A low voltage DC interconnection device with droop characteristics and error correction method

Abstract

The present invention provides a low-voltage DC interconnection device with a droop characteristic and an error correction method, which belongs to the technical field of converter power modules. The device includes a converter power module, a human-machine interface module, and AC and DC circuit breakers. The converter power module is equipped with an independent control unit. The control unit has a DC droop characteristic, which can suppress the circulating current caused by the parallel connection of the DC side of the converter power module. The control unit receives the reference power and droop curve sent by the monitoring background system. While adjusting the DC side output power through the DC droop curve, it will complete the automatic correction function of the DC voltage sampling error based on the sent reference power. The control unit communicates with the human-machine interface module through CAN communication to upload or send corresponding control parameters. The DC sides of the converter power modules are connected together through wires through circuit breakers. The modular low-voltage DC interconnection device of the present invention jointly maintains the DC voltage and can effectively suppress the DC circulating current phenomenon, thereby reducing system costs and enhancing system stability.

Description

Technical Field

[0001] The present invention relates to a low-voltage direct current interconnection device with droop characteristics and an error correction method, belonging to the technical field of converter power modules. Background Art

[0002] The flexible interconnection solution for low-voltage distribution networks integrates the discharge system, power transformation and distribution system, and power-consuming equipment through energy conversion devices. By interconnecting low-voltage flexible DC busbars and leveraging the edge computing capabilities of intelligent converged terminals in substations, it enables real-time monitoring and control of system equipment and develops energy scheduling strategies for the interconnected system. This effectively addresses operational stability and power quality issues associated with the integration of large-scale distributed photovoltaic systems and electric vehicles, improving power supply reliability in substations.

[0003] Since flexible interconnection of low-voltage distribution networks is still in its early stages and relevant standards are relatively loose, the commonly used converter power modules currently on the market have the following main defects:

[0004] 1. The DC voltage on the common DC side of the converter power module needs the upper controller to control the current

[0005] Due to the output error of DC voltage between converter power modules, when multiple converter power modules are operated in parallel, circulating current will be caused, requiring the upper-level controller to perform current sharing control, which is heavily dependent on communication and limits the spatial layout of flexible interconnection of low-voltage distribution networks.

[0006] 2. Sudden change in DC side load causes instantaneous power imbalance on the common DC side of the converter power modules.

[0007] When the converter power modules share a common DC side, due to the inconsistent output impedance of the inverter DC side, even if output current sharing is achieved under the coordinated control of the upper-level control, when the load suddenly changes, due to the difference in DC output impedance of the converter power modules, it will lead to different instantaneous output, and in severe cases, it will cause overload of a single converter power module.

[0008] 3. The DC voltage variation range is very narrow, making DC droop difficult to apply

[0009] The converter power module standard generally requires the output DC voltage accuracy to be within the range of ±2%. Therefore, the slope of DC droop control is very small. A small DC sampling error will cause a large DC power error. Therefore, conventional DC droop is not suitable for low-voltage distribution network flexible interconnection application scenarios.

[0010] 4. The loss of AC / DC conversion will cause the AC power accuracy to decrease

[0011] The assessment index of the DC interconnection device is the AC side. DC droop is used to adjust the current and voltage on the DC side, that is, the DC side power. Since power conversion will cause losses, it will inevitably lead to a reduction in the power control accuracy on the AC side.

[0012] How to solve the above technical problems is a difficult technical problem in this field. Summary of the Invention

[0013] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a low-voltage DC interconnection device with droop characteristics and an error correction method, which can maintain the DC voltage and effectively suppress the DC circulating current phenomenon, thereby reducing system costs and enhancing system stability.

[0014] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0015] In a first aspect, the present invention provides a low-voltage DC interconnection device with droop characteristics, comprising:

[0016] AC circuit breaker: used to complete the opening and closing functions of the low-voltage interconnection device and the AC power grid;

[0017] Human-machine interface module: used for real-time display of operating parameters and start-stop control;

[0018] DC circuit breaker: used to complete the opening and closing functions of the DC side of the low-voltage interconnected device and other low-voltage interconnected devices or DC batteries;

[0019] At least one converter power module: the converter power module is provided with an AC side, a DC side and a control side, wherein the AC side is connected to the power grid through an AC circuit breaker (A), the DC side is connected to other low-voltage DC interconnection devices or a DC battery through a DC circuit breaker (D), and the control side is connected to a human-machine interface module; the converter power module has a DC side droop characteristic, which can simulate the droop characteristic of the battery, realize the DC side parallel operation of multiple power modules in the DC side voltage source mode, and complete the AC / DC bidirectional power conversion function.

[0020] Furthermore, the AC circuit breaker is an AC molded case circuit breaker; and the DC circuit breaker is a DC molded case circuit breaker.

[0021] Furthermore, there are several converter power modules;

[0022] After the AC side of several converter power modules (B) is connected in parallel, they are connected to the grid through the AC circuit breaker (A). After the DC side is connected in parallel, they are connected to other low-voltage DC interconnection devices or DC batteries through the DC circuit breaker (D). Several converter power modules (B) are connected to the human-machine interface module (C).

[0023] Furthermore, the converter power module (B) includes a power topology, a sensor, and a controller;

[0024] The power topology is an AC / DC conversion circuit built with IGBTs. The sensor is arranged in series in the AC / DC conversion circuit to detect parameters such as current and voltage at key points of the AC / DC conversion circuit and transmit them to the controller. After the controller completes the calculation, it controls the switching of the IGBT to realize the power conversion function of the AC / DC conversion circuit.

[0025] The sensors include a current sensor and a voltage sensor provided at the input end of the power topology, and a current sensor and a voltage sensor provided at the output end of the power topology; the current sensor and the voltage sensor are both connected to the controller, and the controller is connected to the human-machine interface module;

[0026] The current sensor and voltage sensor are used to detect the AC voltage of the converter power module, the output AC current of the converter power module, the DC voltage, and the DC current.

[0027] Furthermore, the controller is configured to perform the following actions:

[0028] The AC output current and DC output current of the converter power module are obtained from the current sensor, and the controller obtains the AC three-phase grid voltage and DC voltage from the voltage sensor.

[0029] The DC voltage setting value is calculated based on the collected DC current.

[0030] Dual closed-loop control is completed based on the collected grid voltage, AC current and DC voltage output by the converter power module.

[0031] Furthermore, the DC voltage setting value is calculated based on the collected DC current and the droop curve, including:

[0032] The DC current I is collected by the sensor;

[0033] According to the VI droop curve set in the background, the V corresponding to I is obtained through table lookup or function operation;

[0034] The droop curve is set according to the rated power of the converter power module and the desired DC side voltage fluctuation range.

[0035] The droop equation of the droop curve is:

[0036] V=V0-nI

[0037] Wherein, V is the voltage outputted on the DC side of the converter power module after droop control, V0 is the voltage outputted on the DC side of the converter power module at no load, n is the droop coefficient, and I is the current outputted on the DC side of the converter power module.

[0038] Furthermore, the converter power module (B) is provided with a secondary CT detection channel, and a primary CT is installed in the low voltage section to realize the load current detection function of the low voltage section.

[0039] Furthermore, the device also includes a human-machine interface module, and the converter power module (B) uploads converter power module operating parameters to the human-machine interface module (C) and receives control parameters of the human-machine interface module (C).

[0040] Furthermore, the device is also provided with a monitoring background;

[0041] The converter power module (B) is connected to the monitoring background, receives the DC droop curve sent by the monitoring background, and adjusts the DC side power of the power module through the DC droop curve, thereby indirectly controlling the AC side power.

[0042] Furthermore, the controller also has a real-time calibration function for DC voltage;

[0043] Collect the three-phase current signal on the output side of the converter power module and the three-phase grid-connected point voltage signal, calculate the instantaneous active power P output by the converter power module through the rotating coordinate system, and compare it with the reference active power P issued by the monitoring background system. * By making a difference and performing zero-static-error control through the PI controller, the adjustment amount Udc_adj of the sampling error and the AC / DC power conversion loss error is obtained. The adjustment amount is superimposed on the output command signal of the droop controller to correct the error.

[0044] In a second aspect, the present invention provides an error correction method, comprising the following steps:

[0045] The DC current I is collected by the sensor;

[0046] According to the VI droop curve set in the background, the V corresponding to I is obtained through table lookup or function operation;

[0047] The droop curve is set according to the rated power of the converter power module and the desired DC side voltage fluctuation range.

[0048] The droop equation of the droop curve is:

[0049] V=V0-nI

[0050] Wherein, V is the voltage outputted on the DC side of the converter power module after droop control, V0 is the voltage outputted on the DC side of the converter power module at no load, n is the droop coefficient, and I is the current outputted on the DC side of the converter power module.

[0051] Furthermore, the method further comprises:

[0052] Collect the three-phase current signal on the output side of the converter power module and the three-phase grid-connected point voltage signal, and calculate the instantaneous active power P output by the converter power module through the rotating coordinate system;

[0053] The reference active power P issued by the monitoring background system * Make a difference and use the PI controller to perform zero-static-error control to obtain the adjustment value Udc_adj of the sampling error and the AC / DC power conversion loss error;

[0054] The error can be corrected by adding the adjustment amount to the droop controller output command signal.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] The DC side output voltage of the converter power module of the present invention has a droop characteristic, which can realize the DC side constant voltage mode parallel operation of the converter power module without the need for a communication current sharing signal, and the present invention can realize the correction of the voltage sampling signal and the AC / DC power conversion loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 is a schematic diagram of a converter power module of the present invention;

[0058] Figure 2 It is a schematic diagram of the DC droop curve;

[0059] Figure 3 This is a schematic diagram of the DC droop control system of a traditional converter power module;

[0060] Figure 4 Schematic diagram of the DC droop control system of the converter power module of the present invention. DETAILED DESCRIPTION

[0061] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0062] Example 1:

[0063] like Figure 1 As shown, a converter power module used in low-voltage distribution network flexible interconnection application scenarios has a DC droop characteristic and a DC voltage error correction function, which includes an AC circuit breaker, a human-machine interface module, a DC circuit breaker, and a power conversion module; wherein the AC circuit breaker is an AC circuit breaker and the DC circuit breaker is a DC circuit breaker.

[0064] The converter power module includes a controller and an IGBT main topology driven by the controller. The input end of the IGBT main topology is equipped with a current sensor and a voltage sensor to collect the current and voltage at the input end. The output end of the IGBT main topology is equipped with a current sensor and a voltage sensor to collect the current and voltage at the output end. Both the current sensor and the voltage sensor are connected to the controller, and the controller is connected to the human-machine interface module through the CAN bus.

[0065] The controller of the converter power module has a built-in DC droop control algorithm, which can simulate the battery characteristics according to the DC side output power and the preset droop equation, so that the DC output voltage has droop characteristics.

[0066] The specific droop characteristic curve is as follows: Figure 2 As shown, Figure 2 The horizontal axis is power I, and the vertical axis is frequency V. (I n ,V n ) and (I max ,V max ) are two points in the frequency active power curve, and the droop equation is:

[0067] V=V0-nI

[0068] Wherein, V is the voltage outputted on the DC side of the converter power module after droop control, V0 is the voltage outputted on the DC side of the converter power module at no load, n is the droop coefficient, and I is the current outputted on the DC side of the converter power module.

[0069] The converter power module also has the function of real-time calibration of DC voltage. The schematic diagram of the conventional DC droop control system is as follows: Figure 3 The control system diagram of the present invention is shown in FIG. Figure 4 As shown, in order to correct the DC voltage sampling error and the loss of AC-DC power conversion and improve the control accuracy of AC power, an AC power control loop is added to the outer loop of the control system as shown in Figure 4 As shown: The three-phase current signal (ia, ib, ic) on the output side of the converter power module and the three-phase grid-connected point voltage signal (Uga, Ugb, Ugc) are collected to calculate the instantaneous active power (P) output by the converter power module through the rotating coordinate system, and compared with the reference active power (P) issued by the monitoring background system. * ) is used to make the difference, and the PI controller is used to perform zero-static-error control to obtain the adjustment amount Udc_adj of the sampling error and the AC / DC power conversion loss error. The adjustment amount is superimposed on the output command signal of the droop controller to correct the error.

[0070] This embodiment of the present invention provides a low-voltage DC interconnection device with droop characteristics, including:

[0071] AC circuit breaker: used to complete the opening and closing functions of the low-voltage interconnection device and the AC power grid;

[0072] Human-machine interface module: used for real-time display of operating parameters and start-stop control;

[0073] DC circuit breaker: used to complete the opening and closing functions of the DC side of the low-voltage interconnected device and other low-voltage interconnected devices or DC batteries;

[0074] At least one converter power module: the converter power module is provided with an AC side, a DC side and a control side, wherein the AC side is connected to the power grid through an AC circuit breaker (A), the DC side is connected to other low-voltage DC interconnection devices or a DC battery through a DC circuit breaker (D), and the control side is connected to a human-machine interface module; the converter power module has a DC side droop characteristic, which can simulate the droop characteristic of the battery, realize the DC side parallel operation of multiple power modules in the DC side voltage source mode, and complete the AC / DC bidirectional power conversion function.

[0075] The converter power module (B) includes the power topology, sensors, and controllers;

[0076] The power topology is an AC / DC conversion circuit built with IGBTs. The sensor is arranged in series in the AC / DC conversion circuit to detect parameters such as current and voltage at key points of the AC / DC conversion circuit and transmit them to the controller. After the controller completes the calculation, it controls the switching of the IGBT to realize the power conversion function of the AC / DC conversion circuit.

[0077] The sensors include a current sensor and a voltage sensor provided at the input end of the power topology, and a current sensor and a voltage sensor provided at the output end of the IGBT main topology; the current sensor and the voltage sensor are both connected to the controller, and the controller is connected to the human-machine interface module;

[0078] The current sensor and voltage sensor are used to detect the AC voltage of the converter power module, the output AC current of the converter power module, the DC voltage, and the DC current.

[0079] The converter power module (B) features load current detection in the low-voltage substation, enabling harmonic control, reactive power compensation, and three-phase imbalance suppression. The converter power module (B) has a secondary CT detection channel, and a primary CT (current transformer) is installed in the low-voltage substation, enabling load current detection in the low-voltage substation.

[0080] The converter power module (B) uploads the converter power module operating parameters to the human-machine interface module (C) and receives the control parameters of the human-machine interface module (C).

[0081] Operating parameters include: grid voltage, converter power module output AC current, output active power, reactive power, DC side voltage, current, IGBT temperature, ambient temperature

[0082] Control parameters include: active power setting, operation mode setting

[0083] The device is also equipped with a monitoring background;

[0084] The converter power module (B) is connected to the monitoring background, receives the DC droop curve sent by the monitoring background, and adjusts the DC side power of the power module according to the DC droop curve, thereby indirectly controlling the AC side power;

[0085] Detect the DC output current I of the converter power module, calculate the DC voltage V corresponding to I according to the VI curve, and adjust the DC voltage of the converter power module to V;

[0086] The droop curve is set according to the rated power of the converter power module and the desired DC side voltage fluctuation range.

[0087] The converter power module (B) can dynamically correct the DC side sampling error and the AC / DC power error caused by power topology loss according to the AC power command value issued by the monitoring background, thereby correcting the sampling error and improving the accuracy of the AC command power.

[0088] The controller inside the converter power module (B) uses a fiber optic communication interface to the monitoring background, supports the 61850 communication protocol, and uses CAN communication to the human-machine interface module (C) to perform the following actions:

[0089] The AC output current and DC output current of the converter power module are obtained from the current sensor, and the controller obtains the AC three-phase grid voltage and DC voltage from the voltage sensor.

[0090] The DC voltage setting value is calculated based on the collected DC current and the droop curve.

[0091] Based on the collected grid voltage, AC current and DC voltage output by the converter power module, dual closed-loop control is completed (DC voltage closed-loop control is the outer loop, and AC current closed-loop control is the inner loop)

[0092] The actual output active power P is calculated based on the collected grid voltage and grid current, and the difference between it and the reference power P* sent from the background is sent to the PI controller. The closed-loop control obtains the DC voltage correction value V_adj, which is used to correct the DC voltage.

[0093] After completing the droop adjustment of the monitoring background, the converter power module detects the actual power value on the AC side according to the AC reference power sent by the monitoring background, obtains the DC voltage adjustment component through the proportional-integral controller, and completes the correction of the voltage sampling signal and power conversion loss based on this adjustment component.

[0094] The controller of the converter power module has a built-in DC droop control algorithm, which can simulate the battery characteristics according to the DC side output power and the preset droop equation, so that the DC output voltage has droop characteristics.

[0095] The DC droop control algorithm includes:

[0096] The control system collects the DC current I through the sensor;

[0097] According to the VI droop curve set in the background, the V corresponding to I is obtained by looking up the table or function operation.

[0098] Control the DC side output of the converter power module power corresponding to the DC voltage V

[0099] The droop equation is:

[0100] V=V0-nI

[0101] Where V is the DC output voltage of the converter power module after droop control, V0 is the no-load output voltage of the converter power module, n is the droop coefficient, and I is the DC output current of the converter power module. The converter power module also features real-time DC voltage calibration. It calculates the actual output active power P based on the collected grid voltage and current, subtracts it from the reference power P* issued by the backend, and feeds the result into the PI controller. Closed-loop control generates a DC voltage correction value, V_adj, which is used to correct the DC voltage.

[0102] The schematic diagram of a conventional DC droop control system is as follows: Figure 3 The control system diagram of the present invention is shown in FIG. Figure 4 As shown, in order to correct the DC voltage sampling error and the loss of AC-DC power conversion and improve the control accuracy of AC power, an AC power control loop is added to the outer loop of the control system as shown in Figure 4 As shown: The three-phase current signal (ia, ib, ic) on the output side of the converter power module and the three-phase grid-connected point voltage signal (Uga, Ugb, Ugc) are collected to calculate the instantaneous active power (P) output by the converter power module through the rotating coordinate system, and compared with the reference active power (P) issued by the monitoring background system. * ) is used to make the difference, and the PI controller is used to perform zero-static-error control to obtain the adjustment amount Udc_adj of the sampling error and the AC / DC power conversion loss error. The adjustment amount is superimposed on the output command signal of the droop controller to correct the error.

[0103] Example 2:

[0104] This embodiment provides an error correction method applicable to a converter power module, comprising the following steps:

[0105] The DC current I is collected by the sensor;

[0106] According to the VI droop curve set in the background, the V corresponding to I is obtained through table lookup or function operation;

[0107] The droop curve is set according to the rated power of the converter power module and the desired DC side voltage fluctuation range.

[0108] The droop equation of the droop curve is:

[0109] V=V0-nI

[0110] Wherein, V is the voltage outputted on the DC side of the converter power module after droop control, V0 is the voltage outputted on the DC side of the converter power module at no load, n is the droop coefficient, and I is the current outputted on the DC side of the converter power module.

[0111] Collect the three-phase current signal on the output side of the converter power module and the three-phase grid-connected point voltage signal, and calculate the instantaneous active power P output by the converter power module through the rotating coordinate system;

[0112] The reference active power P issued by the monitoring background system * Make a difference and use the PI controller to perform zero-static-error control to obtain the adjustment value Udc_adj of the sampling error and the AC / DC power conversion loss error;

[0113] The error can be corrected by adding the adjustment amount to the droop controller output command signal.

[0114] Specifically, the method of the present invention includes a controller with a built-in DC droop control algorithm, which can simulate battery characteristics based on the DC side output power and a preset droop equation to enable the DC output voltage to have a droop characteristic.

[0115] 1. The control system collects the grid voltage and the AC current output by the converter power module through sensors.

[0116] 2. Calculate the actual output active power P based on the collected grid voltage and the output AC current of the converter power module, subtract it from the reference power P* sent by the background, and send it to the PI controller. Closed-loop control obtains the DC voltage correction value V_adj, which is used to correct the DC voltage.

[0117] The specific droop characteristic curve is as follows: Figure 2 As shown, Figure 2 The horizontal axis is power I, and the vertical axis is frequency V. (In ,V n ) and (I max ,V max ) are two points in the frequency active power curve, and the droop equation is:

[0118] V=V0-nI

[0119] Wherein, V is the voltage outputted on the DC side of the converter power module after droop control, V0 is the voltage outputted on the DC side of the converter power module at no load, n is the droop coefficient, and I is the current outputted on the DC side of the converter power module.

[0120] The error correction method of the converter power module also has the function of real-time calibration of DC voltage. The schematic diagram of the conventional DC droop control system is as follows: Figure 3 The control system diagram of the present invention is shown in FIG. Figure 4 As shown, in order to correct the DC voltage sampling error and the loss of AC-DC power conversion and improve the control accuracy of AC power, an AC power control loop is added to the outer loop of the control system as shown in Figure 4 As shown: The three-phase current signal (ia, ib, ic) on the output side of the converter power module and the three-phase grid-connected point voltage signal (Uga, Ugb, Ugc) are collected to calculate the instantaneous active power (P) output by the converter power module through the rotating coordinate system, and compared with the reference active power (P) issued by the monitoring background system. * ) is used to make the difference, and the PI controller is used to perform zero-static-error control to obtain the adjustment amount Udc_adj of the sampling error and the AC / DC power conversion loss error. The adjustment amount is superimposed on the output command signal of the droop controller to correct the error.

[0121] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0122] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0123] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0124] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0125] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A low voltage DC interconnection device with droop characteristics, characterized in that: include: AC circuit breaker: used to complete the opening and closing functions of the low-voltage interconnection device and the AC power grid; Human-machine interface module: used for real-time display of operating parameters and start-stop control; DC circuit breaker: used to complete the opening and closing functions of the DC side of the low-voltage interconnected device and other low-voltage interconnected devices or DC batteries; At least one converter power module: the converter power module is provided with an AC side, a DC side, and a control side. The AC side is connected to the power grid through an AC circuit breaker, the DC side is connected to other low-voltage DC interconnection devices or a DC battery through a DC circuit breaker, and the control side is connected to a human-machine interface module. The converter power module has a DC side droop characteristic that can simulate the droop characteristic of a battery, enabling the DC side of multiple power modules to operate in parallel in a DC side voltage source mode. The converter power module includes power topology, sensors and controllers; The power topology is an AC / DC conversion circuit built with IGBTs. The sensor is arranged in series in the AC / DC conversion circuit to detect parameters such as current and voltage at key points of the AC / DC conversion circuit and transmit them to the controller. After the controller completes the calculation, it controls the switching of the IGBT to realize the power conversion function of the AC / DC conversion circuit. The sensors include a current sensor and a voltage sensor provided at the input end of the power topology, and a current sensor and a voltage sensor provided at the output end of the power topology; the current sensor and the voltage sensor are both connected to the controller, and the controller is connected to the human-machine interface module; The current sensor and voltage sensor are used to detect the AC voltage of the converter power module, the output AC current of the converter power module, the DC voltage and the DC current; Based on the collected DC current, the DC voltage setting value is calculated, including: The DC current I is collected by the sensor; According to the VI droop curve set in the background, the V corresponding to I is obtained through table lookup or function operation; The droop curve is set according to the rated power of the converter power module and the desired DC side voltage fluctuation range; The droop equation of the droop curve is: V=V0-nI Wherein, V is the voltage outputted on the DC side of the converter power module after droop control, V0 is the voltage outputted on the DC side of the converter power module at no load, n is the droop coefficient, and I is the current outputted on the DC side of the converter power module.

2. The low-voltage DC interconnection device with droop characteristics according to claim 1, characterized in that: The AC circuit breaker is an AC molded case circuit breaker; the DC circuit breaker is a DC molded case circuit breaker; There are several converter power modules; After the AC sides of several converter power modules are connected in parallel, they are connected to the grid through an AC circuit breaker. After the DC sides are connected in parallel, they are connected to other low-voltage DC interconnection devices or DC batteries through a DC circuit breaker. Several converter power modules are connected to the human-machine interface module.

3. The low-voltage DC interconnection device with droop characteristics according to claim 1, characterized in that: The controller is used to perform the following actions: The AC output current and DC output current of the converter power module are obtained from the current sensor, and the controller obtains the AC three-phase grid voltage and DC voltage from the voltage sensor; According to the collected DC current, the DC voltage setting value is calculated; Dual closed-loop control is completed based on the collected grid voltage, AC current and DC voltage output by the converter power module.

4. The low-voltage DC interconnection device with droop characteristics according to claim 1, characterized in that: The converter power module is equipped with a secondary CT detection channel, and a primary CT is installed in the low-voltage section to implement the load current detection function in the low-voltage section. The device further includes a human-machine interface module. The converter power module uploads converter power module operating parameters to the human-machine interface module and receives control parameters of the human-machine interface module.

5. The low-voltage DC interconnection device with droop characteristics according to claim 1, characterized in that: The device is also provided with a monitoring background; The converter power module is connected to the monitoring background, receives the DC droop curve sent by the monitoring background, and adjusts the DC side power of the power module according to the DC droop curve, thereby indirectly controlling the AC side power.

6. The low-voltage DC interconnection device with droop characteristics according to claim 5, characterized in that: The controller also has a real-time calibration function for DC voltage; Collect the three-phase current signal on the output side of the converter power module and the three-phase grid-connected point voltage signal, calculate the instantaneous active power P output by the converter power module through the rotating coordinate system, and compare it with the reference active power P issued by the monitoring background system. * By making a difference and performing zero-static-error control through the PI controller, the adjustment amount Udc_adj of the sampling error and the AC / DC power conversion loss error is obtained. The adjustment amount is superimposed on the output command signal of the droop controller to correct the error.

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