Doubly Salient Electromagnetic Machine Research Articles

Analysis and Design of Embedded High-Temperature Doubly Salient Electro-Magnetic Starter/Generator for Aviation

In view of the high temperature operation characteristics of the embedded starter/generator for the more electric engine (MEE), the influence of material property change on motor performance at high temperature is studied. Furthermore, considering the influence of high temperature, the electromagnetic calculation of doubly salient electro-magnetic machine (DSEM) is carried out, and the excitation design principle of DSEM under high temperature is pointed out. The performance of DSEMs using DW310 silicon steel and 1J22 iron-cobalt alloy material was compared. Based on the silicon steel material, the structural parameters of DSEM are analyzed. According to the key parameters obtained from structural parameter analysis, Box-Behnken method and genetic algorithm were used to carry out the multi-parameter and multi-objective optimization design. The optimization objectives include excitation current, voltage ripple and cogging torque, to meet the torque and power quality requirements of MEE. Then the performance of DSEM at room temperature and high temperature is analyzed by the finite element method, which verifies the effectiveness of the design. Finally, a high-temperature and high-speed DSEM prototype was processed. At the same time, in order to cooperate with the test, a DSEM ground simulation test system platform for MEE was built to test the prototype. Its design experience lays a foundation for the embedded DSEM design of more electric aircraft.

Fault-Tolerant Control of Doubly Salient Electromagnetic Generator Based on Capacitor Split-Phase Bridge Converter Under Loss of Excitation

Doubly salient electromagnetic machine (DSEM) has the advantages of simple construction, easy power generation control and convenient fault de-excitation, making it a promising application in the aviation field. Aviation power generation system puts forward higher requirements for the reliability of generators. Despite the various studies on the fault-tolerant control of DSEM, there are few studies on fault-tolerant control of excitation fault in aviation power generation system. Therefore, the main purpose of this paper is to achieve fault-tolerant power generation (FTPG) system for doubly salient electromagnetic generator (DSEG) on the event of excitation fault and improve the fault tolerance ability of the system, while can improve output power and reduce copper loss of DSEG under loss of excitation. This paper analyses the basic principle of normal power generation about DSEG, establishes its equivalent circuit after excitation loss, and dissects the control strategy for the FTPG with loss of excitation based on a bridge converter. Besides, this paper also proposes a fault-tolerant control system and its control strategy based on a capacitor split-phase bridge (CSPB) converter for DSEG, with higher generated power as well as lower copper loss. Based on the above hypothesis, experiments are performed on a power generation system for 12/8 pole DSEG to verify the feasibility of the proposed method.

The Currents Coordinative Control Strategy for Integrated Motor-Drive and Battery-Charging System Based on the Split-Field-Winding DSEM in Driving Mode

This paper proposes a currents coordinative control strategy for the integrated motor-drive and battery-charging (IMB) system based on the split-field-winding doubly salient electromagnetic machine (DSEM) in driving mode, where the field windings are reused as the filter inductance of the front-end DC-DC converter. The combined strategy of maximum field current and the minimum copper loss control methods with respect to the error between the reference and feedback speed of DSEM is given. Compared to the traditional constant field control of DSEM, the copper loss in steady-state operation could be reduced significantly for higher efficiency, especially in light load conditions, and the maximum output power could also be obtained to improve the dynamic performance of the proposed system. The effectiveness and reliability of the proposed control strategy are verified by simulation and experiment results.

Torque Ripple Reduction Strategy for Doubly Salient Electromagnetic Machine Based on Current Given Function

Torque ripples caused by the particular doubly salient structure of the doubly salient electromagnetic machine (DSEM) restrict its application in the field requiring high performance. This article employs the current given function (CGF) to propose a torque ripple reduction strategy for DSEM to enhance the torque capability. The optimal current profile for minimizing the copper loss is obtained based on the theoretical analysis. It is found that the obtained three-phase currents are distributed according to the phase torque coefficient that represents the torque capability of each phase. Then, to minimize the torque ripple and copper loss, four CGFs are proposed to distribute the reference current of each phase according to the torque characteristics of DSEM. Finally, the influence of overlap angle on the proposed strategy is analyzed to select the reasonable CGF and overlap angle under different operating conditions through simulation, improving the current tracking performance and torque–ampere ratio. The simulation and experimental results demonstrate the effectiveness of the proposed strategy in suppressing torque ripple and improving the torque–ampere ratio.

Fault-Tolerant System Design for Doubly Salient Electromagnetic Machine Under Loss of Excitation

Aiming at the problem that the traditional doubly salient electromagnetic machine (DSEM) cannot work when the excitation loss occurs, this article designs and analyzes a fault-tolerant DSEM for excitation loss, and the torque ripple suppression strategy under the fault-tolerant operation is studied. First, the characteristics of the output torque of DSEM before and after excitation-loss is analyzed, and a DSEM with a novel winding configuration is proposed to improve the fault tolerance. Second, under normal/excitation-loss conditions, the structure parameters of the fault-tolerant DSEM are analyzed to reveal the influence of the motor structure on its performance. Then, the steady-state torque of the fault-tolerant DSEM is compared with the traditional DSEM and the switched reluctance motor with the same size, which proves the effectiveness of the fault-tolerant design. By analyzing the inductance and torque characteristics, a torque ripple suppression strategy is proposed for the fault-tolerant DSEM without increasing the complexity of the system. Finally, a prototype is developed, and the experimental results verify the fault-tolerant capability of the prototype and the effectiveness of the proposed torque ripple suppression strategy. The research results of this article provide a specific implementation method for the fault-tolerant system design of DSEM under excitation loss.

3-D Global Thermal Analysis of DSEM Considering the Temperature Difference Between Excitation and Armature Coils

The complexity of winding distribution of doubly salient electro-magnetic machine (DSEM) results in its uneven temperature distribution, and its temperature rise characteristics under different working conditions need to be further studied. Different from the thermal analysis method of uniformly distributed electrical machine, this article proposes a time-saving thermal analysis method for the new topology of DSEM. In view of the sensitive change of DSEM excitation loss with temperature, the magnetic-thermal bidirectional coupling method is adopted. Considering the temperature difference between excitation and armature coils, a detailed thermal model is established for the armature-excitation slot. The number of bidirectional coupling iterations of finite-element method is reduced by steady-state temperature prediction. Then the temperature distribution of DSEM is analyzed in detail, and the variation of the temperature distribution under different operating conditions is studied. The temperature rise characteristics of a three-phase 12/8-pole prototype are tested to verify the correctness of the proposed method. The research results can provide reference for the temperature evaluation of DSEM and its electromagnetic and cooling design.

Torque Performance Improvement of Doubly Salient Electromagnetic Machine by Harmonic Current Injection With Optimized Magnetomotive Force Ratio

The doubly salient electromagnetic machine (DSEM) has simple and reliable structure while suffering from the problem of torque ripple due to the salient pole structure. In order to improve the torque performance, this paper proposes a collaborative optimization method of harmonic current injection and proportion of the armature magnetomotive force (MMF) and field MMF based on the optimized rotor pole arc coefficient. The theory of torque generation and the influence of rotor pole arc coefficient on torque characteristics are analyzed. The relationship between the copper loss and the total MMF is investigated. The influence of MMF proportion on the average torque and torque ripple is studied. The effect of harmonic current injection on torque performance is further analyzed on the basis of the optimized rotor pole arc coefficient. Finally, the 12/10-pole DSEM prototype is developed and the experiment is conducted to verify the analysis.

An Improved Direct Instantaneous Torque Control of Doubly Salient Electromagnetic Machine for Torque Ripple Reduction

The doubly salient electromagnetic machine (DSEM) is a suitable candidate in many industrial applications due to its simple construction and low manufacture cost. However, the doubly salient structure and the conventional square-wave control method lead to the large torque ripple in the DSEM. In this article, an improved direct instantaneous torque control (DITC) method is proposed to suppress the inherent torque ripple and enhance the torque capability of the DSEM. The maximum torque characteristics of the DSEM are obtained and analyzed with the finite-element method. Besides, the ideal phase current waveform to realize the low torque ripple is constructed according to the maximum torque characteristics. Then, the operation principle of the proposed DITC method is derived from the maximum torque characteristics. The proposed DITC method is implemented on a prototype of 12/8-pole DSEM drive system. The influence of the commutation angle parameters on the proposed DITC method is analyzed through simulation and experimental results. The simulation and experimental results indicate that the proposed DITC method can realize the smooth torque operation and high torque-ampere ratio simultaneously. Finally, the simulation and experiment under the step reference torque condition are performed to test the dynamic performance of the proposed DITC method.

The Optimized Triloop Control Strategy of Integrated Motor-Drive and Battery-Charging System Based on the Split-Field-Winding Doubly Salient Electromagnetic Machine in Driving Mode

An integrated motor-drive and battery- (IMB) charging system based on the split-field-winding doubly salient electromagnetic machine (DSEM) is proposed in this article, where field winding of DSEM is integrated as the filter inductance of the front-end dc-dc converter. In the driving mode, the coupling relationship between the front-end dc-dc converter and rear-end inverter for DSEM is deduced, and the corresponding basic control method is given to achieve independent control of the front-end dc-dc converter and rear-end inverter based on the power balance of the cascade converter. Due to the constraints analysis of the IMB system in the dynamic procedure, an optimized triloop control strategy of speed, power, and dual-threshold voltage is proposed to improve output performance. Finally, the simulation model and experimental platform are established to verify the effectiveness and the steady and dynamic performance of the IMB system with the proposed driving control strategy.

Two-Step Rotor Position Estimation Method for Doubly Salient Electromagnetic Starter-Generator Over Zero and Low Speeds Range

Doubly salient electromagnetic machine (DSEM) can constitute a novel aero starter-generator (SG) system, and position sensorless control of DSEM is a key technology to improve system reliability and power density. This article proposes a novel two-step rotor position estimation scheme for doubly salient electromagnetic starter-generator (DSESG) over zero and low speeds range. Based on the corresponding relation between the minimal phase self-inductance and rotor sector, the rotor position estimation is made by searching the minimal phase self-inductance, which is carried out through two comparing steps of two proper phase self-inductances, and each comparing step is implemented according to the magnitude relation of two parallel-connected phase currents. Then, the selection method of the diagnostic pulsewidth is studied by overall considering the rotor position estimation precision and the low speeds sensorless startup performance. Furthermore, the possible estimation error introduced by the limited resolution of the practical current sensor is analyzed, and a quasi-three-phase six-state conduction mode is put forward as the compensation strategy to guarantee the low speeds sensorless startup performance, in which three boundary sectors with different conduction states are added. Finally, the experiments on a 12/8-pole DSESG validate the correctness and feasibility of the proposed strategies.

Initial rotor alignment method for doubly salient electromagnetic machine position sensorless startup

The initial rotor alignment process plays an important role in `align and go' which is a simple, implementable and widely industrial used position sensorless startup method. To deal with the possible jitter and reverse in the initial startup process, this Letter proposes a novel initial rotor alignment method for the position sensorless startup of the doubly salient electromagnetic machine (DSEM). According to the analysis of the generated electromagnetic torque, the relation between the alignment pulse and stable locating position is studied at first. Then, to improve the initial startup performance, the alignment pulse of switching on two upper transistors and one lower transistor is proposed to be injected as the alignment pulse since the stable locating position is around the middle point of rotor sector; it owns the benefit of better selection for the initial energising phase windings. The initial sensorless startup performance is desired to be improved in terms of no jitter or reverse. The experiments of initial alignment, as well as, the full process of the sensorless startup based on `align and go' on a 12/8-pole DSEM validate the flexibility and effectiveness of the proposed method.

Operating Performance Enhancing Method for Doubly Salient Electromagnetic Machine Under Light Load Condition

Nowadays, more and more electric machines are demanded to operate under wide ranges of speed and load conditions. This paper deals with the operating performance enhancing method for doubly salient electromagnetic machine (DSEM) under light load condition. With the finding that the power loss can be decreased with reduced field current, and there's regulated space for the distribution of field current and armature current under light load condition. A novel control method with field current inner loop and speed outer loop is proposed for DSEM, the system driving efficiency is desired to be improved. Meanwhile, the cogging torque which is a main ripple source of DSEM torque can be decreased with the reduced filed current, so the output torque performance can be enhanced as well. In addition, the armature reaction of the proposed control method is researched, and the influence on the filed current control during commutation process is theoretically analyzed. The experiments on a 12/8-pole DSEM validate the correctness and flexibility of the proposed control method.

Position Sensorless Control for Doubly Salient Electromagnetic Machine With Improved Startup Performance

It is an effective approach to estimate rotor position of doubly salient electromagnetic machine (DSEM) from self-inductances, which changes with rotor position. To overcome the restrictions of low estimation accuracy as well as the inevitable commutation lag in the conventional sensorless startup method, this paper proposes a novel rotor angular position estimating technique for the DSEM sensorless startup. It starts with injecting three test pulses A + C- (phase A is connected to the positive rail of dc bus, and phase C is connected to the ground rail), B + A- and C + B- on armature windings, so two-phase series self-inductances can be identified according to the resultant currents. Then, the estimating expression of the DSEM rotor angular position is further obtained based on the geometrical relation in the rectangle composed of self-inductances, and the inevitable commutation lag in startup process is likely to be eliminated with the estimated rotor angular position. Moreover, the error of rotor angular position introduced by the nonideal linearity of self-inductances are analyzed in detail, and the boundaries of neighboring sectors are distinguished from normal sectors to compensate the estimation error of rotor angular position. Finally, to enhance the output torque performance during the DSEM startup process, a novel selection method for test pulses concerning rotor sector is developed. Compared to the conventional method, a quicker and superior startup performance is achieved since no negative torque is generated by the test pulses. The experiments on a 12/8-pole DSEM validate the correctness and feasibility of the proposed sensorless control methods.

Dual-Pulse Mode Control of a High-Speed Doubly Salient Electromagnetic Machine for Loss Reduction and Speed Range Extension

In this article, a dual-pulse mode control of a high-speed doubly salient electromagnetic machine (DSEM) for efficiency improvement over a wide speed range is investigated and implemented. The dual-pulse mode control method and operation principle are introduced. The influence of excitation angles and field current on the operation performance is analyzed by finite-element method based on the back electromotive force (EMF) and inductance characteristics. The loss distribution for various speed and load torque requirement is attained, and the control parameters are optimized. The excitation angle can reduce the back EMF at high speed through transformer EMF and flux-weakening armature reaction. A prototype of 12/8-pole DSEM drive system is developed and dual-pulse mode control in high-speed operation under low dc-link voltage is implemented. Both the simulated and measured results show that the torque capacity of the DSEM is improved and the loss is reduced over a wide speed range.

Self-Tuning Control of Advanced Angles for Doubly Salient Motor Drive System

Due to the advantages of simple mechanical structure, high reliability, and high power density, a doubly salient electromagnetic machine (DSEM) has wide application prospects in many areas. Many driving strategies for the DSEM have been developed in recent years, including the standard angle control, the three-state advanced angle control, the six-state advanced angle control, the nine-state advanced angle control, etc. Compared with standard angle control, the driving strategies with advanced angles can further increase the output torque and reduce the torque ripples in the medium/high-speed region. However, the advanced angles are very difficult to select, and the commonly used field-circuit co-simulation method by enumerating advanced angles consumes a lot of time. In addition, once the working condition changes, the advanced angles should be reselected. In this article, self-tuning control of advanced angles based on a several-angle alternating method is proposed, which is carried out by iteratively calculating the advanced angles according to the working conditions. The operating principle of the proposed method is analyzed in detail, together with the change in the pattern of advanced angles and the output characteristics of DSEM. In addition, the implementation method is described, with the upper limitation of advanced angles being selected. Finally, the effectiveness and the feasibility of the proposed method are verified by field-circuit co-simulations and experiments.

An Integrated Motor-Drive and Battery-Charging System Based on Split-Field-Winding Doubly Salient Electromagnetic Machine

In this paper, an integrated motor-drive and battery-charging (IMB) system with a doubly salient electromagnetic machine (DSEM) is proposed to be implemented for electric vehicles. In the driving mode, the front-end dc/dc converter is employed to boost the battery voltage to improve the speed range and acceleration ability of the DSEM. The field windings distribution of a 12/10-pole DSEM is arranged for the constant self-inductance, and adopted as the inductance of the front-end dc/dc converter to eliminate the traditional filter inductance and excitation loss of the machine. In the charging mode, the windings of DSEM could be exploited as the filter inductances to obtain the unity power factor operation and constant current charging ability. The simulations and experiments have been accomplished to verify the feasibility of the independent field current control method for the proposed IMB system.

Indirect measurement and extreme learning machine based modelling for flux linkage of doubly salient electromagnetic machine

Doubly salient electromagnetic machines (DSEMs), which are characterised with fault tolerance, low cost, high reliability, and de-excitation ability, are gaining more and more attention in safety-critical and hash environment applications, such as the aircraft generation systems. Nevertheless, the non-linear and strong coupled characteristics of the flux linkage is the obstruct crux in DSEM modelling. The DSEM model is the critical part of the system model, which is the foundation of theoretical analysis, control strategy developing, and stability analysis. This study is aimed to demonstrate the feasibility of indirect flux linkage measurement method, as well as the effectiveness of the extreme learning machine (ELM)-based flux linkage modelling method. The basic principles of the indirect measurement are analysed and the measurement processes excluding rotor-clamping devices are proposed. The ELM is employed to high-precision flux linkage modelling with high efficiency. A three-phase 12/8-pole DSEM is tested to confirm the validity of the proposed modelling method. Both finite element analysis and experimental results are presented, verifying the effectiveness of the indirect flux linkage measurement and the ELM-based modelling method.

Research on control strategies for doubly salient electromagnetic machine

The doubly salient electromagnetic machine (DSEM) is a kind of variable reluctance machine, which is different from the conventional AC electric machines. The standard angle control and the three-state angle-advanced control are traditional control strategies for DSEM, with dead zone existing. Six-SAA (SSAA) control is a newly proposed control strategy with no dead zone. Compared to traditional control strategies, it can increase output torque, and reduce the torque ripple. However, it is hard to select proper advanced angles in SSAA control. In this study, a 12/8-pole DSEM has been studied. Then, several control strategies for DSEM are presented, and the operating principles are analysed in detail. After that, a new control strategy is proposed, and its characteristic during commutation stage is analysed. Besides, the optimal advanced angles are deduced, with its variation characteristics, and the comparison of these control strategies are conducted by finite element simulation. With the proposed control strategy, a higher-output torque can be acquired in a wide-speed range, and meanwhile, the selection of advanced angles is simplified. Finally, the theoretical analysis is verified by simulations and experimental results.

Torque Density Improvement of Doubly Salient Electromagnetic Machine With Asymmetric Current Control

Due to the introduction of field winding, the doubly salient electromagnetic (DSEM) machine is featured with good torque production capability. However, this capability is limited by the problems of the phase current reversal and excessive back- electromotive force with traditional control methods. In this paper, a new control method, namely asymmetric current control (ASCC), is proposed to further improve the output torque. Two control angles α and γ are introduced to implement the current-angle control. Simultaneously, the pulse width modulation control is utilized to shape the waveform of phase current. Consequently, the torque is increased drastically because of more effective phase current waveforms, which presents the asymmetry of positive and negative half period. Furthermore, the reluctance torque resulting from the interaction between self-inductance and asymmetric phase current exerts favorable effects on the torque output. By field-circuit-coupled analysis, the ASCC method for a 1.3 kW prototype is analyzed and compared with other traditional control methods. Laboratory testing of the 1.3 kW DSEM machine driven by the new control method confirms the validity of theoretical analysis and simulation improvement of torque. The simulation and experimental results show that the torque and power density can be improved to 1.5 times by the proposed control method.

Iron Loss Analysis of Doubly Salient Brushless DC Generators

The doubly salient electromagnetic machine (DSEM) is a kind of variable reluctance machine, which is different from the conventional ac electric machines. A new 24/16-pole DSEM is presented, and the configuration and operation principle are discussed. Based on the comprehensive study of the field distribution feature, the DSEM is separated into eight sections to investigate the iron loss distribution. In order to predict the iron loss of the doubly salient electromagnetic generator (DSEG), the flux density variations of each section are resolved into radial and circumferential waveforms, and Fourier transform is utilized in consideration of harmonic components. A calculation model of iron loss is established, and the coefficients are determined by the measured data at different speeds. The iron loss distribution of the DSEG is investigated. The proportion of iron loss to copper loss is further analyzed under different load conditions. Moreover, the influences of speed, air-gap length, and field current on iron loss are analyzed and summarized. Finally, the calculation and analysis of iron loss are verified by experimental results.