DC content control for an inverter

A control for a pulse-width modulated (PWM) inverter having a pair of switches which are alternately operated in accordance with a PWM control waveform having rising and falling edges to develop AC output power, comprising:

• a memory having a series of digital words stored therein representing intervals between rising and falling edges of a stored PWM waveform;
• means for detecting the magnitude and polarity of a DC component in the AC output power;
• an adder/subtractor having a first set of add/subtract inputs coupled to the memory, a second set of add/subtract inputs which receive a signal representing the magnitude of the DC component, a control input which receives a signal representing the polarity of the DC component and an output at which a series of modified interval words are developed;
• a counter which develops a counter output;
• and
• a comparator which compares each modified interval word against the counter output to produce the PWM control waveform;
• wherein a rising or falling edge of the PWM control waveform is adjusted by the adder/subtractor relative to a corresponding rising or falling edge of the stored PWM waveform to reduce the magnitude of the DC component.

A control for a pulse-width modulated (PWM) inverter having a pair of switches which are alternately operated in accordance with a PWM control waveform having rising and falling edges to develop AC output power, comprising:

• a memory having a plurality of series of digital words stored therein wherein each series represents intervals between rising and falling edges of a stored PWM waveform;
• means for detecting the magnitude and polarity of a DC component in the AC output power;
• an adder/subtractor having a first set of add/subtract inputs coupled to the memory, a second set of add/subtract inputs which receive a signal representing the magnitude of the DC component, a control input which receives a signal representing the polarity of the DC component and an output at which a series of modified interval words are developed;
• a counter which develops a counter output;
• and a comparator which compares each modified interval word against the counter output to produce the PWM control waveform;
• wherein a rising or falling edge of the PWM control waveform is adjusted by the adder/subtractor relative to a corresponding rising or falling edge of the stored PWM waveform to reduce the magnitude of the DC component.

A method of controlling a pulse-width modulated (PWM) inverter having a pair of switches which are alternately operated in accordance with a PWM control waveform having rising and falling edges to develop AC output power, the method comprising the steps of:

• providing a memory having a plurality of series of digital words stored therein wherein each series represents intervals between rising and falling edges of a stored PWM waveform;
• detecting the magnitude and polarity of a DC component in the AC output power;
• providing an adder/subtractor having a first set of add/subtract inputs coupled to the memory, a second set of add/subtract inputs which receive a signal representing the magnitude of the DC component, a control input which receives a signal representing the polarity of the DC component and an output at which a series of modified interval words are developed;
• providing a counter which develops a counter output;
• and
• sequentially comparing each modified interval word against the counter output to produce the PWM control waveform;
• wherein a rising or falling edge of the PWM control waveform is adjusted by the adder/subtractor relative to a corresponding rising or falling edge of the stored PWM waveform to reduce the magnitude of the DC component.