New limiting algorithms for space vector modulated three-phase four-leg voltage source inverter

Abstract

This paper proposes two novel limiting algorithms for three-phase four-leg voltage source inverters to constrain the command vector inside the polyhedron defined by the boundaries of the inverter linear operating range. The first algorithm uses an inscribed ellipsoid on the polyhedron, and the second one is based on the polyhedron, and the second one is based on the polyhedron boundary planes. A detailed description, with the key points required for a digital implementation of space vector and limiting algorithms, is given. In addition, the output voltages and the inductors currents are dynamically controlled by means of MIMO servo system in dq0 coordinates. These controllers are designed using an optimal discrete linear quadratic regulator technique, which ensures stability for the system at all operating conditions. In order to provide smooth transitions among the different modes of operation, nonlinear MIMO anti-windup algorithms are proposed to dynamically update the controllers servo variables. Finally, experimental results on a 15 kVA PWM inverter fully controlled by a DSP controller, TMS320F241, has been used to validate the feasibility of the proposed algorithm and to demonstrate the performance of the overall system.