Sensorless Control Of Permanent Magnet Synchronous Motors Based On High Frequency Pulsating Signal Injection

Permanent Magnet Synchronous Motor(PMSM)has been widely used in electric drive systems because of its simple structure,high power density and high efficiency.Information of rotor position,which is mainly detected by mechanical position sensors,is essential in a PMSM control system,Installation of mechanical sensors,however,gives rise to increase in volume,weight and costs of the system and prevents PMSMs from being used in rigor environments such as high temperature and strong chemical erosion.Hence,the technology of detecting rotor position from electrical signals is proposed and has come into the spotlight in electric drive system research.The paper reviews the technology of detecting rotor position from electrical signals and classifies it according to the speed range.The review shows rotor position detection at low speeds is more difficult than that in high speed range.The paper studies in-depth the rotor position detection of a surface-mounted PMSM(SPMSM)at low speeds based on high frequency pulsating signal injection.The paper discusses structures,characteristics and applications of PMSMs,introduces several classic and modern control strategies of PMSMs,and summarizes research status of position detection methods based on electrical signals.The paper establishes the mathematical model of a PMSM,analyzes the principle of vector control,coordinate transformation,and current control strategies,and based on the analysis introduces the high frequency pulsating signal injection method.In the existing methods,the signal extraction and modulation method at low speeds is relatively mature.Nevertheless,in the process of initial rotor position detection,multiple types of signals need to be injected into the stator,which is tedious.In order to simplify the detection process,the paper proposes three novel methods of initial rotor position detection based on the nonlinear saturation characteristics of d-axis flux.These methods only need to inject high frequency voltage signal which is much simplier than the existing methods.In the high frequency pulsating voltage injection method,two low-pass filters are needed to filter out high frequency components of the feedback currents in d-and q-axes,which complicates the detection system.Moreover,the stability of rotor position detection system depends on the variations of motor parameters and the frequency of injected voltage.To avoid these drawbacks,the paper studies high frequency current injection and firstly introduces the principle of this method.The method,however,has specific requirements for bandwidths of current regulators.The problem of signal delay in the process of rotor position detection remains unsolved also.Hence,the paper proposes a novel rotor position observer,discusses optimal design of the current regulators and structure of the novel position observer,and proposes a method of initial rotor position detection.In order to reduce the influence of step signal on the detection prision of rotor position observer,the paper puts forward the q-axis current feed-forward compensation,which compensates the step signal according to the q-axis current and motor paprameters.In addition,the paper presents stability analysis of this compensation strategy.In high frequency pulsating current injection method,the rotor position is extracted from the command voltage instead of the actual measurement due to the lack of voltage sensors,which results in position estimation error.To avoid the problem,the paper proposes a novel current regulator structure,in which second-order generalized integrators are applied.With this structure,the rotor position can be obtained from current signal.Design process of the proposed current regulator structure is firstly introduced.Then the rotor position and speed detection system are designed.At last,detection errors in steady and dynamic processes and stability of the detection system are analyzed.As amplitude of the signal used for rotor position detection is relatively small in high frequency pulsating signal injection methods,the influence of system hardware is non-negligible.Hence,the paper theoretically analyzes the position detection errors of high frequency pulsating voltage and current injection methods considering inverter nonlinearities,motor parameter asymmetries and current detection errors.Expressions of these errors are derived.To eliminate these errors,the paper puts forward the wave trap method and the dual filter method and further compares advantages and disadvantages of these two methods.Finally,the paper designs hardware platform and the software system of the PMSM control system based on a RT-LAB,and carries out experiments to verify the research.