Research On The PI Controller Strategy For Speedloop Of Permanent Magnetic Synchronous Motor

At present,in the servo drive field with small and medium power and high precision,Permanent Magnet Synchronous Motor(PMSM)has become the mainstream because of its simple structure,high power density,high efficiency and smooth operation.The majority of conventional servo control systems apply PI controller,however,PMSM is a multi-variable and nonlinear controlled object and is affected by many uncertain interior and exterior disturbances in practical application,thus conventional PI controller is difficult to meet the strong stability and robustness requirements of servo system.The relationship between conventional PI controller parameters and system performance is unclear and the parameters setting is difficult.In order to solve the problem,a new PI controller based on the equation of state is introduced in this paper.When we design a traditional controller,the structure of the controller is selected firstly,and then the performance of the system using the controller is analysed.However,the new PI controller in this paper is just the opposite.The attenuation law of tracking error is designed first,based on which the structure of the controller is deduced.The new PI controller has a simple structure,parameters easily set and is adapative to varies input.By using the new PI controller,the speed control system is corrected to be a two-order system with overshoot in step response even when the damping ratio is unit.Futhermore,the new PI control system is an one-degree-of-freedom(1DOF)control system,which can not adjust the tracking performance and disturbance rejection property independently.The speed control system has good tracking performance for step response when using IP controller,i.e.,there is no overshoot in step response,but has also a poor tracking performance for continuously varying input.To solve the problem,a variable structure PI controller is proposed in this paper,acts as an IP controller when the input is a step signal and a PI controller when the input is a continuously varying signal.The secret to get a variable structure PI controller is the use of input differential feedforward and clamping integrator.In order to improve the tracking performance of conventional IP controller,an optimal IP controller is proposed at first.The optimal IP controller helps the control system obtain fastest response with zero overshoot in step response when the damping ratio is unit.However,the optimal IP control system still has a poor tracking performance for continuously varying input.Similarly,a PI controller with different reference gain is propsed.The controller is equivalent to IP controller when reference gain is zero and PI controller when the reference gain is one.The new PI controller,variable structure PI controller and variable input gain PI controller are all 1DOF controllers,thus tracking performance and disturbance rejection performance of the system are completely coupled,which makes it hard to ensure the two performances to be good simultaneously.To solve the problem,two kinds of two-degree-of-freedom(2DOF)PI controller based on conventional 2DOF controllers are proposed in this paper,then two variable structure 2DOF PI controllers are designed with the method of judging input type in variable input gain PI controller.The two variable structure 2DOF PI controllers cover all advantages of 1DOF PI conteollers mentioned above,additionally,make tracking performance and disturbance rejection performance decoupled,thus two performances can be adjusted independently and be good simultaneously.Because of these advantages,variable structure 2DOF PI controllers are very practical in engineering,especially suitable for high-performance speed-servo field.