Research On Topology And Control Strategy Of Electrolytic-less Capacitor Drive System With Low DC-Link Voltage Ripple

Permanent magnet synchronous motor is widely used in aerospace,industrial production,household appliances and many other fields for its high power density,wide speed range and simple structure.However,the traditional motor drive system has the disadvantages of short life,low reliability and low power density due to the use of large-capacity electrolytic capacitor,which does not meet the performance requirements of motor drive system with high reliability and long life.The electrolytic-less capacitor drive system can effectively solve the above problems.However,due to the substantial reduction of the DC-link capacitance,the grid-side power factor of the motor drive system is low and the torque ripple on the motor side is large,which limits the application of electrolytic-less capacitor drive system in high-performance occasions.Therefore,in view of the shortcomings of the current electrolytic-less capacitor drive system,this thesis will improve the system from the two aspects of control strategy and topology structure to obtain high power factor and achieve high performance operation of the motor at the same time.Firstly,in view of the low power factor in the traditional electrolytic-less capacitor drive system,the control strategy based on the power of the inverter is studied.By analyzing the relationship between grid-side current and inverter power,the condition for the system to obtain high power factor is expounded.A power control algorithm based on proportional integral resonance(PIR)controller is proposed to track the inverter power rapidly under the condition of normal motor speed regulation.It solves the problem that the traditional PI controller is difficult to track the sinusoidal signal and the PR controller is difficult to track the given power due to the small gain in the low frequency band,improves the power factor of the system,and further improves the waveform quality of the grid-side current.Then,aiming at the problem of large torque ripple caused by DC-link voltage ripple,this thesis proposes a new topology structure of the electrolytic-less capacitor drive system.Through adding decoupling unit between the uncontrolled diode rectifier and three-phase voltage source inverter units,grid ripple power is buffered.Therefore,the topology can realize the low DC-link voltage ripple,which effectively reduces the motor torque ripple.In this thesis,the working mode of the circuit is analyzed in detail,and on this basis,the corresponding control strategy is proposed,and the selection of key devices in the system is deduced.Finally,an experimental platform with TMS320F28335 as the main control chip is built based on theoretical analysis and simulation verification.The experimental results show that the new type of electrolytic-less capacitor motor drive system proposed in this thesis can achieve high power factor,low harmonic content of grid current and low torque ripple on the motor side,which is beneficial to the application of the electrolytic-less capacitor system in high-performance occasions.