Research On Multi-condition Reliability Design Of Position-sensorless Control For Permanent Magnet Synchronous Machines

Since the trend of more-electrification and more-intelligence in industry has swept the world,the transformation of energy has become the only way for modern industrial development.As the core of electric drive system,the electrical machine has attracted wide attention from various sectors in both industry and academia.Among all electrical machines,the permanent magnet synchronous machine(PMSM)has been widely employed thanks to its inherent advantages in high operating efficiency,high starting torque,and small size.Its application scenarios involve various fields such as precision servo control,traction drive of transportation equipment,and wind power generation.As a commonly used control scheme for PMSM,the field oriented control can easily achieve ideal performance for both speed and torque controls.However,the rotation coordinate transformation of the field oriented control algorithm requires accurate real-time measurement of rotor position information.Therefore,it is often necessary to install a high-precision mechanical position sensor on the rotor shaft for the real-time measurement of rotor position.However,position sensors are generally quite expensive and will inevitably increase the complexity and volume of whole drive system and reduce its reliability.In response to this problem,the position-sensorless control based on measured current and voltage signals from the electrical machine has came into being,which can take the place of position sensors in some applications.Currently,the position-sensorless control for PMSMs can be divided into three main categories: saliency based methods,fundamental model based methods,and openloop position-sensorless control schemes.Different position-sensorless schemes have their own advantages and disadvantages and are suitable for different operating conditions.However,under some special working conditions,the existing conventional position-sensorless control schemes are difficult to achieve ideal control performance,and may even fail to start or become unstable.In response to this problem,the core content of this thesis aims to realize the position-sensorless control of PMSM under special working conditions,and the algorithm design of reliability is also investigated.As a summary,on the basis of studied three major categories of position-sensorless control,the issues in reliability design existing in three special working conditions are properly solved.The specific research contents of this paper can be summarized as follows:(1)A study on position sensorless control schemes based on high-frequency injection for detection of machine saliency,sliding mode observer for PMSM model,and open-loop V/F and I/F controls is conducted.The basic principle and implementation process of each scheme has been investigated,and relevant experimental verifications are conducted,which lays a theoretical and engineering application foundation for solving the reliability design problem in position-sensorless controls under special working conditions.(2)The sensorless control scheme of PMSM under the free-running state is firstly studied,which improves the reliability when the PMSM is under control again after the power is restarted.For the free-running conditions that may appear in application scenarios such as electric vehicles,this thesis uses a combined control schemes with high-frequency pulse voltage injection and short pulse injection to realize the initial position detection,polarity judgement and position estimation of PMSMs under freerunning.Finally,the position-sensorless control of PMSM could be quickly restored under free-running conditions after the power restart.(3)A flexible switching scheme for position sensorless control in the full speed range of PMSM is studied,and the reliability of the PMSM running under different types of sensorless control algorithms together with their switching to each others is improved.Aiming to solve the problem that a single sensorless control scheme is difficult to apply to the full speed range(zero speed,low speed,high speed),this thesis has proposed a flexiable switching scheme between the high-frequency injection method(applicable to zero and low speed)and the sliding mode position-observer(applicable to medium and high speed).It uses the high-frequency injection method to start at zero speed and run at low speed,and realizes the flexible transition with the sliding mode position-observer by a proposed weight function based switching method under the medium and high speed conditions,by which the position-sensorless control in the full speed range is achieved finally.(4)The initial position detection and the low-speed stable startup and operation methods for nonsalient-pole PMSMs are studied,which improves the reliability of open-loop startup of nonsalient-pole PMSM,and realizes a reliable application of highfrequency injection based position-sensorless control in nonsalient-pole PMSM.However,due to the magnetic saliency of nonsalient-pole PMSM is approximately zero,it is often difficult for the high-frequency injection based position-sensorless control to realize its initial position detection and start-up at standstill.Thus,thisthesis proposes a high-frequency impedance measurement based detection of initial rotor position of nonsalient pole PMSM,together with its polarity judgement.On this basis,a three-step starting scheme is proposed to realize the open-loop stable start and operation of nonsalient-pole PMSM,and a further switching from open-loop control to closed-loop field oriented control is achieved finally.Through the above solution,the nonsalient-pole PMSM can be well-controlled and a high reliable initial position detection,start-up and position-sensorless control is also achieved.In summary,on the basis of typical sensorless control schemes,the modeling analysis and design of corresponding solutions for three special working conditions have been investigated in this thesis,and all theories have been verified through experiments.The experimental results show that the proposed control schemes can realize a reliable position-sensorless control of PMSM under the above-mentioned special working conditions.Therefore,the corresponding works not only have theoretical significance,but also have good application values.