Part 3 ― Motor Control Solutions for Key Application Sectors

Industrial Applications ― Processing power of SH-2 and SH-2A Cores Is Put To Work Where Precise Real-time Control Is Needed

Advanced real-time control is required for AC servo drives, general-purpose inverters, and other industrial applications where high speed, high precision, and low vibration drive operation are necessary. The difficult requirements of these motor control applications can only be met by high-performance microcomputers. Popular solutions are the 32-bit SuperH devices positioned at the top-end of Renesas' broad range of controller-oriented products. The SH7211, for example, uses the SH-2A core and has up to 512Kbytes of on-chip flash memory.

Industrial systems such as semiconductor manufacturing equipment, high-speed machining centers, and industrial robots with fast, powerful three-phase AC motors require high-speed, high-precision, and low-vibration motor control. These needs can be met with devices such as AC servo drives and general-purpose inverters. The latest AC servo drives are achieving higher levels of speed and precision, while also shrinking in size and decreasing in cost. Communication functions for linked systems are becoming faster and more sophisticated, too. Implementing a control system that can cope with the highly responsive performance of three-phase AC motors requires not only a high level of CPU performance, but also other enhancements, including better pulse width modulation (PWM) performance and a high-speed memory interface.

Top-end designs for controlling three-phase AC electric motors in industrial applications require a microcomputer that operates in the 100 to 200MHz range or higher. Even mid-level to low end designs need microcomputers that run at speeds as high as 50 to 80MHz. Faster clock inputs provide better resolution for the timers and improve PWM accuracy. Among the other microcomputer features often required are internal USB support and a 16/32-bit external expansion port for connecting to an external ASIC. Microcomputers that offer integrated USB support make it easy to design motor control electronics that connect to a PC to simplify system maintenance.

Like AC servo drives, general-purpose inverters are also achieving higher speeds while getting smaller. Moreover, the trend toward introducing low-cost models for China and other Asian countries is making cost control critical to remaining competitive. Inverters require high levels of microcomputer speed and performance. High-end equipment requires 100MHz speed or more, mid-range equipment requires 60 to 80MHz, and low-end AC servo drives need 30 to 50MHz. Other requirements include faster, more precise A/D converters and internal USB support. For top-end AC servo control applications, the microcomputer must have a 16-bit or similar expansion bus suitable for connecting to an external ASIC.

Renesas motor control solutions for AC servo drives, general-purpose inverters, and similar applications are 32-bit SuperH microcomputers designed for use in embedded systems. The mainstream models have SH-2 or SH-2A CPU cores (see Figure). The SH-2 CPU core has a Harvard architecture and operates from 20 to 100MHz. The more powerful SH-2A CPU core has a superscalar configuration based on the SH-2 CPU and operates at speeds up to 200MHz. It uses parallel flash memory access to achieve a very high level of processing performance: 480 MIPS when running at 200MHz.

Topping the range of SuperH solutions for the most demanding industrial motor control applications is the recently announced the SH2A-Dual device. This single-chip, multi-core 32-bit microcomputer uses two SH-2A cores to achieve very high performance: 960MIPS. Each of the cores includes a CPU, FPU, instruction cache, data cache, and user RAM (URAM). This enables the processing in each core to be executed with a minimum of accesses to external memory for maximum throughput. The advanced semiconductor technology Renesas has put into this device will make possible future motor control applications with unprecedented performance characteristics.

Currently, though, the most popular SH-2A based device for high-end industrial motor control applications is the SH7211, the first device with the SH-2A core to offer on-chip flash memory. It operates at 160MHz and delivers 320 MIPS processing performance. There are 512Kbytes of internal flash memory and 32Kbytes of internal RAM. Integrated peripheral functions include a new 16-bit PWM timer (MTU2 or MTU2S), a 12-bit A/D converter, and an 8-bit D/A converter (see Figure 1).

For mid-range industrial motor control applications, the optimum choices are the devices in the SH7080 series. They use the SH-2 core, can access the up to 512Kbytes of high-speed internal flash memory in a single clock cycle at the maximum operating frequency of 80MHz, and deliver 104 MIPS performance at that speed.

Electric motor control solutions with the SH-2 CPU core include the microcomputers in the SH7147 group, which incorporate an internal CAN (Controller Area Network) interface and have a maximum operating frequency of 64 or 80MHz. They offer up to 256K bytes of flash memory with single-cycle access capability and an MTU2 or MTU2S 16-bit PWM timer. Their analog input interface includes a 16-channel (8ch + 8ch) A/D converter with 12-bit resolution, along with six sample-and-hold circuits. Together, these on-chip peripheral functions can be used to simultaneous sample of all three phases (three circuits per module) of a three-phase industrial AC motor.

For less-demanding applications the devices in the more economical SH7125 series ― the first members of the SH/Tiny product line ― have an SH-2 CPU that runs at speeds up to 50MHz and incorporate functions specifically designed for motor control. Their features include 128Kbytes or 64Kbytes of flash memory, the MTU2 16-bit PWM timer, and a 10-bit A/D converter. One version of these low pin-count, small size microcomputers has a compact 10mm-square LQFP package with 48-pins.

Looking into the future, the solutions Renesas plans to release for industrial motor control applications include a single-chip microcomputer that combines the SH2A-Dual core with internal flash memory.