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A three-level self-synchronizing hysteresis current regulator with constant switching frequency

While hysteresis current control offers the benefits of a fast dynamic response and inherent overcurrent protection, its variable switching frequency and inherent two-level switching response make it unsuitable for many applications. This paper presents a new approach for three-level hysteresis control of a single phase grid-connected inverter that overcomes these limitations. The strategy adjusts the hysteresis band magnitude in response to variations in the inverter average output voltage, to achieve constant switching frequency using only one hysteresis comparator and without requiring DC offset compensation or current error zero-crossing measurement. The inverter average voltage is also used to estimate the phase of the incoming grid voltage, to create a current reference for the regulator at any required power factor. The result is a robust sensorless hysteresis current regulator suitable for three-level grid connected applications that operates with a constant switching frequency.