Design Of BLDCM Drive System Without Capacitor

Brushless DC machine(BLDCM) has been widely used in domestic and industrial applications due to its advantages of high power density, simple-control and quick dynamic response, etc. However, comparing with the permanent magnetic synchronous machine(PMSM), its torque ripple is large, which will degrade the performance of the power system. In the meantime, the volume of the control system is strictly limited. In this thesis, design of BLDCM drive system without capacitor is investigated.Firstly, the drop phenomenon of the inductor current in the traditional PI control algorithm during commutation period of the BLDCM, when the Buck capacitor is small, is analyzed. The one-cycle control algorithm of controlling the inductor current stable is proposed. The proposed control algorithm can keep the inductor current nearly stable during commutation comparing with the PI control algorithm.Then, the current resonance phenomenon is investigated. It is pointed that the reason is that the system damping is too small. The active damping methods applied in the traditional LCL filter is combined with BLDCM in this paper. Three active damping methods are proposed. This algorithm does not need to add the actual resistance and it uses the control algorithm to replace the actual one. As a result, it can achieve good performance of phase current during commutation when the Buck capacitor is small and the torque ripple is suppressed.Lastly, this thesis tries to control the phase current directly from the control purpose of BLDCM. A novel converter without capacitor is proposed to drive the BLDCM. Compared with the traditional Buck converter, the bus capacitor is removed and a switch and a diode is added in parallel with the inductor. The phase current of BLDCM is controlled directly. The novel converter can uplift the bus voltage of the inverter without delay during commutation, which can suppress the commutation torque ripple. The current peak and the current resonance can be solved. The good performance of BLDCM can be achieved and the volume of the driving system is reduced greatly.The corresponding simulations and experiments are conducted to verify the feasibility of the proposed methods and its effectiveness in suppressing the torque ripple of BLDCM.