High Power Factor Control Strategy Research Of Single Phase Grid Connected Permanent Magnet Synchronous Motor Driver Without Electrolytic Capacitor

Single-phase grid connected the motor drive system without the electrolytic capacitor utilizes the small film capacitor as the dc-link capacitor and eliminates the power factor circuits.The system can be applied to the home appliance field,such as the variable frequency air conditioner and washing machine,because of its high power density and the high grid power factor.However,the dc-link voltage drops to zero periodly and it is difficult to control the motor.The conventional motor methods cannot fix this problem.The motor drive system has drawn the worldwide researchers’ attraction.The high gird power factor strategy of the motor drive system has been researched deeply in this thesis.Firstly,the mathematical relstionship between the grid input current and the inveter power is given.And the relationship between the grid input power factor and the bus voltage is analyzed.The small-signal model of the system is dedued and the dc-link capacitance is related with the bus voltage effective value,the line impedance value and the system power effective value.Further,the total harmonics distortion of the grid current is different according to the change of the dc-bus vltage minimum value.All of these provide theoretical basis in the further research.Secondly,the mathematical model of the permanent magnet syschronous motor is established in the syschronous reference frame.The conventional control methods are introduced and they are the direct torque control,the field-weakening control,the maxmum torque per ampere,the unit power factor control.The simulation results based on MATLAB/Simulink verified the above methods.Igoring the voltage drop on the d-and q-axis reductance and dc-link capacitor instantous power,q-axis current reference is given according to the relationship between the q-axis current and the grid input power.Regarding the effect of the dc-link capacitor instantous power,the q-axis current angle is modified.The constant d-axis current reference is derived,considering the dc-link voltage constraint.To improve the power factor,the ac component is added to the constant d-axis current reference.The performance of the proposed method was verified by the simulation results.Assuming that the voltage drop on the d-and q-axis redutance is ignorable,the current reference is proposed according to the intersection point between the bus voltage constraint curve and the power curve.To control the inverter output power following the reference,the calculated d-and q-axis voltages are added to the decoupling voltages by the feedforward compasation.The simulation results validated the performance of the proposed method.Finally,the experimental platform of the motor system was established,including the hardware and software design.The early experiment of the proposed strategy has been done,and the experiment results demonstrated the validity of the proposed control strategy.