Motorized crane and control method thereof

Abstract

To provide a motorized crane capable of stably maintaining desired cargo handling efficiency with lower fuel consumption, and a control method thereof.SOLUTION: The power generation system includes a power storage device 5 having a plurality of sets of inverters 2 and motors 3 and three storage batteries 4, a power generation device 6A, and an arithmetic device 7. In the discharging control, the power storage device 5 is discharged to supply DC power to the inverters 2, the inverters 2 convert the DC power into AC power, and the motors 3 are driven by the AC power, and in the charging control, when the SOC of the power storage device 5 is less than a preset lower limit La, the power generation device 6A generates power to charge the power storage device 5, and when the SOC of the power storage device 5 exceeds a preset upper limit Lb, the power generation device 6A stops generating power.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electric crane and a control method thereof, and more particularly to an electric crane and a control method thereof that can stably maintain a desired cargo handling efficiency with lower fuel consumption. [Background technology]

[0002] Patent Document 1 proposes a crane that travels using power supplied from a high-power battery and performs crane operations such as swinging and / or winching. The crane described in Patent Document 1 runs and performs crane operations using only the power from the high-power battery, so no fuel is consumed during loading and unloading. However, the number of crane operations is greatly dependent on the charge capacity of the high-power battery. Even if the charge capacity of the high-power battery of the crane described in Patent Document 1 were increased, charging of the high-power battery would be unavoidable.

[0003] Electric cranes operated at container terminals are required to maintain a cargo handling efficiency of approximately 17 containers per hour for three to four consecutive hours. Therefore, even if the crane described in Patent Document 1 were operated at a container terminal, the aforementioned performance requirement could not be met because container handling would be interrupted every time the crane was charged, resulting in a decrease in cargo handling efficiency. Therefore, electric cranes use electricity generated by a power generator to cover the electricity required for container handling. However, because the power generator is constantly running, reducing fuel consumption is an issue. Therefore, further development is needed to enable electric cranes to stably maintain the desired cargo handling efficiency with lower fuel consumption. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2024-2730 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide an electric crane that can stably maintain a desired cargo handling efficiency with lower fuel consumption and a control method thereof. [Means for solving the problem]

[0006] The electric crane of the present invention that achieves the above-mentioned object is an electric crane that includes a plurality of sets of inverters and electric motors, an electric storage device having one or more storage batteries, and a power generation device, and further includes a calculation device that executes discharge control and charge control of the electric storage device, wherein in the discharge control, the electric storage device discharges and DC power is supplied to the inverter, the inverter converts the DC power to AC power, and the electric motor is driven by the AC power, and in the charge control, when the charging rate of the electric storage device is below a predetermined lower limit value, the power generation device generates power and charges the electric storage device, and when the charging rate of the electric storage device exceeds a predetermined upper limit value, power generation by the power generation device is stopped.

[0007] The control method for an electric crane of the present invention is a control method for an electric crane including a plurality of sets of inverters and electric motors, a power storage device having one or more storage batteries, a power generation device that outputs DC power, and a computing device, wherein the computing device performs discharge control and charge control for the power storage device, the discharge control involves discharging the power storage device to supply DC power to the inverter, converting the DC power to AC power using the inverter, and driving the electric motor with the AC power, and the charge control involves causing the power generation device to generate power and charge the storage battery when the charging rate of the power storage device is below a predetermined lower limit value, and controlling to stop power generation by the power generation device when the charging rate of the power storage device exceeds a predetermined upper limit value. [Effects of the Invention]

[0008] According to the present invention, the power required for loading and unloading is provided by discharging the power storage device, and the power generation device operates intermittently based on the charge rate of the power storage device, regardless of the loading and unloading status driven by the electric motor. This reduces fuel consumption by the power generation device compared to continuous operation of the power generation device. Furthermore, even if the power required for loading and unloading is provided solely by discharging the power storage device, the charge rate of the power storage device can be appropriately maintained by intermittent operation of the power generation device, thereby reducing the frequency of interruptions to loading and unloading solely for the purpose of charging the power storage device. As a result, the desired loading and unloading efficiency can be stably maintained with lower fuel consumption. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is an explanatory diagram illustrating a main part of an embodiment of a motorized crane. [Figure 2] FIG. 10 is an explanatory diagram illustrating a main part of another embodiment of the motorized crane. [Figure 3] FIG. 1 is a flowchart illustrating the steps of a control method for an electric crane. [Figure 4] FIG. 1 is a graph illustrating a test cycle path. [Figure 5] FIG. 2 is a graph illustrating the transition of the capacity retention rate of a storage battery. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an electric crane and a control method thereof according to the present invention will be described based on an embodiment shown in the drawings.

[0011] The main parts of the embodiments of motorized cranes 1A and 1B illustrated in FIGS. 1 and 2 show the power systems of the motorized cranes 1A and 1B. These motorized cranes 1A and 1B are operated at a container terminal and handle containers. The only difference between the motorized cranes 1A and 1B is the power generation system 6A (a DC generator unit: a combination of an internal combustion engine 10, an AC generator 11, and a rectifier circuit 12) and the power generation system 6B (a fuel cell unit: a combination of a fuel cell 13 and a fuel tank 14), which will be described later. The motorized cranes 1A and 1B have a common configuration, except for the power generation system 6A (a DC generator unit: a combination of an internal combustion engine 10, an AC generator 11, and a rectifier circuit 12) and the power generation system 6B (a fuel cell unit: a combination of a fuel cell 13 and a fuel tank 14). The motorized cranes 1A and 1B each include multiple sets of inverters 2 and motors 3, a power storage device 5 having at least one or more storage batteries (secondary batteries) 4, the power generation systems 6A and 6B, and a computing device 7. The motor 3 is installed for, for example, traveling, traversing a trolley, and raising and lowering a hoisting device.

[0012] In this control method for a motorized crane using the motorized cranes 1A and 1B, the arithmetic device 7 executes discharge control and charge control, which will be described later in detail in FIG. 3. In the discharge control, when containers are being loaded and unloaded, that is, when direct current (DC) power is converted to alternating current (AC) power by the inverters 2 and the motors 3 are driven by the AC power, the power storage device 5 is discharged to supply DC power to the inverters 2. In the discharge control illustrated in FIG. 3, when the state of charge of the power storage device 5 is below a lower limit value La, the power generation devices 6A and 6B are caused to generate power and charge the charging devices, and when the state of charge of the charging devices 5 is above an upper limit value Lb, power generation by the power storage devices 6A and 6B is stopped. In this way, in this control method, the DC power required for container loading and unloading by the motorized cranes 1A and 1B is supplied by discharging the power storage device 5, and the power generation devices 6A and 6B operate intermittently based on the state of charge of the power storage device 5. This is advantageous in achieving both a reduction in the amount of fuel consumed by the power generation devices 6A and 6B and a reduction in the frequency of interruptions to cargo handling work due to charging of the power storage device 5. The charging rate of the power storage device 5 will be described later.

[0013] First, we will explain the details of the motorized cranes 1A and 1B shown in Figures 1 and 2. In Figures 1 and 2, dashed lines indicate the flow of AC power, solid lines indicate the flow of DC power, and dashed arrows indicate signal lines.

[0014] Various known cranes can be used for the motorized cranes 1A and 1B. The motorized cranes 1A and 1B are, for example, gantry cranes and transfer cranes. The motorized cranes 1A and 1B are not limited to cranes operated in container terminals, but may also be overhead cranes, bucket unloaders, jib cranes, stacker cranes, etc.

[0015] Various known DC-AC inverters and three-phase motors can be combined and used as multiple sets of inverters 2 and motors 3. Each inverter 2 converts DC power into three-phase AC power and supplies the converted three-phase AC power to each motor 3, which is then controlled to drive the motor 3 at a desired rotation speed. When motorized cranes 1A and 1B are transfer cranes, these inverters 2 and motors 3 are used, for example, for traveling, for traversing the trolley, and for raising and lowering the hoisting device.

[0016] 1 and 2, auxiliary equipment such as lighting devices and hydraulic supply systems are not shown, but actual motorized cranes 1A and 1B are equipped with various known auxiliary equipment. These auxiliary equipment are connected to the power storage device 5 via an inverter, and are supplied with DC power from the power storage device 5, as are the multiple sets of inverters 2 and electric motors 3, or AC power converted by the inverter. In this way, in motorized cranes 1A and 1B, all equipment related to cargo handling operations is motorized, and the power for all of these equipment is supplied by discharging the power storage device 5 (discharging each storage battery 4).

[0017] Various known storage batteries (secondary batteries) such as lithium ion batteries can be used as the storage battery 4. A single storage battery 4 has multiple packs (battery packs) connected in parallel and / or series. The pack is configured, for example, using a cell-to-module (CTM) system, in which a module (battery pack) combining multiple cells, a protection circuit, a battery management system (BMS), a charge / discharge circuit, a cooling mechanism, and the like are housed in a single case. The storage battery 4 may also be packed using a cell-to-pack (CTP), cell-to-body (CTB), cell-to-chassis (CTC), or other system.

[0018] The power storage device 5 has three storage batteries 4 connected in parallel (three systems). Having multiple storage batteries 4 (multiple systems) connected in parallel in the power storage device 5 is advantageous for increasing the overall charge / discharge capacity of the power storage device 5 while ensuring ease of maintenance in the event of a failure and a stable power supply. The number of storage batteries 4 provided in the power storage device 5 is not limited to multiple, and may be one if the performance conditions required for motorized cranes at container terminals (for example, a performance condition of maintaining a cargo handling efficiency of about 17 items per hour for 3 to 4 consecutive hours) are met. Furthermore, the number of storage batteries 4 provided in the motorized cranes 1A and 1B may be two (two systems) or more than three.

[0019] This power storage device 5 further has two chopper circuits 8 and three multiplexing DC reactors 9, and the multiplexing DC reactors 9 are multiplexed in the number of chopper circuits 8. In this power storage device 5, one storage battery 4 is connected to each of the two chopper circuits 8 via one multiplexing DC reactor 9. That is, in this power storage device 5, two chopper circuits 8 are connected in parallel to each inverter 2, and three storage batteries 4 are connected in parallel.

[0020] The chopper circuit 8 may be a DC-DC converter having a known armature chopper control (switching) circuit (e.g., a thyristor chopper circuit). The multiplexed DC reactor 9 is formed by multiplexing DC reactors equal in number to the number of chopper circuits 8. Known DC reactors may be used for these DC reactors. Generally, in order to adjust the voltage and current of the DC power charged and discharged to the storage batteries 4 to desired values, one storage battery 4 is connected in series to one chopper circuit 8 via one DC reactor (a non-multiplexed DC reactor). Therefore, if the power storage device 5 has multiple storage batteries 4, the same number of chopper circuits 8 and DC reactors as the number of storage batteries 4 are required. However, the greater the number of storage batteries 4, the greater the number of chopper circuits 8, which makes the entire device heavier, larger, and more expensive. Therefore, by connecting one storage battery 4 in series to each chopper circuit 8 via a multiplexed DC reactor 9 in which DC reactors are multiplexed, the number of chopper circuits 8 can be made smaller than the number of storage batteries 4. As a result, it is advantageous in suppressing the increase in the overall size and cost of the power storage device 5, which would otherwise be caused by having multiple storage batteries 4.

[0021] Charging and discharging in the power storage device 5 is controlled by a calculation device 7, which will be described later. When the power storage device 5 has a plurality of storage batteries 4 and at least two or more chopper circuits 8, it becomes possible to control each chopper circuit 8 separately for discharging and charging. The two chopper circuits 8 may be bidirectional circuits for charging and discharging, or one of the two chopper circuits 8 may be dedicated to discharging and the other chopper circuit 8 may be dedicated to charging. In the embodiment, the two chopper circuits 8 are synchronized to be controlled to charge or discharge simultaneously.

[0022] When the power storage devices 5 of the motorized cranes 1A, 1B are performing cargo handling, the respective storage batteries 4 may be discharged simultaneously or may be discharged one by one at a different timing, and when the power storage devices 5 are charged, the respective storage batteries 4 may be charged simultaneously or may be charged one by one at a different timing. In the embodiment, when the power storage devices 5 are discharging, all of the respective storage batteries 4 are discharged simultaneously, and when the power storage devices 5 are charging, the respective storage batteries 4 are charged individually at different timings.

[0023] The discharge capacity [Ah] of the power storage device 5 (total discharge capacity of the three parallel-connected storage batteries 4) can be selected arbitrarily according to the specifications of the motorized cranes 1A, 1B. When the motorized cranes 1A, 1B are transfer cranes, the discharge capacity of one storage battery 4 may be such that the transfer crane can operate continuously for about one hour by discharging only from one storage battery 4 and can load and unload 15 to 20 containers. For example, the discharge capacity of one storage battery 4 is 225 Ah or more and 50 Ah or less, and the total discharge capacity of the three parallel-connected storage batteries 4 is 75 Ah or more and 150 Ah or less.

[0024] Known power generation devices that consume fuel to generate electricity and output DC power can be used for the power generation devices 6A and 6B. The power generation devices 6A and 6B are connected in series to the power storage device 5 and also to each inverter 2. That is, the power storage device 5 and each inverter 2 are connected in parallel to the power generation devices 6A and 6B. The power generation device 6A is a DC generator unit that combines an internal combustion engine 10, an AC generator 11, and a rectifier circuit 12, and the power generation device 6B is a fuel cell unit that combines a fuel cell 13 and a fuel tank 14.

[0025] The power generation units 6A and 6B are selectable, and the choice of which one to use can be made at will. The term "selectable" means that the selected power generation unit can be used without substantially changing the configuration of the motorized cranes 1A and 1B other than the power generation units 6A and 6B. In other words, the power generation capacities of the power generation units 6A and 6B are roughly equivalent and interchangeable. The degree of equivalence means, for example, that the difference in power generation capacity between the power generation units 6A and 6B is within a range of ±20 kW. By being able to select between the power generation units 6A and 6B with roughly equivalent power generation capacities, the motorized cranes 1A and 1B can be adapted to suit the environment of the container terminal. For example, the power generation unit 6A (internal combustion engine 10 using a fuel other than hydrogen) can be used until the fuel supply infrastructure for the fuel cell 12 is installed at the container terminal, and the power generation unit 6B can be used after the fuel supply infrastructure for the fuel cell 13 is installed.

[0026] The power generation capacity of the power generation units 6A and 6B can be selected arbitrarily depending on the specifications of the power storage device 5, but it is sufficient if it is large enough to fully charge the power storage device 5, which is charged at a rate of approximately 30% to 50%, in about one hour. For example, if the motorized cranes 1A and 1B are transfer cranes, the power generation capacity of the power generation unit 6A is preferably 40 kW (55 kVA) or more and 100 kW (115 kVA) or less. Furthermore, the power generation capacity of the power generation unit 6B is preferably 40 kW or more and 80 kW (100 kVA) or less. The smaller the power generation capacity, the more advantageous it is for the power generation units 6A and 6B to be made smaller.

[0027] The power generation device 6A is a DC generator unit that combines an internal combustion engine 10, an AC generator 11, and a rectifier circuit 12. Various known internal combustion generators (motor-driven generators) can be used for the combination of the internal combustion engine 10 and the AC generator 11. The fuel used in the internal combustion engine 10 is, for example, fossil fuel, biofuel, ammonia, hydrogen, etc.

[0028] The rectifier circuit 12 is a known X-phase rectifier circuit (where X=3×2) using rectifier elements such as diodes, thyristors, GTO thyristors, and IGBTs (insulated gate bipolar transistors). n (where n=0, 1, 2, 3) can be used. The rectifier circuit 12 preferably has a reactor or a capacitor as a countermeasure against harmonics. For example, if the rectifier circuit 12 is configured as a three-phase bridge rectifier circuit (three-phase full-wave rectifier circuit), it preferably has a smoothing reactor or a smoothing capacitor.

[0029] In this embodiment, an AC generator 11 with a power generation capacity of 100 kW or less is used as the power generation device 6A. The smaller the power generation capacity, the smaller the size of the AC generator 11, and the smaller its heat capacity. For AC generators 11 with such small heat capacity, transient temperature rises caused by AC resistance due to high-frequency magnetic fields generated by currents containing harmonic components can cause malfunctions, making harmonic countermeasures important. Therefore, a known 12-phase thyristor rectifier circuit or a 24-phase rectifier circuit may be used for the rectifier circuit 12. For example, a known 12-phase rectifier circuit includes one or a pair of transformers and a pair of three-phase bridge rectifier circuits. The transformers generate three-phase AC currents with different phases, and each of the generated three-phase AC currents is rectified by a respective three-phase bridge rectifier circuit. Even in these 12-phase rectifier circuits or 24-phase rectifier circuits, smoothing reactors and smoothing capacitors can be used as additional countermeasures against harmonics.

[0030] The rectifier circuit 12 of this embodiment is configured as a 12-phase rectifier circuit including a pair of three-phase rectifiers 15a, 15b and three AC reactors 16. The pair of three-phase rectifiers 15a, 15b are connected in series with each other via a connection point with the AC generator 11. Each of the three-phase rectifiers 15a, 15b is, for example, a six-pulse rectifier using three diodes as rectifying elements. Each of the AC reactors 16 is disposed on each electric wire between the three-phase rectifier 15b and the connection point. Each of the AC reactors 16 delays the phase of the three-phase AC flowing through the three-phase rectifier 15b relative to the phase of the three-phase AC flowing through the three-phase rectifier 15a. In other words, each of the AC reactors 16 adjusts the phase difference between the respective three-phase ACs. The phase difference between the three-phase AC currents flowing through the three-phase rectifier 15a and the three-phase rectifier 15b can be selected arbitrarily, and is, for example, 60°.

[0031] In this rectifier circuit 12, the phase difference between the three-phase AC currents flowing through the three-phase rectifiers 15a and 15b is adjusted by the AC reactors 16. This means that the rectifier circuit 12 is simpler than the previously known 12-phase rectifier circuit, which adjusts the phase difference using a transformer, and therefore can rectify (convert AC power to DC power) more efficiently. Furthermore, known 12-phase rectifier circuits using a transformer suffer from a problem of increased voltage drop during rectification when 12-phase rectification is converted to 6-phase rectification due to an imbalance in the impedance or number of turns in the transformer. However, this problem is less likely to occur in this rectifier circuit 12, since it does not use a transformer. Furthermore, because the rectifier circuit 12 uses diodes as rectifying elements, no control is required within the circuit. Therefore, by using this rectifier circuit 12, a power generator 6A can be provided that is less expensive than a power generator using a circuit that uses thyristors as rectifying elements.

[0032] The power generation device 6B is a combination of a fuel cell 13 and a fuel tank 14. For example, the fuel of the fuel cell 13 is hydrogen and the oxidant is oxygen. The fuel cell 13 may be a known fuel cell that generates DC power by chemically reacting a fuel with an oxidant, such as a polymer electrolyte fuel cell (PEFC), a phosphoric acid fuel cell (PAFC), a dissolved carbonate fuel cell (MCFC), or a solid oxide fuel cell (SOFC). The fuel for the fuel cell 13 is stored in the fuel tank 14. In this power generation device 6B, power generation in the fuel cell 13 is controlled by controlling the supply of fuel from the fuel tank 14.

[0033] The arithmetic device 7 is configured as a computer, and various data are input and stored therein, and this data is used to process the data and control each device. Various known computers can be used as the arithmetic device 7. The arithmetic device 7 has a central processing unit (CPU), a main storage unit (memory), and an auxiliary storage unit (e.g., a HDD). There may be multiple arithmetic devices 7, and the multiple arithmetic devices 7 may individually control each inverter 2 and charge / discharge the power storage device 5.

[0034] Next, a control method for the motorized cranes 1A, 1B will be described in detail. In this control method, the arithmetic device 7 executes discharge control and charge control. Since discharge control and charge control cannot be executed simultaneously, execution of discharge control is stopped when charge control is executed. The charge control causes the power generation devices 6A, 6B to perform intermittent operation. Intermittent operation does not refer to the operating state of the internal combustion engine 10 of the power generation device 6A, but refers to the repeated generation and halt of power generation of the power generation devices 6A, 6B. In other words, intermittent operation refers to the presence or absence of power output from the power generation devices 6A, 6B, but does not refer to the presence or absence of fuel consumption in the power generation devices 6A, 6B. For example, in the power generation device 6A, the internal combustion engine 10 may be idling while power generation is stopped; however, in this embodiment, the internal combustion engine 10 stops using fuel and is therefore stopped.

[0035] In the discharge control, the power storage device 5 discharges and supplies DC power to the inverter 2, the inverter 2 converts the DC power to AC power, and the electric motor 3 is driven by the AC power. That is, the discharge control is executed based on whether or not the electric motor 3 is being driven. In the motorized cranes 1A, 1B of the embodiment, the supply of power to the auxiliary machinery is also covered by the discharge of the power storage device 5. That is, the discharge control is executed constantly while the motorized cranes 1A, 1B are operating, except for the period when the charge control is being executed.

[0036] In the charge control illustrated in Fig. 3, when the state of charge of the power storage device 5 is below a preset lower limit La, the power generation devices 6A and 6B are made to generate power to charge the power storage device 5, and when the state of charge of the power storage device 5 is above a preset upper limit Lb, control is executed to stop the power generation of the power generation devices 6A and 6B. The above-mentioned discharge control and this charge control cannot be executed simultaneously, so when the charge control is executed, the discharge control must be stopped. Specifically, when the power generation devices 6A and 6B are made to generate power by the charge control, the execution of the discharge control is stopped to stop the discharge of all the storage batteries 4. Next, the DC power output by the power generation of the power generation devices 6A and 6B is supplied to both the operating inverter 2 and each storage battery 4, so that all the storage batteries 4 are charged simultaneously without interrupting the container loading and unloading operation.

[0037] The charging rate of the power storage device 5 indicates the charging rate when the power storage device 5 is regarded as one rechargeable battery. For example, if the power storage device 5 has only one storage battery 4, the filling rate of that storage battery 4 is used as the charging rate of the power storage device 5. If the power storage device 5 has multiple storage batteries 4, each storage battery 4 is regarded as one storage battery, and the average value of the charging rates of the storage batteries 4 is used as the charging rate of the power storage device 5. In this embodiment, since the power storage device 5 has three storage batteries 4, the average value of the charging rates of the three storage batteries 4 is used as the charging rate of the power storage device 5 in the following description of the discharge control procedure. It is assumed that the multiple storage batteries 4 have the same full charge capacity.

[0038] In step S110, the arithmetic device 6 acquires the state of charge (average state of charge (SOC) of each storage battery 4) of the power storage device 5. The state of charge of the storage battery 4 is acquired by the arithmetic device 6 via a battery management system (BMS) that the storage battery 4 has.

[0039] The charging rate of the storage battery 4 represents the state of charge of the storage battery 4, where a fully charged state of a brand new, undegraded storage battery 4 is set to 100% and a fully discharged state is set to 0%. This charging rate is a value calculated by {(full charge capacity - discharge capacity) / full charge capacity} x 100(%).

[0040] In step S120, the arithmetic device 6 executes data processing to determine whether or not the charging rate of the power storage device 5 is less than a preset lower limit value La. In step S130, the arithmetic device 6 executes data processing to determine whether or not the charging rate of the power storage device 5 is greater than a preset upper limit value Lb.

[0041] The lower limit value La and the upper limit value Lb can be set to any value within a usable range of the charging rate of the power storage device 5. If all of the storage batteries 4 in the power storage device 5 are like new, this range is, for example, a charging rate range of 30% to 90%. If all of the storage batteries 4 in the power storage device 5 are nearing the end of their life, this range is a charging rate range of 21% to 72%, because the charging capacity of storage batteries 4 nearing the end of their life is approximately 70% smaller than the charging capacity of storage batteries 4 in like-new condition. For example, the lower limit value La and the upper limit value Lb may be set to values ​​within a usable range of the charging rate of storage batteries 4 nearing the end of their life. Furthermore, the computing device 7 may perform data processing to vary the lower limit value La and the upper limit value Lb based on the degree of deterioration of the storage batteries 4.

[0042] The lower limit La may take into consideration the amount of power consumed between the start of power generation by the power generation devices 6A, 6B and the time when they are able to output DC power, relative to the lower limit of the usable range of the charging rate of the power storage device 5. The time required for the power generation devices 6A, 6B to cold start from the start of power generation until they are able to output DC power includes the time required for the internal combustion engine 10 to cold start and the time required for the AC generator 11 and fuel cell 13 to stably generate power after starting power generation. Therefore, these times need to be determined in advance, the amount of power consumed by the motorized cranes 1A, 1B during this time period estimated, and the charging rate equivalent to this estimated amount of power added to the lower limit of the usable range. The lower limit La may be, for example, approximately 5% to 15% larger than the lower limit of the usable range of the charging rate of the power storage device 5.

[0043] The upper limit value Lb may take into consideration the amount of regenerative power generated by each electric motor 3 after the power generation of the power generation devices 6A, 6B stops relative to the upper limit of the usable range of the charging rate of the power storage device 5. When the motorized cranes 1A, 1B are transfer cranes, the electric motors 3 used to raise and lower the hoisting devices generate regenerative power when the hoisting devices are lowered. If the electric motors 3 generate regenerative power immediately after charging control is completed when the charging rate of the power storage device 5 is at the upper limit of the usable range, charging the power storage device 5 with this regenerative power will result in overcharging. Therefore, the amount of regenerative power generated by the electric motors 3 may be estimated in advance, and a charging rate equivalent to the estimated amount of regenerative power may be subtracted from the upper limit of the usable range. The upper limit value Lb may be, for example, approximately 5% to 15% smaller than the upper limit of the usable range of the charging rate of the power storage device 5.

[0044] When all the storage batteries 4 in the power storage device 5 are like new and the usable range of the charging rate of the power storage device 5 is between 30% and 90%, for example, the lower limit La is a value within the range of between 35% and 45% and the upper limit Lb is a value within the range of between 75% and 85%. When all the storage batteries 4 in the power storage device 5 are nearing the end of their life and the usable range of the charging rate of the power storage device 5 is between 21% and 72%, the limit La is a value within the range of between 26% and 36%, and the upper limit Lb is a value within the range of between 57% and 67%.

[0045] In step S120, if it is determined that the charging rate of the power storage device 5 is less than the lower limit La, the process proceeds to step S140, and if it is determined that the charging rate of the power storage device 5 is equal to or greater than the lower limit La, the process proceeds to step S130. In step S130, if it is determined that the charging rate of the power storage device 5 is greater than the upper limit Lb, the process proceeds to step S150, and if it is determined that the charging rate of the power storage device 5 is equal to or less than the upper limit Lb, the process returns to step S110.

[0046] In step S140, the arithmetic device 7 controls the power generation devices 6A and 6B to generate power by consuming fuel and charge the power storage device 5, and in step S150, the arithmetic device 7 controls the power generation devices 6A and 6B to stop generating power. In the power generation device 6A, power generation is controlled by controlling the drive of the internal combustion engine 10. In the power generation device 6B, power generation is controlled by controlling the supply of fuel to the fuel cell 13.

[0047] In this discharge control, power generation by the power generation devices 6A, 6B is controlled based only on the charge rate of the power storage device 5, regardless of the drive status of each electric motor 3 and auxiliary equipment, i.e., the power usage status of the motorized cranes 1A, 1B. In other words, the power generation devices 6A, 6B operate intermittently while the motorized cranes 1A, 1B are in operation.

[0048] As described above, according to this embodiment, the power required for loading and unloading is supplied by discharging the power storage device 5, and the power generation devices 6A and 6B are controlled based on the charge rate of the power storage device 5 (the average charge rate of each storage battery 4) and operate intermittently while the motorized cranes 1A and 1B are loading and unloading containers. This allows the charge rate of the power storage device 5 to be maintained appropriately, reducing the frequency of interruptions to loading and unloading operations to charge the power storage device 5. Furthermore, the amount of fuel consumed by the power generation devices 6A and 6B can be reduced compared to continuous operation. As a result, the performance requirement of maintaining a loading and unloading efficiency of approximately 17 units per hour for approximately 3 to 4 hours can be met with lower fuel consumption.

[0049] Furthermore, according to this embodiment, the electric cranes 1A and 1B, which consume a large amount of power, mainly discharge the power storage device 5 to supply the power required for loading and unloading containers. The power generation devices 6A and 6B generate power only when the charge rate of the power storage device 5 drops. In other words, the frequency of fuel-consuming power generation is significantly reduced. Therefore, even if a diesel engine that uses fossil fuels is used as the internal combustion engine 10 of the power generation device 6A, greenhouse gas emissions can be reduced. Furthermore, by using an ammonia engine or a hydrogen engine that uses ammonia or hydrogen as fuel as the power generation device 6A, or a fuel cell 13 as the power generation device 6B, greenhouse gas emissions can be reduced to zero. As such, this embodiment provides the electric cranes 1A and 1B that are excellent in environmental protection, which greatly contributes to achieving environmental goals such as carbon neutrality and zero emissions.

[0050] In this embodiment, the power generation units 6A and 6B are selectable, and the optimum power generation unit can be selected each time. For example, in the initial stage, a diesel engine is used as the internal combustion engine 10 as in the past, and in the next stage, an ammonia engine, a hydrogen engine, or a fuel cell 13 is used as the internal combustion engine 10. In this way, greenhouse gas emissions can be reduced in stages, and ultimately reduced to zero.

[0051] The charging control illustrated in Fig. 3 above is control performed while the motorized cranes 1A, 1B are in operation. When the operation of the motorized cranes 1A, 1B is stopped, the power generation devices 6A, 6B may be caused to generate power to charge the power storage device 5 regardless of the charging rate of the power storage device 5.

[0052] When the power storage device 5 has multiple storage batteries 4, the charging rate of each storage battery 4 can be treated as the charging rate of an individual power storage device 5. In the discharge control, all the storage batteries 4 are discharged simultaneously, so the charging rate of the power storage device 5 (the average value of the charging rates of each storage battery 4) is approximately equal to the charging rate of each storage battery 4. Therefore, the charging control may be performed based on the individual charging rates of each storage battery 4 instead of the charging rate of the power storage device 5 (the average value of the charging rates of each storage battery 4). In this case, the charging control is performed when the charging rate of one storage battery 4 falls below the lower limit La, but the charging rates of the other two storage batteries 4 are also near the lower limit La. Therefore, whether the average value of the charging rates of each storage battery 4 or the individual charging rates of each storage battery 4 is used, the frequency of power generation by the power generation devices 6A and 6B is approximately the same. [Example]

[0053] Table 1 below shows whether or not each actual crane (Examples 1 to 6, Comparative Example) with a similar configuration to the electric crane 1A shown in Fig. 1 can handle eight hours of continuous cargo handling and whether or not it can handle four hours of continuous cargo handling under different conditions. Each actual crane was made to handle cargo according to the test cycle path shown in Fig. 4.

[0054] [Table 1]

[0055] The actual crane used was a transfer crane for container handling equipped with three sets of inverters 2 and electric motors 3: one for traveling, one for traversing the trolley, and one for raising and lowering the spreader (hoisting device). Each actual crane used three parallel-connected storage batteries 4, each consisting of 18 battery packs, as the power storage device 5. The discharge capacity of each storage battery 4 was 48 Ah. Two chopper circuits 8 and three multiplexed DC reactors 9 were used to connect the three storage batteries 4. Furthermore, each actual crane used a diesel engine fueled by light oil as the internal combustion engine 10 of the power generation device 6A, and a 12-phase rectifier circuit equipped with a pair of three-phase rectifiers 15a, 15b and three AC reactors 16 as the rectifier circuit 12.

[0056] The loading / unloading efficiency [units / h] is the target value for loading / unloading of each actual machine, and indicates the number of containers loaded per hour. The power generation capacity [kW] indicates the power generation capacity of the AC generator 11. During charging control, the capacity of the DC power output from the AC generator 11 and charged to each storage battery 4 of the power storage device 5 via the rectifier circuit 12 is approximately 80% of the power generation capacity. In the comparative example, the power generation capacity is 0 [kW] because loading / unloading was performed only by discharging the power storage device 5 without generating power from the power generation device 6A. During charging control, the lower limit La was set to a charging rate of 40% and the upper limit Lb was set to a charging rate of 80%. During charging control, the internal combustion engine 10 was operated at idle while the power generation of the power generation device 6A was stopped.

[0057] Each actual machine was made to load and unload a 40.6 ton 20-foot test weight as a test container between points A and B. Under the cycle conditions, the power consumption for traveling [kW] and the main hoisting distance [cm] at point A (the lifting distance of the hoisting tool at point A) were adjusted to achieve the loading and unloading efficiency. In Examples 3 and 6, the loading and unloading efficiency was set to 35 [pieces / h], and the actual machine was not run, so the power consumption for traveling was 0 [kW].

[0058] In the test cycle path shown in Figure 4, the horizontal axis represents time [s] and the vertical axis represents speed [%]. The dashed line in Figure 4 represents the time change in the running speed of the actual machine, the dashed line represents the time change in the traverse speed of the actual machine, and the solid line represents the time change in the spreader lift (main hoist) speed of the actual machine. A speed of 100% represents the rated speed, with the rated running speed of 90 m / min, the traverse speed of 70 m / min, and the main hoist speed of 23 m / min. Following this test cycle path, each actual machine shuttled a test container between points A and B immediately after starting the test. Then, without a test weight attached, the hoist shuttled between points A and B. Assuming that the hoist shuttled between points A and B, a back-power resistor was used to consume power equivalent to the amount consumed in one run. The time required for each operation was calculated based on the speed and cycle conditions of each operation, and the cycle time required to load one test weight was calculated based on the time required for each operation. The calculated cycle time / unit was compared with the inverse of the loading efficiency to adjust the waiting time.

[0059] To determine whether continuous loading and unloading was possible, the change in the charge rate of the power storage device 5 (the average charge rate of each storage battery 4) when each actual machine was subjected to continuous loading and unloading for 8 or 4 hours was estimated based on the loading and unloading time and SOC change in Table 1, and a determination was made as to whether the estimated change exceeded the judgment criterion. Continuous loading and unloading for 8 or 4 hours means that the power storage device 5 in which loading and unloading was interrupted was not charged during the 8 or 4 hours. The judgment criterion was set based on the usable range of the charge rate of the power storage device 5. The usable range of a new storage battery 4 is between 30% and 90%, and the upper limit of the charge rate of each storage battery 4 drops to 70% near the end of its life. Therefore, the judgment criterion was set at 42% (90% - 30% = 60% x 0.7).

[0060] The change in the charge rate of the power storage device 5 over eight hours of continuous loading and unloading is -21.6% (-2.7% x 8) for Example 1, -38.0% (-1.9% x 20) for Example 2, -28.0% (-3.5% x 8) for Example 3, 28.8% (1.6% x 16) for Example 4, 76% (9.5% x 8) for Example 5, and 65.6% (8.2% x 8) for Example 6. The change in the charge rate of the power storage device 5 over four hours of continuous loading and unloading is 36% (9.5% x 4) for Example 5 and 32.8% (8.2% x 4) for Example 6. Therefore, in Examples 1 to 4, the change in the charge rate of the power storage device 5 over eight hours of continuous loading and unloading is below the judgment criterion, and it is therefore clear that there is no need to interrupt loading and unloading to charge the power storage device 5 during continuous loading and unloading for eight hours or less. In Examples 5 and 6, the change in the charge rate of the power storage device 5 during eight hours of continuous loading and unloading exceeded the evaluation criteria, but the change in the charge rate of the power storage device 5 during four hours of continuous loading and unloading was below the evaluation criteria. Therefore, in Examples 5 and 6, it is clear that during eight hours of continuous loading and unloading, it is necessary to interrupt loading and unloading to charge the power storage device 5, but during four hours of continuous loading and unloading, it is not necessary to interrupt loading and unloading to charge the power storage device 5. In the comparative example, the SOC change in approximately 0.8 hours is 41%. This means that approximately 16 containers can be loaded and unloaded in approximately 0.8 hours without generating electricity from the power generation device 6A. However, in the comparative example, loading and unloading must be interrupted approximately every 0.8 hours to generate electricity from the power generation device 6A and charge the power storage device 5, which means that 16 containers per hour cannot be loaded and unloaded for four hours continuously, resulting in low loading and unloading efficiency.

[0061] Cranes operated at container terminals are required to maintain a handling efficiency of approximately 17 units per hour for approximately 3 to 4 consecutive hours. It can be seen that Examples 1 to 6 fully satisfy this performance condition. A handling efficiency of 35 [units / h] corresponds to the handling efficiency during loading and unloading on a ship. Therefore, it can be seen that Examples 3 and 6 can also be applied to loading and unloading on a ship. Furthermore, it can be seen that Examples 1 to 6 allow the power generation capacity of the AC generator 11 to be reduced to a maximum of 40 kW, that is, the AC generator 11 can be made even more compact.

[0062] The expected SOC change amount and the test-obtained SOC change amount are roughly the same in each of Examples 1 to 6. Therefore, the simulation results can be used to develop and manufacture an appropriate motorized crane according to the specifications of the container terminal.

[0063] In Examples 1 to 6, the frequency of charging and discharging the power storage device 5 (each storage battery 4) is high. The higher the frequency of charging and discharging the power storage device 5, the shorter the life of the power storage device 5 tends to be. Therefore, the progress of deterioration of the power storage device 5 was predicted using a computer simulation.

[0064] Figure 5 shows the results of a simulation using an electric crane with the same configuration as Example 1 in Table 1 above, where a cargo handling efficiency of 17 [units / h] was achieved. In this simulation, one set of cargo handling was defined as a total of eight hours per day, followed by a one-hour shutdown for charging the power storage device 5. The solid line in Figure 5 shows the results of one set per day in an environment with an ambient temperature of 25°C, the dashed line shows one set per day in an environment with an ambient temperature of 30°C, the dashed line shows two sets per day in an environment with an ambient temperature of 25°C, and the dashed double-dashed line shows two sets per day in an environment with an ambient temperature of 30°C. The capacity retention rate indicates the percentage of the maximum charge rate of a non-degraded, like-new storage battery 4 in a fully charged state (the maximum usable range of the storage battery 4), with 100% being the maximum charge rate. Because the storage battery 4 reaches the end of its life due to its electrical characteristics at a capacity retention rate of around 60%, a capacity retention rate of 70% was set as the criterion for determining the end of its life.

[0065] Under the most severe conditions indicated by the two-dot chain line, it takes about 6.6 years for the capacity retention rate to fall below 70%, and about 9.3 years for the capacity retention rate to fall below 60%. Considering that the lifespan of the structural components of the cells of the storage battery 4 is generally about 10 years, it can be seen that the lifespan of the storage battery 4 in an electric crane configured similarly to that of Example 1 is within a practical range.

[0066] Table 2 below shows the fuel consumption [L / h] when the same container was loaded and unloaded for three hours by actual electric cranes (Examples 7 and 8) in which the power generation capacity of the AC generator 11 and the lower limit value La and upper limit value Lb in the charge control were different from those of Example 1 in Table 1 above, and the operating state of the internal combustion engine 10 was different when power generation was stopped.The power generation capacity of the actual cranes in Examples 7 and 8 was 60 kW.The lower limit value La in the charge control was 40%, and the upper limit value Lb was 90%.

[0067] [Table 2]

[0068] The fuel consumption in Example 8 is about 75% of the fuel consumption in Example 7. In other words, it is clear that the operating state of the internal combustion engine 10 during power generation stop is more preferably a stopped state in which no fuel is consumed than an idling operation.

[0069] Although the embodiments of the present invention have been described above, the motorized crane and control method of the present invention are not limited to the specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0070] 1A, 1B Electric Crane 2 inverters 3 Electric motor 4. Storage battery 5. Energy storage device 6A, 6B power generation equipment 7 Computing device 8 Chopper Circuit 9 Multiplexed DC reactor 10 Internal combustion engine 11 AC generator 12 Rectifier circuit 13 Fuel Cell 14 Tank 15a, 15b three-phase rectifier 16 AC reactor La lower limit Lb upper limit

Claims

1. An electric crane including a plurality of inverter and motor sets, a power storage device having one or more storage batteries, and a power generation device, a computing device that executes discharge control and charge control of the power storage device, In the discharge control, the power storage device is discharged to supply DC power to the inverter, the inverter converts the DC power into AC power, and the electric motor is driven by the AC power. In the charging control, when the charging rate of the power storage device is below a preset lower limit value, the power generation device generates electricity to charge the power storage device, and when the charging rate of the power storage device exceeds a preset upper limit value, power generation by the power generation device stops.

2. The motorized crane according to claim 1 , wherein the stopping of power generation by the power generation device stops the use of fuel by the power generation device.

3. 2. The motorized crane according to claim 1, wherein the power generating device is a DC generator unit or a fuel cell unit, and the power generating capacity is 40 kW or more and 100 kW or less.

4. 4. The motorized crane according to claim 3, wherein the DC generator unit comprises an internal combustion engine, an AC generator, and a rectifier circuit, the rectifier circuit being a 12-phase rectifier circuit.

5. 5. The motorized crane according to claim 4, wherein the 12-phase rectifier circuit includes a pair of three-phase rectifiers and three AC reactors, the pair of three-phase rectifiers are connected in series via a connection point with the AC generator, and each of the AC reactors is disposed in an electric wire between one of the pair of three-phase rectifiers and the connection point.

6. The motorized crane according to claim 1 , wherein the power storage device includes three or more of the storage batteries connected in parallel.

7. 7. The motorized crane according to claim 6, wherein the power storage device includes chopper circuits whose number is smaller than the number of the storage batteries, and multiplexed DC reactors whose number is the same as the number of the storage batteries, the multiplexed DC reactors are multiplexed by the number of the chopper circuits, and one storage battery is connected to each of the chopper circuits via one of the multiplexed DC reactors.

8. A control method for an electric crane including a plurality of sets of inverters and electric motors, a power storage device having one or more storage batteries, a power generation device that outputs DC power, and a computing device, The computing device controls discharging and charging of the power storage device, In the discharge control, the power storage device is discharged to supply DC power to the inverter, the inverter converts the DC power into AC power, and the electric motor is driven by the AC power. In the charge control, when the charging rate of the power storage device is below a preset lower limit value, the power generation device is caused to generate power to charge the storage battery, and when the charging rate of the power storage device exceeds a preset upper limit value, the control method for an electric crane performs control such that power generation of the power generation device is stopped.

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