Control techniques for improving the static and dynamic performance of switch-mode DC-AC inverters

Abstract

Switch-mode DC-AC inverters are widely used in AC power conditioning systems. These systems require the inverters to provide qualified performance in terms of stability, accurate steady-state regulation, low total harmonic distortion (THD) and fast transient response. In general, conventional linear controllers are used to serve such purposes. However, in some applications, the inverters with conventional linear controllers cannot always satisfy the design specifications. For this reason, over the years, different control methodologies have been proposed to enhance the performance of inverters. This thesis is devoted to the study of effective control methodologies to improve the static and dynamic performance of DC-AC inverter systems. Control methods based on small-signal models and large-signal models are thoroughly investigated. We begin with the investigation of THD suppression in inverters using repetitive control (RC) which is based on small-signal models. Detailed analysis and design of the control system demonstrate the effectiveness of RC in harmonic elimination and THD suppression. However, RC suffers from slow dynamic response. In order to deal with this deficiency, sliding mode control (SMC) techniques are integrated into RC. As a result, a sliding mode repetitive control (SMRC) method is proposed and developed. It is shown that both fast transient response and low THD are achieved by the proposed SMRC method. For the purpose of further improving the static and dynamic performance of inverters, boundary control (BC) based on large-signal models is investigated. The phenomenon of switching frequency variation caused by BC law is analyzed. A BC method with ripple-derived switching surface is proposed to limit the variation of the switching frequency of the inverters while preserving the fast dynamic response and accurate steady-state regulation. All the analytical results are verified through experiments. The main contributions of this thesis are summarized as follows: 1. The analysis and design of the repetitive controller for harmonic elimination and THD suppression in pulse-width modulation (PWM) inverter systems are presented. A method of analyzing the RC system from the frequency response viewpoint is introduced. Based on this method, a systematic way of optimizing the design of the system is proposed. 2. A fast response low harmonic distortion SMRC scheme that combines the useful features of the SMC and RC is proposed for inverters. Excellent transient response and precise steady-state regulation can be achieved simultaneously. 3. A thorough study of the switching frequency variation in inverter systems with BC is provided. An enhanced BC method with ripple-derived switching surface is developed and implemented in an inverter. The proposed BC method is capable of limiting the switching frequency variation while maintaining the characteristics of fast dynamic response and accurate steady-state regulation.