JP7828379B2 - crane - Google Patents

Description

The present invention relates to a crane, and more specifically to a crane that suppresses an increase in the current value output from a power supply device due to the occurrence of an inrush current.

The numerous cranes used to load and unload goods at logistics facilities such as container terminals use electric motors powered by a common power supply (e.g., a substation) to perform operations such as loading and unloading containers and traveling. The allowable current value of the power supply device is set on the assumption that all of the equipment and devices at the logistics facility (including the electric motors of each of the numerous cranes) are driven by their rated current. In other words, as long as each of the electric motors of each of the numerous cranes is driven by its rated current, the current value output from the power supply device will not exceed the allowable current value.

However, each of the many cranes operates independently, and there are cases where the timing of inrush currents (starting currents) overlaps immediately after the electric motors of the many cranes begin powering. The peak current value of the inrush current is greater than the rated current value, and if the number of overlapping inrush current occurrences becomes excessive, the current output from the power supply device temporarily exceeds the allowable current value, causing the power supply device to shut down. This results in a stagnation of cargo handling throughout the logistics facility.

A yard crane has been proposed in which the allowable power that the power receiving unit can transmit is limited to be less than the power supplied to the cargo handling motor when the motor is under maximum load, and even when the power receiving unit is connected to a power supply unit, if the power supplied to the cargo handling motor and traveling motor is insufficient, power is supplied from a charging/discharging unit (see Patent Document 1). In the crane proposed in Patent Document 1, when the weight of the container is greater than a predetermined weight, two types of power, power output from the power receiving unit and power output from the charging/discharging unit, are supplied to the hoisting motor and trolley drive motor; when the weight of the container is less than the predetermined weight, only the power output from the power receiving unit is supplied to those motors.

The above-mentioned inrush current occurs immediately after the electric motor begins powering, and occurs regardless of the weight of the container or the load on the electric motor. Therefore, with the proposed crane, even if an inrush current occurs in the electric motor when the container weight is less than a specified weight, power will not be supplied to the charging/discharging unit. As such, because the proposed crane does not specifically target inrush currents, measures to prevent the power supply system from shutting down due to overlapping inrush currents among multiple cranes require consideration specific to inrush currents. Therefore, there is room for improvement in more reliably suppressing increases in the current value of AC power output from the power supply system due to the occurrence of inrush currents.

JP 2009-137749 A

The object of the present invention is to provide a crane that more reliably suppresses increases in the current value of AC power output from a power supply device due to the occurrence of inrush current.

The crane of the present invention, which achieves the above-mentioned objectives, comprises a converter that converts AC power from a power supply device into DC power, an inverter that converts the DC power output from the converter into AC power, and an electric motor driven by the AC power output from the inverter. The current value of the DC power output from the converter is limited to a limited current value that is equal to or greater than the rated current value of the converter and is smaller than the peak current value due to inrush current generated when the electric motor is powered, and the crane is characterized by comprising a power storage device connected in parallel with the inverter to the converter during at least the time period during which the current value of the AC power supplied from the inverter to the electric motor exceeds the limited current value.

According to the present invention, the current value of the DC power output from the converter is limited. If an inrush current occurs during power running of the electric motor, a shortage of DC power will occur from the converter to the inverter, but this shortage is made up for by the power storage device. In other words, a power shortage will not occur when an inrush current occurs, and an increase in the current value output from the power supply device due to the occurrence of an inrush current can be more reliably suppressed. This prevents the current value of the AC power output from the power supply device from exceeding a predetermined value, and the current value can be maintained below the predetermined value.

FIG. 1 is an explanatory diagram illustrating an embodiment of a crane. 10 is an explanatory diagram illustrating an example of fluctuations in current value over time in an electric motor driven in power running mode. FIG. FIG. 2 is an explanatory diagram illustrating the power system of FIG. 1; FIG. 4 is an explanatory diagram illustrating an example of fluctuations in current value over time in a converter. FIG. 3 is an explanatory diagram illustrating an example of the correlation between the charge capacity and the voltage value in the power storage device. FIG. 2 is an explanatory diagram illustrating an example of the flow of electric power in the power system when the electric motor is regeneratively driven. FIG. 2 is an explanatory diagram illustrating an example of the flow of power in a power system when an inrush current occurs during power running of an electric motor. 10 is an explanatory diagram illustrating an example of the flow of power in the power system when an inrush current does not occur during power running of the electric motor; FIG. FIG. 10 is an explanatory diagram illustrating a modified example of the crane embodiment. FIG. 10 is an explanatory diagram illustrating the power system of FIG. 9 .

The crane of the present invention will be described below based on the embodiment shown in the drawings.

The embodiment of the crane 10 (10a, 10b) illustrated in Figure 1 is a crane used for loading and unloading at a logistics facility 1. This crane 10 is equipped with a power system 20 that takes measures against inrush current, as described below, to maintain the current value of the AC power output from the power supply device 7 shared by the various devices and equipment (including the crane 10) at the logistics facility 1 below a predetermined value.

The logistics facility 1 represents a container terminal. The logistics facility 1 may be any of a variety of well-known logistics facilities, such as a container terminal or warehouse facility that serves as a logistics hub. The logistics facility 1 also includes a manufacturing facility that produces and ships various types of steel plates. In the logistics facility 1, cargo 3 transported by multiple pieces of transportation equipment 2 is temporarily stored in a storage area 4, and the stored cargo 3 is then transported to the outside by the multiple pieces of transportation equipment 2. The transportation equipment 2 is any of a variety of well-known vehicles that transport cargo 3. Examples of the transportation equipment 2 include ships and vehicles that transport containers as cargo 3 in a container terminal. The storage area 4 is an area where cargo 3 is temporarily stored. The storage area 4 in a container terminal corresponds to a storage lane where multiple containers are stored as cargo 3. The multiple cranes 10 may be any of a variety of well-known cranes used to load and unload cargo 3 at the logistics facility 1. The multiple cranes 10 in a container terminal include transfer cranes (yard cranes) 10a and gantry cranes 10b. In addition to the numerous cranes 10 used as cargo handling equipment, the container terminal also has an on-site chassis 5 for transporting containers.

The crane 10 comprises a girder 11, a trolley 12, a hoisting device 13, a leg structure 14, a traveling device 15, a control device 16, and a power system 20 (described later and shown in Figure 3). The girder 11 supports the hoisting device 13 by suspending it via the trolley 12. The trolley 12 is configured to be able to move laterally along the girder 11 in the direction of extension of the girder 11. The hoisting device 13 is configured to be able to be raised and lowered vertically by a wire suspended from the trolley 12. The leg structure 14 supports the girder 11 from above. At least two traveling devices 15 are arranged spaced apart in the direction of extension of the girder 11 in a plan view and are attached to the lower end of the leg structure 14. The traveling devices 15 allow the crane 10 to travel in a direction perpendicular to the direction of extension of the girder 11.

The control device 16 controls each operation of the crane 10 (the traverse operation of the trolley 12, the lifting and lowering operation of the hoisting device 13, and the traveling operation of the crane 10 using the traveling device 15). The control device 16 can be implemented using a variety of well-known computers. The control device 16 is not limited to a single computer, but can also be configured using multiple computers (for example, a combination of a personal computer and a programmable logic controller (PLC)).

The power system 20 supplies power to operate each device (trolley 12, hoisting device 13, traveling device 15) based on commands from the control device 16. Details of this power system 20 will be described later.

The management system 6 receives and stores various data and processes them. The management system 6 can use various known computers. The management system 6 manages the cargo 3 at the logistics facility 1 and instructs the control devices 16 of the numerous cranes 10 to handle the cargo 3. Specifically, the management system 6 creates handling data indicating the cargo 3 to be handled by the cranes 10 based on the scheduled arrival and departure dates of the transportation equipment 2 and the number of cargo 3 entering and leaving the storage area 4. The management system 6 then transmits the handling data to the control devices 16 of the numerous cranes 10, which then instructs the numerous cranes 10 to handle the cargo. In a container terminal, the management system 6 has multiple programs, including a program for managing the handling of cargo 3 onto ships by the transportation equipment 2, a program for managing the cargo 3 in the storage area 4, and a program for transmitting handling data as work instructions to the numerous cranes 10 and on-site chassis 5. The management system 6 is not limited to a single computer, and may be composed of multiple computers, each dedicated to a specific program.

The power supply device 7 supplies AC power to each of the multiple cranes 10 and is a common device for all of the multiple cranes 10. The power supply device 7 can be a publicly known private power plant or extra-high voltage substation. In one example of a logistics facility 1, an extra-high voltage substation is used as the power supply device 7. AC power is supplied from the power supply device 7 to each of the multiple cranes 10 using a power supply device 8, shown by the dashed dotted line in the figure. The power supply device 8 can be a variety of publicly known power supply devices, such as a combination of a contact wire, a bus bar and a current collector, or a combination of a cable reel and a power cable.

Figure 2 shows an example of fluctuations in the current value of AC power supplied from the inverter 22 to the electric motor 23 over time during an operating period ΔT, from the start to the end of a predetermined operation to power a predetermined electric motor 23 of the power system 20. The current value of the AC power supplied from the inverter 22 to the electric motor 23 (the current value of the DC power output from the converter 21) increases to a peak current value Ip, an inrush current greater than the rated current, immediately after the electric motor 23 starts powering. The inrush current then reaches a substantially constant rated current value Ir. The period ΔTp during which the inrush current occurs occurs at the beginning of the operating period ΔT. The rated current value Ir, the peak current value Ip, and the period ΔTp are each predetermined based on the specifications of the inverter 22 and the electric motor 23 of the power system 20. The peak current value Ip is, for example, approximately 1.7 to 2.2 times the rated current value Ir. The period ΔTp is, for example, approximately 1.5 to 2.5 seconds.

The allowable current value Ia of the power supply device 7 is set based on the overall power consumption of the logistics facility 1. For example, in a container terminal, in addition to the numerous cranes 10 and management systems 6, a wide variety of devices and equipment consume power, such as lighting equipment, power sources for reefer containers in the storage area 4, and gate equipment. The allowable current value Ia of the power supply device 7 is set assuming that all of these devices and equipment are driven at rated current. The allowable current value Ia is also set assuming that the electric motors 23 of the numerous cranes 10 are powered at rated current Ir. Specifically, the allowable current value Ia is set to a value greater than the current value output from the power supply device 7 if all of the devices and equipment in the logistics facility 1 were driven at rated current.

As mentioned above, the peak current value Ip due to inrush current is greater than the rated current value Ir. Therefore, as a countermeasure against inrush current, it is possible to set the allowable current value Ia of the power supply device 7 based on the peak current value Ip, but this would increase the cost of the power supply device 7. Therefore, in order to reduce the cost of the power supply device 7 while operating the logistics facility 1 stably, countermeasures against inrush current are necessary.

The power system 20 illustrated in FIG. 3 has measures in place to deal with the inrush current described above. Specifically, in the power system 20, the current value of the DC power output from the converter 21 is limited to a limit current value Ib. The power system 20 also includes a power storage device 24 connected in parallel with the inverter 22 during periods that include times when the current value of the AC power supplied from the inverter 22 to the electric motor 23 exceeds the limit current value Ib. Therefore, in the power system 20, if an inrush current occurs in the electric motor 23 and the AC power supplied from the inverter 22 to the electric motor 23 is insufficient due to limitations imposed by the converter 21, the shortage is compensated for by the DC power stored in the power storage device 24. In this way, the power system 20 incorporates both a configuration that limits the current value of the DC power output from the converter 21 and a configuration that includes a power storage device 24 that compensates for the power shortage caused by the limitation, thereby providing measures to deal with inrush current. The power system 20 is described in detail below.

The power system 20 comprises one converter 21, multiple inverters 22 (22a-22d), multiple electric motors 23 (23a-23d), and one power storage device 24. The number of converters 21 is not limited to one; there may be multiple converters 21 depending on the amount of power supplied to the multiple inverters 22. The multiple inverters 22 and multiple electric motors 23 include a traverse inverter 22a and a traverse motor 23a that move the trolley 12 traversely, a lift inverter 22b and a lift motor 23b that raise and lower the hoist 13, a travel inverter 22c and a travel motor 23c that drive the traveling device 15, and a vibration suppression inverter 22d and a vibration suppression motor 23d that suppress vibration of the hoist 13. The number and types of inverters 22 and electric motors 23 vary depending on the specifications of the crane 10. For example, in gantry crane 10b, lift inverter 22b and lift motor 23b serve to raise and lower the boom (part of girder 11) extending from leg structure 14. Note that power system 20 may also have a separate inverter and electric motor for raising and lowering the boom. Also, depending on the mechanism used to stop the sway of the hoisting device 13, anti-sway inverter 22d and anti-sway motor 23d may not be included. The number of power storage devices 24 is not limited to one, and may be multiple depending on the charging capacity.

The converter 21 converts the AC power output from the power supply device 7 into DC power and supplies the DC power to each device of the crane 10, such as each inverter 22 and the control device 16, via a common line 25. The converter 21 receives AC power from the power supply device 7 via the power feeder 8, high-voltage panel 27, and high-voltage transformer 28. The converter 21 generates DC power according to the various voltages used by the crane 10. Examples of the various voltages include 385V and 400V.

The converter 21 can be any of a variety of known AC-DC converters. It is preferable to use a bidirectional (charge-discharge) converter as the converter 21. By using a bidirectional converter as the converter 21, it is possible to supply surplus power generated by the regenerative drive of the electric motor 23 to other cranes 10 via the power supply device 8. If a bidirectional converter is not used as the converter 21, it is preferable that the power system 20 include a resistor that converts surplus power generated by the regenerative drive of the electric motor 23 into heat and dissipates the heat.

The converter 21 is electrically connected to the control device 16 via signal line 26. The current value of the DC power output from the converter 21 is limited to a limit current value Ib by the control device 16. Note that if a converter control device capable of controlling the current value of the DC power output from the converter 21 is provided separately from the control device 16 and the current value can be limited to the limit current value Ib by this converter control device, then there is no need to connect the converter 21 to the control device 16 via signal line 26. The converter control device may be included in the converter 21, or may be provided separately from the converter 21 on the crane 10.

Figure 4 shows an example of the fluctuation in the current value of the converter 21 over time during an operating period ΔT from the start to the end of a predetermined operation to power a predetermined electric motor 23. The current value of the DC power output from the converter 21 (the current value of the DC power supplied to the inverter 22) is limited to a limit current value Ib. The limit current value Ib is equal to or greater than the rated current value Ir and smaller than the peak current value Ip of the inrush current generated when the electric motor 23 is powered. The limit current value Ib can be set to any value equal to or greater than the rated current value Ir and smaller than the peak current value Ip. However, a value between 1.0 and 1.5 times (including both 1.0 and 1.5) the rated current value Ir is desirable. If the limit current value Ib is smaller than the rated current value Ir, the output current value of the converter 21 will always be smaller than the rated current value Ir, which will interfere with the operation of each device. Furthermore, if the limit current value Ib is 1.5 times or more the rated current value Ic, the effectiveness of the inrush current countermeasure will be reduced. The limit current value Ib can also be set based on the peak current value Ip instead of the rated current value Ic. For example, the limit current value Ib can be set to a value between 0.5 times and 0.8 times (including 0.5 and 0.8 times) the peak current value Ip. However, when setting the peak current value Ip as the reference, it is necessary to ensure that the output current value does not fall below the rated current value Ir.

The inverter 22 converts the DC power output from the converter 21 into AC power and supplies the converted AC power to the electric motor 23. The electric motor 23 is driven by the AC power supplied from the inverter 22. The rotational power obtained by driving the electric motor 23 is used to power the operation of each device (the traverse movement of the trolley 12, the lifting and lowering movement of the hoisting device 13, and the traveling movement of the crane 10 by the traveling device 15).

Various known inverters and electric motors can be used for the inverter 22 and the electric motor 23, respectively. The inverter 22 is electrically connected to the control device 16 via signal lines 26. The inverter 22 adjusts the amount of power supplied to the electric motor 23 in response to commands from the control device 16, thereby adjusting the rotational speed of the electric motor 23. The electric motor 23 operates various devices by powering and regenerating the inverter 22. For example, during the traverse movement of the trolley 12 and the travel movement of the crane 10 using the traveling device 15, the electric motor 23 is powered to perform acceleration and constant-speed movement, and is regenerated to perform deceleration. Furthermore, during the lifting and lowering of the hoisting device 13, the electric motor 23 is powered to perform the lifting movement (hoisting up movement) and regeneratively driven to perform the lowering movement (hoisting down movement). When the electric motor 23 is powered, power supplied from the inverter 22 is consumed, and when it is regeneratively driven, power is generated by the regenerative drive of the electric motor 23.

The power storage device 24 can be any of a variety of well-known power storage devices, such as a secondary battery (storage battery) or a power storage device (capacitor). Examples of secondary batteries include lithium-ion batteries and nickel-metal hydride batteries. Examples of power storage devices include electric double-layer capacitors. The power storage device 24 is not particularly limited, and can be selected appropriately taking into account the advantages and disadvantages of each.

The power storage devices 24 are connected in parallel with the respective inverters 22 to the converter 21 at least during the period when the current value of the AC power supplied from the inverters 22 to the electric motors 23 exceeds the limit current value Ib. The power storage devices 24 only need to be connected to the common line 25 during that period, and may be connected to the common line 25 via a switch or other such device controlled by the control device 16, or a branch.

It is more desirable that the power storage devices 24 be constantly connected in parallel with the respective inverters 22 of the converter 21. Constant connection means that the power storage devices 24 are connected to the common line 25 without using switches or other switches or branching devices. A connection method in which the power storage devices 24 are constantly connected in parallel with the inverters 22 of the converter 21 is known as the float charging method. Connecting the power storage devices 24 using this connection method enables the automatic charging and discharging of the power storage devices 24. This eliminates the need for complex data processing and control processes required for trickle charging methods to counter inrush currents, making it easier to counter inrush currents. Furthermore, if the charge capacity (SOC) of the power storage devices 24 becomes low, they can be automatically charged.

The power storage device 24 has a power storage control device 24a. A known battery management system (BMS) can be used as the power storage control device 24a. The power storage control device 24a monitors the voltage, current, temperature, and state of charge (SOC) of each cell as the status of the power storage device 24. The power storage control device 24a also adjusts the charging and discharging of each cell inside the power storage device 24. Note that, depending on the power storage device 24, it may not be necessary to adjust the charging and discharging using the power storage control device 24a.

Figure 5 shows an example of the correlation between the charge capacity (SOC) and voltage value (natural potential, open circuit voltage: OCV) of the power storage device 24. The voltage value of the power storage device 24 increases as the charge capacity increases and decreases as the charge capacity decreases. A lower limit voltage value Va is set for the voltage value, at which the electric motor 23 no longer operates as instructed by the control device 16. The lower limit voltage value Va is lower than the rated voltage value Vc of the converter 21. The lower limit voltage value Va is, for example, 85% or more of the rated voltage value Vc. This lower limit voltage value Va varies depending on the specifications of the inverter 22 and the electric motor 23. The charge capacity at which the voltage value reaches the lower limit voltage value Va is set as the lower limit charge capacity Sa of the power storage device 24. If full discharge (complete discharge) is defined as 0% and full charge (complete charge) is defined as 100%, the lower limit charge capacity Sa is, for example, approximately 20%.

If the charge capacity of the storage device 24 is equal to or greater than the lower limit charge capacity Sa, an inrush current occurs during power running of the electric motor 23. If the power output from the converter 21 is insufficient to supply power to the inverter 22, the storage device 24 discharges DC power to compensate for the shortfall. Furthermore, if the charge capacity is less than the lower limit charge capacity Sa, the storage device 24 charges with DC power output from the converter 21 in accordance with the difference between the rated voltage value Vc of the converter 21 and its own voltage value. At this time, the storage device 24 is charged to the upper limit charge capacity Sb, at which the voltage value becomes the rated current value Vc. Additionally, if the storage device 24 is not fully charged, it charges with power generated during regenerative operation of the electric motor 23. At this time, the storage device 24 can be charged beyond the upper limit charge capacity Sc until it is fully charged (100%). When the charge capacity is fully charged, charging is stopped to prevent overcharging. To prevent overcharging, charging may be stopped when the storage device 24 reaches a charge capacity less than full charge. The charge capacity just before full charge, at which charging stops, is, for example, around 80%.

When the converter 21 and the control device 16 are connected via signal line 26, the control device 16 not only transmits commands regarding the rotational speed of the electric motor 23 to the inverter 22, but also controls the limiting of the current value of the DC power output from the converter 21 and the lifting of the limit. Specifically, the control device 16 is connected to the power storage control device 24a via signal line 26 and constantly monitors the charge capacity of the power storage device 24. The control device 16 compares the charge capacity with the lower limit charge capacity Sa and executes data processing to impose a limit on the current value of the DC power output from the converter 21 if the charge capacity is equal to or greater than the lower limit charge capacity Sa. On the other hand, the control device 16 executes data processing to lift the limit on the current value of the DC power output from the converter 21 if the charge capacity is less than the lower limit charge capacity Sa. By executing such data processing, it is possible to avoid a situation in which, when an inrush current occurs in the electric motor 23, the power storage device 24 is unable to make up for the shortfall, resulting in a delay in the operation of the electric motor 23. Therefore, by connecting the converter 21 and the control device 16 via signal line 26, it becomes possible to limit the converter 21's output current value and control the release of that limit, which is advantageous in eliminating the impact of the limit on the loading and unloading operations of the crane 10.

The various loading and unloading operations, namely the travel of the crane 10 by the traveling device 15, the lateral movement of the trolley 12, and the lifting and lowering of the hoisting device 13, may be performed simultaneously. For example, the lifting and lowering operation of the hoisting device 13 may be initiated while the trolley 12 is moving laterally, or the lateral movement of the trolley 12 may be initiated while the hoisting device 13 is moving laterally. When multiple loading and unloading operations are performed simultaneously on a single crane 10, the control device 16 can adjust each loading and unloading operation so that the electric motor 23 is regeneratively driven during one loading and unloading operation and the electric motor 23 is powered during the other loading and unloading operation. In this case, the power shortage caused by an inrush current in the electric motor 23, which is powered by limiting the current value of the DC power output from the converter 21, can be covered by the power generated by the regeneratively driven electric motor 23.

At the logistics facility 1, each of the numerous cranes 10 performs loading and unloading operations at its own timing. Therefore, the control device 16 may release the restriction on the current value of the DC power output from the converter 21 based on the timing of each loading and unloading operation. Specifically, the timing of each loading and unloading operation is aggregated by the management system 6, and based on the aggregated timing, the management system 6 identifies a timing at which the inrush current generation periods ΔTp of the cranes 10 do not overlap. The identified timing is then transmitted from the management system 6 to each control device 16. Next, at the timing received, the control device 16 releases the restriction on the current value of the DC power output from the converter 21 or changes the value of the limit current value Ib.

In this way, by connecting the control device 16 and the converter 21 via the signal line 26, the control device 16 can limit the output current value of the converter 21, lift the limit, or change the value of the limit current value Ib, depending on the charge capacity of the power storage device 24 and the power supply status of the power supply device 7. When determining whether to limit or lift the limit, the control device 16 should prioritize ensuring that the current value of the power supply device 7 does not exceed the allowable current value Ia. While the impact of the limit on the loading and unloading operations of the cranes 10 is limited to a reduction in the loading and unloading efficiency of a single crane 10, a shutdown of the power supply device 7 will result in the halt of all loading and unloading operations at the logistics facility 1, significantly reducing loading and unloading efficiency. Therefore, prioritizing ensuring that the current value of the power supply device 7 does not exceed the allowable current value Ia is advantageous in avoiding a situation in which the power supply device 7 shuts down.

Next, we will explain the operation of the embodiment of the crane 10. Specifically, we will explain the operation of the crane 10 in a series of operations in which the hoisting device 13 lowers to grab the load 3, and then the hoisting device 13 raises to lift the load 3.

Figure 6 shows the flow of power during the lowering operation of the hoisting device 13. When the hoisting device 13 is lowered, the lifting motor 23b is driven regeneratively. The power generated by this regenerative drive is supplied from the hoisting device inverter 22b via the common line 25 to the converter 21 and the power storage device 24. The power supplied to the converter 21 is consumed via the power supply device 8 for powering operations of other cranes 10 (traverse operation of the trolley 12, lifting operation of the hoisting device 13, and traveling operation of the crane 10 by the traveling device 15). The power supplied to the power storage device 24 is stored in the power storage device 24 unless the charge capacity of the power storage device 24 is not fully charged.

Figure 7 shows the flow of power while an inrush current is occurring in the lift motor 23b immediately after the lifting device 13 begins to rise. When the lifting device 13 begins to rise, the lift motor 23b is powered. The power consumed by the lift motor 23b during this powered operation (power supplied to the lifting device inverter 22b) is primarily supplied by the power supplied from the converter 21. However, because the current value of the DC power output from the converter 21 is limited to the limit current value Ib, if an inrush current occurs immediately after the lift motor 23b begins to operate, the DC power supplied from the converter 21 alone is insufficient. At this time, DC power stored in the storage device 24 is supplied to the lift inverter 22b via the common line 25 to make up for the shortfall.

Figure 8 shows the flow of power after the inrush current generated in the lifting motor 23b subsides during the lifting operation of the hoisting tool 13. If the charge capacity of the power storage device 24 falls below the lower limit charge capacity Sa by compensating for the shortfall caused by the inrush current generated in the lifting motor 23b, the power supplied from the converter 21 is stored in the power storage device 24. In this way, by charging the power storage device 24 using the float charging method, it is possible to avoid a situation where the charge capacity is insufficient and the shortfall caused by the inrush current during the next powering operation cannot be compensated for.

As described above, according to this embodiment, the current value of the DC power output from the converter 21 is limited. If an inrush current occurs when the electric motor 23 is powered, the power supplied from the converter 21 to the inverter 22 will be insufficient. However, this shortfall is made up for by the power storage device 24. In other words, a power shortage will not occur when an inrush current occurs, and an increase in the current value output from the power supply device 7 due to the occurrence of an inrush current can be more reliably suppressed. This prevents the current value output by the power supply device 7 from exceeding the allowable current value Ia, and the current value can be maintained below the allowable current value Ia. This is advantageous in avoiding situations where the power supply device 7 is shut down, and contributes to improved loading and unloading efficiency by ensuring stable loading and unloading at the logistics facility 1.

Furthermore, according to this embodiment, the inverter 22 and the power storage device 24 are always connected in parallel to the converter 21, so that the power storage device 24 automatically compensates for any shortfall in power supply to the inverter 22 caused by limitations on the converter 21's output current value. Furthermore, the power storage device 24, whose charge capacity has become low, can automatically charge the converter 21's output power. In this way, this embodiment, while having a relatively simple configuration, can maintain the output current value of the power supply device 7 below the allowable current value Ia by taking measures against inrush current.

Next, we will explain variant 1 of the crane 10A embodiment.

Each of the cranes 10A illustrated in FIG. 9 is equipped with an independent power supply device 30. It is not necessary for all cranes 10A in the logistics facility 1 to be equipped with a power supply device 30. For example, depending on the logistics facility 1, each transfer crane 10a may be equipped with an independent power supply device 30, and each gantry crane 10b may receive power from a common power supply device 7.

The power system 20A illustrated in FIG. 10 differs from the power system 20 described above in that its power source is a power supply device 30. The power supply device 30 includes an internal combustion engine 31 that uses hydrogen fuel and a generator 32 that rotates using the power of the internal combustion engine 31. The internal combustion engine 31 can be any of various known engines that use hydrogen fuel. The generator 32 can be any of various known generators. By limiting the current value of the DC power output from the converter 21 to the limited current value Ib, the current value of the AC power output from the generator 32 is similarly limited to the limited current value Ib. Accordingly, the internal combustion engine 31 can operate at a roughly constant rotational speed without needing to significantly increase its rotational speed. It is desirable to set the power supply device 30 so that the fuel efficiency of the internal combustion engine 31 is maximized when the current value of the AC power output from the generator 32 is at the rated current value Ir. For example, fuel efficiency can be adjusted by adjusting the specifications of the internal combustion engine 31 and the generator 32, or the speed ratio between the rotational speed of the internal combustion engine 31 and the rotational speed of the generator 32.

According to variant 1, the current value of the DC power output from the converter 21 is limited to the limited current value Ib, which is smaller than the peak current value Ip, so the current value of the AC power output from the power supply device 30 can be prevented from exceeding the limited current value Ib. In other words, by maintaining the current value of the AC power output from the generator 32 below the limited current value Ib, a significant increase in the rotational speed of the internal combustion engine 31 is suppressed. This allows the internal combustion engine 31 to operate at a rotational speed that is advantageous for fuel efficiency, which is advantageous for improving fuel efficiency.

Immediately after the internal combustion engine 31 starts operating, the power generated by the generator 32 may not reach the desired amount of power. Therefore, the power stored in the power storage device 24 can be used until the power generated by the generator 32 stabilizes. This is advantageous for shortening the time required to start the crane 10.

Although an embodiment of the present invention has been described above, the crane of the present invention is not limited to a specific embodiment, and various modifications and variations are possible within the scope of the present invention.

The control device 16 may adjust the charging and discharging of the power storage device 24 via the power storage control device 24a. The control device 16 controls the loading and unloading operations of the crane 10 (the traverse operation of the trolley 12, the lifting and lowering operation of the hoisting device 13, and the traveling operation of the crane 10 using the traveling device 15). In other words, the control device 16 can roughly predict the power balance and the timing of inrush current occurrence during the loading and unloading cycle. Therefore, the control device 16 may control the charging and discharging of the power storage device 24 based on the predicted power balance and the timing of inrush current occurrence. For example, if the charge capacity of the power storage device 24 falls below the lower limit charge capacity Sa and charging of the power storage device 24 begins, the control device 16 controls the end of the charging based on the power balance and the timing of inrush current occurrence. In this way, by charging and discharging the power storage device 24 based on the loading and unloading cycle of the crane 10 and the timing of inrush current occurrence, it is possible to avoid situations where the power storage device 24 is unable to take measures against inrush current or is unable to charge.

7 Power supply device 8 Power supply device 10 Crane 16 Control device 20 Power system 21 Converter 22 Inverter 23 Electric motor 24 Power storage device 25 Common line 26 Signal line

Claims (7)

A crane including a converter that converts AC power from a power supply device into DC power, an inverter that converts the DC power output from the converter into AC power, and an electric motor that is driven by the AC power output from the inverter,
a current value of the DC power output from the converter is limited to a limited current value that is equal to or greater than a rated current value of the converter and is smaller than a peak current value due to an inrush current generated when the electric motor is driven in power running mode,
a power storage device connected in parallel with the inverter to the converter at least during a time including a time during which a current value of AC power supplied from the inverter to the electric motor is greater than the limited current value. The crane described in claim 1, wherein the power storage device is always connected in parallel with the inverter to the converter. The crane described in claim 1 is equipped with a control device connected to the converter via a signal line and performing data processing to limit the current value of the DC power output from the converter to the limited current value. The crane described in claim 3, wherein the control device performs data processing to monitor the charge capacity of the power storage device, limit the current value of the DC power output from the converter to the limited current value when the charge capacity is equal to or greater than a preset lower limit charge capacity, and lift the limit on the current value when the charge capacity is less than the lower limit charge capacity. The crane described in claim 1, wherein the limit current value is greater than or equal to 1.0 times and less than or equal to 1.5 times the rated current value of the converter. The crane described in claim 1, wherein the power supply device is shared by multiple cranes operated at a logistics facility, and AC power is supplied from the power supply device to the converter via a power feeder. The crane described in claim 1, wherein the power supply device includes an internal combustion engine that uses hydrogen fuel and a generator that rotates using the power of the internal combustion engine.