Voltage measurement

The VSR block of the imperix Power library models a voltage measurement in Simulink and PLECS. It reproduces the measurement bandwidth of the selected imperix sensor, so that a simulated control loop sees the same measurement dynamics as the real hardware.

The block supports the VSR-500-HBW high-bandwidth sensor and the VSR-1000-ISO galvanically isolated sensor. It also supports the previous-generation DIN800V.

Measurement chain and modeled effects

On imperix hardware, a voltage measurement passes through three stages. The sensor converts the measured voltage into a low-voltage signal. This signal reaches the controller’s analog input through an RJ45 cable, where it is sampled. In the control model, the ADC block converts the sampled value back into volts using the selected sensor’s sensitivity.

In simulation, the voltage measurement block represents the first stage. It connects two electrical nodes and outputs the voltage between them, filtered by the selected sensor’s measurement bandwidth. Sampling and quantization are modeled by the ADC block.

The voltage measurement block models only the measurement bandwidth. It does not model noise, offset, sensitivity error, saturation beyond the measurement range, or common-mode voltage rejection.

Measurement bandwidth and modeling levels

The voltage measurement block represents a sensor as either an ideal measurement or an ideal measurement followed by a first-order low-pass filter (LPF). The time constant of the LPF follows from the measurement bandwidth:

$$(1) \quad \quad \tau = \frac{1}{2\pi f_{BW}}, \qquad H(s) = \frac{1}{1 + s\tau}$$

where \(f_{BW}\) is the bandwidth in Hz and \(\tau\) the time constant in s.

Two modeling levels are available, Simple (A) and Detailed (B). Sensor are modeled with the LPF only when its bandwidth lies within the frequency range of the selected level. Otherwise, it is modeled as ideal.

The measurement bandwidth becomes relevant when the crossover frequency exceeds about one tenth of the bandwidth. The same holds when \(\tau\) is not small compared with the sampling period. In these cases, the Detailed (B) level should be used, so that the simulated phase margin matches the hardware.

Sensor	Bandwidth setting	Time constant \(\tau\)	Simple	Detailed
VSR-500-HBW	3 MHz	53 ns	Ideal	Ideal
VSR-500-HBW	300 kHz	530 ns	Ideal	Ideal
VSR-1000-ISO	100 kHz	1.6 µs	Ideal	LPF
VSR-1000-ISO	10 kHz	16 µs	Ideal	LPF
DIN800V	100 kHz	16 µs	Ideal	LPF

Simulink block

Port specification

Parameters

• Use global configurations: when ticked, the block takes its modeling level from the CONFIG block, so that one setting applies to all blocks of the model. Untick it to give this block its own modeling level, for instance, the Detailed level for one slow measurement only.
• Modeling level: Simple models every sensor as ideal. Detailed adds the LPF. Select Detailed when the measurement bandwidth affects the control loop.
• Voltage sensor: selects the modeled sensor and, therefore, its bandwidth. Select the sensor installed on the hardware.

PLECS block

Port specification

Parameters

• Modeling level: Simple models every sensor as ideal. Detailed adds the LPF. Select Detailed when the measurement bandwidth affects the control loop.
• Voltage sensor: selects the modeled sensor and, therefore, its bandwidth. Select the sensor installed on the hardware.

Probe signals

The following signals can be monitored with a PLECS Probe block. Comparing them shows how measurement bandwidth affects a given waveform.

• True value [V]: the actual voltage between the two electrical ports, in volts.
• Sensor output [V]: the voltage delivered by the modeled sensor, in volts.