Methods to reduce device power consumption - accurate measurement

Some predict that the world's energy demand is likely to exceed the energy supply. The U.S. Department of Energy estimates that the total energy consumption in the United States is expected to increase by 30% to 5 trillion kilowatts in 2035, while the planned development of energy, including renewable energy, will only increase by 22% during the same period.

In addition, strategies for energy management are primitive and inefficient, resulting in reduced reliability and stability in the energy distribution process. Engineers are working to improve the efficiency of energy use in all electronic products, including commercial equipment, home appliances, industrial motors, and network equipment. However, it is also necessary to understand how energy is consumed in a closed-loop system to produce beneficial effects and reduce waste. Improving efficiency is only one of many factors. Changing consumers' indifference to efficiency can be achieved through intelligent monitoring of power consumption, which can provide energy-saving options.

The data generated by accurate power consumption measurement and continuous monitoring can be submitted to the local data and control network. Once the data reaches the network, many kinds of power consumption improvement measures with minimal compromise can be automatically given. In fact, such a data network can guide us to improve our lifestyle, for example, when the air conditioner fails, it will not be incomprehensible.

Accurate measurement will provide the information necessary to understand, verify, report and correct equipment power consumption or power allocation. Consumers need to prepare for inevitable changes in the way electricity bills are settled and how to balance the obligations of their choices. What will happen when we are faced with electricity bills of $3.00 per kWh on a regular basis? That day is coming.

Measure and control at every load point

To achieve high efficiency through intelligent power management and consumer choice, accurate measurement of overall equipment power is required, such as the total power consumed by the entire device, but also at the load point, such as an air conditioner, dishwasher, computer, or lighting fixture.

Smart meters can measure electricity consumption on a daily basis, which provides consumers with the best way to change their electricity usage patterns. In order to improve automatic control methods and provide consumers with various options and value-added services, each device must be connected to a local data and control network to monitor and allow control of various loads within the building. Through power measurement and usage statistics, corresponding services can be provided to consumers, such as maintenance scheduling. Such a network can be implemented using a variety of configurations and protocols, depending on the application.

Local data and control networks, including precise power measurement, can help consumers and businesses reduce high costs by identifying how power is used. Users who can see the difference between using air conditioning for about $200 per month (use value) or the difference between using a dryer at noon instead of 7 p.m. (time value of use) are more likely to change their usage patterns.

Data that was previously available only through expensive high-end meters can now be collected for just a few dollars per load point. Power factor (PF) and apparent power (VA) information can be easily obtained, and these parameters can be used to optimize power allocation budgets, such as predicting equipment maintenance time and understanding the fatigue level of aging systems.

Figure 1 depicts the power consumption of a laptop computer powered by two different power adapters. Even if the actual load is the same, the power supplied from the power line can vary greatly. This valuable information is now easily available. The statistical results can be used to adjust the operating behavior of the device. A small drop in voltage or line frequency may indicate a power failure and cause the device to enter protection mode. [page]

Figure 1 Power curves of a laptop computer using two different power adapters in power-on, stable operation, and power-off states

The zero-crossing information of the AC voltage can also be used for timing, which can reduce the arcing generated when the relay contacts separate and close. When this information is obtained in a low-cost and low-power manner, many improvements can be made to the equipment. When transitioning from qualitative evaluation to quantitative measurement, the return on investment is also easier to quantify and control, so accurate measurement is very necessary. Figure 2 describes a very easy-to-use data acquisition system.

Figure 2 A USB-based power socket monitoring demonstration device using the 78M6612 SoC chip

The importance of accuracy

The implementation of intelligent power management algorithms requires a clear description of actual power consumption and actual needs, which requires measurements with considerable accuracy. Currently, on-chip systems are very common, enabling every device to become an intelligent instrument. For example, Teridian's 78M6612 AC power monitoring SoC can measure currents from 10mA to 20A, and the measurement error is less than 0.5% over the temperature range of -40°C to +85°C.

Achieving high measurement accuracy requires high resolution, high precision, and a wide dynamic range. Many general-purpose MCUs are limited in measurement accuracy because they only have 10- or 12-bit ADCs. The 78M6612 has a 22-bit ADC with very high dynamic range and accuracy. Dynamic range affects more than just accuracy. Measuring across a wide dynamic range allows the same circuit to monitor different areas of application, making costs lower.