Power conversion device and power storage system
Patent Information
- Application Number
- JP2023143285
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-09-04
- Publication Date
- 2025-03-14
Smart Images
Figure 2025035927000001_ABST
Abstract
Description
[Technical field]
[0001] The present invention relates to a power conversion device and a power storage system. [Background technology]
[0002] Conventionally, a switching power supply device having an overcurrent protection means is known (see Patent Document 1). Also known is a switching power supply that can keep the average value of the inductor current almost constant and minimize changes in the oscillation frequency even if the load is in an overcurrent or short-circuit state (see Patent Document 2). [Prior art document] [Patent documents] [Patent Document 1] JP 2003-047237 A [Patent Document 2] JP 2005-210822 A Summary of the Invention [Problem to be solved by the invention]
[0003] It is desirable to protect the power converter and devices connected to the power converter from overcurrent. [Means for solving the problem]
[0004] In an embodiment of the present invention, there is provided a power conversion device. The power conversion device may include a DC battery. The power conversion device may include a non-isolated DCDC converter provided between one or more of the DC batteries and a DC bus to which a bus voltage is applied. Any of the power conversion devices may include a current limiting means for limiting at least one of an input current to the non-isolated DCDC converter and an output current from the non-isolated DCDC converter. In any of the power conversion devices, the non-isolated DCDC converter may convert a battery voltage of the DC battery to the bus voltage and output the bus voltage to the DC bus when discharging the DC battery. In any of the power conversion devices, the non-isolated DCDC converter may convert the bus voltage to the battery voltage and output the bus voltage to the DC battery when charging the DC battery. In any of the power conversion devices, the current limiting means may be connected between the non-isolated DCDC converter and the DC battery, or between the non-isolated DCDC converter and the DC bus.
[0005] In any of the power conversion devices described above, the current limiting means may limit at least one of an input current and an output current of the non-isolated DC-DC converter, independently of a conversion operation of the non-isolated DC-DC converter.
[0006] In any of the above power conversion devices, the power conversion device may further include a reference potential line set to a reference potential. In any of the above power conversion devices, the current limiting means may be a circuit in which a limiting switch for limiting a current and a freewheeling diode are connected in series. In any of the above power conversion devices, the anode of the freewheeling diode may be connected to the reference potential line, and the limiting switch may be connected to an input section or an output section of the non-isolated DC-DC converter. In any of the above power conversion devices, a connection point between the limiting switch and the freewheeling diode may be connected to the input section or the DC bus.
[0007] In any of the power conversion devices described above, the limit switch may be a semiconductor switch.
[0008] In any of the power conversion devices described above, the current limiting means may maintain a current value of the input current or the output current at or below a constant value larger than zero.
[0009] In any of the above power conversion devices, the current limiting means may control the current value to be below the certain value by switching the semiconductor switch when the current value of the DC bus exceeds a first reference value, and may cut off the input current or the output current when the current value does not fall below a second reference value after a determination time has elapsed and the value of the bus voltage does not become equal to or greater than a predetermined voltage value.
[0010] In another embodiment of the present invention, there is provided a power storage system. The power storage system may include a plurality of the power conversion devices described above.
[0011] The power storage system may include a plurality of the DC batteries connected to each of the power conversion devices.
[0012] Any of the power storage systems described above may include a common DC bus to which a plurality of the power conversion devices are connected. Any of the power storage systems described above may include a power conditioner connected to the DC bus.
[0013] The above summary of the invention does not list all of the features of the present invention. Also, subcombinations of these features may also be inventions. [Brief description of the drawings]
[0014] [Figure 1] FIG. 1 is a diagram showing an example of a power storage system 100 including a power conversion device 10 according to a first embodiment of the present invention. [Diagram 2] 2 is an enlarged view of the power conversion device 10, the DC battery 20, and the DC bus 30. FIG. [Diagram 3] 3 is a diagram illustrating an example of a current limiting operation of the power conversion device 10 of FIG. 2. [Figure 4] 5 is a diagram illustrating another example of the current limiting operation of the power conversion device 10 in FIG. [Diagram 5] 11 is a diagram showing another example of the arrangement of the power conversion device 10, the DC battery 20, and the DC bus 30. FIG. [Figure 6] FIG. 6 is a diagram illustrating an example of a current limiting operation of the power conversion device 10 of FIG. [Figure 7] 7 is a diagram illustrating another example of the current limiting operation of the power conversion device 10 of FIG. 5. FIG. [Figure 8] FIG. 2 is a diagram illustrating another configuration example of the power conversion device 10. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] The present invention will be described below through embodiments of the invention, but the following embodiments do not limit the scope of the invention according to the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention.
[0016] In this specification, the expression "connected" is not limited to a direct connection without other elements, but also includes an indirect connection via other elements. Furthermore, in this specification, the expressions "connected between ... and ...", "provided between ... and ...", or "disposed between ... and ..." are not intended to limit the physical arrangement, but rather mean "electrically connected between ... and ...".
[0017] FIG. 1 is a diagram showing an example of a power storage system 100 including a power conversion device 10 in a first embodiment of the present invention. The power storage system 100 is connected to a power facility, stores power from the power facility, and supplies power to the power facility. The power facility includes, for example, a power generation facility using renewable energy. The power storage system 100 stores surplus power in the power generation facility, and supplies power from the power storage system 100 when there is a power shortage in the power generation facility. The power facility may be a power grid. The power storage system 100 supplies power to the power system, and stores power from the power system.
[0018] The power storage system 100 includes one or more power conversion devices 10, one or more DC batteries 20, a DC bus 30, a power conditioner 40, and a transformer 50. The power storage system 100 may include a plurality of power conversion devices 10 and a plurality of DC batteries 20. The DC battery 20 may be a secondary battery. The DC battery 20 outputs a predetermined battery voltage. A power conversion device 10 is provided for each DC battery 20. In other words, a DC battery 20 is connected to each power conversion device 10. The power conversion device 10 is provided between the DC battery 20 and the DC bus 30. The power conversion device 10 converts (e.g., boosts) the battery voltage to a bus voltage, which is the voltage of the DC bus 30. The battery voltage is a voltage at an output terminal of the DC battery 20. The power conversion device 10 may convert (e.g., step-down) the bus voltage to a battery voltage to charge the DC battery. The power conversion device 10 includes a non-isolated DC-DC converter. 1 shows three power conversion devices 10 and three DC batteries 20, the power storage system 100 may include more or fewer power conversion devices 10 and DC batteries 20. The structure of the power conversion device 10 will be described later.
[0019] One or more DC batteries 20 are connected to the DC bus 30, and a bus voltage is applied to the DC bus 30. In this example, the DC battery 20 is provided with a power conversion device 10, so that the multiple power conversion devices 10 are connected to the common DC bus 30. Each power conversion device 10 may operate so that the bus voltage of the DC bus 30 is maintained at a predetermined value. The DC bus 30 in this example has a high potential line 32 and a reference potential line 24. The reference potential line 24 is connected to the low voltage side terminals of each DC battery 20. The high potential line 32 is connected to the output terminals of each power conversion device 10. The bus voltage in this example is the voltage at the high potential line 32.
[0020] The power conditioner 40 converts DC power and AC power. The power conditioner 40 is connected to the DC bus 30 and the transformer 50. The power conditioner 40 converts the DC power of the DC bus 30 into AC power and supplies it to the transformer 50. The power conditioner 40 also converts the AC power of the transformer 50 into DC power and supplies it to the DC bus 30. The power conditioner 40 of this example has a capacitor C1 that is charged by the bus voltage of the DC bus 30 or the voltage from the transformer. The power conditioner 40 of this example includes a three-phase inverter that converts the DC power from the capacitor C1 into AC power and converts the AC power from the transformer into DC power. The three-phase inverter has switches SW1 to SW6, and the switches SW1 and SW2, the switches SW3 and SW4, and the switches SW5 and SW6 correspond to each arm of the three-phase inverter. An inductor ALC1 is connected to the connection point of the switches in each arm. A capacitor may be provided between each inductor ALC1 and the reference potential. However, the structure of the power conditioner 40 is not limited to this. The power conditioner 40 only needs to be able to convert DC power and AC power into each other.
[0021] The transformer 50 converts the voltage of the AC power. The transformer 50 converts the voltage of the AC power output from the power conditioner 40 and outputs it to the power equipment. The transformer 50 also converts the voltage of the AC power of the power equipment and outputs it to the power conditioner 40.
[0022] 2 is an enlarged view of the power conversion device 10, the DC battery 20, and the DC bus 30 in FIG. 1. The power conversion device 10 includes a non-isolated DCDC converter 12 and a current limiting means 22. The non-isolated DCDC converter 12 is provided between the DC battery 20 and the DC bus 30. When discharging the DC battery 20, the non-isolated DCDC converter 12 converts (boosts) the battery voltage Vbat of the DC battery 20 to a bus voltage Vbus higher than the battery voltage Vbat and outputs the voltage to the DC bus 30, and when charging the DC battery 20, the non-isolated DCDC converter 12 converts (steps down) the bus voltage Vbus to a battery voltage Vbat and outputs the voltage to the DC battery 20. Here, the battery voltage Vbat when discharging the DC battery 20 may be the output voltage of the DC battery 20, and the battery voltage Vbat when charging the DC battery 20 may be the charging voltage of the DC battery 20.
[0023] The non-insulated DCDC converter 12 has an inductor L1, a capacitor C11, and a conversion switch SW12. A current I1 from the DC battery 20 flows through the inductor L1. The conversion switch SW12 converts the voltage by switching whether or not the current of the inductor L1 is supplied to the capacitor C11. The non-insulated DCDC converter 12 may further have a step-down switch SW11 for step-down operation arranged between the inductor L1 and the capacitor C11. The inductor L1 is an inductor used for step-up and step-down, and may be different from the inductance component of the wiring. The conversion switch SW12 and the step-down switch SW11 may be MOSFETs or IGBTs. In this specification, the wiring or terminal into which the current flows into the non-insulated DCDC converter 12 may be referred to as the input part of the non-insulated DCDC converter 12, and the wiring or terminal from which the current flows out may be referred to as the output part of the non-insulated DCDC converter 12. In FIG. 2, the wiring connecting the DC battery 20 and the non-isolated DC-DC converter 12 serves as an input section 28, and a high-potential line 26 on the DC bus 30 side, which will be described later, serves as an output section.
[0024] The power conversion device 10 includes a reference potential line 24 set to a reference potential, and a high potential line 26 having a potential higher than the reference potential by a voltage Vc of a capacitor C11. The reference potential may be a ground potential. The capacitor C11 is disposed between the high potential line 26 and the reference potential line 24. One end of the capacitor C11 is connected to the high potential line 26 between the step-down switch SW11 and a limit switch SW13 described later. The reference potential line 24 may be common to the DC battery 20 and the DC bus 30. The high potential line 26 may be connected to a high potential line 32 of the DC bus 30 via a limit switch SW13 described later.
[0025] When the non-isolated DC-DC converter 12 is boosting, the conversion switch SW12 is repeatedly turned on and off. In this specification, the repeated on and off of a switch is sometimes referred to as switching. When the conversion switch SW12 is turned on, a current I1 from the DC battery 20 flows to the inductor L1, and energy is stored in the inductor L1. When the conversion switch SW12 is turned off, the energy stored in the inductor L1 and the energy from the DC battery 20 are stored in the capacitor C11. The energy from the inductor L1 and the DC battery 20 is transmitted to the capacitor C11 via the freewheeling diode of the step-down switch SW11. The conversion switch SW12 is repeatedly turned on and off, thereby boosting the voltage Vc of the capacitor C11. The capacitor C11 supplies the voltage Vc to the DC bus 30. As a result, the non-isolated DC-DC converter 12 boosts the battery voltage Vbat to the bus voltage Vbus. That is, when boosting, the non-isolated DC-DC converter 12 of this example operates as a boost chopper circuit.
[0026] When the non-isolated DCDC converter 12 is stepping down, the step-down switch SW11 is repeatedly turned on and off. When the step-down switch SW11 is turned on, a current flows from the DC bus 30 or the capacitor C11 to the DC battery 20, and energy is stored in the inductor L1 and also supplied to the DC battery 20. When the step-down switch SW11 is turned off, the energy stored in the inductor L1 is supplied to the DC battery 20. While the step-down switch SW11 is off, the energy of the inductor L1 flows through the loop of the DC battery 20, the conversion switch SW12, and the inductor L1 via the freewheel diode of the conversion switch SW12. By repeatedly turning on and off the step-down switch SW11, the DC battery 20 is charged with the battery voltage Vbat, which is lower than the bus voltage Vbus. That is, when stepping down, the non-isolated DCDC converter 12 of this example operates as a step-down chopper circuit.
[0027] The current limiting means 22 limits at least one of the input current to the non-isolated DCDC converter 12 and the output current from the non-isolated DCDC converter 12 when at least one of them becomes an overcurrent. In FIG. 2, the input current during the step-up operation is indicated by I1, and the output current is indicated by I2. During the step-down operation, a current in the opposite direction to the current I1 becomes the output current, and a current in the opposite direction to the current I2 becomes the input current. The current limiting means may be connected between the non-isolated DCDC converter and the DC battery, or between the non-isolated DCDC converter and the DC bus. The current limiting means 22 of this example is connected between the capacitor C11 and the DC bus 30. The current limiting means 22 of this example limits the current I2. The current limiting means 22 may be a semiconductor switch such as a transistor, which will be described later. The current limiting means 22 may further include a mechanical switch, not shown. The mechanical switch may be opened after the current limiting operation of the current limiting means 22 described later, to electrically separate the cause of the overcurrent from the non-isolated DC-DC converter 12. This allows the circuit to be completely open, and also provides doubly good protection for the power conversion device 10 and other components in the event of damage to the current limiting means 22.
[0028] When a non-isolated boost DCDC converter is used for a battery, the short-circuit impedance of the battery is small and the boost DCDC converter itself does not have a function to limit the output current, so an overcurrent will flow when the DC bus 30 is short-circuited. In the case of the non-isolated DCDC converter 12 of this example, when the DC bus 30 is short-circuited, an overcurrent will flow from the DC battery 20 through the inductor L1 and the freewheeling diode of the step-down switch SW11. By providing a current limiting means 22, the DC battery 20, the non-isolated DCDC converter 12, and the DC bus 30 can be protected against an overcurrent.
[0029] The current limiting means 22 limits at least one of the input current and the output current, independent of the conversion operation of the non-insulated DCDC converter 12. Being independent of the conversion operation of the non-insulated DCDC converter 12 may mean limiting the current at a timing or standard different from the step-up / step-down operation of the non-insulated DCDC converter 12, or may mean limiting the current by another element different from the non-insulated DCDC converter 12.
[0030] The current limiting means 22 of this example is a circuit in which a limiting switch SW13 for limiting the current and a free wheel diode Dd11 are connected in series. The limiting switch SW13 is connected to the input or output of the non-insulated DC-DC converter 12. The limiting switch SW13 of this example is connected to the output of the non-insulated DC-DC converter 12 and is connected to a capacitor C11. The free wheel diode Dd11 is provided between the limiting switch SW13 and the reference potential line 24. The free wheel diode Dd11 has a role of securing a current path for a current flowing through a current limiting inductor L2 described later during the off period of the limiting switch SW13. The free wheel diode Dd11 of this example has a cathode connected to the limiting switch SW13 and an anode connected to the reference potential line 24. The free wheel diode Dd11 may be a MOSFET, an IGBT with a free wheel diode connected in parallel, or even a modularized version of the IGBT.
[0031] In the current limiting means 22 of this example, a connection point between the limiting switch SW13 and the freewheeling diode Dd11 is connected to the DC bus 30. The limiting switch SW13 limits the current I2. A current limiting inductor L2 may be provided between the connection point and the DC bus 30. The inductance component of the wiring may be used as the current limiting inductor L2.
[0032] The limit switch SW13 may be a semiconductor switch. As an example, the limit switch SW13 may be a MOSFET or an IGBT. A mechanical switch such as a breaker takes a time of tens of milliseconds to turn on and off, whereas a semiconductor switch can switch on and off in the order of microseconds. By switching the semiconductor switch and smoothing the current flowing at that time with an inductor, the current limiting means 22 maintains the current value of the input current or the output current at a constant value greater than 0. The constant value is greater than the current value during steady operation or the rated current value, and may be 5 times or less, 2 times or less, 1.5 times or less, or 1.2 times or less of the current value.
[0033] For example, the value of the limited current limited by the current limiting means 22 may be set based on a parameter specific to the power conversion device 10, such as a rated current value of the DC battery 20 connected to the power conversion device 10 or an output rated current of the power conversion device 10. This allows the value of the limited current to be set for each power conversion device 10 even if the capacity of at least one of the multiple DC batteries 20 and / or the overcurrent tolerance of at least one of the multiple power conversion devices 10 are different in the system of FIG.
[0034] The current limiting means 22 of this example may cut off the current when the current value of the output current exceeds the upper limit value, and may pass the current when the current value of the output current is equal to or lower than the lower limit value. This allows the output current to be maintained between the upper limit value and the lower limit value. The current limiting means 22 may repeat on-off at a predetermined duty ratio when the current value of the output current exceeds the upper limit value. The duty ratio may be a constant value regardless of the output current, and the on period may be shorter as the output current increases. This allows the output current to be suppressed. In the example of FIG. 2, the limiting switch SW13 is switched and the current I2 is smoothed by the current limiting inductor L2, so that the value of the current I2 can be maintained at a constant value greater than 0. The operation at that time will be described below. The power conversion device 10 may include a control unit that controls each switch. The operation of each switch of the power conversion device 10 described in this specification may be performed by the control unit. The control unit may have a signal generating unit that supplies a gate signal to each switch.
[0035] FIG. 3 is a diagram showing an example of a current limiting operation of the power conversion device 10 of FIG. 2. In FIG. 3, the current limiting operation will be described by taking the boost operation as an example. The power conversion device 10 normally switches the conversion switch SW12 to boost the battery voltage Vbat to the bus voltage Vbus. Symbols SW13 and SW12 represent the gate signals of the limiting switch SW13 and the conversion switch SW12. Each switch is turned on when the gate signal is at H level and turned off when the gate signal is at L level. The limiting switch SW13 is always on during a period when no current limiting is performed during the boost operation. In this example, the limiting switch SW13 is also a semiconductor switch. During a normal boost operation without current limiting, a predetermined current I1 is input from the DC battery 20 to the power conversion device 10, and the power conversion device 10 outputs a predetermined current I2 to the DC bus 30. The DC bus has a predetermined bus voltage Vbus.
[0036] In this example, when a power converter 10 or a load device (not shown) is added to the DC bus 30 during normal boost operation, the capacitor C11 of the power converter 10 or the capacitor of the load device is charged from the DC bus 30, or the DC bus 30 is temporarily short-circuited. The insertion of a capacitor refers to the insertion of a capacitor in parallel with the DC bus 30 between the high potential line 32 and the reference potential line 24 on the DC bus 30 side, and is performed, for example, when a power converter 10 is added. The value of the current I2 of the DC bus increases due to the insertion of the capacitor or the short circuit of the DC bus 30. The current limiting means 22 switches the semiconductor switch (limiting switch SW13) when the value of the current I2 of the DC bus 30 exceeds a first reference value. The first reference value may be the value of the rated current. As a result, the current limiting means 22 controls the value of the current I2 to be equal to or less than the above-mentioned constant value.
[0037] The switching frequency of the limit switch SW13 at this time may be higher than the switching frequency of the conversion switch SW12 during the boost operation. As an example, the switching frequency of the limit switch SW13 is 5 times or more and 10 times or less than the switching frequency of the conversion switch SW12. This allows the inductance of the current limiting inductor L2 to be reduced. For example, if there is a 5 times difference between the switching frequencies of the limit switch SW13 and the conversion switch SW12, the inductance of the current limiting inductor L2 may be about 1 / 5 of the inductance of the inductor L1. Also, if the inductance of the wiring can cover the inductance of the current limiting inductor L2, the current limiting inductor L2 can be omitted.
[0038] The dashed dotted line in the I2 column in the figure indicates the behavior of the current I2 when the current is not controlled by the current limiting means 22. When the current is not controlled, the current I2 increases abruptly.
[0039] When the limit switch SW13 is in a switching state, the conversion switch SW12 is turned off. When the conversion switch SW12 is turned off, the voltage Vc of the capacitor C11 is greater than the battery voltage Vbat, so the current I1 decreases to 0 A. In addition, the bus voltage Vbus decreases due to the insertion or short-circuiting of a capacitor in the DC bus 30.
[0040] If the current value falls below the first reference value within the judgment time, the power conversion device 10 may stop switching the limit switch SW13 and keep it in the on state, and start switching the conversion switch SW12. That is, the boost operation may be resumed. If a capacitor is inserted into the DC bus 30, the current I2 temporarily increases to charge the capacitor, but if the capacitor is charged, the current I2 decreases. If the DC bus 30 is temporarily short-circuited, the current I2 decreases when the short circuit is released. In either case, the bus voltage Vbus gradually increases. If the current value falls below the first reference value within the judgment time, the overcurrent is temporary. According to this example, the output current I2 during the judgment time is maintained at a predetermined current greater than 0, so that the boost operation can be resumed immediately after the judgment time has elapsed.
[0041] When the boost operation is stopped, the charge stored in the capacitor C11 of the non-isolated DC-DC converter 12 is discharged, and the voltage Vc of the capacitor C11 decreases. Since the current I1 flows even if the step-down switch SW11 and the conversion switch SW12 are both off, the limit switch SW13 is turned off as described below.
[0042] Fig. 4 is a diagram showing another example of the current limiting operation of the power conversion device 10 of Fig. 2. The power conversion device 10 of this example also performs a boost operation under normal conditions, as in the case of Fig. 3. The symbols in the figure are the same as those in Fig. 3. This example shows a case where the DC bus 30 is continuously short-circuited.
[0043] When the DC bus 30 is short-circuited and the current I2 exceeds the first reference value, the limit switch SW13 starts switching and controls the current I2 to a certain value or less, as in the case of Fig. 3. At that time, the conversion switch SW12 stops switching and turns off, as in the case of Fig. 3.
[0044] In this example, since the DC bus 30 continues to be short-circuited, the current I2 does not fall below the first reference value even after the judgment time has elapsed, and the bus voltage Vbus does not increase. If the current value does not fall below the first reference value even after the judgment time has elapsed, it is considered that the short circuit is caused by a fault. The current limiting means 22 may cut off the input current or the output current if the current value does not fall below the second reference value after the judgment time has elapsed and the bus voltage Vbus value does not become equal to or greater than a predetermined voltage value. In this example, the second reference value is equal to the first reference value. The predetermined voltage value may be the value of the bus voltage Vbus in normal operation, may be 80% of the bus voltage Vbus in normal operation, or may be 50% of the bus voltage Vbus in normal operation.
[0045] In this example, the current I2 is cut off by turning off the limit switch SW13 that is switched on after the judgment time has elapsed. In this case, the conversion switch SW12 remains off. The current limiting means 22 may cut off the input current or the output current if the current value of the current I2 does not fall below the second reference value when the judgment time has elapsed. The current limiting means 22 may cut off the input current or the output current if the value of the bus voltage Vbus does not become equal to or greater than the predetermined voltage value when the judgment time has elapsed.
[0046] When using a mechanical switch such as a breaker or a fuse to protect the device from overcurrent, the current cannot be interrupted within a short time unless the current value is approximately 1000 times the rated current. In addition, even if the current value temporarily increases due to the insertion of a capacitor or a temporary short circuit rather than a failure of the DC bus 30, the voltage conversion operation of the power conversion device 10 is completely stopped, and it takes time to resume the voltage conversion operation. As shown in the example of FIG. 3 and FIG. 4, by controlling the current value using a semiconductor switch, the behavior of the current during the judgment time can be monitored while suppressing the increase in current. This makes it possible to determine whether the DC bus 30 is faulty or the current value is temporarily increased, and also to quickly resume the voltage conversion operation. In addition, it is possible to suppress the sudden release of the charge stored in the capacitor C11.
[0047] Since the value of the current I2 is smaller than the current I1, the current capacity of the element of the current limiting means 22 may be small. Furthermore, even when it is determined that the DC bus 30 has failed and the current path is cut off, since the current value is limited, it is not necessary to consider the condition of 1000 times the rated current or the like for the current capacity of the element, and it may be suitable for the rated current. Note that a separate mechanical switch may be provided to cut off the current path, and the current may be cut off by turning off the mechanical switch. In this case, the same effect can be obtained. The required breaking capacity of the mechanical switch in this case may also be equivalent to the rated current, rather than 1000 times or more the rated current.
[0048] In the example of Fig. 4, after the short circuit continues and the limit switch SW13 is turned off, a retry operation may be performed to manually or automatically turn the limit switch SW13 on again. If the value of the current I2 at that time is equal to or less than the second reference value, a transition to normal boost operation may be made, and if the value of the current I2 is greater than the second reference value, the limit switch SW13 may be turned off again. As an example, the retry operation may be performed up to three times before transitioning to normal boost operation. Alternatively, if a retry operation is performed once and the short circuit continues, it is not necessary to perform the retry operation until the cause of the short circuit is eliminated.
[0049] 5 is a diagram showing another example of the arrangement of the power conversion device 10, the DC battery 20, and the DC bus 30. The configurations of the non-isolated DC-DC converter 12, the DC battery 20, and the DC bus 30 in this example are the same as those in the example in FIG. 2, except that each switch is a MOSFET. The current limiting means 22 in this example is provided between the DC battery 20 and the inductor L1. In this example, the reference potential line 24 may also be common to the DC battery 20, the power conversion device 10, and the DC bus 30. The high potential line 26 and the high potential line 32 may be connected.
[0050] The current limiting means 22 of this example may also be a switch. The switch may be a semiconductor switch such as a transistor, or may be a mechanical switch. The current limiting means 22 of this example also has a limiting switch SW13 and a free-wheeling diode Dd11. However, the limiting switch SW13 of this example is connected to the DC battery 20. The free-wheeling diode Dd11 of this example is provided between the limiting switch SW13 and the reference potential line 24. The free-wheeling diode Dd11 of this example has a role of securing a current path for the current flowing through the inductor L1 during the off period of the limiting switch SW13. The free-wheeling diode Dd11 of this example also has a cathode connected to the limiting switch SW13 and an anode connected to the reference potential line 24. The limiting switch SW13 of this example is a MOSFET, which is a type of semiconductor switch. The connection point between the limiting switch SW13 and the free-wheeling diode Dd11 is connected to the inductor L1.
[0051] When the non-isolated DC-DC converter 12 operates as a step-up chopper, the limit switch SW13 is turned on and the conversion switch SW12 switches. When the non-isolated DC-DC converter 12 operates as a step-down chopper, the step-down switch SW11 switches.
[0052] The current limit during the boost operation will be described. The current limiting means 22 of this example limits the input current to the non-isolated DCDC converter 12. In this example, the limiting switch SW13 switches, and the current I1 flowing at that time is smoothed by the inductor L1 to limit the input current. In this example, the current limiting means 22 may maintain the current value of the input current or the output current at a constant value greater than 0, as in the case of FIG. 2. In this example, the inductor L1 of the non-isolated DCDC converter 12 can be used as the current limiting means 22, so the number of parts can be reduced. In addition, the battery voltage Vbat, which is lower than the bus voltage Vbus, is applied to the current limiting means 22, so that the withstand voltage of the elements can be designed to be low. In this example, the limiting switch SW13 may be a MOSFET, and the step-down switch SW11 and the conversion switch SW12 may be IGBTs. Also, the power conversion device 10 may include a control unit, as in the case of FIG. 2.
[0053] Fig. 6 is a diagram showing an example of a current limiting operation of the power conversion device 10 of Fig. 5. As in the case of Fig. 3, the power conversion device 10 of this example also switches the conversion switch SW12 during normal operation when no current limiting is performed, and boosts the battery voltage Vbat to the bus voltage Vbus. Other symbols and the like that overlap with Fig. 3 refer to the same things as in Fig. 3, and therefore explanations thereof will be omitted.
[0054] This example also shows a case where a capacitor is inserted into the DC bus 30 or the DC bus 30 is temporarily short-circuited during normal boost operation. The value of the DC bus current I2 increases due to the insertion of the capacitor or the short-circuiting of the DC bus 30. The current limiting means 22 switches the semiconductor switch (limiting switch SW13) when the value of the current I2 of the DC bus 30 exceeds a first reference value. The first reference value may be the value of the rated current in this example as well.
[0055] When the limit switch SW13 switches on, the current I1 is limited. The limited current I1 is referred to as current I1'. On the other hand, in this example, the current limiting means 22 is provided between the DC battery 20 and the non-isolated DC-DC converter 12, so the charge stored in the capacitor C11 is released all at once and the current I2 increases rapidly. After the charge of the capacitor C11 is released, the value of the current I2 becomes equal to the value of the current I1'. The current limiting means 22 controls the value of the current I2 to a constant value or less. Here, the constant value in this example may be the value of the current I1', and may exclude a temporary increase in the current value due to the discharge of the capacitor.
[0056] The dashed line in the I2 column in the figure shows the behavior of the current I2 when the current is not controlled by the current limiting means 22. When the current is not controlled, the DC battery 20 is discharged and the current I2 increases rapidly.
[0057] 3, in this example, as the capacitor inserted in the DC bus 30 is charged or the short circuit is removed, the bus voltage Vbus of the DC bus 30 increases. Accordingly, the value of the current I2 decreases.
[0058] If the current value falls below the second reference value within the determination time, the power conversion device 10 may stop switching the limit switch SW13 and keep it on again, and may start switching the conversion switch SW12. That is, the power conversion device 10 may resume the boost operation. The second reference value may be equal to the first reference value, and may be 80%, 50%, or 30% of the value of the current I1'. If the current value falls below the second reference value within the determination time, the overcurrent is temporary, and according to this example, the boost operation can be resumed immediately. Unlike the case of FIG. 3, the determination time may include the period after the voltage Vc of the capacitor C11 becomes smaller than the battery voltage Vbat.
[0059] Fig. 7 is a diagram showing another example of the current limiting operation of the power conversion device 10 of Fig. 5. The power conversion device 10 of this example also performs a boost operation during normal operation when no current limiting is performed, as in the case of Fig. 6. The symbols in the figure are the same as those in Fig. 6. This example shows a case where the DC bus 30 is continuously short-circuited.
[0060] When the DC bus 30 is short-circuited and the current I2 exceeds the first reference value, the limit switch SW13 starts switching and controls the current I1 to the current I1', as in Fig. 6. At that time, the conversion switch SW12 stops switching and is turned off, as in Fig. 6.
[0061] In this example, since the DC bus 30 continues to be short-circuited, the current I2 does not fall below the second reference value even after the judgment time has elapsed, and the bus voltage Vbus does not increase. The fact that the current value does not fall below the second reference value even after the judgment time has elapsed is considered to be a short circuit caused by a fault. Therefore, the current limiting means 22 may cut off the input current or the output current when the current value does not fall below the second reference value after the judgment time has elapsed and the bus voltage Vbus value does not become equal to or greater than a predetermined voltage value. The predetermined voltage value may be the value of the bus voltage Vbus under normal conditions, may be 80% of the bus voltage Vbus under normal conditions, or may be 50% of the bus voltage Vbus under normal conditions.
[0062] In this example, the current I1 is cut off by turning off the limit switch SW13 that is switched on after the judgment time has elapsed. The current limiting means 22 may cut off the input current or the output current if the value of the current I2 does not fall below the second reference value when the judgment time has elapsed. The current limiting means 22 may cut off the input current or the output current if the value of the bus voltage Vbus does not become equal to or greater than the predetermined voltage value when the judgment time has elapsed. Also, a retry operation similar to that of FIG. 4 may be performed.
[0063] 3 and 4, in this example, too, a semiconductor switch is used to control the current value and the behavior of the current value is monitored during a judgment time in constant current operation, making it possible to determine whether the DC bus 30 is faulty or the current value is temporarily increased, and voltage conversion operation can be resumed quickly. Furthermore, even when it is determined that the DC bus 30 is faulty and the current path is cut off, the current capacity of the element may be low because the current value is limited. Note that in this example, a separate mechanical switch may be provided to cut off the current path, and the current may be cut off by turning off the mechanical switch.
[0064] Fig. 8 is a diagram showing another configuration example of the power conversion device 10. The power conversion device 10 of this example is different from the power conversion device 10 of Fig. 5 in the configuration of the non-isolated DCDC converter 12. The current limiting means 22 of this example is provided between the DC battery 20 and the non-isolated DCDC converter 12, but may be provided between the non-isolated DCDC converter 12 and the DC bus 30 as in Fig. 2. The operation of the current limiting means 22 is the same as the operation described in Fig. 2 to Fig. 7, so the description will be omitted.
[0065] The power conversion device 10 of this example includes a reference potential line 24 set to a reference potential as in FIG. 2 and FIG. 5, and a high potential line 26 having a potential higher than the reference potential by the voltage Vc of the capacitor C11. The non-insulated DCDC converter 12 of this example has four switches arranged in series between the high potential line 26 and the reference potential line 24. The four switches are called the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 from the high potential line 26 side. The non-insulated DCDC converter 12 has an inductor L1 with one side connected between the second switch S2 and the third switch S3. The non-insulated DCDC converter 12 has a second capacitor C12 arranged in parallel with the second switch S2 and the third switch S3. That is, the non-insulated DCDC converter 12 of this example is a three-level flying capacitor type chopper.
[0066] 2 and 5, the DC battery 20, the power converter 10, and the DC bus 30 of this embodiment share the same reference potential line 24, so that no high-frequency voltage is generated between the DC battery 20 and the DC bus 30 even if each switch performs a switching operation. In addition, the non-isolated DC-DC converter 12 of this embodiment can easily create a high step-up ratio (bus voltage Vbus / battery voltage Vbat), so that it can handle a high bus voltage Vbus. Furthermore, if the voltage Vc2 of the second capacitor C12 is set to half the bus voltage Vbus, the voltage applied to each switch is also half the bus voltage Vbus, so that the withstand voltage of the elements can be suppressed to half the bus voltage Vbus.
[0067] Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It is clear to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the description of the claims that such modifications and improvements can also be included in the technical scope of the present invention. [Explanation of symbols]
[0068] 10 power conversion device, 12 non-isolated DC / DC converter, 20 DC battery, 22 current limiting means, 24 reference potential line, 26 high potential line, 28 input section, 30 DC bus, 32 high potential line, 40 power conditioner, 50 transformer, 100 power storage system
Claims
1. A non-isolated DC-DC converter provided between a DC battery and a DC bus to which one or more of the DC batteries are connected and to which a bus voltage is applied; a current limiting means for limiting at least one of an input current to the non-insulated DC-DC converter and an output current from the non-insulated DC-DC converter; Equipped with When discharging the DC battery, the non-isolated DC-DC converter performs an operation of converting a battery voltage of the DC battery into the bus voltage and outputting the bus voltage to the DC bus, and when charging the DC battery, the non-isolated DC-DC converter performs an operation of converting the bus voltage into the battery voltage and outputting the battery voltage to the DC battery; The current limiting means is connected between the non-isolated DC-DC converter and the DC battery, or between the non-isolated DC-DC converter and the DC bus. Power conversion equipment.
2. The current limiting means limits at least one of an input current and an output current of the non-isolated DC-DC converter independently of a conversion operation of the non-isolated DC-DC converter. The power conversion device according to claim 1 .
3. The power conversion device further includes a reference potential line set to a reference potential, the current limiting means is a circuit in which a limiting switch for limiting a current and a free-wheeling diode are connected in series; The anode of the free wheel diode is connected to the reference potential line, The limit switch is connected to an input or an output of the non-isolated DC-DC converter, A connection point between the limit switch and the free wheel diode is connected to the input section or the DC bus. The power conversion device according to claim 1 .
4. The limit switch is a semiconductor switch. The power conversion device according to claim 3 .
5. The current limiting means maintains the current value of the input current or the output current at or below a constant value greater than 0. The power conversion device according to claim 4.
6. The current limiting means controls the current value to be equal to or less than the certain value by switching the semiconductor switch when the current value of the DC bus exceeds a first reference value, and cuts off the input current or the output current when the current value does not fall below a second reference value after a determination time has elapsed and the bus voltage value does not become equal to or greater than a predetermined voltage value. The power conversion device according to claim 5 .
7. A plurality of the power conversion devices according to claim 1; A plurality of the DC batteries connected to each of the power conversion devices; A power storage system comprising:
8. A common DC bus to which a plurality of the power conversion devices are connected; a power conditioner connected to the DC bus; The power storage system of claim 7 further comprising: