Outdoor Fan Brake Sequence for PMSM Inverter Heat Protection
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Solution Overview
Problem
Existing air conditioner technologies face challenges in safely and securely braking a permanent magnet synchronous motor when the outdoor fan is rotated by an external force, leading to inefficiencies and potential damage due to irreversible flux losses and heat generation, especially when trying to stop or shift modes during high or low rotation speeds.
Innovation Solution
An air conditioner system with an inverter control unit and current detection unit that operates a brake sequence to decrease the outdoor fan's rotation, followed by a drive sequence for power running, utilizing line-to-line short circuits and PWM control to manage voltage and current effectively, preventing transient currents and heat-related issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If line-to-line short circuit is caused between permanent magnet synchronous motors to protect the inverter from regenerative voltage, then the inverter is protected, but when motors are rotating at high speed, inductance component increases and power factor degrades, so a lot of braking power cannot be obtained and the short circuit state is maintained for a long time causing heat generation and potential breakage
Solution Approach 1:
The control unit performs preliminary detection of the rotation direction of the outdoor fan before executing the short-circuit braking operation. By detecting the rotation direction in advance and determining the appropriate short-circuit phase, the system prepares the optimal braking configuration beforehand, ensuring effective braking power is applied immediately when short-circuit braking is initiated, rather than attempting gradual braking that would prolong the operation and generate excessive heat.
Solution Approach 2:
The control unit changes the phase of the short-circuit braking operation based on the detected rotation direction of the outdoor fan. By adjusting the short-circuit phase parameter to match the rotation direction, the system optimizes the braking effectiveness, enabling the short-circuit operation to generate sufficient braking power even at high rotation speeds, thereby reducing the duration of the braking operation and minimizing heat generation.
2Force
If transistors are ignited with a certain ratio to obtain braking force, then braking is achieved, but the direct-current voltage of the inverter is raised by repetitions of ignition and arc-extinguishing, which may cause circuit breakage
Solution Approach 1:
The invention extracts and eliminates the problematic repetitive ignition and arc-extinguishing process from the braking operation. Instead of using ratio-based transistor ignition that causes voltage fluctuations, the system applies continuous short-circuit braking with optimized phase control, removing the source of voltage rise and circuit stress while maintaining effective braking force.
Solution Approach 2:
The invention converts the potentially harmful short-circuit current into a beneficial braking force through phase-optimized control. By aligning the short-circuit phase with the rotation direction of the outdoor fan, the system transforms what could be a destructive repetitive ignition process into a smooth, continuous braking operation that generates consistent braking force without causing voltage fluctuations or circuit stress.
3Force
If the ignition ratio is set to 100% to maximize braking force, then braking effectiveness is improved, but transient current due to ignition is generated, and in permanent magnet synchronous motors, irreversible flux losses occur reducing motor efficiency
Solution Approach 1:
The control unit performs preliminary detection of the outdoor fan's rotation direction before executing the short-circuit braking operation. This advance detection allows the system to determine the optimal short-circuit phase in advance, ensuring that the braking operation is applied in the most efficient manner from the start, maximizing braking force while minimizing energy loss and avoiding the need for high ignition ratios that would cause irreversible flux losses.
Solution Approach 2:
The control unit changes the short-circuit phase parameter based on the detected rotation direction, optimizing the braking operation to achieve maximum effectiveness with minimum energy loss. This parameter adjustment ensures that the short-circuit braking aligns with the motor's magnetic field configuration, reducing irreversible flux losses while maintaining strong braking force.
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
Enables secure and swift mode shifting to power running, preventing irreversible flux losses and heat-related damage, while maintaining efficient operation of the permanent magnet synchronous motor.
Implementation Method 1
a braking force is obtained by causing line-to-line short circuit between motors
Implementation Method 2
an inverter of which power is supplied from a direct-current power supply and which applies a voltage to the permanent magnet synchronous motor
Data Source
AI summary
An air conditioner includes: an outdoor fan provided in an outdoor unit; a permanent magnet synchronous motor that drives the outdoor fan; an inverter that uses a DC power source as a power source and applies a voltage to the permanent magnet synchronous motor; an inverter control means that controls the output voltage of the inverter; and a shunt resist connected between the DC power source and the inverter. If the outdoor fan is rotating due to an external force while the inverter is stopped, the inverter control means causes the inverter to operate using a brake sequence that brakes the rotation of the outdoor fan, and then causes the inverter to operate using a drive sequence that power-drives the outdoor fan.