Soft turn off protection during short circuit – During short circuit or heavy load, the saturation (collector) voltage of the IGBT will increase. When this voltage will increase beyond a threshold limit the gate voltage of the IGBT will be turned off smoothly through a high impedance path. This is in order to protect the IGBT from fast di/dt which will cause high fly back voltage that may damage the IGBT during turn off.

During short circuit the current through the IGBT is very high. If you suddenly turn off the IGBT during this time, the rate of change of current (di/dt) will be very high. Due to the high di/dt, the lead inductance of the IGBT itself will produce a high fly back voltage which will damage the IGBT. This cannot be protected using any external snubber or diode clamping. Hence, turning off the IGBT smoothly during short circuit is very important. This way the di/dt will be very less and there will not be any fly back voltage that can cause any damage to the IGBT.

A low cost 16 character single line LCD will be of scrolling type, showing ‘your company name’ and the status of the inverter such as batt voltage, mains voltage, and inverter output voltage, inverter standby on/off, charger on/off, mains / solar charging and many more.

It is very simple to handle and very easy to set the values in the menu driven set-up mode. In the menu driven set-up, we can see all the parameters in LCD like battery low – 21V, inverter voltage – 220V etc. By using the Up & Down keys, we can change the values. For ex: Battery low – 21V, by using the ‘Up’ key, you can increase the value to 21.2, 21.3 ….22, 23… By using the ‘down’ key you can decrease the value to 20.8, 20.7…..20, 19…If you want to set battery low at 21.4V, press the ‘enter’ key at 21.4 then this value will be fed to the memory and battery low will be set for 21.4V. There is no need of any preset. (In the conventional method of using a preset, we cannot view the set voltage, after setting the preset, we have to evaluate by varying the battery voltage and check if the battery low warning and cut is coming at the set voltage. Moreover, due to the mechanical vibrations and ageing, there are chances for the preset to shift the set position)

Single phase prevention – For loads like motor and star-delta transformers if one or more phases are missing or missing phase is linked with the other phase (for example – in a three phase connection, if the three phases are R,Y and B. If R is missing and Y is linked with R, then the result will be Y,Y,B) In such conditions, it may result in the load drawing heavy current and may cause damage of the motor / transformer. The DSP will sense these errors and cut off the mains from the output and the inverter will switch on.

In this case, the LCD will indicate faulty condition as “Single Phase” along with buzzer warning.

Phase imbalance – If all phases are correct but the voltages in each phase are imbalanced then the motor or three phase star-delta transformers will draw high current and may result in damaging.

For example: If all phase angle of R, Y, B are correct but R and Y = 230V and B = 100V, then the phase imbalance occurs.

In such conditions, the mains input will cut off from the output and the inverter will provide the supply.

In this case, the LCD will indicate faulty condition as “Phase Imbalance” along with buzzer warning.

Phase sequence error – In a three phase motor, if the connecting sequence is R-Y-B or Y-B-R or B-R-Y the motor will rotate clockwise. But, if the connecting sequence is B-Y-R or Y-R-B or R-B-Y then the motor will rotate anti-clockwise. This will cause severe problems in industries. The DSP will sense the phase sequence of the AC input, if it is reversed the mains input will cut off from the output and the inverter will provide the supply.

In this case, the LCD will indicate faulty condition as “Phase sequence error” along with buzzer warning.

User settable

- online / offline

- single phase / three phase

In the menu driven set-up, you have the option of selecting ‘online’ or ‘offline’. If you select ‘offline’ the system will work as offline inverter. If you select ‘online’ the system will lock the inverter frequency with the mains frequency so there will not be any oscillation in the output voltage because of the beat frequency between mains and inverter. You should use a separate online charger for this.

In the menu driven set-up, you have the option of selecting ‘single phase’ or ‘three phase’. If you select ‘single phase’ the system will work as single phase inverter. Then you can use only two IGBT half bridge modules and two IGBT driver boards. In this case you can take 15KVA maximum. If you select ‘three phase’ the system will work as three phase inverter. You should use three IGBT half bridge modules and three IGBT driver boards. In this case you can take 30KVA maximum.