SLAA517F May   2012  – August 2021 MSP430F6720A , MSP430F6720A , MSP430F6721A , MSP430F6721A , MSP430F6723A , MSP430F6723A , MSP430F6724A , MSP430F6724A , MSP430F6725A , MSP430F6725A , MSP430F6726A , MSP430F6726A , MSP430F6730A , MSP430F6730A , MSP430F6731A , MSP430F6731A , MSP430F6733A , MSP430F6733A , MSP430F6734A , MSP430F6734A , MSP430F6735A , MSP430F6735A , MSP430F6736 , MSP430F6736 , MSP430F6736A , MSP430F6736A

 

  1.   Trademarks
  2. 1Introduction
  3. 2System Diagrams
  4. 3Hardware Implementation
    1. 3.1 Power Supply
      1. 3.1.1 Resistor Capacitor (RC) Power Supply
    2. 3.2 Analog Inputs
      1. 3.2.1 Voltage Inputs
      2. 3.2.2 Current Inputs
  5. 4Software Implementation
    1. 4.1 Peripherals Setup
      1. 4.1.1 SD24 Setup
    2. 4.2 Foreground Process
      1. 4.2.1 Formulas
        1. 4.2.1.1 Voltage and Current
        2. 4.2.1.2 Power and Energy
    3. 4.3 Background Process
      1. 4.3.1 Voltage and Current Signals
      2. 4.3.2 Phase Compensation
      3. 4.3.3 Frequency Measurement and Cycle Tracking
      4. 4.3.4 LED Pulse Generation
  6. 5Energy Meter Demo
    1. 5.1 EVM Overview
      1. 5.1.1 Connections to the Test Setup for AC Voltages
      2. 5.1.2 Power Supply Options and Jumper Settings
    2. 5.2 Loading the Example Code
      1. 5.2.1 Opening the Project
  7. 6Results and Calibration
    1. 6.1 Viewing Results
    2. 6.2 Calibrating the Meter
      1. 6.2.1 Gain Correction
      2. 6.2.2 Phase Correction
      3. 6.2.3 Metrology Results
  8. 7References
  9. 8Schematics
  10. 9Revision History

4.2.1.2 Power and Energy

Power and energy are calculated for a frame’s worth of active and reactive energy samples. These samples are phase corrected and passed on to the foreground process that uses the number of samples (sample count) and use the formulas listed below to calculate total active and reactive powers.

Equation 3. P ACT =Kp× ∑ n=1 Sample count v(n)×i(n) Sample count
Equation 4. P REACT =Kp× ∑ n=1 Sample count v 90 (n)×i(n) Sample count

Where,

  • v90 (n) = Voltage sample at a sample instant ‘n’ shifted by 90°
  • Kp = Scaling factor for power

The consumed energy is then calculated based on the active power value for each frame in similar way as the energy pulses are generated in the background process except that:

Equation 5. E ACT =P ACT ×Sample count

For reactive energy, the 90° phase shift approach is used for two reasons:

  • This allows us to measure the reactive power accurately down to very small currents.
  • This conforms to international specified measurement method.

Because the frequency of the mains varies, it is important to first measure the mains frequency accurately and then phase shift the voltage samples accordingly. This is discussed in Section 4.3.3.

The phase shift consists of an integer part and a fractional part, the integer part is realized by providing an N samples delay. The fractional part is realized by a fractional delay filter (refer to: Phase compensation).