"Addressing Voltage Drop Challenges in Inverter Circuits: Troubleshooting and Solutions

 "Troubleshooting and Solutions for Addressing Voltage Drop Challenges in Inverter Circuits

Inverter voltage drop becomes a significant problem whenever PWM is used in an inverter to enable a sine wave output, especially if the parameters are not calculated properly.

You may have seen a lot of concepts for sine wave and pure sine wave inverters employing PWM feeds or SPWM integrations on this website. The idea is excellent and gives the user the necessary sine wave equivalent outputs, but they appear to have problems with output voltage loss under load.

This post is going to show us how to fix this problem using thinking and basic math. First of all, We need to know that the power an inverter puts out depends on the voltage and current we put into the transformer. The power of the inverter really relies on the voltage and the current that we put into the transformer. So when we are using an inverter we have to think about the voltage and the current that we are putting into the transformer because this is what determines the power of the inverter. In the rest of this discussion we will try to figure out the way to solve this problem by setting things up correctly. We will be talking about inverters. How to make them work better. The inverter is the key, to solving this problem so we need to understand how the inverter works.

Square Wave Inverter Output Voltage Analysis

The waveform as illustrated below is generally seen across the power devices in a square wave inverter circuit, which delivers the current and voltage to the appropriate transformer winding in accordance with the MOSFET conduction rate utilizing this square wave: Here, we can observe that the waveform's equal ON/OFF times correspond to a peak voltage of 12V and a duty cycle of 50%.

To continue the analysis The average voltage induced across the appropriate transformer winding must first be determined. If we use a center-tap 12-0-12V/5-amp transformer and apply 12V @ 50% duty cycle to one of the 12V windings, we can determine the average voltage induced within that winding and MOSFET drain as follows: 12 x 50% = 6V

This means the transformer is getting all the power it needs, and it will give out all the power it should. because when something is using the power from the transformers, it will not lose any power. The 60 watts the transformer is using is the same as what the transformer can handle which is 12 volts times 5 amps, and that is 60 watts. So even if something that uses 60 watts of power is connected to the transformer, it will still work at its best, and the transformer will keep giving out the amount of power.

Analysing an Inverter Output Voltage Based on PWM

The power MOSFETs are already operating with a 50% duty cycle from the main oscillator, as was previously discussed. Now assume we apply a PWM chopping across the gates of the power MOSFETs, say at a rate of 50% duty cycle. The average voltage across the MOSFET gates is now reduced to: This again means that the previously computed 6V average is now additionally impacted by this PWM feed with a 50% duty cycle.

The maximum voltage is 12V. If we split 6V in half, we get 3V. There are two halves to a winding, and each half gives us an average of 3V. It is 6V if we add these two parts of the winding together. We get 30 watts of power when we use 5 amps and 6 volts. The transformer should be able to handle more power than this. We're only getting half of what the transformer can do with the 6V.

 

When the transformer isn't in use, it looks like the output voltage is 310V. The voltage can drop to 150V very quickly when we use the transformer. The average power we are putting in is half of what we think it is because the peaks of the transformer are 12V. When you multiply the 6V output of the transformers by 5 amps, you get 30 watts of power. This is what we get when we turn on the transformers at 6V.

We must simultaneously address two parameters in order to resolve this problem: Using PWM chopping, we must ensure that the transformer winding matches the average voltage value given by the source. so that the output AC does not decrease when under load, and the current of the winding must be specified properly.

Consider the case in the example above where the addition of a 50% PWM reduced the input to the winding's rating to 3V. To reinforce and address this situation, we must guarantee that the winding of the trafo is rated at 3 V as well. The transformer in this instance must therefore be rated at 3-0-3 V.

Current Transformer Specifications

Always keep in mind that in these circumstances, if the output voltage is measured without a load, one may observe an unnatural increase in the output voltage value that may appear to be greater than 600 V. The fact that the peak is always 12V even if the average value produced across the MOSFETs is 3V may explain why this occurs. However, if you chance to notice this high voltage without a load attached, there is no need to be concerned because as soon as a load is connected, the voltage will instantly drop to 220V. Having said that, if consumers find it unsettling to observe such elevated voltage levels without a load, this can be fixed by additionally implementing an output voltage regulator circuit, which I have already covered in one of my earlier postings and which you can equally successfully utilize with this idea.

As an alternative, you can neutralize the rising voltage display by connecting a 0.45uF/600V capacitor across the output or any capacitor with a rating similar to that. This will also help to filter out the PWMs and provide a sine wave with a gradually increasing frequency.

The Important Issue

In the example we talked about earlier, we saw that using a 50% PWM chopping meant we had to use a 3-0-3V transformer for a 12V supply. This meant the user had to buy a 20-amp transformer to get 60 watts, which does not make sense. If 3V needs 20 amps to make 60 watts, then 6V would need 10 amps to do the thing, and that seems like a lot less to handle. If we use 9V we can use a 6.66 amp transformer, which seems even better. The average voltage depends on how long the PWM is on. So what this means is that to get an average voltage, on the transformer we just need to turn the PWM on for a longer time. This is another way to fix the problem of the voltage dropping in PWM-based inverters. Use the comment section to tell us what you think and ask any questions you have about this subject.