solar inverter

INVERTER 

what is solar power inverter?

In electrical systems,current has different types they are,

• Direct current (DC): Current always flows in the same direction between those two terminals.

•  Alternating current(AC): The direction of the current reverses, or alternates, 60 times per second or 50 times per second

 How do solar inverter works?

By connecting the DC system to input part, AC power is obtained from the output part.Solar inverters are composed of two different units: 

•  Convert Unit: Here, the voltage comes as DC to the system and is converted into AC by means of MOSFET and other electronic components.

By switching alternating MOSFET we mean, when the first signal is positive, the second signal will be negative and when the first signal becomes negative, the second signal becomes positive.This process is periodically and get AC output. 

• Amplifier Unit: Transformers are electrical components that are used to increase or decrease the AC values on the grid.

for example:there is a system connected to the input of the transformer which is 200V,4A but 1000V voltage is required from the output. What is the output current?

P (power) = I (current) x V (Voltage)
P-input = 200 x 4 = 800W
P-out = 1000 x (I-out)
800 = 1000 x (I-out)
I-out = 0.8A

In the picture below, you can see how a transformer unit works and turns ratio

 

Types of Solar Panel Power Inverters

There are two different power inverter types according to the grid connections:

• stand alone(off-grid)inverter:They are the inverters that work separately from the grid. Electronic devices are connected to the inverter output directly. The main reason why they work separately from the grid is because there is no hardware that would enable them to work synchronously with the grid.

Stand-Alone inverters have DC input and AC output units. Output wave doesn't necessarily have to be full sine. 

• Grid-tie(synchronous)inverter:These are the inverters that are connected to the grid. The grid tie inverter must synchronize its frequency with that of the grid (e.g. 50 or 60 Hz) using a local oscillator and limit the voltage to no higher than the grid voltage.In the picture below you can see grid-tie power inverter connection.Grid-tie inverters are also designed to quickly disconnect from the grid if the utility grid goes down,the grid tie inverter will shut down to prevent the energy it transfers from harming any line workers who are sent to fix the power grid. You can find grid tie inverters in the market with more power and voltage options. It is a more commonly used product.Grid tie inverter having galvanic isolation and Maximum power point tracking(MPPT).

Working principle of Grid tie inverter:
 
DC to DC converter: The input voltage is first raised by the boost converter formed with inductor L1, MOSFET Q1, diode D1 and capacitor C2.By switching of Power MOSFET Q2-Q5 ,Q3-Q4 alternatively at the periodic time get isolating converted output DC voltage.T1 can be a so-called step-up type to amplify the input voltage
DC to AC converter:conversion stage turns DC into AC by using another full bridge converter. It consists of IGBT Q6-Q9 and LC-filter L3, C4.The IGBTs Q6-Q7,Q8-Q9 work as electronic switches that operate in PWM mode. This topology requires anti-parallel freewheeling diodes to provide an alternate path for the current when the switches are off. These diodes are either included within IGBTs or added externally.Solar panels provide different power in different points of their volt-ampere (V-I) characteristic. The point in the V-I curve where output power is maximum is called maximum power point (MPP). The solar inverter must assure that the PV modules are operated near their MPP. This is accomplished with a special control circuit in the first conversion stage called MPP tracker (MPPT).