Zero-voltage starting circuit for flow battery

Abstract

The invention provides a zero-voltage starting circuit for a flow battery. The zero-voltage starting circuit comprises a transformer unit used for converting high-voltage alternating current output by a power grid into low-voltage alternating current; the filter is used for converting the low-voltage alternating current output by the transformer unit into three-phase alternating current voltages with the same frequency, the same amplitude and the sequential phase difference of 120 degrees; the inverter power unit is used for converting the alternating-current voltage output by the filter into direct-current voltage; and the direct current / direct current converter unit is used for transmitting the direct current voltage output by the inverter power unit to the flow battery, so that the battery works in a step-down direct current circuit mode, constant current charging is carried out on the battery, and floating voltage of the flow battery is established, so that the floating voltage reaches a direct current voltage threshold value for normal working. Zero-voltage starting of the battery can be achieved through the direct current / direct current converter unit, the initial voltage of the flow battery is established, the floating voltage reaches the working voltage threshold value of a single-stage inversion power unit, and the flow battery has the advantages of being small in size, low in cost and stable in performance.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid flow batteries, and in particular to a zero-voltage starting circuit for a liquid flow battery. Background Art

[0002] With the large-scale use of distributed power sources, more and more unstable factors have been caused in the power grid. At present, large-scale energy storage systems contribute to the stability of the power grid and realize the peak-shaving and valley-filling effect of the power grid. Liquid flow battery energy storage systems are widely used in large-scale power energy storage due to their advantages such as large scale, long life, fast response and low maintenance cost.

[0003] Compared with traditional batteries, the initial voltage of flow batteries is close to 0 volts, and zero-voltage initial charging must be performed first to reach the starting voltage threshold of the converter before the converter can work properly. Currently on the market, the main charging methods for flow batteries are transformer step-down initial charging or independently configured mobile DC-to-DC charging equipment. These two methods are complicated to implement. Considering that the transformer winding coil causes the device to be bulky, and the corresponding conversion circuit must be matched, the implementation method is complicated and the cost is relatively expensive. Since flow battery systems usually need to handle a large current and voltage range, the size and weight of the equipment may be large, the heat dissipation capacity is limited, and additional cooling devices may be required, which increases the complexity of the system. Independently configured DC-to-DC mobile devices are often expensive due to their portability and specific functions. Summary of the invention

[0004] Based on the problems existing in the prior art, the technical means adopted by the present invention are as follows: a zero-voltage starting circuit for a flow battery, comprising:

[0005] Transformer unit: used to convert high-voltage AC power output from the power grid into low-voltage AC power;

[0006] Filter: used to convert the low-voltage AC power output by the transformer unit into AC voltages with the same three-phase frequency, equal amplitude, and phases that are 120 degrees apart from each other;

[0007] Inverter power unit: used to convert the AC voltage output by the filter into a DC voltage;

[0008] DC / DC converter unit: used to transmit the DC voltage output by the inverter power unit to the flow battery, so that the battery operates in a step-down DC circuit mode, charges the battery with a constant current, and establishes a floating pressure of the flow battery so that the floating pressure reaches the DC voltage threshold for normal operation.

[0009] Furthermore, it also includes a first switch for switching the grid voltage and outputting it to the transformer unit.

[0010] Further: the inverter power unit includes a three-phase filter reactor and a three-phase filter capacitor;

[0011] The three-phase filter reactor and the three-phase filter capacitor are connected in parallel.

[0012] Furthermore: the three-phase filter reactor includes a three-phase bridge arm composed of 6 fully controlled main switches with anti-parallel diodes.

[0013] Further: also including a second switch, a third switch and a fourth switch;

[0014] One end of the second switch and one end of the third switch are both connected to one end of the flow battery;

[0015] The other end of the second switch and one end of the fourth switch are connected to one end of the inverter power unit;

[0016] The other end of the fourth switch is connected to one end of the DC / DC converter unit.

[0017] Further: the DC / DC converter unit includes an IGBT module, a diode and a reactor;

[0018] One end of the IGBT module is connected to the fourth switch;

[0019] The other end of the IGBT module is connected to one end of the reactor and the cathode of the diode;

[0020] The cathode of the diode is connected to the inverter power unit and the other end of the flow battery.

[0021] The present invention provides a zero-voltage starting circuit for a liquid flow battery, which can realize zero-voltage starting of the battery through a DC / DC converter unit, establish the initial voltage of the liquid flow battery, and make the floating pressure reach the working voltage threshold of a single-stage inverter power unit. The invention has the advantages of small size, low cost and stable performance. Compared with the prior art, zero-voltage starting of the liquid flow battery can be realized without setting a step-down transformer on the user side or independently configuring a mobile DC-DC charging device. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0023] Figure 1 This is a structural diagram of a zero-voltage starting circuit for a flow battery according to the present invention;

[0024] In the figure: 1. All-vanadium liquid flow battery, 2. Second switch, 3. Inverter power unit, 4. Filter, 5. Transformer, 6. First switch, 7. Power grid, 8. Third switch, 9. DC / DC converter unit, 10. Fourth switch. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Figure 1 FIG. 1 is a schematic diagram of a zero-voltage starting circuit structure of a flow battery according to an embodiment of the present invention. Figure 1 As shown, the zero-voltage starting circuit of the flow battery provided in this embodiment includes: a second switch 2, an inverter power unit 3, a filter 4, a transformer 5, a first switch 6, a third switch 8, a DC / DC converter unit 9, and a fourth switch 10.

[0027] The flow battery 1 may include an all-vanadium flow battery, a sodium-sulfur battery, etc.

[0028] Filter: used to convert the low-voltage AC power output by the transformer unit into AC voltages with the same three-phase frequency, equal amplitude, and phases that are 120 degrees apart from each other;

[0029] Inverter power unit: used to convert the AC voltage output by the filter into a DC voltage;

[0030] DC / DC converter unit 9: used to transmit the DC voltage output by the inverter power unit to the flow battery, so that the battery operates in a step-down DC circuit mode, charges the battery with a constant current, and establishes a floating pressure of the flow battery so that the floating pressure reaches a DC voltage threshold for normal operation.

[0031] The DC / DC converter unit 9 and the inverter power unit 3 can realize a bidirectional working state;

[0032] The grid unit 7 and the transformer unit 5 belong to the power supply unit, and both the grid unit 7 and the transformer unit 5 are located in the power distribution station;

[0033] The grid unit 7 is used to transmit high voltage AC power to the transformer unit 5. The transformer unit 5 is connected to the grid unit 7 and the first switch 6 respectively.

[0034] The transformer unit 5 is used to transform the high voltage AC power into low voltage AC power, and transmit the low voltage AC power to the filter 5. Specifically, the transformer unit 5 transforms the high voltage AC power into 315V low voltage AC power, and inputs the AC low voltage power into the filter 4.

[0035] DC / DC converter unit: used to transmit the DC voltage output by the inverter power unit to the flow battery, establish the floating pressure of the flow battery, so that the floating pressure reaches the DC voltage threshold for normal operation.

[0036] Charging the flow battery 1 is divided into an initial charging mode and a normal charging mode, wherein the zero-voltage starting mode is connected to the grid through a DC / DC converter unit and an inverter power unit 3 .

[0037] The inverter power unit includes a three-phase filter reactor and a three-phase filter capacitor;

[0038] The three-phase filter reactor and the three-phase filter capacitor are connected in parallel.

[0039] The three-phase filter reactor comprises a three-phase bridge arm consisting of six fully controlled main switches with anti-parallel diodes.

[0040] The circuit also includes a second switch, a third switch and a fourth switch;

[0041] One end of the second switch and one end of the third switch are both connected to one end of the flow battery;

[0042] The other end of the second switch and one end of the fourth switch are connected to one end of the inverter power unit;

[0043] The other end of the fourth switch is connected to one end of the DC / DC converter unit.

[0044] The DC / DC converter unit includes an IGBT module, a diode and a reactor;

[0045] One end of the IGBT module is connected to the fourth switch;

[0046] The other end of the IGBT module is connected to one end of the reactor and the cathode of the diode;

[0047] The cathode of the diode is connected to the inverter power unit and the other end of the flow battery.

[0048] A method for operating a zero-voltage starting circuit for a flow battery comprises the following steps:

[0049] S1: Specifically, when the converter station outputs low-voltage AC power to initially charge the flow battery 1, in order to make the inverter power unit 3 work normally, the first switch 6 is first closed to start the inverter power unit 3, and a DC bus voltage is generated in the capacitor C1. The inverter power unit is running. Specifically, the filter 4 outputs three AC voltages with the same frequency, equal amplitude, and phase difference of 120 degrees;

[0050] S2: Close the second switch, the third switch, and the fourth switch to provide a prerequisite for the normal operation of the DC / DC converter unit 9.

[0051] During the power conversion stage of the zero-voltage start-up process of the flow battery, the DC / DC converter unit 9 is operated in a step-down DC circuit mode to start charging the battery with a constant current and restore the normal working state of the battery.

[0052] Compared with the prior art, the zero-voltage starting circuit of the flow battery provided by the present invention does not need to set a step-down transformer on the user side to achieve voltage reduction. Through the DC / DC converter unit 4, it has the advantages of small size, low cost and stable performance.

[0053] The initial charging circuit of the flow battery further includes a filter unit 4, which is respectively connected to the transformer 5 and the inverter power unit 3. The filter unit 4 is used to filter the output current of the inverter power unit 3. The filter unit 4 includes a three-phase filter reactor and a three-phase filter capacitor.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A zero-voltage starting circuit for a flow battery, characterized in that: include: Transformer unit: used to convert high-voltage AC power output from the power grid into low-voltage AC power; Filter: used to convert the low-voltage AC power output by the transformer unit into AC voltages with the same three-phase frequency, equal amplitude, and phases that are 120 degrees apart from each other; Inverter power unit: used to convert the AC voltage output by the filter into a DC voltage; DC / DC converter unit: used to transmit the DC voltage output by the inverter power unit to the flow battery, so that the battery operates in a step-down DC circuit mode, charges the battery with a constant current, and establishes a floating pressure of the flow battery so that the floating pressure reaches the DC voltage threshold for normal operation.

2. A zero-voltage starting circuit for a flow battery according to claim 1, characterized in that: It also includes a first switch for switching the grid voltage to be output to the transformer unit.

3. A zero-voltage starting circuit for a flow battery according to claim 1, characterized in that: The inverter power unit includes a three-phase filter reactor and a three-phase filter capacitor; The three-phase filter reactor and the three-phase filter capacitor are connected in parallel.

4. A zero-voltage starting circuit for a flow battery according to claim 1, characterized in that: The three-phase filter reactor comprises a three-phase bridge arm consisting of six fully controlled main switches with anti-parallel diodes.

5. The zero-voltage starting circuit of a flow battery according to claim 1, characterized in that: Also comprising a second switch, a third switch and a fourth switch; One end of the second switch and one end of the third switch are both connected to one end of the flow battery; The other end of the second switch and one end of the fourth switch are connected to one end of the inverter power unit; The other end of the fourth switch is connected to one end of the DC / DC converter unit.

6. A zero-voltage starting circuit for a flow battery according to claim 1, characterized in that: The DC / DC converter unit includes an IGBT module, a diode and a reactor; One end of the IGBT module is connected to the fourth switch; The other end of the IGBT module is connected to one end of the reactor and the cathode of the diode; The cathode of the diode is connected to the inverter power unit and the other end of the flow battery.

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