Feedback Linearization Based Flow Rate Control for Centrifugal Pump in Coupled-Tank Water Meter Testing System

Abstract

A permanent magnet direct current (PMDC) motor centrifugal pump is intended to be used as the water supply unit in a feedback linearization based coupled-tank water meter testing system. Flow rate generated by the pump corresponds to the input variable for implementing the input-output feedback linearization to this single-input-single-output (SISO) system. The pump motor is driven by an Arm Cortex M7 based microcontroller applying the pulse-width modulation (PWM) strategy at various frequencies and pwm methods. It is aimed to determine a suitable PWM frequency and driving method in order to provide a stable flow rate at the desired duty cycle values. An H-Bridge driver integrated circuit (L298N) is used in both fast decay and slow decay modes for driving the pump motor. Flow rate measurements are carried out at 4 range of frequencies between 100 Hz and 20 kHz for each mode. Fast decay mode in low pwm frequency (100Hz) results in higher deviations at the steady-state flow rate. However, slow decay mode provides a faster reduction in motor speed despite the slower current decay, which improves the flow rate stability and minimize deviations at constant pwm duty cycle values. High pwm switching frequencies increase the energy losses resulting in a lower driving voltage range, which reduces the effective range of selection for pwm duty cycle setting of flow rate adjustment. 1 kHz PWM frequency combined with the slow-decay driving mode achieves good performance in terms of linear regression and wider range for pwm duty cycle to flow rate transformation.