To enhance the outage quality of a distribution system with a high penetration of PV renewable energy, this paper proposes a coordinating control strategy for an on-load tap changer (OLTC) of the main transformer in a distribution substation and PV smart inverters. The voltages at the end-points of all distribution feeders that are served by the main transformer and the power generation of each PV system are collected using a SCADA system. The hourly tap position of the OLTC is then derived from the daily profiles of feeder voltage and the injected power that is generated by all PV systems along the feeder. Thereafter, the PV smart inverters perform autonomous control of reactive power compensation so that the voltage at the point of common coupling (PCC) can be fixed at the specified voltage level. To demonstrate the effectiveness of the proposed voltage control strategy, a main transformer, which serves six feeders of the Taiwan Power Company (Taipower) with high PV penetration, was considered in a case study. The proposed coordinating control of the OLTC and PV smart inverters dramatically improved the voltage quality of the distribution feeder and enabled the effective mitigation of the impact of large PV integration in the distribution system.

This paper presents the innovative control scheme of renewable ancillary services to support the system operation of a bulk power system with high penetration of renewable energy. The smart inverters of PV systems can be controlled to adjust the renewable generation of real and reactive power according to the variation of system voltage and frequency. The dispatch control of renewable ancillary services is integrated with the energy management system (EMS) to achieve the coordination control of renewable energy and synchronous generators. The sensitivity factors of renewable system was applied to determine the generation curtailment for the mitigation of line overloading. The ancillary service of reactive power compensation by renewable energy was considered to improve the system voltage quality. The emergency generation control of renewable systems with fast ramping up capability was applied to illustrate the effectiveness of renewable ancillary service to improve the system frequency response after sudden generator tripping. Based on the computer simulation of an actual power system with large renewable energy to be integrated, the functions of virtual synchronous generators by the photovoltaic (PV) systems and wind farms have to be applied to ensure the successful steady state operation and to improve the system transient stability for severe disturbance contingency.

This article proposes a fault identification method that is embedded in an asset management system (AMS) to identify the faulted location based on the fault flags reported from the fault indicators (FIs). The fault identification model based on the Petri-net technology is developed using the distribution network topology generated by a geographic information system. The proposed method uses the data set of fault flags generated by FIs, the statuses of circuit breakers, the available precurrent and postcurrent measurements of FIs, and the loadings of distribution feeders and laterals. The hybrid communication system is applied to provide two-way communication between the control center and FIs. The AMS with the embedded fault identification method can dispatch the repair crews to the fault location faster to accelerate the customer service restoration. A distribution feeder of Taiwan Power Company was selected for the computer simulation to demonstrate the effectiveness of the proposed method by using the communication-capable FIs to identify the exact fault location of distribution lines after a short circuit fault occurs in a distribution system.

This paper presents the power quality assessment of a hot strip mill with cycloconverters for an integrated steel- making facility. Due to the stochastic operation characteristics of cycloconverters, the electric power consumed by the hot strip mill fluctuates dramatically with the harmonic currents of different integer orders and non-integer orders. Both of the harmonic distortion and voltage flicker problems have been introduced to deteriorate the power quality of the industrial customer. To mitigate the harmonic pollution and provide proper reactive power compensation at the same time, two single-tuned and three high-pass passive filters have been therefore applied according to the harmonic load flow analysis. After removing the resistor due to flash over damage, the 6.8^th order high-pass filter has been converted to be a single-tuned filter. The impact of harmonic distortion on the existing filters and other equipments is investigated in this paper to ensure the harmonic distortion of the hot strip mill to be within the tolerance limit with the new configuration. To represent the harmonic current injection more accurately for the harmonic load flow analysis, the harmonic currents generated by cycloconverters are determined by field measurement. It is found that the total voltage harmonic distortion THD_v solved by computer simulation is very close to the actual harmonic distortion. According to the harmonic load flow analysis, the serious harmonic pollution problem introduced by the cycloconverter drive system can be mitigated effectively by the implementation of proposed harmonic filter banks. Besides, the voltage flicker problem due to dramatic variation of large reactive power consumption of the hot strip mill can be solved by proper control of cycloconverters.

This paper proposes an innovative transformer management system (TMS) for energy control of customer loads and photovoltaic (PV) systems to solve the problems of transformer overloading and over voltage due to power injection by PV renewable energy. The operation status of distribution transformers is monitored by transformer terminal unit (TTU) and reported to the control master station via the hybrid communication system. The demand response of customer load control is activated to reduce the loading level of transformers for mitigation of overloading problem. For the residential customers with installation of roof top PV system, the TTU is applied to perform the power factor control of smart inverter to prevent the over voltage problem. The hybrid communication system consisting of power line carrier, radio frequency and optical fiber is used to provide two-way communication for data collection and controls of customer loads and PV system. According to the field testing of the proposed TMS in Taipower, the adaptive energy control of customer loads according to the over loading level of distribution transformer is executed to support the demand response for peak load shaving effectively. The over voltage problem due to PV power injection has also been solved by TTU for control of PV smart inverters to perform the proper reactive power compensation.