Improved estimation scheme for disturbance due to dead time and inverter nonlinearity in inverter‐fed PMSM drive

Abstract

An improved estimation scheme for disturbance due to the dead time and inverter nonlinearity in an inverter-fed permanent magnet synchronous motor (PMSM) drive is presented. The proposed scheme is based on a signal processing and harmonic component extraction and does not require any additional circuits nor parameter information. Furthermore, it is faster to estimate the disturbance as compared with the conventional method based on harmonic analysis. The effectiveness of the proposed scheme is verified through comparative simulations.Introduction: To prevent shoot-through in the DC link caused by simultaneous conduction of both switches in one inverter leg, a dead time should be inserted in a pulse-width modulation (PWM) inverter-fed permanent magnet synchronous motor (PMSM) drive. This distorts nonlinearly the inverter output voltage, eventually, providing the phase current distortion, torque pulsation, harmonic loss and degradation of control performance [1]. In addition to the dead time, the inverter nonlinearity exists in the PWM inverter caused by the inherent non-ideal characteristics of switching devices, such as the finite turn-on/-off time and voltage drops.To deal with such a problem, various approaches have been proposed. Although early attempts are based on the off-line method, recent researches are using on-line schemes because it is not easy to compensate such nonlinearity exactly by the off-line basis. Some on-line strategies require an additional hardware, such as a look-up table or detecting circuit [2]. In addition, these schemes compensated only the dead time without considering inverter nonlinearity. To overcome the limitation requiring additional hardware, on-line basis techniques using observer or adaptation schemes have been proposed [1,3]. Although good performance is obtained, the work in [1] still has the drawback that the estimator has to track the time-varying disturbances. Even though this study has considered the parameter uncertainty as well as the inverter nonlinearity, only partial parameter variations are considered and the compensator design is too complex. In particular, the disturbance voltages due to the dead time and inverter nonlinearity have a sixth-order harmonic component in the synchronous frame, which makes estimator design difficult at high speed. However, most conventional works have tried to estimate such inverter nonlinearity only at the synchronous frame where the current controller is designed.It is only recently that an estimator was designed at the stationary frame where the disturbance due to the dead time and inverter nonlinearity can be considered as slowly time-varying [3]. This scheme transforms a periodically time-varying disturbance into a slowly timevarying one. It is effective considering that the transformed disturbance does not change periodically with time. However, the estimating performance is still dependent on parameter variations because it uses a model-based approach. To obtain the estimating performance irrespective of parameter variations wi...