Filter circuit, photovoltaic inverter and photovoltaic system

Abstract

The application discloses a filter circuit, a photovoltaic inverter and a photovoltaic system, and belongs to the technical field of power electronics. The filter circuit comprises an inductive component, a plurality of first capacitors, a plurality of second capacitors and at least one on-off switching unit. The inductive component comprises a negative winding and a plurality of positive windings, a negative input terminal is used for being electrically connected with the negative poles of a plurality of direct current sources, and positive input terminals are used for being electrically connected with the positive poles of the direct current sources respectively. The first end of each first capacitor is electrically connected with the negative input terminal, and the second end of the first capacitor is electrically connected with the corresponding positive input terminal. The first end of each second capacitor is electrically connected with a negative output terminal, and the second end of the second capacitor is electrically connected with the corresponding positive output terminal. The on-off switching unit is arranged on a target line formed by the positive winding, the corresponding first capacitor and the corresponding second capacitor, and the on-off switching unit makes the target line open when the corresponding direct current source has no output power. The amplitude of the differential mode inductance reduction is reduced, and the differential mode filtering effect is improved.

Description

Technical Field

[0001] This application belongs to the field of power electronics technology, and in particular relates to a filter circuit, a photovoltaic inverter, and a photovoltaic system. Background Technology

[0002] Photovoltaic inverter products typically have multiple boost circuits. The input of each boost circuit is used to connect to a DC source, and the output signal of the DC source needs to be filtered for EMI (Electromagnetic Interference) at the input of each boost circuit.

[0003] In related technologies, multi-mode common-mode inductors are increasingly used in filter circuits. However, existing multi-mode common-mode inductors are prone to problems such as a decrease in differential-mode inductance and a reduction in differential-mode insertion loss, resulting in poor differential-mode filtering performance. Summary of the Invention

[0004] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application proposes a filter circuit, a photovoltaic inverter, and a photovoltaic system that reduces the magnitude of differential mode inductance reduction and prevents differential mode noise from being transmitted to subsequent circuits through an open-circuit target line, thereby improving the differential mode filtering effect.

[0005] In a first aspect, this application provides a filter circuit, which includes:

[0006] An inductor assembly includes a negative winding and multiple positive windings. The negative winding has a negative input terminal and a negative output terminal, and the positive winding has a positive input terminal and a positive output terminal. The negative input terminal is used to connect to the negative terminal of multiple DC sources, and the positive input terminal is used to connect to the positive terminal of each DC source respectively.

[0007] Multiple first capacitors, each first capacitor having its first terminal electrically connected to the negative phase input terminal, and its second terminal being electrically connected to the positive input terminal of the corresponding positive winding.

[0008] Multiple second capacitors, the first terminal of each second capacitor is electrically connected to the negative phase output terminal, and the second terminal of each second capacitor is electrically connected to the positive output terminal of the corresponding positive winding.

[0009] At least one on / off switching unit is disposed on the target line formed by the positive winding and its corresponding first and second capacitors. The on / off switching unit is configured to open the target line when the corresponding DC source has no output power, or to turn on the target line when the corresponding DC source has output power.

[0010] According to one embodiment of this application, the on / off switching unit includes a magnetic element, which is disposed between the positive input terminal and the second terminal of the first capacitor, and / or the magnetic element is disposed between the positive output terminal and the second terminal of the second capacitor.

[0011] Magnetic components are resistive to alternating current signals.

[0012] According to one embodiment of this application, the magnetic element includes:

[0013] A ferrite bead is connected in series between the positive input terminal and the second terminal of the first capacitor, and / or a ferrite bead is connected in series between the positive output terminal and the second terminal of the second capacitor.

[0014] According to one embodiment of this application, the on / off switching unit includes: a switching circuit, wherein the switching circuit is disposed in the branch where the first capacitor is located, and / or the switching circuit is disposed in the branch where the second capacitor is located;

[0015] The switching circuit is configured to disconnect when the DC source has no output power, or to turn on when the DC source has output power.

[0016] According to one embodiment of this application, the switching circuit, located in the branch where the first capacitor is located, includes:

[0017] The first resistor, with its first end electrically connected to the negative phase input terminal;

[0018] The second resistor has its first end electrically connected to the second end of the first resistor, and its second end is electrically connected to the positive input terminal of the first capacitor.

[0019] The switching transistor has its first terminal electrically connected to the second terminal of the first capacitor, its second terminal electrically connected to the corresponding positive input terminal of the first capacitor, and its driving terminal electrically connected to the connection node of the first resistor and the second resistor.

[0020] According to one embodiment of this application, the switching transistor is a bipolar transistor, the collector of the bipolar transistor is electrically connected to the second terminal of the first capacitor, and the emitter of the bipolar transistor is electrically connected to the corresponding forward input terminal of the first capacitor. The switching circuit further includes:

[0021] The third resistor has its first end electrically connected to the connection node of the first and second resistors, and its second end electrically connected to the base of the transistor.

[0022] The third capacitor has its first terminal electrically connected to the base of the transistor, and its second terminal electrically connected to the second terminal of the second resistor and the corresponding positive input terminal of the first capacitor.

[0023] According to one embodiment of this application, the filter circuit includes multiple on / off switching units, and each target line is provided with an on / off switching unit.

[0024] Secondly, this application provides a photovoltaic inverter, which includes the aforementioned filter circuit, multiple DC-DC conversion circuits and inverter circuit. The input side of the filter circuit is used to connect to a DC source. The input side of each DC-DC conversion circuit is electrically connected to the output side of the filter circuit. The output side of each DC-DC conversion circuit is electrically connected to the DC side of the inverter circuit. The AC side of the inverter circuit is used to connect to the power grid or a load.

[0025] Thirdly, this application provides a photovoltaic system comprising multiple photovoltaic strings and the aforementioned photovoltaic inverter, wherein the photovoltaic inverter is electrically connected to the photovoltaic strings.

[0026] According to one embodiment of this application, the positive terminal of at least one photovoltaic string is electrically connected to a plurality of positive input terminals in an inductor component.

[0027] According to various embodiments of the present application, the filter circuit, photovoltaic inverter, and photovoltaic system have the following characteristics: when the DC source has no output power, the target line connected to the on / off switching unit is open-circuited. The open-circuited target line does not form a parallel relationship with the target line corresponding to the DC source with output power, thereby reducing the magnitude of the differential mode inductance reduction and preventing differential mode noise from being transmitted to subsequent circuits through the open-circuited target line, thus improving the differential mode filtering effect.

[0028] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0029] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0030] Figure 1 This is a schematic diagram of the structure of a filter circuit in related technologies;

[0031] Figure 2 This is a schematic diagram of the differential-mode noise path in a filter circuit in related technologies;

[0032] Figure 3 This is one of the structural schematic diagrams of the filter circuit provided in the embodiments of this application;

[0033] Figure 4 This is a schematic diagram of the structure of the inductor assembly provided in an embodiment of this application;

[0034] Figure 5 This is a schematic diagram of the differential-mode noise path of the filter circuit provided in the embodiments of this application;

[0035] Figure 6This is a second schematic diagram of the filter circuit provided in the embodiments of this application;

[0036] Figure 7 This is a schematic diagram of the structure of the photovoltaic inverter provided in the embodiments of this application;

[0037] Figure 8 This is a schematic diagram of the structure of the photovoltaic system provided in the embodiments of this application.

[0038] Figure label:

[0039] Filter circuit 10, on / off switching unit 11, switching circuit 110, DC-DC converter circuit 20, inverter circuit 30, photovoltaic string, inductor component L, negative winding L1, positive winding L2, first to third capacitors C1 to C3, first to third resistors R1 to R3, ferrite bead P, and switching transistor Q. Detailed Implementation

[0040] The embodiments of this application are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0041] In the following description, a "circuit" refers to a conductive loop consisting of at least one element or sub-circuit connected by an electrical or electromagnetic link. When an element or circuit is said to be "coupled to" or "connected to" another element, or when an element / circuit is said to be "coupled at" or "connected at" two nodes, it can be directly coupled to or connected to the other element, or there may be intermediate elements. The connection between elements can be physical, logical, or a combination thereof. Conversely, when an element is said to be "directly coupled to" or "directly connected to" another element, it means that there are no intermediate elements between them.

[0042] In the description, the terms "first," "second," etc., are used to distinguish similar objects, not to describe a specific order or sequence. It should be understood that such numerical descriptors can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class, not limited in number; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0043] Furthermore, the use of terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicates that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0044] Photovoltaic inverters typically have multiple DC-DC converter inputs. The input terminals of these DC-DC converters are connected to a DC power source, and each input signal requires EMI (Electromagnetic Interference) filtering. The mainstream solution is to use a CLC (Common Mode Filter) topology. However, this requires a common-mode inductor on the input side of each DC-DC converter, resulting in a large and costly filter circuit. Furthermore, when multiple DC-DC converter inputs of a photovoltaic inverter share the same DC power source, the positive and negative currents of each converter can become unequal, leading to common-mode inductor saturation and loss of filtering effectiveness.

[0045] Reference Figure 1 In related technologies, multi-mode common-mode inductors are increasingly being used to solve the problem of inductor saturation caused by uneven power current distribution, while also reducing costs. However, when multiple windings share a single magnetic core, the X capacitance between the windings is equivalent to high-frequency conduction, which is equivalent to multiple windings being connected in parallel. This results in less leakage flux, reduced leakage inductance, and consequently, reduced differential-mode inductance and differential-mode insertion loss.

[0046] Reference Figure 2 When some DC sources connected by multiple windings have no power output, the X capacitor in the differential mode path corresponding to the DC source with no power output will cause differential mode noise to be transmitted to subsequent circuits. Figure 1 When the first DC source has power output, and the second, third, and fourth DC sources have no power output, the windings of the second, third, and fourth sources are essentially connected in parallel with the first winding. This reduces the differential-mode inductance generated by the first winding, and some differential-mode noise will be transmitted to subsequent circuits through the X capacitors corresponding to the second, third, and fourth windings, resulting in poor differential-mode filtering.

[0047] This application proposes a filter circuit, a photovoltaic inverter, and a photovoltaic system that reduces the magnitude of differential mode inductance reduction and prevents differential mode noise from being transmitted to subsequent circuits through an open-circuit target line, thereby improving the differential mode filtering effect.

[0048] Reference Figure 3One embodiment of this application provides a filter circuit 10, which includes: an inductor component L, a plurality of first capacitors C1, a plurality of second capacitors C2, and at least one on / off switching unit 11. The inductor assembly L includes a negative winding L1 and multiple positive windings L2. The negative winding L1 has a negative input terminal and a negative output terminal, and the positive windings L2 have a positive input terminal and a positive output terminal. The negative input terminal is used to connect to the negative terminal of multiple DC sources, and the positive input terminal is used to connect to the positive terminal of each DC source. The first terminal of each first capacitor C1 is connected to the negative input terminal, and the second terminal of each first capacitor C1 is connected to the positive input terminal of the corresponding positive winding L2. The first terminal of each second capacitor C2 is connected to the negative output terminal, and the second terminal of each second capacitor C2 is connected to the positive output terminal of the corresponding positive winding L2. The on / off switching unit 11 is disposed on the target line formed by the positive winding L2 and its corresponding first capacitor C1 and second capacitor C2. The on / off switching unit 11 is configured to open the target line when the corresponding DC source has no output power, or to turn on the target line when the corresponding DC source has output power.

[0049] Reference Figure 4 The structure of an inductor assembly L typically consists of multiple positive windings L2 sharing a common negative winding L1 with a single magnetic core. Each positive winding L2 corresponds to a positive input terminal, which is the end of the inductor assembly L used to connect to the positive terminal of a DC source. The positive output terminal is the end of the inductor's positive winding L2 furthest from the positive input terminal. The negative input terminal is the end of the inductor assembly L used to connect to the negative terminal of a DC source, and the negative output terminal is the end of the inductor's negative winding furthest from the negative input terminal.

[0050] The DC power source can be a photovoltaic string or a battery, and its type can be selected according to the actual application scenario. There is no limitation here.

[0051] It is understandable that the number of forward input terminals in inductor component L is the same as the number of forward output terminals. The specific number of forward input terminals and forward output terminals can be selected according to the actual application scenario. For example, inductor component L can be a 4-in-1 inductor or a 6-in-1 inductor. A 4-in-1 inductor has four forward input terminals and four forward output terminals, while a 6-in-1 inductor has six forward input terminals and four forward output terminals. The following explanation uses inductor component L as a 4-in-1 inductor as an example.

[0052] As an example, the filter circuit 10 can be installed in a photovoltaic inverter. The photovoltaic inverter may include four DC-DC converters 20, with each positive output terminal electrically connected to the positive terminal of the DC-DC converter 20 and each negative output terminal electrically connected to the negative terminal of the DC-DC converter 20.

[0053] Each positive winding L2 of the inductor assembly L is electrically connected to a first capacitor C1 and a second capacitor C2 in a one-to-one correspondence. Each first capacitor C1 is electrically connected between the negative input terminal and the positive input terminal of its corresponding positive winding L2, and each second capacitor C2 is electrically connected between the negative input terminal and the positive output terminal of its corresponding positive winding L2. The leakage inductance of the inductor assembly L is equivalent to a differential mode inductance between the first capacitor C1 and the second capacitor C2. The first capacitor C1 and the second capacitor C2 connected across the same positive winding L2 together with the positive winding L2 form the target circuit. The target circuit and the negative winding L1 together form the transmission path for the differential mode signal.

[0054] When the DC source connected to the positive winding L2 has power output, there is power current on the target line where the positive winding L2 is located. Part of the differential mode noise is reflected back to the DC source through the negative phase input terminal and the first capacitor C1. The other part of the differential mode noise is reflected back to the DC source after passing through the negative phase output terminal, the second capacitor C2 and the positive winding L2.

[0055] The on / off switching unit 11 is installed on the target line and can switch the target line between a conducting state and an open state. The specific type of the on / off switching unit 11 can be selected according to the actual application scenario and is not limited here. For example, the on / off switching unit 11 may include a switching circuit.

[0056] When the DC source has output power, the switching unit 11 turns on the target line, and differential-mode noise is reflected back to the DC source through the target line. When the DC source has no output power, the switching unit 11 turns off the target line. The winding on the disconnected target line is equivalent to not being connected in parallel with the winding on the turned-on target line, thereby reducing the reduction in leakage inductance, which in turn reduces the reduction in differential-mode inductance. In addition, differential-mode noise will not be transmitted from the disconnected target line to subsequent components, thereby improving the differential-mode filtering effect.

[0057] It should be noted that the number of on / off switching units 11 can be selected according to the actual application scenario. For example, when the inductor component L in the filter circuit 10 is a four-in-one inductor, the number of on / off switching units 11 can be 1, 2, 3 or 4.

[0058] Reference Figure 5 As an example, in the filter circuit 10 including the four-in-one inductor, each target line is provided with an on / off switching unit 11. The DC source connected to the first positive winding L2 has output power, while the DC sources connected to the other three positive windings L2 do not have output power. Therefore, the target line where the first positive winding L2 is located is on, and the target lines where the other three positive windings L2 are located are open. The path of differential mode noise can be equivalent to... Figure 5As shown in the path, the second positive winding L2, the third positive winding L2, and the fourth positive winding L2 are not connected in parallel with the first positive winding L2, so that the four-in-one inductor maintains its original high differential mode component, that is, maintains the differential mode inductance and improves the differential mode filtering effect.

[0059] According to the filter circuit 10 of this application, when the DC source has no output power, the target line connected to the on / off switching unit 11 is open. The open target line and the target line corresponding to the DC source with output power do not form a parallel relationship, which reduces the magnitude of the differential mode inductance reduction, and the differential mode noise will not be transmitted to the subsequent circuit through the open target line, thereby improving the differential mode filtering effect.

[0060] In some embodiments, the on / off switching unit includes a magnetic element disposed between the positive input terminal and the second terminal of the first capacitor C1, and / or the magnetic element disposed between the positive output terminal and the second terminal of the second capacitor C2; the magnetic element is resistive to AC signals.

[0061] The magnetic element is positioned between the positive input terminal and the second terminal of the first capacitor C1, or between the positive output terminal and the second terminal of the second capacitor C2, i.e., the magnetic element is positioned in the main power path. When the DC source has output power, the main power path primarily transmits DC signals. The magnetic field of the magnetic element does not change under DC signals, therefore its inductive reactance is zero, which can be equivalent to a short circuit. When the DC source has no output power, the main power path primarily transmits differential-mode noise current, which is typically a high-frequency AC signal. Within a certain frequency range, the inductive reactance of the magnetic element gradually increases with increasing frequency; therefore, for high-frequency differential-mode noise current, the magnetic element exhibits a high impedance state.

[0062] By utilizing the different impedances of magnetic components to DC signals and high-frequency AC signals, the target path can be made to conduct when the corresponding DC source has output power and disconnect when the corresponding DC source does not have output power. The main power path carries a large DC current and voltage when the DC source has output power, while the magnetic component is in a short-circuit state under DC signal conditions, which can reduce the damage to the component caused by large voltage or large current.

[0063] Magnetic elements are provided between the positive input terminal and the second terminal of the first capacitor C1, and between the positive output terminal and the second terminal of the second capacitor C2. This allows the other magnetic element to continue functioning even if one of the magnetic elements fails, thus improving the reliability of the filter circuit 10.

[0064] In some embodiments, the ferrite bead P is connected in series between the positive input terminal and the second terminal of the first capacitor C1, and / or the ferrite bead P is connected in series between the positive output terminal and the second terminal of the second capacitor C2.

[0065] The ferrite bead P can be fully saturated when a DC current passes through it, but will not saturate when a high-frequency current passes through it. When the ferrite bead P is saturated, it is in a conducting state, and the target circuit is also in a conducting state; when the ferrite bead P is unsaturated, it presents high impedance, and the target circuit is in an open circuit state.

[0066] When the DC source has output power, the power current flowing through the ferrite bead P is DC, causing the ferrite bead P to saturate. This enables the target circuit where the ferrite bead P is located to conduct when the corresponding DC source has output power. When the DC source has no output power, only the differential mode noise current flows through the ferrite bead P. Differential mode noise is a type of high-frequency signal. At this time, the ferrite bead P will not saturate and will exhibit high impedance. This enables the target circuit where the ferrite bead P is located to be open when the corresponding DC source has no output power.

[0067] By having the ferrite bead P exhibit different states under DC current and differential mode noise current, the corresponding target line can be open when the DC source has no output power and closed when the DC source has output power. The open target line and the closed target line do not form a parallel relationship, which reduces the magnitude of the differential mode inductance reduction, and the differential mode noise will not be transmitted to the subsequent circuit through the open target line, thus improving the differential mode filtering effect.

[0068] The ferrite bead P is connected in series between the positive input terminal and the second terminal of the first capacitor C1, or in series between the positive output terminal and the second terminal of the second capacitor C2. That is, the ferrite bead P is located in the main power path, and can switch between saturated and unsaturated states according to the current in the main power path. No other components need to be introduced, saving costs.

[0069] Reference Figure 6 In some embodiments, the on / off switching unit includes: a switching circuit 110, which is disposed in the branch where the first capacitor C1 is located, and / or the switching circuit 110 is disposed in the branch where the second capacitor C2 is located. The switching circuit 110 is configured to be disconnected when the DC source has no output power, or to be turned on when the DC source has output power.

[0070] The first capacitor C1 or the second capacitor C2 is equivalent to an open circuit for DC. Therefore, when the DC source has output power, the DC current on the main power path will not pass through the branch where the first capacitor C1 or the second capacitor C2 is located.

[0071] The switching circuit 110 is connected in series with the first capacitor C1 or the second capacitor C2. That is, the switching circuit 110 is set in the branch where the first capacitor C1 or the second capacitor C2 is located. In this case, it is not necessary for the components in the switching circuit 110 to have the ability to withstand high voltage or high current. The selection range of electronic components in the switching circuit 110 is larger and the cost is lower.

[0072] When switch circuit 110 is turned on, its corresponding target line is turned on; when switch circuit 110 is turned off, its corresponding target line is turned off. Switch circuit 110 is turned off when the DC source has no output power, ensuring that its corresponding target line is open when the DC source has no output power. Switch circuit 110 is turned on when the DC source has output power, ensuring that its corresponding target line is turned on when the DC source has output power. The open-circuit target line and the turned-on target line do not form a parallel relationship, reducing the magnitude of the differential-mode inductance reduction. Furthermore, differential-mode noise will not be transmitted to subsequent circuits through the open-circuit target line, improving the differential-mode filtering effect.

[0073] In some other embodiments, the first terminal of the switching circuit 110 is electrically connected to the second terminal of the second capacitor C2, the second terminal of the switching circuit 110 is electrically connected to the positive input terminal of the second capacitor C2, and the switching circuit 110 is configured to disconnect when the DC source has no output power.

[0074] The working principle and technical effect of the switch circuit 110 connected in series with the second capacitor C2 can be referred to the aforementioned embodiment, and will not be repeated here.

[0075] In other embodiments, a switching circuit 110 is provided in both the branch where the first capacitor C1 is located and the branch where the second capacitor C2 is located, so that when one switching circuit 110 fails, the other switching circuit 110 can continue to function, thereby improving the reliability of the filter circuit 10.

[0076] In some embodiments, the switching circuit 110 is disposed in the branch where the first capacitor C1 is located. The switching circuit 110 includes a first resistor R1, a second resistor R2, and a switching transistor Q. The first end of the first resistor R1 is electrically connected to the negative input terminal; the first end of the second resistor R2 is electrically connected to the second end of the first resistor R1, and the second end of the second resistor R2 is electrically connected to the positive input terminal corresponding to the first capacitor C1; the first end of the switching transistor Q is electrically connected to the second end of the first capacitor C1, the second end of the switching transistor Q is electrically connected to the positive input terminal corresponding to the first capacitor C1, and the driving end of the switching transistor Q is electrically connected to the connection node of the first resistor R1 and the second resistor R2.

[0077] The first resistor R1 and the second resistor R2 are connected in series and electrically connected between the negative input terminal and the positive input terminal. When the DC source has output power, there is a working voltage between the negative input terminal and the positive input terminal. The working voltage is applied to the driving terminal of the switching transistor Q after being divided by the first resistor R1 and the second resistor R2, which can drive the switching transistor Q to conduct.

[0078] The specific type of the switching transistor Q can be selected according to the actual application scenario, and there is no limitation here. For example, the switching transistor Q can be a transistor, a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), or an IGBT (Insulated-Gate Bipolar Transistor), etc.

[0079] The driving terminal of the switch Q is electrically connected to the connection node of the first resistor R1 and the second resistor R2. When the DC source has output power, the voltage at the driving terminal of the switch Q is the voltage divided by the second resistor R2. By adjusting the resistance values ​​of the first resistor R1 and the second resistor R2, the switch Q can be turned on when the DC source has output power and turned off when the DC source has no output power.

[0080] In some embodiments, the switching transistor Q is a transistor, with its collector electrically connected to the second terminal of the first capacitor C1, and its emitter electrically connected to the corresponding forward input terminal of the first capacitor C1. The switching circuit 110 further includes a third resistor R3 and a third capacitor C3. The first terminal of the third resistor R3 is electrically connected to the connection node of the first resistor R1 and the second resistor R2, and the second terminal of the third resistor R3 is electrically connected to the base of the transistor. The first terminal of the third capacitor C3 is electrically connected to the base of the transistor, and the second terminal of the third capacitor C3 is electrically connected to both the second terminal of the second resistor R2 and the corresponding forward input terminal of the first capacitor C1.

[0081] Transistors are current-driven devices. When the DC source has output power, the voltage across the second resistor R2 is converted into a driving current through the third resistor R3, driving the transistor to conduct. The third capacitor C3 is electrically connected between the base of the transistor and the forward input terminal of the first capacitor C1, which can filter out high-frequency interference signals in the driving current and improve the accuracy of switching.

[0082] In some embodiments, the filter circuit 10 includes a plurality of on / off switching units 11, and each target line is provided with an on / off switching unit 11.

[0083] Each target line is equipped with an on / off switching unit 11. When the DC source corresponding to any one or more target lines has no power output, the target line can be cut off, maintaining the original high differential mode component of the inductor component L, thereby improving the differential mode filtering effect.

[0084] Reference Figure 7One embodiment of this application proposes a photovoltaic inverter, which includes the aforementioned filter circuit 10, multiple DC-DC converter circuits 20, and inverter circuit 30. The input side of the filter circuit 10 is used to connect to a DC source. The input side of each DC-DC converter circuit 20 is electrically connected to the output side of the filter circuit 10. The output side of each DC-DC converter circuit 20 is electrically connected to the DC side of the inverter circuit 30. The AC side of the inverter circuit 30 is used to connect to the power grid or a load.

[0085] In the filter circuit 10, the positive and negative input terminals of the inductor component L are electrically connected to the DC source. Each positive output terminal is electrically connected to the positive terminal of the DC-DC converter 20, and the negative output terminal is electrically connected to the negative terminal of the DC-DC converter 20. The electrical signal output from the DC source is filtered by the filter circuit 10 and then transmitted to the DC-DC converter 20. The DC-DC converter 20 can be a boost circuit or a buck circuit, etc.

[0086] The output sides of each DC-DC converter circuit 20 are connected in parallel and then electrically connected to the DC side of the inverter circuit 30. The inverter circuit 30 converts the DC power output from the DC-DC converter circuit 20 into AC power and supplies it to the power grid or load.

[0087] The specific structure and filtering principle of the filter circuit 10 can be referred to in the aforementioned embodiments, and will not be repeated here.

[0088] According to the photovoltaic inverter of this application, when the DC source has no output power, the target line connected to the on / off switching unit 11 is open. The open target line and the target line corresponding to the DC source with output power do not form a parallel relationship, which reduces the magnitude of the differential mode inductance reduction, and the differential mode noise will not be transmitted to the subsequent circuit through the open target line, thereby improving the differential mode filtering effect.

[0089] Reference Figure 8 One embodiment of this application proposes a photovoltaic system including a plurality of photovoltaic strings 40 and the aforementioned photovoltaic inverter, wherein the photovoltaic inverter is electrically connected to the photovoltaic strings 40.

[0090] The photovoltaic string 40 is equivalent to the DC source in the aforementioned embodiment. The positive terminal of each photovoltaic string 40 is electrically connected to the positive input terminal of the inductor component L, and the negative terminal of each photovoltaic string 40 is electrically connected to the negative input terminal of the inductor component L. The filter circuit 10 is used to filter the DC power output by the photovoltaic string 40.

[0091] The specific structure and filtering principle of the photovoltaic inverter can be referred to in the aforementioned embodiments, and will not be repeated here.

[0092] According to the photovoltaic system of this application, when the DC source has no output power, the target line connected to the on / off switching unit 11 is open. The open target line and the target line corresponding to the DC source with output power do not form a parallel relationship, which reduces the magnitude of the differential mode inductance reduction, and the differential mode noise will not be transmitted to the subsequent circuit through the open target line, thereby improving the differential mode filtering effect.

[0093] In some embodiments, the positive terminal of at least one photovoltaic string is electrically connected to a plurality of positive input terminals in an inductor component.

[0094] The negative winding L1 of the inductor component L shares the same magnetic core with multiple positive windings L2. The sum of the currents in each positive winding L2 is equal to the current in the negative winding L1. When the negative terminals of each photovoltaic string are electrically connected to the negative input terminals of the inductor component L, even if the positive terminal of the same photovoltaic string is electrically connected to two or more of the positive input terminals, there will be no current imbalance.

[0095] As an example, the inductor assembly is a four-in-one inductor. Switching units are provided on / off on the target paths of the first, second, and third positive windings L2, but not on the target path of the fourth positive winding L2. There are two photovoltaic strings. The first and second positive windings L2 are electrically connected to the positive terminal of the first photovoltaic string, and the third and fourth positive windings L2 are electrically connected to the positive terminal of the second photovoltaic string. When the first photovoltaic string has output power and the second photovoltaic string has no output power, the target path of the third positive winding L2 is disconnected. Differential-mode noise will not be transmitted to subsequent circuits through the target path of the third positive winding L2. Therefore, this embodiment can improve the differential-mode filtering effect when multiple positive windings L2 are connected to the same photovoltaic string.

[0096] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. A filter circuit, characterized in that, include: An inductor assembly includes a negative winding and multiple positive windings. The negative winding has a negative input terminal and a negative output terminal, and the positive winding has a positive input terminal and a positive output terminal. The negative input terminal is used to be electrically connected to the negative terminal of multiple DC sources, and the positive input terminal is used to be electrically connected to the positive terminal of each DC source respectively. Multiple first capacitors, each first capacitor having its first terminal electrically connected to the negative phase input terminal, and each first capacitor having its second terminal electrically connected to the corresponding positive input terminal of the positive winding. Multiple second capacitors, the first end of each second capacitor is electrically connected to the negative phase output terminal, and the second end of each second capacitor is electrically connected to the positive output terminal of the corresponding positive winding. At least one on / off switching unit is disposed on the target line formed by the positive winding and its corresponding first capacitor and second capacitor. The on / off switching unit is configured to open the target line when the corresponding DC source has no output power, or to turn on the target line when the corresponding DC source has output power.

2. The filter circuit according to claim 1, characterized in that, The on / off switching unit includes a magnetic element, which is disposed between the positive input terminal and the second terminal of the first capacitor, and / or the magnetic element is disposed between the positive output terminal and the second terminal of the second capacitor; The magnetic element is in a resistive state to AC signals.

3. The filter circuit according to claim 2, characterized in that, The magnetic element includes: A magnetic bead, wherein the magnetic bead is connected in series between the positive input terminal and the second terminal of the first capacitor, and / or the magnetic bead is connected in series between the positive output terminal and the second terminal of the second capacitor.

4. The filter circuit according to claim 1, characterized in that, The on / off switching unit includes a switching circuit, which is located in the branch where the first capacitor is located, and / or the switching circuit is located in the branch where the second capacitor is located; The switching circuit is configured to be disconnected when the DC source has no output power, or to be turned on when the DC source has output power.

5. The filter circuit according to claim 4, characterized in that, The switching circuit is located in the branch where the first capacitor is located, and the switching circuit includes: A first resistor, the first end of which is electrically connected to the negative phase input terminal; The second resistor has a first end electrically connected to the second end of the first resistor, and the second end of the second resistor is electrically connected to the positive input terminal corresponding to the first capacitor. The switching transistor has its first end electrically connected to the second end of the first capacitor, its second end electrically connected to the forward input terminal corresponding to the first capacitor, and its driving end electrically connected to the connection node of the first resistor and the second resistor.

6. The filter circuit according to claim 5, characterized in that, The switching transistor is a bipolar junction transistor (BJT). The collector of the BJT is electrically connected to the second terminal of the first capacitor, and the emitter of the BJT is electrically connected to the corresponding forward input terminal of the first capacitor. The switching circuit further includes: The third resistor has its first end electrically connected to the connection node of the first resistor and the second resistor, and its second end electrically connected to the base of the transistor. The third capacitor has its first terminal electrically connected to the base of the transistor, and its second terminal electrically connected to the second terminal of the second resistor and the forward input terminal corresponding to the first capacitor.

7. The filter circuit according to any one of claims 1-6, characterized in that, The filtering circuit includes multiple on / off switching units, and each target line is provided with an on / off switching unit.

8. A photovoltaic inverter, characterized in that, The device includes a filter circuit, a plurality of DC-DC converter circuits, and an inverter circuit according to any one of claims 1-7. The input side of the filter circuit is used to connect to a DC source. The input side of each DC-DC converter circuit is electrically connected to the output side of the filter circuit. The output side of each DC-DC converter circuit is electrically connected to the DC side of the inverter circuit. The AC side of the inverter circuit is used to connect to the power grid or a load.

9. A photovoltaic system, characterized in that, It includes multiple photovoltaic strings and a photovoltaic inverter according to claim 8, wherein the photovoltaic inverter is electrically connected to the photovoltaic strings.

10. The photovoltaic system according to claim 9, characterized in that, At least one of the positive terminals of the photovoltaic string is electrically connected to a plurality of the forward input terminals of the inductor assembly.

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