Control-oriented modelling and adaptive control of a single-phase quasi-Z-source inverter

One key feature of Z-source and quasi-Z-source converters is the inclusion of a fully reactive network (the Z network) between input voltage source and inverter bridge. The inclusion of the Z network enables the possibility of utilizing the so-called shoot-through mode, i.e. the simultaneous activation of both switches in a single inverter bridge leg. Typical control strategies for these converters involve two separate objectives: (a) the control of Z-network variables (capacitor voltages) aimed at regulating the Z-network-to-inverter-bridge voltage and (b) standard inverter bridge output control. Modelling and control of the Z-network behavior, aiming at objective (a), is complicated by the fact that the current drawn from the Z-network by the inverter bridge during non shoot-through may be discontinuous and cannot be considered constant, especially in the case of a single-phase inverter. Our main contribution is to derive an adequately simple and sufficiently useful control-oriented model for the Z-network variables, taking full account of the variability of the aforementioned current and hence avoiding restrictive assumptions on the load or the PWM modulation strategy. A second contribution is to derive, based on the Z-network model, an adaptive control law able to compensate for large-signal variations. Successful operation is illustrated by means of a simulation example.