| Due to magnetization and design problems, the back-emf of the BLDC(Brushless DC) motors used in industry area mostly is similar to sine wave ratherthan ideal trapezoidal wave, the torque ripple would increase greatly if the six stepcontrol mode is adopted in the control system, therefore, it is important to explorehow to reduce current harmonics and torque ripple. In addition, the phase currentlags behind the phase back-emf, which further lead to the decrease in output torque,when BLDC motors operate in high speed area, and traditional PID control theorycan’t guarantee the performance in wide speed range, hence it is necessary to studythe maximum torque per ampere and adaptive PID control of BLDC motors toensure the performance in wide speed range.Firstly, the operating principle of twelve step control mode is introduced, thefourier series decomposition method is adopt to compare and analysis the phasevoltage and phase current harmonics under six step control mode and twelve stepcontrol mode. A simulation model was also built based on a sine-wave back-emfBLDC motor by S-function method in order to simulate the current harmonics andtorque ripples under two control modes. The simulation results showed thatcompared with six step control mode, twelve step control mode could effectivelyinhibit current harmonics and reduce torque ripples.Secondly, lead angle control strategy is studied to slove the problem thatfundamental phase current lags behind fundamental phase back-emf. The optimallead angle calculation methods are analyzed based on the introduction of theoperation principle of lead angle control method. The system simulation model wasfurther improved. the simulation results showed that the optimal lead angle controlmethod was applicable. In order to increase the system control precision and thereliability of the systems which adopt the resolver as rotor position sensor, denoisingand fault detection theory based on wavelet transform was explored, the simulationresults showed that the db3wavelet could effectively reduce the noise and extractthe fault information.Thirdly, the system losses under six step control mode and twelve step controlmode are compared. The switch trigger signals of power modules were generated byPWM_ON modulation method. The conduction losses and switch losses under twocontrol modes were compared theoretically. Finite element method was used toanalyze the loss of the motor. The losses of the control system are almost the sameunder both control approaches. However, compared with six step control mode, thetwelve step control mode can effectively reduce motor losses, which further increases the efficiency of the system. In addition, the optimal lead angle controlmethod could further increase the efficiency.Fourthly, in order to ensure the dynamic and static performance of the motoroperated in wide speed range, especially when the speed and load is changingsuddenly, fuzzy adaptive PID control algorithm is explored. Through choosesuitable fuzzification and defuzzification methods, membership functions, fuzzyreasoning methods and fuzzy control rules, a fuzzy adaptive PID regulator module isbuilt. The simulation results showed that fuzzy adaptive PID control strategy couldensure the good performance of the motor in wide speed range.Finally, a DSP-based digital BLDC motor control system was designed andconstructed to verify and validate the effectiveness of the control strategies. Thehardware system mainly includes the DSP and its peripheral circuits, fault detectionand protection circuit based on the CPLD, signal conditioning circuit and IPM drivecircuit. The design of software includes the twelve step control strategy and leadangle control method. The related control approaches are studied experimentally.The experimental results verify the correctness of theoretical analysis. |
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