Power supply system

Abstract

This prevents a portion of the power from the charging equipment from being recirculated to the charging connector without being used to charge the first or second battery. [Solution] A power supply system in which the first battery has a larger number of battery cells than the second battery, and the control device controls the first and second inverters so that the remaining capacity of the first battery and the remaining capacity of the second battery are equal when charging in parallel.

Description

Technical Field

[0006] , , ,

[0001] The present disclosure relates to a power supply system.

Background Art

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, as a power supply system, there has been devised one that includes a first battery and a second battery and a charging connector, and that can charge the first battery via a first charging path and the second battery via a second charging path using power from a charging facility connected to the charging connector. In such a power supply system, during parallel charging, part of the power from the charging facility may flow back to the charging connector without being used for charging the first battery or the second battery.

[0005] The main object of the power supply system of the present disclosure is to suppress part of the power from the charging facility from flowing back to the charging connector without being used for charging the first battery or the second battery.

Means for Solving the Problems

[0006] The power supply system of the present disclosure employs the following means to achieve the main objective described above. The power supply system of the present disclosure comprises a first battery and a second battery, each having a plurality of battery cells; a motor having a three-phase coil; a first inverter connected to the first battery via a first positive electrode line and a negative electrode line and connected to one end of the three-phase coil; a second inverter connected to the second battery via a second positive electrode line and the negative electrode line and connected to the other end of the three-phase coil; a charging connector connected to the first positive electrode line and the negative electrode line and electrically connectable to a charging device; and a control device that, when charging the first and second batteries in parallel using power from the charging device, fixes one upper arm of the first and second inverters to the ON position and controls the duty cycle of the other upper arm and lower arm. The first battery has a larger number of battery cells than the second battery, and the control device controls the first and second inverters during parallel charging so that the remaining capacity of the first battery and the remaining capacity of the second battery are equal. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic diagram of the power supply system and charging stand according to the embodiment of this disclosure. [Figure 2] An explanatory diagram showing the flow of current during parallel charging. [Modes for carrying out the invention]

[0008] Embodiments for implementing this disclosure will be described with reference to the drawings. Figure 1 is a schematic diagram of a power supply system and charging station according to an embodiment of this disclosure. The power supply system 10 is installed in an electric vehicle or a hybrid vehicle and comprises a battery 12, a motor 20, a first inverter 22, a second inverter 24, a switching circuit 30, a charging circuit 40, and a system electronic control unit (hereinafter referred to as "system ECU") 50 as a control device. The power supply system 10 is capable of charging the battery 12 using power from a charging station 80 installed at home or a charging station.

[0009] Battery 12 comprises a first battery 13 and a second battery 14, each having multiple battery cells. The first battery 13 and the second battery 14 are configured as lithium-ion secondary batteries or nickel-metal hydride secondary batteries, respectively, with a rated voltage slightly lower than the first voltage Vs1 (e.g., 400V). The positive terminal of the first battery 13 is connected to the first positive line 31, and the negative terminal of the second battery 14 is connected to the negative line 33. The negative terminal of the first battery 13 is connected to the positive terminal of the second battery 14 via a series line 35. A series relay Rs is attached to the series line 35. Therefore, by turning on the series relay Rs, the first battery 13 and the second battery 14 are connected in series with each other.

[0010] The motor 20 is configured as a three-phase AC motor having, for example, a rotor in which permanent magnets are embedded in the rotor core, and a stator in which three-phase (U-phase, V-phase, W-phase) coils are wound around the stator core. The first inverter 22 comprises six transistors T11 to T16 as switching elements, and six diodes D11 to D16 connected in parallel to each of the six transistors T11 to T16. The transistors T11 to T16 are arranged in pairs, with two on each side acting as the source and sink sides with respect to the first positive line 31 and the negative line 33. Each connection point of a pair of transistors T11 to T16 is connected to one end of the three-phase (U-phase, V-phase, W-phase) coils of the motor 20. A first capacitor 26 for smoothing is connected to the first positive line 31 and the negative line 33. The second inverter 24, like the first inverter 22, is equipped with six transistors T21-T26 and six diodes D21-D26 as switching elements. Transistors T21-T26 are arranged in pairs, with two on each side, acting as the source and sink sides for the second positive line 32 and the negative line 33. Each connection point of a pair of transistors T21-T26 is connected to the other end of the three-phase (U-phase, V-phase, W-phase) coil of the motor 20. A second capacitor 28 for smoothing is connected to the second positive line 32 and the negative line 33. Hereinafter, transistors T11-13 and T21-T23 of the first and second inverters 22 and 24 may be referred to as the "upper arm," and transistors T14-T16 and T24-T26 may be referred to as the "lower arm."

[0011] The switching circuit 30 includes, in addition to the first positive line 31, second positive line 32, negative line 33, series line 35, and series relay Rs described above, a parallel line 36, a first parallel relay Rp1, and a second parallel relay Rp2. The parallel line 36 connects the negative terminal of the first battery 13 to the negative line 33. The first parallel relay Rp1 is attached to the parallel line 36. The second parallel relay Rp2 is attached to the second positive line 32.

[0012] The charging circuit 40 includes a charging line 42 connected to the first positive electrode line 31 and the negative electrode line 33, and a charging connector 44 connected to the charging line 42. The charging connector 44 is configured to be connectable to the stand connector 82 of the charging stand 80.

[0013] The system ECU 50 includes a microcomputer with a CPU, ROM, RAM, flash memory, input / output ports, and communication ports, as well as various drive circuits and various logic ICs. Signals from various sensors are input to the system ECU 50. Examples of these sensors include a voltage sensor 13v that detects the voltage Vb1 of the first battery 13, a temperature sensor 13t that detects the temperature Tb1 of the first battery 13, a voltage sensor 14v that detects the voltage Vb2 of the second battery 14, and a temperature sensor 14t that detects the temperature Tb2 of the second battery 14. Other examples include a rotation position sensor 20a that detects the rotational position of the rotor of the motor 20, current sensors 20u, 20v, and 20w that detect the currents Iu, Iv, and Iw flowing through each phase (U phase, V phase, and W phase) of the motor 20, a voltage sensor 26v that detects the voltage VH of the first capacitor 26, and a voltage sensor 28v that detects the voltage VL of the second capacitor 28. Furthermore, a current sensor 31i for detecting the current Ip1 flowing through the first positive electrode line 31 and a current sensor 32i for detecting the current Ip2 flowing through the second positive electrode line 32 are also included. Note that when the series relay Rs is in the off state and the first parallel relay Rp1 and the second parallel relay Rp2 are in the on state, that is, when the first battery 13 is connected to the first positive electrode line 31 and the negative electrode line 33 and the second battery 14 is connected to the second positive electrode line 32 and the negative electrode line 33, the current Ip1 flowing through the first positive electrode line 31 is equal to the current flowing through the first battery 13, and the current Ip2 flowing through the second positive electrode line 32 is equal to the current flowing through the second battery 14. Furthermore, when the series relay Rs is ON and the first parallel relay Rp1 and the second parallel relay Rp2 are OFF, that is, when the first battery 13 and the second battery 14 are connected in series, the current Ip1 flowing through the first positive electrode line 31 is equal to the current flowing through the first battery 13 and the second battery 14.

[0014] The system ECU 50 calculates the charge levels SOC1 and SOC2 of the first battery 13 and the second battery 14, as well as the open-circuit voltages OCV1 and OCV2, and the allowable input powers Win1 and Win2. The charge levels SOC1 and SOC2 are calculated, for example, based on the integrated value of the current Ip1 (current flowing to the first battery 13) flowing through the first positive line 31 and the integrated value of the current Ip2 (current flowing to the second battery 14) flowing through the second positive line 32 when the series relay Rs is off and the first parallel relay Rp1 and the second parallel relay Rp2 are on, and the integrated value of the current Ip1 (current flowing to the first battery 13 and the second battery 14) flowing through the first positive line 31 when the series relay Rs is on and the first parallel relay Rp1 and the second parallel relay Rp2 are off. The open-circuit voltages OCV1 and OCV2 are derived, for example, by applying the charge ratios SOC1 and SOC2 to a predetermined map, which is determined by experiments, analyses, or machine learning, as a relationship between the charge ratios SOC1 and SOC2 and the open-circuit voltages OCV1 and OCV2. The allowable input powers Win1 and Win2 are derived, for example, by applying the charge ratios SOC1 and SOC2 and temperatures Tb1 and Tb2 to a predetermined map, which is determined by experiments, analyses, or machine learning, as a relationship between the charge ratios SOC1 and SOC2 and temperatures Tb1 and Tb2 and the allowable input powers Win1 and Win2.

[0015] The system ECU 50 outputs control signals to the first and second inverters 22 and 24, as well as control signals to each relay. These relays include the series relay Rs, the first parallel relay Rp1, and the second parallel relay Rp2. The system ECU 50 can communicate with the charging station's electronic control unit (hereinafter referred to as the "stand ECU") 86 of the charging station 80.

[0016] The charging stand 80 comprises a stand connector 82, a power supply device 84, and a stand ECU 86. The stand connector 82 is configured to be connectable to the charging connector 44 of the power supply system 10. The power supply device 84 is connected to an AC power source such as a household power supply or a commercial power supply, and is configured to convert AC power from the AC power source to DC power and adjust the output power (output voltage and output current) to be output to the stand connector 82. The stand ECU 86, like the system ECU 50, is equipped with a microcomputer. Signals from various sensors are input to the stand ECU 86. Examples of these sensors include a voltage sensor (not shown) that detects the output voltage Vs of the power supply device 84, and a current sensor (not shown) that detects the output current Is of the power supply device 84. The stand ECU 86 outputs control signals to the power supply device 84. As described above, the stand ECU 86 is capable of communicating with the system ECU 50. Examples of charging stations 80 include a first-voltage station where the supplied power voltage is a first voltage Vs1 (e.g., 400V), a second-voltage station where the supplied power voltage is a second voltage Vs2 (e.g., 800V) which is higher than the first voltage Vs1, and a third-voltage station in which either the first voltage Vs1 or the second voltage Vs2 can be selectively set as the supplied power voltage.

[0017] In the power supply system 10 of this embodiment, when the motor 20 is used as a driving motor, the first battery 13 and the second battery 14 are connected in series by turning on the series relay Rs and turning off the first parallel relay Rp1 and the second parallel relay Rp2, and the motor 20 is driven by the first inverter 22 using power from the first battery 13 and the second battery 14.

[0018] Furthermore, in the power supply system 10, when the charging connector 44 and the stand connector 82 of the charging stand 80 are connected, the system ECU 50 selects parallel charging if the voltage of the power supplied by the charging stand 80 is a first voltage Vs1, and selects series charging if the voltage of the power supplied by the charging stand 80 is a second voltage Vs2. Since series charging is not central to the present invention, a detailed description is omitted.

[0019] In parallel charging, the first battery 13 and the second battery 14 are connected in parallel as seen from the charging connector 44 by turning off the series relay Rs and turning on the first parallel relay Rp1 and the second parallel relay Rp2, and the first battery 13 and the second battery 14 are charged using power from the charging stand 80. Figure 2 is an explanatory diagram showing the current flow during parallel charging. In the figure, the thick solid line with an arrow indicates the charging current of the first battery 13, and the thick dashed line with an arrow indicates the charging current of the second battery 14. In parallel charging, the first battery 13 is charged by the current flowing in the following order from the charging connector 44 to the positive terminal line of the charging line 42, the first positive terminal line 31, the first battery 13, the parallel line 36 (first parallel relay Rp1), the negative terminal line 33, the negative terminal line of the charging line 42, and the charging connector 44, as shown by the thick solid line with an arrow in Figure 2. This current path is called the "first charging path". The second battery 14 is charged by current flowing in the following order, as shown by the thick dashed line with arrow in Figure 2: from the charging connector 44, through the positive terminal line of the charging line 42, the first positive terminal line 31, the first inverter 22, the motor 20, the second inverter 24, the second positive terminal line 32 (second parallel relay Rp2), the second battery 14, the negative terminal line 33, the negative terminal line of the charging line 42, and finally through the charging connector 44. This current path is referred to as the "second charging path".

[0020] In the power supply system 10 of this embodiment, the first battery 13 and the second battery 14 are each equipped with multiple battery cells of the same type. The number of battery cells N1 in the first battery 13 is greater than the number of battery cells N2 in the second battery 14. In parallel charging, the first and second inverters 22 and 24 are controlled so that the charge level SOC1 of the first battery 13 and the charge level SOC2 of the second battery 14 are the same. Now, since the number of battery cells N1 in the first battery 13 is greater than the number of battery cells N2 in the second battery 14, the open-circuit voltage OCV1 of the first battery 13 is higher than the open-circuit voltage OCV2 of the second battery 14. At this time, step-down control is performed as the control of the first inverter 22. In step-down control, the upper arm of the second inverter 24 is fixed to ON (the lower arm is fixed to OFF), and the upper and lower arms of the first inverter 22 are controlled on a duty cycle. As a result, a portion of the power from the charging station 80 is stepped down by the first inverter 22 and the motor 20 and supplied to the second battery 14.

[0021] Here, we will explain why the number of battery cells N1 in the first battery 13 is greater than the number of battery cells N2 in the second battery 14, and why the first and second inverters 22 and 24 are controlled so that the charge level SOC1 of the first battery 13 and the charge level SOC2 of the second battery 14 are the same. The second charging path passes through the first inverter 22, motor 20, and second inverter 24, and therefore has a higher impedance than the first charging path. For this reason, by setting the number of battery cells in the first battery 13 and the second battery 14 to be the same and controlling the first and second inverters 22 and 24 so that the charge level SOC1 of the first battery 13 and the charge level SOC2 of the second battery 14 are equal, boost control is performed. In boost control, the upper arm of the first inverter 22 is fixed to ON (the lower arm is fixed to OFF), and the upper and lower arms of the second inverter 24 are controlled on a duty cycle. When boost control is performed, current flows in the following order from the charging connector 44 to the positive line of the charging line 42, the first positive line 31, the upper arm of the first inverter 22, the motor 20, the transistor that is turned on on the lower arm side of the second inverter 24, the negative line 33, the negative line of the charging line 42, and finally to the charging connector 44. In other words, a portion of the power from the charging connector 44 is returned to the charging connector 44 without being used to charge the first and second batteries 13 and 14, resulting in a longer charging time. In this embodiment, since the open-circuit voltage OCV1 of the first battery 13 is greater than the open-circuit voltage OCV2 of the second battery 14, buck control is performed. Therefore, since the boost control of the first and second inverters 22 and 24 is suppressed, it is possible to suppress the return of a portion of the power from the charging stand 80 to the charging connector 44 without being used to charge the first and second batteries 13 and 14, thereby suppressing a longer charging time.

[0022] According to the power supply system 10 of the present embodiment described above, by making the number N1 of battery cells of the first battery 13 larger than the number N2 of battery cells of the second battery 14 and controlling the first and second inverters 22 and 24 so that the power storage ratio SOC1 of the first battery 13 and the power storage ratio SOC2 of the second battery 14 are the same, it is possible to suppress the reflux of a part of the power from the charging stand 80 to the charging connector 44 without being used for charging the first and second batteries 13 and 14.

[0023] As described above, the embodiments for implementing the present disclosure have been described. However, the present disclosure is not limited to such embodiments, and it is needless to say that the present disclosure can be implemented in various forms without departing from the gist of the present disclosure.

Explanation of Reference Numerals

[0024] 13 First battery, 14 Second battery, 50 System ECU.

Claims

[Claim 1] A power supply system comprising: a first battery and a second battery, each having a plurality of battery cells; a motor having a three-phase coil; a first inverter connected to the first battery via a first positive electrode line and a negative electrode line and connected to one end of the three-phase coil; a second inverter connected to the second battery via a second positive electrode line and a negative electrode line and connected to the other end of the three-phase coil; a charging connector connected to the first positive electrode line and the negative electrode line and electrically connectable to a charging device; and a control device that, when charging the first and second batteries in parallel using power from the charging device, fixes one of the upper arms of the first and second inverters in the ON position and controls the duty cycle of the other upper arm and lower arm, wherein The first battery has a larger number of battery cells compared to the second battery. The control device controls the first and second inverters so that the remaining capacity of the first battery and the remaining capacity of the second battery are equal during parallel charging. Power supply system.

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