Direct-current converter suitable for multi-voltage-level bipolar direct-current distribution network and electrical equipment
By combined with the voltage balancer and three -level DC converter, the problem of uneven voltage of the point capacitor in the traditional three -level DC converter was solved, and the multi -voltage level output and system reliability were realized.
Patent Information
- Application Number
- CN202411424199.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-12
- Publication Date
- 2025-01-21
AI Technical Summary
When the input or output series capacitor is uneven, the traditional three-level DC converter causes the voltage stress of the switching device and the capacitor to increase, the output voltage and current waveform distortion, and the three-level working state of the power device cannot be achieved.
The DC converter structure including voltage balance and three -level DC converter is adopted. The voltage balance converts the voltage on the DC bus into two voltages and outputs it to the three levels of DC transformers. The latter converts it to preset Positive voltage and preset negative voltage form three voltage level outputs.
The voltage balancer overcomes the problem of uneven voltage balancing of the midpoint capacitor of the traditional three-level DC converter, realizes multi-voltage output, supports bus access of different voltage levels, and avoids the problem of voltage balancing of the midpoint capacitor of the three-level circuit output. , improving the reliability of the system.
Smart Images
Figure CN119340954A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of direct current converters, and in particular to a direct current converter and electrical equipment suitable for a multi-voltage level bipolar direct current distribution network. Background Art
[0002] The switch stress of the three-level DC converter is half of the input DC voltage. It is widely used in applications with high input voltage and high output power. This topology can not only achieve output of three different voltage levels, but also achieve flexible adjustment of the output voltage.
[0003] However, if the input or output series capacitors of the converter are not voltage-balanced, it will not only increase the voltage stress of the switching devices and capacitors, but also cause the circuit output voltage and current waveforms to be distorted or fail to achieve the three-level working state of the power device. Summary of the invention
[0004] The present invention proposes a DC converter suitable for a multi-voltage level bipolar DC distribution network, the DC converter comprising: a voltage balancer and a three-level DC converter; A voltage balancer, the input end of which is connected to the DC bus, and the first output end and the second output end are connected to the three-level DC converter; The midpoint of the three-level DC converter is connected to the midpoint of the voltage balancer to form a neutral line; The voltage balancer is used to convert the voltage on the DC bus into a first voltage and a second voltage, and output the voltages to the first input terminal and the second input terminal of the three-level DC converter through the first output terminal and the second output terminal respectively; The three-level DC converter is used to convert the first voltage and the second voltage into a preset positive voltage and a preset negative voltage respectively and then output them, thereby forming three voltage level outputs with the neutral line.
[0005] Optionally, the number of the three-level DC converter is multiple; The midpoint of each of the three-level DC converters is connected to the midpoint of the voltage balancer to form a neutral line; The first input end of each of the three-level DC converters is connected to the first output end of the voltage balancer; the second input end of the at least one three-level DC converter is connected to the second output end of the voltage balancer; Each of the three-level DC converters is used to convert the first voltage and the second voltage into corresponding preset positive voltage and preset negative voltage respectively and then output them.
[0006] Optionally, the number of the voltage balancers is multiple; The voltage balancers are connected in parallel; the first output end of each voltage balancer is connected to the first input end of the at least one three-level DC converter; the second input end of each voltage balancer is connected to the second input end of the at least one three-level DC converter; The values of the first voltage and the second voltage output by each of the voltage balancers are respectively the same.
[0007] Optionally, the voltage balancer comprises: A first switching device, a second switching device, a first capacitor, a second capacitor and a first inductor; The first switch device and the second switch device are arranged in series between the positive electrode and the negative electrode of the DC bus; the first capacitor and the second capacitor are arranged in series between the positive electrode and the negative electrode of the DC bus; The first end of the first inductor is connected to the second end of the first switch device and the first end of the second switch device; the second end of the first inductor is connected to the second end of the first capacitor and the first end of the second capacitor.
[0008] Optionally, the three-level DC converter comprises: A first two-level conversion circuit, a first input terminal of which is connected to a first output terminal of the voltage balancer; A second two-level conversion circuit, a first input terminal of which is connected to the second output terminal of the voltage balancer; The second input terminal of the first two-level circuit and the second input terminal of the second two-level circuit are connected to the midpoint of the voltage balancer; The first two-level conversion circuit is used to convert the first voltage into a preset positive voltage and then output it; The second two-level conversion circuit is used for converting the second voltage into a preset negative voltage and then outputting it; The values of the preset positive voltage and the preset negative voltage are opposite to each other.
[0009] Optionally, the first two-level conversion circuit includes: a second inductor, a first switching device, a second switching device and a third capacitor; A first end of the second inductor is connected to a first output end of the voltage balancer, and a second end of the second inductor is connected to a first end of the first switching device and a first end of the second switching device; The second end of the second switch device is connected to the first end of the third capacitor; The second end of the first switch device and the second end of the third capacitor are connected to the midpoint of the voltage balancer; The second two-level conversion circuit comprises: a third inductor, a third switch device, a fourth switch device and a fourth capacitor; A first end of the third inductor is connected to the second output end of the voltage balancer, and a second end of the third inductor is connected to the second end of the third switch device and the second end of the fourth switch device; The second end of the fourth switch device is connected to the second end of the fourth capacitor; A first terminal of the third switch device and a first terminal of the fourth capacitor are connected to a midpoint of the voltage balancer.
[0010] Optionally, the first two-level conversion circuit includes: a fourth inductor, a fifth switch device, a sixth switch device and a fifth capacitor; A first end of the fifth switch device is connected to the first output end of the voltage balancer, and a second end of the fifth switch device is connected to the first end of the sixth switch device and the first end of the fourth inductor; The second end of the sixth switch device is connected to the first end of the fifth capacitor; The second end of the fifth switch device and the second end of the fifth capacitor are connected to the midpoint of the voltage balancer; The second two-level conversion circuit comprises: a fifth inductor, a seventh switch device, an eighth switch device and a sixth capacitor; A first end of the seventh switch device is connected to the second output end of the voltage balancer, and a second end of the seventh switch device is connected to the second end of the eighth switch device and the first end of the fifth inductor; The second end of the fifth inductor is connected to the second end of the sixth capacitor; A first terminal of the eighth switching device and a first terminal of the sixth capacitor are connected to a midpoint of the voltage balancer.
[0011] Optionally, the switching device is a MOS tube or an IGBT tube.
[0012] The present invention also provides an electrical device, which includes the DC transformer suitable for a multi-voltage level bipolar DC distribution network.
[0013] Optionally, the electrical device further includes: A rectifier; the input end of the rectifier is connected to the power grid, and the output end is connected to the input end of the voltage balancer in the DC converter suitable for multi-voltage level bipolar DC distribution network; The rectifier is used to rectify the AC voltage of the power grid and output it to the voltage balancer; Alternatively, the electrical device further comprises: A DC-DC circuit, the input end of which is connected to a DC power supply, and the output end of which is connected to the input end of a voltage balancer in the DC converter suitable for a multi-voltage level bipolar DC distribution network; The DC-DC circuit is used to convert the voltage of the direct current power supply and output it to the voltage balancer.
[0014] The present invention provides a DC converter suitable for a multi-voltage level bipolar DC distribution network, the DC converter comprising: a voltage balancer and a three-level DC converter; the voltage balancer, the input end is connected to the DC bus, the first output end and the second output end are connected to the three-level DC converter; the midpoint of the three-level DC converter is connected to the midpoint of the voltage balancer to form a neutral line; the voltage balancer is used to convert the voltage on the DC bus into a first voltage and a second voltage, and output them to the first input end and the second input end of the three-level DC converter through the first output end and the second output end respectively; the three-level DC converter is used to convert the first voltage and the second voltage into a preset positive voltage and a preset negative voltage respectively, and then output them, so as to form three voltage level outputs with the neutral line. The present invention combines the voltage balancer and the three-level DC converter, and uses the voltage balancer to overcome the disadvantage of uneven voltage of the midpoint capacitor of the traditional three-level DC converter. BRIEF DESCRIPTION OF THE DRAWINGS
[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.
[0016] Figure 1 It is a structural schematic diagram of an embodiment of a DC converter applicable to a multi-voltage level bipolar DC distribution network of the present invention; Figure 2 It is a structural schematic diagram of another embodiment of the DC converter applicable to a multi-voltage level bipolar DC distribution network of the present invention; Figure 3 It is a structural schematic diagram of another embodiment of the DC converter applicable to a multi-voltage level bipolar DC distribution network of the present invention; Figure 4 It is a structural schematic diagram of a voltage balancer of an embodiment of a DC converter applicable to a multi-voltage level bipolar DC distribution network of the present invention; Figure 5 It is a structural schematic diagram of another embodiment of the DC converter applicable to a multi-voltage level bipolar DC distribution network of the present invention; Figure 6 It is a structural schematic diagram of another embodiment of the DC converter applicable to a multi-voltage level bipolar DC distribution network of the present invention; Figure 7 It is a structural schematic diagram of an embodiment of an electrical device of the present invention; Figure 8 It is a schematic structural diagram of another embodiment of the electrical equipment of the present invention.
[0017] Description of Figure Numbers:
[0018] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION
[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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.
[0020] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.
[0021] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" 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 an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.
[0022] In addition, in the present invention, descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.
[0023] DC microgrids have natural advantages over traditional AC distribution networks for renewable energy generation, energy storage devices, and new DC load access. There are two main system architectures for low-voltage DC microgrids: unipolar system and bipolar system. Compared with unipolar systems, DC microgrids with bipolar system architecture can provide positive and negative symmetrical two-level DC bus voltages to meet the access of DC loads and distributed power sources of different voltage levels, and when one of them fails and stops operating, the other can still operate normally, with a high safety redundancy factor. When a bipolar system is connected to an asymmetric load, the voltage of the two-pole bus will be unbalanced. The switch stress of the three-level DC converter is half of the input DC voltage, and it is widely used in applications with high input voltage and high output power. This topology can not only achieve output of three different voltage levels, but also achieve flexible adjustment of the output voltage, but its input or output capacitors are used in series, and usually need to have a voltage balancing function. If the input or output series capacitors of the converter are not voltage-balanced, it will not only increase the voltage stress of the switch devices and capacitors, but also cause the circuit output voltage and current waveforms to be distorted or the power device cannot achieve a three-level working state. Therefore, many scholars have studied the voltage balancing control methods of three-level converters from different perspectives, including feedforward control, zero-sequence voltage control, dual PWM control, differential mode current control, and RLC voltage balancing circuits. However, the above voltage balancing methods are usually only used to solve the voltage balancing problem of equipment or devices, and the voltage balancing control is relatively complex, and is rarely directly applied to bipolar DC distribution networks.
[0024] The present invention provides a DC converter suitable for a multi-voltage level bipolar DC distribution network, aiming to solve the output capacitor voltage balancing problem of a three-level circuit in the prior art.
[0025] Reference Figure 1 As shown, the DC converter suitable for a multi-voltage level bipolar DC distribution network includes: a voltage balancer and a three-level DC converter; A voltage balancer, the input end of which is connected to the DC bus, and the first output end and the second output end are connected to the three-level DC converter; The midpoint of the three-level DC converter is connected to the midpoint of the voltage balancer to form a neutral line; The voltage balancer is used to convert the voltage on the DC bus into a first voltage and a second voltage, and output the voltages to the first input terminal and the second input terminal of the three-level DC converter through the first output terminal and the second output terminal respectively; The three-level DC converter is used to convert the first voltage and the second voltage into a preset positive voltage and a preset negative voltage respectively and then output them, thereby forming three voltage level outputs with the neutral line.
[0026] It should be noted that the voltage balancer is a non-isolated DC conversion device. By introducing a neutral line, a DC power supply system of one voltage level is transformed into two DC power supply systems of equal voltage levels. In addition, the other two DC buses in the output DC bus except the neutral line are shared with the input DC bus. At the same time, the sum of the output voltage must be equal to the input voltage. As an independent power conversion device, the device only processes the power of the unbalanced part of the DC power supply system. It is required that it is not affected by the previous and next stage conversion devices. The topology structure and control method should be simple and easy to implement, so that it can be flexibly and conveniently distributed in occasions where voltage balance is required. In particular, in a distributed DC power supply system, an independent DC voltage balancer device is used at the user end where voltage balance is required. Even if a voltage balancer in the system fails and stops working, it will not affect the normal operation of the entire DC system, thereby improving the flexibility and reliability of the system. From the above content, it can be seen that the voltage balancer can handle the unbalanced power between the two output ends, allowing the voltage at both ends of the subsequent connected circuit to be unbalanced.
[0027] Reference Figure 1 The input end of the voltage balancer is connected to the DC bus, the first output end and the second output end are connected to the three-level DC converter; the midpoint of the three-level DC converter is connected to the midpoint of the voltage balancer to form a neutral line.
[0028] The introduction of a voltage balancer can balance the voltage of the positive and negative buses, but the bus voltage between the poles is fixed and cannot be adjusted. Building a new bus voltage and voltage balancer system will lead to a significant increase in cost. Although the three-level DC converter can achieve voltage regulation and output of three different voltage levels, this type of converter generally has the problem of midpoint capacitor voltage balancing. The present invention combines the two to overcome the shortcomings of traditional three-level DC converters and voltage balancers, and provides a DC converter suitable for multi-voltage level bipolar DC distribution networks.
[0029] The voltage balancer is used to convert the voltage on the DC bus into a first voltage and a second voltage, and output the voltages to the first input terminal and the second input terminal of the three-level DC converter through the first output terminal and the second output terminal respectively; The three-level DC converter is used to convert the first voltage and the second voltage into a preset positive voltage and a preset negative voltage respectively and then output them, thereby forming three voltage level outputs with the neutral line.
[0030] It should be noted that the output end of the three-level DC converter is connected to a load, and the load may cause the midpoint capacitor of the three-level DC converter to have an uneven voltage during operation; that is, the working state of the load affects the output voltage value of the three-level DC converter. In order to maintain the preset positive voltage and the preset negative voltage at the output end of the three-level DC converter, the values of the first voltage and the second voltage output by the voltage balancer may change. Therefore, the first voltage and the second voltage change dynamically. The preset positive voltage and the preset negative voltage are determined by the R&D personnel; the specific electrical components and component parameters in the voltage balancer and the three-level DC converter can be selected according to the determined preset positive voltage and the preset negative voltage.
[0031] The three voltage levels are output as follows: 1) Preset positive voltage and neutral voltage.
[0032] 2) Preset negative voltage and neutral voltage.
[0033] 3) Preset positive voltage and preset negative voltage.
[0034] Among them, the neutral voltage is zero.
[0035] The present invention aims at the problem of single output voltage level of bipolar DC microgrid constructed by voltage balancer, and combines the advantages of adjustable output voltage of three-level DC converter topology (input and output are not grounded), to construct a DC converter suitable for multi-voltage level bipolar DC distribution network; it can not only solve the problem of single output voltage level of voltage balancer, support the access of buses with different voltage levels, but also convert the three-level converter into two independent two-level circuits for control, avoiding the problem of capacitor voltage balancing at the output midpoint of the three-level circuit, and improving the reliability of the system. Compared with the traditional single voltage level voltage balancer, its specific advantages are as follows: 1) Support multi-voltage level bus access.
[0036] 2) It has at least 2 adjustable voltage ports to meet the access requirements of loads of different voltage levels or DC sources.
[0037] 3) The converter control is simple and there is no problem of capacitor midpoint voltage equalization.
[0038] In one embodiment, referring to Figure 1 The input ends of the voltage balancer and the three-level DC converter are respectively connected to the two ends of the V1 DC bus. The midpoint of the voltage balancer and the midpoint of the three-level converter are connected and output to form a neutral line. The positive and negative poles of the balancer input bus and the neutral line constitute two sets of symmetrical bipolar outputs (+V1 / 2, 0) and (0, -V1 / 2). The output positive and negative poles of the three-level DC converter and the neutral line constitute three voltage level outputs (+V2, 0), (0, -V2), and (+V2, -V2).
[0039] The present invention provides a DC converter suitable for a multi-voltage level bipolar DC distribution network, the DC converter comprising: a voltage balancer and a three-level DC converter; the voltage balancer, the input end is connected to the DC bus, the first output end and the second output end are connected to the three-level DC converter; the midpoint of the three-level DC converter is connected to the midpoint of the voltage balancer to form a neutral line; the voltage balancer is used to convert the voltage on the DC bus into a first voltage and a second voltage, and output them to the first input end and the second input end of the three-level DC converter through the first output end and the second output end respectively; the three-level DC converter is used to convert the first voltage and the second voltage into a preset positive voltage and a preset negative voltage respectively, and then output them, so as to form three voltage level outputs with the neutral line. The present invention combines the voltage balancer and the three-level DC converter, and uses the voltage balancer to overcome the disadvantage of uneven voltage of the midpoint capacitor of the traditional three-level DC converter.
[0040] In one embodiment, the number of the three-level DC converters is multiple; The midpoint of each of the three-level DC converters is connected to the midpoint of the voltage balancer to form a neutral line; The first input end of each of the three-level DC converters is connected to the first output end of the voltage balancer; the second input end of the at least one three-level DC converter is connected to the second output end of the voltage balancer; Each of the three-level DC converters is used to convert the first voltage and the second voltage into corresponding preset positive voltage and preset negative voltage respectively and then output them.
[0041] Reference Figure 2 As shown, this embodiment uses a voltage balancer to balance the voltages of multiple three-level DC converters. It should be noted that the voltages output by the voltage balancer to the multiple three-level DC converters are consistent, namely, the first voltage and the second voltage; however, each three-level DC converter has its corresponding preset positive voltage and preset negative voltage; the preset positive voltage and preset negative voltage of different three-level DC converters may be different. Therefore, this embodiment expands multiple ports for the DC converter of the voltage level bipolar DC distribution network by increasing the number of three-level DC converters connected to the output end of the voltage balancer, so that it has more voltage level outputs.
[0042] It is easy to understand that the preset positive voltage and preset negative voltage corresponding to each three-level DC converter are determined by R&D personnel. Specifically, the preset positive voltage and preset negative voltage corresponding to the three-level DC converter connected to the load are determined according to the working voltage and power of the load to be connected.
[0043] It is easy to understand that the processing capacity of a single voltage balancer is limited and may not be able to handle the capacitor unequal voltage problem of multiple three-level DC converters. Figure 3 , in one embodiment, the number of the voltage balancers is multiple; The voltage balancers are connected in parallel; the first output end of each voltage balancer is connected to the first input end of the at least one three-level DC converter; the second input end of each voltage balancer is connected to the second input end of the at least one three-level DC converter; The values of the first voltage and the second voltage output by each of the voltage balancers are respectively the same.
[0044] It should be noted that all DC converters are connected in parallel, that is, the input ends of all DC converters are interconnected and connected to the DC bus, the first output ends are interconnected, and the second output ends are interconnected. The first output end outputs a preset positive voltage of each DC converter, and the second output end outputs a preset negative voltage of each DC converter. This embodiment improves the problem of voltage imbalance of the DC converter suitable for a multi-voltage level bipolar DC distribution network by connecting DC converters in parallel. It is easy to understand that the first output ends of all DC converters are interconnected, and the second output ends are interconnected; in order to avoid current circulation and voltage fluctuations, all DC converters need to output the same voltage value, that is, the value of the first voltage output by each voltage balancer is the same, and the value of the second voltage output is the same.
[0045] Reference Figure 4 , the voltage balancer comprises: A first switch device S1, a second switch device S2, a first capacitor C1, a second capacitor C2 and a first inductor L1; The first switch device S1 and the second switch device S2 are arranged in series between the positive electrode and the negative electrode of the DC bus; the first capacitor C1 and the second capacitor C2 are arranged in series between the positive electrode and the negative electrode of the DC bus; A first end of the first inductor L1 is connected to a second end of the first switch device S1 and a first end of the second switch device S2 ; a second end of the first inductor L1 is connected to a second end of the first capacitor C1 and a first end of the second capacitor C2 .
[0046] Among them, the first switch device S1 and the second switch device S2 are fully controlled switch devices (such as MOSFET or IGBT), which can support bidirectional power flow; the first capacitor C1 and the second capacitor C2 are busbar equalizing capacitors of the voltage balancer, and the first inductor L1 is the filter inductor of the voltage balancer.
[0047] It should be noted that the control signals received by the controlled ends of the first switch device S1 and the second switch device S2 are provided by an external circuit, and the DC converter outputs the first voltage and the second voltage by controlling the on and off of the first switch device S1 and the second switch device S2.
[0048] The three-level DC converter comprises: A first two-level conversion circuit, a first input terminal of which is connected to a first output terminal of the voltage balancer; A second two-level conversion circuit, a first input terminal of which is connected to the second output terminal of the voltage balancer; The second input terminal of the first two-level circuit and the second input terminal of the second two-level circuit are connected to the midpoint of the voltage balancer; The first two-level conversion circuit is used to convert the first voltage into a preset positive voltage and then output it; The second two-level conversion circuit is used for converting the second voltage into a preset negative voltage and then outputting it; The values of the preset positive voltage and the preset negative voltage are opposite to each other.
[0049] It should be noted that since the midpoint of the three-level DC converter is connected to the midpoint of the voltage balancer to form a neutral line, the three-level DC converter can be disassembled into two two-level DC conversion circuits with equal input voltages. The two two-level DC conversion circuits can work independently, and the voltage balancer bears the unbalanced power. Both the two-level DC conversion circuits and the voltage balancer can independently control the output voltage according to the voltage and current double closed-loop mode of the traditional two-level circuit, thereby ensuring that the circuit achieves multi-voltage stable output while avoiding the voltage balancing problem of the output capacitor of the traditional three-level circuit, thereby improving the reliability of the circuit.
[0050] It is easy to understand that the three-level DC converter converts the first voltage and the second voltage into a preset positive voltage and a preset negative voltage respectively and then outputs them; correspondingly, the first two-level conversion circuit converts the first voltage into a preset positive voltage and then outputs it; the second two-level conversion circuit converts the second voltage into a preset negative voltage and then outputs it. It can be determined whether the three-level DC converter outputs the first voltage and the second voltage after boosting or after stepping down the first voltage and the second voltage according to the comparison between the load working voltage and the first voltage and the second voltage output by the voltage balancer.
[0051] In one embodiment, the first two-level conversion circuit includes: A second inductor L2, a third switch device S3, a fourth switch device S4 and a third capacitor C3; A first end of the second inductor L2 is connected to a first output end of the voltage balancer, and a second end thereof is connected to a first end of the third switch device S3 and a first end of the fourth switch device S4; The second end of the fourth switch device S4 is connected to the first end of the third capacitor C3; The second end of the third switch device S3 and the second end of the third capacitor C3 are connected to the midpoint of the voltage balancer; The second two-level conversion circuit comprises: a third inductor L3, a fifth switch device S5, a sixth switch device S6 and a fourth capacitor C4; A first end of the third inductor L3 is connected to the second output end of the voltage balancer, and a second end of the third inductor L3 is connected to the second end of the fifth switch device S5 and the second end of the sixth switch device S6; The second end of the sixth switch device S6 is connected to the second end of the fourth capacitor C4; A first terminal of the fifth switch device S5 and a first terminal of the fourth capacitor C4 are connected to a midpoint of the voltage balancer.
[0052] It should be noted that, in this embodiment, the two two-level conversion circuits are both boost circuits.
[0053] The second inductor L2, the third switch device S3, the fourth switch device S4 and the third capacitor C3 form a first boost type two-level conversion circuit; the third inductor L3, the fifth switch device S5, the sixth switch device S6 and the fourth capacitor C4 form a second boost type two-level conversion circuit. The first boost type two-level conversion circuit and the second boost type two-level conversion circuit form a boost type three-level DC converter. The value of the preset positive voltage output by the first boost type two-level conversion circuit can be changed by controlling the on / off of the fifth switch device S5 and the sixth switch device S6; the value of the preset negative voltage output by the second boost type two-level conversion circuit can be changed by controlling the on / off of the fifth switch device S5 and the sixth switch device S6.
[0054] Reference Figure 5 In one example, the voltage balancer output port voltage is ±375 V, and the three-level converter output port voltage is ±750 V. The voltage balancer part realizes the positive and negative voltage balancing function of the input 750V bus, eliminating the influence of unbalanced load on the positive and negative voltages.
[0055] The third capacitor C3 and the fourth capacitor C4 are output side voltage equalization and filtering capacitors of the three-level DC converter. The first inductor L1 and the second inductor L2 are BOOST inductors.
[0056] In another embodiment, the first two-level conversion circuit includes: a fourth inductor L4, a seventh switch device S7, an eighth switch device S8 and a fifth capacitor C5; A first end of the seventh switch device S7 is connected to the first output end of the voltage balancer, and a second end thereof is connected to the first end of the eighth switch device S8 and the first end of the fourth inductor L4; The second end of the eighth switch device S8 is connected to the first end of the fifth capacitor C5; The second end of the seventh switch device S7 and the second end of the fifth capacitor C5 are connected to the midpoint of the voltage balancer; The second two-level conversion circuit comprises: a fifth inductor L5, a ninth switch device S9, a tenth switch device S10 and a sixth capacitor C6; A first end of the ninth switch device S9 is connected to the second output end of the voltage balancer, and a second end thereof is connected to the second end of the tenth switch device S10 and a first end of the fifth inductor L5; The second end of the fifth inductor L5 is connected to the second end of the sixth capacitor C6; The first end of the tenth switch device S10 and the first end of the sixth capacitor C6 are connected to the midpoint of the voltage balancer. It should be noted that, in this embodiment, the two two-level conversion circuits are both step-down circuits.
[0057] The fourth inductor L4, the seventh switch device S7, the eighth switch device S8 and the fifth capacitor C5 form a first buck-type two-level conversion circuit; the fifth inductor L5, the ninth switch device S9, the tenth switch device S10 and the sixth capacitor C6 form a second buck-type two-level conversion circuit. The first buck-type two-level conversion circuit and the second buck-type two-level conversion circuit form a buck-type three-level DC converter. The value of the preset positive voltage output by the first buck-type two-level conversion circuit can be changed by controlling the on / off of the seventh switch device S7 and the eighth switch device S8; the value of the preset negative voltage output by the second buck-type two-level conversion circuit can be changed by controlling the on / off of the ninth switch device S9 and the tenth switch device S10.
[0058] Reference Figure 6 In one example, the voltage balancer output port voltage is ±375 V, and the three-level converter output port voltage is ±110 V. The voltage balancer part realizes the positive and negative voltage balancing function of the input 750V bus, eliminating the influence of unbalanced load on the positive and negative voltages.
[0059] The fifth capacitor C5 and the sixth capacitor C6 are output side voltage equalization and filtering capacitors of the three-level DC converter. The fourth inductor L4 and the fifth inductor L5 are BUCK step-down inductors.
[0060] It should be noted that the control signals received by the controlled ends of the third switching device S3 to the tenth switching device S10 are provided by an external circuit; which may be a control unit in the microgrid system.
[0061] The switch device is a fully controlled device, and the switch device can be a MOS tube or an IGBT tube.
[0062] The present invention also proposes an electrical device, which includes the DC converter suitable for a multi-voltage bipolar DC distribution network. The specific structure of the DC converter suitable for a multi-voltage bipolar DC distribution network refers to the above embodiment. Since the electrical device adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be repeated here one by one.
[0063] In one example, refer to Figure 7 , the electrical device further comprises: A rectifier; the input end of the rectifier is connected to the power grid, and the output end is connected to the input end of the voltage balancer in the DC converter suitable for multi-voltage level bipolar DC distribution network; The rectifier is used to rectify the AC voltage of the power grid and output it to the voltage balancer.
[0064] In this example, the AC power of the power grid is used to provide power to the voltage balancer. Since the input end of the voltage balancer can only input DC power, the AC power of the power grid is first rectified and then output to the voltage balancer.
[0065] Or, refer to Figure 8 , the electrical device further comprises: A DC-DC circuit, the input end of which is connected to a DC power supply, and the output end of which is connected to the input end of a voltage balancer in the DC converter suitable for a multi-voltage level bipolar DC distribution network; The DC-DC circuit is used to convert the voltage of the direct current power supply and output it to the voltage balancer.
[0066] The DC power source may be a battery, and the DC-DC circuit converts the voltage output by the DC power source into an operating voltage range within which the voltage balancer can operate normally. In addition, the DC-DC circuit may also improve voltage quality and reduce ripple.
[0067] The above descriptions are only optional embodiments of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent structural changes made using the contents of the present invention's specification and drawings, or directly / indirectly applied in other related technical fields, are included in the patent protection scope of the present invention.
Claims
1. A DC converter suitable for a multi-voltage bipolar DC distribution network, characterized in that: The DC converter comprises: a voltage balancer and a three-level DC converter; A voltage balancer, the input end of which is connected to the DC bus, and the first output end and the second output end are connected to the three-level DC converter; The midpoint of the three-level DC converter is connected to the midpoint of the voltage balancer to form a neutral line; The voltage balancer is used to convert the voltage on the DC bus into a first voltage and a second voltage, and output the voltages to the first input terminal and the second input terminal of the three-level DC converter through the first output terminal and the second output terminal respectively; The three-level DC converter is used to convert the first voltage and the second voltage into a preset positive voltage and a preset negative voltage respectively and then output them, thereby forming three voltage level outputs with the neutral line.
2. The DC converter suitable for a multi-voltage bipolar DC distribution network according to claim 1, characterized in that: The number of the three-level DC converters is multiple; The midpoint of each of the three-level DC converters is connected to the midpoint of the voltage balancer to form a neutral line; The first input end of each of the three-level DC converters is connected to the first output end of the voltage balancer; the second input end of the at least one three-level DC converter is connected to the second output end of the voltage balancer; Each of the three-level DC converters is used to convert the first voltage and the second voltage into corresponding preset positive voltage and preset negative voltage respectively and then output them.
3. The DC converter suitable for a multi-voltage bipolar DC distribution network according to claim 2, characterized in that: The number of the voltage balancers is multiple; The voltage balancers are connected in parallel; the first output end of each voltage balancer is connected to the first input end of the at least one three-level DC converter; the second input end of each voltage balancer is connected to the second input end of the at least one three-level DC converter; The values of the first voltage and the second voltage output by each of the voltage balancers are respectively the same.
4. The DC converter suitable for a multi-voltage bipolar DC distribution network according to any one of claims 1 to 3, characterized in that: The voltage balancer comprises: A first switching device, a second switching device, a first capacitor, a second capacitor and a first inductor; The first switch device and the second switch device are arranged in series between the positive electrode and the negative electrode of the DC bus; the first capacitor and the second capacitor are arranged in series between the positive electrode and the negative electrode of the DC bus; The first end of the first inductor is connected to the second end of the first switch device and the first end of the second switch device; the second end of the first inductor is connected to the second end of the first capacitor and the first end of the second capacitor.
5. The DC converter suitable for a multi-voltage bipolar DC distribution network according to any one of claims 1 to 3, characterized in that: The three-level DC converter comprises: A first two-level conversion circuit, a first input terminal of which is connected to a first output terminal of the voltage balancer; A second two-level conversion circuit, a first input terminal of which is connected to the second output terminal of the voltage balancer; The second input terminal of the first two-level circuit and the second input terminal of the second two-level circuit are connected to the midpoint of the voltage balancer; The first two-level conversion circuit is used to convert the first voltage into a preset positive voltage and then output it; The second two-level conversion circuit is used for converting the second voltage into a preset negative voltage and then outputting it; The values of the preset positive voltage and the preset negative voltage are opposite to each other.
6. The DC converter suitable for a multi-voltage bipolar DC distribution network according to claim 5, characterized in that: The first two-level conversion circuit comprises: a second inductor, a third switch device, a fourth switch device and a third capacitor; A first end of the second inductor is connected to a first output end of the voltage balancer, and a second end of the second inductor is connected to a first end of the third switch device and a first end of the fourth switch device; The second end of the fourth switch device is connected to the first end of the third capacitor; The second end of the third switch device and the second end of the third capacitor are connected to the midpoint of the voltage balancer; The second two-level conversion circuit comprises: a third inductor, a fifth switch device, a sixth switch device and a fourth capacitor; A first end of the third inductor is connected to the second output end of the voltage balancer, and a second end of the third inductor is connected to the second end of the fifth switch device and the second end of the sixth switch device; The second end of the sixth switch device is connected to the second end of the fourth capacitor; A first terminal of the fifth switching device and a first terminal of the fourth capacitor are connected to a midpoint of the voltage balancer.
7. The DC converter suitable for a multi-voltage bipolar DC distribution network according to claim 5, characterized in that: The first two-level conversion circuit comprises: a fourth inductor, a seventh switch device, an eighth switch device and a fifth capacitor; The first end of the seventh switch device is connected to the first output end of the voltage balancer, and the second end is connected to the first end of the eighth switch device and the first end of the fourth inductor; The second end of the eighth switch device is connected to the first end of the fifth capacitor; The second end of the seventh switch device and the second end of the fifth capacitor are connected to the midpoint of the voltage balancer; The second two-level conversion circuit comprises: a fifth inductor, a ninth switch device, a tenth switch device and a sixth capacitor; The first end of the ninth switch device is connected to the second output end of the voltage balancer, and the second end is connected to the second end of the tenth switch device and the first end of the fifth inductor; The second end of the fifth inductor is connected to the second end of the sixth capacitor; A first terminal of the tenth switching device and a first terminal of the sixth capacitor are connected to a midpoint of the voltage balancer.
8. The DC converter suitable for a multi-voltage bipolar DC distribution network according to any one of claims 6 to 7, characterized in that: The switch device is a MOS tube or an IGBT tube.
9. An electrical device, characterized in that: The electrical equipment includes a DC converter suitable for a multi-voltage level bipolar DC distribution network as described in any one of claims 1 to 8.
10. The electrical device according to claim 9, characterized in that The electrical device further comprises: A rectifier; the input end of the rectifier is connected to the power grid, and the output end is connected to the input end of the voltage balancer in the DC converter suitable for multi-voltage level bipolar DC distribution network; The rectifier is used to rectify the AC voltage of the power grid and output it to the voltage balancer; Alternatively, the electrical device further comprises: A DC-DC circuit, the input end of which is connected to a DC power supply, and the output end of which is connected to the input end of a voltage balancer in the DC converter suitable for a multi-voltage level bipolar DC distribution network; The DC-DC circuit is used to convert the voltage of the direct current power supply and output it to the voltage balancer.