Fuzzy set applications in power systems have been attracting growing interest. The primary motivation for this interest stems from the desire to model uncertainties which arise from practical considerations in developing expert systems and/or numerical methods for complex systems. This paper reviews the current status of fuzzy mathematical approaches to power system problems and suggest directions for further development.
In this paper, we propose a method of approximate reasoning for fuzzy control based on α-level-set decomposition of fuzzy sets by quantized α. This method can be easily implemented with analog hardware. We also investigated 4 defuzzifying methods, which are suitable for this configuration. The influence of quantization levels of α on output from fuzzy inference engine is investigated. It is concluded that 4 quantization levels give sufficient result for fuzzy control performance of DC servo system. The hardware implementation of this reasoning operation method and of the defuzzification by gravity center method, which is directly converted to PWM actuating signal, is also presented.
The stabilization of power systems has been an important subject for a reliability, due to the large scale and complexity. For improving a controllability of stabilization, several stabilizing methods have been studied, such as nonlinear and robust controls. The purpose of this paper is to construct a sliding mode control based on fuzzy model for electric power systems. A fuzzy model composed of the fuzzy inference is introduced to treat the nonlinearity of the system. The consequent part of a fuzzy process law is constructed by a linear system. The sliding mode control using optimal switching vector is applied to each linear system of a process law, and a control input is given by a fuzzy inference for sliding mode control input. Then the method becomes nonlinear and robust control. In order to demonstrate the control effect of the proposed method, numerical simulation is performed by using 3 machine-9 bus power system with an automatic voltage regulator and a governor as controllers. The method gives good control effect for both small and large oscillations.
Electric power system has been associated with a lot of uncertainties, such as constant change of loads and system operation, because of becoming large scale and complexity. A fuzzy control has been applied to some of power system studies. The aim of this paper is to propose a method of stabilizing control based on fuzzy theory for electric power system and to apply it numerically and experimentally for a one-machine infinite bus power system. The method is constructed under the knowledge of the equal-area method used for the transient stability analysis. In the method, variables of condition parts and rules are simplified, and the number of membership functions of fuzzy control is minimized, by a coordinate transformation with the rotation angle on the phase plane. Furthermore, we discuss the stabilizing control during fault condition. The proposed method gives a good efficiency during fault, because it has great potential that the implementation of fuzzy control does not always require the use of a mathematical model and the control input can be determined in a short time using only a qualitative statement of control rules. Simulation results for numerical calculation and experimentation show that the method yields good system dynamic performance.
Power system stability is essential to reliable and economical operation of power system. The quick-response excitation control with PSS is used as a power system stability improvement measure at generator. This method, however, is not always sufficient to apply in a wide operation range of power system configuration, load flow, and so on. This paper includes results of experiments of fuzzy excitation control system on AC/DC Power System Simulator of CRIEPI. This control system is verified to improve power system stability and has better performance than the conventional excitation control on a one and two machine to infinite bus system.
It has been made clear that a superconducting magnetic energy storage (SMES) is very effective for power system stabilization. The control methods proposed for power system stabilization by SMES are such as the pole assignment, the optimum control and so on, each of which, however, has its drawbacks. The application of fuzzy control is considered in order to overcome these drawbacks. This paper is concerned with the power system stabilization by fuzzy control of the active and reactive power of SMES. First, the adequate fuzzy control rules of a SMES for the model power system is derived. Then, in order to alleviate the dependence of the fuzzy control on the operating condition and the fault, we propose a method, which adjusts the fuzzy parameter according to the operating condition and the fault using a neural network. The validity of the proposed method is examined by computer simulations.
Power system control equipment needs higher sensitivity and operational reliability than convential one. Advanced voltage control equipment needs reducting the frequency of tap changes and improving the characteristics (the relationship between the actual voltage and reference voltage) of the voltage meet today's power system requirement. However, these objectives are in a trade-off relationship. Studies of voltage control based on knowledge base suitable for electric power systems can satisfy these objectives using fuzzy inference. Comparing with a corresponding conventional equipment, the new equipment improved the deviation of 30min. average voltage of 30%. This paper describes the design concept of new voltage control equipment using fuzzy inference. In addition, performance of field test results are described along with rules fo fuzzy inference, membership functions, and the deviation of 30min. average voltage through the detailed simulation.
This paper presents a new solution method for computing the maximum loading point of a bulk power system under the condition where the loads of the nodes can be parameterized by a scaler which is the loading level of the system. A special loading model, in which the loading level of the system depends on the voltage magnitude of a loading node, is adopted for the purpose of releasing the loadflow computation from the ill-condition near and at the maximum loading point. The loading level of the system is unknown in the abovementioned loading model. The maximum loading point is obtained by so adjusting the operating parameter as to achieve the maximum loading. The operating parameter is adjusted in the converging process of the Newton Raphson's iterative computation. The adjustment is computed by a way based on the least squares estimation using the data set which is obtained from its own iteration process. It is shown in numerical examples that the proposed method is satisfactorily rapid, stable, and accurate.
The experimental data in the FUJI-1 closed cycle MHD generator with helium working gas have been discussed by a quasi-one dimensional numerical simulation based on two temperature model. The effects of large fluid loss in the generator and of insufficient plasma condition at the generator inlet are analyzed by assuming the large apparent skin friction coefficient in channel and low electron temperature and density at the inlet, respectively. It may be concluded that the main cause of unexpected experimental results is ascribed to the undesirable plasma growth from various experimental cause.
It is interested in the current limiting fuses that generate high arc voltage and show remarkable current limiting effect. We experimentally investigate the mechanism of high arc voltage generation in the insulated capillary of inorganic material. The insulated capillary with small inner diameter is made of Pyrex glass. The test sample is consisted of the insulated capillary, a slender copper wire fuse element strained along the center axis in the insulated capillary and the fuse element terminals. The test sample is put in the enclosed vessel that could withstand high pressure. Arc current, arc voltage and pressure generated during the experimental period are observed. It is shown that the change of arc voltage waveform depends on dimension of the insulated capillary, arc current density and pressure in the vessel. The maximum pressure closely depends on the evaporated fuse element material during arc period, is reached after arc current zero due to a narrow compressible air channel. It is clear that the maximum of arc voltage is dominated by evaporated fuse element vapor density.