Design Of Digital Power Amplifier Based On Sliding Mode Control

Active magnetic bearing with high speed,high precision,low loss and other fine features.In active magnetic bearing systems,control signal is converted to electromagnetic energy by power amplifier,its performance will directly affect the requirements of system for rapidity,accuracy,stability.The DC bus of the magnetic bearing power amplifier currently widely use the finished switching power supply,not specifically designed for the characteristics of magnetic bearing systems,DC output voltage can not be dynamically adjusted,no load parameter identification and fault self-diagnosis functions.A active magnetic bearing digital power amplifier based on sliding mode control is designed in the paper to deal with these problems,including a digital power amplifier and a Buck converter that provides constant and adjustable DC bus voltage for the digital power amplifier.It has the ability to online identification of load parameters,fault diagnosis and system protectionThe digital power amplifier selects a half-bridge topology with simple control,excellent performance,and moderate cost.PI control and three-level control strategy are adopted by controller,which is simple and reliable.The three-level digital power amplifier is compared with the two-level digital power amplifier,the output current ripple will decrease with the freewheel time.Sliding mode control is chosen for buck converter,which is insensitive to changes in internal and external parameters of the system,and has strong robustness.The digital power amplifier uses TMS320F28335 high-performance digital signal processing device as the control core and is responsible for signal acquisition,data processing and control output.The analog to digital conversion module acquires voltage and current signals.The pulse width modulation module outputs PWM signal to drive power MOSFET.The serial communications interface module to achieve communication with the host computer software.The system test result shows that the designed digital power amplifier has stable output current waveform,high precision(steady-state error less than 20mA),small ripple(current ripple about 20mA),high linearity(0.67%),fast dynamic response,and wide frequency response range.After the sliding mode control Buck converter is added into digital power amplifier,better amplitude-frequency characteristics and transmission characteristics,higher linearity,but the algorithm processing time is increased,which causes the relative lag of phase-frequency characteristics.