Power leveling device

Abstract

To provide a power leveling device with versatility capable of preventing voltage flicker to solve a problems of peak current.SOLUTION: A power leveling device is constituted of: a power input unit 1 for inputting power of a power supply; a power storage device 3 which can charge and discharge power; a charge control circuit 2 connected with the power input unit 1 to convert current from the power supply into current which can be charged to the power storage device 3; a discharge control circuit 4 which converts current from the power storage device 3 into the same kind of current as that of the power supply; and a power output unit 5 for outputting power by current converted by the discharge control circuit 4 to the outside.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a power leveling device.

Background Art

[0002] Conventionally, resistance welding has been used to join metal workpieces to be welded. In resistance welding, the workpieces to be welded are overlapped, the welding portion is clamped by electrodes, and current is passed while applying a predetermined pressure. Then, the workpieces to be welded can be fusion-bonded by Joule heat generated by the contact resistance at the joint portion.

[0003] In a resistance welder, a large current (peak current) is required instantaneously when welding. Then, due to the repeated change in the voltage of the electric wire line, voltage flicker that adversely affects equipment inside or outside the factory, such as repeated brightening and darkening of lighting, occurs, which becomes a problem. Conventionally, in order to prevent such voltage flicker, a flicker prevention device that passes a compensation current has been disclosed (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Disclosure of the Invention

Problems to be Solved by the Invention

[0005] On the other hand, when multiple resistance welders are used and their peak currents overlap, there is a problem that the current capacity of the factory is exceeded. In order to increase the current capacity of the factory, special power distribution work is required, but this sometimes costs as much as several hundred million yen.

[0006] In the conventional voltage flicker prevention device, it was possible to prevent voltage flicker, but it was not possible to solve the peak current problem. In addition, the conventional voltage flicker prevention device also had the problem of lack of versatility.

[0007] Therefore, an object of the present invention is to provide a versatile power leveling device that can prevent voltage flicker and solve the peak current problem.

Means for Solving the Problems

[0008] To achieve the above object, the power leveling device of the present invention includes a power input unit for inputting the power of a power source, a power storage device capable of charging and discharging power, a charging control circuit connected to the power input unit for converting the current from the power source into a current capable of charging the power storage device, a discharge control circuit for converting the current from the power storage device into a current of the same type as the power source, and a power output unit for outputting the power generated by the current converted by the discharge control circuit to the outside.

[0009] In this case, it is preferable to include a bypass circuit that connects the power input unit and the power output unit.

[0010] Further, it is preferable that the charging control circuit controls the current or voltage to be charged to the power storage device according to the voltage of the power storage device.

[0011] Further, the power storage device can preferably use a lithium-ion capacitor.

[0012] Further, the charging control circuit can use a converter that converts the alternating current of the power source into a direct current of a predetermined constant current.

[0013] Further, the discharge control circuit can use an inverter that converts the direct current from the power storage device into an alternating current having the same voltage and the same cycle as the power source.

[0014] In addition, the charging control circuit can use a converter that converts the direct current of the power supply into a constant current of a predetermined voltage.

[0015] In addition, the discharging control circuit can use a converter that converts the direct current from the power storage device into a direct current having the same voltage as the power supply.

Advantages of the Invention

[0016] The power leveling device of the present invention can charge the power of the power supply into the power storage device, level it, and use it, so that voltage flicker can be prevented and the problem of peak current can be solved. In addition, since the power leveling device of the present invention outputs the same type of power as the power supply, it has versatility.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0018] Hereinafter, the power leveling device of the present invention will be described. As shown in FIG. 1, the power leveling device of the present invention mainly includes a power input unit 1, a charging control circuit 2, a power storage device 3, a discharging control circuit 4, and a power output unit 5. Further, a bypass circuit 6 may be provided.

[0019] [1] Power Input Unit The power input unit 1 is for inputting the power of the power supply 8. Here, as shown in FIGS. 3 to 5, the power supply 8 means a power supply source of AC or DC power. The AC mainly corresponds to three-phase AC or single-phase AC, but may also be two-phase AC or other polyphase AC. Also, in Japan, voltages such as 100V and 200V are used, but it is not limited to this, and various voltages are used in each country. Therefore, the form of the power input unit 1 may be appropriately selected to match the shape of the output unit (socket) determined by the type of power of the power supply 8. For example, the output units of the power supply 8 in Japan include various sockets such as single-phase 100V, single-phase 200V, and three-phase 200V. The power input unit 1 may use a plug that matches each socket. Also, if the power supply 8 outputs DC power, a power input unit 1 that matches the type of the output unit may be used. Also, the power input unit 1 is not limited to a plug, and may simply have only terminals for inputting the power of the power supply 8.

[0020] [2] Power storage device The power storage device 3 can charge and discharge power. As the power storage device 3, various ones can be used. In the power leveling device of the present invention, those having high output, responsiveness, high charge / discharge efficiency, high stored power amount, and low self-discharge rate are preferable.

[0021] A. Output and responsiveness Output means the amount of electricity that can be output at one time. The larger the output, the more capable it is of handling large currents. In the power leveling device of the present invention, when using power for equipment 9 such as a resistance welder, a power storage device 3 having an output capable of handling large currents is required. In particular, a power storage device 3 having an output capable of handling large currents of 1000 A or more is preferred. Also, responsiveness means the speed at which the power storage device 3 can follow and charge and discharge when the input or output fluctuates. In the power leveling device of the present invention, when using power for equipment 9 such as a resistance welder, an output responsiveness that can quickly discharge from the power storage device 3 is required. Also, after using the equipment 9, an input responsiveness that can quickly charge the power storage device 3 is required. Here, there is a positive correlation between the responsiveness of the power storage device 3 and the rated electrical output of the power storage device 3. In other words, the larger the rated electrical output of the power storage device 3, the higher the responsiveness of the power storage device 3, and the smaller the rated electrical output of the power storage device 3, the lower the responsiveness of the power storage device 3.

[0022] B. Charge and discharge efficiency Charge and discharge efficiency means the ratio of the discharge capacity to the charge capacity charged during charging when the power storage device 3 is charged under predetermined conditions and then discharged. The higher the charge and discharge efficiency, the more preferably the electrical energy can be used without waste. Here, there is a negative correlation between the charge and discharge efficiency of the power storage device 3 and the DC resistance of the power storage device 3. In other words, if the DC resistance of the power storage device 3 is small, the charge and discharge efficiency of the power storage device 3 will be high, and if the DC resistance of the power storage device 3 is large, the charge and discharge efficiency of the power storage device 3 will be low.

[0023] C. Stored electric energy The stored power amount means the amount of power that can be stored in the power storage device 3. If the stored power amount of the power storage device 3 is small, the voltage will rapidly decrease due to discharge. Therefore, when using the power storage device 3 for a device 9 that requires a large amount of power such as a resistance welder, a high stored power amount is necessary to maintain the voltage even when using sufficient power continuously. To increase the stored power amount of the power storage device 3, the modules used in the power storage device 3 can be paralleled or the voltage can be increased by increasing the number of series cells. Incidentally, as will be described later in the explanation of the charge control circuit 2, if it is about twice the peak voltage of the power supply 8, it is possible to boost the voltage using an LC resonance circuit without using a transformer. Therefore, the upper limit voltage of the power storage device 3 may be set to be less than or equal to the magnitude that can boost the voltage of the power supply 8 using the LC resonance circuit. Specifically, the power storage device 3 may adjust the number of series cells so that it is about twice the peak voltage of the power supply 8, and further adjust the stored power amount by the number of parallel modules.

[0024] D. Self-discharge rate The self-discharge rate means the rate at which the amount of power stored in the power storage device 3 decreases due to self-discharge over a predetermined time. If the self-discharge rate of the power storage device 3 is high, the voltage will rapidly decrease due to discharge. Therefore, when using it for a device 9 that requires a large amount of power such as a resistance welder, a low self-discharge rate with substantially no self-discharge is required so that the voltage of the power storage device 3 can be maintained for a long time.

[0025] Figure 2 is a diagram for explaining various devices that store energy. As shown in the figure, these devices are classified by the stored power amount [Wh] and the maximum output [W]. The left side of the dashed line 500 in Figure 2 is a device with a small DC resistance and a high charge-discharge efficiency, and the right side of the dashed line 500 is a device with a large DC resistance and a low charge-discharge efficiency. Table 1 shows the responsiveness, charge-discharge efficiency, and self-discharge rate of a lithium-ion capacitor, a superconducting magnetic energy storage (SMES), an electric double layer capacitor, or a nickel-metal hydride battery, a lithium-ion battery, and a lead-acid battery as secondary batteries.

[0026]

Table 1

[0027] As described above, since the power storage device 3 applied to this power leveling device is required to have high output, high responsiveness, high charge / discharge efficiency, high stored power amount, and low self-discharge rate, as shown in FIG. 2 and Table 1, it is preferable to use a "lithium ion capacitor", "SMES", or the like. Note that the power storage device 3 can also be assembled in parallel or in series in order to increase the maximum output and the stored power amount. Further, the power storage device 3 may be provided with various protection circuits inside, such as an overcharge protection circuit for protecting the power storage device 3 from overcharging, an over-discharge protection circuit for protecting it from over-discharging, a temperature protection circuit for protecting it from overheating, and a current protection circuit for protecting it from overcurrent.

[0028] [3] Charge control circuit In order to charge the power storage device 3, usually the power of the power source 8 cannot be used as it is, and it is necessary to use a voltage and current of an appropriate form for the power storage device 3. For example, a lithium ion capacitor requires direct current instead of alternating current for charging. Also, a lower limit voltage and an upper limit voltage are defined to prevent deterioration and the like. Further, in order to increase the charging speed, it is preferable to use a constant current as large as possible within a range that does not adversely affect the lithium ion capacitor. Therefore, the power leveling device of the present invention includes a charge control circuit 2 that is connected to the power input unit 1 and converts the current from the power source 8 into a current that can charge the power storage device 3.

[0029] The charging control circuit 2 may be controlled in any way as long as it can convert the current from the power source 8 into a current capable of charging the power storage device 3. Preferably, however, it is more preferable to control the current or voltage to be charged to the power storage device 3 according to the voltage of the power storage device 3. For example, the charging control circuit 2 can perform constant current control so as to maintain a constant current until the current from the power source 8 reaches a first voltage that does not exceed the upper limit voltage of the power storage device 3. Further, after the voltage of the power storage device 3 reaches the first voltage, the charging control circuit 2 can also perform constant voltage control so as to maintain a constant second voltage within a range that does not exceed the upper limit voltage of the power storage device 3. Thereby, the power storage device 3 can be rapidly charged.

[0030] As the charging control circuit 2, a well-known one that has been conventionally known can be used. For example, as shown in FIGS. 3 and 4, when the power source 8 is an alternating current such as three-phase alternating current or single-phase alternating current, a converter that converts the alternating current of the power source 8 into a direct current of a predetermined constant current can be used as the charging control circuit 2. The converter may convert the alternating current into a direct current of a constant current that is equal to or higher than the lower limit voltage and equal to or lower than the upper limit voltage at which the power storage device 3 can be charged. As the converter, for example, one that performs PWM (Pulse Width Modulation) control on a switching element 21 such as a thyristor or a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) can be used. By controlling the on-off of the switching element 21, the alternating current of the power source 8 can be rectified into a direct current, and the voltage and current of the direct current can be adjusted. Further, the charging control circuit 2 may further include a smoothing reactor 25 or the like for reducing the pulsating current on the DC side of the rectifier circuit.

[0031] In addition, in the discharge control circuit described later, in order to output only by PWM (Pulse Width Modulation) control as a step-down type at the lower limit voltage of the power storage device 3, it is preferable to boost in the charge control circuit and charge the power storage device 3. As a result, there is no need to boost in the discharge control circuit, so there is an advantage that it can be considerably simplified in terms of capacity compared to the case where the boost section is reduced in the charge circuit. When it is desired to boost the voltage of the power supply 8, a transformer may be provided in the charge control circuit 2. Also, if it is about twice the peak voltage of the power supply 8, it is possible to boost using an LC resonance circuit without using a transformer. In this case, the power storage device 3 may use one with an upper limit voltage equal to or less than the magnitude that can boost the voltage of the power supply 8 with the LC resonance circuit. Specifically, one with an upper limit voltage of about twice the peak voltage of the power supply 8 may be used.

[0032] Also, as shown in FIG. 5, when the power supply 8 is DC, a converter that converts the DC of the power supply into a predetermined constant current can be used as the charge control circuit 2. The converter may convert the DC into a DC constant current equal to or higher than the lower limit voltage at which the power storage device 3 can be charged and equal to or lower than the upper limit voltage. As the converter, a conventionally known step-up type DC-DC converter may be used. For example, a step-up type DC-DC converter that PWM (Pulse Width Modulation) controls a switching element 21 such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) can be used.

[0033] [4] Discharge control circuit The discharge control circuit 4 is for converting the current from the power storage device 3 into a current of the same type as that of the power source 8. Here, converting into a current of the same type as the power source 8 means, for example, when the power source 8 is a three-phase alternating current, converting the current from the power storage device 3 into a three-phase alternating current having the same voltage and the same frequency as that of the power source 8. Also, when the power source 8 is a single-phase alternating current, it means converting the current from the power storage device 3 into a single-phase alternating current having the same voltage and the same frequency as that of the power source 8. Further, when the power source 8 is a direct current, it means converting the current from the power storage device 3 into a direct current having the same voltage as that of the power source 8. Thus, since the current output from the power output unit 5 of the power leveling device of the present invention is of the same type as the current supplied from the power source 8 at the power input unit 1, it is a very versatile device applicable to various loads.

[0034] As the discharge control circuit 4, a well-known one that has been conventionally known can be used. For example, as shown in FIGS. 3 and 4, when the power source 8 is a three-phase alternating current, an inverter that converts the direct current from the power storage device 3 into a three-phase alternating current having the same voltage and the same frequency as that of the power source 8 can be used. Also, when the power source 8 is a single-phase alternating current, an inverter that converts the direct current from the power storage device 3 into a single-phase alternating current having the same voltage and the same frequency as that of the power source 8 can be used. As the inverter, a conventionally known one may be used. For example, one that performs PWM (Pulse Width Modulation) control on a switching element 41 such as an IGBT (Insulated Gate Bipolar Transistor) can be used. By controlling the on-off of the switching element 41, the direct current from the power storage device 3 can be made into an alternating current, and the voltage, current, and waveform of the alternating current can be adjusted. Also, the discharge control circuit 2 may further include an AC reactor 45 or the like for smoothing the waveform on the AC side.

[0035] Also, as shown in FIG. 5, when the power supply 8 is DC, a converter can be used to convert the current from the power storage device 3 into DC with the same voltage as the power supply 8. As the converter, a conventionally known step-down DC-DC converter may be used. For example, a step-down DC-DC converter that PWM (Pulse Width Modulation) controls a switching element 41 such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) can be used.

[0036] [5] Power output unit The power output unit 5 is for outputting the power generated by the current converted by the discharge control circuit 4 to an external device 9. The form of the power output unit 5 may be selected to be the same as that of the output unit (outlet) of the power supply 8. For example, there are various plugs such as single-phase 100V, single-phase 200V, and three-phase 200V in Japanese plugs, and the power output unit 5 may use an outlet suitable for each plug. Also, the power output unit 5 is not limited to an outlet and may simply have terminals for outputting power.

[0037] [6] Bypass circuit Also, for example, when the power storage device 3 is not sufficiently charged and the voltage is below the lower limit voltage, or when a malfunction occurs in the power storage device 3, the charge control circuit 2, the discharge control circuit 4, etc., an output abnormality such as voltage, waveform, frequency, etc. may occur in the power output unit 5. Also, various other abnormalities such as temperature abnormality of the power storage device 3 may occur. Therefore, the power leveling device of the present invention may further include a bypass circuit 6 that connects the power input unit 1 and the power output unit 5. Thereby, even when various abnormalities such as the above-described output abnormality and temperature abnormality occur, the charge control circuit 2, the power storage device 3, and the discharge control circuit 4 can be bypassed, and the power of the power supply 8 can be directly supplied from the power input unit 1 to the power output unit 5 via the bypass circuit 6. In particular, since the current output by the power output unit 5 of the power leveling device of the present invention is of the same type as the current supplied from the power supply 8 by the power input unit 1, the power input unit 1 and the power output unit 5 can be connected by a bypass circuit 6 having a simple configuration.

[0038] As the bypass circuit 6, any circuit may be used as long as it can connect the power input unit 1 and the power output unit 5 and output the power of the power supply from the power output unit 5. For example, as shown in FIGS. 3 to 5, the bypass circuit 6 may be composed of a bypass line 61 connecting the power input unit 1 and the power output unit 5 and a bypass switch 62 for turning on or off the current flowing through the bypass line 61. Further, the bypass circuit 6 may further include an input-side switch 63 for dissociating the power input unit 1 from the charge control circuit 2 and an output-side switch 64 for dissociating the discharge control circuit 4 from the power output unit 5. In this case, when the bypass switch 62 is OFF, the input-side switch 63 and the output-side switch 64 may be turned ON, and when the bypass switch 62 is ON, the input-side switch 63 and the output-side switch 64 may be turned OFF.

[0039] The ON or OFF of the bypass switch 62, the input-side switch 63, and the output-side switch 64 can be switched manually or automatically when an abnormality such as the above-described output abnormality or temperature abnormality occurs. The above-described abnormality may be detected using abnormality detection means such as well-known voltage detection means, current detection means, and temperature detection means.

[0040] When automatically switching the ON or OFF of the bypass switch 62, the input-side switch 63, and the output-side switch 64, the bypass circuit 6 may further include bypass control means for controlling the switching of the ON or OFF of these switches.

[0041] The bypass control means controls, for example, to turn off the bypass switch 62 and cut off the bypass line when the abnormality detection means does not detect an abnormality, that is, in a normal case. Also, the input-side switch 63 and the output-side switch 64 are turned ON, and the power input unit 1 and the power output unit 5 are connected via the charge control circuit 2, the power storage device 3, and the discharge control circuit 4 to control the current to flow to the power output unit.

[0042] Also, when the abnormality detection means detects an abnormality, the bypass control means controls to turn off the input side switch 63 and the output side switch 64 to disconnect and dissociate the charging control circuit 2 to the discharging control circuit 4. Further, the bypass switch 62 is turned on to connect the power input section 1 and the power output section 5 via the bypass line 61, and controls to allow the current of the power source to flow to the power output section.

Explanation of Signs

[0043] 1 Power input section 2 Charging control circuit 3 Power storage device 4 Discharging control circuit 5 Power output section 6 Bypass circuit 8 Power source 9 Equipment 21 Switching element 25 Smoothing reactor 41 Switching element 45 AC reactor 61 Bypass line 62 Switch 63 Input side switch 64 Output side switch

Claims

1. a power input section for inputting power of the power supply; A power storage device capable of charging and discharging power; a charge control circuit connected to the power input section and converting a current from the power source into a current capable of charging the power storage device; a discharge control circuit for converting a current from the power storage device into a current of the same type as that of the power source; a power output unit for outputting to an outside the power generated by the current converted by the discharge control circuit; A power leveling device comprising:

2. 2. The power leveling device according to claim 1, further comprising a bypass circuit connecting said power input section and said power output section.

3. 3. The power leveling device according to claim 1, wherein the charge control circuit controls a current or a voltage charged to the power storage device in accordance with a voltage of the power storage device.

4. 3. The power leveling device according to claim 1, wherein the power storage device is a lithium ion capacitor.

5. 3. The power leveling device according to claim 1, wherein the charge control circuit is a converter that converts the AC power from the power source into a DC power with a predetermined constant current.

6. 6. The power leveling device according to claim 5, wherein the discharge control circuit is an inverter that converts a direct current from the power storage device into an alternating current of the same voltage and period as the power source.

7. 3. The power leveling device according to claim 1, wherein the charge control circuit is a converter that converts the direct current of the power supply into a predetermined constant current.

8. 8. The power leveling device according to claim 7, wherein the discharge control circuit is a converter that converts the direct current from the power storage device into a direct current having the same voltage as that of the power source.

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