MCUs for motor inverter drives cut code size, speed development

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By eeNews Europe

Renesas designed the RX23T Group of microcontrollers to enable highly precise control of inverter circuits employed in energy-efficient electric home appliances, industrial machinery, and office equipment. Based on the fast RX core, the 32-bit MCUs are suitable for building high-performance inverter control systems for applications such as DC motor control in energy-efficient electric home appliances such as refrigerators, air conditioners, washing machines, vacuum cleaners, and fans; entry-level to mid-range industrial equipment such as general-purpose inverters, electrical tools, and drones; and office equipment. The functions are optimised for inverter drive control, including the inclusion of an on-chip floating point unit (FPU).

These MCUs provide an optimised subset of the functions of the RX62T Group, which has a track record in the inverter control field, designed specifically for use in three-phase inverter drive applications.

Precise inverter control and reduced development time for mid-range and entry-level devices; inverter control requires a large number of arithmetic operations involving decimal points, and it is useful to perform these using a floating-point arithmetic unit. However, cost constraints on mid-range and affordably priced power-efficient electric home appliances and industrial equipment have prevented the use of expensive microcontrollers with on-chip FPUs. Instead, the most common approach has been to develop software for a fixed-point arithmetic unit. The new RX23T Group MCUs incorporate an on-chip FPU without increased costs, eliminating the need to implement the decimal position shifting required when using a fixed-point arithmetic unit. This simplifies the software configuration. The on-chip peripheral functions are also optimised for single inverter drive, boosting the cost-to-performance ratio and making it possible to add high-precision inverter control to mid-range and entry-level products.

High power efficiency for even lower power consumption in inverter products; the RX23T MCUs feature the RXv2 core (4.55 CoreMark/MHz (target), among the best in the industry) and DSP functionality, allowing operation processing to be maintained with no loss of real-time responsiveness when performing inverter control (sensor-less vector control), even when the CPU is not running at high speed. Current consumption in low-power mode (data retained in RAM) is only 450 nA (typ.). This power efficiency claimed as being among the best in the industry, enabling inverter products with lower power consumption.

Support for 5 V peripheral I/O makes it easier to implement measures to reduce effects of electromagnetic noise from inverter drive; as systems become more power efficient and the power supply voltage drops, it becomes necessary to take steps to prevent electromagnetic noise from peripheral components from adversely affecting high-precision control because MCUs become more susceptible to such interference when the power supply voltage is low. Supporting a 5 V power supply voltage, the new RX23T Group MCUs are less vulnerable to inverter drive noise than MCUs using a 3 V power supply, reducing the number of components required to reduce the noise effects.

Samples of the RX23T MCUs are available now in package pin counts ranging from 48- to 64-pins and on-chip flash memory capacities ranging from 64 to 128 kB for a total of 12 individual products. Mass production is scheduled to begin in August 2015. Integrated development environment (CS+, e2 studio) and code generator support tools are scheduled to be available from June 2015. Renesas also plans to expand its lineup of motor control application notes and solutions.



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