Inverter Motor Control for Low-Temperature Surge Protection
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Solution Overview
Problem
Conventional PWM control inverter devices for electric motors face issues with surge voltage generation due to equivalent series resistance (ESR) of capacitors, especially at low temperatures, which can damage semiconductor elements and limit motor current, reducing the operating range of electric motors, particularly in cold environments.
Innovation Solution
A method and apparatus that adjust motor current by estimating the rotational position of the rotor and controlling the inverter circuit to supply a direct current smaller than the maximum acceptable motor current value when the capacitor temperature is low, and switching to alternating current once the temperature allows for sufficient torque production, using a temperature detecting section, memory section, rotor position estimating section, and inverter device control section to manage the motor current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the maximum acceptable motor current value is limited with a large safety margin to account for ESR variation, then component damage from surge voltage is prevented, but the operating range of the electric motor is reduced
Solution Approach 1:
The control device performs preliminary warming-up of the capacitor by controlling the inverter circuit to operate in a state that generates heat in the capacitor before normal motor operation. This preliminary action reduces the ESR of the capacitor in advance, allowing the motor current to be increased to values that would otherwise be restricted by safety margins, thereby expanding the operating range while maintaining component protection.
Solution Approach 2:
The invention changes the temperature parameter of the capacitor through controlled heating operation. By operating the inverter circuit to warm up the capacitor, the ESR parameter of the capacitor is reduced from its high low-temperature value to a lower high-temperature value, enabling higher motor currents to be supplied safely and thus expanding the motor's operating range.
2Reliability
If the motor current is limited at low temperatures to prevent surge voltage damage, then semiconductor elements are protected, but sufficient torque for starting the electric motor cannot be produced
Solution Approach 1:
The control device executes a warming-up operation before motor start-up when the capacitor temperature is low. During this preliminary phase, the inverter circuit is controlled to generate heat in the capacitor, reducing its ESR. Once the ESR is reduced sufficiently, the motor current can be increased to produce the required starting torque without risking semiconductor element damage from surge voltage.
Solution Approach 2:
The invention implements a two-stage periodic control strategy: first a warming-up period where the inverter operates to heat the capacitor and reduce ESR, then a normal operation period where full motor current can be supplied. This periodic alternation between different operational states allows the system to overcome the low-temperature limitation and achieve sufficient starting torque while maintaining component protection.
3Reliability
If the ESR of the capacitor is high at low temperatures, then surge voltage is generated that can damage components, but the capacitor cannot be operated without current limitation
Solution Approach 1:
The invention changes the temperature parameter of the capacitor through controlled heating operation. By operating the inverter circuit to warm up the capacitor, the ESR parameter of the capacitor is reduced from its high low-temperature value to a lower high-temperature value, enabling higher motor currents to be supplied safely and thus expanding the motor's operating range.
Solution Approach 2:
The warming-up operation continuously supplies current to the capacitor through the inverter circuit to generate heat and reduce ESR. This continuous useful action of heating the capacitor maintains the ESR at an acceptable level, allowing the system to operate with high motor current supply capability while continuously protecting components from surge voltage damage.
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 prevents component damage from surge voltage while ensuring sufficient torque is produced for electric motor operation, even at low temperatures, by dynamically adjusting the motor current based on capacitor temperature and rotor position, thereby extending the operating range of electric motors in cold conditions.
Implementation Method 1
The inverter device includes an inverter circuit and a capacitor connected to an input of the inverter circuit
Implementation Method 2
The capacitor has a resistance element caused by the resistance of an electrode or depending on characteristics of a dielectric body. Such a resistance element is called 'equivalent series resistance (ESR)'
Implementation Method 3
Conventionally, a PWM control inverter device for controlling an electric motor is known
Implementation Method 4
The inverter device uses a power transistor or an IGBT (insulated gate bipolar transistor) as a control element
Data Source
Figure 1
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AI summary
A method for controlling a motor current supplied to an electric motor by using an inverter device is provided. The inverter device includes an inverter circuit and a capacitor connected to an input of the inverter circuit. The method includes controlling the inverter circuit in such a manner as to supply an alternating electric current to the electric motor after the temperature of the capacitor reaches a temperature at which a maximum acceptable motor current value becomes greater than or equal to a value at which the torque necessary for starting the electric motor is produced.