| By the development of high frequency switch, low frequency transformer has been withdrawn from many domains. But in the domain of UPS, linear power amplifier and the inverter output low frequency AC, for the purpose of isolation and change voltage, there is no choice but to use low frequency transformer. In order to reduce the size and weight of the transformer, as the development of high frequency switching technology, it is possible that the high frequency transformer replaces the low frequency transformer. The conventional converter has two power transfer levels. The first one is to obtain high frequency, and the second one is to obtain low frequency AC voltage.A novel topology of power transfer with high frequency transformer is proposed in this paper. This novel topology has one inverter, and changing voltage, isolation, and power transfer are completed by the high frequency transformer. The novel system has two-novelty points comparing to tradional system. The first, this system configuration is consisted of a new type of compound flyback converter, bi-directional high frequency rectifier, high frequency filter and controller. A new type of compound flyback converter is two flyback converters with only one transformer core and secondary coil. It completes changing voltage, isolation, and power transfer. The second, at the high frequency primary coil, when switch turn on with control signal (the SPWM pulse is modulated), in the positive or negative semi-period of low frequency modulation signal, transformer coil with same direction voltage. The magnetic flux of transformer core will increase step by step. At the end, it leads to magnetic flux saturation. So the converter can't work in order. The magnetic reset by each pulse is proposed in this paper. That is how to controlmodulation ratio and let the increase of magnetic flux with each high frequency pulse reset to zero. So it will avoid magnetic flux saturation.The operation of the proposed system is thoroughly analyzed and how to control modulation ratio meets each pulse magnetic reset is deduced. The principle of operation are illustrated and verified on emulation and experimental results. |
