A Z-source converter is an unique x-shaped impedance network called Z-source impedance network that couples the converter main circuit to the power source. The converter may be of all conversion types -if it is of ac-to-dc type, the z-source converter is called z-source inverter. Since 2003 when this recently conversion concept appeared [1], it proved able to solve many conversion problems. In this paper it's superiority compared to traditional solutions are shown. There are also small disadvantages and limitations revealed.

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The paper presents a PWM control system of a sinusoidal voltage using a single-phase inverter that comprises at the output a LC low-pass filter with resistive load. The PWM control strategy of a sinusoidal voltage and the optimization of the control loop via the modulus criterion, for step input signals, are presented. The steady-state error of the PWM control system is analyzed for sinusoidal input signal and methods for reducing the steady-state error by increasing the switching frequency and by adding an integral element series to the modulus criterion optimized controller are presented. If analyzed as a linear system, the addition of an integral element would make the system unstable, due to a double pole in the origin, but it is shown that by analyzing the system as a nonlinear system having an ideal relay-type nonlinearity, stability is preserved. Further, knowing that the steady-state error for sinusoidal input can be nullified by introducing a resonant element, a new utilization of a resonant element is proposed, namely its introduction instead of the integral element in the optimal transfer function according to the modulus criterion. The theoretical considerations are confirmed by simulation results.