Novel motor-drive unit features optics-based commutation
Stationary/rotating switches and associated electronics installed outside the main motor housing offer protection from heat and dirt and permit easy replacement. Rotor coil leads brought out through the bearing via slots in the motor shaft help implement the design.
It may look like an ordinary ac or dc motor and consist of familiar mechanical parts, but that’s where similarities end for DynaMotor —a variable-speed brushless motor-drive package from DynaMotors Inc.— which applies optically controlled solid-state switches (transistors) embedded in its rotor windings to control current, hence torque. Moreover, control occurs at the source of torque.
DynaMotor incorporates patented “Dynamic Rotor” technology that operates the switches at low frequency rather than high frequency associated with PWM, reducing RFI/EMI motor noise problems by up to 99%, says the company. This also is said to eliminate traditional costs related to reducing RFI; for example, eliminating use of filters, isolation transformers, special cables, and grounding brushes, according to Douglas Toman, DynaMotors vice president and GM.
With Dynamic Rotor technology, speed and torque control take place in the armature. Each rotating switch in the rotor is appropriately turned on/off as it passes stationary light-emitting diodes (LEDs) on the motor's end-bell. Time duration of switch closure determines speed and torque level. “Closing the switch for a longer period produces more torque and increases the speed,” says Toman. “Since multiple coils on the rotor can be energized simultaneously and controlled individually, continuous smooth torque can be produced.” Direction of rotation likewise is simply controlled. DynaMotor is reversed by turning on LEDs on the opposite side of each stator pole. No contactors or additional power electronics are needed. Besides optical control, the switches can be actuated by a magnetic or RF method, Toman explains.
Built-in feedback; 5,000 rpm max
DynaMotor is billed as a “self-contained, closed-loop drive system,” due to its simple internal optical speed sensor for speed feedback. It further eliminates the need for an external encoder. “Speed can be controlled manually with a potentiometer or keypad or automatically by transducer or serial link, etc.,“ adds Toman. Other features include high torque at low speed; conformance to CE standards; and lower cost and improved reliability—from less wiring, electronic circuitry, and parts—because of one integrated motor and controller package.
DynaMotors Inc. has optimized its design for various applications. It has extensively tested prototype motors and has run numerous beta-test sites for field evaluation of DynaMotor since its original announcement of this technology. Today, products are available in NEMA 48 frame up to 1 hp and NEMA 56 frame to 2 hp (both with single-phase input and ODP and TEFC enclosures); speed capability is up to 5,000 rpm. The company also is working on non-NEMA frame motors for very low speeds—under 100 rpm.
—Frank J. Bartos, Control Engineering, executive editor