Power Converter VSM Control for Overcurrent and Step-Out Suppression
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Solution Overview
Problem
Voltage control-type virtual synchronous machines cannot effectively control current, leading to potential overcurrents and instability during system disturbances, which can cause the power converter to stop simulating a synchronous power generator.
Innovation Solution
A control device that includes a power generator simulation unit to generate a voltage command value based on AC voltage and current, with integrators to stabilize angular frequency and phase, and a signal generation unit to control the power converter, limiting integrator outputs to prevent overcurrents and maintain synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage control-type virtual synchronous machine control is used to operate as a voltage source, then the power converter can simulate synchronous machine behavior, but overcurrent cannot be controlled and may occur during system disturbance
Solution Approach 1:
The patent changes the control parameter from pure voltage control to a composite control that includes both voltage control and current limiting. The current limiting command value is generated by comparing the detected current with a reference current value, and when overcurrent is detected, the voltage command value is adjusted to limit the current while maintaining voltage control capability.
Solution Approach 2:
The patent introduces a current limiting command value as an intermediary control signal that mediates between the voltage control requirement and the overcurrent prevention requirement. This intermediate control layer allows the system to balance both objectives by adjusting the voltage command based on current conditions.
2Object-affected harmful factors
If compensation means is used to suppress overcurrent by setting compensation output voltage command value on the control circle, then overcurrent is suppressed, but the synchronous power generator enters a state where it cannot synchronize with the power system
Solution Approach 1:
The patent implements dynamic control by continuously monitoring the current condition and adjusting the voltage command value in real-time. When overcurrent is detected, the control mode dynamically switches to current limiting; when normal operation is restored, it returns to voltage control. This dynamic adjustment maintains synchronization while suppressing overcurrent.
Solution Approach 2:
The patent uses feedback control by continuously detecting the AC current and comparing it with the reference current value. The detected current condition feeds back to the control unit, which adjusts the voltage command value accordingly. This closed-loop feedback ensures that current limiting is applied only when necessary, maintaining system synchronization.
3Object-affected harmful factors
If the output voltage command value is moved outside the control circle to suppress overcurrent, then overcurrent is suppressed, but step-out occurs in performing control that simulates the synchronous power generator
Solution Approach 1:
The patent applies partial action by implementing current limiting only when overcurrent is detected, rather than continuously constraining the voltage command to the control circle. This partial application of current limiting suppresses overcurrent while allowing the system to maintain normal voltage control and synchronization during normal operation, avoiding step-out.
Data Source
AI summary
A control device includes a power generator simulation unit to generate a voltage command value, and a signal generation unit to generate a control signal for the power converter. The power generator simulation unit includes a first integrator to time-integrate a first difference between effective power and a target value of the effective power and output a first angular frequency, a second integrator to time-integrate the first angular frequency and output a phase of an AC voltage, and a voltage command generation unit to generate the voltage command value based on the AC voltage, a target value of the AC voltage, and the phase. When a voltage difference between the AC voltage and the target value of the AC voltage is greater than a threshold, the first integrator outputs a difference between an angular frequency of the AC voltage and a reference angle frequency as the first angular frequency.