Search

The increase in wind power penetration leads to the risk of energy supply interruption in integrated electricity‐heat energy systems (IHES). This paper presents an analytical‐based approach for the efficient operational reliability evaluation of the IHES. The wind power distribution characteristic model considering correlation is constructed based on Hidden Markov Model (HMM). To reduce computational complexity, a critical system state identification (CSSI) method is proposed that characterises both random device failures and wind power uncertainty. Under each critical system state, the analytical function relationship between the reliability index and the uncertainty factors is established based on the virtual stochastic response surface (VSRS) method. The analytical function can directly calculate the reliability index when the wind power output varies, avoiding a large number of repeated calculations of the optimal load‐shedding model of the system and reducing the time required for reliability assessment. This allows the operator to evaluate the operational reliability of the integrated energy system in real‐time. The numerical simulation of the test system combining the IEEE 33‐node distribution system and the existing 28‐node heating system proves the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The finite‐control‐set model predictive control (FCS‐MPC) can achieve a high output and fast control response. However, the size of the candidate vector set of FCS‐MPC must be very huge to achieve a satisfactory steady‐state control performance. Although some studies suggest that the candidate vector set can be expanded by increasing the number of vectors in one period or directly defining new virtual vectors, there is a tricky contradiction between improving the steady‐state control performance and reducing the computational burden. It makes the online realization difficult. This study presents a hierarchical search approach based FCS‐MPC of three‐level converter fed permanent magnet synchronous motor (PMSM) driving systems. The optimal vector is obtained by continuously shrinking the vector space, so that only 30 prediction calculations are needed to evaluate more than 20,000 candidate vectors. Consequently, the proposed method can achieve the excellent steady‐and transient‐state control performance online. Moreover, since the optimal vector is chosen directly from the vector set, the linear‐and over‐modulation are unified. No special treatment is necessary for over‐modulation driving systems, because the reference voltage is decided naturally by the cost function of FCS‐MPC. Some experimental results are shown finally to prove the correctness and feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents an in‐depth analysis for the two‐variable impedance model of a grid‐connected system. The two‐variable model describes the impedance using the frequency as well as the operating point variable. The impedance‐based stability analysis method cannot be directly applied because the conventional models are derived for a specific steady‐state operating point and the operating point varies during operation. Thus, this paper develops a new analysis method to shed light on the role the two‐variable model plays instability analysis. The proposed method not only analyzes the system stability at different operating points, but also enables the controller design to ensure system stability. Experimental results are presented to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Grid‐connected inverter have been extensively used in the renewable energy grid‐connect systems, such as solar and wind. Interaction between the grid and the inverter may generate harmonic resonances that lead to reduced power quality and even instability. To analyse the stability of the inverter‐grid system using impedance‐based stability criterion, inverter impedance has to be known. Impedance measurement in the dq‐domain requires the precise synchronous phase angle to obtain accurate measurement. For impedance measurement in the stationary frame, inaccuracy usually results from not considering the effects of grid impedance and the frequency coupling. A new impedance measurement method in the stationary frame is proposed to obtain accurate measurement. The proposed method takes into account the grid impedance and its interaction with the inverter. Thus, it overcomes the limitations of current impedance measurement methods. More important, the proposed method enables accurate stability analysis results, whereas current methods may fail. Simulation and experimental results are presented to demonstrate the effectiveness of the proposed measurement method. [ABSTRACT FROM AUTHOR]

The interaction between wind farm and power grid may cause the stability issue in the wind farm integration system. Practically, the integration system contains many collector feeders, and one feeder connects a large number of wind turbine generators. Moreover, frequency coupling effect is introduced in all parts of the wind farm system due to the asymmetrical controller of the wind turbine converter. So, it is complicated to analyse the stability of the whole integration system. This study proposes the modular admittance model for wind farm, which is easy to expand for modelling and analysis of the whole integration system. In addition, the operation condition of wind turbine generators in wind farm varies with the prevailing wind speed. The system stability may alter constantly according to the wind speed. How to effectively evaluate the system stability in the entire wind speed operation space is also a challenge. Thus, for wind farm system, this study develops an approach with two‐variable admittance model and criterion based on magnitude and phase contours plot to overcome this problem. The proposed admittance model and stability analysis approach are verified by simulation. [ABSTRACT FROM AUTHOR]