Abstract: A standby power supply system is provided for supplying normal AC power to a critical load from an AC power source during normal operating conditions, and for supplying emergency AC power to the load during failure of the AC power source. During normal operation, the standby power supply system actively neutralizes undesirable harmonic components in the input current drawn by the load. The standby power supply system includes a power conversion device having a DC side coupled to a back-up power source and an AC side in parallel with the load and the AC source. A harmonic distortion sensor senses a harmonic distortion current component of a load current drawn by the load during normal operating conditions. A controller is responsive to the harmonic distortion sensor for causing the power conversion device to produce a harmonics neutralizing current to substantially neutralize the harmonic distortion current component produced by the load.

Abstract: A standby power supply system is provided for supplying normal AC power to a critical load from an AC power source during normal operating conditions, and for supplying emergency AC power to the load during failure of the AC power source. During normal operation, the standby power supply system actively neutralizes undesirable harmonic components in the input current drawn by the load. The standby power supply system includes a power conversion device having a DC side coupled to a back-up power source and an AC side in parallel with the load and the AC source. A harmonic distortion sensor senses a harmonic distortion current component of a load current drawn by the load during normal operating conditions. A controller is responsive to the harmonic distortion sensor for causing the power conversion device to produce a harmonics neutralizing current to substantially neutralize the harmonic distortion current component produced by the load.

Abstract: A full bridge DC-DC series-resonant power converter is operated at a constant switching frequency using a phase delay between the transistor legs of the bridge to control the output voltage. All power semiconductor devices switch on and switch off at approximately zero volts while operating at a constant switching frequency which is above the resonant frequency of the resonant tank circuit. Zero-voltage switching increases the efficiency of the power converter and allows high frequency operation which minimizes component volumes. Constant frequency operation simplifies design of the magnetic components, confines the EMI spectrum to known frequencies and simplifies EMI design, and reduces the voltage and current excursions and thus reduces the peak component stress.