CN114362497A

CN114362497A - Electronic capacitor, converter and electronic capacitor control method thereof

Info

Publication number: CN114362497A
Application number: CN202210261056.7A
Authority: CN
Inventors: 潘年安
Original assignee: Sungrow Power Supply Co Ltd
Current assignee: Sungrow Power Supply Co Ltd
Priority date: 2022-03-17
Filing date: 2022-03-17
Publication date: 2022-04-15
Anticipated expiration: 2042-03-17
Also published as: CN114362497B

Abstract

The application provides an electronic capacitor, a converter and an electronic capacitor control method thereof, wherein the electronic capacitor is connected between the anode and the cathode of a direct current bus of the converter through a bridge circuit, and the midpoint of the bridge circuit is also connected with the midpoint of the direct current bus through an energy exchange element; the bridge circuit can be controlled to work to supply low-frequency current required by the converter through the energy exchange element; that is, this application replaces the electrolytic capacitor among the prior art with electronic capacitor to solve the low frequency fluctuation problem of converter midpoint voltage, has avoided the problem that electrolytic capacitor brought with high costs, bulky, weight is big, moreover, replaces electrolytic capacitor with electronic capacitor and can also promote the life-span of converter, promotes the security of converter.

Description

Electronic capacitor, converter and electronic capacitor control method thereof

Technical Field

The present disclosure relates to the field of power electronics technologies, and in particular, to an electronic capacitor, a converter, and a method for controlling the electronic capacitor.

Background

With the rapid development of photovoltaic power generation, the capacity of the inverter is larger and larger, and particularly the capacity requirement of a three-phase high-power group string type inverter on a bus capacitor is correspondingly increased; most of the current technical solutions for realizing the bus capacitor are as shown in fig. 1, and the film capacitor provides a smoothing function for high-frequency ripple current in a mode of combining the film capacitor with the electrolytic capacitor, and the electrolytic capacitor provides a capacitance value to suppress low-frequency fluctuation caused by an inverter modulation algorithm.

That is, in the prior art, the problem of low-frequency fluctuation of the midpoint voltage of the high-power string inverter is solved by adding the electrolytic capacitor; however, electrolytic capacitors have disadvantages in terms of cost, volume, weight, and safety.

Disclosure of Invention

In view of the above, the present application provides an electronic capacitor, a converter and a method for controlling the electronic capacitor, so as to reduce cost, volume and weight and improve safety.

In order to achieve the above purpose, the present application provides the following technical solutions:

the application provides in a first aspect an electronic capacitor for use between dc buses of a converter, the electronic capacitor comprising: bridge circuit and energy exchange element; wherein,

two ends of the bridge circuit are respectively connected with the anode and the cathode of the direct current bus;

the middle point of the bridge circuit is connected with one end of the energy exchange element;

and the other end of the energy exchange element is connected with the midpoint of the direct current bus.

Optionally, the bridge circuit includes: an upper bridge arm and a lower bridge arm;

the upper bridge arm and the lower bridge arm are connected in series, and a connection point is used as a midpoint of the bridge circuit;

the other end of the upper bridge arm is connected with the anode of the direct current bus;

the other end of the lower bridge arm is connected with the negative electrode of the direct current bus.

Optionally, the upper bridge arm and the lower bridge arm respectively include: at least one first switching tube with a diode; when the number of the first switch tubes in the bridge arm is more than 1, the first switch tubes are connected in parallel; or,

the upper bridge arm and the lower bridge arm respectively comprise: at least one second switching tube and at least one diode connected in reverse parallel.

Optionally, the upper bridge arm and the lower bridge arm respectively include: two switch tube modules connected in series;

each switch tube module respectively includes: at least one first switching tube with a diode; when the number of the first switch tubes in the switch tube module is more than 1, the first switch tubes are connected in parallel; or,

each switch tube module respectively includes: at least one second switching tube and at least one diode connected in reverse parallel.

Optionally, the method further includes: the first diode module and the second diode module;

the negative electrode of the first diode module is connected with the connection point of the two switch tube modules in the upper bridge arm;

the anode of the first diode module is connected with the cathode of the second diode module, and the connecting point is connected with the middle point of the direct current bus;

and the anode of the second diode module is connected with a connection point of the two switch tube modules in the lower bridge arm.

Optionally, the first diode module and the second diode module respectively include: one diode, or at least two diodes connected in parallel.

Optionally, the energy exchange element is: an inductor, or, alternatively, a transformer winding.

A second aspect of the present application provides a converter comprising: the controller and a main circuit controlled by the controller; the bus capacitor between the positive and negative poles of the direct current bus in the main circuit comprises: at least two sets of thin film capacitors and at least one electronic capacitor as described in any of the above first aspects; wherein:

the group of thin film capacitors is arranged between the positive electrode and the midpoint of the direct current bus;

the other group of the thin film capacitors is arranged between the negative electrode and the midpoint of the direct current bus;

at least three ports of the electronic capacitor are respectively connected with the anode, the cathode and the midpoint of the direct current bus;

the two thin film capacitors are used for realizing a wave smoothing function for high-frequency ripple current;

the electronic capacitor is used for providing low-frequency current required by the converter according to the control of the controller.

Optionally, the main circuit includes an inverter circuit having a dc side connected to the dc bus;

the inverter circuit comprises a three-phase bridge arm; each phase bridge arm is respectively as follows: a Conergy NPC half-bridge topology, an NPC half-bridge topology, or an active neutral point clamped ANPC half-bridge topology.

Optionally, the main circuit further includes: and the filter is connected with the alternating current side of the inverter circuit.

Optionally, the main circuit further includes: and at least one DC/DC conversion circuit with one side connected to the DC bus.

A third aspect of the present application provides an electronic capacitance control method for an inverter, applied to a controller in the inverter according to any one of the second aspects, the electronic capacitance control method including:

acquiring a ripple current reference value of a midpoint of a direct current bus in the converter;

judging whether the ripple current reference value is larger than a preset threshold value or not;

if the ripple current reference value is larger than the preset threshold value, controlling an electronic capacitor in the converter to generate corresponding low-frequency current by taking the ripple current reference value as a given value;

and if the ripple current reference value is less than or equal to the preset threshold value, the electronic capacitor is not controlled to work.

Optionally, obtaining a ripple current reference value of a midpoint of a dc bus in the converter includes:

acquiring output current of each phase of an inverter circuit in the converter, and determining per-unit modulation voltage of each phase of a bridge arm of the inverter circuit;

and calculating the current flowing through the midpoint of the direct current bus according to the output current of each phase and the per-unit modulation voltage of each phase bridge arm to obtain the current serving as the ripple current reference value.

Optionally, determining per-unit modulation voltage of each phase bridge arm of the inverter circuit includes:

and calculating to obtain per unit modulation voltage of the corresponding bridge arm according to the real-time duty ratio of each phase of bridge arm of the inverter circuit.

Optionally, calculating the current flowing through the midpoint of the dc bus according to the output current of each phase and the per-unit modulation voltage of each phase bridge arm, including:

for each phase of the inverter circuit, respectively calculating the product of the output current and the absolute value of the per unit modulation voltage;

and subtracting the sum of the products of each phase from the sum of the output currents of each phase to obtain the current.

and taking the current detection result flowing through the midpoint of the direct current bus as the ripple current reference value.

Optionally, controlling the electronic capacitor in the converter to generate a corresponding low-frequency current given by the ripple current reference value includes:

generating a modulation signal for each switching tube in the electronic capacitor by taking the ripple current reference value as a given value;

and controlling the corresponding switch tube in the electronic capacitor to act by the modulation signal, and providing the low-frequency current to the midpoint of the direct current bus.

According to the electronic capacitor, a bridge circuit is connected between the anode and the cathode of a direct current bus of a converter, and the midpoint of the bridge circuit is also connected with the midpoint of the direct current bus through an energy exchange element; the bridge circuit can be controlled to work to provide a low-frequency current converter required by the converter through the energy exchange element; that is, this application replaces the electrolytic capacitor among the prior art with electronic capacitor to solve the low frequency fluctuation problem of converter midpoint voltage, has avoided the problem that electrolytic capacitor brought with high costs, bulky, weight is big, moreover, replaces electrolytic capacitor with electronic capacitor and can also promote the life-span of converter, promotes the security of converter.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings to be used in the description of the embodiments or the prior art will be briefly introduced below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

Fig. 1 is a schematic structural diagram of a bus capacitor provided in the prior art;

fig. 2a and fig. 2b are schematic structural diagrams of an electronic capacitor according to an embodiment of the present disclosure;

fig. 3a and fig. 3b are two circuit diagrams of the electronic capacitor provided in the embodiment of the present application, respectively;

FIG. 4 is a schematic structural diagram of a converter provided in an embodiment of the present application;

fig. 5a, 5b, and 5c are circuit diagrams of bridge arms of each phase in the inverter circuit according to the embodiment of the present disclosure, respectively;

FIG. 6 is a schematic diagram of another structure of a converter provided in the embodiments of the present application;

fig. 7 and fig. 8 are two flowcharts of an electronic capacitance control method of a converter according to an embodiment of the present application, respectively;

fig. 9 is a schematic diagram of an equivalent application structure of a converter provided in an embodiment of the present application.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In this application, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The application provides an electronic capacitor to reduce cost, volume and weight and improve safety.

The electronic capacitor is applied between the dc buses of the converter, and specifically includes, referring to fig. 2 a: a bridge circuit 101 and an energy exchange element 102; wherein,

two ends of the bridge circuit 101 are respectively connected with a positive electrode BUS + and a negative electrode BUS-of the direct current BUS; the middle point of the bridge circuit 101 is connected with one end of the energy exchange element 102; the other end of the energy exchange element 102 is connected to the midpoint O of the dc bus.

In practical applications, the bridge circuit 101, as shown in fig. 2b, specifically includes: upper arm 111 and lower arm 112; wherein, the upper bridge arm 111 and the lower bridge arm 112 are connected in series, and the connection point is used as the midpoint of the bridge circuit 101; the other end of the upper bridge arm 111 is connected with a positive electrode BUS + of the direct current BUS; the other end of the lower arm 112 is connected to the negative BUS-of the dc BUS.

The specific working principle is as follows:

during the operation of the converter, the action of a switching tube of an internal conversion circuit, such as an inverter circuit with a direct current side connected with a direct current bus, brings voltage fluctuation with a certain frequency to a midpoint O of the direct current bus; since the frequency of the ripple is lower than the switching frequency in the inverter circuit, the ripple is referred to as low-frequency ripple. In this case, the bridge circuit 101 may be controlled by any controller, such as a controller in the converter, to supply a required low-frequency current to the midpoint O of the dc bus through the energy exchange element 102, so as to replace the electrolytic capacitor in the prior art to solve the problem of low-frequency fluctuation of the midpoint voltage of the converter.

This electronic capacitor that this embodiment provided, through above-mentioned structure and principle, can replace the electrolytic capacitor among the prior art to solve the low frequency fluctuation problem of converter midpoint voltage, avoided the problem that electrolytic capacitor brought with high costs, bulky, weight is big, moreover, replace electrolytic capacitor with electronic capacitor and can also promote the life-span of converter, promote the security of converter.

On the basis of the above embodiment, in practical applications, the energy exchange element 102 of the electronic capacitor may specifically be an inductor, or may also be implemented by taking a winding in a transformer nearby; as long as the corresponding energy exchange function can be realized, depending on the application environment, the energy exchange device is within the protection scope of the present application.

The bridge circuit 101 of the electronic capacitor can be implemented in various forms, and two specific alternatives are provided in the embodiment:

(1) referring to fig. 3a, the bridge circuit 101 may be a half-bridge configuration.

In this case, upper arm 111 and lower arm 112 may include: at least one first switching tube with diodes (Q1 and Q2 as shown in fig. 3 a); in practical applications, in order to meet the corresponding power requirement, the number of the first switching tubes in each bridge arm may also be greater than 1, and the first switching tubes in each bridge arm are equivalent to Q1 or Q2 shown in fig. 3a after being connected in parallel.

Alternatively, upper arm 111 and lower arm 112 may include: at least one second switching tube and at least one diode connected in reverse parallel, when both are one, the structure is the same as that shown in fig. 3 a.

The types and the number of the devices are selected and set according to the specific application environment, and the devices are within the protection scope of the application.

In FIG. 3a, one end of the switch tube Q1 is connected to the positive BUS + of the DC BUS, and one end of the switch tube Q2 is connected to the negative BUS-of the DC BUS; a connection point a1 between the switching tubes Q1 and Q2 is connected to one end of an inductor L1 as the energy exchange element 102, and the other end of the inductor L1 is connected to a midpoint O of the dc bus.

The controller can enable the electronic capacitor to generate current injected into the midpoint O of the direct current bus by controlling the actions of the switching tubes Q1 and Q2, and further solve the problem of low-frequency fluctuation of the midpoint voltage of the converter.

(2) Referring to fig. 3b, the bridge circuit 101 may also be an NPC (neutral point clamped) structure.

In this case, upper arm 111 and lower arm 112 include: two switching tube modules connected in series (Q3, Q4, Q5 or Q6 as shown in fig. 3 b).

Specifically, each switch tube module can include respectively: at least one first switching tube with a diode (as shown in fig. 3 b); when the number of the first switch tubes in the switch tube module is greater than 1, the first switch tubes are connected in parallel, and the equivalent structure of the switch tube module is the same as that shown in fig. 3 b.

Alternatively, each switch tube module may include: at least one second switching tube and at least one diode connected in reverse parallel, when both are one, the structure is the same as that shown in fig. 3 b.

In this case, the electronic capacitor further includes: a first diode module (D1 as shown in fig. 3 b) and a second diode module (D2 as shown in fig. 3 b);

the cathode of the first diode module D1 is connected to the connection point of the two switch tube modules in the upper arm 111; the anode of the first diode module D1 is connected with the cathode of the second diode module D2, and the connection point A3 is connected with the midpoint O of the direct current bus; the positive pole of second diode module D2 is connected to the junction of the two switching tube modules in lower leg 112.

In practical applications, the first diode module D1 and the second diode module D2 may include: one diode, or at least two diodes connected in parallel.

In fig. 3b, switching tubes Q3, Q4, Q5 and Q6 are connected in series in sequence, one end of the switching tube Q3 is connected with the positive BUS + of the dc BUS, and one end of the switching tube Q6 is connected with the negative BUS-of the dc BUS; the connection point of the switching tube Q4 and the switching tube Q5 is used as a switching tube branch midpoint a2 and is connected with one end of an inductor L2 used as the energy exchange element 102; the connection point of the first diode module D1 and the second diode module D2 in series is used as a diode branch midpoint A3, is connected with the other end of the inductor L2, and is connected with a midpoint O of the direct current bus.

The controller can enable the electronic capacitor to generate current injected into the midpoint O of the direct current bus by controlling the operations of the switching tubes Q3, Q4, Q5 and Q6, and further solve the problem of low-frequency fluctuation of the midpoint voltage of the converter.

In practical applications, other structures may be adopted to implement the bridge circuit 101, and fig. 3a and 3b are only two alternative examples, but not limited thereto; other configurations that provide the low frequency current, as controlled by the controller, are also within the scope of the present application.

Another embodiment of the present application further provides a converter, as shown in fig. 4, including: a controller (not shown in the figure) and a main circuit controlled by the controller; the BUS capacitance 10 between the positive BUS + and the negative BUS-of the DC BUS in the main circuit comprises: at least two sets of thin film capacitors C1 and C2, and, an electronic capacitor 11; wherein:

each group of thin film capacitors can be realized by connecting a plurality of thin film capacitors in series and in parallel, which is shown in the prior art; a group of film capacitors C1 is arranged between the positive electrode BUS + of the direct current BUS and the midpoint O; another set of film capacitors C2 is disposed between the negative electrode BUS-of the DC BUS and the midpoint O. The two thin film capacitors have the same function as those in the prior art, and are mainly used for realizing a smoothing function for high-frequency ripple current in the converter.

The structure and principle of the electronic capacitor 11 can be seen in the above embodiment, and it has at least three ports, respectively connected with the positive BUS +, the negative BUS-and the midpoint O of the DC BUS; the electronic capacitor 11 is used for providing low-frequency current required by the converter according to the control of the controller. The low-frequency current is low-frequency ripple current of a level corresponding to the switching frequency of the converter, and the electronic capacitor 11 replaces an electrolytic capacitor in the prior art, so that the problem of bus low-frequency ripple of the converter can be solved. In practical applications, the electronic capacitor 11 may be integrated inside the converter or externally applied to the converter, and is not limited herein, and is within the protection scope of the present application.

The ripple current command of the controller to the electronic capacitor 11 may be specifically determined according to an actual detection result, or may be obtained through internal calculation, and the obtaining manner is not limited, for example, the obtaining of the ripple current reference value injected by the electronic capacitor 11 may be based on the output current of the converter and the real-time duty ratio of the converter bridge arm side to calculate the current injected into the midpoint O of the bus capacitor 10, and the current is used as the ripple current reference in the ripple current command; in practical applications, any way of obtaining the ripple current command through calculation inside the controller is within the protection scope of the present application.

The converter provided by the embodiment uses the electronic capacitor 11 to replace an electrolytic capacitor in the prior art to solve the problem of low-frequency fluctuation of the midpoint voltage of the converter, so that the problems of high cost, large volume and heavy weight caused by the electrolytic capacitor are avoided, and the service life of the converter can be prolonged and the safety of the converter can be improved by replacing the electrolytic capacitor with the electronic capacitor 11.

On the basis of the above embodiment, the main circuit of the converter at least includes a conversion circuit, such as the inverter circuit 20 shown in fig. 4, and generally, the ac side of the inverter circuit 20 is also provided with a corresponding ac filter 30. When the converter circuit is the inverter circuit 20 shown in fig. 4, the converter is an inverter; when the converter circuit is other circuits, such as a DC/DC converter circuit, or an AC/DC converter circuit, it is within the scope of the present application depending on the specific application environment.

The dc side of the inverter circuit 20 is connected to a dc bus, and may specifically include a three-phase bridge arm; the implementation form of each phase bridge arm may adopt various schemes in the prior art, for example, may be a coherence NPC half-bridge topology shown in fig. 5a, an NPC half-bridge topology shown in fig. 5b, or an ANPC (Active neutral point clamped) half-bridge topology shown in fig. 5 c; but not limited thereto, other topologies that can implement the inversion function are also within the scope of the present application.

In addition, as shown in fig. 6, the main circuit may further include: at least one DC/DC conversion circuit 40 with one side connected to the DC bus, such as a BOOST circuit commonly used in a photovoltaic grid-connected scenario or a bidirectional DC/DC conversion circuit commonly used in an energy storage grid-connected scenario. The other side of each DC/DC conversion circuit 40 is connected to a corresponding DC source, such as a photovoltaic string or a battery cluster. The parallel application of the plurality of DC/DC conversion circuits 40 enables the inverter to be a high power string inverter.

Another embodiment of the present invention further provides a method for controlling an electronic capacitor of a converter, which is applied to a controller in the converter according to any of the above embodiments, and the structure and principle of the converter are described in the above embodiments, and are not described herein again.

Referring to fig. 7, the method for controlling the electronic capacitor specifically includes:

and S11, acquiring a ripple current reference value of the midpoint of the direct current bus in the converter.

The step S11 may specifically be: directly taking a current detection result flowing through the midpoint of the direct current bus as a ripple current reference value, and requiring that the midpoint of the direct current bus in the converter is provided with a corresponding current detection module; alternatively, the step S11 may also include the steps shown in fig. 8:

s101, obtaining output current of each phase of an inverter circuit in the converter, and determining per unit modulation voltage of each phase bridge arm of the inverter circuit.

Referring to fig. 9, the bus capacitors In the converter are equivalent to two half bus capacitors C, and during the operation of the converter, the current flowing through the upper half bus capacitor C is Ip, the current flowing through the lower half bus capacitor C is In, and the current flowing through the midpoint O of the dc bus is Im, which is specifically divided into currents Ima, Imb, and Imc flowing into the arms of each phase.

When step S101 is executed, the output currents Ia, Ib, and Ic of the respective phases may be obtained by sampling. And through the calculation inside the controller software, normalized modulation voltages Vma, Vmb and Vmc of the three-phase bridge arms can be calculated according to the real-time duty ratios of the bridge arms of each phase of the inverter circuit.

And S102, calculating to obtain the current flowing through the midpoint of the direct current bus in the operation process of the converter as a ripple current reference value according to the output current of each phase and the per-unit modulation voltage of each phase bridge arm.

Based on normalized modulation voltages Vma, Vmb and Vmc of the three-phase bridge arms, currents Ima, Imb and Imc flowing through the midpoint O of each phase of bridge arm can be calculated, and the sum of the three currents is the current Im flowing through the midpoint O of the direct-current bus in the operation process of the converter.

Specifically, taking phase C as an example, the output current is Ic, and the current flowing from the midpoint O into the bridge arm of the phase is Imc; in the working process of an inverter bridge arm: when the Pulse Width Modulation (PWM) is carried out in a positive half PWM (Pulse Width Modulation) period Modulation mode, the potential of a point C is switched by a positive bus and a midpoint bus, the conducting time of the positive bus and the midpoint bus is determined by a unit Modulation voltage Vmc in each switching period, and the current Imc = (1-Vmc) × Ic flowing through the midpoint can be obtained; when in negative half-cycle modulation, Imc = (1+ Vmc) × Ic; based on the positive and negative period expression, it can be uniformly expressed as Imc = (1- | Vmc |) × Ic.

Similarly, currents flowing from the midpoint O of the A, B-phase bridge arm can be obtained as Ima = (1- | Vma |) × Ia, Imb = (1- | Vmb |) × Ib, respectively.

This gives:

Im = Ima+Imb+Imc = Ia+Ib+Ic - (|Vma|×Ia + |Vmb|×Ib +|Vmc|×Ic)。

that is, in practical application, the step S102 may be specifically divided into:

(1) for each phase of the inverter circuit, the product of the output current and the absolute value of the corresponding per unit modulation voltage is calculated. That is, | Vma | × Ia, | Vmb | × Ib, | Vmc | × Ic in the above formula are calculated.

(2) And subtracting the sum of the products of the phases from the sum of the output currents of the phases to obtain the current.

The sum of the output currents of the phases is: ia + Ib + Ic; the sum of the above products for each phase is: (| Vma |. times Ia + | Vmb |. times Ib + | Vmc |. times Ic); and calculating the difference between the two values to obtain the current Im flowing through the midpoint O of the direct current bus in the operation process of the converter.

After the step S11 is completed, the step S12 is executed.

And S12, judging whether the ripple current reference value is larger than a preset threshold value.

If the ripple current reference value is greater than the preset threshold, executing step S13; if the ripple current reference value is less than or equal to the predetermined threshold, step S14 is executed.

And S13, controlling the electronic capacitor in the converter to generate corresponding low-frequency current by taking the ripple current reference value as a given value.

In practical applications, the step S13 may be specifically divided into:

(1) and generating a modulation signal for each switching tube in the electronic capacitor by taking the ripple current reference value as a given value.

(2) And controlling the corresponding switch tube in the electronic capacitor to act by using the modulation signal, and providing low-frequency current for the midpoint of the direct current bus.

Based on the output current of the converter and the real-time duty ratio of the bridge arm side of the converter, the current injected into the midpoint of the bus capacitor is calculated, and the current is taken as a given value to control the electronic capacitor to provide corresponding low-frequency current, so that the problem of low-frequency fluctuation of the midpoint voltage of the converter can be solved by replacing an electrolytic capacitor in the prior art; the problems of high cost, large volume and heavy weight caused by the electrolytic capacitor are avoided, and the service life of the converter can be prolonged and the safety of the converter can be improved by replacing the electrolytic capacitor with the electronic capacitor.

And S14, not controlling the electronic capacitor to work.

When the ripple current reference value is less than or equal to the preset threshold value, it indicates that the ripple is low, and at this time, if the electronic capacitor is controlled to work, the efficiency of the converter is affected, so that each switching tube in the electronic capacitor is turned off at this time.

The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, the system or system embodiments are substantially similar to the method embodiments and therefore are described in a relatively simple manner, and reference may be made to some of the descriptions of the method embodiments for related points. The above-described system and system embodiments are only illustrative, wherein the units described as separate parts may or may not be physically separate, and the parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.

Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative components and steps have been described above generally in terms of their functionality in order to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

In the above description of the disclosed embodiments, the features described in the embodiments in this specification may be replaced or combined with each other to enable those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An electronic capacitor, applied between direct current buses of an inverter, comprising: bridge circuit and energy exchange element; wherein,

2. The electronic capacitor of claim 1, wherein the bridge circuit comprises: an upper bridge arm and a lower bridge arm;

3. The electronic capacitor of claim 2, wherein the upper leg and the lower leg each comprise: at least one first switching tube with a diode; when the number of the first switch tubes in the bridge arm is more than 1, the first switch tubes are connected in parallel; or,

4. The electronic capacitor of claim 2, wherein the upper leg and the lower leg each comprise: two switch tube modules connected in series;

5. The electronic capacitor of claim 4, further comprising: the first diode module and the second diode module;

6. The electronic capacitor of claim 5, wherein the first diode module and the second diode module each comprise: one diode, or at least two diodes connected in parallel.

7. The electronic capacitor according to any of claims 1 to 6, wherein the energy exchange element is: an inductor, or, alternatively, a transformer winding.

8. A transducer, comprising: the controller and a main circuit controlled by the controller; the bus capacitor between the positive and negative poles of the direct current bus in the main circuit comprises: at least two sets of thin film capacitors and at least one electronic capacitor as claimed in any one of claims 1 to 7; wherein:

9. The converter according to claim 8, characterized in that the main circuit comprises an inverter circuit with a direct current side connected with the direct current bus;

10. The converter according to claim 9, further comprising in the main circuit: and the filter is connected with the alternating current side of the inverter circuit.

11. The converter according to any one of claims 8 to 10, characterized in that the main circuit further comprises: and at least one DC/DC conversion circuit with one side connected to the DC bus.

12. An electronic capacitance control method of a converter, applied to a controller in the converter according to any one of claims 8 to 11, the electronic capacitance control method comprising:

13. The electronic capacitance control method of the converter according to claim 12, wherein obtaining a ripple current reference value of a dc bus midpoint in the converter comprises:

14. The electronic capacitance control method of the converter according to claim 13, wherein determining per-unit modulation voltages of the inverter circuit phase legs comprises:

15. The electronic capacitance control method of a converter according to claim 13, wherein calculating a current flowing through a midpoint of the dc bus from the output current of each phase and the per-unit modulation voltage of each phase bridge arm includes:

16. The electronic capacitance control method of the converter according to claim 12, wherein obtaining a ripple current reference value of a dc bus midpoint in the converter comprises:

17. The electronic capacitance control method of a converter according to any one of claims 12 to 16, wherein controlling the electronic capacitance in the converter to generate a corresponding low frequency current given the ripple current reference value comprises: