Application Research Of DPWM Over Modulation In Asynchronous Motor Vector Speed Control System

With the development of AC speed control theory and power electronictechnology, asynchronous motor has a superior control performance similar toDC motor. Regard the idea that torque and excitation component independentcontrol in DC motor as a guide, a vector control model based on rotor fluxorientation emerge as the times require. At present, the asynchronous motor hasobvious price advantage and is easy to maintain, so it occupies an importantplace in practical applications and its use accounts for more than50%marketdriven power. A commitment to study of asynchronous motor speed regulationstill has potential application value. In this paper, the vector control method andthe inverter modulation strategy of three-phase asynchronous motor are treatedas the main content, aiming at improving related indexes of system performance.Firstly, the rotor fux oriented vector control fundamental theory isexpatiated in detail. After analysing dynamic mathematical model, inductionmotor can be converted to M-T rotating coordinate system by the vectortransformation equation, according to the rotor field oriented three-phase statorcurrents are decoupled and calculated to obtain the separating torque current component and excitation current component. In addition, bicyclic structure oftorque control and flux control subsystem is simplified properly, thus get theM-T axis voltage command outputs to the inverter.After that, the design of optimization program focuses on invertermodulation strategy. Discontinuous pulse width modulation (DPWM) strategyallows each inverter bridge arm just switches in2/3fundamental period. In viewof over-modulation technique contributing to a more efficient DC voltage energyuse, DPWM modulation strategy and over-modulation technique are combined，harmonic distortion and switching losses are two mutual restraint indicators,when pursuiting both optimization of the two index compromised balance isnecessary. Based on traditional voltage space vector pulse width modulation(SVPWM), the correct switching control pulse output is analyzed when DPWMworks in the over-modulation area.Whereafter the overall scheme is established which includes bothrotor-flux-orientation vector speed control and DPWM modulation. Simulationbuilt based on Matlab/Simulink software is a reference object used to verify it.The results show that the overall scheme for improving the DC side voltage,reducing the switching losses and reducing the harmonic distortion has certaineffect, whether the system is in steady state or dynamic transition process, thespeed can follow the given value quickly and accurately, other indicators ofspeed performance are also in correct reaction.Finally, taking the three-phase diode bridge rectifier6R130G-120as uncontrollable rectifier and using IPM intelligent power module PM30RSF060as the inverter hardware platform is builded. By the way make a simpleintroduction of the filter circuit, driving circuit, detection circuit, protectioncircuit and fault processing circuit. TMS320F2812is software control coreboard for C language programming in CCS3.3development platform whichincludes main program and six subroutines. Subroutines were all about signals’acquisition and computation, controlling methods’ implement and inverteroutput trigger pulses’ generation. After debugging of hardware and softwarecombination, both DPWM over modulation and traditional SVPWM methodswere used to verify the vector control system. The experimental results showedthat DPWM over modulation and vector control are reasonable and efficient.