Detailed models are presented for the stationary and synchronous sine-triangle current regulators. Analytical and test results are compared for purposes of model verification and regulator evaluation. The results demonstrate the limitations of the two most often used current regulators and the robustness of the synchronous current regulator. The stationary sine-triangle and hysteretic current regulators are shown to have steady-state characteristics that depend on slip, operating frequency, and motor impedance. In contrast the synchronous regulator, because it lacks these dependencies, exhibits ideal steady-state current regulator characteristics without sacrificing bandwidth. Moreover, the complexities traditionally associated with the synchronous regulator are overcome with a simple equivalent implementation.

A New Synchronous Current Regulator and an Analysis of Current-Regulated PWM Inverters

The evolution of power electronics and its control has been mainly driven by industry applications and influenced by the development achieved in several technologies, such as power semiconductors, converter topologies, automatic control, and analog and digital electronics. Digital signal processors (DSPs), in particular, have experienced an exponential development in processing power, which until now has not been fully exploited for control purposes in power converters and drive applications. Presently, the control system technology finds itself in a paradigm-changing tipping point, in which more demanding control goals, system flexibility, and functionalities required by emerging applications are driving the control system technology development, in addition to stabilization and robustness, which was the main focus in the past. This article walks briefly through the history of the mainstream power converter control scene, with an emphasis on the more recent introduction of predictive control, and gives a glimpse on the challenges and possibilities ahead. Special attention is given to finite control set (FCS)-model predictive control (MPC), because of its simplicity, flexibility, inherent adaptation to power electronic circuits and their discrete nature, both in the finite amount of switching states and the digital implementation with microprocessors.

Model Predictive Control: MPC's Role in the Evolution of Power Electronics

An induction motor is the most frequently used electric machine in high-performance drive applications. Control schemes of such drives require an exact knowledge of at least some of the induction motor parameters. Any mismatch between the parameter values used within the controller and actual parameter values in the motor leads to a deterioration in the drive performance. Numerous methods for induction machine on-line and off-line parameter estimation have been developed exclusively for application in high-performance drives. This paper aims at providing a review of the major techniques used for the induction motor parameter estimation. The paper is illustrated throughout with experimental and simulation examples related to various parameter estimation techniques.

A review of RFO induction motor parameter estimation techniques

Field orientation has emerged as a powerful tool for controlling ac machines such as inverter-supplied induction motors. The dynamic performance of such a drive is comparable to that of a converterfed four quadrant dc drive. The complex functions required by filed-oriented control may be executed by microprocessors on line, thus greatly reducing the necessary control hardware. It is shown that the flux signals may be derived from sensing coils or, with some compromise in performance, from the stator voltages and currents. The speed signal is obtained from a digital tachometer. Results from a 2-kW experimental drive are given.

Field-Oriented Control of a Standard AC Motor Using Microprocessors

The sensitivity of the parameters of a rotor-flux-oriented system using rotor flux estimation is discussed, and a stator-flux-oriented scheme is developed. Since the estimation of the stator flux is independent of the leakage, the steady-state performance of the stator-flux-oriented system is insensitive to the leakage inductance. A decoupler is designed to minimize the coupling in the stator-flux reference frame, improving the dynamic performance of the system. Digital simulation is carried out to show that the performance of the stator-flux-oriented system is superior to that of a detuned rotor-flux-oriented system. >

A stator flux oriented induction machine drive

SummaryThe dynamic interactions of AC-machines are far more complex than those of DC-machines and important quantities are not directly measurable. This has given rise to considerable difficulties in designing high performance AC-drive controls. About 20 years ago, they were overcome by the emergence or new methods of control, using moving frames of reference determined by the angular position or flux waves, hence called field orientation. Their application requires extensive on-line signal processing that can only be realised economically with microprocessors or special digital hardware.The paper presents a review of this evolution, which has matured in less than 2 decades from research studies to a universally accepted method for controlling AC-machines. The method of field orientation has proved to be well adaptable to all types of power converters and AC-machines; modifications and extensions to include self-tuning and adaptive features are possible. It now seems to be generally accepted that field or...

30 Years Space Vectors, 20 Years Field Orientation, 10 Years Digital Signal Processing with Controlled AC-Drives, a Review (Part 1)

With the recent advances of power transistors and microprocessors it has become possible to design high-dynamic-performance ac-servo drives free of moving contacts using synchronous or asynchronous motors. Both schemes have their particular strengths. A general control principle, based on field or rotor orientation, is described which has been realized with a state-of-the-art microcomputer, where all the signal processing, including modulation of the inverter, is performed by software. Extensive tests have been carried out with different motors to compare the characteristics of the various types of drives.

Werner Leonhard

Papers

Field-Oriented Control of a Standard AC Motor Using Microprocessors

30 Years Space Vectors, 20 Years Field Orientation, 10 Years Digital Signal Processing with Controlled AC-Drives, a Review (Part 1)

Microprocessor-Controlled AC-Servo Drives with Synchronous or Induction Motors: Which is Preferable?

Microprocessor-controlles AC-servo drives with synchronous or induction motors: which is preferable?

Adjustable-speed AC drives