Testing for energy efficiency
Guest columnist Clive Davis of Yokogawa Europe describes how measuring technologies play their part in the drive to design more energy efficient systems and products, both from the point of view of ensuring optimum energy efficiency and meeting the compliance targets of international standards and the related legislation.
Even in a familiar area of home electronics, technologies to reduce power consumption are seen in devices, circuit designs, structure designs and software control technologies.
These technologies include improving the efficiency of power supplies and motor drives by using inverters, using LED for lighting apparatus, and applying intelligent technologies to control the operation of equipment with reduced energy consumption. In the technology development process, component and equipment characteristics must be quantified, and it is important to measure the power consumption of products by power meters with guaranteed traceability.
In the latest generation of digital power analysers a number of new functions are included for electrical power and efficiency measurements in a range of industries from inverter and drive design to alternative energy systems.
A key feature of this product is the ability to make up to six power input measurements, which makes it possible to perform efficiency tests between the input and output of products such as inverters, matrix converters, motors, fans and pumps.
The instrument has a power measurement bandwidth from DC and 0.1Hz to 1MHz, and basic power measurement accuracy is 0.1% of reading plus 0.05% of range.
A motor evaluation function makes it possible to measure the rotation speed, torque, and output (mechanical power) of motors from rotation sensor and torque meter signals. The input signal from the rotation sensor and torque meter can be selected from analogue signals (DC voltage) or pulse signals.
In addition, A-phase, B-phase, and Z-phase input terminals make it possible to detect the rotation direction and electrical angle.
For the first time in the high-precision power analyser industry, an event trigger function is incorporated to capture only a particular event. A trigger can be set for measured values that fall out of a pre-selected range, and the analyser will only store, print or save data that meets the trigger condition.
Many of today’s power conversion circuits use energy-saving switching techniques which can cause highly distorted voltage or current waveforms with high harmonic content. To measure these waveforms accurately, the new analyser uses high-resolution 16-bit analogue-digital converters with a digitising rate of 2MS/s (megasamples per second).
It is now possible to simultaneously measure voltage, current fundamental wave, harmonic components, and harmonic distortion factor (THD) in the harmonic measurement mode, along with the conventional voltage and current RMS values in the normal measurement mode. In addition, up to the 500th order harmonic can be measured for fundamental frequencies.
The analyser is capable of performing two-line simultaneous harmonic measurements with one unit for the first time in the industry. The ability to simultaneously measure harmonics for the input and output signals not only reduces the switching time but also makes it possible to perform simultaneous data analysis for the input and output.
The dual harmonic measurement function makes it possible to simultaneously measure the harmonic content and perform harmonic analysis on two different sources, such as the input and output of an inverter, variable-speed motor drive, lighting ballast, uninterruptible power supply or similar devices. The normal power parameters and harmonic data are measured simultaneously, providing for faster and more accurate power analysis.
The ability to make multiple measurements in a single unit makes the unit ideally suited to the performance testing of multiple appliances on a production line. A single instrument can perform high-precision power evaluation on up to six items of equipment, measuring voltage, current, power, frequency, power factor, and harmonic distortion factor. An independent integration function is available for each input element to start and stop integration. Since data can be collected remotely by communicating with just a single analyser, it is easy to create the appropriate test programs.
As indicated above, power generation and conversion efficiency measurements are vital in new energy markets, including photovoltaic and wind power generation. For example, energy generated by photovoltaic cell modules and wind turbines is converted from DC to AC by a power conditioner.
Furthermore, the voltage is converted by a charge control unit for the storage battery. Minimising losses in these conversion processes improves efficiency in the overall energy system. The instrument’s ability to provide up to six channels of power inputs per unit makes it possible to measure the voltage, current, power, and frequency (for AC) before and after each converter, as well as converter efficiency and charging efficiency.
A new programmable digital filter function enhances the capability to remove unnecessary harmonic components and noise superimposed on signals such as from an inverter or variable-speed motor drive. This filter can be set independently for each input element, from 100Hz to 100kHz in 100Hz increments.
An analogue filter is also provided for 300kHz and 1MHz filtering on each input element.
For photovoltaic power generation applications, a maximum peak power tracking measurement is available to maximise the harvested power generated by photovoltaic cells. To accomplish this, the analyser is capable of measuring voltage, current and power peak values and calculating the derived parameters.
A power integration function is also available which can be used to measure the amou nt of power sold or purchased in grid interconnection applications. An average active power function makes it possible to measure power consumption under conditions where the power fluctuates greatly.
Power measurements on fluorescent and LED lights are another key application. Since the switching frequency of fluorescent lights can be tens of kilohertz, a wide range power measurement is required. In addition, dimming control using PWM modulation circuit is used with LED lights.
The new analyser provides a wide range from DC to up to 5MHz to allow the resultant harmonic signals to be evaluated.
Input/output efficiency measurements are also necessary on the inverter motors used for electric vehicles. Here, the analyser’s ability to perform up to six power input measurements makes it possible to evaluate the battery’s charge and discharge characteristics, and test and evaluate the efficiency between the input and output of inverters.
The motor evaluation function makes it possible to simultaneously monitor changes in the voltage, current, and power, as well as changes in the rotation speed and torque.
Similar considerations apply to high-order harmonic measurements on aircraft power supplies and power measurements in ‘green’ IT data centre servers.