A Sensorless Vector Control Scheme with High Bandwidth Current Loop for Surface Mounted Permanent Magnet Synchronous Machine Based on High Frequency Square Wave Type Voltage Injection

Abstract

Thanks to stator flux based observer running at middle and high speed and various high frequency injection (HFI) methods operating in zero and low speed region, position sensorless field oriented vector control system of permanent-magnet synchronous machine (PMSM) has attracted much attention. Nowadays, Most of HFI methods adopt sinusoidal type voltage at high frequency as injection signal, its frequency being one-tenth of PWM switching frequency or so. Restricted by low pass filters (LPFs) and/or band pass filters (BPFs) used, the control system is implemented with narrow current loop bandwidth and high-frequency audible noise. In order to solve these problems, this paper proposes a new HFI method based on square wave, with its injection frequency equivalent to PWM switching one. Also LPFs and BPFs are replaced with a new demodulation method and then rotor position and velocity can be estimated with rotor position observer. To validate the proposed scheme, a prototype is designed with DSP-TMS320F28335. Whole control system has been designed including initial rotor position determination, magnetic polarity judgment and rotor position and speed estimation by the proposed HFI scheme in low-speed region. Experiments show that the proposed schemes are of good dynamic performance and no additional audible noise is added, its bandwidth of current loop being 500Hz, which approach to that of vector control system of PMSM with encoder. Introduction Information of rotor position plays very important part in high-performance servo drive system of PMSM. It can be measured directly from encoder or resolver, or obtained indirectly from estimation methods by means of voltages and currents measured from endpoints of PMSM. Among these sensorless methods, various observer based strategies and high frequency injection (HFI) based methods attract more attention during last two decades, particular the later [1-6]. In principle, observer strategies for rotor position estimation is based on the magnitude of electro-magnetic-force (EMF) at stator, therefore these strategies are only adaptable at high and middle speed. Various HFI methods provide a good means to obtain rotor position and speed at low or even zero speed. They employ constructional asymmetry of rotor, or magnetic asymmetry stimulated by high frequency injection signals to get information of rotor position and speed. So far, according to waveform of which high frequency is injected, these methods can be divided into two types: one is sinusoidal HFI method, the other being square wave HFI one. Usually, the sinusoidal HFI method is more often utilized than later. For sinusoidal HFI method, the signal frequency of which is about onetenth of PWM switching frequency. Restricted by low pass filters (LPFs) and/or band pass filters (BPFs) used, the control system is only implemented with narrow current loop bandwidth and highfrequency audible noise [7-12]. In order to solve these problems, this paper presents a square wave based HFI scheme, the frequency of which being equal to the PWM frequency. Combined a new demodulation method International Conference on Modeling, Simulation and Big Data Analysis (MSBDA 2019) Copyright © 2019, the Authors. Published by Atlantis Press. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/). Advances in Computer Science Research, volume 91