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Popular Articles (December 2014)

Includes the top 50 most frequently downloaded documents for this publication according to the most recent monthly usage statistics.
  • 1. A new algorithm for rapid tracking of approximate maximum power point in photovoltaic systems

    Page(s): 16 - 19
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB) |  | HTML iconHTML  

    This paper presents a new algorithm for tracking maximum power point in photovoltaic systems. This is a fast tracking algorithm, where an initial approximation of maximum power point is (MPP) quickly achieved using a variable step-size. Subsequently, the exact maximum power point can be targeted using any conventional method like the hill-climbing or incremental conductance method. Thus, the drawback of a fixed small step-size over the entire tracking range is removed, resulting in reduced number of iterations and much faster tracking compared to conventional methods. The strength of the algorithm comes from the fact that instead of tracking power, which does not have a one-to-one relationship with duty cycle, it tracks an intermediate variable β, which has a monotonically increasing, one-to-one relationship. The algorithm has been verified on a photovoltaic system modeled in Matlab-Simulink software. The algorithm significantly improves the efficiency during the tracking phase as compared to a conventional algorithm. It is especially suitable for fast changing environmental conditions. The proposed algorithm can be implemented on any fast controller such as the digital signal processor. All the details of this study are presented. View full abstract»

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  • 2. A multiple-input DC-DC converter topology

    Page(s): 6 - 9
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (250 KB) |  | HTML iconHTML  

    A new topology for multiple energy source conversion is presented. The topology is capable of interfacing sources of different voltage-current characteristics to a common load, while achieving a low part count. A fixed frequency switching strategy is investigated and the resulting operating modes are analyzed. The analysis is verified by experimentation. The results show that the converter is an enabling technology for power diversification and optimization. View full abstract»

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  • 3. The nearest three virtual space vector PWM - a modulation for the comprehensive neutral-point balancing in the three-level NPC inverter

    Page(s): 11 - 15
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (504 KB) |  | HTML iconHTML  

    This letter presents a new modulation approach for the complete control of the neutral-point voltage in the three-level three-phase neutral-point-clamped voltage source inverter. The new modulation approach, based on the virtual space vector concept, guarantees the balancing of the neutral-point voltage for any load (linear or nonlinear) over the full range of converter output voltage and for all load power factors, the only requirement being that the addition of the output three-phase currents equals zero. The implementation of the proposed modulation is simple according to the phase duty-ratio expressions presented. These expressions are only dependent on the modulation index and reference vector angle. The performance of this modulation approach and its benefits over other previously proposed solutions are verified experimentally. View full abstract»

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  • 4. Electronic controlled device for the analysis and design of photovoltaic systems

    Page(s): 57 - 62
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (744 KB) |  | HTML iconHTML  

    The characterization and design of photovoltaic systems is a difficult issue due to the variable operation atmospheric conditions. With this aim, simulators and measurement equipments have been proposed. However, most of them do not deal with real atmospheric conditions. This letter proposes an electronic device that first measures the real evolution of the I-V characteristic curves of photovoltaic modules and generators, and then physically emulates in real time these curves to test photovoltaic inverters. The device consists of a dc-dc converter, a microcontroller and a data storage unit. The two operation modes (emulation and measurement) are digitally driven by the microcontroller. The converter current is controlled by means of a variable-hysteresis control loop, whose reference is provided by the microcontroller. In addition, a digital voltage control loop is designed to find out the complete characteristic curves of the photovoltaic generators. A 15-kW prototype is designed and built that can measure three times per second the characteristic curves of up to seven generators and then emulate their electrical behavior to test photovoltaic inverters. With the proposed device, the optimal configuration and performance of photovoltaic modules and generators, as well as the operation of photovoltaic inverters can be thoroughly analyzed under real atmospheric conditions. View full abstract»

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  • 5. Single-phase Z-source PWM AC-AC converters

    Page(s): 121 - 124
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB) |  | HTML iconHTML  

    The letter proposes a new family of simple topologies of single-phase PWM ac-ac converters with a minimal number of switches: voltage-fed Z-source converter and current-fed Z-source converter. By PWM duty-ratio control, they become "solid-state transformers" with a continuously variable turns ratio. All the proposed ac-ac converters in this paper employ only two switches. Compared to the existing PWM ac-ac converter circuits, they have unique features: providing a larger range of output ac voltage with buck-boost, reversing or maintaining phase angle, reducing in-rush and harmonic current, and improving reliability. The operating principle and control method of the proposed topologies are presented. Analysis, simulation, and experimental results are given using the voltage-fed Z-source ac-ac converter as an example. The analysis can be easily extended to other converters of the proposed family. The proposed converters could be used in voltage regulation, power regulation, and so on. View full abstract»

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  • 6. DC analysis technique for inductive power transfer pick-ups

    Page(s): 51 - 53
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (227 KB) |  | HTML iconHTML  

    Inductively coupled power transfer (ICPT) systems are now being used in applications where their efficiency and stability are critically important. In this paper, an ICPT pick-up is analyzed under conditions where the pick-up tuning is assumed to be essentially perfect, and all diodes are assumed to have continuous current flow in them. The analysis proceeds by replacing the existing parallel resonant tank and rectifier circuit with a DC source and transformer equivalent, thereby reducing the complexity of the circuit, and eliminating the diodes. The DC equivalent is shown to have the same energy storage and power capability as the original circuit and is accurate under all loadings for both transient and steady-state conditions. With this simplification, analytic transfer functions for the pick-up with respect to its excitation current and its control switch duty cycle are developed. The ICPT system model is shown to have multiple poles, with complex zeroes on the right half plane. The model allows a sophisticated controller to be designed to give the ICPT system the required stability at high efficiency. View full abstract»

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  • 7. Z-source inverter for adjustable speed drives

    Page(s): 33 - 35
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB) |  | HTML iconHTML  

    This paper presents a Z-source inverter system and control for adjustable speed drives (ASD). The Z-source inverter employs a unique LC network to couple the inverter main circuit to the diode front end. By controlling the shoot-through duty cycle, the Z-source can produce any desired output AC voltage, even greater than the line voltage. As results, the new Z-source inverter system provides ride-through capability under voltage sags, reduces line harmonics, and extends output voltage range. Simulation results are presented to demonstrate the new features. View full abstract»

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  • 8. Modeling of capacitor impedance in switching converters

    Page(s): 136 - 140
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB) |  | HTML iconHTML  

    Switched capacitor (SC) converters are gaining acceptance as alternatives to traditional, inductor-based switching power converters. Proper design of SC converters requires an understanding of all loss sources and their impacts on circuit operation. In the present work, an equivalent resistance method is developed for analysis, and equivalent resistance formulae are presented for various modes of operation. Quasiresonant converters are explored and compared to standard SC converters. Comparisons to inductor-based switching power converters are made. A number of capacitor technologies are evaluated and compared for applications to both SC converters and inductor-based converters. The resulting model can be used to accurately predict and optimize converter performance in the design phase. View full abstract»

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  • 9. Buck or boost tracking power converter

    Page(s): 131 - 134
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB) |  | HTML iconHTML  

    A cascade of buck and boost converter is presented here. The control operates in a manner that the converter is either in buck or boost (BOB) mode on a cycle by cycle basis. It transitions between the modes seamlessly to provide a tracking power conversion function for modulating the power supply of a variable envelope radio frequency (RF) power amplifier. The control algorithm and its implementation using switched capacitor circuits is described. Simulation and measured experimental results including converter efficiency, tracking accuracy, and spectrum at the output of the RF power amplifier are provided. This control technique allows seamless transition between the buck and boost modes while tracking RF envelopes with bandwidth greater than 100 kHz, and maintaining extreme accuracy and extremely low ripple. The efficiency of this converter operating at 1.68 MHz is close to 90% over a wide range of conversion ratios. The area of the power converter is extremely small allowing this to be integrated into a cellular telephone. The controller was integrated as part of a larger power management IC as well as a discrete IC. View full abstract»

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  • 10. Simple topologies of PWM AC-AC converters

    Page(s): 10 - 13
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (337 KB) |  | HTML iconHTML  

    This letter proposes a new family of simple topologies of PWM AC-AC converters with minimal switches. With extension from the basic DC-DC converters, a series of AC-AC converters such as buck, boost, buck-boost, Cuk, and isolated converters are obtained. By PWM duty ratio control, they become a "solid-state transformer" with a continuously variable turns ratio. All the proposed AC-AC converters in this paper employ only two switches. Compared to the existing circuits that use six switches or more, they can reduce cost and improve reliability. The operating principle and control method of the proposed topologies are presented. Analysis and simulation results are given using the Cuk AC-AC converter as an example. The analysis can be easily extended to other converters of the proposed family. View full abstract»

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  • 11. PWM methods to handle time delay in digital control of a UPS inverter

    Page(s): 1 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB) |  | HTML iconHTML  

    With the popularity of micro-processors, digital controllers are widely used in uninterruptible power supply (UPS) inverters. These digital control systems of UPS inverters require a time interval for sampling and computation, which sometimes affects the performance of inverters. In this paper, the problem of time delay in digital control of a UPS inverter is discussed. Then two novel pulsewidth modulation (PWM) methods, the two-polarity PWM method and the asymmetric PWM method, are proposed to handle the time-delay problem. Both of these PWM methods can achieve a wide range of duty ratio between 0.05-0.95, which is independent of inverter model. Furthermore, they are easy to implement using a digital micro-controller. Experimental results are presented in the paper to verify feasibility of the proposed PWM methods. View full abstract»

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  • 12. Low-input-voltage, low-power boost converter design issues

    Page(s): 96 - 99
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB) |  | HTML iconHTML  

    Issues associated with boost converter design and performance are investigated when a low input voltage is used. Low-input-voltage sources include single fuel cells, single solar cells, and thermoelectric devices. The primary context is interfacing single micro fuel cells to portable electronic loads, such as mobile phones. Efficiency and circuit startup are the two most difficult issues for a low-cost design. It is shown in theory and experiment that the boost converter has a voltage collapse point. A simple startup technique is proposed that is appropriate for some applications. View full abstract»

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  • 13. A constant-frequency method for improving light-load efficiency in synchronous buck converters

    Page(s): 24 - 29
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB) |  | HTML iconHTML  

    The low-voltage synchronous rectifier buck topology suffers from low efficiency at light loads due to dissipation that does not scale with load current. In this paper we present a method for improving light-load efficiency in synchronous buck converters by reducing gate drive losses. We propose a new gate drive technique whereby the gate voltage swing dynamically scales with load current such that gate drive loss is traded for conduction loss. Since conduction losses scale with the square of load current, an optimal gate swing exists that, at light loads, is shown to be less than the supply voltage. Using this method we obtain a 6.25% increase in converter efficiency at a load current of 10 mA and operating at a constant switching frequency of 2 MHz. View full abstract»

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  • 14. A 3-D space vector modulation generalized algorithm for multilevel converters

    Page(s): 110 - 114
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (347 KB) |  | HTML iconHTML  

    A three-dimensional (3-D) space vector algorithm of multilevel converters for compensating harmonics and zero sequence in three-phase four-wire systems with neutral is presented. The low computational cost of the proposed method is always the same and it is independent of the number of levels of the converter. The conventional two-dimensional (2-D) space vector algorithms are particular cases of the proposed generalized modulation algorithm. In general, the presented algorithm is useful in systems with or without neutral, unbalanced load, triple harmonics and for generating 3-D control vectors. View full abstract»

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  • 15. Implementation of pulse-width-modulation based sliding mode controller for boost converters

    Page(s): 130 - 135
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB) |  | HTML iconHTML  

    This letter addresses the various issues concerning the implementation of a pulse-width modulation (PWM) based sliding mode (SM) controller for boost converters. The methods of modeling the system and translation of the SM control equations for the PWM implementation are illustrated. It is shown that the control technique is easily realized with simple analog circuitries. Various experiments are conducted to test the static and dynamic performances of the system. View full abstract»

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  • 16. Three-dimensional space vector modulation in abc coordinates for four-leg voltage source converters

    Page(s): 104 - 109
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (561 KB) |  | HTML iconHTML  

    Four-leg inverters have been selected as one of the preferred power converter topologies for applications that require a precise control of neutral current, like active filters. The main advantage of this topology lies in an extended range for the zero sequence voltages and currents. However, the addition of a fourth leg extends the space vectors from two to three dimensions, making the selection of the modulation vectors more complex. Most of the algorithms that deal with this problem require an /spl alpha//spl beta//spl gamma/ transformation. This paper presents a new space vector modulation algorithm using abc coordinates (the phase voltages) avoiding the /spl alpha//spl beta//spl gamma/ transformation. Thanks to the use of abc coordinates, the algorithm is much simpler and more intuitive than in /spl alpha//spl beta//spl gamma/ representation, drastically reducing the complexity of modulation algorithm and the computational load associated to it. View full abstract»

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  • 17. Self-tuning dead-time compensation method for voltage-source inverters

    Page(s): 72 - 75
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (360 KB) |  | HTML iconHTML  

    A new method of dead-time compensation is proposed, capable of self-tuning to the inverter and load properties. The tuning, performed real-time, relies on parameter selection of a generic compensation characteristic. During the parameter search, the quality of compensation is being continuously assessed against the harmonic distortion of output currents. The method enjoys very effective compensation of both harmonic and linear distortion caused by dead time and other parasitic agents. View full abstract»

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  • 18. A three-phase symmetrical multistage Voltage multiplier

    Page(s): 30 - 33
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB)  

    A three-phase symmetrical Cockcroft-Walton (CW) multistage voltage multiplier (VM) is proposed. It consists of one smoothing column and six oscillating columns. The oscillating columns are connected to three-phase power through center-tap transformers. The capacitors of the smoothing column are charged six times per cycle by six oscillating columns and are discharged six times through the load, unlike the conventional symmetrical VM in which they are charged and discharged twice per cycle. The three-phase symmetrical structure completely eliminates the first five harmonic components of load-generated voltage ripple. Theoretical analysis indicates that the proposed three-phase symmetrical CW-VM has one-third the voltage ripple and voltage drop of the conventional single-phase symmetrical CW-VM. Experimental and simulation results of the proposed three-phase symmetrical CW-VM as well as of the conventional single-phase symmetrical CW-VM are presented. A comparison shows that the three-phase symmetrical CW-VM has significantly less voltage ripple, half the voltage drop, and a fourfold increase in output power over the conventional single-phase symmetrical CW-VM. View full abstract»

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  • 19. Synthetic-ripple modulator for synchronous buck converter

    Page(s): 148 - 151
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB) |  | HTML iconHTML  

    Comprising a hysteretic comparator and a ripple synthesizer, the synthetic-ripple modulator (SRM) allows voltage-hysteretic modulation to be realized in low-voltage buck converters where the natural voltage ripple is too small for reliable hysteretic operation. Circuit implementation, steady-state operation, and design equations are described for an SRM controlling a buck dc-dc converter. The basics are verified experimentally by a buck converter switched at 420 kHz and delivering 10 A at 1.8 V. View full abstract»

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  • 20. Improved power flow control for contactless moving sensor applications

    Page(s): 135 - 138
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB) |  | HTML iconHTML  

    An improved power flow control method for contactless moving sensor applications is proposed. The method allows the design of a system where sensors with different power ratings or a wide range of load variations can be implemented. A phase-controlled variable inductor is used to tune the resonant circuit of the power pickups of an inductively coupled power transfer (ICPT) system according to the actual power requirements of the sensors, thereby, helping to reduce the power losses without affecting the maximum power transfer capacity. Soft switching is achieved in the variable inductor control, and the effect of the equivalent tuning parameters on the power flow is analyzed theoretically. Simulation results show that a significant improvement of the existing controllers is achieved at no load or very lightly loaded conditions. View full abstract»

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  • 21. Online grid measurement and ENS detection for PV inverter running on highly inductive grid

    Page(s): 77 - 82
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB) |  | HTML iconHTML  

    Photovoltaic (PV) and other sources of renewable energy are being used increasingly in grid-connected systems, for which stronger power quality requirements are being issued. Continuous grid monitoring should be considered so as to provide safe connections and disconnections from the grid. This letter gives an overview of the methods used for online grid measurement with PV inverters. Emphasis is placed on a method based on the injection of a noncharacteristic harmonic in the grid. Since this injection is regarded as a disturbance for the grid, different issues, i.e., the influence on total harmonic distortion (THD), the accuracy of line impedance measurement and the ENS (German abbreviation of Main Monitoring units with allocated Switching Devices) detection are studied. Laboratory results conducted on an existing PV inverter are presented to demonstrate the behavior of the PV inverter under different grid conditions. Some of the injection parameters are tuned in order to get an accurate measurement of line impedance. View full abstract»

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  • 22. Three-step impedance criterion for small-signal stability analysis in two-stage DC distributed power systems

    Page(s): 83 - 87
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (402 KB) |  | HTML iconHTML  

    Small-signal stability analysis methods based on an impedance criterion originate from the minor loop gain method and are gradually utilized in two-stage DC distributed power systems. In this paper, we conclude that the impedance criterion directly dependent on output impedance Z/sub o/(s) of the source subsystem and input impedance Z/sub i/(s) of the load subsystem is possible but gives an incorrect stability analysis for systems with a regulated source subsystem. Through introducing a mapped pure impedance of the load subsystems and the preliminary system, we develop a general three-step impedance criterion, with which a correct small-signal stability analysis can be guaranteed, regardless of the type of source subsystem. Furthermore, we introduce the application of the three-step impedance criterion in two small-signal stability analysis cases and utilize it in an example system to predict the stability shift process arising from the variation on the load resistance and input voltage value. View full abstract»

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  • 23. Multilevel dynamic voltage restorer

    Page(s): 125 - 130
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (552 KB) |  | HTML iconHTML  

    This letter presents the implementation and control of a high voltage dynamic voltage restorer (HVDVR) for use in power distribution network to compensate for sags in utility voltages. The proposed HVDVR is implemented using a multilevel inverter topology with isolated DC energy storage, allowing the direct connection of the HVDVR to the distribution network without using a bulky and costly series injection transformer. A control algorithm, incorporating P+resonant and Posicast compensators, is also presented for controlling the HVDVR with perfect reference voltage tracking and effective damping of transient voltage oscillations at the instant of sag compensation. Finally, simulation results are presented to verify the performance of the proposed multilevel HVDVR. View full abstract»

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  • 24. Small-signal and signal-flow-graph modeling of switched Z-source impedance network

    Page(s): 111 - 116
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB) |  | HTML iconHTML  

    The Z-source inverter is a recently proposed converter topology that uses a unique X-shaped impedance network on its dc side for achieving both voltage-buck and boost capabilities. In the process of designing control schemes for the Z-source inverter, knowledge of the transfer function representing its unique dc impedance network is essential. Toward this end, this letter presents dynamic small-signal modeling of the Z-source impedance network using perturbed mathematical analysis and a signal-flow graph with parasitic components taken into consideration. In particular, the developed average control-to-output model reveals the presence of a right-hand-plane zero in the network transfer function, whose trajectories with variations in network parameters can be studied using classical root-locus analyses. Using the graphical signal-flow modeling approach, various disturbance-to-output transfer functions can also be derived with their parameter sensitivity similarly studied. Lastly, simulation and experimental results are presented for verifying the dynamic phenomena identified in this letter. View full abstract»

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  • 25. Constant and high switching frequency torque controller for DTC drives

    Page(s): 76 - 80
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB) |  | HTML iconHTML  

    The letter presents a new method of increasing the switching frequency of a direct torque control (DTC) of induction machines. The method simply replaces the hysteresis comparator of the conventional DTC drives with a triangular waveform-based constant switching frequency controller. By synchronizing the digital signal processor (DSP) sampling with a triangular waveform and with an appropriate systematic controller design, a high switching frequency DTC drive is possible without requiring a high-frequency space-vector modulator. The implementation of the controller is simple and operates based on waveform comparisons; in this letter it is implemented using a combination of a DSP and a field programmable gate array device. Simulation and experimental results indicate that the controller both reduces the torque ripple and maintains a constant switching frequency. View full abstract»

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  • 26. Interpreting small signal behavior of the synchronous buck converter at light load

    Page(s): 144 - 147
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (544 KB) |  | HTML iconHTML  

    The pulse-width-modulation (PWM) buck converter with synchronous rectifiers operating at light load is usually modeled by its continuous conduction mode (CCM) model. However, the actual power-stage small-signal control-to-output response shows a different behavior from what the traditional CCM model predicts, specifically, more damping around the double-pole frequency, instead of more resonance. This paper presents a modified small-signal light-load model for a synchronous buck converter. The developed model accurately predicts the actual small-signal behavior of a PWM converter at light load. The derived averaged switch model for light load can also be used for the small-signal models of the other basic PWM converters operating in CCM at light load. View full abstract»

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  • 27. Variable-frequency predictive digital current mode control

    Page(s): 113 - 116
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB) |  | HTML iconHTML  

    A variable-frequency predictive digital control method for the inductor current in switched-mode converters is introduced in this letter. This method is predictive in nature because the transistor off-time required for achieving the target current is calculated ahead of time. The transistor on-time is kept constant, which results in variable switching frequency. The control laws for continuous and discontinuous modes of operation of the three basic converters are derived. Stability and robustness criteria are presented. The variable-frequency predictive control obviates the need for current-loop compensation and has the advantages of single-cycle response and relatively simple implementation. The control method is demonstrated in a digital signal processor (DSP) for a boost power factor corrector (PFC), which shows excellent current tracking and a very low harmonic distortion of the line current. View full abstract»

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  • 28. A simple model for flux weakening in surface PM synchronous machines using back-to-back thyristors

    Page(s): 54 - 57
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB) |  | HTML iconHTML  

    Flux weakening in surface permanent magnet (PM) synchronous machines is revisited in this letter. The condition for achieving infinite constant power speed ratio (CPSR) is explained from the machine equivalent circuit and phasor diagram point of view. Back-to-back thyristors, or triac, switches feeding the three phases of a surface PM synchronous machine will be shown to be equivalent to a simple series reactance with respect to fundamental component behavior. Using such switches is equivalent to adding a series inductance to the machine. This additional inductance helps extend the CPSR of surface PM synchronous machines. This is significant because extending the CPSR of surface PM machines is usually a challenging task due to the presence of low-permeability surface magnets and the resulting low machine inductance. View full abstract»

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  • 29. Time domain comparison of pulse-width modulation schemes

    Page(s): 64 - 68
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (374 KB) |  | HTML iconHTML  

    This paper shows that classical space vector modulation (SVM) is functionally identical to double-sided uniform-sampled pulse width modulation (UPWM). Consequently, direct conclusions about harmonic distortion, losses, DC bus utilization, and ease of implementation are made that clarify some existing misconceptions about SVM. Since UPWM is conceptually simple and involves few steps, it is possible that computation may be reduced in practice. UPWM algorithms can avoid the sector and switch sequence tracking tasks in an SVM algorithm. The linear modulation range extension "inherent" to SVM is associated with triplen harmonic injection, and does not provide advantages over conventional third-harmonic injection techniques. The equivalence of SVM and UPWM means that SVM has spectral distortion in baseband as is known to occur in UPWM. This has implications for naturally-sampled sine-triangle PWM (NPWM)-which is known not to generate baseband distortion. View full abstract»

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  • 30. A leakage-inductance-based ZVS two-inductor boost converter with integrated magnetics

    Page(s): 67 - 71
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB) |  | HTML iconHTML  

    A two-inductor boost converter topology has conduction loss and transformer utilization advantages in converting low-voltage higher current inputs to high output voltages. In this letter, a new zero-voltage switching (ZVS) two-inductor boost converter with integrated magnetics is proposed. In the new topology, the two current source inductors, a resonant inductor and a two-winding transformer, are integrated into one single magnetic core with three windings. Two windings simultaneously perform the functions of the current source inductors and the transformer primary. The transformer leakage inductance forms the resonant inductance. This leads to a much more compact converter design with a significant reduction in the number of core and winding components. A theoretical analysis establishes the operating point of the ZVS converter. Both of the theoretical and experimental waveforms, including flux waveforms for the legs of the integrated core structure, are presented at the end of the letter. View full abstract»

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  • 31. A passive auxiliary circuit achieves zero-voltage-switching in full-bridge converter over entire conversion range

    Page(s): 141 - 143
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB) |  | HTML iconHTML  

    A passive auxiliary circuit is proposed to achieve zero-voltage-switching (ZVS) over the entire conversion range in a full-bridge (FB) pulse-width modulated (PWM) converter (FBZVS converter) with minimum conduction loss penalty. The stored energy in the auxiliary circuit is minimal under the full-load condition. It increases progressively as the load current decreases. The proposed auxiliary circuit is passive, simple and can be viewed as an add-on to the conventional FBZVS converter. The principle of operation is described and the performance is demonstrated on a 100 kHz, 500 W prototype. View full abstract»

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  • 32. A voltage-balanced phase-shifted three-level DC/DC converter operating from high-input voltage

    Page(s): 74 - 77
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (399 KB) |  | HTML iconHTML  

    A voltage-balanced phase-shifted three-level DC/DC converter is proposed. Its switch voltage stress is ensured to be only one-half of the input voltage and its four-step operation can reduce considerably the output inductor current ripple. Moreover, it features a small filter, no voltage unbalance problem, static/dynamic sharing of the switch voltage, high-efficiency, and high-power density. It is very suitable for high power converters operating from a high-input voltage. View full abstract»

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  • 33. Effects of machine speed on the development and detection of rolling element bearing faults

    Page(s): 19 - 21
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (177 KB) |  | HTML iconHTML  

    This research investigates the effects of a variable machine speed on machine vibration and the implications for bearing fault detection. These effects are important to understand because when ignored they can significantly hinder the ability to detect bearing faults. Experimental results verify that a variable machine speed can directly and nonlinearly alter the level of machine vibration. This is due to differences in mechanical damping and resonance at various machine speeds. While this effect is difficult to notice in healthy machines, it can become significant as bearing health degrades. An additional effect that speed can exert is on the rate of development of a bearing fault. Variations in speed can actually retard or temporarily mask the increase in machine vibration due to a bearing fault. This phenomenon is observed in experimental trials as the bearing fault enters an advanced and more deteriorated stage. This can inadvertently make a machine appear healthy even though a bearing failure is imminent. However, by understanding these effects, a more skillful application of the available condition monitoring tools in variable speed applications is achieved. View full abstract»

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  • 34. A ripple control buck regulator with fixed output frequency

    Page(s): 61 - 63
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB) |  | HTML iconHTML  

    This paper presents a ripple control buck regulator for stepping down high-voltage adaptor or battery supplies to low-voltage CPU core supply in notebook computers. Methods and circuits are proposed to achieve fixed switching frequency operation. The control loop adjusts delay of the controller and thus controls the output frequency. This is done by using a phase-frequency detector (PFD) to lock the frequency of switching signal with the input clock. The delay value is determined automatically according to operating conditions. Simulation results showed fast load and line transient responses and fixed frequency operations in steady states. In addition, stability of the regulator is shown under a very low output-to-input voltage ratio condition that is difficult for conventional PWM controllers. View full abstract»

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  • 35. A 3-D generalized direct PWM algorithm for multilevel converters

    Page(s): 85 - 88
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    A three-dimensional (3-D) generalized direct pulse width modulation (PWM) algorithm is proposed for multilevel converters in a three-phase, four-wire system. It is proved to be equivalent to the newly proposed generalized 3-D space vector modulation (SVM). However, the direct PWM greatly simplifies the calculation process and is much easier to implement in digital controllers. The direct PWM can be used in all applications needing a 3-D control vector, such as active filters, uninterruptible power supplies, etc. Simulation and experimental results are given to show the validity of the proposed control strategy. View full abstract»

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  • 36. Minimum current magnitude control of surface PM synchronous machines during constant power operation

    Page(s): 53 - 56
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB) |  | HTML iconHTML  

    The dual-mode inverter control (DMIC) was initially developed to provide broad constant power speed range (CPSR) operation for a surface mounted permanent magnet machine (PMSM) having low inductance. The DMIC interfaces the output of a common voltage source inverter (VSI) to the PMSM through an ac voltage controller. The ac voltage controller consists of three pairs of anti-parallel silicon controlled rectifiers (SCRs), one anti-parallel SCR pair in series with each winding of the motor. In a recent paper a fundamental frequency model of DMIC type controllers was developed using an equivalent reactance interpretation of the in-line SCRs. In this work, the same fundamental frequency model is used to show that the DMIC may have considerable loss reduction benefits even if the motor winding inductance is large. Specifically, it is shown that the SCRs enable maximum watts per rms amp control during constant power operation. The rms motor current can be minimized for any given power level and sufficiently large speed with DMIC. A fixed winding inductance and a conventional inverter can only be optimized for a single speed and power level. The performance predicted by the fundamental frequency model of the DMIC is compared to that of a conventional PMSM drive where the motor has sufficiently large inductance to achieve an infinite CPSR. It is shown that the SCRs can reduce motor current by a factor of 0.7071 at high speed and rated power. This would reduce the motor copper losses by 50% and reduce the conduction losses in the VSI by 29.3%. At less than rated power the percentage of motor/VSI loss reduction enabled by the SCRs is seen to be even larger. View full abstract»

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  • 37. Thermal design based on surface temperature mapping

    Page(s): 125 - 129
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (840 KB) |  | HTML iconHTML  

    A method of extracting a conservative thermal model from an existing PCB assembled converter is investigated. This improves upon thermal management by increasing the thermal management contribution of the PCB itself. A thermal calibration loop is proposed in which a given converter is analyzed and data extracted, in order to create a thermal map of the surface temperature from which the component layout and thermal profiles can be estimated. Thermal figures of merit are vital to quantify the thermal adjustments, recorded in this thermal map, which are required during thermal calibration. The thermal figures of merit are also flexible enough to allow for specific optimization objectives such as high power density, or overall reliability. Two graphical means to predict temperature profiles required in the thermal calibration loop have been investigated: a thermal resistor network method with a purely analytical approach, suitable for relatively small systems where the geometry and loss analysis are simple (fewer than ten components), or a more elaborate method using a finite difference method algorithm, implemented in a spreadsheet environment. Both provide flexible means for PCB thermal layout and provide straightforward graphical visualization. A case study illustrates the complete design method. View full abstract»

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  • 38. Adjustable shunt regulator based control systems

    Page(s): 93 - 96
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (313 KB) |  | HTML iconHTML  

    Adjustable shunt regulators known as TL431 are extensively used to build the control systems in switched-mode converter applications. The resulting control system is typically a two-loop system, where one loop defines the low frequency behavior, and the other loop the higher frequency behavior, respectively. The shunt regulator is regarded to possess characteristics similar to an operational amplifier, even if it is basically a transconductance amplifier having current as an output signal instead of voltage as well as positive feedback instead of negative feedback. The small-signal response of a shunt regulator shows that it may be modeled as a voltage-controlled current source with a small transconductance gain and an equivalent capacitor as output impedance, which may be extracted from the open-loop frequency response by inspection. The variance in the parameters may be high depending on the manufacture, and operating point, i.e., cathode current, which is normally chosen to be close to 1 mA due to the specifications. The analysis shows, however, that the cathode current should be at least 5 mA for stable equivalent circuit parameters. If low cathode current is used, the control system may not be better than a Zener diode replacing the shunt regulator. View full abstract»

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  • 39. A lossless active clamping circuit for current doubler topologies

    Page(s): 92 - 95
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB) |  | HTML iconHTML  

    This letter presents a new lossless clamping circuit on the secondary side for DC-DC converters with a current-doubler structure. This circuit reduces ringing on secondary-side rectifiers due to leakage inductance. The ringing loss is recovered to the load. As a result, efficiency is improved, and the voltage stress on secondary-side rectifiers is reduced significantly. These improvements allow DC-DC topologies with a current doubler to operate efficiently at high switching frequencies. The operating principle of the clamping circuit is detailed. Simulations and experimental results validate the proposed technique. View full abstract»

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  • 40. Fault interrupting methods and topologies for interior PM machine drives

    Page(s): 139 - 143
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB) |  | HTML iconHTML  

    This work investigates methods to interrupt the phase currents induced when interior permanent magnet (IPM) machine drives suffer short-circuit or uncontrolled generator mode faults. A fault-tolerant silicon switch is proposed in which the antiparallel diode in a reverse-blocking inverter switch is replaced by a thyristor. A reduced-parts-count fault-interrupting topology is also proposed which consists of delta-connected thyristors inserted at the center star point of wye-connected IPM machine stator windings. Control of the proposed reduced-parts-count fault-tolerant drive is discussed and simulation results are presented to verify operation of the proposed topology. View full abstract»

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  • 41. A switching control strategy based on output regulation subspaces for the control of induction motors using a three-level inverter

    Page(s): 29 - 32
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (329 KB) |  | HTML iconHTML  

    In this work we present the design of a new switching control strategy for a three-level converter aimed to improve the performance of a direct torque control (DTC) for induction machines, special attention is given to the reduction of torque ripple. As in classical DTC, the proposed technique is aimed to directly regulate the outputs: torque and flux amplitude. We show that classical DTC can be considered as a particular case of the proposed control strategy. The proposed criterion to design the switching control sequence is based on a quadratic criterion of the output errors plus a prediction in one-step ahead, and an interesting partition of the input state space generated by the output regulation subspaces (ORS) to facilitate the selection of the control vector for reducing the computational load. As a result, a control vector is selected without the requirement of an auxiliary space vector or any other modulation technique. Simulations results using the proposed control technique confirm the validity of this approach. View full abstract»

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  • 42. Analysis of thermoelectric coolers by a spice-compatible equivalent-circuit model

    Page(s): 63 - 66
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB) |  | HTML iconHTML  

    The objective of this work was to develop a PSPICE-compatible equivalent circuit of a thermoelectric cooler (TEC). Equivalent circuits are convenient tools for power electronics engineers since they help in presenting a problem in electronic circuit terms and can assist in the design of power stages and the control circuitry and algorithms. A methodology is developed for extracting the parameters of the proposed model from manufacturers' data of TECs. The present model is compatible with PSPICE or other electronic circuit simulators. An important feature of the model is its ability to generate small-signal transfer functions that can be used to design feedback networks for temperature-control applications. Several examples of successful utilization of the model are presented. Data of many different manufacturers were examined and the model parameters were extracted. In all cases, the model was found to reproduce accurately the performance of commercial TECs. The accuracy of the model was also verified by experiments. View full abstract»

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  • 43. Estimative current mode control technique for DC-DC converters operating in discontinuous conduction mode

    Page(s): 20 - 23
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB) |  | HTML iconHTML  

    A new control technique for DC-DC converters is introduced and applied to a boost converter operating in discontinuous conduction mode (DCM). In contrast to conventional control methods, the principal idea of the proposed control scheme is to obtain samples of the required signals and estimate the required switch-on time. The proposed technique is applicable to any converter operating in DCM, including power factor correctors (PFC), however, this letter mainly focuses on boost topology. In this letter, the main mathematical concept of a new control algorithm is introduced, as well as the robustness investigation of the proposed method with simulation and experimental results. View full abstract»

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  • 44. Improvement of light-load efficiency using width-switching scheme for CMOS transistors

    Page(s): 105 - 110
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (920 KB) |  | HTML iconHTML  

    This paper presents a derivation of the optimum width of transistors to minimize losses in monolithic CMOS buck converters. The high optimal width requires a tapered inverter chain gate driver. A technique called "width switching" is presented. It can be integrated with the inverter chain to maintain maximum converter efficiency over a wide power range, particularly at light load. Experimental results are presented from a chip containing CMOS transistors optimized for power levels between 50 mW and 200 mW. Challenges in implementing the width-switching scheme and other applications are also discussed. View full abstract»

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  • 45. Capacitor voltage balancing in full binary combination schema flying capacitor multilevel inverters

    Page(s): 2 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (267 KB) |  | HTML iconHTML  

    Recently, the full binary combination schema (FBCS) method has been introduced to control the flying capacitor multilevel inverter. This method has the primary advantage that the number of voltage levels can be increased for a given number of semiconductor devices when compared to the conventional control methods. However, due to the difficulty of balancing the capacitors, the new schema requires fixed floating sources to provide the DC voltages. This paper reveals an approach of balancing the capacitors, thus expanding the application fields of FBCS inverters to the family of the flying capacitor multilevel inverters under the condition of choosing a suitable modulation index. Simulation results demonstrate the proposed voltage balancing control. View full abstract»

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  • 46. Using magnetic coupling to eliminate right half-plane zeros in boost converters

    Page(s): 58 - 62
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB) |  | HTML iconHTML  

    A dynamic analysis of the boost converter with an output filter reveals that magnetic coupling between inductors allows transfer of the zeros to the left half-plane of the control-to-output transfer function. Similar results requiring smaller magnetic components are obtained by combining magnetic coupling with damping of the output filter. The analysis is based on the application of the Routh-Hurtwitz's criterion to the numerator of the transfer function in order to derive the design conditions for the converter parameters. A design example illustrates the procedure, and experimental results verify the theoretical predictions. The application of these techniques will allow the design of high efficiency voltage boost-based regulators with dynamic behavior similar to buck-derived structures. View full abstract»

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  • 47. Secondary control for a series reactive compensator based on a voltage-source PWM inverter

    Page(s): 117 - 120
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB) |  | HTML iconHTML  

    This work describes a secondary control scheme of a series reactive compensator for a power system based on a single voltage-source pulse-width-modulated (PWM) inverter. The controllable capacitive reactance can be used as a supplementary control variable for the secondary (external) controller (SC) of a series capacitive reactance compensator to improve the dynamic transient and damping performances of the power system. From the viewpoint of agent-based global dynamic optimization of a system, the selection and use of suitable input signals for the SC are investigated. Detailed simulation results show that the SC with local feedback loop (LFL) has a powerful control performance; however, it requires the controllable compensation for a reference change due to different operating conditions. On the other hand, the SC with global feedback loop (GFL) avoids the need of reference compensation; moreover, its dynamic control performance is improved when the dual inputs (frequency and active power signal) are used, compared to when only the frequency is used as an input signal. View full abstract»

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  • 48. Characterization of SiC Schottky diodes at different temperatures

    Page(s): 54 - 57
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (564 KB) |  | HTML iconHTML  

    The emergence of silicon carbide (SiC) based power semiconductor switches, with their superior features compared with silicon (Si) based switches, has resulted in substantial improvement in the performance of power electronics converter systems. These systems with SiC power devices have the qualities of being more compact, lighter, and more efficient; thus, they are ideal for high-voltage power electronics applications. In this study, commercial Si pn and SiC Schottky diodes are tested and characterized, their behavioral static and loss models are derived at different temperatures, and they are compared with respect to each other. View full abstract»

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  • 49. A nonlinearity compensation method for a matrix converter drive

    Page(s): 19 - 23
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB)  

    This paper presents a new method to compensate the nonlinearities for matrix converter drives. The nonlinearities of matrix converter drives such as commutation delay, turn-on and turn-off time of the switching devices, and on-state switching device voltage drop is corrected by a new matrix converter model using the direction of current. The proposed method does not need any additional hardware or complicated software and it is easy to realize by applying the algorithm to the conventional vector control. The proposed compensation method is applied for high-performance induction motor drives using a 3-kW matrix converter system without a speed sensor. Experimental results show the proposed method provides good compensating characteristics. View full abstract»

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  • 50. Modeling the sequential switching shunt series regulator

    Page(s): 7 - 13
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB) |  | HTML iconHTML  

    This letter characterizes, in terms of the bandwidth and limit cycle frequency of its constituent subsystems, the sequential switching shunt series regulator -S4R, a high-efficiency, low-mass and volume power cell devised to power the next generation of regulated power buses in telecommunication spacecrafts. Transconductance power source modeling is used to obtain linear and nonlinear models. These are used to establish a design control strategy which involves the dynamic response in large load requirements or at the end of the satellite life. Simulations and experimental results are also given to demonstrate the validity of the model. View full abstract»

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