Virtual Synchronous Converter Control for Grid Fault Overcurrent
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Voltage control-type virtual synchronous machines are unable to flexibly suppress overcurrents during grid faults, as their protection mechanisms have fixed limits and cannot adapt to varying overcurrent magnitudes, leading to potential power converter shutdowns.
Innovation Solution
A control device for power converters that includes a generator simulating unit, first and second command generating units, and an overcurrent suppression mechanism, which sets an overcurrent level based on output current and AC voltage, filters the fundamental frequency component, limits its amplitude, and calculates a voltage command value to manage overcurrents effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If fixed limit values are used in the overcurrent protection unit, then the protection mechanism is simple to implement, but the system cannot flexibly suppress overcurrents of varying magnitudes during grid faults
Solution Approach 1:
The patent applies dynamics by making the limit values dynamic rather than fixed. The first and second limit values are dynamically adjusted based on the magnitude of detected overcurrents, allowing the system to adapt to varying overcurrent conditions. This resolves the contradiction by enabling flexible suppression (improving adaptability) while maintaining a relatively simple control structure (managing complexity).
Solution Approach 2:
The patent changes the parameters of the protection mechanism by adjusting the limit values based on overcurrent magnitude. When overcurrent magnitude increases, the first limit value is set to a larger value to allow higher current passage, while the second limit value is set to a smaller value for stricter suppression. This parameter adaptation resolves the contradiction between flexibility and complexity.
2Reliability
If the first limit value is set large to allow overcurrent passage, then power converter shutdown is prevented, but current control capability is reduced
Solution Approach 1:
The patent segments the overcurrent protection into two distinct limit values with different functions: the first limit value controls the magnitude of fundamental frequency components to prevent shutdown, while the second limit value suppresses harmonic components to maintain control capability. This segmentation resolves the contradiction by assigning different control roles to different limit values.
Solution Approach 2:
The patent applies local quality by treating different frequency components differently. The first limit value applies to fundamental frequency components where higher limits prevent shutdown, while the second limit value applies to harmonic components where stricter limits maintain control. This localized approach resolves the contradiction between reliability and control capability.
3Reliability
If strict overcurrent suppression is applied to prevent converter shutdown, then equipment protection is improved, but power output is reduced during grid faults
Solution Approach 1:
The patent dynamically adjusts the first limit value based on overcurrent magnitude. When overcurrent is severe, a larger first limit value allows more current to pass, maintaining power output. When overcurrent is moderate, a smaller first limit value provides stricter suppression for equipment protection. This dynamic adjustment resolves the contradiction between protection and productivity.
Solution Approach 2:
The patent changes the first limit value parameter according to overcurrent conditions. By setting the first limit value to a larger value when needed, the system allows sufficient current for power output while still providing protection through the second limit value. This parameter change strategy resolves the contradiction between equipment protection and power output maintenance.
Data Source
AI summary
A control device includes a generator simulating unit to generate a phase of output voltage of a power converter by simulating characteristics of a synchronous generator, a first voltage command generating unit to generate a first voltage command value of output voltage of the power converter so that an AC voltage of a power grid attains a target voltage, a setting unit to set an overcurrent level, and a second command generating unit to generate a second voltage command value by limiting the first voltage command value based on the overcurrent level. The control device further includes a signal generating unit to generate a control signal for the power converter, based on the phase generated by the generator simulating unit and the second voltage command value.