| In recent years,China's increasingly haze pollution.One of the main causes of pollution is the exhaust emissions of traditional fuel vehicles.From China's current market capacity and technical level,the speed of 40-60km/h low-speed electric vehicles with good economic performance?energy saving?low cost?easy charging and other advantages,is the most economical?the most environmentally friendly and the most easy to promote transportation of the second and third tier cities.It's China's green transport strategy choice.Motor drive control system is the key components of electric vehicle operation,Its control performance affects the electric vehicle power and continued mileage.The motors currently used in low-speed electric vehicles mainly include: Brushless DC motor(BLDC)? permanent magnet synchronous motor(PMSM)and AC induction motor(ACIM).BLDC are typically controlled with six-step commutation method.Although the control mode is simple,but the operation efficiency is low?the torque ripple is large and has low control accuracy.Because of the back-EMF of PMSM is sine wave,so vector control is usually used.Its torque ripple is small?operation efficiency is high and Its speed performance is good,but its manufacturing cost is very high,and the presence of back-EMF has also reduced its reliability.ACIM also use vector control,although the efficiency is lower than PMSM,but it has good speed performance?high reliability and low cost.Considering of the cost of low-speed electric vehicles and application scenarios,this paper selects the most widely used ACIM as the research object.Firstly,analyze the structure and working principle of ACIM,Simultaneously the mathematical model of three coordinate systems is established.On this basis,analyze the ACIM vector control principle,then,the principle of voltage space vector pulse width modulation(SVPWM)in vector control is analyzed.Aiming at the current application of SVPWM,a dead time compensation method based on time is proposed,which reduces the current distortion,running noise and torque ripple effectively due to the current distortion caused by the dead time of the switching device.Next,a sensorless control algorithm based on adaptive sliding-mode speed observer is proposed to solve the problem that the low speed electric vehicle speed sensor is easy to be damaged and difficult to be repaired.This method effectively eliminates the ripple of the motor speed in high frequency range in the sliding-mode observer in the motor control system without speed sensor.At the same time,the simulation model is established by MATLAB/Simulink.The simulation results show that the method has good current and speed followability.On the basis of the theoretical analysis,Using NXP-KV58F1M0VLQ22 as the master chip designed the smallest system.The chip has a DSP and FPU unit so the operation speed is very fast,which provides a reliable hardware foundation for the realization of complex control algorithms.On the basis of the minimum system,Aiming at the application requirements of 5KW AC induction motor for low speed electric vehicle,the overall design of hardware and software system is carried out.Finally,match the selected motor and controller with the experimental platform.From the waveform analysis and the actual test data can be seen,the controller designed in this paper satisfies the application requirements of the low speed electric vehicle and can operate normally under the condition that the sensor is damaged. |
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