Patent Application
20140232324
The present invention is related to battery systems, and in particular to battery charging systems.
Battery systems are typically comprised of a plurality of individual batteries (sometimes referred to as “battery cells”) connected either in parallel or in series with one another to provide a desired output to a load. Placing the plurality of battery cells in series with one another allows the system to supply loads with higher output voltages and is therefore desirable in many applications.
Connecting batteries in series has a number of benefits over parallel connected batteries during discharge, but presents a number of challenges during charging operations. For example, each battery cell may be characterized by a different source impedance. As a result, the charging voltage applied to the stack of series-connected battery cells may be unevenly distributed across each of the plurality of battery cells, resulting in each battery cell being exposed to a different charging voltage. As a result, some battery cells may be subject to overvoltage conditions, while others do not receive a charging voltage sufficient to fully charge the battery cell.
A battery charging system comprises a battery charger, a first battery, a second battery connected in series with the first battery, and first and second voltage regulation circuits. The battery charger provides a charging output to the series-connected first and second batteries. The first voltage regulation circuit is connected in parallel with the first battery and provides a first conductive current path that bypasses the first battery in response to a voltage across the first battery exceeding a threshold value. A second voltage regulation circuit is connected in parallel with the second battery and provides a second conductive current path that bypasses the second battery in response to a voltage across the second battery exceeding a threshold value.
Battery charger 12 is connected in series with batteries 14a and 14b to provide a charging voltage to batteries 14a and 14b. The charging voltage required depends on the number of series-connected batteries and the rated voltage of the batteries. For example, if batteries 14a and 14b are each 12 Volt (V) batteries, then battery charger 12 would need to provide a 24V charging voltage in order to fully charge both batteries. As discussed above, however, variation in the source impedances Rb1 and Rb2 of each respective battery 14a and 14b may result in variations in the voltage applied across each battery. In some instances, this may result in an overvoltage being applied to either battery 14a or 14b.
Voltage regulation circuits 16a and 16b are connected in parallel with batteries 14a and 14b, respectively, to regulate the voltage provided to batteries 14a and 14b. Because voltage regulation circuits 16a and 16b are connected in parallel with batteries 14a and 14b, respectively, the voltage applied to the batteries will be the same voltage applied to the voltage regulation circuits. For example, with respect to battery 14a and voltage regulation circuit 16a, the voltage applied to battery 14a is also applied across voltage regulation circuit 16a. If the voltage applied across battery 14a is less than an overvoltage threshold then voltage regulation circuit 16a remains non-conductive and charging current provided by battery charger 12 is applied to battery 14a and then to battery 14b. However, if the voltage across battery 14a exceeds an overvoltage threshold then voltage regulation circuit 16a creates a conductive current path that bypasses battery 14a, thereby decreasing the voltage across battery 14a. In this way, voltage regulation circuits 16a and 16b regulate the voltage applied to batteries 14a and 14b respectively. Importantly, the charging voltage supplied by battery charger 12 remains unchanged regardless of the state of voltage regulation circuits 16a and 16b, such that the full charging potential of battery charger is applied to remaining battery 14b without overcharging battery 14a.
In the embodiment shown in
In addition to selection of breakdown voltages associated with Zener diodes D1 and D2, the diodes and associated wiring are sized to handle the full capacity of current supplied by battery charger 12. That is, voltage regulation circuits 16a and 16b are not merely monitoring circuits that are not likely to be required to handle the full charging current associated with battery charger 12. Rather, voltage regulation circuits 16a and 16b are expected during normal operation to create conductive bypass paths around batteries 14a or 14b through which a maximum current associated with battery charger 12 may flow. In some embodiments, battery charge controller 18 detects when each of the batteries 14a and 14b are fully charged, either by directly monitoring the voltage across each battery or the voltage across the entire stack of batteries (depending on t he type of load). In response to a determination that all batteries have been fully charged, battery charge controller 18 may stop the charging operation. However, in other embodiments, battery charger 12 may remain On in a float-charge mode in which substantially all of the current supplied by battery charger 12 flows through Zener diodes D1 and D2. In one embodiment, battery charger 12 is current-limited (i.e., will not supply a current above a threshold level), and Zener diodes D1 and D2 are sized to handle the maximum current level that may be supplied by battery charger 12.
In the embodiment shown in
In contrast with approaches in which a detected overvoltage condition across one battery or battery cell results in the voltage supplied by the battery charger being decreased, the embodiment shown in
Battery charger controller 18 is responsible for detecting faults in voltage regulation circuits 16a and 16b and in response to a detected fault taking action to protect batteries 14a and 14b. In addition, battery charger controller 18 may be responsible for determining when the batteries are fully charged, such that battery charger 12 can be turned Off. In the embodiment shown in
During normal charging operations, voltage regulation circuits 16a and 16b are responsible for regulating the voltage across respective batteries 14a and 14b to prevent overvoltage conditions. However, a fault condition associated with either voltage regulation circuit 16a or 16b could result in an overvoltage being applied to one or both batteries 14a or 14b. For example, if Zener diode D1 is damaged and does conduct at the expected breakdown voltage then an overvoltage may be applied to battery 14a. This fault condition is detected by battery charger controller 18 if the monitored voltage across battery 14a increases above the breakdown voltage of Zener diode D1. Based on a detected fault condition, battery charger controller 18 operates in a fault protection mode in which batteries 14a and 14b are protected by either reducing the voltage supplied by battery charger 12 or turning Off battery charger 12 altogether. Battery charger controller 18 may also store information related to the detected fault, including the voltage regulation circuit in which the fault occurred to accommodate repair and/or replacement of the faulty circuit.
Although separate from the fault protection functions provided by battery charger controller 18, the controller may also be utilized to determine when the batteries have been fully charged such that the charging operation can be ended. There are a number of methods by which battery charger controller 18 may determine whether the charging operation is complete. In one embodiment, battery charger controller 18 compares monitored voltages from across each battery to a threshold value to determine whether each of the plurality of batteries 14a and 14b are fully charged. In another embodiment, battery charger controller 18 monitors the voltage across the entire stack of batteries to determine whether the charging operation is complete. If battery charger controller 18 determines that the charging operation is complete, then battery charger controller 18 instructs battery charger 12 to stop charging.
At step 24, battery charging system 10 operates in a normal operating mode in which battery charger 12 provides a full output voltage to begin charging batteries 14a and 14b and voltage regulation circuits 16a and 16b regulate the voltage supplied to prevent overvoltage conditions. During normal operation, battery charger controller 18 is not responsible for regulating the voltage across batteries 14a and 14b or regulating the output voltage supplied by battery charger 12. Rather, voltage regulating circuits 16a and 16b individually regulate the voltage across respective batteries 14a and 14b by creating conductive paths bypassing respective batteries 14a and 14b as required to maintain the voltage across each battery below an overvoltage threshold value.
At step 26, battery charge controller 18 monitors the voltage across each of the plurality of batteries 14a and 14b. At step 28, battery charger controller 18 determines whether a fault condition exists with respect to any of the voltage monitoring circuits based on whether one or more of the monitored voltages exceeds an overvoltage threshold value. A monitored voltage that exceeds the overvoltage threshold value indicates that the corresponding voltage regulation circuit has experienced a fault condition (e.g., Zener diode is “popped” open, and cannot create a conductive path).
If a fault is detected at step 28, then at step 30 battery charger controller 18 operates in a fault protection mode. In one embodiment, operation in the fault protection mode includes decreasing the voltage provided by battery charger 12 to prevent the fault condition from causing an overcharging of the battery associated with the detected fault. If no fault condition is detected at step 28, then at step 32 battery charger controller determines whether the charging operation is complete. As discussed above, battery charger controller may make this determination based on the voltages monitored across each of the plurality of batteries 14a and 14b, voltage monitored across the entire stack of battery cells, or based on other well-known methods. In one embodiment, this includes comparing the monitored voltages to a charge complete value to determine whether each of the plurality of batteries 14a and 14b are fully charged. If the charging operation is not complete, then monitoring of the plurality of batteries continues at step 26. A determination of whether the charging operation is complete may also depend on whether the battery charging system is operating in a normal mode or in a fault protection mode. If the voltage supplied by battery charger 12 is reduced in a fault protection mode, then the threshold used to determine whether the charging operation is complete may be reduced.
If the charging operation is complete, as evidenced by the monitored voltage across the plurality of batteries 14a and 14b, then the charging process is stopped at step 34.
Once again battery charger 42 is connected in series with batteries 44a and 44b. Voltage regulation circuits 46a and 46b are connected in parallel with batteries 44a and 44b, respectively, to regulate the voltage across batteries 44a and 44b to a value less than an overvoltage threshold. In the embodiment shown in
In contrast with the embodiment described with respect to
In the embodiment shown in
To ensure that during normal operation, current flows through voltage regulation circuits 46a and 46b, but not through fault detection circuits 48a or 48b, respectively, the breakdown voltage of Zener diodes D3 and D4 must be higher than the breakdown voltage of Zener diodes D1′ and D2′. In one embodiment, because of the expectation that current will not flow through components associated with fault detection circuits 48a and 48b (e.g., through Zener diodes D3 and D4, and current sense resistors Rc1 and Rc2), these components and the wire associated with these components can be sized according to the expectation that they will not be required to handle large currents. In contrast, the expectation associated with the components associated with voltage regulation circuits 46a and 46b is that large currents will regularly be flowing through these components in order to regulate the voltage across batteries 44a and 44b, respectively. However, the trade-off associated with sizing the components associated with fault detection circuits 48a and 48b smaller than the components associated with voltage regulation circuits 46a and 46b is that the protection capability of fault detection circuits 48a and 48b is decreased.
In one embodiment, in response to a fault condition detected by fault detection circuit 48a or 48b, battery charger controller 50 may reduce the voltage provided by battery charger 42 to a level that will not result in overvoltage faults or may stop the charging operation altogether. Although fault detection circuits 48a and 48b provide a conductive path bypassing the battery to which the overvoltage is applied, and therefore will act to regulate the voltage across batteries 44a and 44b, it may be still be desirable to decrease the voltage supplied by battery charger 42 to prevent fault detection circuits 48a and 48b from being required to handle the full charging currents provided by battery charger 12. That is, in one embodiment it is more cost-effective to size components associated with fault detection circuits 48a and 48b to be capable of handling bypass currents for only a short period of time long enough to detect a fault condition and decrease the voltage supplied by the battery charger as opposed to regulating the voltage across the battery. However, in other embodiments components associated with fault detection circuits 48a and 48b may be sized to provide both fault detection and regulation, in which case battery charger controller 50 may maintain the full charging voltage supplied by battery charger 42. In this embodiment, battery charger controller 50 would then be responsible for detecting faults in fault detection circuits 48a and 48b based on the monitored voltage across batteries 44a and 44b, respectively, and would decrease the voltage supplied by battery charger 44 if a fault is detected within fault detection circuit 48a or 48b as indicated by the monitored voltage exceeding the breakdown voltage associated with Zener diodes D3 and D4.
Because of the presence of fault detection circuits 48a and 48b, battery charger controller 50 is not required to monitor the voltage across each battery for fault conditions. However, battery charger controller 50 may still monitor the voltage across each battery and/or the battery across the entire stack of batteries to determine whether the charging operation is complete. If battery charger controller 50 determines that the charging operation is complete, then battery charger controller 50 ends the charging operation. In other embodiments, battery charger controller 50 may not be required to monitor the voltages across each battery independently, but rather, may rely only on the feedback provided by fault detection circuits 48a and 48b.
The following are non-exclusive descriptions of possible embodiments of the present invention.
A battery charging system includes a battery charger, a first battery connected in series with the battery charger, a second battery connected in series with the first battery and the battery charger, and first and second voltage regulation circuits. The first voltage regulation circuit is connected in parallel with the first battery to provide a first conductive current path that bypasses the first battery in response to a voltage across the first battery exceeding a threshold value. The second voltage regulation circuit is connected in parallel with the second battery to provide a second conductive current path that bypasses the second battery in response to a voltage across the second battery exceeding a threshold value.
The battery charging system of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components.
wherein the first voltage regulation circuit includes a Zener diode connected in parallel with the first battery, wherein the Zener diode has a breakdown voltage selected to provide the first conductive current path bypassing the first battery in response to the voltage across the first battery exceeding the threshold value;
a battery charger controller connected to monitor the voltage across the first battery and the voltage across the second battery and to provide commands to the battery charger based on the monitored voltages across the first and second batteries;
wherein the battery charger operates in a current-limited mode to provide charging current to the first and second batteries, wherein the battery charger controller turns Off the battery charger when based on the monitored voltages across the first and second batteries both batteries have been fully charged;
wherein the battery charger controller detects a fault in the first voltage regulation circuit when the monitored voltage across the first battery exceeds the threshold value and detects a fault in the second voltage regulation circuit when the monitored voltage across the second battery exceeds the threshold value;
wherein the battery charger controller controls the battery charger to reduce output voltage of the battery charger in response to a detected fault in either the first voltage regulation circuit or the second voltage regulation circuit;
wherein the battery charger controller controls the battery charger to stop the charging operation in response to a detected fault in either the first voltage regulation circuit or the second voltage regulation circuit;
further including a first fault detection circuit connected in parallel with the first battery and the first voltage regulation circuit that detects faults in the first voltage regulation circuit, wherein in response to a detected fault in the first voltage regulation circuit the first fault detection circuit provides a first backup conductive path that bypasses the first battery and generates a first output indicating the detected fault in the first voltage regulation circuit; and a second fault detection circuit connected in parallel with the second battery and the second voltage regulation circuit that detects faults in the second voltage regulation circuit, wherein in response to a detected fault in the second voltage regulation circuit the second fault detection circuit provides a second backup conductive path that bypasses the second battery and generates a second output indicating the detected fault in the second voltage regulation circuit;
wherein the first fault detection circuit includes a Zener diode having a breakdown voltage greater than the threshold value, a current sense resistor connected in series with the Zener diode, wherein the Zener diode and the current sense resistor are connected in parallel with the first battery, and a current detection circuit connected to detect current in the current sense resistor, wherein the Zener diode conducts current in response to the voltage across the first battery exceeding the threshold value without the first regulation circuit providing the first conductive path bypassing the first battery, wherein in response to current detected through the current sense resistor the current detection circuit provides the first output indicating a fault condition in the first voltage regulation circuit;
further including a battery charger controller connected to receive the first and second outputs provided by the first and second fault detection circuits and to provide control instructions to the battery charger, respectively, wherein in response to an indication of a fault condition in either the first or second voltage regulation circuits the battery charger controller decreases the output voltage provided by the battery charger.
A method of regulating the charging of first and second series-connected batteries includes operating in a normal mode in which voltages across the first and second batteries are regulated by first and second voltage regulation circuits connected in parallel with the first and second batteries, respectively, wherein the first and second voltage regulation circuits are non-conductive when the voltage across the first and second batteries, respectively, is less than a threshold value and conductive when the voltage across the first and second batteries, respectively, is greater than a threshold value, monitoring the voltage across the first battery and the voltage across the second battery, and operating in a protection mode in response to the monitored voltage across either the first or second battery exceeding a second threshold value, wherein output voltage of a battery charger is reduced in the protection mode.
The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components;
wherein the second threshold value is greater than the first threshold value;
wherein the first threshold value is defined by the breakdown voltage of a first Zener diode connected in parallel with the first battery;
wherein the second threshold value is defined by a breakdown voltage of a second Zener diode connected in series with current sense resistor and together connected in parallel with the first battery and the first Zener diode, wherein operation in the protection mode is entered when current flow is detected through the current sense resistor.
A battery charging regulation and protection system for use with first and second series-connected batteries includes a first voltage regulation circuit connected in parallel with the first battery that provides a first conductive current path that bypasses the first battery in response to a voltage across the first battery exceeding a threshold value, a second voltage regulation circuit connected in parallel with the second battery that provides a second conductive current path that bypasses the second battery in response to a voltage across the second battery exceeding a threshold value, and a battery charger controller connected to monitor voltage across the first battery and voltage across the second battery, wherein the battery charger controller detects a fault in the first voltage regulation circuit and/or the second voltage regulation circuit if the voltage monitored across the first battery and/or the voltage monitored across the second battery exceeds a second threshold value;
wherein the second threshold value is equal to or greater than the first threshold value;
wherein the battery charger controller reduces the voltage across the series connected first and second batteries in response to a detected fault in either the first voltage regulation circuit or the second voltage regulation circuit;
wherein the first voltage regulation circuit includes a Zener diode connected in parallel with the first battery, wherein the Zener diode has a breakdown voltage selected to provide the first conductive current path bypassing the first battery in response to the voltage across the first battery exceeding the threshold value;
wherein the first voltage regulation circuit further includes a light-emitting diode connected in series with the Zener diode that provides a visual indication that the first voltage regulation circuit is working properly when current flows through the first conductive current path;
wherein the first voltage regulation circuit includes a plurality of Zener diodes connected in series with one another and in parallel with the first battery, wherein a number of Zener diodes employed and breakdown voltages of the plurality of Zener diodes is selected to provide the first conductive current path bypassing the first battery in response to the voltage across the first battery exceeding the threshold value.
While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
