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Research On Some Key Technologies Of Virtual Synchronous Generator Applying To Photovoltaic Micro-grid

Posted on:2016-07-16Degree:DoctorType:Dissertation
Country:ChinaCandidate:L YangFull Text:PDF
GTID:1312330461952316Subject:Power electronics and electric drive
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Energy is the material foundation for the development of human society. Man's using of energy developed from firewood to fossil energy such as coal, petroleum and natural gas, and then to electricity generated by water, wind,solar power and other clean energy. Each development procedure evolves with giant leap in productivity and important progress of civilization. At present, along with the economic growth and population growth, the world demand for energy will continue to increase. While the traditional coal, petroleum and other energy are badly depleted, the development of new energy sources has become a large-scale implementation of the strategic direction by the world. China is not only faced with a shortage of conventional energy sources, environmental pollution also faced the grim reality of the problem, and the country has made a corresponding reduction in unit GDP carbon emissions directional statement, therefore, the development of new energy and resolving their access to the grid is and importance and urgency issue. The "guidance on the development of natural gas distributed energy" shows that by 2020 national distributed power system installed capacity will reach 50 million kilowatts, the development of distributed power is unstoppable. Common distributed power solar photovoltaic, wind power, microturbines, fuel cells. The because of distributed PV is clean, unlimited, without geographical restrictions, operation and maintenance of a small amount, and many little, more and more attention. In recent years, the rapid development of distributed photovoltaic power generation, wind power generation has gone beyond to become the fastest growing clean energy. By the end of 2013, the global distributed PV is about 92 GW, accounting for 48% of the total amount of distributed generation, and come out on top of world in the field of distributed energy. Early China has promulgated the "Golden Sun Demonstration Project", "Solar Roofs Plan" and so on, measures for the development of distributed power in 2014, and net of cumulative PV installed capacity of 28.05 million kilowatts, an increase of 60%, of which 23.38 million photovoltaic power plants kilowatts, distributed 4.67 million kilowatts. PV generating about 25 billion kwh, an increase of over 200%. In 2020, if the existing and new buildings in China, 10% of the roof area and 15% of the facade area can be used in photovoltaic power generation, distributed PV could reach 1000 GW.Microgrid is a new technologies based on distributed generation under the circumstances of new energy resource generation. It is a kind of advanced "miniature" power system technology management system.The use of micro grid obviously enhance the scale of access of distributed power supply, greatly improve the reliability of power supply, Promote the flexible and interactive smart power technology and power grid coordination operation technology development, has become a hot topic of research in the world. At present, many countries and regions continue to explore application of micro grid technology, construction of microgrid is the implementation of the project, access to a large number of results, and accumulated valuable experience. The EU 5th Framework Programme and the Sixth Framework Programme Project of dispersed micro source grid connected, micro grid and distribution network connection, micro coordination management of network and distribution network, micro grid on the grid influence of a large number of studies. United States to solve the multiple micro network technical difficulties and the establishment of a set of control, protection and energy management in one of the large scale micro grid platform, in Vermont and also completed the construction of rural micro grid demonstration area. At present, the development of micro grid growing, Many countries including China, but also the construction of a number of demonstration projects, and achieved certain results. With the rise of PV installed capacity, the instability of a single photovoltaic power generation system, the lower energy density, power adjustable gradually reflected poor shortcomings, obstacles and restrictions on the photovoltaic power generation is also growing. In order to ensure the healthy development of photovoltaic power generation, solar protection can provide stable power supply for large-scale proposed photovoltaic micro-grid solutions. Since the concept of micro-grid power generation system is that the power supply and the load placed in the same area, therefore, particularly suitable for low energy density of new energy photovoltaic power generation and other distributed generation. Meanwhile, take a variety of micro-grid power supply in the form of internal high reliability supply, PV can be completely overcome the weaknesses of instability, fully promote large-scale photovoltaic power generation access. After the grid inverter connected via distributed between PV and micro-grid and grid-connected inverter features have been digging and affirmed its beneficial effects, but still can not ignore the challenges of large number of distributed photovoltaic access to micro-grid safe and stable operation. Existing distributed micro-grid photovoltaic grid-connected inverters using conventional grid strategy, fast response, almost no moment of inertia, it is difficult to adjust to participate in the grid can not provide the necessary voltage and frequency support for photovoltaic micro-grid, will not be able to stabilize relatively poor micro-grid to provide the necessary damping effect, the lack of a valid and micro-network "synchronize" mechanism.Synchronous generator inertia and VVVF control characteristics is helpful to improve the stability of power grid. If the grid connected inverter of distributed power supply from the external characteristic simulation part or simulated synchronous generator rotational inertia and adjusting the frequency and the voltage control characteristic, can improve the stability of the distributed system. Based on this idea, there has been introduced in grid-connected inverter power similar to the outer ring of the voltage and frequency droop characteristics of synchronous generator, to get the grid inverter droop control strategy. Virtual synchronous generator technology refers to learn mechanical equations and electromagnetic equations synchronous generator to control the grid inverters and inverter makes the mechanism and the external characteristics can be comparable with the synchronous generator, which is particularly suitable for connected to the storage function with distributed between PV and micro-grid, is expected to play an important role in the future of photovoltaic micro-grid.This paper gets financial aid from the item of "based on virtual synchronous generator distributed power grid key technology research"(project number 50907060),which belongs to the project of national "One Thousand People Plan", and the National 863 high technology project "containing microgrid key technology research"(Project No. 2011AA05A107) funding, and gains some valuable research results on key technologies applicable on PV virtual synchronous generator system of micro-grid. The conclutions achieved are mainly as the following aspects:(1) Optimize the theory of virtual synchronous generator system analysis framework, and put forward a complete virtual synchronous generator control strategy to realize the control of the process of virtual synchronous generator power of the phase. On the basic functions of the virtual synchronous motor on the basis of the research, analysis of the tuning method based on optimal quadratic system tuning of key parameters can be accurate simulation of the synchronous generator inertia and damping, ensure the virtual synchronous generator output active and reactive power agree with the traditional synchronous generator in the dynamic process of oscillation characteristics. Based on an enhanced phase-locked loop(PLL) pre synchronization control strategy and improve the grid voltage distortion in the precision of PLL, avoid the grid voltage over zero distortion and LC filter parameter tolerance influence on control effect, can effectively guarantee the grid synchronization inverter output voltage, frequency, amplitude and phase can no static error tracking of grid voltage, so as to effectively reduce the impact of grid connected current is studied. Design the virtual synchronous generator system based on independent midline module, inverter synchronous increase independent line module, using double loop control, voltage outer loop using bipolar double zero adjustment, implementation of virtual synchronous generator of three-phase four wire system to supply the power and unbalanced neutral current control. And for the photovoltaic micro grid islanded and grid connected operation mode and handover process design the control strategy, enable virtual synchronous generator with grid connected and islanded mode operation mode.(2)Aiming at the intermittent and instability of distributed PV caused by virtual synchronous generator system DC bus voltage deviation, this paper proposes the use of bi-directional DC-DC converter as the energy storage system and the DC bus of the intermediate links, to control the power flow between them. Detailed analysis of the synchronous machine is suitable for virtual bi-directional DC converter, elaborated based on the triple transformation half interleaved topology and complementary PWM modulation toward the control strategy, based on the actual situation of photovoltaic cells and batteries, a wide range of proposed bus voltage control strategy. Experimental verification of the performance benefits of bi-directional DC converter, on the one hand, virtual synchronous generator to provide a stable DC bus voltage; on the other hand, to achieve the energy storage battery charge and discharge management to ensure reliable and efficient storage batteries can be stored and release energy.(3) Design an improved synchronous inverter model. The the large disturbance in the process of the grid is not considered in former thesis, the paper conduct an complementary research on the characteristics of virtual synchronous generator during disturbance. Further analysis of the virtual synchronous generator dynamic process demonstrated performance., by constructing a virtual excitation controllers, governor and SG characteristic simulation unit, and the terminal voltage of the component is introduced dual closed-loop PI controller such synchronous inverter only in steady, And in the three-phase short-side, the pressure-side electricity dq mutations can process large disturbance and consistent with the parameters of the SG has a dynamic response. And in Matlab / Simulink simulation environment to verify the effectiveness of the control strategy, to fully simulate synchronous generators, photovoltaic micro-grid helps to study the stability of the grid reference of stability analysis. More importantly, you can further develop contains micro-grid stability analysis multiple inverters, micro-computing network protection, research and other aspects of electric vehicle charging inverter-based synchronization.(4)Design a virtual synchronous generator synchronous inverter core device. Two aspects of the design from the hardware part of the main circuit parameter design and software components control parameters were introduced, and the main circuit and control parameters for design simulation and experimental analysis. For three-phase four-leg inverter topology synchronization, the hardware design of the output LCL filter parameters, independent middle inductance parameter, the power switch, the driver circuit protection circuitry, digital control chips. Software section analyzes the sagging coefficient Dp and Dq, inertia coefficient J and K design. The use of saber software simulated the steady-state and transient of 10 kW synchronous inverter prototype phase operating characteristics.
Keywords/Search Tags:Photovoltaic micro grid, distributed generation, virtual synchronous generator, pre-synchronization
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