The Development On Low-voltage Inverter And Research On Asynchronous Motor Indirect Torque Control Strategy

Since the 20th century, with the development of power electronics technology, particularly large-scale integrated circuits and computer control technology, high-performance AC Speed control System has achieved in and rapidly developed. In the variable speed transmitting domain, it has taken the place of DC variable speed system, and obtained significant energy savings results in wind driven generator, pumps and so on. This paper focused on two aspects on AC speed control system.1. Hardware circuits:Based on In-depth study of the Inverter hardware circuit, this paper discusses the principle and design of general-purpose inverter, using DSP TMS320LF2407A as the control core, applying IGBT as apparatus of the inverter. This paper carries out parameter calculation and selection on the inverter main circuit devices including IGBT, rectifier bridge, filter electrolytic capacitors, voltage and current sensors, and improves control circuit including using of a control circuit chip (ADS8365) as the A/D converter module, increasing PC-CAN communication module circuit and designing drive protection circuit corresponding IGBT. On this basis, this paper designs and develops a 100KVA prototype inverter and currently the prototype is debugging.2. Control strategy:As is known to everyone, in low-speed range (n<0.25 n N), asynchronous motor traditional direct torque control method exists some problems , for example, low frequency switch, unfixed switching frequency ,torque ripple and so on. This paper adopts the indirect torque control method (ISC) to solve the above problems.Directly in the stator frame analysis, indirect torque control calculates the flux and torque without complex vector rotation transformation. From the perspective of control, ISC control system takes PI adjuster with continuous output to adjust the flux and torque of inverter and adopts random variable amplitude and phase voltage vector. From the above, the magnetic chain of ISC control system maintains circular trajectory and space voltage vector and magnetic flux variation can be accurately calculated, so ISC control system is a continuous precise control method.The paper realizes matlab simulation of indirect torque control system based on SVPWM. On the basis of the research on simulation, ISC control system is programmed, in AC speed control experimental platform.The simulation and experimental results show that ISC control system can effectively reduce the the torque ripple at low-speed and improve the current and magnetic flux waveform.