A micro-energy system contains a variety of energy conversion and storage equipment. The energy consumption characteristics of energy conversion equipment usually strongly depends on the operation conditions. Based on the improved coupling model of micro energy system under different working conditions which describes characteristics of the system more accurately. Firstly, the optimal planning problem is modeled with an aim of system economy. Then, considering the uncertainties of renewable energy input, load and environmental factors, scenarios under variable off-design conditions are introduced. In order to reduce the complexity of the solution, the optimal problem is divided into master problem of equipment capacity configuration and primal problem of multistage power allocation by decomposition method. Finally, a micro-energy system which involves electricity, natural gas, and heat is configured under the proposed model and the linear model respectively. The result shows that the off-design conditions of
Uncertainty analysis of power system time-domain simulation is mainly concerned with the study of the influence of uncertainty factors in power system on time-domain simulation results. It provides an important reference for analyzing the transient stability of power system under uncertain conditions. A method based on generalized polynomial chaos(gPC)is proposed for uncertainty analysis of time-domain simulation. Approximately, the method assumes that there exists a polynomial relationship between variables and random factors at any time. The solution procedure is as follows. Firstly, the optimal orthogonal polynomial basis function is acquired to approximate the random input variables and unknown variables. Then, by Galerkin method, the stochastic equations which describe the system's transient process are transformed into the corresponding deterministic equations. Finally, by solving these equations, the polynomial approximation coefficients of unknown variables are obtained, which can be used to calculate
Modular multilevel converter(MMC)is very suitable for medium voltage and high voltage wind power generation system due to its advantages in many aspects. However, the capacitor voltage of each sub-module(SM)fluctuates widely in low frequency large current condition of the generator, which leads to large capacitors of the SMs. A novel method is proposed to suppress the capacitor voltage fluctuation of the SM with the circulating current injection based on the negative sequence double frequency circulation controller. And the basis is given for choosing the initial phase of the injected circulating current and the choice of SM capacitance based on the method. For the increase of the double frequency circulation with this strategy, a set of tradeoff coefficients characterizing the effect of voltage suppression relative to the increase of circulating current is presented. It is pointed out that the coefficient should be chosen according to the system requirements to meet the overall performance. Simulation result
The small-signal impedance modeling of modular multilevel converters(MMCs)is the key for the resonance and stability analysis of MMC-based power systems. MMC is a converter system featuring multi-frequency, nonlinearity and periodically time-varying operation trajectory due to its complex internal dynamics. Hence, traditional small-signal methods cannot be directly applied to MMC. The AC-side small-signal impedance of MMC is modeled by the harmonic linearization method, which has taken into consideration the harmonic circulating current and capacitor voltage steady-state ripples. Furthermore, the influence of the circulating current control on the AC-side impedance of MMC is analyzed. A detailed time-domain simulation model of a three-phase MMC is built by using MATLAB/Simulink and the analytical models are validated by simulation results.
Owing to the use of active-standby hosts to process all the real-time data, the current supervisory control and data acquisition(SCADA)system is faced with more and more severe challenges in terms of data throughput capacity, real-time performance, scalability, reliability and whatnot. A novel distributed SCADA system is proposed and its architecture and some related key technologies such as distributed resource and task management, distributed real-time data management, and distributed data processing are discussed. The system has broken through the bottleneck of the existing SCADA data processing mode, which can effectively improve the performance of the SCADA system and adapt to the development of future power grid dispatching and control operation.
The high proportion of renewable energy generation connected with the grid has brought great pressure to the peak-shaving of electric power systems. Using energy storage for auxiliary peak-shaving is an effective way to solve this problem. However, the high cost of energy storage limits its large-scale application. To make full use of the peak-shaving function of the limited energy storage and reduce the load demand for energy storage capacity, this paper proposes a practical method to develop the combination of energy storage and normal, deep, given oil and start-stop regulation ways for peak-shaving. The calculation models of the technical index based on the probability of lack of peak load and the economic index based on the annual cost of peak-shaving are developed. The curved surfaces of technical and economic indices of the combined peak-shaving scheme are built. The combined peak-shaving scheme at the junction of technical and economic curved surfaces is the optimal one under different renewable energy
In view of the microgrid consisting of inverters controlled by droop method, a frequency regulation strategy for the microgrid in the islanded mode is studied. Through the modeling and analysis of the microgrid system, as well as the equivalent and simplification of transfer functions, a parameter correction formula for the frequency regulation controller has been derived. When the system condition changes result in distribution ratio altering, output impedance changing and the varying of access number of inverters connected to the microgrid, the controller is able to adjust parameters online for quick restoring the system frequency to stability. Experimental results show that, the system frequency can quick recover to the given value and keep steadily due to the parameter auto-adjustment algorithm. This work is supported by National Natural Science Foundation of China(No. 51541703)and Innovative Research Team Funded Program of Guangdong Province(No. 2011N015).
The application of the heat storage tank in combined heat and power(CHP)units can contribute to improving the cogeneration system's abilities in peak-load regulation and wind power consumption. Since the use of the heat storage tank increases the difficulty in optimal dispatching, a novel power scheduling strategy based on two linear models is proposed to coordinate the operation of CHPs and heat storage tank. For the proposed scheduling strategy, the operation state of heat storage tank can be pre-judged, and the two technical indexes including the rate of wind power curtailment and the growth rate of running cost are taken into account. According to the adjustments of electric power and thermal power, wasted wind power and running cost can be reduced, respectively. Furthermore, an optimal dispatching plan is obtained in consideration of the uncertainty of wind power generation. Numerical examples are conducted to demonstrate the effectiveness of the proposed scheduling strategy in achieving efficient utiliz
In order to quantify the harmonic contributions on the point of common coupling(PCC), a new method based on waveform matching is proposed. Firstly, a model of linear regression equation between harmonic voltage amplitude and harmonic current amplitude is established, which avoids the direct measurement of harmonic phase. In consideration of the error to the equation brought by the fluctuation of the background harmonic, the dynamic time warping(DTW)distance is used to analyze the harmonic data to select the sub sequences of high similarity. The utility equivalent harmonic impedance is estimated by the least square method, and then the customer harmonic contributions are calculated. The results of simulation and field measurement analysis show that the method has high accuracy and can restrain the influence of the fluctuating harmonic in the background. This work is supported by National Natural Science Foundation of China(No. 51477029).