Control of DC-DC converters for DC charging

Abstract

An electrical system may include a rechargeable energy storage system (RESS) and a direct current - direct current (DC - DC) converter. The DC - DC converter is connected to the RESS and configured to be connected to a DC charging station. The DC - DC converter is configured to selectively connect the RESS to the DC charging station so as to selectively supply a charging current to the RESS during a recharge operation.

Description

Technical Field

[0001] The present disclosure relates to an electrical system that can charge a battery from a direct current (DC) charging device serving as a current source via a DC-DC converter. Background Art

[0002] A direct current - direct current (DC-DC) converter converts a direct current (DC) source from one voltage level to another voltage level. For example, a switched DC-DC converter can convert one DC voltage level to another DC voltage level by temporarily storing input energy and then releasing the stored energy at a different voltage to the output. Summary of the Invention

[0003] An exemplary electrical system for increasing the voltage supplied by a DC charging station is disclosed herein. The electrical system may include a rechargeable energy storage system (RESS) and a direct current - direct current (DC-DC) converter. The DC-DC converter is connected to the RESS and configured to be connected to the DC charging station. The DC-DC converter is configured to selectively connect the RESS to the DC charging station, thereby selectively providing a charging current to the RESS during a recharge operation.

[0004] In other features, the DC-DC converter includes a first switch and a second switch.

[0005] In other features, the first switch and the second switch include voltage-controlled semiconductor switches.

[0006] In other features, the voltage-controlled semiconductor switch includes at least one of a silicon insulated gate bipolar transistor (IGBT), a silicon carbide metal oxide semiconductor field effect transistor (MOSFET), a silicon superjunction MOSFET, a gallium nitride (GaN) field effect transistor (FET), a SiC junction gate field effect transistor (JFET), a wide bandgap (WBG) device, or an ultra-wide bandgap (UWBG) device.

[0007] In other features, the first switch and the second switch are configured to operate in complementary operating states.

[0008] In other features, the electrical system includes a controller that is operably connected to the DC-DC converter and configured to operate the DC-DC converter to selectively connect the RESS to the DC charging station based on a gate signal provided to at least one of the first switch or the second switch.

[0009] In other features, the controller is further configured to compare an input DC-DC converter voltage with a predetermined voltage threshold and selectively operate the first switch to boost the voltage stored in a pre-charge capacitor, where the pre-charge capacitor is charged using power provided by the RESS.

[0010] An exemplary electrical system for increasing the voltage supplied by a DC charging station is disclosed. The electrical system may include a rechargeable energy storage system (RESS) and a direct current - direct current (DC - DC) converter. The DC - DC converter is connected to the RESS and configured to be connected to the DC charging station. The DC - DC converter is configured to selectively connect the RESS to the DC charging station so as to selectively supply a charging current to the RESS during a recharge operation.

[0011] Among other features, the DC - DC converter includes a first switch and a second switch.

[0012] Among other features, the first switch and the second switch include voltage - controlled semiconductor switches.

[0013] Among other features, the voltage - controlled semiconductor switch includes at least one of a silicon insulated - gate bipolar transistor (IGBT), a silicon carbide metal - oxide - semiconductor field - effect transistor (MOSFET), a silicon super - junction MOSFET, a gallium nitride (GaN) field - effect transistor (FET), a SiC junction - gate field - effect transistor (JFET), a wide - bandgap (WBG) device, or an ultra - wide - bandgap (UWBG) device.

[0014] Among other features, the first switch and the second switch are configured to operate in complementary operating states.

[0015] Among other features, the electrical system includes a controller that is operably connected to the DC - DC converter and configured to operate the DC - DC converter to selectively connect the RESS to the DC charging station based on a gate signal provided to at least one of the first switch or the second switch.

[0016] Among other features, the controller is further configured to compare an input DC - DC converter voltage with a predetermined voltage threshold and selectively operate the first switch to boost the voltage stored in a pre - charge capacitor, wherein the pre - charge capacitor is charged using power provided by the RESS.

[0017] A method is disclosed that includes comparing, via a controller, an input DC - DC converter voltage of a direct current - direct current (DC - DC) converter with a predetermined voltage threshold and selectively operating a first switch of the DC - DC converter to boost the voltage stored in a pre - charge capacitor, wherein the pre - charge capacitor is charged using power provided by a rechargeable energy storage system (RESS). The method further includes selectively operating a second switch of the DC - DC converter to boost a charger current to a predetermined charging current threshold such that the charger current recharges the RESS.

[0018] Among other features, the charger current is provided by a DC charging station.

[0019] Among other features, the DC charging station includes a DC fast charging station capable of outputting power in the range from about fifty kilowatts (50 kW) to about three hundred and fifty kilowatts (350 kW).

[0020] Among other features, the first switch and the second switch include voltage-controlled semiconductor switches.

[0021] Among other features, the voltage-controlled semiconductor switch includes at least one of a silicon insulated gate bipolar transistor (IGBT), a silicon carbide metal oxide semiconductor field effect transistor (MOSFET), a silicon super junction MOSFET, a gallium nitride (GaN) field effect transistor (FET), a SiC junction gate field effect transistor (JFET), a wide bandgap (WBG) device, or an ultra-wide bandgap (UWBG) device.

[0022] Among other features, the first switch and the second switch are configured to operate in complementary operating states.

[0023] From the description provided herein, further applicable fields will become apparent. It should be understood that the description and specific examples are for illustrative purposes only and are not intended to limit the scope of the present disclosure. Description of the Drawings

[0024] The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present disclosure in any way.

[0025] Figure 1 is a schematic diagram of an exemplary motor vehicle connected to a non-vehicle-mounted DC charging station;

[0026] Figure 2 is a block diagram of an exemplary direct current (DC) charging circuit, i.e., an electrical system, according to an exemplary embodiment;

[0027] Figure 3 is a circuit schematic diagram of an exemplary electrical system according to an exemplary embodiment; and

[0028] Figure 4 is a flowchart showing an exemplary process for charging a vehicle's RESS via a non-vehicle-mounted power source according to an exemplary embodiment. Detailed Description

[0029] The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application, or uses.

[0030] Figure 1An exemplary direct current (DC) charging circuit 10 is shown as part of a motor vehicle 20. The vehicle 20 is depicted as performing a DC fast charging operation, wherein the DC charging circuit 10 is electrically connected to an off-board DC charging station 30 via a charging port 11 and a charging cable 15, such as using an SAE J1772 charging connector or other suitable regional or national standard charging plug or connector. The present disclosure is independent of the specific charging standard ultimately adopted in the DC fast charging operation involving the DC charging station 30, and therefore the above examples are merely illustrative. For example, the DC charging station 30 can be a DC fast charging station capable of supplying power to the vehicle 20, wherein the power output ranges between about fifty kilowatts (50kW) to about three hundred and fifty kilowatts (350kW). In another possible embodiment, the vehicle 20 can be charged from a second vehicle capable of providing charging power to the vehicle 20.

[0031] The DC charging circuit 10 can be used as part of a motor vehicle 20 and other electrical systems such as a fixed or mobile power station robot or platform. For transport applications, non-motor vehicles such as aircraft, ships, and rail vehicles can enjoy similar benefits. The DC charging circuit 10 can be used as part of a powertrain of a mobile system (such as the exemplary vehicle 20). For consistency of description, the following will be described in the context of a motor vehicle and the application of the DC charging circuit 10 as a component of the vehicle 20, but the present disclosure is not limited to this embodiment.

[0032] Figure 1 The vehicle 20 includes a body 12 and drive wheels 14. The body 12 may define or include a charging port 11 at a user accessible location. The vehicle 20 may be implemented differently as having Figure 2 and Figure 3 A plug-in electric vehicle having an onboard rechargeable energy storage system (RESS) 120 as shown and described below, wherein the RESS is a type of vehicle that can be used, for example, Figure 1 The RESS 120 may be configured to selectively recharge a multi-cell lithium-ion DC battery pack, a zinc-air DC battery pack, a nickel-metal hydride DC battery pack, or a lead-acid DC battery pack at an off-board DC charging station 30. During operation of the vehicle 20, the RESS 120 may provide power to one or more powertrain components / traction drive components of the vehicle 20, such as an electric motor (EM) (e.g., a traction motor), to generate motor torque and transmit it to the drive wheels 14 to propel the vehicle 20, or to perform other useful work on the vehicle 20.

[0033] Figure 2A block diagram of a DC charging circuit 10 for a vehicle 20 according to various embodiments is shown. As shown, the DC charging circuit 10 includes a controller 105, which may include at least one processor and at least one memory for storing computer-readable instructions. The memory includes a tangible non-transitory memory, such as a read-only memory, which may be an optical memory, a magnetic memory, a flash memory, or other memory. The controller 105 also includes a sufficient amount of random access memory, electrically erasable programmable read-only memory, etc., as well as a high-speed clock, analog-to-digital and digital-to-analog circuits, input / output circuits and devices, and appropriate signal conditioning and buffering circuits.

[0034] The DC charging circuit 10 also includes a gate driver 110 and a direct current - direct current (DC-DC) converter 115. The controller 105 is operably connected to the gate driver 110 and the DC-DC converter 115. Based on control signals issued by the controller 105, the gate driver 110 controls one or more switches within the DC-DC converter 115, as described in more detail below with reference to Figure 3 In various embodiments, the controller 105 may include a pulse width modulator that provides a pulse width modulation signal to the gate driver 110. The gate driver 110 may operate the DC-DC converter 115 based on the signal received from the pulse width modulator.

[0035] As shown, the DC charging circuit 10 also includes an on-board rechargeable energy storage system (RESS) 120, which is adapted to store high-voltage electrical energy for propelling an electric drive vehicle (e.g., Figure 1 the vehicle 20).

[0036] The RESS 120 may be a deep-cycle, high ampere capacity battery system, rated at a voltage of approximately four hundred (400) to approximately eight hundred (800) volts direct current (VDC) or higher, e.g., depending on the required vehicle range, vehicle gross weight, and the rated power of various loads that draw power from the RESS 120 in various embodiments. However, it should be understood that the RESS 120 may also have other rated voltages. The RESS 120 may include one or more high-voltage, independently rechargeable battery packs.

[0037] When a DC charging station 30 is connected to the vehicle 20, e.g., when the charging cable 15 of the DC charging station 30 is connected to the charging port 11 of the vehicle 20, the DC charging station 30 delivers electrical energy to the DC-DC converter 115 to charge the RESS 120.

[0038] Figure 3A circuit schematic diagram of a DC charging circuit 10 according to an exemplary embodiment of the present disclosure is shown. As shown, the DC-DC converter 115 may include a first switch 205 and a second switch 210. In an exemplary embodiment, the switches 205, 210 include voltage-controlled semiconductor switches controlled by control signals provided by a controller 105 through a gate driver 110. In various embodiments, the switches 205, 210 include voltage-controlled switching devices in the form of silicon insulated gate bipolar transistors (IGBTs), silicon carbide (SiC) metal oxide semiconductor field effect transistors (MOSFETs), silicon (Si) superjunction MOSFETs, gallium nitride (GaN) field effect transistors (FETs), SiC junction gate field effect transistors (JFETs), other wide bandgap (WBG) or ultra-wide bandgap (UWBG) semiconductor power switching devices, or other suitable switches having corresponding gates, where a gate signal is applied to the corresponding gate to change the on / off state of a given switch.

[0039] As Figure 3 shown, the gate driver 110 is operably connected to the gates 215, 220 of the switches 205, 210 and provides gate signals to the corresponding gates to control the corresponding switches 205, 210 to either operate in an off state to prevent current flow or in an on state to allow current flow. The gate driver 110 may include an inverter 225 that inverts the gate signal provided by the gate driver 110. For example, the output 230 of the gate driver 110 is connected to the gate 220 of the second switch 210, and the output 235 of the inverter 225 is connected to the gate 215 of the switch 205. Based on this configuration, the switches 205, 210 operate in complementary states, where when one of the switches 205, 210 is in the on state, the other of the switches 205, 210 is in the off state.

[0040] The DC charging circuit 10 may further include a pre-charge capacitor 230 and a discharge resistor 235 connected in parallel. The pre-charge capacitor 230 and the discharge resistor 235 are connected between the positive terminal 240 and the negative terminal 245.

[0041] The DC charging circuit 10 further includes an inductor 250 between nodes 255 and 260. Node 255 includes an electrical node to which the positive terminal of the pre-charge capacitor 230 and the discharge resistor 235 are connected. Node 260 includes an electrical node that can be used as an input to the switches 205, 210. For example, depending on the operation of the DC charging circuit 10, electrical energy can be transferred to one of the switches 205, 210 via the inductor 250. The DC charging circuit 10 may further include an output capacitor 265. The pre-charge capacitor 230, the discharge resistor 235, the inductor 250, and the output capacitor 265 may include any suitable values according to the present disclosure.

[0042] When the DC charging station 30 is connected to the DC charging circuit 10, the DC charging station 30 serves as a current source for the DC-DC converter 115. As discussed in more detail herein, boost mode techniques can be used to provide sufficient electrical energy to the RESS 120 for charging purposes. For example, boost mode techniques can be used to address the internal resistance 270 and internal inductance 275 associated with the RESS 120.

[0043] Figure 4 is a flowchart of an exemplary process 400 for selectively recharing the RESS 120 via an off-board power source (e.g., the DC charging station 30), which serves as a current source having a maximum voltage lower than the maximum voltage of the RESS 120. The various blocks of process 400 can be executed by the controller 105. Process 400 begins at block 402. At block 405, a vehicle charging command is received at the controller 105. For example, when the connector of the charging cable 15 docks with the charging port 11, the vehicle charging command can be provided to the controller 105.

[0044] At block 410, it is determined whether the input DC-DC converter voltage is greater than or equal to a predetermined voltage threshold. The controller 105 can use one or more sensors (not shown) deployed in the DC charging circuit 10 to determine whether the input DC-DC converter voltage is greater than or equal to the predetermined voltage threshold. For example, one or more sensors can include voltage sensors that determine voltage values at one or more nodes in the DC charging circuit 10. In some embodiments, the input DC-DC converter voltage can include the voltage stored by the precharge capacitor 230.

[0045] If the input DC-DC converter voltage is less than the predetermined voltage threshold, then at block 415, the controller 105 causes the gate driver 110 to generate a control signal that operates the control switch 205. For example, the gate driver 110 can transmit a control signal such that a buck mode duty cycle is applied to the gate 215 to cause the DC-DC converter 115 to operate in a buck operating mode, thereby boosting the voltage stored by the precharge capacitor 230 to the predetermined voltage threshold. During the buck operating mode, the precharge capacitor 230 is charged to the predetermined voltage threshold via the power provided by the RESS 120.

[0046] When the input DC-DC converter voltage is greater than or equal to a predetermined voltage threshold, at block 420, the controller 105 causes the gate driver 110 to output a control signal to switches 205, 210 according to a boost mode duty cycle to boost the charging current to a predetermined charging current threshold. In an exemplary embodiment, the predetermined charging current threshold may be about one hundred and twenty-five amperes (125 A). However, it should be understood that other predetermined charging current thresholds may be selected based on the recharge operation. In various embodiments, the switch 210 of the DC-DC converter 115 (and based on the complementary nature of switches 205, 210, switch 205) is controlled via a control signal applied to gate 220 to control the charging current provided to the RESS 120. The boost mode duty cycle can control the amplitude of the charging current such that the charging current is boosted to the predetermined charging current threshold. The charging current can be supplied from the DC charging station 30 to the RESS 120 via switch 205. In some cases, the controller 105 causes the gate driver 110 to output a control signal with a dead time between the complementary signals applied to gates 215 and 220 to mitigate current shoot-through via switches 205 and 210.

[0047] At block 425, it is determined whether the charging operation is complete. For example, the controller 105 can compare the voltage stored in the RESS 120 with a RESS voltage threshold. If the voltage stored in the RESS 120 is greater than or equal to the RESS voltage threshold, the charging operation is complete. If the charging operation is not complete, the process 400 returns to block 420.

[0048] Otherwise, at block 430, the controller 105 causes the charging current to decrease by operating switch 210 in the off state. At block 435, the controller 105 causes both switches 205, 210 to transition to the off state, and the voltage stored in the pre-charge capacitor 230 is discharged via the discharge resistor 235. Then the process 400 ends at block 440.

[0049] The description of the present disclosure is merely exemplary in nature, and variations that do not depart from the gist of the present disclosure are intended to fall within the scope of the present disclosure. These variations should not be regarded as departing from the spirit and scope of the present disclosure.

Claims

1. An electrical system for increasing the voltage supplied by a DC charging station, comprising: Rechargeable Energy Storage System (RESS); and a DC-DC converter, connected to the RESS and configured to be connected to the DC charging station, wherein the DC-DC converter is configured to selectively connect the RESS to the DC charging station so as to selectively supply a charging current to the RESS during a recharge operation, and wherein the DC-DC converter includes: a positive terminal; a negative terminal connected to the RESS; a pre-charge capacitor connected between the positive terminal and the negative terminal; an input node on the positive terminal; a first switch connected between the input node and the negative terminal; and a second switch connected between the input node and the RESS, wherein when the input DC-DC converter voltage is less than a predetermined voltage threshold, the second switch is controlled to boost the voltage stored in the pre-charge capacitor to the predetermined voltage threshold, and wherein when the input DC-DC converter voltage is greater than or equal to the predetermined voltage threshold, the first switch and the second switch are controlled to boost the charging current to a predetermined charging current threshold of the RESS.

2. The electrical system according to claim 1, wherein, The DC-DC converter further includes an inductor disposed between a point connecting the pre-charge capacitor on the positive terminal and the input node.

3. The electrical system according to claim 2, wherein, The first switch and the second switch include voltage-controlled semiconductor switches.

4. The electrical system according to claim 3, wherein, The voltage-controlled semiconductor switch includes at least one of a silicon insulated gate bipolar transistor (IGBT), a silicon carbide metal oxide semiconductor field effect transistor (MOSFET), a silicon super-junction MOSFET, a gallium nitride (GaN) field effect transistor (FET), a SiC junction gate field effect transistor (JFET), a wide bandgap (WBG) device, or an ultra-wide bandgap (UWBG) device.

5. The electrical system according to claim 2, wherein, The first switch and the second switch are configured to operate in complementary operating states.

6. The electrical system according to claim 2, further comprising: A controller, operably connected to the DC-DC converter and configured to operate the DC-DC converter to selectively connect the RESS to the DC charging station based on a gate signal provided to at least one of the first switch or the second switch.

7. The electrical system according to claim 6, further comprising an output capacitor connected between the positive terminal and the negative terminal of the RESS.

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