Apparatus and method to prevent saturation of interphase transformers

A power circuit, comprising:

• an inverter generating a set of inverter pole output signals;
• a set of interphase transformers connected to said inverter, said set of interphase transformers receiving said set of inverter pole output signals and producing a set of combined inverter pole output signals;
• a main transformer connected to said set of interphase transformers, said main transformer receiving said combined inverter pole output signals and producing load output signals;
• and
• a switch firing control circuit including:
• a module to execute a standard switch firing scheme to produce a set of inverter pole output signals including a first inverter pole output signal and a second inverter pole output signal, said first inverter pole output signal having a predetermined phase displacement from said second inverter pole output signal,
• a module to identify a system transient, and
• a module to execute a system transient switch firing scheme such that said inverter reduces said predetermined phase displacement between said first inverter pole output signal and said second inverter pole output signal in the presence of said system transient and restores said predetermined phase displacement between said first inverter pole output signal and said second inverter pole output signal after said system transient.

A method of operating a voltage sourced inverter, said method comprising the steps of:

• generating a set of inverter pole output signals for application to a set of interphase transformers, said set of inverter pole output signals including a first inverter pole output signal and a second inverter pole output signal, said first inverter pole output signal having a predetermined phase displacement from said second inverter pole output signal;
• identifying a system transient;
• reducing said predetermined phase displacement between said first inverter pole output signal and said second inverter pole output signal in the presence of said system transient;
• and
• restoring said predetermined phase displacement between said first inverter pole output signal and said second inverter pole output signal when said system transient is completed.