Harmonic modulation for charge balance of multi-level power converters

A control circuit to control a multi-level power conversion system, the control circuit comprising:

• a pulse width modulation (PWM) circuit to generate switching control signals having a duty cycle to operate switches to control a voltage signal at a switching node, the duty cycle being adjustable in different switching cycles, and each switching cycle including a respective first sub-cycle with a first sub-cycle duration and a respective second sub-cycle with a second sub-cycle duration;
• an output control circuit to generate a duty cycle signal to control the duty cycle according to a feedback signal, to regulate an output signal at an output node that is coupled to the switching node;
• a ramp generator circuit to generate a ramp signal to the PWM circuit to control the given switching cycle's first and second sub-cycle durations;
• a slope adjustment circuit coupled with the ramp generator circuit to control a slope of the ramp signal according to a difference voltage on a difference voltage input;
• and
• a subtractor having a capacitor voltage input coupled to a capacitor of the power conversion system, an input voltage input coupled to an input node of the power conversion system, and a difference voltage output coupled to the difference voltage input.

A method of controlling a multi-level power conversion system, the method comprising:

• generating pulse width modulation (PWM) signals having a duty cycle to operate switches to convert an input signal at an input node into an output signal at an output node, the duty cycle being adjustable in different switching cycles, each switching cycle including a respective first sub-cycle with a first sub-cycle duration and a respective second sub-cycle with a second sub-cycle duration;
• controlling the duty cycle according to a feedback signal in a given switching cycle to regulate the output signal;
• controlling the given switching cycle's first and second sub-cycle durations to control a voltage across a capacitor of the power conversion system while maintaining the given switching cycle's duty cycle;
• and
• the controlling the durations including subtracting half of a voltage of the input signal from a voltage across the capacitor to produce a difference voltage that controls the durations.