Asymmetric non-isolated buck converter, single-phase to two-phase converter and single-phase to three-phase converter

Abstract

The invention discloses an asymmetric non-isolated buck converter, a single-phase to two-phase converter and a single-phase to three-phase converter, and belongs to the technical field of converters, the asymmetric non-isolated buck converter comprises a cascaded buck unit and a non-isolated unit, the buck unit comprises one or more cascaded buck modules, each buck module comprises a first rectifier, and the output end of the first rectifier is vacant; the non-isolation unit comprises one or more cascaded non-isolation conversion modules. According to the invention, a traditional transformer structure with large volume and heavy weight is completely cancelled, and the number of devices is reduced while the power density of the converter is improved; and voltage reduction is carried out through the no-load voltage reduction unit, so that the voltage reduction capability is higher, and the input and output phase shift angle range can be expanded to a certain extent.

Description

Technical Field

[0001] The present invention relates to the technical field of converters, and in particular to an asymmetric non-isolated buck converter, a single-phase-two-phase converter and a single-phase-three-phase converter. Background Art

[0002] High-power transformers have been widely used in power conversion fields such as AC / DC hybrid distribution networks, electric locomotive traction, and industrial special power supplies. Currently, common transformers in high-voltage and high-power application scenarios are mainly divided into general transformers and power electronic transformers that realize energy transfer through power electronic devices:

[0003] (1) General transformer structure such as Figure 1 As shown, it utilizes winding to generate a magnetic field and uses a magnetic core material to conduct magnetism to transfer energy, and achieves voltage increase or decrease by changing the number of turns of the winding.

[0004] (2) Buck converter based on multi-winding transformer such as Figure 2 As shown, it consists of a multi-winding power frequency transformer, a front-stage rectifier, and a rear-stage inverter. The output voltage is matched with the load voltage amplitude by adjusting the transformer turns ratio, and the frequency and phase of the inverter output voltage can also be controlled.

[0005] (3) Traditional isolated power electronic transformers such as Figure 3 As shown, the DC voltage generated by the front-stage rectifier can be raised or lowered through the medium and high frequency transformer of the isolated DC-DC, and then AC power is generated through the control of the inverter stage, thereby achieving the matching of the input AC voltage amplitude with the voltage amplitude, frequency and phase required by the load.

[0006] The above transformer has the following technical features:

[0007] For example Figure 1 The power frequency transformer shown has a simple design and high reliability. It can match the input and output AC voltage amplitudes by adjusting the transformation ratio. However, it is large in size, has serious loss and heat generation problems, and the power frequency transformer cannot adjust the frequency and phase. Therefore, it is difficult to adapt to the actual needs of various working conditions.

[0008] For example Figure 2 The step-down converter with a multi-winding transformer shown is simple to manufacture and has low cost, but requires the addition of a larger power frequency transformer and is not suitable for occasions requiring lightweighting.

[0009] For example Figure 3 The power electronic transformer shown has many advantages such as a wide voltage regulation range and arbitrary phase shifting, but its structure is complex and uses a large number of switching devices. It still has the disadvantages of large size, severe power dissipation and heat generation. Summary of the invention

[0010] The object of the present invention is to overcome the problems of the prior art and to provide an asymmetric non-isolated buck converter, a single-phase to two-phase converter and a single-phase to three-phase converter.

[0011] The objective of the present invention is achieved through the following technical scheme: an asymmetric non-isolated buck converter, comprising a cascaded buck unit and a non-isolated unit, the buck unit comprising one or more cascaded buck modules, the buck module comprising a first rectifier, and the output end of the first rectifier is vacant; the non-isolated unit comprises one or more cascaded non-isolated modules, the non-isolated module comprises a second rectifier and an inverter cascaded in sequence, the first rectifier and the second rectifier are cascaded on the input side, and the inverter is cascaded on the output side.

[0012] In one example, a first capacitor is connected in parallel to the output end of the first rectifier, and the positive and negative ends of the first capacitor are left vacant.

[0013] In one example, a second capacitor is connected in parallel between the second rectifier and the inverter.

[0014] In one example, the first rectifier, the second rectifier, and the inverter are all full-bridge circuits.

[0015] In one example, the first rectifier and the second rectifier are full-bridge circuits, and the inverter is a half-bridge circuit.

[0016] In one example, the upper and lower bridge arms of the two bridge arms in the full-bridge circuit each include a switching device, and the upper and lower bridge arms of the half-bridge circuit each include a switching device, forming a two-level full-bridge half-bridge converter.

[0017] In one example, the upper and lower bridge arms of the two bridge arms in the full-bridge circuit each include two switching devices, and the upper and lower bridge arms of the half-bridge circuit each include two switching devices, forming a three-level full-bridge half-bridge converter.

[0018] The present invention also includes a single-phase to two-phase converter, comprising two cascaded asymmetric non-isolated buck converters formed by any of the above-mentioned example compositions or replacement combinations, wherein one phase voltage is drawn from each asymmetric non-isolated buck converter to form a single-phase to two-phase converter.

[0019] The present invention also includes a single-phase to three-phase converter, comprising three cascaded asymmetric non-isolated buck converters formed by any of the above-mentioned example compositions or replacement combinations, wherein one phase voltage is drawn from each asymmetric non-isolated buck converter to form a single-phase to three-phase converter.

[0020] It should be further explained that the technical features corresponding to the above examples can be combined or replaced with each other to form a new technical solution.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention completely eliminates the traditional transformer structure with large volume and heavy weight, improves the power density of the converter and reduces the number of devices; at the same time, compared with the traditional non-isolated power electronic transformer, the present invention has a stronger step-down capability by stepping down the voltage with an unloaded step-down unit, and can expand the phase shift angle range of the input and output to a certain extent; further, the second rectifier and inverter cascaded in the non-isolated module can convert the DC power supply into AC power supply to supply the external load. When the external AC power supply needs to be converted back to DC power supply, the inverter can work in the rectification mode, that is, the converter topology of the present invention can work in four quadrants, realize bidirectional transmission of active and reactive power, and can also control the input and output, shift the phase (by controlling the switching state of the switching devices in the rectifier and inverter), and other operations.

[0023] 2. When the input and output of the converter of the present invention are both full-bridge, the step-down ratios of 9:2, 18:2 and 27:2 can be achieved; the converter input is full-bridge and the output is half-bridge, which combines the characteristics of full-bridge and half-bridge converters to meet specific power conversion requirements, thereby achieving a larger step-down ratio at a lower cost. For example, when the output is 1 motor, the step-down ratio of 9:1 meets the power supply requirements of mines, and when the output is 2 motors, the step-down ratio of 18:1 meets the application requirements of vehicle-mounted traction converters. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The specific implementation methods of the present invention are further described in detail below in conjunction with the accompanying drawings. The accompanying drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The same reference numerals are used in these drawings to represent the same or similar parts. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0025] Figure 1 It is a schematic diagram of an existing power frequency transformer;

[0026] Figure 2 It is a schematic diagram of an existing input multi-winding power electronic transformer;

[0027] Figure 3 It is a schematic diagram of an existing power electronic transformer;

[0028] Figure 4 A schematic diagram of an asymmetric non-isolated buck converter provided as an example of the present invention;

[0029] Figure 5 A schematic diagram of a converter with a step-down module and two non-isolated modules provided as an example of the present invention;

[0030] Figure 6A structural diagram of a two-level full-bridge and half-bridge circuit provided for an example of the present invention;

[0031] Figure 7 A structural diagram of a three-level full-bridge and half-bridge circuit provided for an example of the present invention;

[0032] Figure 8 A schematic diagram of a single-phase to three-phase converter provided as an example of the present invention. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] In the description of the present invention, ordinal numbers (eg, “first and second,” “first to fourth,” etc.) are used to distinguish objects and are not limited to the order and should not be understood as indicating or implying relative importance.

[0035] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0036] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] In one example, an asymmetric non-isolated buck converter, the input and output ends of which are respectively connected to the high-voltage side and the low-voltage side, includes a cascaded buck unit and a non-isolated unit, which may be a sequentially cascaded buck unit and a non-isolated unit, or a sequentially cascaded non-isolated unit and a buck unit, or a sequentially cascaded buck unit, a non-isolated unit and a buck unit. Among them, the buck unit includes one or more cascaded buck modules, the buck module includes a first rectifier, the output end of the first rectifier is vacant, forming a buck module with no load; when the buck unit includes multiple buck modules, multiple first rectifiers are cascaded on the input side. The non-isolated unit includes one or more cascaded non-isolated modules, the non-isolated module includes a sequentially cascaded second rectifier and an inverter; when the non-isolated unit includes multiple non-isolated modules, multiple second rectifiers are cascaded on the input side, and multiple inverters are cascaded on the output side. The buck unit is cascaded with the non-isolated unit, that is, the first rectifier and the second rectifier are cascaded on the input side, and the inverter is cascaded on the output side. Preferably, a first capacitor is connected in parallel to the output end of the first rectifier, and the positive and negative ends of the first capacitor are left vacant. Preferably, a second capacitor is connected in parallel between the second rectifier and the inverter. The first rectifier and the second rectifier are both single-phase single-module rectifiers, which are full-bridge circuits or half-bridge circuits formed by switching devices; the inverter is a single-phase inverter submodule, which is a full-bridge circuit or half-bridge circuit formed by switching devices. According to different voltage level requirements and switching device selections, a certain no-load module can be added on the high-voltage side to bear the DC side voltage drop. Conversely, when the external AC power supply needs to be converted back to a DC power supply, the converter topology of the present invention can also achieve the function of boosting.

[0038] Furthermore, the asymmetric non-isolated buck converter of the present invention comprises a cascaded buck unit and a non-isolated unit, the buck unit comprises a plurality of cascaded buck modules, and the non-isolated unit comprises a plurality of cascaded non-isolated modules. The specific topological connection form is as follows: Figure 4 As shown, the positive end of the input single-phase electricity is connected to the positive end of the input of the first step-down module of the power electronic transformer through the reactor, the negative end of the input of the first step-down module is connected to the positive end of the input of the second step-down module, and so on, the negative end of the input of the last step-down module is connected to the positive end of the input of the first non-isolated module, the negative end of the input of the first non-isolated module is connected to the positive end of the input of the second non-isolated module, and then connected to the last non-isolated module in sequence. The positive end of the output single-phase electricity is connected to the positive end of the output of the first non-isolated module of the power electronic transformer, the negative end of the output of the first non-isolated module is connected to the positive end of the output of the second non-isolated module, the negative end of the output of the second non-isolated module is connected to the positive end of the output of the third non-isolated module, and then connected to the last non-isolated module in sequence.

[0039] Among them, the DC capacitors on some modules on the high-voltage side are not connected to the load (the capacitors on the output side of the step-down module are not connected to the load to form an unloaded module), and other non-isolated modules have the same structure as traditional non-isolated power electronic transformers. The DC side parts of the rectifier and inverter are connected to the positive and negative poles of the same capacitor. The positive and negative poles of the capacitor connected to the first non-isolated module on the high-voltage side are respectively connected to the positive and negative poles on the DC side of the rear-stage inverter in the first non-isolated module, and the positive and negative poles of the capacitor connected to the second non-isolated module on the high-voltage side are respectively connected to the positive and negative poles on the DC side of the rear-stage inverter in the second non-isolated module, and so on. The positive and negative poles of the capacitor connected to the last non-isolated module on the high-voltage side are respectively connected to the positive and negative poles on the DC side of the rear-stage inverter on the last non-isolated module.

[0040] Furthermore, the cascade converter allows 1 / 3 of the modules to be unloaded, so the ratio of the number of unloaded modules to loaded modules of the converter of the present invention is 1:2, that is, the ratio of the number of buck modules to non-isolated modules is 1:2. Figure 5 As shown, the power electronic transformer of the present invention can be formed by one step-down module (one no-load) and two non-isolated modules (two loaded).

[0041] In one example, the first rectifier, the second rectifier, and the inverter are all full-bridge circuits, that is, the first rectifier, the second rectifier, and the inverter all include two bridge arms: a first bridge arm and a second bridge arm, and the upper and lower bridge arms of the first bridge arm and the second bridge arm are each provided with a switch device or multiple series switch devices. When the input and output are all full-bridge, a step-down ratio of 9:2, 18:2, and 27:2 can be achieved.

[0042] In one example, the first rectifier and the second rectifier are full-bridge circuits, and the inverter is a half-bridge circuit. The first rectifier and the second rectifier each include two bridge arms: a first bridge arm and a second bridge arm, and the upper and lower bridge arms of the first bridge arm and the second bridge arm are each provided with a switch device, and the inverter includes only one bridge arm, and the upper and lower bridge arms are provided with a switch device. Further, if Figure 5-6As shown, at this time, the converter includes a buck module and two non-isolated modules, the two non-isolated modules are a first non-isolated module and a second non-isolated module connected in cascade, the first rectifier in the buck module is a first full-bridge circuit, the second rectifier in the first non-isolated module is a second full-bridge circuit, the second rectifier in the second non-isolated module is a third full-bridge circuit, the inverter in the first non-isolated module is a first half-bridge circuit, and the inverter in the second non-isolated module is a second half-bridge circuit. The upper and lower bridge arms of the first bridge arm and the second bridge arm in the first full-bridge circuit, the second full-bridge circuit, and the third full-bridge circuit each include a switching device, and the upper and lower bridge arms of the half-bridge circuit each include a switching device, forming a two-level full-bridge and half-bridge converter (high level, low level). At this time, the midpoint (common connection point) between the two switching devices in the first bridge arm of the first full-bridge circuit is connected to the AC power supply, the common connection point of the second bridge arm in the first full-bridge circuit is connected to the common connection point of the first bridge arm in the second full-bridge circuit, the common connection point of the second bridge arm in the second full-bridge circuit is connected to the common connection point of the first bridge arm in the third full-bridge circuit, and the common connection point of the second bridge arm in the third full-bridge circuit is connected to the AC power supply. Two series capacitors are connected in parallel at both ends of the second bridge arm in the first full-bridge circuit to achieve step-down output. Further, the second full-bridge circuit is cascade-connected to the first half-bridge circuit, and two series capacitors are connected in parallel between the second full-bridge circuit and the first half-bridge circuit, and the midpoints of the two series capacitors are connected to the common connection point of the second half-bridge circuit; the third full-bridge circuit is cascade-connected to the second half-bridge circuit, and two series capacitors are connected in parallel between the third full-bridge circuit and the second half-bridge circuit. At this time, the output positive and negative ends of the single-phase voltage are respectively drawn from the common connection point of the first half-bridge circuit and the two series capacitors connected in parallel between the third full-bridge circuit and the second half-bridge circuit.

[0043] In one example, the upper and lower bridge arms of the two bridge arms in the full-bridge circuit each include two switching devices, and the upper and lower bridge arms of the half-bridge circuit each include two switching devices, forming a three-level full-bridge half-bridge converter. Figure 5 , Figure 7As shown, at this time, the converter includes a buck module and two non-isolated modules, the two non-isolated modules are the first non-isolated module and the second non-isolated module connected in cascade, the first rectifier in the buck module is the first full-bridge circuit, the second rectifier in the first non-isolated module is the second full-bridge circuit, the second rectifier in the second non-isolated module is the third full-bridge circuit, the inverter in the first non-isolated module is the first half-bridge circuit, and the inverter in the second non-isolated module is the second half-bridge circuit. The upper and lower bridge arms of the first bridge arm and the second bridge arm in the first full-bridge circuit, the second full-bridge circuit, and the third full-bridge circuit each include two series switching devices, and the upper and lower bridge arms of the half-bridge circuit each include two series switching devices, forming a three-level full-bridge half-bridge converter (high level, low level, neutral level). Preferably, at this time, in the three full-bridge circuits and the two half-bridge circuits, the two switching devices of the upper bridge arm and the two switching devices of the lower bridge arm are connected through two series diodes, the midpoints between the two series diodes of the two bridge arms in the buck module are connected to each other, and the midpoints between the two series diodes of the three bridge arms in the non-isolated module are connected to each other. At this time, the midpoint (common connection point) between the four switch devices in the first bridge arm of the first full-bridge circuit is connected to the AC power supply, the common connection point of the second bridge arm in the first full-bridge circuit is connected to the common connection point of the first bridge arm in the second full-bridge circuit, the common connection point of the second bridge arm in the second full-bridge circuit is connected to the common connection point of the first bridge arm in the third full-bridge circuit, and the common connection point of the second bridge arm in the third full-bridge circuit is connected to the AC power supply. Two series capacitors are connected in parallel at both ends of the second bridge arm in the first full-bridge circuit, and the midpoints of the two series capacitors are connected to the midpoints of the diodes corresponding to the two bridge arms in the buck module, so as to achieve buck output. Furthermore, the second full-bridge circuit is connected in cascade with the first half-bridge circuit, and two series capacitors are connected in parallel between the second full-bridge circuit and the first half-bridge circuit, and the midpoints of the two series capacitors are connected to the midpoints of the diodes corresponding to the three bridge arms in the first non-isolated module; the third full-bridge circuit is connected in cascade with the second half-bridge circuit, and two series capacitors are connected in parallel between the third full-bridge circuit and the second half-bridge circuit, and the midpoints of the two series capacitors are connected to the midpoints of the diodes corresponding to the three bridge arms in the second non-isolated module. At this time, the output positive and negative ends of the single-phase voltage are respectively drawn from the common connection point of the first half-bridge circuit and the two series capacitors connected in parallel between the third full-bridge circuit and the second half-bridge circuit.

[0044] The present invention also includes a single-phase-to-two-phase converter, comprising two cascaded asymmetric non-isolated buck converters formed by any one or more of the above examples or a replacement combination, wherein one phase voltage is respectively drawn from the non-isolated unit in each asymmetric non-isolated buck converter to form a single-phase-to-two-phase converter to adapt to different power supply demand scenarios.

[0045] The present invention also includes a single-phase to three-phase converter, such as Figure 8As shown, three cascaded asymmetric non-isolated buck converters are formed by any one of the above examples or multiple examples or a replacement combination, and one phase voltage is respectively drawn from the non-isolated unit in each asymmetric non-isolated buck converter to form a single-phase-three-phase converter to adapt to different power supply demand scenarios.

[0046] The above specific implementation methods are detailed descriptions of the present invention. It cannot be determined that the specific implementation methods of the present invention are limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions and substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. An asymmetric non-isolated buck converter, It is characterized in that It includes a cascaded buck unit and a non-isolated unit, the buck unit includes one or more cascaded buck modules, the buck module includes a first rectifier, and the output end of the first rectifier is vacant; the non-isolated unit includes one or more cascaded non-isolated modules, and the non-isolated module includes a second rectifier and an inverter cascaded in sequence.

2. The asymmetric non-isolated buck converter according to claim 1, It is characterized in that A first capacitor is connected in parallel to the output end of the first rectifier, and the positive and negative ends of the first capacitor are left vacant.

3. The asymmetric non-isolated buck converter according to claim 1, It is characterized in that A second capacitor is connected in parallel between the second rectifier and the inverter.

4. The asymmetric non-isolated buck converter according to claim 1, It is characterized in that The first rectifier, the second rectifier and the inverter are all full-bridge circuits.

5. The asymmetric non-isolated buck converter according to claim 1, It is characterized in that The first rectifier and the second rectifier are full-bridge circuits, and the inverter is a half-bridge circuit.

6. The asymmetric non-isolated buck converter according to claim 5, It is characterized in that The upper and lower bridge arms of the two bridge arms in the full-bridge circuit each include a switch device, and the upper and lower bridge arms of the half-bridge circuit each include a switch device, forming a two-level full-bridge half-bridge converter.

7. The asymmetric non-isolated buck converter according to claim 5, It is characterized in that The upper and lower bridge arms of the two bridge arms in the full-bridge circuit each include two switch devices, and the upper and lower bridge arms of the half-bridge circuit each include two switch devices, forming a three-level full-bridge half-bridge converter.

8. A single-phase to two-phase converter, It is characterized in that The asymmetric non-isolated buck converter according to any one of claims 1 to 7 is comprised of two cascaded ones, wherein one phase voltage is drawn from each asymmetric non-isolated buck converter to form a single-phase to two-phase converter.

9. A single-phase to three-phase converter, It is characterized in that The invention comprises three cascaded asymmetric non-isolated buck converters as claimed in any one of claims 1 to 7, wherein one phase voltage is respectively drawn from each asymmetric non-isolated buck converter to form a single-phase to three-phase converter.

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