Harmonic currents generated by the voltage-source active rectifier

Share of current harmonics, which is taken from the power net, increases with the use of diode and thyristor rectifiers (so-called characteristic harmonics of current). One of the ways to minimize these harmonics is to use the active rectifier. The principle of operation of active rectifier is based on correct switching of transistors, which allows the two basic functions: a) to keep the first harmonic of current in phase with the first harmonic of voltage, power factor is approximately one, b) to achieve almost sinusoidal current, which is taken from the grid. Characteristic harmonics in the spectrum of the current, which is drawn from the grid by active rectifier, are negligible. There appear new harmonics in the spectrum of the current; these new harmonics are produced by switching frequency of transistors. These harmonics are little dependent on load. That can cause the fact that the proportional value of the examined harmonics is high, although the absolute value is actually low. This paper briefly describes the voltage-source active rectifier and its workings. The main part is devoted to results from simulations and measurements in the laboratory.