Grid-connected and off-grid smooth switching system of micro-grid and switching device and method thereof

Abstract

The invention discloses a microgrid grid-connected and off-grid smooth switching system and a switching device and method thereof, and the method comprises the steps: in a grid-connected mode, the operation mode of an energy storage inverter is a PQ control mode, and whether a power grid starts to be disconnected or not is detected in real time; when it is detected that the power grid starts to be disconnected, the operation mode of the energy storage inverter is immediately switched into a constant current control mode; after a preset waiting period, detecting whether the power grid is disconnected or not; if the power grid is detected to be disconnected, detecting whether a gateway of the power grid trips; and if the gateway of the power grid trips, the operation mode of the energy storage inverter is switched to a V / F control mode, and grid-connected and off-grid switching is completed. When it is detected that the power grid starts to be disconnected, the operation mode of the energy storage inverter is immediately switched into the constant current control mode, the current is stabilized within the current upper limit value, current overshoot is controlled, and system stability is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of microgrids, and in particular to a microgrid on-grid and off-grid smooth switching system and a switching device and method thereof. Background Art

[0002] A microgrid is a small power system that integrates distributed energy (such as solar energy, wind energy, fuel cells, etc.), energy storage systems, and loads. It can be connected to the main grid (grid-connected mode) or it can operate independently after being disconnected from the main grid (off-grid mode). The flexibility of microgrids makes them play an important role in improving energy efficiency, increasing the resilience of power systems, and promoting the application of renewable energy. Due to the different structures and parameters of the systems in grid-connected and off-grid modes, when switching between grid-connected and off-grid modes, the system transfer function will mutate, resulting in current shocks and voltage oscillations. Summary of the invention

[0003] In order to solve the technical problems existing in the background technology, the present invention proposes a microgrid on-grid and off-grid smooth switching system and a switching device and method thereof.

[0004] The present invention proposes a method for smooth switching of microgrids on and off the grid based on a constant current mode, comprising:

[0005] In grid-connected mode, the energy storage inverter operates in PQ control mode, detecting in real time whether the grid starts to disconnect;

[0006] When it is detected that the grid starts to disconnect, the operation mode of the energy storage inverter is immediately switched to a constant current control mode;

[0007] After a preset waiting period, detect whether the grid has been disconnected;

[0008] If the detection grid is disconnected, then check whether the gateway of the grid is tripped;

[0009] If the gateway of the power grid has tripped, the operation mode of the energy storage inverter will be switched to V / F control mode to complete the off-grid switching.

[0010] Preferably, real-time detection of whether the power grid starts to disconnect specifically includes:

[0011] Detect and record the current of the power grid in real time and lock the current value;

[0012] When the current of the power grid is outside the preset standard current range, it is determined that the power grid begins to be disconnected.

[0013] Preferably, detecting whether the power grid is disconnected specifically includes:

[0014] Check whether the voltage of the power grid is stable;

[0015] If yes, then detect whether the voltage of the power grid reaches or exceeds the preset voltage value;

[0016] If so, it is determined that the power grid is disconnected;

[0017] If not, the detection grid is not disconnected.

[0018] Preferably, after detecting that the power grid is not disconnected, the method further comprises:

[0019] The energy storage inverter in the constant current control mode increases the output constant current until the voltage of the power grid reaches or exceeds the preset voltage value.

[0020] Preferably, after detecting whether the gateway of the power grid is tripped, the method further includes:

[0021] If the gateway of the power grid does not trip, it will send a crash message to the upper computer after waiting for the preset fair period.

[0022] The present invention also proposes a microgrid on-grid and off-grid smooth switching device based on a constant current mode, comprising: a detection module and a control module;

[0023] The detection module is used to detect in real time whether the power grid begins to disconnect;

[0024] When the detection module detects that the power grid begins to disconnect, the control module is used to immediately switch the operation mode of the energy storage inverter to a constant current control mode;

[0025] The detection module is also used to detect whether the power grid has been disconnected after a preset waiting period;

[0026] If the detection grid is disconnected, then check whether the gateway of the grid is tripped;

[0027] If the gateway of the power grid has tripped, the control module is also used to switch the operation mode of the energy storage inverter to the V / F control mode to complete the off-grid switching.

[0028] Preferably, after the detection module detects that the grid is not disconnected, the control module is further used to enable the energy storage inverter in the constant current control mode to increase the output constant current until the voltage of the grid reaches or exceeds the predetermined voltage value.

[0029] Preferably, when the detection module detects that the gateway of the power grid has not tripped, the control module is further configured to send a crash message to the upper computer after waiting for a preset fair period.

[0030] The present invention also proposes a microgrid on-grid and off-grid smooth switching system based on a constant current mode, comprising: a microgrid on-grid and off-grid smooth switching device based on a constant current mode and an energy storage inverter as described in any one of the above items, and the microgrid on-grid and off-grid smooth switching device based on a constant current mode is connected to the energy storage inverter.

[0031] In the present invention, the proposed microgrid on-grid and off-grid smooth switching system and its switching device and method detect in real time whether the grid begins to disconnect. Once it is detected that the grid begins to disconnect, the operation mode of the energy storage inverter is immediately switched to a constant current control mode to stabilize the current within the current upper limit value to control current overshoot and ensure system stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The figure is a schematic diagram of the principle of the PQ control method of the energy storage inverter in one embodiment of the present invention.

[0033] Figure 2 A schematic diagram of the principle of a V / F control method of an energy storage inverter in an embodiment of the present invention.

[0034] Figure 3 The present invention is a flowchart of a method for smooth switching of a microgrid on and off-grid based on a constant current mode in an embodiment of the present invention. DETAILED DESCRIPTION

[0035] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0036] It should be noted that in grid-connected mode, the energy storage inverter adopts PQ control mode; in off-grid mode, the energy storage inverter adopts V / F control mode.

[0037] In order to complete the on-grid and off-grid switching of the microgrid, refer to Figure 3 The present invention proposes a method for smooth switching of microgrids on and off the grid based on a constant current mode, comprising:

[0038] In grid-connected mode, the energy storage inverter operates in PQ control mode;

[0039] Real-time detection of whether the power grid begins to disconnect;

[0040] When it is detected that the grid starts to disconnect, the operation mode of the energy storage inverter is immediately switched to a constant current control mode;

[0041] After a preset waiting period, detect whether the grid has been disconnected;

[0042] If the detection grid is disconnected, then check whether the gateway of the grid is tripped;

[0043] If the gateway of the power grid has tripped, the operation mode of the energy storage inverter will be switched to V / F control mode to complete the off-grid switching.

[0044] The present invention applies to real-time detection of whether the power grid begins to disconnect. Once the power grid is detected to be disconnected, the operation mode of the energy storage inverter is immediately switched to a constant current control mode to stabilize the current within the current upper limit value to control current overshoot and ensure system stability.

[0045] In this embodiment, real-time detection of whether the power grid starts to disconnect specifically includes:

[0046] Detect and record the current of the power grid in real time and lock the current value;

[0047] When the current of the power grid is outside the preset standard current range, it is determined that the power grid begins to be disconnected.

[0048] In this embodiment, detecting whether the power grid is disconnected specifically includes:

[0049] Check whether the voltage of the power grid is stable;

[0050] If yes, then detect whether the voltage of the power grid reaches or exceeds the preset voltage value;

[0051] If so, it is determined that the power grid is disconnected;

[0052] If not, the detection grid is not disconnected.

[0053] In a further embodiment, after detecting that the power grid is not disconnected, the method further includes:

[0054] The energy storage inverter in the constant current control mode increases the output constant current until the voltage of the power grid reaches or exceeds the preset voltage value.

[0055] In this embodiment, after detecting whether the gateway of the power grid is tripped, the method further includes:

[0056] If the gateway of the power grid does not trip, it will send a crash message to the upper computer after waiting for the preset fair period, so that the staff can deal with the abnormality or fault in time.

[0057] In this embodiment, the operation mode of the energy storage inverter is switched to a constant current control mode, specifically including:

[0058] Make the energy storage inverter output a constant current, which is less than or equal to the current upper limit value, to control current overshoot and ensure system stability.

[0059] In this embodiment, in the dq-abc coordinate system, the calculation formula for the actual output power of the energy storage inverter in the PQ control mode is:

[0060]

[0061] In the formula, P and Q are the actual active power and reactive power of the energy storage inverter, respectively.d 、i d are the instantaneous voltage and current of the grid d axis, u q 、i q are the instantaneous voltage and current of the grid q axis respectively;

[0062] When connected to the grid, the output voltage is clamped by the grid voltage, ignoring its disturbance. After the phase-locked loop and coordinate transformation, u q =0;

[0063] You can make u d The calculation formula of the actual power of the energy storage inverter in PQ control mode is:

[0064]

[0065] That is, the active power and reactive power of the energy storage inverter can be respectively transmitted through the current i d ,i q Realize power decoupling control.

[0066] According to the above calculation formula, the PQ control system structure of the energy storage inverter can be obtained: Figure 1 .

[0067] Taking active power control as an example, the open-loop transfer function G k1 (s) is:

[0068]

[0069] Where: k p1 , k i1 k is the current inner loop PI regulator parameter; dp , k di is the power outer loop PI regulator parameter, R is the filter inductor equivalent resistance, s is the Laplace transform variable, and L is the filter inductor.

[0070] In this embodiment, the calculation formula for the constant voltage of the energy storage inverter in V / F control mode is:

[0071]

[0072] After Laplace transformation and power decoupling of the constant voltage calculation formula, the V / F control system structure of the energy storage inverter under off-grid control is obtained as follows: Figure 2 .

[0073] Among them, taking voltage control as an example, the open-loop transfer function G k2 (s) is:

[0074]

[0075] Where: k p2 , ki2 k is the current inner loop PI regulator parameter; vp , k vi is the voltage outer loop PI regulator parameter, and C is the capacitor.

[0076] The present invention also proposes a microgrid on-grid and off-grid smooth switching device based on a constant current mode, comprising: a detection module and a control module;

[0077] The detection module is used to detect in real time whether the power grid begins to disconnect;

[0078] When the detection module detects that the power grid begins to disconnect, the control module is used to immediately switch the operation mode of the energy storage inverter to a constant current control mode;

[0079] The detection module is also used to detect whether the power grid has been disconnected after a preset waiting period;

[0080] If the detection grid is disconnected, then check whether the gateway of the grid is tripped;

[0081] If the gateway of the power grid has tripped, the control module is also used to switch the operation mode of the energy storage inverter to the V / F control mode to complete the off-grid switching.

[0082] In this embodiment, when the detection module detects whether the power grid is disconnected,

[0083] Check whether the voltage of the power grid is stable;

[0084] If yes, then detect whether the voltage of the power grid reaches or exceeds the preset voltage value;

[0085] If so, it is determined that the power grid is disconnected;

[0086] If not, the detection grid is not disconnected.

[0087] In a further embodiment, after the detection module detects that the grid is not disconnected, the control module is further configured to cause the energy storage inverter in the constant current control mode to increase the output constant current until the voltage of the grid reaches or exceeds a predetermined voltage value.

[0088] In this embodiment, when the detection module detects that the gateway of the power grid has not tripped, the control module is also used to send a crash message to the upper computer after waiting for a preset fair period, so that the staff can handle the abnormality in time.

[0089] The length of the fair cycle is related to the time the grid is disconnected and the time it takes for the grid gateway to trip.

[0090] In this embodiment, after the control module is used to switch the operation mode of the energy storage inverter to the constant current control mode, it is also used to make the energy storage inverter output a constant current, and the constant current is less than or equal to the current upper limit value to control current overshoot and ensure system stability.

[0091] The present invention also proposes a microgrid on-grid and off-grid smooth switching system based on a constant current mode, comprising: a microgrid on-grid and off-grid smooth switching device based on a constant current mode and an energy storage inverter as described in any one of the above items, and the microgrid on-grid and off-grid smooth switching device based on a constant current mode is connected to the energy storage inverter.

[0092] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for smooth switching of microgrid on and off-grid based on constant current mode, characterized in that: include: In grid-connected mode, the energy storage inverter operates in PQ control mode, detecting in real time whether the grid starts to disconnect; When it is detected that the grid starts to disconnect, the operation mode of the energy storage inverter is immediately switched to a constant current control mode; After a preset waiting period, detect whether the grid has been disconnected; If the detection grid is disconnected, then check whether the gateway of the grid is tripped; If the gateway of the power grid has tripped, the operation mode of the energy storage inverter will be switched to V / F control mode to complete the off-grid switching.

2. The method for smooth switching between microgrid and off-grid based on constant current mode according to claim 1, characterized in that: Real-time detection of whether the power grid is disconnecting, including: Detect and record the current of the power grid in real time and lock the current value; When the current of the power grid is outside the preset standard current range, it is determined that the power grid begins to be disconnected.

3. The method for smooth switching between microgrid and off-grid based on constant current mode according to claim 1, characterized in that: Detect whether the power grid is disconnected, including: Check whether the voltage of the power grid is stable; If yes, then detect whether the voltage of the power grid reaches or exceeds the preset voltage value; If so, it is determined that the power grid is disconnected; If not, the detection grid is not disconnected.

4. The method for smooth switching between microgrid and off-grid based on constant current mode according to claim 3, characterized in that: After detecting that the power grid is not disconnected, it also includes: The energy storage inverter in the constant current control mode increases the output constant current until the voltage of the power grid reaches or exceeds the preset voltage value.

5. The method for smooth switching between microgrid and off-grid based on constant current mode according to claim 1, characterized in that: After detecting whether the gateway of the power grid is tripped, it also includes: If the gateway of the power grid does not trip, it will send a crash message to the upper computer after waiting for the preset fair period.

6. A microgrid on-grid and off-grid smooth switching device based on constant current mode, characterized in that: include: Detection module and control module; The detection module is used to detect in real time whether the power grid begins to disconnect; When the detection module detects that the power grid begins to disconnect, the control module is used to immediately switch the operation mode of the energy storage inverter to a constant current control mode; The detection module is also used to detect whether the power grid has been disconnected after a preset waiting period; If the detection grid is disconnected, then check whether the gateway of the grid is tripped; If the gateway of the power grid has tripped, the control module is also used to switch the operation mode of the energy storage inverter to the V / F control mode to complete the off-grid switching.

7. The microgrid on-grid and off-grid smooth switching device based on constant current mode according to claim 6, characterized in that: After the detection module detects that the grid is not disconnected, the control module is further used to enable the energy storage inverter in the constant current control mode to increase the output constant current until the voltage of the grid reaches or exceeds the preset voltage value.

8. The microgrid on-grid and off-grid smooth switching device based on constant current mode according to claim 6, characterized in that: When the detection module detects that the gateway of the power grid has not tripped, the control module is further used to send a crash message to the upper computer after waiting for a preset fair period.

9. A microgrid on-grid and off-grid smooth switching system based on constant current mode, characterized in that: include: According to the microgrid on-grid and off-grid smooth switching device based on constant current mode and the energy storage converter as described in any one of claims 6 to 8, the microgrid on-grid and off-grid smooth switching device based on constant current mode is connected to the energy storage converter.

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