A small brushless DC motor is used to rotate a helical antenna element to a specific radiation phase in order to beam scan a mechanical phased array antenna. To control the position of micro brushless DC motors, a new system is being developed. An algorithm controller with a proportional sliding mode and super twisting surface is created for velocity control. A position PID controller and a velocity profile technique are used to regulate the rotation of the intermediate process. The system is built on an FPGA hardware experiment platform after the control system simulation model is established in Simulink to confirm the viability of the plan.
Simulated and experimental findings show that the tiny brushless DC motor can accurately drive the antenna to follow the preset velocity profile curve, and the rotation angle reaches 180° within a 50 ms control time. The residual error at the balancing position is less than 3°, as is the position tracking deviation in the intermediate phase.
1. System Structure
Fig. 1 displays the brushless DC motor position control system. The gearbox system connects the brushless DC motor to the helical antenna unit, and the encoder built into the rear end provides back real-time data on rotor position and speed. FPGA serves as the primary control chip in the control circuit. The control circuit regulates the three-phase inverter in the drive circuit, which produces three-phase voltage that drives the motor to revolve. After being sampled by the ADC, the phase current signal of the winding is fed to the control circuit. The brushless DC motor is driven by the control system using the vector control method, which reduces torque ripple. Three closed loops make up the entire control system.
The brushless DC motor is driven by the control system using the vector control method, which reduces torque ripple. The entire control loop consists of three closed loops: the current loop, the speed loop, and the position loop. To increase the robustness of the system, the speed loop uses a proportional sliding mode surface-super helical second-order sliding mode controller, and the position loop uses a PI controller. The rotational position of the antenna element is controlled at an intermediate process level using a PID controller in conjunction with a velocity profile technique.
Fig. 1. The position control system of BLDC motor
2. Second-order sliding mode controller for the speed loop
Fast and accurate response times are essential for the rotation process of the antenna unit, but so is strong system robustness. A powerful, reliable control strategy is the second-order sliding mode control approach. It not only maintains the robustness compared to the conventional sliding mode control, but also lessens chattering of the regulated quantity. The second-order sliding mode super-helix algorithm (STA) is used by the speed loop controller, and its discrete algorithm expression is
(1) Where: iq* is the target current of the current loop; λ and α are the control parameters; s is the sliding modulus; sign(x) is the sign function; is the speed error. Due to the small rated current of the micro BLDC motor, it is necessary to limit the current loop input. In order to reduce the influence of current limitation, STA is improved, and a new construction method of sliding mode s is adopted, as shown in formula (2).
