ECM Motor Bus Current Feedback for Constant Air Volume
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Solution Overview
Problem
Existing methods for controlling constant air volume in HVAC systems using electronically commutated motors (ECM motors) are costly and prone to control failures, often requiring complex computing capacity and malfunctioning air flowmeters.
Innovation Solution
A method employing a simple mathematical model and algorithms to control the rotational speed of the ECM motor using a microprocessor, bus current detection, and inverter circuit to maintain constant air volume, reducing production costs and improving control accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If air flowmeter is directly installed in the air duct to obtain constant air volume, then air volume control is achieved, but production cost increases and the air flowmeter often malfunctions causing control failure
Solution Approach 1:
The patent extracts the air volume control function from the air flowmeter and implements it through the motor controller by monitoring bus current. This removes the need for a separate air flowmeter device, reducing device complexity while maintaining control reliability through the existing motor control system.
Solution Approach 2:
The motor controller is given multiple functions: it not only controls the motor speed but also monitors bus current to determine air volume and performs closed-loop control. This multi-functionality eliminates the need for separate air flowmeter hardware, reducing device complexity while maintaining reliable control.
2Reliability
If monitoring the static pressure of the system to adjust the rotational speed is used to control constant air volume, then air volume control is achieved, but production cost increases
Solution Approach 1:
The patent replaces the mechanical static pressure monitoring system with an electrical measurement system that monitors bus current. This substitution uses electrical parameters already available in the motor control system, eliminating the need for separate pressure sensors and reducing production cost while maintaining control accuracy.
Solution Approach 2:
The motor controller uses its own existing bus current measurement capability to determine air volume and perform control, without requiring external pressure monitoring equipment. This self-service approach leverages existing system resources, reducing production cost while maintaining control accuracy.
3Measurement precision
If strong computing capacity of the MCU of the motor controller is used to control constant air volume, then control accuracy is improved, but production cost increases
Solution Approach 1:
The patent changes the control parameter from complex torque calculations to simple bus current monitoring. By using the relationship between bus current and air volume, the system achieves accurate control with simple comparison operations, reducing MCU computing capacity requirements while maintaining control accuracy.
Solution Approach 2:
The patent uses a simplified control approach that monitors only bus current rather than performing complete torque calculations. This partial action (monitoring only the necessary parameter) achieves sufficient control accuracy without requiring excessive computing capacity, reducing production cost.
Data Source
AI summary
A method for controlling constant air volume of an ECM motor in an HVAC system. The method includes: a) acquiring a target air volume Qset input from an external, determining a function Itad=f(n) corresponding to the target air volume Qset by the microprocessor, in which Itad represents a bus current, n represents a rotational speed of the motor; b) acquiring a calculated bus current Itad according to the rotational speed n and the function Itad=f(n), and detecting a real-time bus current Ibus; and c) comparing the calculated bus current Itad with the real-time bus current Ibus by the microprocessor for closed-loop control; when Itad>Ibus, increasing the rotational speed n of the motor; when Itad<Ibus, decreasing the rotational speed n of the motor; and when Itad=Ibus, stopping regulating the rotational speed n and returning to B) for continuing the control of the constant air volume.