Stability Control Of Ultra-high-speed Electric Air Compressor For Fuel Cell Of Vehicles

Fuel cell vehicles have advantages of high energy efficiency,zero emissions,and no pollution.As an important direction for development of new energy vehicles,they have been extensively studied by scholars and companies in recent years.Fuel cell electric air compressor for vehicles delivers compressed air to the stack,where it electrochemically reacts with hydrogen to generate electricity.In order to meet needs of fuel cell vehicles for a wide range of power,high-power fuel cells must be used,which requires further improvement of the air supply flow and pressure ratio.The electric air compressor is mainly composed of compressor and permanent magnet synchronous motor(PMSM).The structure and speed of compressor affect the air supply flow and pressure ratio.Before major breakthrough is made in structural design of compressor,the speed of PMSM must develop towards high speed and ultra-high speed,so ultra-high-speed electric air compressors have become development trend.In the typical PMSM control method,the d and q axis stator voltage are calculated by the PID controller tracking d and q axis stator current reference.If the calculated d and q axis stator voltage are incorrect,it will cause the d and q axis stator current instability,which in turn produces torque fluctuations and speed fluctuations.In order to improve the stability of ultra-high-speed electric air compressor,this research starts from the construction of dynamic model of ultra-high-speed electric air compressor,and conducts in-depth research on its stability analysis and stability control.The main research contents are as follows:Firstly,introduce structure and working principle of ultra-high-speed electric air compressor,derive expression of phase current in static coordinate system,perform Clark and Park transformations,and establish dynamic model of PMSM in the synchronous rotating coordinate system;consider shape of the impeller blade,the pressure component in the direction of the blade speed is derived,and the impeller load torque model is established according to pressure distribution on the blade surface;impeller load torque model and PMSM model are combined to perform linear affine transformation and time scale transformation to establish a dimensionless dynamic model of ultra-high-speed electric air compressor.Secondly,based on the dimensionless ultra-high-speed electric air compressor dynamic model,the equilibrium point is calculated.Considering the dimensionless load torque and d and q-axis stator voltages,the Routh-Hurwitz criterion,Hopf and Fold bifurcation theory are used to derive stability conditions of equilibrium point;the calculation method of the stability region of ultra-high-speed electric air compressor is proposed,and the ultra-high-speed electric air compressor is analyzed.The bifurcation that exists during the operation of ultra-high-speed electric air compressor.Numerical analysis shows that the boundary value of dimensionless d-axis stator voltage stability region is-22,and this value increases with the decrease of the q-axis stator voltage;the boundary values of dimensionless q-axis stator voltage stability region are 0.5 and 3,and the stability region increases with d-axis stator voltage increases.Thirdly,calculate d and q-axis stator voltage stability domains of the ultra-high-speed electric air compressor under different electromagnetic torques,and finally obtain the three-parameter stability domain division results of electromagnetic torque,d and q-axis stator voltage.Combined with the PMSM vector control architecture,the stability control module is designed to ensure that the d and q axis stator voltages of the ultra-high-speed electric air compressor can be in the stable range during operation.Simulation analysis shows that ultra-high-speed electric air compressor has two instability phenomena during process of static speed adjustment to the highest speed.After the stability control is carried out,q-axis stator voltage suddenly drops to 275.3V and 251.6V,respectively,and d-axis stator voltage is maintained at-128.3V and increased to-102.7V respectively.The controlled d and q-axis stator voltages are in the stable region.Finally,in order to verify effectiveness of stability control method,the experimental equipment was carried out,and the stability control test bench of ultra-high-speed electric air compressor was built.Design the experimental methods for speed control response experiment with or without the stability control method,and compare the speed fluctuation and torque fluctuation of ultra-high-speed electric air compressor with or without the stability control method.The experimental results show that the maximum speed fluctuation amplitude when the stability control method is not adopted is 287.32 rpm.After the stability control method is adopted,and the maximum speed was increased to 154336 rpm,the speed fluctuation amplitude can be kept below20 rpm.The total time to reach the maximum speed is only 20 ms later than that without the stability control method.