Power Quality Test Procedures for Plug-In Electric Vehicle Chargers
This recommended practice provides test procedures for evaluating PEV chargers for the parameters established in SAE J2894/1, Power Quality Requirements for Plug-In Electric Vehicle Chargers.
In addition, this Recommended Practice provides procedures for evaluating EVSE/charger/battery/vehicle systems in terms of energy efficiency, which is a subset of power quality. This expansion of scope from J2894/1 was requested by the stakeholders, and it provides relevance to the system level analyses that are current in state and federal processes. In accordance, the scope includes the energy storage system and the input and output of that system.
In consideration of evaluation, a system boundary is established. The system boundary defines the tested elements and the measurement points. The system boundary for most of the systems expected to be evaluated under this Recommended Practice is shown in Figure 1. In this system boundary the parts of the battery charging system that are included for evaluation are the EVSE, the battery charger (BC), the system powering auxiliary loads, and the battery. It should be noted that this is a change from the original text of J2894/1, but it was essential for the purposes of system analysis to include all the elements, such as the EVSE, to evaluate efficiency and response to events. In terms of power quality and efficiency, the effects of this change should be minor. Note that no distinction is made about the battery or the auxiliary loads, which may include fans, chillers, or other thermal management devices. Note that some systems may require multiple measurement points to capture all auxiliary loads.
Figure 2 shows the system boundary for an off-board charging system.
Figure 3 shows the special case of an EVSE under test with a testing tool.
Note that all systems include an EVSE device. EVSE devices can introduce variance in test results. Therefore, all system test results must be recorded for, and are only valid for the tested combinations.
Auxiliary loads include all of the separable electrical loads on the vehicle while charging and discharging that are necessary for safe and effective operation and sufficient battery life, but are separate from energy going into the battery that later does work.
Examples of auxiliary loads:
Active battery cooling and heating system components
Data systems or telematics
Cabin comfort systems
12V system support (charging auxiliary, or starting, battery)
In 2011 SAE issued power quality requirements for plug-in electric vehicle (PEV) chargers in response to rising sales of PEVs and concerns about their potential impact on utility systems and on other devices connected adjacent to them. Electrical power is delivered upon demand, and utility systems are impacted by demand, or power, and the duration of that demand. Distinctions must be made about real power, which does work, and apparent power, which is the impact on the electrical system. The integration of transportation and the electric grid imposes concerns about not only serving demand and making sure that not only are existing deliveries made, but the additional load of vehicle chargers as well. Utilities must work to ensure reliability and quality of service. Computer equipment and controls are impacted negatively by distortions such as harmonics, so PEV chargers, like most all electronics, must limit potentially disruptive effects. In addition to impacts of equipment on the grid, the equipment itself must be reliable and effective when presented with effects impressed upon it, as can occur with the wide variety of loads and conditions that could emerge on the modern grid. Therefore, criteria were established to ensure that PEV charging equipment could continue to operate after encountering such grid events. These recommendations were presented in SAE J2894/1, Power Quality Requirements for Plug-In Electric Vehicle Chargers. This recommended practice provides the test procedures for measuring the criteria.
Since the power quality recommended practice was issued, interest has emerged for measuring and regulating energy efficiency of battery charging systems, on state and federal levels. Battery chargers have historically only been judged for efficiency instantaneously on a power conversion basis, as battery charging systems also include a battery, which is a variable energy reservoir, and a vehicle with auxiliary systems and controls. However, recent efforts have established energy efficiency measurement methods based on a systems approach. With these methods, grid energy input is measured against useful output. As there is not yet clear direction on things like “allowable” auxiliary loads, this recommended practice maintains the measurements in separate bins and provides suggested limits.
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