PWM controlled neutral point clamped multilevel converter

A neutral point clamped, multilevel level converter, comprising:

• a DC voltage link;
• a first capacitor coupling one side of the DC link to a neutral point;
• a second capacitor coupling another side of the DC link to the neutral point;
• a plurality of phase legs, each phase leg including switches, each phase leg coupled to an AC node;
• a current sensor associated with each AC node;
• and
• a controller generating a PWM signal to control the switches, the controller generating a current zero sequence component in response to current sensed at each of the current sensors, the controller adjusting a modulation index signal in response to the current zero sequence component to produce the PWM signal;
• wherein the controller combines the current zero sequence component with a voltage zero sequence component to provide a combined zero sequence component, the controller adjusting the modulation index signal in response to the combined zero sequence component to produce the PWM signal.

A neutral point clamped, multilevel level converter, comprising:

• a DC voltage link;
• a first capacitor coupling one side of the DC link to a neutral point;
• a second capacitor coupling another side of the DC link to the neutral point;
• a plurality of phase legs, each phase leg including switches, each phase leg coupled to an AC node;
• a current sensor associated with each AC node;
• and
• a controller generating a PWM signal to control the switches, the controller generating a current zero sequence component in response to current sensed at each of the current sensors, the controller adjusting a modulation index signal in response to the current zero sequence component to produce the PWM signal;
• wherein the controller changes a sign of the current zero sequence component in response to an operating mode of the converter.