Micro inverter and current measurement method

Abstract

The present application provides a micro inverter and a current measurement method. The micro inverter comprises: a primary-side circuit, which is adapted to be connected to a photovoltaic module and converts a direct current outputted by the photovoltaic module into an alternating current; a transformer, a primary-side winding of the transformer being coupled to the primary-side circuit, and the transformer being used for stepping up or stepping down of the voltage of the alternating current converted by the primary-side circuit; a secondary-side circuit, a secondary-side winding of the transformer being coupled to the secondary-side circuit, and the secondary-side circuit being used for converting the alternating current after voltage stepping up or stepping down into a power frequency alternating current and outputting the power frequency alternating current to a power grid by means of an output port; and a current measurement circuit, comprising a current transformer, the current transformer being located between the secondary-side winding of the transformer and the secondary-side circuit, and the current measurement circuit being used for collecting a high-frequency alternating current of the secondary-side winding by means of the current transformer, and on the basis of the high-frequency alternating current, measuring the alternating current outputted by the output port. The device in the alternating current measurement circuit in the present application has a small size and low cost, and is beneficial to being used in the micro inverter.

Description

A micro inverter and current detection method

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of China on September 21, 2023, with application number 202311235636.X, and priority to the Chinese patent application entitled “A Micro Inverter and Current Detection Method”, all contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of electric power technology, and in particular to a micro inverter and a current detection method. Background Art

[0003] Microinverters can directly convert the DC power of photovoltaic panels into AC power and are currently widely used in residential photovoltaic power generation systems. Currently, AC current detection primarily relies on sampling devices installed at the AC grid-connected port. For example, adding a power-frequency current transformer and subsequent conversion circuitry to the AC grid-connected port enables detection of the grid-connected AC current. However, power-frequency current transformers are relatively large, making them difficult to install, making them unsuitable for use in microinverter scenarios, and they are also relatively expensive.

[0004] Summary of the Invention

[0005] The present application provides a micro-inverter and a current detection method. Since the AC detection circuit in the micro-inverter is arranged between the secondary winding of the transformer and the secondary circuit, the AC detection circuit detects the high-frequency current of the secondary winding of the transformer. The higher the current frequency, the smaller the volume of the coil. Therefore, the current transformer in the AC detection circuit in the present application is small in size and low in cost, which is conducive to use in the micro-inverter.

[0006] In a first aspect, a micro inverter is provided, comprising: a primary circuit, the primary circuit being used to connect to a photovoltaic module and convert the direct current output by the photovoltaic module into alternating current; a transformer, the primary winding of the transformer being coupled to the primary circuit, the transformer being used to step up or step down the alternating current converted by the primary circuit; a secondary circuit, the secondary winding of the transformer being coupled to the secondary circuit, the secondary circuit being used to convert the stepped-up or stepped-down alternating current into industrial frequency alternating current, and being used to output the industrial frequency alternating current to a power grid through an output port; a current detection circuit, the current detection circuit comprising a current transformer, the current transformer being located between the secondary winding of the transformer and the secondary circuit, the current detection circuit being used to collect high-frequency alternating current from the secondary winding through the current transformer, and to detect the alternating current output from the output port based on the high-frequency alternating current, wherein the frequency of the high-frequency alternating current is greater than the frequency of the industrial frequency alternating current.

[0007] In an embodiment of the present application, a current detection circuit is used to detect the high-frequency current of the secondary winding of the transformer, and detects the AC power at the port of the power grid based on the high-frequency current of the secondary winding of the transformer, thereby achieving the goal of obtaining the AC power at the power grid port indirectly by collecting the high-frequency current of the secondary winding of the transformer instead of directly collecting the AC power at the power grid port. Since the AC detection circuit detects the high-frequency current of the secondary winding of the transformer, and since the higher the frequency, the smaller the volume of the coil, the device in the AC detection circuit in the embodiment of the present application is small in size and low in cost, which is conducive to use in a micro-inverter. In addition, since the current detection circuit is located between the secondary winding and the secondary circuit of the transformer, the identification response speed for faults in the transformer or the primary circuit is faster and more efficient, thereby better protecting the inverter.

[0008] In conjunction with the first aspect, in a first possible implementation, the microinverter further includes a controller, the current detection circuit further includes a sampling circuit, a switching circuit, and an integrating filter circuit, the primary side of the current transformer is connected between the secondary winding of the transformer and the secondary circuit, the secondary side of the current transformer is connected to the sampling circuit, the sampling circuit is connected to the integrating filter circuit via the switching circuit, and the switching circuit includes a switching transistor. The controller is configured to control the on / off switching transistor in the switching circuit so that the integrating filter circuit restores the output voltage of the sampling circuit, and the AC power restored by the integrating filter circuit is consistent with the current, voltage, or frequency of the AC power output from the output port.

[0009] In an embodiment of the present application, a controller controls the on or off of a switch tube in a switching circuit so that the integral filter circuit restores the output voltage of the sampling circuit. The AC power restored by the integral filter circuit is a continuous port AC power of the power grid. The parameters of the obtained port AC power are more comprehensive and accurate, which is conducive to the AC power output by the micro-inverter being incorporated into the power grid, and further, the safety of the power grid can be guaranteed.

[0010] In combination with the first possible implementation of the first aspect, in a second possible implementation, the sampling circuit includes two sampling resistors and a sampling capacitor. The two sampling resistors are connected in series at both ends of the secondary side of the current transformer. One end of the sampling capacitor is connected to the connection midpoint of the two sampling resistors, and the other end is grounded.

[0011] In combination with the first possible and second possible implementations of the first aspect, in a third possible implementation, the secondary circuit includes a bridge arm and two capacitors, the two capacitors are connected in series and in parallel with the bridge arm, the bridge arm includes an upper half bridge arm and a lower half bridge arm, the connection point of the upper half bridge arm and the lower half bridge arm is connected to one end of the secondary winding of the transformer, and the connection point of the two capacitors is connected to the other end of the secondary winding of the transformer, the upper half bridge arm and the lower half bridge arm each include a group of switching tubes, the two switching tubes included in each group of switching tubes each include a parallel freewheeling diode, and the freewheeling directions of the two parallel freewheeling diodes of each group of switching tubes are opposite. The switching circuit includes two groups of controllable switches. The controller is used to control the conduction or shutoff of the switching tubes in the switching circuit so that the integral filter circuit restores the voltage output by the sampling circuit, including: the controller is used to control the conduction or shutoff of the two groups of controllable switches according to the state of the four switching tubes included in the bridge arm and the current direction of the secondary winding of the transformer, so that the integral filter circuit restores the output voltage of the sampling circuit.

[0012] In an embodiment of the present application, the controller controls the on or off of the two groups of controllable switches according to the states of the four switching tubes included in the bridge arm and the current direction of the secondary winding of the transformer, so that the integral filter circuit restores the output voltage of the sampling circuit, and the voltage polarity output by the integral filter circuit is consistent with the voltage polarity output by the secondary circuit, so as to ensure that the voltage output by the integral filter circuit is the port AC power of the power grid, so that the port AC power of the power grid is obtained more reliably through the voltage output by the integral filter circuit. Furthermore, it is beneficial for the micro-inverter to invert the DC power output by the photovoltaic module into AC power and then integrate it into the power grid, thereby ensuring the safety of the power grid.

[0013] In combination with the third possible implementation method of the first aspect, in a fourth possible implementation method, the controller is used to control the conduction or shutdown of the two groups of controllable switches according to the state of the four switching tubes included in the bridge arm and the current direction of the secondary winding of the transformer, including: when the two switching tubes included in the upper half bridge arm are turned on or the two switching tubes included in the lower half bridge arm are turned on, or when only one of the four switching tubes is turned on, the controller is used to control one group of the two controllable switches to be turned on and the other group of controllable switches to be turned off according to the current direction of the secondary winding of the transformer and the voltage polarity of the output end of the secondary circuit.

[0014] In an embodiment of the present application, when the two switch tubes included in the upper half bridge arm are turned on or the two switch tubes included in the lower half bridge arm are turned on, or when only one of the four switch tubes is turned on, the controller is used to control one of the two groups of controllable switches to be turned on and the other group of controllable switches to be turned off according to the current direction of the secondary winding of the transformer and the voltage polarity of the output end of the secondary circuit, so as to ensure that the voltage output by the integral filter circuit is the port AC power of the power grid, so that the port AC power of the power grid is obtained more reliably through the voltage output by the integral filter circuit. Furthermore, it is beneficial for the micro inverter to invert the DC power output by the photovoltaic module into AC power and then integrate it into the power grid, thereby ensuring the safety of the power grid.

[0015] In combination with the third possible implementation method of the first aspect, in a fifth possible implementation method, the controller is used to control the conduction or shutdown of two groups of controllable switches according to the state of the four switching tubes included in the bridge arm and the current direction of the secondary winding of the transformer, including: when one switching tube in the upper half bridge arm and one switching tube in the lower half bridge arm are turned on, or, when two switching tubes in the upper half bridge arm and one switching tube in the lower half bridge arm are turned on, or, when one switching tube in the upper half bridge arm and two switching tubes in the lower half bridge arm are turned on, the controller is used to control the two groups of controllable switches to be alternately turned on or off according to the current direction of the secondary winding of the transformer.

[0016] In an embodiment of the present application, when at least one switch tube in the upper half bridge arm is turned on and at least one switch tube in the lower half bridge arm is turned on, it is possible that the current direction of the secondary winding of the transformer is the same but the voltage polarity of the output end of the secondary circuit is different, or it is possible that the current direction of the secondary winding of the transformer is different but the voltage polarity of the output end of the secondary circuit is the same. Therefore, the controller controls the two groups of controllable switches to be alternately turned on or off according to the specific conduction status of the switch tube and the current direction of the secondary winding of the transformer, so as to ensure that the voltage output by the integral filter circuit is the port AC power of the power grid, so that it is more reliable to obtain the port AC power of the power grid through the voltage output by the integral filter circuit. Furthermore, it is beneficial for the micro inverter to invert the DC power output by the photovoltaic module into AC power and then integrate it into the power grid, thereby ensuring the safety of the power grid.

[0017] In combination with the fifth possible implementation of the first aspect, in a sixth possible implementation, the upper half bridge arm includes a switch tube S8 and a switch tube S6, and the lower half bridge arm includes a switch tube S5 and a switch tube S7. The controller is used to control the two groups of controllable switches to be alternately turned on or off according to the current direction of the secondary winding of the transformer, including: when the switch tube S6 is turned on, the current direction of the secondary winding of the transformer is positive, and the controller controls one group of controllable switches to be turned on according to the positive current direction of the secondary winding of the transformer, or, when the switch tube S8 is turned on, the current direction of the secondary winding of the transformer is negative, and the controller controls one group of controllable switches to be turned on according to the negative current direction of the secondary winding of the transformer; when the switch tube S5 is turned on, the current direction of the secondary winding of the transformer is positive, and the controller controls the other group of controllable switches to be turned on according to the positive current direction of the secondary winding of the transformer, or, when the switch tube S7 is turned on, the current direction of the secondary winding of the transformer is negative, and the controller controls the other group of controllable switches to be turned on according to the negative current direction of the secondary winding of the transformer.

[0018] In the embodiment of the present application, the controller controls the two groups of controllable switches to conduct alternately according to the specific conduction conditions of the switch tube and the current direction of the secondary winding of the transformer, so as to ensure that the voltage output by the integral filter circuit is the port AC power of the power grid, thereby obtaining the port AC power of the power grid through the voltage output by the integral filter circuit more reliably. Furthermore, it is beneficial for the micro-inverter to invert the DC power output by the photovoltaic module into AC power and then integrate it into the power grid, thereby ensuring the safety of the power grid.

[0019] In combination with the sixth possible implementation manner of the first aspect, in a seventh possible implementation manner, one group of controllable switches is connected between one end of the two sampling resistors connected in series and the inverting input terminal of the integral filter circuit, one end of the two sampling resistors connected in series is connected to the non-identical end of the secondary winding of the transformer, and another group of controllable switches is connected between the other end of the two sampling resistors connected in series and the inverting input terminal of the integral filter circuit, one end of the two sampling resistors connected in series is connected to the identical end of the secondary winding of the transformer, and the midpoint of the connection between the two sampling resistors is connected to the non-identical input terminal of the integral filter circuit.

[0020] In combination with any one of the third to seventh possible implementations of the first aspect, in an eighth possible implementation, each group of controllable switches includes two switching tubes and a freewheeling resistor; wherein the sources of the two switching tubes in each group of controllable switches are connected, wherein the drains of the two switching tubes in one group of controllable switches are respectively connected to one end of the two sampling resistors connected in series and the inverting input end of the integral filter circuit, and the drains of the two switching tubes in the other group of controllable switches are respectively connected to the other end of the two sampling resistors connected in series and the inverting input end of the integral filter circuit, the two switching tubes in each group of controllable switches respectively include a freewheeling diode connected in parallel, and the freewheeling directions of the two freewheeling diodes in parallel in each group of controllable switches are opposite, and the two ends of the freewheeling resistor are connected in parallel to the drains of the two switching tubes. Alternatively, the drains of the two switching tubes in each group of controllable switches are connected, wherein the sources of the two switching tubes in one group of controllable switches are respectively connected to one end of the two sampling resistors connected in series and the inverting input end of the integral filter circuit, and the sources of the two switching tubes in the other group of controllable switches are respectively connected to the other end of the two sampling resistors connected in series and the inverting input end of the integral filter circuit, the two switching tubes in each group of controllable switches respectively include a freewheeling diode connected in parallel, and the freewheeling directions of the two freewheeling diodes in parallel in each group of controllable switches are opposite, and the two ends of the freewheeling resistor are connected in parallel to the sources of the two switching tubes; the gates of the two switching tubes in each group of controllable switches are connected, and the controller is used to control the conduction or shutdown of the two groups of controllable switches by controlling the gates of the switching tubes to input a high level or a low level.

[0021] In an embodiment of the present application, each group of controllable switches includes two switching tubes, and each of the two switching tubes is connected in parallel with a freewheeling diode, and the freewheeling directions of the two diodes are opposite. When the four switching tubes in the secondary circuit are in the dead zone, the two switching tubes with opposite freewheeling directions can, on the one hand, prevent the current of the integral filter circuit from being reversely input into the secondary circuit through the current transformer, thereby avoiding damage to the switching tube in the secondary circuit; on the other hand, it can also prevent the current of the current transformer from being input into the integral filter circuit, thereby avoiding damage to the integral filter circuit. In addition, each group of controllable switches also includes a freewheeling resistor. When the four switching tubes in the secondary circuit are in the dead zone, the current of the integral filter circuit can be consumed by the freewheeling resistor, thereby playing a role in protecting the integral filter circuit.

[0022] In combination with the eighth possible implementation manner of the first aspect, in a ninth possible implementation manner, the switching circuit further includes a signal control circuit, which includes two groups of push-pull circuits, which are respectively connected to the two groups of controllable switches; each group of push-pull circuits includes two signal switching tubes, two voltage-dividing resistors and a capacitor, one of which is an N-channel switching tube and the other is a P-channel switching tube, the base of one of the signal switching tubes is connected to the controller, the emitter of one of the signal switching tubes is grounded, the collector of one of the signal switching tubes is connected in series with a voltage-dividing resistor and then connected to the base of the other signal switching tube, the base of the other signal switching tube is connected in series with another voltage-dividing resistor and then grounded through a capacitor, the emitter of the other signal switching tube is connected to the other voltage-dividing resistor and the capacitor, and the collector of the other signal switching tube is connected to the gate of the two switching tubes in one group of controllable switches; the controller is used to control the conduction or shutdown of the two groups of controllable switches by inputting a high level or a low level into the base of the control signal switching tube.

[0023] In combination with the ninth possible implementation of the first aspect, in a tenth possible implementation, each push-pull circuit also includes two additional protection resistors, one of which is connected to the base of one of the signal switching tubes, and the other is connected to the collector of the other signal switching tube.

[0024] In the embodiment of the present application, for one of the signal switch tubes connected to the controller in any group of push-pull circuits, a protection resistor is set at the base of the signal switch tube. The protection resistor can share part of the voltage, thereby preventing the voltage U between the base and emitter of the switch tube from GE For another signal switch tube, the protection resistor has a similar function, which can prevent the damage of the switch tube in the switching circuit caused by the voltage between the base and emitter of the signal switch tube being too large.

[0025] In combination with any one of the first to tenth possible implementation methods of the first aspect, in the eleventh possible implementation method, the integral filter circuit includes an operational amplifier, a filter resistor, and a filter capacitor; the inverting input terminal of the operational amplifier is connected in series with the filter resistor and then connected to the two ends of the two sampling resistors connected in series; the non-inverting input terminal of the operational amplifier is connected to the midpoint of the connection of the two sampling resistors; and the two ends of the filter capacitor are respectively connected to the inverting input terminal of the operational amplifier and the output terminal of the operational amplifier.

[0026] In combination with the eleventh possible implementation method of the first aspect, in a twelfth possible implementation method, the integral filter circuit also includes two other protection resistors, one of which is connected in parallel at both ends of the filter capacitor, and the other is connected to the non-inverting input terminal of the operational amplifier.

[0027] In an embodiment of the present application, during the process of the integral filter circuit performing integral filtering on the sampling resistor, the filter capacitor is in a state of charging for a long time, and the operational amplifier may quickly become saturated. Since the protection resistor is connected in parallel to both ends of the capacitor, the voltage across the filter capacitor can be released through the protection resistor, thereby achieving the purpose of protecting the integral filter circuit, thereby allowing the protection integral filter circuit to operate normally. In addition, a protection resistor is connected in series with the positive input end of the integral filter circuit, and the protection resistor is connected to the connection point of the two sampling resistors. Generally, a reference bias voltage is set at the connection point. If there is no protection resistor, it is equivalent to directly connecting the connection point to the positive input end of the integral filter circuit, resulting in damage to the integral filter circuit.

[0028] In combination with any one of the first to twelfth possible implementations of the first aspect, in a thirteenth possible implementation, the sampling circuit, the switching circuit, the integral filter circuit, and the controller are integrated into a chip.

[0029] In a second aspect, a current detection method is provided, which is applied to an inverter, and the method includes: controlling four switching tubes in a secondary circuit connected to the secondary winding of the transformer in the inverter to turn on or off, the secondary circuit being used to convert the frequency of the alternating current output by the secondary winding of the transformer into industrial frequency alternating current, and outputting the industrial frequency alternating current to the power grid through the output port; controlling the on or off of two groups of controllable switches in the current detection circuit according to the states of the four switching tubes and the current direction of the secondary winding of the transformer, so that the integral filter circuit in the current detection circuit restores the output voltage of the sampling circuit in the current detection circuit, the current detection circuit is located between the secondary winding of the transformer and the secondary circuit, and the alternating current restored by the integral filter circuit is consistent with the current, voltage or frequency of the alternating current output from the output port.

[0030] In combination with the second aspect, in a first possible implementation method, the two groups of controllable switches are controlled to be turned on or off according to the state of the four switching tubes and the current direction of the secondary winding of the transformer, including: when the two switching tubes included in the upper half bridge arm are turned on or the two switching tubes included in the lower half bridge arm are turned on, or when only one of the four switching tubes is turned on, one group of the two groups of controllable switches is controlled to be turned on and the other group of controllable switches is turned off according to the current direction of the secondary winding of the transformer.

[0031] In combination with the second aspect, in a second possible implementation method, the two groups of controllable switches are controlled to be turned on or off according to the state of the four switching tubes and the current direction of the secondary winding of the transformer, including: when one switching tube in the upper half bridge arm and one switching tube in the lower half bridge arm are turned on, or when two switching tubes in the upper half bridge arm and one switching tube in the lower half bridge arm are turned on, or when one switching tube in the upper half bridge arm and two switching tubes in the lower half bridge arm are turned on, the two groups of controllable switches are controlled to be alternately turned on or off according to the current direction of the secondary winding of the transformer.

[0032] In combination with the second possible implementation method of the second aspect, in a third possible implementation method, the upper half bridge arm includes a switch tube S8 and a switch tube S6, and the lower half bridge arm includes a switch tube S5 and a switch tube S7, and the two groups of controllable switches are controlled to be alternately turned on or off according to the current direction of the secondary winding of the transformer, including: when the switch tube S6 is turned on, the current direction of the secondary winding of the transformer is positive, and the controller controls one group of controllable switches to be turned on according to the positive current direction of the secondary winding of the transformer, or, when the switch tube S8 is turned on, the current direction of the secondary winding of the transformer is negative, and one group of controllable switches is controlled to be turned on according to the negative current direction of the secondary winding of the transformer; when the switch tube S5 is turned on, the current direction of the secondary winding of the transformer is positive, and the controller controls the other group of controllable switches to be turned on according to the positive current direction of the secondary winding of the transformer, or, when the switch tube S7 is turned on, the current direction of the secondary winding of the transformer is negative, and the other group of controllable switches is controlled to be turned on according to the negative current direction of the secondary winding of the transformer.

[0033] For the technical effects that may be achieved in the second aspect, please refer to the description of the technical effects that can be achieved in any possible implementation method of the first aspect above, and no further details will be given here. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG1 is a schematic diagram of a micro-inverter system.

[0035] FIG2 is a schematic diagram of a circuit topology of a micro inverter.

[0036] FIG3 is a schematic diagram of detecting AC current using a power frequency current transformer.

[0037] FIG4 is a schematic diagram of a micro inverter provided in an embodiment of the present application.

[0038] FIG5 is a schematic diagram of another micro inverter provided in an embodiment of the present application.

[0039] FIG6 is a schematic diagram of another micro inverter provided in an embodiment of the present application.

[0040] FIG7 is a schematic diagram of current flow in a secondary circuit connected to a secondary winding of a transformer provided in an embodiment of the present application.

[0041] FIG8 is a schematic diagram of another micro inverter provided in an embodiment of the present application.

[0042] FIG9 is another schematic diagram of current flow in a secondary circuit connected to a secondary winding of a transformer provided in an embodiment of the present application.

[0043] FIG10 is a schematic diagram of another micro-inverter provided in an embodiment of the present application.

[0044] FIG11 is another schematic diagram of current flow in a secondary circuit connected to a secondary winding of a transformer provided in an embodiment of the present application.

[0045] FIG12 is a schematic diagram of another micro-inverter provided in an embodiment of the present application.

[0046] FIG13 is a schematic diagram of a current detection method provided in an embodiment of the present application.

[0047] FIG14 is a schematic diagram of another micro-inverter provided in an embodiment of the present application.

[0048] FIG15 is a schematic diagram of another micro inverter provided in an embodiment of the present application.

[0049] FIG16 is a schematic diagram of a current detection method provided in an embodiment of the present application. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present application will be described below with reference to the accompanying drawings.

[0051] In the description of the embodiments of the present application, unless otherwise specified, “ / ” means or, for example, A / B can mean A or B; “and / or” in this article is merely a way to describe the association relationship of associated objects, indicating that three relationships can exist, for example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone.

[0052] In the embodiments of the present application, prefixes such as "first" and "second" are used only to distinguish different description objects and have no limiting effect on the position, order, priority, quantity or content of the described objects. The use of prefixes such as ordinal numbers to distinguish description objects in the embodiments of the present application does not constitute a restriction on the described objects. For the statement of the described objects, please refer to the description in the context of the claims or embodiments, and the use of such prefixes should not constitute an unnecessary restriction. In addition, in the description of this embodiment, unless otherwise specified, the meaning of "plurality" is two or more.

[0053] References to "some embodiments" and the like in this specification mean that a particular feature, structure, or characteristic described in connection with that embodiment is included in one or more embodiments of the present application. Thus, phrases such as "in some embodiments" and the like that appear in different places in this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "including," "comprising," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0054] Microinverters can directly convert the DC power from photovoltaic panels into AC power and are currently widely used in household photovoltaic power generation systems. Figure 1 shows a schematic diagram of a microinverter system. A microinverter is connected to a photovoltaic panel, converting the DC power from the panel into AC power. Multiple microinverters are connected in parallel to output AC power to the grid.

[0055] Since the AC power connected to the grid must meet the grid connection requirements, it is very important to detect the AC power on the grid side. The detected parameters such as the amplitude and frequency of the AC current are very important for the closed-loop control of the micro-inverter during operation.

[0056] Figure 2 is a schematic diagram of a microinverter circuit topology. The primary circuit (dashed box ①) consists of an H-bridge, with the middle dashed box ② containing a transformer. Ls represents the transformer's leakage inductance or the inductance connected in series with the transformer. The secondary circuit (dashed box ③) consists of a half-bridge circuit consisting of four switches (including S5, S6, S7, and S8) and two bridge-arm capacitors (including Cs1 and Cs2), connected to the output filter (dashed box ④). Photovoltaic modules convert solar energy into direct current (DC) through the photovoltaic effect. This DC is then inverted by the H-bridge into alternating current (AC). This AC is then transformed by the transformer and fed into the half-bridge circuit, which converts the AC into industrial frequency current. The converted industrial frequency current is filtered by the filter and then enters the grid.

[0057] Currently, the detection of AC side current mainly focuses on setting up sampling devices at the AC grid-connected port. The following describes the existing AC side current detection technology with reference to FIG3.

[0058] Figure 3 shows a schematic diagram of using a power-frequency current transformer to detect AC current. By adding a power-frequency current transformer and subsequent conversion circuitry (such as the resistor and current transformer peripheral circuitry shown in the figure) to the AC grid-connected port, grid-connected AC current detection is achieved. However, power-frequency current transformers are relatively large, making them difficult to install, unsuitable for use in micro-inverter scenarios, and are relatively expensive.

[0059] Based on this, the present application provides a micro inverter. Since the AC detection circuit in the micro inverter is arranged between the secondary winding of the transformer and the secondary circuit, the AC detection circuit detects the high-frequency current of the secondary winding of the transformer. The higher the current frequency, the better the signal transmission performance. Therefore, the current transformer in the AC detection circuit is small in size and low in cost, which is conducive to use in the micro inverter.

[0060] 4 is a schematic diagram of a micro-inverter provided in an embodiment of the present application. The micro-inverter includes a primary circuit 410 , a transformer 420 , a secondary circuit 430 , and a current detection circuit 440 .

[0061] One end of the primary circuit 410 is used to input a DC voltage Vdc, and the other end of the primary circuit 410 is connected to the primary winding of the transformer 420. The primary circuit 410 is used to convert the DC voltage Vdc input by the photovoltaic module into AC power, which includes a high-frequency AC rectangular wave signal.

[0062] In the embodiments of the present application, the primary circuit 410 may be an H-bridge circuit, such as a half-bridge circuit, a full-bridge circuit, or other circuit capable of converting direct current into high-frequency alternating current. The primary circuit may include multiple H-bridge circuits, such as multiple half-bridge circuits connected in series or in parallel, or a half-bridge circuit and a full-bridge circuit connected in series or in parallel, without limitation.

[0063] Transformer 420 is used to step up or down the AC power output by the primary circuit. Transformer 420 can be designed with a secondary leakage inductance equal to Ls. Alternatively, referring to FIG4 , transformer 420 can be designed with a very small leakage inductance, with a separate inductive element Ls connected in series. This embodiment of the present application uses a separate inductor Ls as an example.

[0064] The secondary circuit 430 is used to convert the stepped-up or stepped-down AC power into industrial frequency AC power, and to output the industrial frequency AC power to the power grid through the output port.

[0065] In the embodiment of the present application, the AC power output by the secondary winding of transformer 420 is high frequency. Secondary circuit 430 can convert this high frequency AC power into industrial frequency AC power. The converted industrial frequency AC power also includes some noise. Secondary circuit 430 can filter the converted industrial frequency AC power and output the filtered AC power to the power grid.

[0066] The current detection circuit 440 includes a current transformer, which is located between the secondary winding of the transformer 420 and the secondary circuit 430. The current detection circuit 440 is used to collect the high-frequency alternating current of the secondary winding through the current transformer, and detect the alternating current output from the output port based on the high-frequency alternating current. The frequency of the high-frequency alternating current is greater than the frequency of the industrial frequency alternating current.

[0067] Generally, the relationship between a coil's inductive reactance, frequency, and inductance is: inductive reactance = 2*π*frequency*inductance. Since frequency and inductive reactance are proportional, under the same conditions, the higher the frequency, the higher the inductive reactance, meaning fewer turns are required to manufacture the coil, and thus the coil's volume is smaller. Because the current detection circuit 440 in this embodiment detects the high-frequency current of the secondary winding of transformer 430, the current transformer in current detection circuit 440 is smaller than the power-frequency current transformer in FIG. 3 , making it suitable for use in microinverters. In addition, since the current detection circuit 440 is located between the secondary winding of the transformer 420 and the secondary circuit 430, if a fault occurs in the transformer 420 or the primary circuit 410, in the scheme shown in Figure 3, the current needs to flow through the secondary circuit to detect the fault, resulting in damage to the switching tube in the secondary circuit. However, the embodiment of the present application can detect the fault current on the secondary winding side of the transformer. Therefore, compared with the scheme of detecting the AC port in Figure 3, the embodiment of the present application can perform fault detection on the energy front side, with faster response speed and higher efficiency, and can respond to faults more quickly.

[0068] In an embodiment of the present application, the current detection circuit 440 is used to detect the AC power at the power grid port through the high-frequency current of the secondary winding of the transformer 430, thereby obtaining the AC power at the power grid port indirectly by collecting the high-frequency current of the secondary winding of the transformer 420 instead of directly collecting the AC power at the power grid port. Since the AC detection circuit 440 detects the high-frequency current of the secondary winding of the transformer 420, and since the higher the frequency, the smaller the volume of the coil, the device in the AC detection circuit 440 in the present application is small in size and low in cost, which is conducive to use in a micro-inverter. In addition, since the current detection circuit 440 is located between the secondary winding of the transformer 420 and the secondary circuit 430, the identification response speed for faults in the transformer or primary circuit is faster and more efficient, thereby better protecting the inverter.

[0069] Figure 5 is a schematic diagram of another micro-inverter provided in an embodiment of the present application. In one embodiment, the micro-inverter further includes a controller 450. The current detection circuit 440 further includes a sampling circuit 442, a switching circuit 443, and an integrating filter circuit 444. The primary side of the current transformer 441 is connected between the secondary winding of the transformer 420 and the secondary circuit 430. The secondary side of the current transformer 441 is connected to the sampling circuit 442. The sampling circuit 442 is connected to the integrating filter circuit 444 via the switching circuit 443. The switching circuit 443 includes a switching transistor.

[0070] The controller 450 is used to control the on or off of the switch tube in the switch circuit 443 so that the integral filter circuit 444 restores the output voltage of the sampling circuit 442, and the restored AC power after integral filtering is consistent with the current, voltage or frequency of the AC power output from the output port.

[0071] In one embodiment, the sampling circuit 442 includes two sampling resistors R1 and R2 and a sampling capacitor C1. The two sampling resistors R1 and R2 are connected in series and connected to the two ends of the secondary side of the current transformer 441. One end of the sampling capacitor C1 is connected to the midpoint of the connection between the two sampling resistors R1 and R2, and the other end is grounded.

[0072] In this embodiment of the present application, the primary side of the current transformer 441 is connected between the secondary winding of the transformer 420 and the secondary circuit 430. The high-frequency alternating current flowing from the secondary winding of the transformer flows through the primary side of the current transformer 441. The current transformer 441 transmits the high-frequency alternating current to the secondary side of the current transformer 441 through electromagnetic induction. The high-frequency current flows through the two sampling resistors R1 and R2, and the integral filter circuit 444 integrates and filters the voltage across one of the sampling resistors. The specific sampling resistor voltage that is integrated and filtered by the integral filter circuit 444 is described below.

[0073] In the embodiment of the present application, there are no excessive restrictions on the resistance values ​​of the sampling resistors R1 and R2. In other words, the resistance values ​​of the sampling resistors R1 and R2 can be equal or different. The current transformer 441 can be a step-down current transformer. The sampling circuit 442, the switching circuit 443, and the integration filter circuit 444 can be integrated into a chip. Alternatively, the sampling circuit 442, the switching circuit 443, the integration filter circuit 444, and the controller 450 described below can be integrated into a chip.

[0074] Integrating filter circuit 444 integrates and filters the voltage across one of the sampling resistors. By setting the parameters of the components in integrating filter circuit 444, the waveform of the voltage output by integrating filter circuit 444 can be made substantially consistent with the waveform of the current output by the secondary circuit. Therefore, the voltage output by integrating filter circuit 444 is the AC power at the grid port, thereby achieving the goal of obtaining the AC power at the grid port indirectly by collecting the high-frequency current of the secondary winding of transformer 420 rather than directly collecting the AC power at the grid port. Because the parameters of the AC power restored by integrating filter circuit 444 are consistent with those of the AC power output at the output port, that is, the waveform of the voltage output by integrating filter circuit 444 is substantially consistent with the waveform of the current output by the secondary circuit, the waveform of the voltage output by integrating filter circuit 444 can be used to determine whether the AC power output by the secondary circuit meets the grid connection requirements. If the requirements are met, the AC power output by the microinverter is connected to the grid to ensure grid security. In addition, the current data at the grid-connected point is also an input parameter for realizing the circuit topology control inside the micro-inverter. For example, the controller 450 can control the conduction and shutdown of the switch tubes in the primary circuit and the secondary circuit in the micro-inverter according to the voltage output by the integral filter circuit 444.

[0075] In an embodiment of the present application, the controller 450 controls the on or off of the switch tube in the switching circuit so that the integral filter circuit 444 restores the output voltage of the sampling circuit. The AC power restored by the integral filter circuit is the continuous port AC power of the power grid. The parameters of the obtained port AC power are more comprehensive and accurate, which is conducive to the AC power output by the micro inverter being integrated into the power grid, and further, the safety of the power grid can be guaranteed.

[0076] FIG6 is a schematic diagram of another micro-inverter provided in an embodiment of the present application. In one embodiment, the secondary circuit includes a bridge arm and two capacitors CS1 and CS2. The two capacitors CS1 and CS2 are connected in series and in parallel with the bridge arm. The bridge arm includes an upper half bridge arm and a lower half bridge arm. The connection point of the upper half bridge arm and the lower half bridge arm is connected to one end of the secondary winding of the transformer 420. The connection point of the two capacitors CS1 and CS2 is connected to the other end of the secondary winding of the transformer. The upper half bridge arm and the lower half bridge arm each include a set of switching tubes, each set of switching tubes includes two switching tubes, and the two switching tubes each include a parallel freewheeling diode. The freewheeling directions of the two parallel freewheeling diodes in each set of switching tubes are opposite.

[0077] In an embodiment of the present application, the switching circuit 443 includes two groups of controllable switches K1 and K2, wherein one group of controllable switches K1 is connected between one end of the two sampling resistors R1 and R2 connected in series and the inverting input end of the integral filter circuit 444, and one end of the sampling resistors connected in series is connected to the non-identical end of the secondary winding of the transformer; the other group of controllable switches K2 is connected between the other end of the two sampling resistors R1 and R2 connected in series and the inverting input end of the integral filter circuit 444, and one end of the sampling resistors connected in series is connected to the identical end of the secondary winding of the transformer, and the midpoint of the connection between the two sampling resistors R1 and R2 is connected to the non-identical input end of the integral filter circuit 444.

[0078] The controller 450 is used to control the conduction or shutdown of the switch tube in the switching circuit 443, so that the integral filter circuit 444 restores the output voltage of the sampling circuit 442, including: the controller 450 is used to: control the conduction or shutdown of the two groups of controllable switches according to the status of the four switch tubes included in the bridge arm and the current direction of the secondary winding of the transformer, so that the integral filter circuit 444 restores the output voltage of 442 in the sampling circuit.

[0079] In the embodiment of the present application, the upper half bridge arm and the lower half bridge arm each include two switching tubes, and the two switching tubes included in each bridge arm constitute a bidirectional switch. The switching tube in the embodiment of the present application can specifically be a metal-oxide-semiconductor field-effect transistor (MOSFET), or an insulated gate bipolar transistor (IGBT) or a gallium nitride (GaN) high electron mobility transistor (HEMT), etc. Specifically, the upper half bridge arm or the lower half bridge arm can be composed of two discrete switching tubes, or can be composed of a module integrating two switching tubes, or can be composed of a monolithic bidirectional (conducting or blocking) device (such as a monolithic bidirectional GaN device). For example, the upper half bridge arm includes a switch tube S8 and a switch tube S6 connected in series, and the lower half bridge arm includes a switch tube S5 and a switch tube S7 connected in series.

[0080] Each switch tube in the embodiment of the present application includes a parallel freewheeling diode, which can be called a body diode.

[0081] Referring to Figure 6, it can be seen that the controller 450 controls K1 to close and K2 to disconnect, the integral filter circuit 444 is connected in parallel at both ends of R1, and the integral filter circuit 444 performs integral filtering on the voltage across R1; the controller 450 controls K2 to close and K1 to disconnect, the integral filter circuit 444 is connected in parallel at both ends of R2, and the integral filter circuit 444 performs integral filtering on the voltage across R2.

[0082] In this embodiment of the present application, the on / off state of the two controllable switches in switch circuit 443 is dependent on the states of the four switch transistors S8, S6, S5, and S7 in the bridge arm. See below for details. The general principle is that controller 450 controls the on / off state of the two controllable switches to ensure that the polarity of the voltage output by integrating filter circuit 444 is consistent with that of the voltage output by secondary circuit 430. This ensures that the waveform of the voltage output by integrating filter circuit 444 matches the waveform of the AC current at the power grid port.

[0083] In an embodiment of the present application, the controller 450 controls the on or off of the two groups of controllable switches K1 and K2 according to the states of the four switching tubes included in the bridge arm and the current direction of the secondary winding of the transformer 420, so that the integral filter circuit 444 restores the output voltage of the sampling circuit, and the voltage polarity output by the integral filter circuit 444 is consistent with the voltage polarity output by the secondary circuit 430, so as to ensure that the voltage output by the integral filter circuit 444 is the port AC power of the power grid, so that the port AC power of the power grid obtained by the voltage output by the integral filter circuit 444 is more reliable. Furthermore, it is beneficial for the micro-inverter to invert the DC power output by the photovoltaic module into AC power and then integrate it into the power grid, thereby ensuring the safety of the power grid.

[0084] The following will describe how the controller 450 specifically controls the on or off of the two groups of controllable switches according to the states of the four switch tubes included in the bridge arm and the current direction of the secondary winding of the transformer 420 in combination with the accompanying drawings.

[0085] In one embodiment, the controller 450 is configured to control the on or off of the two groups of controllable switches according to the states of the four switching tubes included in the bridge arm and the current direction of the secondary winding of the transformer 420, including:

[0086] When the two switching tubes included in the upper half bridge arm are turned on or the two switching tubes included in the lower half bridge arm are turned on, or when only one of the four switching tubes is turned on, the controller 450 is used to control one group of the two groups of controllable switches to be turned on and the other group of controllable switches to be turned off according to the current direction of the secondary winding of the transformer 420.

[0087] Case 1: The two switches included in the upper half bridge arm are turned on

[0088] In the embodiment of the present application, the switches S8 and S6 of the upper half bridge arm are turned on, and the current direction of the secondary winding of the transformer includes two directions, as shown in FIG7 , one of which flows out from the same-name end of the secondary winding of the transformer, passes through the inductor Ls, the switch S6, the switch S8, the filter capacitor C X1 , bridge arm capacitance C S2 Return to the non-identical end of the secondary winding of the transformer (as shown in (a) in Figure 7). The other is the non-identical end of the secondary winding of the transformer flowing out through the bridge arm capacitor C S2 , filter capacitor C X1 , switch S8, switch S6, and inductor Ls return to the same end of the secondary winding of the transformer (as shown in (b) of Figure 7). The current paths of the two current loops are the same, but the current directions are different.

[0089] In the embodiment of the present application, the direction of the current on the secondary side of the current transformer CT is set to be positive from left to right and negative from right to left.

[0090] (1) Referring to (a) in FIG7 , for the current flowing out of the same-name terminals of the secondary winding of the transformer, the voltage at the output terminal of the secondary circuit is positive at the top and negative at the bottom (hereinafter referred to as the forward voltage). In order to make the voltage polarity output by the integral filter circuit 444 consistent with the voltage polarity of the output terminal of the secondary circuit 430, the controller controls the controllable switch K2 to be turned on, as shown in FIG8 . This is because the current flows out of the same-name terminals of the secondary winding of the transformer 420. Since the same-name terminals of the current transformer CT are not in the same direction, the current direction of the secondary side of the current transformer CT is forward. The current flows through the sampling resistors R1 and R2, and the potential at point o is higher than the potential at point q. When the switch K2 is turned on, the integral filter circuit 444 integrates the voltage across the sampling resistor R2. Since the potential at point p across the sampling resistor R2 is higher than the potential at point q, point p is connected to the positive input terminal of the integral filter circuit, and point q is connected to the negative input terminal of the integral filter circuit. In other words, the high potential end of the sampling resistor R2 is connected to the non-inverting input end of the integral filter circuit, and the low potential end of the sampling resistor R2 is connected to the inverting input end of the integral filter circuit, so that the voltage output by the integral filter circuit 444 is a positive voltage. Therefore, the polarity of the voltage output by the integral filter circuit 444 is consistent with the polarity of the voltage output by the secondary circuit 430, so as to ensure that the voltage output by the integral filter circuit 444 is the port AC power of the power grid.

[0091] If the controller 450 controls the controllable switch K1 to be conductive, the integrating filter circuit 444 integrates the voltage across the sampling resistor R1. Since the potential at point o of the sampling resistor R1 is higher than the potential at point p, and point o is connected to the inverting input terminal of the integrating filter circuit, and point p is connected to the non-inverting input terminal of the integrating filter circuit, in other words, the high-potential end of the sampling resistor R1 is connected to the inverting input terminal of the integrating filter circuit 444, and the low-potential end of the sampling resistor R1 is connected to the non-inverting input terminal of the integrating filter circuit 444. As a result, the voltage output by the integrating filter circuit 444 is a negative voltage, and the polarity of the voltage output by the integrating filter circuit 444 is inconsistent with the polarity of the voltage output by the secondary circuit 430. As a result, the voltage output by the integrating filter circuit 444 is inconsistent with the AC power at the grid port, and the AC power at the grid port cannot be obtained from the voltage output by the integrating filter circuit 444.

[0092] (2) Referring to (b) in FIG7 , for the current flowing out of the non-coinciding terminals of the secondary winding of the transformer, the voltage at the output terminal of the secondary circuit is negative at the top and positive at the bottom (hereinafter referred to as negative voltage). In order to make the polarity of the voltage output by the integral filter circuit 444 consistent with the polarity of the voltage at the output terminal of the secondary circuit 430, the controller controls the controllable switch K2 to be turned on, as shown in FIG8 . This is because the current flows out of the non-coinciding terminals of the secondary winding of the transformer. Since the coinciding terminals of the current transformer CT are not in the same direction, the current direction of the secondary side of the current transformer is negative. The current flows through the sampling resistors R1 and R2, and the potential at point o is lower than the potential at point q. When switch K2 is turned on, the integral filter circuit 444 integrates the voltage across the sampling resistor R2. Since the potential at point p across the sampling resistor R2 is lower than the potential at point q, point p is connected to the positive input terminal of the integral filter circuit 444, and point q is connected to the negative input terminal of the integral filter circuit 444. In other words, the high potential end of the sampling resistor R2 is connected to the negative phase input end of the integral filter circuit 444, and the low potential end of the sampling resistor R2 is connected to the positive phase input end of the integral filter circuit 444, so that the voltage output by the integral filter circuit 444 is also a negative voltage. Therefore, the polarity of the voltage output by the integral filter circuit 444 is consistent with the polarity of the voltage output by the secondary circuit 430, so as to ensure that the voltage output by the integral filter circuit 444 is the port AC power of the power grid.

[0093] If the controller 450 controls the controllable switch K1 to be conductive, the integrating filter circuit integrates the voltage across the sampling resistor R1. Since the potential at point o of the sampling resistor R1 is lower than the potential at point p, and point o is connected to the inverting input terminal of the integrating filter circuit 444, and point p is connected to the non-inverting input terminal of the integrating filter circuit 444, in other words, the high-potential end of the sampling resistor R1 is connected to the non-inverting input terminal of the integrating filter circuit 444, and the low-potential end of the sampling resistor R1 is connected to the non-inverting input terminal of the integrating filter circuit 444, the voltage output by the integrating filter circuit 444 is a positive voltage. This results in a polarity inconsistency between the voltage output by the integrating filter circuit 444 and the voltage output by the secondary circuit 430, making it impossible to obtain AC power from the grid port via the voltage output by the integrating filter circuit 444.

[0094] Case 2: The two switches in the lower half bridge arm are turned on

[0095] In the embodiment of the present application, the switches S5 and S7 of the lower half bridge arm are turned on, and the current direction of the secondary winding of the transformer includes two directions, as shown in Figure 9. One direction is to flow out from the same end of the secondary winding of the transformer, through the inductor Ls, the switch tube S5, the switch tube S7, the filter capacitor C X1 , the bridge arm capacitor CS1 returns to the non-identical end of the transformer secondary winding (as shown in (a) in Figure 9). The other is the non-identical end of the transformer secondary winding flowing out, passing through the bridge arm capacitor C S1 , filter capacitor C X1 , switch S7, switch S5, and inductor Ls return to the same end of the secondary winding of the transformer (as shown in (b) of Figure 9). The current paths of the two current loops are the same, but the current directions are different.

[0096] (1) Referring to (a) in FIG9 , for the current flowing out of the same-name terminal of the secondary winding of the transformer, the voltage at the output terminal of the secondary circuit is a negative voltage. In order to make the polarity of the voltage output by the integral filter circuit consistent with the polarity of the voltage at the output terminal of the secondary circuit, the controller 450 controls the controllable switch K1 to be turned on, as shown in FIG10 . This is because, when the switch K1 is turned on, the integral filter circuit 444 integrates the voltage across the sampling resistor R1. Since the same-name terminals of the current transformer CT are not in the same direction, the current direction of the secondary side of the current transformer is positive, and the current flows through the sampling resistors R1 and R2. The potential at point o of the sampling resistor R1 is higher than the potential at point p, and point o is connected to the inverting input terminal of the integral filter circuit 444, and point p is connected to the non-inverting input terminal of the integral filter circuit 444. In other words, the high potential end of the sampling resistor R1 is connected to the inverting input end of the integrating filter circuit 444, and the low potential end of the sampling resistor R1 is connected to the non-inverting input end of the integrating filter circuit 444, so that the voltage output by the integrating filter circuit 444 is also a negative voltage. Therefore, the polarity of the voltage output by the integrating filter circuit 444 is consistent with the polarity of the voltage output by the secondary circuit 430, so as to ensure that the voltage output by the integrating filter circuit 444 is the port AC power of the power grid.

[0097] (2) Referring to (b) in FIG9 , for the current flowing out of the non-coinciding terminals of the secondary winding of the transformer, the voltage at the output terminal of the secondary circuit is a positive voltage. In order to make the polarity of the voltage output by the integral filter circuit 444 consistent with the polarity of the voltage at the output terminal of the secondary circuit 430, the controller controls the controllable switch K1 to be turned on, as shown in FIG10 . This is because, when the switch K1 is turned on, the integral filter circuit integrates the voltage across the sampling resistor R1. Since the coinciding terminals of the current transformer CT are not in the same direction, the current direction of the secondary side of the current transformer is negative. The current flows through the sampling resistors R1 and R2. The potential at point p of the sampling resistor R1 is higher than the potential at point o. Point p is connected to the positive-inverting input terminal of the integral filter circuit 444, and point o is connected to the negative-inverting input terminal of the integral filter circuit 444. In other words, the high potential end of the sampling resistor R1 is connected to the non-inverting input end of the integral filter circuit 444, and the low potential end of the sampling resistor R1 is connected to the inverting input end of the integral filter circuit, so that the voltage output by the integral filter circuit 444 is also a positive voltage. Therefore, the polarity of the voltage output by the integral filter circuit 444 is consistent with the polarity of the voltage output by the secondary circuit 430, so as to ensure that the voltage output by the integral filter circuit 444 is the port AC power of the power grid.

[0098] For the case where only one of the four switching tubes is turned on, please refer to the above case 1 or case 2 for the specific control strategy, which will not be repeated here.

[0099] In an embodiment of the present application, when the two switch tubes included in the upper half bridge arm are turned on or the two switch tubes included in the lower half bridge arm are turned on, or when only one of the four switch tubes is turned on, the controller 450 is used to control one of the two groups of controllable switches to be turned on and the other group of controllable switches to be turned off according to the current direction of the secondary winding of the transformer 420 and the voltage polarity of the output end of the secondary circuit 430, so as to ensure that the voltage output by the integral filter circuit 444 is the port AC power of the power grid, so that the port AC power of the power grid obtained by the voltage output by the integral filter circuit 444 is more reliable. Furthermore, it is beneficial for the micro inverter to invert the DC power output by the photovoltaic module into AC power and then integrate it into the power grid, thereby ensuring the safety of the power grid.

[0100] In one embodiment, the controller 450 is configured to control the on or off of the two groups of controllable switches according to the states of the four switching tubes included in the bridge arm and the current direction of the secondary winding of the transformer 420, including:

[0101] When one switch tube in the upper half bridge arm and one switch tube in the lower half bridge arm are turned on, or when two switch tubes in the upper half bridge arm and one switch tube in the lower half bridge arm are turned on, or when one switch tube in the upper half bridge arm and two switch tubes in the lower half bridge arm are turned on, the controller 450 is used to control the two groups of controllable switches to be alternately turned on or off according to the current direction of the secondary winding of the transformer 420.

[0102] In an embodiment of the present application, when at least one switch tube in the upper half bridge arm is turned on and at least one switch tube in the lower half bridge arm is turned on, it is possible that the current direction of the secondary winding of the transformer is the same but the voltage polarity of the output end of the secondary circuit is different, or it is possible that the current direction of the secondary winding of the transformer is different but the voltage polarity of the output end of the secondary circuit is the same. Therefore, the controller 450 controls the two groups of controllable switches K1 and K2 to be alternately turned on or off in combination with the specific conduction status of the switch tube and the current direction of the secondary winding of the transformer 420, so as to ensure that the voltage output by the integral filter circuit 444 is the port AC power of the power grid, so that the port AC power of the power grid is obtained more reliably through the voltage output by the integral filter circuit 444. Furthermore, it is beneficial for the micro-inverter to invert the DC power output by the photovoltaic module into AC power and then integrate it into the power grid, thereby ensuring the safety of the power grid.

[0103] In one embodiment, the upper half bridge arm includes switch tubes S8 and S6, and the lower half bridge arm includes switch tubes S5 and S7. The controller is used to control the two groups of controllable switches to be alternately turned on or off according to the current direction of the secondary winding of the transformer, including:

[0104] When the switch tube S6 is turned on, the current direction of the secondary winding of the transformer is positive, and the controller controls one group of controllable switches to be turned on according to the positive current direction of the secondary winding of the transformer; or when the switch tube S8 is turned on, the current direction of the secondary winding of the transformer is negative, and the controller controls one group of controllable switches to be turned on according to the negative current direction of the secondary winding of the transformer;

[0105] When the switch tube S5 is turned on, the current direction of the secondary winding of the transformer is positive, and the controller controls another group of controllable switches to turn on according to the positive current direction of the secondary winding of the transformer. Or, when the switch tube S7 is turned on, the current direction of the secondary winding of the transformer is negative, and the controller controls another group of controllable switches to turn on according to the negative current direction of the secondary winding of the transformer.

[0106] In the embodiment of the present application, it is assumed that the current of the secondary winding of the transformer is in a positive direction from left to right, and the current of the output end of the secondary circuit is in a positive direction from top to bottom.

[0107] Case 3: At least the upper bridge arm switch S6 and the lower bridge arm switch S5 are turned on

[0108] (1) The upper half bridge arm switch tube S6 and the lower half bridge arm switch tube S5 are turned on

[0109] In the embodiment of the present application, the switch tube S6 of the upper half bridge arm and the switch tube S5 of the lower half bridge arm are turned on, and the current loop of the secondary winding of the transformer includes two paths, as shown in Figure 11. One is to flow out from the same-name end of the secondary winding of the transformer, through the inductor Ls, the switch tube S6, the freewheeling diode on the switch tube S8, the filter capacitor CX1, and the bridge arm capacitor CS2, and return to the non-same-name end of the secondary winding of the transformer, as shown in (a) of Figure 11. The other is to flow out from the same-name end of the secondary winding of the transformer, through the switch tube S5, the freewheeling diode on the switch tube S7, the filter capacitor CX1, and the bridge arm capacitor C S1 , and the inductor Ls returns to the same end of the secondary winding of the transformer, as shown in (b) of Figure 11. The current paths of the two current loops are different, but the current directions are the same.

[0110] A. For the current loop passing through the switch tube S6

[0111] Referring to (a) in Figure 11 , the current flowing through the secondary winding of the transformer is in the forward direction, and the voltage at the output of the secondary circuit is in the forward direction. To ensure that the polarity of the voltage output by the integrating filter circuit 444 is consistent with the polarity of the voltage at the output of the secondary circuit 430, the controller 450 controls the controllable switch K2 to conduct. This is because the current flows from the same-name terminal of the secondary winding of the transformer 420, the current direction of the secondary side of the current transformer is in the forward direction, and the current flows through the sampling resistors R1 and R2, resulting in a higher potential at point o than at point p. When switch K2 is turned on, the integrating filter circuit integrates the voltage across the sampling resistor R2. Since the potential at point p across the sampling resistor R2 is higher than the potential at point q, point p is connected to the non-inverting input of the integrating filter circuit 444, and point q is connected to the inverting input of the integrating filter circuit 444. In other words, the high potential end of the sampling resistor R2 is connected to the non-inverting input end of the integral filter circuit 444, and the low potential end of the sampling resistor R2 is connected to the inverting input end of the integral filter circuit 444, so that the voltage output by the integral filter circuit 444 is a positive voltage. Therefore, the polarity of the voltage output by the integral filter circuit 444 is consistent with the polarity of the voltage output by the secondary circuit 430, so as to ensure that the voltage output by the integral filter circuit 444 is the port AC power of the power grid.

[0112] B. For the current loop passing through the switch tube S5

[0113] Referring to FIG. 11( b ), the current flowing through the secondary winding of the transformer is positive, while the voltage at the output of the secondary circuit is negative. To ensure that the polarity of the voltage output by the integrating filter circuit 444 is consistent with the polarity of the voltage at the output of the secondary circuit 430, the controller 450 controls the controllable switch K1 to conduct. This is because, when switch K1 is turned on, the integrating filter circuit 444 integrates the voltage across the sampling resistor R1. Since the potential at point o of the sampling resistor R1 is higher than that at point p, point o is connected to the inverting input of the integrating filter circuit 444, and point p is connected to the non-inverting input of the integrating filter circuit 444. In other words, the high potential end of the sampling resistor R1 is connected to the inverting input end of the integrating filter circuit 444, and the low potential end of the sampling resistor R1 is connected to the non-inverting input end of the integrating filter circuit 444, so that the voltage output by the integrating filter circuit 444 is also a negative voltage. Therefore, the polarity of the voltage output by the integrating filter circuit 444 is consistent with the polarity of the voltage output by the secondary circuit 430, so as to ensure that the voltage output by the integrating filter circuit 444 is the port AC power of the power grid.

[0114] (2) The upper half bridge arm switch tubes S6 and S8 and the lower half bridge arm switch tube S5 are turned on

[0115] This method has an additional current loop compared to (1) in case 3, that is, the current flows out from the non-identical end of the secondary winding of the transformer and passes through the bridge arm capacitor C S2 , filter capacitor CX1 , switch tube S8, switch tube S6, and inductor Ls return to the same-name end of the secondary winding of the transformer. Based on the analysis of the above situation 1, in this mode, the controller controls switch K2 to be turned on.

[0116] (3) The upper half bridge arm switch tube S6 and the lower half bridge arm switch tubes S7 and S5 are turned on

[0117] This method has an additional current loop compared to (1) in case 3, that is, the current flows out from the non-identical end of the secondary winding of the transformer and passes through the bridge arm capacitor C S1 , filter capacitor C X1 , switch tube S7, switch tube S5, and inductor Ls return to the same-name end of the secondary winding of the transformer. Based on the analysis of the above situation 2, in this mode, the controller controls switch K1 to be turned on.

[0118] In summary, the controller can control the switch K1 or the switch K2 to be alternately turned on or off according to the specific conduction status of the switch tube and the current direction of the secondary winding of the transformer.

[0119] Case 4: At least the upper bridge arm switch S8 and the lower bridge arm switch S7 are turned on

[0120] (1) The upper half bridge arm switch tube S8 and the lower half bridge arm switch tube S7 are turned on

[0121] In the embodiment of the present application, the switch tube S8 of the upper half bridge arm and the switch tube S7 of the lower half bridge arm are turned on, and the current loop of the secondary winding of the transformer includes two paths. One is that the current flows out from the non-identical end of the secondary winding of the transformer, passes through the bridge arm capacitor CS2, the filter capacitor CX1, the switch tube S8, the freewheeling diode on the switch tube S6, and the inductor Ls, and returns to the identical end of the secondary winding of the transformer. The other is that the current flows out from the non-identical end of the secondary winding of the transformer, passes through the bridge arm capacitor CS1, the filter capacitor CX1, the switch tube S7, the freewheeling diode on the switch tube S5, and the inductor Ls and returns to the identical end of the secondary winding of the transformer. The current paths of the two current loops are different, but the current directions are the same.

[0122] A. For the current loop passing through the switch tube S8

[0123] According to the above analysis, the controller controls the switch K2 to be turned on.

[0124] B. For the current loop passing through the switch tube S7

[0125] According to the above analysis, the controller controls the switch K1 to be turned on.

[0126] (2) The upper half bridge arm switch tubes S8 and S6 and the lower half bridge arm switch tube S7 are turned on

[0127] This method has an additional current loop compared to (1) in case 4, that is, the current flows out from the non-identical end of the secondary winding of the transformer and passes through the bridge arm capacitor C S2 , filter capacitor C X1 , switch tube S8, switch tube S6, and inductor Ls return to the same-name end of the secondary winding of the transformer. Based on the analysis of the above situation 1, in this mode, the controller controls switch K2 to be turned on.

[0128] (3) The upper half bridge arm switch tube S8 and the lower half bridge arm switch tubes S7 and S5 are turned on

[0129] This method has an additional current loop compared to (1) in case 4, that is, the current flows out from the non-identical end of the secondary winding of the transformer and passes through the bridge arm capacitor C S1 , filter capacitor C X1 , switch tube S7, switch tube S5, and inductor Ls return to the same-name end of the secondary winding of the transformer. Based on the analysis of the above situation 2, in this mode, the controller controls switch K1 to be turned on.

[0130] In summary, the controller 450 can control the switch K1 or the switch K2 to be alternately turned on or off according to the specific conduction status of the switch tube and the current direction of the secondary winding of the transformer.

[0131] In the embodiment of the present application, the controller 450 controls the two groups of controllable switches to conduct alternately according to the specific conduction conditions of the switch tube and the current direction of the secondary winding of the transformer, so as to ensure that the voltage output by the integral filter circuit 444 is the port AC power of the power grid, thereby obtaining the port AC power of the power grid through the voltage output by the integral filter circuit 444 more reliably. Furthermore, it is beneficial for the micro-inverter to invert the DC power output by the photovoltaic module into AC power and then integrate it into the power grid, thereby ensuring the safety of the power grid.

[0132] In the embodiment described above, the switch circuit includes two groups of controllable switches K1 and K2 as an example. The switch circuit can also be a signal switch tube. Please refer to the following for details.

[0133] In one embodiment, each group of controllable switches includes two switch tubes and a freewheeling resistor; wherein,

[0134] The sources of the two switching tubes in each group of controllable switches are connected, the drains of the two switching tubes in one group of controllable switches are respectively connected to one end of the two sampling resistors connected in series and the inverting input end of the integral filter circuit 444, and the drains of the two switching tubes in the other group of controllable switches are respectively connected to the other end of the two sampling resistors connected in series and the inverting input end of the integral filter circuit 444, the two switching tubes in each group of controllable switches respectively include a freewheeling diode connected in parallel, and the freewheeling directions of the two freewheeling diodes in parallel in each group of controllable switches are opposite, and the two ends of the freewheeling resistor are connected in parallel to the drains of the two switching tubes; or,

[0135] The drains of the two switching tubes in each group of controllable switches are connected, the sources of the two switching tubes in one group of controllable switches are respectively connected to one end of the two sampling resistors connected in series and the inverting input end of the integral filter circuit 444, and the sources of the two switching tubes in the other group of controllable switches are respectively connected to the other end of the two sampling resistors connected in series and the inverting input end of the integral filter circuit 444. The two switching tubes in each group of controllable switches each include a freewheeling diode connected in parallel, and the freewheeling directions of the two freewheeling diodes in each group of controllable switches are opposite. The two ends of the freewheeling resistor are connected in parallel to the sources of the two switching tubes.

[0136] The gates of the two switch tubes in each group of controllable switches are connected, and the controller 450 is used to control the on or off of the two groups of controllable switches 443a by inputting a high level or a low level to the gates of the controllable switches.

[0137] FIG12 is a schematic diagram of another micro-inverter provided in an embodiment of the present application. The source electrodes of the two switching transistors in each group of controllable switches shown in FIG12 are connected. For one group of switching transistors V1 and V2, the switching transistors V1 and V2 are respectively connected to one end of the two sampling resistors connected in series (such as point o in the figure) and the inverting input terminal of the integral filter circuit 444. The drain electrodes of the two switching transistors V3 and V4 in the other group of controllable switches are respectively connected to the other end of the two sampling resistors connected in series (such as point q in the figure) and the inverting input terminal of the integral filter circuit 444. A freewheeling resistor R3 is connected in parallel to the drain electrodes of the switching transistors V1 and V2.

[0138] It should be noted that each group of controllable switches shown in the figure includes two switching tubes, and each of these two switching tubes is connected in parallel to a freewheeling diode, and the freewheeling directions of these two diodes are opposite. This is mainly because during the switching process of the four switching tubes S5 to S8, it is possible that the switching tubes are in a dead zone, that is, all four switching tubes are turned off. In this case, the controller 450 controls the switching tubes in the two groups of controllable switches to be turned off. Because the freewheeling directions of the two diodes connected in parallel to the two switching tubes in each group of switching tubes are opposite, this can, on the one hand, prevent the current of the integrating filter circuit from being reversely input into the secondary circuit through the current transformer, thereby preventing damage to the switching tubes in the secondary circuit; on the other hand, it can also prevent the current of the current transformer from being input into the integrating filter circuit, thereby preventing damage to the integrating filter circuit.

[0139] In addition, each group of controllable switches also includes a freewheeling resistor, which is connected in parallel to the drains of the two switching tubes, and can play a protective role for the integral filter circuit. As described above, during the switching process of the four switching tubes S5 to S8, it is possible that the switch tubes are in a dead zone, that is, all four switching tubes are turned off. At this time, the controller 450 controls the switching tubes in the two groups of controllable switches to turn off. Because the freewheeling directions of the two diodes connected in parallel to the two switching tubes in each group of switching tubes are opposite, the current of the integral filter circuit can be prevented from being reversely input to the secondary circuit through the current transformer. However, due to the presence of the freewheeling resistor, the current of the integral filter circuit can be consumed by the freewheeling resistor, thereby playing a role in protecting the integral filter circuit.

[0140] In one embodiment, the switch circuit further includes a signal control circuit 443b, and the signal control circuit 443b includes two groups of push-pull circuits, and the two groups of push-pull circuits are respectively connected to the two groups of controllable switches 443a.

[0141] Each push-pull circuit includes two signal switching tubes, two voltage-dividing resistors and a capacitor, one of the signal switching tubes is an N-channel switching tube, and the other signal switching tube is a P-channel switching tube. The base of one of the signal switching tubes is connected to the controller 450, the emitter of one of the signal switching tubes is grounded, the collector of one of the signal switching tubes is connected in series with a voltage-dividing resistor and then connected to the base of the other signal switching tube, the base of the other signal switching tube is connected in series with another voltage-dividing resistor and then grounded through the capacitor, the emitter of the other signal switching tube is connected to the other voltage-dividing resistor and the capacitor, and the collector of the other signal switching tube is connected to the gates of two switching tubes in one group of controllable switches.

[0142] The controller 450 is used to control the on or off of the two groups of controllable switches 443a by inputting a high level or a low level into the base of the control signal switch tube.

[0143] Referring to FIG. 12 , for one set of push-pull circuits, the switch tube Q2 is an N-channel switch tube, and the switch tube Q1 is a P-channel switch tube. The base of the switch tube Q2 is connected to the controller 450, the emitter of the switch tube Q2 is grounded, the collector of the switch tube Q2 is connected in series with a voltage-dividing resistor R11 and then connected to the base of the switch tube Q1. The base of the switch tube Q1 is connected in series with another voltage-dividing resistor R9 and then grounded through a capacitor C3. The emitter of the switch tube Q1 is connected to the other voltage-dividing resistor R9 and the capacitor C3. The collector of the other signal switch tube Q1 is connected to the gates of two switch tubes V1 and V2 in one set of controllable switches.

[0144] It should be noted that the switch tube Q2 connected to the controller 450 is an N-channel switch tube, and the switch tube Q1 connected to the gate of the switch tube in the controllable switch is a P-channel switch tube. This is because the switch tube Q2 connected to the controller is an N-channel switch tube, the emitter of the switch tube Q2 is grounded, and the controller 450 controls the input of a high level to the base of the switch tube Q2. The voltage U between the base and emitter of the switch tube Q2 is be is positive (assuming U be When the switch Q2 is turned on, the collector of the switch Q2 is also grounded. Since the collector of the switch Q2 is connected to the base of the switch Q1, the base of the switch Q1 is grounded. The VCC network connected to the emitter of the switch Q1 outputs a positive voltage. Since the switch Q1 is a P-channel switch and the voltage U between the base and emitter of the switch Q1 is be is negative, so the switch tube Q1 can be turned on, and further, V1 and V2 can be controlled to be turned on.

[0145] If the switch tube Q2 is a P-channel switch tube and the switch tube Q1 is an N-channel switch tube, or if the switch tubes Q1 and Q2 are both N-channel switch tubes or both P-channel switch tubes, the solution of the present application cannot be implemented.

[0146] Taking the switching tubes Q1 and Q2 as N-channel switching tubes as an example, the controller 450 controls the input of a high level to the base of the switching tube Q2, and the voltage U between the base and emitter of the switching tube Q2 is be is positive (assuming U be When the switch Q2 is turned on, the collector of the switch Q2 is also grounded, which is equivalent to the base of the switch Q1 being grounded. The VCC network connected to the emitter of the switch Q1 outputs a positive voltage. At this time, the voltage U between the base and emitter of the switch Q1 is be is positive. Since the switch tube Q1 is an N-channel switch tube, the switch tube Q1 cannot be turned on, and V1 and V2 cannot be turned on.

[0147] Similarly, the conduction principle of the switching tubes Q3 and Q4 is the same as that of the switching tubes Q1 and Q2, and will not be repeated here.

[0148] It should also be noted that the signal control circuit 443b is not limited to the two sets of push-pull circuits shown in the above embodiment. The signal control circuit 443b can also be an OC gate circuit or an OD gate circuit. As long as the circuit can output high and low levels, this application can be applied.

[0149] In one embodiment, the integration filter circuit includes an operational amplifier, a filter resistor R5, and a filter capacitor C2. The inverting input terminal of the operational amplifier is connected in series with the filter resistor and then connected to both ends of the two sampling resistors connected in series; the non-inverting input terminal of the operational amplifier is connected to the midpoint of the connection between the two sampling resistors; and the two ends of the filter capacitor C2 are connected to the inverting input terminal of the operational amplifier and the output terminal of the operational amplifier, respectively.

[0150] In the embodiment of the present application, the relationship between the output voltage of the integral filter circuit 444 and the input voltage is:

[0151] Among them, U o is the output voltage of the integral filter circuit, U i is the input voltage of the integration filter circuit, t1 and t2 are the start time and end time of integrating the input voltage respectively.

[0152] In the embodiment of the present application, the on / off state of the controllable switches K1 and K2 is related to the on / off state of the switch in the secondary circuit 430. The integral filter circuit 444 performs integral filtering on the sampling resistor based on the on / off state of the controllable switches K1 and K2. Generally, if the on / off state of the switch in the secondary circuit 430 changes, the integral filter circuit 444 restarts the calculation of the start time of the integral filtering of the voltage across the sampling resistor.

[0153] For example, assuming that during the time period from 9:00 to 9:10, the switches S8 and S6 in the secondary circuit 430 are turned on, the controller 450 controls the controllable switch K2 to be turned on, and the integral filter circuit 444 performs integral filtering on the voltage across R2, that is, Assume that during the period from 9:10 to 9:15, the switches S5 and S7 in the secondary circuit 430 are turned on, the controller 450 controls the controllable switch K1 to be turned on, and the integral filter circuit 444 performs integral filtering on the voltage across R1, that is, Therefore, the voltage output by the integration filter circuit 444 is consistent with the AC power at the port of the power grid.

[0154] The following table lists the output levels of G1 and G2 when different switches are turned on, in conjunction with Table 1. Table 1 only lists some of the possible situations.

[0155] Table 1

[0156] Referring to Table 1, it can be seen that when only one switch, only the upper arm, or only the lower arm is turned on, the controller controls G1 or G2 to output a high level, that is, controls V1 and V2 to be turned on, or controls V3 and V4 to be turned on. When at least one switch in the upper arm is turned on and at least one switch in the lower arm is turned on, the controller controls G1 and G2 to alternately output high levels, that is, controls the switch groups V1 and V and V3 and V4 to be turned on alternately.

[0157] The following description will be made by taking as examples only the upper half bridge arm and at least one switch tube in the upper half bridge arm and at least one switch tube in the lower half bridge arm being turned on.

[0158] Case 1: The two switches S8 and S6 included in the upper half bridge arm are turned on

[0159] As mentioned above, when switches S8 and S6 are turned on, the current in the secondary winding of the transformer has two directions, as shown in (a) and (b) of Figure 7. The two current loops have the same current path but different current directions.

[0160] (1) Referring to (a) in FIG7 , for the current flowing out of the same-name end of the secondary winding of the transformer, the voltage at the output end of the secondary circuit is positive at the top and negative at the bottom (hereinafter referred to as the forward voltage). In order to make the voltage polarity output by the integral filter circuit consistent with the voltage polarity at the output end of the secondary circuit, the controller controls the switching tubes V3 and V4 to be turned on, so that the voltage polarity output by the integral filter circuit is consistent with the voltage polarity output by the secondary circuit. Therefore, in order to make the switching tubes V3 and V4 turned on, the controller controls the gate of the switching tube Q4 to output a high level. When the gate of the switching tube Q4 is input with a high level, since the emitter of the switching tube Q4 is grounded, the voltage U between the gate and emitter of the switching tube Q4 is GE When the switch tube Q4 is turned on, it is equivalent to the collector of the switch tube Q4 being grounded. Since the emitter of the switch tube Q3 is connected to the capacitor C3, the voltage U between the gate and emitter of the switch tube Q3 is GE The voltage is negative, so the switch tube Q3 is turned on. The collector of the switch tube Q3 is connected to G2 in the controllable switch, that is, G2 inputs a high level, thereby turning on the switch tubes V3 and V4.

[0161] (2) Referring to (b) in FIG7 , for the current flowing out of the non-coincidental terminals of the secondary winding of the transformer, the control strategy is similar to that described above and will not be described in detail.

[0162] Case 3: At least the upper bridge arm switch S6 and the lower bridge arm switch S5 are turned on

[0163] (1) The upper half bridge arm switch tube S6 and the lower half bridge arm switch tube S5 are turned on

[0164] As described above, when switches S6 and S5 are turned on, the current loop of the secondary winding of the transformer has two paths, as shown in FIG11(a) and FIG11(b). The two current loops have different current paths but the same current direction.

[0165] A. For the current loop passing through the switch tube S6

[0166] Referring to FIG. 11 (a), the current flowing through the secondary winding of transformer 420 is in the forward direction, and the voltage at the output of secondary circuit 430 is in the forward direction. To ensure that the polarity of the voltage output by integrating filter circuit 444 is consistent with the polarity of the voltage at the output of secondary circuit 430, controller 450 controls switches V3 and V4 to be turned on. This ensures that the polarity of the voltage output by integrating filter circuit 444 is consistent with the polarity of the voltage output by secondary circuit 430. Therefore, to turn on switches V3 and V4, controller 450 controls the gate of Q4 to output a high level, thereby ultimately causing the input of G2 to be high, turning on switches V3 and V4.

[0167] B. For the current loop passing through the switch tube S5

[0168] Referring to FIG. 11( b ), the current flowing through the secondary winding of transformer 420 is positive, and the voltage at the output of secondary circuit 430 is negative. To ensure that the polarity of the voltage output by integrating filter circuit 444 is consistent with that of the voltage output by secondary circuit 430, controller 450 controls switches V1 and V2 to be conductive. This ensures that the polarity of the voltage output by integrating filter circuit 444 is consistent with that of the voltage output by secondary circuit 430. Therefore, to enable switches V1 and V2 to be conductive, controller 450 controls the gate of Q2 to output a high level, thereby ultimately enabling the input of G1 to be high, thereby enabling switches V1 and V2 to be conductive.

[0169] In summary, when at least the upper-half-bridge-arm switch tube S6 and the lower-half-bridge-arm switch tube S5 are turned on, the controller controls the switch tubes V1 and V2 or the switch tubes V3 and V4 to be alternately turned on or off according to the current direction of the secondary winding of the transformer and the voltage polarity of the output end of the secondary circuit.

[0170] To better understand the solution of the present application, the following description is made in conjunction with Figure 13. Figure 13 is a schematic diagram of a current detection method provided in an embodiment of the present application, and the current detection method may include steps S130 to S144.

[0171] S130: Whether only the switch tube of the upper half bridge arm or only the switch tube of the lower half bridge arm is turned on.

[0172] If yes, go to step S132; if no, go to step S314.

[0173] S312, control G1 or G2 to input high level.

[0174] Specifically, in step S316, the upper bridge arm S8 and / or S6 is turned on, and a high level is input to G2. In step S318, the lower bridge arm S5 and / or S7 is turned on, and a high level is input to G1.

[0175] S314 , whether at least one switch tube in the upper half bridge arm and at least one switch tube in the lower half bridge arm are turned on.

[0176] If not, go to step S140; if so, go to step S142.

[0177] S140, G1 and G2 all input low level.

[0178] S142, control G1 and G2 to input high level alternately.

[0179] Specifically, in S144, when the switch tube S6 is turned on, the current direction of the secondary winding of the transformer is positive, and G2 inputs a high level, or, when the switch tube S8 is turned on, the current direction of the secondary winding of the transformer is negative, and G2 inputs a high level; when the switch tube S5 is turned on, the current direction of the secondary winding of the transformer is positive, and G1 inputs a high level, or, when the switch tube S7 is turned on, the current direction of the secondary winding of the transformer is negative, and G1 inputs a high level.

[0180] Figure 14 is a schematic diagram of another micro-inverter provided in an embodiment of the present application. In one embodiment, each push-pull circuit further includes two additional protection resistors, one of which is connected to the base of one of the signal switching transistors, and the other is connected to the collector of the other signal switching transistor.

[0181] In the embodiment of the present application, one set of push-pull circuits may further include two additional protection resistors R8 and R10, wherein the protection resistor R10 is connected to the base of the switch tube Q2, and the other protection resistor R8 is connected to the collector of the other switch tube Q1. Another set of push-pull circuits may further include two additional protection resistors R12 and R14, wherein the protection resistor R14 is connected to the base of the switch tube Q4, and the other protection resistor R12 is connected to the collector of the other switch tube Q3.

[0182] In the embodiment of the present application, the main function of the protection resistors R8 and R10 is to protect the switch tube in the push-pull circuit. For example, the controller 450 controls the input of a high level to the base of the switch tube Q2. The base voltage of the switch tube Q2 is greater than the emitter voltage. If the voltage U between the base and emitter of the switch tube Q2 is be If the voltage U between the base and emitter of the switch tube Q2 is greater than the turn-on voltage, the switch tube Q2 can be turned on. beIf the voltage U between the base and emitter of the switch tube Q2 is too large, it will cause the base voltage to oscillate, thereby causing damage to the base. In the embodiment of the present application, a protection resistor R10 is set at the base of the switch tube Q2. The protection resistor R10 can share part of the voltage, thereby preventing the voltage U between the base and emitter of the switch tube Q2 from oscillating. be In addition, the protection resistor R10 can also play the role of current limiting. If the voltage U between MCU1 and the base and emitter of the switch tube Q2 is too large, the base of the switch tube Q2 will be damaged. be The voltage difference between the two is large. Without the protective resistor R10, the current flowing through the base of the switch tube Q2 is large, which may damage the switch tube Q2. In the embodiment of the present application, a protective resistor R10 is provided at the base of the switch tube Q2. Due to the increased resistance, the current flowing through the base of the switch tube Q2 can be reduced, thereby protecting the switch tube Q2. The function of the protective resistor R8 is similar and will not be repeated here.

[0183] The functions of the protection resistors R12 and R14 are similar to those of the protection resistors R8 and R10 described above, and are not described in detail herein.

[0184] In one embodiment, the integration filter circuit 444 further includes two other protection resistors R6 and R7, wherein one protection resistor R7 is connected in parallel across the filter capacitor C2, and the other protection resistor R6 is connected to the non-inverting input terminal of the operational amplifier.

[0185] In the embodiment of the present application, the positive input terminal of the integrating filter circuit 444 is connected in series with a protective resistor R6 and then connected to the connection point of the two sampling resistors R1 and R2 (point p in the figure). Generally, a reference bias voltage Vref is set at point p. If there is no protective resistor R6, it is equivalent to directly connecting point p to the positive input terminal of the integrating filter circuit 444. Due to voltage fluctuations, the integrating filter circuit may be damaged. In the embodiment of the present application, a protective resistor R6 is connected in series with the non-inverting input terminal of the operational amplifier. Even if the voltage fluctuates, the protective resistor R6 can reduce the interference with the integrating filter circuit caused by the voltage fluctuation, reduce the possibility of damage to the integrating filter circuit, and thus play a role in protecting the integrating filter circuit.

[0186] The primary function of protective resistor R7 is to prevent integration filter circuit 444 from malfunctioning due to saturation of the operational amplifier. While integration filter circuit 444 is integrating and filtering the sampling resistor, filter capacitor C2 remains charged for an extended period, potentially causing the operational amplifier to quickly saturate. Because protective resistor R7 is connected in parallel across capacitor C2, the voltage across filter capacitor C2 can be released through protective resistor R7, thereby protecting integration filter circuit 444 and enabling it to function properly.

[0187] It should be noted that, in the above examples, the switch tubes Q1 to Q4 are described using triodes as an example. In some embodiments, the switch tubes Q1 to Q4 may also be MOSFETs without limitation.

[0188] Based on this, the structure of the current detection circuit and the corresponding control strategy are introduced above. In some embodiments, the current detection circuit can also be of other forms of structure, which will be explained below in conjunction with FIG15.

[0189] Figure 15 is a schematic diagram of another micro-inverter provided in an embodiment of the present application. In this embodiment, the current detection circuit shown in Figure 15 is substantially identical to the circuit in the primary topology. The on / off logic of switches S15, S16, S17, and S18 shown in the figure is identical to that of switches S5, S6, S7, and S8 in the primary topology, respectively. Furthermore, the capacitances of capacitors CS11 and CS12 are identical to those of capacitors CS1 and CS2 in the primary topology, respectively. Filter circuit 2 has the same filtering effect as the filter circuit in the primary topology.

[0190] The sampling resistor Rac and the DC bias circuit are used to convert current into voltage for easy sampling by the controller. Where Vref is the bias voltage.

[0191] In the embodiment of the present application, the controller can obtain the AC power at the grid port according to the voltage across the sampling resistor Rac and the resistance value of the sampling resistor Rac.

[0192] Figure 16 is a schematic diagram of a current detection method provided by an embodiment of the present application. It should be understood that the description of the method embodiment corresponds to the description of the device embodiment. Therefore, for matters not described in detail, please refer to the device embodiment above and will not be repeated here.

[0193] The current detection method is applied to the inverter, and the current detection method includes steps S160-S162:

[0194] S160 controls the four switching tubes in the secondary circuit of the inverter connected to the secondary winding of the transformer to turn on or off. The secondary circuit is used to convert the frequency of the AC power output by the secondary winding of the transformer into industrial frequency AC power, and output the industrial frequency AC power to the power grid through the output port.

[0195] S162, according to the status of the four switching tubes and the current direction of the secondary winding of the transformer, the two groups of controllable switches in the current detection circuit are controlled to be turned on or off, so that the integral filter circuit in the current detection circuit restores the output voltage of the sampling circuit in the current detection circuit. The current detection circuit is located between the secondary winding of the transformer and the secondary circuit. The AC power restored by the integral filter circuit is consistent with the current, voltage or frequency of the AC power output from the output port.

[0196] In one embodiment, the on or off of two groups of controllable switches are controlled according to the states of the four switching tubes and the current direction of the secondary winding of the transformer, including: when the two switching tubes included in the upper half bridge arm are turned on or the two switching tubes included in the lower half bridge arm are turned on, or when only one of the four switching tubes is turned on, one group of the two groups of controllable switches is controlled to be turned on and the other group of controllable switches is turned off according to the current direction of the secondary winding of the transformer.

[0197] In one embodiment, the two groups of controllable switches are controlled to be turned on or off according to the states of the four switching tubes and the current direction of the secondary winding of the transformer, including: when one switching tube in the upper half bridge arm and one switching tube in the lower half bridge arm are turned on, or when two switching tubes in the upper half bridge arm and one switching tube in the lower half bridge arm are turned on, or when one switching tube in the upper half bridge arm and two switching tubes in the lower half bridge arm are turned on, the two groups of controllable switches are controlled to be alternately turned on or off according to the current direction of the secondary winding of the transformer.

[0198] In one embodiment, the upper half bridge arm includes a switch tube S8 and a switch tube S6, and the lower half bridge arm includes a switch tube S5 and a switch tube S7. The two groups of controllable switches are controlled to be alternately turned on or off according to the current direction of the secondary winding of the transformer, including: when the switch tube S6 is turned on, the current direction of the secondary winding of the transformer is positive, and one group of controllable switches is controlled to be turned on according to the positive current direction of the secondary winding of the transformer, or, when the switch tube S8 is turned on, the current direction of the secondary winding of the transformer is negative, and the controller controls one group of controllable switches to be turned on according to the negative current direction of the secondary winding of the transformer; when the switch tube S5 is turned on, the current direction of the secondary winding of the transformer is positive, and the other group of controllable switches is controlled to be turned on according to the positive current direction of the secondary winding of the transformer, or, when the switch tube S7 is turned on, the current direction of the secondary winding of the transformer is negative, and the controller controls the other group of controllable switches to be turned on according to the negative current direction of the secondary winding of the transformer.

[0199] An embodiment of the present application further provides a computer-readable storage medium storing computer instructions for implementing the method executed by the controller in the above method embodiment.

[0200] An embodiment of the present application further provides a computer program product comprising instructions, which, when executed by a computer, enables the computer to implement the method executed by the controller in the above method embodiment.

[0201] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A micro inverter, characterized in that: include: A primary circuit, the primary circuit is used to connect to the photovoltaic module and convert the direct current output by the photovoltaic module into alternating current; A transformer, wherein the primary winding of the transformer is coupled to the primary circuit, and the transformer is used to step up or step down the alternating current converted by the primary circuit; A secondary circuit, the secondary winding of the transformer is coupled to the secondary circuit, the secondary circuit is used to convert the stepped-up or stepped-down alternating current into industrial frequency alternating current, and to output the industrial frequency alternating current to a power grid through an output port; A current detection circuit, wherein the current detection circuit includes a current transformer, wherein the current transformer is located between the secondary winding of the transformer and the secondary circuit, and the current detection circuit is used to collect high-frequency alternating current of the secondary winding through the current transformer, and detect the alternating current output from the output port based on the high-frequency alternating current, wherein the frequency of the high-frequency alternating current is greater than the frequency of the industrial frequency alternating current.

2. The micro inverter according to claim 1, characterized in that: The micro inverter further includes a controller, the current detection circuit further includes a sampling circuit, a switching circuit, and an integral filter circuit, the primary side of the current transformer is connected between the secondary winding of the transformer and the secondary circuit, the secondary side of the current transformer is connected to the sampling circuit, the sampling circuit is connected to the integral filter circuit through the switching circuit, and the switching circuit includes a switching tube; The controller is used to: The switch tube in the switch circuit is controlled to be turned on or off so that the integral filter circuit restores the output voltage of the sampling circuit, and the alternating current restored by the integral filter circuit is consistent with the current, voltage or frequency of the alternating current output by the output port.

3. The micro inverter according to claim 2, characterized in that: The sampling circuit includes two sampling resistors and a sampling capacitor. The two sampling resistors are connected in series and connected to two ends of the secondary side of the current transformer. One end of the sampling capacitor is connected to the connection midpoint of the two sampling resistors, and the other end is grounded.

4. The micro inverter according to claim 2 or 3, characterized in that: The secondary circuit includes a bridge arm and two capacitors, the two capacitors are connected in series and then connected in parallel with the bridge arm, the bridge arm includes an upper half bridge arm and a lower half bridge arm, the connection point of the upper half bridge arm and the lower half bridge arm is connected to one end of the secondary winding of the transformer, and the connection point of the two capacitors is connected to the other end of the secondary winding of the transformer, the upper half bridge arm and the lower half bridge arm each include a group of switch tubes, each group of the switch tubes includes two switch tubes, the two switch tubes respectively include a parallel freewheeling diode, the freewheeling directions of the two parallel freewheeling diodes of each group of the switch tubes are opposite, and the switch circuit includes two groups of controllable switches; The controller is used to control the on or off of the switch tube in the switch circuit so that the integral filter circuit restores the output voltage of the sampling circuit, including: The controller is used to: The two groups of controllable switches are controlled to be turned on or off according to the states of the four switch tubes included in the bridge arm and the current direction of the secondary winding of the transformer, so that the integral filter circuit restores the output voltage of the sampling circuit.

5. The micro inverter according to claim 4, characterized in that: The controller is used to control the on or off of the two groups of controllable switches according to the states of the four switch tubes included in the bridge arm and the current direction of the secondary winding of the transformer, and includes: When the two switch tubes included in the upper half bridge arm are turned on or the two switch tubes included in the lower half bridge arm are turned on, or when only one of the four switch tubes is turned on, the controller is used to control one group of the two groups of controllable switches to be turned on and the other group of controllable switches to be turned off according to the current direction of the secondary winding of the transformer.

6. The micro inverter according to claim 4, characterized in that: The controller is used to control the on or off of the two groups of controllable switches according to the states of the four switch tubes included in the bridge arm and the current direction of the secondary winding of the transformer, and includes: When one switch tube in the upper half bridge arm and one switch tube in the lower half bridge arm are turned on, or when two switch tubes in the upper half bridge arm and one switch tube in the lower half bridge arm are turned on, or when one switch tube in the upper half bridge arm and two switch tubes in the lower half bridge arm are turned on, the controller is used to control the two groups of controllable switches to be alternately turned on or off according to the current direction of the secondary winding of the transformer.

7. The micro inverter according to claim 6, characterized in that: The upper half bridge arm includes a switch tube S8 and a switch tube S6, the lower half bridge arm includes a switch tube S5 and a switch tube S7, and the controller is used to control the two groups of controllable switches to be alternately turned on or off according to the current direction of the secondary winding of the transformer, including: When the switch tube S6 is turned on, the current direction of the secondary winding of the transformer is positive, and the controller The positive current direction of the secondary winding of the transformer controls one of the controllable switches to be turned on, or, when the switch tube S8 is turned on, the current direction of the secondary winding of the transformer is negative, and the controller controls one of the controllable switches to be turned on according to the negative current direction of the secondary winding of the transformer; When the switch tube S5 is turned on, the current direction of the secondary winding of the transformer is positive, and the controller controls another group of controllable switches to be turned on according to the positive current direction of the secondary winding of the transformer; or, when the switch tube S7 is turned on, the current direction of the secondary winding of the transformer is negative, and the controller controls another group of controllable switches to be turned on according to the negative current direction of the secondary winding of the transformer.

8. The micro inverter according to claim 7, characterized in that: One of the groups of controllable switches is connected between one end of the two sampling resistors connected in series and the inverting input end of the integral filter circuit, one end of the two sampling resistors connected in series is connected to the non-same-name end of the secondary winding of the transformer, the other group of controllable switches is connected between the other end of the two sampling resistors connected in series and the inverting input end of the integral filter circuit, one end of the two sampling resistors connected in series is connected to the same-name end of the secondary winding of the transformer, and the connection midpoint of the two sampling resistors is connected to the non-same-name input end of the integral filter circuit.

9. The micro inverter according to any one of claims 4 to 8, characterized in that: Each group of controllable switches includes two switch tubes and a freewheeling resistor; wherein, The sources of the two switch tubes in each group of the controllable switches are connected, wherein the drains of the two switch tubes in one group of the controllable switches are respectively connected to one end of the two sampling resistors connected in series and the inverting input end of the integral filter circuit, and the drains of the two switch tubes in another group of the controllable switches are respectively connected to the other end of the two sampling resistors connected in series and the inverting input end of the integral filter circuit, the two switch tubes in each group of the controllable switches respectively include a freewheeling diode connected in parallel, and the freewheeling directions of the two freewheeling diodes in parallel in each group of the controllable switches are opposite, and the two ends of the freewheeling resistor are connected in parallel to the drains of the two switch tubes; or, The drain electrodes of the two switch tubes in each group of the controllable switches are connected, wherein the source electrodes of the two switch tubes in one group of the controllable switches are respectively connected to one end of the two sampling resistors connected in series and the inverting input end of the integral filter circuit, and the source electrodes of the two switch tubes in another group of the controllable switches are respectively connected to the other end of the two sampling resistors connected in series and the inverting input end of the integral filter circuit, the two switch tubes in each group of the controllable switches respectively include a freewheeling diode connected in parallel, and the freewheeling directions of the two freewheeling diodes in parallel in each group of the controllable switches are opposite, and the two ends of the freewheeling resistor are connected in parallel to the sources of the two switch tubes; The gates of the two switch tubes in each group of the controllable switches are connected, and the controller is used to control the on or off of the two groups of the controllable switches by controlling the gates of the switch tubes to input a high level or a low level.

10. The micro inverter according to claim 9, characterized in that: The switch circuit further includes a signal control circuit, the signal control circuit includes two groups of push-pull circuits, and the two groups of push-pull circuits are respectively connected to the two groups of controllable switches; Each group of push-pull circuits includes two signal switch tubes, two voltage-dividing resistors and a capacitor, wherein one of the signal switch tubes is an N-channel switch tube, and the other signal switch tube is a P-channel switch tube, wherein the base of one of the signal switch tubes is connected to the controller, the emitter of one of the signal switch tubes is grounded, the collector of one of the signal switch tubes is connected in series with one of the voltage-dividing resistors and then connected to the base of the other signal switch tube, the base of the other signal switch tube is connected in series with another voltage-dividing resistor and then grounded through the capacitor, the emitter of the other signal switch tube is connected to the other voltage-dividing resistor and the capacitor, and the collector of the other signal switch tube is connected to the gates of the two switch tubes in one group of controllable switches; The controller is used to control the on or off of the two groups of controllable switches by controlling the base input of the signal switch tube to be high level or low level.

11. The micro inverter according to claim 10, characterized in that: Each group of the push-pull circuits also includes two other protection resistors, one of which is connected to the base of one of the signal switch tubes, and the other is connected to the collector of the other signal switch tube.

12. The micro inverter according to any one of claims 2 to 11, characterized in that: The integral filter circuit includes an operational amplifier, a filter resistor, and a filter capacitor; The inverting input terminal of the operational amplifier is connected in series with the filter resistor and then connected to both ends of the two sampling resistors in series; The non-inverting input terminal of the operational amplifier is connected to the connection midpoint of the two sampling resistors; Two ends of the filter capacitor are connected to the inverting input end of the operational amplifier and the output end of the operational amplifier respectively.

13. The micro inverter according to claim 12, characterized in that: The integral filter circuit also includes two other protection resistors, one of which is connected in parallel to both ends of the filter capacitor, and the other is connected to the non-inverting input terminal of the operational amplifier.

14. The micro inverter according to any one of claims 2 to 13, characterized in that: The sampling circuit, the switch circuit, the integral filter circuit and the controller are integrated in a chip.

15. A current detection method, the method being applied to an inverter, characterized in that: The method comprises: Controlling the on or off of four switch tubes in the secondary circuit connected to the secondary winding of the transformer in the inverter, wherein the secondary circuit is used to convert the alternating current output by the secondary winding of the transformer into industrial frequency alternating current, and output the industrial frequency alternating current to the power grid through the output port; The on or off of two groups of controllable switches in the current detection circuit are controlled according to the states of the four switching tubes and the current direction of the secondary winding of the transformer, so that the integral filter circuit in the current detection circuit restores the output voltage of the sampling circuit in the current detection circuit. The current detection circuit is located between the secondary winding of the transformer and the secondary circuit. The AC power restored by the integral filter circuit is consistent with the current, voltage or frequency of the AC power output by the output port.

16. The current detection method according to claim 15, characterized in that: The controlling the on or off of the two groups of controllable switches according to the states of the four switch tubes and the current direction of the secondary winding of the transformer includes: When the two switch tubes included in the upper half bridge arm are turned on or the two switch tubes included in the lower half bridge arm are turned on, or when only one of the four switch tubes is turned on, one group of the two groups of controllable switches is controlled to be turned on and the other group of controllable switches is turned off according to the current direction of the secondary winding of the transformer.

17. The current detection method according to claim 16, characterized in that: The controlling the on or off of the two groups of controllable switches according to the states of the four switch tubes and the current direction of the secondary winding of the transformer includes: When one switch tube in the upper half bridge arm and one switch tube in the lower half bridge arm are turned on, or when two switch tubes in the upper half bridge arm and one switch tube in the lower half bridge arm are turned on, or when one switch tube in the upper half bridge arm and two switch tubes in the lower half bridge arm are turned on, the two groups of controllable switches are controlled to be alternately turned on or off according to the current direction of the secondary winding of the transformer.

18. The current detection method according to claim 17, characterized in that: The upper half bridge arm includes a switch tube S8 and a switch tube S6, the lower half bridge arm includes a switch tube S5 and a switch tube S7, and the two groups of controllable switches are controlled to be alternately turned on or off according to the current direction of the secondary winding of the transformer, including: When the switch tube S6 is turned on, the current direction of the secondary winding of the transformer is positive, and the controller controls one group of controllable switches to be turned on according to the positive current direction of the secondary winding of the transformer; or, when the switch tube S8 is turned on, the current direction of the secondary winding of the transformer is negative, and the controller controls one group of controllable switches to be turned on according to the negative current direction of the secondary winding of the transformer; When the switch tube S5 is turned on, the current direction of the secondary winding of the transformer is positive, and the controller controls another group of controllable switches to be turned on according to the positive current direction of the secondary winding of the transformer; or, when the switch tube S7 is turned on, the current direction of the secondary winding of the transformer is negative, and the controller controls another group of controllable switches to be turned on according to the negative current direction of the secondary winding of the transformer.

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