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Volume 48 (Oct 12, 2005)
Inverter control microcontrollers: Making air conditioners quieter, more energy efficient and capable of fine-tuned temperature control
Inverters are used in most popular products
What first comes to mind when you think of consumer appliances that incorporate inverter technology (Note 1)? Air conditioners are perhaps what come to mind for many. However, inverters are also used in a vast array of other consumer appliances, including washing machines and refrigerators. In addition to their use in consumer appliances, they are employed in products for which motors are indispensable, such as elevators, robots, electric power steering and electric bicycles. Moreover, this technology is employed in non-motor driven products such as electromagnetic cooking devices (IH cooking heaters, etc.) and fluorescent lights. Using air conditioners as an example, let's take a look at how inverter technology is used in the operation of products like these.
Making air conditioners quieter, more energy efficient and capable of fine-tuned temperature control
Air conditioners are one of the biggest power-consuming appliances used in the home. So if you're going to use an air conditioner in your home, you naturally want one that can be run inexpensively and quietly. That's where inverter technology comes into play. To explain how, let's use temperature setting as an example. If you set the temperature to 25°C in the summer for an air conditioner without inverter control, the air conditioner will automatically turn itself off once the room temperature drops below 25°C, and will then turn back on when the temperature rises above 25°C. This makes it necessary for the air conditioner to repeatedly turn itself on and off, and a great deal of electricity is wasted due to fluctuations in room temperature above and below the preset temperature. Moreover, the noise of the power switch turning on and off can become an annoyance. In the case of an inverter air conditioner, however, it is possible to maintain a fixed temperature without having to repeatedly turn the power on and off (Figure 1). The compressor inside the air conditioner's outdoor component changes the compression rate of the refrigerant gas, thereby making it possible to adjust the temperature. In actuality, this adjustment is carried out by changing the revolution speed of the motor inside the compressor. Since the revolution speed can be smoothly controlled over a wide range by varying the frequency of the motor's power switch, inverter control makes it possible for air conditioners to not only be more energy efficient and quieter, but also capable of fine-tuned temperature control.
Microcontrollers: The key to inverter control
Microcontrollers hold the key to inverter control and influence the performance of inverter systems. To smoothly control motor revolution, microcontrollers calculate the optimum driving force when minor wobbling occurs due to load fluctuations, and this wobbling can then be eliminated through feedback processing. In addition, fine-tuned control makes it possible to keep power loss at a minimum while the motor is running. Microcontrollers, with their fast interrupt response time and high computational ability per unit time, are capable of creating clear power waveforms, and thus of improving the energy-saving capabilities of systems (Figure 2).
NEC Electronics produces products that are well suited to consumer device and industrial applications because of their extensive variety of frequencies, ROM sizes and packages for on/off control, stepping motor control and inverter control (Figure 3). For example, the 32-bit V850E2/ME3™ microcontroller, which realizes a maximum operating frequency of 200 MHz, is the ideal product for industrial-use inverters requiring ultra-high-speed processing. The 8-bit µPD78F0714 microcontroller and 32-bit V850ES/IK1™ microcontroller are equipped with optimum circuit functions for inverter control, including A/D converters, protection circuits and reset IC and low-voltage detection functions. Both microcontrollers are mainly used for inverter control of refrigerators and other such appliances.
Moreover, the V850E/IA4™ and V850E/IA3™ have been newly commercialized for inverter control appliances requiring high performance and low cost. These products are equipped with circuit functions optimized for inverter control such as A/D converters synchronized with inverter timers for sine-wave inverter control, which has been adopted in air conditioners of recent years, and protection circuits that increase the safety of systems. These microcontrollers also incorporate external ICs such as operational amplifiers and comparators, which are indispensable for system configuration. These two products, as well as the previously mentioned V850ES/IK1, are equipped with nearly identical functions, thus enabling software compatibility.
NEC Electronics' inverter control microcontrollers, which provide high performance, user-friendliness and safety, have acquired a favorable reputation with many set manufacturers, and as a result achieved a high share in the market. As we work to further expand our product lineup to maintain pace with the development of new applications, we will continue to offer products that allow our customers to improve system performance and keep costs down as well as realize the succession of development resources.
Note 1: Inverter technology refers to technology that produces AC power from DC power. In the case of air conditioners, 50/60 Hz of AC power is first converted into DC power, and then inverter technology is used to once again convert the DC power into AC power and rotate the motor.
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