Optimization And Control Of A Parallel Pump System During Operating Regulations

Parallel pump systems are widely used in many industries,including municipal water supply and drainage systems,chemical industries,power systems and irrigation systems.Therefore,the reliability of parallel pump systems are crucial to energy saving and avoiding destructive accidents.Pumps are often designed with large design margins due to safety reasons,and are often selected with large safe margins in consideration of the possible production capacity expansions,demand changes and other reasons.These reasons make centrifugal pumps are often too large for their pipeline systems,which cause the centrifugal pumps operating in large flow condition areas.If a pump operates in its large flow condition for a long-term,it cannot perform efficiently and will deduce its reliability,thereby resulting in massive energy waste and high failure rate.The existing operating condition regulation methods,including throttling regulation,frequency regulation and pump series/parallel regulation,do not optimize the actual operating points of pumps,so the pumps are still possible to operate in large off-design points,which deduces the life of pumps.In order to improve the off-design operating problems in pump systems,this thesis proposes an optimization method to balance the reliability and efficiency of centrifugal pumps by optimizing the number of centrifugal pumps to put into operation and the suitable head loss across the control valve.The main contents of this thesis include the following aspects:(1).To study the check valve opening and closure during pump switch process,a parallel pump test rig is constructed and the three dimensional model of the check valve is built.The tran-sient behaviours of the check valve during its opening and closure,the inner flow field and the factors affecting the water-hammer caused by the check valve closure are analyzed us-ing transient numerical simulations.According to the results,the pressure loss of the check valve in fully open condition is relatively small and can be omitted in the following studies;the pressure fluctuation during the check valve closure is also negligible under experimental conditions.(2).The optimization model of the parallel pump system is built using the analysis of pump char-acteristics,frequency conversion and pump parallel operations.The optimization model aims at the minimum power consumption subjecting to the restraint that the actual pump operation points are restricted to a nearby area of its best efficiency point.The optimization model is solved using particle swarm optimization.The results show that the operation conditions and the reliability of the pumps are improved.(3).Using the previous optimization results,the pump-valve combined control system is mod-elled,the flow and pressure are controlled simultaneously.The pump-valve combined control system is a multi-input-multi-output nonlinear system with time delays.The time delays are balanced using extended Smith predictor,the nonlinearity is solved using input-output lin-earization.Three control methods are applied to solve the control system.The results show that the fuzzy adaptive method presents the best tracking and anti-disturbance performance and achieved the tracking of the previous optimization results.(4).Based on the pump-valve optimization theory,a industry-oriented dual-stage PID optimiza-tion method is proposed to overcome the calculation complexity of the particle swam opti-mization and the fuzzy adaptive controller.This method is based on the conventional PID frequency conversion method,by adding the optimizer,it can properly choose the proper number of pumps to put into operation and can optimize the operating point of the pumps by adjusting the control valve.The whole calculation is embedded into a PLC,therefore the dual-stage PID method is simple and stable,and can be conveniently extended to other industry projects.This thesis presents an optimization method based on the improvement of the actual operating point of centrifugal pumps for parallel pump systems,which enables the centrifugal pumps oper-ate within the best operating areas,therefore ensures centrifugal pumps a high reliability and low energy consumption.The fuzzy adaptive control enables the system to operate in the optimized operating point.This thesis also developed of a dual-stage PID optimization method,which is simple,stable and suitable for industrial applications.The experimental results show that the pro-posed method can effectively improve the operating point of the centrifugal pump and improve the reliability of the centrifugal pump,so as to solve the problem of the off-design operating condition of centrifugal pumps in practical engineering applications.