Photovoltaic energy storage hybrid system and control method thereof

Abstract

The invention discloses a photovoltaic energy storage hybrid system and a control method thereof. The photovoltaic energy storage hybrid system includes a photovoltaic power generation device, an energy storage device, a DC bus, a first DC / DC converter, a first controller for controlling the output of the first DC / DC converter, a second DC / DC converter arranged between the energy storage device and the DC bus, a second controller for controlling the second DC / DC converter in order to stabilize a DC bus voltage, a DC / AC converter arranged between the DC bus and the tail end of a distribution network, and a third controller for controlling the DC / AC converter. The second controller, by detecting the voltage applied to the DC bus and comparing the same with a preset reference voltage, controls the second DC / DC converter according to a comparison result so as to charge or discharge the energy storage device, and then restores the DC bus voltage to the reference voltage so as to stabilize the voltage at the tail end of the distribution network and greatly improve the power quality of users at the tail end of the distribution network.

Description

technical field [0001] The invention relates to the field of power quality management, in particular to a photovoltaic energy storage hybrid system and a control method thereof. Background technique [0002] For a long time, power companies have focused their research on the governance of power quality problems in medium and high voltage systems, while paying less attention to power quality problems in low-voltage distribution networks (mainly focusing on short-term voltage sags and swelling of low-voltage distribution networks (such as: DVR, UPS, etc.) issues), especially in rural low-voltage distribution networks. The terminal voltage problems of low-voltage distribution network are generally divided into high voltage and low voltage. For the high voltage problem at the end of the low distribution network, the main reasons are: 1) The extensive use of cable lines in the urban power grid; 2) The load power factor is too low; 3) A large number of distributed power sources a...

AI Technical Summary

Problems solved by technology

For the problem of high voltage at the end of the low distribution network, the main reasons are: 1) The extensive use of cable lines in the urban power grid; 2) The load power factor is too low; 3) A large number of distributed power sources are connected

The high voltage at the end will easily cause the electrical equipment to heat up, even cause equipment damage, and affect the power transmission from the grid to the load, and may cause the system to collapse.

For the low voltage problem at the end of the low distribution network, the main reasons are: 1) The power load has obvious seasonality, is scattered and far away from the power point, and the peak-to-valley difference is large; 2) The line is long, the cross-sectional area of ​​the wire is insufficient, the power supply radius is large, severe phase imbalance

The low voltage at the end will affect the normal operation of the equipment, shorten its service life, and cause great losses to both the user and the power company.

[0003] At present, the main means to solve the terminal high voltage problem are: on the one hand, manage and control the grid-connected power factor, this method requires no investment, and the effect is good, but it does not consider the reactive power of the load; on the other hand, install inductive reactive power compensation devices, such as Shunt reactors, etc., can effectively suppress overvoltage, but switching and maintenance are not very convenient, and will increase line loss under certain conditions

The control measures for the terminal low-voltage problem include: 1) Optimizing the power grid structure can improve the power quality in a large area, but requires a certain amount of investment; 2) Reactive power compensation, such as parallel connection of passive capacitors, can achieve reactive power balance and improve reactive power. Power and voltage levels, but there is no systematic capacity evaluation standard and equipment switching and maintenance are difficult, so it is difficult to apply to power grids with many nodes and complex structures; installing active power electronic devices such as SVG can realize inductive and capacitive reactive power. 3) The automatic on-load voltage regulation of the distribution transformer can carry out two-way regulation very well, the voltage regulation range is wide, the load bearing capacity is strong, and the voltage stabilization effect is relatively ideal , but requires real-time adjustment and frequent operation, which increases maintenance costs

[0004] In the field of photovoltaic systems, photovoltaic grid-connected generally adopts DC-DC-AC topology. The front-stage DC-DC converter of this structure realizes the maximum energy tracking of photovoltaic power generation devices and provides appropriate DC bus voltage by using MPPT controller. Level DC-AC converter completes grid-connected power supply, and stabilizes the intermediate DC bus flow so that all the electric energy obtained by the photovoltaic power generation device can be injected into the distribution network. The power grid provides stable and reliable power supply, but on the contrary, it will exacerbate the fluctuation of power transmission and make the problem of high and low voltage at the end of the distribution network more prominent, and the post-stage DC-AC converter is in the form of pure active energy injection, which does not have the ability to The ability of the distribution network to perform reactive power regulation

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