Grid Power Converter Current Control During Voltage Drops
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Solution Overview
Problem
Conventional grid connection power conversion devices struggle to maintain stable operation during instantaneous voltage drops in commercial three-phase power systems, particularly when the system voltage is unbalanced, leading to potential overcurrents and instability in the upstream power system.
Innovation Solution
A grid connection power conversion device equipped with an instantaneous voltage detection circuitry and output current control circuitry that reduces the output current to a minimum value based on the maximum three-phase instantaneous voltage and line voltages, ensuring stable operation by limiting the output current and preventing overcurrents, even during unbalanced voltage conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the output current is continuously output up to its upper limit value to achieve continuous operation performance during power system faults, then the continuous operation performance is improved, but the upstream power system may become unstable through system impedance when many distributed power supplies are connected
Solution Approach 1:
The patent applies dynamics by making the output current limit dynamic rather than fixed. The output current control circuitry adjusts the upper limit value of output current based on detected system conditions (voltage levels, fault status). During normal operation, the inverter can output at full capacity, but during instantaneous voltage drops or unbalanced conditions, the limit is automatically reduced to prevent upstream system instability, thus resolving the contradiction between continuous operation and system stability.
2Measurement precision
If the phase angle detection is used to generate AC power matching the commercial power system, then the power matching is improved, but the phase angle cannot be accurately detected when low voltage fault such as instantaneous voltage drop occurs
Solution Approach 1:
The patent introduces an intermediary mechanism - the output current control circuitry acts as a mediator between the phase angle detection system and the inverter output. When voltage drops occur and phase angle detection becomes unreliable, the control circuitry uses alternative methods (such as storing previous valid phase angle information or using voltage waveform zero-crossing detection) to maintain adequate phase synchronization, thereby maintaining both detection accuracy and operational reliability.
3Stability of the object's composition
If the output current is limited to maintain stability during instantaneous voltage drop, then the system stability is improved, but the output power is reduced
Solution Approach 1:
The patent applies periodic action by implementing time-based control strategies. During instantaneous voltage drops, the output current limit is temporarily reduced only for the duration of the fault condition. The control circuitry monitors the system voltage and automatically restores the full output current capacity once normal voltage levels are recovered, thus maintaining system stability during critical periods while preserving full power output capability during normal operation.
Data Source
AI summary
A grid connection power conversion device for connecting a distributed power supply to a three-phase commercial power system is provided. The power conversion device comprises an inverter, an instantaneous voltage detection circuitry to detect a maximum three-phase instantaneous voltage value of the commercial power system, a line voltage detection circuitry to detect a maximum value of each of three line voltages, an instantaneous voltage drop detection circuitry to detect an instantaneous voltage drop, and an output current control circuitry to control an output current value from the inverter. When the instantaneous voltage drop detection circuitry detects an instantaneous voltage drop, the output current control circuitry reduces the output current value from the inverter to an output current value corresponding to a minimum value among the four maximum voltage values which are the maximum three-phase instantaneous voltage value and the maximum values of the three line voltages.