Green Systems

Further efforts to save energy are essential to overcome the environmental issues facing us. One essential point in achieving this will be reducing wasted power at the system level through efforts to make control as efficient as possible. As key components of many products, semiconductor devices have a big part to play in this area. Both hardware innovations and software design technologies play important roles in contributing to the realization of more environmentally friendly products.
This page introduces examples of eco-friendly technologies used in application systems. For specific examples of such applications, please refer to our Green Applications page.

Switching to Renewable Energy Sources

Realization of a low-carbon society is an urgent task if we are to solve the problem of global warming. We must switch from a power generation model dependent on fossil fuels to one that employs renewable energy sources such as solar and wind. In like manner, a move in future from automobiles that consume fossil fuels to plug-in hybrid vehicles and electric vehicles is also being widely considered.
However, the amount of power that can be produced by renewable energy sources such as solar and wind is affected by a variety of natural conditions. To ensure the stable operation of large-scale power systems, many countries are actively promoting the construction of smart grids , a new type of power distribution grid system employing information technology (IT).
Electronics technology is absolutely indispensable to achieving a switchover to renewable energy sources. Furthermore, it can be said that semiconductor technology will play an extremely large role in this process by making possible equipment that runs on less power, more efficient power conversion, and more.

Technologies for Reducing the Power Consumption of the System

One technological approach to reducing the power consumption of the entire system is to focus on reducing the amount of power that goes to waste. Such an approach must deal, for example, with issues such as "whether too much power is being consumed when equipment is in standby mode" or "which power consuming components need to be optimized in order to achieve the greatest efficiency for the system as a whole". Examples are presented below of some ways systems can be made more efficient.

1) Reducing Wasteful Power Consumption

To boost energy efficiency at the system level in everything from IT to household appliances and electronics, "system technologies" are needed that are effective in cutting power consumption through approaches such as main power supply control, reducing standby power consumption, and positive adoption of inverter circuits to implement such control. Some examples are presented below.

(a) Shutting Off the Main Power Supply When Equipment Not Operating

Scheduled Operation:

An operating schedule is determined beforehand, and the main power supply is turned on only when it is needed. Alternately, if processing must be performed at regular intervals, a timer is used to turn on the main power supply only when processing is performed. This approach is particularly effective for large-scale equipment used in factories and the like.

Operation Control Using Sensors:

Proximity or motion sensors are used to provide control so that the equipment operates only when someone is present and is shut off when it is not required.

Control via a Network:

A local area network (LAN) or the like is used to provide control so that only the required equipment is powered on.

(b) Reducing Standby Power Consumption

In cases where it is not possible to cut off the main power supply, such as equipment in which a timer function alone must continue operating, power can be supplied only to enable the clock to operate and cut off to all other modules. One point to keep in mind regarding this method of reducing standby power consumption is that the device used for control continues to consume power.

Sleep Function:

Microcontrollers and SoC devices require a sleep function. It enables the power consumption of the device to be reduced dramatically, either by halting operation of all blocks that are not essential or by switching to an extremely low operating frequency. Recent semiconductor products offer the user a variety of low-power modes to select from to match the operating conditions.

Power Supply Intermittent Operation Mode:

When processing must be performed at regular intervals, power is supplied only when processing takes place.

Low-Power Converter for Standby:

Large-capacity power devices generally have somewhat lower power supply efficiency at lower output levels, so a separate low-capacity power supply can be provided to supply power only in standby mode.

(c) Reducing Power Consumption During Operation

In the case of familiar examples in the home, such as air conditioners and refrigerators, it is also necessary that thoroughgoing efforts be made at the design stage to reduce power consumption at the system level. It is particularly important to increase the energy efficiency of motors, which convert electric power into motive force, and inverters are ideal for this purpose. An inverter works by converting the commercial AC power supply output into DC, generating an AC voltage from the DC voltage, and using the output to drive a motor. For example, if a piece of equipment is connected directly to a 100 V commercial power supply with a frequency of 50 Hz or 60 Hz, an inverter can be used to control the voltage amplitude and frequency, and the drive phase, making it a highly effective technology for reducing the operating power consumption.

2) Higher Energy Conversion Efficiency and Fine-Grained Control: Details of Inverter Control

Fine-grained inverter control loop (Click to enlarge)

In applications such as factory automation equipment or household appliances, it is necessary to manage factors like temperature, humidity, rotation rate, and flow volume in addition to time. An air conditioner, for example, uses a motor to turn the compressor and performs control to bring the indoor temperature to the setting value by using the operating principle of a heat pump. A sensor constantly monitors the indoor temperature, and the temperature is raised or lowered toward the target value by controlling the operation of the motor and the control valves.
If only simple on/off control was available, it would be necessary to run the motor (compressor) at full power every time the indoor temperature deviated from the setting value, resulting in very inefficient use of energy. A method for controlling energy conversion is needed in order both quickly to attain the specified temperature and to achieve fine-grained maintenance and management of temperature settings.
Today inverter control is widely used for this purpose. Inverter control is a technology that provides free control over the voltage and frequency of the power supply. It enables efficient power conversion and fine-grained control.
Renesas supplies a variety of microcontrollers for inverter control applications, including the RX600 Series with advanced PWM functions and multichannel A/D converters on-chip, in addition to high-performance power devices such as IGBTs and MOSFETs. In this way we have made an important contribution to the widespread adoption of inverter technology. Please see the following section for an overview of inverter technology.

Inverters: A Fundamental Technology for Saving Energy in the Consumer and Industrial Fields

Technologies for Boosting the Power Conversion Efficiency of Power Supply Equipment

Renesas turned its attention to smart grids early on and now supplies a variety of solutions that are instrumental in their implementation. We already supply devices supporting the ZigBee specification for Near Field Communication (NFC) as well as power line communication (PLC), both of which are part of the communication infrastructure forming the foundation of a smart grid.

The power supplies in factories and homes use alternating current (AC). Most electrical products, such as household appliances, home electronics, and personal computers, incorporate a power supply circuit that converts the AC into direct current (DC). Inevitably, the operation of these AC/DC power converters entails some amount of energy loss.
As demand for personal computers and servers grows with the increasing importance of information technology (IT), and as the rising standard of living in developing countries means that more and more electrical products are in use, the loss during power conversion becomes too significant to be ignored. Finding ways to reduce the hidden waste arising within the power supplies of products that use electric power is a key issue. Methods to achieve this goal include the following.

1) Digital Control to Improve the Power Conversion Efficiency of Power Supplies

By improving the efficiency of the power supplies in a large number of electrical products it is possible to boost power conversion efficiency worldwide. Approaches such as the following can be used to increase power supply efficiency.

• Using low-loss power devices (transistors with low on-resistance, low-loss, fast-recovery diodes, etc.)
• High-efficiency circuit design (improved multilevel inverters, gradation control, high-efficiency UPS configurations, etc.)
• Using soft switching converters (resonant converters, zero-voltage switches) This is a way to reduce the switching loss of power devices. It enables use of a higher switching frequency and smaller coils, making it an effective way to make the power supply more compact.

High-performance power supplies such as these have more complex control requirements, so attention is turning to digital control methods as alternatives to conventional analog control. Using a digital control system for the power supply means that a processor or digital signal processor (DSP) can be used to perform the necessary operation processing and allows support for a variety of control methods simply by making changes to the software.

2) Increasing Use of Digitally Controlled Power Supply Technology in UPS Systems

Large-scale IT data centers employ uninterruptable power supply (UPS) systems to ensure that power will continue to be supplied to the servers and other IT equipment even in the event of a power failure. Online UPS systems, which ensure not even a momentary interruption in the supply when a power failure occurs, provide excellent reliability. However, since UPS systems use internal batteries to store power, they are constantly performing AC to DC to AC power conversion.
Particularly in data centers where IT equipment is stored at a high density, the energy loss accompanying power conversion is a major issue. In addition, a substantial investment in climate control equipment is needed to deal with the heat generated by the lost energy.
To improve energy efficiency in cases such as these, new control methods and control circuits that provide better power conversion efficiency are being proposed and developed, both for large UPS systems used in data centers and for compact UPS products as well. This has spurred demand for complex control systems that cannot be implemented with conventional control methods.
Digital control methods provide the solution. In particular, flexible digital control technology employing microcontrollers can be incorporated into UPS systems. The RX600 Series integrates a floating-point unit used principally for running control algorithms, multiple A/D converters for analog signal detection, and high-performance PWM drive functions. It can perform DSP signal processing while at the same time carrying out the interrupt control and communication functions for which microcontrollers are well suited, making it possible to build UPS systems that deliver low power conversion loss and high efficiency.

Power Supplies: Digitally Controlled Power Supplies, Power Factor Correction, Digitally Controlled UPS Systems, Battery Control

Every piece of electrical or electronic equipment requires a power supply. The function of a power supply is efficiently to convert power from a commercial power source or battery into electricity in the required format. If the efficiency of the conversion can be improved even a little, this translates directly into a reduction in power consumption.
Renesas has contributed to improved power conversion efficiency by supplying from early on a variety of widely used DC/DC converters, PWM ICs, critical conduction mode interleaved PFC ICs providing an improved power factor, and battery control ICs for high-precision remaining battery charge detection. We are working to further improve compactness and power efficiency by offering MOSFET products such as 6 mm × 6 mm DrMOS devices employing SiP technology.
In recent years interest in digitally controlled power supplies and UPS systems with fully digital power control has increased. The digitizing of power supplies opens up many new possibilities, including high efficiency with flexible control by software and centralized control of large-scale power supply systems through the use of communication functions.
In a digitally controlled power supply, a switching device employing a PWM circuit is used for power control. Digital high-speed feedback calculation makes it possible to achieve superior power supply performance. The RX600 Series integrates a floating-point unit used principally for running control algorithms, multiple A/D converters for analog signal detection, and high-performance PWM drive functions, making it possible to build UPS systems that deliver low power conversion loss and high efficiency. The greater interest in digitally controlled power supplies in recent years owes a lot to substantial increases in the performance delivered by semiconductor devices such as processors and power devices.