High Precision And Low Speed Servo Control Of PMSM Based On Position Observer Algorithm

With the development of modern industry towards automation and intelligence,the electrical motor is playing an increasingly important role in reality.Compared with the DC motor,induction motor and other conventional motors,the perma nent magnet synchronous machine(PMSM)has advantages such as high torque density,high energy conversion efficiency and small moment of inertia.Thus,it has been widely used in high-precision servo machining,manipulator,textile and other industrial automation fields.In order to achieve high-precision vector control of PMSM,high accuracy rotor position is usually needed,and consequently a high-precision position sensor is usually installed.However,the high-precision position sensor is usually expens ive and will significantly increase the manufacturing cost of the system.Therefore,in some products with strict cost control,the low-cost low-resolution position sensor is usually empoyed,whereas it is difficult to meet the requirements of high-precision control.And the sensorless control technology is still difficult to meet the requirements in high-precision control field.In summary,the rotor position estimation technology that can reduce costs and meet high-precision control has become a research focus in both industry and academia.Therefore,the position interpolation control algorithms based on average speed method,average acceleration method and position observer method are seperately studied in this thesis.At the same time,the position estimation based on the SMO and the high frequency square wave injection method is studied,and a high-precision estimation of rotor position is realized,and the effectiveness of the proposed algorithm is verified in both simulations and experiments.Key contents of this thesis are listed as follows:(1)The position interpolation control algorithms based on the average velocity method and average acceleration method are studied.T he characteristics of output signals of low-resolution position sensor have been analyzed at the beginning,and it is found that the discrete position signal is difficult to meet the requirements in high-precision servo control.Then it investigates how to use the discrete position signal to estimate the continuous states of rotor position and speed,and deduces the position interpolation control algorithm model b ased on the average speed method and the average acceleration method,respectively,and realize s the continuous rotor position and speed estimation.(2)The position interpolation control algorithm based on SMO is studied.Both average speed method and average acceleration method usually have poor dynamic response when there is an abrupt change in moto r speed or external load.To solve this problem,a position interpolation control algorithm based on SMO is proposed.It estimates the rotor position via the combination of SMO and PLL,and uses the difference of the estimated rotor position to interpol ate the discrete position signal,which significantly improves the estimation accuracy of rotor position.(3)The position interpolation control algorithm based on hig h frequency square wave injection is investigated.Although the structure of the SMO is simple and easy for implementation in engineering,it is impossible to identify the initial pole position of the motor,and has a poor accuracy at low speed.Therefore,this paper has a further study on the high frequency square wave injection method which is suitable for zero and low speed applications.It is based on the injection of square wave signal being of the same switching frequency of PWM in the estimated d-axis,and uses the filter free separation technology to separate the fundamental freq uency and high frequency response currents,so as to estimate the rotor position and speed.Secondly,in order to estimate the initial position polarity of rotor,a set of d-axis voltage pulse signal is injected to identify the positive and negative polari ty of permanent magnet.Finally,the difference of estimated rotor position is used for the interpolation of the discrete position signals,which can obviously improve the estimation accuracy of rotor position in low speed region.