Direct-drive Permanent Magnet Synchronous Motor Research Articles

Design of Direct-drive Permanent Magnet Synchronous Motor for Cryogenic Valve

This paper presents a novel design of a low-speed and high-torque cryogenic direct-drive PMSM. A new simplified model is proposed to address the inaccuracy of the electro-thermal coupling model of the common cryogenic PMSM design. The coupling model focuses on the influence of the winding copper loss on the resistance, which improves the accuracy of calculating the temperature distribution and resistance value. Compared with FEM, the error of the calculation results is 4.8 %. A new design method is proposed to address the problem that the common low-temperature PMSM designs lead to a rise in the copper loss. Measuring the improvement of the magnet performance in low temperature, the method reduces the turns of the coil, which significantly reduces the amount of copper loss. Compared with common methods, the amount of copper loss reduces 29.5%. Furthermore, a prototype is fabricated and tested, the results of which verifies the rationality of the design.

Neutral-point voltage control of the three-level inverter in permanent magnet synchronous motor based direct-drive belt conveyor

Combined with the operation condition of belt conveyor and the running state of low speed direct-drive permanent magnet synchronous motor (PMSM), the reason for the high fluctuation of the neutral-point voltage (NPV) in the three-level inverter with the conventional method is analyzed. An improved NPV control strategy based on self-optimization of the switching sequence is proposed to ensure that the NPV could be completely controlled with the minimal number of switching times. A test platform with a 800 kW low speed PMSM is built, where the proposed NPV control strategy is implemented on a digital processor using the programming language C. Compared with the conventional method, the experimental results show that the NPV fluctuation of the proposed method can be reduced by a ratio of 46.3% to 89.5% at the least cost of the switching loss increase and the low-frequency harmonics in the output current can also be mitigated.

Research on internal model control and hybrid modulation strategy of a MW-level direct-drive PMSM for traction drives in electric locomotive

Aiming at the problem of motor control performance degradation caused by the cross-coupling and low switching frequency condition in the high-power direct-drive permanent magnet synchronous motor (PMSM) control system, a robust current control of PMSM based on internal model control (IMC) and hybrid pulse width modulation (PWM) is proposed and applied to the control of a MW-level direct-drive PMSM in electric locomotive traction system. Firstly, combined with the characteristics of the low switching frequency of the electric locomotive inverter, a hybrid PWM strategy is adopted. Secondly, the IMC of PMSM is designed, and the IMC is adopted to solve the problems of more control parameters and cross-coupling of direct-drive PMSM in the d-q axis under low switching frequency, which improves the robustness of the whole locomotive system. Finally, the experiments have been carried out on a 1.2 MW direct-drive PMSM for traction system in electric locomotive, the correctness and effectiveness of IMC and hybrid PWM strategy are verified.

A novel online method for locating fault coil in direct‐drive permanent magnet synchronous motor with inter‐turn short‐circuit fault using search coil array

This study presents a fault coil localisation approach for a direct-drive permanent magnet synchronous motor (DDPMSM) with inter-turn short-circuit fault (ISF) using the search coil (SC) array. The SCs are wound around specific stator tooth of DDPMSM through the proposed SC array arrangement principle, which reduces the invasiveness of the fault coil localisation method. The SCs are classified as several search coil groups (SCGs), the differential between SC back electromotive forces (EMFs) in the same SCGs (δ1) and SC residual back EMF (δ2) are used as fault indicators for ISF localisation. The peak values extracted from δ1 and δ2 are the basis for diagnosing ISF. Hence, the proposed approach does not need a complicated signal processing algorithm, and it is less complex. First, the SC back EMF analytical model is developed to investigate the mapping relationship between the back EMF of each SC and fault coil location. Second, fault coil localisation indicators for ISF are analysed based on the proposed analytical model, and the exact ISF localisation approach is presented. Finally, two basic installation units and the arrangement principle of SC array in DDPMSM are proposed. Simulation and experimental results justify the effectiveness of the selected fault indicators and the feasibility of the proposed SC array for diagnosing ISF.

Robust Adaptive Current Control of a 1.2-MW Direct-Drive PMSM for Traction Drives Based on Internal Model Control With Disturbance Observer

In order to improve the efficiency of the electric locomotive, the MW-level direct-drive permanent magnet synchronous motor (DD-PMSM) is used to replace the original traction motor and gearbox in the electric locomotive. However, the DD-PMSM parameters will change with the operating conditions during the operation of the electric locomotive, and the absence of the gearbox in direct drives increases the sensitivity of the control performance to uncertainties in the drive system. In order to solve the problems, a novel robust adaptive (RA) current control of MW-level DD-PMSM for traction drives based on internal model control with disturbance observer (IMCDO) is proposed in this article. IMCDO is simply designed as the estimated uncertainty function, and simple control law is derived based on the Lyapunov function to guarantee the system stability and improve the antidisturbance performance. Then, in order to adjust the internal model disturbance observer properly, the observer gain selection criteria are given by using the stability analysis based on the discrete Lyapunov function. The proposed method in the article is verified on a 1.2-MW DD-PMSM, and the comparative experiments demonstrate the validity and effectiveness of the proposed method.

Rotor Position Tracking Control for Low Speed Operation of Direct-Drive PMSM Servo System

In this article, a rotor position tracking control (RPTC) strategy is proposed to effectively reduce the speed fluctuation for a direct-drive permanent magnet synchronous motor servo system operating at a low speed with different torque disturbances. In this article, considering the derivative relationship between the rotor position and speed, a speed command is converted to a real-time rotor position trajectory, and then a position-current two-loop control with the RPTC controller is proposed based on the internal model method to smoothly track the rotor position. In addition, the parameter design of the RPTC controller from the perspectives of robust stability and antidisturbance capability is investigated as well. The comparative simulation and experimental results demonstrate that, at a low speed, the proposed RPTC strategy has a good speed performance for both periodic and nonperiodic torque disturbances. Moreover, it enjoys a simple implementation for not requiring the precise speed feedback and specific torque disturbance information.

Fault coil location of inter‐turn short‐circuit for direct‐drive permanent magnet synchronous motor using knowledge graph

Inter-turn short-circuit fault (ISF) degrades its reliability and may cause serious catastrophes for direct-drive permanent magnet synchronous motor (DDPMSM). Fault location technology can reduce maintenance time, increase the mean time between failure (MTBF), and then improve the reliability of DDPMSM. Hence, an intelligent fault locating system for DDPMSM is proposed in this paper. This system proposes a knowledge graph (KG) based diagnostic tool for detection and location of the fault coil. First, the fault model of the DDPMSM with multiple branches parallel winding is established, which is used to analyze the fault characteristics of motor. Second, the BDC and BRC are proposed as the fault indicator. The effectiveness and robustness of fault indicator are analyzed. Then, the KG system are designed and established according to the relationship between fault indicator and location of fault coil. Finally, the system is tested by data under different fault and operation conditions. The test results showed that the proposed fault locating system can detect and locate the fault coil in early stage. The minimum ratio of shorted turns to branch turns that can be detected is 0.52%. The minimum ratio of shorted turns to branch turns that can be located is 6.25%.

Novel modelling method based on winding sub‐element of direct‐drive permanent magnet synchronous motor

Owing to its many benefits, including convenient and short computing time, the analytical model (AM) is widely used in the performance analyse of the permanent magnet synchronous motor (PMSM). The existing analytical models based on phase winding cannot sufficiently speculate about the contribution of the coil to the performances of direct-drive PMSM (DDPMSM) with series coils and multiple branches. Hence, in this work, a novel AM for the DDPMSM is proposed. This model, which is based on the winding sub-element, can analyse the influence of coil on motor performance. First, the structure and key parameters of the DDPMSM are reported. Second, an inductance matrix, which considers the spatial disposition of coils and the characteristics of large self-inductance and small mutual inductance, is constructed. Then, the influence of the coil on motor performance is analysed based on the proposed AM. Finally, the results of AM, finite-element model and experiment are compared. The results validate the correctness of the proposed AM. Furthermore, the proposed AM can speculate about the contribution of a coil in the DDPMSM performances with satisfactory accuracy.

Speed Ripple Reduction of Direct-Drive PMSM Servo System at Low-Speed Operation Using Virtual Cogging Torque Control Method

In this article, a virtual cogging torque (VCT) control method to reduce the speed ripple of direct-drive permanent magnet synchronous machine servo system under low-speed conditions is proposed. Compared with other factors, at low speeds, the cogging torque is the main factor that deteriorates the drive performance, even induces speed oscillations. Especially in this article, due to volume limitation, the cogging torque is designed larger than normal one in order to remove the need of brake. Based on the model of permanent magnet synchronous motor, the cause and effect of the cogging torque are analyzed. Inspired by the characteristic of cogging torque, the VCT control method is proposed and investigated to significantly reduce the speed ripple at low speeds. The main idea of this proposed control method is to produce a proper VCT and continuously move the corresponding virtual stable equilibrium point to drive the rotor smoothly. In addition to the principle of this control method, its analysis and implementation are studied as well. Simulation and experimental results from the prototype demonstrate that the proposed control method is correct and valid, and it is simple and effective to smooth the speed at low-speed operations.

A Novel Analytical Method of Inductance Identification for Direct Drive PMSM with a Stator Winding Fault Considering Spatial Position of the Shorted Turns

This paper presents a novel analytical method (NAM) of inductance identification for a direct drive permanent magnet synchronous motor (DDPMSM) with a stator winding fault (SWF), which considers the spatial position of the shorted turns. First, the structure of the DDPMSM is introduced and its key parameters are reported. Second, the NAM on the inductance identification is elaborated. The inductance analytical expressions of the faulty coil are derived in detail, in which the inductances of the faulty coil and the fault branch can be quickly calculated according to the spatial position coordinates of fault turns. Then, the model of DDPMSM with SWF is established. Finally, using the NAM, finite-element method (FEM), and the simplified analytical method (SAM), the inductances of the faulty coil and the branch are calculated under different fault conditions. Additionally, the fault current of the faulty coil is also studied, where the value of the fault current reflects the fault severity. The comparisons among the FEM, NAM, and SAM show that the accuracy of the NAM is higher than that of the SAM.

A Novel Direct-Drive Permanent Magnet Synchronous Motor with Toroidal Windings

A direct-drive motor has the merits of low speed, high torque, and elimination of mechanical deceleration mechanisms, and is widely used in various fields. A novel direct-drive permanent magnet synchronous motor is presented herein, in which all coils are wrapped around the stator yoke in the same orientation. The structure of the novel direct-drive permanent magnet synchronous motor with toroidal windings (N-TWDDPMSM) is introduced and its operating principle is analyzed by describing the variation in the armature magnet field versus time. Furthermore, based on the same power grade and mechanical size, several finite-element models of motors with different windings are established using Magnet software to analyze the distribution of magnetic field, back-electromotive force (back-EMF), power-angle characteristics, loss characteristics, etc. Compared with the traditional permanent magnet synchronous motor (T-PMSM), the traditional permanent magnet synchronous motor with toroidal windings (T-TWPMSM), and the N-TWDDPMSM, the N-TWDDPMSM shows advantages of low speed and high torque, and the feasibility and superiority of the N-TWDDPMSM are verified.

A Physical Faulty Model Based on Coil Sub-Element for Direct-Drive Permanent Magnet Synchronous Motor With Stator Winding Short-Circuit Faults

As winding short-circuit faults (WSF) in a direct-drive permanent magnet synchronous motor (DDPMSM) degrade its reliability and may cause serious catastrophes, fault detection and diagnosis for the DDPMSM are necessary. The performances analyses of motor under WSF are the basis of fault detection and diagnosis. An efficient and accurate faulty model is a great tool for evaluating motor performances under various WSF. Hence, this paper proposes a novel physical faulty model (PFM) based on the coil sub-element for the DDPMSM with the WSF. Fault position can be examined by differentiating the inductance and the electromotive force of the coil sub-element. This model can evaluate motor performances under various WSF, especially inter-turn short-circuit fault in different positions of the same slot, without changing the internal structure of model. The faults are set by connecting the desired taps as in the practical motor. First, the structure and parameters of the DDPMSM are reported. Second, the inductance calculation matrix, which considers the spatial position of the fault, is constructed. Then, the proposed PFM is established. The motor performances under various WSF are evaluated. Finally, the results of PFM, finite element model and experiment are compared. The results validate the correctness of the proposed PFM.

PID controller optimized by genetic algorithm for direct-drive servo system

The latest development trend of direct-drive electro-hydraulic servo technology is discussed. The working principle, system model and system control theory of an electro-hydraulic servo system are studied. The dynamic behavior of the direct-drive electro-hydraulic servo system is highly nonlinear, structure uncertainty. Considering that the standard PID controller cannot fulfill all the demands, it is necessary to use advanced means for compensation. A PID controller optimized by genetic algorithm for an electro-hydraulic servo system direct driven by a permanent magnet synchronous motor is proposed. The genetic algorithm is applied to optimize the parameters of the PID controller. The simulation and experiment research of one direct-drive electro-hydraulic servo system are carried out to verify the response properties of the proposed controller. The step signal tracking responses of the servo system with different parameters of PID controller are, respectively, reported. In addition, a feedforward PID controller using genetic algorithm optimization is also designed for the direct-drive servo system. The simulation and experiment results show that the feedforward PID controller using genetic algorithm optimization has good dynamic response characteristics in the electro-hydraulic servo system based on a direct-drive permanent magnet synchronous motor.

Noise Analysis and Improvement of a Permanent Magnet Synchronous Motor by Dynamic Error Budgeting

Abstract: This paper presents the mechatronic analysis and performance estimation for a single axis rotational servo system with direct-drive permanent magnet synchronous motor (PMSM). To identify the dominant noise sources acting in the motor control system, physical modeling together with dynamic error budgeting are applied. The analysis is carried out for two modes of operation, zero velocity and constant velocity. The current sensor is identified as the major noise source. It is experimentally verified, that an improvement of the current measurement system yields an improvement of the position noise by a factor of 6.3.

Direct-Drive Permanent Magnet Synchronous Motor in the Application of New Energy Vehicles

This paper introduces the new energy vehicles drive system for the future development trend, analysis and comparison in the new energy vehicles drive motor technical indicators. By Ansolf analysis software to optimize the motor rotor, to improve the air gap flux density and the electric potential sine.

300W급 이중 공극 구조 PMSM 설계 및 출력 특성에 관한 연구

This paper suggests the dual-gap for generating power and increasing the torque of a direct-drive permanent magnet synchronous motor in a hybrid-cycle. To consider easy coil winding, we applied a structure of dual-gap for the permanent magnet synchronous motor (PMSM). Because the torque of PMSM with the dual-gap is very large, we are designed the appropriate specifications of the PMSM by selected the appropriate dual-gap slot and poles combination. The prototype model is selected by design theory for increasing torque and maximizing output power of PMSM. And the detailed structure design of the model was designed by the loading distribution method. The PMSM models were analyzed by finite element method. Finally, we have suggested appropriate rotor structure has benefit to further increasing torque and prevent decreasing of the output power in PMSM with dual-gap.

A New SVPWM Dead-Time Compensation Strategy for Low Speed Direct-Drive Motor

Traditional space vector pulse-width modulation (SVPWM) algorithm included complex calculations like triangle functions and square root, which increased execution time of the program. A novel SVPWM algorithm calculating modulation functions of three phases through stationary αβ components of reference voltage vectors was proposed here to solve the problem, which was composed of only simple four arithmeticoperations. The method simplified traditional SVPWM and improved real-time performance of digital control system. However, dead-time effect still existed in novel SVPWM algorithm. And it will lead to distortions of low speed direct-drive PMSM phase currents, brought increase of speed fluctuation, resulted in unstable operating of servo system. This paper analyzed details of error voltage vectors led by dead-time effect, researched relationship between error voltage vectors and polarities of three phase currents, and put forward a novel dead-time compensation strategy that decreased influence of zero current clamping. Simulation results showed that this strategy can effectively compensate effects of dead-time error voltage vector and improve wave forms of phase currents, which increased operating performance of low speed direct-drive PMSM.

Research on Cogging Torque for Low-Speed and Direct-Drive PMSM

The paper attempts to present some effective methods to reduce cogging torque for low-speed and direct-drive(LSDD) permanent magnet motor.

Robust High Bandwidth Discrete-Time Predictive Current Control with Predictive Internal Model—A Unified Approach for Voltage-Source PWM Converters

This paper presents a robust high bandwidth discrete-time predictive current control scheme for voltage-source pulsewidth-modulated (VS-PWM) converters. First, to achieve high bandwidth current control characteristics, a digital predictive current controller with delay compensation is adopted. The compensation method utilizes a current observer with an adaptive internal model for system uncertainties. The predictive nature of both the current observer and the internal model forces the delays elements to be equivalently placed outside the closed loop system. Second, to ensure perfect tracking of the output current in the presence of uncertainties and providing means for attenuating low- and high- frequency system disturbances, the frequency modes of the disturbances to be eliminated should be included in the stable closed loop system. Toward this, an adaptive internal model for the estimated uncertainty dynamics is proposed. To cope with the high bandwidth property of the lump of uncertainties in VS-PWM converter applications, the disturbance slowly varying assumption is relaxed in the proposed controller. The relaxation is achieved by adopting a curbing sliding-mode-based feedback gain vector within the internal model observation system. Comparative evaluation tests were carried out on a grid-connected VS-PWM converter and a direct drive permanent magnet synchronous motor (DD-PMSM) drive system to demonstrate the validity and effectiveness of the proposed control scheme at different operating conditions.

A Newly Designed Instantaneous-Torque Control of Direct-Drive PMSM Servo Actuator With Improved Torque Estimation and Control Characteristics

In this paper, a newly designed instantaneous-torque-control scheme with improved instantaneous-torque estimation and control characteristics in a direct-drive permanent-magnet synchronous motor (DD-PMSM) is presented. A hybrid control structure that combines the internal-model principle and the variable-structure control approach is proposed. The appropriate control voltage vector is determined using the control effort of the variable-structure torque and d-axis current controllers combined with the estimated dynamic back-EMF vector in a feedforward control manner. Subsequently, the dynamic back-EMF vector, which contains the flux-harmonics information, is included in the reference voltage generation as an internal model. As a result, better disturbance rejection can be obtained with the proposed cascaded control structure. To robustly obtain the instantaneous-torque information, an adaptive motor model is proposed. The adaptive model is realized by adopting recursive estimators to estimate unknown machine electrical quantities and parameters. In addition to its robust estimation performance, the proposed adaptive model includes the dynamic model of the estimated disturbance to enhance the estimation characteristics. Experimental results are presented to demonstrate the validity and effectiveness of the proposed instantaneous-torque-control scheme.