KR20120110368A - Electric excavator system - Google Patents

Abstract

PURPOSE: An electric excavator system is provided to eliminate restriction to a work space by separating and combining a power supply unit and a power receiving unit. CONSTITUTION: An electric excavator system comprises an electric excavator including a power supply unit(100) and a power receiving unit(200). The power supply unit comprises a power box(110), a cable drum(120), a drum drive unit(122) controlling rotation of the cable drum, and a cable guide(130). The power receiving unit includes a driving motor generator(230) as an engine for a driving source. The driving motor generator receives power of an AC power source in a state a DC power source is converted into the AC power source through an inverter(220). The inverter is controlled by a controller(240). The driving motor generator is connected to a hydraulic pump(260). [Reference numerals] (110) Power box; (120) Cable drum; (122) Drum drive unit; (130) Cable guide; (210a,201b,210c) Storage battery; (212) Overcharge prevention unit; (214) Stored power amount detection unit; (215) Charging and discharging control unit; (220) Inverter; (230) Driving motor generator; (232) Rotation motor generator; (240) Controller; (250) Alarm unit; (260) Hydraulic pump; (270) Hydraulic control valve; (274) Boom cylinder; (276) Arm cylinder; (278) Bucket cylinder; (280) Conversion switch; (AA) External power; (BB) Legend; (CC) Mechanical problem; (DD) Electrical problem; (EE) Hydraulic motion

Description

Electric Excavator System {ELECTRIC EXCAVATOR SYSTEM}

The present invention relates to an electric excavator, and more particularly, having a storage battery therein, so that the work can be performed in a state in which the power supply unit and the power receiving unit are separated, so that the work can be performed remotely without space limitation, and the charging of the storage battery provided therein is provided. The present invention relates to an electric excavator system including an electric excavator having an improved power supply unit and a power receiver unit to control discharge to be performed uniformly to increase the life of a storage battery.

In general, an excavator is a construction machine with various work functions, such as excavation work to dig or fill the ground during construction and civil works, breaker work such as soil and rock crushing, compactor work such as soil compaction, and crusher work such as cutting. Say.

Such an excavator is usually equipped with an engine such as a diesel engine to obtain driving power, and uses the power of the engine to drive a hydraulic pump, and supply hydraulic oil discharged from the hydraulic pump to a hydraulic actuator such as a hydraulic motor or a hydraulic cylinder. As a result, each work part such as a traveling crawler or tire rotation, a boom, an arm, a bucket, or the like is operated.

Since such a well-known excavator is equipped with an engine such as a diesel engine, it has the advantage of being able to work freely without being restricted in the work place.

However, diesel, which is a fossil fuel, is gradually being depleted, and the necessity of alternative energy is seriously raised, and fuel costs are high, and fuel consumption is particularly high due to the peculiarity of heavy equipment.

As part of solving this problem, an electric excavator using electric energy has been disclosed.

The disclosed electric excavator, for example, by replacing the engine for driving the excavator with an electric motor, as shown in the example of FIG. 1 and by supplying the power for driving the motor from an external power source through the cable 10 to reduce the fuel cost by more than 70% For example, an external power box 20, a cable drum 22 to wind the cable 10, and a cable guide 24 to pivot the cable 10 so as to supply power from the outside. And an induction guide 30 installed in the excavator to guide the cable 10 guided out through the cable guide 24 to the excavator safely.

Therefore, the driving of the excavator uses an engine-powered motor mounted on the excavator, and the various work functions of the excavator use the hydraulic operation through the hydraulic pump as it is, but control the driving of the hydraulic pump by an electric motor. The function was performed as is.

However, since the electric excavator is structured to be powered using the cable 10, the range in which the excavator can operate is limited.

That is, since the work can be performed only within the range of the cable 10, the working radius is very limited, and the remote work is not possible, which causes a lot of inconveniences.

In addition, even if the remote operation is possible by using a battery, because the capacity of the battery has a limit, it is also difficult to work for a long time.

As a means for solving the problem, a method of selectively switching the battery using a plurality of batteries as needed may be proposed, and in addition, a method for extending the service life may be better.

In general, a battery used in an electric excavator is composed of a plurality of cells, all initially have the same performance, but as the operation of the electric excavator increases the performance of the cells of the battery.

Nevertheless, since the output of the motor is usually controlled based on the maximum output the battery can produce, after a certain point, the battery cells are discharged in a state exceeding the allowable discharge output. Shortened.

In addition, when the charge and discharge of the battery is not performed uniformly, the shortening of the life of the battery is further accelerated.

The present invention was made in view of the above-mentioned problems in the prior art, and was created to solve this problem. In the cable type electric excavator, the operating range of the excavator is extended to a farther distance than the cable, thereby expanding the scope of work possible and maximizing the work efficiency. In addition to the use of a plurality of batteries, the application range is broadened so that long-range work can be stably performed for a long time, but overcharging and overdischarging can be prevented depending on the condition of the battery. Equipped with a charge and discharge control unit Its main purpose is to provide an electric excavator system.

An electric excavator system having a charge / discharge control unit of the present invention for achieving the above object is provided with a power box including a plurality of control buttons, winding or unwinding a power box that receives an external power source and switches to a charging voltage. Power supply consisting of a cable drum, a drum drive for controlling the rotation of the cable drum, a cable guide connected to the power box and guided so that the charging cable wound on the cable drum is not tangled or twisted; and, the cable is connected / disconnected At least one battery including a cable connector and a motor generator and a controller, and charged with electricity supplied through regenerative braking of the motor and the motor generator, an overcharge preventing unit connected to the battery and preventing overcharging under the control of the controller, It is connected to the battery and detects the potential difference of the battery and outputs it to the controller. Power receiving unit consisting of a charge detection unit, an inverter connected to the storage battery and an inverter that converts the DC power of the storage battery into an AC power supply under the control of the controller and supplies it to the motor generator, and an alarm unit connected to the controller to send an alarm when the detection potential of the battery is lower than the reference potential. Consist of; The power receiver may include a charge / discharge control unit configured to detect charging or discharging states of the storage batteries so that charging and discharging may be performed while driving the storage cells within a predetermined voltage or current range.

The power supply unit is further provided with a switching switch for switching the connection between the battery and the inverter under the control of the controller when the potential of each battery is lower than the reference potential; The controller further includes a memory unit in which a discharge output value according to a state of charge (SOC) of the battery and an internal resistance value for each temperature is stored as a table; A temperature sensor is further installed in the storage battery; The controller further includes an operation unit calculating a current and a voltage based on a potential value detected by the temperature sensor and the charge detection unit, and dividing the voltage by a current to calculate an internal resistance, and stored in a memory unit corresponding to the calculated internal resistance. According to an exemplary embodiment of the present invention, there is provided a battery discharge output control apparatus of an electric excavator, wherein the discharge output is controlled according to an experimental internal resistance table value.

In this case, the controller is characterized in that the discharge output control of the battery is stopped when the battery falls below the reference potential.

According to the present invention, by separating the power supply unit and the power receiving unit can remove the constraints of the work space, improve the work efficiency, eco-friendly, reduce fuel costs, long distance work for a long time, as well as charging individual batteries Since the discharge can be performed at a constant voltage and current range, the life of the battery can be extended.

1 is an exemplary view of a conventional cable type electric excavator.
2 is a block diagram illustrating the construction of the electric excavator system according to the present invention.
3 is a circuit diagram according to an embodiment of the charge / discharge control unit.
4 is a schematic block diagram showing a configuration for battery control of an electric excavator according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The electric excavator system according to the present invention has the concept of a conventional cable type electric excavator as described above, and receives power when necessary, including the charging concept, and uses the charged power when working, and uses the voltage required for the work. It is configured to detect whether it is secured and to charge it when necessary.

In this regard, reference is made to FIG. 2, which shows a block diagram of an electric excavator system according to the invention.

As shown in FIG. 2, the electric excavator system according to the present invention includes an electric excavator equipped with a power supply unit 100 and a power receiver 200.

At this time, the power supply unit 100 is installed in a place for supplying power from the outside as before, the power receiver 200 is installed in the excavator body.

In addition, the power receiver 200 is provided with a cable connector (meaning a plug and a socket) to be connected to the power supply unit 100.

More specifically, as shown in FIG. 2, the power supply unit 100 includes a power supply box 110, a cable drum 120, and a drum driver 122 and a cable guide 130 that control rotation of the cable drum 120. ).

In this case, the power box 110 is provided with a plurality of control switches, so that the external power is connected to supply the necessary power supplied from the external power source to the power receiver 200 when connected to the power receiver 200. It is designed.

In addition, the power supply unit 100 may be installed in plural as necessary, if the working radius is large, by installing a plurality at appropriate intervals to provide ease of connection through the power receiver 200 to further improve workability. Can be.

In addition, the cable drum 120 facilitates cable management to a short distance as well as to a long distance while winding or releasing a cable (Cable) for transmitting power controlled through the power box 110.

In this case, the cable drum 120 may be driven by a power source, the drive motor may be a drive motor, it may also be controlled by the drum drive unit (122).

In addition, the cable guide 130 may have a structure of a structure that guides the cable to be supplied so as not to be tangled or twisted, as it is, as shown in FIG. 1.

In this case, the cable guide 130 guides the cable drawn out from the cable drum 120 in which the cable is wound so as to smoothly withdraw the cable to a predetermined length range.

On the other hand, the power receiving unit 200 includes a driving motor generator 230 as a driving driving source, the driving motor generator 230 is in the form of AC power in the state in which the DC power is switched to the AC power through the inverter 220 Will be powered by

In this case, the inverter 220 is controlled by the controller 240.

In addition, the driving motor generator 230 is connected to the hydraulic pump 260 to be controlled through the controller 240.

In addition, the power supply unit 200 according to the present invention further includes a swing motor generator 232 capable of rotating the excavator body mounted with the boom 360 ° with respect to the main body.

In addition, they take the form of an electric motor and a generator to obtain electrical energy through regenerative braking, and the regenerative electricity obtained through regenerative braking is recovered and stored in the battery 210.

As such, since the regenerative braking can be used to accumulate electricity to the storage battery 210, it is possible to reduce heat generation due to driving and to recycle energy.

Of course, the swing motor generator 232 is also controlled by the controller 240.

In addition, the controller 240 may include a predetermined memory.

In addition, a hydraulic control valve 270 is connected to the hydraulic pump 260, and the hydraulic oil discharged by the hydraulic pump 260 is boom cylinder 274 and an arm cylinder according to the control sequence of the hydraulic control valve 270. 276, the bucket cylinder 278 is driven.

That is, since only the drive of the hydraulic pump 260 is electrically coupled, the controller 240 is controlled by the controller 240 to selectively receive the driving force of the driving motor generator 230, but the hydraulic oil generated by the driving of the hydraulic pump 260 thereafter. The hydraulic circuit associated with the supply of is made as before through the opening and closing control of the hydraulic control valve 270.

And the power receiver 200 is provided with a battery (210a, 210b, 210c) for supplying power to the driving motor generator 230, the battery (210a, 210b, 210c) is to supply sufficient power for driving the excavator Has the capacity to Since the storage batteries 210a, 210b, and 210c are DC-type, as described above, DC power is supplied to the traveling motor generator 230 through the inverter 220 to AC power, and a plurality of batteries are installed and the charging voltage is constant. That is, it includes a switching switch 280 to be replaced with another storage battery when it falls below the reference potential to work.

In this case, the changeover switch 280 is installed between the inverter 220 and the storage batteries 210a, 210b, and 210c, and is controlled by the controller 240.

Here, the three storage batteries 210a, 210b, 210c has been described as an example, but this is only a preferred embodiment and can be installed more of course.

Therefore, when three or more batteries are used while changing a single battery, the working time can be extended by that amount, and the working efficiency can be improved for a long time at a long distance.

In addition, the storage batteries 210a, 210b, and 210c are connected to the cable drawn out through the cable guide 120 and the cable connector and configured to be chargeable.

In other words, in a state in which a proper amount of power is charged, the driving motor generator 230 may be driven by being separated from the power supply unit 100 to freely expand and expand the working range of the excavator.

However, as described above, when the charged power falls below a certain level, it is difficult to perform the operation of the excavator, so it can be solved by checking the connection in advance and switching the connection to another battery having a sufficient amount of storage. Accordingly, the work efficiency does not need to be moved back to the power supply unit 100 for charging during the remote work.

To this end, in the present invention, the storage capacity detection unit 214 is further installed in the storage batteries 210a, 210b, and 210c, and at the same time, the overcharge preventing unit 212 can prevent damage to the storage batteries 210a, 210b and 210c due to overcharging. ) And a charge / discharge control unit 215 is installed.

At this time, the overcharge prevention unit 212 and the power storage detection unit 214 are all connected to the controller 240 is configured to be controlled by the controller 240, these overcharge protection unit 212 and the power storage detection unit to prevent overcharge It is preferable to have a kind of circuit form, such as a circuit and a capacitance detection circuit.

In addition, the capacitance detecting unit 214 detects the internal resistance that changes according to SOC (State Of Charge) and temperature of the batteries 210a, 210b, and 210c, and a method of estimating potential by estimating an electric potential. The amount of electricity stored in the 210a, 210b, and 210c, that is, the potential can be detected. The simplest method detects the voltages of both ends of the batteries 210a, 210b, and 210c, and transmits them to the controller 240, and the controller 240. Is preferably configured to check and control the charging by comparing the received detection potential with a reference potential required for driving.

In addition, when it is determined that the potential of the battery currently being used is lower than the reference potential through the storage amount detecting unit 214, the changeover switch 280 is connected to the inverter 220 with an adjacent storage battery having sufficient storage capacity under the control of the controller 240. Switch.

The charge / discharge control unit 215 is configured to be connected between the cable guide 130, the power switch 280 and the pre-rotational power generator 232, the driving motor generator 230 and the storage battery (210a, 210b, 210c) reference voltage To compare the voltages of the batteries 210a, 210b, and 210c, and compare the reference current and the discharge current of the batteries 210a, 210b, and 210c to charge or discharge the batteries 210a, 210b, and 210c. Charge and discharge of the storage battery (210a, 210b, 210c) to be performed within the range of.

That is, the charge / discharge control unit 215 compares the reference voltage with the voltage of each of the batteries 210a, 210b, and 210c so that the voltage of each of the batteries 210a, 210b, and 210c exceeds a predetermined voltage range including the reference voltage. When the charge of each of the storage battery (210a, 210b, 210c) is cut off. In addition, when the discharge current of each of the batteries 210a, 210b and 210c is out of a range of current values including the reference current by comparing the discharge current and the reference current of each of the batteries 210a, 210b and 210c. The discharge of the 210a, 210b, and 210c is blocked. As a result, the charge / discharge control unit 215 allows each of the storage batteries 210a, 210b, and 210c to be uniformly charged or discharged.

In FIG. 2, the charge / discharge control unit 215 and the power switch 280 are connected by one control and power line, and the charge / discharge control unit 215 and all the storage batteries 210a, 210b, and 210c are also connected by one control and power line. Although illustrated as being, the charge / discharge control unit 215 and the power switch 280 may be configured to control each of the storage batteries 210a, 210b, and 210c independently of the charge / discharge control unit 215, respectively. In order to supply the power of the 210c to the power switch 280 individually, the control and the power corresponding to the number of the storage batteries 210a, 210b and 210c are connected. The cable guide 130 or the charge / discharge control unit 215 and the storage batteries 210a, 210b and 210c may also independently control the charging and discharging control unit 215 to charge the respective storage batteries 210a, 210b and 210c. Control corresponding to the number of accumulators 210a, 210b, and 210c to divide the input power of the pre-rotational motor generator 232 or the traveling motor generator 230, respectively, and supply them independently to the capacitors 210a, 210b, and 210c. And a storage battery 210a, 210b, 210c by a power supply line.

3 is an example of a circuit configuring the charge / discharge control unit 215.

As shown in FIG. 3, the precharge controller controls a voltage error amplifier ERROR AMP that amplifies and outputs an error ERROR of a voltage command V_ref, a capacitor, and a battery feedback voltage V_fb, and a current command I_ref and charge / discharge. The output error amplifier consists of a current error amplifier that amplifies and outputs the error of feedback current (I_fb) flowing through the capacitor and battery, and consists of two diodes connected to the voltage error amplifier output and two resistors connected to the current error amplifier output. It has charge / discharge switching circuit part and is connected to the non-inverting input (+) terminal of the voltage follower so that the diode and the resistor are connected in common to drive the charge control signal, and the diode and the resistor are connected in common to drive the discharge control signal. Is connected to the non-inverting input (+) terminal of the voltage follower so as to drive the charge / discharge control signal. There is a driver circuit section, and in the charging section, the drain of the N-type field effect transistors (FET1, FET2) is connected to a positive power supply terminal (+ V), and a voltage follower is provided. The output of the amplifier is connected to the gate resistors R3 and R4 of the FETs FET1 and FET2, respectively. In the discharge part, the drain of the P-type FETs FET3 and FET4 has a negative power supply terminal (-V). And a circuit in which the output of the voltage follower amplifier IC4 is connected to the gate resistors of the FETs FET3 and FET4, respectively.

In the case of the charging unit, resistors used for current limiting during charging and discharging are connected in common with the source of the N-type FETs (FET1, FET2) and the source of the discharge unit (P3). Since the drain-source resistance value is small when the FETs are connected in parallel, overcurrent may flow toward the smaller RDS value among the FETs connected in parallel when there are no resistors. Thus, adding resistors with a larger resistance value than RDS can be used to balance charge / discharge currents of parallel-connected FETs.

In the above configuration, the reference voltage V_fb and the feedback current I-fb are compared with the reference voltage V_ref and the reference current I_ref as the voltages and currents of the storage batteries 210a, 210b, and 210c, respectively. When driving the 210b and 210c, the voltage and the current of each of the storage batteries 210a, 210b and 210c are compared with the reference voltage and the reference current to control charging and discharging in a constant voltage range and current range.

The charge / discharge control unit 215 is not limited to the above example, and various circuit configurations for controlling charging and discharging of the storage battery may be applied according to reference voltage and reference current values.

Further, as shown in FIG. 4, the temperature sensors 290 are installed in the storage batteries 210a, 210b, and 210c, respectively, and the temperature sensor 290 is connected to the controller 240 to detect the detected temperature value of the controller ( 240).

In addition, the controller 240 includes an operation unit 292 and a memory unit 294, and includes an operation unit 292 according to the temperature detection value of the temperature sensor 290 and the detection value of the power storage detection unit 214. The memory unit 294 controls the discharge output of the storage batteries 210a, 210b, and 210c.

That is, the maximum allowable discharge output is controlled based on the SOC (state of charge) and the temperature of the batteries 210a, 210b, and 210c, which are internal to the batteries 210a, 210b, and 210c by these factors. This is because the resistance is different.

Accordingly, in the present invention, the driving conditions of the present invention are stored in the memory unit 294 in a state in which the internal resistance change of SOC and temperature storage batteries 210a, 210b, and 210c and the ideal discharge output value thereof are stored as table values through experiments. The internal resistance is calculated according to the method, and the value is compared with the stored value stored in the memory unit 294 to control the discharge output of the batteries 210a, 210b, and 210c to a value corresponding thereto. 210c) enables management.

At this time, the method of measuring the internal resistance is determined by the value of the voltage change divided by the current when the current flows to the battery to be tested, and when the internal resistance is determined in this way through the following equation (Equation 1), (Equation 2) The discharge output P can be determined.

----------------(식1)

---------------- (Eq. 1)

------------------------(식2)

------------------------ (Equation 2)

(R: internal resistance, ΔV: difference between the maximum voltage (V _LIMIT ) and the current voltage (V _CURRENT ) of the battery)

Here, if the output P is a negative value, the discharge output is a positive value. If the output P is a negative value, the discharge output is a charge output. In the present invention, since only an electric motor excluding a generator is used, the charge output will not be discussed.

As a result, in the present invention, the controller 240 receives the potential value detected through the capacitance detection unit 214, calculates an amount of change in current and voltage in the calculation unit 292, calculates an internal resistance, and stores the battery temperature at that temperature. The battery 210a, 210b, by adjusting the temperature detected by the sensor 290 and the value corresponding to the calculated internal resistance from the table value stored in the memory unit 294 to the discharge output presented in the table accordingly. The life of 210c) can be extended.

In addition, when the storage batteries 210a, 210b, and 210c are below the reference voltage, it is preferable to stop the discharge output adjustment.

In addition, the alarm unit 250 is connected to the controller 240.

The alarm unit 250 is preferably configured to flash the warning light while emitting an alarm sound so that the excavator driver can see visually.

The alarm unit 250 is operated under the control of the controller 240 when the detection potential of the storage batteries 210a, 210b, and 210c of the power storage detection unit 214 does not reach the reference potential. By driving toward the power supply unit 100 to connect the cable provided in the power supply unit 100 to the power receiver 200 to perform the charging operation.

In this case, the alarm unit 250 may generate an alarm for each discharge of each battery, and may be configured to generate an alarm when all the batteries are discharged. Preferably, only the warning lamp flashes during discharge of each battery. When all of the batteries are discharged, it is particularly preferable to generate a warning light and an alarm sound so that the batteries can be recognized visually.

In addition, the term "discharge" described in the present invention is not defined as a discharge concept commonly used, but is defined as meaning when the potential of the battery falls below a reference potential (a proper potential required for driving an excavator).

The present invention having such a configuration has the following operational relationship.

First, when the working radius is not far from the power supply unit 100 and is within the length of the cable, the power supply unit 100 and the power receiver unit through the cable connector without having to separate the power supply unit 100 and the power receiver 200. While maintaining the connection state 200, the work that can be done through the electric excavator, such as excavation work, breaker work, crusher work, etc. are performed.

In this case, since the power is continuously supplied through the power supply unit 100, the driving power and the working power (for driving the hydraulic pump) are sufficient without sufficient force.

On the other hand, if the working radius is out of the cable length is supplied with sufficient power from the power supply unit 100 to sufficiently charge the power required for the storage batteries (210a, 210b, 210c) provided in the power receiving unit 200 or already charged state To be in.

Thus, when charging is complete, the cable connector is disconnected so that the power supply unit 100 and the power receiver 200 are separated.

Here, the output control of the storage batteries (210a, 210b, 210c) according to the discharge, as described above, the table value corresponding to the temperature value detected by the temperature sensor 290 and the arithmetic internal resistance value (stored in the memory unit) It is controlled in accordance with the present invention), so that abrupt discharge change can be suppressed, thereby extending the service life.

Then, the excavator is driven by using the power stored in the storage battery (210a, 210b, 210c), and after moving to the working place to drive the hydraulic pump 260 under the control of the controller 240 to perform the necessary work. .

In addition, when the warning light flashes through the alarm unit 250 during operation, the driver only needs to recognize that the battery is changing.

At the same time, the changeover switch 280 switches the connection between the storage battery and the inverter 220 to a new storage battery under the control of the controller 240.

Then, since the excavator can always be supplied with a power source above the reference potential, there is no problem in driving the driving motor generator 230, and thus, a long distance operation can be performed.

If the audio-visual alarm is generated through the alarm unit 250 even after the operation continues or during the operation, the driver recognizes that the battery needs to be stored, and drives the excavator toward the power supply unit 100 to connect the cable connector. By connecting the power supplied from the power supply unit 100 to charge the storage battery (210a, 210b, 210c), and if sufficient power storage is done again disconnect the cable and then move to the work place to work.

At this time, if a plurality of power supply unit 100 is installed in accordance with the working radius, the time required to move the excavator for charging, thereby reducing the charging time has the advantage that the work efficiency is improved.

As such, the electric excavator system according to the present invention utilizes storage batteries 210a, 210b, and 210c to drive the traveling motor generator 230 replacing the engine, as well as driving the hydraulic pump 260 to drive the excavator. Because it can do various tasks, it can improve the work efficiency and save energy.

First of all, by using a plurality of storage batteries (210a, 210b, 210c) can work for a long time even in the long-distance work has the advantage of significantly improved work efficiency.

100: power supply unit 110: power box
120: cable guide 200: power receiver
210a, 210b, 210c: Storage battery
215: charge and discharge control unit 220: inverter
230: electric motor 240: controller
250: alarm unit 260: hydraulic pump
270: hydraulic control valve 280: changeover switch
290: temperature sensor 292: calculation unit
294 memory section

Claims (3)

An electric excavator system comprising an electric excavator having a power supply and a power receiver;
The power receiver includes a cable connector and a controller that can be connected / disconnected the cable of the power supply unit for supplying external power to the electric excavator, and at least one storage battery for charging the electricity obtained through the regenerative braking of the power and the motor generator An overcharge preventing unit connected to the battery and preventing overcharging under the control of the controller; a charge detection unit connected to the battery and detecting a potential difference of the battery and outputting the same to the controller; An alarm unit that is connected to an inverter and a controller supplied to an electric generator by switching to a power source, and outputs an alarm when the detection potential of the battery is lower than the reference potential. Even if charging / discharging during driving is performed within the range Charge-discharge control unit for;
Electric excavator system, characterized in that comprises a. The method according to claim 1;
The power supply unit is provided with a switching switch for switching the connection between the battery and the inverter under the control of the controller when the potential of each battery is lower than the reference potential;
The controller further includes a memory unit in which a discharge output value according to a state of charge (SOC) of the battery and an internal resistance value for each temperature is stored as a table;
A temperature sensor is further installed in the storage battery;
The controller is provided with a calculation unit for calculating the current and the voltage based on the potential value detected from the temperature sensor and the charge detection unit, and then divide the voltage by the current to calculate the internal resistance;
And the discharge output is controlled according to an experimental internal resistance table value stored in a memory unit corresponding to the calculated internal resistance. The method according to claim 2,
And the controller stops controlling the discharge output of the battery when the battery falls below the reference potential.

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