Speed Sensorless Control for Permanent Magnet Synchronous Motor Direct Torque Control Systems

Speed sensorless technology for Permanent Magnet Synchronous Motor (PMSM) Direct Torque Control (DTC) systems represents an advanced control strategy widely adopted in high-performance drives. This technology employs optimized control algorithms to estimate motor speed, eliminating the need for traditional mechanical sensors while enhancing system reliability and cost-effectiveness.

Core Principles In sensorless DTC systems, motor state observers (such as sliding mode observers, extended Kalman filters, or flux observers) are implemented to estimate rotor position and speed in real-time. The algorithm processes measured voltage and current signals through electromagnetic equation solutions, typically involving mathematical models like: - Stator flux estimation: ψ_s = ∫(V_s - R_s I_s)dt - Torque calculation: T_e = (3/2)p(ψ_α I_β - ψ_β I_α) The derived speed information is then fed back into the DTC control loop to maintain closed-loop operation. Code implementation often involves discrete-time integration methods and angle calculation using arctangent functions.

Advantages Cost Reduction: Eliminates need for optical encoders or resolvers, reducing hardware costs and maintenance complexity Enhanced Robustness: Avoids mechanical sensor vulnerabilities to environmental disturbances (vibration, temperature variations), suitable for harsh operating conditions Fast Dynamic Response: Combines DTC's inherent rapid torque response with sensorless technology for optimized system performance. Implementation typically uses hysteresis controllers and switching table algorithms for quick duty cycle updates.

Technical Challenges Speed estimation accuracy at low/zero-speed conditions, parameter sensitivity (e.g., motor resistance variations), and anti-interference capabilities require continuous improvement through advanced observer algorithms or adaptive compensation mechanisms. Common solutions include: - Parameter identification algorithms using recursive least squares methods - High-frequency signal injection techniques for low-speed operation - Robust observer designs with stability proof verification

Application Scenarios Widely applied in electric vehicles, industrial servo systems, and wind power generation, particularly excelling in volume-sensitive, cost-critical, or high-reliability applications where compact design and maintenance-free operation are prioritized.