Optimized FPGA Implementation of PWAM-Based Control of Three—Phase Nine—Level Quasi Impedance Source Inverter

Inherent buck-boost capability, reduced component count, controlled power injection and multilevel operation are some of the advantages which makes cascaded qZSI popular for integrating the generated solar energy with the utility grid. Phase-Shifted Carrier PWM (PSCPWM) and Pulse Width Amplitude Modulation (PWAM) are the most popular techniques for achieving multilevel qZSI operation. Generally, closed loop control implementation of three - phase qZSI system consists of large number of slave controllers (placed locally for voltage control) and one centralized master controller (for grid integration or load current control). Since the aim is to control single system with this highly distributed control structure, issues of clock pulse and interrupt signal synchronization, hardware and software redundancy are common in these implementations. This limits the utilization factor and step size of these control boards. To address these issues, either more optimized solutions must be suggested, or distribution of control structure must be reduced. In this paper, closed loop control of nine - level three - phase qZSI system is implemented using single FPGA control board thereby eliminating above said problems. Since, PWAM control algorithm is more complex than PSCPWM, FPGA based implementation for PWAM control is discussed. Critical implementation processes consisting of DAC - ADC interfacing, FPGA code per unitization, PI Controller realization and different clock pulse utilization are presented. For highlighting and comparing the resource consumption, PWAM and PSCPWM modulation are compared in terms of device utilization. Transient analysis and control algorithm are presented and validated during both starting and load transient conditions by means of simulation results. Finally, hardware results of these modulation methods are discussed and analyzed.