A modular multilevel DC active power filter scheme based on optimal parameter design for the CFETR N-NBI accelerator grid power supply

A DC active power filter (DAPF) based on a modular multilevel converter scheme is proposed for the accelerator grid power supply (AGPS) in a neutral beam injector system, to reduce the DC bus voltage ripple of AGPS. It works better than adding capacitors directly to the DC bus. This will help reduce the output voltage ripple of the AGPS at rated operating conditions, improve the focus state of the extraction beam, and reduce the occurrence of breakdown conditions. The scheme is special in that each module can compensate one frequency component of the ripple current, and the maximum switching frequency is not more than 4 times the ripple frequency. The electrical parameters of all DAPF modules (switching states and module capacitor voltages) are optimal values obtained through an optimal parameter design algorithm. In the process of applying the algorithm, two types of APF modules are distinguished, which have different switching frequencies and ripple suppression effects to adapt to different occasions. The simulation results show that each module can reduce the relative frequency component of the ripple by about 80% under the optimal parameters. Similar results are obtained by the 400V AGPS prototype and 20 V DAPF prototype. The ripple reduction scheme can be applied to other high-power applications with DC bus.