In a power converter apparatus, such as an uninterruptible power supply, a phase reference signal is generated responsive to a DC voltage on a DC bus. A magnitude reference signal may be generated responsive to a phase current of an AC bus and/or the DC voltage on the DC bus. Power is transferred between the AC and DC busses responsive to the phase reference signal and the magnitude reference signal. Generation of the phase reference signal may include generating a DC voltage error signal responsive to the DC voltage on the DC bus, generating a phase offset signal responsive to the DC voltage error signal, and generating the phase reference signal responsive to the phase offset signal. Generation of the magnitude reference signal may include generating a volt-amperes reactive (VAR) error signal responsive to the phase current and generating the magnitude reference signal responsive to the VAR error signal.