CN110022077B - Topology structure of power composite modular multilevel solid state transformer for AC/DC hybrid distribution network - Google Patents

Abstract

The invention discloses a power composite type solid-state transformer topological structure for an alternating-current and direct-current hybrid power distribution network. A branch is led out from the middle point of each of the three-phase upper and lower bridge arms of the modular multilevel converter and is connected with the high-frequency transformer through a DC blocking capacitor to form a new high-frequency power circulation path, high-frequency components are simultaneously superposed in a target modulation signal, and the energy of the high-voltage side is led into the high-frequency transformer through the high-frequency circulation path in a high-frequency power form and is transmitted to the low-voltage side, so that the high-voltage side input stage and the middle-side isolation stage are subjected to integrated power conversion by adopting a power composite idea, the power conversion stage number is effectively reduced, the power conversion is more integrated. Meanwhile, the high-frequency transmission power in the invention can not flow to a high-voltage direct-current port or a fundamental frequency alternating-current port, and a trap constant-frequency selection device is not needed.

Description

Power composite modular multilevel solid state transformer for AC/DC hybrid distribution network device topology

technical field

The invention belongs to the technical field of high-voltage and high-power power electronics, and mainly relates to a power composite solid-state transformer topology structure oriented to an AC-DC hybrid distribution network.

Background technique

In the traditional AC distribution network, the power transformer is the key device to realize voltage level conversion and electrical isolation. However, due to its single function, the need for a large number of magnetic materials, and the inability to directly access or process DC power, it cannot meet the needs of future intelligent Therefore, solid-state transformers based on fully-controlled power electronic devices emerge as the times require.

Solid-state transformers, also known as power electronic transformers, electronic power voltages or smart transformers, were rated as one of the ten most promising technologies by the American MIT magazine in 2011, and are one of the key devices for flexible energy routing in the future distribution network. . Compared with traditional power transformers, solid-state transformers have five major advantages: 1) flexible and continuous input voltage/current, output voltage/current control capability, bidirectional controllable power transmission; 2) integrated harmonic/reactive/non-power Power quality management capabilities such as balance compensation and dynamic voltage recovery; 3) Direct access to and processing of DC power, which is more conducive to the flexible interconnection of AC-DC hybrid systems; 4) Full power electronic fault management capabilities, short fault processing time, no need Additional relay protection device; 5) Less use of magnetic materials, no need for transformer oil, more environmentally friendly.

However, the existing solid-state transformers cannot completely replace the traditional power transformers. In addition to the high device cost caused by the power electronic device's own manufacturing process, it is also mainly limited by key issues such as low power density and low transmission efficiency. At present, many researchers have proposed the topology of solid-state transformers, but generally the high-voltage side adopts modular multi-level converters or cascaded H-bridge converters, and the intermediate side adopts ISOP or independent DAB converters for DC-DC conversion. , the power conversion stages are too many, the whole device is bulky and the efficiency is low. Invention patent CN 106787861 A discloses a modular multi-level full-bridge resonant power electronic transformer topology, which constructs a high-frequency transmission path on each phase arm of a star-connected cascade H bridge, but does not have a high-voltage DC interface , which cannot be directly connected to the electric energy in the form of high-voltage direct current; the invention patent CN 107623456 A discloses a MMC-based multi-port power electronic transformer topology and its control method, and the invention patent CN 107612407 A discloses a high power density power electronic transformer topology Structure and control method thereof. Invention patent CN 108832825 A discloses a high-power density multi-port power electronic transformer topology. These three invention patents all draw out high-frequency power by constructing a high-frequency power flow path, but they all need to be configured Frequency selection devices such as notch filters and high-pass filters are used to guide the power flow in the form of high frequency and low frequency as needed, and the cost is relatively high.

SUMMARY OF THE INVENTION

Purpose of the invention: Aiming at the problems that the existing solid-state transformers have many transformation stages and low transmission efficiency, and the existing power composite solid-state transformers rely on frequency selection devices, the present invention proposes a power composite modularization for AC-DC hybrid distribution network. Multilevel solid state transformer topology.

Technical solution: The topology structure of the power composite modular multi-level solid-state transformer for the AC/DC hybrid distribution network of the present invention includes: a modular multi-level converter on the high-voltage side, and a high-frequency AC-DC converter on the middle side. and the inverter on the low-voltage side; the modular multi-level converter and the high-frequency AC-DC converter are all three-phase structures, and the phases of the two are in one-to-one correspondence; each phase of the modular multi-level converter There are two upper and lower bridge arms, the upper and lower bridge arms each have two upper and lower sub-bridge arms, and each sub-bridge arm includes a unit module and a filter inductor connected in series; the unit module includes one or more sub-modules connected in cascade, each One sub-module is a double half-bridge structure; in any phase of the modular multi-level converter, the upper end of the upper sub-bridge arm in the upper bridge arm is connected to the positive pole of the input end of the high-voltage DC power supply, and the lower sub-bridge arm in the lower arm is connected to the positive pole of the input end of the high-voltage DC power supply. The lower end is connected to the negative pole of the input end of the high-voltage DC power supply, and the connection point of the upper and lower bridge arms is connected to the one-phase port of the input end of the three-phase high-voltage AC power supply; each phase of the high-frequency AC-DC converter includes a DC blocking capacitor and a high-frequency transformer. and an H-bridge rectifier; in any phase of the high-frequency AC-DC converter, the positive and negative poles of the primary side of the high-frequency transformer are connected across the upper and lower sides of the corresponding phase in the modular multi-level converter through a series-connected DC blocking capacitor. The two midpoints of the bridge arms, the positive and negative poles of the secondary side of the high-frequency transformer are connected to the two midpoints of the left and right bridge arms of the H-bridge rectifier; the upper and lower arms of the H-bridge rectifier in each phase of the high-frequency AC-DC converter The midpoint and the midpoint of the lower bridge arm are respectively connected to the positive pole and the negative pole of the inverter.

Further, the inverter is a three-phase four-wire half-bridge structure for converting the low-voltage DC signal into a low-voltage AC signal.

Further, the low-voltage side further includes a parallel capacitor, and two ends of the parallel capacitor are respectively connected to the positive electrode and the negative electrode of the inverter.

Further, in each phase on the high-voltage side, the superimposed high-frequency components of the two groups of sub-bridge arms in the upper and lower arms have the same amplitude and opposite phases, and the lower sub-arm in the upper arm and the upper sub-arm in the lower arm are superimposed. The high frequency components have the same amplitude and phase.

Further, the DC blocking capacitor in the middle-side high-frequency AC-DC converter can not only prevent the electric energy in the form of DC from flowing into the high-frequency path, but also can be combined with the filter inductance in each sub-bridge arm to form an LC resonance circuit.

Beneficial effect: Compared with the prior art, the main feature of the present invention is that the high-voltage side modular multi-level converter and the middle side high-frequency AC-DC converter adopt the idea of power compounding to perform integrated power conversion, and plan a new The high-frequency power flow path integrates the high-voltage side input stage and the middle-side isolation stage, which effectively reduces the number of power conversion stages and makes the power conversion more integrated; at the same time, the superimposed high-frequency components effectively utilize the common mode and differential mode components. The combination characteristics of the high-frequency components make the high-frequency components present common-mode properties for themselves, while presenting differential-mode properties for high-voltage DC and high-voltage fundamental frequency AC ports.

Therefore, the present invention can directly access and process electric energy in the form of DC; the newly planned high-frequency power flow path neither affects the high-voltage DC port nor the fundamental frequency AC port, no additional frequency selection device is required, and the cost is higher. It can effectively reduce the number of power conversion stages, thereby making the power conversion more integrated, the power density is further improved, and the power transmission efficiency is further improved.

Description of drawings

Figure 1 is a topology diagram of a power composite modular multi-level solid-state transformer for AC/DC hybrid distribution network;

Figure 2 is a structural diagram of a high-voltage side modular multi-level unit module;

FIG. 3 is a schematic diagram of superposition of high-frequency modulation components.

Detailed ways

The technical solutions of the present invention will be specifically explained below with reference to the accompanying drawings.

As shown in Figure 1, the power composite modular multilevel solid state transformer topology structure of the present invention includes: a modular multilevel converter on the high voltage side, a high frequency AC-DC converter on the middle side and an inverter on the low voltage side . Modular multilevel converters are used to convert high-voltage three-phase AC or high-voltage DC into high-voltage high-frequency AC. The middle-side high-frequency AC-DC converter is used to convert the high-voltage high-frequency AC obtained by the modular multi-level converter into low-voltage DC. The inverter is a three-phase four-wire half-bridge structure, which is used to convert low-voltage DC into three-phase four-wire low-voltage AC. The modular multilevel converter and the high-frequency AC-DC converter are all three-phase structures, and each phase of the two is in one-to-one correspondence.

The high-voltage side modular multi-level converter includes a high-voltage AC voltage source input end, a plurality of unit modules and a plurality of filter inductors. Wherein, each phase of the modular multilevel converter has two upper and lower bridge arms, and the upper and lower bridge arms each have two upper and lower sub-bridge arms, and each sub-bridge arm includes a unit module and a filter inductor connected in series. The unit module includes one or more sub-modules that are cascaded, and each sub-module is a double-half bridge structure. As shown in Figure 2, the double-half-bridge sub-module consists of two half-bridges connected in series. The DC positive pole of the bridge is connected, and the AC output of the two half bridges is used as the AC output of the sub-module. Since the double half-bridge structure increases the voltage output range of the sub-module, the voltage output capability of the unit module can be increased without increasing the number of unit modules, and a high-frequency voltage equivalent to the amplitude of the fundamental frequency voltage can be provided. In any phase of the modular multilevel converter, the upper end of the upper sub-bridge arm in the upper arm is connected to the positive pole of the input end of the high-voltage DC power supply (ie, the positive busbar of the high-voltage DC power supply), and the lower end of the lower sub-bridge arm in the lower arm is connected to It is connected to the negative pole of the input terminal of the high-voltage DC power supply (ie, the positive busbar of the high-voltage DC power supply), and the connection point of the upper and lower bridge arms is connected to the first-phase port of the input terminal of the three-phase high-voltage AC power supply.

The middle-side high-frequency AC-DC converter includes three DC blocking capacitors, three single-phase high-frequency transformers and three single-phase H-bridge rectifiers. The three DC blocking capacitors, three single-phase high-frequency transformers and three single-phase H-bridge rectifiers belong to three phases, and each phase includes a DC blocking capacitor, a single-phase high-frequency transformer and a single-phase H-bridge rectifier . One end of the three DC blocking capacitors is connected to the midpoint of the three-phase upper bridge arm of the high-voltage side modular multilevel converter (that is, the connection point of the upper and lower sub-bridge arms in each upper bridge arm of the three-phase), and the other end is connected to the high-frequency The upper ends of the primary sides of the transformers are connected, and the lower ends of the primary sides of the three high-frequency transformers are respectively connected with the midpoints of the three-phase lower arms of the high-voltage side modular multilevel converter (that is, the upper and lower sub-bridges in the lower arms of the three-phase). The upper and lower ends of the secondary sides of the three high-frequency transformers are respectively connected with the midpoints of the left and right bridge arms of the three single-phase H-bridge rectifiers. In other embodiments, one end of the three DC blocking capacitors may be connected to the midpoint of the three-phase lower bridge arm of the high-voltage side modular multilevel converter, and the other end may be connected to the lower end of the primary side of the high-frequency transformer. The upper end of the primary side of the frequency transformer is connected to the midpoint of the three-phase upper bridge arm of the high-voltage side modular multi-level converter respectively, forming a high-frequency power flow path, and the secondary ends of the three high-frequency transformers are respectively connected with the three single-phase H The midpoints of the left and right bridge arms of the bridge rectifier are connected. The midpoint of the upper bridge arm and the midpoint of the lower bridge arm of the H-bridge rectifier in each phase of the high-frequency AC-DC converter are respectively connected to the positive pole and the negative pole of the low-voltage side inverter.

The high-voltage side modular multi-level converter and the middle-side high-frequency AC-DC converter use the idea of power compounding to perform integrated power conversion. It is connected to the high-frequency AC-DC transformer path), and at the same time superimposes the high-frequency component in the target modulation signal, and the energy on the high-voltage side is introduced into the high-frequency AC-DC transformer in the form of high-frequency power through this high-frequency flow path and It is transmitted to the low-voltage side, so that the transmission power of the high-voltage side input stage and the intermediate-side isolation stage is combined, which effectively reduces the number of power conversion stages and makes the power conversion more integrated.

In addition, the three phases of the high-voltage side modular multi-level converter are symmetrical and equal. In each phase of the high-voltage side, the two sets of sub-bridge arms in the upper and lower arms have the same amplitude and opposite phase of superimposed high-frequency components. The amplitude and phase of the superimposed high-frequency components of the lower sub-bridge arm and the upper sub-bridge arm of the lower sub-bridge arm are the same, as shown in FIG. 3 . In this way, the high-voltage side does not need additional frequency selection devices (such as notch filters, low-pass filters, etc.) to prevent high-frequency AC from entering the high-voltage fundamental frequency AC and high-voltage DC ports, so that the transmitted high-frequency power does not affect the high-voltage The DC port does not affect the fundamental frequency AC port.

The DC blocking capacitor in the middle-side high-frequency AC-DC converter can not only prevent the electric energy in the form of DC from flowing into the high-frequency path, but also can combine with the sub-bridge arm inductance to form an LC resonance circuit.

In addition to the inverter, the low-voltage side also includes a parallel capacitor, two ends of the parallel capacitor are respectively connected to the positive and negative electrodes of the inverter, and the parallel capacitor plays the role of DC voltage regulation.

The inverter on the low-voltage side is used to convert low-voltage DC into low-voltage AC, so that the topology has four general ports of high-voltage AC, high-voltage DC, low-voltage AC and low-voltage DC, which is suitable for AC-DC hybrid distribution network.

Claims (5)

1. A power composite type modular multilevel solid-state transformer topological structure facing an alternating current-direct current hybrid power distribution network comprises a modular multilevel converter positioned at a high-voltage side, a high-frequency AC-DC converter positioned at a middle side and an inverter positioned at a low-voltage side; the modular multilevel converter and the high-frequency AC-DC converter are both of a three-phase structure, and the phases of the modular multilevel converter and the high-frequency AC-DC converter are in one-to-one correspondence;

Each phase of the modular multilevel converter is provided with an upper bridge arm and a lower bridge arm, each upper bridge arm and each lower bridge arm are respectively provided with an upper sub-bridge arm and a lower sub-bridge arm, and each sub-bridge arm comprises a unit module and a filter inductor which are connected in series; the unit module comprises one or more cascaded sub-modules, and each sub-module is in a double half-bridge structure; the double-half-bridge structure is formed by connecting two half-bridges in series, the direct current negative electrode of the upper half-bridge is connected with the direct current positive electrode of the lower half-bridge, and the alternating current outputs of the two half-bridges are used as the alternating current outputs of the sub-modules; in any phase of the modular multilevel converter, the upper end of an upper sub-bridge arm in an upper bridge arm is connected with the positive pole of the input end of the high-voltage direct-current power supply, the lower end of a lower sub-bridge arm in a lower bridge arm is connected with the negative pole of the input end of the high-voltage direct-current power supply, and the connecting point of the upper and lower bridge arms is connected with one phase port of the input end of the three-phase high-voltage alternating-;

Each phase of the high-frequency AC-DC converter comprises a blocking capacitor, a high-frequency transformer and an H-bridge rectifier; in any phase of the high-frequency AC-DC converter, the positive and negative poles of the primary side of the high-frequency transformer are bridged to two middle points of the upper and lower bridge arms of the corresponding phase in the modular multilevel converter through the serially connected blocking capacitors, and the positive and negative poles of the secondary side of the high-frequency transformer are bridged to two middle points of the left and right bridge arms of the H-bridge rectifier; and the middle point of the upper bridge arm and the middle point of the lower bridge arm of the H-bridge rectifier in each phase of the high-frequency AC-DC converter are respectively connected to the anode and the cathode of the inverter.

2. The power composite modular multilevel solid-state transformer topology structure oriented to the alternating current-direct current hybrid power distribution network according to claim 1, characterized in that: the inverter is in a three-phase four-wire half-bridge structure and is used for converting a low-voltage direct current signal into a low-voltage alternating current signal.

3. The power composite modular multilevel solid-state transformer topology structure oriented to the alternating current-direct current hybrid power distribution network according to claim 1, characterized in that: the low-voltage side further comprises a parallel capacitor, and two ends of the parallel capacitor are connected to the positive electrode and the negative electrode of the inverter respectively.

4. The power composite modular multilevel solid-state transformer topology structure oriented to the alternating current-direct current hybrid power distribution network according to claim 1, characterized in that: in each phase of the high-voltage side, the superposed high-frequency components of the two groups of sub bridge arms in the upper bridge arm and the lower bridge arm are the same in amplitude and opposite in phase, and the superposed high-frequency components of the lower sub bridge arm in the upper bridge arm and the superposed high-frequency components of the upper sub bridge arm in the lower bridge arm are the same in amplitude and phase.

5. the topological structure of the power composite type modular multilevel solid-state transformer oriented to the alternating current-direct current hybrid power distribution network according to claim 1, wherein the DC blocking capacitor in the high-frequency AC-DC converter at the middle side can not only prevent electric energy in a direct current form from flowing into a high-frequency path, but also can be combined with the filter inductor in each sub-bridge arm to form an L C resonant circuit.

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