Inverter-Motor

In general, the rated voltage of the output appliance needs to equal or exceed the supply input voltage. Further details may be found in the inverter manufacturer's application data.

The output AC voltage would be in proportion to the output frequency, subjected to the maximum input voltage.

Inverters, plus rectifiers for DC, can be designed to convert from any voltage, AC or DC, to any other voltage, also AC or DC, at any desired frequency. The output power can never exceed the input power, but efficiencies can be high, with a small proportion of the power dissipated as waste heat.

Maximum inverter output voltage is a function of the DC bus voltage. Essentially, the RMS inverter output voltage is limited to DC bus voltage x 0.7072. For a motor requiring, for example, 380V at 50Hz, the DC bus voltage needs to be not less than 537V. It can be higher, but not (significantly) lower.

Within limits - yes. The inverter can run motors of the same voltage as the 3 phase input down to about 1/4 voltage. Lower voltage motors may cause problems with insulation breakdown if they are of old design as the inverter "pulses" quite high voltage even though the "RMS" is carefully controlled.

When you set up the inverter, you will have to enter the nominal motor voltage with a few other parameters.

Thank you for the comments. But what i m asking is that the inverter specifies only input voltage dc, Max 2min RMS current and rated power, nothing about "ac output voltage". If i need to connect a device of a particular voltage, how can i know whether the inverter is suitable for it?

for eg: if the inverter is of 48VDC input , 200A (RMS) max, 10KVA and i want to connect an induction motor of 400Vac 3 phase with 5KW power.As you can see here inverter doesnt specifies whether it is for a 400VAC output? Is it related to the power between the inverter and the motor? i m not sure please help me with this.....

Dear Sujinvipin,

output voltage is supposed to be the mains voltage where the inverter is sold. Probably 230 V in your case, hence 400 V phase-to-phase (check motor windings and how voltage is specified - star or delta? What is the starting system?). Voltage is not power dependent.

kbaker, max rms ouptut voltage can reach DCbus x 0.8166 (less the voltage drops on the IGBTs).

brgds

Snel

Reading the manual would help.

Is it possible to connect a 50Vac induction motor?

By the way can you please explain about the specification of

19/33V delta/wye (connected in wye) and 33/57V delta/wye (connected in delta) i didnt understand clearly.

The inverter will give you some defined voltage. If you need a different voltage, you may use a transformer (with heavy duty insulation to whitstand the weird waveform you get from an inverter).

brgds

Snel

You can connect a 50 Vac motor, but the output power will we lower

I guess only 43% of the original output power.

Inverter specification as i have given indicates 2 min max RMS current,does it mean the current it delivers at starting for 2min and then return to normal. in case of induction motors connected to the inverter output , does this mean starting or locked rotor current ?

If the inverter is capable to deliver 200 A rms during 2 min, and there is no additional information like S2 - 2 min or S6 - 20% Then I would use this inverter only during maximum 2 minutes.

Depending on the actual mechanical load of the connected motor, this motor will need less of more current. This current has to be supplied by the inverter.

The internal temperature of the inverter will rise as a result of inefficiencies. This temperature rise will limit the number of practical applications.

You can use this inverter for an application that only needs power during a short time, like an door opener that moves the heavy door only in the morning to open the gate and in the evening to close the gate.

It can only deliver power during 2 minutes, and when is delivers power, the output current must be limited to max 200 A rms.

I hope you see the difference between an application that has a 20 % duty cycle or an application with a 100% duty cycle.

100% duty cycle indicates continuous use, like a pump that runs for hours.

You bet you can, don't forget to wear your PPE..

No you cant connect to any voltage.The inverter manufacturer must have specifications for the output voltages and power.Check for the output voltage and power rating in the manual,or supply the input and measure the output voltage for single or three phase.You should contact the manufacturer as well to be sure.Avoid making wrong connections that may damage the inverter or your load.

Patrick whowha

Rudy.leurs,

In an inverter specification i have seen, Peak current= 450A rms(2min) , Boost current= 540A(10sec) & continues current=180Arms(60sec),

So according to this data, doesnt it mean that the peak or max current is just happening at the initial start up, just as i told previously as Starting current ?

Secondly, can you tell me what is "Boost current" ?

Boost current or boost as used in an inverter is the possibility to allow a larger current than normally suspected at low speed.

At low speed, the drives output voltage is also low. (the ratio Voltage / frequency must be kept constant.)

But this low voltage is devided over

• the ohmic resistance of the motor windings and the ohmic resistance of the supply leads between motor and inverter
• the rest of the voltage is used to create magnetic flux (which results in torque)

Because the voltage over supply leads and motor winding is almost constant, there is almost no voltage left over to create torque.

With the boost function you can increase the output voltage to overcome this fysical problem.

In your example, boost current = 540A (10 sec) , you have to be sure that acceleration has finished before the 10 seconds are passed. Additionally, you can increase the output voltage during boost which results in an higher current and motor torque. The limit will be 540 A

After start up, you current must decrease to maximum 180 A rms and the drive must be switched off within 60 seconds.

Keep in mind that this means that you can not drive a load for a longer time than one minute.

Everybody is guessing in circles now. Please provide a URL to YOUR invertor's specifications so that some science can be applied to obtaining an answer for you.