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5、 Quality Requirements for Plug-In Electric Vehicle Chargers RATIONALE The proliferation of nonlinear loads such as switching power supplies, variable frequency drives and battery chargers have led to a higher level of concern over the impacts of power quality. More precisely there are three major re
6、asons for these concerns: 1. Sensitive microprocessor based devices are more susceptible to power variances. 2. The increased number of non-linear devices has resulted in the rise of harmonics onto the power system leading to reduced system reliability.3. The vast networkability of devices has led t
7、o larger consequences from failure. Ultimately, the success of widespread plug-in electric vehicle (PEV) charging depends in major part to the reliability of both the electric grid and the charger. To meet the needs of PEV operators, PEV chargers must be sufficiently robust, reliable and cost effect
8、ive. In order to achieve this goal, vehicle and equipment manufacturers along with electric utility companies must understand the characteristics of the AC service to which the charger will be connected, as well as the impact chargers can have on service quality. The charger is the “conduit” through
9、 which energy moves from the AC line to the vehicles battery. For practical purposes, it is the charger that controls power quality. FOREWORD Designers and the vehicle manufactures that implement PEV battery chargers must understand the characteristics of the AC service to which the equipment will b
10、e connected if they are to develop products that are sufficiently robust, reliable and cost effective to satisfy the needs of the PEV owner. The charger designer and vehicle manufacturer must also understand that the battery charger can have a significant impact on the quality of the AC service to w
11、hich it is connected. The information presented in this Recommended Practice may be used by charger power supply designers, managers of charger development programs, and an electric utility. NOTE: This SAE Recommended Practice is intended as a standard practice and is subject to change to keep pace
12、with experience and technical advances Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE J2894-1 Issued DEC2011 Page 2 of 16 TABLE OF CONTENTS 1. SCOPE 32. REFERENCES 32.1 Applicable Documents 33.
13、DEFINITIONS . 44. CHARGER POWER QUALITY PARAMETERS . 64.1 Displacement Power Factor 64.2 4.2 Power Conversion Efficiency 74.3 4.3 Total Harmonic Current Distortion 84.4 4.4 Current Distortion at Each Harmonic Frequency 94.5 Inrush Current . 95. CHARACTERISTICS OF THE AC SERVICE . 105.1 Voltage Range
14、 115.2 Voltage Swell 115.3 Voltage Surge . 115.4 Voltage Sag . 115.5 Voltage Distortion 125.6 Momentary Outage . 125.7 Frequency Variation 125.8 Portable (Self) Generation / Distributed Energy Resources . 126. CHARGING CONTROL 136.1 Utility Messaging . 136.2 Communication . 136.3 Cold Load Pickup 13
15、6.4 Load Rate (Soft Start) . 14APPENDIX A 15FIGURE 1 AC LINE VOLTAGE/LINE CURRENT PHASE RELATIONSHIP 6FIGURE 2 TYPICAL INPUT CIRCUIT 7FIGURE 3 COLD LOAD PICK-UP the vehicle inlet and the coupler. The charge coupling is actually a take-apart transformer, the coupler comprising the transformer primary
16、 and the vehicle inlet housing the transformer secondary. 3.7 ON-BOARD CHARGER A charger located on the vehicle for the purpose of delivering DC energy to the PEVs energy storage device. Typically requires an AC input from an external EVSE. 3.8 OFF-BOARD CHARGER A charger located externally to vehic
17、le for the purpose of delivering DC energy to the PEVs energy storage device. Typically requires an AC input from the sites electrical infrastructure. 3.9 DC CHARGING A method that uses a dedicated off-board direct current (DC) BEV or PHEV supply equipment to provide energy from an appropriate off-b
18、oard charger to the BEV or PHEV in either private or public locations. 3.10 ELECTRIC VEHICLE SUPPLY EQUIPMENT (EVSE) The conductors, including the ungrounded, grounded, and equipment grounding conductors, the electric vehicle connectors, attachment plugs, and all other fittings, devices, power outle
19、ts, or apparatuses installed specifically for the purpose of delivering energy from the premises wiring to the electric vehicle. Charging cords with NEMA 5-15P and NEMA 5-20P attachment plugs are considered EVSEs. 3.11 FREQUENCY VARIATION The normal range of variation of the AC line frequency. 3.12
20、MOMENTARY OUTAGE A complete loss of AC line voltage for a 12 Cycles (200 ms) or more. 3.13 VOLTAGE RANGE The normal range of variability of the AC line voltage. Voltage Range is generally expressed as a “percent of nominal“ of the nominal value of line voltage varies regionally. Copyright SAE Intern
21、ational Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE J2894-1 Issued DEC2011 Page 6 of 16 3.14 VOLTAGE SAG A reduction in the AC line voltage below the normal range of variability, typically of relatively short duration,
22、typically 30 to120 cycles (500 ms to 2000 ms). 3.15 VOLTAGE SURGE (TRANSIENT) A temporary increase in the AC line voltage far beyond the normal range of variability that is evidenced by a sharp brief discontinuity of the waveform, typically of very short duration (sub-cycle) 3.16 VOLTAGE SWELL A tem
23、porary increase in the AC line voltage of more than 10% of the normal range of variability at the power frequency, typically of relatively short duration of half a cycle to a few s (8ms 5000ms) 4. CHARGER POWER QUALITY PARAMETERS 4.1 Displacement Power Factor Total power factor is defined as the rat
24、io of real power in Watts to apparent power in Volt-Amps, and is expressed by the following formula: Displacement Power Factor = Real Power (kW) / Apparent Power (kVA) If voltage distortion is negligible, total power factor is equal to the product of displacement power factor and distortion power fa
25、ctor. Displacement power factor, which is the ratio of real power to apparent power at the fundamental frequency (50Hz / 60 Hz), is a measure of the phase shift that occurs between line voltage and line current when the AC line is loaded with a linear load having reactive characteristics, such as an
26、 AC motor. The line current is sinusoidal in shape, but either leads or lags the line voltage in phase (Figure 1). FIGURE 1 - AC LINE VOLTAGE/LINE CURRENT PHASE RELATIONSHIP Distortion power factor is the ratio of fundamental current to total rms current. The line current distortion is normally the
27、result of non-linear loading of the AC line. Most switching power supplies, except those that incorporate active power factor correction, use full wave bridge rectifiers with capacitive input filters to perform AC to DC conversion from the line (Figure 2). The rectified AC peak charges the input cap
28、acitor to produce a DC voltage nearly equal to the peak line voltage. Because the capacitor is peak charged, the diodes in the bridge rectifier are reverse biased for most of the AC sine wave, forward biasing only near the peak of the line voltage where V(line) exceeds V(cap) + 2 x V(diode). The “re
29、sulting currents are highly distorted from the ideal sine wave, and contain harmonics of the fundamental line frequency. Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE J2894-1 Issued DEC2011 Pag
30、e 7 of 16 FIGURE 2 TYPICAL INPUT CIRCUIT Maintaining a high input power factor is important for two reasons. A. Maintaining a high power factor minimizes reactive line current and harmonic currents of the fundamental line frequency. Because available power is limited by available line current which
31、is in turn limited by the circuit breaker protecting the line, minimizing reactive and harmonic currents maximizes the line current which is actually available for true power delivery. B. Minimizing reactive and harmonic currents minimizes heating of the AC service conductors for a specified deliver
32、ed power. This permits optimal utilization of infrastructure and may eliminate the need to perform a service upgrade when EV battery chargers are installed. The recommended minimum values for total power factor are defined in Table 1 below. These values are specified for operation at the full rated
33、output power of the charger. Recommended Displacement Power Factor Values AC Level 1 AC Level 2 DC 95% 95% 95% TABLE 1 - MINIMUM RECOMMENDED GUIDELINES FOR TOTAL POWER FACTOR 4.2 4.2 Power Conversion Efficiency Power conversion efficiency is a measure of how efficiently the charging equipment proces
34、ses power from its input terminals to its output terminals. Power conversion efficiency can be measured over the total charging cycle or at any point in the charging cycle. Due to the typical battery charging profile, the charger efficiency will be greatly reduced at the “finishing off“ part of the
35、chargingcycle, when minimal power is delivered. Efficiency is most important when the charger is delivering maximum power to the load because low power conversion efficiency at full output may constitute a significant power loss. Power conversion efficiency is defined as a ratio of the charger input
36、 power to the charger output power per the following equation: Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE J2894-1 Issued DEC2011 Page 8 of 16 Power Conversion Efficiency (%) = DC Power (kW)
37、at Charger Output / AC Power (kW) at the Charger Input x 100 Full power efficiency is this ratio measured at the rated full power output of the charger. Because all power processing systems have loss, power efficiency is always less than 100%. Full power efficiency is important for two reasons. A. A
38、n efficient charger reduces battery recharge time by optimally accessing energy from the AC line and delivering it to the battery. Since all electric services are current limited (therefore power limited) less wasted power equals greater power delivery to the battery which reduces charge time. B. Hi
39、gh power conversion efficiency is consistent with the underlying philosophy of emissions reduction. A highly efficient charger reduces the required energy production for a given energy transfer to the vehicle, thereby, reducing the pollutants produced by the energy production process.Recommended min
40、imum values for power conversion efficiency are specified in Table 2. These values are specified at the full rated power of the charger into a resistive load. Note: System energy efficiency defines how the system uses the energy that the charger delivers. The charger cannot control how the system us
41、es energy. Therefore, it is not possible to specify system energy efficiency as a controlled parameter for a charger. Conversely, power conversion efficiency does not dictate how the system uses energy. It is a function of the design of the charger and therefore can be specified as a controlled para
42、meter for the charger. Recommended Full Power Conversion Efficiency AC Level 1 AC Level 2 DC 90% 90% 90% TABLE 2 - MINIMUM RECOMMENDED GUIDELINES FOR FULL POWER CONVERSION EFFICIENCY 4.3 4.3 Total Harmonic Current Distortion Periodic waveforms can be broken down into component sine waves which are r
43、eferred to as harmonics of the fundamental wave form. These harmonic frequencies are integer multiples of the fundamental frequency of the periodic wave form. Each harmonic has a specific amplitude and phase with respect to the fundamental. The vector sum of all harmonics produces the original perio
44、dic wave form. If the periodic waveform is a “pure“ sinusoid, then only the fundamental frequency is present. There are no harmonics. Any undesired departure from the purely sinusoidal wave shape is referred to as harmonic distortion. Total harmonic distortion (THD) is the root mean square of each i
45、ndividual harmonic distortion. It is desirable for any current drawn from the AC line to have a fundamental frequency equal to the line frequency (50/60 Hz) with no harmonic distortion. This is because only fundamental current contributes significantly to true power delivery. Harmonic currents do no
46、t contribute to true power because the product of the undistorted line voltage and the harmonic currents, averaged over one full cycle of the AC line, is always equal to zero. In short, harmonic currents that flow on the AC line contribute nothing to true power delivery. They simply heat the wire an
47、d, in so doing, waste energy. Harmonic currents can also cause distortion of the AC line voltage. This is dependent on the line impedance (l x R drops) and the presence of resonances due to the capacitances and inductances in the system. This distortion, if severe enough, may cause other equipment c
48、onnected to the line to malfunction or even sustain damage. Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE J2894-1 Issued DEC2011 Page 9 of 16 Institute of Electrical and Electronics Engineers (IEEE) 519 is a guide for utilities on limiting the amount of harmonic voltage and current distortion allowed on their system. The guide specifies that the total harmonic distortion of the voltage waveform for voltages below 69 kV should not exceed 5 percent. In addition, no individual volt
