Cascade Control for Refrigerant Compressor Heat Flow Management
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Solution Overview
Problem
The existing methods for controlling the compressor in refrigerant circuits of battery-electric vehicles are complex due to the nonlinear relationship between refrigerant pressure and heat flow, particularly when cooling the vehicle battery, which affects the efficiency of thermal management and cooling capacity.
Innovation Solution
A method involving a cascade control system where an inner control loop regulates the compressor's power based on heat flow deviation and an outer control loop manages the target heat flow, allowing for more robust and faster control by separating refrigeration circuit control from temperature control and accounting for nonlinearities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If compressor speed is controlled based on refrigerant pressure upstream of the compressor, then the temperature control requirements can be met, but the control complexity increases due to the nonlinear relationship between refrigerant pressure and heat flow
Solution Approach 1:
The patent changes the control parameter from refrigerant pressure to compressor speed, with the target value for compressor speed being determined based on the heat flow requirement and the actual heat flow. This parameter transformation simplifies the control by directly linking compressor speed to the heat flow requirement rather than indirectly through refrigerant pressure, which has a nonlinear relationship with heat flow.
Solution Approach 2:
The patent implements a feedback control mechanism where the target value for compressor speed is continuously adjusted based on the deviation between the required heat flow and the actual heat flow. The control unit determines the target compressor speed by considering the heat flow requirement, actual heat flow measurement, and their deviation, creating a closed-loop feedback system that simplifies the overall control complexity.
2Measurement precision
If the nonlinear relationship between refrigerant pressure and heat flow is considered, then accurate temperature control is achieved, but the control response time increases
Solution Approach 1:
The patent directly controls compressor speed based on heat flow requirements rather than indirectly controlling through refrigerant pressure. This direct parameter control eliminates the need to account for nonlinear relationships in the control calculation, thereby reducing computational complexity and improving response time while maintaining temperature control precision through feedback adjustment.
Solution Approach 2:
The control unit proactively determines the target compressor speed based on the heat flow requirement before the temperature deviation becomes significant. By calculating the required heat flow and determining the appropriate compressor speed in advance, the system can respond more quickly to thermal management needs without waiting for temperature deviations to accumulate.
3Power
If indirect cooling via a cooling circuit is used for the vehicle battery, then the cooling capacity can be increased, but the relationship between refrigerant pressure and heat flow becomes more complex
Solution Approach 1:
The patent changes the control approach by directly measuring or calculating the actual heat flow in the cooling circuit and using this information to determine the target compressor speed. This direct heat flow-based control simplifies the control relationship by establishing a direct link between the cooling requirement and compressor operation, bypassing the complex nonlinear relationship between refrigerant pressure and heat flow that characterizes indirect cooling systems.
Solution Approach 2:
The patent introduces heat flow as an intermediary parameter that mediates between the cooling circuit requirements and the compressor control. By using heat flow as the intermediate variable, the system can accurately control the cooling capacity of the indirect cooling circuit without dealing with the complex nonlinear relationship between refrigerant pressure and heat flow, thereby simplifying the overall control architecture.
Data Source
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AI summary
The invention relates to a method for controlling a compressor in a refrigerant circuit, the method comprising the following steps: S1. Determining a thermal target state; S2. Determining a target heat flow dQSet or a quantity proportional thereto, at least partially based on the thermal target state; S3. Determining an actual heat flow dQIact or a quantity proportional thereto and determining a heat flow deviation ΔQ between the actual heat flow dQIact and the target heat flow dQSet or between the quantity proportional to the actual heat flow dQIact and the quantity proportional to the target heat flow dQSet; S4.Control of the compressor in a cascade control system, wherein an inner control loop (R1) of the cascade control system controls a power, in particular a speed, of the compressor at least partially on the basis of the heat flow deviation ΔQ determined in step S3, and an outer control loop (R2) controls the target heat flow dQSetpoint at least partially on the basis of the thermal target state determined in step S1.