Control Strategy For Generators Of Gas Pressure Energy Recovery Power Systems

Gaseous energy and industrial by-products such as natural gas,exhaust gas of internal combustion engine,blast furnace gas,etc.are firstly pressurized to high pressure in the gas source and then sent to the transportation network.During the transportation process,they are regulated step by step and supplied to downstream users for use or discharge.High-pressure gas contains a lot of pressure energy.However,this part of pressure energy is not recovered and reused in the existing transportation and pressure regulation technical process,resulting in energy waste.In order to achieve efficient use of energy and reduce energy waste,this thesis designs and develops a gas pressure energy recovery power generation system,which uses an expander to recover the pressure energy of high-pressure gas for driving a permanent magnet synchronous generator to rotate and generate electricity.The gas pressure energy recovery system is susceptible to changes in the gas consumption of downstream users,making the output torque of the expander fluctuate,thus reducing the power generation quality of the system.Therefore,the system has high requirements on the performance of the PMSG control strategy.For this reason,this thesis firstly addresses the problem that the PI controller parameters of the outer loop control loop cannot be adaptively adjusted in the direct torque control of the PMSG,and proposes a fuzzy PI-based speed outer loop control method,which takes the error between the generator speed and the set value and its rate of change as input,and outputs the torque set value of the PMSG through the designed fuzzy rules,which improves the performance of the speed outer loop control compared with the PI controller This method improves the control effect of the speed outer loop compared with the PI controller.On this basis,the required fuzzy rules are more complex and computationally intensive when the power generation system requires high control accuracy.For this reason,this thesis further proposes an external loop control method for rotational speed based on second-order active disturbance rejection control.The method first realizes the extraction of the differential of the error signal by designing a tracking differentiator for the control strategy,so that the system enters the steady state quickly and without overshoot;then,the rotational speed and angular acceleration of the permanent magnet synchronous generator are selected as state variables,and a second-order expansion state observer is constructed to realize the observation and compensation of the system state variables as well as the total disturbance;finally,the Non-linear State error feedback control law is established for the error feedback control.This method further improves the control performance of the speed external loop controller under the system in the disturbance-prone operating conditions while reducing the computational effort of the control system.On the other hand,in the torque inner-loop loop of the direct torque control strategy,the loop width of the hysteresis comparator has a large impact on the torque control effect.When the loop width is large,it will increase the error of torque and magnetic chain;when the loop width is small,it will increase the switching frequency of the converter as well as the loss;when the loop width is set to a fixed value,the voltage vector obtained by checking the voltage vector table will make the torque fluctuate in a small range.To address the above problem of the converter switching frequency instability due to the strong nonlinearity between the hysteresis loop comparator and the voltage vector switching table,resulting in the fluctuation of the PMSG torque,this thesis designs the torque inner-loop model prediction controller,which takes the generator torque and magnetic chain stability as the optimization target and calculates the optimal control quantity(voltage switching vector)in the prediction time domain,thus improving the control performance;and to override the control of the PMSG(a process called delay compensation in this thesis)to eliminate the control delay caused by signal transmission and program operation,to improve the real-time control response,and to further reduce the generator torque fluctuation.Based on the above research,an experimental platform for gas pressure energy recovery power generation system is designed and developed in this thesis.Using high pressure air generated by an air compressor as the gas source,the proposed control strategy is experimentally studied by changing the valve opening downstream of the expander and simulating the conditions where the expander output torque fluctuates due to the change in the expander outlet pressure caused by the change in the gas consumption of the downstream users.The TMS320F28335 chip is used as the main control chip to implement the fuzzy PI model predictive direct torque control strategy and the active disturbance rejection model predictive direct torque control strategy proposed in this thesis.At the same time,in order to verify the performance of the proposed control strategy,this paper designs four additional control strategies for experimental comparison,namely,traditional direct torque control,fuzzy PI direct torque control,model predictive direct torque control(outer-loop PI controller+inner-loop model predictive controller)and active disturbance rejection direct torque control strategy.The experimental results show that,among the proposed control methods,the self-rejecting model prediction direct torque control strategy has the best control effect,reduces the speed and torque fluctuations of the PMSG,and effectively suppresses the current harmonics.