EP3602730A1

EP3602730A1 - Battery fleet charging system

Info

Publication number: EP3602730A1
Application number: EP17905750.0A
Authority: EP
Inventors: Andrew H. REBELE; Kerwin M. LOUKUSA; Keith A. MULLINS; Michael V. SCHAEFER; Joel M. REITER
Original assignee: Pure Watercraft Inc
Current assignee: Pure Watercraft Inc
Priority date: 2017-04-10
Filing date: 2017-04-10
Publication date: 2020-02-05
Also published as: CN110870157A; WO2018190796A1; EP3602730A4

Abstract

A battery fleet charging system for charging one or more batteries simultaneously at independently controlled charge rates. The disclosed charging system can intelligently distribute an available charging power among multiple battery chargers, either symmetrically or asymmetrically, as specified by a central controller to regulate the power used by each battery charger.

Description

BATTERY FLEET CHARGING SYSTEM

TECHNICAL FIELD

[1] The disclosed technology relates to battery charging systems and in particular to systems for charging multiple sets of batteries.

BACKGROUND

[2] Existing battery charging systems are designed to charge a single battery or battery pack, usually at a constant charge rate. If there are multiple battery packs that need to be charged, multiple charging systems are required or the battery packs must be charged one at a time, even if there is excess charge power available. A fleet operator who maintains multiple rechargeable electric devices must therefore purchase and operate multiple charging systems. Such systems generally operate independently without regard to the total charging power available and without regard to how the other charging systems are charging their batteries. The result is a possibility that the charging systems will overload the available power source while providing little flexibility for how power can be directed to the various batteries to be charged.

[3] Given these problems there is a need for a charging system that provides an operator the flexibility to control how devices in their fleet are charged and that efficiently uses the total amount of charging power available.

SUMMARY

[4] To address the above mentioned problems and others, the disclosed technology relates to a battery charging system that employs multiple channels to simultaneously charge multiple battery packs at independently controlled charge rates. A central controller intelligently instructs each channel to deliver a selectable amount of power to charge the batteries in the channel. In one embodiment, the central controller instructs battery chargers associated with each of the channels to deliver all or nearly all of the charging power available from a source to charge the batteries.

[5] In one embodiment, the system includes a power source that is rated to provide a maximum amount of charging power that is available to charge multiple batteries that are arranged in different channels. A number of battery chargers associated with the different channels are individually controllable to charge one or more batteries with a selectable amount of power. A central controller receives information from the batteries to be charged and directs the battery chargers in a channel to charge the batteries with a selectable amount of power. In one embodiment, the central controller controls the power delivered by each of the battery chargers so that the total amount of power delivered is equal, or nearly equal, to the maximum amount of charging power that is available from the power source.

BRIEF DESCRIPTION OF THE DRAWINGS

[6] Figure 1 illustrates a battery charging system in accordance with an embodiment of the disclosed technology;

[7] Figure 2 depicts a central controller and a single battery charger for a channel in accordance with an embodiment of the disclosed technology;

[8] Figure 3 illustrates a rechargeable battery and a number of electrical connections to a battery charger for a channel in accordance with an embodiment of the disclosed technology; and

[9] Figure 4 shows a pair of diodes that connect an individual set of battery cells to power cables to improve safely in accordance with an embodiment of the disclosed technology.

DETAI LED DESCRIPTION

[10] As indicated above, the disclosed technology relates to a battery charging system that can be used to charge a fleet of vehicles. In the embodiment discussed below, the vehicles are electric boats that are powered by one or more rechargeable batteries. However, it will be appreciated that other vehicles or devices having rechargeable batteries could also be charged such as cars, motorcycles, lawn mowers or other equipment, drones and the like.

[11] Figure 1 shows a representative environment where the charging system of the disclosed technology can be used. In the example shown, a fleet operator owns a number of electric boats B1 -B3 that are powered by rechargeable battery packs. A power source 50 typically includes an AC to DC converter that converts commercial AC power from the grid into a variable DC voltage. The DC voltage produced is often unregulated and fluctuates depending on the instantaneous load placed on the commercial grid. The power source 50 has a maximum power rating such as 1 .5 KW, 6 KW, 10 KW etc. The power source 50 supplies the power required to charge the batteries in each of the boats.

[12] Rather than allocating a fixed amount of power from the power source 50 to a number of battery chargers that charge the battery packs in each boat, the charging system of the disclosed technology uses a central controller 100 to variably control the amount of power to be used by a battery charger in each of a number of different channels. For example, the batteries of boats B2 and B3 may be nearly charged while the batteries of boat B1 may be mostly depleted. Therefore, the central controller 100 can direct a battery charger 1 10a associated with the boat B1 to use more of the capacity of the power source 50 than the power used by the battery

chargers 1 10b and 1 10c to charge the batteries of boats B2 and B3 respectively.

[13] In one embodiment, each of the battery chargers 1 10 for the different boats is controllable to use between 0-100% of the capacity of the power source 50 to charge its respective batteries. For example, if the power source 50 has a rating of 6 KW, then each of the battery chargers 1 10a-1 10c for the three channels can use between 0 and 6KW of charging power for its respective battery load. Of course, the total power used by the battery chargers in all the channels together cannot exceed the maximum power rating of the power source 50 and the battery charger for each channel should not charge its associated batteries at a rate that exceeds the charging capacity of the batteries. Continuing with the example shown, if the batteries in boat B1 need to be charged quickly, then the battery charger 1 10a may be directed to use 4KW of charging power while the remaining 2KW of charging power is split evenly between the battery chargers for the other two channels. Alternatively, battery charger 1 10a may be controlled to use all 6KW of charging power and the battery chargers for the other two channels are turned off. The central controller 100 can therefore divide the power used by the battery charger in each channel as necessary.

[14] In one embodiment of the invention, the central controller 100 controls the battery chargers in each of the channels so that the total power used is equal to (or nearly equal to) the maximum power rating of the power source 50.

[15] In one embodiment, the central controller 100 is a microcontroller-based system that is programmable to control how much power is used by the battery chargers in each of the channels. The microcontroller is programmed to receive information from each of the battery packs to be charged and may be programmed to implement one of a number of different charging routines or schedules. For example, the battery chargers of each channel may be controlled so that the battery packs of all the vehicles in the fleet are fully charged by a specific time. Alternatively, the microcontroller 100 may be programmed to control the battery charger in a channel so that the battery packs with the lowest voltage are charged with more power than the battery packs associated with other battery chargers. When all the battery packs achieve some nominal level of charge, the available power can be evenly divided between the battery chargers.

[16] In one embodiment, the central controller 100 has an input mechanism 102 for changing a program that determines how the central controller divides the charging power between the battery chargers in each of the channels. Such an input mechanism 102 can include a keyboard or keypad and may include an associated display 104 that an operator can use to enter commands to change the programming of the central controller. In another embodiment, the central controller includes one or more ports 106 (USB, Ethernet, serial ports, parallel ports or the like) that receives the programming commands for the microcontroller. In yet another embodiment, the central controller includes a wireless communication chipset (WiFi, Bluetooth, cellular, satellite etc.) that allows the central controller to be programmed wirelessly from a remote computer 108.

[17] Figure 2 illustrates further details of a battery charger 1 10 associated with a single channel and its connections to the central controller 100. The battery chargers associated with the other channels are constructed in the similar manner. In one embodiment, each battery charger has the same maximum power that it can use to charge the battery packs in its channel. However, it is possible that some battery chargers may have a greater power capacity than others. The central controller 100 knows the maximum power capacity of the battery charger for each channel.

[18] In the embodiment shown, the battery charger 1 10 includes a pulse width modulation (PWM) battery charging circuit 150 than can operate in either a constant current (CC) or constant voltage (CV) mode under the direction of a signal sent from the central controller 100. An enable line from the central controller 100 to the PWM battery charging circuit 150 allows the central controller to turn on and turn off the battery charging circuit. A 12 volt power source 154 is provided to supply power to circuitry, such as the battery management system, in the battery packs to be charged. Signal conditioning circuits 156 and 158 condition and provide isolation for communication signals and an interlock signal transmitted to and from the battery packs being charged as will be described below.

[19] In some embodiments, the battery charger 1 10 also includes feedback circuitry 160 that monitors an output charging voltage and an output current produced by the PWM battery charging circuit 150. Signals representative of the output voltage and current are fed back to inputs (such as A/D converters) on the central controller 100. By multiplying the output voltage and the output current from the PWM battery charging circuit 150, the central controller 100 estimates the power being delivered by the battery charger 1 10.

[20] In one embodiment, the central controller 100 sends one or more PWM signals having a duty cycle that is proportional to the power that should be used by the battery charger 1 10. For example, a pulse with a duty cycle of 50% of the maximum duty cycle for a pulse is interpreted to mean that the battery charger is to operate at 50% of its maximum power rating etc. Other methods of signaling the battery charger 1 10 could also be used, such as by providing an analog voltage or current or by providing a digital signal (e.g. 0-255) etc.

[21] As will be understood by those skilled in the art of battery charging, the PWM battery charging circuit 150 can be programmed to deliver a specific charging current while letting the voltage required to produce such a current vary. Alternatively, the battery charging circuit 150 can be programmed to deliver a specific voltage regardless of the current required to produce such a voltage. Most modern rechargeable batteries are charged by supplying a constant current specified by the manufacturer. The optimal rate can be reported by a battery management system to the central controller 100 as explained below. Once the battery pack reaches a particular voltage value, some battery chemistries require the batteries to be charged with a constant voltage (and variable current) until the battery pack is fully charged. Other charging schemes are also possible depending the type of batteries to be charged and the programming of the central controller 100.

[22] In the embodiment shown, the central controller 100 supplies a variable value signal to the PWM battery charging circuit 150 representing a value between 0 and 100% of the power of the power source 50 to be used in charging the batteries for that channel. Alternatively, the number may represent between 0-100% of the total power that can be delivered by the PWM battery charger 150 (which may be different than the total power available from the power source). For example, if the PWM battery charging circuit 150 can deliver at most 4KW of charging power, then a value of 50% may represent 2KW and a value of 100% may represent 4KW even if the total power available from the power source is 6KW.

[23] In one embodiment, a battery management system associated with each battery pack to be charged reports the voltage of the battery pack to the central controller 100 over a communication link (e.g. CAN communication link). The central controller 100 determines if the battery pack should be charged with a constant current or a constant voltage. Assuming that a constant current is used, a current is selected so that the power used by the battery charger is less than or equal to the maximum power that should be used by the battery charger and that is within the safe charging range for the batteries to be charged. If a constant voltage is to be used to charge the battery pack, then a voltage is selected so that that the power used by the battery charger is less than or equal to the maximum power that should be used by the battery charger 1 10 and that is within the safe charging range for the batteries to be charged.

[24] Figure 3 shows some of the internal components of a battery pack 300 to be charged with the charging system in accordance with an embodiment of the disclosed technology. The configuration of batteries in a battery pack may vary but in one embodiment, each battery pack 300 includes six serially connected modules of 80 rechargeable battery cells 310 for a total of 480 battery cells per battery pack. A vehicle such as an electric boat may include several battery packs that are connected in parallel to provide sufficient current to drive the vehicle.

[25] In the embodiment shown, the battery pack 300 has an input port I and an output port O. These names are assigned as a convenience as the ports are functionally equivalent. The input port I receives a cable connector with wires connected to a vehicle charging receptacle and to power bus cables that the vehicle uses to draw power during operation. Internal connections are provided within the battery pack between the input port I and the output port O to put some of the contacts in the input port in parallel with contacts in the output port so that multiple batteries can be daisy chained together (e.g. by connecting a cable from an input port of one battery pack to an output port of another battery pack). A battery management system 320 in the battery pack is provided to monitor and report one or more battery conditions such as, but not limited to, the internal temperature of the batteries, the charge or discharge current from the battery cells 310, the voltage of the battery cells, the number of times the battery pack has been recharged, the charge/discharge rate C for arrangement of battery cells 310.

[26] The battery management system 320 controls the position of a number of switches S1 and S2 that connect the positive and negative terminals of the arrangement of battery cells 310 to the power cables in the vehicle. If the battery management system detects that the batteries are overheating, that the output current current is too high or there is some other anomaly occurring in the batteries, then the battery management system can independently operate to open the switches S1 and S2 and disconnect the battery pack from the power cables.

[27] As indicated above, the battery management system communicates information to and from the central controller 100 using a communication bus such as a set of CAN (controller area network) lines of the type commonly used in electric vehicles. Internal connections within the battery pack 300 put the connectors for the CAN lines in parallel between the input port I and the output port O so that the CAN lines for each daisy chained battery in a vehicle are in parallel. In another embodiment, each battery pack can be equipped with a wireless communication chip set to communicate signals wirelessly.

[28] A 12 volt line and a ground line are connected to the input port I to supply power the battery management system 320. When the 12 volt signal is applied with the switch S3 open, the battery management system 320 reports information to the central controller including information about its set of battery cells 310. Such battery information can include the serial number of the battery pack, the number of charging cycles applied to the battery pack, maximum charging current and voltage for the batteries in the battery pack, etc. In one embodiment, the battery management system 320 selectively connects the 12 volt line to a connector on the output port using a switch S3. When battery management system is instructed to close the switch S3 to power a next battery that is daisy chained to the output port O. The battery management system of that battery pack reports its information on the CAN leads and so on, until the last battery pack in the vehicle is reached. In this way, the central controller knows how many battery packs are in a vehicle and what the state of charge is for each set of batteries in each battery pack. [29] In the embodiment shown, the battery pack 300 is connected to an interlock line that is run serially from the input port to the output port. The interlock line returns back from the last connected battery pack to the central controller 100 through the signal conditioning circuit 158 in the battery charger 1 10 to form a continuous electrical path through each of the battery packs to be charged. If the interlock line is broken by disconnecting one of the battery packs from the circuit, the central controller will be alerted and can take appropriate action such as disabling its output.

[30] As indicated above, each of the sets of battery cells 310 is connected to the power cables via a pair of switches S1 and S2. The switches are controlled by the battery management system 320. The battery management system can disconnect the battery cells from the power cables if it detects a fault in the battery or an unsafe condition occurs. Alternatively, the battery management system can connect the battery cells to the power cables by closing the switches S1 and S2 upon instructions from the central controller.

[31] As will be appreciated by those skilled in the art, the battery cells of different battery packs in a vehicle may be at different voltages when they are to be recharged. In one embodiment, in order to avoid connecting two battery packs with unequal voltages in parallel, the central controller 100 instructs a battery management system 320 to connect the batteries in the battery pack with the lowest voltage to the power cables so that the lowest charged battery pack is charged first. Once the voltage of that battery pack rises to the voltage of the batteries in another battery pack, then those batteries are connected to the power cables to charge. This process can continue until all the sets of battery cells are connected in parallel to the battery charger for that channel. Depending on the particular state of charge of the batteries, the batteries may be charged with a constant current or a constant voltage. The central controller 100 may direct the PWM charging circuit to adjust the current or voltage depending on the number of battery packs to be charged, the maximum current or voltage that can be delivered to the connected battery packs and the total power being delivered by the charging circuit.

[32] As additional battery packs in a particular channel are connected to the battery charger, the central controller 100 reads the voltage and current produced by the PWM charging circuit 150 to know how much power is being delivered by the battery charger. The central controller then can adjust the amount of power to be used by the battery charger for a particular channel so the total power is less than or equal to the total amount of charging power available from the power source and so that the charging power delivered is within the safe operating range of the batteries in the channel.

[33] In one embodiment, the central controller 100 commands each of the battery chargers in each of the channels to use an amount of power such that that the total amount of power used is equal to (or nearly equal to) the maximum power that can be provided by the power source 50. The central controller 100 therefore can independently control the power delivered by the battery charger of each channel.

[34] In one embodiment, the voltage and current outputs of the PWM battery charging circuit 150 are used to determine when to switch from a constant current charging mode to a constant voltage charging mode. In another embodiment, the battery management system 320 of each battery pack periodically reports the voltage of its batteries and those values are used by the central controller to determine how to charge the batteries.

[35] The electronics of the charging system also perform safety checks continuously during operation to monitor for dangerous conditions that may be present in the system. If dangerous conditions are noted they are logged and the appropriate action is taken to prevent a harmful situation being presented to the user. [36] Figure 4 illustrates an additional feature that can be added to each set of battery cells. The addition of two diodes on the positive terminal of the battery cells, along with a single pole double throw (SPDT) switch can be used to prevent current flow between battery cells at different voltages. For example, during discharge, the SPDT switch is connected to Diode 2, which allows current to flow out of the set of battery cells when the voltage of the battery cells is greater than the voltage at the high side terminal, but prevents current flow in the opposite direction when the voltage at the high side terminal is greater than the voltage of the set of battery cells. Similarly, during charging the SPDT switch is connected to Diode 1 , which allows current to flow into the set of battery cells when the voltage at the high side terminal is greater than the voltage of the set of battery cells, but prevents current flow in the opposite direction when the voltage of the set of battery cells is greater than the voltage at the high side terminal.

[37] An additional safety feature is that the default switch location is connected to Diode 1 (i.e., when the battery pack is not in use), which ensures that no current can flow from the battery cell terminals. This is a redundant safety feature since there is typically another switch (Low Side Contactor in Figure 4) whose default position is OPEN, also preventing current flow from the battery cell terminals when not in use.

[38] There are additional benefits to having independent control of battery pack contactors. For example, if one set of battery cells indicates a fault, the central controller can request that its contactor be opened, which suspends charging to that battery pack while continuing to charge other battery packs connected to the same channel. This capability also allows additional battery packs to be connected to a channel at any time, regardless of its output , and the charger will evaluate its state of charge and take action to equalize its voltage with the other battery cells.

[39] The disclosed charging system has been designed with sophisticated safety protocols to ensure safety of the user, the batteries being charged, and the charging system itself. As shown in the figures, each charging channel requires communication between the batteries and the central controller, and certain conditions must be satisfied before charging will be initiated. Once all conditions have been satisfied, the central controller sends a request to the battery pack to close an internal electrically controlled switch (contactor), which establishes an electrically conductive path between the energy storage devices (e.g. cells) within the battery pack and the external connectors. Likewise, the charging system closes its own internal electrically controlled switch to enable power to the external connectors. Furthermore, if communication between the charging system and a battery pack indicates an unsafe condition, or if communication is lost, the electrically controlled switches revert to the open condition to halt charging. This safety protocol also reduces the risk of electrical shock at the external connectors when not mated.

[40] Potential uses of the disclosed technology include applications where multiple batteries need to be recharged simultaneously. This may include all types of electric vehicle charging, battery powered consumer electronics, battery powered tools, etc. The invention provides the most value to organizations that maintain a plurality of battery-powered items.

[41] While the present invention has been described with particular embodiments, it should be clear to one skilled in the art that additional embodiments are contemplated without departing from the intended scope and coverage of the disclosure. The scope of the invention is further described in the following claims.

Claims

CLAIMS We Claim:

1. A battery fleet charging system comprising:

an AC-to-DC power stage configured to provide charging power for charging battery packs in two or more channels;

a battery charger for each of the channels that is configured to deliver an amount of charging power to the battery packs in a channel; and

a central controller configured to control the power delivered by each of the battery chargers either symmetrically or asymmetrically.

2. The battery fleet charging system of claim 1 wherein the central controller is configured to direct a battery management system in each battery pack to selectively connect or disconnect batteries to be charged in the battery pack to charging power.

3. The battery fleet charging system of claim 1 , wherein each battery charger uses pulse width modulation.

4. The battery fleet charging system of claim 3 wherein the central controller receives feedback of a voltage and current provided by each battery charger.

5. The battery fleet charging system of claim 4 wherein the central controller is programmable to implement different charging routines.

6. The battery fleet charging system of claim 1 , wherein each channel includes two or more battery packs and each battery pack includes a set of battery cells with a positive terminal and two diodes on the positive terminal and a single pole double throw (SPDT) switch that is operated by a battery management system to prevent current flow between the two or more batteries packs in a channel at different voltages.

7. The battery fleet charging system of claim 1 further comprising a communication link between the batteries to be charged and the central controller.

8. A method of simultaneously charging two or more battery packs in a battery fleet charging system at independently controlled charge rates and intelligently distributing available charge power among the two or more battery packs up to a maximum charge power, either symmetrically or asymmetrically, comprising the steps of:

a) monitoring conditions of the two or more battery packs in different channels;

b) drawing AC power from a power grid and converting it into DC power; and c) using a central controller to direct a battery charging circuit in each channel to supply DC power to charge the battery packs in the channel so that a sum of DC power supplied by each of the battery charging circuits equals the maximum charge power.

9. The method of claim 8, further comprising: using a pulse width modulation signal from the central controller to control the DC power supplied by each battery charging circuit.

10. The method of claim 9, further comprising: monitoring an output voltage and charge current of each battery charging circuit at the central controller in real time to adjust the pulse width modulation signal.

1 1. The method of claim 8, further comprising requesting a voltage of the two or more battery packs in a channel and charging a battery pack with a lower voltage before connecting the two or more battery packs in parallel to charge.

12. The method of claim 8, further comprising continuously performing safety

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RECTMED SHEET (RULE 91) checks including receiving communications at the central controller from each battery packs during charging.

13. The method of claim 12, further comprising sending a request to the two or more battery packs to close an internal electrically controlled switch or contactor once predetermined conditions are met, thereby establishing an electrically conductive path between batteries in a battery pack and the external connectors.

14. The method of claim 8, further comprising communicating between battery pack and the central controller wired or wireless data exchange.

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RECT ED SHEET (RULE 91)