Power Electronics

Integration Key to Efficient Variable Speed Motion Control

Today, around 40% of the world's energy is used to produce electricity, of which about half is consumed by electric motors. An estimated 7 billion motors are produced each year to control motion in refrigerators, air conditioners, washing machines, elevators, factory automation and automobiles. Due to cost, less than 20% of these motors use electronic controls of different levels of complexities.

The trend is shifting rapidly to the use of advanced electronic control for motor drives. This fast adoption is driven by a combination of energy-efficiency regulations and programs, such as Energy Star, Blue Angel and Green Mark, together with performance requirements for precise control of torque and speed.

However, the design of these electronic control units involves digital, analog and power circuitry. Designers are faced with the challenges of achieving high performance at relatively low cost for the high-volume appliance and light industrial markets, while minimizing the design risk to meet tight design schedules using components with form factors and integration levels that simplify manufacturing.

An integrated design platform is required for these motor control design challenges. The chipsets must contain compatible digital controller, analog gate drivers and sensor signal-processing chips, power silicon and power modules.

As high-performance applications often demand fast computation and update rates to satisfy the growing demand for higher dynamic performance, digital controllers are moving from 8-bit and 16-bit MCU to 32-bit RISC or DSP. Motion programming requires the specific skill of writing motion action into all sequential computational descriptions, which consist of thousands of lines of instructions. The code maintenance cost is usually a hidden cost that doesn't show up at the start of development phase.

A new class of dedicated control engine, the Motion Control Engine (MCE), is emerging. The MCE off-loads the computation intensive portions to a parallel processing engine. These engines incorporate configurable control blocks necessary to perform closed-loop controls and motion hardware peripherals. One significant advantage of the MCE over a conventional microprocessor or DSP is the very short computation time to complete a closed-loop control algorithm with deterministic timing. Fast computation directly influences the dynamic performance of torque and speed of a servo system.

Increasingly, high-voltage ICs (HVICs) may be used to integrate all analog circuits onto a single chip with multiple functions, including gate drive, current sensing, bias supply control and other glue functions. Because these HVICs must operate in a high-voltage and noisy environment, special design techniques must be used to combat the inevitable issues of overvoltage, overcurrent and other noise spikes not commonly encountered in less-demanding applications.

In addition, a new type of integrated power module (IPM) may be deployed to integrate the power silicon with the analog control IC. The module uses IGBT technology matched with a hyperfast diode. In addition to the IGBT power switches, the modules contain a 3-phase monolithic gate-driver IC, matched to the drive requirements of the IGBTs to generate the most efficient power switch consistent with minimum noise generation and maximum ruggedness.

Integrated design platforms for electronic motor drive control offer a compelling argument to manufacturers to adopt variable speed motion as a higher performing and viable cost-effective alternative to electro-mechanical techniques.

From the designer's perspective, the integrated design platform approach blends the best silicon, packaging, processes and software to optimize performance while simplifying the design task to meet critical cost targets and bringing products to market faster.

David Tam joined International Rectifier in 1986 in the R&D department as a design engineer, and designed the world's first single-chip 500-V buck switching regulator and half-bridge gate driver products. In 1993, he formed IR's Power Integrated Circuit Group to design and market power IC products for the motor drive, lighting, automotive and power supply applications. In 2001, Tam ran the Field Application Engineering group and led a team to develop new system architecture for power systems. In 2003, he formed the Consumer and Industrial Business Unit.

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