Performance Optimization Analysis of Hybrid Excitation Generator with the Electromagnetic Rotor and Embedded Permanent Magnet Rotor for Vehicle

To solve the problems of the non-adjustable magnetic field of the permanent magnet (PM) generator, large excitation loss and high failure rate of electric excitation generator, this paper proposes a parallel electromagnetic and PM hybrid excitation generator (HEG). The designed generator adopts a high power density PM rotor composed of built-in tangential PM steel and V-shaped PM steel and a salient-pole electromagnetic rotor (EMR) with short axial length, less electromagnetic loss, simple and reliable structure. By adjusting the axial length of two rotors and the size of magnetomotive force sources, the generator can adjust the rotor power distribution to meet various power requirements. Meanwhile, the HEG can adjust the electromagnetic magnetic field (EMMF) by adjusting the size and direction of the excitation current, and then can adjust the size of the synthetic magnetic field to achieve the purpose of stabilizing output voltage. In this paper, the magnetic circuit model of the HEG is established by using the equivalent magnetic circuit (EMC) method, and the rationality of the designed magnetic circuit is verified and analyzed by the finite element method. The prototype is trial-manufactured and tested, and the results show that the designed HEG has a wide magnetic regulation range, stable output voltage, and good output performance.


I. INTRODUCTION
Hybrid excitation generator (HEG) for vehicle not only has the characteristics of high efficiency and high power density of the permanent magnet (PM) generator but also has the flexible magnetic field regulation of the electric excitation generator [1][2][3][4][5] . Moreover, it can effectively solve the problem that the output voltage is difficult to stabilize due to the variation of the operating condition of the generator, and it has become the development direction of vehicle generators in the future [6,7] . For the hybrid excitation power generation system, many researchers have carried out a lot of research. And the hybrid excitation topology mainly includes three types: PM steel in stator, PM steel in rotor, and parallel structure [8][9][10] . Most generator types of "PM steel in stator" are flux-switching machines. In this structure, the stator is usually composed of several toothed blocks to form a circular ring, the PM steel is embedded in the middle of the connection of two stator blocks, and the electromagnetic winding (EMW) is wound on the outside of the PM steel or on the adjacent stator teeth to form a hybrid excitation structure [11][12][13][14] . For example, reference [15] proposed a C-type hybrid excitation flux-switching machine. Its stator was spliced by C-type stator blocks, the PM steel was embedded in the splice, and the EMW was wound on the outside of the PM steel. Reference [16] proposed an E-type hybrid excitation flux-switching motor, which can reduce the PM steel by half compared with the C-type structure. The type of " PM steel in rotor " usually designs PM steel inside the rotor core and winds EMW around the rotor pole or the stator [17][18][19] . For example, reference [20] proposed a HEG with an adjustable magnetic field. Its EMW was axially wound on the left and right sides of the stator, and the PM steel was tangentially embedded in the rotor core. A salient pole hybrid excitation synchronous generator was proposed in [21]. Its rotor was composed of two salient poles and four PM poles. The EMW was wound on the salient pole, and the PM steel was embedded in the PM pole. The type of "parallel structure" is usually designed with its PM rotor and electromagnetic rotor (EMR) in parallel and coaxial, and the magnetic field generated by them is synthesized in the main air gap [22][23][24] . For example, reference [25] proposed a hybrid excitation motor with claw-pole rotor and surface-mounted PM rotor in parallel. In this structure, the EMW is axially wound inside of the inner end of the rotor, and the PM steel is attached to both sides of the claw pole to form the outer end of the rotor. Reference [26] proposed a hybrid excitation motor with a magnetic bypass structure. In this motor, the EMW is on the outside of the stator, and the electromagnetic magnetic field (EMMF) is transmitted to the stator through a special magnetic conductor.
To sum up, the EMMF of the type of "PM steel in stator" usually passes through the PM steel, which has some problems such as large magnetoresistance of the EMMF and irreversible demagnetization of the PM steel. Whereas, the circuit of EMMF in the type of "PM steel in rotor" is usually long and has many additional air gaps, which can lead to the low magnetic field regulation efficiency. The EMMF and PM magnetic field of the "parallel structure" are relatively independent and do not affect each other. The efficiency of magnetic field regulation is high, but the axial length of the rotor increases, and the volume of HEG is relatively large [27,28] . Through comprehensive comparison, the "parallel structure" has the advantages of small excitation loss and good magnetic regulation characteristics, and it has excellent development potential. Therefore, the paper proposes a parallel structure HEG. The structure adopts a new type of combined-pole PM rotor with a pair of V-shaped PM steel in the middle of two built-in tangential PM steels. The rotor magnetic field of each pole of this design jointly provided by multiple PM steels, which has high magnetic field strength and high power density, and can effectively avoid the depression of the induced electromotive force' peak caused by the weak magnetic field in the center of the rotor pole of single PM steel structure. The EMR adopts a salient-pole structure with simple structure and short axial length. Compared with the traditional claw-pole structure, the excess space of the axial EMW is much less than the length of the yoke of the claw pole. Therefore, the effective axial length of the synthetic rotor is reduced, which can effectively reduce the effective axial length of the stator core and armature winding, and can effectively reduce copper consumption. The performance comparison between the designed HEG and the existing parallel HEG is shown in Table 1. Claw-pole and built-in PM HEG [29] Built-in tangential PM rotor Claw-pole EMR One stator core and one set of armature windings The power adjustment range is extensive, and the power is easy to distribute.
The claw pole yoke located in the center of the two rotors occupies the effective length of the stator.
Claw-pole and surface mounted PM HEG [25] The PM steel is pasted on the brackets on both sides of claw.
Variable clawpole EMR with claw separated from yoke One stator core and one set of armature windings The space on both sides of the claw pole is effectively used, and the volume of the HEG is small.
The PM magnetic field is weak, the structure is complex, and the structural strength is low.
Hybrid excitation power generation with bypass magnetic circuit [26] Built-in tangential PM rotor Bypass EMR with variable claw-pole magnetic bridge One stator core and one set of armature windings The magnetic bridge is used to transfer the EMMF to reduce the effective axial length.
Two air gaps are added in the EMR, the magnetic circuit of EMMF is long, and the magnetic resistance increases.
Flux modulated HEG [30][31][32][33] Surfacemounted PM rotor Magnetic flux modulation electromagnetic part Parallel double stator and parallel double armature windings The power adjustment range is extensive, and the power is easy to distribute.
The combination of two types of power generation forms has a complex structure and complex control system.
PM-Inductor HEG [34] Surfacemounted PM rotor Inductor power generation part One stator core and one set of armature windings The power adjustment range is extensive, and the power is easy to distribute.
The axial length of the generator is greatly increased, and the efficiency of the inductive power generation part is low.

The HEG designed in this paper
Buil-in combined-pole PM rotor Salient-pole EMR One stator core and one set of armature windings The structure is simple and reliable, the power adjustment range is extensive, and the power is easy to distribute.
The axial length is the sum of the axial lengths of two rotors.
It can be seen from Table 1 that the PM part of parallel HEG mainly adopts the surface-mounted structure or built-in tangential PM rotor. For the surface-mounted PM rotor, the rotation of the rotor of high-speed generator is easy to cause the PM steel to fall off due to centrifugal force. Moreover, since the PM steel faces the main air gap directly, the armature reaction magnetic field passes through it directly, which is easy to cause the demagnetization of PM steel under high-power conditions. For the built-in tangential PM rotor, the PM steel is built on both sides of the rotor magnetic pole. Based on the principle of minimum magnetic circuit, the magnetic field generated by PM steel is mostly distributed on both sides of the PM steel, that is, on both sides of the rotor magnetic pole. It can lead to the weak magnetic field in the center of the rotor magnetic pole, uneven magnetic field distribution in the main air gap, and depression of the induced electromotive force' peak [35][36][37] . In order to solve these problems, a combined-pole PM rotor is proposed in this paper. Compared with the conventional tangential PM rotor, two V-shaped PM steels are added in the middle of the two tangential PM steels. This design has a significant gathering effect of magnetic field and high rotor power density compared with the conventional rotor. Table 1 also shows that the electromagnetic part of parallel HEG mainly adopts claw-pole structure, variable claw-pole structure, flux modulation generator, or inductor generator. Among them, the effective axial length of the conventional claw pole is in the middle of the claw, and there is an extended length of claw pole' yoke on both sides. Therefore, in the middle of the two parallel rotors, the yoke of the claw pole occupies part of the axial length, which increases the volume and armature winding loss of the HEG. The variable claw-pole structure usually adopts a special magnetic conduction structure to introduce the PM magnetic field or the EMMF into the main air gap. The magnetic circuit of this kind of structure is usually long, and there are many additional air gaps. Moreover, the magnetic conduction structure distributed on both sides of the axial direction also increases the volume of the HEG. And the HEG using flux modulation generator and inductor generator instead of electromagnetic part mainly adopts double stator and double armature winding structure, which leads to the complexity of its structure and control system. Considering these problems, the salient-pole EMR is adopted in this paper. The rotor has a simple structure, flexible axial length adjustment, no additional air gap, and small magnetoresistance. Meanwhile, the axial length of the EMW is short, which does not occupy the volume of the HEG.
Compared with the parallel HEG currently developed, the designed HEG has significant advantages and better output performance. Meanwhile, the HEG can adjust the power distribution of two rotors by adjusting the axial length and magnetic potential source of the PM rotor and the EMR, so as to meet a variety of power requirements. From the above, the designed HEG has high research value.
The rest of this paper is organized as follows. Section II analyzes the magnetic field of the HEG, establishes the equivalent magnetic circuit (EMC) model, and carries out analytical calculation. Section Ⅲ establishes the finite element analysis model of the HEG and solves its electromagnetic parameters to compare and analyze the effectiveness of the EMC method. Meanwhile, the magnetic field distribution and magnetic field regulation characteristics are analyzed to verify the rationality of the magnetic field design. Section Ⅳ uses the finite element method and prototype test method to analyze the output performance and application performance of the designed HEG. Finally, conclusions are drawn in Section V.

II. STRUCTURE AND MAGNETIC CIRCUIT MODEL OF HEG
The rotor of HEG is composed of salient-pole EMR and combined-pole PM rotor. Two rotors are coaxial and installed in parallel. The center of the two rotors is designed with magnetic isolation bushing, which can not only reduce axial leakage magnetic flux but also reserve space for EMW of EMR. The structure of HEG is shown in Fig. 1, and the main technical parameters of the generator are shown in Table 2   As shown in Fig. 1, the PM rotor of HEG is a combinedpole structure and composed of the tangential PM steel and V-shaped PM steel. In order to reduce the leakage flux, a semicircular air gap is set at the outer end of the tangential PM steel, a triangular air gap is set at its inner end, a wedgeshaped air gap is set at the outer end of the V-shaped PM steel, and a through V-shaped air gap is set at the inside of two V-shaped PM steels.
For the designed combined-pole PM rotor, the magnetic field of the rotor is mainly based on the magnetic field provided by the tangential PM steel, and the magnetic field of the V-shaped PM steel plays an auxiliary role. The magnetic flux of each pole is jointly provided by multiple PM steels, and its magnetic circuit analysis diagram is shown in Fig  Under one magnetic pole of PM rotor, the main magnetic circuit of PM steel is: N pole of tangential PM steel → rotor core → air gap → stator core → air gap → rotor core → S pole of tangential PM steel → rotor core → N pole of tangential PM steel. As shown in the main magnetic circuit 1 in Fig. 2. Meanwhile, the V-shaped PM steel is built in the center of the rotor pole, and the polarity of it is opposite to that of tangential PM steel under one rotor pole. Therefore most of the magnetic field generated by tangential PM steel will go to the main air gap pass through V-shaped PM steel directly. This part of the magnetic circuit is: N pole of tangential PM steel → rotor core → S pole of V-shaped PM steel → air gap → stator core → air gap → N pole of V-shaped PM steel → rotor core → S pole of tangential PM steel → rotor core → N pole of tangential PM steel. It can be seen in the main magnetic circuit 2 in Fig. 3.
In order to simplify the analysis, the two main magnetic circuits are calculated separately, and the total magnetic flux of each pole is calculated as the sum of the magnetic flux of main magnetic circuit 1 and main magnetic circuit 2. Among them, the tangential PM steel provides the magnetic field in two main magnetic circuits, respectively. Therefore, its magnetomotive force and internal magnetic conductivity in each main magnetic circuit are calculated by half. Moreover, since the leakage magnetic circuit can be calculated only once, the leakage fluxes at the inner end and the outer end of the tangential PM steel are calculated in the main magnetic circuit 1, and the remaining leakage fluxes are calculated in the main magnetic circuit 2. Based on this, the EMC diagrams of main magnetic circuit 1 and main magnetic circuit 2 of PM rotor are shown in Fig. 3. To simplify the analysis, the permeances of the leakage magnetic circuit at the inner end and outer end of the tangential PM steel are combined into one magnetic circuit through the parallel formula. The combined total leakage magnetic flux is recorded as tr  , and the combined permeance is recorded as tr Similarly, the permeances of the leakage magnetic circuit at the inner end and outer end of V-shaped PM steel are also calculated together. The combined total leakage magnetic flux is recorded as cr  , and the combined permeance is recorded as cr G , where 1 2 cr cr cr The simplified EMC models of main magnetic circuit 1 and main magnetic circuit 2 are shown in Fig. 4. The analytical equations of the simplified equivalent models of main magnetic circuit 1 and main magnetic circuit 2 can be solved by the node method of the magnetic circuit, respectively: By solving the two equivalent models respectively, the analytical expressions of main magnetic flux and leakage magnetic flux of each part can be obtained as follows:   For the magnetic field of the PM rotor, the effective magnetic flux  In equations (1) and (2), the magnetomotive force and internal permeance of tangential PM steel and V-shaped PM steel can be calculated according to the above formula, and the other permeance and leakage permeance can be calculated as: where r G is the permeance of magnetic circuit in rotor core, The direction of the magnetic circuit of the EMR changes with the direction of the excitation current, and the main magnetic circuit is: the pole body of N pole → air gap → stator core → air gap → the pole body of S pole → the yoke of rotor → the pole body of N pole. The leakage flux is mainly distributed between the two magnetic poles. And the magnetic circuit of the EMR is shown in Fig. 5.

Main magnetic circuit
Leakage magnetic circuit

FIGURE 5. Magnetic circuit analysis diagram of EMR
According to the analysis of the magnetic circuit, the EMC diagram of the EMR is drawn and shown in Fig. 6.
In Fig. 6 Author Name: Preparation of Papers for IEEE Access (February 2017) VOLUME XX, 2017 8 The analytical expressions of magnetic flux obtained by solving the EMC model of the EMMF are as follows: Since the internal resistance of the EMW is very small, 1 em G is equivalent to 0, so it is ignored. The magnetomotive force generated by the EMW can be calculated as: where f I is the current of the EMW, and f N is the number of turns of the EMW. The leakage permeance stl G between the stator teeth is calculated as the leakage permeance with one tooth width and two slot widths, which can be calculated as: The synthetic magnetic field of the HEG is the synthesis of the PM magnetic field and the EMMF in the main air gap, and its EMC diagram is shown in Fig. 7  In Fig. 7, ar G is the leakage permeance between the PM rotor and the EMR. According to the EMC diagram, the total main magnetic flux of the HEG can be calculated as follows: The total coefficient of leakage magnetic flux of the HEG can be calculated as:

III. MAGNETIC FIELD SIMULATION ANALYSIS OF THE HEG
In order to analyze the output performance of the HEG, it's finite element model is established by using the finite element software, and is shown in Fig. 8. To solve the magnetic flux, the solving surfaces of the magnetic flux a-i are drawn and shown in Fig. 9. In Fig. 9, surface a, surface b, and surface c are used to solve the total magnetic flux generated by the tangential PM steel, the V-shaped PM steel, and the EMW respectively, surface d is used to solve the effective magnetic flux of per pole of the stator, surface e and surface f are used to solve the leakage magnetic flux at the outer end and the inner end of the tangential PM steel respectively, surface g and surface h are used to solve the leakage magnetic flux at the outer end and the inner end of the V-shaped PM steel respectively, and surface i is used to solve the leakage magnetic flux between two salient poles. Using the solving surfaces and the finite element model, we can calculate the magnetic flux of each part, and the result, compared with the EMC method, is shown in Table 3  TABLE Ⅲ CALCULATION As shown in Table 3, the magnetic flux of each part calculated by the EMC model is basically the same as that calculated by the finite element method, and the calculated leakage flux coefficient is 1.222, which is smaller than the result of the finite element method, but the result can prove that the EMC method is reasonable. Using the finite element model, the distribution of the magnetic field of the PM magnetic field and the EMMF are simulated and shown in Fig. 10.

The PM magnetic feild
The EMMF According to Fig. 10, the PM magnetic field is mainly based on the magnetic circuit 2. The leakage magnetic flux is mainly distributed at the ends of the tangential PM steel. Fig.  10 also shows that the distribution of magnetic field lines is the same as the analysis results of EMC, which can prove that the EMC design method is effective and is suitable for the design and analysis of hybrid excitation magnetic circuits.
The synthetic magnetic field of the HEG is mainly based on the PM magnetic field, which gives full play to the advantages of high magnetic field intensity and high power density of the PM rotor. Meanwhile, it will weaken the EMMF, reduce the excitation loss effectively and improve the output efficiency of the generator. The EMMF mainly plays a role in adjusting the size of the synthetic magnetic field and stabilizing the output voltage. The magnetic flux density vector diagram of the HEG under different excitation currents is simulated and shown in Fig. 11.  Fig. 11 shows that when the excitation current is positive, the direction of the EMMF is consistent with that of the PM magnetic field. Under this conduction, the EMMF plays the role of increasing the magnetic field, the synthetic magnetic field increases, and the output voltage of the generator increases too. When the excitation current is reversed, the direction of the EMMF is opposite to that of the PM magnetic field. Under this conduction, the EMMF plays the role of weakening the magnetic field, the synthetic magnetic field decreases, and the output voltage decreases too. It can also be seen in Fig. 11 that when the excitation current increases from 2A to 3A, the magnetic field intensity of the stator part corresponding to the EMR increases significantly, which shows that with the increase of the excitation current, the EMMF increases, and the increasing and weakening effect of the EMMF on the synthetic magnetic field increases. The diagram of the magnetic flux density of HEG under different excitation currents is shown in Fig. 12.

If=1A
If=2A If=3A If=4A It can be seen from Fig. 12 that with the increase of excitation current, the magnetic flux density of the stator part corresponding to the EMR increases, the magnetic flux density of the stator teeth and stator yoke can reach 1.6T, and the distribution of magnetic field become more uniform. And when the excitation current increases to 4A, the main magnetic circuit of the PM rotor, the EMR, and the stator core does not reach saturation, which indicates that the EMR can still work normally when the excitation current is large, it can complete the role of increasing and reducing magnetic field. Fig. 12 also shows that the saturation of the magnetic field mainly exists at both ends of the tangential PM steel and the outer end of the V-shaped PM steel, these two parts are the leakage magnetic circuit, and those parts can force the magnetic flux to the effective magnetic flux path, increase the magnetic field strength of the main magnetic circuit and reduce the leakage flux loss. From the above analysis, the magnetic field design of HEG is reasonable.

IV. OUTPUT PERFORMANCE ANALYSIS OF HEG
When the excitation current increases from 0A to 3A, and the interval is 1A, the speed of the generator increases from 500r/min to 4000r/min, and the step is 500r/min, the output voltage of the HEG is simulated and shown in Fig. 13.   13 shows that under the same speed, the output voltage of the HEG increases with the increase of the excitation current. And under the same excitation current, the output voltage increases almost linearly with the rise of the speed, which shows that the HEG has good regulation characteristics at different speeds. Set the generator speed is 3000r/min and the excitation current is 0A and 2A, respectively, the curve of output voltage with load current, namely external characteristic curve of the HEG, is simulated and shown in Fig. 14. Fig. 14 shows that when the generator operates with the load, the speed and excitation current remain unchanged, the output voltage of the generator decreases linearly with the increase of load current. Therefore, to maintain the stable output voltage, it is necessary to adjust the size and direction of the excitation current continuously. It can also be seen that under the rated load, when the excitation current is 0A and 2A, the output voltage is 10V and 29V, respectively. It shows that when the speed is 3000r/min, the excitation current of 2A can ensure that the generator output voltage reaches the rated voltage. The calculated power characteristic curves under different excitation currents are shown in Fig. 15.  Fig. 15 shows that when the speed is 3000r/min, and the excitation current is 0A, the peak output power is 420W, whereas when the excitation current of the HEG is 2A, the peak output power is 1156W. And under the rated load condition, the output power is 1100W, which means that the HEG can ensure the rated power output under the rated condition.
When the speed of HEG is 3000 r/min, change the generator load, and stabilize the output voltage at the rated voltage by adjusting the excitation current, the relationship of the excitation current and the load current, namely the regulation characteristics, can be obtained. And the regulation characteristic curves of HEG and electric excitation generator are simulated and compared as shown in Fig. 16. It can be seen from Fig. 16 that when the load current is small, the HEG needs to input reverse excitation current to weaken the air-gap magnetic field and maintain the output voltage at 28 V. With the increase of load current, to maintain the stability of output voltage, both HEG and electric excitation generator need to increase the excitation current, but the excitation current required by HEG is much less than that of electric excitation generator. Therefore, the HEG with low excitation current demand can avoid the problems of large excitation heating, large excitation loss, and the decline of output efficiency.
To verify the effectiveness of the simulation analysis, the prototype of the designed HEG is trial-manufactured, the test platform is built, and the prototype test is carried out. The main structural parameters of the HEG are shown in Table 4, and the prototype and test bench are shown in Fig. 17 and Fig.  18, respectively. a) The s tator The whole machine b) Under the rated speed condition of the generator, the noload output voltage of the prototype when the excitation current in different directions and sizes is tested, and the noload characteristic curve of the generator is obtained and shown in Fig. 19 with the simulation results. It can be seen from Fig. 19 that the change trend of the noload characteristic curve of the HEG obtained by prototype test and finite element analysis is consistent, and the values of test result are slightly smaller than the simulation result when the excitation current is large, but the maximum deviation between them is less than 5V, which proves that the simulation result of the HEG is effective. It can be seen that when the excitation current changes from -3A to 3 A, the output voltage of the generator increases almost linearly with the increase of excitation current, from 17V to 92V, whereas when the excitation current, with forward or reverse direction, is greater than 3A, the increasing and decreasing trend of the output voltage of the HEG decreases, at those time, the EMMF tends to be saturated and the regulation effect is weakened. Meanwhile, it shows that the HEG has a wide voltage regulation range, and the output voltage can change between 11V to 95V by changing the magnitude and direction of the excitation current.
When the speed of HEG is 3000 r/min, and the excitation current is 2A, the external characteristic of the HEG is tested and is shown in Fig.20 with the simulation result. It can be seen from Fig. 20 that the variation trend of the external characteristic curve of the HEG obtained by the prototype test and the simulation is consistent, and the deviation between them is more minor, which can verify the effectiveness of finite element analysis. Meanwhile, under the condition of constant generator speed and excitation current, the output voltage of the generator decreases almost linearly with the increase of load current, and the load current under rated load condition is 35.7A, and the output voltage can reach 28V. So, the generator can output rated voltage under rated working conditions.
When the speed of HEG is 3000 r/min, changing the load of the generator, and stabilizing the output voltage at the rated voltage by adjusting excitation current, the regulation characteristic curves can be obtained by the test and the simulation, as shown in Fig. 21.  Fig. 21 shows that when the generator load is 200W, the excitation current needs to be -0.6A. At this time, the direction of the EMMF is opposite to that of the PM magnetic field, the EMMF weakens the synthetic magnetic field to stabilize the output voltage at 28V. When the generator is under the rated load condition, the excitation current is 2.3A, the direction of the EMMF is the same as that of the PM magnetic field, the EMMF plays the role of increasing the synthetic magnetic field, and ensuring that the output voltage rises to 28V. Therefore, the stability of output voltage can be effectively guaranteed by changing the excitation current.
When the load power of the HEG is 980W, 1000W, and 1020W, respectively, the performance test of the HEG is carried out from low speed to high speed, and the results are shown in Table 5. It can be seen from Table 5 that when the generator speed changes from 2000 r/min to 4800 r/min and the load power changes from 980W to 1020W, the HEG can stabilize the output voltage between 26.3V and 28.6V, it means that the design of HEG is effective.

V. CONCLUSIONS
The paper proposes a HEG with salient-pole EMR and combined-pole PM rotor in parallel and coaxial. The generator is mainly composed of PM magnetic field and assisted by EMMF, so as to have the advantages of high power density, less electromagnetic loss, large magnetic field strength, and wide magnetic regulation range. The magnetic circuit models of the PM magnetic field, the EMMF, and the synthetic magnetic field are established by using the EMC method. And used this model, the magnetic flux of PM steel and the EMW, the leakage magnetic flux and the effective magnetic flux are calculated to get the leakage flux coefficient, and the result is 1.222. To verify the effectiveness of the EMC method, the finite element model is established and analyzed by finite element software. Meanwhile, the magnetic field regulation characteristic of the HEG is analyzed by the finite element model. It shows that changing the size and direction of excitation current can effectively change the size and direction of the EMMF and the size of the synthetic magnetic field, so as to achieve the purpose of stabilizing output voltage. The prototype is trialmanufactured and tested. And the results show that when the excitation current is from -3A to 3A, the output voltage of the designed HEG increases almost linearly from 15V to 90V, under the rated load condition, the output voltage can be stable at 28V, and the designed HEG has good voltage stabilizing performance.