Variable Speed Motor Direct Power Control for Constant Airflow in HVAC
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Solution Overview
Problem
Current constant airflow control methods for HVAC systems using torque as a key control variable are inaccurate, complex, and costly, and do not effectively manage energy conservation and environmental standards due to the difficulty in determining torque and its association with steady-state control.
Innovation Solution
The method involves direct power control using a function P=f(n) to calculate motor input power based on rotation speed, with real-time bus current and voltage measurements, allowing for closed-loop control, which is more accurate and cost-effective for steady-state airflow control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If torque control is used for constant airflow control, then control capability is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces mechanical torque control with direct electrical power control. Instead of using complex mechanical torque sensors and vector control systems, the invention directly controls motor input power through electrical parameters (voltage and current measurements), substituting a complex mechanical control system with a simpler electrical control approach that achieves the same constant airflow objective
Solution Approach 2:
The patent extracts the essential control variable from torque control by focusing directly on power control. Rather than controlling torque through multiple intermediate steps (current control, flux control, torque calculation), the invention extracts and directly controls the power parameter P=f(n), simplifying the control chain while maintaining constant airflow capability
2Reliability
If torque control is used for constant airflow control, then control capability is improved, but manufacturing cost increases
Solution Approach 1:
The patent uses inexpensive electrical measurement components (voltage and current sensors) instead of expensive torque sensors and complex control hardware. By measuring electrical parameters that are already present in the motor system and calculating power from these measurements, the invention avoids costly additional components while achieving accurate constant airflow control
Solution Approach 2:
The patent replaces expensive mechanical torque control systems with affordable electrical power control. By using electrical measurements and calculations rather than mechanical torque sensing and control mechanisms, the invention significantly reduces manufacturing costs while maintaining control accuracy
3Measurement precision
If airflow meter is mounted for constant airflow control, then control accuracy is improved, but device cost and complexity increase
Solution Approach 1:
The patent uses motor input power as an intermediary variable to indirectly control and monitor airflow. Instead of directly measuring airflow with complex meters, the invention uses power measurements (voltage and current) as intermediaries that correlate with airflow conditions, allowing constant airflow control through power regulation without direct airflow sensing
4Measurement precision
If complex calculation formulas are used for constant airflow control, then control accuracy is improved, but processing time and CPU requirements increase
Solution Approach 1:
The patent changes the control parameter from torque (which requires complex vector control calculations) to direct power control using the formula P=f(n). This parameter change simplifies the mathematical relationships involved, allowing accurate constant airflow control with basic arithmetic operations rather than complex logarithmic or polynomial calculations
Data Source
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AI summary
The present invention discloses a method of constant airflow control of motor direct power control and a HVAC system using the same. The method comprises the following steps of: step A), starting a motor controller to receive a target airflow IN-CFM; step B), acquiring a corresponding function P=f(n) according to the target airflow IN-CFM; step C), entering a direct power controlled constant airflow control mode: controlling a motor to reach a steady working point (pt, nt) along a control track of the function P=f(n); step D), calculating the real-time input power Pi of the motor according to operating parameters of the motor, and calculating ΔP=|Pt-Pi|; step E), keeping the current working point if ΔP is less than a set value Pset; step F), calculating whether the operating time of a speed loop is reached if ΔP is greater than or equal to the set value Pset, and keeping the current working point if the operating time of the speed loop is not reached; and step G), entering a speed control circuit to adjust the speed if the time is already reached, so as to realize a new working point (Pi, ni) on the track, i.e., letting pt=Pi and nt=ni, and returning to step C. The present invention is particularly suitable for the airflow control at a steady state, and has simple algorithm, low requirements for CPU operation, low cost and high control accuracy.