Grid Control With Frequency-Dependent Droop Gain Stability
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Solution Overview
Problem
Existing grid stabilization control methods using proportional control with a single gain can lead to deteriorated control stability due to time lag elements and other influences.
Innovation Solution
A grid system with a distribution grid, a voltage source device, a detector, a power conversion device, and a grid control unit that calculates a power command value to provide a drooping characteristic, while performing control computation with a predetermined frequency characteristic. This frequency characteristic includes a first control gain value for direct current and a second control gain value for higher frequencies, which is lower than the first control gain value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If proportional control with a single gain is used to provide drooping characteristic, then the drooping characteristic is maintained, but control stability deteriorates due to time lag elements
Solution Approach 1:
The control gain is segmented into frequency-dependent components: a first control gain for low frequency range (including DC) and a second control gain for high frequency range. This segmentation allows different gain values to be applied to different frequency components, resolving the contradiction between maintaining drooping characteristic and ensuring control stability.
Solution Approach 2:
The control gain is made dynamic by introducing frequency dependence. The control computation unit dynamically selects or transitions between the first control gain and the second control gain based on the frequency characteristics of the input signal, allowing the system to adaptively maintain stability while preserving drooping characteristic.
2Adaptability or versatility
If the control gain is set high to ensure the slope of drooping characteristic, then the drooping characteristic is maintained, but control stability is impaired
Solution Approach 1:
Different control gains are applied to different frequency ranges: the first control gain (higher value) is applied to low frequency range to maintain drooping characteristic, while the second control gain (lower value) is applied to high frequency range to ensure control stability. This local differentiation resolves the contradiction between maintaining drooping slope and ensuring stability.
Solution Approach 2:
The control gain parameter is changed based on frequency characteristics. The control computation unit modifies the gain parameter dynamically, using a higher gain value for low frequencies and a lower gain value for high frequencies, thereby resolving the contradiction between maintaining drooping characteristic and ensuring control stability.
Data Source
AI summary
A power conversion device inputs or outputs a power for changing a state quantity of a distribution grid to which a voltage source device is connected, to or from the distribution grid. A grid control unit calculates a power command value of the power conversion device such that a drooping characteristic is provided for compensating for a deviation from a control target of the state quantity obtained from an output of a detector. A frequency characteristic of control computation for calculating a power command value from the deviation in the system control unit is defined such that a first control gain value in a first frequency range including direct current is set corresponding to a slope of the drooping characteristic, and a second control gain value in a second frequency range including higher frequencies than the first frequency range is set to be lower than the first control gain value.