Calculate motor current in amps for three-phase, single-phase, or DC motors from power and voltage with efficiency and power factor.
- All Physics Calculators
- All Electrical Calculators
- Stepper Motor Voltage Calculator
- AC Current Calculator
- Motor Startup Current Calculator
- HP to Current Calculator
Inverter Voltage Formula
The inverter voltage calculator uses the ideal average output voltage relationship between the DC bus voltage, the difference in modulation indices, and the inverter output voltage.
V_I = V_{dc} \cdot d_mTo solve for DC bus voltage:
V_{dc} = \frac{V_I}{d_m}To solve for the difference in modulation indices:
d_m = \frac{V_I}{V_{dc}}- VI = inverter voltage, or average output voltage
- Vdc = DC bus voltage supplied to the inverter
- dm = difference in modulation indices, dimensionless
Enter any two values and leave the third blank. The calculator rearranges the same formula to find the missing value. Voltage inputs can be entered in mV, V, or kV, and the calculation is performed after converting voltage values to volts.
A positive dm gives a positive average output voltage. A negative dm gives a negative average output voltage. In many PWM applications, dm is usually between -1 and +1.
Voltage Units and Modulation Index Reference
| Unit | Meaning | Equivalent in volts |
|---|---|---|
| mV | millivolt | 1 mV = 0.001 V |
| V | volt | 1 V = 1 V |
| kV | kilovolt | 1 kV = 1000 V |
| dm value | Resulting output | Example with 400 V DC bus |
|---|---|---|
| 1 | Full positive average output | 400 V |
| 0.5 | Half positive average output | 200 V |
| 0 | Zero average output | 0 V |
| -0.5 | Half negative average output | -200 V |
| -1 | Full negative average output | -400 V |
Example Calculations
Example 1: Calculate inverter voltage
You have a DC bus voltage of 600 V and a modulation index difference of 0.35.
V_I = V_{dc} \cdot d_mV_I = 600 \cdot 0.35 = 210\text{ V}The inverter average output voltage is 210 V.
Example 2: Calculate modulation index difference
You have an inverter average output voltage of -120 V and a DC bus voltage of 400 V.
d_m = \frac{V_I}{V_{dc}}d_m = \frac{-120}{400} = -0.3The difference in modulation indices is -0.3.
FAQ
Is inverter voltage the same as DC bus voltage?
No. The DC bus voltage is the input supply to the inverter. The inverter voltage in this calculator is the average output voltage determined by multiplying the DC bus voltage by dm. If dm is 0.5, the average output voltage is half of the DC bus voltage.
Can dm be negative?
Yes. A negative dm means the calculated average output voltage is negative relative to the chosen reference polarity. For example, with a 300 V DC bus and dm = -0.4, the average output voltage is -120 V.
Does this calculate RMS AC output voltage?
No. This calculator uses an average output voltage formula. It does not calculate RMS AC voltage, switching ripple, harmonic content, dead-time effects, semiconductor voltage drops, or inverter losses.
