Multimeter - Measure voltages and currents specified in dialog boxes of SimPowerSystems blocks

Library

Measurements

Description

The Multimeter block is used to measure voltages and currents of the measurements described by the dialog boxes of SimPowerSystems blocks.

The powerlib blocks listed in the following table have a special parameter (Measurements) that allows you to measure voltages or currents related to the block. Choosing voltages or currents through this measurement parameter is equivalent to connecting an internal voltage or current measurement block inside your blocks. The measured signals can be observed through a Multimeter block placed in your circuit.

Drag the Multimeter block into the top-level system of your circuit and double-click the icon to open the dialog box.

Block Name	Block Name
AC Current Source	PI Section Line
AC Voltage Source	Saturable Transformer
Breaker	Series RLC Branch
Controlled Current Source	Series RLC Load
Controlled Voltage Source	Surge Arrester
DC Voltage Source	Three-Level Bridge
Distributed Parameter Line	Three-Phase Harmonic Filter
Linear Transformer	Three-Phase Load (Series and Parallel)
Multi-Winding Transformer	Three-Phase Branch (Series and Parallel)
Mutual Inductance	Three-Phase Transformer (Two and Three Windings)
Parallel RLC Branch	Universal Bridge
Parallel RLC Load	Zigzag Phase-Shifting Transformer

Sign Conventions for Voltages and Currents

When you measure a current using a Current Measurement block, the positive direction of current is indicated on the block icon (positive current flowing from + terminal to – terminal). Similarly, when you measure a voltage using a Voltage Measurement block, the measured voltage is the voltage of the + terminal with respect to the – terminal. However, when voltages and currents of blocks from the Elements library are measured using the Multimeter block, the voltage and current polarities are not immediately obvious because blocks might have been rotated and there are no signs indicating polarities on the block icons.

Unlike Simulink signal lines and input and output ports, the Physical Modeling connection lines and terminal ports lack intrinsic directionality. The voltage and current polarities are determined, not by line direction, but instead by block orientation. To find out a block orientation, first click the block to select it. Then enter the following command:

get_param(gcb,'Orientation')

The following table indicates the polarities of the currents and voltages measured with the Multimeter block for single-phase and three-phase RLC elements (branches or loads), surge arresters, and single-phase and three-phase breakers. The table also indicates the polarities of their state variables (inductor currents and capacitor voltages).

Block Orientation	Positive Current Direction	Measured Voltage
`right`	left —> right	Vleft – Vright
`left`	right —> left	Vright – Vleft
`down`	top —> bottom	Vtop – Vbottom
`up`	bottom —> top	Vbottom – Vtop

The natural orientation of the blocks (that is, their orientation in the Element library) is right for horizontal blocks and down for vertical blocks.

For single-phase transformers (linear or saturable), with the winding connectors appearing on the left and right sides, the winding voltages are the voltages of the top connector with respect to the bottom connector whatever the block orientation (right or left). The winding currents are the currents entering the top connector.

For three-phase transformers, the voltage polarities and positive current directions are indicated by the signal labels used in the Multimeter block. For example, Uan_w2 = phase A-to-neutral voltage of the Y connected winding #2, Iab_w1 = winding current flowing from A to B in the delta-connected winding #1.

Dialog Box and Parameters

Available Measurements

The Available Measurements list box shows the measurements in the Multimeter block. Use the >> button to select measurements from the Available Measurements list box. Click the Update button to refresh the list of available measurements in the Multimeter block.

The measurements in the list box are identified by the name of the block where the measurement is done. The type of measurement (voltage measurement, current measurement, or flux) is defined by a label preceding the block name. See the reference sections of blocks listed in the previous table for a description of these measurements.

Selected Measurements

The Selected Measurements list box shows the measurements sent to the output of the block. You can reorder the measurements by using the Up, Down, and Remove buttons. The +/– button allows you to reverse the polarity of any selected measurement.

Plot selected measurements

If selected, displays a plot of selected measurements using a MATLAB^® figure window. The plot is generated when the simulation stops.

Output type

Specifies the format of the output signals when the block is used in a phasor simulation. The Output signal parameter is disabled when the block is not used in a phasor simulation. The phasor simulation is activated by a Powergui block placed in the model.

Set to Complex to output the selected measurements as complex values. The outputs are complex signals.

Set to Real-Imag to output the real and imaginary parts of the measurements. For each selected measurement, the multimeter outputs the real and imaginary parts.

Set to Magnitude-Angle to output the magnitude and angle of the selected measurements. For each selected measurement, the multimeter outputs the magnitude and angle values.

Set to Magnitude to output the magnitude of the selected measurements.

Example

The power_compensated demo uses a Multimeter block to measure the voltage across the secondary winding of a Saturable Transformer block and the currents flowing through two Series RLC Load blocks.

A Multimeter block is dragged into the model. In the dialog box of the 250 MVA block, set the Measurements parameter to All measurements (V,I,flux). In the 110 Mvar1 block, set it to Branch voltage and in the 110 Mvar2 block, set it to Branch voltage and current.

The output of the Multimeter block is connected to a Scope block in order to display the measurements during the simulation. In addition, you can select the Plot selected measurements parameter to display a plot of selected measurements when simulation stops.

Open the Multimeter block dialog box and select the signals you want to observe, as shown on the Dialog Box and Parameters section. Notice the labels used to define the available measurements in the Multimeter block. See the reference section of the Saturable Transformer block and Series RLC Load block for a description of these labels.

Start the simulation. After 0.4 seconds, the simulation stops and a MATLAB figure window opens to display the selected measurements in the Multimeter block.