In the last decades, multilevel converters have been developed usually for medium-voltage high-power applications. They have become a mature solution for the increasing power demand of multiple applications such as renewable energy systems, power quality improvement, and motor drives. In this paper, the operation of multilevel converters is addressed focusing on control and modulation techniques for different well-known applications. The new developments are presented as an extension of conventional methods for two-level voltage-source converters which are still the mainstream solution for most cases.

Multilevel Converters: Control and Modulation Techniques for Their Operation and Industrial Applications

In this paper, a fast voltage control strategy of three-phase AC/DC pulsewidth modulation (PWM) converters applying a feedback linearization technique is proposed. First, incorporating the power balance of the input and output sides in system modeling, a nonlinear model of the PWM converter is derived with state variables such as AC input currents and DC output voltage. Then, by input-output feedback linearization, the system is linearized and a state feedback control law is obtained by pole placement. With this control scheme, output voltage responses become faster than those in a conventional cascade control structure. For robust control to parameter variations, integrators are added to the exact feedback control law. Since the fast voltage control is feasible for load changes, it is shown that the DC electrolytic capacitor size can be reduced. In addition, the capacitor current is analyzed for size reduction of the capacitor. As is usual with PWM converters, the input current is regulated to be sinusoidal and the source power factor can be controlled at unity. The experimental results are provided to verify the validity of the proposed control algorithm for a 1.5 kVA insulated gate bipolar transistor PWM converter system.

DC-bus voltage control of three-phase AC/DC PWM converters using feedback linearization

This paper presents a comprehensive analysis of a pulse- width modulated (PWM) ac-to-dc voltage source converter under phase and amplitude control. A general mathematical model of the converter, which is discontinuous, time-variant, and nonlinear, is first established. To obtain closed-form solutions, the following three techniques are used: Fourier analysis, transformation of reference frame, and small signal linearization. Three models, namely, a steady-state dc model, a low-frequency small-signal ac model, and a high-frequency model, are consequently developed. Finally, three solution sets, namely, the steady-state solution, various dynamic transfer functions, and the high- frequency harmonic components, are obtained from the three models. The theoretical results are verified experimentally.

Analysis of an ac-to-dc Voltage Source Converter Using PWM with Phase

A comprehensive analysis is presented of a pulse-width modulated AC-to-DC voltage source converter under phase and amplitude control. A general mathematical model of the converter, which is discontinuous, time-variant, and nonlinear, is first established. To obtain closed-form solutions, the following three techniques are used: Fourier analysis; transformation of reference frame; and small-signal linearization. Three models, namely, a steady-state DC model, a low-frequency small-signal AC model, and a high-frequency model, are consequently developed. Finally, three solution sets, namely, the steady-state solution, various dynamic transfer functions, and the high-frequency harmonic components, are obtained from the three models. The theoretical results were verified experimentally. >

Analysis of an AC-to-DC voltage source converter using PWM with phase and amplitude control

A variable speed wind turbine is disclosed comprising a turbine rotor that drives a doubly-fed induction generator, a matrix converter which converts variable frequency output into constant frequency output, and a control unit and a protection circuit for the matrix converter. Power is circulated in the system allowing for sensorless detection of rotor position and better output ratios of power from the system.

Variable speed wind turbine having a matrix converter

A high-performance control method for a voltage-type pulsewidth-modulated voltage-type converter is introduced. Starting from the modeling of the converter, power-factor control and five types of DC voltage control are discussed. The stability and responses of these control methods are analyzed and compared with the root locus method and by digital simulation. The most promising approach, which uses current feedforward control, is applied to the drive test of an induction motor, and its excellent performance is confirmed. >

M. Yano

Papers

A high performance control method of a voltage-type PWM converter