New Energy Electric Drive Sensors Resolver: Self-Learning And Failure Mode Analysis

**1. Overview of Resolverin New Energy Electric Drive Systems 

A resolver is a common sensor in new energy electric drive systems, primarily converting the axial rotation's angular position and angular velocity into electrical signals. Its structure mainly includes the resolver stator and rotor, with the most commonly used type being the variable reluctance resolver.

**2. Working Principle of Resolver**

The core structure of a resolver lies in its winding design, primarily consisting of excitation windings R1 and R2 and two sets of orthogonal feedback windings S1, S3 and S2, S4, all meticulously arranged on the stator. In normal operating conditions, high-frequency excitation signals are applied to R1 and R2, generating a sinusoidal current. The signals induced in the feedback windings have a clear functional relationship with the motor's rotational speed. Therefore, by thoroughly analyzing these feedback signals, we can accurately determine the motor's rotational state.

**3. Determining the Zero Position of the Electric Drive Resolver**

Determining the motor's zero position is crucial as it affects the motor control precision. In the early stages of new energy electric drive development, software functionality was limited, and zero position calibration was typically done using a specific zero-setting instrument, followed by software adjustments. However, this method has a significant drawback: it cannot correct the zero position angle during use, leading to deteriorating control precision over time.

To address this issue, self-learning zero position angle technology for resolvers has emerged. This technology integrates a self-learning algorithm into the motor controller, allowing the controller to automatically detect and correct the zero position deviation between the resolver and the motor. During the self-learning process, the controller first obtains the actual deviation value through specific test procedures (e.g., static or dynamic tests). Once the deviation value is acquired, the controller stores this information and automatically compensates during subsequent motor control operations. This enables the controller to more accurately control the motor's operational state based on the calibrated resolver signals, thereby improving control precision and performance.

A common self-learning algorithm is based on back electromotive force (EMF) learning, with a zero position angle PI regulator as the core. The diagram below illustrates the self-learning process of the zero position in a hybrid system. It sets the current control by setting iq to 0 and assigning a value to id, then calculates Vd (d-axis voltage) and uses it as the reference input for the zero position angle. The Vd output from the controller's current loop serves as feedback, and the zero position angle regulator outputs the converged zero position angle.

**4. Common Failure Modes of Resolvers**

- **Electromagnetic Interference (EMI)**

In new energy electric drive systems, the motor, controller, and other electrical components can generate electromagnetic interference. If the resolver's anti-interference capability is weak, these interference signals may affect its normal operation, leading to signal distortion or loss. Previously, shielding was used around resolvers to prevent EMI. However, this practice has largely been discontinued because the resolver operates at a higher frequency than the motor’s electromagnetic frequency, and as long as it is not too close to high-voltage lines, EMI is generally not an issue.

- **Asymmetry in Sine and Cosine Windings**

Misalignment in the assembly of the resolver stator and rotor can cause an uneven distribution of the magnetic field gap. This uneven distribution can lead to asymmetry in the sine and cosine windings, resulting in unequal amplitudes of the sine and cosine signals.

- **Impedance Mismatch Leading to System Instability**

Impedance is a critical factor affecting signal transmission. If the impedance of the resolver does not match that of other parts of the control system, it may cause signal reflection, attenuation, or distortion, thereby affecting the stability and performance of the entire system.

**Conclusion**

As a crucial sensor in new energy electric drive systems, the resolver is essential for precise motor control. We must also pay attention to potential failure modes in practical applications and take appropriate measures for prevention and handling. Only then can we ensure the stable operation and high efficiency of new energy electric drive systems.