A resolver sensor primarily consists of a stator, rotor, excitation winding, sine winding, and cosine winding. The stator is fixed to the motor housing, while the rotor is coaxially connected to the motor rotor, typically featuring a salient pole structure.
Without it, an EV wouldn't even know which way to spin! The resolver acts like the motor's "sensory nerves," precisely tracking rotor position in real-time to deliver butter-smooth acceleration.
The Function of the Resolver Sensor
The resolver sensor is essentially a type of rotary transformer, and its operating principle is based on the effect of electromagnetic induction.
A high-frequency sinusoidal AC reference signal-with constant amplitude and fixed frequency (typically 10 kHz)-is applied to the excitation winding (which serves as the primary winding). When the salient-pole rotor (directly connected to the motor shaft) rotates, it alters the air gap between the rotor and the two stator windings-namely the Sin and Cos windings-thereby modulating the magnetic coupling strength between them. These two windings are spatially arranged with a strict 90-degree electrical phase difference.
he waveforms of the Sin and Cos output signals exhibit envelopes (Outline of amplitude variation) that closely approximate ideal sine and cosine curves, respectively. Although the frequency of the Sin and Cos output signals remains consistent with that of the excitation signal, their amplitudes vary continuously and precisely according to sinusoidal and cosinusoidal functions as the rotor's angular position changes.
The MCU decodes and processes the signal fed back from the resolver sensor to accurately determine the real-time operating status of the motor (including position, speed, and rotation direction), thereby enabling high-precision closed-loop vector control of the motor.
These parameters form the foundation for ensuring the normal operation of the resolver sensor and achieving high-precision decoding. In practical applications, it is essential to refer to the exact values specified for the specific vehicle model or sensor.
How to Test a Resolver Sensor
Core Principle: First external, then internal; first static, then dynamic.
Visual Inspection
Housing：Check the housing at the sensor mounting area on the motor for defects such as cracks or deformation.
Connector： Check for bent, corroded, loose, or otherwise damaged pins.
Wiring Harness： Inspect the cables from the sensor to the controller for signs of wear, peeling, crushing, or melting due to high temperatures.
2,Static Resistance Measurement (Offline Testing)
Disconnect the sensor from the driver! Use a multimeter to measure the resistance between the pins of each winding.
Measurement Items：Excitation Winding Resistance (Exc+ and Exc-):
Measure the resistance of the excitation winding.
Sine Winding Resistance (Sin+ and Sin-) and Cosine Winding Resistance (Cos+ and Cos-):
The resistances of these two windings should be nearly identical (very close) and approximately 1.5 to 3 times that of the excitation winding.
Insulation Resistance Between Windings:
Measure the resistance between any winding and the housing (ground), as well as between different windings. All values should be infinite (megaohm level) to ensure no short circuits or leakage.
Result Interpretation：
Normal: All resistance values meet the specifications in the manual, and the Sin and Cos winding resistances are symmetrical.Open Circuit: Resistance is infinite → Internal winding breakage.
Short Circuit: Resistance is close to zero → Inter-turn short circuit within the winding or short between pins.
Resistance Deviation: Abnormal resistance in one phase or asymmetry between Sin and Cos winding resistances → Indicates potential sensor performance degradation.
