Inverter and grid-connected and off-grid switching device thereof

Abstract

The utility model discloses an inverter and a grid-connected and off-grid switching device thereof, which can prevent overcurrent protection from being mistakenly triggered in the grid-connected and off-grid switching process, and also can prevent the phenomenon that grid connection or off-grid cannot be successfully switched due to overcurrent triggering. A grid-connected and off-grid switching device of an inverter comprises an inductor used for being connected with an inverter bridge arm of the inverter and a current sampling device used for sampling current on the output side of the inductor, and the inductor and the current sampling device are connected through an electric power connecting line. The grid-connected and off-grid switching device further comprises a filtering module arranged between the inductor and the current sampling device, the filtering module comprises a filtering capacitor, one end of the filtering capacitor is connected to the electric power connecting line and located between the inductor and the current sampling device, and the other end of the filtering capacitor is grounded.

Description

TECHNICAL FIELD

[0001] The utility model belongs to photovoltaic energy storage field relates to a kind of inverter and its parallel and off-grid switching device. BACKGROUND

[0002] Energy storage inverter generally has grid-connected operation state and off-grid operation state, in grid-connected operation state, the AC side of energy storage inverter is connected to power grid to convert DC from photovoltaic panel or battery into AC and feed to power grid;In off-grid operation state, the AC side of energy storage inverter is disconnected from power grid, and the load is powered by the battery of energy storage inverter.Therefore, the inverter bridge arm of energy storage inverter will be connected to a parallel and off-grid switching device, which realizes the connection or disconnection switching with power grid, i.e.the switching between grid-connected operation state and off-grid operation state.However, some inverters are prone to trigger overcurrent protection of inverter during parallel and off-grid operation state conversion, especially when the load is empty.

[0003] The above information disclosed in the BACKGROUND section is only intended to enhance the understanding of the background of the present application, and therefore it can include information that does not constitute the prior art known to those of ordinary skill in the art. SUMMARY

[0004] Therefore, the utility model provides an improved parallel and off-grid switching device of inverter and an inverter using such parallel and off-grid switching device, which avoids false triggering of overcurrent protection during parallel and off-grid switching process, and also avoids the phenomenon that the inverter cannot successfully convert to grid-connected or off-grid due to triggering of overcurrent.

[0005] The utility model adopts the following technical solutions:

[0006] A parallel and off-grid switching device of inverter, comprising an inductor for connecting the inverter bridge arm of inverter and a current sampling device for sampling the output side current of the inductor, the inductor and the current sampling device are connected through power connection line;

[0007] The parallel and off-grid switching device further comprises a filter module arranged between the inductor and the current sampling device, the filter module comprises a filter capacitor, one end of the filter capacitor is connected to the power connection line and located between the inductor and the current sampling device, and the other end of the filter capacitor is grounded.

[0008] In a preferred embodiment, resistors are connected in parallel on both sides of the filter capacitor, one end of the resistor is connected to the power connection line and located between the inductor and the current sampling device, and the other end of the resistor is grounded.

[0009] In a more preferred embodiment, the discharge time constant of the filter capacitor is less than the completion time of grid-connected to off-grid of the grid-connected and off-grid switching device.

[0010] In a further preferred embodiment, the resistance value of the resistor is 1-1000KΩ, and the capacitance value of the filter capacitor is 1-1000uf.

[0011] In a preferred embodiment, the grid-connected and off-grid switching device comprises a plurality of the power connection lines, each of which is provided with the inductor and the current sampling device, and each of which is connected with one of the filter modules.

[0012] In a preferred embodiment, the current sampling device comprises a current sensor.

[0013] In a preferred embodiment, the inductor and the inverter bridge arm are connected with a relay for switching between grid-connected and off-grid of the inverter.

[0014] The utility model discloses still uses following technical scheme:

[0015] An inverter comprising an inverter circuit, the inverter circuit comprising an inverter bridge arm, the inverter further comprising the grid-connected and off-grid switching device, and the grid-connected and off-grid switching device being connected to the inverter bridge arm.

[0016] In a preferred embodiment, the inverter is a single-phase or three-phase inverter, the inverter circuit is an H4 bridge, an H5 bridge or an H6 inverter circuit, and the inverter circuit is connected to the power grid through the grid-connected and off-grid switching device.

[0017] In a preferred embodiment, the inverter further comprises an overcurrent protection circuit, and the current sampling device of the grid-connected and off-grid switching device and the input end of the overcurrent protection circuit are electrically connected.

[0018] The utility model adopts the above scheme and has the following advantages:

[0019] In the grid-connected and off-grid switching device for the inverter, the current sampling device is located at the back side of the filter capacitor, so that even if the inverter wave and the capacitor residual voltage are inconsistent, the inrush current will not be detected by the current sampling device, and the overcurrent will not be triggered, solving the problem that the grid-connected to off-grid conversion of the energy storage product cannot be successfully converted due to the triggering of overcurrent protection under no-load and light load, ensuring that the load is continuously powered during power failure and can work normally. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical scheme of the utility model, the following will be briefly introduced the drawing needed to be used in the embodiment description, obviously, the drawing in the following description is only some embodiments of the utility model, for the ordinary skilled person in the art, under the premise of not paying the creative labor, other drawings can also be obtained according to these drawings.

[0021] Figure 1 It is a circuit diagram of a storage inverter according to the embodiment of the utility model.

[0022] Figure 2 It is a circuit diagram of a storage inverter for a comparative example. DETAILED DESCRIPTION

[0023] The preferred embodiments of the utility model will be described in detail below in combination with the drawings, so that the advantages and features of the utility model can be more easily understood by the person skilled in the art.It needs to be explained here that the description of these embodiments is used to help understanding the utility model, but does not constitute the limitation to the utility model.

[0024] EMBODIMENT

[0025] Figure 1 A storage inverter according to the embodiment is shown.The storage inverter includes an inverter circuit 200 and an on-off grid switching device 100, as shown in the drawing. Figure 1 The inverter can be a single-phase or three-phase inverter, and the inverter circuit 200 can be one of H4 bridge, H5 bridge or H6 inverter circuit.The on-off grid switching device 100 is connected to the inverter bridge arm, and the inverter circuit 200 is connected to the power grid or load through the on-off grid switching device 100. Figure 1 A three-phase storage inverter using H6 bridge inverter circuit is taken as an example to be described in detail.

[0026] The on-off grid switching device 100 of the inverter includes an inductor for connecting the inverter bridge arm and a current sampling device for sampling the output side current of the inductor, and the inductor and the current sampling device are connected through a power connection line.The on-off grid switching device 100 further includes a filter module 104 arranged between the inductor and the current sampling device, and the filter module 104 includes a filter capacitor, one end of the filter capacitor is connected to the power connection line and located between the inductor and the current sampling device, and the other end of the filter capacitor is grounded.The two sides of the filter capacitor are connected in parallel with a resistor, one end of the resistor is connected to the power connection line and located between the inductor and the current sampling device, and the other end of the resistor is grounded.The on-off grid switching device 100 includes a plurality of power connection lines, and the inductor and the current sampling device are respectively arranged on each power connection line, and each power connection line is connected with one filter module 104.

[0027] For Figure 1The three-phase inverter shown, the inverter circuit 200 has three inverter bridge arms 201, 202 and 203, the first inverter bridge arm 201 through the first power connection line 101 connected to the grid or load, the second inverter bridge arm 202 through the second power connection line 102 connected to the grid or load, the third inverter bridge arm 203 through the third power connection line 103 connected to the grid or load. The first power connection line 101 is provided with a first inductor L1 and a first current sampling device Am1, the middle node of the first inductor L1 and the first current sampling device Am1 is connected to the filter capacitor C1 and one end of a resistor R, the other end of the filter capacitor C1 and the resistor R is at the same potential as the ground BUSN. The second power connection line 102 is provided with a second inductor L2 and a second current sampling device Am2, the middle node of the second inductor L2 and the second current sampling device Am2 is connected to the filter capacitor C2 and one end of a resistor R, the other end of the filter capacitor C2 and the resistor R is at the same potential as the ground BUSN. The third power connection line 103 is provided with a third inductor L3 and a third current sampling device Am3, the middle node of the third inductor L3 and the third current sampling device Am3 is connected to the filter capacitor C3 and one end of a resistor R, the other end of the filter capacitor C3 and the resistor R is at the same potential as the ground BUSN.

[0028] The resistance of each resistor R is 1-1000KΩ, and the capacitance of the filter capacitors C1, C2 and C3 is 1-1000uf, so that the discharge time constant of the filter capacitors C1, C2 and C3 is less than the completion time of the grid-connected to off-grid switching of the off-grid switching device 100.

[0029] The current sampling devices Am1, Am2 and Am3 specifically include current sensors for detecting the current value flowing through the inductor.

[0030] The inductor L1, L2 or L3 and the inverter bridge arm 201, 202 or 203 are connected with a relay, by controlling the contact closure or opening of the relay, to realize the switching of the inverter between the grid-connected operation state and the off-grid operation state. The drive end or drive circuit of the relay is electrically connected with the control unit of the inverter.

[0031] The inverter further comprises an overcurrent protection circuit, and the current sampling devices of the off-grid switching device 100 and the input end of the overcurrent protection circuit are electrically connected. The overcurrent protection circuit is an electric current protection action when the electric current exceeds a predetermined maximum value. When the current flowing through the protected element exceeds the preset value, the current protection action is taken, and the selectivity of the action is ensured by timing, for example: causing the circuit breaker to trip or sending an alarm signal. The overcurrent protection circuit is not the improvement point of the present application, and the overcurrent protection circuit known in the prior art can be used.

[0032] Comparative example

[0033] Figure 2The other parallel and off-grid switching device 100 of the inverter is shown, and the difference from the embodiment is only that the current sampling devices Am1, Am2, Am3 and the front and back positions of the filter module 104 are different, and the rest is basically the same as the embodiment. Referring to Figure 2 As shown, the current sampling devices Am1, Am2, Am3 on each power connection line 101, 102, 103 are arranged between the inductors L1, L2, L3 and the filter capacitors C1, C2, C3, that is, the inductors and the current sampling devices on each power connection line are located before the resistors and the filter capacitors.

[0034] In the comparative example, due to the power consumption, the resistance in parallel with the filter capacitor C1 / 2 / 3 cannot be too small, and is generally several hundred kilo-ohms, and the capacitance of the filter capacitor is generally uf level, so the residual voltage discharge time constant of the filter capacitor is several seconds: time constant f=RC. The parallel-to-off-grid conversion time of the energy storage inverter requires 10ms to complete the conversion, which is much larger than the time constant of the discharge of the filter capacitor C1 / 2 / 3, so the voltage of the filter capacitor cannot be discharged completely during the conversion process and there will be residual voltage. Because the filter capacitor has residual voltage, the size of the residual voltage cannot be determined and there is no test circuit to know the size, and if the voltage cannot be consistent with the residual voltage when the off-grid inverter generates waves, the capacitor will be charged or discharged at a very high speed to generate a surge current. Because the current sampling devices Am1 / 2 / 3 are between the inverter circuit 200 and the filter capacitor, the surge current will be monitored by the sensor to trigger the overcurrent protection; this problem will cause the parallel-to-off-grid conversion of the energy storage inverter to fail under light load and no load, and will cause the load to be powered off and unable to work normally.

[0035] On the contrary, in the embodiment, the current sampling devices Am1 / 2 / 3 are moved to the back of the filter capacitor, so that even if the inverter wave generation is inconsistent with the residual voltage of the capacitor, the surge current will not be detected by the current sensor, and the overcurrent will not be triggered, solving the problem that the parallel-to-off-grid conversion of the energy storage inverter cannot be successfully converted under no load and light load due to the triggering of the overcurrent protection, and ensuring that the load equipment is continuously powered during power failure and can work normally at all times.

[0036] As shown in the specification and claims, the terms "comprise" and "include" only indicate the inclusion of the steps and elements explicitly identified, and these steps and elements do not constitute an exclusive list, and the method or device can also include other steps or elements. The term "and / or" used herein includes any combination of one or more related listed items.

[0037] It can be further understood that "multiple" in the present disclosure means two or more, and other quantifiers are similar.

[0038] It should be noted that, unless otherwise specified, when a certain feature is referred to as "connected" to another feature, it can be directly connected to the other feature or indirectly connected to the other feature.

[0039] The above embodiment is only for illustrating the technical concept and characteristics of the present application, is a preferred embodiment, the purpose is that the person skilled in the art can understand the content of the present application and implement it, and cannot limit the protection scope of the present application. Any equivalent transformation or modification according to the principle of the present application should be covered within the protection scope of the present application.

Claims

1. A grid-connected / off-grid switching device for an inverter, comprising an inductor for connecting an inverter bridge arm of the inverter and a current sampling device for sampling the current on the output side of the inductor, wherein the inductor and the current sampling device are connected via a power connection line; Its features are, The grid-connected / off-grid switching device further includes a filtering module disposed between the inductor and the current sampling period. The filtering module includes a filtering capacitor, one end of which is connected to the power connection line and located between the inductor and the current sampling device, and the other end of which is grounded.

2. The grid-connected / off-grid switching device according to claim 1, characterized in that, A resistor is connected in parallel across the two sides of the filter capacitor. One end of the resistor is connected to the power connection line and located between the inductor and the current sampling device, while the other end of the resistor is grounded.

3. The grid-connected / off-grid switching device according to claim 2, characterized in that, The discharge time constant of the filter capacitor is less than the grid-to-offline switching time of the grid-connected switching device.

4. The grid-connected / off-grid switching device according to claim 3, characterized in that, The resistance of the resistor is 1 to 1000KΩ, and the capacitance of the filter capacitor is 1 to 1000uF.

5. The grid-connected / off-grid switching device according to any one of claims 1 to 4, characterized in that, The grid-connected / off-grid switching device includes multiple power connection lines, each of which is equipped with an inductor and a current sampling device, and each power connection line is connected to a filtering module.

6. The grid-connected / off-grid switching device according to any one of claims 1 to 4, characterized in that, The current sampling device includes a current sensor.

7. The grid-connected / off-grid switching device according to any one of claims 1 to 4, characterized in that, A relay is connected between the inductor and the inverter bridge arm to enable switching between grid-connected and off-grid operation of the inverter.

8. An inverter comprising an inverter circuit, said inverter circuit including an inverter bridge arm, characterized in that, The inverter further includes a grid-connected / off-grid switching device as described in any one of claims 1 to 7, the grid-connected / off-grid switching device being connected to the inverter bridge arm.

9. The inverter according to claim 8, characterized in that, The inverter is a single-phase or three-phase inverter, and the inverter circuit is an H4 bridge, H5 bridge, or H6 inverter circuit. The inverter circuit is connected to the power grid through the grid-connected / off-grid switching device.

10. The inverter according to claim 8, characterized in that, The inverter also includes an overcurrent protection circuit, and the current sampling device of the grid-connected switching device is electrically connected to the input terminal of the overcurrent protection circuit.

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