Government agencies that define the standardization of energy efficiency metrics continue to be a manufacturers force behind the development of the next generation electric vehicle powertrains. These metrics require manufacturers to have high confidence in their measurements and motivate the optimization of efficiency. The use of purpose-built instruments for the development of electric powertrains ensures compliance with these standards and enables further optimization beyond regulation.
The Environmental Protection Agency follows SAE J1634 “Battery Electric Vehicle Energy Consumption and Range Test Procedure” as the testing criteria for determining vehicle energy consumption and range testing of electric vehicles (MPG equivalency). SAE J1711 is a similar standard for plug-in hybrid electric vehicles. Table 1 provides examples of electrical energy measurements in SAE J1634.
|Battery Ampere-Hour Capacity||DC Amp Hours|
|Discharge Energy||DC Watt Hours|
|DC Discharge Amp-Hours||DC Amp Hours|
|Power Outlet Voltage||AC Volts (RMS)|
|AC Recharge Energy||AC Watts Hours|
|DC Recharge Amp-Hours||DC Amp Hours|
SAE J1634 makes the following requirements on electrical energy measurements:
The measurement of electrical kinetic energy is performed by making voltage and current measurements, computing electrical power, and performing a gapless integration of power over time (Figure 1).
Similarly, the measurement of mechanical kinetic energy in a rotating machine is typically performed by making torque and speed measurements, computing mechanical power and integrating power over time. The efficiency of the conversion electrical kinetic energy to mechanical kinetic energy is computed from the ratio of electrical input energy to the mechanical output energy. A power analyzer is a purpose-built instrument intended for making both the electrical and mechanical energy measurements (Figure 2). A power analyzer will provide highly detailed published accuracy specifications with NIST traceability (Figure 3). Power analyzers are often called out in standards documents as the preferred measurement devices for electrical measurements and are regularly found in the engineering laboratories of manufacturers and government agencies responsible for ensuring compliance. SAE J1634 Battery Electric Vehicle Energy Consumption and Range Test presumes that computations for electrical energy measurement will be performed by a power analyzer.
EV powertrain systems are often comprised of multiple AC to DC, DC to DC and motor and inverter drive components, each component in the stage contributing to the overall system efficiency. Figure 4 shows an example traction motor and drive system comprised of a DC input, variable speed 3-phase inverter, and a variable speed motor.
Measurement points 1-4 denote the points of electrical power measurement in the system, with point M denoting the measurement of mechanical output power. Power analyzers allow engineers to take high confidence measurements at each one of these stages, quantifying the efficiency of each component in the system (inverter, motor), enabling the maximization of overall powertrain efficiency. A power analyzer can also be used to evaluate the efficiency of other electrical components in the vehicle such as charging systems shown in Figure 5.
Power analyzers provide a concrete measure of efficiency throughout the system; however, each individual component carries its own complexity. Each sub-component presents unique engineering challenges to optimization and integration. A new motor control algorithm in the inverter might require the use of a positional feedback sensor such as Hall-effect, encoder, or resolver. As shown in Figure 6, the feedback from these signals are often high-speed, multi-channel, and require complex mathematics to decode position, direction, and speed.
Figure 7 shows an example output of an AC inverter driving a motor. Modern inverters use high-speed pulsed power electronics (PWM), resulting in complex high-voltage, high-frequency output waveforms of voltage and current. These signals present several engineering challenges such as harmonics, electromagnetic interference, and the ability to make high-voltage measurements in a safe manner.
Understanding how each of these subsystems are interacting and determining proper operation is key to optimizing the efficiency at each stage. Design, validation, and test engineers are faced with challenging questions when trying to understand the performance of the entire system. Examples of these challenges include:
Optimization and integration of the individual components of a complex EV system require instrumentation that is flexible enough to handle a wide range of signals not found in conventional oscilloscopes or data acquisition systems. A ScopeCorder is a purpose-built instrument for the development of electromechanical systems such as motors and drives. A modular design enables the evolution of the instrument as the engineering needs change. A unique array of digital and analog input modules combined with real-time math enable the decoding of complex sensor data such as encoders and resolvers. High-voltage, high-sample rate modules offer isolated inputs up to 1000V allowing safe measurements on complex pulsed power signals. Communication modules such as CAN/FD decode digital bus signals into engineering units for correlation with the rest of the system IO. Figure 9 shows the array of input modules including voltage, temperature, strain, frequency, acceleration, logic, and various digital communications.
Standards such as SAE J1634 establish test methods that provide parity in the market as government agencies attempt to steer manufacturers toward more energy efficient vehicles. Precision power analyzers are purpose-built tools for providing reliable mechanical and electrical energy measurements allowing manufacturers to confidently comply with standard testing procedures. The complexity of electric vehicles challenges engineers with a multitude of signals that conventional instrumentation does not easily accommodate. ScopeCorders provides a unique solution to mechatronic measurements and allows engineers to better answer the challenging questions that arise when analyzing the performance of an entire system. Yokogawa Test and Measurement is an industry leader in providing a full range of instruments for energy measurement and mechatronics development including power analyzer and ScopeCorders.
Yokogawa, the world's largest manufacturer of energy and power analyzers and meters, provides a broad choice of digital power analyzers to satisfy all requirements.