WO2012136145A1

WO2012136145A1 - Method, circuit, and high-voltage transformer for implementing high-voltage inversion by using low-voltage inversion

Info

Publication number: WO2012136145A1
Application number: PCT/CN2012/073586
Authority: WO
Inventors: 李永盼
Original assignee: Li Yongpan
Priority date: 2011-04-07
Filing date: 2012-04-06
Publication date: 2012-10-11
Also published as: CN102739097B; CN102739097A

Abstract

A method, circuit, and high-voltage transformer for implementing high-voltage inversion by using low-voltage inversion, comprising: setting inputs of M number of three-phase low-voltage inverter circuits (2A, 2B, 2C, and 2D) as direct current voltages (V_DCA, V_DCB, V_DCC, and V_DCD) electrically isolated from each other; three-phase output voltages (U1, V1, W1, U2, V2, W2, U3, V3, W3, U4, V4, and W4) of each low-voltage inverter circuit respectively connecting in series directly or coupled in series via transformers (31, 32, 33, 34, 35, and 36) to corresponding phases (U, V, and W), thereby acquiring a three-phase high-voltage alternating current output; respectively serial-connecting directly two phases among the three-phase outputs of the three three-phase low-voltage inverter circuits to high-voltage alternating current output ends of the corresponding phases, then respectively using common output ends outputted by the two phases of the three low-voltage inverter circuits as three-phase output ends of high-voltage inverter circuits; and then using a pulse-width modulation scheme respectively on the three-phase low-voltage inverter circuits, inverting the direct current voltage input into a three-phase symmetrical PWM alternating current output voltage. The method, circuit, and high-voltage transformer is capable of achieving high-voltage alternating current output by coupling in series via the transformers any three and more than three three-phase low-voltage inverter outputs.

Description

Method, circuit and high voltage converter for realizing high voltage inverter by low voltage inverter

The invention relates to a power electronic technology, in particular to a method, a circuit and a high voltage converter for realizing a high voltage inverter by using a low voltage inverter, which is specifically: obtaining a high voltage alternating current by connecting a plurality of three-phase low voltage inverter circuits through a transformer coupling series A three-phase power inversion method, a circuit, and a high voltage converter based on the method and the circuit. Background technique

As an important part of power-saving technology, high-voltage power conversion technology is gaining widespread attention. As a core component of power conversion, solid state power electronic switches such as insulated gate transistors

The (IGBT) voltage level has reached 6500V, which enables AC power conversion below 2500V, but for higher grid voltages, power conversion still cannot be directly performed.

Methods of power conversion, including "AC-DC" (rectifier) methods and "DC-AC" (inverter) methods. Due to the voltage and cost constraints of power electronic switches, in the case of medium and high voltage, the unit is connected in series with multiple pulse width modulation (PWM) high voltage inverter method. The inverter method inverts the multi-channel low-voltage direct currents isolated from each other into the same-number of low-voltage single-phase alternating currents, and these low-voltage single-phase alternating currents are further divided into three groups of symmetrical, and each group of single-phase alternating currents can be sequentially connected in series. Single-phase high-voltage AC voltage output, one end of three high-voltage AC high-voltage outputs are connected together, and the other end is used as three output terminals of high-voltage AC voltage. With a certain PWM distribution strategy of the low-voltage inverter, a three-phase symmetrical multi-level high-voltage AC voltage can be obtained at three outputs.

The high-voltage inverter with this inverter method has a good output voltage waveform, low output voltage change rate, low material cost, and convenient maintenance. However, since each low-voltage inverter is a single-phase output, each low-voltage DC voltage is often obtained by rectification and filtering. When the output frequency is low, DC power The fluctuation of the pressure is large, which causes the output harmonic current to increase. If the load of the high voltage converter is the motor, it will also affect the starting performance and low speed running performance of the motor. Increasing the DC filter capacitor can improve, but it also degrades the input current characteristics of the converter. In addition, the low-voltage converter's pre-stage filter capacitor has large capacity, high price and short life, which not only increases the cost of the high-voltage inverter, but also increases the maintenance workload during actual use.

In view of the above shortcomings of the unit series multiplexed PWM high voltage inverter method, in 1998, E. Cengelci proposed a three in "A New Medium-voltage PWM Inverter Topology for Adjustable-speed Drives, IEEE Paper No. IPCSD 98-83". The phase-voltage inverter output is designed by a transformer-coupled series to increase the output AC voltage of the main circuit of the inverter.

1A is a schematic diagram of main circuit wiring of the medium voltage inverter, wherein the medium voltage inverter includes three three-phase low voltage inverters (belonging to a low voltage converter) 2A, 2B, 2C and three single-phase transformers 31, 32 33. The DC input of three three-phase low-voltage inverters (such as 2A) is isolated from each other and equal in voltage (such as V _DCA ); each low-voltage inverter (such as 2A) inverts the low-voltage DC voltage (such as V _DCA ) into the required Three-phase AC; The inverter bridges of each of the low-voltage converters 2A, 2B, and 2C are controlled by PWM. The PWM signals of the corresponding switches in the inverter bridges have the same reference wave, and the carrier waveforms are the same and the phases are different from each other by 120°. The low-voltage converters (such as 2A) each have an output (such as ul) as the output of the medium-voltage inverter connected to the load, such as motor 5; the other two outputs (such as vl and wl) are connected to the output-coupled transformer (such as 32, 33). Among them, the three single-phase coupled transformers 31, 32, and 33 in Figure 1A are all 1:1, and operate in the wu, vw, and uv phases of the three-phase low-voltage converter, respectively, so a three-phase transformer 3A can be used. To achieve this, as shown in FIG. 1B, the power of the three-phase transformer is only equivalent to 1/3 of the output power of the medium voltage inverter.

With the transformer coupled series of the low-voltage inverter output described above, the output voltages of the medium-voltage converter are:

UuV=UuVl+UuV2+UuV3,

U =UvWl+UvW2+UvW3, UuV=U\VUl+UwU2+UwU3; thus making the output available.

The low-voltage inverters use phase-shift modulation, and the output voltage ripples of the low-voltage inverters can cancel each other, so that the medium-voltage inverter can realize multi-level output, thus not only reducing the output current ripple, It also reduces the rate of change of the output voltage.

The three-phase low-voltage inverter output transformer coupled with the series-connected medium-voltage inverter directly uses the three-phase inverter, which improves the DC voltage fluctuation caused by the single-phase inverter of the unit series multiple PWM high-voltage inverter, and thus can Reduce the number of pre-filter capacitors in the inverter. However, the disadvantage is that only three levels of superposition can be achieved, and it is difficult to directly implement high-voltage power inversion by the low-voltage inverter.

If the high-voltage output is obtained by the above-mentioned three-phase low-voltage inverter output transformer coupling series, as shown in FIG. 2, the output of the nine three-phase low-voltage inverters 2A to 2I is firstly driven by three three-phase coupling transformers. 3A, 3B, 3C are coupled in series to realize three medium voltage inverters. The output of the three medium voltage inverters is connected to the high voltage output through the 3D coupling of the first phase three-phase transformer, and the number of coupling transformers is increased to four. The type of transformer has been increased to 2 types (the transformer 3A ~ 3C power is 1/9 of the high-voltage inverter output power, the transformer 3D power is 1/3 of the high-voltage inverter power), and the total power is increased to 2/3 of the main transformer. In this way, not only the cost is increased, but also a three-phase low-voltage inverter combination of 3, 9, and 27... can be realized, and the application is not flexible enough. Summary of the invention

In view of this, the main object of the present invention is to provide a method, a circuit and a high voltage converter for implementing high voltage inverter using low voltage inverter to overcome the unit series multiple PWM high voltage inverter method and the existing three-phase low voltage inverter output. The three-phase low-voltage inverter output of three or more three-phase low-voltage inverter outputs can be realized by the high-voltage inverter mode of the three-phase transformer coupling in series to achieve the above purpose. The technical solution of the present invention is realized in this way. :

A method for realizing high-voltage inverter by using a low-voltage inverter, the method comprising the following steps: A. setting an input of the M three-phase low-voltage inverter circuits to DC voltages that are electrically isolated from each other; B. The three-phase output voltages of the low-voltage inverter circuits are directly connected in series or through a single-phase transformer to the corresponding phase to obtain three-phase high-voltage AC output; the output terminals of the low-voltage inverter circuits pass through a single phase. Winding connection of the transformer;

C. Directly connecting two of the three-phase outputs of the three three-phase low-voltage inverter circuits to the high-voltage AC output terminal of the corresponding phase, and then outputting the common outputs of the two-phase outputs of the three low-voltage inverter circuits As the three-phase output of the high-voltage inverter circuit;

D. Finally, each three-phase low-voltage inverter circuit is inverted into a three-phase symmetrical PWM AC output voltage by a pulse width modulation PWM method, and each three-phase low-voltage inverter circuit corresponds to an output AC. The PWM voltage reference wave is the same, the carrier waveform is the same, and the phase is sequentially different.

360° /M; where M is a natural number greater than or equal to 3.

Wherein, step B obtains a three-phase high-voltage current output, which is specifically:

Bl, directly connecting part of the output phase of the M minus MOD (M, 3) low-voltage inverter circuits to the corresponding phase high-voltage AC output, and the remaining output phases are coupled and isolated by the single-phase transformer, and then connected in series to the corresponding phase high-voltage AC output. MOD ( M, 3 ) denotes the remainder of M divided by 3;

B2. If the number M of low-voltage inverter circuits is not an integral multiple of 3, there are still other low-voltage inverter circuits. All three output phases are respectively coupled and isolated by a single-phase transformer and connected to the corresponding phase high-voltage AC output.

The single-phase transformer has the same structure, and three single-phase transformers belonging to different output phases are combined into one three-phase transformer. If all three-phase transformers are used for coupling isolation, at least Ceil (2M/) is required. 3) minus one three-phase transformer; wherein, M is a natural number greater than or equal to 3, and the Ceil() is a ceiling function, indicating that the real number is rounded up.

A circuit for realizing high voltage inverter by using a low voltage inverter, the circuit comprising: M three-phase low-voltage inverter circuits, Ceil (2M/3) minus one three-phase transformer; and the three-phase low-voltage inverter circuits The input voltage is DC and is electrically isolated from each other; the M three-phase low-voltage inverter circuits are the most Divided into 3 groups:

The first group includes three three-phase low-voltage inverter circuits, wherein each of the low-voltage inverter circuits has two output phases directly connected in series to the corresponding phase output of the high-voltage inverter circuit, and the remaining one output phase is separately coupled through the three-phase transformer. Connected in series to the corresponding phase output of the high voltage inverter circuit;

If M is not an integer multiple of 3, there is a second group of low-voltage inverter circuits, including MOD(M,

3) a low-voltage inverter circuit, the MOD (M, 3) represents the remainder of M divided by 3; the three-phase output of each of the second low-voltage inverter circuits is respectively coupled to the high-voltage inverter circuit through three-phase transformer coupling isolation Corresponding phase output;

If M is a natural number greater than or equal to 6, other low-voltage inverter circuits are used as the third group, wherein one output phase of each low-voltage inverter circuit is directly connected in series to the corresponding output phase of the high-voltage inverter circuit, and the other two output phases respectively pass The three-phase transformer is coupled and isolated and connected in series to the corresponding output phase of the high voltage inverter circuit;

The outputs of the respective low voltage inverter circuits are not directly connected;

The common ends of the two phases directly outputted in series by the first group of low voltage inverter circuits are respectively used as the three-phase output terminals of the high voltage inverter circuit;

Where M is a natural number greater than or equal to 3; the Ceil() is a ceiling function, indicating that the real number is rounded up.

The M three-phase low-voltage inverter circuits have the same structure; each three-phase low-voltage inverter circuit respectively inverts the output DC voltage into a three-phase symmetric PWM AC output voltage by PWM mode, and the corresponding output of each three-phase low-voltage inverter circuit AC PWM voltage reference wave.

All of the three-phase transformers have the same number of winding turns.

A high voltage converter, comprising: a main transformer, 3N three-phase low voltage converters, 2N-1 three-phase output transformers and a main controller; the phase shifting main transformer is a three-phase multi-side winding Transformer, the primary winding is connected to the three-phase high-voltage power grid, and the secondary winding includes 3N roads that are electrically isolated from each other and output voltages are equal, each channel is a symmetrical three-phase output, for each three-phase low voltage The converter has a secondary winding connected thereto; the output of the low voltage converter is respectively connected to the load of the high voltage converter or the winding of the three-phase coupling transformer; each low voltage converter is respectively connected to the main controller; wherein, the natural number is .

Wherein, the main transformer is a three-phase phase-shifting transformer, and a phase difference of 20/Ν between the secondary windings of each path; or

The secondary windings are divided into L groups, and the secondary windings in the group have the same phase, and the phase between the secondary windings of each group is 60/L degrees, wherein N and L are natural numbers, and 3Ν is an integer multiple of L.

The low voltage converter includes a three-phase uncontrolled rectifier bridge (21), a DC filter circuit (22), a three-phase full-control inverter bridge (23), and a control drive circuit (24); wherein, the three-phase rectifier bridge (21) The AC side a, b, c terminals are used as the input of the low-voltage converter, and connect one phase three-phase secondary winding of the phase-shifting main transformer, its DC side, n-end and DC filter circuit (22) and three-phase full-control inverter bridge The DC side of (23) is connected, and the AC side u, v, w ends of the three-phase full-controlled inverter bridge (23) serve as the output of the low-voltage converter; the control drive circuit (24) is connected to the main controller through the optical fiber. Receiving a PWM signal from the main controller, controlling the solid state power switch (231 ~ 236) of the three-phase full control inverter bridge (23), and transmitting the operation information of the low voltage converter to the main controller.

The six winding turns of the three-phase output transformers are the same; the primary windings of the three-phase output transformer are connected to the two output ends of the same low-voltage converter; the secondary windings of the three-phase output transformer are respectively connected to the high-voltage converter Corresponding phase output.

The reference signals of the inverter control PWM signals corresponding to the solid state switches in the three-phase full-control inverter bridges (23) of the three-phase low-voltage converters are the same, the carrier shapes are the same, and the phases are sequentially different by 120/N degrees, wherein N is Natural number.

The method, circuit and high voltage converter for realizing high voltage inverter by low voltage inverter provided by the invention have the following advantages:

1. Directly adopting three-phase low-voltage inverter, which improves the DC voltage fluctuation caused by single-phase inverter of the unit multiplexed PWM high-voltage inverter, thereby reducing the pre-stage filter capacitance in the inverter. 2. It can realize any three-phase inverter superposition of three or more stages, and can directly realize three-phase high-voltage power inverter by three-phase low-voltage inverter;

3. Compared with the nesting scheme of three-phase low-voltage inverter output connected by transformer in series, the total capacity of the output transformer is significantly reduced, and the application is more flexible. DRAWINGS

1A is a schematic diagram of a main circuit of a conventional transformer coupled series medium voltage inverter;

1B is a schematic diagram of a three-phase output transformer of a conventional transformer-coupled series medium voltage inverter; FIG. 2 is a schematic diagram of a main circuit of a two-stage nested transformer coupled series high voltage inverter;

3A is a schematic diagram of a three-phase output transformer of a low-voltage inverter output transformer coupled series high-voltage inverter circuit according to the present invention. FIG. ;

3D is a schematic diagram showing the waveform of the output voltage synthesis of the TL coupled series high voltage inverter circuit of the 4 low voltage inverter according to the present invention;

4A is a schematic diagram of a 6-voltage low-voltage inverter-output transformer coupled series high-voltage inverter circuit according to the present invention;

4B is a series diagram of a series connection of a low voltage inverter of the present invention: :1 coupled series high voltage inverter circuit; FIG. 4C is a schematic diagram of a three-phase output transformer of a low voltage inverter of the present invention;

Main circuit of transformer coupled series high voltage converterFig. 5B is a schematic diagram of the circuit of the three-phase low voltage converter of the present invention 5C is a schematic view showing the synthesis of the output voltage of the output transformer-connected series high voltage converter of the 6 low voltage inverter according to the present invention;

5D is a schematic diagram of the input current synthesis of the output transformer-connected series high voltage converter of the 6 low voltage inverter according to the present invention;

6A is a schematic diagram of a main circuit of nine low-voltage converter coupled series high-voltage converters according to the present invention; FIG. 6B is a schematic diagram of a three-phase output transformer corresponding to FIG. 6A.

Fig. 6C is a diagram showing the voltage coupling series relationship of the high voltage converter shown in Figs. 6A and 6B.

[Main part symbol description]

1: Phase shifting main transformer

11: Three-phase primary winding

12A-12I: secondary winding

2A-2I: Three-phase low-voltage inverter (circuit)

21: Three-phase rectifier bridge

22: DC filter circuit

23: Three-phase (full control) inverter bridge

24: Control drive circuit

31-39: Single phase output transformer

3A-3E: Three-phase output transformer

4, the main controller

5: Motor

6, high voltage power grid. detailed description

The method, circuit and high voltage converter of the present invention are further described in detail below with reference to the accompanying drawings and embodiments of the invention.

The invention provides an output of any three or more three-phase low-voltage inverters A method in which a transformer is coupled in series to obtain a high-voltage AC output, and a high-voltage inverter circuit based on the high-voltage inverter method is described below in conjunction with a specific circuit.

3A is a schematic diagram of a high voltage inverter circuit implemented by four three-phase low voltage inverter circuits according to an embodiment of the present invention, wherein input voltages of the four low voltage inverter circuits (such as 2A) are DC voltages (such as V _DCA ), and Electrically isolated from each other.

Figure 3B shows the method of connecting the output of four three-phase low-voltage inverter circuits through transformer coupling. The elliptical symbol in the figure indicates that the corresponding output is directly connected in series to the output phase of the high-voltage inverter, and the box symbol indicates that the corresponding output passes. The transformer is isolated and connected in series to the output phase of the high-voltage inverter; the symbols in the ellipse and the box indicate the source of the voltage, such as uvl in the ellipse, which represents the voltage component in series in the UV output phase of the high-voltage inverter circuit from the three-phase The output voltage ul-vl of the low-voltage inverter circuit 2A, wu2 in the block indicates that the voltage component in the output phase of the high-voltage inverter circuit WU comes from w2-u2 of the three-phase low-voltage inverter circuit 2B, and the like.

The three-phase output voltages (such as ul-vl, vl-wl, wl-ul) of each low-voltage inverter circuit (such as 2A) are respectively connected in series to the UV, VW, and WU phases of the high-voltage inverter circuit to obtain three-phase high-voltage AC. Output; three of the low-voltage inverter circuits 2A, 2B, 2C have two output phases, such as 2A ul-vl phase and wl-ul phase, 2B u2-v2 phase and v2-w2 phase, 2C v3- The w3 phase and the w3-u3 phase are directly connected in series to the corresponding phase output of the high voltage inverter circuit; the remaining output phases of the three low voltage inverter circuits, such as the vl-wl phase of 2A, the w2-u2 phase of 2B, 2C The u3-v3 phase is coupled and isolated by the transformers 32, 33, and 31, respectively, and connected in series to the VW, WU, and UV phase outputs of the high voltage inverter circuit.

In Figure 3A, there are four three-phase low-voltage inverter circuits. Since 4 is not an integer multiple of 3, there is also a low-voltage inverter circuit 2D, and all three output phases u4-v4, v4-w4, w4-u4 pass through The transformers 34, 35, 36 are coupled and isolated and respectively connected to the AC output of the high voltage inverter circuit UV, VW, WU phase;

In Figure 3A, there is no direct connection between the outputs of the low voltage inverter circuits; Low-voltage inverter circuits 2A, 2B, 2C, each having two-phase outputs (such as ul-vl and wl-ul of 2A, u2-v2 and v2-w2 of 2B, v3-w3 and w3-u3 of 2C) are directly connected in series to The high-voltage inverter circuit AC output of the corresponding phase; the common terminals ul, v2, and w3 of the two-phase output of the low-voltage inverter circuits 2A, 2B, and 2C serve as U, V, and W three-phase output terminals of the high-voltage inverter circuit, respectively.

Each three-phase low-voltage inverter circuit (such as 2A) inverts the input DC voltage (such as V _DCA ) into a three-phase symmetric PWM AC output voltage (such as ul-vl, vl-wl, and wl-ul) through PWM mode. The three-phase low-voltage inverter circuit 2A, 2B, 2C, 2D corresponds to the output AC PWM voltage reference wave, the carrier waveform is the same, the phase difference is 90° (360° /4), which can make each low-voltage inverter circuit The corresponding phase, such as ul-vl of 2A, u2-v2 of 2B, u3-v3 of 2C, u4-v3 of 2D, and u4-v4 of 2D, have low-frequency component waveforms and phases that are identical but the pulses are sequentially shifted, so that each low-voltage inverter circuit The carrier components of the corresponding phase outputs can cancel each other, thus not only achieving multi-level output of the high-voltage inverter circuit, but also reducing the rate of change of the output voltage of the high-voltage inverter circuit, and reducing the output ripple voltage, thereby enabling The lower PWM modulation frequency is compared. Figure 3D shows the waveform of the PWM output voltage of each low-voltage inverter circuit and the output voltage of the high-voltage inverter circuit. RefU and RefV are low-voltage inverter circuits (including 2A, 2B). , 2C, 2 D) U-phase and V-phase PWM reference waves, Cl, C2, C3, C4 are PWM carriers of low-voltage inverter circuits 2A, 2B, 2C, 2D, respectively, V _UV1 , V _UV2 , V _UV3 , V _UV4 are low voltage respectively The inverter circuit 2A, 2B, 2C, 2D corresponds to the voltage between the output terminals ul-vl, u2-v2, u3-v3, u4-v4 of the UV phase of the high voltage inverter circuit, and V _uv is the output terminal UV of the high voltage inverter circuit Between the voltages. The input three-phase voltage of the four three-phase low-voltage inverter circuits in the figure is the same, and the output thereof is coupled in series through the transformer, and the level of the output voltage can be up to nine levels. As shown in Figure 3D:

It can be seen that the output of the high voltage inverter circuit is 4 times that of the low voltage inverter circuit. If the above-mentioned low-voltage inverter units use different input DC voltages, the number of levels of the output voltage will be more, and the high-voltage inverter method provided by the present invention can also be applied. In addition, sinusoidal PWM modulation is used in Fig. 3D, and the effectiveness of the method provided by the present invention is not affected if other modulation methods are used.

In FIG. 3B, the output voltage of the three-phase low-voltage inverter circuit coupled in series by the transformer includes vl-wl of 2A, w2-u2 of 2B, u3-v3 of 2C, and u4-v4, v4- of inverter circuit 2D. W4, w4- _u 4, it can be seen that each phase of the corresponding three-phase high-voltage output has two voltage outputs (such as vl-wl and v4- _w 4), so two three-phase transformers can be used to achieve 6 Isolated coupling of the road voltage. Figure 3C shows a three-phase voltage isolation connection method using a three-phase transformer. One transformer 3A realizes the voltage coupling output of vl-wl, w2-u2, u3-v3, and the other transformer 3B realizes u4-v4, _V 4-w4, w4-u4 voltage coupled output. If a single-phase transformer is used to couple the output, the power of each single-phase transformer is 1/^ of the output power of the low-voltage inverter circuit. A total of 6 transformers are required. If two three-phase transformers are used to couple the output, the power of each transformer. Both are equal to the output power of the low-voltage inverter circuit; 实现 implemented with a three-phase transformer, which can reduce the total power of the coupling transformer.

The low-voltage inverter output shown in Figure 3B is not unique by transformer-coupled series combination. Figure 3B is just a series connection.

Assume that the number of low-voltage inverter circuits used is M. If all three-phase transformers are used for coupling isolation, the number of three-phase transformers is at least Ceil (2M/3) -1; here, the Ceil ( ) is a ceiling function, which means that the real number is rounded up, such as Ceil(3.1)=4, Ceil(3.9)=4. In Fig. 3B, if the number of low-voltage inverter circuits is M=4, the number of three-phase transformers is required to be at least two, as shown in Fig. 3C. Increasing the number of transformers can also achieve series output, but it is not economical.

As another embodiment. FIG. 4A provides a scheme for realizing three-phase high-voltage inverter by connecting nine output of three low-voltage three-phase inverter circuits through nine single-phase transformers, and FIG. 4B is a schematic diagram of a series connection mode of output voltages of the corresponding low-voltage inverter circuits. The above nine single-phase output transformers can also be replaced by three three-phase transformers, and an implementation is shown in Figure 4C. The comparison of the output-coupling series high-voltage inverter scheme of the six three-phase low-voltage inverter circuits of FIG. 4A and the four three-phase low-voltage inverter circuits shown in FIG. 3A has the following differences:

1) 6 DC voltages that are electrically isolated from each other are required as inputs to the respective low voltage inverter circuits;

2) There are 6 three-phase low-voltage inverter circuits, which are integer multiples of 3. All low-voltage inverter circuits have partial output voltage directly connected to the output voltage of the high-voltage inverter circuit; 3 three-phase low-voltage inverter circuits 2A, 2B, 2C, respectively, two output phases are directly connected in series to the corresponding high-voltage phase output, and the other three three-phase low-voltage inverter circuits 2D, 2E, 2F have one output phase directly connected in series to the corresponding high-voltage phase output, and other outputs. The phase is respectively coupled to the corresponding high voltage phase output through the transformer coupling; 3) the AC PWM carrier phase of the three-phase low voltage inverter circuit is sequentially different by 60° (ie 360° 16 );

4) The output voltage of the high-voltage inverter circuit is 6 times that of the low-voltage inverter circuit, and the number of levels can be as high as 13 5) The number of output-coupled three-phase transformers is 3.

Other aspects are the same as in the case of four three-phase low-voltage inverter circuits or are easily derived from the case of four low-voltage inverter circuits.

The multi-phase low-voltage inverter output of the invention is connected to the high-voltage inverter method by transformer coupling in series, and can be applied to the high-voltage converter to realize the "AC-AC" conversion of the three-phase high-voltage alternating current, so as to be applied to the AC motor speed regulation. And other fields.

To this end, the present invention also provides a three-phase high voltage power converter, please refer to FIG. 5A, the high voltage power converter as shown, including phase shifting main transformer 1, six (N=2) three-phase low voltage transform 2A ~ 2F, three three-phase coupled output transformers 3A ~ 3C and main controller 4.

The phase shifting main transformer 1 is a three-phase multi-side winding transformer. The primary winding 11 terminal is used as the input of the high-voltage converter, and is connected to the three-phase high-voltage power grid 6. The secondary winding includes six 12A to 12F, and the six outputs are electrically isolated from each other. The voltages are equal, and the three-phase outputs of each channel (such as 12A) are symmetrical; for each three-phase low-voltage converter (such as 2A), there is a secondary winding (such as 12A) connected to it. There is a phase difference between the secondary windings (12A ~ 12F), and the phases are 10° out of phase (ie 60 / 6 = 10).

5B is a schematic circuit diagram of the above three-phase low-voltage converter, each three-phase low-voltage converter (such as 2A) includes a three-phase uncontrolled rectifier bridge 21, a DC filter circuit 22, a three-phase full-control inverter bridge 23, and a control drive. Circuit 24. The AC sides a, b, c of the three-phase rectifier bridge 21 serve as inputs to the low-voltage converter, and connect a three-phase secondary winding (such as 12A) of the phase-shifted main transformer 1, and its DC side p, n and DC filter circuit 22, The DC side of the three-phase inverter bridge 23 is connected, and the AC sides u, v, w of the three-phase inverter bridge 23 serve as outputs of the low voltage converter (e.g., 2A). The control driving circuit 24 is connected to the main controller 4 through the optical fiber, receives the PWM signal from the main controller 4, controls the solid state power switches 231 to 236 of the three-phase inverter bridge 23, and operates the operation information of the low voltage converter (such as 2A). Send to the main controller 4.

The high-voltage converter has 6 three-phase low-voltage converters 2A ~ 2F, and the wiring diagram of the corresponding three-phase output transformer is the same as Figure 4C. The output of the low-voltage converter (eg 2A) is connected to the winding of the high-voltage converter 5 or the three-phase coupling transformer (eg 3A, 3B, 3C). Taking FIG. 5A as an example, the low-voltage converters 2A, 2B, and 2C each have one output terminal ul, v2, and w3 connected to one terminal of the load, and the other two output terminals are respectively connected to the primary winding of the three-phase output transformer 3A. And the secondary windings of the 3B, 3C; and the output terminals of the low voltage converters 2D, 2E, 2F are respectively connected to the primary winding and the secondary winding of the output transformers 3B, 3C. All six windings of the three three-phase output transformers 3A, 3B, and 3C have the same number of turns, and the three secondary windings are independent leads; the secondary windings of the output transformer (such as vl-u4 of 3B) are respectively connected to the high voltage converter. Corresponding phase (UV) output. Of course, there are other connections between the three-phase coupled output transformers 3A, 3B, 3C and the low-voltage converters 2A-2F, and only such connections are given here as an example.

For the connection mode of the above-mentioned coupled output transformer, the voltage synthesis relationship diagram is the same as that of Fig. 4B, and the three-phase line voltage output of the high voltage converter is:

VuV=Vuvi+VuV2+VuV3+VuV4+VuV5+VuV6

Vvw- vw 1 + vW2+ yW3 +VvW4+ vW5 + yW6

Where: V _uv is the line voltage between the 11 and V phases of the high voltage converter, and V _UV1 ~ V _UV6 are the line voltages between the 11 and V phases of the low voltage inverter 2 8~2, respectively; other U _w , U _{wu is} similar and will not be described again.

The solid-state switches 231 ~ 236 of the inverter bridge 23 of the low-voltage converter (such as 2A) are controlled by PWM signals, and the reference signals of the PWM signals corresponding to the solid-state switches (such as 231) of the low-voltage converters are the same, and the carrier frequencies are the same. There is a phase difference. For the six low-voltage converters outputted in series with the high-voltage converter shown in Figure 5A, the PWM carrier phases are sequentially different by 60° (N=2, 120° /2=60°).釆 With the above modulation combination, the low-frequency components of the output voltage of each low-voltage converter are the same, and the voltage pulses are shifted from each other. Combined with the previous voltage synthesis formula, it can be concluded that six low-voltage converters are connected in series through a transformer, and the output voltage of the high-voltage converter is equal to six times the output voltage of the low-voltage converter. In addition, the line voltages of different low-voltage converters can only be changed sequentially, so that the high-voltage converter can be multi-level output, thereby limiting the rate of change of the output voltage.

Figure 5C shows the output voltage synthesis waveform between the U and V phases of the six-stage low-voltage converter coupled-output high-voltage converter, where RefU and RefV are the U and V phases of the inverter bridge of the low-voltage converter, respectively.

PWM reference wave, CI C6 is the PWM carrier of the low-voltage converter 2A, ... 2F inverter bridge (phase difference is 60°), Vuvi V _UV6 is the line between the 11 and V phases of the low-voltage converter 2A 2F Voltage, V _uv is the line voltage between the 11 and V phases of the high voltage converter. As can be seen from Figure 5C, the output line voltage potential of the high voltage converter can be as many as 13.

Main transformer secondary winding 12A corresponding to each low voltage converter 2A, 2B 2F

The voltage phases between 12F are sequentially different by 10. , not only can make each three-phase low-voltage converter (2A

The DC bus voltage ripple of 2F) cancels each other, thereby reducing the influence of the DC ripple voltage of the low-voltage converter on the output voltage of the high-voltage converter, and also causing the main transformer 1 caused by the low-voltage converter (2A, 2B, ..., 2F) The phase of the primary current is shifted by 10° in sequence, which can improve the input current characteristics of the high-voltage inverter. Figure 5D is a waveform diagram of the A-phase input current of the high-voltage converter of the output-coupled series of the six-stage low-voltage converter, wherein I _A1 , ... I _A6 are the low-voltage converters 2 A, 2B, ..., respectively. The primary current component of phase A of the main transformer caused by 2F, I _A is the total primary phase current of phase A. Obviously, the harmonic current of I _A is significantly lower than that of the primary current component (such as I _A1 ) caused by each low voltage converter.

The output of nine 660V three-phase low-voltage converters is coupled in series by five three-phase transformers to achieve a high-voltage converter of 6KV voltage level. Figure 6A shows the main circuit of a nine-phase low-voltage converter coupled high-voltage converter. Figure 6B shows the external wiring diagram of the corresponding three-phase output transformer, and Figure 6C shows the output coupling series diagram of the high-voltage converter. In this case, since the number of secondary windings of the phase-shifted main transformer is large, the phase shifting method can be taken, for example: nine three-phase secondary windings are divided into three groups (L=3), three of each group The output voltages of the secondary windings (such as 12A, 12B, and 12C) have the same phase, and the output voltages of the secondary windings of each group are in phase difference of 20° (60 / /3). The inverter PWM carrier phases of the respective low voltage converters are sequentially shifted by 40. (N=3, 120° /3).耦合 With the coupling scheme of the nine low-voltage converters, the power of each three-phase output transformer is roughly 1/9 of that of the main transformer, and the total power of the five output transformers is only 5/9 of the main transformer, as described in Figure 2. Compared to the two-stage nested coupled output scheme of the low-voltage converter, the total output transformer capacity is reduced by 1/6.

The above is only the preferred embodiment of the present invention and is not intended to limit the scope of the present invention.

Claims

Claim

A method for realizing high voltage inversion using a low voltage inverter, characterized in that the method comprises the following steps:

A. The inputs of the M three-phase low-voltage inverter circuits are set as DC voltages that are electrically isolated from each other; B. The three-phase output voltages of the respective low-voltage inverter circuits are directly connected in series or through a single-phase transformer to the corresponding phase, Obtaining a three-phase high-voltage AC output; the output ends of the low-voltage inverter circuits are connected by a winding of a single-phase transformer;

360. /M; where M is a natural number greater than or equal to 3.

2. The method for realizing high voltage inversion using low voltage inverter according to claim 1, wherein the three-phase high voltage current output is obtained in step B, specifically:

3. The method for realizing high voltage inversion using low voltage inverter according to claim 1, wherein said single phase transformer has the same structure and will respectively belong to three said single outputs of different output phases. The phase transformers are combined into a three-phase transformer. If all three-phase transformers are used for coupling isolation, at least Ceil (2M/3) minus one three-phase transformer is required; where M is a natural number greater than or equal to 3, Ceil( ) is a ceiling function, which means that the real number is rounded up.

4. A circuit for implementing high voltage inverter using low voltage inverter, wherein the circuit comprises: M three-phase low voltage inverter circuits, Ceil (2M/3) minus one three-phase transformer; The input voltage of the phase low voltage inverter circuit is DC and is electrically isolated from each other; the M three-phase low voltage inverter circuits are divided into three groups at most:

If M is not an integer multiple of 3, the low voltage inverter circuit also has a second group including MOD (M, 3) low voltage inverter circuits, and the MOD (M, 3) represents the remainder of M divided by 3; The three-phase outputs of the respective low-voltage inverter circuits are respectively coupled to the corresponding phase outputs of the high-voltage inverter circuit after being coupled and isolated by the three-phase transformer;

5. The circuit for implementing high voltage inverter using low voltage inverter according to claim 4, wherein the M three-phase low voltage inverter circuits have the same structure; each three-phase low voltage inverter circuit is respectively connected The PWM method is used to invert the output DC voltage into a three-phase symmetric PWM AC output voltage, and each of the three-phase low-voltage inverter circuits corresponds to an output AC PWM voltage reference wave.

6. The circuit for implementing high voltage inverter using low voltage inverter according to claim 4, characterized in that all of the three-phase transformers have the same number of winding turns.

7. A high voltage converter, comprising: a main transformer, 3N three-phase low voltage converters, 2N-1 three-phase output transformers and a main controller; the phase shifting main transformer is a three-phase multiple The edge winding transformer has a primary winding connected to the three-phase high-voltage power grid, and the secondary winding includes 3N paths electrically isolated from each other and having the same output voltage, each of which is a symmetric three-phase output, and each of the three-phase low-voltage converters has a secondary side The winding is connected thereto; the output of the low voltage converter is respectively connected to the load of the high voltage converter or the winding of the three-phase coupling transformer; each low voltage converter is respectively connected to the main controller; wherein, Ν is a natural number.

The high-voltage converter according to claim 7, wherein the main transformer is a three-phase phase-shifting transformer, and a phase difference of 20/Ν between the secondary windings of each of the paths; or

The high voltage converter according to claim 7, wherein the low voltage converter comprises a three-phase uncontrolled rectifier bridge (21), a DC filter circuit (22), and a three-phase full-control inverter bridge (23). And a control driving circuit (24); wherein, the AC side & b, c terminals of the three-phase rectifier bridge (21) serve as an input of the low voltage converter, and connect a three-phase secondary winding of the phase shifting main transformer, the DC side thereof, The n-side is connected to the DC filter circuit (22) and the DC side of the three-phase full-control inverter bridge (23), and the AC side u, v, w terminals of the three-phase full-control inverter bridge (23) are used as the low-voltage converter The output of the control drive circuit (24) is connected to the main controller through the optical fiber, receives the PWM signal from the main controller, and controls the solid state power switch (231 ~ 236) of the three-phase full control inverter bridge (23), and The operation information of the low voltage converter is sent to the main controller.

10. The high voltage converter according to claim 7, wherein each of the three phase inputs The six winding turns of the transformer are the same; the primary windings of the three-phase output transformer are connected to the two output ends of the same low-voltage converter; the secondary windings of the three-phase output transformer are respectively connected to the corresponding phase outputs of the high-voltage converter.

The high voltage converter according to claim 8 or 9, wherein the reference of the inverter control PWM signal corresponding to the solid state switch in the three-phase full-control inverter bridge (23) of each three-phase low-voltage converter The waves are the same, the carrier shapes are the same and the phases are different by 120/N degrees, where N is a natural number.