Expandable phase modular transformer, using method and DC-DC converter

Abstract

The invention belongs to the technical field of transformers, and discloses an expandable phase modular transformer, a use method and a DC-DC converter, and the transformer is characterized in that one end of a low-voltage bridge module is connected with a primary-side high-voltage bridge, and the other side of the low-voltage bridge module is connected with a secondary-side high-voltage bridge; the low-voltage bridge module comprises n parallel modules which are connected in parallel; each parallel module comprises two input ends and two output ends; one end of one input end of each parallel module is connected with the first end of the primary side high-voltage bridge, and the other input end of each parallel module is connected with the low-voltage bridge; a plurality of parallel switch tubes are arranged in the low-voltage bridge; the other end of the low-voltage bridge is connected with the first end of the first inductor Lk; a low-voltage bridge capacitor C9 is connected in parallel in each low-voltage bridge; the second end of the first inductor Lk is connected with the first end of the second inductor Lm and the first end of the primary side of the transformer. The embedded full bridge is adopted, so that the transformer effectively counteracts leakage inductance reactance, and optimal operation at any frequency is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of transformers, and particularly relates to an expandable phase modular transformer, a usage method and a DC-DC converter. Background Art

[0002] Traditional power systems require new transformer technologies to support the efficient access and transmission of renewable energy. However, the intermittent characteristics of renewable resources may lead to voltage deviations in microgrids, thereby affecting the stability and operation of the system. With the development of smart grid technology, it is required that transformers have a higher level of intelligence and be able to achieve self-monitoring, remote control and fault diagnosis to improve the stability and reliability of the grid. Moreover, the bulky size of transformers also limits the development of transformer technology. With the application of new materials and the development of power electronics technology, transformers can be integrated with power electronic devices (such as inverters, rectifiers, etc.) to form new energy conversion and control solutions. And today, with the rapid development of high-frequency technology, new transformer designs can operate at higher frequencies, providing higher power density and efficiency. Along with the increasing global attention to energy efficiency, and the rapid development of energy storage systems, data center power supplies and transportation electrification, the demand for high-power, high-density isolated DC-DC converters has been promoted. However, due to the trade-off between thermal management, leakage inductance minimization and insulation requirements, designing high-power and high-frequency transformers faces huge challenges.

[0003] The Chinese patent publication number is CN101399498A, and the patent application named DC conversion power supply device and method for improving DC conversion power supply device includes: a transformer; a primary side circuit of the transformer; a secondary side circuit of the transformer, and the secondary side circuit includes a rectifying circuit with a shaping transformation function for transforming the square wave voltage output by the transformer to form a DC output voltage; a control unit, which controls the secondary side circuit of the transformer according to the DC output voltage and adjusts the DC output voltage to make the DC output voltage a stable target value. The present invention also discloses a method for improving a DC conversion power supply device, including: coupling a rectifying circuit with a shaping transformation function on a secondary winding to transform the square wave voltage output by the transformer to form a DC output voltage; monitoring the DC output voltage, and adjusting the DC output voltage according to the DC output voltage to make the DC output voltage a stable target value. By applying the present invention, the dynamic performance of the DC conversion power supply can be improved. However, the transformer of this patent application cannot cancel the leakage inductance reactance to ensure optimal operation at any frequency. Summary of the Invention

[0004] In order to overcome the problems existing in the above-mentioned prior art, the object of the present invention is to provide an expandable phase modular transformer, a usage method and a DC-DC converter. This transformer solves this problem through its simple open-loop control and natural current sharing, enabling it to be paralleled and expanded to different rated powers. This transformer overcomes the problems of transformer parallel connection and resonant point displacement in the design of traditional bidirectional DC converters. By adopting an embedded full bridge, the transformer of the present invention effectively cancels out the leakage inductance reactance, ensuring optimal operation at any frequency. In addition, the present invention also retains the inherent advantages of the transformer in the design of traditional bidirectional DC converters, including voltage gain independent of load, simple open-loop control, zero-voltage switching over the full load range, and low circulating current.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows: In the first aspect, the present invention provides an expandable phase modular transformer, including a low-voltage bridge module; one end of the low-voltage bridge module is connected to the primary high-voltage bridge, and the other side is connected to the secondary high-voltage bridge; the low-voltage bridge module includes n parallel modules connected in parallel with each other; each parallel module includes a low-voltage bridge, a first inductor L k , a second inductor L m and a transformer; each parallel module includes two input terminals and two output terminals; one end of one input terminal of each parallel module is connected to the first end of the primary high-voltage bridge, and the other input terminal is connected to the low-voltage bridge; the low-voltage bridge has a plurality of switch tubes connected in parallel; the other end of the low-voltage bridge is connected to the first end of the first inductor L k ; a low-voltage bridge capacitor C9 is connected in parallel in each low-voltage bridge; the second end of the first inductor L k is connected to the first end of the second inductor L m and the first end of the primary side of the transformer; the second end of the second inductor L m and the second end of the primary side of the transformer are both connected to the second end of the primary high-voltage bridge; the two ends of the secondary side of the transformer are respectively connected to the two input terminals of the secondary high-voltage bridge.

[0006] Optionally, the number of parallel modules connected in parallel in the low-voltage bridge module is not less than two.

[0007] Optionally, the transformer is a high-frequency transformer.

[0008] Optionally, the low-voltage bridge includes a first field-effect transistor Q1, a second field-effect transistor Q2, a third field-effect transistor Q3, and a fourth field-effect transistor Q4; the source of the first field-effect transistor Q1 is connected to the low-voltage bridge capacitor C9 and the source of the third field-effect transistor Q3; the drain of the first field-effect transistor Q1 is connected to the source of the second field-effect transistor Q2; the drain of the second field-effect transistor Q2 is connected to the second end of the ninth capacitor C9 and the drain of the fourth field-effect transistor Q4; the drain of the third field-effect transistor Q3 is connected to the first end of the first inductor L k and the source of the fourth field-effect transistor Q4.

[0009] In a second aspect, the present invention provides a DC-DC converter, including the expandable phase modular transformer described above, and a primary-side high-voltage bridge and a secondary-side high-voltage bridge; both the primary-side high-voltage bridge and the secondary-side high-voltage bridge have a first input terminal, a second input terminal, a first output terminal, and a second output terminal; the first input terminal and the second input terminal of the primary-side high-voltage bridge are connected to a power supply; the transformer includes a primary-side induction coil and a secondary-side induction coil; the first input terminal and the second input terminal of the secondary-side high-voltage bridge are respectively connected to the first end and the second end of the secondary-side induction coil.

[0010] Optionally, the drain of the first field-effect transistor Q1 is connected to the first output terminal of the primary-side high-voltage bridge; the second end of the second inductor L m of each parallel module is connected to the second output terminal of the primary-side high-voltage bridge.

[0011] Optionally, the primary-side high-voltage bridge includes: a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, a first field-effect transistor S1, a second field-effect transistor S2, a third field-effect transistor S3, and a fourth field-effect transistor S4; capacitors are connected in parallel with the first field-effect transistor S1, the second field-effect transistor S2, the third field-effect transistor S3, and the fourth field-effect transistor S4; the drain of the first field-effect transistor S1 is connected to the negative pole of the power supply, and the negative pole of the power supply is connected to the first end of the first capacitor C1; the source of the first field-effect transistor S1 is connected to the first end of the fourth capacitor C4 and the drain of the second field-effect transistor S2; the source of the second field-effect transistor S2 is connected to the second end of the first capacitor C1; the second end of the fourth capacitor C4 is the first output terminal of the primary-side high-voltage bridge; the drain of the third field-effect transistor S3 is connected to the positive pole of the power supply, and the positive pole of the power supply is connected to the first end of the second capacitor C2; the source of the second field-effect transistor S2 is connected to the first end of the third capacitor C3 and the drain of the fourth field-effect transistor S4; the second end of the third capacitor C3 is the second output terminal of the primary-side high-voltage bridge.

[0012] Optionally, the secondary side includes: a fifth capacitor C5, a sixth capacitor C6, a seventh capacitor C7, an eighth capacitor C8, a fifth field-effect transistor S5, a sixth field-effect transistor S6, a seventh field-effect transistor S7, and an eighth field-effect transistor S8; the fifth capacitor C5, the sixth capacitor C6, the seventh capacitor C7, and the eighth capacitor C8 are all connected in parallel with a capacitor; the source of the fifth field-effect transistor S5 is connected to the second end of the sixth capacitor C6 and the drain of the sixth field-effect transistor S6; the drain of the fifth field-effect transistor S5 is connected to the negative pole of the power supply and the first end of the seventh capacitor C7; the source of the sixth field-effect transistor S6 is connected to the second end of the seventh capacitor C7; the drain of the seventh field-effect transistor S7 is connected to the first end of the eighth inductor C8; the source of the seventh field-effect transistor S7 is connected to the drain of the eighth field-effect transistor S8; the source of the eighth field-effect transistor S8 is connected to the second end of the eighth inductor C8.

[0013] Optionally, the low-voltage bridge capacitor C9 is a ceramic capacitor; the first inductor L k and the second inductor L m are both air-core inductors.

[0014] In a third aspect, the present invention provides a method for using the expandable phase modular transformer, including the following steps: In a half cycle, turn off the second field-effect transistor Q2 and the third field-effect transistor Q3, and then by turning on the first field-effect transistor Q1 and the fourth field-effect transistor Q4, natural zero-voltage switching is achieved; In another half cycle, perform the same zero-voltage switching analysis on the switched second field-effect transistor Q2 and the third field-effect transistor Q3, so that all switches of the low-voltage bridge achieve zero-voltage switching.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The expandable phase modular transformer, the method for using the same, and the DC-DC converter of the present invention can achieve the parallel connection of transformers and improve the current sharing ability. In the design of a single transformer, high frequency and high power are essentially a trade-off. By the parallel connection of high-frequency and low-power transformers, different rated powers can be extended, and through the cooperation of switching tubes, zero-voltage switching (ZVS) of the switching tubes can be achieved. The transformer of the present invention can be used in power grids or substations as well as in power transmission and distribution, which can improve the economic efficiency of operation and reduce the reserve capacity. Description of the Drawings

[0016] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the disclosure of the present invention in any way. Additionally, the shapes, proportional dimensions, etc. of the components in the drawings are only schematic and are used to assist in understanding the present invention, rather than specifically defining the shapes and proportional dimensions of the components of the present invention. In the drawings: Figure 1 is a topological diagram of the expandable phase modular transformer applied to the DC-DC converter of the present invention.

[0017] Figure 2 is a schematic diagram of multi-stage parallel connection of the expandable phase modular transformer applied to the DC-DC converter of the present invention. Detailed implementation manners

[0018] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0019] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0020] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper", "lower", "horizontal", "inner", etc. are used to indicate the orientation or positional relationship, they are based on the orientation or positional relationship shown in the accompanying drawings or the orientation or positional relationship in which the product of the present invention is usually placed during use. This is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0021] When an element is referred to as being "disposed on" another element, it can be directly on the other element or there can be intervening elements. When an element is considered to be "connected" to another element, it can be directly connected to the other element or intervening elements may be present. The terms "vertical", "horizontal", "left", "right", and similar expressions used herein are for illustrative purposes only and do not denote the only embodiments. When the term "horizontal" appears, it does not require the component to be absolutely horizontal, but it can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and it does not mean that the structure must be completely horizontal, but it can be slightly inclined.

[0022] It should be noted that like reference numerals and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures. In the description of the present invention, it is to be understood that the terms "comprising" and "including" indicate the presence of the described features, wholes, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or their groups.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used herein in the description of the present invention are for the purpose of describing particular embodiments only and are not intended to limit the present invention. As used in the description of the present invention and the appended claims, unless the context clearly dictates otherwise, the singular forms "a", "an", and "the" are intended to include the plural forms.

[0024] The present invention will be described in detail below with reference to the accompanying drawings.

[0025] As Figure 1 shown, a DC-DC converter of the present invention includes an expandable phase modular transformer, as well as a primary side high-voltage bridge and a secondary side high-voltage bridge.

[0026] The expandable phase modular transformer includes a low-voltage bridge module. One end of the primary side high-voltage bridge is connected to a power source, and the other end is connected to the secondary side high-voltage bridge through the low-voltage bridge module.

[0027] The low-voltage bridge module includes n parallel modules connected in parallel with each other.

[0028] The parallel module includes a low-voltage bridge, a first inductor L k , a second inductor L mand a transformer; each parallel module includes two input terminals and two output terminals. One end of one input terminal of each parallel module is connected to the first end of the primary high-voltage bridge, and the other input terminal is connected to the low-voltage bridge; there are multiple parallel switching tubes in the low-voltage bridge.

[0029] The other end of the low-voltage bridge is connected to the first end of the first inductor L k ; a low-voltage bridge capacitor C9 is connected in parallel in each low-voltage bridge; the second end of the first inductor L k is connected to the first end of the second inductor L m and the first end of the primary side of the transformer. The second end of the second inductor L m and the second end of the primary side of the transformer are both connected to the second end of the primary high-voltage bridge; the two ends of the secondary side of the transformer are respectively connected to the input terminals of the secondary high-voltage bridge.

[0030] Both the primary high-voltage bridge and the secondary high-voltage bridge have a first input terminal, a second input terminal, a first output terminal, and a second output terminal; the first input terminal and the second input terminal of the primary high-voltage bridge are connected to the power supply; the transformer includes a primary-side induction coil and a secondary-side induction coil; the first input terminal and the second input terminal of the secondary high-voltage bridge are respectively connected to the first end and the second end of the secondary-side induction coil.

[0031] The secondary side includes: a fifth capacitor C5, a sixth capacitor C6, a seventh capacitor C7, an eighth capacitor C8, a fourteenth capacitor C 14 , a fifteenth capacitor C 15 , a sixteenth capacitor C 16 , a seventeenth capacitor C 17 , a fifth field-effect transistor S5, a sixth field-effect transistor S6, a seventh field-effect transistor S7, an eighth field-effect transistor S8; the source electrode of the fifth field-effect transistor S5 is connected to the second end of the sixth capacitor C5 and the drain electrode of the sixth field-effect transistor; the drain electrode of the fifth field-effect transistor S5 is connected to the negative electrode of the power supply and the first end of the seventh capacitor C7; the source electrode of the sixth field-effect transistor S6 is connected to the second end of the seventh capacitor C7; the drain electrode of the seventh field-effect transistor S7 is connected to the first end of the eighth inductor C8, and the source electrode of the seventh field-effect transistor S7 is connected to the positive electrode of the power supply and the drain electrode of the eighth field-effect transistor; the source electrode of the eighth field-effect transistor is connected to the second end of the eighth inductor C8.

[0032] The low-voltage bridge includes a first field-effect transistor Q1, a second field-effect transistor Q2, a third field-effect transistor Q3, and a fourth field-effect transistor Q4; the source of the first field-effect transistor Q1 is connected to the low-voltage bridge capacitor C9 and the source of the third field-effect transistor Q3; the drain of the first field-effect transistor Q1 is connected to the source of the second field-effect transistor Q2 and the first output terminal of the primary high-voltage bridge; the drain of the second field-effect transistor Q2 is connected to the second end of the ninth capacitor C9 and the drain of the fourth field-effect transistor Q4; the drain of the third field-effect transistor Q3 is connected to the first end of the first inductor L k and the source of the fourth field-effect transistor Q4.

[0033] The second end of the second inductor L m of each parallel module is connected to the second output terminal of the primary high-voltage bridge.

[0034] The primary high-voltage bridge includes: a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, a first field-effect transistor S1, a second field-effect transistor S2, a third field-effect transistor S3, and a fourth field-effect transistor S 4、 The first field-effect transistor S1, the second field-effect transistor S2, the third field-effect transistor S3, and the fourth field-effect transistor S4 are respectively connected in parallel with a tenth capacitor C 10 , an eleventh capacitor C 11 , a twelfth capacitor C 12 , and a thirteenth capacitor C 13 ; the drain of the first field-effect transistor S1 is connected to the negative pole of the power supply, and the negative pole of the power supply is connected to the first end of the first capacitor C1. The source of the first field-effect transistor S1 is connected to the first end of the fourth capacitor C4 and the drain of the second field-effect transistor S2.

[0035] The source of the second field-effect transistor S2 is connected to the second end of the first capacitor C1; the second end of the fourth capacitor C4 is the first output terminal of the primary high-voltage bridge; the drain of the third field-effect transistor S3 is connected to the positive pole of the power supply, and the positive pole of the power supply is connected to the first end of the second capacitor C2; the source of the second field-effect transistor S2 is connected to the first end of the third capacitor C3 and the drain of the fourth field-effect transistor S4; the second end of the third capacitor C3 is the second output terminal of the primary high-voltage bridge.

[0036] The secondary side includes: a fifth capacitor C5, a sixth capacitor C6, a seventh capacitor C7, an eighth capacitor C8, a fifth field-effect transistor S5, a sixth field-effect transistor S6, a seventh field-effect transistor S7, and an eighth field-effect transistor S8.

[0037] The fifth capacitor C5, the sixth capacitor C6, the seventh capacitor C7, and the eighth capacitor C8 are respectively connected in parallel with the fourteenth capacitor C 14 , the fifteenth capacitor C 15 , the sixteenth capacitor C 16 , the seventeenth capacitor C 17 ; The source of the fifth field-effect transistor S5 is connected to the second end of the sixth capacitor C6 and the drain of the sixth field-effect transistor S6; The drain of the fifth field-effect transistor S5 is connected to the negative pole of the power supply and the first end of the seventh capacitor C7; The source of the sixth field-effect transistor S6 is connected to the second end of the seventh capacitor C7; The drain of the seventh field-effect transistor S7 is connected to the first end of the eighth inductor C8; The source of the seventh field-effect transistor S7 is connected to the drain of the eighth field-effect transistor S8; The source of the eighth field-effect transistor S8 is connected to the second end of the eighth inductor C8.

[0038] The first field-effect transistor Q1, the second field-effect transistor Q2, the third field-effect transistor Q3, and the fourth field-effect transistor Q4 are connected in a capacitive half-bridge pairwise. The tenth capacitor C 10 , the eleventh capacitor C 11 , the twelfth capacitor C 12 , the thirteenth capacitor C 13 are all connected in parallel on both sides of the field-effect transistor, which is to prevent the transistors on the same side from conducting in series and causing a short circuit.

[0039] The first inductor L k is a leakage inductance, and the second inductor L m is an exciting inductance.

[0040] Among them, the field-effect transistors on the primary side require the input voltage to be strictly positive, which is achieved by introducing a common-mode bias voltage u gn in the high-voltage bridge. The field-effect transistors of the high-voltage bridge of the transformer are arranged in a half-bridge structure, using transistors with single-pole voltage blocking ability, so that it has a clear commutation path and can achieve a high switching frequency and a moderate switching node overvoltage. When operating in a half-bridge, assuming its duty cycle is 50%, the phase with the instantaneous lowest grid phase voltage turns on the primary-side and secondary-side transistors simultaneously during one-third of the grid cycle. Thus, the potential of the input-stage reference point n is always clamped to the most negative phase voltage, and thus u gn is strictly limited to be positive.

[0041] In the case of an integrated low-voltage bridge, the low-voltage bridge with a floating DC capacitor C9 replaces the resonant capacitor of the transformer in a traditional DC-DC converter. V b is the voltage across C9. V c is the output voltage of the low-voltage bridge, and its amplitude is equal to V b . For the current, i priand i scc are the currents passing through the primary and secondary coils of the transformer. Since the primary side and the secondary side have the same field-effect transistors, the first field-effect transistor Q1, the second field-effect transistor Q2, the third field-effect transistor, and the fourth field-effect transistor Q4 of the low-voltage bridge all have a 90° phase delay compared to the fifth field-effect transistor S5, the sixth field-effect transistor S6, the seventh field-effect transistor S7, and the eighth field-effect transistor S8, and are driven by two high-voltage bridge signals.

[0042] Since the low-voltage drive signal has a 90° delay from the high-voltage drive signal, when the first field-effect transistor Q1, the second field-effect transistor Q2, the third field-effect transistor Q3, and the fourth field-effect transistor Q4 of the low-voltage bridge are turned on or off, the current i pri will reach its peak. Therefore, during the switching transition of the low-voltage bridge, the two poles of i pri will not change.

[0043] During the no-load period of the low-voltage bridge, the current i pri remains at its peak, and the voltage V b on the low-voltage bridge is small, so the output capacitance of the devices of the low-voltage bridge switch can be ignored. In addition, by optimizing and shortening the dead time of the low-voltage bridge, the losses caused by the dead time can be reduced. For the triangular wave i pri , the capacitor C9 will be alternately charged and discharged, and the ripple on C9 can be derived as: Equation 1 Where: V b is the voltage of the capacitor C9, ΔV b is the change in the voltage of the capacitor C9, L k is the inductance value of the inductor L k , C9 is the capacitance value of the capacitor C9, and f n is the rated frequency.

[0044] To meet the requirement of the ripple voltage, the capacitance value of the low-voltage bridge capacitor C9 is selected.

[0045] According to the superposition principle, the original equivalent circuit diagram can be decomposed into two parts, namely the high-voltage bridge part and the low-voltage bridge part. In the branch circuit of the high-voltage bridge, the circuit will always charge the low-voltage bridge capacitor C9 of the low-voltage bridge. In the branch circuit of the low-voltage bridge, there is only one excitation power source.

[0046] In the steady state, assuming the transformer turns ratio is 1:1, the input voltage V in should be equal to the output voltage V out .

[0047] Equation 2 Where: Vin is the input voltage on the primary side of the transformer, and Vout is the output voltage on the secondary side of the transformer. Since the drive signals of the high-voltage bridges on the primary and secondary sides are the same, V pri and V sec should have the same amplitude and phase angle.

[0048] Equation 3 Where: Vpri is the voltage across the primary-side coil, and Vsec is the voltage across the secondary-side coil.

[0049] For the current i T and the component i T1 should be equal to 0 under steady state; otherwise, this current will continue to charge and discharge the floating low-voltage bridge capacitor C9. Therefore, i T should be equal to i T2 . This steady state is a stable equilibrium point and thus does not require control.

[0050] Equation 4 Where: i T1 is the current flowing through the first low-voltage bridge of the parallel module, and i T2 is the current flowing through the second low-voltage bridge module.

[0051] Since i T is in the stage of V pri or V Sec under steady state, this current is dedicated to transmitting the actual power. For different output frequencies P, the amplitude of i T will be adjusted by V b . Since I out is equal to 0.5I T , the steady-state value of the voltage V b can be derived as Equation 5 Where: Vb is the voltage applied to the low-voltage bridge capacitor C9; P is the output power; Lk is the inductance value of the first inductor Lk, and Vin(out) is the input-output voltage.

[0052] The floating voltage V b applied to the low-voltage bridge is proportional to f s , P, L k and 1 / V in(out) .

[0053] Equation 6 Where: V b is the voltage applied to the low-voltage bridge capacitor C9; f sis the rated frequency; P is the output power; Lk is the inductance value of the first inductor Lk, V in(out) is the input-output voltage.

[0054] Through a lower-voltage-level device, the low-voltage bridge can be embedded in the high-frequency transformer. Since V pri is equal to V sec at steady state, the output voltage V c of the low-voltage bridge is directly applied to L k , which means that the voltage drop across L k is completely offset by the output of the embedded low-voltage bridge. Therefore, the transformer of the present invention does not require resonance tuning and can always operate optimally at any switching frequency f s .

[0055] To increase the rated current, due to the too-high power density, transformer-stage parallel connection is more ideal than converter-stage parallel connection. After converting all the embedded electronic parameters from the secondary side to the primary side, the corresponding equivalent circuit can be simplified. All the low-voltage bridges and two high-voltage bridges are replaced by the square voltage Vc, and V pri and V sec According to Kirchhoff's voltage law, the terminal voltage V AB can be written as Equation 7 where: V AB is the terminal voltage during transformer-stage parallel connection; L kN is the inductance value of the Nth inductor L k ; i TN is the current value flowing through the Nth low-voltage bridge; V cN is the voltage across the N low-voltage bridges at time t; r wn is the equivalent resistance of the low-voltage bridge.

[0056] According to the previous analysis, the voltage drop across the first inductor L k will be completely offset by the corresponding voltage V c under steady state. Therefore, the total voltage drop of each electronic transformer can be written as Equation 8 Due to the unique structure of the transformer designed in the present invention, it can perform convenient transformer-stage parallel connection to increase the rated power. According to Kirchhoff's voltage law, during transformer-stage parallel connection, its terminal voltage V AB is Equation 9 Under steady state, the voltage drops across the 1st to Nth first inductors L k will be completely offset by the corresponding V c1-N voltage. Therefore, the total voltage drop across each multi-stage parallel-connected transformer can be expressed as Formula 10 The current distribution of each parallel embedded electronic module is Formula 11 Define i r1-N as the resonant current passing through each transformer. Considering the resistance R of each embedded module ω1-N , the resonant impedance Z of each transformer N can be expressed as Formula 12 From this formula, it can be deduced that the current distribution between the resonant branches is Formula 13 When all the resonant slots have the same resonant frequency, since the voltage drops of the first to the nth first inductors L k will be completely offset by the low-voltage bridge capacitors C9 of the first to the nth resonances, the current shunt should be the same as in Formula 12.

[0057] Since the current sharing performance of this transformer is decoupled from the first inductor Lk, this transformer will have a natural and stable current sharing performance, and due to the positive temperature coefficient of the resistance, current sharing can always be achieved.

[0058] A method for using the expandable phase modular transformer described above includes the following steps: Since there is a 90° delay between the low-voltage bridge drive signals (the first field-effect transistor Q1, the second field-effect transistor Q2, the third field-effect transistor Q3, and the fourth field-effect transistor Q4) and the high-voltage bridge drive signals (the first field-effect transistor S1, the second field-effect transistor S2, the third field-effect transistor S3, the fourth field-effect transistor S4, the fifth field-effect transistor S5, the sixth field-effect transistor S6, the seventh field-effect transistor S7, and the eighth field-effect transistor S8), when the low-voltage bridge switch is turned on or off, the current i pri will reach its peak.

[0059] Therefore, during the switching transition of the low-voltage bridge, the polarity of i pri will not change. For example, for the rectification from the second field-effect transistor Q2 and the third field-effect transistor Q3 to the first field-effect transistor Q1 and the fourth field-effect transistor Q4, i pri will remain in a good state within a very short dead time.

[0060] Before the second field-effect transistor Q2 and the third field-effect transistor Q3 are turned off, the current i priwill pass through the channels of the second field-effect transistor Q2 and the third field-effect transistor Q3. When the second field-effect transistor Q2 and the third field-effect transistor Q3 are turned off, the positive current i pri will flow through the diodes of the first field-effect transistor Q1 and the fourth field-effect transistor Q4. i pri After passing through the diodes of the second field-effect transistor Q2 and the third field-effect transistor Q3, natural soft switching can be obtained through the first field-effect transistor Q1 and the fourth field-effect transistor Q4. In the other half cycle, the same soft switching can be performed on the second field-effect transistor Q2 and the third field-effect transistor Q3, which means that all switches of the low-voltage bridge can achieve natural soft switching similar to this.

[0061] During the no-load period of the low-voltage bridge, the current ipri remains at the peak value, and the voltage Vb on the low-voltage bridge is very small. Therefore, the device output capacitance of the low-voltage bridge switches can be ignored. In addition, the dead time of the low-voltage bridge can be optimized and shortened to reduce the losses caused by the dead time. For the triangular wave ipri, the low-voltage bridge capacitor C9 will be alternately charged and discharged, and the ripple on the low-voltage bridge capacitor C9 can be derived as: Equation 14 To meet the requirements of the ripple voltage, the capacitance value of the low-voltage bridge capacitor C9 is selected.

[0062] Considering the capacitors C pri and C sec on both sides of the high-voltage bridge, at a turns ratio of 1:1, Ctotal is derived as Equation 15 Where: C pri is the input capacitance, and C sec is the output capacitance.

[0063] Assume that the input voltage V in and the output voltage V out are both 400V, and the rated power is 12kM. The leakage inductance L k of the transformer is 1460nH, and the magnetizing inductance L m is 25μH. By determining the magnetizing inductance L m , the stop time Td can be derived. Considering i m later, the relationship between i pri , i sec and i m is written as: Equation 16 Where: ipri is the input current and isec is the output current.

[0064] Before the second field effect transistor S2 and the third field effect transistor S3 are turned on, V pri and V sec both drop to 0, which means that the high-voltage bridge obtains a soft-switching function.

[0065] To achieve transformer-stage parallelism and proportionally amplify the total power, two separate external inductors L pri and L sec are respectively provided on the primary side and the secondary side. If there are N embedded electronic modules in parallel, each electronic unit should provide the magnetization current on average. If the total power needs to be increased, more electronic modules can be stacked. Therefore, the electromagnetic induction in each electronic unit should be updated according to the latest total number of parallel units. However, this is not desirable for modular and scalable designs because the design of the transformer air gap is related to the number of parallel electronic modules.

[0066] With the help of L pri and L sec , both the high-voltage bridges on the primary side and the secondary side can achieve soft switching without an air gap and the corresponding L m . The current flowing through each electronic module can be dedicated to transmitting the actual power.

[0067] In the above embodiments, the device elements involved are all conventional device elements unless otherwise specified. The structural settings, working methods, or control methods involved are all conventional settings, working methods, or control methods in this field unless otherwise specified.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not restrictive. Other modifications or equivalent replacements made by those of ordinary skill in the art to the technical solutions of the present invention should be covered within the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solutions of the present invention.

Claims

1. An expandable phase modular transformer, characterized in that, It includes a low-voltage bridge module; one end of the low-voltage bridge module is connected to the primary-side high-voltage bridge, and the other side is connected to the secondary-side high-voltage bridge; the low-voltage bridge module includes n parallel modules; the parallel module includes a low-voltage bridge, a first inductor L k , a second inductor L m and a transformer; each parallel module includes two input terminals and two output terminals; one end of one input terminal of each parallel module is connected to the first end of the primary-side high-voltage bridge, and the other input terminal is connected to the low-voltage bridge; the low-voltage bridge has a plurality of parallel switch tubes; the other end of the low-voltage bridge is connected to the first end of the first inductor L k ; a low-voltage bridge capacitor C9 is connected in parallel in each low-voltage bridge; the second end of the first inductor L k is connected to the first end of the second inductor L m and the first end of the primary side of the transformer; the second end of the second inductor L m and the second end of the primary side of the transformer are both connected to the second end of the primary-side high-voltage bridge; the two ends of the secondary side of the transformer are respectively connected to the two input terminals of the secondary-side high-voltage bridge.

2. The expandable phase modular transformer according to claim 1, characterized in that, The number of parallel modules in the parallel connection in the low-voltage bridge module is not less than two.

3. The expandable phase modular transformer according to claim 1, characterized in that, The transformer is a high-frequency transformer.

4. The expandable phase modular transformer according to claim 1, characterized in that, The low-voltage bridge includes a first field-effect transistor Q1, a second field-effect transistor Q2, a third field-effect transistor Q3, and a fourth field-effect transistor Q4; the source electrode of the first field-effect transistor Q1 is connected to the low-voltage bridge capacitor C9 and the source electrode of the third field-effect transistor Q3; the drain electrode of the first field-effect transistor Q1 is connected to the source electrode of the second field-effect transistor Q2; the drain electrode of the second field-effect transistor Q2 is connected to the second end of the ninth capacitor C9 and the drain electrode of the fourth field-effect transistor Q4; the drain electrode of the third field-effect transistor Q3 is connected to the first end of the first inductor L k and the source electrode of the fourth field-effect transistor Q4.

5. A DC-DC converter, characterized in that, It includes an expandable phase modular transformer according to any one of claims 1 to 4, as well as a primary-side high-voltage bridge and a secondary-side high-voltage bridge; both the primary-side high-voltage bridge and the secondary-side high-voltage bridge have a first input terminal, a second input terminal, a first output terminal, and a second output terminal; the first input terminal and the second input terminal of the primary-side high-voltage bridge are connected to a power supply; the transformer includes a primary-side induction coil and a secondary-side induction coil; the first input terminal and the second input terminal of the secondary-side high-voltage bridge are respectively connected to the first end and the second end of the secondary-side induction coil.

6. A DC-DC converter according to claim 5, wherein, The drain of the first field effect transistor Q1 is connected to the first output terminal of the primary side high-voltage bridge; the second ends of the second inductors L of each parallel module are all connected to the second output terminal of the primary side high-voltage bridge. m ​ 7. A DC-DC converter according to claim 5, characterized in that, The primary-side high-voltage bridge includes: a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, a first field-effect transistor S1, a second field-effect transistor S2, a third field-effect transistor S3, and a fourth field-effect transistor S4; capacitors are connected in parallel to the first field-effect transistor S1, the second field-effect transistor S2, the third field-effect transistor S3, and the fourth field-effect transistor S4; the drain of the first field-effect transistor S1 is connected to the negative pole of the power supply, and the negative pole of the power supply is connected to the first end of the first capacitor C1; the source of the first field-effect transistor S1 is connected to the first end of the fourth capacitor C4 and the drain of the second field-effect transistor S2; the source of the second field-effect transistor S2 is connected to the second end of the first capacitor C1; the second end of the fourth capacitor C4 is the first output terminal of the primary-side high-voltage bridge; the drain of the third field-effect transistor S3 is connected to the positive pole of the power supply, and the positive pole of the power supply is connected to the first end of the second capacitor C2; the source of the second field-effect transistor S2 is connected to the first end of the third capacitor C3 and the drain of the fourth field-effect transistor S4; the second end of the third capacitor C3 is the second output terminal of the primary-side high-voltage bridge.

8. A DC-DC converter according to claim 5, characterized in that, The secondary side includes: a fifth capacitor C5, a sixth capacitor C6, a seventh capacitor C7, an eighth capacitor C8, a fifth field-effect transistor S5, a sixth field-effect transistor S6, a seventh field-effect transistor S7, and an eighth field-effect transistor S8; capacitors are connected in parallel to the fifth capacitor C5, the sixth capacitor C6, the seventh capacitor C7, and the eighth capacitor C8; the source of the fifth field-effect transistor S5 is connected to the second end of the sixth capacitor C6 and the drain of the sixth field-effect transistor S6; the drain of the fifth field-effect transistor S5 is connected to the negative pole of the power supply and the first end of the seventh capacitor C7; the source of the sixth field-effect transistor S6 is connected to the second end of the seventh capacitor C7; the drain of the seventh field-effect transistor S7 is connected to the first end of the eighth inductor C8; the source of the seventh field-effect transistor S7 is connected to the drain of the eighth field-effect transistor S8; the source of the eighth field-effect transistor S8 is connected to the second end of the eighth inductor C8.

9. A DC-DC converter according to claim 5, characterized in that, The low-voltage bridge capacitor C9 is a ceramic capacitor; the first inductor L k and the second inductor L m are both air-core inductors.

10. A method for using an expandable phase modular transformer according to any one of claims 1 to 4, characterized in that, It includes the following steps: In a half cycle, turn off the second field-effect transistor Q2 and the third field-effect transistor Q3, and then realize natural zero-voltage switching by turning on the first field-effect transistor Q1 and the fourth field-effect transistor Q4. In another half cycle, the same zero-voltage switching analysis is performed on the switching second field-effect transistor Q2 and the third field-effect transistor Q3, enabling all switches of the low-voltage bridge to achieve zero-voltage switching.

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