Inverter Control Device Mitigating Overcurrents During Voltage Drops
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Solution Overview
Problem
Existing inverter control systems fail to effectively suppress overcurrents caused by abrupt changes in system voltage, leading to unnecessary tripping of circuit breakers due to increased ripple current from AC capacitors during voltage fluctuations.
Innovation Solution
An inverter control apparatus that includes system voltage detection, differentiation, and correction current instruction value calculation to adjust the current instruction value for the inverter, using a correction current instruction value calculated based on the differential value of the system voltage, thereby controlling the inverter to mitigate overcurrents during voltage changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the system voltage drops, then the amplitude of ripple current increases, but the fundamental wave component of output current does not reach protective operation level
Solution Approach 1:
The patent changes the parameter of current instruction value based on the detected system voltage level. When voltage drops are detected, the control device adjusts the current instruction value to account for the increased ripple current amplitude, allowing the fundamental wave component to be properly distinguished from ripple components and preventing false protective operations.
2Reliability
If the inverter is controlled after detecting system voltage drop, then overcurrent suppression is attempted, but abrupt voltage variations cause AC capacitor to repeat charge and discharge
Solution Approach 1:
The control device performs preliminary detection of system voltage variations and calculates correction current instruction values before the AC capacitor completes excessive charge-discharge cycles. By proactively adjusting the current instruction value based on detected voltage changes, the system prevents abrupt voltage variations from causing severe capacitor stress and overcurrent conditions.
Solution Approach 2:
The patent implements a feedback mechanism where the control device continuously detects system voltage, calculates the differential value to identify abrupt changes, and adjusts the current instruction value accordingly. This closed-loop feedback controls the AC capacitor's charge-discharge behavior, preventing excessive current fluctuations while maintaining stable operation during voltage variations.
3Reliability
If the circuit breaker trips due to overcurrent from AC capacitor, then protective operation occurs, but the fundamental wave current did not require protection
Solution Approach 1:
The control device dynamically adjusts the current instruction value parameter based on system voltage conditions. By calculating correction values from the differential of system voltage and applying them to the current instruction, the device ensures that only genuine overcurrent conditions trigger protective operations, while ripple-induced current increases during voltage drops do not cause unnecessary tripping.
Data Source
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AI summary
There is provided an inverter control apparatus (2) which controls an inverter (1) interconnected to an alternating-current power system (9). A capacitor (6) is on an alternating-current side of the inverter (1). The apparatus detects the system voltage (Vr) of the alternating-current power system (9), calculates the differential value of the detected system voltage (Vr), calculates a correction current instruction value (Ic) for correcting a current instruction value (Ir0) set for the output current (Iiv) of the inverter (1), based on the calculated differential value of the system voltage (Vr), corrects the current instruction value (Ir0) based on the calculated correction current instruction value (Ic), and controls the inverter (1), based on the corrected current instruction value (Ir1).