Resonant link PFN charger and modulator power supply

In applications such as large PFN chargers and power modulator power must be drawn from the 50/60/400 Hz utility grid with acceptable total harmonic distortions and without large inrush currents. A common mitigating practice is to use standard twelve or eighteen-pulse rectification circuits that require large, bulky and expensive utility power transformers and large harmonic filtering. SAIC has developed a Resonant Link (also known as AC-Link) electronic transformer that draws controlled harmonic power from the utility grid with less than 1.5 % total harmonic distortion. The active rectification is performed utilizing the Resonant Link inverter “soft switching” operation at switching frequencies of 15 to 20 kHz using commercial IGBTs or other available solid state switching devices. To step up or step down to the required voltage, a small high frequency and efficient nanocrystalline transformer, operating at the inverter frequency is used, with its leakage inductance being utilized as part of the inverter output resonant circuit. The secondary rectified output DC has no 360 Hz components and can be regulated to better than 1% with minimum passive filtering, or can be used to charge up a capacitor bank in a controlled manner. A Resonant Link based system could be configured to yield a power density between 2-6 MW/m3 and at a fraction of the weight and cost of conventional approaches. In addition, the soft switching topology yields in excess of 97% efficiency.