Keywords: sine–wave VSI, voltage source inverters, dead–time distortion, THD, total harmonic distortion, predictive algorithm, DSP based control, sine–triangle modulation, digital signal processing, simulation
A predictive algorithm for minimising dead–time distortions in sine–wave VSI with L–C output filter
In many applications, single–phase sine–wave inverters are operated with low–pass filters at the output to deliver a low–distortion sinusoidal voltage to the load. In such cases, it is essential that the output be as close to a sinusoid as possible. However, conventional bridge–type inverters, which must be operated with some dead time, suffer from dead–time distortion problems. This effect distorts the output voltage–waveform from its sinusoidal nature to one having significant amounts of low–frequency harmonics. In such cases, dead–time distortion is minimised by employing some suitable algorithm. This paper presents one such algorithm, predictive in nature, for minimising dead–time distortion in the output voltage of a sinusoidal Voltage Source Inverter (VSI) with L–C filter at the output. The algorithm operates by sensing only the load–current. Performance of this algorithm is verified for a single–phase full–bridge inverter, first by simulations and then via experiments, employing Digital Signal Processors (DSP) based inverter. It achieves THD values lesser than 3% for a wide range of load magnitudes and power–factors.