Brushless DC (BLDC) motors are widely utilized in low-cost applications due to their simple manufacturing and Hall-sensor-based control. The BLDC motors are often controlled using the 120-degree commutation logic, which naturally approximates the maximum torque per Ampere operation. The application of the 180-degree commutation mode is also possible and may be advantageous since this mode has higher dc voltage utilization, although it comes at the cost of higher torque ripple. This paper proposes a new strategy to mitigate torque ripples of the 180-degree commutated BLDC motors with PWM voltage control. This method calculates a varying duty ratio during each switching interval based on the reference and estimated electromagnetic torque. The effectiveness of the proposed torque ripple reduction algorithm is demonstrated by both simulations and experimental results on a typical industrial BLDC motor.
See more IEEE XploreFaults and unbalanced operation of generators in power systems require appropriate models in electromagnetic transient (EMT/EMTP-type) simulation programs used for system studies. Therefore, it is essential to have computationally efficient models of synchronous machines that can also predict the unbalanced conditions and generator protection operation that is often realized by monitoring the neutral circuit current. The so-called constant-parameter voltage-behind-reactance (CP-VBR) machine models have recently been introduced for widely used nodal-analysis-based EMTP simulators as computationally advantageous alternatives to the traditional qd0 models. This paper advances the previous work and generalizes the CP-VBR model to include the floating neutral point by extending the equivalent conductance matrix that is used for interfacing within the EMTP solution. The new model is implemented in the PSCAD/EMTDC program and is demonstrated to have advantages over the built-in traditional qd0 model in studies with unbalanced faults.
See more IEEE XploreBrushless DC (BLDC) motors are widely used in various applications today. The two commonly used control methods include the maximum torque per ampere (MTPA) control and maximum torque per volt (MTPV) control, which can be easily implemented through different advances in firing angle. However, both of those methods also have their limitations and drawbacks. The MTPA may not produce enough torque to satisfy operation requirements, especially during high-speed operation. The MTPV method, while capable of delivering higher torque, results in higher losses. This paper proposes a novel flux-weakening (FW) control strategy to enable the BLDC motors to operate within a higher speed range, produce sufficient torque, and minimize the magnitude of stator current. The proposed method applies the MTPA at low speeds, and at higher speeds or when high torque is required, it smoothly transitions to the FW region. The proposed method is demonstrated to have improved dynamic response, a wider speed/torque operating range, and higher efficiency (compared to MTPV).
See more IEEE XploreModels of electrical machines are essential in electromagnetic transient programs (EMTP) that are commonly used for studies of power systems. Recently, a voltage-behind-reactance (VBR) model has been developed for synchronous machines as an alternative to the conventional qd0 model which has advantageous properties in terms of interfacing and accuracy when using large simulation time steps. This paper presents a multirate implementation method for the VBR models of the synchronous machines in EMTP solution. The multirate algorithm separates the VBR machine model into fast subsystem (that includes the stator interfacing circuit and uses small time steps) and slow subsystem (that includes the rotor history terms and mechanical subsystem and uses larger time steps). The presented computer studies demonstrate the computational gains offered by the proposed multirate VBR model.
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