A single-phase power electronic transformer and its application system

Abstract

The present invention discloses a single-phase power electronic transformer and its application system, belonging to the field of power electronic power conversion, and mainly solving the deficiencies of existing power electronic transformers such as many power conversion stages, low efficiency, poor reliability, and difficulty in realizing high-voltage applications. The single-phase power electronic transformer includes 2 high-frequency isolation DC / DC modules, and can achieve single-phase isolation AC / AC conversion and isolation AC / DC conversion through electrical interconnection. At the same time, through the combination of single-phase power electronic transformers, three-phase AC / AC type power electronic transformers and three-phase AC / DC type power electronic transformers can be realized. The single-phase power electronic transformer and its application system are based on modular design, can achieve functions such as electrical isolation, continuous voltage regulation, phase-shifting control, frequency modulation control, and harmonic suppression, and have the characteristics of simple structure, convenient use and maintenance, high efficiency, low cost, good reliability, and can be easily extended to high-voltage application occasions, and can be widely applied to power transformers, isolated rectifiers and inverters.

Description

Technical Field

[0001] The present invention relates to a single-phase power electronic transformer and its application system, belonging to the technical field of power electronic power conversion, especially realizing isolation voltage regulation, phase shift, and frequency modulation conversion from AC to AC, isolation voltage regulation conversion from AC to DC, and isolation voltage regulation and frequency conversion conversion from DC to AC, and is particularly applicable to power transformer, rectifier, and inverter systems. Background Art

[0002] Traditional power transformers are still the main measures for realizing power conversion at present due to their advantages such as simple structure, low cost, high efficiency, and good reliability. However, with the continuous deterioration of problems such as harmonic current, reactive current, and unbalanced current in the power grid, the operating losses of traditional power transformers are prominent, and the failure rate of transformers has increased significantly. In addition, due to their large volume and single function, traditional power transformers cannot meet the higher requirements for the access of a large number of distributed energy sources and electric vehicle charging in the future.

[0003] With the rapid development of power electronic technology, in the 1970s, another way to realize power conversion - the concept of power electronic transformer (PET) or solid-state transformer (SST) was proposed. After more than 40 years of development, the research on power electronic transformers has been continuously deepened. At the present stage, the topologies of power electronic transformers are divided into single-stage structure, two-stage structure, and three-stage structure. The more cascaded stages there are, the richer the functions are. However, existing power electronic transformers have problems such as low reliability, low efficiency, complex control, and high cost, and it is also very complex to realize high-voltage applications with existing solutions. Summary of the Invention

[0004] The purpose of the present invention is to solve the above problems and provide a high-efficiency single-phase power electronic transformer and its application system. The single-phase power electronic transformer and its application system are mainly realized based on a high-efficiency high-frequency isolation DC / DC converter, and meet isolation voltage regulation, phase shift, and frequency modulation conversion from AC to AC, isolation voltage regulation conversion from AC to DC, and isolation voltage regulation and frequency conversion conversion from DC to AC.

[0005] The present invention adopts the following technical solutions.

[0006] A single-phase power electronic transformer includes 2 identical high-frequency isolation DC / DC modules. It is characterized in that a pair of same-polarity DC terminals on the primary side of the 2 high-frequency isolation DC / DC modules are connected together to form a primary center terminal, and the other pair of same-polarity DC terminals are used as the primary AC terminals of the single-phase power electronic transformer; a pair of same-polarity DC terminals on the secondary side of the 2 high-frequency isolation DC / DC modules are connected together to form a secondary center terminal, and the other pair of same-polarity DC terminals are used as the secondary AC terminals of the single-phase power electronic transformer.

[0007] The single-phase power electronic transformer as described above is characterized in that the high-frequency isolation DC / DC module includes M identical high-frequency isolation DC / DC sub-modules, and diodes are connected in parallel on the primary DC side and the secondary DC side of each high-frequency isolation DC / DC sub-module; the connection mode of the M high-frequency isolation DC / DC sub-modules is that the primary DC sides are connected in parallel and the secondary DC sides are connected in series, or the primary DC sides are connected in series and the secondary DC sides are connected in parallel; the high-frequency isolation DC / DC sub-module is composed of N high-frequency isolation DC / DC converters connected in parallel, that is, the primary DC sides of the N high-frequency isolation DC / DC converters are connected in parallel, and at the same time, their secondary DC sides are connected in parallel.

[0008] The single-phase power electronic transformer as described above is characterized in that the high-frequency isolation DC / DC converter includes a half-bridge circuit, a high-frequency transformer, a high-frequency inductor and a capacitor; m primary windings and n secondary windings of the high-frequency transformer are wound on a magnetic core and share a magnetic path; one end of each primary winding of the high-frequency transformer is connected to the midpoint of the corresponding half-bridge circuit through a high-frequency inductor L Sp and is connected to the midpoint of the corresponding half-bridge circuit, and the capacitor C Hp and C Lp are connected in series and then connected in parallel on the DC bus of the corresponding primary half-bridge circuit, and the series midpoint is connected to the other end of the primary winding; one end of each secondary winding of the high-frequency transformer is connected to the midpoint of the corresponding half-bridge circuit through a high-frequency inductor L Ss and is connected to the midpoint of the corresponding half-bridge circuit, and the capacitor C Hs and C Ls are connected in series and then connected in parallel on the DC bus of the corresponding secondary half-bridge circuit, and the series midpoint is connected to the other end of the secondary winding; the DC buses of the m primary half-bridge circuits of the high-frequency transformer are connected in series in sequence according to positive and negative polarities, and the DC buses of the n secondary half-bridge circuits of the high-frequency transformer are connected in series in sequence according to positive and negative polarities.

[0009] The single-phase power electronic transformer as described above is characterized in that it further includes two single-phase AC filters and a single-phase converter; the primary AC terminals and the secondary AC terminals of the single-phase power electronic transformer are respectively connected to the primary and secondary single-phase AC filters; at the same time, the AC terminals of the single-phase converter are connected to the secondary AC terminals of the single-phase power electronic transformer.

[0010] The single-phase power electronic transformer as described above is characterized in that the secondary AC terminals of the single-phase power electronic transformer are connected together and together with the secondary center terminal form the secondary DC side terminals of the single-phase power electronic transformer.

[0011] The single-phase power electronic transformer as described above is characterized in that it further includes a single-phase AC filter and a DC filter; the single-phase AC filter is connected to the primary AC terminals of the single-phase power electronic transformer; the DC filter is connected to the secondary DC terminals of the single-phase power electronic transformer.

[0012] A three-phase AC / AC power electronic transformer application system, comprising a three-phase AC filter and a Δ / Y connection selector, is characterized in that it further comprises the single-phase power electronic transformer as described above; the primary AC terminals of the 3 single-phase power electronic transformers are connected to the primary three-phase AC filter via a series-connected primary Δ / Y connection selector; the secondary AC terminals of the 3 single-phase power electronic transformers are connected to the secondary three-phase AC filter via a series-connected secondary Δ / Y connection selector.

[0013] The three-phase AC / AC power electronic transformer application system as described above is characterized in that it further comprises a three-phase converter; the three-phase converter is connected in parallel to the connection line between the three-phase AC filter and the Δ / Y connection selector.

[0014] A three-phase AC / DC power electronic transformer application system, comprising a three-phase AC filter and a Δ / Y connection selector, is characterized in that it further comprises the single-phase power electronic transformer as described above; the primary AC terminals of the 3 single-phase power electronic transformers are connected to the three-phase AC filter via a series-connected Δ / Y connection selector; the secondary DC terminals of the 3 single-phase power electronic transformers are directly connected in parallel one-to-one; the secondary DC terminals are connected to a DC filter.

[0015] A cascading method for a single-phase power electronic transformer is characterized in that the primary AC terminals of multiple single-phase power electronic transformers are connected in series, and the secondary AC terminals and the center terminals are connected in parallel one-to-one; alternatively, the primary AC terminals and the center terminals of multiple single-phase power electronic transformers are connected in parallel one-to-one, and the secondary AC terminals are connected in series.

[0016] The structure of the present invention is simple, based on modular design, and can achieve functions such as electrical isolation, continuous voltage regulation, phase-shift control, frequency modulation control, harmonic suppression, fast fault isolation, and reactive power compensation. It is convenient to use and maintain, has high efficiency, low cost, good reliability, and can be easily extended to high-voltage application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a single-phase power electronic transformer shown in the present invention.

[0018] Figure 2 is a high-frequency isolation DC / DC module shown in the present invention.

[0019] Figure 3 is a high-frequency isolation DC / DC sub-module shown in the present invention.

[0020] Figure 4 is a high-frequency isolation DC / DC converter shown in the present invention.

[0021] Figure 5It is a single-phase power electronic transformer with a filter shown in the present invention.

[0022] Figure 6 It is an AC / DC single-phase power electronic transformer shown in the present invention.

[0023] Figure 7 It is an AC / DC single-phase power electronic transformer with a filter shown in the present invention.

[0024] Figure 8 It is an application system of an AC / AC three-phase power electronic transformer with a filter shown in the present invention.

[0025] Figure 9 It is an application system of an AC / DC three-phase power electronic transformer with a filter shown in the present invention.

[0026] Figure 10 It is a cascading method of a single-phase power electronic transformer with the primary side in parallel and the secondary side in series shown in the present invention.

[0027] Figure 11 It is a cascading method of a single-phase power electronic transformer with the primary side in series and the secondary side in parallel shown in the present invention.

[0028] Figure 12 It is the Δ-type connection structure of the Δ / Y connection selector shown in the present invention.

[0029] Figure 13 It is the Y-type connection structure of the Δ / Y connection selector shown in the present invention. Specific embodiments

[0030] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0031] Figure 1 A single-phase power electronic transformer shown includes two identical high-frequency isolation DC / DC modules No.1 and No.2. A pair of positive DC terminals on the primary side of the two high-frequency isolation DC / DC modules are connected together to form the primary center terminal O p , and the other pair of negative DC terminals on the primary side serve as the primary AC terminals A p and N p ; A pair of negative DC terminals on the secondary side of the two high-frequency isolation DC / DC modules are connected together to form the secondary center terminal O s , and the other pair of positive DC terminals serve as the secondary AC terminals A s and N s .

[0032] Figure 2A high-frequency isolated DC / DC module as shown includes M identical high-frequency isolated DC / DC sub-modules. The primary DC sides of the M high-frequency isolated DC / DC sub-modules are connected in series, that is, the negative pole of the primary DC side k is connected to the positive pole of the primary DC side k + 1, where k ranges from 1 to M - 1. The positive pole of the primary DC side 1 and the negative pole of the primary DC side M form the primary DC terminals of the high-frequency isolated DC / DC module. The secondary DC sides of the M high-frequency isolated DC / DC sub-modules are connected in parallel, that is, the positive poles of the secondary DC sides of the M identical high-frequency isolated DC / DC sub-modules are connected together, and the negative poles of the secondary DC sides of the M identical high-frequency isolated DC / DC sub-modules are connected together, and they form the secondary DC terminals of the high-frequency isolated DC / DC module.

[0033] Figure 3 A high-frequency isolated DC / DC sub-module as shown includes N parallel high-frequency isolated DC / DC converters and two diodes. That is, the primary DC sides of the N high-frequency isolated DC / DC converters are connected in parallel to form the primary DC terminals of the high-frequency isolated DC / DC sub-module, and at the same time, the secondary DC sides are also connected in parallel to form the secondary DC terminals of the high-frequency isolated DC / DC sub-module. A diode is connected in parallel to each of the primary and secondary DC terminals of the high-frequency isolated DC / DC sub-module. The anode of the diode is connected to its negative-polarity DC terminal, and the cathode of the diode is connected to its positive-polarity DC terminal.

[0034] Figure 4 A high-frequency isolated DC / DC converter as shown includes a half-bridge circuit, a high-frequency transformer, a high-frequency inductor, and a capacitor. The m primary windings and n secondary windings of the high-frequency transformer Tx are wound on a magnetic core and share a magnetic path. One end of each primary winding of the high-frequency transformer is connected to the midpoint A of its corresponding half-bridge circuit through a high-frequency inductor L Sp and the capacitor C Hp and C Lp of the primary winding are connected in series and then connected in parallel to the DC bus of the corresponding primary half-bridge circuit. The series midpoint B is connected to the other end of the primary winding. One end of each secondary winding of the high-frequency transformer is connected to the midpoint a of its corresponding half-bridge circuit through a high-frequency inductor L Ss and the capacitor C Hs and C Ls of the secondary winding are connected in series and then connected in parallel to the DC bus of the corresponding secondary half-bridge circuit. The series midpoint b is connected to the other end of the secondary winding. The m DC buses of the primary half-bridge circuits of the high-frequency transformer are connected in series in sequence according to positive and negative polarities, and the n DC buses of the secondary half-bridge circuits of the high-frequency transformer are connected in series in sequence according to positive and negative polarities.

[0035] The high-frequency isolated DC / DC converter can be a forward converter, a flyback converter, a resonant converter, a phase-shifted full-bridge converter, and other high-frequency isolated DC / DC converters that achieve isolated DC conversion.

[0036] Figure 5 A single-phase power electronic transformer with a filter, including two single-phase AC filters, a single-phase converter and Figure 1 the single-phase power electronic transformer shown; the primary AC terminals and secondary AC terminals of the single-phase power electronic transformer are respectively connected to the single-phase AC filters on the primary side and secondary side; at the same time, the AC terminals of the single-phase converter are connected to the secondary AC terminals of the single-phase power electronic transformer. The single-phase converter mainly realizes functions such as harmonic suppression, reactive power compensation, and energy storage for peak shaving and valley filling, and energy storage, photovoltaic, and wind power generation can also be connected to the DC side of the single-phase converter.

[0037] Figure 6 An AC / DC single-phase power electronic transformer shown is Figure 1 For the single-phase power electronic transformer shown, its secondary AC terminals A s and N s are connected together and together with the secondary center terminal O s constitute the secondary DC terminals of the single-phase power electronic transformer.

[0038] Figure 7 A filter-equipped AC / DC single-phase power electronic transformer shown includes Figure 6 the AC / DC single-phase power electronic transformer shown, a single-phase AC filter, and a DC filter; the single-phase AC filter is connected to the primary AC terminals of the single-phase power electronic transformer; the DC filter is connected to the secondary DC terminals of the single-phase power electronic transformer.

[0039] Figure 8 A filter-equipped AC / AC three-phase power electronic transformer application system shown includes a three-phase AC filter, a Δ / Y connection selector, a three-phase converter, and a single-phase power electronic transformer as shown in Figure 1 The primary AC terminals of the three single-phase power electronic transformers are connected to the primary three-phase AC filter through a series-connected primary Δ / Y connection selector, and at this time the primary Δ / Y connection selector is in Δ connection; the secondary AC terminals of the three single-phase power electronic transformers are connected to the secondary three-phase AC filter through a series-connected secondary Δ / Y connection selector, and at this time the secondary Δ / Y connection selector is in Y connection; the three-phase converter is three-phase four-wire and is connected in parallel on the line between the secondary three-phase AC filter and the secondary Δ / Y connection selector. The three-phase converter mainly realizes functions such as harmonic suppression, reactive power compensation, and energy storage for peak shaving and valley filling, and energy storage, photovoltaic, and wind power generation can also be connected to the DC side of the three-phase converter.

[0040] Figure 9 A filter-equipped AC / DC three-phase power electronic transformer application system shown includes a three-phase AC filter, a Δ / Y connection selector, a DC filter, and Figure 6The single-phase power electronic transformer shown. The primary AC terminals of three single-phase power electronic transformers are connected to a three-phase AC filter through a series-connected Δ / Y connection selector, and at this time the Δ / Y connection selector is in the Y connection; the secondary DC terminals of the three single-phase power electronic transformers are directly connected in parallel one by one, that is, A s1 、A s2 and A s3 are connected together, and the secondary DC terminal O s1 、O s2 and O s3 are connected together; the secondary DC terminals are connected to a DC filter.

[0041] Figure 10 A cascading method for a single-phase power electronic transformer with parallel primary and series secondary shown, and this single-phase power electronic transformer realizes AC / DC conversion. The primary AC terminals of the single-phase power electronic transformer are directly connected in parallel one by one, that is, the primary terminals A p1 to A pm are connected together, the primary terminals O p1 to O pm are connected together, and the primary terminals N p1 to N pm are connected together. At the same time, the secondary DC terminals are connected in series in turn, that is, the terminal O sk is connected to A s(k+1) , and k changes from 1 to m - 1.

[0042] Figure 11 A cascading method for a single-phase power electronic transformer with series primary and parallel secondary shown, and this single-phase power electronic transformer realizes AC / AC conversion. The secondary AC terminals of the single-phase power electronic transformer are directly connected in parallel one by one, that is, the secondary terminals A s1 to A sm are connected together, the secondary terminals O s1 to O sm are connected together, and the secondary terminals N s1 to N sm are connected together. At the same time, the primary AC terminals are connected in series in turn, that is, the terminal N pk is connected to A p(k+1) , and k changes from 1 to m - 1.

[0043] Figure 12 The Δ connection structure of the Δ / Y connection selector shown, and the six AC terminals of three single-phase power electronic transformers are connected in the following way: the terminal A, the terminal A1 and the terminal N3 are connected together, the terminal B, the terminal N1 and the terminal A2 are connected together, and the terminal C, the terminal N2 and the terminal A3 are connected together. Figure 13The Y-type connection structure of the Δ / Y connection selector shown, the six AC terminals of the three single-phase power electronic transformers are connected in the following manner: terminal A is connected to terminal A1, terminal B is connected to terminal A2, terminal C is connected to terminal A3, and terminals N, N1, N2, and N3 are connected together.

Claims

1. A single-phase power electronic transformer includes 2 identical high-frequency isolation DC / DC modules, characterized in that, The primary side of two high-frequency isolated DC / DC modules has a pair of like-polarity DC terminals connected together to form a primary center terminal, and the other pair of like-polarity DC terminals serves as the primary AC terminals of the single-phase power electronic transformer; the secondary side of two high-frequency isolated DC / DC modules has a pair of like-polarity DC terminals connected together to form a secondary center terminal, and the other pair of like-polarity DC terminals serves as the secondary AC terminals of the single-phase power electronic transformer. The isolation voltage regulation transformation from AC to AC, from AC to DC, or from DC to AC is achieved through the single-phase power electronic transformer.

2. The single-phase power electronic transformer according to claim 1, characterized in that, The high-frequency isolated DC / DC module includes M identical high-frequency isolated DC / DC sub-modules, and diodes are connected in parallel on the primary DC side and the secondary DC side of each high-frequency isolated DC / DC sub-module; the connection method of the M high-frequency isolated DC / DC sub-modules is that the primary DC sides are connected in parallel and the secondary DC sides are connected in series, or the primary DC sides are connected in series and the secondary DC sides are connected in parallel; the high-frequency isolated DC / DC sub-module is composed of N high-frequency isolated DC / DC converters connected in parallel, that is, the primary DC sides of the N high-frequency isolated DC / DC converters are connected in parallel, and at the same time, their secondary DC sides are connected in parallel.

3. The single-phase power electronic transformer according to claim 2, characterized in that, The high-frequency isolated DC / DC converter described above includes a half-bridge circuit, a high-frequency transformer, a high-frequency inductor, and a capacitor; m primary windings and n secondary windings of the high-frequency transformer are wound on a magnetic core and share a magnetic path; one end of each primary winding of the high-frequency transformer is connected to the midpoint of the corresponding half-bridge circuit through a high-frequency inductor L Sp connected to the midpoint of its corresponding half-bridge circuit, and the capacitor C Hp and C Lp are connected in series and then paralleled on the DC bus of the corresponding primary half-bridge circuit, and the series midpoint is connected to the other end of the primary winding; one end of each secondary winding of the high-frequency transformer is connected to the midpoint of the corresponding half-bridge circuit through a high-frequency inductor L Ss connected to the midpoint of its corresponding half-bridge circuit, and the capacitor C Hs and C Ls are connected in series and then paralleled on the DC bus of the corresponding secondary half-bridge circuit, and the series midpoint is connected to the other end of the secondary winding; the DC buses of the m primary half-bridge circuits of the high-frequency transformer are connected in series in sequence according to the positive and negative poles, and the DC buses of the n secondary half-bridge circuits of the high-frequency transformer are connected in series in sequence according to the positive and negative poles.

4. The single-phase power electronic transformer according to claim 1 or 2, characterized in that, It also includes two single-phase AC filters and a single-phase converter; the primary AC terminals and the secondary AC terminals of the single-phase power electronic transformer are respectively connected to the primary and secondary single-phase AC filters; at the same time, the AC terminals of the single-phase converter are connected to the secondary AC terminals of the single-phase power electronic transformer.

5. The single-phase power electronic transformer according to claim 1 or 2, characterized in that, The secondary AC terminals of the single-phase power electronic transformer are connected together to form the secondary DC side terminals of the single-phase power electronic transformer together with the secondary center terminal.

6. The single-phase power electronic transformer according to claim 5, characterized in that, It also includes a single-phase AC filter and a DC filter; the single-phase AC filter is connected to the primary AC terminals of the single-phase power electronic transformer; the DC filter is connected to the secondary DC terminals of the single-phase power electronic transformer.

7. A three-phase AC / AC type power electronic transformer application system includes a three-phase AC filter and a Δ / Y connection selector, characterized in that, It also includes the single-phase power electronic transformer as described in claim 1 or claim 2; the primary AC terminals of the three single-phase power electronic transformers are connected to the primary three-phase AC filter through a series-connected primary △ / Y connection selector; the secondary AC terminals of the three single-phase power electronic transformers are connected to the secondary three-phase AC filter through a series-connected secondary △ / Y connection selector.

8. The three-phase AC / AC type power electronic transformer application system according to claim 7, characterized in that, It also includes a three-phase converter; the three-phase converter is connected in parallel on the connection line between the three-phase AC filter and the △ / Y connection selector.

9. A three-phase AC / DC type power electronic transformer application system includes a three-phase AC filter and a Δ / Y connection selector, characterized in that, It also includes the single-phase power electronic transformer as described in claim 5; the primary AC terminals of the three single-phase power electronic transformers are connected to the three-phase AC filter through a series-connected △ / Y connection selector; the secondary DC terminals of the three single-phase power electronic transformers are directly connected in parallel one by one; the secondary DC terminals are connected to the DC filter.

10. A cascading method for a single-phase power electronic transformer, the method is implemented based on the single-phase power electronic transformer according to any one of claims 1 to 6, characterized in that, The primary AC terminals of multiple single-phase power electronic transformers are connected in series, and the secondary AC terminals and the center terminals are connected in parallel one by one; or, the primary AC terminals and the center terminals of multiple single-phase power electronic transformers are connected in parallel one by one, and the secondary AC terminals are connected in series.

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