Power electronic transformer based on hybrid topology

Abstract

The invention discloses a hybrid topology-based power electronic transformer, and belongs to the technical field of power electronic transformers, the hybrid topology-based power electronic transformer comprises a first isolation unit, a second isolation unit and a non-isolation unit, the first isolation unit comprises a first rectifier and a first inverter which are in cascade connection in sequence, and the first rectifier and the first inverter are vacant; the second isolation unit comprises a second rectifier, an isolation DC-DC module and a second inverter which are sequentially cascaded, and the non-isolation unit comprises a third rectifier and a third inverter which are sequentially cascaded; the first isolation unit, the second isolation unit and the non-isolation unit are in cascade connection, the first isolation unit and the second isolation unit are arranged at the head end and / or the tail end, and the non-isolation unit is arranged at the middle stage. The no-load and isolation DC-DC module is introduced, so that part of short-circuit paths can be blocked, the size is small, and the cost is low; the available vector boundary can be further expanded through cooperation of the no-load DC-DC module and the isolation DC-DC module, and the no-load voltage-sharing capability is compensated.

Description

Technical Field

[0001] The invention relates to the technical field of power electronic transformers, and in particular to a power electronic transformer based on a hybrid topology. Background Art

[0002] For the same-phase traction power supply system, an active power compensation device can be used to compensate for the harmonic reactive power required by the traction load, thereby reducing the number of excessive phases in the traction power supply system and improving the power quality. The commonly used active power compensation device is a power electronic transformer. Due to the requirements of ultra-high voltage application scenarios, multi-module cascade power electronic transformers are commonly used. Due to the capacitor short-circuit problem, isolated power electronic transformers are generally used, which are mainly divided into the following types:

[0003] like Figure 1 The fully isolated power electronic transformer shown in the figure achieves isolation of the input and output ports through the isolated DC-DC structure in the middle, thereby avoiding the problem of capacitor short circuit. In addition, the isolation transformer on the DC-DC module is a high-frequency transformer, which has the advantages of high efficiency and relatively small size.

[0004] like Figure 2 The power electronic converter with input and output isolation of industrial frequency transformer shown in the figure reduces the input and output voltages to bearable low-voltage single-phase electricity through a multi-tap industrial frequency transformer, realizes high-power transmission by connecting multiple converters in parallel, and adds a transformer transformation link while avoiding the capacitor short-circuit problem.

[0005] For the first topology (fully isolated power electronic transformer), the input and output are completely isolated, thus avoiding the problem of capacitor short circuit. The system has a wide operating range, but the isolation module is expensive and relatively large in size, and there will be certain power losses.

[0006] The second topology (power electronic converter with input and output isolation by industrial frequency transformer) has a simple structure and low cost, but the introduction of an ultra-high voltage industrial frequency transformer leads to problems of huge size and weight, as well as high power loss. Summary of the invention

[0007] The purpose of the present invention is to overcome the problems of the prior art and provide a power electronic transformer based on a hybrid topology.

[0008] The object of the present invention is achieved through the following technical solutions: A power electronic transformer based on a hybrid topology, comprising a first isolation unit, a second isolation unit and a non-isolation unit, the first isolation unit comprising a first rectifier and a first inverter connected in series, the output end of the first rectifier and the input end of the first inverter are both vacant; the second isolation unit comprises a second rectifier, an isolation DC-DC module and a second inverter connected in series, and the non-isolation unit comprises a third rectifier and a third inverter connected in series;

[0009] The first isolation unit, the second isolation unit and the non-isolation unit are connected in cascade, the first isolation unit and the second isolation unit are arranged at the head end and / or the tail end, and the non-isolation unit is arranged at the middle stage.

[0010] In an example, the power electronic transformer includes one or more first isolation units and one or more second isolation units.

[0011] In one example, an unused first capacitor is connected in parallel to the output end of the first rectifier, and an unused second capacitor is connected in parallel to the input end of the first inverter.

[0012] In one example, a third capacitor is connected in parallel between the second rectifier and the isolated DC-DC module, and a fourth capacitor is connected in parallel between the isolated DC-DC module and the second inverter.

[0013] In one example, a fifth capacitor is connected in parallel between the third rectifier and the third inverter.

[0014] In one example, the isolated DC-DC module is a dual active bridge converter, including an input-side rectifier bridge, a transformer, and an output-side rectifier bridge that are cascaded in sequence.

[0015] In one example, the power electronic transformer includes a first isolation unit, a second isolation unit, and N non-isolation units, and power control of the isolated DC-DC module includes:

[0016] Collect input voltage V s 、Input current I s , the DC voltage V of the isolated DC-DC module dc ;

[0017] According to V s ,I s 、V dc Calculate the minimum power P transmitted by the isolated DC-DC module under different input current, input voltage and modulation conditions j , corresponding to the actual power P dc-dc Satisfaction: P dc-dc =max(0,Pj); the minimum power P j The calculation expression is:

[0018]

[0019] Wherein, R1 represents the average equivalent load of the second isolation unit;

[0020] According to the actual power P dc-dc The transmission power of the isolated DC-DC module is distributed, and the transmission power of the isolated DC-DC module is introduced into the isolated DC-DC module control strategy to change the power transmission size.

[0021] It should be further explained that the technical features corresponding to the above-mentioned examples of power electronic transformers can be combined or replaced with each other to form a new technical solution.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention introduces a first isolation unit with no-load at the head end and / or tail end of the power electronic transformer, and introduces a second isolation unit with an isolated DC-DC module at the head end and / or tail end of the power electronic transformer. Both the no-load and isolated DC-DC modules can block part of the short-circuit path, and the cooperation between the no-load and isolated DC-DC modules can further expand the available vector boundary, greatly expand the input and output phase shift angle, and make up for the no-load voltage equalization capacity. At the same time, compared with the existing isolated power electronic transformer, the present invention has a low no-load cost, and only introduces two isolation units at the head end and / or tail end, which optimizes the cost, volume and weight of the traditional PET.

[0024] 2. The isolated DC-DC module of the present invention is a dual active bridge converter, which cooperates with the rectifier and inverter in each second isolation unit and non-isolation unit, has four-quadrant working characteristics, and the energy between the source and the load can flow in any direction to realize bidirectional transmission of energy; by controlling the switching tubes in the rectifier and the inverter, the voltage phase, frequency and amplitude of the output voltage can be adjusted. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The specific implementation methods of the present invention are further described in detail below in conjunction with the accompanying drawings. The accompanying drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The same reference numerals are used in these drawings to represent the same or similar parts. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0026] Figure 1 It is a schematic diagram of the circuit structure of an existing fully isolated power electronic transformer;

[0027] Figure 2 It is a schematic diagram of the circuit structure of an existing power electronic converter with input and output isolation of an industrial frequency transformer;

[0028] Figure 3 A schematic diagram of the circuit structure of a power electronic converter with an unloaded and isolated DC-DC module at each head end provided in an example of the present invention;

[0029] Figure 4 A schematic diagram of the circuit structure of a power electronic converter with an unloaded and isolated DC-DC module at each end provided by an example of the present invention;

[0030] Figure 5 A schematic diagram of the circuit structure of a power electronic converter with an unloaded head end and an isolated DC-DC module at the tail end provided as an example of the present invention;

[0031] Figure 6 An isolated DC-DC module direct power control block diagram provided for an example of the present invention;

[0032] Figure 7 A topological structure diagram of a power electronic converter in a traction power supply system provided as an example of the present invention. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] In the description of the present invention, it should be noted that the directions or positional relationships indicated by "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. are directions or positional relationships based on the drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the use of ordinal numbers (e.g., "first and second", "first to fourth", etc.) is to distinguish objects, and is not limited to this order, and cannot be understood as indicating or implying relative importance.

[0035] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0036] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] In one example, a power electronic transformer (Power Electronic Transformer, PET) based on a hybrid topology includes a first isolation unit, a second isolation unit, and a non-isolation unit, all of which have a voltage conversion function. The first isolation unit includes a first rectifier and a first inverter in cascade, and the output end of the first rectifier and the input end of the first inverter are both vacant, that is, the first rectifier and the first inverter are unloaded, and the short-circuit path is blocked by the unloaded part. The second isolation unit includes a second rectifier, an isolation DC-DC module (high-frequency DC-DC module), and a second inverter in cascade, and the isolation DC-DC module includes an isolation transformer, thereby achieving electrical isolation and blocking the short-circuit path. The non-isolation unit includes a third rectifier and a third inverter in cascade, and realizes voltage conversion processing. In the present invention, the first rectifier, the second rectifier, and the third rectifier are all single-phase single-module rectifiers, and the first inverter, the second inverter, and the third inverter are all single-phase inverters.

[0038] The first isolation unit, the second isolation unit, and the non-isolation unit are connected in cascade, that is, the input sides of the first rectifier, the second rectifier, and the third rectifier are connected in cascade, and the output sides of the first inverter, the second inverter, and the third inverter are connected in cascade to form a power electronic transformer, and the first isolation unit and the second isolation unit are arranged at the head end and / or the tail end, and the non-isolation unit is arranged at the middle stage. Preferably, the number of the first isolation unit, the second isolation unit, and the non-isolation unit can be one or more.

[0039] When the first isolation unit and the second isolation unit are only arranged at the head end, the power electronic transformer includes a head end unit and an intermediate unit connected in cascade. The head end unit is a first isolation unit and a second isolation unit connected in cascade. The head end unit can also be a second isolation unit and a first isolation unit connected in cascade. The first isolation unit and the second isolation unit in the head end unit can be arranged alternately. The intermediate unit is one or more non-isolated units connected in cascade. Figure 3 As shown, at this time, the power electronic transformer includes a head-end unit and an intermediate-stage unit connected in cascade in sequence. The head-end unit is a first isolation unit and a second isolation unit connected in cascade in sequence, and the intermediate-stage unit is two cascaded non-isolated units. At this time, a first isolation unit, a second isolation unit, and two non-isolated units are cascaded.

[0040] When the first isolation unit and the second isolation unit are both arranged only at the tail end, the middle-level units and the tail end units are sequentially cascaded, the middle-level units are one or more non-isolated units connected in cascade, the tail end unit is the first isolation unit and the second isolation unit connected in cascade, the tail end unit can also be the second isolation unit and the first isolation unit connected in cascade, and the first isolation unit and the second isolation unit in the tail end unit can be arranged alternately. Figure 4 As shown, at this time, the power electronic transformer includes an intermediate stage unit and a tail end unit connected in cascade in sequence. The intermediate stage unit is two cascaded non-isolated units, and the tail end unit is a first isolation unit and a second isolation unit connected in cascade in sequence. At this time, two non-isolated units, a first isolation unit, and a second isolation unit are cascaded.

[0041] When the first isolation unit and / or the second isolation unit are arranged at the head end and the tail end, the power electronic transformer comprises a head end unit, an intermediate unit and a tail end unit connected in cascade in sequence. The head end unit is a first isolation unit and a second isolation unit connected in cascade, or the head end unit is a second isolation unit and a first isolation unit connected in cascade, or the head end unit is one or more first isolation units, or the head end unit is one or more second isolation units. When the head end unit is provided with both the first isolation unit and the second isolation unit, the first isolation unit and the second isolation unit can be arranged alternately; the intermediate unit is one or more non-isolated units connected in cascade; the tail end unit is a first isolation unit and a second isolation unit connected in cascade, or the tail end unit is a second isolation unit and a first isolation unit connected in cascade, or the tail end unit is one or more first isolation units, or the tail end unit is one or more second isolation units. When the tail end unit is provided with both the first isolation unit and the second isolation unit, the first isolation unit and the second isolation unit can be arranged alternately. Figure 5 As shown, at this time, the power electronic transformer includes a head-end unit, an intermediate-stage unit and a tail-end unit connected in cascade in sequence, the head-end unit is a first isolation unit, the intermediate-stage unit is two cascaded non-isolation units, and the tail-end unit is a second isolation unit. At this time, a first isolation unit, two non-isolation units, and a second isolation unit are cascaded.

[0042] In the power electronic transformer of the present invention, the input positive end of the first-stage first isolation unit or the second isolation unit arranged at the head end and the input negative end of the last-stage first isolation unit or the second isolation unit arranged at the tail end are connected to a high-voltage power grid of one phase (α phase) of the traction transformer, the output positive end of the first-stage first isolation unit or the second isolation unit arranged at the head end and the output negative end of the last-stage first isolation unit or the second isolation unit arranged at the tail end are connected to a high-voltage power grid of another phase (β phase) of the traction transformer, and the high-voltage power grid of another phase (β phase) of the traction transformer is connected to the traction network. Further, the input positive end of the first-stage first isolation unit or the second isolation unit arranged at the head end is connected to a high-voltage power grid of one phase (α phase) of the traction transformer via a first reactor, and the output positive end of the first-stage first isolation unit or the second isolation unit arranged at the head end is connected to a high-voltage power grid of another phase (α phase) of the traction transformer via a second reactor.

[0043] In one example, if Figure 3-5 As shown, the output end of the first rectifier is connected in parallel with a first capacitor, the input end of the first inverter is connected in parallel with a second capacitor, and the first capacitor and the second capacitor are left vacant. Further, a third capacitor is connected in parallel between the second rectifier and the isolation DC-DC module, and a fourth capacitor is connected in parallel between the isolation DC-DC module and the second inverter to achieve isolation and filtering functions. Further, a fifth capacitor is connected in parallel between the third rectifier and the third inverter to achieve isolation and filtering functions.

[0044] In one example, the isolated DC-DC module is a dual active bridge (DAB) converter, including a sequentially cascaded input side rectifier bridge, a converter, and an output side rectifier bridge, wherein the input side rectifier bridge and the output side rectifier bridge are preferably full-bridge circuits composed of transistors. Optionally, the DC-DC converter is a converter containing a resonant circuit. In this example, the DC-DC converter is a dual active bridge converter, which cooperates with the rectifier and inverter in the non-isolated unit, and thus has a four-quadrant operating characteristic, and energy can flow in any direction between the source and the load.

[0045] In one example, a power electronic transformer includes a first isolation unit, a second isolation unit, and N non-isolation units, and power control of an isolated DC-DC module includes:

[0046] Collect input voltage V s 、Input current I s , the DC voltage V of the isolated DC-DC module dc ; Among them, the isolated DC-DC module is a dual active bridge converter, including an input side rectifier bridge, a converter and an output side rectifier bridge cascaded in sequence.

[0047] According to V s ,I s 、Vdc Calculate the minimum power P transmitted by the isolated DC-DC module under different input current, input voltage and modulation conditions j , corresponding to the actual power P dc-dc Satisfaction: P dc-dc =max(0,Pj); the minimum power P j The calculation expression is:

[0048]

[0049] Wherein, R1 represents the average equivalent load of the second isolation unit;

[0050] According to the actual power P dc-dc The transmission power of the isolated DC-DC module is distributed, and the transmission power of the isolated DC-DC module is introduced into the isolated DC-DC module control strategy to change the power transmission size.

[0051] Specifically, when the power electronic transformer includes a first isolation unit, a second isolation unit and N non-isolation units, the minimum power P transmitted by the isolated DC-DC module under different input current, input voltage and modulation conditions is j The calculation process is as follows:

[0052] The modulation wave signal is defined as (N+2)msinωt, and the average modulation wave signal of the no-load and isolated DC-DC modules is: R1 is the average equivalent load of the second isolation unit; R2 is the average equivalent load of the non-isolation unit. At this time, the equivalent loads R1 and R2 satisfy:

[0053]

[0054] Among them, i s represents instantaneous current; m represents the modulation degree of the modulation signal; ω represents the angular frequency; t represents time; and E represents the minimum voltage change unit.

[0055] Then, the input current amplitude I s The relationship with load can be expressed as:

[0056]

[0057] Where Vs satisfies:

[0058] V s =(N+2)mE;

[0059] Then the instantaneous current i s satisfy:

[0060]

[0061] According to the relationship between the equivalent loads R1 and R2 and i s Integrating the expression yields:

[0062]

[0063] Then the equivalent load R2 is obtained as:

[0064]

[0065] Combining the equivalent load R2 expression, the instantaneous current expression, and V dc =(N+2)E, m=Vs / V dc , simplify the R1 expression to:

[0066]

[0067] Therefore, at different currents I s 、V s And the total DC voltage V dc Under these conditions, the minimum power transmitted by the isolated DC-DC module is:

[0068]

[0069] Since the power transmitted by the isolated DC-DC module cannot be negative, the actual power satisfies P dc-dc =max(0,P j ).

[0070] Furthermore, the transmission power of the isolated DC-DC module is introduced into the isolated DC-DC module control strategy, such as Figure 6 As shown, including:

[0071] According to the actual power P dc-dc , the compensation power △P* generated by the PI controller is calculated to obtain the synthetic given power P0*; wherein, the compensation power △P* is calculated by the PI controller based on the error between the actual output DC voltage U2 of the secondary side of the isolated DC-DC module and the expected output voltage U2*.

[0072] Calculate the given duty cycle D based on the synthesized given power P0* and the DC voltage of the converter in the isolated DC-DC module * , when the converter output reaches a steady state, the duty cycle D * The actual duty cycle D is consistent with the actual duty cycle D.

[0073] The actual duty cycle D is input into the modulation module to obtain a switching signal, and the switching of the converter in the isolated DC-DC module is controlled based on the switching signal.

[0074] The present invention establishes the relationship between the input current and the load, performs integral calculation, and calculates the minimum power of the DC-DC module under different input current, input voltage and modulation conditions by combining the expression of the modulation wave signal and the equivalent load, and then distributes the transmission power of the isolated DC-DC module according to the actual power, which can quickly respond to the input voltage and current changes, reduce the loss in energy transmission, improve the converter efficiency in the isolated DC-DC module, and ensure the converter operation efficiency; at the same time, the transmission power of the isolated DC-DC module is controlled to be minimum, which can reduce the required transformer capacity and reduce the cost.

[0075] Combining the above power electronic transformer examples, a preferred example of the present invention is obtained, such as Figure 7 As shown, at this time, the power electronic transformer includes a head-end unit, an intermediate unit and a tail-end unit connected in cascade in sequence. In this example, the head-end unit is a first isolation unit, the intermediate unit is a plurality of non-isolated units, and the tail-end unit is a second isolation unit. At this time, the first isolation unit and the second isolation unit are respectively arranged at the first stage of the head end and the last stage of the tail end. At this time, the specific topological connection form is as follows Figure 6 As shown, the positive end of the input single-phase electricity is connected to the positive end A1P of the first isolation unit of the power electronic transformer through the inductor L1, the inductor L1 is connected to the α-phase high-voltage power grid of the traction transformer, the negative end A1N of the first isolation unit is connected to the A2P of the first non-isolated unit, the A2N of the first non-isolated unit is connected to the A3P of the second non-isolated unit, and then connected to the n-1th non-isolated unit in sequence, the negative end An-1N of the n-1th non-isolated unit is connected to the positive end AnP of the second isolation unit, and the negative end AnN of the second isolation unit is connected to the α-phase high-voltage power grid of the traction transformer. The positive end of the output single-phase electricity is connected to the positive end B1P of the first isolation unit of the power electronic transformer through the inductor L2, the negative end B1N of the first isolation unit is connected to B2P of the first non-isolated unit, B3N of the first non-isolated unit is connected to B3P of the second non-isolated unit, and so on, and are connected to the n-1th non-isolated unit in sequence, the negative end Bn-1N of the n-1th non-isolated unit is connected to the positive end BnP of the second isolation unit, the negative end BnN of the second isolation unit is connected to the β-phase high-voltage power grid of the traction transformer, and the β-phase high-voltage power grid of the traction transformer is connected to the traction network.

[0076] In the first isolation unit, the capacitors on the rectifier and inverter sides of the no-load module are separated from each other, and the capacitors on the rectifier and inverter sides of the non-isolated unit are combined into one capacitor. The second isolation unit adds an isolated DC-DC module between the rectifier and inverter sides for power transmission. For example, in the first isolation unit, the positive end of capacitor C11 is connected to the positive pole of the rectifier, and the negative end of capacitor C11 is connected to the negative end of the rectifier; the positive end of capacitor C12 is connected to the positive pole of the inverter, and the negative end of capacitor C12 is connected to the negative end of the inverter. For the non-isolated unit, the structure of the first non-isolated unit is used as an example for explanation. Capacitor C21 and capacitor C22 are combined into one capacitor C2, and the positive end and negative end are respectively connected to the positive pole and negative pole of the rectifier side and the inverter side. For the second isolation unit with an isolated DC-DC module, one side of the positive and negative ends of the capacitor Cn1 is connected to the positive and negative electrodes of the rectifier respectively, and the other side is connected to the positive and negative input electrodes of the DAB converter respectively; one side of the positive and negative ends of the capacitor Cn2 is connected to the positive and negative electrodes of the inverter respectively, and the other side is connected to the positive and negative output electrodes of the DAB converter respectively.

[0077] The no-load module in the first isolation unit and the isolated DC-DC module in the second isolation unit of the present invention can both block part of the short-circuit path, thereby increasing the input and output phase shift angle. The difference between the two is that adding an isolated DC-DC module requires an additional 8 switch tubes, a transformer and a capacitor, which is costly. The no-load module only needs to add a capacitor, which is low in cost, but the no-load module is limited by the voltage-sharing capacity, and it is difficult to reach the range boundary of the theoretical phase shift angle. Therefore, an isolated DC-DC module is introduced on the basis of adding the no-load module, which expands the available vector boundary and makes up for the voltage-sharing capacity of the no-load module. At the same time, compared with the isolated power electronic transformer, the non-isolated unit that occupies the main part of the present invention cancels part of the intermediate isolated DC-DC of the isolated power electronic transformer, and there is no need to use an ultra-high voltage power frequency transformer, that is, the present invention proposes a topological structure with a small number of power conversion stages, low device cost and small size. In addition, the position and number of the no-load module and the isolated DC-DC of the present invention are theoretically unlimited, and can be changed according to user needs, which is versatile.

[0078] The above specific implementation methods are detailed descriptions of the present invention. It cannot be determined that the specific implementation methods of the present invention are limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions and substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A power electronic transformer based on hybrid topology, characterized in that: The invention comprises a first isolation unit, a second isolation unit and a non-isolation unit, wherein the first isolation unit comprises a first rectifier and a first inverter which are cascaded in sequence, and the output end of the first rectifier and the input end of the first inverter are both vacant; the second isolation unit comprises a second rectifier, an isolation DC-DC module and a second inverter which are cascaded in sequence, and the non-isolation unit comprises a third rectifier and a third inverter which are cascaded in sequence; The first isolation unit, the second isolation unit and the non-isolation unit are connected in cascade, the first isolation unit and the second isolation unit are arranged at the head end and / or the tail end, and the non-isolation unit is arranged at the middle stage.

2. The power electronic transformer based on hybrid topology according to claim 1, characterized in that: The power electronic transformer includes one or more first isolation units and one or more second isolation units.

3. The power electronic transformer based on hybrid topology according to claim 1, characterized in that: An unused first capacitor is connected in parallel to the output end of the first rectifier, and an unused second capacitor is connected in parallel to the input end of the first inverter.

4. The power electronic transformer based on hybrid topology according to claim 1, characterized in that: A third capacitor is connected in parallel between the second rectifier and the isolated DC-DC module, and a fourth capacitor is connected in parallel between the isolated DC-DC module and the second inverter.

5. The power electronic transformer based on hybrid topology according to claim 1, characterized in that: A fifth capacitor is connected in parallel between the third rectifier and the third inverter.

6. The power electronic transformer based on hybrid topology according to claim 1, characterized in that: The isolated DC-DC module is a dual active bridge converter, comprising an input side rectifier bridge, a transformer and an output side rectifier bridge which are cascaded in sequence.

7. The power electronic transformer based on hybrid topology according to claim 1, characterized in that: The power electronic transformer includes a first isolation unit, a second isolation unit and N non-isolation units, and power control of the isolated DC-DC module includes: Collect input voltage V s 、Input current I s , the DC voltage V of the isolated DC-DC module dc ; According to V s ,I s 、V dc Calculate the minimum power P transmitted by the isolated DC-DC module under different input current, input voltage and modulation conditions j , corresponding to the actual power P dc-dc Satisfaction: P dc-dc =max(0,Pj); the minimum power P j The calculation expression is: Wherein, R1 represents the average equivalent load of the second isolation unit; According to the actual power P dc-dc The transmission power of the isolated DC-DC module is distributed, and the transmission power of the isolated DC-DC module is introduced into the isolated DC-DC module control strategy to change the power transmission size.

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