Research On Energy Recovery And Reuse Devices For AC Motor Speed Regulating System

Since the beginning of 21 st century,with the rapid development of the economy and the continuous improvement of people's living standards,the consumption of fossil energy(such as oil,coal,and natural gas,etc.)is increasing,and China will face increasingly serious environmental problems and energy crises.Energy conservation and consumption reduction will become an important issue for companies in all operating conditions.In the power industry,Electric power consumption of motor accounts for about 64% of the country's total electricity consumption.In the industrial field,electric power consumption of motor reaches more than 75%.In the “12th Five-Year Plan”,the energy saving transformation project of the motor system is the most important part of the energy conservation project.In recent years,with the rapid development of variable frequency control technology,it has become one of the current research hotspots to tap new energy-saving methods in the AC motor variable frequency speed regulation system.The motor usually needs frequent start and brake in industrial production,so there is a large amount of regenerative braking energy.At present,the electrical energy generated by the motor braking is usually dissipated by the electrical resistance in the form of thermal energy in most AC motor frequency control,resulting in a huge waste of energy.In this paper,according to the characteristics of braking energy and in comparison with various energy storage modes,the super capacitor is selected as the energy storage unit to recover the braking energy produced by the AC motor speed control system,and a kind of energy recovery and reuse device for AC motor speed control system is designed to achieve the secondary use of the energy generated by the motor during braking.According to the functions of the energy recovery and reuse device in the AC motor speed control system,the overall structure of the system is designed.The charging and discharging methods of the super capacitor were analyzed.The mathematical model was used to describe the efficiency of the super capacitor constant current charging and discharging.The working mode of the bidirectional DC/DC converter was designed according to the different operating conditions of the AC motor.The non-isolated interleaved parallel topology was adopted to reduce the output current ripple and ensure the stability of the motor operation.According to the set parameters valve of super capacitor and bi-directional DC/DC converter,the parameters of the super capacitor and the main components of the converter are specifically designed and selected.Combining with the actual operating characteristics of the load AC motor,the control objectives of the braking energy recovery and reuse device in different working modes are described;according to the control objectives,the power controller,state recognition and mode switching controller,bidirectional DC/ DC converter controller and super capacitor constant current and constant voltage charging controller are designed respectively to realize the overall coordinated control of the device.On the basis of theoretical analysis,relevant hardware design of the device for energy recovery and reuse of brake energy is carried out,including state recognition and control circuit,pattern recognition and control output circuit,voltage and current sampling circuit and bidirectional DC/DC converter PWM circuit and The IGBT module drive circuit and the control interface circuit and then the overall design of the braking energy recovery and reuse device of the AC motor speed control system are completed.An experimental platform for the energy recovery and reuse device of the AC motor speed control system with a power of 2 kW was set up.The study of charge discharge characteristics of super capacitor and steady and dynamic characteristics of bi-directional DC/DC converter,as well as the simulation experiment of variable load power and the impact verification experiment were carried out.Finally,the feasibility,stability and dynamic performance of the designed energy recovery and reuse device are verified.