Direct Motor Power Control for Constant Airflow in HVAC Systems
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Solution Overview
Problem
Current methods for constant airflow control in HVAC systems using torque as a control variable are complex, costly, and difficult to measure, making them unsuitable for steady-state control and consumer understanding, and are constrained by hardware and software limitations.
Innovation Solution
A direct power control method for PM motors in HVAC systems, using a concise algorithm that measures and adjusts motor input power to maintain constant airflow, with a motor controller that detects real-time bus current and voltage to calculate and control motor speed, allowing for low-cost, high-precision control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If torque control is used for constant airflow control, then the control can be implemented, but the system complexity increases and measurement difficulty arises
Solution Approach 1:
The patent changes the control parameter from torque (mechanical variable) to input power (electrical variable). This parameter substitution simplifies the control system because electrical parameters can be directly measured from the power supply side without complex mechanical sensors, while still achieving the same constant airflow control objective.
Solution Approach 2:
The patent replaces the mechanical torque measurement and control system with an electrical power measurement and control system. By controlling input power instead of torque, the system eliminates the need for complex torque sensors and mechanical measurement devices, reducing overall system complexity while maintaining control effectiveness.
2Reliability
If torque control is used for constant airflow control, then the control can be implemented, but the measurement precision decreases
Solution Approach 1:
The patent substitutes mechanical torque measurement with electrical power measurement. Electrical parameters (voltage and current) can be measured with high precision using standard electrical sensors, avoiding the measurement errors and difficulties associated with mechanical torque sensing, thereby improving overall measurement precision.
3Measurement precision
If air flow meter is directly installed for constant airflow control, then the control accuracy is improved, but the cost increases and reliability decreases
Solution Approach 1:
The patent uses input power as an intermediary parameter to indirectly control airflow instead of directly measuring airflow with a flow meter. By establishing the relationship between input power and airflow characteristics, the system achieves airflow control through power measurement, eliminating the need for fragile flow meters and improving system reliability.
Solution Approach 2:
The patent creates a control model that copies the airflow control function through electrical power measurement rather than direct mechanical airflow measurement. This virtual copying approach allows the system to achieve the same control objective without the physical constraints and failure modes of traditional flow meters.
4Measurement precision
If complex calculations (logarithmic or high-order polynomials) are used for constant airflow control, then the control accuracy is improved, but the computational requirements and cost increase
Solution Approach 1:
The patent changes the control parameter to input power, which has a more direct and simpler relationship with motor speed and airflow characteristics. This parameter substitution allows the use of simpler computational models compared to torque-based control, reducing the need for complex logarithmic or high-order polynomial calculations while maintaining control accuracy.
Data Source
AI summary
Systems and methods for providing constant airflow based on direct motor power control and advanced motor system modeling are described. A power and speed of a motor may be determined based on static pressure in the system. A target airflow rate for the system may be obtained, and a target motor power that yields the target airflow rate in the system may be determined based on the determined speed of the motor and the obtained target airflow rate for the system. A determination of whether the determined motor power is approximately equal to the target motor power may be made, and the power of the motor may be adjusted when the motor power is not approximately equal to the target motor power.