Battery Pack Arrangement

A traction battery pack(s) 102 may be constructed from a variety of chemical formulations. Typical battery pack chemistries are lead acid, nickel-metal hydride (NIMH) or Lithium-Ion. Figure 1 shows a typical traction battery pack(s) 102 in a simple series configuration of N battery cell(s) 104. Other traction battery pack(s) 102, however, may be composed of any number of individual battery cells connected in series or parallel or some combination thereof. A typical system may have a one or more controllers, such as a battery Energy Control Module (BECM 108) that monitors and controls the performance of the traction battery pack(s) 102. The BECM 108 may monitor several battery pack level characteristics such as pack current 112, pack voltage 114 and pack temperature 110. The BECM 108 may have non-volatile memory such that data may be retained when the BECM 108 is in an off condition. Retained data may be available upon the next key cycle. 

In addition to the pack level characteristics, there may be battery cell(s) 104level characteristics that are measured and monitored. For example, the terminal voltage, current, and temperature of each battery cell(s) 104 may be measured. A system may use a sensor module(s) 106 to measure the battery cell(s) 104  characteristics. Depending on the capabilities, the sensor module(s) 106 may measure the characteristics of one or multiple of the battery cell(s) 104. The traction battery pack(s) 102 may utilize up to N.sub.c sensor module(s) 106 to measure the characteristics of all the battery cell(s) 104. Each sensor module(s) 106 may transfer the measurements to the BECM 108 for further processing and coordination. The sensor module(s) 106 may transfer signals in analog or digital form to the BECM 108. In some embodiments, the sensor module(s) 106functionality may be incorporated internally to the BECM 108. That is, the sensor module(s) 106hardware may be integrated as part of the circuitry in the BECM 108 and the BECM 108 may handle the processing of raw signals. 

It may be useful to calculate various characteristics of the battery pack. Quantities such a battery power capability and battery state of charge may be useful for controlling the operation of the battery pack as well as any electrical loads receiving power from the battery pack. Battery power capability is a measure of the maximum amount of power the battery can provide or the maximum amount of power that the battery can receive for the next specified time period, for example, 1 second or less than one second. Knowing the battery power capability allows electrical loads to be managed such that the power requested is within limits that the battery can handle. 

Battery pack state of charge (SOC) gives an indication of how much charge remains in the battery pack. The battery pack SOC may be output to inform the driver of how much charge remains in the battery pack, similar to a fuel gauge. The battery pack SOC may also be used to control the operation of an electric or hybrid-electric vehicle. Calculation of battery pack or cell SOC can be accomplished by a variety of methods. One possible method of calculating battery SOC is to perform an integration of the battery pack current over time. One possible disadvantage to this method is that the current measurement may be noisy. Possible inaccuracy in the state of charge may occur due to the integration of this noisy signal over time. Calculation of battery pack or cell SOC can also be accomplished by using an observer, whereas a battery model is used for construction of the observer, with measurements of battery current, terminal voltage, and temperature. Battery model parameters may be identified through recursive estimation based on such measurements. 

The accuracy of voltage and current sensor measurement depend on many factors. Noise may impact the signal that is measured. For example, accuracy of a hall-effect type current sensor may depend on shielding the sensor and conductors from environmental magnetic fields. Biases in the sensor measurements may also be present. Prior art systems may utilize current measurements taken prior to contactor closing to calculate a current measurement bias. Before the contactor closes, there should be no current flowing. 

A battery management system may estimate various battery parameters based on the sensor measurements. Current and voltage sensor biases and inaccuracies may be time-varying in nature. Therefore, pre-contactor close compensation may not be accurate enough over the entire operating time of the sensors. The short sample time before the contactor is closed only allows limited sampling of the current sensor. The pre-contactor close samples may not be accurate due to the rise time of the current sensor from BECMstart-up. Another significant issue may be the lack of exact synchronization in voltage and current measurements. Battery parameter identification depends on well-defined inputs (current) and outputs (terminal voltage). A loss of synchronization between the signals may result in measured data that does not accurately represent the real battery behavior which may lead to erroneous parameter estimation