Secondary Frequency Stochastic Optimal Control in Independent Microgrids with Virtual Synchronous Generator-Controlled Energy Storage Systems
Abstract
:1. Introduction
- (1)
- To solve the independent MG system uncertainty problem—resulting from the power fluctuation of renewables, load disturbance, and measurement noise—an uncertain state-space model for secondary frequency regulation with VSG-controlled ESSs and traditional synchronous generators is established. In the model, a participation factor dynamic configuration method for secondary frequency regulation based on the battery’s state of charge (SOC) is proposed to optimally control the ESSs, which will prevent the overcharge or overdischarge problems and prolong the ESSs’ service life.
- (2)
- According to the proposed uncertain state-space model for secondary frequency regulation in independent MGs, based on stochastic optimal control theory, an improved linear quadratic Gaussian (LQG) controller is designed to solve the established uncertain state-space model. In the controller design process, the weighting matrices determining the dynamic control performance are optimized by combining the loop transfer recovery (LTR) technology and distributed estimation algorithm. Compared with the PID and μ-synthesis control approaches, our proposed controller has a faster response speed and smaller overshoot, while the robustness is similar to the benchmark controllers.
2. Frequency Regulation Modelling in Independent Microgrids
2.1. State-Space Model for Secondary Frequency Regulation of Independent Microgrid
2.1.1. Traditional Synchronous Generator
2.1.2. Virtual Synchronous Generator-Controlled Energy Storage System
2.1.3. Power Conservation Equation
2.1.4. Secondary Frequency Regulation Participation Factor Dynamic Configuration Method
2.2. Establishment of Uncertain State-Space Model of Secondary Frequency Regulation in Independent Microgrid
3. Secondary Frequency Regulation Controller Design
4. Experiment and Performance Evaluation
4.1. Dynamic Performance Analysis with Different Control Algorithms
4.2. Performance Evaluation of Control Algorithms under Different Renewable and Load Power Fluctuations
4.3. Analysis of Energy Storage Units’ Operating Status with Variable Participation Factors Strategy
5. Conclusions
Author Contributions
Funding
Conflicts of Interest
References
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Parameters of Traditional Synchronous Generators | Diesel Generator | Micro-Gas Generator |
Time constant of speed governor TG (s) | 0.1 | 0.1 |
Time constant of generator TT (s) | 3 | 8 |
Droop coefficient R (Hz/pukW) | 2.5 | 2.5 |
Rotary inertia M (pukW·s/Hz) | 0.12 | 0.15 |
Damping coefficient D (pukW/Hz) | 0.1 | 0.05 |
Adjustable power capacity E (kW·h) | 110 | 85 |
Parameters of Renewable Generation Systems | Wind Power Generator | PV System |
Baseline active output power | 50 | 30 |
Variance of active output power fluctuation | 15 | 10 |
Parameters of VSG-Controlled ESSs | ESS1 | ESS2 |
Droop coefficient R (Hz/pukW) | 2.5 | 2.05 |
Virtual rotary inertia (pukW·s/Hz) | 0.2 | 0.17 |
Virtual damping coefficient (pukW/Hz) | 0.19 | 0.22 |
Initial SOC value (%) | 80 | 60 |
Constant η (%) | 95 | 95 |
Rated active power PN (kW) | 50 | 30 |
Adjustable capacity E (kW·h) | 36 | 20 |
Variance | Scenario 1 | Scenario 2 | Scenario 3 | Scenario 4 |
---|---|---|---|---|
Wind power generator | +20% | −40% | - | - |
PV generator | +45% | −30% | - | - |
Power load | - | - | +50% | −40% |
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Yang, T.; Zhang, Y.; Wang, Z.; Pen, H. Secondary Frequency Stochastic Optimal Control in Independent Microgrids with Virtual Synchronous Generator-Controlled Energy Storage Systems. Energies 2018, 11, 2388. https://doi.org/10.3390/en11092388
Yang T, Zhang Y, Wang Z, Pen H. Secondary Frequency Stochastic Optimal Control in Independent Microgrids with Virtual Synchronous Generator-Controlled Energy Storage Systems. Energies. 2018; 11(9):2388. https://doi.org/10.3390/en11092388
Chicago/Turabian StyleYang, Ting, Yajian Zhang, Zhaoxia Wang, and Haibo Pen. 2018. "Secondary Frequency Stochastic Optimal Control in Independent Microgrids with Virtual Synchronous Generator-Controlled Energy Storage Systems" Energies 11, no. 9: 2388. https://doi.org/10.3390/en11092388