Calculate single-phase real and reactive power
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The Power Measurement block measures the real and reactive power of an element in a single-phase network. The block outputs the power quantities for each frequency component you specify. For three-phase measurements, consider using the Three-Phase Power Measurement block.
Use this block to measure power for both sinusoidal and nonsinusoidal periodic signals.
Set the Sample time parameter to
continuous-time operation, or explicitly for discrete-time operation.
Specify a vector of all frequency components to include in the power output using the Harmonic numbers parameter:
To output the DC component, specify
To output the component corresponding to the fundamental frequency, specify
To output components corresponding to higher-order harmonics, specify
n > 1.
For each specified harmonic k, the block calculates the real power Pk and reactive power Qk from the phasor equation:
G is equal to
0.25for the DC component (k = 0) and
0.5for the AC components (k > 0).
is the phasor representation of the k-component input voltage.
is the complex conjugate of , the phasor representation of the k-component input current.
The block estimates the real-time k-component voltage and current phasors using these relationships:
In these phasor equations:
V(t) and I(t) are the input voltage and current, respectively.
T is the period of the input signal, or equivalently the inverse of its base frequency F.
If the input signals have a finite number of harmonics n, the total real power P and total reactive power Q can be calculated from their components:
The summation for Q does not include the DC component (k = 0) because this component only contributes to real power.
v — Input voltage
Voltage across element from which to measure power, in V.
i — Input current
Current through element from which to measure power, in A.
P — Real power
scalar or vector
Real power for selected frequency components, in W. If the Harmonic numbers parameter value is a scalar, this output is also a scalar.
Q — Reactive power
scalar or vector
Reactive power for selected frequency components, in var. If the Harmonic numbers parameter value is a scalar, this output is also a scalar.
Base frequency (Hz) — Fundamental frequency
60 (default) | positive number
Fundamental frequency corresponding to component k=1.
Harmonic numbers — Frequency components
[0 1 2 3] (default) | scalar or vector
Frequency components to include in the output. Specify either a scalar value corresponding to the desired component or a vector of all desired components.
The value k = 0 corresponds to the DC component.
The value k = 1 corresponds to the fundamental frequency.
Values k > 1 correspond to higher-level harmonics.
If you specify a vector, the order of the power outputs correspond to the order of this vector.
Sample time — Block sample time
0 (default) | positive number
Time between consecutive block executions. During execution, the block produces outputs and, if appropriate, updates its internal state. For more information, see What Is Sample Time? and Specify Sample Time.
For continuous operation, set this property to
0. For discrete
operation, specify the sample time explicitly as a positive number. This block does not
support inherited sample time.
If this block is in a masked subsystem, or other variant subsystem that allows either continuous and discrete operation, promote the sample time parameter. Promoting the sample time parameter ensures correct switching between the continuous and discrete implementations of the block. For more information, see Promote Block Parameters on a Mask.