Multi-output power supply with series voltage compensation capability for Magnetic Resonance Imaging system

In Magnetic Resonance Imaging system, the most powerful device is gradient driver, which is also one of the key components to realize fast imaging with high quality. To meet the requirements of high-end MRI products, the power rating of the gradient driver increase from several hundred-kVA to 1MVA and even higher in the future. Commonly the gradient driver applies full bridge cascade technology and needs a lot isolated DC source with high power capability. To provide solution to this requirement, several technology platforms have been developed. This paper presents one of the most attractive options. In the proposed power supply structure, an AC pre-regulator and a multi-winding transformer are combined together with diode rectifiers to provide multiple isolated DC outputs. The AC pre-regulator compensates the utility voltage variation by injecting voltage to the input line through a series transformer, and that make the multi-winding transformer get a stable input. With this solution, the DC outputs voltage is only determined by the transformer leakage inductance and load current. Compared with high frequency DC-DC conversion methods, this scheme does not need high frequency magnetic devices and capacitors, which are difficult to build and high cost for high power application. The switching devices (IGBTs) in this option can also operate at a much lower frequency (several kHz) to reduce the switching loss, and lower switching frequency also benefit the device selection. Beside that the rectifiers applied at the secondaries of the multi-winding transformer operate at line frequency and that benefits the device selection and cost too. Here in this paper, the control algorithm of the power supply is presented and discussed. Both its self-performance and co-operation with the amplifier are evaluated with Saber simulation. The results indicate the attractiveness of the proposed scheme.