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

The 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 boundary planes. A detailed description is given which sets out the key points required for a digital implementation of space vector and limiting algorithms. In addition, the output voltages and the inductor currents are dynamically regulated by means of a MIMO servo controller in dq0 co-ordinates. These controllers are designed using an optimal discrete linear quadratic regulator technique, which ensures stability for the system at all operating conditions. To provide smooth transitions among the different modes of operation, nonlinear MIMO anti-windup algorithms are proposed to dynamically update the controller servo variables. Finally, experimental results on a 15 kVA PWM inverter fully controlled by a DSP controller, TMS320F241, have been used to validate the feasibility of the proposed algorithm and to demonstrate the performance of the overall system performance.