Detailed explanation of the design and implementation of a 600W sine wave inverter (Part 2)

1.SPWM main chip

2. Main transformer

The main transformer is the key to the success of the inverter . The magnetic core used in the main transformer of this machine is EE55 , made of PC40. I bought a high-quality skeleton in Hangzhou Electronic Market, vertical, with 11 plus 11 feet and 1.2MM feet. Winding data: primary 2T plus 2T, using 10 0.93 wires. The total area of ​​the primary wire is 6.8 square MM, and the secondary is a 0.93 wire, wound with 60T.

C) Continue to wind the high voltage winding and complete the other 30 turns. It is important to note that the winding direction of these 30 turns should be the same as the inner 30 turns. If one layer cannot be wound, wind the remaining turns in another layer.

D) After winding the high-voltage winding, wrap it with three layers of high-temperature tape, and then fold down the wire ends of the low-voltage winding that were originally left on it (see Figure 3), ready to be welded to the legs of the frame. Paint stripping can be used to remove the paint. Use a cotton swab to dip a little paint stripping agent and apply it to the wire ends. After a while, the paint will fall off and you can weld it.

E), and then wrap the entire winding with several layers of high-temperature tape. The appearance of the wound wire package should be full and smooth.

F), now you can insert the core. Before inserting the core, you need to clean the joint surface of the core. I use tape to stick it a few times to clean all the powder on the joint surface of the core. Insert the core and tighten it with tape. If conditions permit, use glue to fix the joint of the core.

I found that the leakage inductance of transformers wound in this way is relatively small. In the past, when winding with copper tape, the leakage inductance was generally above 0.8uH, but now it can be below 0.4uH. I think the reason is: because the copper tape needs to be soldered to the lead-out wire, a tin pile is left, and when winding the high-voltage winding, there is a gap in the middle, resulting in loose coupling. The figure below is a schematic diagram of the leakage inductance test.

If conditions permit, a withstand voltage test must be done. The insulation of any low-voltage winding to the high-voltage winding must be above 1500V so that it can be used with confidence.

3. AC output filter magnetic ring

For a pure hand-made hobbyist like me, winding this magnetic ring is also a headache.

The magnetic ring is a 40MM diameter iron silicon aluminum magnetic ring. A 1.18 wire is used to wind 90 turns on it. The wire length is about 4.5 meters. If a magnetic ring with a magnetic permeability of 125 is used, the inductance is about 1.5mH. If a magnetic ring with a magnetic permeability of 90 is used, the inductance is about 1mH. I have done experiments and used two such magnetic rings. Each inductance is above 0.7mH and it can work normally. There are two layers when winding. The first layer is 45 turns. Because the circumference of the outer and inner rings of the magnetic ring is different, when winding the first layer, the wires of the inner ring should be arranged closely, and the wires of the outer ring should leave a gap between each turn. When winding the second layer, the inner ring is stacked on the first layer of wires, and the outer ring is embedded in the gap of the first layer of wires. Only in this way can the coil look good. Of course, it seems that whether it looks good or not does not affect the use. The following is the online store where I bought the magnetic ring on Taobao (no intention to advertise for the merchant, just to facilitate friends to purchase). Note that you must wear gloves when winding this magnetic ring, otherwise the wire will cause blisters on you.