Water circulation system for air conditioning system and control method thereof
Solution Overview
Problem
Large commercial refrigeration systems face challenges in maintaining stable pressure differences across air-conditioning outdoor units due to nonlinear characteristics and tight coupling of actuators and pressure disturbances, leading to system vibrations, shutdowns, and potential damage to components like outdoor heat exchangers or water pipes.
Innovation Solution
A control method for the water circulation system that employs a PID control step for stable operation and a feed forward control step during state changes, along with split range control and nonlinear compensation, to maintain a stable pressure difference across air-conditioning outdoor units, using a state machine to manage the actuator and bypass valve operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If PID control is used for pressure difference control in water circulation system, then system stability is improved, but system vibration occurs and severe disturbances cannot be overcome due to nonlinear characteristics and tight coupling of actuators and pressure disturbances
Solution Approach 1:
The feed forward control obtains a control quantity in advance based on the relationship between operating states and pressure difference, and adjusts the actuator and bypass valve before severe disturbances occur. This preliminary action prevents system vibration and instability that would otherwise occur with PID control alone under nonlinear conditions.
Solution Approach 2:
The system uses PID control as feedback control to maintain pressure difference stability during normal operation. The feedback mechanism continuously monitors the pressure difference and adjusts control quantities to compensate for deviations, ensuring stable operation while working in conjunction with feed forward control for disturbance rejection.
2Speed
If feed forward control is used to quickly respond to state changes, then response speed is improved, but control precision may be compromised due to system nonlinear characteristics
Solution Approach 1:
The feed forward control obtains a control quantity in advance based on pre-established relationships between operating states (such as water valve opening degrees) and pressure difference. This allows the system to respond quickly to state changes while maintaining control precision through the pre-calculated control strategy that accounts for system nonlinearities.
Solution Approach 2:
After feed forward control adjusts the system, PID feedback control takes over to fine-tune the pressure difference and eliminate any remaining deviations. This two-stage control approach combines the speed of feed forward with the precision of feedback, resolving the contradiction between response speed and control precision.
3Stability of the object's composition
If actuator frequency and bypass valve opening are controlled to maintain pressure difference, then pressure stability is improved, but tight coupling between actuators and pressure disturbances causes system vibration
Solution Approach 1:
The feed forward control obtains control quantities in advance based on the relationship between operating states and pressure difference, allowing the actuator and bypass valve to be adjusted proactively before pressure disturbances occur. This prevents system vibration and energy waste associated with reactive PID control adjustments.
Solution Approach 2:
The system changes the control parameters (actuator frequency and bypass valve opening degree) based on the feed forward control quantity derived from operating state relationships. By dynamically adjusting these parameters proactively, the system maintains pressure stability while avoiding the energy inefficiency of continuous PID corrections.
Data Source
AI summary
A water circulation system for air conditioning system and a control method thereof, wherein the water circulation loop comprises: a main loop provided with air-conditioning indoor units, air-conditioning outdoor units and an actuator, and a bypass branch connected between upstream and downstream of the air-conditioning outdoor units and provided with a bypass valve; the control method comprises: S100, starting the water circulation system after receiving a start command; S200, executing a PID control step after initialization and a first preset time period of the water circulation system; S300, executing a feed forward control step when the operating states of the air-conditioning indoor units and/or the air-conditioning outdoor units are changed, and going back to execute the PID control step after a second preset time period; and S400, executing a shutdown step of the water circulation system after receiving a shutdown command.