Luigi Malesani

Current control techniques for three-phase voltage-source PWM converters: a survey

The aim of this paper is to present a review of current control techniques for three-phase voltage-source pulsewidth modulated converters. Various techniques, different in concept, have been described in two main groups: linear and nonlinear. The first includes proportional integral (stationary and synchronous) and state feedback controllers, and predictive techniques with constant switching frequency. The second comprises bang-bang (hysteresis, delta modulation) controllers and predictive controllers with on-line optimization. New trends in current control-neural networks and fuzzy-logic-based controllers-are discussed, as well. Selected oscillograms accompany the presentation in order to illustrate properties of the described controller groups.

Comparison of current control techniques for active filter applications

This paper presents the comparative evaluation of the performance of three state-of-the-art current control techniques for active filters. The linear rotating frame current controller, the fixed-frequency hysteresis controller, and the digital deadbeat controller are considered. The main control innovations, determined by industrial applications, are presented, suitable criteria for the comparison are identified, and the differences in the performance of the three controllers in a typical parallel active filter setup are investigated by simulations.

Robust dead-beat current control for PWM rectifiers and active filters

The paper analyses the stability limitations of the digital dead-beat current control applied to voltage-source three-phase converters used as PWM rectifiers and/or active filters. In these applications the conventional control algorithm, as used in drive applications, is not sufficiently robust and stability problems may arise for the current control loop. The current loop is, indeed, particularly sensitive to any model mismatch and to the possibly incorrect identification of the model parameters. A detailed analysis of the stability limitations of the commonly adopted dead-beat algorithm, based on a discrete-time state space model of the controlled system, is presented. A modified line voltage estimation technique is proposed, which increases the controls robustness to parameter mismatches. The results of the theoretical analysis and the validity of the proposed modification to the control strategy are finally verified both by simulations and by experimental tests.

AC/DC/AC PWM converter with reduced energy storage in the DC link

The paper introduces the family of quasi-direct converters, i.e., forced-commutated AC/DC/AC power converters including small energy storage devices in the DC link. In particular, the case of the three-phase to three-phase quasi-direct power converter is considered. Since energy storage minimization calls for instantaneous input/output power balance, a proper control strategy is needed. The paper describes a simple and effective control technique which also provides high-power factor and small distortion of the supply currents. After a discussion of the general properties of quasi-direct power converters, design criteria of both power and control sections are given, and experimental results of a 2-kVA prototype are reported. >

Three-Phase AC/DC PWM Converter with Sinusoidal AC Currents and Minimum Filter Requirements

A pulsewidth modulation (PWM) control technique suitable for fully controlled three-phase ac/dc converters is analyzed, which gives sinusoidal input currents and ideally smoothed dc voltage. The technique allows four-quadrant operation and full-range control of the input power factor. An extension to a simplified converter scheme, capable of one-quadrant operation, is also considered. Operation of the converter is analyzed under both ideal and actual conditions. Control implementation and design criteria are discussed and experimental results are reported.

High-performance hysteresis modulation technique for active filters

A new, substantial improvement of the hysteresis current control method for voltage source inverters is presented. A simple and fast prediction of the hysteresis band is added to a linearized version of the phase-locked loop control, thus ensuring constant switching frequency and tight control of the position of modulation pulses. This allows high accuracy in tracking highly distorted current waveforms and minimizes the ripple in multiphase systems. The implementation of this technique is very simple and robust, employing only a small number of conventional inexpensive analog and logic components. It does not require trimmings or tunings, giving the control the capability to adjust itself to the different operating conditions. The proposed method is compared with the most diffused modulation techniques, demonstrating its superior performance in responding to the most demanding conditions met in active filters. The behavior of the method has been fully verified by simulation and by experimental tests.

Improved constant-frequency hysteresis current control of VSI inverters with simple feed-forward bandwidth prediction

An improved implementation of the constant-frequency hysteresis current control of three-phase voltage source inverters is presented. A simple, self adjusting analog prediction of the hysteresis band is added to the phase-locked-loop control to ensure constant switching frequency even at high rate of output voltage change, such as required in active filters, fast drives and in other high demanding applications. This provision also improves the relative position of phase modulation pulses, thus reducing the current ripple. The prediction method is robust and uses a small number of inexpensive components. It does not require trimming or tunings, giving the whole system the capability to adjust itself to different load conditions. Thus the control becomes suitable to hybrid or monolithic integration. In the paper, the basic principles are described, and a detailed stability analysis is done. The control performance is illustrated both by simulated and experimental results.

High Efficiency Quasi-Resonant DC Link Three-phase Power Inverter for Full-Range PWM

A quasi-resonant dc link soft switching inverter is presented, capable of PWM operation. It requires only two additional switches, and allows loss limitation in the resonant circuit. The modulation method adopted is able to perform true PWM operation at any modulation index. Simulated and experimental results are reported, confirming the effectiveness of the proposed solution.

Digital adaptive hysteresis current control with clocked commutations and wide operating range

A new hysteresis current control technique for voltage source inverters is proposed, which uses digital calculation to predict the proper band amplitude in order to minimize the error and give a switching frequency synchronized with a clock. The technique is self-adapting to supply and load parameters, and is easily extended to three-phase systems using the decoupling approach already proposed by the same authors. The proposed technique exhibits both the advantages typical of the hysteresis methods, and those of the digital controls. The implementation of the control is done by means of a standard microcontroller and simple additional circuitry. Simulations and experimental tests confirmed the advantages and the excellent performance of the new modulation method. >

A synchronized resonant DC link converter for soft-switched PWM

A resonant DC link scheme for soft-switched inverters is proposed, where the link oscillation can be synchronized with inverter modulation. The scheme is able to operate with reduced commutation losses at a high switching frequency. Synchronization compatibility allows the development of suitable modulation techniques, which ensure improved waveform accuracy. The system performance and control strategies are verified both by simulation and by experimental tests, confirming the effectiveness of the proposed scheme.<<ETX>>