(R) SAE Electric Vehicle Inductive Coupled Charging
|Publication Date:||1 November 1999|
1. Scope--This SAE Recommended Practice establishes the minimum interface compatibility requirements for electric vehicle (EV) inductively coupled charging for North America.
This part of the specification is applicable to manually connected inductive charging for Levels 1 and 2 power transfer. Requirements for Level 3 compatibility are contained in Appendix B. Recommended software interface messaging requirements are contained in Appendix A.
This type of inductively coupled charging is generally intended for transferring power at frequencies significantly higher than power line frequencies. This part of the specification is not applicable to inductive coupling schemes that employ automatic connection methods or that are intended for transferring power at power line frequencies.
1.1 General Inductive Charging System Description--The basic principle behind inductive charging is that the two halves of the inductive coupling interface are the primary and secondary of a two-part transformer. When the charge coupler (i.e., the primary) is inserted in the vehicle inlet (i.e., the secondary), power can be transferred magnetically with complete electrical isolation just as it occurs in a standard transformer. The number of turns (windings) on the secondary is "matched" to the vehicle's battery pack voltage so that the same charger can charge any vehicle.
The charger converts utility power to high frequency AC (HFAC) power (130 kHz to 360 kHz). The high frequency operation is utilized to reduce the size and mass of the on-vehicle portion of the transformer. The vehicle inlet is the power inlet on the vehicle which receives the HFAC from the charger. The HFAC is converted into DC to charge the batteries. An on-vehicle charge controller continuously monitors the state of the batteries during charging and controls the charger output power level via an IR communications link between the vehicle inlet and the charger (the charger's communications interface is physically imbedded in the charge coupler). The charge controller signals the charger to stop charging when it determines that the batteries are completely charged or a fault is detected during the charging process.
The following steps correspond with the diagram in Figure 1, and describe the closed-loop charging system.
a. Vehicle charge controller determines desired current into batteries. **
b. Vehicle charge controller transmits charger output power request to charger via an IR communications interface. **
c. Charger controls input current from utility based on charger output power request from vehicle charge controller. **
d. Charger converts 60 Hz utility power to HFAC power.
e. HFAC power is magnetically coupled from the coupler (primary) to the vehicle inlet (secondary).
f. HFAC power is rectified/filtered to DC to charge the vehicle batteries.
g. Process repeats until the vehicle charge controller determines the batteries are fully charged. **
NOTE--Items with ** indicate control loop.