An Overview and Minimum Fault Ramp Rate Analysis of Impedance Based Circuit Breaker Topologies

In the advent of recent developments in a higher efficiency Direct Current (DC) system, the DC microgrid proves to be a permissible future to match the load demand with distributed power generation. The distribution of the DC power system benefits more than the Alternate Current (AC) power system, and due to recent developments, many researchers focus on DC microgrid. DC microgrid system has the advantage of direct interfacing with Renewable energy sources (RES) and energy storage systems (ESS), making the system highly efficient and distinct. Since the protective devices used in AC power systems do not support DC applications, there are challenges in designing and implementing a proper protection device for DC microgrid, which includes the breaking of fault current and the rapid response in handling fault current, capability to overcome the fault and cost of implementing. Unlike traditional circuit breakers that work with a fixed voltage source, Z-Source Breakers are capable of interrupting current in systems with variable voltage sources, making it appropriate for applications involving renewable energy sources, microgrids and energy storage systems. These breakers use a unique Z-Source network to provide enhanced flexibility and reliability in managing electrical faults in modern power grids. This study intends to analyses the recent growth in the impedance-based DC circuit breaker and DC microgrid’s fault characteristics.


I. INTRODUCTION
DC microgrids have significant advantages over conventional AC power systems compared with power efficiency, power density and flexible operation.The growth of usage in Renewable energy has increased the need for integration, transmission and distribution of DC microgrids.However, DC power transmission/distribution is not particularly effective as there is no rapid or reliable fault protection mechanism, especially for low to medium power levels and multi-terminal DC system topologies.
The Protection scheme determines the reliability of the microgrid system; ongoing research is working to provide a reliable protection scheme for the grid and islanded mode The associate editor coordinating the review of this manuscript and approving it for publication was Arturo Conde .
of operation in the microgrid.The typical protective devices used in DC microgrids are Fuses, Relays, Switches and Circuit breakers.Traditional methods remain ineffective in protecting DC microgrids owing to factors like bidirectional power flow, variable fault current during the islanded mode, and the dynamic behaviour of distributed energy sources [1], [2].Another problematic element to deal with in a fault condition is the rapid voltage drop caused by the rise in the negative impedance of power converters [3].The other issues involved in protecting microgrids are blinding zones, false tripping, islanding issues, recloser, response time and variation in short circuit level [4].
The existing current response-based electromechanical breaker (MCB) has its limitations with slow response time and acting only at high peak fault current limit.Later introduced Solid-state circuit breakers (SSCB) have overcome these issues, and they have provided protection schemes for Low Voltage Direct Current (LVDC) and Medium Voltage Direct Current (MVDC) applications [5], [6].Power semiconductor devices like IGBT, IGCT, MOSFET and SCR are gate-driven by fault current sensor circuits, which are fast response and efficient circuit breakers [7].Despite several advantages, some challenges need to be addressed: • Reducing the ON-state loss.
• Increasing surge current capability.
• Decreasing OFF-state leakage current.The combination of MCB and SSCB leads to the development of a hybrid circuit breaker (HCB), which performs efficiently in fault interruption and removes the dissipated fault current.Still, the response time depends on the ultra-fast switch [8].
Impedance source circuit breaker or Z-source circuit breaker (ZSCB) is the improved version of SSCB; unlike SSCB, it can autonomously respond to and interrupt faults without additional sensor circuits.Inspired by the Z-source inverter's ability to short course its DC bus while its Z-source provides boost mode, the ZSCB is developed.Based on the different inverter topologies, many ZSCB topologies supporting unidirectional and bidirectional power flow have been proposed for shipboard protection and other microgrid applications.Coordinated protection can be achieved in multiple ZSCB or with Fuse by enabling a gate driver circuit to control the thyristor [9], [10].The paper discusses the various protection devices for DC microgrids and provides a detailed topological review of ZSCB.Section II presents the analysis comparison of protective devices of DC microgrid.Section III shares a detailed review of the category of ZSCB.Section IV briefly compares different Coupled ZSCB topologies and their performance using Matlab Simulink 2018a and real time simulation, followed by recommendations for future development for ZSCB applications.

II. PROTECTIVE DEVICES FOR DC MICROGRID
Since DC circuits lack natural zero-crossing, protection mechanisms designed for AC systems do not applicable to DC circuits [11].So, DC microgrids require protective devices like fuses, DC circuit breakers, fault current limiters, mechanical switches and breaker-less.A highly reliable microgrid should focus on abnormal fault current detectors, fault isolation & quick restoration.One of the promising protective devices is the DC circuit breaker (DCCB), which isolates the fault and restores the system.Generally, a DCCB should have the following features: High reliability, fast response, low power loss, more extended life period, low cost and compact [12].Some types of DCCB are Hybrid CB, Solid-state CB, and Z-source CB.Due to the presence of many power electronics devices in the DC microgrid, a fault might lead to an unexpected voltage drop in the DC bus, resulting in severe damage to nearby equipment in the system.

A. FUSE
Fuses are an inexpensive protecting device and classic structure, mainly preferred for low-voltage AC and DC systems.
And they are categorized as fast response and time-delay model.In general, fuses are preferably used in DC motor protection.The fuse must be selected based on voltage and current rating, interrupting capability, temperature and maximum circuit fault current [13].In [14] fuse trip characteristic with two boundary curves is depicted in Figure 1.a, the minimum melting curve, which serves as a lower limit and measures the minimum overcurrent that causes the melting the link.Full opening curve, which represents the upper barrier and shows that the fuse has completely blown and the circuit has opened.The few merits of a fuse are low cost and no maintenance required, and it clears inrush and surge currents; it reacts faster compared to Circuit Breaker.Despite being widely used, there are still certain negative aspects.Replacement is required after fault clearance.It cannot be used in high-load applications and cannot differentiate between permanent faults and transients.

B. MECHANICAL CIRCUIT BREAKER (MCB)
MCB is usually identified with an electric arc and magnetization during fault current interruption.Using only an MCB is not recommended because of its low response time, longer trip delay, nuisance tripping and limited interruption capability; it has many advantages like low power loss and low cost.The circuit consists of three paths in parallel termed as (a) the nominal path has a mechanical switch S; (b) the switching path consists of a series resonance and (c) the energy-absorbing path is given by a surge arrest.Current travels through the nominal path during normal operation, when a high amplitude oscillating current flows between the nominal and commutation channels during the fault period when switch S opens.A zero-crossing current happens in the nominal path if the oscillating current amplitude is greater than the DC fault current [15].
Figure 1(b) is a conceptual diagram of a mechanical DC circuit breaker.The combined mechanical switch with a z-source breaker [16], [17] and solid-state circuit breaker provides higher sensitivity and reliability.Mechanically switched Z-source provides high operative efficiency with an average cost, which is advantageous [18].The setback of MCB is that the fault interruption operation is slow, which takes approximately 50 -100 ms, and it is more sensitive to vibration.

C. SOLID-STATE CIRCUIT BREAKER (SSCB)
Semiconductor switches using thyristors, gate turnoff thyristors (GTOs), insulated gate bipolar transistors (IGBTs), and integrated gate-commutate thyristors (IGCTs) are used as DCCB for fast-time response operation.Using a thyristor with low conduction loss minimizes the cost of SSCB.Figures 1(d) and 1(e) show a conventional bidirectional solid-state DC circuit breaker using IGCTs and IGBTs [19], [20].At ideal conditions, the current flows through the semiconductor device to the load, and when a fault occurs, the fault sensor detects the fault and commutates to turn off.Bidirectional solid-state DC circuit breaker using IGCT.(c).Bidirectional solid-state DC circuit breaker using IGBT [18].(e).Design of classical Z-source breaker [23].(f).Proactive hybrid circuit breaker [12].
The semiconductor device turns off and opens the circuit.The varistor connected across the semiconductor dampens the breaker's reverse fault current [20], [21].Though the SSCB is proven to have an ultrafast operation, minimum turnoff time, and fast fault current interruption, they are expensive and have high on-state losses and power loss.

D. Z-SOURCE CIRCUIT BREAKER (ZSCB)
A new breaker topology is introduced with a critical feature such as natural commutation, auto-disconnect of load due to fault with the primary control circuit, isolation of the fault to source, highly coordinated, fault limiting ability with the bidirectional operation will interrupt the DC power concerning a fault.An L-C resonant circuit earlier connected in the inverter input circuit, with further development is used in the breaker.The first introduced series-connected impedance based breaker design is considered the classical Z-source breaker model [12], [22], [23] as depicted in figure 1(e).Based on circuit components Z-source breaker design, is sub-classified into series ZSCB, parallel ZSCB and crossed ZSCB.Z-source DCCB is highly reliable, with fast response and less fault interruption time, isolating fault by natural commutation at critical fault conditions.It is evident that the Z-source breaker effectively acts only for large fault transients.

E. HYBRID CIRCUIT BREAKER (HCB)
A hybrid circuit breaker (HCB) is a new topology in CB's, combining both the MCB and the SSCB.Hence, when the solid-state DC circuit breaker and mechanical switch are integrated, it results in a fast and effective solution.Few upper 145044 VOLUME 11, 2023 Authorized licensed use limited to the terms of the applicable license agreement with IEEE.Restrictions apply.
hands of HCBs are low power loss, fast response and absence of arc at the mechanical contacts [24], [25].
Figure 1(f) shows the Conceptual design circuit of a proactive hybrid circuit breaker.There are three branches connected in parallel in the proactive hybrid circuit breaker circuit.They are the main semiconductor-based circuit breaker (MB) and semiconductor load commutation switch (LCS) connected in series with an ultra-fast disconnector (UFD) and MOV.Unlike the MB branch, the current will flow through the LCS and the UFD during regular operation.The LCS will open instantly during a fault, and the current will be commutated to the MB branch.Following the UFD will operate within 2 ms, isolating the LCS from the faulted section; thus, the MB will break the current.The SSCB portion of the HCB makes extensive use of semiconductor devices such as IGBT, IGCT, and GTOs [26], [27], [28].In recent times, third-generation wideband gap semiconductors based on silicon carbide and gallium nitrate, such as IGCT and Metal Semiconductor Field Effect Transistor (MESFET), have been employed in HCB [31], [32].These semiconductor-based HCBs are preferable than others due to their rapid switching speed and improved performance at greater temperatures.

F. FAULT CURRENT LIMITER (FCL)
Fault current limiter (FCL) aids in limiting the uninterrupted fault current to the load; it is classified as high-temperature superconducting FCL and solid-state FCL.High-temperature superconducting (HTS) FCLs minimize fault currents by integrating impedance into the fault current path.The short circuit current rises during the fault period, and the solid-state switch in the fault current limiter turns ON & OFF at very high speed.FCL limits short circuit current by adjusting its turn-on and turn-off time [31], [32].SFCL not only suppresses fault current but also compensates for the bus voltage sag [33].
Superconducting Fault Current Limiter (SFCL) limits the fault current before it reaches the first cycle.Researchers prioritize the location where SFCL will be commutated in the circuit to gain higher efficiency.A significant advantage of SFCL is that it is competent to limit fault current before it exceeds the threshold value [34].The FCL responds quickly, no control strategies are required, reduces thermal and mechanical stresses and improves the switching equipment's life span.In addition, it improves power quality, thereby reducing voltage sag and swell during faults.However, they require adequate cooling provisions and need attention to thermal instabilities.

III. CLASSIFICATION OF IMPEDANCE BASED DC CIRCUIT BREAKER
Inspired from various impedance-based power converter topologies, the application of impedance-based circuit breakers is developed by varying or rearranging the resonance components in the original Z source network to overcome the traditional solid-state DC circuit breaker [50].Discusses different power converter topologies; generally, ZCB can be categorized as inductor-based and coupled inductor-based, depending on its topological identification.

A. INDUCTOR BASED DC CIRCUIT BREAKER 1) Z-SOURCE CIRCUIT BREAKER
Applying an impedance-source network in the inverter provides buck and boost operation between the source and the inverter; this motivates the application of an impedance-source network in the DC circuit breaker.In [23], a ZSCB design is proposed initially for unidirectional DCCB applications and is simulated using Matlab.Figure 1 d design from [24, 51 and 52] is considered the classical Z-source circuit breaker model; it uses SCR as the primary switching element series to a crossed l-c source resonant circuit with damping resistance and diode.At a fault instance at the load end of the ZSCB, the fault current will flow through the crossed capacitance to the impedance circuit and force the SCR to reverse commutate, and the SCR gate voltage is maintained at zero by an external circuit.The two series LC branch connected with the fault region starts resonance to supply the fault.The source is isolated from the fault, resulting in reduced fault impedance.By Kirchhoff's voltage law, when the voltage across the capacitor and inductor becomes equal, the output voltage to the load becomes zero.In [52], a parallel Z-source connection proposed in which the Z-source is inline with the transmission; the CB shares the common ground connection of the source In [53], a modified ZSCB is proposed based on the Classical ZSCB, introducing unidirectional and bidirectional protection for medium voltage DC ship power systems.The CB proposed is considered to differentiate and identify fault from transients in load, achieved by modifying the classical design by adding a resistor in the crossed Z source path along with a snubber-type circuit in the load.This addition serves the purpose of reducing the harmonics in output, and it also prevents CB from false tripping for transients in load.A simulated modified bidirectional CB is applied on the star and ring-connected DC bus system; external breaker coordination is used to limit auxiliary breakers to turn off.A new Unidirectional ZSCB is proposed in [54]; the configuration resembles an H bridge with two pairs of LC filters connected parallel to an SCR.The unbalanced passive elements in the circuit make the step response critical, so the selection of symmetrical components makes the architecture more complex.

2) SERIES Z-SOURCE CIRCUIT BREAKER
Even though the classical model satisfies the purpose of a circuit breaker by isolating the fault from the source, the frequency response is abominable due to harmonics.The previously proposed parallel z source topology allows a common ground path; since the capacitors are in line with the source, the impact of fault current will be enormous [55].The Z-source series circuit breaker (ZSCB) is introduced by modifying the classical Z-source breaker design to overcome this issue by providing a common path to ground the circuit breaker, as given in Figure 2(a).
In [39] and [56], two Series Z Source circuit breaker (SZSCB) designs are proposed by adding capacitors in parallel to the source as a current divider.Current resistors or inductors are fault limiters to protect this capacitor from high faults.The circuit design with a fault limiter resistor and an inductor connected along with the capacitor were tested, and the inductor's performance was successful.In [57], two modified bidirectional SZCB are designed and tested; the simulated and hardware results are compared.The findings show that this model cannot detect faults due to small transients and steady-state overload conditions.Similarly, in [55], a new bidirectional series ZSCB is presented with a fault current limiter and manual tripping circuit; it can limit fault current, interrupt steady-state current and control the direction of power flow.
The source-connected capacitor is parallel to the ground to reduce the fault current and provide a common ground path [40].During a fault, the SCR turns off to form a series LC connection, and the capacitor will supply the fault current instead of the source.The designed SZSCB can act autonomously to protect the system only based on the fault current magnitude.To provide different triggering schemes for protection, manual tripping of the Z-source breaker is introduced in [58].By adding a semi-controlled device in the breaker, manual tripping is initiated, and an artificial fault current with a large magnitude can be induced comparatively with less loss than an SCR in the conduction path.A brief comparison of bidirectional SZSCB proposed in [23] and [58] with the new design presented in [59] states that, while commutation of thyristor, a spike in current may appear due to reverse recovery.With this current spike in input, the coordination of the circuit breaker might be affected.The proposed design restricts the spike current in input, and it provides a reverse voltage equal to the source voltage to increase the turn-off time of the thyristor.A setback of the proposed design is during interruption of a fault occurring in the load end; a portion of the fault current might reflect toward the source.There are issues involved in SZSCB; an undesirable flow of power and a negative flow of current in the load will occur during the opening and reclosure of the SZSCB.
The proposed SZSCB design in [60], with a parallel snubber circuit and an additional two IGBT's, assists in the seamless operation of the opening and reclosure of the CB.The mutual assistance of both the IGBT's avoids dissipated power and reverses power flow.Still, compared with other designs, the power loss will increase due to additional power semiconductor devices.In [61], the proposed modified SZSCB with an additional impedance source shows reduced fault clearing time than the coupled ZSCB, parallel ZSCB and other SZSCB topologies.

B. COUPLED INDUCTOR BASED DC CIRCUIT BREAKER
The applications of Z-source breakers in the DC bus system led to research on a more sophisticated and compact design [62].Introduces coupled inductor for the application of impedance source in DC circuit breaker as given in figure 4 a; with this implementation, the size of the inductor is fairly reduced, and the quantity of the passive components is minimal.The following section briefs the different coupled inductor topologies used for DC circuit breakers.

1) COUPLED INDUCTOR CIRCUIT BREAKER
The autonomous and rapid operation of the Z source circuit breakers makes it desirable for DC protection, leading to advancement by creating a Coupled inductor circuit breaker.In [63], they proposed coupled inductor CB circuits for unidirectional protection.Rather than monitoring the current flowing in the main path, the proposed circuit measures the fault current between the added capacitor and load in the short path.At steady-state operation, shown in Figure 3(a), the current flows from the source through the SCR and the coupled inductor to the load.If a fault occurs in the load end, the fault current flows through the capacitor and secondary winding of the coupled inductor; the fault current, followed by the primary winding, turns the SCR to off state, as shown in Figure 3(b).The modified proposed circuit is practically tested for medium DC voltage applications, and the inductance leakage effect of source impedance is considered during testing.Added resistor and diode across the short path capacitor enhances charging the capacitor, and the additional switch S2 acts as a manual switch to turn off the CB.
Improved to the previous circuit, in [64], a bidirectional coupled inductor CB is proposed, and it is tested using simulation tools for a Ring DC bus microgrid system.For the designed ring bus microgrid, different control schemes to control multiple CB's is tested and analysed.The 145046 VOLUME 11, 2023 Authorized licensed use limited to the terms of the applicable license agreement with IEEE.Restrictions apply.proposed independent control, paired control scheme, and central control scheme are tested.The manual switch control provided continuous operation without creating significant disturbances, and the proposed paired control scheme with some limitations does offer a proper operational scheme.The comparison study of a novel coupled inductor circuit breaker with a single inductor circuit breaker conducted in [65], states the size of inductor is larger than the ZSCB with a reduced fault peak current.

2) T-Z SOURCE CIRCUIT BREAKER
Based on the T-source inverter and Trans-Z source inverter, a novel T-source circuit breaker is proposed in [66].This proposed CB overcomes constraints due to the fault current flow to the source, common ground and input harmonic resonance of ZSCB.By varying the transformer's turn ratio, the current gain of the circuit breaker can be determined.The circuit comprises an SCR followed by two winding coupled transformers and a capacitor that resembles a T-shape network, as in Figure 3(c) the current flows from the SCR and the transformer's primary to the load at normal conditions.
145048 VOLUME 11, 2023 Authorized licensed use limited to the terms of the applicable license agreement with IEEE.Restrictions apply.
When a fault occurs at the load end, fault current flows from the capacitor to the secondary winding of the transformer.If the fault current reflected to the primary winding exceeds the source current, SCR commutates to turn off state, isolating the fault reaching the source as given in figure 3(d) [67].Proposes a bidirectional T-source circuit breaker based on the previous model [66], and the proposed model could successfully interfere with short circuit faults in bidirectional load flow.The results show that the SCR current naturally becomes zero through the coupling T-source network and removes the short-circuit current.Recent study proposes an interesting combination of a T-source circuit breaker with a shunt and series compensator to overcome grid transients [37].The proposed model achieves to provide series voltage and shunt current compensation for small signal and large signal stability for a rated system capacity of 5kW, 270V system.

3) Y-Z SOURCE CIRCUIT BREAKER
Bidirectional protection using ZSCB and Coupled inductor circuit breaker requires four inductors of two transformers to achieve bidirectional power flow and interruption.The novel Y-source circuit breaker requires only a three-winding transformer to achieve bidirectional protection [68].The source side winding is considered T1, and the load side winding with reverse power flow is T2, and both share the secondary winding L2 connected series with a capacitor, as given in Figure 3(e).At steady-state conditions, current flows through the primary winding to the load and no current flows through the secondary winding L2.When a fault occurs at the load side, the discharge current of the capacitor flows through the secondary winding, as in Figure (f).Due to the mutual inductance, the reverse current flowing through the primary will lead to the source current, which force commutes the SCR.In [68], the minimum value for the coupling level of the transformer and the fault conductance to interrupt the fault is suggested.The proposed model is simulated and tested for various faults in a 12-bus 2.5kV microgrid system, and their ability for sequential operation is verified.
In [69] a new unidirectional YZSCB is proposed with a wideband gap IGCT as the semiconductor switching device for Nasa N3-X space aircraft application.Where the proposed breaker has the capacity to limit the fault peak current of 2031A around 20µs with efficiency around 99%.

4) O-Z SOURCE CIRCUIT BREAKER
The O-Z Source circuit breaker (OZSCB) proposed design in [71] is uncomplicated with limited components compared with other Bidirectional CB, as shown in Figure 4 (g).The performance of the OZSCB is tested without a snubber circuit and with MOV and damping resistor diode during fault conditions, as in Figure 4(h).Damping resistor and diode application are effective for resonance due to the inductors, while MOV is more effective in damping resonance due to the grid and source inductance.A new conception of equivalent capacitance is introduced in [70] to determine the coupled inductor-based breaker capacitance for determining the minimum fault ramp rate.As a result, autonomous fault interruption, symmetrical configurable fault current thresholds and common grounding are achieved as benefits, but the reflected fault current source is only reduced but not eliminated.A modified OZSCB proposed in [71] claims to be a more efficient breaker than the classical OZSCB breaker by varying the current direction of the inductor terminal by achieving a lower starting current than the existing models.

5) -Z SOURCE CIRCUIT BREAKER
The proposed model in [72] and [73] offers a compact and better protection device with no reverse flow current to the source, as shown in Figure 3(i).Based on the trans-Z source inverter topology, the Ã-Z source circuit breaker ( ZSCB) protects from instantaneous and overload step faults of Uni & Bidirectional applications.The fault interruption principle is different in this model; during the fault, the forward voltage experienced by N1 induces a positive voltage across N2.The previously charged capacitor at steady-state mode will discharge to commutate the SCR off, as shown in Figure 3(j).After commutation, resonance starts between the breaker's impedance network and the fault path.SCR remains turned off until the N1 voltage becomes negative and the snubber dampens dissipated energy.For fast discharging of the capacitor current, the turns ratio of the transformer needs to be greater than one, and the SCR with a high voltage rating is required.

IV. COMPARISON OF IMPEDANCE BASED SOURCE CIRCUIT BREAKERS
Table 2 compares different ZSCB topologies, features and their intended applications.The motivation driven by the advancement of different topologies is to reduce the passive and switching components in the circuit, reduce the voltage stress on the switching device, reduce the power loss, and improve the system's reliability.Different topology modifications have enhanced features from the traditional model, like the proposed modified SZCB in [53], which has limited the negative fault current flow.In addition to this comparison, the defined Minimum fault ramp rate of different topologies is given in Table 3 to simplify the application preference of the CB.In [71], the minimum value of the capacitor in the circuit breaker to be considered for OZSCB and ZSCB topologies is mentioned for the modelling of the CB.s Considering that the load resistance value RL is 30 ohms and the load capacitor value CL is 480µF, the Kmin values for different breaker topologies are analysed from the defined equations in Table 3.And the analysed minimum fault ramp rate value Kmin for different breaker topologies, as in Figure 4(c), it is preferred that SZSCB from [47] has the least minimum fault ramp rate compared to other topologies.
Simulink and carried loop testing in Opal RT OP4500 to compare the breaker topologies.Figures 4(a  interruption and breaker reclosing.Fault analysis for Line -Line fault is carried out in this study; at 5 seconds, a fault is applied at the load end for 0.5ms.The auto reclosing of SZSCB inhibits ample delay time, but it is rapid in fault interruption due to less minimum fault ramp rate.In the case of TZSCB and YZSCB, the time to interrupt the fault is significant, and the time to auto-reclose is less.From the comparison of all the listed breakers, SCB does rapid fault interruption with less time taken to auto-reclose.The fault interrupting operation and auto reclosing period varies based on the Kmin values.Also, if the LC values are not adequately designed based on Kmin, the time taken for fault interruption and auto reclosing may vary, resulting in a delayed response. a proper design of L&C is required based on the operating voltage and considering the Kmin value for the breaker to work efficiently and reliably.Figure 5(a) depicts the software in loop testing carried out in Opal RT OP4500 kit which provides the real time simulation results using FPGA processor.For real time analysis, a solar panel installed in smart grid laboratory with the technical specifications as mentioned above in table 4 is considered as input.With a resistive load of 30 the SCB breaker's fault interruption and reclosing capability is tested, by running a MATLAB Simulink model of SCB in Opal RT.The results are verified through analog to digital module of the DSO.A Line -Line fault is analyzed by applying a fault for a period of 5 sec, where the SCB breaker takes 250 µs to interrupt the fault with no reflecting fault current to 145052 VOLUME 11, 2023 Authorized licensed use limited to the terms of the applicable license agreement with IEEE.Restrictions apply.the source.The voltage characteristics of the breaker to reach zero during fault interruption is shown in figure 5(b).And the residual voltage and the voltage at the breaker terminal where the fault is interrupted is given in figure 5(c).The figure 5(d) gives the breaker interrupting voltage with respect to SCR voltage where the SCR is tripped exactly at the instance of fault which proves the occurrence of natural commutation.Figure 5(e) shows the reclosing voltage of breaker terminal and the inductor voltage after the breaker is reclosed.The existence of voltage spike in breaker terminal is due to the switching voltage stress in the thyristor at the moment of reclosing the breaker.

V. CONCLUSION
This literature presents the different protective devices available for DC protection and the Impedance source breaker topology for DC microgrid application.Impedance-source converter topologies have inspired the development of circuit breakers to overcome protection issues in DC networks.Overcoming the limitations of the traditional ZSCB, many converter topologies are applied for breaker operations, and several converter topologies like distributed Z source, embedded Z source, TSTS Z source, and improved Trans Z source are yet to be designed, tested and applied for the breaker application.The existing breaker topology can be modified further to develop better-performing protection devices.Z-Source Breakers represent a critical innovation in the field of electrical engineering, with the capacity to revolutionize power system protection, energy management, and grid integration.Their importance in enhancing the resilience and adaptability of power systems in an era of renewable energy and evolving energy demands cannot be understated.As we continue to advance in the pursuit of sustainable and reliable energy solutions, Z-Source Breakers will undoubtedly remain at the forefront of this transformative journey.Further the breaker can be enhanced with wideband semiconductor devices for better performance in high voltage applications.Along with implementing intelligent electronic instruments for control operation, efficient and reliable synchronized operation of breakers in microgrids can be achieved.This study was conducted on a real-time simulator opal RT platform licensed version in the smart grid laboratory, VIT Chennai.

FIGURE 4 .
FIGURE 4. (a).Load voltage characteristics of different Z source circuit breakers topologies.(b).Load current characteristics of different Z source circuit breakers topologies.(c) Calculation of minimum fault ramp rate of different impedance based circuit breaker topologies.
) and 4(b) exhibit the load current I L and voltage V L characteristics of the four topologies mentioned above four topologies during fault

TABLE 1 .
Literature review of various dc protective devices.Authorized licensed use limited to the terms of the applicable license agreement with IEEE.Restrictions apply.

TABLE 1 .
(Continued.) Literature review of various dc protective devices.

TABLE 2 .
Comparison of impedance based circuit breaker topologies

TABLE 3 .
Minimum fault ramp rate equation of various breaker topologies.

TABLE 4 .
Technical specifications of the solar PV.