Inverter for driving 3 phase motors

[marifhossain]

dead time inverter mosfet controls

I designed a three phase inverter for a 48 volt 3 phase ac motor. What I did was I designed a small chopper for generating 4 slit power supplies. One split supply for the lower three IGBTs of the Three Phase MOSFET/IGBT bridge and the other three for the three high side IGBTs. I used AT89c2051 for generating the pulses for driving the high side and low side IGBTs and used PWM algorithm.

But one problem was there and a very nasty one was Shoot-through. MOSFETS/IGBTs bursted and short circuited the DC power source at the moment of starting the motor. I suspect that the problem was at the Microcontroller outputs of the AT89c2059 which are all 1 at the begining. So what I did was installed a Relay before the inverter line. The control circuit was enegised first and stable pulses was started and after a small delay time (1 sec or 2) the relay started and gave power to the inverter. This improved the stability of the circuit a lot and only once in a hundred times the IGBTs gone after that. But still I could not make it 100% ok.
I believe the Microcontroller "Hangs" while the Motor starts and takes heavy loads.

Now I want to design 400 volt inverter. But before that I would like to have some comments. If anyone of you have block diagrams or complete circuit diagram of any professional frequency inverter?

I am a microcontroller programmer and I can program SPWM algorithm to it but I need my inverter power circuit to be stable first. Any help from professional inverter designers?

 

[IanP]

400 volt 3 phase inverter

Some comments on power-on reset:
I assume you use proper, external POR circuit that gives you ≈0.2-0.5s reset pulse.
During this time the MOSFET drivers should be disabled. First thing you do after initialization of the microcontroller is to set one of its I/O pins LOW and make AND function of RESET and this pin to still maintain disable stage on the MOSFET drivers. In the meantime the CPU stabilizes and for the time being the drivers remain disabled.
Then the CPU releases the disable line and the inverter can start its operation.

Also, I hope that you implemented ramping algorithms so from a motor point of view starting looks like a "soft" start. This prevents hugh power surges on the supply line(s) which can cause the CPU to "hang up".

Next thing is to provide good isolation (optical) between control unit and drivers, and in many cases dc-dc converter, or dedicated low-power-step-down transformer just to supply the control circuitry (CPU, ....).

Maybe my post is not coherent, and I elaborated on different issues, but this is what have gone through my mind when I first read your story..

 

[marifhossain]

3 phase ac motors using inverter power supply

Thanks for your reply. Your informations will surely help me.

Can you help me finding some proffesional inverter schematics and circuit diagrams?

I am a microcontroller programmer for a long time and I will be able to take care of the SPWM and soft start algorithm. But I need my Power circuits to be stable first.

Thanks in advance.

 

[marie65]

three or 3 phase motor inverter schematic

Try this apps from freescale (former motorola)
**broken link removed**
**broken link removed**
**broken link removed**

and you can find many others at https://www.freescale.com/webapp/sp...046&Device=All&DocTypeKey=10KscRcb&Results=25

 

[Mesut_yigit]

simple algorithm three phase inverter

Recently I made a similar circuit for 280 Volt AC induction motor.

I came across the same conduction of low and high sides of IGBT driver at the same time problem.

In my circuit , IGBT block was actuating with Logic 0 applied to gates. I was using just upper side PWM. I put 3 gates of 74HCT32 NOR gate between the IGBT and upper PWM inputs of IGBT block. The second inputs of Nor gates was tied together as an enable pin and connected to a PIN of my PIC microcontroller. During the power up or , motor Idle , I was disabling the outputs to prevent IGBTS burning.
In your case you must use an AND gate to block control signals when unnecessary.

The most important thing yo have to consider is the "Dead time" of IGBTs. When you cut the drive signal , an IGBT does not turn off immediately. If you switch on the lower IGBT of the same phase output , immediately after its upper counterpart, due to dead time , that branch becomes short and burns IGBT(s). You must wait a proper time to drive the IGBTs of the same phase. This time is typically around 20 us. but you must check the data sheets.

Same problem happens generally with the edge aligned PWM scheme. If you are using HW PWM, check if your UC has center aligned PWM possibility.

The last point : Use a suitable ramp before the motor reach the full current. If it reach the full current without no movement , IGBTS will suffer from the exceeding currents. You must consider to put an current sense circuit over the IGBT bridge. This both helps you to protect IGBTs and implement the advanced possibilities like semi vector control , or optimised curves for start and stop ramps.

Using proper gate insulation will also defeats many problems which glitches and noises may disturb your drive system.

Strong pull ups / pull downs will also improve the noise immunity.

 

[marifhossain]

three phase inverters motor pwm

Thanks marie65 and Mesut for sharing.

Actually I was thinking that instead of using AND, NOR and other gate combination, GALs or PALs will reduce number of chips and also noise problems.

I am lloking for good documentations for Vector Control Mechanim. What is Vector Control? Where is it used and why?

 

[ogunyemi]

what is 3 phase idler motor

Please, I want to design 1kva 3-phase inverter using mosfet. I need advice on how best to go about it and the complete circuit diagram.

 

[mnn77]

hello...marifhossain
can u help me to to generate spwm for 1 phase full wave with AT89C2051-24PI???