Flying capacitor balancing

A controller for a multilevel flying capacitor power converter comprising a plurality of pairs of switching elements in a nested arrangement, including at least a first pair of switching elements and a second pair of switching elements, wherein the first pair is an innermost pair, wherein the switching elements of the first pair are coupled together at a switching node, wherein the switching elements of the second pair are coupled to respective switching elements of the first pair, the multilevel power converter further comprising one or more flying capacitors, including at least a first flying capacitor connected across the first pair of switching elements, the controller comprising:

• first control logic configured to calculate a duty cycle command value for driving the switching elements;
• and
• second control logic configured to generate, based on the duty cycle command value, a first pulse width modulated, PWM, control signal for the first pair of switching elements and a second PWM control signal for the second pair of switching elements,
• the first PWM control signal comprising a series of first pulses at a switching frequency and the second PWM control signal comprising a series of second pulses at the switching frequency, each pulse having a start and an end,
• wherein a first switching element of the first pair is controlled by the first PWM control signal and a second switching element of the first pair is controlled by the complement of the first PWM control signal,
• wherein a first switching element of the second pair is controlled by the second PWM control signal and a second switching element of the second pair is controlled by the complement of the second PWM control signal,
• wherein the second control logic comprises voltage balancing logic configured to detect a difference between a voltage on the first flying capacitor and a reference voltage for that flying capacitor;
• and
• responsive to detecting said difference, to modify a width of the first pulses,
• wherein the voltage balancing logic is further configured to modify a width of the second pulses,
• wherein the width of the first pulses is modified by changing a timing of an edge of each first pulse, and the width of the second pulses is modified by changing a timing of an edge of each second pulse.

An apparatus comprising:

• a controller operative to:
• receive a reference voltage;
• receive a signal indicating a magnitude of a voltage across a flying capacitor disposed in a power converter, the power converter operative to convert an input voltage into an output voltage via control of current through an inductor;
• and
• based on comparison of the received signal to the reference voltage, adjust pulse width modulation control of a network of switches in the power converter to adjust the magnitude of the voltage across the flying capacitor.