Hysteresis current control operates by switching the load current so that it is maintained within a fixed band around a current reference signal. Another way to think about this is that the current error, the difference between the load current and the reference current, is maintained within a small positive and negative band. In this applet it is shown how the current is generated and how well the hysteresis current controller operates. 

In this example the current error is not always kept inside the hysteresis band as there is coupling between the phases. This is because when the switching state of the all the phases is the same a zero voltage vector is generated and control of the current is lost. Therefore it is possible to have current excursions outside of the hysteresis band (maximum excursion is twice the hysteresis band). Using this applet it is possible to zoom in and see the detail of the switching action and observe the current excursion outside of the hysteresis band.

• To start the hysteresis controller, click on the “GO” button. When the current error reaches a hysteresis limit then one of the switches changes state and the current error vector moves (normally) away from the limit.
• The position of the zoom window can be changed by moving the red line on the waveforms.
• The amplitude and phase of the load voltage can be changed by moving the red dot on the load voltage waveform.