Dynamic Current-Limitation Strategy of Grid-Forming Inverters Based on SR Latches
Abstract
:1. Introduction
- The proposed dynamic current-limitation strategy based on SR latch logic not only suppresses transient overcurrents during grid-voltage drops but also effectively addresses the issue of irregular toggling of virtual impedance. Furthermore, it enables rapid power recovery after fault clearance.
- The virtual-impedance method with power reference regulation based on grid codes is proposed for enhancing transient synchronization stability, and transient synchronization instability is effectively avoided under grid fault. The inverter reaches a new operating point quickly after the grid fault, and the dynamic performance is improved effectively.
- The proposed method is similar to the hardware SR latch, which has high speed and is not affected by time-triggered interruptions. Therefore, both the real-time triggering of SR hardware and the flexibility of digital controllers are taken into account, and the inverter control and fast overcurrent protection can be realized by digital control.
2. Mathematical Model of Grid-Forming Inverters
2.1. System Description
2.2. Power Control
3. GFM Inverter Operation Characteristics under Grid Faults
4. Dynamic Current-Limitation Strategy with Virtual Impedance and Power Limitation
5. Simulation and Experiment Verification
5.1. Simulation Verification
5.2. Experiment Verification
6. Conclusions
- SR latch-based virtual impedance control scheme can retain current-limitation ability during grid fault. In addition, compared with other current-limitation schemes, the proposed current-limitation method can not only avoid the saturation of the voltage loop, but also avoid the repeated switching of virtual impedance.
- Virtual impedance control with a power modification can effectively achieve fault current limitation without synchronization instability problems during grid fault.
- The event-triggered control logic is applied in a digital controller, which can suppress the inrush current induced by time delay.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Current-Limitation Method | Advantage | Defect |
---|---|---|
High-power device | Strong overcurrent ability | High cost |
Current loop limitation [15,16,17,18] | Simple design and control | Voltage loop saturation, may fail to restore [18] |
Output power limitation | Avoid voltage loop saturation | Ignore dynamic response |
Virtual impedance [20,21,22,23,24,25] | Avoid voltage loop saturation, good to restore | Difficulty in switching |
Voltage loop limitation [26,27] | Good to restore | Anti-saturation algorithm complexity, low applicability [28,29,30] |
S | R | State |
---|---|---|
1 | 0 | 1 |
0 | 1 | 0 |
0 | 0 | hold |
Parameter | Value | Parameter | Value |
---|---|---|---|
DC bus voltage Udc | 800 V | Grid-side equivalent inductance Lg | 5 mH |
Switching frequency fs | 10 kHz | Grid-side equivalent resistance Rg | 0.9 Ω |
Inductance Lf | 10 mH | Reactive droop coefficient Dq | 3 × 10−4 |
Capacitance Cf | 50 μF | Active droop coefficient Dp | 3.33 × 10−4 |
Current controller P gain kip | 50 | Active power reference Pref | 20 kW |
Virtual resistor Rv | 1 Ω | Voltage controller P gain kup | 0.5 |
Virtual inductance Lv | 5 mH | Voltage controller I gain kui | 100 |
Voltage magnitude reference value E | 311 V | Frequency reference ωref | 50 Hz |
Parameter | Value | Parameter | Value |
---|---|---|---|
DC bus voltage Udc | 800 V | Grid-side equivalent inductance Lg | 10 mH |
Switching frequency fs | 10 kHz | Current controller I gain kii | 333 |
Inductance Lf | 3 mH | Reactive droop coefficient Dq | 2 × 10−4 |
Capacitance Cf | 100 μF | Active droop coefficient Dp | 3 × 10−4 |
Current controller P gain kip | 30 | Active power reference Pref | 20 kW |
Virtual resistor Rv | 2 Ω | Voltage controller P gain kup | 0.15 |
Virtual inductance Lv | 5 mH | Voltage controller I gain kui | 75 |
Voltage magnitude reference value E | 311 V | Frequency reference ωref | 50 Hz |
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Zhang, H.; Ma, J.; Li, X. Dynamic Current-Limitation Strategy of Grid-Forming Inverters Based on SR Latches. Electronics 2024, 13, 3432. https://doi.org/10.3390/electronics13173432
Zhang H, Ma J, Li X. Dynamic Current-Limitation Strategy of Grid-Forming Inverters Based on SR Latches. Electronics. 2024; 13(17):3432. https://doi.org/10.3390/electronics13173432
Chicago/Turabian StyleZhang, Huajie, Junpeng Ma, and Xiaopeng Li. 2024. "Dynamic Current-Limitation Strategy of Grid-Forming Inverters Based on SR Latches" Electronics 13, no. 17: 3432. https://doi.org/10.3390/electronics13173432