Patent Application
20110163716
Plug-in hybrid electric vehicles and battery electric vehicles typically include a battery charger that may receive electrical energy from an electrical grid via a wall outlet and provide electrical energy to a traction battery and/or other electrical loads.
An automotive vehicle power system may include a battery charger having an input and output. The battery charger may receive electrical energy via the input when the input is electrically connected with an electrical power source. The battery charger may also reduce a current provided at the output from a commanded value to a target value that varies according to a temperature of the battery charger if the temperature falls within a predetermined range of temperatures.
When charging a vehicle from an AC line, there is a desire to ensure that power limits of the charger are not exceeded. Charger components, for example, may heat up when excessive power is being drawn from the AC line, when excessive ambient temperatures occur, and when there is a loss of cooling, etc. A typical approach for limiting the heating of charger components is to terminate the charge when excessive heating occurs. This termination of charging may result in customer dissatisfaction.
Certain battery chargers described herein provide power for charging both a low voltage (LV) vehicle battery and a high voltage (HV) vehicle battery. These chargers may also measure the voltage and current at the output of both the HV and LV systems, and control the HV output current and the LV output voltage set point. This form of low voltage control may result in the LV system supplying smooth regulated output LV voltage for control electronics by supplying all required current to maintain the set point voltage up to the limit of the converter design. While the HV output may have both a smooth voltage and current (hence, power output can be maintained), the LV power output can fluctuate as loads turn on and off in the vehicle.
The general equation relating the input power, Pacline, to the charger output power is
where VHV and VHV are the measured high voltage output voltage and current respectively, VLV and ILV are the measured low voltage output voltage and current respectively, and ηHV and ηLV are the conversion efficiencies between the AC line and the high voltage output and low voltage output respectively.
The efficiency of conversion varies with power output, input voltage, converter temperature, internal charger component power draw and other factors. This efficiency represents losses in the charging system resulting in thermal dissipation within the charger (and a corresponding temperature rise above ambient). These losses have fixed components such as the power required to run the logic, linear components that vary primarily with the amount of power processed by the charger electronics, and second order losses primarily due to losses in the wiring and other conductive elements. These losses can be approximated as
Chr grLoss≈K2*Iout2R+K1*Vout*Iout+K0 (2)
where the constants K0, K1 and K2 relate the temperature rise to those components of power loss described above.
Typically in converters containing a magnetic path for isolation of the AC line from the DC side, a significant portion of the losses at high power levels is due to the resistive component, R. Considering (2), a reduction in output current by half will reduce the resistive loss component by a factor of four.
Hence, a step in controlling charger temperature may be to reduce the LV charge rate to a low level (e.g., 13.2 V). While this change may result in an immediate reduction in the charger loss, the slow response of the heat sink mass will slow any temperature decrease in the heat sink, thus avoiding rapid resumption of the LV charge rate. The heat sink temperature can be further controlled by varying the IHV output proportional to the temperature rise, again resulting in a stable control of temperature.
This control scheme may offer an additional advantage because high temperature conditions often occur during high rate charging where Iout is near the charger rated maximum. The second order term in (2) will dominate the control resulting in stable operation of the charger with only slightly reduced output current.
Thus, a control equation (assuming the LV charge rate has been reduced) can be rewritten as
where ImaxHV is the maximum design output current of the charger, Tmax is the desired temperature for the charger at which to reduce its output to zero (e.g., 60° C.), Tcharger is the charger temperature, and Tmin is the desired temperature for the charger at which to first begin reducing its output (e.g., 55° C.).
Referring to
The battery charger 12 is configured to receive electrical power from an electrical grid (or other power source) 26. For example, the vehicle 10 may be plugged into a wall outlet such that the battery charger 12 is electrically connected with the electrical grid 26 via, in this example, a ground fault interrupter (GFI) 22 (or similar device) and fuse box 24. Line, neutral and ground wires are shown, in this example, electrically connecting the battery charger 12 and grid 26. The ground wire is electrically connected to a chassis (not shown) within the vehicle 10. The ground wire is also electrically connected with the neutral wire and ground at the fuse box 24. Other electrical configurations, such as a 240 V arrangement with L1, L2 and ground wires, are of course also possible.
The controller 18 may command that electrical energy be provided to either/both of the loads 14, 16. For example, the controller 18 may command the battery charger 12 to provide a specified charge current to the traction battery 14 and/or a specified charge voltage to the auxiliary battery 16. Hence in the embodiment of
Referring to
Returning to operation 30, if yes, it is determined whether the charger temperature is greater than or equal to 62° C. at operation 34. If yes, the auxiliary battery charge voltage is set to a charge sustaining value at operation 36. The battery charger 12, for example, may set the voltage output set point to the low voltage loads 16 to 13.2 V (or some other charge sustaining value). At operation 38, the high voltage battery charge current is set according to the charger temperature. For example, the battery charger 12 may set the current output to the high voltage loads 14 to zero if the charger temperature is 67° C. or more, and based on the charger temperature if the charger temperature is less than 67° C. and greater than or equal to 62° C. according to the following relations:
where iHV is the high voltage output current, Tcharger is the charger temperature, Tuplim is, in this example, 67° C., icmd is the commanded high voltage output current, and Tlwrlim is, in this example, 62° C. Other temperature thresholds may also be used. At operation 42, it is determined whether the battery charge is complete. For example, the battery charger 12 may determine whether its actual state of charge is equal to its target state of charge in any suitable/known fashion. If yes, the algorithm ends. If no, the algorithm returns to operation 28.
Returning to operation 34, if no, the high voltage battery charge current is set equal to the commanded value. For example, the battery charger 12 may set the current output to the high voltage loads 14 equal to the value commanded by the controller 18. The algorithm then proceeds to operation 42.
The algorithms disclosed herein may be deliverable to/implemented by a processing device, such as the battery charger 12 or controller 18, which may include any existing electronic control unit or dedicated electronic control unit, in many forms including, but not limited to, information permanently stored on non-writable storage media such as ROM devices and information alterably stored on writeable storage media such as floppy disks, magnetic tapes, CDs, RAM devices, and other magnetic and optical media. The algorithms may also be implemented in a software executable object. Alternatively, the algorithms may be embodied in whole or in part using suitable hardware components, such as Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), state machines, controllers or other hardware components or devices, or a combination of hardware, software and firmware components.
While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.
