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Difference between On Grid Inverter and Off Grid Inverter

This article will introduce on grid inverters and off grid inverters, discuss the working principles of off grid inverters and on grid inverters, as well as their differences.

Inverter Basics

Inverter refers to a device that converts DC power (such as storage battery) into AC power (usually 220V, 50Hz sine wave). It is composed of inverter bridge, control logic and filter circuit. Inverters are widely used in air conditioners, home theaters, electric grinding wheels, electric tools, sewing machines, DVD, VCD, computers, TVs, washing machines, range hoods, refrigerators, video recorders, massagers, fans, lighting and other fields. When working or traveling, the inverter can be connected to the battery to drive the electrical appliances and various tools to work. By the cigarette lighter, a car power inverter outputs continuous power of 40W, 75W, 120W, 150W to 300W. The more powerful inverter power supply should be connected to the battery through the connecting wire. Various electrical appliances can be used in the car by connecting household appliances to the output of the power converter.

On Grid Inverter Basics

On grid inverters are also called grid tie inverters, which are generally divided into solar PV power generation on grid inverters, wind power generation grid tie inverters, power equipment generation on grid inverters, and other equipment generation grid tie inverters. The biggest advantage of on grid inverter is the high power and low cost of the system.

Schematic diagram of on grid inverter

Grid tie inverters are generally used in the system of large-scale solar photovoltaic power stations. Many parallel photovoltaic strings are connected to the DC input of the same centralized inverter. Generally, three-phase IGBT power modules are used for higher power, and field effect transistors are used for lower power. At the same time, it uses a DSP conversion controller to improve the quality of the generated power, making it very close to a sine wave current.

Off Grid Inverter Basics

The off grid inverter can work independently after leaving the grid, which is equivalent to forming an independent small grid. It mainly controls its own voltage and can be regarded as a voltage source. Off grid inverters can carry loads such as resistance-capacitive and motor-inductive loads. It has fast response, anti-interference, strong adaptability and practicability, so it is the preferred power product for emergency power supply and outdoor power supply.

Schematic diagram of off-grid inverter

Generally, off grid inverters need to be connected to batteries, because its PV power generation is unstable, and the load is also unstable, requiring batteries to balance energy. When the photovoltaic power generation is greater than the load, the excess energy charges the battery. When the photovoltaic power generation is less than the load, the insufficient energy is provided by the battery.

How does an on grid inverter work in an off-grid manner?

Sometimes, an on grid inverter can be used directly as an off-grid inverter.

Grid tie inverter sends energy directly to the grid, so the frequency and phase of the grid must be tracked. It is equivalent to a current source. Of course, there are also some inverters that have low voltage ride-through capability and can be used for PQ adjustment.

Off grid inverter is equivalent to building an independent small power grid by itself. It mainly controls its own voltage, but in fact it is a voltage source.

On grid inverter does not require energy storage, but its energy cannot be controlled. As much energy as photovoltaic generates, it sends as much energy to the grid. Off grid inverters generally require energy storage and do not send energy to the grid, and the grid has no right to interfere.

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