Research On Optimal Control Technology Of Uninterruptible Power Supply In Chemical Instrument System

Due to the continuous innovation of electronic technology,the degree of automation in the traditional chemical industry has been significantly improved,making the frequency of use of chemical instrumentation systems increase.In order to reduce the impact of emergency power failure of the instrumentation system on the chemical industry,an uninterruptible power supply should be used to power the chemical instrumentation system;on the other hand,in the complex chemical environment,the instrumentation equipment is subject to increasingly serious harmonic pollution,which not only affects the measurement results of the instrumentation,but also leads to misoperation of the equipment which can overheat the line or even cause a fire.In summary,it can be seen that improving the harmonic optimization capability of the uninterruptible power supply of chemical instrumentation system is of great significance to the stability of chemical instrumentation system.In this paper,we analyze and study the optimization control of the power factor correction(PFC)module and inverter module of the uninterruptible power supply of the chemical instrumentation system,and its main contents include the following.(1)The operating principle of the PFC circuit is analyzed,a small-signal model of the PFC circuit based on conventional dual-loop PI control is established,and the causes of harmonics generated by the PFC input current are derived from the model analysis.The method of reducing the voltage loop cutoff frequency is used to solve the problem of input current harmonics.The analysis shows that reducing the voltage loop cutoff frequency has the problem of slow dynamic response of the PFC output voltage,and the existing PI control has the problem of steady-state error in the control of the PFC input current.(2)To address the output voltage problem of the conventional PI control-based PFC module,the optimal control strategy of PFC current is proposed.For the current loop,the DQ current decoupling scheme in rotating coordinate system is proposed to achieve static-free tracking of the input current in rotating coordinate system through PI control,thus improving the system stability;for the voltage loop,the output voltage harmonics are suppressed by introducing a 100 Hz trap to indirectly improve the quality of the current waveform.The simulation and analysis of the steady-state output waveform,dynamic response waveform and inductor current harmonics of the PFC module based on the current-optimized control strategy and the conventional PI control are conducted to verify the feasibility and superiority of the proposed current-optimized control strategy.(3)For the common periodic harmonic problem in the inverter output voltage,the optimized control strategy of repetitive PI is adopted.Selecting the appropriate Q value on the basis of repetitive control can improve the stability of the system.By designing a second-order low-pass filter,the high-frequency components in the system are filtered out.For the existence of resonant spikes in the controlled object,by introducing a comb trap filter,not only can the fixed frequency band be attenuated,but also has the characteristic of zero phase shift.Due to the existence of a certain degree of phase lag in the inverter itself and the second-order low-pass filter,phase compensation is performed by introducing an overrun link.To address the problem of poor dynamic characteristics of the repetitive controller,the system dynamic capability and periodic harmonic suppression capability are improved by combining repetitive control with PI control.Finally,simulation experiments are conducted for the optimized control of repetitive PI and the conventional PI control,and the waveforms of the output voltage steady-state response and the output voltage harmonic analysis plots of the two control schemes under rectified load are compared to verify the superiority of repetitive PI control.(4)A 2k W uninterruptible power supply prototype was built to experimentally verify the current-optimized control strategy proposed by the PFC module and the repetitive PI control strategy proposed by the inverter module.The experiments show that the PFC inductor current based on the current-optimized control strategy can follow the mains voltage.The inverter output voltage waveform based on repetitive PI control is a perfect sine wave,and the dynamic response is fast during sudden load and load shedding,and the output voltage remains sinusoidal when dealing with rectified loads.