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A HESM-Based Variable Frequency AC Starter-Generator System for Aircraft Applications Zhuoran Zhang , Senior Member, IEEE, Ye Liu , Student Member, IEEE, and Jincai Li , Student Member, IEEE
Abstract—With the development of more electric aircraft, higher demand for electrical energy is put forward in generation systems. The constant speed drive is eliminated in variable frequency ac (VFAC) generation systems, which makes integrated startergenerator (SG) can be realized. Considering the inherent defects of wound rotor synchronous SG systems, such as the complex starting excitation methods and rotating rectifiers, this paper proposes a VFAC SG system based on hybrid excitation synchronous machines (HESMs) for aircraft applications. The key technology of HESM-based VFAC SG system is to regulate the field current in such a way that three major modes of VFAC SG system operation for aircraft applications, namely, engine starting operation, transition mode, and generating operation, can be realized effectively. The simulation model of HESM-based VFAC SG system is built and analyzed. A prototype HESM-based VFAC SG system has been designed and developed for experimental verification. The starting operation, transition mode, and generating operation of the prototype HESM-based VFAC SG system are implemented. The feasibility of HESMs to VFAC SG system for safety-critical aircraft applications has been validated. Index Terms—Brushless machine, generation system, hybrid excitation synchronous machine, more electric aircraft, starter-generator.
I. INTRODUCTION P TO now, the power of traditional aircraft, initially generated by fuel, can be divided into two parts, the primary power, which is converted to propulsive power by the engine, and the secondary power, including mechanical power, hydraulic power, pneumatic power and electrical power [1]. On conventional aircraft, four kinds of secondary power, including electrical power, mechanical power, pneumatic power and hydraulic power, are miscellaneously distributed to supply all the on-board systems, including landing gear, braking and flight control, air conditioning, pressurization, de-icing, avionics and so on. As for pneumatic and hydraulic systems, they also have
U
Manuscript received December 29, 2017; revised July 25, 2018; accepted August 26, 2018. Date of publication August 30, 2018; date of current version November 21, 2018. This work was supported in part by the National Natural Science Foundation for Excellent Young Scholar of China under Award 51622704, in part by the Jiangsu Provincial Science Funds for Distinguished Young Scientists under Award BK20150033, and in part by the Fundamental Research Funds for the Central Universities under Grant NE2014102. Paper no. TEC-01027-2017. (Corresponding author: Zhuoran Zhang.) The Authors are with the Center for More-Electric-Aircraft Power System, College of Automation Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China (e-mail:,
[email protected];
[email protected];
[email protected]). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TEC.2018.2867906
a risk of leaks which are generally difficult to be located and accessed [2]. The characteristics of such secondary power configuration are summarized as following: 1) Complex power distribution system. 2) Low energy conversion efficiency. 3) Low reliability, difficult to maintain. Furthermore, future legislation with respect to climate change demands a radical change on the entire aircraft, as it is not sufficient to optimize the current aircraft sub-systems and components individually to achieve these goals [3]. In order to simplify the secondary power and improve reliability, the electrical power capacity is increased to replace the other three kinds of secondary power, defined as more electric aircraft (MEA). The MEA concept is based on utilizing electric power to drive aircraft subsystems which are driven by a combination of hydraulic, electric, pneumatic, and mechanical power transfer systems [4]. The whole power system is much simplified in MEA, which offers the following distinct advantages. 1) Reduction of aircraft weight. 2) Efficient energy management. 3) High reliability and maintenance. 4) Low operating costs. 5) Low environmental impact. On conventional aircraft, an additional starter is needed for engine start. After the engine starts, the generator supplies electrical power for onboard electric loads. With the increasing electrical power capacity in an MEA, it is possible to use the original electrical machine to start the engine, namely starter-generator (SG). On MEA, the SG operates as a motor in starting mode and operates as a generator in generating mode. The SG reduces the onboard weight and simplifies the structure of accessory gearbox. The ac power system is the most widely applied architecture for aircrafts. Because of constant speed drives (CSDs), the generator cannot operate as a starter to start the engine in constant speed constant frequency (CSCF) generation system. In variable speed constant frequency (VSCF) generation system and variable speed variable frequency (VSVF) generation system, the CSD is eliminated which makes it possible to realize SG system [5]. Compared with VSCF generation system, VSVF generation system is simpler, in which the electronics power converter is eliminated. VSVF generation system is a simple and reliable option at this stage. In order to reduce the weight of the aircraft generation system and increase the output power capacity, the requirement on the power density of the generator becomes higher [6]. Wound rotor synchronous machines (WRSMs) are the typical generator used
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ZHANG et al.: HESM-BASED VARIABLE FREQUENCY AC STARTER-GENERATOR SYSTEM FOR AIRCRAFT APPLICATIONS
Fig. 1.
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Diagram of VFAC SG system.
in aircraft applications so far. The power generation technology of WRSM is relatively mature. However, as a starter, the starting excitation methods of WRSM are complex. The rotating rectifier is adopted to realize brushless structure in WRSM. Due to the existence of rotating rectifier, the maximum rotor speed is restricted, and the reliability is decreased. As a promising candidate, the hybrid excitation synchronous machine (HESM) is of growing interest due to the prominent controllability of air-gap flux. Since the air-gap flux is produced by the permanent magnets and field windings, it can be weakened or strengthened by regulating the magnitude and direction of field current [7]–[10]. For the superiority regarding high power density and simple brushless structure, HESM possesses considerable applicability for aircraft generation systems by integrating the advantages of permanent magnet synchronous machine (PMSM) and WRSM. An HESM-based high voltage DC generation system for aircraft applications is proposed in [11] and optimized in [12]. Another SG system based on a high torque density HESM has been proposed for hybrid electric vehicles in [13]. As can be seen, many HESM topologies with high torque and power density have been proposed. However, most HESMs are not suitable for VFAC generation system in aircraft applications due to the a nonsinusoidal back EMF. The back EMF of HESM with magnetic shunting rotor in [14] is highly sinusoidal by avoiding axial flux in the stator core, which makes it suitable for AC SG system. Simple brushless structure without rotating rectifier enables the HESM to be suitable for high-speed operation. Compared to WRSM-based VFAC SG system, the starting control strategy of the HESM-based VFAC SG system is simple and easy to implement. This paper studies the applicability of an HESM with magnetic shunting rotor to a variable frequency AC (VFAC) SG system for safety-critical aircraft applications, which has been proposed and briefly introduced in [15]. The simulation model of HESM-based VFAC SG system is built and analyzed. A prototype HESM-based VFAC SG system has been designed and developed for experimental verification. The starting operation, transition mode and generating operation of the HESM-based VFAC SG system are completed in the experiment. The contribution of this paper is to propose a promising solution where an HESM replaces a WRSM as an SG in aircraft applications. II. VFAC SG SYSTEM CONFIGURATION AND OPERATION MODES As shown in Fig. 1, the VFAC SG system performs both engine starting and power generating for aircraft applications. The VFAC SG system operates at three major modes for aircraft power system.
Fig. 2.
Typical engine starting process.
Fig. 3.
Load torque and starting torque characteristics.
A. Mode I: Engine Starting Operation Fig. 2 shows the typical engine starting process. There is a minimum speed which the engine must attain before engine ignition n1 , namely light-up speed. As shown in Fig. 3, the speed n2 is named self-sustaining speed when the load torque is zero. In engine starting operation, the starting contactor (SC) is closed and the SG operates as a starter to drive the engine rotor. When the engine reaches the light-up speed, the engine begins igniting. Then the engine and the SG work together to accelerate the engine to a certain speed, namely cutoff speed. As a starter, the SG must meet the following two requirements. The output torque of SG must be larger than the maximum resistance moment of engine. The output power of SG must be large enough to accelerate the engine to the cutoff speed. B. Mode II: Transition Mode When the engine reaches the cutoff speed, the SC and generator circuit breaker (GCB) are opened, then the SG operates in no-load condition, namely transition mode. The engine is controlled by engine control unit (ECU) to accelerate to the idling speed. C. Mode III: Generating Operation When the engine reaches the idling speed and then the rated output voltage of the SG is detected by generator control unit (GCU), the GCB is closed, and the SG starts operating in generating operation.
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Fig. 5.
Self-excitation principle in generating operation.
Fig. 6.
Rotor mechanical design of the HESM.
Fig. 4. Proposed HESM-based VFAC SG system. (a) System configuration. (b) Machine structure.
III. PROPOSED HESM-BASED VFAC SG SYSTEM The proposed HESM-based VFAC SG system is shown in Fig. 4, which consists of an HESM with magnetic shunting rotor and a SG control unit (SGCU). SGCU is made up of a starter control unit (SCU) and a GCU. The SCU is consist of an H bridge and an inverter, which is used to control the field current and armature current to start the engine. The GCU is made up of a rectifier and an H bridge, which is used to control the field current to realize constant voltage output in generating operation. It should be noted that GCU and SCU share one H bridge. There are two sets of three-phase windings in the stator, namely main power winding and field power winding. The presented HESM has a unique feature of the same stator core with WRSM and a simple rotor structure, as shown in Fig. 4(b). The stationary circular magnetic bridge is fixed on the end shield with auxiliary air-gaps between magnetic bridge and rotor cores to realize a simple brushless excitation structure, which improves the reliability and stability at high speed. With the unique features, the proposed HESM-based VFAC SG system offers the following distinct advantages. 1) The rotating rectifier is eliminated and a simple brushless structure is realized by the fixed magnetic bridge, which makes the reliability of the system improved. 2) Compared to WRSM, the field power capacity of the proposed HESM is reduced effectively, which makes the efficiency of the system can be improved. 3) Due to the introduction of field windings, the excitation control strategy of output voltage regulation is similar to that in WRSM.
4) The starting control strategy of armature current is similar to that of PMSM due to the permanent magnetic field. With a proper coordinated operation between field current and armature current, the starting performance can be optimized. In starting operation, the DC power supplies the starting power and excitation power, which is provided by the auto transformer rectifier unit (ATRU) connected to the ground power unit or the APU generation system. A proper starting control strategy is critical to the engine starting. An optimized control strategy that utilizes the coordinated operation between the field current and d-axis current is proposed in [15], which can be adopted to improve starting performance. The whole speed range is divided into three operating regions with respect to the different field current levels: region I (maximum field current), region II (field current decreases with the increasing speed), region III (field current keeps zero). Especially in region II, field current and d-axis current are both adopted to realize maximum output torque under a constant armature current. In transition mode, the HESM SG starts operating in no-load condition once the speed reaches the cutoff speed. In generating operation, as shown in Fig. 5, the field current is provided by the field power winding and regulated by GCU to realize a constant output voltage. The three sets of windings, including main power winding, field power winding and DC field winding, realize the highly reliable self-excitation in generating operation, which is required for aircraft generation system. As shown in Fig. 6, the high-strength titanium alloy endring and sleeve are both adopted to improve the rotor structure strength. The distribution of rotor stress and deformation at 14000 rpm are illustrated in Fig. 7, which shows the rotor can keep stable operating in the whole speed range.
ZHANG et al.: HESM-BASED VARIABLE FREQUENCY AC STARTER-GENERATOR SYSTEM FOR AIRCRAFT APPLICATIONS
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where ud , uq and uf are the d-axis, q-axis and field voltage, id , iq and If are the d-axis, q-axis and field current, ψd , ψq and ψpm are the d-axis, q-axis and PM flux linkage, Rs and Rf are the stator winding and field winding resistance, Ld , Lq and Msf are the d-axis, q-axis and mutual inductance between armature windings and field windings, ulim is the maximum armature voltage, ilim is the maximum armature current. Fig. 7. Rotor stress and deformation distribution of the optimized rotor at 14 000 rpm. (a) Stress. (b) Deformation.
IV. MODELING AND SIMULATION PERFORMANCE A. Mathematical Model of the HESM The HESM with magnetic shunting rotor is developed from spoke-type PMSM and therefore the mathematical model of HESMs can be constructed by integrating the field current with that of PMSMs. Magnetic saturation, iron loss and temperature dependences are neglected to simplify the mathematical model of HESMs. The mathematical model for the HESM has been established in [16], briefly introduced as follows. The flux-linkage equation can be written as ψd = Ld id + Msf If + ψpm (1) ψq = Lq iq The voltage equation is expressed as ⎧ dψd ⎪ ⎪ ud = − ωψq + Rs id ⎪ ⎪ dt ⎪ ⎪ ⎨ dψq + ωψd + Rs iq uq = ⎪ dt ⎪ ⎪ ⎪ ⎪ dI di ⎪ ⎩ uf = Rf If + Lf f + Msf d dt dt
(2)
By substituting (1) into (2), the voltage equation can be obtained as ⎧ did dI ⎪ ⎪ + Msf dtf − ωLq iq + Rs id ⎪ ud = Ld ⎪ dt ⎪ ⎪ ⎨ diq (3) + ω (Ld id + Msf If + ψpm ) + Rs iq uq = Lq ⎪ dt ⎪ ⎪ ⎪ ⎪ dI di ⎪ ⎩ uf = Rf If + Lf f + Msf d dt dt Then the electromagnetic torque can be calculated by 3 np (iq ψd − id ψq ) 2 3 = np [ψpm iq + Msf If iq + (Ld − Lq ) id iq ] (4) 2 The differential items in (3) are zero in the steady state and the stator resistance voltage drop can be neglected in high speed condition. Then the feasible operation range is restricted by u 2 lim (5) (Ld id + ψpm + Msf If )2 + (Lq iq )2 ≤ ω Tem =
i2d + i2q ≤ i2lim
(6)
B. HESM SG Modeling In order to build an accurate model of the proposed HESMbased VFAC SG system, the modeling method of the HESM SG is analyzed. One of the difficulties and key technology is the integration of starter and generator in HESM SG modeling. The starter and generator models are built based on the mathematical model of the HESM separately and then encapsulated as HESM SG model, as shown in Fig. 8. There is another particular saliency factor feature of the HESM SG which is caused by adjusting the d-axis armature reaction flux path to axial flux path in Fig. 10, where the saturation degree can be controlled by the field current. The q-axis armature reaction flux path keeps same with that of spoke-type PMSM and the q-axis inductance can be considered as a constant. With a proper field current, the axial flux can be reduced close to zero and the d-axis inductance is larger than q-axis inductance. The saliency factor can be adjusted by the field current. Considering the non-linear relationship between d-axis inductance and field current, the d-axis inductance data is calculated by three-dimensional finite element method and then the lookup-algorithm is adopted to improve the precision of the HESM SG model. C. HESM-Based VFAC SG System Modeling As shown in Fig. 9, a simulation model of the proposed HESM-based VFAC SG system based on the HESM SG model is built and simulated. The parameters of the investigated HESM SG is shown in Table I. As shown in Fig. 11, the d-axis inductance versus field current is calculated by three-dimensional finite element method and adopted to improve the precision of the HESM SG model. In the simulation, a reduced mechanical moment of inertia is used to reduce the simulation time effectively. In order to verify the applicability of HESM with magnetic shunting rotor to a VFAC SG system for safety-critical aircraft applications, the three operation modes for aircraft power system are simulated by the proposed HESM-based VFAC SG system model. Considering the highest speed 3000 r/min which can be achieved in the test platform, the speed adopted in the simulation is pressed by 1/3. The cutoff speed, DC bus voltage and rated phase voltage are set to 2000 r/min, 90 V, 38.3 V respectively corresponding to the speed. The motion equation of the machine is given by Jm
dω = Te − TL − λω dt
(7)
where Jm is the mechanical moment of inertia, ω is the mechanical speed, TL is the load torque, and λ is the damping coefficient.
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Fig. 8.
Proposed HESM SG model.
Fig. 9.
Proposed HESM-based VFAC SG system model. TABLE I PARAMETERS OF HESM SG
Fig. 10.
d-axis armature reaction flux path.
As shown in Fig. 12, the optimized control strategy that utilizes the coordinated operation between the field current and d-axis current can be adopted to improve the output torque of the HESM SG. It can be seen that a higher acceleration can be achieved with a higher output torque of the HESM SG from the motion equation. The load torque vs. speed characteristic
adopted to analyze the starting performance is shown in Fig. 13. With only field current flux-weakening strategy, the highest speed 1750 r/min is lower than the cutoff speed, which may lead to the engine starting failure. The d-axis current and coordinated operation flux-weakening strategies can both accelerate the engine to the cutoff speed. The starting performance with the d-axis current and coordinated operation flux-weakening strategies is shown in Fig. 14. Compared to the d-axis current
ZHANG et al.: HESM-BASED VARIABLE FREQUENCY AC STARTER-GENERATOR SYSTEM FOR AIRCRAFT APPLICATIONS
Fig. 11.
D-axis inductance versus field current.
Fig. 12.
Torque speed characteristics with different control strategies.
Fig. 13.
Load torque vs. speed curve adopted in the process of simulation.
flux-weakening strategy, the starting time can be reduced efficiently with the coordinated operation flux-weakening strategy. As shown in Fig. 15, the whole operation modes have been implemented based on the coordinated operation flux-weakening strategy, including engine starting, transition and generating. Fig. 16 shows the generating performance according to the rotor speed performance in Fig. 15. A sudden increasing load and sudden dumping load happened at 0.7 s and 0.8 s
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Fig. 14. Starting performance with different control strategies. (a) Rotor speed with d-axis current flux-weakening strategy. (b) Input current with d-axis current flux-weakening strategy. (c) Rotor speed with coordinated operation flux-weakening strategy. (d) Input current with coordinated operation fluxweakening strategy.
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Fig. 15.
Rotor speed performance in the whole process. Fig. 17.
Fig. 16.
Generating performance. (a) Phase voltage. (b) Field current.
respectively. As shown in Fig. 16, the phase voltage changes when a sudden load is added to the system or the speed changes, and it can be seen that the phase voltage amplitude can be kept constant with field current regulation. Hence, it illustrates that the HESM SG can provide a constant output voltage for safety-critical aircraft applications. V. IMPLEMENTATION AND EXPERIMENTAL VALIDATION To confirm the feasibility of the HESM-based VFAC SG system, as shown in Fig. 17, a 12 kVA system has been developed
Experimental platform of the HESM-based VFAC SG system.
Fig. 18. No-load characteristic. (a) No-load back-EMF with 0 A field current at 2000 rpm. (b) No-load voltage regulating characteristic at different speed.
according to the parameters in Table I and the control algorithm is implemented on the system. Experiments are carried out on the platform. Fig. 18 shows the no-load characteristic of the HESM with different field currents. Fig. 18(a) indicates that the harmonic components of the phase voltage and phase current is low. Fig. 18(b) shows the phase voltage can be regulated by field current. The sinusoidal phase voltage and phase voltage regulating characteristic of the HESM SG make it suitable for VFAC SG systems.
ZHANG et al.: HESM-BASED VARIABLE FREQUENCY AC STARTER-GENERATOR SYSTEM FOR AIRCRAFT APPLICATIONS
Fig. 21.
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Transition process of the HESM-based VFAC SG system.
Fig. 19. Measured torque speed characteristics with different flux-weakening control strategies.
Fig. 22. Generating performance of the HESM-based VFAC SG system. (a) Sudden load at 1280 rpm. (b) Speed variation.
Fig. 20. Starting performance of the prototype HESM-based VFAC SG system. (a) D-axis current flux-weakening strategy with 0 A field current. (b) Coordinated operation flux-weakening strategy.
The torque speed characteristics with d-axis current, field current and coordinated operation flux-weakening strategies are measured and compared as shown in Fig. 19, which are in good agreement with the previous theoretical studies in Fig. 12. It can be seen that the starting time can be reduced by the coordinated operation flux-weakening strategy. Fig. 20 indicates the starting performance under a constant load torque 10 Nm of the prototype HESM-based VFAC SG system. The starting time is about 5.5 seconds with d-axis current flux-weakening strategy with 0 A field current and the starting time is reduced to about 3.5 seconds with coordinated
operation flux-weakening strategy. Fig. 21 shows the transition mode of the HESM-based VFAC SG system. The generating performance of the HESM-based VFAC SG system under sudden load and speed variation operations is also validated and the constant output voltage can be realized by regulating field current in Fig. 22. Apart from the aforementioned three major modes of operation, the HESM-based VFAC SG system can also satisfy the other requirements of safety-critical aircraft applications, such as the limitation of short circuit current in case of fault. As shown in Fig. 23, the short-circuit current of the HESM can be reduced by field current, which is significant to VFAC SG systems for safety-critical aircraft applications. It can be observed that the HESM-based VFAC SG system is suitable for safety-critical aircraft applications.
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Fig. 23.
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Short-circuit current vs. field current of the HESM.
VI. CONCLUSION In this paper, a new HESM-based VFAC SG system is developed as a promising solution for aircraft applications. In the HESM-based VFAC SG system, the rotating rectifier is eliminated and the simple brushless structure of the HESM is realized, which makes the reliability of the system is improved further. The efficiency of the HESM-based VFAC SG system is improved for the low field power capacity. The GCU in the HESM-based VFAC SG system can continue to adopt the control strategy of WRSM-based VFAC SG system. The starting control strategy of armature current is similar to that of PMSM due to the permanent magnetic field. With a proper coordinated operation between field and armature currents, the starting control strategy can be optimized. For these features, the HESM-based VFAC SG system is a competitive candidate for safety-critical aircraft applications. The three main operating modes of VFAC SG system have been validated by simulated and experiment results. The feasibility of the HESM with magnetic shunting rotor in the VFAC SG systems has been preliminarily verified. REFERENCES [1] X. Roboam, B. Sareni, and A. D. Andrade, “More electricity in the air: Toward optimized electrical networks embedded in more-electrical aircraft,” IEEE Ind. Electron. Mag., vol. 6, no. 4, pp. 6–17, Dec. 2012. [2] J. A. Rosero, J. A. Ortega, E. Aldabas, and L. Romeral, “Moving towards a more electrical aircraft,” IEEE Aerosp. Electro. Syst. Mag., vol. 22, no. 3, pp. 3–9, 2007. [3] B. Srimoolanathan, “Aircraft electrical power systems—charged with opportunities,” Aerosp. Defense Executive Briefing Frost Sullivan, Nov. 2008. [4] N. Morioka, M. Takeuchi, and H. Oyori, “Moving to an All-Electric aircraft system,” IHI Eng. Rev., vol. 47, no. 1, pp. 33–39, 2014. [5] K. Emadi and M. Ehsani, “Aircraft power systems: Technology, state of the art, and future trends,” IEEE Aerosp. Electron. Syst. Mag., vol. 15, no. 1, pp. 28–32, Jan. 2000. [6] P. Wheeler and S. Bozhko, “The more electric aircraft: Technology and challenges.,” IEEE Electrific. Mag., vol. 2, no. 4, pp. 6–12, Dec. 2014. [7] J. A. Tapia, F. Leonardi, and T. A. Lipo, “Consequent-pole permanent magnet machine with extended field-weakening capability,” IEEE Trans. Ind. Appl., vol. 39, no. 6, pp. 1704–1709, Nov./Dec. 2003. [8] B. Nedjar, S. Hlioui, Y. Amara, L. Vido, M. Gabsi, and M. L´ecrivain, “A new parallel double excitation synchronous machine,” IEEE Trans. Magn., vol. 47, no. 9, pp. 2252–2260, Sep. 2011.
[9] Y. Wang and Z. Deng, “Hybrid excitation topologies and control strategies of stator permanent magnet machines for DC power system,” IEEE Trans. Ind. Electron., vol. 59, no. 12, pp. 4601–4616, Dec. 2012. [10] Q. Zhang, S. Huang, and G. Xie, “Design and experimental verification of hybrid excitation machine with isolated magnetic paths,” IEEE Trans. Energy Convers., vol. 25, no. 4, pp. 993–1000, Dec. 2010. [11] N. Patin, L. Vido, E. Monmasson, J. P. Louis, M. Gabsi, and M. Lecrivain, “Control of a hybrid excitation synchronous generator for aircraft applications,” IEEE Trans. Ind. Electron., vol. 55, no. 10, pp. 3772–3783, Oct. 2008. [12] A. Nasr, S. Hlioui, M. Gabsi, M. Mairie, and D. Lalevee, “Design optimization of a hybrid-excited flux-switching machine for aircraft-safe DC power generation using a diode bridge rectifier,” IEEE Trans. Ind. Electron., vol. 64, no. 12, pp. 9896–9904, Dec. 2017. [13] C. Liu, K. T. Chau, and J. Z. Jiang, “A permanent-magnet hybrid brushless integrated starter–generator for hybrid electric vehicles,” IEEE Trans. Ind. Electron., vol. 57, no. 12, pp. 4055–4064, Dec. 2010. [14] Z. R. Zhang, Y. G. Yan, S. S. Yang, and B. Zhou, “Principle of operation and feature investigation of a new topology of hybrid excitation synchronous machine,” IEEE Trans. Magn., vol. 44, no. 9, pp. 2174–2180, Sep. 2008. [15] Z. Zhang, J. Li, Y. Liu, Y. Xu, and Y. Yan, “Overview and development of variable frequency AC generators for more electric aircraft generation system,” Chinese J. Electrical Eng., vol. 3, no. 2, pp. 32–40, Sep. 2017. [16] Z. Zhang, Y. Liu, B. Tian, and W. Wang, “Investigation and implementation of a new hybrid excitation synchronous machine drive system,” IET Electric Power Appl., vol. 11, no. 4, pp. 487–494, Apr. 2017.
Zhuoran Zhang (M’09–SM’12) received the B.S. degree in measurement engineering and the M.S. and Ph.D. degrees in electrical engineering from the Nanjing University of Aeronautics and Astronautics (NUAA), Nanjing, China, in 2000, 2003, and 2009, respectively. Since 2003, he has been a member of the faculty with the Department of Electrical Engineering, NUAA, where he is currently a Full Professor and the Vice-Director of the Jiangsu Provincial Key Laboratory of New Energy Generation and Power Conversion. From February 2012 to Junuary 2013, he was a Visiting Professor with Wisconsin Electric Machines and Power Electronics Consortium, University of Wisconsin-Madison, U.S. From 2016 to 2017, he was with the Commercial Aircraft Corporation of China, Ltd., and was appointed as the Deputy Director of electrical system designers of C919 civil jet aircraft. His research interests include design and control of permanent magnet machines, hybrid excitation electric machines, and doubly salient electric machines for aircraft power, electric vehicles and renewable energy generation. He has authored or coauthored more than 120 technical papers and one book, and is the holder of 30 issued patents in these areas. Ye Liu (S’16) received the B.S. degree in electrical engineering in Nanjing University of Aeronautics and Astronautics, Nanjing, China, in 2014. He is working towards the Ph.D. degree in electrical engineering at Nanjing University of Aeronautics and Astronautics, Nanjing, China. His main research interests include design and control of hybrid excitation electrical machines.
Jincai Li (S’17) received the B.S. degree in electrical engineering from Henan University of Urban Construction, Pingdingshan, China, in 2012 and the M.S. degree in electrical engineering from Shanghai Dianji University, Shanghai, China, in 2015. He is currently working toward the Ph.D. degree in electrical engineering at the Center for More-Electric- Aircraft Power System, Nanjing University of Aeronautics, Nanjing, China. His main research interests include design and control of brushless synchronous starter/generator and electrical power generation system for MEA.
