JPH11332134A - Power storage system - Google Patents

Abstract

(57) Abstract: An object of the present invention is to provide a power storage system that reduces a loss generated in a non-insulated commercial AC transformer and improves the efficiency of a bidirectional power converter. The present invention comprises a non-grounded DC power storage device and a non-isolated bidirectional power converter connected to a commercial AC power supply and having a non-insulated commercial AC transformer. In the power storage system, a switch 4 that bypasses the commercial AC transformer 2 and a switch 5 that does not bypass the commercial AC transformer 2 are provided, and when the DC power storage device 3 is charged, the switch 4 is bypassed, and when the DC power storage device 3 is discharged, the switch 4 is not bypassed. It is characterized in that the switch 5 is turned on.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power storage system capable of improving power conversion efficiency during charging by bypassing a commercial AC transformer when charging a DC power storage device.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional example of a DC power storage system composed of a commercial AC power supply, a DC power storage device and an insulated bidirectional power converter. In the figure, 1 is a commercial AC power supply, 2 is a non-insulated commercial AC transformer, 3 is a DC power storage device, and 6 is a bidirectional power converter. The bidirectional power converter 6 serves as a rectifier for the commercial AC power supply 1 when charging the DC power storage device 3 and as an inverter connected to the commercial AC power supply 1 when discharging from the DC power storage device 3. Perform the operation. That is, at the time of discharging, DC is converted to AC, but the phase is coordinated with that of commercial AC so that the current can be applied so that the current can be applied.
At the time of charging, the line voltage Vm is boosted to the voltage Vdc across the DC power storage system, and at the time of discharging, Vdc is increased.
Is reduced to Vm. Therefore, the line voltage Vm
The relationship between the maximum value Vmp and the voltage Vdc of the DC power storage device is expressed by the following equation.

Vdc> Vmp or Vdc = Vmp The maximum value of the line voltage Vc of the commercial AC power supply 1 is
If Vcp is low and Vcp> Vdc, then Vcp> Vmp. Therefore, the non-insulated commercial AC transformer 2 is used to boost Vm to Vc. If there is no non-insulated commercial AC transformer 2, power cannot be supplied from the DC power storage device 3 to the commercial AC power supply 1.

In general, lead-acid batteries and sodium-sulfur batteries are often used as DC power storage devices, but the voltage Vdc of these batteries is lower during discharge than during charge due to the influence of wiring resistance and internal resistance. . Therefore, whether to use a non-insulated commercial AC transformer is determined by the relationship between the voltage Vdc and the line voltage Vc at the time of discharging of the DC power storage device.

[0005]

In the conventional method, when the relationship between the voltage Vdc at the time of discharging of the DC power storage device and the maximum value Vcp of the line voltage is Vcp> Vdc, non-insulated commercial AC power is used. A transformer was used. At the time of charging, even if Vcp <Vdc or Vcp = Vdc and the non-insulated commercial AC transformer becomes unnecessary, the current is passed through the non-insulated commercial AC transformer. There is a problem that the efficiency of the bidirectional power converter is reduced due to the loss generated in the commercial AC transformer.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a power storage system that reduces a loss generated in a non-insulated commercial AC transformer and improves the efficiency of a bidirectional power converter. And

[0007]

In order to achieve the above object, a power storage system according to the present invention comprises an ungrounded DC power storage device, and a non-insulated type DC power storage device connected to the DC power storage device and a commercial AC power supply. In a power storage system including a non-isolated bidirectional power converter having a commercial AC transformer, a switch that bypasses the commercial AC transformer and a switch that does not bypass the commercial AC transformer are provided, and when the DC power storage device is charged, A switch to be bypassed is turned on, and a switch not to be bypassed is turned on when discharging.

[0008] The present invention takes the above measures,
In the non-insulated power storage system, the efficiency of the bidirectional power converter can be improved when the DC power storage device is charged.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention. In the figure, 1 is a commercial AC power supply, 60 is a non-isolated bidirectional power converter, 2 is a non-insulated commercial AC transformer, 3 is a non-grounded DC power storage device, and 4 and 5 are changeover switches. Commercial AC power supply 1 is u
Phase, v-phase, and w-phase, and the w-phase line connected to the w-phase is grounded. The u-phase line, v-phase line, and w-phase line of the commercial AC power supply 1 are connected to a switch S via a non-insulated commercial AC transformer 2.
The fixed terminals of the switches S2u, S2v, and S2w are respectively connected to the movable terminals of the high-frequency switches S3u, S3v, and S3w via the corresponding inductors Lu, Lv, and Lw. Each is connected correspondingly. The switch S2u,
S2v and S2w constitute the changeover switch 5. The u-phase line, the v-phase line, and the w-phase line of the commercial AC power supply 1 are connected to the movable terminals of the switches S1u, S1v, and S1w, respectively, and the fixed terminals of the switches S1u, S1v, and S1w correspond to the corresponding terminals. Switches S2u, S2v, S2
w is connected to the fixed terminal. These switches S1u, S1
v and S1w constitute the changeover switch 4. The changeover switch 4 and the changeover switch 5 are connected in parallel. A capacitor Cuv is connected between the fixed terminal of the switch S2u and the fixed terminal of the switch S2v.
A capacitor Cvw is connected between the fixed terminal of the switch S2w and the fixed terminal of the switch S2w. A capacitor Cuw is connected between the fixed terminal of the switch S2u and the fixed terminal of the switch S2w.
Is connected. The high frequency switches S3u, S3v, S
3w fixed terminals Hu, Hv, Hw are DC power storage devices 3
And the high-frequency switches S3u and S3
The fixed terminals Lu, Lv, Lw of v, S3w are connected to the negative terminal of the DC power storage device 3. The DC power storage device 3
The capacitor Cd is connected between the positive terminal and the negative terminal. The non-insulated commercial AC transformer 2, changeover switches 4, 5, high-frequency switches S3u, S3v, S3w, inductors Lu, Lv, Lw, capacitors Cuv, Cvw,
Cuw and Cd constitute the bidirectional power converter 60.

The bidirectional power converter 60 serves as a rectifier for the commercial AC power supply 1 when charging the DC power storage device 3 and connects to the commercial AC power supply 1 when discharging from the DC power storage device 3. Performs high-frequency switching operation as an inverter. At the time of discharging, DC is converted to AC, but it is coordinated with the commercial AC so that current can be applied with good phase matching. At the time of charging, a step-up operation of increasing the line voltage Vm to the voltage Vdc across the DC power storage device 3 is performed, and at the time of discharging, a step-down operation of decreasing Vdc to Vm is performed. Further, at the time of charging, the changeover switch 4 is turned on (conduction), and the changeover switch 5
Is turned off (cut off), and the switch 4 is turned off at the time of discharging,
The changeover switch 5 is turned on. This allows the current to bypass the non-insulated transformer 2 during charging, thereby preventing loss from occurring in the non-insulated transformer. The DC power storage device 3 has an internal resistance, and the voltage during charging is higher than the voltage during discharging. The switching unit of the bidirectional power converter 60 not only converts alternating current and direct current to each other, but also can change the voltage according to the switching frequency. However, the change width has a range as shown in FIG. At the time of discharging, it is necessary to use the non-insulated commercial AC transformer 2 to boost the voltage. However, at the time of charging, the voltage can be changed within the transforming range of the switching unit. It becomes unnecessary.

Next, the conditions under which the non-insulated commercial AC transformer 2 can be bypassed during charging will be described. FIG. 2 shows an example of a voltage condition to which the present invention is applied. Here, 7 is the waveform of the charging voltage of the DC power storage device 3, 8 is the waveform of the discharging voltage of the DC power storage device 3, and 9 is the commercial voltage V.
The waveform of c is shown. T represents one cycle of the commercial AC power supply 1. The discharge voltage of the DC power storage device 3 is the commercial AC power source 1
Therefore, it is necessary to match Vc and Vm using the non-insulated commercial AC transformer 2. On the other hand, since the charging voltage of the DC power storage device 3 is higher than the line voltage maximum value Vcp of the commercial AC power supply 1,
It is possible to control by switching of the inverter unit so that m becomes the same voltage as Vc. Therefore, it is not necessary to use the non-insulated commercial AC transformer 2 during charging. As shown in FIG. 2, the discharge voltage of the DC power storage device 3 is lower than the maximum line voltage Vcp of the commercial AC power supply 1, and the charging voltage of the DC power storage device 3 is the maximum line voltage of the commercial AC power supply 1. The present invention can be applied under a voltage condition higher than Vcp.

That is, according to the present embodiment, it is possible to prevent the loss in the non-insulated commercial AC transformer 2 during charging, which was impossible in the conventional example. For example, if the power conversion efficiency of the bidirectional power converter 60 is 90% and 20% of the loss occurs in the non-insulated commercial AC transformer 2, the present invention reduces the charging loss by 20%. The efficiency increases to about 92%.

[0013]

As described above, according to the present invention, in a non-isolated power storage system, the loss generated in the non-insulated commercial AC transformer by bypassing the non-insulated commercial AC transformer during charging. Can be deleted. Therefore, the efficiency of the power storage system during charging can be improved. In addition, as the DC power storage device, a lead storage battery, a capacitor, a sodium-sulfur battery, or the like can be considered.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a waveform diagram showing voltage conditions to which an embodiment of the present invention is applied.

FIG. 3 is a circuit diagram showing a conventional power storage system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Commercial AC power supply 2 Non-insulated commercial AC transformer 3 DC power storage device 4, 5 Changeover switch 60 Bidirectional power converter

Claims (1)

[Claims] 1. An ungrounded DC power storage device, and a non-isolated bidirectional power converter connected to the DC power storage device and a commercial AC power supply and having a non-insulated commercial AC transformer. In the power storage system, a switch that bypasses the commercial AC transformer and a switch that does not bypass the commercial AC transformer are provided, and the switch that bypasses the DC power storage device is turned on when charging, and the switch that is not bypassed is discharged when the DC power storage device is discharged. A power storage system characterized by the following.