Method and apparatus for balancing voltages of multi-level inverter DC link

The present disclosure discloses a method and an apparatus implementing the method for balancing voltages of a DC link of a multi-level inverter, wherein the DC link is divided into two halves by a neutral point connection. The disclosure further discloses an apparatus implementing the method. The method comprises injecting a periodic common-mode voltage injection signal to a common-mode voltage reference and a periodic power injection signal to a power reference of the inverter. The power injection signal has the same frequency as the common-mode voltage injection signal. A phase shift between the common-mode voltage injection signal and the power injection signal is constant. Amplitude of at least one of the common-mode voltage injection signal and the power injection signal is controlled on the basis of a difference between voltages over the two halves of the DC link.