Контрольная работа по дисциплине «Английский язык» для ТулГУ

Контрольная работа заочника   по дисциплине «Иностранный язык (английский язык)» на тему «Исследование классических режимов питания распределительной сети переменного / постоянного тока» ISSN: (Print) 2234-8972 (Online) Journal homepage: https://www.tandfonline.com/loi/tjee20   Research on the classic power supply modes of AC/DC distribution network Shigong Jiang, Weihong Yang, Yunfei Wang and Hongjun Li State Power economic research Institute, Beijing, China   ABSTRACT With the rapid development of distributed generation and power electronic technology, it is a tendency to develop the DC distribution network based on the AC type. And it is an urgent need to solve the problem of reasonably planning of AC/DC distribution network. In this paper, the application scenarios of AC/DC distribution network are analyzed based on the distribution characters of power sources and loads. The basic modules are analyzed, and the DC voltage grade sequences, electric power network structure, equipment, configuration of distribution automation are proposed. Furthermore, 5 classic power supply modes are proposed according to the analyzed application scenarios. The research results provide technical reference for the future AC/DC distribution network planning and design.  

1. Introduction

The AC/DC distribution network has advantages on reliability, power supply distance and environmental friendliness. It can be used to solve the shortage of line corridor, improve the power quality and distributed generation access. It is a tendency to develop the AC/DC distribution network based on the traditional AC distribution network[1,2]. Establish the classic power supply mode is an effective way to normalize the planning and improve the standardizing pattern of AC/DC distribution network [3]. Furthermore, the basic modules such as the DC voltage grade sequences, electric power network structure and equipment are the fundamental contents. Actually, the DC distribution technique has been applied into some domain such as communication, ships and rail transit, the corresponding researches and standards of DC power supply in these domains are formulated [4–7]. In the July of 2005, the SC6.31 working team of International Council on Large Electric Systems (CIGRE) was established to research and generalize DC distribution technique in medium voltage, and the medium voltage is confirmed between 1.5 and 100 kV [3]. The national standard of medium and low voltage of DC distribution system is formulating for the popularization and application of DC distribution network in China. Some countries and scientific institutions has carried out relevant researches about DC distribution technique, but most of the demonstration projects focused on low voltage [8–10]. In 2011, an AC/DC distribution was proposed by North Carolina State University (NCSU), 120 VAC and 400VDC are applied, the DC/DC converters and DC/AC inverters are installed in the system for the power supply of AC loads, PV and DC loads [11]. A bipolar construction is proposed by Osaka University, and the DC bus is ±170V. Each pole can satisfied the various loads via power electronic equipment [12]. 3 typical topologies, which includes the radiation, hand-in-hand and circular ring, are proposed by ZheJiang University, also the control and protection strategies are comparatively analyzed [13]. The typical topologies are shown in Figure 1. In this paper, the Chapter I introduces the research status of the DC distribution network. In Chapter II, the principle of classification and application scenarios classifies are discussed. In Chapter III, the basic module including DC voltage grade sequences, electric power network structure, equipment and configuration of distribution automation are studied. In Chapter IV, 5 classic power supply modes and the relevant parameters are proposed. The conclusion is summarized in Chapter V.  

2. Classification of application scenarios

2.1. The classified principle of application scenarios The application scenarios are the key motivating factor to accelerate the development of AC/DC distribution network. For meeting the demands of different application scenarios, the voltage grades sequences, power network structures, and equipment need to be optimal configurated. The application scenarios of AC/DC distribution network present based on the internal and exterior factors. And the main classified principle includes the types and distribution of DC sources and loads, also the advantages of DC distribution system is needed to be considered. As the applications of electric vehicle charging station, energy storage power station, electric traction and renewable energy generation system exist differences, the characteristic of application scenarios are different. 2.2. Application scenarios of AC/DC distribution network In this paper, 5 application scenarios are proposed according to the classified principle, which includes concentration area of DC loads, industrial park, remoulding of load center in cities, assembling the renewable energy sources and the interconnection of different distribution subareas. (1)  Concentration area of DC loads In this scenario, the data centers, electric vehicle charging station, rail transit and other DC loads are supplied by medium and low voltage. Each mentioned DC load need corresponding AC/DC converter in AC distribution system, but they can be supplied by DC distribution system which accesses to the AC power grid via centralized converter. With this pattern, the efficiency and reliability can be improved. (2)  Industrial park In industrial park, the main DC loads includes converters, electrolytic furnaces, precise electronic instruments, central air conditioning, elevators, the proportion of DC load is more than 40%. Also, renewable energy generation systems are involved. So, the power supply capacity, reliability and power quality are highly rigorous. With the same power line corridor, DC distribution system can achieve bigger transmission capacity and be convenient for renewable energy accessing. (3)  Remoulding of load center in cities As the social development, urban size becomes bigger, and the loads increase sharply in city centers. With the AC distribution network, the power line corridors are shortage and the remoulding will be costly. Using DC distribution system to realize the remoulding of load center in cities is an effective way. The transmission capacity can be up to 1.5, when the existing power lines are preserved. (4)  Assembling the renewable energy sources Normally, photovoltaic power generation and energy storage systems need inverters to connect to utility AC grids. The wind driven generators need AD/DC/AC converters to transform the electric power. With DC distribution network to assemble the renewable energy sources, the DC/AC inverters can be ignored and only voltage amplitude need to be controlled, the reliability and efficiency can be improved. (5)  Interconnection of different distribution subareas In normal AC distribution network, different distribution subareas are connected via switches. When some of the subareas break down, the loads transmission is realized by control the connecting switches. But the system can not meet the demands of closed loop operation, if the phase difference is existing between different subareas. With DC converters, the parallel operation between different subareas can be achieved and the power flow control can be realized in real time.

3. Basic modules

As the components of the classic power supply modes, the power supply module, distribution automation module, power source access module and load access module need to be analyzed. 3.1. Power supply module Power supply module includes the voltage grade sequences, power network structure and equipment. The voltage grade sequence is confirmed considering the capacity, distribution characters of power sources and loads in different application scenarios, the transmission capacity and distance of different voltage level, the interconnection with AC distribution network. 3 voltage grade sequences are proposed for different application scenarios. (1)  ±35 kV/±10 kV/1.5 kV(0.75 kV)/0.4 kV(0.24 k V); (2)  ±100 kV(±50 kV)/±35 kV/±10 kV/1.5 kV(0.75  kV); (3)  ±100 kV(±50 kV)/±35 kV/±10 kV; Based on the power supply reliability demand, the power network structure can be divided into 4 types, which are radiation, hand-in-hand, circular ring and back-to-back. The radiation structure is mainly used in the situation that power sources and loads are dispersive, and the demand of reliability is not rigorous. When the medium voltage bus has fault, the DC distribution network will break down. In hand-in-hand structure, the power comes from two different sources, and the 2 DC medium voltage buses are standby for each other. The loads, distributed generations and energy storage systems access to different voltage level buses. The reliability is higher than radiation structure. In circular ring structure, the power sources come from high level AC grid or large-scale renewable energy power generations. The power sources connect to the DC bus via DC/DC or AC/DC converters. One of the converters applies V/f control to offer the voltage reference, the other converters apply P/Q control strategy. And the DC or AC loads, distributed generations and energy storage systems are supply by DC bus via DC/DC or DC/AC converters. The circular ring structure can cover more regions and be convenient for load accessing. The power flow can be controlled easily and the reliability is higher, but the configuration of protection and control is complex and the investment is costly. In back-to-back structure, the AC/DC/AC converter is used to connect different AC distribution subareas. The closed-loop operation and power balance are realized. Mainly, it is used to solve the problem that the partition running of AC distribution network caused by short-circuit current exceeding limit. In addition, the development progress of the AC/DC converters, DC/DC converters, breakers and the other distribution equipment are considered to be applied into the classic power supply modes. 3.2. Distribution automation module The distribution automation module is including fault handling strategy, communication mode and protection. The characters of loads, power supply reliability are mainly considered to configure the Distribution automation scheme. The fault handling can be divided into centralized type and distributed type. The communication modes are mainly used optical fiber communication and carrier communication, wireless communication is also considered according to the reliability requirement. The load switches and breakers are considered which are used to coordinate with the defensive function of power electric equipment. 3.3. Power source access module The distribution automation module is including fault handling strategy, communication mode and protection. The characters of loads, power supply reliability are mainly considered to configure the Distribution automation scheme. The fault handling can be divided into centralized type and distributed type. The communication modes are mainly used optical fiber communication and carrier communication, wireless communication is also considered according to the reliability requirement. The load switches and breakers are considered which are used to coordinate with the defensive function of power electric equipment. 3.4. Load access module Same with power source access module, the load access module includes access point, access mode and access voltage, the access pattern need to consider the load capacity, the types of loads and other factors in different application scenarios. The main access pattern includes single and double circuit, the access point includes the DC buses of ±110 kV~ ±35 kV converter stations, also the switching station and ring main unit of medium voltage.    

4. 4. The analysis of classic power supply modes

Based on the analysis of application scenarios, 5 classic power supply modes are proposed, DC voltage grade sequences, power network structures, equipment parameters, automation configuration of each classic power supply mode are described in details. 4.1. Classic power supply mode I In this application scenario, most of the loads are DC type, such as charging station of electric vehicle and rail transit power supply. DC voltage grade sequences is ±3 5 kV/±10 kV/1.5 kV(0.75 kV)/0.4 kV(0.24 kV). The distribution network structure is hand-in-hand, AC loads are supplied by DC power via inverters, the basic structure is shown as Figure 2, and the AC/DC converters, DC/DC converters, inverters and breakers are applied for the interconnecting with AC grids and accessing of the loads and distributed generations. The medium voltage convertor stations need to configure optical fiber communication, the optical fiber communication or carrier communication can be employed in the low voltage equipment. The main capacities of DC distribution equipment are shown in Table 1. 4.2. Classic power supply mode II This classic power supply mode is proposed based on the application scenarios of industrial park. The loads includes induction machines, electrolytic furnace, elevators and other medium voltage DC loads, the proportion of DC loads is more than 40%. DC voltage grade sequences is  ±100  kV(±50  kV) /±35 kV/±10 kV/1.5 kV(0.75 kV). The distribution network structure is hand-in-hand, shown as Figure 3, but the difference with Classic power supply mode I is the AC loads are supplied by AC power. And also, the AC/ DC converters, DC/DC converters, inverters and breakers are equipped for loads and distributed generation accessing. The high and medium voltage convertor stations need to configure optical fiber communication, also the carrier communication can be selected in the low voltage equipment. The main capacities of DC distribution equipment are shown in Table 2. 4.3. Classic power supply mode III According to the application scenario of load centers remoulded in cities, most of the DC loads are illumination, inverter appliances and electronic equipment. Considering the power supply reliability requirement and economy, the radiation type is applied, which is shown in Figure 4. The AC/DC and DC/DC converters are used to supply DC load. Because the loads in residential area are in low voltage range, the DC voltage grade sequences is ±35 kV/±10 kV/1.5 kV（0.75 kV） /0.4 kV. The DC loads, energy storage systems and DGs are connecting to the medium voltage DC Bus via DC/ DC converters. AC loads connect to the AC utility grid via transformers. The medium voltage convertor stations need to configure optical fiber communication, and the optical fiber communication or carrier communication can be employed in the low voltage equipment. The main capacities of DC distribution equipment in this mode are shown in Table 3. 4.4. Classic power supply mode IV Assembling the renewable energy sources is also an important application scenario. In this mode, the renewable energy is assembled and delivered to power transmission network via AC/DC distribution or consumed locally. The DC voltage grade sequences is ±35 kV/±10 kV/1.5 k V(0.75 kV)/0.4 kV. To satisfy the reliability requirement and distribution characters of renewable energies, the circular ring structure is applied, which is shown in Figure 5. The AC/DC converters, DC/DC converters, inverters and breakers are equipped to satisfy loads and renewable energy sources accessing. Also, the optical fiber communication or carrier communication are applied in this scenario. The main capacities of DC distribution equipment in this mode are shown in Table 4. 4.5. Classic power supply mode V In this application scenario, the AC/DC distribution network is used to realize the interconnection of different AC distribution subareas, power flow control and short-circuit current reduction. Considering the load is less, DC voltage grade sequences is ± 100( ± 50)/±35 kV/±10 kV. The back-to-back structure is applied, which is shown in Figure 6. The AC/DC converter is equipped only and the optical fiber communication is applied. The main capacities of DC distribution equipment in this mode are shown in Table 5.

5. Conclusion

Considering to the load categories and capacity, power supply reliability requirement, power sources categories, 5 AC/DC distribution network application scenarios including concentration area of DC loads, industrial park, remoulding of load center in cities, assembling the renewable energy sources and the interconnection of different distribution subareas are proposed. The basic modules include power supply, distribution automation, power source access and load access are proposed for planning and designing standardly. According to the analysis results of application scenarios and basic modules, 5 classic power supply modes are proposed, the DC voltage grade sequences, distribution network structure, equipment capacity and communication configuration are analyzed in details.