WO2020035969A1 - Dc power supply - Google Patents

Abstract

A reactor-attached connection switching circuit capable of selecting a series connection or a parallel connection of two batteries further has a step-up mode, a step-down mode, and a transient mode. The reactor connects a series transistor to one of two parallel transistors. The connection point between the reactor and the series transistor is connected to one of the two parallel transistors via a reactor demagnetization diode. When the temperature of the batteries is low, a bidirectional DC/DC converter connected to the batteries alternately executes a step-up operation and a step-down operation to heat the batteries.

Description

DC power supply

The present invention relates to a DC power supply having a bidirectional DCDC converter, and more particularly to a DC power supply including a vehicle battery.

The EV has a battery temperature management system that cools the battery with a cool airflow in a high temperature environment and warms the battery with a warm airflow in a low temperature environment. This battery temperature management system consumes battery electrical energy and EV internal space. For this reason, efficient use of EV batteries is required.

Vehicle DC power supplies having a bidirectional DCDC converter are known. Switched battery devices that switch between serial connection and parallel connection of two batteries are also known. The two batteries connected in parallel have an equivalent resistance value of 1/4 as compared to the two batteries connected in series. As a result, a parallel connection can have half the battery loss of a series connection. However, the switched battery device has a problem that the DC link voltage changes suddenly due to connection switching.

Patent Document 1 proposes a switched battery device with a reactor shown in FIG. The series transistor 3 connects the batteries 1 and 2 in series. The parallel transistors 4 and 5 connect the batteries 1 and 2 in parallel. The reactor 7 suppresses a sudden change in the DC link voltage due to connection switching. However, the switched battery device shown in FIG. 1 has a problem that the reactor 7 always generates power loss.

Patent Document 2 proposes another switched battery device with a reactor shown in FIG. The series transistor 3 connects the batteries 1 and 2 in series. The parallel transistors 4 and 5 connect the batteries 1 and 2 in parallel. Reactor 7A is connected to battery 1 in series. Reactor 7B is connected in series with battery 2. The voltages of the batteries 1 and 2 are output through the output transistor 6.

The switched battery device with a reactor shown in FIG. 2 can execute a DC link voltage boosting operation. As a result, the number of turns of the stator coil can be increased. Further, the inverter current and its resistance loss can be reduced. In other words, reactors 7A and 7B realize both smooth connection switching and DC link voltage boosting. However, the switched battery device with a reactor shown in FIG. 2 has a problem that the reactors 7A and 7B always generate power loss.

Patent 4353222 Patent 5492040

An object of the present invention is to provide a DC power supply that can efficiently use battery energy.

In one aspect of the invention, a DC power supply comprising a switched battery device with a reactor has a bidirectional DCDC converter. This bidirectional DCDC converter includes a series transistor that connects two batteries in series, two parallel transistors that connects two batteries in parallel, a reactor that is connected in series with the two batteries, and a voltage of the two batteries and the reactor. And an output transistor that outputs the sum of The reactor is arranged between one of the two parallel transistors and the series transistor. Further, a connection point between the reactor and the series transistor is connected to one of the two parallel transistors through a diode for reactor discharge.

Thus, in the parallel mode in which the two batteries are connected in parallel, the batteries can perform discharging and charging without passing through the reactor. When the series transistor is turned off, a degaussing current for reducing magnetic energy stored in the reactor flows through the diode.

According to one aspect, the controller includes: a parallel mode in which two batteries are connected in parallel; a series mode in which two batteries are connected in series; a boost mode in which a voltage higher than the total voltage of the two batteries is output; And a transient mode in which an intermediate voltage of the series mode and the series mode is output, and a step-down mode in which two batteries are charged in series. As a result, the power supply efficiency in the parallel mode can be improved, and the mode can be smoothly changed.

According to another aspect, the controller inhibits turning on the parallel transistor and the series transistor connected to the defective battery. As a result, normal battery discharge can be continued, and the reliability of the power supply is improved.

According to another aspect and another aspect of the invention, the controller alternately performs the boost mode and the buck mode when the battery temperature is low. Thereby, the battery can be efficiently heated. As a result, the internal resistance of the battery is reduced, and the efficiency of the DC power supply is improved. After all, the DC power supply of the present invention is particularly suitable for a battery for an electric vehicle.

According to another aspect, the alternating implementation of the boost mode and the buck mode is performed by the main battery and the smoothing capacitor. In another preferred embodiment, the alternating operation of the boost mode and the buck mode is performed by the main battery and the auxiliary battery. As a result, manufacturing costs can be reduced.

FIG. 1 is a wiring diagram showing an example of a conventional booster battery device. FIG. 2 is a wiring diagram showing another example of a conventional booster battery device. FIG. 3 is a wiring diagram showing an embodiment of the DC power supply of the present invention. FIG. 4 is a diagram illustrating an example of the relationship among the motor speed, the maximum current, and the DC link voltage. FIG. 5 is a schematic wiring diagram showing the accumulation mode of the boost mode. FIG. 6 is a schematic wiring diagram showing an output mode of the boost mode. FIG. 7 is a schematic wiring diagram showing the accumulation mode of the transient mode. FIG. 8 is a schematic wiring diagram showing the degaussing mode of the transient mode. FIG. 9 is a schematic wiring diagram showing the accumulation mode of the step-down mode. FIG. 10 is a schematic wiring diagram showing the free wheeling mode of the step-down mode. FIG. 11 is a flowchart showing a control example in the motor mode. FIG. 12 is a schematic wiring diagram showing one modified embodiment. FIG. 13 is a schematic wiring diagram for explaining the battery internal heating operation. FIG. 14 is a flowchart for explaining the battery internal heating operation.

A preferred embodiment of the DC power supply of the present invention will be described with reference to FIG. This DC power supply for applying a DC link voltage Vdc to an inverter (not shown) for driving a traction motor of an electric vehicle includes a battery 1, a battery 2, and a connection switching circuit 10. The rated voltages of batteries 1 and 2 are equal. Each of the batteries 1 and 2 can employ a capacitor.

The connection switching circuit 10, which is essentially a bidirectional DCDC converter, includes a series transistor 3, parallel transistors 4 and 5, an output transistor 6, a reactor 7, and a diode 8. Transistors 3-6 each consist of an IGBT with an anti-parallel diode. This DC power supply applies a DC link voltage Vdc to a positive power supply line 11 and a negative power supply line 12.

The positive power supply line 11 is connected to the negative power supply line 12 through the output transistor 6, the battery 2, the reactor 7, the series transistor 3, and the battery 1. The connection point between the negative electrode of the battery 2 and the reactor 7 is connected to the negative power supply line 12 through the parallel transistor 4. The connection point between the output transistor 6 and the positive electrode of the battery 2 is connected to the positive electrode of the battery 1 through the parallel transistor 5. The connection point between the reactor 7 and the series transistor 3 is connected to the cathode electrode of the diode 8. The anode electrode of the diode 8 is connected to the negative power supply line 12.

The controller 100 that controls the connection switching circuit 10 has a motor mode for supplying a power supply current to an inverter (not shown) and a regenerative mode for charging the batteries 1 and 2. The motor mode has a parallel mode, a series mode, a boost mode, and a transient mode.

FIG. 4 shows an example of the relationship among the maximum power supply current Imax, the motor speed Vm, and the DC link voltage Vdc. When the motor speed Vm reaches the speed value V1 and the maximum power supply current Imax exceeds the first predetermined value, switching from the parallel mode 20 to the serial mode 30 is executed. When the motor speed Vm reaches the speed value V2 and the maximum power supply current Imax exceeds the second predetermined value, a change from the serial mode 30 to the boost mode 40 is executed. The transient mode 50 is executed during a switching period for switching between the parallel mode 20 and the serial mode 30. The first and second predetermined values each have a hysteresis characteristic.

In the parallel mode 20, the series transistor 3 is turned off. When the voltage difference between the batteries 1 and 2 is higher than a predetermined value, the higher one of the batteries 1 and 2 supplies the power supply current through the anti-parallel diode of the parallel transistor. Thereby, the voltage difference between batteries 1 and 2 is reduced. When the voltages of batteries 1 and 2 are approximately equal, battery 1 supplies half of the supply current through parallel transistor 5 and battery 2 supplies the other half of the supply current through parallel transistor 4. Discharging batteries 1 and 2 in parallel mode 20 is advantageous when batteries 1 and 2 have different states of degradation. The low deterioration battery can be discharged by bypassing the high deterioration battery.

In series mode 30, parallel transistors 4 and 5 are turned off and series transistor 3 is turned on. Thus, the DC link voltage Vdc becomes the sum of the voltages of the batteries 1 and 22.

In the boost mode 40, the series transistor 3 is turned on, and the parallel transistors 4 and 5 are subjected to PWM control. Preferably, the parallel transistors 4 and 5 are turned on at the same time and turned off at the same time. This boost mode includes an accumulation mode and an output mode that are executed alternately.

The accumulation mode will be described with reference to FIG. The output transistor 6 is turned off, and the parallel transistors 4 and 5 are turned on. The circulating current I1 flowing through the battery 1, the series transistor 3, the reactor 7, and the parallel transistor 4 increases, and the reactor 7 stores magnetic energy. Similarly, the circulating current I2 flowing through the battery 2, the parallel transistor 5, the series transistor 3, and the reactor 7 increases, and the reactor 7 stores magnetic energy. When the voltage difference between the batteries 1 and 2 is higher than a predetermined value, only the parallel transistor connected to the higher one of the batteries 1 and 2 is turned on. Thereby, the voltage difference between batteries 1 and 2 is reduced.

The output mode will be described with reference to FIG. The parallel transistors 4 and 5 are turned off. A power supply current I substantially equal to the sum of the circulating currents I1 and I2 is supplied to the inverter through the output transistor 6. The DC link voltage Vdc is the sum of the voltages of the battery 1, the reactor 7, and the battery 2. DC link voltage Vdc is adjusted by adjusting the duty ratio of parallel transistors 4 and 5. As a result, the connection switching circuit 10 operates as a step-up chopper type DCDC converter.

Transient mode 50 will be described with reference to FIGS. The parallel transistors 4 and 5 are turned off, and the series transistor 3 is PWM-controlled. FIG. 7 shows an accumulation period in which the series transistor 3 is turned on. The DC link voltage Vdc is the voltage sum of the battery 1, the reactor 7, and the battery 2. Reactor 7 generates a back electromotive force to suppress an increase in power supply current I. For this reason, the DC link voltage Vdc becomes lower than the sum of the voltages of the batteries 1 and 2.

FIG. 8 shows a demagnetization period in which the series transistor 3 is turned off. Reactor 7 allows power supply current I to flow through diode 8, reactor 7, battery 2, and output transistor 6. Reactor 7 generates a voltage in the same direction as battery 2 in order to suppress a decrease in power supply current I. For this reason, the DC link voltage Vdc becomes higher than the voltage of the battery 2.

In the transient mode in which the change from the parallel mode to the series mode is instructed, the on-duty ratio of the series transistor 3 is gradually changed from 0 to 1. Thereby, the DC link voltage Vdc is gradually changed from 150V to 300V. In the transient mode in which a change from the serial mode to the parallel mode is instructed, the on-duty ratio of the series transistor 3 is gradually changed from 1 to 0. Thereby, the DC link voltage Vdc is gradually changed from 300V to 150V. Preferably, this transient mode is less than a few seconds.

The regenerative mode has a parallel mode 20, a series mode 30, a transient mode 50, and a step-down mode 60. The parallel mode 20 and the series mode 30 of the regenerative mode are essentially the same as those of the motor mode. However, when the parallel mode of the regenerative mode is started, a voltage difference between the batteries 1 and 2 is detected. When this voltage difference exceeds a predetermined value, only the parallel transistor connected to the lower voltage battery is turned on. When this voltage difference is less than a predetermined value, both the parallel transistors 4 and 5 are turned on. The transient mode 50 of the regenerative mode is also essentially the same as the transient mode of the motor mode. However, during the demagnetization period when the series transistor 3 is turned off, the reactor 7 charges the batteries 1 and 2 in parallel through the respective anti-parallel diodes of the transistors 3-5. Charging batteries 1 and 2 in parallel mode 20 is advantageous when batteries 1 and 2 have different states of degradation. The low degradation battery can be charged by bypassing the high degradation battery. Further, charging in the step-down mode is advantageous when the deterioration states of the batteries 1 and 2 are different. The freewheeling current flowing through the low-deterioration battery increases due to the freewheeling current flowing through the high-deterioration battery.

In the step-down mode 60 shown in FIGS. 9 and 10, the series transistor 3 is turned on, the parallel transistors 4 and 5 are turned off, and the output transistor 6 is PWM-controlled. Since the antiparallel diode of the series transistor 3 is turned on, the turning on of the series transistor 3 can be omitted.

FIG. 9 shows an accumulation period in which the output transistor 6 is turned on. DC link voltage Vdc is applied to battery 2, reactor 7, and battery 1. The batteries 1 and 2 are charged in series by the regenerative current Ir, and the reactor 7 stores magnetic energy. The difference between the DC link voltage Vdc and the sum of the voltages of the batteries 1 and 2 is absorbed by the reactor 7.

FIG. 10 shows a free wheeling period in which the output transistor 6 is turned off. Reactor 7 circulates freewheeling current (I1 + I2). Freewheeling current I1 flowing through reactor 7, series transistor 3, battery 1, and parallel transistor 4 charges battery 1. The freewheeling current I2 flowing through the reactor 7, the series transistor 3, the parallel transistor 5, and the battery 2 charges the battery 2. Freewheeling currents I1 and I2 flow through the antiparallel diodes of parallel transistors 4 and 5. However, it is also possible to turn on the parallel transistors 4 and 5. As a result, the connection switching circuit 10 executes the step-down chopper operation of the bidirectional DCDC converter.

Further, the connection switching circuit 10 executes a countermeasure for failure of the batteries 1 and 2. The connection switching circuit 10 disconnects the defective batteries when one of the batteries 1 and 2 is defective and the other is normal. When the battery 1 is defective, the transistors 3 and 5 are turned off and the transistor 4 is turned on. Similarly, when battery 2 is defective, transistors 3 and 4 are turned off and transistor 5 is turned on. After all, the connection switching circuit 10 operates the normal battery in the parallel mode. Thereby, even if one of the two batteries 1 and 2 fails, driving of the traction motor can be realized.

Controller 100 also has a battery heating mode. Generally, this battery heating mode is executed when the temperature of batteries 1 and 2 is lower than a predetermined value. In the heating mode, the step-up mode and the step-down mode are alternately executed. When the DC link voltage Vdc reaches the first predetermined value, the step-up mode ends and the step-down mode starts. When the DC link voltage Vdc reaches the second predetermined value, the step-down mode ends and the step-up mode starts. The first predetermined value is higher than the second predetermined value. It is preferable that the first predetermined value and the second predetermined value are changed according to the driving environment.

According to the boost mode shown in FIGS. 5 and 6, the batteries 1 and 2 discharge the discharge current Id. According to the step-down mode shown in FIGS. 9 and 10, batteries 1 and 2 are charged by charging current Ic. As a result, the batteries 1 and 2 supply the inverter current (Id-Ic) to the inverter (not shown). As a result, a charging current Ic and a discharging current Id higher than the inverter current (Id-Ic) required by the inverter flow through the batteries 1 and 2. As a result, the batteries 1 and 2 are rapidly heated by the charging current Ic and the discharging current Id. When the temperature of the batteries 1 and 2 reaches a predetermined value, the heating mode is ended.

FIG. 11 is a flowchart illustrating the control operation of the controller 100 in the motor mode. First, it is determined whether switching from the serial mode S to the parallel mode P or switching from the parallel mode P to the serial mode S has been instructed (S100). When the mode switching is commanded, the PWM control of the series transistor 3 is executed (S102). Thereby, the DC link voltage Vdc is gradually changed.

Next, it is determined whether or not heating of batteries 1 and 2 has been commanded (S104). When the heating is commanded, a heating mode H in which the step-up mode and the step-down mode are alternately performed is executed. (S106). Thereby, batteries 1 and 2 are quickly heated. It is preferable that the step-up mode and the step-down mode are executed under the condition that the DC link voltage Vdc is maintained within a predetermined range.

Next, it is determined whether or not the boost mode B has been commanded (S108). When the boost mode B is commanded, the parallel transistors 4 and 5 are PWM-controlled, and the boost mode B is executed (S110). Next, it is determined whether or not a battery failure has occurred (S112). When a battery failure occurs, the above-described failure countermeasures are executed (S114).

The advantages of the DC power supply of this embodiment composed of a booster battery device with a reactor will be described. The DC power supply of this embodiment has a parallel mode in addition to the DC mode, similarly to the conventional DC power supply shown in FIGS. This parallel mode reduces the power loss of batteries 1 and 2. Further, the DC power supply of this embodiment has a boost mode like the conventional DC power supply shown in FIG. Therefore, the number of turns of the stator coil can be increased, and the power loss of the inverter can be reduced.

Further, the DC power supply of this embodiment has an excellent advantage that the power loss of the reactor 7 becomes zero in the parallel mode. In the low-speed and high-torque region, the parallel mode supplies a large current to the inverter. The parallel mode occupies most of the running time of electric vehicles and hybrid vehicles. Therefore, the DC power supply of this embodiment has improved efficiency, and the cooling mechanism of the reactor 7 is simplified. Further, according to this embodiment, the reliability regarding battery failure is improved.

Further, the DC power supply of this embodiment has a heating mode in which the step-up mode and the step-down mode are alternately executed at a low temperature. Thereby, the cold batteries 1 and 2 can be quickly heated. The internal resistance of the battery is high at low temperatures. Therefore, battery loss increases when the battery temperature is low. According to this embodiment, there is no need to heat the batteries 1 and 2 with an external electric heater.

The DC power supply of this embodiment requires transistors 3-6. However, the transistor 3-5 can adopt a relatively low voltage type as compared with the output transistor 6. Therefore, the transistor 3-5 can have a low on-resistance. This means that the power loss and manufacturing cost of the transistor 3-5 can be reduced. Since the diode 8 is used only during a very short transition period, a small diode can be used.

FIG. 12 shows a modification of the DC power supply shown in FIG. FIG. 12 has a reactor 7 and a diode 8 at different positions compared to FIG. Reactor 7 connects series transistor 3 and the positive electrode of battery 1. Diode 8 connects the connection point between reactor 7 and series transistor 3 to the positive electrode of battery 2. The DC power supply shown in FIG. 12 has essentially the same operation as the DC power supply shown in FIG.

Another embodiment is described with reference to FIGS. The battery of an EV parked outdoors during the winter is extremely cold, which increases battery loss. The above-described battery heating method in which charging and discharging are repeated between the smoothing capacitor of the inverter and the main battery has a possibility that the batteries 1 and 2 cannot be kept sufficiently warm due to the small-capacity smoothing capacitor. This problem is solved by alternate charging and discharging between the EV main battery and the auxiliary battery. This battery heating method using an auxiliary battery can be employed in a conventional EV battery system.

In FIG. 13, an auxiliary battery 500 having a rated voltage of 12 V is connected to batteries 1 and 2 through an insulated bidirectional DCDC converter 400. Converter 400 transfers DC power between batteries 1 and 2 and auxiliary battery 500. Connection switching circuit 10, which is another bidirectional DCDC converter, connects batteries 1 and 2 and smoothing capacitor 200. The smoothing capacitor 200 is connected to a pair of DC input terminals of a three-phase inverter (not shown). Connection switching circuit 10 exchanges DC power between batteries 1 and 2 and smoothing capacitor 200.

FIG. 14 is a flowchart showing a battery heating routine for controlling the battery heating system shown in FIG. First, it is determined whether battery heating by use of the smoothing capacitor 200 has been requested (S200). If Yes, the accumulation mode (S202) in which the transistor 3-5 is turned on and the transistor 4-5 are turned off. The boost mode (S204) is sequentially executed. Thereby, the smoothing capacitor 200 is charged. Next, an accumulation mode in which the transistor 6 is turned on (S206) and a free wheeling mode in which the transistor 6 is turned off (S208) are sequentially executed. Thereby, the batteries 1 and 2 are heated.

Next, it is determined whether battery heating by use of the auxiliary battery 500 has been requested (S210). If Yes, a charging operation for charging the auxiliary battery 500 (S212) and discharging the auxiliary battery are performed. The discharging operation (S214) is sequentially performed. Thereby, the batteries 1 and 2 are heated. Further, auxiliary battery 500 is heated. Next, it is determined whether or not the temperature Tb of the batteries 1 and 2 is higher than a predetermined threshold value Tth. If Yes, the routine ends, and if No, this routine is executed again.

The previously described battery heating mode is preferably performed early in the winter. The controller is started 30 minutes before the predicted operation start time calculated from the learned past operation start time. Thus, useless power consumption can be reduced.

Claims (8)

A controller for controlling a bidirectional DCDC converter connecting the first charge device and the second charge device, wherein the controller includes: a boost mode for transmitting power from the first charge device to the second charge device; and the second charge device. A DC power supply having a step-down mode for transmitting power from the device to the first charge device,
The bidirectional DCDC converter includes a series transistor for connecting two batteries as the first charge device in series, two parallel transistors for connecting the two batteries in parallel, and a memory for storing magnetic energy. A reactor, an output transistor connecting the two batteries to the second charge device, and a discharge diode for discharging the reactor;
The reactor is disposed between one of the two parallel transistors and the series transistor;
The direct-current power supply, wherein the discharge diode is connected to a connection point connecting the reactor and the series transistor. The DC power supply according to claim 1, wherein the second charge device comprises a smoothing capacitor for smoothing an output voltage of the DCDC converter. The controller includes: a parallel mode in which the two batteries are connected in parallel; a series mode in which the two batteries are connected in series; a boost mode in which a voltage higher than a total voltage of the two batteries is output; 2. The DC power supply according to claim 1, having a transient mode for outputting an intermediate voltage of the series mode, and a step-down mode for charging the two batteries in series. The DC power supply according to claim 3, wherein the controller prohibits the on-operation of the parallel transistor and the series transistor connected to the defective battery when one of the two batteries is defective. 4. The DC power supply according to claim 3, wherein the controller alternately executes the step-up mode and the step-down mode to heat the main battery when the temperature of the battery is lower than a predetermined value. A controller for controlling a bidirectional DCDC converter connecting the first charge device and the second charge device, wherein the controller includes: a boost mode for transmitting power from the first charge device to the second charge device; and the second charge device. A DC power supply having a step-down mode for transmitting power from the device to the first charge device,
The first charge device includes a main battery that supplies power to an automobile traction motor,
The DC power supply, wherein the controller alternately executes the step-up mode and the step-down mode to heat the main battery when the temperature of the main battery is lower than a predetermined value. 7. The DC power supply according to claim 6, wherein the second charge device includes a smoothing capacitor for smoothing an output voltage of the DCDC converter. 7. The DC power supply according to claim 6, wherein the second power storage means comprises a low-voltage battery for driving an auxiliary device of the vehicle.

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