Calculate DC bus voltage, inverter average output voltage, or modulation index difference from any two values and units for inverter calculations.

Inverter Voltage Calculator

Enter any two values to calculate the third. (For typical PWM duty/modulation values, dm is usually between -1 and +1.)

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Inverter Voltage Formula

The following formula is used to calculate the inverter’s average (line-to-line) output voltage for a simple two-leg PWM inverter / H-bridge model, where dm represents the difference between the two legs’ modulation indices (or duty ratios).

VI = Vdc * dm

Variables:

  • Where VI  is the inverter voltage (volts), interpreted here as the average differential output voltage
  • Vdc is the DC bus voltage (volts) 
  • dm is the difference in modulation indices (dimensionless), typically dm = dA − dB (often between −1 and +1)

To calculate this inverter voltage, multiply the DC bus voltage by the difference in modulation indices. (Note: other definitions of “inverter voltage” such as AC fundamental RMS require different formulas and scaling factors.)

How to Calculate Inverter Voltage?

The following example problem outlines how to calculate the Inverter Voltage.

Example Problem #1:

  1. First, determine the DC bus voltage (volts). In this example, the DC bus voltage (volts) is measured to be 95.
  2. Next, determine the difference in modulation indices. For this problem, the difference in modulation indices is calculated to be .45.
  3. Finally, calculate the Inverter Voltage using the formula above: 

VI = Vdc * dm

Inserting the values from above and solving the equation with the input values gives: 

VI = 95 * .45 = 42.75 (volts)

FAQ

What is the significance of the DC bus voltage in an inverter’s operation?

The DC bus voltage is the inverter’s DC supply and sets the maximum possible output voltage magnitude (along with the modulation strategy and load). In general, a higher DC bus voltage allows a higher achievable output voltage for the same modulation settings.

How does the difference in modulation indices affect inverter voltage?

In this simplified model, the average output voltage is proportional to dm. Increasing the magnitude of dm increases the output voltage magnitude, and the sign of dm determines the output polarity.

Can the formula for calculating inverter voltage be applied to any type of inverter?

No. This relationship is a simplified average-voltage model (often used when thinking in terms of PWM duty/modulation and DC-equivalent output). Many practical cases—especially where “inverter voltage” means the AC fundamental (phase vs line-to-line, peak vs RMS, SPWM vs SVPWM, and topology)—use different formulas and scaling factors.