Transmission power distribution method for isolation DC-DC module in hybrid topology power electronic transformer

Abstract

The invention discloses a transmission power distribution method for an isolation DC-DC module in a hybrid topology power electronic transformer, and belongs to the technical field of power distribution, and the method comprises the steps: collecting an input voltage Vs, an input current Is, and a DC voltage Vdc of the isolation DC-DC module; and establishing a relationship between the input current and the equivalent load, performing integral calculation in combination with the instantaneous current, calculating the minimum power Pj transmitted by the isolated DC-DC module under different circuit conditions in combination with the expressions of the modulated wave signal and the equivalent load and Vs, Is and Vdc, and further distributing the transmission power for the DC-DC module. By calculating the minimum power of the DC-DC module under the conditions of different input currents, input voltages and modulation degrees, the transmission power of the isolated DC-DC module is distributed according to the actual power, the input voltage and current changes can be quickly responded, the loss in energy transmission is reduced, the efficiency of a converter in the isolated DC-DC module is improved, and the operation efficiency of the converter is ensured; and meanwhile, the transmission power of the isolation DC-DC module is controlled to be minimum, the required transformer capacity can be reduced, and the cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of power distribution, and in particular to a transmission power distribution method of an isolated DC-DC module in a hybrid topology power electronic transformer. Background Art

[0002] Hybrid topology power electronic transformer is an advanced power electronic device that combines multiple power electronic converter topologies to achieve more efficient, flexible and reliable power conversion. This transformer is usually used in medium and high voltage distribution networks and can provide voltage conversion, isolation, reactive power compensation, harmonic filtering and other functions. In hybrid topology power electronic transformers, the transmission power distribution of isolated DC-DC modules is a key technical challenge. Power distribution of isolated DC-DC modules can ensure system stability, improve system efficiency, extend equipment life and adapt to different working conditions. At present, the power of isolated DC-DC modules is generally not adjusted directly, but the power output of non-isolated conversion units is adjusted by power transmission difference. In order to make the isolated DC-DC module respond quickly to different working conditions, how to determine the power transmission size of the isolated DC-DC module when the input voltage, current and DC voltage change is an urgent problem to be solved. Summary of the invention

[0003] The purpose of the present invention is to overcome the problems of the prior art and provide a transmission power distribution method for an isolated DC-DC module in a hybrid topology power electronic transformer.

[0004] The object of the present invention is achieved through the following technical solutions: a transmission power distribution method of an isolated DC-DC module in a hybrid topology power electronic transformer, the method is applied to a power electronic transformer, the power electronic transformer comprises a cascaded first isolation conversion unit, a second isolation conversion unit and a non-isolation conversion unit, the first isolation conversion unit and the second isolation conversion unit are arranged at the head end and / or the tail end, and the non-isolation conversion unit is arranged at the middle stage; the first isolation conversion unit comprises a first rectifier and a first inverter cascaded in sequence, the output end of the first rectifier and the input end of the first inverter are both vacant;

[0005] The method comprises the following steps:

[0006] Collect input voltage V s 、Input current I s , the DC voltage V of the isolated DC-DC module dc ;

[0007] Define the modulation wave signal and equivalent load, establish the relationship between the input current and the equivalent load, perform integral calculation based on the instantaneous current, and then solve the equivalent load. Combine the expressions of the modulation wave signal and the equivalent load, and according to V s ,Is 、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);

[0008] According to the actual power P dc-dc Distribute the transmission power of the isolated DC-DC module.

[0009] In one example, the relationship between input current and equivalent load is:

[0010]

[0011] Among them, i s represents instantaneous current; k represents the number of first isolation conversion units; l represents the number of second isolation conversion units; N represents the number of non-isolation conversion units; m represents modulation degree; ω represents angular frequency; t represents time; E represents the minimum voltage change unit; R 1 represents the total average equivalent load of the second isolation conversion unit; R 2 Represents the total average equivalent load of the non-isolated conversion unit.

[0012] In one example, the input voltage V s The expression is:

[0013] V s =(N+k+l)mE;

[0014] Wherein, m represents the modulation degree; E represents the minimum voltage change unit.

[0015] In one example, the instantaneous current i s The expression is:

[0016]

[0017] Wherein, k represents the number of first isolation conversion units; l represents the number of second isolation conversion units; N represents the number of non-isolation conversion units; m represents the modulation index; ω represents the angular frequency; t represents the time; E represents the minimum voltage change unit; R 1 represents the total average equivalent load of the second isolation conversion unit; R 2 Represents the total average equivalent load of the non-isolated conversion unit.

[0018] In one example, the total average equivalent load R of the non-isolated conversion unit is 2 for:

[0019]

[0020] Where m represents the modulation degree; R 1 represents the total average equivalent load of the second isolation conversion unit.

[0021] In one example, the total average equivalent load R of the second isolation conversion unit is 1 for:

[0022]

[0023] In one example, the minimum power transmitted by the isolated DC-DC module is:

[0024]

[0025] In one example, after allocating transmission power to the isolated DC-DC module, the method further includes:

[0026] According to the actual power P dc-dc , the compensation power generated by the PI controller is calculated to obtain the synthetic given power;

[0027] Calculate the given duty cycle D based on the synthesized given power 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.

[0028] The actual duty cycle D is input into the modulation module to obtain a switching signal, and the power of the converter in the isolated DC-DC module is controlled based on the switching signal.

[0029] It should be further explained that the technical features corresponding to the above examples can be combined or replaced with each other to form a new technical solution.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] 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.

[0033] Figure 1 A schematic diagram of a power electronic converter circuit structure provided for an example of the present invention;

[0034] Figure 2 A method flow chart provided for an example of the present invention;

[0035] Figure 3 A block diagram of direct power control of an isolated DC-DC module provided as an example of the present invention. DETAILED DESCRIPTION

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] In one example, a transmission power distribution method of an isolated DC-DC module is applied to a hybrid topology power electronic transformer, the power electronic transformer including a first isolation conversion unit with a voltage conversion function, a second isolation conversion unit and a non-isolation conversion unit, the first isolation conversion unit including a first rectifier and a first inverter in series, 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 conversion unit includes a second rectifier, an isolation DC-DC module (high-frequency DC-DC module) and a second inverter in series, and the isolation DC-DC module includes an isolation transformer, thereby achieving electrical isolation and blocking the short-circuit path. The non-isolation conversion unit includes a third rectifier and a third inverter in series, realizing 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. Preferably, 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, and 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 conversion unit, and thus has a four-quadrant working characteristic, and energy between the source and the load can flow in any direction.

[0041] The first isolation conversion unit, the second isolation conversion unit, and the non-isolation conversion 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 conversion unit and the second isolation conversion unit are arranged at the head end and / or the tail end, and the non-isolation conversion unit is arranged at the middle stage. Preferably, the number of the first isolation conversion unit, the second isolation conversion unit, and the non-isolation conversion unit can be one or more.

[0042] When the first isolation conversion unit and the second isolation conversion unit are both arranged only at the head end, the power electronic transformer comprises a head end unit and an intermediate unit connected in cascade in sequence. The head end unit is a first isolation conversion unit and a second isolation conversion unit connected in cascade. The head end unit may also be a second isolation conversion unit and a first isolation conversion unit connected in cascade. The first isolation conversion unit and the second isolation conversion unit in the head end unit may be arranged alternately. The intermediate unit is one or more non-isolation conversion units connected in cascade.

[0043] When the first isolation transformation unit and the second isolation transformation unit are both only arranged at the tail end, this includes intermediate-level units and tail-end units connected in cascade sequence, the intermediate-level units are one or more cascade-connected non-isolated transformation units, the tail-end unit is a cascade-connected first isolation transformation unit and a second isolation transformation unit, the tail-end unit may also be a cascade-connected second isolation transformation unit and a first isolation transformation unit, and the first isolation transformation unit and the second isolation transformation unit in the tail-end unit may be alternately arranged.

[0044] When the first isolation conversion unit and / or the second isolation conversion unit are arranged at the head end and the tail end, the power electronic transformer includes 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 conversion unit and a second isolation conversion unit connected in cascade, or the head end unit is a second isolation conversion unit and a first isolation conversion unit connected in cascade, or the head end unit is one or more first isolation conversion units, or the head end unit is one or more second isolation conversion units. When the head end unit is provided with both the first isolation conversion unit and the second isolation conversion unit, the first isolation conversion unit and the second isolation conversion unit can be arranged alternately; the intermediate unit is one or more non-isolated conversion units connected in cascade; the tail end unit is a first isolation conversion unit and a second isolation conversion unit connected in cascade, or the tail end unit is a second isolation conversion unit and a first isolation conversion unit connected in cascade, or the tail end unit is one or more first isolation conversion units, or the tail end unit is one or more second isolation conversion units. When the tail end unit is provided with both the first isolation conversion unit and the second isolation conversion unit, the first isolation conversion unit and the second isolation conversion unit can be arranged alternately. Figure 1 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 conversion unit, the intermediate-stage unit is two cascaded non-isolation conversion units, and the tail-end unit is a second isolation conversion unit. At this time, a first isolation conversion unit, two non-isolation conversion units, and a second isolation conversion unit are cascaded.

[0045] The present invention introduces a first isolation conversion unit with no load at the head end and / or tail end of the power electronic transformer, and introduces a second isolation conversion 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 of 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 capability. 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 conversion units at the head end and / or tail end, which optimizes the cost, volume and weight of the traditional PET.

[0046] The transmission power distribution method of the isolated DC-DC module is applied to the above-mentioned power electronic transformer, such as Figure 2 As shown, the method now includes the following steps:

[0047] S1: Collect input voltage V s 、Input current I s , the DC voltage V of the isolated DC-DC module dc .

[0048] 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 which are cascaded in sequence.

[0049] S2: Define the modulation wave signal and equivalent load, establish the relationship between the input current and the equivalent load, perform integral calculation based on the instantaneous current, and then solve the equivalent load. Combine the expressions of the modulation wave signal and the equivalent load, and 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).

[0050] Preferably, the minimum power P transmitted by the isolated DC-DC module under different input current, input voltage and modulation conditions is derived in advance. j The calculation expression of s ,I s 、V dc Substitute the minimum power P j The calculation expression can quickly get the minimum power P j , and then determine the actual power range.

[0051] S3: According to the actual power P dc-dc Distribute the transmission power of the isolated DC-DC module.

[0052] In one example, the relationship between input current and equivalent load is:

[0053]

[0054] Among them, i s represents instantaneous current; k represents the number of first isolation conversion units; l represents the number of second isolation conversion units; N represents the number of non-isolation conversion units; m represents modulation degree; ω represents angular frequency; t represents time; E represents the minimum voltage change unit; R 1 represents the total average equivalent load of the second isolation conversion unit; R2 Represents the total average equivalent load of the non-isolated conversion unit.

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

[0056]

[0057] Where Vs satisfies:

[0058] V s =(N+k+l)mE

[0059] Then the instantaneous current i s satisfy:

[0060]

[0061] According to the equivalent load R 1 and R 2 The relationship satisfied and i s Integrating the expression yields:

[0062]

[0063] Then we get the equivalent load R 2 for:

[0064]

[0065] Combined with equivalent load R 2 The expression and instantaneous current expression give the equivalent load R 1 for:

[0066]

[0067] Since V dc =(N+2)E, m=Vs / V dc , R 1 The expression simplifies to:

[0068]

[0069] 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:

[0070]

[0071] Since the power transmitted by the isolated DC-DC module cannot be negative, the actual power satisfies P dc-dc =max(0,Pj ).

[0072] In one example, after allocating transmission power to the isolated DC-DC module, as shown in FIG. Figure 3 As shown, it also includes:

[0073] S41: 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 P 0 *; where the compensation power △P* is calculated by the PI controller based on the actual output DC voltage U of the secondary side of the isolated DC-DC module 2 With the expected output voltage U 2 *The error is calculated.

[0074] S42: Calculate the given duty cycle D according to 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.

[0075] S43: Inputting the actual duty cycle D into the modulation module to obtain a switching signal, and performing switching control on the converter in the isolated DC-DC module based on the switching signal, thereby achieving transmission power control on the isolated DC-DC module.

[0076] 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.

[0077] 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 method for distributing transmission power of an isolated DC-DC module in a hybrid topology power electronic transformer, the method being applied to a power electronic transformer, characterized in that: The power electronic transformer comprises a cascaded first isolation conversion unit, a second isolation conversion unit and a non-isolation conversion unit, wherein the first isolation conversion unit and the second isolation conversion unit are arranged at the head end and / or the tail end, and the non-isolation conversion unit is arranged at the middle stage; The first isolation conversion unit includes 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 method comprises the following steps: Collect input voltage V s 、Input current I s , the DC voltage V of the isolated DC-DC module dc ; Define the modulation wave signal and equivalent load, establish the relationship between the input current and the equivalent load, perform integral calculation based on the instantaneous current, and then solve the equivalent load. Combine the expressions of the modulation wave signal and the equivalent load, and 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); According to the actual power P dc-dc Distribute the transmission power of the isolated DC-DC module.

2. The transmission power distribution method of the isolated DC-DC module in the hybrid topology power electronic transformer according to claim 1 is characterized in that: The relationship between input current and equivalent load is: Among them, i s represents instantaneous current; k represents the number of first isolated conversion units; l represents the number of second isolated conversion units; N represents the number of non-isolated conversion units; m represents the modulation index; ω represents the angular frequency; t represents time; E represents the minimum voltage change unit; R1 represents the total average equivalent load of the second isolated conversion unit; R2 represents the total average equivalent load of the non-isolated conversion unit.

3. The transmission power distribution method of the isolated DC-DC module in the hybrid topology power electronic transformer according to claim 1, characterized in that: The input voltage V s The expression is: V s =(N+k+l)mE; Wherein, m represents the modulation degree; E represents the minimum voltage change unit.

4. The transmission power distribution method of the isolated DC-DC module in the hybrid topology power electronic transformer according to claim 1 is characterized in that: The instantaneous current i s The expression is: Among them, k represents the number of first isolation conversion units; l represents the number of second isolation conversion units; N represents the number of non-isolation conversion units; m represents the modulation index; ω represents the angular frequency; t represents time; E represents the minimum voltage change unit; R1 represents the total average equivalent load of the second isolation conversion unit; R2 represents the total average equivalent load of the non-isolation conversion unit.

5. The transmission power distribution method of the isolated DC-DC module in the hybrid topology power electronic transformer according to claim 1, characterized in that: The average equivalent load R2 of the non-isolated conversion unit is: Wherein, k represents the number of first isolation conversion units; l represents the number of second isolation conversion units; N represents the number of non-isolation conversion units; m represents the modulation degree; and R1 represents the total average equivalent load of the second isolation conversion unit.

6. The transmission power distribution method of the isolated DC-DC module in the hybrid topology power electronic transformer according to claim 1, characterized in that: The total average equivalent load R1 of the second isolation conversion unit is: Wherein, k represents the number of first isolation conversion units; l represents the number of second isolation conversion units; N represents the number of non-isolation conversion units; m represents the modulation degree; and R1 represents the total average equivalent load of the second isolation conversion unit.

7. The transmission power distribution method of the isolated DC-DC module in the hybrid topology power electronic transformer according to claim 1, characterized in that: The minimum power P transmitted by the isolated DC-DC module j for: Wherein, k represents the number of first isolation conversion units; l represents the number of second isolation conversion units; N represents the number of non-isolation conversion units; m represents the modulation degree; and R1 represents the total average equivalent load of the second isolation conversion unit.

8. The transmission power distribution method of the isolated DC-DC module in the hybrid topology power electronic transformer according to claim 1, characterized in that: After allocating transmission power to the isolated DC-DC module, it also includes: According to the actual power P dc-dc , the compensation power generated by the PI controller is calculated to obtain the synthetic given power; Calculate the given duty cycle D based on the synthesized given power 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. The actual duty cycle D is input into the modulation module to obtain a switching signal, and the power of the converter in the isolated DC-DC module is controlled based on the switching signal.

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