同步磁阻电机最优电流角控制

对于同步磁阻电机在运行过程中受到磁路饱和与电压极限的影响,本文提出了最优电流角控制策略。采用Ansoft软件对电机内部磁场进行有限元仿真,对dq轴电感的耦合与饱和现象进行拟合,并利用拟合结果得到最优电流角随负载转矩变化的轨迹,以实现同步磁阻电机最大转矩电流比(MTPA)控制;同时考虑电压、电流极限对电机运行的影响,使电机在高速运行时可以实现空载到满载的稳定运行。通过建立考虑磁路饱和的同步磁阻电机数学模型进行仿真验证,而实验结果也说明了该方案的可行性与有效性。     

Maximum torque control of stator-flux-oriented induction machinedrive in the field-weakening region

In a conventional stator-flux-oriented (SFO) induction machine drive system, the field-weakening method is used to vary the stator-flux reference in proportion to the inverse of the rotor speed. This paper investigates why the maximum torque capability cannot be obtained in a conventional SFO system. This paper proposes a new selection method of flux reference to obtain maximum torque capability in the field-weakening region by considering voltage, torque, and current limits. The proposed method is verified by simulation and experiment with a 5 hp induction motor drive     

实现感应电机宽范围最大转矩控制的电流优化策略

针对广泛应用于数控机床主轴驱动系统中的交流感应电机,提出了一种新的宽范围运行的电流优化控制策略。根据感应电机在不同速段的转矩特性,充分考虑逆变器的输出电压限制、电机本体的电流约束条件及最大转差频率限制,以输出最大转矩为目标,得出了全速范围内的最优电流控制轨迹和感应电机宽范围转矩输出最大化的电流优化分配指导原则。在此基础上,设计了一种工程实现算法,依据电机实际运行的状态变量实现恒转矩区、恒功率区与恒电压区的快速平滑过渡,完成了对最优电流控制轨迹的逼近。实验结果证明了提出方法的有效性,可以实现感应电机宽范围运行的最大转矩输出,并且使系统具有较快的动态响应性能。     

一种异步电机定子磁链弱磁控制方法

本文提出了一种电动汽车用异步电机的定子磁链弱磁控制方法,通过引入定子参考电压与逆变器能提供的电压值的比较,确定电机的运行区域,进而确定能够输出最大转矩的励磁电流,再结合给定转矩求出定子磁链参考值。本方法采用定子参考电压与母线电压对应值的比较,仅需简单计算即能实现恒转矩、恒功率、降功率区域的平滑过渡。在逆变器和电机的电压、电流能力一定时,能够输出最大转矩。无需转子磁链定向,适用于定子磁链控制的场合。通过动态调整转矩给定限制值可保证电机稳态运行不过流。仿真和实验结果证明了本方法的有效性。     

Practical Wide-speed-range Sensorless Control System for Permanent Magnet Reluctance Synchronous Motor Drives via Active Flux Model

This article introduces a control strategy to obtain near-maximum available torque in a wide speed range with sensorless operation via the active flux concept for permanent magnet-reluctance synchronous motor drives. A new torque dq current reference calculator is proposed, with reference torque limited by the torque/speed envelope and by maximum current constraint. This solution approximates the maximum torque per ampere below base speed and also in the flux-weakening region, where voltage limitations impose constraints on the allowable dq currents with less computational effort. Comprehensive digital simulation results (1–6000 rpm) and experimental results (50–3000 rpm at low inverter available DC voltage of 12 V_dc instead of 48 V_dc) demonstrate the effectiveness of the proposed sensorless control strategy in a wide speed range, with stable and reliable operations up to a speed equal to eight times the machine base speed (constant power speed range = 8).     

基于开关序列的永磁同步电机模型预测磁链控制

为了消除传统的模型预测转矩控制(Model predictive torque control,MPTC)算法中的权重因子,减小计算量并提高稳态控制精度,本文提出了一种基于开关序列的永磁同步电机模型预测磁链控制(Model predictive flux control- switching sequence,MPFC-SS)算法。首先,通过分析电磁转矩和磁链的关系,将对转矩和定子磁链幅值的控制等效转换为对d、q轴磁链的控制,避免了权重因子的设计;其次,采用定子磁链无差拍预测控制计算所需的参考电压矢量,并根据其所在扇区选择对应开关序列;然后,基于磁链无差拍预测控制原则,计算开关序列中基本矢量的最优作用时间,有效减小电流谐波和转矩脉动,实现定子磁链的准确跟踪。最后,对传统MPTC和所提算法进行了实验对比研究,结果表明：所提算法具有计算量小、电磁转矩脉动小、电流谐波含量低等优点。     

Simulation Study on On-Line MTPA/MTPV Trajectory Tracking in PMSMs with Power Management

Abstract

This paper proposes an on-line maximum torque per ampere (MTPA)/maximum torque per voltage (MTPV) trajectory tracking method in permanent magnet synchronous machines (PMSMs) with power management. The on-line MTPA/MTPV machine current trajectory tracking algorithm is developed from PMSM model. Maximum source current and machine current are regulated to enhance hardware protection during machine current trajectory tracking. The maximum source current management is achieved by iterating within the current trajectory tracking algorithm over continuous torque command modifications based on power flow analysis, and the maximum machine current management is achieved by torque command limiting based on current angle modulation. Different from the existing techniques in literature, the proposed method has an unique feature of providing on-line regulation of source current, while maintaining on-line MTPA/MTPV trajectory tracking in PMSMs. It also provides machine and inverter overcurrent regulation to enhance their protection. In addition, the proposed method is flexible to tune and does not require off-line calibration. The effectiveness of the proposed method is confirmed by simulation results in MATLAB.     

Direct Flux Field-Oriented Control of IPM Drives With Variable DC Link in the Field-Weakening Region

This paper presents the direct flux control of an interior permanent-magnet (IPM) motor drive in the field-weakening region. The output torque is regulated by the coordinated control of the stator flux amplitude and the current component in quadrature with the flux, and it is implemented in the stator flux reference frame. The control system guarantees maximum torque production taking into account voltage and current limits, in particular in case of large dc-link variations. The field-oriented control does not necessarily require an accurate magnetic model of the IPM motor, and it is able to exploit the full inverter voltage at different dc-link levels with no additional voltage control loop. The feasibility of the proposed control method is investigated in discrete-time simulation, then tested on a laboratory rig, and finally implemented on board of an electric scooter prototype. The motor under test is an IPM permanent-magnet-assisted synchronous reluctance machine, with high-saliency and limited permanent-magnet flux.     

Design and Control of an Axial-Flux Machine for a Wide Flux-Weakening Operation Region

This paper describes the strategy to design and control an axial-flux (AxF) surface-mounted permanent-magnet machine for achieving a wide flux-weakening (FW) operating region. By using a slotted stator with fractional-slot windings and additional cores enclosing end windings, the AxF machine satisfies the specification of a wide constant-power speed range. The design procedure is presented for increasing FW capability while obtaining low-harmonic back electromotive force and low cogging torque. This technique is applied to design an 8-Nldrm AxF prototype machine that exhibits about 3 : 1 FW range. To the aim of exploiting full capability of the machine, an FW controller is designed and implemented. This controller utilizes the voltage difference between the current regulator and the output voltage, limited by a voltage source inverter. With this method, the output torque in the FW region is higher than that achieved using the conventional FW method based on the voltage-magnitude feedback. The goodness of both design and control algorithm is proved by experimental tests on a prototype.     

Maximum torque control of an induction machine in the fieldweakening region

In this paper, a new approach to the induction machine control that ensures the production of maximum torque per ampere over the entire field weakening region is presented. Considering the limitations of voltage and current, the optimal current condition for yielding the maximum torque is obtained. Also, since the onset of the field weakening operation is automatically adjusted according to the flux level, the current limit and the voltage limit, smooth and precise transition can be obtained. The proposed scheme is verified through simulation and experiment with a 5-hp laboratory induction motor drive system     

Acceleration tests to determine salient pole synchronous motorinrush currents and torques

Determining torque and current at locked rotor and various slips during the acceleration test on a synchronous machine is very tedious and time consuming. Induction and synchronous machines behave similarly during acceleration except that synchronous machine acceleration can include a pulsation torque. Because of the salient poles, conditions exist where the synchronous motor has minimum torque at quadrature axis and maximum torque at direct axis during locked rotor or stall. Since synchronous machines do not have large numbers of rotor bars in the amortisseur winding, like the induction motor has in the squirrel cage, their stall times tend to be shorter. Due to the shorter stall time and large starting torque, locked-rotor torque and current are generally determined from acceleration tests conducted at reduced voltage rather than by tests at stand-still. Data showing that saturation effects impact both torque and current are presented in this paper. The data shows that the voltage index that has to be applied to the torque and current measured at reduced voltage varies with speed and can be obtained from a series of acceleration tests     

Optimum torque control of permanent-magnet AC Machines in the field-weakened region

This paper presents a novel current regulation algorithm for permanent-magnet ac (PMAC) machines that provides maximum torque-per-ampere capability in the entire field-weakened region. The algorithm provides robust current regulation with maximum efficiency and torque capability for PMAC machines despite significant changes in the voltage source and machine parameters. The algorithm identifies when the current regulator starts to saturate and determines the optimum d-axis current command for the machine. The q-axis current command is determined from the torque command and d-axis current feedback. When the voltage angle reaches the maximum angle, the current magnitude is decreased to provide maximum torque per ampere. Experimental results from a machine prototype show that the algorithm provides good overall dynamic response and smooth transitions into the field-weakened region with maximum torque-per-ampere capability in all four quadrants of operation.     

Locked-rotor and acceleration testing of large inductionmachines-methods, problems, and interpretation of the results

The measurement of locked-rotor current, torque, and power factor has been a standard test for induction machines for many years. Measurement of torque has evolved from using a brake, a dynamometer, a torque arm, and scale, through strain gauges and load cells to acceleration tests. The test must be of short duration to prevent damage to the machine and large machines present problems because of facility limitations in either kilovoltampere or torque measurement. A single test at reduced voltage when prorated to operating voltage by the square of the ratio of rated voltage to test voltage neglects the impact of saturation and results in significantly lower values of predicted torque and current. This paper discusses several methods for performing the locked-rotor and the speed-torque tests on large machines. It also discusses some of the problems associated with the test methods and shows how the tests can be performed and the results evaluated to account for saturation effects. Finally, the paper shows how to extract some machine circuit parameters from the test data     

无刷直流电机低力矩波动控制方法

针对无刷直流电机力矩波动，本文提出提高换流电压的电流控制PWM方法。给出了改进的硬件线路，并与传统方法控制进行仿真比较，对改善电流波形和降低力矩脉动取得比较好的效果。     

Evaluation and implementation of a system to eliminate arbitraryload effects in current-based monitoring of induction machines

This paper presents a method for removing the load effects from the monitored quantity of the machine. Fault conditions in induction machines cause the magnetic field in the airgap of the machine to be nonuniform. This results in harmonics in the stator current of the motor which can be measured in order to determine the health of the motor. However, variations in the load torque which are not related to the health of the machine typically have exactly the same effect on the load current. Previously presented schemes for current-based condition monitoring ignore the load effect or assume it is known. Therefore, a scheme for determining machine health in the presence of a varying load torque requires some method for separating the two effects. This is accomplished by comparing the actual stator current to a model reference value which includes the load effects. The difference between these two signals provides a filtered quantity, independent of variations of the load, that allows continuous on-line condition monitoring to be conducted without concern for the load condition. Simulation and test results illustrate the effects on the spectrum of the monitored quantity for both constant and eccentric airgaps when in the presence of an oscillating load     

Modified direct torque control method for induction motor drives based on amplitude and angle control of stator flux

This paper proposes design and implementation of a direct torque controlled induction motor drive system. The method is based on control of separation between amplitude and angle of reference stator flux for determining reference stator voltage vector in generating PWM output voltage for induction motors. The objective is to reduce electromagnetic torque ripple and stator flux droop which result in a decrease in current distortion in steady-state condition. In addition, the proposed technique provides simplicity of a control system. The direct torque control is based on the relationship between instantaneous slip angular frequency and rotor angular frequency in adjustment of the reference stator flux angle. The amplitude of the reference stator flux is always kept constant at rated value. The system has been implemented to verify its capability such as torque and stator flux responses, stator phase current distortion both during dynamic and steady state with load variation, and low speed operation.     

Torque-ripple minimization in modular permanent-magnet brushless machines

This paper discusses the suitability of four-phase, five-phase, and six-phase modular machines, for use in applications where servo characteristics and fault tolerance are key requirements. It is shown that an optimum slot number and pole number combination exists, for which excellent servo characteristics could be achieved, under healthy operating conditions, with minimum effects on the power density of the machine. To eliminate torque ripple due to residual cogging and various fault conditions, the paper describes a novel optimal torque control strategy for the modular permanent-magnet machines operating in both constant torque and constant power modes. The proposed control strategy enables ripple-free torque operation to be achieved, while minimizing the copper loss under voltage and current constraints. The utility of the proposed strategy is demonstrated by computer simulations on a four-phase fault-tolerant drive system.     

Stator-flux-based vector control of induction machines in magneticsaturation

In many variable-torque applications of induction machines, it is desirable to operate the machine at high flux levels, thus allowing the machine to produce higher torques. This can lead to saturation of the main flux path, introducing cross-coupling effects which can severely disrupt the performance of controllers dependent on knowledge of the machine's magnetic parameters. Stator flux-oriented torque-control schemes need not depend on the magnetic parameters of the machine and, hence, are potentially more robust and easier to implement in magnetic saturation than rotor-flux-oriented control. In this paper, the authors present and analyze a stator-flux-oriented torque-control scheme. This controller only requires knowledge of the stator voltage, stator current, and stator resistance. An analytical expression for the maximum achievable torque output of the machine using a linear magnetics model is compared with values calculated using a nonlinear magnetics model incorporating saturation of the main flux path and is shown to be a good approximation at high flux levels, when the main flux path is heavily saturated. Experiments carried out on a 3 hp 1800 RPM wound-rotor induction machine show smooth operation of the control scheme at torque levels up to at least four times rated torque     

Modeling Split-Phase Induction Motors With Center-Tapped Windings and Asynchronous Torque Dips

This paper puts forward an analytical method for calculating the performance of a split-phase induction machine, where the auxiliary winding can be connected to a center tap on the main winding. Some manufacturers produce machines like this to allow for dual voltage operation. The method utilizes an impedance matrix so that a variety of connections are possible. The analysis is described in full and tested experimentally. Asynchronous torque dips are included in the method, and these are clearly shown.     

基于嵌合转矩法的虚拟同步机多回路保结构稳定分析

虚拟同步发电机(virtual synchronous generator,VSG)控制系统结构复杂、耦合性强,传统的稳定性分析方法无法分析系统内部各交互回路间的相互作用机理问题。基于此,文章提出一种基于嵌合转矩法的多回路保结构稳定分析方法。首先,基于模块化建模思想及模块重构建立了VSG并网的多回路交互保结构模型;其次,基于嵌合转矩法建立各交互回路间的回路阻尼转矩,形成分析-结构联通对应关系;然后,详细分析多回路系统中关键回路和关键参数的精确溯源方法,对VSG系统内各环节间的阻尼竞争及互激等规律进行了深入分析;最后,以VSG控制下的单机无穷大系统为例进行仿真验证。结果表明:VSG控制系统中电压控制环和电流控制环的直轴分量和交轴分量存在交互影响。其交互回路间阻尼转矩的恶性竞争以及负向激励导致了系统机电振荡模式失稳。该方法在捕捉系统失稳机制的基础上,还能为实际参数配置优化提供借鉴基础,具有一定应用价值。