A grid-connected control method and device for inverter

Abstract

The present invention outputs direct current to alternating current for a load system by setting a grid-connected control device and a grid-connected control method of an inverter; and compares the output power of direct current with the load power by setting a relay switching system between a DC / DC system and a DC / AC system; and compares the output power of alternating current with the load power by setting a grid-connected output circuit; ensures the safety of the inverter grid-connected system by a double comparison system; prevents excessive output and failure of the inverter bridge circuit; reconverts alternating current by setting a diode rectifier circuit on the grid-connected output circuit; and performs circuit compensation by directly going off-grid without the need for a DC / AC system when the load requires direct current.

Description

Technical Field

[0001] The present invention relates to the technical field of inverters, and in particular to a grid-connected control method and device for an inverter. Background Art

[0002] An inverter is a device that converts DC power into AC power. It includes an inverter bridge, control logic and filter circuit. The existing inverter circuit needs to be connected to the grid and then connected to the applicable circuit. The invention patent with publication number CN117879045A discloses a multi-path staggered parallel Her IC inverter current sharing control system and control method; including a DC bus input end; a DC bus total voltage sampling unit and a DC bus total filter capacitor are arranged in parallel at the DC bus input end; an inverter output total capacitor is arranged in parallel at the AC output end, and an inverter voltage sampling unit is arranged in parallel on the inverter output total capacitor; the current difference problem generated when multiple inverter units are connected in parallel is solved; and the invention patent with publication number CN117748593A discloses a grid-connected and off-grid switching control method for energy storage converters, and includes detecting the working state of the energy storage converter, specifically including the working state of the energy storage converter being a grid-connected working state and the working state of the energy storage converter being an off-grid working state, and can quickly switch between the two operating modes of grid-connected and off-grid, and can operate in both grid-connected mode and off-grid mode. Formula; the invention patent with publication number CN117895813A discloses a control method for a photovoltaic VSG inverter based on an improved reaching law integral sliding mode; by performing feedforward decoupling control on the mathematical model of the three-phase inverter in the dq coordinate system, the separate control of the dq axis voltage and current is realized; and the inverter in the prior art needs to perform a ratio detection on the maximum withstand current and voltage of the grid-connected circuit load and the current and voltage output by the inverter when connected to the grid; to determine whether the inverter can be output; and the output current and voltage of the inverter need to be converted and calculated because it is a conversion of direct current to alternating current; the comparison method is relatively complicated; and it is also necessary to decide whether to go off-grid based on the current demand of the grid-connected load; and circuit compensation is generally required after going off-grid, which requires the setting of a compensation circuit at the same time.

[0003] 1. Technical issues to be resolved

[0004] In order to solve the above technical problems, the present invention provides a grid-connected control method and device for an inverter.

[0005] (II) Technical solution

[0006] A grid-connected control device for an inverter; comprising a grid-connected circuit load voltage detection system, a grid-connected load circuit power detection system, a DC / DC output system 100, a DC / DC power output detection system, a relay switching system 110, an inverter DC / AC output system, a DC / AC output power detection system, a grid-connected output circuit, a grid-connected load system, and a grid-connected circuit load demand conversion system.

[0007] Furthermore; the DC / DC output system 100 is connected to the DC / DC power output detection system; a relay switching system 110 is provided on the DC / DC power output detection system; the DC / DC output system 100 is connected in parallel with the DC / AC output system through the relay switching system 110; the DC / AC output system is connected with the DC / AC output power detection system; the DC / AC output system is connected in parallel with the grid-connected load system through the grid-connected output circuit.

[0008] Furthermore, the grid-connected load circuit power detection system detects and records the maximum load current and voltage of the circuit.

[0009] Furthermore, the DC / DC output system 100 includes a power output device U0, U0 is connected to the DC / DC output circuit connected to the relay switching system 110, and the DC / DC output circuit is provided with two current branches in parallel; a capacitor C1 is provided on the first current branch; and a varistor Rv is provided on the second current branch.

[0010] Furthermore, the relay switching system 110 includes a relay T1 and a relay T2, the relay switch T1 is connected to the positive pole connecting wire of the power output device U0; the relay switch T2 is connected to the negative pole connecting wire of the power output device U0, and the DC / DC power output detection system controls the opening and closing of the relay switching system 110; the power detected by the DC / DC power output detection system is compared with the parameters of the grid-connected load circuit power detection system.

[0011] Furthermore, the inverter DC / AC output system 120 is connected in parallel with a bridge inverter circuit; the bridge inverter circuit includes an inverter switch V1 and a V1 transistor matched with the inverter switch V1; an inverter switch V2 and a V2 transistor matched with the inverter switch V2, an inverter switch V3 and a V3 transistor matched with the inverter switch V3; an inverter switch V4 and a V4 transistor matched with the inverter switch V4, and the corresponding inverter switch is opened and closed within a unit time by inputting a corresponding frequency value into the transistor.

[0012] Furthermore, the inverter DC / AC output system is connected in parallel with a grid-connected load system through a grid-connected output circuit; the grid-connected output circuit includes a grid-connected output circuit 130 connected to the grid-connected load system e1 and a grid-connected output circuit 140 connected to the grid-connected load system e2; the grid-connected output circuit 130 is connected in parallel with a first diode rectifier circuit and a circuit connected with a switch K1.

[0013] Furthermore, the grid-connected output circuit 140 is connected in parallel with a second diode rectifier circuit and a circuit connected with a switch K2.

[0014] Further, initially, the voltage at both ends of the current flowing through the grid-connected load systems e1 and e2 is detected by the grid-connected load circuit power detection system; the maximum load current of the grid-connected load systems e1 and e2 is recorded as I0; the maximum load voltage is V0; before the power output device U0 outputs power; the relay switch T1 and the relay switch T2 of the relay switching system 110 are disconnected; a current loop is formed by setting two parallel current branches on the DC / DC output circuit; on this basis, the current and voltage of the DC / DC power output system are detected by the DC / DC power output detection system; and the detection result is compared with the maximum load current and the maximum load voltage of the grid-connected load system; when the comparison result is less than I0 and V0; the relay switch T1 and the relay switch T2 are opened; the DC / DC output circuit completes the DC current output to the inverter DC / AC output system; if the comparison result is greater than I0 and V0; the relay switch T1 and the relay switch T2 continue to be closed.

[0015] Furthermore, when the DC / AC output system of the inverter inputs a DC current, the switches K1 and K2 on the grid-connected output circuit and the two diode rectifier circuits are first disconnected; the d and q axis components U of the inverter output voltage are calculated by converting the two-phase stationary coordinate system to the rotating coordinate system. d and U q ; and the d-axis and q-axis components of the inverter output current I d and I q ; Compare the calculated voltage and current values ​​with the maximum load current and maximum load voltage of the grid-connected load system; when the comparison result is less than I0 and V0; continue to disconnect the two diode rectifier circuits on the grid-connected output circuit; open switches K1 and K2; complete the grid-connected operation of the inverter DC / AC output system; when the comparison result is greater than I0 and V0; continue to disconnect the grid-connected output circuit.

[0016] Further; according to the grid-connected circuit load demand conversion system to detect the DC and AC power demand of the load system; and according to the demand to determine the inverter DC / AC output system grid and off-grid.

[0017] Furthermore, when it is detected that the load system continuously requires AC power, the two diode rectifier circuits are continuously disconnected when the output current, voltage and power are normal, so that the DC / AC output system continues to output grid-connected power; when it is detected that the load system requires DC power, the switches K1 and K2 are disconnected; the two diode rectifier circuits are opened, so that multiple diodes rectify the AC power output by the DC / AC output system into DC power to output the load system.

[0018] (3) Beneficial effects;

[0019] The present invention outputs direct current to alternating current for a load system by setting a grid-connected control device and a grid-connected method of an inverter; compares the output power of direct current with the load power by setting a relay switching system between a DC / DC system and a DC / AC system; and compares the output power of alternating current with the load power by setting a grid-connected output circuit; ensures the safety of the inverter grid-connected system by a double comparison system; prevents excessive output power and failure of the inverter bridge circuit; reconverts alternating current by setting a diode rectifier circuit on the grid-connected output circuit; and performs circuit compensation by directly disconnecting from the grid without the need for a DC / AC system when the load requires direct current. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Attached Figure 1 This is the circuit diagram of the inverter grid-connected system.

[0021] Attached Figure 2 This is a schematic diagram of the grid-connected output circuit.

[0022] Attached Figure 3 Output power detection process for DC / DC output system

[0023] Attached Figure 4 Output power detection process for DC / AC output system DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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.A grid-connected control device for an inverter; comprising a grid-connected circuit load voltage detection system, a grid-connected load circuit power detection system, a DC / DC output system 100, a DC / DC power output detection system, a relay switch system 110, an inverter DC / AC output system, a DC / AC output power detection system, a grid-connected output circuit, a grid-connected load system, and a grid-connected circuit load demand conversion system; the DC / DC output system 100 is connected to the DC / DC power output detection system; the DC / DC power output detection system is provided with a relay switch system 110; the DC / DC output system 100 is connected in parallel with a DC / AC output system; the DC / AC output system is connected to a DC / AC output power detection system; the DC / AC output system is connected in parallel to a grid-connected load system through a grid-connected output circuit; the grid-connected load circuit power detection system detects and records the maximum load current and voltage of the circuit; the DC / DC output system 100 includes a power output device U0, U0 is connected to the DC / DC output circuit and connected to a relay switching system 110, and two current branches are provided in parallel on the DC / DC output circuit; a capacitor C1 is provided on the first current branch; a varistor Rv is provided on the second current branch; the relay switching system 110 includes a relay T1 and a relay T 2, the relay switch T1 is connected to the positive connection wire of the power output device U0; the relay switch T2 is connected to the negative connection wire of the power output device U0, the DC / DC power output detection system controls the opening and closing of the relay switch system 110; the power detected by the DC / DC power output detection system is compared with the parameters of the grid-connected load circuit power detection system; the inverter DC / AC output system 120 is connected in parallel with a bridge inverter circuit; the bridge inverter circuit includes an inverter switch V1 and a V1 transistor matched with the inverter switch V1; an inverter switch V2 and a V2 transistor matched with the inverter switch V2, an inverter switch V3 and a V4 transistor matched with the inverter switch V 3; the inverter switch V4 and the V4 transistor matched with the inverter switch V4, by inputting the corresponding frequency value into the transistor to open and close the corresponding inverter switch in unit time; the inverter DC / AC output system is connected in parallel with the grid-connected load system through the grid-connected output circuit; the grid-connected output circuit includes a grid-connected output circuit 130 connected to the grid-connected load system e1 and a grid-connected output circuit 140 connected to the grid-connected load system e2; the grid-connected output circuit 130 is connected in parallel with a first diode rectifier circuit and a circuit connected with a switch K1; the grid-connected output circuit 140 is connected in parallel with a second diode rectifier circuit and a circuit connected with a switch K2.

Claims

1. A grid-connected control device for an inverter; The invention comprises a grid-connected circuit load voltage detection system, a grid-connected load circuit power detection system, a DC / DC output system 100, a DC / DC power output detection system, a relay switching system 110, an inverter DC / AC output system 120, a DC / AC output power detection system, a grid-connected output circuit, a grid-connected load system, and a grid-connected circuit load demand conversion system; the DC / DC output system 100 is connected to the DC / DC power output detection system; the DC / DC power output detection system is provided with a relay switching system 110; the DC / DC output system 100 is connected in parallel with the DC / AC output system via the relay switching system 110; the DC / AC output system is connected to the DC / AC output power detection system; the DC / AC The output system is connected in parallel with a grid-connected load system through a grid-connected output circuit; the grid-connected load circuit power detection system detects and records the maximum load current and maximum load voltage of the grid-connected load circuit; the DC / DC output system 100 includes a power output device U0, and the DC / DC output circuit is connected in parallel with two current branches; a capacitor C1 is provided on the first current branch; a varistor Rv is provided on the second current branch; the relay switching system 110 includes a relay T1 and a relay T2, the relay switch T1 is connected to the positive pole connecting wire of the power output device U0; the relay switch T2 is connected to the negative pole connecting wire of the power output device U0, and the DC / DC power output detection system controls the opening and closing of the relay switching system 110; The inverter DC / AC output system 120 is connected in parallel with a bridge inverter circuit; the bridge inverter circuit includes: an inverter switch V1 and a V1 transistor matched with the inverter switch V1; the bridge inverter circuit also includes an inverter switch V2 and a V2 transistor matched with the inverter switch V2; an inverter switch V3 and a V3 transistor matched with the inverter switch V3; an inverter switch V4 and a V4 transistor matched with the inverter switch V4; the bridge inverter circuit is used to open and close the corresponding inverter switch within a unit time according to the input corresponding frequency value; The inverter DC / AC output system is connected in parallel with a grid-connected load system through a grid-connected output circuit; the grid-connected output circuit includes a grid-connected output circuit 130 connected to the grid-connected load system e1 and a grid-connected output circuit 140 connected to the grid-connected load system e2; the grid-connected output circuit 130 is connected in parallel with a first diode rectifier circuit and a circuit connected with a switch K1.

2. The grid-connected control device of the inverter according to claim 1; characterized in that: The grid-connected output circuit 140 is connected in parallel with a second diode rectifier circuit and a circuit connected with a switch K2.

3. A method for controlling a grid-connected inverter of a grid-connected inverter control device according to any one of claims 1 to 2; characterized in that: The voltages at both ends of the grid-connected load system e1 and the grid-connected load system e2 are detected by the grid-connected load circuit power detection system; the maximum load current I0 and the maximum load voltage V0 of the grid-connected load system e1 and the grid-connected load system e2 are recorded; before the power output device U0 outputs power, the relay switch T1 and the relay switch T2 of the relay switching system 110 are disconnected; a current loop is formed by two current branches connected in parallel with the DC / DC output circuit; the current and voltage of the DC / DC power output system are detected by the DC / DC power output detection system; the detection result is compared with the maximum load current and the maximum load voltage of the grid-connected load system; if the detected current is less than I0 and the detected voltage is less than V0; the relay switch T1 and the relay switch T2 are opened; The DC / DC output circuit completes the DC current output to the inverter DC / AC output system; if the detected current is greater than I0 and the detected voltage is greater than V0, the relay switch T1 and the relay switch T2 continue to be closed.

4. The grid-connected control method of the inverter according to claim 3, characterized in that: When the DC / AC output system of the inverter inputs DC current, the switches K1 and K2 on the grid-connected output circuit and the two diode rectifier circuits are first disconnected; the d-axis and q-axis components U of the inverter output voltage are calculated by converting the two-phase stationary coordinate system to the rotating coordinate system. d and U q ; and the d-axis and q-axis components of the inverter output current I d and I q ; Compare the calculated voltage and current values ​​with the maximum load current and maximum load voltage of the grid-connected load system; if the detected current is less than I0 and the detected voltage is less than V0; Continue to disconnect the two diode rectifier circuits on the grid-connected output circuit; open switch K1 and switch K2 to complete the grid-connected operation of the inverter DC / AC output system; If the detected current is greater than I0 and the detected voltage is greater than V0, the grid-connected output circuit continues to be disconnected.

5. The grid-connected control method of the inverter according to claim 4, characterized in that: According to the load demand of the grid-connected circuit, the conversion system detects the DC and AC power demand of the load system; according to the demand, the grid connection and off-grid connection of the inverter DC / AC output system are determined.

6. The grid-connected control method of the inverter according to claim 5, characterized in that: When it is detected that the load system continuously requires AC power, the two diode rectifier circuits are continuously disconnected when the output current, voltage and power are normal, so that the DC / AC output system continues to output grid-connected power; when it is detected that the load system requires DC power; the switches K1 and K2 are disconnected; the two diode rectifier circuits are opened, so that multiple diodes rectify the AC power output by the DC / AC output system into DC power for output to the load system.

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