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terça-feira, 31 de agosto de 2021

A study on emergency power generation system at waterworks by cooperation of ESS and emergency generator-Lee Hyoung Mook- Department of Electrical Engineering Graduate School, Chonnam National University -2021








A study on the emergency power generation system of waterworks by the cooperation of ess and emergency generator by  Lee Hyoung Mook
 Department of Electrical Engineering Graduate School, Chonnam National University (Supervised by Professor Sung-Jun Park)

 (Abstract) 

Recently, as awareness of the finiteness of fossil energy, environmental pollution, and the dangers of nuclear power generation has grown, the direction of energy policy in domestic is changing to improve economic efficiency including denuclearization and a stable supply. In accordance with this policy direction, the operation of aging nuclear power plants is suspended and the construction of new nuclear power plants is being canceled. However, the power supply and demand problem due to the decrease in nuclear power generation sources can be overcome with distributed power using renewable energy and active idle resources. In the smart grid using distributed power, demand management, power quality, and power reliability improvement are important factors, and related research is ongoing. In this paper, we proposed an uninterruptible system consisting of an emergency generator and a short-cycle ESS, and proposed an integrated operation algorithm that can provide stable power to the consumer and improve power reliability

 Research on uninterruptible systems using ESS has been conducted before. However, in order to secure a long back-up time, a large-capacity battery system is required. This greatly increases the overall system cost, so there is no problem in the functional part, but in the field of construction cost, the economical efficiency of the unit price was not suitable, so the commercialization stage was not progressed. Recently, various studies using emergency generators, which were temporarily used for emergency power supply in case of power failure, have been conducted. Public institutions and for-profit institutions are also increasingly participating in DR projects for demand resources using emergency generators. In order to use the emergency generator as a demand resource, a power changeover switch is required, but in the beginning, ATS (Automatic Transfer Switch) was widely used. ATS has a disadvantage that power failure occurs within about 100[ms] when switching over. It is participating in the DR project by replacing it with a CTTS (Closed Transition Transfer Switch), which is a complementary uninterruptible power changeover switch. In the case of CTTS, there is a grid tied CTTS (G-CTTS) that directly controls the AVR and governor of an emergency generator to operate in a grid-tied type, and by using this, parallel operation with a power converter is possible. 

The system proposed in this paper is composed of G-CTTS, emergency generator and short-cycle ESS. The rated power capacity of the proposed uninterruptible system is 360kW, and for each component, the inverter is 500kW, the G-CTTS and the emergency generator are 360kW. For short-cycle ESS batteries, 500kWh of carbon batteries were used, and a PC-based PMS operation program was used for power management of the entire system.

 This paper proposes the operation and element technology for the uninterruptible system consisting of an emergency generator and short-cycle ESS. The factors proposed in this paper are largely summarized into five categories.

 First, a large-capacity uninterruptible system configuration consisting of an emergency generator and a UPS was proposed. In a system composed of two voltage sources, power control is mainly handled by the inverter, but in this system, power control is performed by the emergency generator using G-CTTS. When G-CTTS performs power control during two types of parallel operation, the required function of the inverter is lowered, and a large-capacity uninterruptible system can be implemented only by applying a commercial UPS. 
Second, in order to improve the reliability and quick response of the emergency generator in parallel operation, it is necessary to precisely detect the phases of different voltage sources and control the frequency. To this end, we propose a high-precision PLL method that synchronizes the phase of the voltage source to be synchronized at high speed using a virtual d-q coordinate method. 

Third, high-speed response and output of the inverter are important for non-power failure operation. In the case of the output quick response of the inverter, the time required to the rated output increases depending on the capacity. Therefore, it is possible to operate stably only when the time for detecting a power failure is reduced as much as possible. In the case of a site with a large system impedance, the voltage THD increases when the load contains many harmonics. If the voltage condition for power failure detection is sensitively applied, it can be recognized as a power failure even if it is not a power failure. Therefore, we propose a high-speed blackout detection algorithm using Perid Time Shit that can accurately detect blackout at high speed. 

Fourth, as the short-cycle ESS is additionally installed, the capacity to supply power to the customer side increases. When the instantaneous load power increases due to nonlinear loads such as inrush current when starting the motor, the reliability of the system voltage can be enhanced through power cooperation. In case of PCS with uninterruptible function, it has fast output speed, and by using this, we propose an algorithm to cooperate power of two types of power for peak load. Fifth, to secure the reliability of PCS, we propose a PCS structure that allows parallel operation with three power stack modules even if one power stack fails by configuring a 125kW power stack in 4 parallel. In this paper, we proposed a long-cycle uninterruptible system using an emergency generator and a short-cycle ESS, analyzed and proposed the necessary technology to operate it, and developed and manufactured a 500[kW] class G-CTTS and inverter. The proposed study was validated through simulations and experiments.

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