Research On Permanent Magnet Synchronous Motor Phase Current Reconstruction Techniques

Permanent magnet synchronous motor with its many advantages of high powerdensity, high reliability, high accuracy has been widely applied in industrial servofield.Most permanent magnet synchronous motor drive system using closed-loopvector control requires real-time detection of the rotor position and phase windingcurrents today.While both position sensor and current sensor aren’t cheap,preventinga decline in the cost of permannet magnet synchronous motor servo system,limitingthe expansion of its range of applications.In this paper,from the viewpoint ofreducing the number of current sensors to reduce the cost,several phase currentreconstruction methods based on single current sensor are elaborated.First,on the basis of the vector control that SVPWM technology adoped,thebasic principle of phase current reconstruction based on bus current sensor isintroduced.Taking into account the impact of the actual system of non-idealfactors,dividing the current remodeling blind area.Solving the problem of blind areaby pulse shifting,and theoretical analysis shows that the method doesn’t affect theactual output voltage vector.The simulation and experimental results show that theshift pulse method can basically solve the problem of blind area,but it will cause theharmonic content of the current incerases slightly.While solution for the currentreconstruction in case of over-modulation operation is also proposed.Secondly,in order to achieve the completion of the entire region of the voltagevector can be accurately reconstrcucted phase current,pulse insertion method isintroduced.This method isn’t limited by the voltage vectors,current reconstructioncan be completed within any area.And according to the needs of engineeringapplications,pulse insertion based on unipolar current sensor is proposed. Asimplified scheme is given while running in the low modulation region.However,dueto the added pulse,it leads to decrease in bus voltage utilization.It also increases theharmonic content of current, leading to a sharp increase in switching losses.Again,from the view of improving the traditional SVPWM technoology,three-state pulse width modulation technology and hybrid pulse width modulationtechnology are elaborated,describing the working principles of the two modu-lation.Unmeasured areas were theoretical analysed and improved,and the simulationand experimental verification were carried out.Experimental results show that thethree-state pulse width modulation technique can effectively enlarge the effectivearea of the current reconstruction,but it can be seen from the current curve,that itscontrol performance is still less than traditional SVPWM technology.Then,by adjusting the position of the current sensor, you can complete the phase current reconstruction in the majority of the area under the premise of nochange to the traditional vector control algorithm. The advantage of this method isthat it doesn’t degrade the performance of the original closed-loop system.But theparticular installation makes its limited application in IPM,and due to the lack of buscurrent sensor,overcurrent protection functions is somewhat complicated.Then itpoints out some commom errors existed in the current reconstruction,and gives thecorresponding solutuons.Finally,in order to further reduce the cost of the system,this paper introducestwo permanent magnet synchronous motor sensorless technology,dual observermethod and model reference adaptive backstepping method.Elaborating the workingpriciples of the two methods,and combining phase current reconsruction technologywith sesorless technology to be simulated together.Simulation results showthat:double observer method exists in small high-frequency chattering,whichdetermental to system stability.The eatimate of the accuracy of the model referenceadaptive backstepping method is more sensitive to the motor parameters.Overall,oftwo methods to estimate rotor pisition and speed can be more accurately.