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Inverter
The Function of the Inverter 2017-07-18 17:46:55

Generally speaking, the process of converting AC power into DC power is called rectification. The rectifier circuit is called rectifier circuit. The device of actual rectification process is called rectifier or rectifier, and the corresponding DC is converted into AC power The process known as the inverter, the circuit to complete the inverter function as the inverter circuit, the actual inverter process device called inverter equipment or inverter. PV inverter will be issued by the PV module DC into a sine wave current, access to the load or into the grid, the PV system is the core device.


PV inverter according to the use of grid-connected inverter, off-grid inverter, micro-network energy storage inverter three categories, and grid inverter according to power and use can be divided into micro-inverter, Inverter, also known as component inverter, power level 180W to 1000W, suitable for small power generation system; group string inverter Equipment, power in the 1kW to 10kW single-phase inverter for household power generation system, the network voltage of 220V, 4kW to 80kW three-phase inverter for industrial and commercial power generation system, and network voltage for the three-phase 380V. Centralized inverter and distributed inverter, power from 500kW to 1500KW, generally used in large-scale ground power plant.


Grid-connected inverter is a key component connecting the PV array and the power grid. In addition to the DC power that the component sends out into the AC power of the grid, there are the following special functions:


1. Maximum power tracking MPPT function

When the sunshine intensity and ambient temperature changes, the PV module input power exhibits a non-linear change, as shown in the figure, from the figure: the PV module is neither a constant voltage source, nor a constant current source, its power with the output voltage Change and change, and load does not matter. Its output current starts with a horizontal line as the voltage rises. When it reaches a certain power, it decreases as the voltage rises, and when it reaches the open circuit voltage of the module, the current drops to zero.


The output power of PV modules is affected by factors such as sunshine intensity and ambient temperature. When the light intensity decreases, the open circuit voltage decreases, the short circuit current decreases, the maximum output power decreases; when the PV module temperature decreases, the component short circuit current decreases, but the components of the open circuit voltage increases, the maximum output power increases ; MPPT function is the maximum power tracking function, by adjusting the DC voltage and output current, so that the solar module always work at the maximum operating point, the output of the same component Current temperature and maximum power under sunshine conditions.


The common maximum power tracking control method is CVT, the PV module terminal voltage fixed at a fixed value, is characterized by simple control, good stability; power calculation method, current optimization method, perturbation Observation method, incremental conductivity method and other classical control algorithm and the optimal gradient method, fuzzy logic control method, neural network control method and other modern control algorithm.


2. Detection and control of islanding effect

In the normal power generation, the photovoltaic grid-connected power generation system connected to the large power grid, to the power transmission power, but when the power grid, the photovoltaic grid-connected power generation system may still work, and the local load in a separate operating state, This phenomenon is called islanding effect. When the inverter has an island effect, it will be safe for personal safety, power grid operation, the inverter itself caused great security risks, so the inverter network standard, photovoltaic grid-connected inverter must have the island effect detection and control function.


The detection method of the islanding effect is passive detection and active detection. The passive detection method detects the amplitude of the voltage and current of the output of the inverter. The inverter does not add the interference signal to the grid. By detecting the current phase shift and frequency Whether the parameters exceed the specified value, to determine whether the power grid power failure; this approach is not caused by the power grid pollution, there will be no energy loss; and active detection refers to the grid inverter active, regularly imposed some interference on the power grid signal, Such as frequency movement and phase shift, because the grid can be seen as an infinite voltage source, there are power when the interference signal will be absorbed by the power grid, the power grid if the power outage, the interference signal will form a positive feedback, and ultimately the formation of frequency or Voltage exceeded, which can determine whether the island effect occurred.


Related Reading:AC hybrid DC power inverter,DC to AC pure sine wave inverter,high frequency inverter

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