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12 Chapter Two: Motor Controllers and Drivers The BLDC drive type refers to the approach to current switching (commutation). The drive type can be trapezoidal, sinusoidal, or field-oriented control (FOC). As with other areas of BLDC design, choosing the appropriate approach requires balancing trade-offs among cost, performance, efficiency, and processor requirements. The simplest drive type is trapezoidal, which is a popular approach for low-end applications in which higher speeds or starting torque are required. In this six-step commutation approach, current is controlled through two windings energized at one time—one high and one low—with the third always being disconnected from the power source. Because only two windings are on at a time, torque ripple at every stage of commutation occurs, especially at lower speeds. This drive type is the simplest and least expensive. In sinusoidal drives, all three coils are energized at one time, resulting in smoother power delivery than with the trapezoidal approach. Whereas trapezoidal control results in trapezoidal wave forms, sinusoidally commutated BLDC wave forms are smoother and vary sinusoidally as the motor turns, reducing torque ripple and making motor control more precise. Note, however, that this commutation type becomes inefficient at high speeds. Keys to sinusoidal commutation include accurately determining the rotor position and being able to control the current accurately to follow the waveform. "Mistakes during the design of control circuits may result in poor operation of the motor or the inability to rotate. In the worst case, when the design mistakes relate to safety functions, the motor drive may even start a fire." Anton Dianov Senior Firmware Engineer, Samsung Electronics Precise rotor position data is crucial. Even small errors in angle detection can result in operational problems, safety issues, or motor failures. This is one area where BLDC motors have a clear advantage over their brushed DC motor counterparts. Suad Jusuf Senior Manager, AIoT Global, Renesas Electronics