Torque Ripple Reduction And Modulation Strategy For Permanent Magnet Brushless DC Motor Systems

Permanent magnet brushless DC motor (BLDCM) has been widely used inaerospace systems, military equipment, industrial automation equipment andhousehold appliances, because of its advantages of high power density, highefficiency, small size and large output torque. The control strategy, modulationmethod and new inverter topology of BLDCM are studied in this paper, in order tomeet the requirement of high performance, high efficiency, low loss, low cost andhigh reliability in industrial applications.This paper studies the mechanism of the torque ripples and influence of controllerbandwidth caused by different switching modulation strategies for torque ripples ofBLDCM system induced by back electromotive force (BEMF) and currentcommutation, and establishes the mapping between torque and current of the motorduring operations of commutation and non-commutation, based on which proposesoptimal control strategy. The strategy takes the advantage of the line BEMF tooptimize the reference current during the processes of commutation andnon-commutation, so as to suppress the influence of the torque caused by the BEMF.During commutation, low-speed commutation modulation strategy and high-speedcommutation modulation strategy are used according to the different speed ranges andcommutation torque ripple is reduced by controlling the currents of non-commutatedwindings to track the optimized reference current. Integral variable structure control(IVSC) is designed for current controllers by designing appropriate continuouscomponent of controllers to make the switching gain of switching component onlydepends on the parameters disturbances and model uncertainty disturbances,effectively reduces the chattering of controllers from the switching component.Mapping equations between BEMF and current of non-conduction phase areestablished for current distortion caused by BEMF in three-phase four-switch inverterBLDCM drives. Adjusting mechanisms of different adjusting vectors ofnon-conducting phase current are analyzed and three effective vectors modulationstrategy and two effective vectors modulation strategy are proposed. The twomodulation strategies take the advantages of the different adjusting mechanism ofnon-conduction phase current by the adjustment vectors, and inhibits the negative effects of the currents caused by the BEMF, and control the non-conduction phasecurrent to converge to zero, effectively increases the dynamic and static performanceof the current. The duty cycles of adjusting vectors are calculated and the stability ofthe proposed strategies is demonstrated by selecting a candidate Lyapunov function.A boost five-switch three-phase (BFSTP) topology and boost three-effectivevector modulation strategy in BLDCM drives are proposed by studying the operatingcharacteristics of three-phase four-switch inverter and boost circuit for the problemsof load carrying capacity and speed range restriction in low voltage of BLDCMsystem, which make use of adjustment mechanism of straight-through vector to outputvoltage, and achieve the boost of motor system, effectively expand the load carryingcapacity and speed range of BLDCM system in low voltage applications.The hardware platform is set up and experiments are carried out to demonstratethe effectiveness of the proposed current optimization torque ripple reduction strategy,three effective vector modulation strategy, two effective vector modulation strategyand boost three-phase five-switch topology. The experimental results providefact-based support for the theoretical analysis and demonstrate the effectiveness of theproposed strategies.