Abstract : Variable frequency speed control (VFD) for coal mine belt conveyors is widely used, and most speed control equipment employs closed-loop control systems. This article elaborates on the design concept, parameter selection, function settings, and debugging methods of a closed-loop system constructed using a VFD, providing readers with a reference for practical applications. Keywords : VFD; closed-loop system; PID control; speed regulation 0 Introduction A VFD is a static frequency conversion device, currently widely used in the speed control of AC motors. Due to its high-efficiency drive performance and good control characteristics, it has been widely applied in coal mining systems. VFDs have rich control functions, making them very convenient for process control (such as speed, flow rate, air pressure, etc.). Therefore, closed-loop control systems are widely used. The regulators that make up a closed-loop control system mostly adopt PID control algorithms. This function is present in many models of VFDs, but many users are not familiar with it, causing many difficulties in their work. Therefore, based on years of practical experience in VFD application and development, this article introduces the design concept, parameter selection, function settings, and debugging methods of implementing a closed-loop control system using a VFD. 1. Composition of the PID Control System The block diagram of the PID control system is shown in Figure 1. In Figure 1, the given signal is a voltage input signal (0～±5 V or 0～±10 V) or the set value of Pr. 133; the feedback signal is a 4～20 mA current input signal; the PID control consists of proportional control (P), integral control (I), and derivative control (D). Depending on the actual situation, proportional-integral control (PI), proportional-derivative control (PD), or proportional-integral-derivative control (PID) can be used. The regulating effects of proportional-integral control (PI) and proportional-derivative control (PD) are shown in Figure 2. The inverter drive circuit can be regarded as a proportional element, and the equivalent mathematical model of the motor can be regarded as an inertial element. As long as the coefficients (Kp, Ti, Td, Kb) of each element are reasonably selected, the system can work normally. Full text download : Application Practice of PID Closed-Loop Control System for Coal Mine Belt Conveyor Inverter.pdf