Estimation of the flux linkage in a direct-torque-controlled drive

An improved integration method is presented for the estimation of the stator flux linkage for speed- and position-sensorless direct-torque-controlled AC machine drives. The method is based on monitoring the scalar product of the estimated stator flux linkage and the measured stator current. The AC part of the scalar product is extracted using filtering and the correction for the estimated stator flux linkage is formed from that part. Adequate performance is obtained by using simple low-pass filtering. By using adaptive filtering in the extraction, the performance of the drive is excellent. Both simulation and laboratory test results are presented, which show that the presented method works well both in steady state and in transients.     

On the behavior of a current fed synchronous machine drive withoutDC-link inductance

A drive system with synchronous machine and machine-commutated thyristor-inverter is discussed. The current source of this type of drive is realized by a fast switching transistor chopper, and the current is smoothed by the machine reactance and, atypically, by a choke in the DC link. It is shown that operation without link inductance affects the margin angle of the inverter. Hence, the reactive power of the machine has to be increased considerably. To overcome this disadvantage, a special method of control is presented, investigated, and verified by experimental results     

Measurement of rotor load angle of synchronous machines

A measurement system is presented in which an almost immediate and permanent record of steady-state or transient values of rotor load angles of synchronous machines may be obtained utilising an ultraviolet recorder.     

IPM synchronous machine drive response to a single-phase open circuit fault

This paper investigates the steady-state and dynamic response of an interior permanent magnet (IPM) synchronous machine drive to a single-phase open-circuit fault. This fault results in rotational electromagnetic asymmetry on both the stator and rotor, making it difficult to analyze using classical dq-transformation techniques. This paper presents a new dq synchronous-frame machine model that is capable of handling this highly asymmetrical fault condition, including the effects of q axis magnetic saturation. Fault responses with two alternative post-fault control strategies are investigated: (1) opening all of the inverter switches so that the machine behaves as an uncontrolled generator (UCG), with the two unfaulted phases connected to the inverter DC link via the antiparallel diodes; and (2) shorting the two remaining unfaulted phases together using the inverter switches. Results of this investigation show that the fault response is generally more benign using the UCG control strategy, with significantly lower phase currents and pulsating torque than corresponding values delivered using the phase-shorting strategy.     

Improved method of measuring the load angle of synchronous machines

A method is presented for measuring the load angle of a synchronous machine, which has a time delay much shorter than methods previously described. In addition, a signal suitable for control and recording purposes is available with a minimum of further delay.     

Optimization of a synchronous reluctance machine for a sensorless drive with a wide field-weakening range

For more than one century, electrical machines have been utilized for electrical drives. Nowadays, in most applications the electrical machine is fed by an inverter. Three types of machines are available for such purposes: the asynchronous induction machine, the permanent magnet excited synchronous machine and the synchronous reluctance machine. Reluctance machines represent an alternative to the other types when utilized in high-performance drives with a wide speed range. Due to the rotor saliency, these machines have an inherent suitability for a position-sensorless control. The parameters of a 5 kW machine with a maximum speed of 8000 rpm are evaluated by means of nonlinear finite element analyses. With regard to an application in a high-performance drive with a wide field-weakening range and a position-sensorless control scheme, the characteristics are calculated for the conventional reluctance machine as well as the reluctance machine with additional permanent magnets in the rotor. The comparison of the characteristics of the conventional reluctance machine and the permanent magnet assisted reluctance machine clearly shows the improved performance in terms of electromagnetic torque and power factor due to the interior permanent magnets. Thereby, the suitability for the application in position-sensorless drives due to the high effective saliency is preserved.     

Matrix methods for the study of a regulated synchronous machine

A powerful but simple matrix method for the digital computer manipulation of large sets of differential and algebraic equations is introduced to the field of power systems. The method is first illustrated with reference to the linearized equations representing a general-purpose turboalternator model. Subsequently, the form of the system equations obtained as a result of the matrix method is seen to provide a unified approach to the determination of system stability limits using Routh, Nyquist, or eigenvalue methods. The normal state space form of the system equations is also shown to facilitate control studies. A previously suggested performance criterion for an excitation system is generalized, and a systematic method for the simultaneous optimization of governor and exciter control loops is suggested. This method of optimization does not require the evaluation of system transient responses. The manner in which the normal state space form of the system equations leads naturally to the synthesis of controllers which are optimal with respect to a chosen scalar quadratic performance index is indicated. With this form of control, the structure is not defined a priori but emerges from the computational algorithm and it becomes unnecessary to specify the source or the magnitude of the stabilizing signals required to provide an improved dynamic performance. Finally, the matrix method is shown to be effective for the manipulation of the nonlinear machine equations and these are obtained in a new form which is directly amenable to digital or analog computer solution.     

Parameters and volt-ampere ratings of a synchronous motor drive forflux-weakening applications

This paper deals with the selection of the motor parameters and the inverter power ratings for a permanent magnet (PM) synchronous motor drive in order to meet a given flux-weakening torque versus speed characteristic. Appropriate combinations of stator PM flux linkage, d- and q-axis inductances, and inverter current rating at a given voltage are derived, in normalized values, as functions of the specified flux-weakening speed range and torque limits. By means of these sets of data, the drive designer can easily individuate and compare all the suitable synchronous motors (defined by the d- and q-axis inductances and flux linkage) and the related inverter volt-ampere ratings, for the desired flux-weakening performance. Therefore, this paper can be considered a synthesis work rather than an analysis one and can profitably be used for an optimal design of a synchronous motor drive     

Steady-state stability of the doubly fed synchronous machine

The eigenvalues of the linearised equations describing a variable-speed doubly fed synchronous machine are examined to establish steady-state stability boundaries. A limited range of results is confirmed by experiments using a wound-rotor machine fed from the mains and from a cycloconvertor.     

High-efficiency drive due to power factor control of a permanentmagnet synchronous motor

A drive system of a permanent magnet motor without a magnetic position detector is described. Generally, the position data of a magnet is obtained from the terminal voltage of the motor. In the newly developed method, the inverter DC-link current waveform provides the control signal for driving a permanent magnet motor without a detector. Since the power factor of the motor is controlled around 1.0, the motor runs at a higher efficiency than one controlled by the conventional method. Therefore, this control method saves energy. Current pulsation induced by sudden load fluctuations has been studied and its stabilization has been achieved. This paper provides the principle and operation of the new control method, simulated characteristics, and experimental results     

The control of a synchronous machine using optimal control theory

The selection of stabilizing signals to improve power system dynamic behavior is presented. Some results from modern control theory are used to show how such stabilizing signals may be derived systematically for a turboalternator model connected through a double circuit line to an infinite bus. The closed-loop performance of this nonlinear system model with the derived linear optimal controller is then evaluated for a wide range of input disturbances and operating conditions which include three-phase fault studies with autoreclosure.     

A SPICE model of a permanent magnet synchronous motor with a light load

A simple and accurate model of a permanent magnet synchronous motor (PMSM) with a light load is presented in this paper. The light-load condition is always needed in integrated circuit manufacturing machines in order to achieve a fast, accurate and minimum overshoot response. The model proposed here can help a designer to specify the controller's specifications and also to verify the hardware of motor drives. The differential equations of the PMSM are handled by the macromodels in PSPICE^TM. Moreover, it is revealed that the PMSM system is operating in a 4-state mode rather than a 2-state mode. Experimental results are provided to verify the simulation results of this model. The heavy load condition is also simulated.     

Predictive direct torque control for the PM synchronous machine

This paper shows that a predictive digital control combined with the principle of direct torque control (DTC) leads to an excellent dynamic behavior of the synchronous machine with surface-mounted permanent magnets and is a real alternative to the classical field-orientated control. The advantages are a DTC control scheme with constant switching frequency and a predictable torque ripple. The settling times of the torque are reduced compared to the classical field-orientated control. The application in servo drives in which the rotor position is always measured can easily be achieved by using a commercial digital signal processor. Numerous simulations and measurements confirm the theoretical work.     

A novel direct torque controlled interior permanent magnet synchronous machine drive with low ripple in flux and torque and fixed switching frequency

A modified direct torque control (DTC) scheme for interior permanent magnet synchronous machine (IPMSM) is investigated in this paper, which features in very low flux and torque ripple and almost fixed switching frequency. It is based on the compensation of the error flux linkage vector by means of space vector modulation. Modeling and experimental results show that the flux and torque ripples are greatly reduced when compared with those of the basic DTC. With the new scheme, very short sampling time is not essential. All the advantages of the basic DTC are still retained. In addition, fixed switching frequency at different operating conditions becomes possible. The field-weakening control of this drive is also studied; an IPM DTC drive with a wider operation range and lower flux and torque ripple has been achieved experimentally.     

基于有限元法的永磁同步电机铁耗计算

给出了永磁同步电机铁心损耗的计算模型以及铁耗计算的一般方法。通过有限元分析,得出定、转子铁心不同区域磁场的变化规律。综合考虑电机中交变磁场与旋转磁场的影响,对永磁同步电机的铁耗进行了分析计算。给出其不同位置的损耗密度以及电机中各种损耗的含量,为进一步对电机进行优化设计、减少损耗奠定了基础。     

Synchronising and damping torques in a synchronous machine with 2-axis excitation control

Current interest in the use of combined direct- and quadrature-axis excitation-control systems for synchronous machines makes it relevant to consider the basic physics of such a configuration. By studying the synchronising and damping torques, it is possible to assess the effectiveness of this type of control.     

Control characteristics and speed controller design for a highperformance permanent magnet synchronous motor drive

The theory of vector control is applied to the nonlinear model of a permanent magnet synchronous motor to develop a linear model for controller design purposes. The operation and relevant mathematics of a pseudo-derivative feedback controller are presented. Controller designs for three different speeds are then considered, and a comparative evaluation is made on the basis of their large and small-signal behavior. In order to test the large-signal response, the detailed nonlinear model of the machine and a real-time model of the inverter switches are used. Results indicate that a critically damped design done so as to ensure that all control and power signals never saturate gives an extremely poor result. Much better small and large-signal responses are achieved by avoiding this constraint and using Zener diodes instead to limit the commanded input into the inverter. Two designs using this technique are presented, an underdamped design with low speed overshoot and an overdamped design with no speed overshoot. The response of the underdamped design was much quicker than that of the overdamped. However the overdamped design has application when speed overshoot is intolerable     

Control and dynamics of constant-power-loss-based operation ofpermanent-magnet synchronous motor drive system

The operational envelope of electrical machines is limited by the maximum permissible power loss of the machine at any given speed. The control and dynamics of the permanent-magnet synchronous motor (PMSM) drive operating with a maximum power loss versus speed profile is proposed in this paper. The proposed operational strategy is modeled and analyzed. Its comparison to the conventional strategy of limiting current and power to rated values demonstrates the superiority of the proposed scheme. The implementation of the proposed strategy is developed. It is achieved with an outer power loss feedback control loop. This has the advantage of retrofitting the present PMSM drives with the least amount of software/hardware effort. The PMSM drives in this case then can use the existing controllers to implement any torque control criteria, such as constant torque angle, unity power factor, constant air-gap flux linkages, maximum torque per unit current, or maximum-efficiency operation. Experimental verification of the new operational strategy is provided. The concepts presented in this paper can be applied to all other types of motor drives     

Speed tracking control of a permanent-magnet synchronous motor withstate and load torque observer

This paper is concerned with the speed tracking control problem for a permanent-magnet synchronous motor (PMSM) in the presence of an unknown load torque disturbance. After a brief review of the mathematical model of the PMSM, a speed tracking control law using the exact linearization methodology is introduced. The tracking control algorithm is completed by adding an extended observer which provides, on the one hand, the motor speed and acceleration and, on the other hand, estimates the unknown load torque. The stability of the closed-loop system composed of a nonlinear speed tracking controller and an observer is studied by the way of Lyapunov theory. Furthermore, the decoupling of the state observer and the load torque observer is discussed. Finally, a real-time implementation and the experimental results of the proposed control strategy are presented     

Online estimation of the stator resistance and leakage inductance of a four-phase induction machine drive

This paper proposes a technique to determine online the stator resistance and the stator leakage inductance of a four-phase induction machine in a four-phase drive system. These parameters are obtained by solving a least squares minimization problem. The technique is conceived to be used online with the drive strategy without disturbing the machine electromagnetic torque. Experimental results are used to demonstrate the feasibility of the proposed technique.