The purpose of this applet is to examine the impact that connecting the star point of the load to the mid-point of the DC link has on the current waveforms. The applet also presents the implementation of the hysteresis current controller. 

The quality of the generated load current waveform is dependent of the size of the hysteresis band, applied voltage across the inductor and the inductor value. A smaller hysteresis band results in a higher average switching frequency and generally better quality current waveforms. 

When the connection between the load star point and DC mid point is open, there is switching interaction between the phases. As seen in the previous applet the phase current can not always be maintained within the hysteresis band. In the case when the switch is closed and the mid and star points are connected no coupling between the phases now exists and the phase current is always maintained inside the hysteresis band. However there is now a path for current to flow between the two star points.

• Compare the operation of the hysteresis current controller with the neutral switch opened and closed. When the switch is closed there is no coupling between the phases. This can be observed in the current waveforms.
• By changing the hysteresis band width and inductor value the impact on the waveform quality and the average switching frequency can be observed.
• The amplitude of the current reference can be changed. From this it can be seen that the amplitude of the current ripple does not change.
• Change the amplitude and phase angle of the load voltage. At high load voltage amplitudes the current controller does not have enough voltage to control the current within the hysteresis band.