3.5.1 RMS Value

Total three kinds of RMS values can be calculated directly from the output of metrology firmware: RMS value of all harmonics, RMS value of fundamental harmonic and the RMS value of m-th harmonic.

RMS value of all harmonics and RMS value of fundamental harmonic can be calculated as following:

Where, x = [A, B, C], and:

  • K_Ix is the current conversion factor of phase x
  • K_Vx is the voltage conversion factor
  • I_xrms is the fundamental and all harmonics current RMS value
  • V_xrms is the fundamental and all harmonics voltage RMS value
  • I_x1rms is the fundamental harmonic current RMS value
  • V_x1rms is the fundamental harmonic voltage RMS value
  • N is the number of samples in the integration period
  • ACC_I_x is the accumulated fundamental and all harmonics current quantity
  • ACC_V_x is the accumulated fundamental and all harmonics voltage quantity
  • ACC_I_x_F is the accumulated fundamental harmonic current quantity
  • ACC_V_x_F is the accumulated fundamental harmonic voltage quantity
Note:
  • K_Ix and K_Vx are the register values in the metrology control registers.
  • N is the register value in the metrology status registers.
  • ACC_I_x, ACC_V_x, ACC_I_x_F and ACC_V_x_F are the register values in the metrology accumulated output quantities.

After the harmonic analysis feature is enabled, RMS value of m-th harmonic can be calculated:

Where, x = [A, B, C], and:

  • I_xm rms is the m-th harmonic current RMS value of phase x
  • V_xm rms is the m-th harmonic voltage RMS value
  • I_x_m_R is the real part of DFT for m-th harmonic current
  • I_x_m_I is the imaginary part of DFT for m-th harmonic current
  • V_x_m_R is the real part of DFT for m-th harmonic voltage
  • V_x_m_I is the imaginary part of DFT for m-th harmonic voltage
Note:
  • I_x_m_R I_x_m_I, V_x_m_R and V_x_m_I are the register values in metrology harmonic analysis output quantities
  • m is set in the register, FEATURE_CTRL1: HARMONIC_m_REQ[5:0]
  • The voltage/current RMS value is updated every one integration period. INTEGRATION_IRQ will be generated at the end of integration period and this interrupt can be used to update derived quantities.