CN104184356B - A kind of power model group of three-phase power electronic transformer - Google Patents

Abstract

The present invention provides a power module set of a three-phase power electronic transformer. The three-phase power electronic transformer includes a high-voltage filter, the power module set, a fifth power module, and a low-voltage filter; A power module unit connected in series on one side and parallel on the low-voltage side; the power module unit includes a first power module, a capacitor on the high-voltage side, a second power module, a medium/high-frequency transformer and a third power module connected in sequence, and the third power module is connected in parallel on the low-voltage side capacitor. The power electronic transformer also has the function of automatic mutual balance of three-phase electric energy, which can better deal with the asymmetric load on the low-voltage side, and naturally transform the asymmetry of the low-voltage side into the symmetry of the high-voltage side through the topological connection.

Description

A power module group of a three-phase power electronic transformer

technical field

The invention relates to a device in the technical field of power electronic transformers, in particular to a power module group of a three-phase power electronic transformer.

Background technique

The concept of "active distribution network" and continuous practice can solve a series of technical problems brought about by the rapid development and accelerated application of distributed generation technology. The active distribution network aims to improve the active energy distribution ability and economic operation level of the distribution network, actively absorb renewable energy, improve the power supply reliability and power quality level of the distribution network, and make the distribution network more efficient and environmentally friendly. At the same time, the controllability of the distribution network is required to be higher.

As the basic component equipment of the distribution network, the distribution transformer's operation reliability, technical performance and economic indicators will directly affect the power supply reliability, power quality and intelligence of the distribution network. Traditional distribution transformers usually adopt iron-core oil-immersed or dry-type, and the outstanding advantages are good reliability, high efficiency and low price. However, under the background that the power system is facing a series of new challenges, the power transformer, which is the most basic power transmission and transformation device in the power system, has the following shortcomings shown by the single function:

1. The volume and weight are large, and the insulating oil of the transformer pollutes the environment;

2. The no-load loss is high, and the output voltage fluctuates with the load when it is loaded;

3. When a fault occurs on the load side, the fault cannot be isolated and will affect the power supply side;

4. When carrying a nonlinear load, the distorted current is coupled into the power grid through the transformer, which will cause pollution to the power grid;

5. When the voltage on the power supply side is disturbed, it will be transmitted to the load side, resulting in an impact on sensitive loads;

6. Relevant supporting equipment is required to detect and protect it;

7. The ferromagnetic element is non-linear, which causes a large excitation inrush current when it is put into the power grid, and generates harmonic pollution when the iron core is magnetically saturated, resulting in distortion of the voltage and current of the power grid, and increased vibration and noise.

Power electronic transformer (PET) refers to a new type of power transformer realized by power electronic converter and medium/high frequency transformer. Control and power quality control functions. Power electronic transformers can be used as a seamless interface and dynamic control point between the transmission network and distribution network. Energy receiving capacity, reduce network loss, and improve power quality. Power electronic transformers have the following advantages:

1. Small size, light weight, natural air cooling, less environmental pollution, more suitable for urban applications than traditional transformers;

2. It can output DC and AC at the same time to better meet the diverse needs of users;

3. With a DC link, it is very convenient to connect renewable energy such as photovoltaics and wind power and energy storage equipment, so as to improve the utilization rate of renewable energy and the reliability of power supply;

4. It has a high degree of controllability, can realize constant frequency and constant voltage output, and effectively solves the problem of a large number of distributed generation (DG) connected to the transformer. The power factor of the primary side and the secondary side can be adjusted, and the power distribution can be adjusted smoothly and quickly Active power and reactive power flow of the grid, fast compensation for steady state and power balance requirements during faults, which is conducive to improving the active energy distribution capacity and economic operation level of the distribution network;

5. With the function of a circuit breaker, high-power power electronic devices can instantaneously (subtle level) interrupt the large current when the system fails.

6. With intelligent functions, it can not only realize its own self-test, self-diagnosis, self-protection and self-recovery functions, but also realize network communication and interact with other equipment in the distribution network;

7. It can flexibly realize phase number transformation and phase sequence transformation.

Structurally, a power electronic transformer mainly includes two basic elements: a power electronic converter and a medium/high frequency transformer. The power electronic converter mainly includes power electronic devices, controllers, filters and auxiliary equipment, and mainly realizes the waveform control function. The function of medium/high frequency transformers is isolation and voltage level conversion. The frequency usually works at the kilohertz (kHz) level. The purpose of using medium/high frequency transformers is mainly to greatly reduce the size of the transformer, reduce weight, reduce heat dissipation, and improve capacity and efficiency. Wait.

The specific implementation scheme of power electronic transformer is divided into two forms:

1. As shown in Figure 1, a power electronic transformer without a DC link is also called a direct AC/AC type power electronic transformer. The power electronic transformer directly converts the input power frequency AC into high frequency AC on the primary side. After the /high-frequency transformer is coupled to the secondary side, it is directly restored to power frequency AC. During this conversion process, the modulation on the primary side and the demodulation on the secondary side must be synchronized. The power electronic transformer without DC link has the characteristics of less conversion links and simple structure, which can greatly reduce the volume and weight of the transformer, and can conveniently realize the control of the output voltage amplitude of the transformer. The disadvantage is that the controllability is not strong, sometimes it is difficult to contribute to the improvement of power quality, and the power factor of the primary side is not adjustable.

2. As shown in Figure 2, a power electronic transformer with a DC link, also known as an AC/DC/AC type power electronic transformer, converts the input power frequency AC into DC through a rectifier, and then modulates it into a high frequency through an inverter circuit. The square wave is loaded to the primary side winding of the medium/high frequency transformer and coupled to the secondary side winding of the medium/high frequency transformer. Then, the high frequency square wave is rectified into a DC voltage, and then inverted into the required AC output. But in general, its controllability is strong, and it can ensure good power quality on both the primary and secondary sides of the transformer, but the transformation process is relatively complicated, and the number of components required is also large.

The power electronic transformer with DC link is much more controllable than the power electronic transformer without DC link. The pulse width modulation technology (PWM) can realize the flexible control of the voltage, current and power of the high voltage and low voltage sides of the transformer, and has gradually become a power transformer. The main development direction of electronic transformers in the future.

In a new type of power electronic transformer in the invention patent disclosure column with the authorized announcement number CN 101707443B, it is proposed to obtain a common high-voltage DC by connecting multiple MMC bridge arms in parallel, and then use DC capacitors in series to divide the voltage, and then convert them sequentially. Although the high-voltage direct current shared by multiple MMC bridge arms can indeed be used to solve the asymmetry problem. However, since photovoltaic, wind power and other renewable energy sources and energy storage devices are connected to the DC system, the voltage is usually low, and the DC voltage values are not necessarily equal, that is, multiple low-voltage DCs are required instead of one high-voltage DC. Therefore, the advantage of a high-voltage direct current generated by sharing multiple MMC bridge arms cannot be fully utilized, and the disadvantages of the relatively large number of power electronic devices and capacitors used in this scheme have not been effectively offset.

Therefore, it is necessary to propose a new power module group of a three-phase power electronic transformer to solve the above-mentioned problems existing in the prior art.

Contents of the invention

In order to overcome the shortcomings of the above-mentioned prior art, the present invention provides a power module set of a three-phase power electronic transformer.

The solution adopted to achieve the above purpose is:

A power module set of a three-phase power electronic transformer, the three-phase power electronic transformer includes a high-voltage filter, the power module set, a fifth power module, and a low-voltage filter; the improvements are:

The power module group includes power module units connected in series on the high-voltage side and in parallel on the low-voltage side;

The power module unit includes a first power module, a high voltage side capacitor, a second power module, a medium/high frequency transformer and a third power module connected in sequence, and the third power module is connected in parallel with a low voltage side capacitor;

The first power module is used to convert power frequency AC power into DC power; the high-voltage side capacitor is used to provide DC voltage support and power storage; the second power module is used to convert DC power into medium/high frequency AC power; The medium/high frequency transformer is used for voltage level transformation and electrical isolation between the high voltage side and the low voltage side; the third power module is used for converting medium/high frequency AC power into DC power; the low voltage side capacitor is used for providing DC Voltage support and power storage.

Further, the third power module includes one power module or three power modules with the same capacity.

Further, when the third power module includes one power module, the medium/high frequency transformer adopts a transformer with a 1-to-1 structure; the power module unit is a power module unit with an M structure.

Further, when the third power module includes three power modules with the same capacity, the medium/high frequency transformer adopts a transformer with a 1-to-3 structure; the power module unit is a power module unit with an M/3 structure.

Further, for the second power module with the same capacity, the third power module includes one power module with a capacity of L or three power modules with a capacity of 1/3L.

Further, the combination mode of the power module group is determined according to the rated voltage of the high voltage side, the withstand voltage level of the first power module, and the output requirements of the power module group;

According to the number of the power module units, corresponding power can be provided to meet different output power requirements.

Further, if the number of the first power modules connected in series on the AC side is 3n, each phase uses 3n power module units of M structure to form a power module group, reducing the overall number of power modules and corresponding costs, where n is positive integer.

Further, if the number of the AC side series connection of the first power module is 3n+1, and there is no separate DC output requirement, each phase adopts 3n power module units of M structure and 1 power module unit of M/3 structure The module units form a power module group, which reduces the overall number of power modules and corresponding costs, and n is a positive integer.

Further, if the number of AC side series connections of the first power module is 3n+2, and there is no separate DC output requirement, each phase adopts 3n power module units of M structure and 2 power modules of M/3 structure The module units constitute a power module group, so as to reduce the overall number of power modules and corresponding costs, and n is a positive integer.

Further, if the number of the first power module connected in series on the AC side is 3n+1 or 3n+2, and there is a requirement for DC output, each phase adopts an M-structured power module unit and an M/3-structured power module unit. The corresponding combination constitutes the corresponding power module group to meet the corresponding DC output. At the same time, the corresponding combination of the M structure power module unit and the M/3 structure power module unit constitutes the corresponding power module group to meet the corresponding AC output, so as to reduce the power module. The total number of and the corresponding cost, n is a positive integer.

Further, the first power module, the second power module and the third power module all adopt the H-bridge main circuit topology to ensure the bidirectional flow of power during AC-DC conversion;

The four bridge arms of the H-bridge main circuit topology respectively include parallel anti-parallel diodes and power electronic devices that can be turned off;

The turn-off power electronic devices include IGBT, IEGT, GTO, IGCT and BIGT.

Further, on the premise that power does not need to flow bidirectionally, the bridge arms of the H-bridge main circuit topology used by the third power module respectively use rectifier diodes, which simplifies control and reduces the number of devices and costs.

Further, the high-voltage AC side of the power module group is connected to the grid through the high-voltage filter, and the phases are connected in delta or star.

Further, the low-voltage side of the power module group is connected in parallel to form three or more isolated direct current sources to meet different engineering requirements.

Further, the three or more isolated direct current sources can be converted from direct current to industrial frequency alternating current, and then provide industrial frequency alternating current through a low-voltage filter.

Further, each of the three lines of said power frequency AC can be connected in a star connection or a delta connection to provide a three-phase AC interface.

Further, the star connection can lead to a neutral point, realizing a three-phase four-wire system.

Further, the mid/high frequency transformer may not have a tap, or may have a tap; when the tap is drawn out, the power modules on both sides of the mid/high frequency transformer and the corresponding capacitor wiring should be adjusted accordingly.

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

1. The three-phase power electronic transformer of the present invention can realize basic functions such as voltage conversion, electrical isolation, and energy transfer of traditional power transformers; it can realize functions such as bidirectional energy transfer, power flow control, and power quality adjustment of power electronic transformers;

2. The high-voltage side of the power module group of the present invention adopts a series connection method. For different levels of voltage, only the number of series connection of the corresponding power module M1 needs to be calculated, and the corresponding voltage can be withstand according to the corresponding number of power modules connected in series;

3. The low-voltage side of the power module group of the present invention adopts a parallel connection method. For different output powers, only the number of parallel connections of the corresponding power modules needs to be calculated, and the corresponding power can be provided by parallel connection according to the corresponding number of power modules;

4. The three-phase power electronic transformer of the present invention is easy to be modularized, standardized, and redundant, thereby facilitating design, processing, assembly, debugging, and maintenance;

5. The circuit topology of the present invention has the function of automatic mutual balance of three-phase electric energy, which can better deal with the asymmetric load on the low-voltage side, and naturally transform the asymmetry of the low-voltage side into the symmetry of the high-voltage side through the topology connection ;

6. The DC side of the three-phase power electronic transformer of the present invention can be easily connected to renewable energy such as photovoltaics and wind power and energy storage equipment, improving the utilization rate of renewable energy and the reliability of power supply;

7. The three-phase power electronic transformer of the present invention provides two topological structures that can be flexibly applied according to different power levels and control purposes;

8. If the power flow direction does not need to realize bidirectional flow, the corresponding topology structure of the three-phase power electronic transformer of the present invention can be further simplified, the complexity of the control system can be reduced, and the cost of equipment can be saved.

Description of drawings

Figure 1 is a schematic diagram of a power electronic transformer without a DC link;

Figure 2 is a schematic diagram of a power electronic transformer with a DC link;

Fig. 3 is a structural schematic diagram of a mutually balanced three-phase power module group 1 in the present invention;

Fig. 4 is a simplified structural schematic diagram of a mutually balanced three-phase power module group 1 in the present invention;

5 is a schematic structural diagram of a mutually balanced three-phase power module group 2 in the present invention;

Fig. 6 is a simplified structural schematic diagram of a mutually balanced three-phase power module group 2 in the present invention;

FIG. 7 is a schematic diagram of Embodiment 1 of a three-phase power electronic transformer in this embodiment;

Fig. 8 is a schematic diagram of the second embodiment of the three-phase power electronic transformer in this embodiment;

Fig. 9 is a schematic diagram of the third embodiment of the three-phase power electronic transformer in this embodiment;

Fig. 10 is a schematic diagram of the topological structure of the H bridge main circuit in the present invention;

Fig. 11 is a schematic diagram of a DC/DC conversion with an intermediate tap in the present invention;

Fig. 12 is a schematic diagram of diode rectification in the present invention.

detailed description

The specific embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings.

The invention provides a power module group of a three-phase power electronic transformer. The power module group can be used for modularization, can balance asymmetrical loads, and can provide low-voltage direct current. Power electronic transformer (PET) refers to a new type of power transformer realized by power electronic converter and medium/high frequency transformer.

The power module group includes power module units connected in series at the high-voltage side and parallel-connected at the low-voltage side. The power module unit includes a first power module, a high-voltage side capacitor, a second power module, a medium/high frequency transformer, and a third power module connected in sequence. Three power modules are connected in parallel with low-voltage side capacitors; the first power module is used to convert industrial frequency AC power into DC power; the high-voltage side capacitor is used to provide DC voltage support and power storage; the second power module is used to convert DC power into medium/high frequency AC power ; The medium/high frequency transformer is used for voltage level conversion and electrical isolation between the high voltage side and the low voltage side; the third power module is used to convert the medium/high frequency AC power into DC power; the low voltage side capacitor is used to provide DC voltage support and power storage.

The third power module includes one power module or three power modules of equal capacity. When the third power module is one power module, the medium/high frequency transformer adopts a transformer with a 1-to-1 structure; when the third power module includes three power modules, the medium/high frequency transformer adopts a transformer with a 1-to-3 structure. When the third power module includes one power module, the medium/high frequency transformer adopts a transformer with a 1-to-1 structure; the power module unit is a power module unit with an M structure. When the third power module includes three power modules with the same capacity, the medium/high frequency transformer adopts a transformer with a 1-to-3 structure; the third power module unit is a power module unit with an M/3 structure.

For the second power module M2 of the same capacity, the third power module may be one power module with a capacity of L, or include three power modules with a capacity of 1/3L.

In the present invention, the combination mode of the power module group is determined according to the rated voltage of the high-voltage side, the withstand voltage level of the first power module, and the output requirements of the power module group; According to the number of different power module units, corresponding power can be provided to meet different output power requirements.

If the number of AC side series connections of the first power module is 3n, each phase uses 3n M-structure power module units to form a power module group, reducing the overall number of power modules and corresponding costs, and n is a positive integer.

If the number of AC side series connections of the first power module is 3n+1, and there is no separate DC output requirement, each phase is composed of 3n power module units with M structure and 1 power module unit with M/3 structure The power module group reduces the overall number of power modules and the corresponding cost, n is a positive integer.

If the number of AC side series connection of the first power module is 3n+2, and there is no separate DC output requirement, each phase is composed of 3n power module units with M structure and 2 power module units with M/3 structure The power module group is used to reduce the overall number of power modules and the corresponding cost, n is a positive integer.

If the number of the AC side series connection of the first power module is 3n+1 or 3n+2, and there is a requirement for DC output, each phase adopts a corresponding combination of M-structured power module units and M/3-structured power module units The corresponding power module group is used to meet the corresponding DC output. At the same time, the corresponding combination of the M-structure power module unit and the M/3 structure power module unit is used to form the corresponding power module group to meet the corresponding AC output, so as to reduce the overall size of the power module. number and the corresponding cost, n is a positive integer.

The first power module, the second power module and the third power module all adopt the H-bridge main circuit topology to ensure the bidirectional flow of power during AC-DC conversion;

The four bridge arms of the H-bridge main circuit topology respectively include parallel anti-parallel diodes and power electronic devices that can be turned off;

The power electronic devices that can be turned off include IGBT, IEGT, GTO, IGCT, BIGT and the like.

On the premise that no bidirectional flow of power is required, the third power module can also use diodes as rectifier diodes, and the bridge arms of the H-bridge main circuit topology use rectifier diodes to simplify control and reduce equipment quantity and cost.

The high-voltage AC side of the power module group is connected to the grid through the high-voltage filter, and the phases are connected in delta or star. The low-voltage side of the power module group is connected in parallel to form three or more isolated DC sources to meet different engineering requirements.

The above three and above isolated DC sources can be converted from DC to power frequency AC, and the power frequency AC can be provided through a low-voltage filter. The power frequency AC of each three channels can adopt star connection or delta connection to provide a three-phase AC interface.

The star connection can lead out the neutral point to realize the three-phase four-wire system.

There may be no taps drawn out from the middle of the medium/high frequency transformer, or taps may be drawn out. The power modules on both sides of the medium/high frequency transformer and the corresponding capacitor wiring should be adjusted accordingly when the taps are drawn out.

When the third power module with different structures is used, the structures of the power module units are as follows:

1. The first power module unit topology

As shown in FIG. 3 , FIG. 3 is a schematic structural diagram of a mutually balanced three-phase power module group 1 in the present invention. The power module group includes 9 power modules, 3 medium/high frequency transformers and 6 capacitors. The nine power modules are three first power modules M1, three second power modules M2 and three third power modules M3.

3 capacitors are on the high-voltage side, and 3 capacitors are on the low-voltage side, and the 3 capacitors on the low-voltage side can be replaced by a capacitor with a larger capacity.

The first power module M1 is used to convert power frequency AC into DC, the high-voltage side capacitor is used to provide DC voltage support and power storage, the second power module M2 is used to convert DC into medium/high frequency AC, medium/high frequency transformer It is used for voltage level conversion and electrical isolation between the high voltage side and the low voltage side. The third power module M3 is used to convert medium/high frequency AC into DC, and the low voltage side capacitor is used to provide DC voltage support and power storage.

The mutually balanced three-phase power module group has 6 high-voltage AC terminals and 2 low-voltage DC terminals. The six high-voltage AC terminals are A11, A12, B11, B12, C11 and C12. Among them, A11 and A12 are one-way AC access terminals, B11 and B12 are one-way AC access terminals, and C11 and C12 are one-way AC access terminals. The two low voltage DC terminals are respectively DC1+ and DC1-.

The high-voltage AC of phase A is connected to the first power module M1 through A11 and A12, and the first power module M1 converts the power-frequency AC into DC and supplies it to the high-voltage side capacitor.

One end of the second power module M2 is connected to a high-voltage side capacitor, converts DC to medium/high frequency AC, and then connects to a medium/high frequency transformer. The medium/high frequency transformer realizes voltage level conversion and electrical isolation, and then connects to the third power module M3. A11 and a12 of the three power modules M3 form a direct current, which is connected to a low-voltage side capacitor. The wiring between the high-voltage terminals B11 and B12 of phase B to b11 and b12 on the low-voltage side, and the high-voltage terminals C11 and C12 of phase C to c11 and c12 on the low-voltage side are similar, and will not be repeated here.

The high-voltage AC terminals A11 , A12 , B11 , B12 , C11 , and C12 are independent from each other, so as to select the corresponding number of series connection of the first power module M1 according to the corresponding AC voltage.

A11, b11 and c11 at the low-voltage side are connected through a common DC bus DC1+, and a12, b12 and c12 at the low-voltage side are connected through a common DC bus DC1-, which facilitates the mutual balance between the three phases.

The mutually balanced three-phase power module group can realize bidirectional flow of power, that is, it can flow from the high-voltage AC side to the low-voltage DC side, and can also flow from the low-voltage DC side to the high-voltage AC side. If the actual project only needs to realize the one-way flow of power, the corresponding power module can be simplified to reduce the complexity of the control and reduce the cost of the equipment at the same time.

The mutually balanced three-phase power module group in FIG. 3 is adopted in a more simplified schematic diagram, as shown in the simplified structural diagram of the mutually balanced three-phase power module group 1 in FIG. 4 . The power module M in FIG. 4 is an ordered combination of the first power module M1, the high voltage side capacitor, the second power module M2, the medium/high frequency transformer, the third power module M3 and the low voltage side capacitor in FIG. 3 . The simplified schematic diagram in FIG. 4 embodies the characteristic that the power module M can be connected in series at the high voltage side and parallel connected at the low voltage side.

2. The second power module unit topology

As shown in Figure 5, Figure 5 is a schematic diagram of the structure of a mutually balanced three-phase power module group II, the three-phase power module group II includes 15 power modules, three 1-way to 3-way medium/high frequency transformers and 12 capacitors.

The 15 power modules are respectively 3 first power modules M1, 3 second power modules M2 and 9 fourth power modules M4.

Three capacitors are on the high-voltage side, and nine capacitors are on the low-voltage side. Among them, the nine capacitors on the low-voltage side can be replaced by three large-capacity capacitors.

It should be noted that the circuit topology of the fourth power module M4 in FIG. 5 and the third power module M3 in FIG. 3 can be the same, but for the second power module M2 of the same capacity, the capacity of the fourth power module M4 is usually only 1/3 of the third power module M3.

The first power module M1 is used to convert power frequency AC into DC, the high-voltage side capacitor is used to provide DC voltage support and power storage, and the second power module M2 is used to convert DC into medium/high frequency AC, 1 channel to 3 channels The medium/high frequency transformer is used for voltage level conversion and electrical isolation between the high voltage side and the low voltage side, the fourth power module M4 is used to convert medium/high frequency AC into DC, and the low voltage side capacitor is used to provide DC voltage support and power storage.

The mutually balanced three-phase power module group has 6 high-voltage AC terminals and 6 low-voltage DC terminals. The six high-voltage AC terminals are A11, A12, B11, B12, C11 and C12, of which A11 and A12 are one-way AC access terminals, B11 and B12 are one-way AC access terminals, and C11 and C12 are one-way AC access terminals. The six low-voltage DC terminals are DC1a+, DC1a-, DC1b+, DC1b-, DC1c+ and DC1c-, of which DC1a+ and DC1a- are one DC access terminal, DC1b+ and DC1b- are one DC access terminal, and DC1c+ and DC1c- are All the way to the DC access terminal.

The high-voltage AC of phase A is connected to the first power module M1 through A11 and A12. The first power module M1 converts the power-frequency AC into DC and feeds it to the high-voltage side capacitor. One end of the second power module M2 is connected to the high-voltage side capacitor. DC is converted into medium/high frequency AC and then connected with medium/high frequency transformer. The medium/high frequency transformer not only realizes voltage level conversion and electrical isolation, but also realizes the function of 1-way to 3-way. The power of the 3-way is usually evenly distributed.

The three outputs of the low-voltage side of the medium/high frequency transformer are respectively connected to three power modules M4. After each of the three power modules M4 realizes the medium/high frequency AC conversion into DC, it passes through the low-voltage terminals aa11, aa12, ba11, ba12, ca11 and ca12 Connect to three low-voltage side capacitors respectively. Among them, aa11 and aa12 form a direct current, ba11 and ba12 form a direct current, and ca11 and ca12 form a direct current. The high-voltage terminals B11 and B12 of phase B to ab11, ab12, bb11, bb12, cb11 and cb12 on the low-voltage side and the high-voltage terminals C11 and C12 of phase C to ac11, ac12, bc11, bc12, cc11 and cc12 on the low-voltage side are similar. I won't repeat them one by one.

The high-voltage AC terminals A11 , A12 , B11 , B12 , C11 , and C12 are independent from each other, so as to select the corresponding number of power modules M1 connected in series according to the corresponding AC voltage. aa11, ab11 and ac11 on the low-voltage side are connected through the common DC bus DC1a+; aa12, ab12 and ac12 on the low-voltage side are connected through the common DC bus DC1a-; ba11, bb11 and bc11 on the low-voltage side are connected through the common DC bus DC1b+; ba12, bb12 and bc12 are connected through the common DC bus DC1b-, ca11, cb11 and cc11 at the low-voltage side are connected through the common DC bus DC1c+, and ca12, cb12 and cc12 at the low-voltage side are connected through the common DC bus DC1c-.

The mutually balanced three-phase power module group can realize bidirectional flow of power, that is, it can flow from the high-voltage AC side to the low-voltage DC side, and can also flow from the low-voltage DC side to the high-voltage AC side.

A more simplified schematic diagram is adopted for a mutually balanced three-phase power module group in FIG. 5 , as shown in the simplified structure of the mutually balanced three-phase power module group II in FIG. 6 . The power module M/3 in Figure 6 is the first power module M1, the high-voltage side capacitor, the second power module M2, the 1-way to 3-way medium/high frequency transformer, the power module M4 and the low-voltage side capacitor in Figure 5 an ordered combination of .

The simplified schematic diagram in Fig. 6 embodies the feature that the power module M/3 can be connected in series at the high voltage side and can be connected in parallel at the low voltage side.

The power module group 1 in FIG. 4 is to realize the conversion of three ACs and one DC, and the power module group 2 in FIG. 6 is to realize the conversion of three ACs and three DCs.

In the embodiment, a three-phase power electronic transformer based on the above power module unit M and power module unit M/3 is given:

Embodiment 1, a three-phase power electronic transformer based on a power module unit M.

In this embodiment, when the number of AC side series connections of the first power module M1 is 3n, each phase uses 3n power module units of M structure to form a power module group, reducing the overall number of power modules and corresponding costs, where n is positive integer.

As shown in FIG. 7, FIG. 7 is a schematic diagram of Embodiment 1 of the three-phase power electronic transformer in this embodiment. For the required high-voltage AC level voltage, the calculated number of AC-side series connections corresponding to the first power module M1 is 3n, where n is a natural number. If the calculated number of AC side series connection corresponding to the first power module M1 is 3n+1 or 3n+2, as shown in the second and third embodiments below.

For each phase, there are 3n power modules M whose high-voltage AC sides are connected in series, and are connected to corresponding phases of the high-voltage AC side of the power grid through a high-voltage filter. Phases can be connected in star or delta. In the first embodiment, a star connection is adopted between phases.

The 3n*3 direct currents of the 3n*3 power module units M are evenly divided into 3 groups, and finally form 3 direct currents through parallel connection, namely DC1, DC2 and DC3. These three direct currents respectively realize the power conversion from direct current to industrial frequency alternating current through the power module M5, and obtain three alternating current outputs. Three way communication.

The above three ACs are passing through their respective low-voltage filters. Phases are connected in star form, and the neutral line N is drawn out, as shown in Figure 7. The above three-way AC can also be connected in a delta connection.

Embodiment 2, a three-phase power electronic transformer based on the power module unit M and the power module unit M/3.

If the AC side series connection number of the first power module M1 is 3n+1, and there is no separate DC output requirement, each phase uses 3n power module units with M structure and 1 power module unit with M/3 structure to form the power The module group reduces the total number of power modules and the corresponding cost, n is a positive integer.

As shown in FIG. 8, FIG. 8 is a schematic diagram of the second embodiment of the three-phase power electronic transformer in this embodiment. For the required high-voltage AC level voltage, the calculated number of AC-side series connections corresponding to the first power module M1 is 3n+1 (n is a positive integer).

In this embodiment, n is a natural number 1, that is, the number of the first power module M1 connected in series on the AC side is four. Therefore, in this embodiment, for each phase, three power modules M and one power module M/3 are connected in series on the AC side, and are connected to the corresponding phase on the high-voltage AC side of the power grid through a high-voltage filter. Phases can be connected in delta or star. In this embodiment, a delta connection is adopted between phases.

9 DCs of 9 power module units M and 9 DCs of 3 power module units M/3, that is, a total of 18 DCs are evenly divided into 3 groups, namely a11, a12, aa41, aa42, b11, b12, ab41, ab42, c11, c12, ac41, ac42 are the first group, a21, a22, ba41, ba42, b21, b22, bb41, bb42, c21, c22, bc41, bc42 are the second group, a31, a32, ca41, ca42, b31, b32, cb41, cb42, c31, c32, cc41, cc42 are the third group.

The above three groups finally form three direct currents through parallel connection, which are respectively DC1, DC2 and DC3. These three direct currents respectively realize the power conversion from direct current to industrial frequency alternating current through the fifth power module M5, and obtain three alternating current outputs, respectively, a1 and a2 form the first alternating current, b1 and b2 form the second alternating current, and c1 and c2 Form a third exchange. The above three channels of AC pass through their respective low-voltage filters, and the phases are connected in star form, and the neutral line N is drawn out, as shown in the second embodiment in FIG. 8 . The above three-way AC can also be connected in a delta connection.

Embodiment 3, a three-phase power electronic transformer based on the power module unit M and the power module unit M/3.

If the number of AC side series connection of the first power module M1 is 3n+1 or 3n+2, and there is a requirement for DC output, each phase adopts the corresponding combination of M-structured power module units and M/3-structured power module units to form a corresponding The power module group meets the corresponding DC output. At the same time, the corresponding combination of the power module unit of the M structure and the power module unit of the M/3 structure constitutes the corresponding power module group to meet the corresponding AC output, so as to reduce the overall number of power modules And the corresponding cost, n is a positive integer.

As shown in FIG. 9, FIG. 9 is a schematic diagram of the third embodiment of the three-phase power electronic transformer in this embodiment. For the required high-voltage AC level voltage, the calculated number of AC-side series connection corresponding to the first power module M1 is 3n+2 (n is a positive integer).

In this embodiment, n is a natural number 1, that is, the number of AC side series connections of the first power module M1 is five. Therefore, in this embodiment, for each phase, the AC side of 4 power module units M and 1 power module unit M/3 are connected in series, and are connected to the corresponding phase of the high-voltage AC side of the power grid through a high-voltage filter. Connection; this structure can realize AC input, AC output and DC output. The structure of 4 power module units M and 1 power module unit M/3 is taken as an example for further description below.

The phases are connected in a delta connection or in a star connection. In this implementation, a delta connection is adopted between phases.

9 DCs of 9 power module units M and 9 DCs of 3 power module units M/3, that is, a total of 18 DCs are evenly divided into 3 groups, namely a11, a12, aa41, aa42, b11, b12, ab41, ab42, c11, c12, ac41 and ac42 are the first group, a21, a22, ba41, ba42, b21, b22, bb41, bb42, c21, c22, bc41 and bc42 are the second group, a31, a32, ca41, ca42, b31, b32, cb41, cb42, c31, c32, cc41 and cc42 are the third group.

The three groups are connected in parallel to finally form three direct currents, which are respectively DC1, DC2 and DC3. These three direct currents respectively realize the power conversion from direct current to industrial frequency alternating current through the fifth power module M5, and obtain three alternating current outputs, respectively, a1 and a2 form the first alternating current, b1 and b2 form the second alternating current, and c1 and c2 Form a third exchange. The above three channels of AC pass through their respective low-voltage filters, and the phases are connected in a delta, as shown in the third embodiment in FIG. 9 . The three-way AC can also be connected in star form.

In addition, the three direct currents of the three power module units M, that is, a51 and a52 are the first direct currents, b51 and b52 are the second direct currents, and c51 and c52 are the third direct currents. The three direct currents are connected in parallel to form a separate direct current power supply DC4 to provide a separate direct current power supply output and meet corresponding power requirements, as shown in the third embodiment in FIG. 9 .

Embodiment 4, a three-phase power electronic transformer based on the power module unit M and the power module unit M/3.

If the number of AC side series connection of the first power module M1 is 3n+2, and there is no separate DC output requirement, each phase uses 3n power module units with M structure and 2 power module units with M/3 structure to form the power Module group, to reduce the overall number of power modules and the corresponding cost, n is a positive integer.

Assume that n is a natural number 1, that is, the number of AC side series connections of the first power module M1 is five.

For each phase, the AC side of 3 power module units M and 2 power module units M/3 is connected in series, and connected to the corresponding phase of the high-voltage AC side of the power grid through a high-voltage filter; this structure realizes AC input, AC output;

For each phase, the AC sides of three power modules M and two power modules M/3 are connected in series, and are connected to the corresponding phases of the high-voltage AC side of the power grid through a high-voltage filter. Phases can be connected in delta or star. In this embodiment, a delta connection is adopted between phases. Similar to Example 2.

In the topology of the present invention, the first power module M1, the second power module M2, the third power module M3, the fourth power module M4 and the fifth power module M5 can adopt the H-bridge main circuit topology as shown in Figure 10 , in order to realize the conversion of AC and DC, and maintain the bidirectional flow of power.

The H-bridge main circuit topology consists of four turn-off power electronic devices with anti-parallel diodes. The IGCT1, IGCT2, IGCT3, and IGCT4 in the figure are just for illustration, which can be IGBT, IEGT, GTO, and BIGT, etc. electronic devices.

In the topological structure of the present invention, there is no tap in the middle of the medium/high frequency transformer in Fig. 3 and Fig. 5 . According to the needs of actual projects, medium/high frequency transformers with intermediate taps can be used. For example, for the section from the high-voltage side capacitor to the low-voltage side capacitor in Figure 3, the scheme shown in Figure 11 can be used. The scheme shown in Figure 11 can realize the functions of converting from DC to high-frequency AC, and then converting to DC. Since all of them adopt turn-off power electronic devices with anti-parallel diodes, the function of bidirectional power flow is retained.

If there is an actual project that only requires power to flow from the high voltage side to the low voltage side, but not from the low voltage side to the high voltage side, that is, the power flow is only one-way, then for some power modules, it is not necessary to use turn-off power electronics with anti-parallel diodes. devices, and only use diodes, such as the diode rectifier circuit shown in Figure 12. To expand, the diode rectifier circuit in FIG. 12 can be used for the third power module M3 in FIG. 3 and the fourth power module M4 in FIG. 5 to realize the conversion from AC to DC.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application rather than to limit the scope of protection thereof. Although the present application has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: After reading this application, those skilled in the art can still make various changes, modifications or equivalent replacements to the specific implementation methods of the application, but these changes, modifications or equivalent replacements are all within the protection scope of the pending claims of the application.

Claims (13)

1. a kind of power model group of three-phase power electronic transformer, the three-phase power electronic transformer includes hv filtering Device, the power model group, the 5th power model and low voltage filter；It is characterized in that：

The power model group includes connecting and low-pressure side power model unit in parallel in high-pressure side respectively；

The power model unit include be sequentially connected the first power model, high pressure side capacitors, the second power model, in/ High frequency transformer and the 3rd power model, the 3rd power module parallel low-voltage side capacitor；

First power model is used to industrial-frequency alternating current being transformed into direct current；The high pressure side capacitors are used to provide direct current Voltage support and power storage；Second power model is used for DC power conversion into medium/high frequency alternating current；It is described medium/high Voltage class conversion and electrical isolation that frequency power transformer is used between high-pressure side and low-pressure side；3rd power model is used for will Medium/high frequency convert alternating current is into direct current；The low-voltage side capacitor is used to provide DC voltage support and power storage；

The combination of the power model group is according to high-pressure side rated voltage, the resistance to voltage levels of first power model and work( The output of rate module group requires to determine；

Corresponding power can be provided according to the number of the power model unit, different output power requirement is met；

If the AC serial number of first power model is 3n, per mutually using the power model unit structure of 3n M structure Success rate module group, reduces the overall number and corresponding cost of power model, n is positive integer；The M structure is to be sequentially connected The first power model, high pressure side capacitors, the second power model, medium/high frequency power transformer, the 3rd power model and with the 3rd work( The low-voltage side capacitor of rate wired in parallel；

If the AC serial number of first power model is 3n+1, and during without the requirement of single direct current output, per phase Power model group is constituted using the power model unit of 3n M structure and the power model unit of 1 M/3 structure, power is reduced The overall number of module and corresponding cost, n is positive integer；The M/3 structures are the first power model, the high pressure being sequentially connected Side capacitors, the second power model, medium/high frequency power transformer, three respectively connection three-phase the 4th power model and three difference With the low-voltage side capacitor of different 4th power module parallel；

If the AC serial number of first power model is 3n+2, and during without the requirement of single direct current output, per phase Power model group is constituted using the power model unit of 3n M structure and the power model unit of 2 M/3 structures, to reduce work( The overall number of rate module and corresponding cost, n is positive integer；

If the AC serial number of first power model is 3n+1 or 3n+2, and when having direct current output requirement, it is every mutually to use M The respective combination of the power model unit of structure and the power model unit of M/3 structures constitutes corresponding power module group to meet phase The direct current output answered, at the same using M structure power model unit and M/3 structures power model unit respective combination constitute Corresponding power module group is exported with meeting corresponding exchange, and to reduce the overall number and corresponding cost of power model, n is just Integer.

2. a kind of power model group of three-phase power electronic transformer as claimed in claim 1, it is characterised in that：Described 3rd Power model includes the power model of a power model or three identical capacity.

3. a kind of power model group of three-phase power electronic transformer as claimed in claim 2, it is characterised in that：When described When three power models include a power model, the medium/high frequency power transformer uses the transformer of 1 turn of 1 structure；The power mould Module unit is the power model unit of M structure.

4. a kind of power model group of three-phase power electronic transformer as claimed in claim 2, it is characterised in that：When described When three power models include the power model of three identical capacity, the medium/high frequency power transformer using 1 turn of 3 structure transformer； The power model unit is the power model unit of M/3 structures.

5. a kind of power model group of three-phase power electronic transformer as claimed in claim 2, it is characterised in that：When for phase With second power model of capacity, the 3rd power model includes a capacity for L power model or including three capacity For 1/3L power model.

6. a kind of power model group of three-phase power electronic transformer as claimed in claim 1, it is characterised in that：Described first Power model, the second power model and the 3rd power model use H bridge main circuit topologies, and realization ensures in AC-DC conversion The two-way flow of power；

Four bridge arms of the H bridges main circuit topology include anti-paralleled diode in parallel respectively and can turn off power electronics device Part；

The power electronic devices that turns off includes IGBT, IEGT, GTO, IGCT and BIGT.

7. a kind of power model group of three-phase power electronic transformer as claimed in claim 1, it is characterised in that：Do not needing On the premise of to and fro flow of power, the bridge arms of the H bridge main circuit topological structures that the 3rd power model is used is respectively adopted whole Flow diode, simplify control, reduction number of devices and cost.

8. a kind of power model group of three-phase power electronic transformer as claimed in claim 1, it is characterised in that：The power The high-voltage alternating side of module group is connected by the hv filtering device with power network, between phase and phase using triangle connection or star Connection.

9. a kind of power model group of three-phase power electronic transformer as claimed in claim 1, it is characterised in that：The power The low-pressure side of module group is in parallel, forms the DC source of each self-isolation of three tunnels and the above, meets different engineering demands.

10. a kind of power model group of three-phase power electronic transformer as claimed in claim 9, it is characterised in that：Described three The DC source of each self-isolation of road and the above, can carry out direct current and be converted into industrial frequency AC, and providing power frequency by low voltage filter hands over Stream.

11. a kind of power model group of three-phase power electronic transformer as claimed in claim 10, it is characterised in that：Every three tunnel The industrial frequency AC, can there is provided three-phase alternating current interface using star-star connection and delta connection.

12. a kind of power model group of three-phase power electronic transformer as claimed in claim 11, it is characterised in that：The star Shape wiring can draw neutral point, realize three-phase four-wire system.

13. a kind of power model group of three-phase power electronic transformer as claimed in claim 1, it is characterised in that：In described/ Tap can be not brought up in the middle of high frequency transformer, tap can be also drawn；

The both sides power model of the medium/high frequency power transformer and corresponding capacitor wiring should have corresponding adjustment when drawing tap.