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Grid-Connected Power Inverter

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What are the design issues that I should pay attention when construct a Grid-Connected Power Inverter so that the inverter can be connected to power grid without problem? Thanks.
 

These are also called offline. Search for this keyword. In general this is a very old technology with the optimum solutions known. There are commercial encapsulated modules available.

First the line is rectified to produce 200 V DC or so. There are modules that sense the line voltage and change the rectifier configuration for 100 V or 200 V lines.

Then this 200 V is sent to a switching circuit that produces the desired output voltage.

There are special power factor correction modules also available. For commercially sold supplies these are required by law in some countries for supplies over a certain power level which I vaguely remember as 100 W.
 

My colleague constructed one 3-phase grid connected power inverter. However, when he tested the module in lab, the main switchboard was tripped. Is it because of synchronization problem? Thanks.
 

You should contact your local Power distribution company for conditions/permission to do that.
You should pay attention also to power flow in distribution network (+ synchronisation) in order to keep your inverter in normal mode (not overloaded).
REgards.
 

synchronization how ? use analog zero cross detect pll or anything else
 
If I got you ok, you want to connect the output of your inverter to the grid supply?

Then, 2 problems couols occur:
1. You need full synchronisation with the grid supply,
2. There must not be enough voltage difference between the inverter and grid supply, actually they have to be the same or u must be slightly higher in order to supply power to the grid.

Difficult tasks, both.
 

i want to design analog 3 phase grid tie inverter without using micro processor...

so..i got one question here
grid tie inverter usually use local oscillator with the same freq as the grid which is 60hz or 50hz in order to produce pwm right?
can i just substitute local oscillator with the feed from the grid instead.. where 240v step down to 12v(50hz) then compare with triangular wave 15v(60khz) in order to produce pwm.. ?
 

yes you can. in fact, this is exactly how my first grid tied project was done. i can not say if it is ALLOWED to be done this way (IEEE standard) but technically speaking it is surely possible.

but be aware that when the grid varies (or is not available) your converter will get messed up results.

personally.. i'm not convinced that it is the prefered way to go due to possible failure modes. but that's my opinion. i have no idea how the industry people are doing it.

Mr.Cool
 
thanks for your reply mr cool.. here another ques... hope someone can give me some suggestion.. base on my project which is fully analog three phase grid tie inverter... how can i design pure three phase sine wave at 50hz [somewhat like 3 phase oscillator] without relying on the grid, microcontroller or dsp... i want use this sine wave for generate pwm.

i try use phase shift circuit where i can get 3 phase sine wave with 120 degree phase differ to each other... the problem is the magnitude of each sinewave are differ due to the voltage drop.. where it can't be use to compare with triangular wave to produce pwm....
 

Basically, you can synthesize the 3 phase reference voltages from a quadrature (0 and 90°) oszillator, which is also the standard method in a digital inverter controller. But for a grid tied inverter, the reference voltage must be phase locked to the grid, so you can't use a free running oszillator. If you want to have your reference system independant of the actual grid voltage and possibly distorted waveform, a PLL is an option. To track the grid voltage and clean the waveform, use a bandpass.

I don't understand your problem with phase shift, a second order allpass is a very simple circuit, that allows an 0 - 180° variable phase shift and by design exactly reproduces the input magnitude.
 

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