WO2015011879A1

WO2015011879A1 - Power supply system

Info

Publication number: WO2015011879A1
Application number: PCT/JP2014/003542
Authority: WO
Inventors: Masanori Ishigaki; Shuji Tomura; Naoki YANAGIZAWA; Masaki Okamura
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2013-07-25
Filing date: 2014-07-03
Publication date: 2015-01-29
Also published as: JP2015027152A; JP6100640B2

Abstract

DC power supplies (10a, 10b) are electrically connected to smoothing capacitors (Ca, Cb) by way of first and second relays (12a, 12b), respectively. A current limiting circuit (13) is connected to in parallel to the first relay (12a), but not provided for the second relay (12b). At the startup of a power supply system (5), the smoothing capacitor (Ca) is precharged with a current passing through a current limiting resistor (15) with the first and second relays (12a, 12b) turned off and a third relay (14) turned on. After the completion of precharge of the smoothing capacitor (Ca), the smoothing capacitor (Cb) is precharged with a current from the DC power supply (10a) accompanied by periodic on/off control of switching elements (S1-S4) with the first relay (12a) turned on and the second relay (12b) and the third relay (14) turned off.

Description

POWER SUPPLY SYSTEM

The present invention relates to a power supply system, and more particularly to control at the time of startup of a power supply system configured to include a power converter connected across a plurality of DC power supplies and electric power lines.

Various types of power supply systems have been provided in which a plurality of power supplies are combined to supply power to a load. For example, Japanese Patent Laying-Open No. 2012-70514 (PTL 1) describes a configuration of a power converter capable of, by means of control of a plurality of switching elements, switching between an operation mode of carrying out DC/DC conversion with two DC power supplies connected in series (series connection mode) and an operation mode of carrying out DC/DC conversion with two DC power supplies used in parallel (parallel connection mode).

With the power converter described in PTL 1, two DC power supplies can effectively be utilized by selective use of the operation modes, while an output voltage to a load can be controlled.

[PTL 1] Japanese Patent Laying-Open No. 2012-70514

In general, in a power supply system having a DC power supply, a smoothing capacitor is connected in parallel to the DC power supply. Therefore, at the startup of the power supply system, an operation is required in which the smoothing capacitor is charged to the voltage of the DC power supply.

To prevent an excessive inrush current from occurring at the startup, control is generally exerted to charge (precharge) the smoothing capacitor by way of a current limiting circuit. For example, the current limiting circuit is configured by connecting a current limiting resistor and a switch connected in series to each other, in parallel to a main switch connected across the DC power supply and the smoothing capacitor.

By precharging the smoothing capacitor with a current passing through the current limiting resistor with the main switch turned off and then turning on the main switch, the occurrence of an excessive inrush current at the startup can be avoided.

In a power supply system having a plurality of DC power supplies as described in PTL 1, however, the aforementioned current limiting circuit needs to be provided in correspondence to each of the DC power supplies. Therefore, there is a concern for size increase and cost increase due to the increase of circuit elements.

The present invention was made to solve these problems, and an object of the present invention is, in a power supply system including a plurality of DC power supplies, to eliminate the need to provide a current limiting circuit for part of the DC power supplies by precharge control at the system startup.

A power supply system in an aspect of the present invention is a power supply system for outputting a DC voltage (VH) across first and second electric power lines connected to a load. The power supply system includes a first DC power supply, a second DC power supply, a first switch corresponding to the first DC power supply, a second switch corresponding to the second DC power supply, a first capacitor, a second capacitor, a third capacitor, first to fourth switching elements sequentially connected in series across the first and second electric power lines, a first reactor, a second reactor, a current limiting circuit, and a control device configured to control on/off of the first to fourth switching elements and on/off of the first to third switches. The first capacitor is connected in parallel with the first DC power supply by way of the first switch. The second capacitor is connected in parallel with the second DC power supply by way of the second switch. The third capacitor is electrically connected across the first and second electric power lines. The first reactor is electrically connected across a connection node of the second and third switching elements and a positive electrode terminal of the first DC power supply. The second reactor is electrically connected across a connection node of the first and second switching elements and a positive electrode terminal of the second DC power supply. Further, the first DC power supply has a negative electrode terminal electrically connected to the second electric power line, and the second DC power supply has a negative electrode terminal electrically connected to a connection node of the third and fourth switching elements. The current limiting circuit is provided in correspondence with only one DC power supply of the first and second DC power supplies, and is connected in parallel with a corresponding switch of the first and second switches. The current limiting circuit has a third switch and a current limiting resistor connected in series. The control device performs (i) first precharge control for precharging one capacitor of the first and second capacitors that is connected to the third switch and the third capacitor to an output voltage of the one DC power supply by turning on the third switch with the first and second switches turned off at startup of the power supply system, (ii) turns off the third switch and turns on the one switch of the first and second switches in accordance with completion of precharge of the one capacitor, (iii) performs second precharge control for precharging the other capacitor of the first and second capacitors to an output voltage of the other DC power supply of the first and second DC power supplies accompanied by periodic on/off control of the first and fourth switching elements with the one switch turned on and the other switch of the first and second switches and the third switch turned off, (iv) and turns on the other switch in accordance with completion of precharge of the other capacitor.

Preferably, the second precharge control has first switching control and second switching control. The first switching control performs periodic on/off control of the first to fourth switching elements such that a voltage of the other capacitor and the third capacitor rises to a lower voltage of respective output voltages of the first and second DC power supplies. The second switching control performs periodic on/off control of the first to fourth switching elements such that the voltage of the other capacitor and the third capacitor rises to an output voltage of the other DC power supply after the voltage of the other capacitor rises to the lower voltage.

More preferably, the first switching control performs periodic on/off control of the first to fourth switching elements so as to periodically repeat a first operation and a second operation until the voltage of the other capacitor rises to the lower voltage. In the first operation, the first to fourth switching elements are controlled to connect the other capacitor in parallel with the one DC power supply by way of the first and second reactors. In the second operation, the first to fourth switching elements are controlled to electrically connect the one DC power supply and the other capacitor in series across the first and second electric power lines by way of the first and second reactors.

Alternatively, more preferably, the second switching control performs periodic on/off control of the first to fourth switching elements so as to periodically repeat a third operation and a fourth operation until the voltage of the other capacitor rises to the output voltage of the other DC power supply. In the third operation, on/off of the first to fourth switching elements is controlled to form a current circulating path by the one DC power supply and one of the first and second reactors. In the fourth operation, the first to fourth switching elements are controlled to electrically connect the one DC power supply and one of the first and second reactors in series across the first and second electric power lines.

Still preferably, the control device further turns on the other switch without executing periodic on/off control of the first and fourth switching elements, when the output voltage of the other DC power supply is lower than a predetermined voltage at the startup of the power supply system.

Preferably, the power supply system is configured to control the DC voltage by operating with one of a plurality of operation modes selectively applied in a state where the first and second switches are turned on. The plurality of operation modes includes first to sixth modes. In the first mode, a power converter executes DC voltage conversion in parallel between the first and second DC power supplies and the first and second electric power lines by on/off control of the first to fourth switching elements. In the second mode, the power converter executes DC voltage conversion between the first and second DC power supplies connected in series and the first and second electric power lines by keeping the third switching element on and performing on/off control of the first, second and fourth switching elements. In the third mode, the power converter maintains the state where the first and second DC power supplies are connected in series to the first and second electric power lines by keeping on/off of the first to fourth switching elements. In the fourth mode, the power converter executes DC voltage conversion between one of the first and second DC power supplies and the first and second electric power lines by on/off control of the first to fourth switching elements. In the fifth mode, the power converter maintains the state where one of the first and second DC power supplies is electrically connected to the first and second electric power lines and the other one of the first and second DC power supplies is electrically disconnected from the first and second electric power lines by keeping on/off of the first to fourth switching elements. In the sixth mode, the power converter maintains the state where the first and second DC power supplies are connected in parallel to the first and second electric power lines by keeping on/off of the first to fourth switching elements.

According to the present invention, in a power supply system including a plurality of DC power supplies, provision of a current limiting circuit for part of the DC power supplies can be eliminated by precharge control at the system startup.

Fig. 1 is a circuit diagram showing a configuration of a power supply system according to a first embodiment of the present invention. Fig. 2 is a conceptual view for describing an exemplary configuration of a load of the power supply system. Fig. 3 is a chart for describing a plurality of operation modes possessed by a power converter shown in Fig. 1. Fig. 4 is a conceptual view showing an example of properties of two DC power supplies shown in Fig. 1 when implemented by power supplies of different types. Fig. 5 is a flowchart for describing a procedure of precharge control at the startup of the power supply system according to the first embodiment. Fig. 6 is a state transition diagram of Cb precharge. Fig. 7 is a chart for describing circuit operations in first and second precharge modes in Cb precharge. Fig. 8 is a conceptual circuit diagram for describing a circuit operation in the first precharge mode in Cb precharge. Fig. 9 is a conceptual waveform diagram for describing pulse width modulation control for setting a duty ratio in switching control in each precharge mode. Fig. 10 is a conceptual circuit diagram for describing a circuit operation in the second precharge mode in Cb precharge. Fig. 11 is a waveform diagram for describing a first exemplary operation of precharge control in startup processing of the power supply system according to the present embodiment. Fig. 12 is a waveform diagram for describing a second exemplary operation of precharge control. Fig. 13 is a circuit diagram showing a configuration of a power supply system according to a second embodiment of the present invention. Fig. 14 is a flowchart for describing a procedure of precharge control at the startup of the power supply system according to the second embodiment. Fig. 15 is a state transition diagram of Ca precharge. Fig. 16 is a chart for describing circuit operations in first and second precharge modes in Ca precharge. Fig. 17 is a conceptual circuit diagram for describing a circuit operation in the first precharge mode in Ca precharge. Fig. 18 is a conceptual circuit diagram for describing a circuit operation in the second precharge mode in Ca precharge.

Hereinbelow, embodiments of the present invention will be described in detail with reference to the drawings. It is noted that the same or corresponding portions in the drawings have the same reference characters allotted, and detailed description thereof will not be repeated basically.

First Embodiment

Fig. 1 is a circuit diagram showing a configuration of a power supply system 5 according to a first embodiment of the present invention.

Referring to Fig. 1, power supply system 5 includes a plurality of

DC power supplies

10a, 10b and a power converter 50. A load 30 of power supply system 5 is connected across

electric power lines

20 and 21.

In the present embodiment,

DC power supplies

10a and 10b are each implemented by a secondary battery, such as a lithium-ion secondary battery or a nickel-metal hydride battery, or a DC voltage source element having excellent output characteristics, such as an electric double layer capacitor or a lithium-ion capacitor.

Power converter 50 is connected across

DC power supplies

10a and 10b and across

electric power lines

20 and 21. Power converter 50 controls a DC voltage (hereinafter also referred to as an output voltage VH) across

electric power lines

20 and 21 in accordance with a voltage command value VH*. That is,

electric power lines

20 and 21 are provided in common for

DC power supplies

10a and 10b.

Load 30 operates upon receipt of output voltage VH output by power converter 50 across

electric power lines

20 and 21. Voltage command value VH* is set at a voltage suitable for the operation of load 30. Furthermore, load 30 may be configured to be capable of generating electric power for charging

DC power supplies

10a and 10b by regeneration or the like.

Fig. 2 is a conceptual view for describing an exemplary configuration of load 30.

Referring to Fig. 2, load 30 is configured to include a traction motor for an electric powered vehicle, for example. Load 30 includes a smoothing capacitor CH, an inverter 32, a motor-generator 35, a motive power transmission gear 36, and a driving wheel 37.

Motor-generator 35 is a traction motor for generating vehicle driving force, and implemented by, for example, a multiple-phase permanent-magnet type synchronous motor. Output torque of motor-generator 35 is transferred to driving wheel 37 by way of motive power transmission gear 36 formed by a reduction gear and a power split device. The electric-powered vehicle runs with the torque transferred to driving wheel 37. Motor-generator 35 generates electric power with rotary force of driving wheel 37 during regenerative braking of the electric powered vehicle. This generated power is subjected to AC/DC conversion by inverter 32. This DC power can be used as electric power for charging

DC power supplies

10a and 10b included in power supply system 5.

In a hybrid vehicle equipped with an engine (not shown) in addition to the motor-generator, vehicle driving force necessary for the electric-powered vehicle is generated by operating this engine and motor-generator 35 cooperatively. On this occasion, it is also possible to charge

DC power supplies

10a and 10b with electric power generated by rotation of the engine.

In this manner, the electric-powered vehicle collectively represents a vehicle equipped with a traction motor, and includes both of a hybrid vehicle that generates vehicle driving force by an engine and an electric motor, as well as an electric vehicle and a fuel-cell vehicle not equipped with an engine.

The operation of load 30 (motor-generator 35) is controlled such that necessary vehicle driving force or vehicle breaking force is obtained in accordance with a running condition of the electric powered vehicle (representatively, the vehicular speed) and a driver operation (representatively, the operation of an accelerator pedal and a brake pedal). That is, an operating command for load 30 (e.g., a torque command value for motor-generator 35) is set by running control of the electric-powered vehicle. This running control is preferably executed by a high-order ECU different from a control device 40 (Fig. 1).

Referring again to Fig. 1, a smoothing capacitor Ca is connected in parallel with DC power supply 10a by way of a relay 12a. Similarly, a smoothing capacitor Cb is connected in parallel with DC power supply 10b by way of a relay 12b.

Relays

12a and 12b connect

DC power supplies

10a and 10b, respectively, to power converter 50 at the startup of power supply system 5.

A current limiting circuit 13 is provided only for DC power supply 10a. Current limiting circuit 13 is connected in parallel with relay 12a. Current limiting circuit 13 has a relay 14 and a current limiting resistor 15 connected in series. By operating current limiting circuit 13 by turning on relay 14 with relay 12a turned off, smoothing capacitor Ca can be gently precharged by means of a current path passing through current limiting resistor 15.

Relays

12a, 12b and 14 are turned on/off in response to a control signal (not shown) from control device 40. It is noted that any switch whose on/off can be controlled, such as an electromagnetic relay or a semiconductor relay can be employed as

relays

12a, 12b and 14.

In power supply system 5, current limiting circuit 13 is provided in correspondence with DC power supply 10a, while no current limiting circuit is provided for DC power supply 10b and smoothing capacitor Cb. In this manner, the power supply system according to the present embodiment is characterized in that current limiting circuit 13 is not provided in correspondence with every DC power supply, but provision of a current limiting circuit for part of the DC power supplies is eliminated.

Power converter 50 includes switching elements S1 to S4 connected in series across

electric power lines

20 and 21 as well as reactors L1 and L2. In the present embodiment, for the switching elements, IGBTs (Insulated Gate Bipolar Transistors), power MOS (Metal Oxide Semiconductor) transistors, power bipolar transistors, or the like can be used. For switching elements S1 to S4, anti-parallel diodes D1 to D4 are arranged, respectively. On/off of switching elements S1 to S4 can be controlled in response to control signals SG1 to SG4, respectively. That is, switching elements S1 to S4 are respectively turned on when control signals SG1 to SG4 are at a high level (hereinafter referred to as an H level), and are turned off when they are at a low level (hereinafter referred to as an L level).

Switching element S1 is electrically connected across electric power line 20 and a node N1. Reactor L2 is connected across node N1 and a positive electrode terminal of DC power supply 10b. Switching element S2 is electrically connected across nodes N1 and N2. Reactor L1 is connected across node N2 and a positive electrode terminal of DC power supply 10a. Reactor L2 is connected across node N1 and the positive electrode terminal of DC power supply 10b. That is, node N1 corresponds to a connection mode of switching element S1 and S2, and node N2 corresponds to a connection mode of switching elements S2 and S3.

Switching element S3 is electrically connected across nodes N2 and N3. Node N3 is electrically connected to a negative electrode terminal of DC power supply 10b. Switching element S4 is electrically connected across node N3 and electric power line 21. Electric power line 21 is electrically connected to load 30 and a negative electrode terminal of DC power supply 10a. That is, node N3 corresponds to a connection mode of switching elements S3 and S4.

As understood from Fig. 1, power converter 50 is configured to include a step-up chopper circuit in correspondence with each of

DC power supplies

10a and 10b. That is, for DC power supply 10a, a bidirectional current first step-up chopper circuit is formed in which switching elements S1 and S2 serve as upper-arm elements and switching elements S3 and S4 serve as lower-arm elements. Similarly, for DC power supply 10b, a bidirectional current second step-up chopper circuit is formed in which switching elements S1 and S4 serve as upper-arm elements and switching elements S2 and S3 serve as lower-arm elements.

Switching elements S1 to S4 are included in both of a power conversion path formed across DC power supply 10a and electric power line 20 by the first step-up chopper circuit and a power conversion path formed across DC power supply 10b and electric power line 20 by the second step-up chopper circuit.

Control device 40 is implemented by, for example, an electronic control unit (ECU) including a CPU (Central Processing Unit) and a memory neither shown, and is configured to perform arithmetic processing through use of a detection value of each sensor based on maps and programs stored in that memory. Alternatively, at least part of control device 40 may be configured to execute predetermined numeric/logic operation processing by hardware, such as an electronic circuit.

Control device 40 generates control signals SG1 to SG4 for controlling on/off of switching elements S1 to S4, respectively, in order to control output voltage VH to load 30. Furthermore, control device 40 further generates control signals (not shown) for controlling on/off of

relays

12a, 12b and 14.

A voltage sensor 41 detects a voltage Vca of smoothing capacitor Ca. A voltage sensor 42 detects a voltage Vcb of smoothing capacitor Cb. Voltage sensor 43 detects a voltage of smoothing capacitor CH, namely, output voltage VH. Detected values of voltage sensors 41 to 43 are given to control device 40.

It is noted that although not shown in Fig. 1, detectors (voltage sensor, current sensor) for the voltage (hereinafter referred to as Va) and current (hereinafter referred to as Ia) of DC power supply 10a, the voltage (hereinafter referred to as Vb) and current (hereinafter referred to as Ib) of DC power supply 10b, as well as output voltage VH are provided. Furthermore, detectors (temperature sensors) for the temperatures (hereinafter referred to as Ta and Tb) of

DC power supplies

10a and 10b are also preferably provided. The outputs of these detectors are given to control device 40.

In the configuration of Fig. 1, switching elements S1 to S4 correspond to "a first switching element" to "a fourth switching element", respectively, and reactors L1 and L2 correspond to "a first reactor" and "a second reactor", respectively.

Relays

12a, 12b and 14 correspond to "a first switch", "a second switch" and "a third switches ", respectively.

(Operation of Power Converter after Startup)

By system startup processing, power supply system 5 precharges smoothing capacitors Ca and Cb to voltages Va and Vb, respectively, and then operates with

relays

12a and 12b turned on and relay 14 turned off. Details of startup processing will be described later in detail.

Power converter 50 has a plurality of operation modes different in the mode of DC power conversion between

DC power supplies

10a, 10b and electric power line 20.

Fig. 3 shows a plurality of operation modes possessed by power converter 50.

Referring to Fig. 3, the operation modes are roughly divided into a "boosting mode (B)" of boosting output voltage(s) of DC power supply 10a and/or DC power supply 10b following periodic on/off control of switching elements S1 to S4 and a "direct connection mode (D)" of electrically connecting DC power supply 10a and/or DC power supply 10b to electric power line 20 with switching elements S1 to S4 kept on/off.

The boosting mode includes a "parallel boosting mode (hereinafter referred to as a PB mode)" of carrying out parallel DC/DC conversion between

DC power supplies

10a and 10b and electric power line 20 and a "series boosting mode (hereinafter referred to as a SB mode)" of carrying out DC/DC conversion between

DC power supplies

10a and 10b connected in series and electric power line 20. The PB mode corresponds to the "parallel connection mode" in PTL 1, and the SB mode corresponds to the "series connection mode" in PTL 1.

The boosting mode further includes an "independent mode with DC power supply 10a (hereinafter referred to as an aB mode)" of carrying out DC/DC conversion between only DC power supply 10a and electric power line 20 and an "independent mode with DC power supply 10b (hereinafter referred to as a bB mode)" of carrying out DC/DC conversion between only DC power supply 10b and electric power line 20. In the aB mode, DC power supply 10b is unused while being maintained in the state electrically disconnected from electric power line 20 as long as output voltage VH is controlled to be higher than voltage Vb of DC power supply 10b. Similarly, in the bB mode, DC power supply 10a is unused while being maintained in the state electrically disconnected from electric power line 20 as long as output voltage VH is controlled to be higher than voltage Va of DC power supply 10a.

In each of the PB mode, SB mode, aB mode, and bB mode included in the boosting mode, output voltage VH of electric power line 20 is controlled in accordance with voltage command value VH*. Control of switching elements S1 to S4 in each of these modes will be described later.

The direct connection mode includes a "parallel direct connection mode (hereinafter referred to as a PD mode)" of maintaining the state in which

DC power supplies

10a and 10b are connected in parallel to electric power line 20 and a "series direct connection mode (hereinafter referred to as an SD mode)" of maintaining the state in which

DC power supplies

10a and 10b are connected in series to electric power line 20.

In the PD mode, switching elements S1, S2 and S4 are kept on, while switching element S3 is kept off. Accordingly, output voltage VH becomes equivalent to output voltages Va and Vb of

DC power supplies

10a and 10b (strictly, a higher one of Va and Vb). Since the voltage difference between Va and Vb will produce a short-circuit current at

DC power supplies

10a and 10b, the PD mode can be applied limitedly when the voltage difference is small.

In the SD mode, switching elements S2 and S4 are kept off, while switching elements S1 and S3 are kept on. Accordingly, output voltage VH is determined uniquely in accordance with the sum of output voltages Va and Vb of

DC power supplies

10a and 10b (VH=Va+Vb).

Further, the direct connection mode includes a "direct connection mode of DC power supply 10a (hereinafter referred to as an aD mode)" of electrically connecting only DC power supply 10a to electric power line 20 and a "direct connection mode of DC power supply 10b (hereinafter referred to as a bD mode)" of electrically connecting only DC power supply 10b to electric power line 20.

In the aD mode, switching elements S1 and S2 are kept on, while switching elements S3 and S4 are kept off. Accordingly, DC power supply 10b is brought into the state disconnected from electric power line 20, and output voltage VH becomes equivalent to voltage Va of DC power supply 10a (VH=Va). In the aD mode, DC power supply 10b is unused while being maintained in the state electrically disconnected from electric power line 20. It is noted that if the aD mode is applied when Vb>Va holds, a short-circuit current will flow from DC power supply 10b to 10a by way of switching element S2. Thus, Va>Vb is a necessary condition for applying the aD mode.

Similarly, in the bD mode, switching elements S1 and S4 are kept on, while switching elements S2 and S3 are kept off. Accordingly, DC power supply 10a is brought into the state disconnected from electric power line 20, and output voltage VH becomes equivalent to voltage Vb of DC power supply 10b (VH=Vb). In the bD mode, DC power supply 10a is unused while being maintained in the state electrically disconnected from electric power line 20. It is noted that when the bD mode is applied when Va>Vb holds, a short-circuit current will flow from DC power supply 10a to 10b by way of diode D2. Thus, Vb>Va is a necessary condition for applying the bD mode.

In each of the PD mode, SD mode, aD mode, and bD mode included in the direct connection mode, output voltage VH of electric power line 20 is determined depending on voltages Va and Vb of

DC power supplies

10a and 10b, and therefore, cannot be directly controlled. Thus, in each mode included in the direct connection mode, output voltage VH can no longer be set at a voltage suitable for the operation of load 30, so that power loss at load 30 may be increased.

On the other hand, in the direct connection mode, power loss at power converter 50 is significantly suppressed because switching elements S1 to S4 are not turned on/off. Therefore, depending on the operating condition of load 30, there is a possibility that power loss at power supply system 5 as a whole can be suppressed because the amount of decrease in power loss at power converter 50 becomes larger than the amount of increase in power loss at load 30 by applying the direct connection mode.

In Fig. 3, the PB mode corresponds to a "first mode", the SB mode corresponds to a "second mode", and the SD mode corresponds to a "third mode." Further, the aB mode and bB mode correspond to a "fourth mode", the aD mode and bD mode correspond to a "fifth mode", and the PD mode corresponds to a "sixth mode."

Fig. 4 is a conceptual view showing an example of properties of

DC power supplies

10a and 10b when implemented by power supplies of different types. Fig. 4 shows a so-called Ragone plot in which energy is plotted on the horizontal axis and electric power is plotted on the vertical axis. In general, output power and stored energy of a DC power supply have a trade-off relationship. Therefore, a high output is difficult to obtain with a high-capacity type battery, while stored energy is difficult to increase with a high-output type battery.

Therefore, preferably, one of

DC power supplies

10a and 10b is implemented by a so-called high-capacity type power supply having high stored energy, and the other one of them is implemented by a so-called high-output type power supply providing high output power. Then, energy stored in the high-capacity type power supply is used as a constant supply for a long time, and the high-output type power supply can be used as a buffer to output a deficiency caused by the high-capacity type power supply.

In the example of Fig. 4, DC power supply 10a is implemented by a high-capacity type power supply, while DC power supply 10b is implemented by a high-output type power supply. Therefore, an active region 110 of DC power supply 10a has a narrower range of electric power that can be output than an active region 120 of DC power supply 10b. On the other hand, active region 120 has a narrower range of energy that can be stored than active region 110.

At an operating point 101 of load 30, high power is requested for a short time. For example, in an electric-powered vehicle, operating point 101 corresponds to abrupt acceleration caused by a user's accelerator operation. In contrast to this, at an operating point 102 of load 30, relatively low power is requested for a long time. For example, in an electric-powered vehicle, operating point 102 corresponds to continuous high-speed steady running.

For operating point 101, the output from high-output type DC power supply 10b can mainly be applied. On the other hand, for operating point 102, the output from high-capacity type DC power supply 10a can mainly be applied. Accordingly, in an electric-powered vehicle, the running distance with electrical energy can be extended through use of energy stored in the high-capacity type battery for a long time, and acceleration performance in correspondence with a user's accelerator operation can be ensured promptly.

In this manner, by combining DC power supplies of different types and capacitances, stored energy can be used effectively in the whole system taking advantage of characteristics of the respective DC power supplies. Hereinafter, in the present embodiment, an example in which DC power supply 10a is implemented by a secondary battery and DC power supply 10b is implemented by a capacitor will be described. It should be noted that the combination of

DC power supplies

10a and 10b is not limited to this example, but can be implemented by DC power supplies (power storage devices) of the same type and/or the same capacitance.

When the DC power supplies are implemented by batteries, there are possibilities that output characteristics decrease at a low temperature and charging/discharging is restricted at a high temperature in order to suppress progress of deterioration. Particularly in an electric-powered vehicle, a case arises in which a temperature difference occurs between

DC power supplies

10a and 10b because of the difference in mounting position. Therefore, in power supply system 5, there is a case in which it is more effective to use only either one of the DC power supplies in accordance with the operating condition (particularly, the temperature) of

DC power supplies

10a and 10b or in accordance with requests of load 30 as described above. These cases can be handled by providing modes of using only one of

DC power supplies

10a and 10b (aB mode, bB mode, aD mode, and bD mode) as described above.

In this manner, power supply system 5 according to the present first embodiment is capable of operating while selecting from among the plurality of operation modes shown in Fig. 3 in accordance with the operating conditions of

DC power supplies

10a and 10b and/or load 30 such that efficiency in power supply system 5 as a whole is optimized.

(Startup Processing of Power Supply System)

At the startup of power supply system 5, voltages Vca, Vcb and VH of smoothing capacitors Ca, Cb and CH are 0. Therefore, in system startup processing, it is necessary to complete precharging of each of smoothing capacitors Ca, Cb and CH without generating an excessive current.

In the power supply system according to the present embodiment, current limiting circuit 13 is provided for only part of the DC power supplies (in the example of Fig. 1, DC power supply 10a). Therefore, to precharge smoothing capacitor Cb not provided with any current limiting circuit, the following precharge control is executed.

Fig. 5 is a flowchart for describing a procedure of precharge control at the startup of the power supply system according to the first embodiment. Precharge control is achieved by control device 40 controlling on/off of

relays

12a, 12b and 14 as well as switching elements S1 to S4 in accordance with a procedure which will be described below.

Referring to Fig. 5, at the startup of power supply system 5, in step S100, control device 40 first executes precharging of smoothing capacitor Ca (hereinafter also briefly referred to as Ca precharge) by current limiting circuit 13.

In the Ca precharge in step S100, relays 12a and 12b are turned off, while relay 14 is turned on. Accordingly, current limiting circuit 13 operates. Smoothing-capacitor Ca is charged by DC power supply 10a by the current path passing through current limiting resistor 15. An excessive inrush current can thereby be prevented from occurring. When voltage Vca of smoothing capacitor Ca rises to voltage Va of DC power supply 10a, the Ca precharge is completed.

During the Ca precharge, smoothing capacitor CH is also charged by DC power supply 10a by the current path formed by diodes D1 and D2. That is, in the Ca precharge, smoothing capacitors Ca and CH are charged in parallel with the current from current limiting circuit 13. Therefore, at the time when the Ca precharge is completed, VH=Vca=Va holds.

When the Ca precharge is completed, control device 40 in step S150 turns off relay 14 and turns on relay 12a. Accordingly, smoothing capacitor Ca having been precharged and DC power supply 10a are electrically connected to each other not by way of current limiting resistor 15.

Control device 40 further executes in step S200 precharge of smoothing capacitor Cb (hereinafter also referred to as Cb precharge) accompanied by periodic on/off control (switching control) of switching elements S1 to S4. As will be described later, in the Cb precharge, two precharge modes P1 and P2 are sequentially selected with relay 12b turned off.

When voltage Vcb of smoothing capacitor Cb rises to voltage Vb of DC power supply 10b, control device 40 completes the Cb precharge in step S250.

When the Cb precharge is completed, control device 40 turns on relay 12b in step S300. Accordingly, both of smoothing capacitors Ca and Cb having been precharged are brought into the state connected in parallel to

DC power supplies

10a and 10b, respectively, and the startup processing is terminated. In the first embodiment, Ca precharge corresponds to "first precharge control", and Cb precharge corresponds to "second precharge control".

Next, the Cb precharge will be described in more detail.

Fig. 6 shows a state transition diagram of the Cb precharge.

Referring to Fig. 6, when the Cb precharge is started, voltage Vb of DC power supply 10b is first determined. When voltage Vb is approximately 0, there is no possibility that a large current may flow across DC power supply 10b and smoothing capacitor Cb even if relay 12b is turned on. Therefore, in the case where Vb approximately equals 0 holds, and when the Cb precharge is started, the Cb precharge is immediately completed eliminating precharge by switching control, so that relay 12b can be turned on.

Since DC voltage Vb>0 holds at the usual time, precharge mode P1 is selected when the Cb precharge is started. Then, when voltage Vcb of smoothing capacitor Cb rises to around voltage min(Va, Vb), which is a lower one of voltages Va and Vb, by precharge mode P1, precharge mode P1 is terminated, and precharge mode P2 is selected. For example, when voltage Vcb becomes higher than min(Va, Vb)-TH0 (TH0: a predetermined value), precharge mode P1 is terminated.

Further, when voltage Vcb of smoothing capacitor Cb approaches voltage Vb of DC power supply 10b, precharge mode P2 is terminated, and the Cb precharge is completed. Accordingly, relay 12b can be turned on. For example, when voltage Vcb enters the range where Vb-TH1<Vcb<Vb+TH2 (TH1, TH2: predetermined values), precharge mode P2 is terminated. Precharge mode P1 corresponds to "first switching control", and precharge mode P2 corresponds to "second switching control".

Fig. 7 is a chart for describing circuit operations in precharge modes P1 and P2 in the Cb precharge.

Referring to Fig. 7, in each of precharge modes P1 and P2, on/off of switching elements S1 to S4 is controlled in response to a control pulse signal SDp in accordance with a duty ratio Dp.

In precharge mode P1, the pair of switching elements S1 and S3 and the pair of switching elements S2 and S4 are turned on/off complementarily in response to control pulse signals SDp and /SDp. An exemplary operation when Vb>Va holds will be described below.

Fig. 8 shows a circuit operation in precharge mode P1.

Referring to Fig. 8(a), in a period during which switching elements S2 and S4 are on and switching elements S1 and S3 are off, smoothing capacitor Cb is connected in parallel with DC power supply 10a by way of reactors L1 and L2. On this occasion, the amount of increase in current flowing through smoothing capacitor Cb is restricted by reactors L1 and L2 as well as the length of the on period of switching elements S2 and S4. Therefore, an excessive current is not produced. If the circuit operation in Fig. 8(a) is continued, Vcb=Va will hold finally.

Referring to Fig. 8(b), in a period during which switching elements S1 and S3 are on and switching elements S2 and S4 are off, DC power supply 10a and smoothing capacitor Cb are connected in series across

electric power lines

20 and 21 by way of reactors L1 and L2. Accordingly, voltage VH of smoothing capacitor CH rises toward (Va+Vcb). Also on this occasion, the amount of increase in current flowing through smoothing capacitor Cb is restricted by reactors L1 and L2 as well as the length of the on period of switching elements S1 and S3.

Referring again to Fig. 8, in precharge mode P1, duty ratio Dp that determines the ratio between the periods shown in Figs. 8(a) and 8(b) is set within the range where Dp equals or is greater than 0 and is less than Dmax (Dmax<1) in accordance with Equation (1) below.

Dp = (VH-Vcb)/VH ...(1)

Fig. 9 shows a conceptual waveform diagram for describing pulse width modulation control for setting the duty ratio in switching control in each precharge mode.

Referring to Fig. 9, control pulse signal SDp and its inversion signal /SDp are generated based on voltage comparison between duty ratio Dp and a carrier wave CW of a predetermined frequency. In a period during which the voltage of carrier wave CW is larger than duty ratio Dp, control pulse signal SDp is set at a logic low level (hereinafter also referred to as an L level), and control pulse signal /SDp is set at a logic high level (hereinafter also briefly referred to as an H level).

In the period during which control pulse signal SDp is at the L level, switching elements S2 and S4 are on as shown in Fig. 8(a), while in the period during which control pulse signal /SDp is at the L level, switching elements S1 and S3 are on as shown in Fig. 8(b).

At the start of precharge mode P1, VH=Va holds, while Vcb=0 holds. Therefore, duty ratio Dp has an initial value of Dmax. Since Dmax<1 holds, Vcb rises by the circuit operation in Fig. 8(a) being executed for only a short time. Subsequently, duty ratio Dp decreases with rise of Vcb, so that the ratio of the circuit operation shown in Fig. 8(a) increases. Then, the switching operation is finally stopped when the state where Vcb=Va holds is brought about.

Actually, as shown in Fig. 6, precharge mode P1 is terminated when the condition that Vcb>min(Va, Vb)-TH0 (TH0: a predetermined value) holds. Since switching elements S1 and S4 are not turned on simultaneously in precharge mode P1, an inrush current can be prevented from flowing across smoothing capacitors CH and Cb. Therefore, precharge mode P1 is applied while voltage Vcb is low.

Referring again to Fig. 7, in precharge mode P2, switching elements S1 and S4 are kept on, and switching elements S2 and S3 are turned on/off complementarily in response to control pulse signals SDp and /SDp.

Fig. 10 shows a circuit operation in precharge mode P2.

Fig. 10(a) shows a circuit operation in the H level period of control pulse signal /SDp, and Fig. 10(b) shows a circuit operation in the H level period of control pulse signal SDp.

Through Figs. 10(a) and 10(b), switching elements S1 and S4 are maintained on. Therefore, during precharge mode P2, smoothing capacitors Cb and CH are maintained in the state connected in parallel.

On the other hand, by repeating the period during which switching elements S3 and S4 are on shown in Fig. 10(b) and the period during which switching element S3 is off shown in Fig. 10(a), output voltage VH is boosted above voltage Va of DC power supply 10a by the circuit operation of a so-called step-up chopper. That is, in precharge mode P2, smoothing capacitors Cb and CH connected in parallel can be precharged to a voltage higher than voltage Va of DC power supply 10a.

Referring again to Fig. 7, in precharge mode P2, duty ratio Dp that determines the ratio between the periods shown in Figs. 10(a) and 10(b) is set within the range where Dp equals or is greater than 0 and is less than Dmax (Dmax<1) in accordance with Equation (2) below.

Dp = (Vb-Vcb)/Vb ...(2)

Therefore, on/off of switching elements S1 to S4 is controlled by pulse width modulation control shown in Fig. 9 based on duty ratio Dp such that output voltage VH is controlled with VH*=Vcb serving as a voltage command value. Then, the switching operation is finally stopped when the state where VH=Vb holds is brought about. As a result, smoothing capacitor Cb connected in parallel with smoothing capacitor CH can also be precharged until Vcb=Vb holds.

Actually, as shown in Fig. 6, precharge mode P1 is terminated when the condition that Vb-TH1<Vcb<Vb+TH2 (TH1, TH2: predetermined values) holds, and the Cb precharge is completed.

Fig. 11 is a waveform diagram for describing a first exemplary operation of precharge control in startup processing of power supply system 5 according to the present embodiment. Fig. 11 shows an exemplary operation when Vb>Va holds as described above.

Referring to Fig. 11, when the startup of power supply system 5 is instructed, relay 14 of current limiting circuit 13 is turned on at time t1. Accordingly, precharge of smoothing capacitor Ca corresponding to DC power supply 10a provided with current limiting circuit 13 is started.

From time t1, smoothing capacitors Ca and CH are charged with a charging current having passed though current limiting resistor 15. On this occasion, the action of current limiting resistor 15 prevents an excessive charging current from occurring even when relay 14 is maintained on.

At time t2, when voltages Vca and VH of smoothing capacitors Ca and CH become equivalent to voltage Va of DC power supply 10a, relay 12a is turned on in accordance with the completion of the Ca precharge. Furthermore, relay 14 is turned off at time t3. Accordingly, current limiting circuit 13 is stopped, and DC power supply 10a and smoothing capacitor Ca are electrically connected not by way of current limiting resistor 15.

When the Cb precharge is started in accordance with the completion of the Ca precharge, first, precharge mode P1 is started at time t4. In precharge mode P1, smoothing capacitor Cb is charged with a current obtained by switching control by the on/off control of switching elements S1 to S4 described with reference to Figs. 7 and 8, so that voltage Vb rises. Voltage VH also rises in accordance with Va+Vcb.

At time t6, when voltage Vcb of smoothing capacitor Cb is brought into substantial agreement with voltage Vb of DC power supply 10b, precharge mode P2 is terminated, and the Cb precharge is completed. Accordingly, relay 12b is turned on at time t7.

The above-described precharge control at the startup can also be applied similarly in the case where

DC power supplies

10a and 10b have a relationship in which Vb<Va holds.

Fig. 12 is a waveform diagram for describing a second exemplary operation of precharge control in the startup processing of power supply system 5 according to the present embodiment. Fig. 12 shows an exemplary operation when Vb<Va holds as described above in contrast to Fig. 11.

Referring to Fig. 12, at time t1 to time t3, the Ca precharge is executed similarly to Fig. 11, and precharge mode P1 is started at time t4. Accordingly, smoothing capacitor Cb is charged with a current obtained by switching control of switching elements S1 to S4. In precharge mode P1, voltage VH of smoothing capacitor CH rises further from voltage Va.

Since min(Va,Vb)=Vb holds in the example of Fig. 12, when voltage Vcb rises to Vb at time t5, precharge mode P1 is terminated, and precharge mode P2 is started. However, since voltage Vcb has risen to around voltage Vb at the start of precharge mode P2, Vb-TH1<Vcb<Vb+TH2, which is the termination condition for precharge mode P2, will hold immediately at time t6.

As a result, the Cb precharge is completed, so that relay 12b is turned on at time t7. That is, precharge mode P2 is terminated after a very short time period, and the precharge control at the startup of power supply system 5 is completed. At and subsequent to time t7,

DC power supplies

10a and 10b are connected to power converter 50 in the state connected in parallel with smoothing capacitors Ca and Cb by way of

relays

12a and 12b, respectively, similarly to the case of Fig. 11.

As shown in Figs. 11 and 12, smoothing capacitor Cb not provided with any current limiting resistor can be precharged to voltage Vb whether voltages Va and Vb of

DC power supplies

10a and 10b are high or low.

In this manner, in the power supply system according to the first embodiment, smoothing capacitor Cb not provided with any current limiting resistor can be charged with the current obtained by switching control of switching elements S1 to S4 even in the configuration where current limiting circuit 13 is provided only for DC power supply 10a. As a result, with the circuit configuration in which the number of current limiting circuits is smaller than that of DC power supplies, each smoothing capacitor can be precharged without generating an excessive inrush current at the startup of the power supply system. Accordingly, size reduction and cost reduction can be achieved by the reduction of the number of parts of the power supply system.

Second Embodiment

In the first embodiment, the configuration in which provision of current limiting circuit 13 corresponding to DC power supply 10b is eliminated has been described. In a second embodiment, contrary to the first embodiment, startup control in a configuration in which provision of current limiting circuit 13 corresponding to DC power supply 10a is eliminated will be described.

Fig. 13 is a circuit diagram showing a configuration of a power supply system 5# according to the present second embodiment.

Comparing Fig. 13 with Fig. 1, in power supply system 5# according to the second embodiment, current limiting circuit 13 is connected in parallel with relay 12b. On the other hand, relay 12a of DC power supply 10a is not provided with current limiting circuit 13. The configuration of the remaining part of power supply system 5# is similar to power supply system 5 shown in Fig. 1, and detailed description thereof will not be repeated.

In the power supply system according to the second embodiment, since current limiting circuit 13 is provided only for DC power supply 10b, the following precharge control is executed in order to precharge smoothing capacitor Ca not provided with any current limiting circuit.

Fig. 14 is a flowchart for describing a procedure of precharge control at the startup of the power supply system according to the second embodiment. The precharge control is achieved by control device 40 controlling on/off of

relays

12a, 12b, 14 and switching elements S1 to S4 in accordance with a procedure which will be described below.

Referring to Fig. 14, at the startup of power supply system 5#, control device 40 first executes in step S100# precharge (Cb precharge) of smoothing capacitor Cb by current limiting circuit 13.

In the Cb precharge in step S100#, relays 12a and 12b are turned off, while relay 14 is turned on. Accordingly, current limiting circuit 13 operates. Smoothing capacitor Cb is charged by DC power supply 10b by the current path passing through current limiting resistor 15. This can prevent an excessive inrush current from occurring. When voltage Vcb of smoothing capacitor Cb rises to voltage Vb of DC power supply 10b, the Cb precharge is completed.

During the Cb precharge, smoothing capacitor CH is also charged by DC power supply 10b by the current path formed by diodes D1 and D2. That is, in the Cb precharge, smoothing capacitors Cb and CH are charged in parallel with a current from current limiting circuit 13. Therefore, at the time when the Cb precharge is completed, VH=Vcb=Vb holds.

When the Cb precharge is completed, control device 40 in step S150# turns off relay 14 and turns on relay 12b. Accordingly, smoothing capacitor Cb having been precharged and DC power supply 10b are electrically connected to each other not by way of current limiting resistor 15.

Furthermore, control device 40 in step S200# executes precharge (Ca precharge) smoothing capacitor Ca accompanied by periodic on/off control (switching control ) of switching elements S1 to S4. In the Ca precharge, two precharge modes P1 and P2 are selected sequentially with relay 12a turned off.

When voltage Vca of smoothing capacitor Ca rises to voltage Va of DC power supply 10a, control device 40 completes the Ca precharge in step S250#.

When the Ca precharge is completed, control device 40 turns on relay 12a in step S300#. Accordingly, both of smoothing capacitors Ca and Cb having been precharged are brought into the state connected in parallel with

DC power supplies

10a and 10b, respectively, and the startup processing is terminated. In the second embodiment, Cb precharge corresponds to "first precharge control", and Ca precharge corresponds to "second precharge control".

Next, the Ca precharge will be described in more detail.

Fig. 15 shows a state transition diagram of the Ca precharge.

Referring to Fig. 15, when the Ca precharge is started, voltage Vb of DC power supply 10a is first determined. When voltage Va is approximately 0, the Ca precharge is immediately completed eliminating precharge by switching control, so that relay 12a can be turned on.

Since DC voltage Va>0 holds at the usual time, precharge mode P1 is selected when the Ca precharge is started. Then, when voltage Vca of smoothing capacitor Ca rises to around voltage min(Va, Vb) which is a lower one of voltages Va and Vb by precharge mode P1, precharge mode P1 is terminated, and precharge mode P2 is selected. For example, when voltage Vca becomes higher than min(Va, Vb)-TH0 (TH0: a predetermined value), precharge mode P1 is terminated.

Further, when voltage Vca of smoothing capacitor Ca approaches voltage Va of DC power supply 10a, precharge mode P2 is terminated, and the Ca precharge is completed. Accordingly, relay 12a can be turned on. For example, when voltage Vca enters the range where Va-TH1<Vca<Va+TH2 (TH1, TH2: predetermined values), precharge mode P2 is terminated.

Fig. 16 is a chart for describing circuit operations in precharge modes P1 and P2 in the Ca precharge.

Referring to Fig. 16, in each of precharge modes P1 and P2, on/off of switching elements S1 to S4 is controlled in response to control pulse signal SDp in accordance with duty ratio Dp, similarly to the Cb precharge.

Fig. 17 shows a circuit operation in precharge mode P1 in the Ca precharge.

Referring to Fig. 17(a), in a period during which switching elements S2 and S4 are on and switching elements S1 and S3 are off, smoothing capacitor Ca is connected in parallel with DC power supply 10b by way of reactors L1 and L2. On this occasion, the amount of increase in current flowing through smoothing capacitor Ca is restricted by reactors L1 and L2 as well as the length of the on period of switching elements S2 and S4. Therefore, an excessive current is not produced. If the circuit operation in Fig. 17(a) is continued, Vca=Vb will hold finally.

Referring to Fig. 17(b), in a period during which switching elements S1 and S3 are on and switching elements S2 and S4 are off, DC power supply 10b and smoothing capacitor Ca are connected in series across

electric power lines

20 and 21 by way of reactors L1 and L2. Accordingly, voltage VH of smoothing capacitor CH rises toward (Vb+Vca). Also on this occasion, changes in current flowing through smoothing capacitor Cb are restricted by reactors L1 and L2 as well as the length of the on period of switching elements S1 and S3.

Referring again to Fig. 16, in precharge mode P1 in the Ca precharge, duty ratio Dp that determines the ratio between the periods shown in Figs. 17(a) and 17(b) is set within the range where Dp equals or is greater than 0 and is less than Dmax (Dmax<1) in accordance with Equation (3) below.

Dp = (VH-Vca)/VH ...(3)

As described with reference to Fig. 9, since the H level period of control pulse signal /SDp is longer as duty ratio Dp decreases, the period during which switching elements S2 and S4 are on is longer as shown in Fig. 17(a).

Since the initial value of duty ratio Dp is Dmax at the start of precharge mode P1, the circuit operation of Fig. 17(a) is executed for a very short time, so that Vca rises. Subsequently, duty ratio Dp decreases with rise of Vca, so that the ratio of the period of the circuit operation shown in Fig. 17(a) increases. Then, as shown in Fig. 15, precharge mode P1 is terminated when the condition that Vca>min(Va, Vb)-TH0 (TH0: a predetermined value) holds.

Fig. 18 shows a circuit operation in precharge mode P2.

Fig. 18(a) shows a circuit operation in the H level period of control pulse signal /SDp, and Fig. 18(b) shows a circuit operation in the H level period of control pulse signal SDp.

Through Figs. 18(a) and 18(b), switching elements S1 and S2 are maintained on. Therefore, during precharge mode P2, smoothing capacitors Ca and CH are maintained in the state connected in parallel.

On the other hand, by repeating the period during which switching elements S2 and S3 are on shown in Fig. 18(b) and the period during which switching element S3 is off shown in Fig. 18(a), output voltage VH is boosted above voltage Vb of DC power supply 10b by the circuit operation of a so-called step-up chopper. That is, in precharge mode P2, smoothing capacitors Ca and CH connected in parallel can be precharged to a voltage higher than voltage Vb of DC power supply 10b.

Referring again to Fig. 16, in precharge mode P2, duty ratio Dp that determines the ratio between the periods shown in Figs. 18(a) and 18(b) is set within the range where Dp equals or is greater than 0 and is less than Dmax (Dmax<1) in accordance with Equation (4) below.

Dp = (Va-Vca)/Va ...(4)

Therefore, on/off of switching elements S1 to S4 is controlled by pulse width modulation control (Fig. 9) based on duty ratio Dp such that output voltage VH is controlled with VH*=Vca serving as a voltage command value. Then, the switching operation is finally stopped when the state where VH=Va holds is brought about. As a result, smoothing capacitor Ca connected in parallel with smoothing capacitor CH can also be precharged until Vca=Va holds. Actually, as shown in Fig. 15, precharge mode P2 is terminated when the condition that Va-TH1<Vca<Va+TH2 (TH1, TH2: predetermined values) holds, and the Ca precharge is completed.

It is noted that when Va>Vb holds, voltage Vcb can be controlled similarly to the behavior of voltage Vca in the operation waveform diagram of Fig. 11. That is, in Fig. 11, smoothing capacitor Ca can be precharged by exchanging the waveform diagrams of

relays

12a and 12b.

Similarly, when Vb>Va holds, voltage Vcb can be controlled similarly to the behavior of voltage Vca in the operation waveform diagram of Fig. 12. That is, in Fig. 12, smoothing capacitor Ca can be precharged by exchanging the waveform diagrams of

relays

12a and 12b.

In this manner, in the power supply system according to the second embodiment, smoothing capacitor Ca not provided with any current limiting resistor can be charged with the current obtained by switching control of switching elements S1 to S4 even in the configuration where current limiting circuit 13 is provided only for DC power supply 10b. As a result, with the circuit configuration in which the number of current limiting circuits is smaller than that of DC power supplies, each smoothing capacitor can be precharged without generating an excessive inrush current at the startup of the power supply system. Accordingly, size reduction and cost reduction can be achieved by the reduction of the number of parts of the power supply system.

It is described for confirmation that in

power supply systems

5 and 5#, load 30 may be implemented by any apparatus that can operate with a DC voltage controlled by a power converter. That is, although the example in which load 30 is configured to include a traction motor for an electric powered vehicle has been described in the present embodiment, the application of the present invention is not limited to such a load.

It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the claims not by the description above, and is intended to include any modification within the meaning and scope equivalent to the terms of the claims.

5, 5# power supply system; 10a, 10b DC power supply; 12a, 12b, 14 relay; 13 current limiting circuit; 15 current limiting resistor; 20, 21 electric power line; 30 load; 32 inverter; 35 motor-generator; 36 motive power transmission gear; 37 driving wheel; 40 control device; 41-43 voltage sensor; 50 power converter; 101, 102 operating point; 110, 120 active region; CH, Ca, Cb smoothing capacitor; CW carrier wave; D1-D4 anti-parallel diode; Dp duty ratio (precharge control); L1, L2 reactor; N1, N2, N3 node; S1-S4 power semiconductor switching element; SDp, /SDp control pulse signal; SG1-SG4 control signal; VH output voltage; VH* voltage command value.

Claims

A power supply system for outputting a DC voltage across first and second electric power lines connected to a load, comprising:
a first DC power supply;
a second DC power supply;
a first switch corresponding to said first DC power supply;
a second switch corresponding to said second DC power supply;
a first capacitor connected in parallel with said first DC power supply by way of said first switch;
a second capacitor connected in parallel with said second DC power supply by way of said second switch;
a third capacitor electrically connected across said first and second electric power lines;
first to fourth switching elements sequentially connected in series across said first and second electric power lines;
a first reactor electrically connected across a connection node of said second and third switching elements and a positive electrode terminal of said first DC power supply; and
a second reactor electrically connected across a connection node of said first and second switching elements and a positive electrode terminal of said second DC power supply,
said first DC power supply having a negative electrode terminal electrically connected to said second electric power line,
said second DC power supply having a negative electrode terminal electrically connected to a connection node of said third and fourth switching elements, said power supply system further comprising:
a current limiting circuit provided in correspondence with only one DC power supply of said first and second DC power supplies, and connected in parallel with a corresponding switch of said first and second switches; and
a control device configured to control on/off of said first to fourth switching elements and on/off of said first to third switches,
said current limiting circuit having a third switch and a current limiting resistor connected in series,
said control device
performing first precharge control for precharging one capacitor of said first and second capacitors that is connected to said third switch and said third capacitor to an output voltage of said one DC power supply by turning on said third switch with said first and second switches turned off at startup of said power supply system,
turning off said third switch and turning on said one switch of said first and second switches in accordance with completion of precharge of said one capacitor,
performing second precharge control for precharging the other capacitor of said first and second capacitors to an output voltage of the other DC power supply of said first and second DC power supplies accompanied by periodic on/off control of said first and fourth switching elements with said one switch turned on and the other switch of said first and second switches and said third switch turned off, and
turning on said other switch in accordance with completion of precharge of said other capacitor.
The power supply system according to claim 1, wherein said second precharge control has
first switching control to perform periodic on/off control of said first to fourth switching elements such that a voltage of said other capacitor and said third capacitor rises to a lower voltage of respective output voltages of said first and second DC power supplies, and
second switching control to perform periodic on/off control of said first to fourth switching elements such that the voltage of said other capacitor and said third capacitor rises to an output voltage of said other DC power supply after the voltage of said other capacitor rises to said lower voltage.
The power supply system according to claim 2, wherein said first switching control performs periodic on/off control of said first to fourth switching elements so as to periodically repeat a first operation of connecting said other capacitor in parallel with said one DC power supply by way of said first and second reactors and a second operation of electrically connecting said one DC power supply and said other capacitor in series across said first and second electric power lines by way of said first and second reactors, until the voltage of said other capacitor rises to said lower voltage.
The power supply system according to claim 2, wherein said second switching control performs periodic on/off control of said first to fourth switching elements so as to periodically repeat a third operation of forming a current circulating path by said one DC power supply and one of said first and second reactors and a fourth operation of electrically connecting said one DC power supply and one of said first and second reactors in series across said first and second electric power lines, until the voltage of said other capacitor rises to the output voltage of said other DC power supply.
The power supply system according to any one of claims 1 to 4, wherein said control device further turns on said other switch without executing periodic on/off control of said first and fourth switching elements, when the output voltage of said other DC power supply is lower than a predetermined voltage at the startup of said power supply system.
The power supply system according to any one of claims 1 to 5, wherein
said power supply system is configured to control said DC voltage by operating with one of a plurality of operation modes selectively applied in a state where said first and second switches are turned on, and
said plurality of operation modes includes
a first mode of executing DC voltage conversion in parallel between said first and second DC power supplies and said first and second electric power lines by on/off control of said first to fourth switching elements,
a second mode of executing DC voltage conversion between said first and second DC power supplies connected in series and said first and second electric power lines by keeping said third switching element on and performing on/off control of said first, second and fourth switching elements,
a third mode of maintaining the state where said first and second DC power supplies are connected in series to said first and second electric power lines by keeping on/off of said first to fourth switching elements,
a fourth mode of executing DC voltage conversion between one of said first and second DC power supplies and said first and second electric power lines by on/off control of said first to fourth switching elements,
a fifth mode of maintaining the state where one of said first and second DC power supplies is electrically connected to said first and second electric power lines and the other one of said first and second DC power supplies is electrically disconnected from said first and second electric power lines by keeping on/off of said first to fourth switching elements, and
a sixth mode of maintaining the state where said first and second DC power supplies are connected in parallel to said first and second electric power lines by keeping on/off of said first to fourth switching elements.