EVALUATION OF DSP AND FPGA BASED DIGITAL CONTROLLERS FOR A SINGLE-PHASE PWM INVERTER Ariawan Tjondronugroho, Adnan Al-Anbuky, Simon Round, Richard Duke Department of Electrical and Computer Engineering, University of Canterbury, Christchurch, New Zealand Abstract A variety of control strategies have been used to control single-phase inverters for various power electronics applications. Each control strategy has its own advantages and disadvantages. This paper presents a brief assessment of repetitive, sliding mode, current mode and multiple-loop control strategies, as applied to single-phase PWM inverters. Controller implementation has evolved with time from traditional analogue schemes to a range of digital control options. DSP and FPGA based digital controller implementations of the multiple-loop control strategy are examined in detail. Simulated and experimental measurements of the performance of these digital controllers are presented. 1 INTRODUCTION Single-phase Pulse Width Modulated (PWM) inverters have found widespread application in Uninterruptible Power Supplies (UPS) for telecommunication applications. The control strategy of a PWM inverter is one of the key aspects that influence its performance, size and cost. Many closed-loop control strategies with the purpose of improving the output signal quality of a single-phase PWM inverter have been proposed over past decades [1]-[11]. Traditional closed-loop analogue control systems have been implemented at the expense of high complexity and low efficiency due to the large number of components. Since the introduction of microprocessors, the control strategy of power converters has evolved very rapidly. Microprocessor based controllers have proven to be more flexible, reliable and cheaper than the analogue equivalent. However their computational power limits the possibility for implementing complex algorithms [1], [2]. With the computational power of Digital Signal Processors (DSP), complex algorithms can be easily implemented. Nowadays, digital control for power converter applications is becoming very widely used. More processing power can also be obtained by using fully programmable logic devices such as the Field Programmable Gate Array (FPGA). Many fully digital inverter controllers have been reported, each with their own advantages and disadvantages [1]-[8]. This paper presents a general evaluation of different types of closed-loop digital control systems for PWM inverters. Four typical control strategies, namely repetitive, sliding mode, current mode and multiple-loop were evaluated. The efficiency of the controller is measured by means of output signal quality and the complexity of the control algorithms. The multiple-loop control is the most efficient controller. This strategy has been verified by both simulation and experiment, using DSP and FPGA technologies. 2 TYPES OF CONTROLLERS In order to produce a stable and reliable ac waveform, the output signal of an inverter must be regulated by a robust controller. A range of control strategies are available and these will be briefly explained and assessed. 2.1 Repetitive Control Closed-loop regulation of a PWM inverter normally gives satisfactory results, but occasionally it suffers from periodic disturbances. Repetitive control utilises the repetitive nature of disturbances and provides a solution to remove periodic error that occurs in a dynamic system. Figure 1(a) shows a cascaded repetitive control structure. In this system, the repetitive controller is cascaded in between two negative feedback loops of the output voltage. Feedforward repetitive control is shown in Figure 1 (b). The purpose of the tracking controller is to improve the transient response of the system and make it insensitive to external disturbances [6]. Australasian Universities Power Engineering Conference (AUPEC 2004) 26-29 September 2004, Brisbane, Australia