The Research Of High Power High Precision DC Power Supply System

There is an increasing need for high power low ripple high dynamic performance DC power supplies in physical experiment and medical equipments such as accelerators, Tokamak, etc.. For instance ions in a synchro-accelerator are kept within a synchrotron ring and accelerated by magnetic field, to make the magnetic field increasing and decreasing synchronize with the movement of the ions the currents through the magnet coils have to vary following their setting values without delay approximately and to avoid the ions deviating from the track the currents have to have very low ripple(10^-4-10^-5) owning to extremely low ion mass. The power rating of this kind of power supplies may reach to 800V, 3000A. It is challenging to meet both high power and high performance requirements.The development of accelerator power supply has been given a brief survey in this thesis. The problem lies in slow current response and high current ripple. In order to solve these problems a new approach is introduced in this paper where an DC active filter(DAF) based on PWM switching mode is connected with thyristor converter(THC) in parallel, the current through the switching devices of the filter is only 3-5% of load current, the amount of the devices is less, its size is smaller and efficiency is higher. The active filter not only filters out the harmonics generated by the thyristor converter, but also improve dynamics because the switching frequency of the devices is 10-20kHz and its control dead-time is small. Simulation and prototype experiment results show that the system can meet the extremely high steady state and dynamic requirements of the magnets: very low ripple and good following performance.The circuit topology of the proposed power supply and the principle of the DAF are introduced. Two kinds of control systems of the DAF: harmonic voltage control one (HVCS) and harmonic current control time of the current loop of the HCCS and how to measure harmonic voltage or current from the THC are solved. Where a current hysteresis controller with variable hysteresis width is used to the HCCS which not only makes the actual current of the DAF following its setting value without delay but also makes switching frequency fixed approximately. The harmonic signal is achieved by subtracting DC component from measured voltage or current of the THC. Usually the DC component is got by means of a low-pass filter, but the method causes system response delay. A new way where a setting value is adopted stead of the filter output is proposed and does not affect dynamics. It is impossible to meet the extremely high dynamic following requirements of the power supply by using feedback only, therefore feedforward and feedback compound control systems HVCS and HCCS are introduced in the thesis. To realizing feedforward the key is how to achieve the first-order and second-order differential signals of the load current setting value. The signals can be obtained by means of a ramp-function generator with rounding-off and the method is investigated also.The circuit topology of the DC active filter - a PWM converter and a current hysteresis converter are studied which play a great role in improve the system performance The simulation and experiment results show that the system performance by using current hysteresis converter is prior to the PWM converter.The problems have been developed which include how to attain high precision load current, how to get the harmonic current and harmonic voltage fast and precisely, how to over come the fluctuation of power supply input voltage, how to implement a current hysteresis controller withvariable hysteresis.Both of the schemes (HCCS, HVCS) have been deeply studied by means of simulation software MATLAB, the influence of variations of parameter also studied. The simulation results are reasonable and useful to the prototype experiment.Prototype experiment results show that the power supply system has very good dynamical and steady state performance and can satisfy the extremely high desires on current ripple (lxlO"5) and following error (2x10^*) of the synchro accelerator.