Resolver Simulation

IRS cRIO resolver simulator can be used in a National Instruments Compact-RIO chassis to simulate the signal of the resolver sensor of electric motors.

Purpose

This document describes the hardware functionality and the usage of the software interface for IRS resolver simulation module.

Resolver sensor

Resolver sensors are often used in the power-train of electrical or hybrid vehicles. Following figure shows the principle of a typical resolver, where the Excitation winding “R” is rotating. The two stator windings receive the energy from the excitation and generate a signal with an amplitude, depending on the rotor position.

Resolver principle with rotating excitation winding R and stator windings S1 and S2 — Figure 1: Resolver principle

When the Excitation winding is rotating, the two stator windings will show a signal similar to the following figure.

Signals R, S1 and S2 over a rotation angle of 0 to 360 degrees — Figure 2: Resolver signal

For component testing of the power stages of the motor driver, it is often not desired to include an original motor with its sensors in the tester. On the other hand the resolver signal should be generated for both functional test, End-Of-Line test or for lifetime tests during design validation.

Especially for lifetime testing IRS provides test systems which simulate the original motor by means of passive inductive loads. With this setup high phase currents of 400A_rms can be generated, while the power loss is very low, since the energy is stored as reactive power in the load coils.

The inverter, which is tested and generates the phase currents through the load coils, must “see” the same conditions as it would see with a real electric motor in the car. Thus, the sensor signal of the electric machine must be emulated. At this point the Resolver simulation comes into play.

The resolver simulation can simulate the sensor signal of a rotating machine or may emulate specific positions of the electric motor. The module can be controlled by software to stop at certain positions or perform continuous modulation, like a rotating electric motor does. Following figure shows a typical waveform of the resolver simulator:

Oscilloscope capture of excitation, sine and cosine output — Figure 3: typical simulation waveform

RVDT sensor

RVDT (rotary variable differential transformer) is a transformer used for measuring angular displacements. Following figure shows the principle of a typical sensor, where the metal core is rotatable in a limited angular range. The two windings on side “B” receive the energy from the excitation on side “A” and generate a signal with an amplitude depending on the core position. The displacement direction (sign) can be determined by the phase of the output signal compared to the excitation signal (positive angle -> 0°; negative angle -> 180°).

RVDT principle with excitation winding A, rotatable core and two windings B — Figure 4: RVDT principle

Abbreviations

Abbreviation	Description
cRIO	Compact reconfigurable input output module
FIFO	First in first out
FPGA	Field programmable gate array
LUT	Look-up table
MAX	Measurement & Automation Explorer
PGA	Programmable gain amplifier
RPM	Revolutions per minute
RT	Real time
SPI	Serial peripheral interface
VI	Virtual instrument
ResSi	Resolver Simulation
RVDT	Rotary Variable Differential Transformer

Table 2: Abbreviations