Power Converter Voltage Command Control for Isolated AC Stability
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Solution Overview
Problem
Power converters interconnected with AC power systems not connected to a generator face instability during load variations, requiring a control device that ensures stable operation.
Innovation Solution
A control device for self-excited power converters, comprising a phase generation unit, voltage control unit, and command unit, which computes compensation voltage and droop values to stabilize the power converter's operation by adjusting voltage commands based on point-of-interconnection voltage and current deviations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a self-excited power converter is interconnected with an AC power system not connected to a generator, then the power converter can operate without a power supply for the AC power system, but the power converter becomes unstable during load variations
Solution Approach 1:
The control device dynamically adjusts control parameters based on the operational mode (isolated system vs. interconnected system). The determination unit identifies whether the AC power system is isolated or interconnected, and the control unit switches control strategies accordingly - using voltage control for isolated systems and frequency control for interconnected systems, thereby maintaining stability across different operational conditions
Solution Approach 2:
The control device changes control parameters based on system conditions. When operating in an isolated system, the control unit adjusts voltage magnitude and frequency based on load variations. The determination unit monitors system parameters to detect mode changes, and the control unit modifies control parameters in real-time to maintain stable operation during transitions between operational modes
2Productivity
If the power converter operates in an isolated system mode, then it can supply power to AC power system without generator, but voltage and frequency control becomes difficult under load variations
Solution Approach 1:
The control device implements feedback control by continuously monitoring the AC power system's voltage and frequency. The determination unit detects system mode and load conditions, and the control unit adjusts the power converter's output based on this feedback to maintain stable voltage and frequency. This closed-loop control simplifies operation by automatically adapting to load variations without requiring manual intervention
Solution Approach 2:
The control device performs preliminary actions by pre-determining control strategies based on the detected operational mode. When the determination unit identifies an isolated system mode, the control unit proactively switches to appropriate voltage and frequency control algorithms before load variations occur, preparing the system to handle upcoming changes and simplifying the control process
Data Source
AI summary
A control device includes: a phase generation unit to generate a phase of a voltage command for the power converter; a voltage control unit to generate a voltage value of the voltage command; and a command unit to output the voltage command having the phase and the voltage value to the power converter. The voltage control unit includes: a voltage compensator unit to compute a compensation voltage value, based on a voltage deviation of a point-of-interconnection voltage from a reference voltage; a droop calculator unit to compute a first droop value in accordance with a magnitude of a point-of-interconnection current, when the AC power system is an isolated system, the isolated system being the AC power system not connected to a generator; and a calculation unit to calculate the voltage value of the voltage command, based on a difference between the compensation voltage value and the first droop value.