Inverter Current Limit Control for Electric Compressor Overcurrent
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Solution Overview
Problem
In electric compressors, particularly under low-speed high-load conditions, the influence of discharge pulsation leads to an increased risk of overcurrent in AC motors, making stable control challenging.
Innovation Solution
An inverter apparatus with a current detection unit and a limit value control unit that monitors and adjusts the current limit value based on predefined thresholds and time frames to prevent overcurrent by decreasing the current limit value when excessive current is detected and returning it to the original value when conditions improve.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the output current of the motor is increased to expand the operating range of the electric compressor, then the operating range is increased, but the influence of discharge pulsation increases causing overcurrent to occur more frequently
Solution Approach 1:
The current limit value is made dynamic rather than fixed. The control unit adjusts the current limit value based on detected current levels and operating conditions, allowing the system to adapt to discharge pulsation while maintaining high output capability. This resolves the contradiction by enabling the system to operate at high currents when conditions permit while automatically limiting current when discharge pulsation causes overcurrent risk.
Solution Approach 2:
The invention changes the parameter of current limit value based on operating conditions. By monitoring detected current and comparing it against thresholds, the system modifies the current limit parameter in real-time. This allows the operating range to be maximized when conditions are favorable while preventing overcurrent when discharge pulsation occurs, thus resolving the technical contradiction between adaptability and reliability.
2Reliability
If the current limit value is decreased to prevent overcurrent, then overcurrent is prevented, but the output current and operating range are reduced
Solution Approach 1:
The current limit value dynamically adapts to operating conditions rather than being statically reduced. The control unit increases the current limit value when detected current is below thresholds (allowing high output) and decreases it only when discharge pulsation causes overcurrent risk. This dynamic adjustment prevents overcurrent while maintaining high productivity during normal operation.
Solution Approach 2:
The control system periodically evaluates the detected current against thresholds and adjusts the current limit value accordingly. This periodic monitoring and adjustment allows the system to maintain high output current during normal operation while temporarily reducing the limit only when discharge pulsation occurs, thus preventing overcurrent without permanently reducing productivity.
3Reliability
If the current limit value is frequently adjusted to respond to discharge pulsation, then overcurrent is prevented, but the control complexity increases
Solution Approach 1:
The invention uses simple parameter changes based on threshold comparisons rather than complex control algorithms. The control unit compares detected current against predetermined thresholds and adjusts the current limit value accordingly. This simple threshold-based parameter adjustment effectively prevents overcurrent while adding minimal control complexity, resolving the technical contradiction.
Data Source
AI summary
Provided is an inverter apparatus capable of preventing occurrence of overcurrent in an AC motor and stably controlling driving of the AC motor. The inverter apparatus controlling the AC motor included in an electric compressor includes a shunt resistor for detecting current flowing in the AC motor, and a limit value control unit controlling a current limit value for a detected current detected at the shunt resistor. The limit value control unit determines whether the number of times the detected current becomes equal to or more than the first threshold within a first predetermined time is equal to or more than a first number of times. The limit value control unit decreases the current limit value when the number of times the detected current becomes equal to or more than the first threshold within the first predetermined time is equal to or more than the first number of times.