DQ and Direct Torque Models of Brushless Doubly-Fed Machine Implement Brushless Direct Torque Control

The Brushless Doubly-Fed Machine (BDFM) is a special motor structure featuring a brushless rotor design and a stator containing two sets of windings: the power winding and the control winding. By regulating the voltage and frequency of the control winding, variable-speed operation can be achieved while eliminating maintenance issues associated with brushes and slip rings in traditional doubly-fed machines. Code implementation typically involves separate control loops for each winding set with frequency synchronization algorithms.

In control strategies, the dq-axis model and Direct Torque Control (DTC) are two commonly used approaches:

DQ Model: This model employs Park transformation to convert three-phase AC quantities into DC quantities in the dq coordinate system, making control variables more intuitive. The BDFM's dq model typically includes dq-axis equations for both power and control windings. Decoupling control implementation requires coordinate transformation functions (like Clarke-Park transforms) and PID regulators to independently adjust torque and flux. The algorithm structure involves real-time calculation of dq components using trigonometric functions based on rotor position feedback.

Direct Torque Control (DTC): DTC is a control strategy based on hysteresis comparison of flux and torque. It directly controls inverter switching states through estimated flux and torque, achieving fast dynamic response. In BDFM applications, DTC effectively reduces complex calculations found in traditional vector control while enhancing system robustness. Code implementation typically features flux and torque estimators using voltage and current measurements, combined with switching table algorithms that select optimal voltage vectors based on hysteresis band comparisons.

By combining dq modeling with direct torque control, BDFM achieves high control precision and dynamic performance while avoiding reliability issues from slip ring wear in conventional doubly-fed machines. Practical applications demonstrate excellent performance in speed regulation range, torque response, and efficiency optimization, making it suitable for industrial scenarios like wind power generation and pump speed control. The integrated control approach typically requires real-time processors executing flux observation algorithms and adaptive switching frequency modulation routines.