Dealing with linear and nonlinear time delays under model predictive control of power electronic inverters

Performance of any digital control scheme applied to inverters, or any other power electronic structures, can significantly suffer due to time delays. These time delays can be linear and nonlinear. An example of a linear delay is the delay due to sampling, control calculation and application of the new voltage state, which results in a constant delay present in each control cycle. An example of a non-linear delay is the inverter dead-time, which is different depending on the selected switching state and the direction of the load current. Both types of delays are well-known and are addressedin literature. At the same time, the known solutions result in significantly more complicated hardware and/or software implementations. Introduction of MPC to power electronics gives a new and unique opportunity to compensate for both types of the delays in a clear and effective way. This can be done by including the delays, both linear and non-linear, in the model predictions. As an illustration, this paper presents an MPC-based design of closed-loop current control with linear delay compensation for voltage source inverters. The paper also proposes a variable rate MPC-based voltage modulator which combines harmonic suppression with inverter dead-time compensation. The main points of the paper are illustrated by extensive simulation and experimental results.