| Permanent magnet synchronous motors have the advantages of high power density and flexible control,and are currently widely used in the field of electrical transmission.In the traditional permanent magnet motor drive system,in order to reduce the fluctuation of the DC bus voltage,the bus capacitor generally chooses the electrolytic capacitor with a larger capacitance value.However,the electrolytic capacitor has a shorter life as a bus capacitor,and its volume and weight are relatively large.The life of the system is increased,and the volume and weight are increased.Film capacitors have been gradually used in motor drive systems in recent years due to their small size,high reliability and long service life.However,electrolytic capacitor-less motor drivers using film capacitors can not only eliminate the need for power factor correction(PFC),and reduce the volume and cost of the system,and can also extend the service life of the drive system.However,due to the reduction of the bus capacitance value,not only the voltage stabilization ability of the drive system is deteriorated,but also the grid-side current harmonics will appear that can’t meet the harmonic standards.One of key technologies is the need to use advanced inverter control strategies to enable grid-side current harmonics to meet harmonic standards.This paper mainly studies the control technology of power quality improvement on the grid side of the three-phase AC power supply without electrolytic capacitor drive system.In order to construct the grid-side current harmonic suppression strategy,the small signal model of the electrolytic capacitor-less drive system is firstly modeled and analyzed.First,the coefficient model of the motor on the rotating shaft is established,and then the harmonics of the input voltage on the grid side are analyzed,and the main reasons that affect the power quality on the grid side are determined.In addition,on the basis of the established motor mathematical model,an AC small-signal model of the electrolytic capacitor-less motor drive system is established.And consider the influence of motor parameters,vector control mode and controller parameters on the drive system.Finally,the relationship between the grid-side current THD and the harmonics of the bus current is analyzed,and the relationship between the grid-side power quality of the electrolytic capacitor drive system and the system parameters is clarified.In order to improve the input power quality on the grid side,a grid-side current harmonic suppression strategy based on active damping is studied.The system impedance is reshaped by applying active damping control on the inverter side of the drive system to improve the system’s impedance characteristics to specific frequency harmonics,thereby reducing the current harmonic amplitude that is an integer multiple of the bus voltage fluctuation frequency and improving the grid side power quality.This control method controls specific frequencies without increasing the harmonics of other frequencies,and is more flexible in implementation.In addition,the control strategy is controlled based on the harmonic information of the bus voltage,without other information to generate control damping,and will not increase the number of system sensors.Finally,the effectiveness of the studied strategy is verified by simulation.In order to adapt to the non-ideal grid conditions,the weak grid stability and adaptive impedance reshaping control strategy to improve the grid-side power quality of the system under weak grid conditions are studied.Firstly,a modeling analysis of the drive system under the weak grid condition is carried out,and the influence of the weak grid condition on the electrolytic capacitor-less drive system is clarified.Then,based on this,a stability control strategy and an adaptive impedance reshaping control strategy that have better adaptability to weak grid conditions are proposed,which improves the grid-side power quality of the electrolytic capacitor drive system under weak grid conditions,and is verified by simulation.The effectiveness of the strategy studied.Finally,on the basis of mathematical derivation and simulation verification,th e control method studied was verified experimentally on the 5.5k W electrolytic capacitor-less driver platform.The experimental results show that the control strategy can effectively suppress the grid-side current harmonics and improve the grid-side power quality of the electrolytic capacitor-less drive system. |
