This paper has described a technique of calculating voltage and power flow state of a distribution system using the information measured with two or more switches with sensors installed in a distribution system. The proposed technique is that, a set of the power distribution section where two or more switches with a sensor are connected is defined as the large section, and the active power and reactive power consumption in the large section are calculated based on measurement information, voltage (RMS), current (RMS) and power factor. Using the simple distribution system model that consisted of the large sections, the power consumption of the large section is calculated by the power flow calculation to separating power consumption and power distribution loss. It is distributed to the small sections that constitute the large section, and detailed power flow calculation is performed. Verification of the proposal technique and basic estimation of the calculation error were performed using the simple power distribution system model.
Application ofcontrolled series capacitors with antiparallel thyristor combination across the capacitor segment is one of the new and promising countermeasures for enhancement of power system stability. The line reactance can be directly controlled by the controlled series capacitors, hence, it is very effective to apply the capacitors for damping power system disturbances.In this paper, we describe the following.(1) The design method of control system for the segmented series capacitors with thyristor switches is proposed.(2) The effectiveness of the controlled capacitors proposed for power system stabilization is shown with the results of EMTP analysis.(3) The possibility of zero passing missing phenomena of capacitor voltage is indicated by E M F simulation, and a countermeasure is proposed in order to avoid the phenomena. The effects of the countermeasure is indicated by the results of EMTP simulation.
Keywords: HVDC, self-commutated inverter, induction machine, wind power, inverter control HVDC consisted by self-commutated inverters is able to be applied for power transmission that connecting from a remote large windfarm to weak ac system. Most self-commutated HVDC is applied for connection between two ac systems they have synchronous power sources, but it is not suitable for windfarm that consists of induction generators without synchronous power source.This paper proposes a new control for the self-commutated HVDC system connected to large windfarm of induction generators. The windfarm and HVDC system for study is shown in Fig. 1. This system is that the power transmission from an island or the windfarm in marine is assumed. Below, the windfarm side is called "sending side", and the other side is called "receiving side". The windfarm consists of induction generators without synchronous power source. In the sending side, there are 10 wind power generators of 1 MW of rating. The rated output of the windfarm is 10 MW. It is assumed that the wind power generator is the simplest stole type induction generator. The converter is a self-commutated converter of the full bridge composition used IEGT.The receiving side assumes as the general power system. It is referred to as short circuit capacity 20 MVA on the voltage of 33 kV. This is 20/12.5 = 1.6 times in a ratio with direct-current power transmission capacity. When it sees from the direct-current power transmission system, it is a small and weak system. The proposed new control block for sending side inverter is shown in Fig. 2. This control consists of frequency control and voltage control. The frequency compensation that controls the fre- Fig. 1. Windfarm and HVDC system quency of sending side power system is added to frequency control. And the voltage limit compensation that restricts the current of sending side inverter is added to voltage control.Verification of the effect of the proposed control was performed using the windfarm and HVDC system shown in Fig. 1 by EMTP simulation. Figure 3 shows the simulation result at fault on sending side. It is assumed that 5 wind power generators stop at the occurrence of the fault.The dc voltage falls according to the sending side fault, and active power is temporarily poured in so that direct-current voltage may be maintained from the receiving side. Although the active power of sending side after the fault removal becomes half in order for 5 wind power generators to stop, the system can be continuing operation stably. HVDC consisted by self-commutated inverters is able to be applied for power transmission that connecting from a remote large windfarm to weak ac system. Most self-commutated HVDC is applied for connection between two ac systems they have synchronous power sources, but it is not suitable for windfarm that consists of induction generators without synchronous power source. This paper presents new control for the self-commutated HVDC system connected to a large windfarm of induction generators. The effect...
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