Renesas offers single-chip microcomputers that combine the functions required for implementing sophisticated inverter control techniques.

Renesas microcomputers are pervasive technology enablers for a vast range of products, equipment, and systems. They are all around us in consumer electronics products, automotive engine/transmission and safety systems, mobile phones, environmental controls, industrial robots; and financial and security systems — to name just a few applications. This new column in EDGE magazine will put the features of various Renesas microcomputers into perspective by examining specific areas and ways in which they are used. This story, developed with the help of Yuji Mouri, Senior Engineer in the No. 2 High-End RISC Group of the MCU Product Technology Section, covers inverter control applications. "Using microcomputers is an increasingly widespread approach for controlling motors and compressors because this design technique delivers good speed and position control, as well as excellent energy efficiency," Mr. Mouri said.

Inverter control technology for electric motors and compressors has started to appear in various markets recently in response to increasing environmental regulation and demand for energy savings. Especially, its use is growing in home appliances, industrial equipment and automotive applications.

Typical consumer appliance products that use inverters include high-efficiency room air conditioners (outdoor units), refrigerators, and washing machines. Examples from the industrial sector include general-purpose inverters, AC servos, pumps, variable-speed fans, and production-line robots. In automobiles, inverters are used in electrically assisted power steering and air-conditioning compressor controls. Design requirements common to all of these applications are small size, quiet operation, and energy efficiency (see Figure 1).

Significantly, inverter technology is being applied to an expanding array of applications beyond those just mentioned. For example, it's being used in areas such as controllers for electrical water heaters, solar cells and fuel cells. Moreover, inverter-based electronic controls and electric motors are starting to replace fluid pumps and hydraulics in industrial machinery, vehicle sub-systems, construction equipment, and the like.

Microcomputers are the key enabling components for inverter control applications. They execute specific algorithms in software to implement the requisite levels of motor control. The precise control thus achieved allows electric motors to operate more quietly while consuming less energy. "Low-end, mid-range, and high-end microcomputers are used, depending on the situation," said Mr. Mouri. "However, the trend is for customers to want greater improvements in energy efficiency and better performance in other areas. In turn, that is changing the requirements for the microcomputers being sought."

To obtain better energy efficiency and system performance in inverter control applications, design engineers are requiring microcomputers with ever higher levels of performance (see Figure 2). Faster, higher-throughput CPUs are needed to support control techniques that are becoming more sophisticated and complex, so the proportion of inverter-based products that use 32-bit microcomputers is growing. "The industrial sector requires CPUs rated in the 200 to 300MIPS range for applications such as AC servos. And powerful devices are even becoming essential in consumer markets," Mr. Mouri said.

Beyond the customer requests for higher performance, there are requirements that microcomputers provide easy-to-use peripheral modules for the functions essential to inverter control designs. Three-phase PWM output timers with dead-time insertion capabilities and high-speed A/D converters are among the key peripherals needed.

For certain major applications, microcomputers must provide two internal inverter-control timers because one device is used to control two motors. This is the case in some air conditioners, where a single microcomputer controls the compressor motor and the fan motor. Using one device to control both motors of a dual-axis robot is another example. In such applications, the microcomputer must also have sufficient CPU performance to handle the extra processing load imposed by the execution of two control functions.

Other requirements for microcomputer peripheral functions aren't dictated by the inverter control tasks the devices perform, per se, but rather by higher-level system requirements. That is, in many situations — particularly in industrial and automotive applications — an inverter controller is networked with other subsystems as part of a total system solution. In such cases, the microcomputer must provide the appropriate communication interfaces, such as CAN, USB, and high-speed (2 to 5Mbps) UART functions.

To meet the needs of customers building many different types of inverter equipment, Renesas offers a broad range of microcomputers, extending from 8-bit to 32-bit devices (see Figure 3). Devices in the R8C/Tiny series and M16C/Tiny series, which are available in low-pin-count versions and with up to about 100 pins, are effective and economical choices for many basic inverter control applications in the consumer sector. Our H8/300H and M16C microcomputers are optimized for mainstream applications. For inverter applications that use vector-type motor control techniques and therefore require more CPU performance, devices in the SuperH series are ideal solutions. The SuperH chips are the best choice for industrial applications that require high performance and a large pin count.

"The devices in these popular Renesas product lines that are recommended for inverter control designs include a three-phase PWM, A/D converter, and other necessary functions — all on the same chip," Mr. Mouri explained. "Available peripheral sets allow migration from single-inverter control to dual-inverter control." To meet evolving needs in the important and growing inverter applications area, Renesas plans to continue developing new microcomputers beyond those now offered.

In the current Renesas microcomputer lineup, new products in the R8C/24, M16C/28, SH7125 and SH7211F product groups are particularly recommended for inverter control applications (see Table 1). Of course, the optimum device choice depends on the design requirements of the specific application.

. R8C/24 series — The main applications for these single-chip microcomputers include industrial motors and home appliances that use small brushless DC motors or three-phase induction motors. The devices use the R8C/Tiny 16-bit CPU core and are available in 52-pin LQFP and 64-pin FLGA plastic-molded packages. They have a single three-phase PWM output that includes a deadtime capability and is driven by a 16-bit timer that can be selected as the start trigger for the built-in A/D converter. Members of the R8C/25 group within the R8C/24 series also provide two 1KB blocks of data-flash memory that can be used for storing motor constants and other settings, thereby helping to reduce the external component count in motor control applications. For more information, click here .

. M16C/28 group — Suitable for control systems for brushless DC motors and induction motors, these single-chip microcomputers use the 16-bit M16C core and are available in an 80-pin plastic molded LQFP package. The devices have an internal 10-bit A/D converter and can output a single set of PWM waveforms using a 16-bit timer with a three-phase PWM mode. Devices in the M16C/29 series within the M16C/28 group have a single-channel CAN interface for use in automotive or industrial applications where the CAN protocol is used as the serial communication interface.For more information, click here .

. SH7125 group — Recommended for applications such as inverter units that control refrigerator compressors and the drive motors of washing machines and other home appliances, as well as general-purpose industrial inverters, these single-chip microcomputers are members of the SH/Tiny series. They are available in a range of packages, including 48- and 64-pin plastic molded LQFPs. They use the 32-bit SH-2 CPU core — a high-performance (50MHz/65MIPS) 32-bit RISC design that supports highly efficient motor operation and fast response times. The microcomputers can output a single three-phase PWM waveform with deadtime using an internal multifunction timer unit (MTU2). The MTU2 also includes a timer that can be used to measure the encoder input waveform. The microcomputers provide two 10-bit A/D converter units with 2.0?sec conversion times. Both units can measure analog inputs simultaneously, a capability useful for measuring motor currents, among other functions.For more information, click here .

. SH7211F group — Ideal for applications such as industrial robots and AC servos, these microcomputers use the fast, high-throughput (160MHz/320MIPS) 32-bit SH-2A CPU core, and are available in 144-pin plastic molded LQFP packages. They have two timer channels, so they can output two independent PWM waveforms. One timer is the MTU2 peripheral previously mentioned, while the other is the MTU2S, an MTU2 without the three-phase PWM output function. The on-chip 12-bit A/D converter has a conversion speed of 1.25?sec per channel. Three of the analog input pins (AN0 to AN2) have independent sample-and-hold circuits, allowing simultaneous sampling of the U, V, and W motor current phases.For more information, click here .