PV educator

The flyback inverter secondary winding acts as an unfolding stage in a grid connected scnario. The switches associated with them needs gate driver circuits. The question here is that can we consider them as a half bridge circuit so that it is possible to use a half bridge driver ic with it. To answer this consider the Fig. 1 that depicts two different types of unfolding configurations. The working although is same lets consider the one with no center tapping.

During my Ph.D. work, it was a requirement to sense the dc current on the PV side and ac current on the grid side. To sense the current I used a hall effect current sensor LTS25NP. This hall effect sensor is a bit costly however, it is excellent in working and easy to setup. Figure 1 shows this sensor. This sensor has three pins on each side and three in the front side. The three pins of left and right side should be shorted together. The output is from the front side. It should be noted that there are three pins on the front side and an arrow symbol. Arrow symbol shows the flow of current, this means that the positive terminal of the wire should be wired in harmony with the arrow direction.

IR2111 is a half bridge driver that is extensively used in power electronics.  It is an eight pin ic that works only with half bridge configuration. It can not be used individually for low side or high side driver.  Here is the schematic that i designed during my term project.

4N26 and 4N37 are cheap optocoupler that are good for most of the power electronics applications. They are six pin ic with optical isolation. The output is inverted because the output transistor works as a switch. The frequency limit of this ic is explained in this post. The following is the working circuit of optocoupler 4N26 and 4N37.

The gate driver is essential in power electronics because of two basic reasons. First, at high frequency switching applications the switching time is less which means that in order to charge/discharge the mosfet capacitance fast, more current is required. The output current of most optocouplers is not enough to drive the mosfet properly. Secondly, most of the optocoupler output is limited to under 10 V which means that they can operate a mosfet near its threshold voltage, This results in high R_ds resulting in heating the mosfet.

Click to zoom Source : http://www.nrel.gov/ncpv/images/efficiency_chart.jpg

Recently while i was having work with mofet driver ic ICL7667 i noticed that it gets hot  with the output open circuited (not connected to MOSFET). I posted my question in a linkedin group and got the following answers.

Problem : While experimenting the flyback inverter i observed a visible spark on the output of the flyback transformer.

Reason: One of the secondary winding was open possibly because of a dry solder.

Solution: Hunt for the open circuit and solder it properly.