Compressor Motor Braking Using Induced Voltage Feedback
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Solution Overview
Problem
Compressors in refrigeration appliances face challenges in slowing down safely without risking resonant frequency encounters, which requires complex pump designs and poses a risk of the compressor striking the shell during freewheeling.
Innovation Solution
A method involving a controller that determines induced voltages and applies a braking current with decreasing frequency, based on the instantaneous load, to control the rotational speed and ensure reliable motor braking without relying on rotor position determination, using a predefined rotational speed curve and load torque measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the compressor is allowed to freewheel during slowing down, then the braking process is simple, but the compressor may reach resonant frequency and strike the shell
Solution Approach 1:
The patent replaces the mechanical braking approach (short-circuiting windings) with an electrical control approach. The controller continues to supply controlled current to the windings during deceleration, using electromagnetic forces to actively control the rotor position and prevent resonant frequency encounters, thereby eliminating the need for complex mechanical braking systems while ensuring reliability.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the deceleration process and adjusting the current supplied to the windings based on the rotor position and speed. The controller uses this feedback information to maintain optimal braking current, preventing the compressor from reaching resonant frequencies while ensuring smooth and controlled deceleration to a stop.
2Speed
If short circuiting is used to brake the motor below rotational speed mark, then braking is achieved quickly, but the pump design must be complex and robust
Solution Approach 1:
The patent replaces the mechanical short-circuiting braking method with an electrical control method. The controller continues to supply controlled current to the windings during deceleration, using electromagnetic forces to actively control the rotor position and prevent resonant frequency encounters, thereby eliminating the need for complex mechanical braking systems while ensuring reliability.
Solution Approach 2:
The patent changes the control parameters by continuing to supply controlled current to the windings during deceleration instead of short-circuiting them. The controller adjusts the current magnitude and frequency based on the rotor speed and position, maintaining electromagnetic torque control throughout the entire deceleration process, including below the rotational speed mark where back-EMF becomes insufficient for position determination.
3Reliability
If the rotational speed regulator is used below rotational speed mark, then position control is maintained, but the rotor position cannot be reliably determined due to back EMF
Solution Approach 1:
The patent implements feedback control by continuously monitoring the deceleration process and adjusting the current supplied to the windings based on the rotor position and speed. The controller uses this feedback information to maintain optimal braking current, preventing the compressor from reaching resonant frequencies while ensuring smooth and controlled deceleration to a stop.
Solution Approach 2:
The patent replaces the mechanical braking approach (short-circuiting windings) with an electrical control approach. The controller continues to supply controlled current to the windings during deceleration, using electromagnetic forces to actively control the rotor position and prevent resonant frequency encounters, thereby eliminating the need for complex mechanical braking systems while ensuring reliability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for controlled and safe braking of the compressor, reducing the complexity of the pump design and preventing potential shell strikes by maintaining rotor control through induced voltage and load torque considerations, thus ensuring reliable operation and energy efficiency.
Implementation Method 1
voltages induced in the windings are determined and the windings are energized with a braking current at a decreasing frequency, the braking current during braking being a function of the previously determined induced voltages
Data Source
AI summary
A method is provided for braking a compressor of a refrigeration appliance, of an air conditioning appliance or of a heat pump in which the compressor has a brushless motor with windings and a controller for braking the motor. The controller is configured to brake the brushless motor by using a braking current in a controlled manner starting from an operating rotational speed, in which the braking current during the controlled braking is dependent on induced voltages determined before the controlled braking. The method for braking includes rotating the motor at an operating rotational speed, receiving a signal for decelerating, braking or slowing down, determining voltages induced in the windings and supplying a braking current having a decreasing frequency to the windings, in which the braking current during the braking is dependent on the previously determined induced voltages. A compressor and a refrigeration appliance having the compressor are also provided.