Research On The Rotor Flux Observer Design And Field Weakening Control Strategy Of PMSM At Low Carrier Ratio

With the fast development of the motor manufacturing technology and the power electronics technology,permanent magnet synchronous motor(PMSM)has been widely used in all fields of industry,especially in the field of equipment manufacturing,because of its merits of high-power density,fast response and high energy efficiency.A large part of PMSMs is applied in medium and low-end application,so the general drivers are in high demand.Considering the low cost and high performance,the sensorless vector control strategy should have the characteristics,such as the same algorithms,low algorithm complexity and strong robustness in full power ranges.Particularly in the roto flux observer and field weakening control under low carrier ratio,on the one hand,the control strategy of rotor flux observer should have better stability and dynamic characteristics under low carrier ratio,on the other hand,the field weakening control strategy also has excellent dynamic and static performance under low carrier ratio.Under the above background,the following research around the rotor flux observation and field weakening control for the sensorless vector control of PMSM in this thesis is mainly carried out:The vector control strategy based on PMSM mathematical model is introduced,including the building of PMSM mathematical model;tuning of the PI regulator parameters of the speed and current loop;according to the influence of current sampling circuit error,nonlinear factors of inverter and inaccuracy motor parameters on flux model,the defects of open-loop rotor flux observer is discovered;the advantages and disadvantages of the field weakening control strategy based on voltage closed-loop is analyzed,specially under low carrier ratio.In order to verify the effectiveness of the algorithm,three-phase current sensor sampling platform is built and the loading system is setup.Aiming at the problem of inaccurate rotor flux estimation of open-loop rotor flux observer caused by the deviations of the flux model,an adaptive compensation rotor flux observer is proposed.In this method,the DC bias component and high-order harmonic component in the output of the flux integrator are fed back to the input of the flux integrator through the PI regulator,so that the amplitude of the DC bias component and high-order harmonic component in the flux model can be attenuated naturally with time,then the output of the flux integrator only contains the fundamental component,so as to realize the accurate estimation of the rotor flux.This method is suitable for both surface-mounted PMSM(SPMSM)and interior PMSM(IPMSM),and is easy to be realized by low-cost engineering,because of the features of less complexity,less variables,low requirements for hardware circuit and controller.When PMSM works in the field weakening region with low carrier ratio,the performance of rotor flux observer has a great impact on the load capacity and stability of sensorless vector control system.For the instability problem of the adaptive compensation flux observer under low carrier ratio,an adaptive compensation rotor flux observer with feedback delay is proposed,and the new parameter expressions of PI regulator related to carrier ratio is established,so as to improve the performance of flux observer under low carrier ratio and make the response of torque and current loops faster.At the same time,by analyzing the stability of different Euler discretization methods of integrator in discrete domain,combined with the advantages of backward Euler and trapezoidal Euler discretization methods,a new Euler discretization method with carrier ratio weighting factor is proposed to improve the stability of the flux observer under low carrier ratio.Due to the disadvantages of poor dynamic performance of SPMSM field weakening control algorithm based on voltage closed-loop control in the field weakening region with low carrier ratio,a field weakening control strategy with adaptive carrier ratio is also proposed.Based on the voltage closed-loop control,the q-axis voltage control loop is added,and the q-axis voltage constraint is adjusted adaptively with the carrier ratio.Compared with the field weakening control strategy based on voltage closed-loop control,the flux current is regulated in advance by the proposed control strategy,so that the current loop is approximately torque current single-axis regulation during loading or unloading,which is conducive to the rapid response of torque current and improves the dynamic load performance when the carrier ratio is reduced.For improvement of the field weakening control algorithm of IPMSM at low carrier ratio based on voltage closed-loop control,there are not only the same problem as SPMSM,but also the problem that the current loop regulator is easily saturated and result in the out of control of the output voltage distribution.A single PI regulator field weakening control strategy with dynamic torque current limitation is proposed in this paper,which synchronously regulate the torque current and flux current.The sufficient voltage regulation margin under low carrier ratio is ensured the dynamic limitation of torque current.At the same time,by adjusting the dynamic dqaxis current distribution factor,the smooth transition between field weakening region and non field weakening region is realized,and the influence of current efficiency on non field weakening region is reduced.Since the field weakening control strategy is based on the speed loop in motor control,and the control cycle of the speed control loop is usually a fixed value(usually 0.5ms or longer),the dynamic performance is not effected by the reduction of current loop speed or DCbus voltage fluctuation.