Coordinated Scheme of Under-Frequency Load Shedding with Intelligent Appliances in a Cyber Physical Power System
2. Structure of a Cyber Physical Power System
3. Emergency Frequency Control with Consideration of Intelligent Terminal Equipment
3.1. Dynamic Frequency Response of the Power System
3.2. Estimation of Disturbance Scale
3.2.1. Determine the Power Shortage after Disturbance
3.2.2. Estimation of the Disturbance Type
- Type 1:
- The disturbance is regarded as a large disturbance when ∆P ≥ ∆PL. In this situation, the frequency is very likely to fall under the first round action threshold; thus, all intelligent home appliance loads should respond in conjunction with the traditional UFLS measures to prevent a severe frequency drop. The emergency control is aimed at restoring the frequency to the rated value as soon as possible.
- Type 2:
- The disturbance is regarded as a large disturbance when ∆P < ∆PL. In this situation, the frequency is unlikely to fall under the first round action threshold. The control center determines the response proportion of the intelligent home appliances according to the operational condition. The restoration and regulation are aimed at minimizing the control cost.
3.3. Traditional UFLS Scheme and Its Shortage
4. Coordinating Scheme of Intelligent Appliances with UFLS
4.1. Classifications of Intelligent Home Appliances
4.2. Control of Intelligent Home Appliances
4.3. Coordinating Scheme of Intelligent Appliances with UFLS
- The operational condition information of intelligent appliances is transmitted to the control center or slave station for statistics of the load capacity ready for response. The frequency and other status information are collected simultaneously.
- When a disturbance occurs, the response index K of each intelligent appliance is renewed by the control center based on the response capacity of the load and the estimated power shortage and is sent to smart meters.
- The real-time frequency f and its rate of change df/dt are measured by smart meters. When f < fSM1, the non-critical loads are cut off until the frequency has recovered and stabilized; furthermore, if |df/dt| > K, then the critical loads also respond and will be connected to the grid after a certain time interval t; if |df/dt| < K, then the critical loads do not change status until the frequency keeps dropping and reaches f < fSM2. Note that to prevent the shock caused by suddenly switching on a load, which may lead to a second drop of frequency, the reconnection of all disconnected loads is under centralized control.
- The control center collects information on the responding intelligent appliance and the real-time frequency, based on which the coordinating scheme adjusts the threshold value of each UFLS stage.
- When f < fLS, the UFLS devices are triggered on.
4.4. Discussion of the Time Delay in the New Scheme
5. Case Study
- In the proposed method, the power shortage is calculated quickly using the frequency variation ratio. Combined with the different home appliance action strategies obtained by the real-time operation status, the load shedding scale can be significantly limited.
- The early response of the intelligent home appliances can be used to replace part of the passive load shedding resources in the traditional scheme, thereby eliminating the effects of the fault in the power system and decreasing the cost of control.
- Through the positive interaction of power flow and information flow, the coordination of demand-side resources with traditional power system controllable assets can enrich the means of control strategies and increase the flexibility and reliability of the power system.
Conflicts of Interest
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|Action Frequency (Hz)||49.0||48.8||48.6|
|Time Delay (s)||0.2||0.2||0.2|
|Load Shedding Rate (%)||8.0||6.5||6.0|
|Load Shedding Buses||N1005, N1007, |
|N1006, N1010, N1012||N1001, N1002, N1003, N1004, N1011|
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Wang, Q.; Tang, Y.; Li, F.; Li, M.; Li, Y.; Ni, M. Coordinated Scheme of Under-Frequency Load Shedding with Intelligent Appliances in a Cyber Physical Power System. Energies 2016, 9, 630. https://doi.org/10.3390/en9080630
Wang Q, Tang Y, Li F, Li M, Li Y, Ni M. Coordinated Scheme of Under-Frequency Load Shedding with Intelligent Appliances in a Cyber Physical Power System. Energies. 2016; 9(8):630. https://doi.org/10.3390/en9080630Chicago/Turabian Style
Wang, Qi, Yi Tang, Feng Li, Mengya Li, Yang Li, and Ming Ni. 2016. "Coordinated Scheme of Under-Frequency Load Shedding with Intelligent Appliances in a Cyber Physical Power System" Energies 9, no. 8: 630. https://doi.org/10.3390/en9080630