Research On Dead-time Effect Compensation Scheme For A PMSM Servo System

At present, Voltage Source Inverters employing PWM strategies have been extensively used in PMSM servo systems, but dead-time effect is a major factor that degrades the control precision of a high-performance PMSM servo system. Dead-time insertion, voltage drop and other nonlinear characteristics of the switching devices cause an error between their output and reference voltages. This distorted voltage results in error of the currents and generates greater torque ripples, especially when the servo system operates at low speed and light load, which seriously invokes deterioration of the system control performance. Thus, it is necessary to analyze and compensate for the dead-time effect on inverters.A simulation experiment on an established PMSM servo system is run in the MATLAB/Simulink environment, suggesting the good operating performance of this system model. The cause for dead-time effect is analyzed quantitatively, and the effect of dead time and switching devices on-state voltage drop on both output voltage and current is also studied, with a special focus on the relations between the magnitude/ phase variation of the fundamental output voltage and the power factor angle. Additionally, an explaintion is given to the zero-current clamping phenomenon. Afterwards, the adverse dead time and on-state voltage drop effects on the PMSM servo system are verified in the MATLAB/Simulink.Currently, most traditional methods rely on the current polarity detection to compensate the output voltage distortion of inverters. However, accurate detection of current polarity cannot be achieved around the zero current crossing zone because of the interference brought by factors such as PWM noises. To avoid the current polarity detection, some scholars have proposed the time-delay control based compensation method, which, however, faces electrical machine parameter mismatches. To improve compensation accuracy, this thesis proposes an improved compensation scheme, namely the PI-type voltage loop compensation,which measures the real-time output voltage of the inverter online and makes the inverter output voltage dynamically trace its reference voltage through PI regulation. An appropriate selection of proportional and integral parameters is made to ensure highly acceptable dynamic tracing performance, and then curves of d-q voltage errors before and after compensation with respect to stator frequency are obtained. A comparison is made between this proposed method and the time-delay control based method under different switching frequencies using MATLAB/Simulink, and the effectiveness and feasibility of the proposed compensation scheme is confirmed; the PI-type voltage loop compensation scheme is superior to the time-delay control method in terms of the compensation performance.At last, the proposed method is experimentally validated using a d SPACE platform. Waveforms are compared with those of the time delay control based method. The experimental results prove the correctness, feasibility and effectiveness of the PI-type voltage loop compensation method again.