This paper proposes distributionally robust energy-reserve-storage co-dispatch model and method to facilitate the integration of variable and uncertain renewable energy. The uncertainties of renewable generation forecasting errors are characterized through an ambiguity set which is a set of probability distributions consistent with observed historical data. The proposed model minimizes the expected operation costs corresponding to the worst-case distribution in the ambiguity set. Distributionally robust chance constraints are employed to guarantee reserve and transmission adequacy. The more historical data is available, the smaller the ambiguity set is and the less conservative the solution is. The formulation is finally cast into a mixed integer linear programming whose scale remains unchanged as the amount of historical data increases. Inactive constraint identification and convex relaxation techniques are introduced to reduce the computational burden. Numerical results and Monte Carlo simulations on IEEE 118-bus systems demonstrate the effectiveness and efficiency of the propose method.

Conventional pilot protections used for EHV/UHV AC transmission lines require data synchronization between the two terminals of transmission line and their performance is affected by the line capacitive charging current and load conditions. To tackle these problems, this paper proposes a new pilot protection scheme based on two-port network model of AC transmission lines. The new protection scheme calculates the two-port network parameters from the online measurements via sequence components method, then compares the solved parameters with their setting values to distinguish the internal and external faults. It does not require the data synchronization between two terminals of transmission line. Moreover, its performance is not affected by the line capacitive charging current and load conditions. The applicability of the proposed scheme for series compensated lines are also analyzed. Effectiveness and accuracy of the proposed protection scheme have been verified by simulation tests.

As the most suitable main protection for multi-terminal transmission lines represented by T-connections, current differential protection exhibits great performance due to its high reliability and sensitivity. However, considering multiple substations geographically, there are more severe problems of data synchronization for multi-terminal current differential protection than for double-terminal types based on a typical channel. To solve the aforementioned problems, the operating characteristics of multi-terminal line differential protection under different synchronization errors on the - plane are first analyzed. Based on the influence of synchronization errors on the magnitude and phase of the protection operating value, a design method for the restraint current of multi-terminal current differential protection is proposed. To achieve the sensitivity of a high resistance internal fault, as well as the tolerance capability of the data phase-shift error, double restraint coefficients are introduced to optimize the shape and area of the restraint region. Subsequently, the setting method is inferred, which can be used as a reference for an engineering application and the promotion of multi-terminal line differential protection. Finally, the simulation results indicate that the proposed method can significantly improve the criterion security for the case of additional data synchronization errors while maintaining the sensitivity of the internal fault.

When current differential protection is applied to an AC transmission line, synchronous sampling at the two ends is required. The use of GPS synchronization increases the difficulty and cost of project implementation while the use of ‘ping-pong’ synchronization requires that the communication channel has equal transmission and reception delay. To overcome the impact of these issues, power differential protection has been proposed. However, power differential protection cannot fully identify the fault zone for solid single-line-to-ground fault. This paper proposes a novel differential protection approach based on the Tellegen's quasi-power theorem. The approach retains the advantages of current differential protection. Meanwhile, it is not affected by load condition and distributed capacitance. This paper also proposes a time synchronization method based on the Tellegen's quasi-power theorem to calculate and correct the time synchronization error. Therefore, the proposed pilot protection has a high synchronization accuracy and has no requirement on the communication delay. In this paper, different simulation models are established by using MATLAB/Simulink and PSCAD and extensive simulation studies verify the effectiveness of the proposed protection approach and time synchronization method.

Grid-tied power converters are widely adopted in renewable energy integration systems. Reliable operation of such power converters is highly desirable, which relies on effective fault diagnosis and ride-through techniques. In this work we propose a new open-circuit fault diagnosis method for grid-tied power converters based on Tellegen’s Theorem, which is fast in fault detection and accurate in faulty component location. We firstly developed a ’quasi-power’ concept to define the relationship between current and voltage magnitudes for the underlying power converter. The value of the afore-developed quasi-power in this proposal depends solely on the connection state (i.e., the switch position and status) of a power converter, resulting in its good features of robustness to parameter variations and immunity to operation changes. Thereafter, we propose a fault diagnosis method based on the quasi-power of a converter, which is able to identify any faulty component among all the semiconductor switches (i.e., the IGBTs and freewheeling diodes) at a time-scale of only one sampling period. As a case study, the proposed technique is incorporated into a well-known model predictive control framework of a grid-tied two-level power converter, and tested at a lab-constructed test-bench. Experimental results confirm its effectiveness.