Power conversion device

Abstract

The invention provides power conversion equipment. The power conversion equipment comprises a power conversion circuit, a sampling module, a communication module, an isolator, an alternating current end and a controller, under the condition that the alternating current end is connected with a load and disconnected from a power grid, the sampling module is used for outputting a direct current voltage analog signal to the communication module when receiving a voltage signal output by the power conversion circuit; the communication module is used for outputting a digital signal to the isolator when receiving a direct-current voltage analog signal; the isolator is used for sending a digital signal to the controller and electrically isolating the controller from the communication module; and the controller is connected with the power conversion circuit and is used for reducing the direct current component in the voltage signal output by the power conversion circuit under the condition that the digital signal is received. When the power conversion equipment operates in an off-grid mode and supplies power to the load, the direct current component in the voltage signal output to the load can be reduced, and meanwhile the power density of the power conversion equipment is improved.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and particularly to a power conversion device. Background Art

[0002] With the increasing penetration rate of new energy power generation into the grid, more and more photovoltaic devices, energy storage devices, etc. are connected to the grid or load through inverters. Generally, there are differences in the internal resistance and dead time of the switching tubes of different bridge arms in the inverter, resulting in a DC component in the AC voltage output by the inverter. When the inverter is connected to the grid and load, and the inverter converts the DC power output by photovoltaic devices, energy storage devices, etc. into AC power to supply power to the grid, the DC component in the AC voltage output by the inverter will not affect the stable operation of the load. However, when the inverter is disconnected from the grid and supplies power to the load, the DC component in the AC voltage output by the inverter will cause problems such as magnetic saturation and increased harmonics in the load, which has an adverse impact on the operation of the load. Therefore, how to reduce the DC component in the AC voltage output by the inverter when the inverter operates off-grid and supplies power to the load is a technical problem that those skilled in the art urgently need to solve. Summary of the Invention

[0003] This application provides a power conversion device, which can reduce the DC component in the voltage signal output to the load, improve the power density of the power conversion device, and has high reliability and strong applicability when operating off-grid and supplying power to the load.

[0004] In a first aspect, this application provides a power conversion device, which includes a power conversion circuit, a sampling module, a communication module, an isolator, an AC terminal, and a controller; wherein, the power conversion circuit is used to convert the DC power from a photovoltaic module or an energy storage battery into AC power and output the AC power through the AC terminal; when the AC terminal is connected to the load and disconnected from the grid, the sampling module is used to output a DC voltage analog signal to the communication module when receiving the voltage signal output by the power conversion circuit, and the DC voltage analog signal is the DC component in the voltage signal output by the power conversion circuit; the communication module is used to output a digital signal to the isolator when receiving the DC voltage analog signal to filter out the common-mode voltage signal in the DC voltage analog signal; the isolator is used to send a digital signal to the controller and electrically isolate the controller from the communication module; the controller is connected to the power conversion circuit and is used to reduce the DC component in the voltage signal output by the power conversion circuit when receiving the digital signal.

[0005] In this application, when the communication module converts the DC voltage analog signal into a digital signal, since the common-mode voltage signal contained in the DC voltage analog signal will not be converted into a digital signal, the communication module can filter out the common-mode voltage signal after converting the DC voltage analog signal into a digital signal, avoiding the influence of the common-mode voltage signal on the accuracy of adjusting the DC component of the subsequent power conversion device. At the same time, the digital signal output by the communication module can be used to characterize the magnitude of the DC component in the voltage signal output by the power conversion circuit. Then, the controller can obtain the magnitude of the DC component in the voltage signal output by the power conversion circuit according to this digital signal, so as to accurately adjust the reduction of the DC component in the voltage signal output by the power conversion circuit and reduce the adverse effects of the DC component on the load. In addition, the power conversion device also realizes external communication through the communication module, that is, the power conversion device multiplexes the functions of the communication module. While using the communication module to achieve external communication, it also uses the communication module to filter out the common-mode voltage signal, which can simplify the manufacturing process and improve the power density of the power conversion device. Further, the power conversion device electrically isolates the communication module and the controller through an isolator, which can ensure safe, noise-reducing and reliable signal transmission during external communication.

[0006] In a possible implementation manner, the power conversion device further includes a neutral line and a live line. The power conversion circuit is used to connect the AC terminal of the power conversion device through the neutral line and the live line, and the sampling module is connected to the live line and the neutral line; the sampling module is used to output a DC voltage analog signal to the communication module when receiving the voltage signals transmitted on the live line and the neutral line; the voltage signals transmitted on the live line and the neutral line are the voltage signals output by the power conversion circuit. In this application, when the power conversion device includes one or more live lines, the sampling module obtains the voltage signal output by the power conversion circuit by receiving the voltage signals transmitted on the neutral line and the live line, ensuring accurate sampling and avoiding the problem that the voltage signal obtained by the sampling module is inaccurate when the power conversion circuit only receives the voltage signal transmitted on the live line. That is, the sampling module of this application can be applicable to different application scenarios, and the implementation method is simple and has strong applicability.

[0007] In a possible implementation, the power conversion device further includes a first relay and a second relay. The first relay is disposed on the neutral line, and thus the second relay is disposed on the live line; the connection point of the sampling module to the neutral line is located between the first relay and the power conversion circuit, and the connection point of the sampling module to the live line is located between the second relay and the power conversion circuit; the sampling module is configured to receive voltage signals transmitted on the live line and the neutral line when the AC terminal is connected to the load, disconnected from the power grid, and the first relay and the second relay are open; the controller is configured to control the first relay and the second relay to close after the DC component in the voltage signal output by the power conversion circuit is reduced to a target range. In this application, before the power conversion device supplies power to the load, that is, when the AC terminal is connected to the load and disconnected from the power grid, and the first relay and the second relay are open, the power conversion device first adjusts the reduction of the DC component in the voltage signal output by the power conversion circuit, and after the DC component in the voltage signal output by the power conversion circuit is reduced to the target range, then controls the first relay and the second relay to close, which can effectively reduce the adverse effects of the DC component on the load.

[0008] In a possible implementation, the sampling module includes a first capacitor, a first impedance unit, a second impedance unit, and an operational amplifier. The non-inverting input terminal of the operational amplifier is connected to the neutral line through the first impedance unit, the inverting input terminal of the operational amplifier is connected to the live line through the second impedance unit, and the first capacitor is disposed between the non-inverting input terminal and the inverting input terminal of the operational amplifier; the resistance values of the first impedance unit and the second impedance unit are greater than or equal to 1 megaohm. In this application, the resistance values of the first impedance unit and the second impedance unit in the sampling module are greater than or equal to 1 megaohm, so that the first impedance unit, the second impedance unit, and the first capacitor form a low-pass filter, and achieve a good low-pass filtering effect on the received voltage signals transmitted on the live line and the neutral line, thereby filtering out high-frequency AC voltage analog signals and outputting low-frequency DC voltage analog signals. Further, the operational amplifier in the sampling module amplifies the error of the DC voltage analog signals received through the non-inverting input terminal and the inverting input terminal to output a DC voltage analog signal for characterizing the magnitude of the DC component in the voltage signal output by the power conversion circuit, facilitating subsequent adjustment of the reduction of the DC component in the voltage signal output by the power conversion circuit. The structure of the sampling module is simple, easy to implement, and has strong applicability.

[0009] In a possible implementation, the first impedance unit includes a first inductor and a plurality of first resistors connected in series, and the second impedance unit includes a second inductor and a plurality of second resistors connected in series. In this application, the resistance value of the first impedance unit is equal to the total resistance value of the plurality of first resistors. By adjusting the number and resistance value of the first resistors, the total resistance value of the first impedance unit can be made greater than or equal to 1 megohm. Similarly, the resistance value of the second impedance unit is equal to the total resistance value of the plurality of second resistors. By adjusting the number and resistance value of the second resistors, the total resistance value of the second impedance unit can be made greater than or equal to 1 megohm. The structure is simple and easy to adjust. In addition, the first inductor in the first impedance unit and the second inductor in the second impedance unit can filter out high-frequency interference signals in the received voltage signal, improving reliability.

[0010] In a possible implementation, the sampling module further includes a first switch unit and a second switch unit. The first switch unit is connected in series with the first impedance unit, and the second switch unit is connected in series with the second impedance unit. The controller is configured to control the first switch unit and the second switch unit to be turned off when the AC terminal is connected to the power grid or disconnected from the load. In this application, when the AC terminal of the power conversion device is connected to the power grid or disconnected from the load, the controller controls the first switch unit and the second switch unit to be turned off, so that the power conversion device stops receiving the voltage signal output by the power conversion circuit through the sampling module. Then, the power conversion device no longer detects or adjusts the DC component in the voltage signal output by the power conversion circuit, which can reduce the energy consumption of the power conversion device.

[0011] In a possible implementation, the power conversion device further includes a ground wire and a neutral wire, and the neutral wire is connected to the ground wire. The power conversion device further includes a second capacitor, and the second capacitor is connected in parallel with the first impedance unit. In this application, since the first impedance unit is connected to the neutral wire and the operational amplifier, and the operational amplifier is connected to the communication module, the first impedance unit is equivalent to being connected between the ground wire and the communication module. And the second impedance unit is connected to the live wire and the operational amplifier, so that the second impedance unit is equivalent to being connected between the live wire and the communication module. Further, by connecting the first impedance unit in parallel with the second capacitor, the voltage across the first impedance unit can be effectively adjusted, thereby reducing the leakage current generated by the first impedance unit between the ground wire and the communication module, and avoiding the resistance values of the first impedance unit and the second impedance unit being close. When the voltage across the first impedance unit is close to half of the voltage between the live wire and the ground wire, a large leakage current is generated between the ground wire and the communication module, improving safety.

[0012] In a possible implementation, the power conversion device further includes a ground wire and a neutral wire. The neutral wire is connected to the ground wire. The power conversion device further includes a third capacitor. The reference zero potential terminal of the communication module is connected to the ground wire or the neutral wire through the third capacitor. In this application, since the first impedance unit is connected to the neutral wire and the operational amplifier, and the operational amplifier is connected to the communication module, the first impedance unit is equivalent to being connected between the ground wire and the communication module. And the second impedance unit is connected to the live wire and the operational amplifier, so that the second impedance unit is equivalent to being connected between the live wire and the communication module. At the same time, the third capacitor is equivalent to being connected in parallel with the first impedance unit. Thus, the voltage across the first impedance unit can be effectively adjusted, thereby reducing the leakage current generated by the first impedance unit between the ground wire and the communication module, and avoiding the situation where the resistance values of the first impedance unit and the second impedance unit are close. When the voltage across the first impedance unit is close to half of the voltage between the live wire and the ground wire, a large leakage current is generated between the ground wire and the communication module, improving safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 FIG. is a schematic diagram of an application scenario of the power supply system provided by this application;

[0014] Figure 2 FIG. is a schematic diagram of a power conversion device provided by this application;

[0015] Figure 3 FIG. is a schematic diagram of a sampling module provided by this application;

[0016] Figure 4 FIG. is another schematic diagram of a sampling module provided by this application;

[0017] Figure 5 FIG. is yet another schematic diagram of a sampling module provided by this application;

[0018] Figure 6 FIG. is an equivalent connection schematic diagram of a sampling module provided by this application;

[0019] Figure 7 FIG. is another schematic diagram of a power conversion device provided by this application;

[0020] Figure 8 FIG. is yet another schematic diagram of a sampling module provided by this application;

[0021] Figure 9 FIG. is yet another schematic diagram of a power conversion device provided by this application;

[0022] Figure 10 FIG. is yet another schematic diagram of a power conversion device provided by this application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] See Figure 1 , Figure 1It is a schematic diagram of an application scenario of the power supply system provided by this application. The power supply system provided by this application includes an energy storage inverter and a photovoltaic inverter. Among them, the DC terminal of the energy storage inverter is used to connect to the energy storage battery, and the AC terminal of the energy storage inverter is used to connect to the box-type transformer. The energy storage inverter converts the direct current from the energy storage battery into alternating current and outputs the alternating current to the box-type transformer. The box-type transformer transforms and distributes the alternating current to supply power to the power grid. The DC terminal of the photovoltaic inverter is used to connect to the photovoltaic module, and the AC terminal of the photovoltaic inverter is used to connect to the box-type transformer. The photovoltaic inverter converts the direct current from the photovoltaic module into alternating current and outputs the alternating current to the box-type transformer to supply power to the power grid through the box-type transformer. The energy storage inverter and the inverter are both used to provide functions such as power conversion in the power supply system. The energy storage inverter and the photovoltaic inverter can be collectively referred to as power conversion devices.

[0024] In Figure 1 In the application scenario of the power supply system shown, the power conversion device includes multiple bridge arms. By controlling the actions of the switching tubes in each bridge arm, the direct current is converted into alternating current for output. Among them, during the process of the power conversion device converting the direct current, due to the differences in the internal resistance and dead time of the switching tubes in different bridge arms, there is a DC component in the alternating voltage output by the power conversion device. As described in the background art, when the power conversion device is disconnected from the power grid and supplies power to the load, the DC component in the alternating voltage output by the power conversion device will cause problems such as magnetic saturation and increased harmonics in the load, which have an adverse impact on the operation of the load. Therefore, how to reduce the DC component in the alternating voltage output by the power conversion device when the power conversion device is disconnected from the power grid and supplies power to the load is a technical problem that those skilled in the art urgently need to solve.

[0025] For this reason, this application provides a power conversion device. When the power conversion device operates off-grid and supplies power to the load, it can reduce the DC component in the voltage signal output to the load, improve the power density of the power conversion device at the same time, and has high reliability and strong applicability.

[0026] The following takes the power conversion device as a photovoltaic inverter as an example for illustration. The implementation principle of the power conversion device as an energy storage inverter can refer to the following description, and this application will not elaborate on it. Specifically, please refer to Figure 2 , Figure 2 It is a schematic diagram of the power conversion device provided by this application. Figure 2The power conversion device shown includes a power conversion circuit and an AC terminal. The input terminal of the power conversion circuit is used to connect to a photovoltaic module, and the output terminal of the power conversion circuit is used to connect to the AC terminal of the power conversion device. When the power conversion device is disconnected from the power grid and electrically connected to a load, the power conversion circuit can convert the DC power provided by the photovoltaic module into AC power and supply power to the load through the AC terminal. Since there is a DC component in the voltage signal output by the power conversion circuit when the power conversion device operates off-grid and supplies power to the load, it will have an adverse effect on the load. Therefore, a sampling module and a controller are also provided in the power conversion device, which can, when operating off-grid, obtain the magnitude of the DC component in the voltage signal output by the power conversion circuit through the sampling module, and accurately adjust the reduction of the DC component in the voltage signal output by the power conversion circuit according to the magnitude of the DC component through the controller.

[0027] Among them, the sampling module is connected to the output terminal of the power conversion circuit and can collect the voltage signal output by the power conversion circuit. Specifically, when the power conversion circuit outputs a voltage signal, the sampling module receives the voltage signal output by the power conversion circuit. It should be noted that since the magnitude of the DC component in the voltage signal output by the power conversion circuit is positively correlated with the DC voltage analog signal in the voltage signal output by the power conversion circuit, when the sampling module receives the voltage signal output by the power conversion circuit, it can collect the DC voltage analog signal in the voltage signal, and the voltage signal output by the power conversion circuit also includes an AC voltage analog signal. Therefore, when the sampling module receives the voltage signal output by the power conversion circuit, it can filter out the AC voltage analog signal in the voltage signal and then output the DC voltage analog signal. This DC voltage analog signal can represent the magnitude of the DC component in the voltage signal output by the power conversion circuit.

[0028] In addition, it should be noted that since there may be a common-mode voltage signal in the voltage signal output by the power conversion circuit, the DC voltage analog signal collected by the sampling module according to the voltage signal output by the power conversion circuit also includes this common-mode voltage signal, and the presence of this common-mode voltage signal will affect the accuracy of subsequent adjustment of the DC component. Therefore, the power conversion device filters out the common-mode voltage signal in the DC voltage analog signal through the communication module.

[0029] Specifically, the sampling module outputs the collected DC voltage analog signal to the communication module. After receiving the DC voltage analog signal, the communication module performs analog-to-digital conversion on the DC voltage analog signal, that is, converts the DC voltage analog signal into a digital signal. At the same time, since the common-mode voltage signal contained in the DC voltage analog signal will not be converted into a digital signal when the communication module performs analog-to-digital conversion on the DC voltage analog signal, there is no common-mode voltage signal in the digital signal, so that the filtering of the common-mode voltage signal can be achieved. As can be seen from the above, the DC voltage analog signal is used to characterize the magnitude of the DC component in the voltage signal output by the power conversion circuit. Then, the digital signal obtained by performing analog-to-digital conversion on the DC voltage analog signal can also be used to characterize the magnitude of the DC component in the voltage signal output by the power conversion circuit, and the digital signal filters out the interference of the common-mode voltage signal, so that the accuracy of adjusting the DC component can be guaranteed.

[0030] In some feasible embodiments, the communication module can be used not only to filter out the common-mode voltage signal, but also to realize the external communication of the power conversion device. Specifically, the communication module is provided with a communication interface, such as a Universal Serial Bus (USB) interface, an RS485 interface, a CAN communication interface, or an external antenna interface, etc. The communication module can receive the data signal sent by the external device through the communication interface, and can also send the data signal to the external device through the communication interface. The above are only examples and do not constitute a limitation to the present application.

[0031] It can be seen that in the present application, while the power conversion device uses the communication module to realize external communication, it also uses the communication module to perform analog-to-digital conversion on the DC voltage analog signal to filter out the common-mode voltage signal, that is, the communication module is functionally reused, so that the power density of the power conversion device can be improved.

[0032] Further, the power conversion device further includes an isolator. The input end of the isolator is connected to the communication module and is used to receive the digital signal output after the communication module performs analog-to-digital conversion on the DC voltage analog signal. At the same time, the output end of the isolator is connected to the controller and is used to output the received digital signal to the controller. Among them. The input end and the output end of the isolator are separated by an electrical isolation layer, so that electrical isolation between the communication module and the controller can be achieved. It should be noted that when the controller is directly electrically connected to the power conversion circuit in a high-voltage environment (the power conversion circuit performs voltage conversion and adjustment and needs to withstand high voltage and current), the controller also needs to withstand high voltage and current. In order to ensure that the high-voltage environment of the controller does not interfere with the signal transmission of the communication module, the power conversion device electrically isolates the communication module and the controller through the isolator, which can ensure safe, noise-reducing and reliable signal transmission between the communication module and the controller.

[0033] It can be seen that by using an isolator to electrically isolate the communication module and the controller, the power conversion device of the present application enables the communication module to filter out the common-mode voltage signal while ensuring the stability of the external communication function of the communication module.

[0034] Furthermore, after receiving the digital signal sent by the isolator, in order to obtain the magnitude of the DC component in the voltage signal output by the power conversion circuit based on this digital signal, the controller can convert the digital signal from digital to analog. As can be seen from the above, this digital signal can represent the magnitude of the DC component in the voltage signal output by the power conversion circuit, so the analog signal obtained after converting the digital signal from digital to analog can also represent the magnitude of the DC component in the voltage signal output by the power conversion circuit. It can be understood that the controller can output a pulse width modulation signal to the power conversion circuit according to the magnitude of the DC component in the voltage signal output by the power conversion circuit to drive the switching tubes of each arm in the power conversion circuit to act, thereby reducing the DC component in the voltage signal output by the power conversion circuit and reducing the adverse effects caused by the DC component on the load. Exemplarily, assuming that the analog signal obtained by the controller after converting the digital signal from digital to analog is a DC voltage analog signal with a voltage magnitude equal to 2 volts, it means that the magnitude of the DC component in the voltage signal output by the power conversion circuit is 2 volts. Then the controller can control the actions of the switching tubes in each arm to adjust the DC component in the voltage signal output by the power conversion circuit to decrease from 2 volts to 1 volt or 0 volts, etc. The above is only an example and does not constitute a limitation to the present application.

[0035] When the power conversion device provided by this application operates off-grid and supplies power to a load, it receives the voltage signal output by the power conversion circuit through a sampling module. After filtering out the AC voltage analog signal in the voltage signal through the sampling module, it outputs a DC voltage analog signal to the communication module. Since the common-mode voltage signal contained in this DC voltage analog signal will have an adverse effect on the subsequent regulation of the DC component, the power conversion device also performs analog-to-digital conversion on this DC voltage analog signal through the communication module and outputs a digital signal. Among them, the common-mode voltage signal in the DC voltage analog signal will not be converted into a digital signal, so the digital signal output by the communication module filters out the common-mode voltage signal. At the same time, the power conversion device can also achieve external communication through this communication module, that is, by multiplexing the functions of the communication module, the power conversion device can, while using the communication module to perform analog-to-digital conversion on the DC voltage analog signal to filter out the common-mode voltage signal, also use the communication module to achieve external communication, thereby simplifying the manufacturing process and increasing the power density of the power conversion device. Further, the power conversion device receives the digital signal output by the communication module through an isolator and sends the digital signal to the controller through this isolator. This digital signal can represent the magnitude of the DC component in the voltage signal output by the power conversion circuit, enabling the controller to accurately adjust the reduction of the DC component in the voltage signal output by the power conversion circuit based on this digital signal, thereby reducing the adverse effects of the DC component on the load. In addition, the power conversion device electrically isolates the communication module and the controller through the isolator, which can ensure safe, noise-reducing, and reliable signal transmission.

[0036] The power conversion device provided by this application connects to the load through a live wire and a neutral wire, that is, it supplies power to the load using a single-phase system. Optionally, the power conversion device can also add a ground wire to connect to the load to prevent electric shock. Or, the power conversion device connects to the load through three live wires and a neutral wire, that is, it supplies power to the load using a three-phase four-wire system. Or, the power conversion device connects to the grid through three live wires, a neutral wire, and a ground wire, that is, it supplies electrical energy to the load using a three-phase five-wire system. Among them, the neutral wire of the power conversion device, as the wire providing the current loop to the load, can ensure that a power supply loop is formed between the power conversion device and the load. The ground wire of the power conversion device can introduce the leakage current generated in the power conversion device into the ground, ensuring the stability of the power conversion device and the load.

[0037] In some feasible implementation manners, please refer to again Figure 2, when the power conversion device supplies power to the load using a single-phase system, the power conversion device includes a neutral line N and a live line A. Among them, the output end of the power conversion circuit is connected to the AC end of the power conversion device through the neutral line N and the live line A. When the load is connected to the AC end, the power conversion circuit supplies power to the load through the live line A and the neutral line N. In order to collect the voltage signal output by the power conversion circuit, the sampling module is respectively connected to the live line A and the neutral line N, and receives the voltage signals transmitted on the live line A and the neutral line N. The sampling module filters out the AC voltage analog signals in the voltage signals transmitted on the received live line A and neutral line N, and outputs a DC voltage analog signal.

[0038] In some feasible embodiments, a first relay and a second relay are also provided in the power conversion device. The first relay is provided on the neutral line, and the second relay is provided on the live line. When the first relay and the second relay are closed, the power conversion circuit supplies power to the load, and conversely, the power conversion circuit stops supplying power to the load. In order to detect and adjust the reduction of the DC component in the voltage signal output by the power conversion circuit before the power conversion circuit supplies power to the load, thereby reducing the adverse effects of the DC component on the load, the connection point of the sampling module to the neutral line is located between the first relay and the power conversion circuit. At the same time, the connection point of the sampling module to the live line is located between the second relay and the power conversion circuit. When the first relay and the second relay are disconnected, the power conversion device first adjusts the reduction of the DC component in the voltage signal output by the power conversion circuit, and after the DC component in the voltage signal output by the power conversion circuit is reduced to the target range, then controls the first relay and the second relay to close. Among them, the target range refers to the numerical range of the DC component size when the DC component in the voltage signal output by the power conversion circuit is small or negligible. Exemplarily, this target range is specifically less than or equal to 1 volt, which is only an example and does not constitute a limitation of this application. It can be understood that after the power conversion device adjusts the DC component in the voltage signal output by the power conversion circuit to the target range through the controller, and then controls the first relay and the second relay to conduct to supply power to the load, it can ensure that the DC component in the voltage signal when supplying power to the load is small or negligible, thereby effectively reducing the adverse effects of the DC component on the load.

[0039] It should be noted that the number of the first relay and the second relay in the power conversion device can be one or more. For the convenience of description, the following content takes the number of both the first relay and the second relay as two as an example.

[0040] Exemplarily, such as Figure 2As shown, the power conversion device includes a first relay K11, a first relay K12, a second relay K21, and a second relay K22. Specifically, the connection point of the sampling module to the neutral line N is located between the first relay K11 and the power conversion circuit. Before the power conversion circuit supplies power to the load, the first relay K11 and the first relay K12 remain open, and the sampling module collects the voltage signal at the connection point to facilitate subsequent adjustment of the magnitude of the DC component. After the magnitude of the DC component in the voltage signal output by the power conversion circuit is adjusted to the target range, the controller controls the first relay K11 and the first relay K12 to close to supply power to the load. Alternatively, the connection point of the sampling module to the neutral line N is located between the first relay K12 and the first relay K11. Before the power conversion circuit supplies power to the load, the controller first controls the first relay K11 to close and keeps the first relay K12 open, and the sampling module collects the voltage signal at the connection point to facilitate subsequent adjustment of the magnitude of the DC component. After the magnitude of the DC component in the voltage signal output by the power conversion circuit is adjusted to the target range, the controller controls the first relay K12 to close to supply power to the load.

[0041] Similarly, the connection point of the sampling module to the live wire A is located between the second relay K21 and the power conversion circuit, or the connection point of the sampling module to the live wire A is also located between the second relay K22 and the second relay K21. The implementation principle of the controller controlling the second relay K22 and the second relay K21 to open or close can refer to the specific implementation manners of the controller controlling the first relay K11 and the first relay K12 to open or close in the above content, and this application will not elaborate on it.

[0042] In some feasible embodiments, the sampling module specifically includes a first capacitor, a first impedance unit, a second impedance unit, and an operational amplifier. Among them, one end of the first impedance unit is connected to the neutral line to receive the voltage signal transmitted on the neutral line, and one end of the second impedance unit is connected to the live line to receive the voltage signal transmitted on the live line. The first capacitor is disposed between the other end of the first impedance unit and the other end of the second impedance unit, and can form a low-pass filter with the first impedance unit and the second impedance unit to filter out the AC voltage analog signal in the received voltage signal. It should be noted that, in order to ensure the low-pass filtering effect on the AC voltage analog signal in the voltage signal, the resistance value of the first impedance unit is greater than or equal to 1 megohm, and the resistance value of the second impedance unit is also greater than or equal to 1 megohm. Further, in order to obtain the DC voltage analog signal in the voltage signal output by the power conversion circuit, the other end of the first impedance unit is further connected to the non-inverting input terminal of the operational amplifier, and the other end of the second impedance unit is further connected to the inverting input terminal of the operational amplifier. The operational amplifier performs error amplification processing on the voltage signals received at the non-inverting input terminal and the inverting input terminal, and outputs the above-mentioned DC voltage analog signal to the communication module.

[0043] Exemplarily, please refer to Figure 3 , Figure 3 which is a schematic diagram of the sampling module provided by this application. As Figure 3 shown, the sampling module includes a first capacitor C1, a first impedance unit, a second impedance unit, and an operational amplifier OP. The non-inverting input terminal of the operational amplifier OP is connected to the neutral line N through the first impedance unit, the inverting input terminal is connected to the live line A through the second impedance unit, and the first capacitor C1 is disposed between the non-inverting input terminal and the inverting input terminal of the operational amplifier OP. Among them, the first impedance unit includes a plurality of first resistors R1 connected in series, and the second impedance unit includes a plurality of second resistors R2 connected in series.

[0044] In some feasible embodiments, when the power conversion device does not need to supply power to the load, in order to reduce energy consumption, the power conversion device does not adjust the DC component in the voltage signal output by the power conversion circuit, and then the sampling module can stop receiving the voltage signal output by the power conversion circuit. For this purpose, a first switch unit connected in series with the first impedance unit is arranged in the sampling module, and a second switch unit connected in series with the second impedance unit is arranged. When the power conversion device does not need to supply power to the load, the controller controls the first switch unit and the second switch unit to disconnect, so that the sampling module stops receiving the voltage signal output by the power conversion circuit, and then the power conversion device no longer detects or adjusts the DC component in the voltage signal output by the power conversion circuit, thereby reducing the energy consumption of the power conversion device. Similarly, when the power conversion device supplies power to the load or before the power conversion device is about to supply power to the load, the controller controls the above-mentioned first switch unit and the second switch unit to close to detect and adjust the DC component in the voltage signal and reduce the adverse effects of the DC component on the load.

[0045] Exemplarily, please refer to Figure 4 , Figure 4 which is another schematic diagram of the sampling module provided by this application. As Figure 4 shown, the first switch unit in the sampling module is connected in series with the first impedance unit, and the second switch unit is connected in series with the second impedance unit. Among them, Figure 4 the set positions of the first switch unit and the second switch unit shown are only examples. The first switch unit and the second switch unit are specifically controllable switch devices such as relays or triodes, and this application does not limit this.

[0046] In some feasible embodiments, as Figure 4 shown, the first impedance unit further includes a first inductor L1, and the first inductor L1 can filter out high-frequency interference signals on the received neutral line N. Similarly, the second impedance unit further includes a second inductor L2, and the second inductor L2 can filter out high-frequency interference signals on the received live line A.

[0047] In some feasible embodiments, the specific structure of the sampling module can also be as Figure 5 shown, Figure 5 which is another schematic diagram of the sampling module provided by this application. Different from Figure 4 , Figure 5 the sampling module shown also sets a third resistor R3 connected in series with the first impedance unit and a fourth resistor R4 connected in series with the second impedance unit. The third resistor R3 and the fourth resistor R4 can suppress noise interference, improve the purity and signal-to-noise ratio of the signal, and enhance the stability of the circuit. In addition, Figure 5The sampling module shown is also provided with a reference resistor Rref. The reference resistor Rref is connected to the non-inverting input terminal of the operational amplifier OP, and can provide a reference voltage to the operational amplifier OP to set the operating point of the operational amplifier OP, ensuring that the signal output by the operational amplifier OP fluctuates within a normal range and avoiding signal distortion. In addition, Figure 5 The sampling module shown is also provided with a feedback resistor R5. The feedback resistor is arranged between the output terminal and the inverting input terminal of the operational amplifier OP, and can form a negative feedback adjustment, enabling the operational amplifier OP to operate in the linear region. Figure 5 The operational amplifier OP in the sampling module shown is a dual-power operational amplifier, that is, the operational amplifier can operate based on the power supplies +V1 and -V1. Figure 5 What is shown is only an example, and the specific structure of the sampling module can be flexibly adjusted according to actual requirements, and the present application will not give examples one by one here.

[0048] In some feasible implementation manners, it can be known from the above that when the power conversion device supplies power to the load in a single-phase system, the power conversion device can also be connected to the load through a ground wire. The ground wire can introduce the leakage current generated in the power conversion device into the ground to prevent electric shock. It should be noted that when the ground wire of the power conversion device is connected to the neutral wire, since the first impedance unit of the sampling module is respectively connected to the neutral wire and the operational amplifier, and the operational amplifier is connected to the communication module, and the reference zero potential of the operational amplifier is provided by the communication module, the first impedance unit is equivalent to being connected between the ground wire and the reference zero potential terminal of the communication module. Similarly, the second impedance unit in the sampling module is respectively connected to the live wire and the operational amplifier, then the first impedance unit is equivalent to being connected between the live wire and the reference zero potential terminal of the communication module. Exemplarily, please refer to Figure 6As shown, the first impedance unit is equivalently disposed between the ground wire PE and the reference zero potential terminal of the communication module, and the second impedance unit is equivalently disposed between the live wire A and the reference zero potential terminal of the communication module, and the ground wire PE is connected to the neutral wire N. Further, since the resistance values of the first impedance unit and the second impedance unit are close (both greater than or equal to 1 megaohm), according to the principle of resistor voltage division, the voltage division across the first impedance unit is relatively large (close to half of the voltage between the live wire and the ground wire), resulting in a relatively large leakage current between the ground wire PE and the reference zero potential terminal of the communication module. When the operation and maintenance personnel touch the communication module, electric shock may occur, posing a safety hazard. Therefore, in this application, a third capacitor C3 is provided between the reference zero potential terminal of the communication module and the ground wire PE. The third capacitor C3 is connected in parallel with the first impedance unit, which can reduce the voltage division generated by the first impedance unit, thereby reducing the generated leakage current. Exemplarily, when the resistance values of the first impedance unit and the second impedance unit are 2 megaohms, the capacitance value of the third capacitor C3 is set to 10 nanofarads, which can effectively reduce the leakage current. Among them, the third capacitor is specifically disposed inside or outside the communication module, Figure 6 The third capacitor C3 shown is only for equivalent illustration and does not constitute a limitation to this application.

[0049] In some feasible embodiments, the sampling module sets a second capacitor in the sampling module. Exemplarily, please refer again to Figure 5 As shown, the second capacitor C2 is connected in parallel with the first impedance unit in the sampling module. The function of this second capacitor is the same as that of the above-mentioned third capacitor, which can reduce the magnitude of the voltage division generated by the first impedance unit, and thus can reduce the leakage current generated between the ground wire and the communication module when the ground wire and the neutral wire of the power conversion device are connected.

[0050] In some feasible embodiments, when the power conversion device supplies power to a load using a three-phase four-wire system, the specific structure of the power conversion device can be as shown in Figure 7 As shown, Figure 7 This is another schematic diagram of the power conversion device provided by this application. Different from the power conversion device shown in Figure 2 the power conversion device shown in Figure 7 includes three live wires: live wire A, live wire B, and live wire C. The sampling module is respectively connected to the live wire A, live wire B, live wire C, and the neutral wire N to receive the voltage signals transmitted on the live wire A, live wire B, live wire C, and the neutral wire N. Specifically, Figure 7 For the specific implementation manners of the power conversion circuit, sampling module, communication module, isolator, and controller in the power conversion device shown, reference can be made to the specific implementation manners in the above Figures 2 to 6 This application will not elaborate herein.

[0051] In some feasible embodiments, when the power conversion device outputs a voltage signal only through one of the above three live wires, for example, live wire A, the magnitude of the DC component of the voltage signal output by the power conversion device can be characterized by the voltage difference between live wire A and neutral wire N. Therefore, if the sampling module only collects the voltage signals transmitted on live wire A, live wire B, or live wire C, the voltage signals collected by the sampling module cannot accurately characterize the magnitude of the DC component, thereby affecting the accuracy of subsequent DC component regulation. It can be seen that in this application, by receiving the voltage signals transmitted on live wire A and neutral wire N, the sampling module can ensure the accuracy of DC component regulation in different scenarios (when the power conversion device outputs voltage signals through one or more live wires), and has a rich application scenario.

[0052] In some feasible embodiments, a first relay K1 and a second relay K2 are also provided in the power conversion device. Specifically, Figure 7 The setting positions of the connection points of the shown sampling module with live wire A, live wire B, live wire C, and neutral wire N, and the control logic of the controller for each first relay K1 and second relay K2 can refer to the above Figure 2 shown specific embodiments, and the present application will not elaborate herein.

[0053] In some feasible embodiments, Figure 7 The specific structure of the shown sampling module can be as Figure 8 shown, Figure 8 which is another schematic diagram of the sampling module provided by the present application. As Figure 8 shown, the sampling module includes a second capacitor, a first impedance unit, and second impedance units, a first capacitor C1, an operational amplifier OP, a third resistor R3, a fourth resistor R4, a feedback resistor R5, and a reference resistor Rref corresponding to live wire A, live wire B, and live wire C. Among them, the implementation principle of the sampling module for collecting the voltage signals transmitted on live wire B and neutral wire N, and the voltage signals transmitted on live wire C and neutral wire N can refer to the above Figures 2 to 7 shown specific embodiments of the sampling module for collecting the voltage signals transmitted on live wire A and neutral wire N, and the present application will not elaborate herein.

[0054] In some feasible embodiments, as Figure 8 shown, the non-inverting inputs of the three operational amplifiers OP corresponding to live wire A, live wire B, and live wire C are connected to the same first impedance unit and third resistor R3. In some application scenarios, the non-inverting inputs of the three operational amplifiers OP corresponding to live wire A, live wire B, and live wire C can each be connected to a separate first impedance unit and third resistor R3, that is, the non-inverting inputs of each operational amplifier OP do not share a first impedance unit and a third resistor R3, and the present application does not limit this.

[0055] In some feasible embodiments, when the power conversion device supplies power to a load using a three-phase five-wire system, the specific structure of the power conversion device can be as Figure 9 shown. Figure 9 This is another schematic diagram of the power conversion device provided by this application. Different from Figure 7 that shown, Figure 8 the power conversion device shown also includes a ground wire PE, which can introduce the leakage current generated in the power conversion device into the ground to ensure the stability of the power conversion device and the load.

[0056] It can be understood that Figure 9 the setting positions of the connection points of the sampling module in the power conversion device shown to the live wires A, B, C and the neutral wire N, and the control logic of the controller for each first relay K1 and second relay K2 can refer to the above Figure 2 specific embodiments shown, and this application will not elaborate here. Similarly, Figure 9 the specific implementation of the sampling module, communication module, controller and isolator shown can refer to the above Figures 2 to 8 specific embodiments, and this application will not elaborate here.

[0057] In addition, Figure 8 a filtering module is also provided in the power conversion device shown. The filtering module is arranged between the power conversion circuit and the AC terminal. The filtering module can filter the noise and interference output by the power conversion circuit and then provide it to the load to ensure that the output of the power conversion circuit is purer, thereby improving the overall performance of the power conversion device. Specifically, the filtering module includes inductors connected in series to the live wires A, B, and C, and capacitors connected across different live wires. In other application scenarios, the specific structure of the filtering module can be flexibly adjusted, and this application does not limit this.

[0058] In some feasible embodiments, when the power conversion device supplies power to a load using a three-phase five-wire system, the specific structure of the power conversion device can also be as Figure 10 shown. Figure 10 This is another schematic diagram of the power conversion device provided by this application. Different from Figure 9 that shown, Figure 9 the ground wire PE in the power conversion device shown is connected to the neutral wire N.

[0059] It can be understood that Figure 10 the setting positions of the connection points of the sampling module in the power conversion device shown to the live wires A, B, C and the neutral wire N, and the control logic of the controller for each first relay K1 and second relay K2 can refer to the above Figure 2The specific embodiments shown are not elaborated in this application. Similarly, Figure 10 For the specific implementation of the sampling module, communication module, controller, filtering module, and isolator shown, reference can be made to the above Figures 2 to 9 specific embodiments, which are not elaborated in this application.

[0060] Before the power conversion device provided in this application supplies power to the load, the controller first adjusts the reduction of the DC component in the voltage signal output by the power conversion circuit, and after the DC component in the voltage signal output by the power conversion circuit is reduced to the target interval, the first relay and the second relay on the live wire and the neutral wire are controlled to close, which can effectively reduce the adverse effects of the DC component on the load. In addition, when the power conversion device does not need to supply power to the load, the controller controls the first switch unit and the second switch unit in the sampling module to disconnect, so that the sampling module stops receiving the voltage signal output by the power conversion circuit, which can reduce the energy consumption of the power conversion device. In addition, the power conversion device also reduces the generation of leakage current through the second capacitor or the third capacitor, improves the safety of the power conversion device, and has strong applicability. Further, the sampling module uses the first impedance unit, the second impedance unit, and the first capacitor to form a low-pass filter, which can achieve a good low-pass filtering effect on the voltage signals transmitted on the neutral wire and the live wire, and then filter out the high-frequency AC voltage analog signals. Among them, the resistance value of the first impedance unit is equal to the total resistance value of multiple first resistors, and the resistance value of the second impedance unit is equal to the total resistance value of multiple second resistors. By adjusting the number and resistance values of the first resistor and the second resistor, the total resistance values of the first impedance unit and the second impedance unit can be flexibly adjusted, and the structure is simple and easy to implement.

Claims

1. A power conversion device, characterized in that: The power conversion device includes a power conversion circuit, a sampling module, a communication module, an isolator, an AC terminal and a controller; wherein, The power conversion circuit is used to convert direct current from the photovoltaic module or the energy storage battery into alternating current, and output the alternating current through the alternating current terminal; When the AC end is connected to the load and disconnected from the power grid, the sampling module is used to output a DC voltage analog signal to the communication module upon receiving the voltage signal output by the power conversion circuit, wherein the DC voltage analog signal is a DC component in the voltage signal output by the power conversion circuit; The communication module is used to, when receiving the DC voltage analog signal, output a digital signal to the isolator to filter out the common mode voltage signal in the DC voltage analog signal; The isolator is used to send the digital signal to the controller and electrically isolate the controller from the communication module; The controller is connected to the power conversion circuit and is used to reduce the DC component in the voltage signal output by the power conversion circuit when receiving the digital signal.

2. The power conversion device according to claim 1, characterized in that: The power conversion device further includes a neutral line and a live line, the power conversion circuit is used to connect the AC end of the power conversion device through the neutral line and the live line, and the sampling module is connected to the live line and the neutral line; The sampling module is used to output the DC voltage analog signal to the communication module when receiving the voltage signal transmitted on the live wire and the neutral wire; the voltage signal transmitted on the live wire and the neutral wire is the voltage signal output by the power conversion circuit.

3. The power conversion device according to claim 2, characterized in that: The power conversion device further includes a first relay and a second relay, wherein the first relay is arranged on the neutral line, and the second relay is arranged on the live line; the connection point between the sampling module and the neutral line is located between the first relay and the power conversion circuit, and the connection point between the sampling module and the live line is located between the second relay and the power conversion circuit; The sampling module is used to receive the voltage signal transmitted on the live wire and the neutral wire when the AC end is connected to the load and disconnected from the power grid, and the first relay and the second relay are disconnected; The controller is used to control the first relay and the second relay to close after the DC component in the voltage signal output by the power conversion circuit decreases to a target interval.

4. The power conversion device according to claim 2 or 3, characterized in that: The sampling module includes a first capacitor, a first impedance unit, a second impedance unit and an operational amplifier, the same-direction input terminal of the operational amplifier is connected to the neutral line through the first impedance unit, the reverse input terminal of the operational amplifier is connected to the live line through the second impedance unit, and the first capacitor is arranged between the same-direction input terminal and the reverse input terminal of the operational amplifier; the resistance value of the first impedance unit and the resistance value of the second impedance unit are greater than or equal to 1 megohm.

5. The power conversion device according to claim 4, characterized in that: The first impedance unit includes a first inductor and a plurality of first resistors connected in series, and the second impedance unit includes a second inductor and a plurality of second resistors connected in series.

6. The power conversion device according to claim 4 or 5, characterized in that: The sampling module further includes a first switch unit and a second switch unit, the first switch unit is connected in series with the first impedance unit, and the second switch unit is connected in series with the second impedance unit; The controller is used for controlling the first switch unit and the second switch unit to be disconnected when the AC end is connected to the power grid or disconnected from the load.

7. The power conversion device according to any one of claims 4 to 6, characterized in that: The power conversion device further includes a ground line and a neutral line, wherein the neutral line is connected to the ground line. The power conversion device further includes a second capacitor, which is connected in parallel to the first impedance unit.

8. The power conversion device according to any one of claims 1 to 6, characterized in that: The power conversion device also includes a ground wire and a neutral wire, the neutral wire is connected to the ground wire, and the power conversion device also includes a third capacitor, and the reference zero potential end of the communication module is connected to the ground wire or the neutral wire through the third capacitor.

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