Photovoltaic high voltage direct current transmission method using current source type active commutation converter

Abstract

The present specification relates to the technical field of power transmission, and discloses a photovoltaic high-voltage direct-current transmission method based on a current source type active commutation converter, to solve the problems of too high number of power conversion stages, too large power loss and low transmission efficiency of the current source type power transmission system in the existing power transmission system. The photovoltaic high-voltage direct-current transmission system of the current source type active commutation converter comprises, in sequence, a photovoltaic power supply module, a voltage boosting module, a high-voltage direct-current transmission module, a high-voltage active commutation module and a power transmission grid connection module; wherein the voltage boosting module comprises a low-voltage active commutation converter, a medium-frequency transformer and a high-voltage uncontrolled rectification bridge. The present application adopts a current source active commutation converter and a high-voltage uncontrolled rectification bridge on the low-voltage side, and can realize photovoltaic power generation maximum power tracking without an additional DC / DC converter, thereby reducing one level of power conversion, reducing switching loss, adopting an uncontrolled rectification bridge on the sending end high-voltage side, realizing unidirectional energy flow and reducing system cost.

Description

Technical Field

[0001] This document relates to the field of power transmission technology, and in particular to a photovoltaic high-voltage direct current transmission system with a current source type active commutation converter. Background Technology

[0002] At present, the shortage of fossil energy and environmental pollution are prominent problems. New energy sources, represented by solar and wind energy, have become the core of the solution to the energy crisis because they are clean, environmentally friendly and have high utilization rates.

[0003] According to statistics, as of the end of August 2022, wind power installed capacity was approximately 340 million kilowatts, a year-on-year increase of 16.6%, while solar power installed capacity was approximately 350 million kilowatts, a year-on-year increase of 27.2%. Solar power installed capacity surpassed wind power, becoming the third largest energy source after thermal power and hydropower. Solar energy utilization is mainly in the form of grid-connected photovoltaic power generation. With the large-scale development and utilization of photovoltaics, efficient and reliable grid connection technology has become the focus of attention.

[0004] In common large-scale photovoltaic (PV) high-voltage direct current (HVDC) transmission technologies, photovoltaic power is transmitted through a DC / DC converter, an LC inverter, and a power frequency transformer to a sending-end voltage source PV converter. After rectification by the converter, the power is transmitted to a remote receiving-end voltage source PV converter, where it is inverted and connected to the AC grid. However, the PV power conversion process from generation to AC transmission involves numerous stages, resulting in high operating losses. Furthermore, the PV voltage source converter contains a large number of energy storage capacitors, making the device large, heavy, and expensive. Therefore, research on PV HVDC transmission technology is urgently needed. Summary of the Invention

[0005] This specification provides a 1V HVDC transmission system using a current-source active phase-commutation converter to address the problems of excessively high power conversion stages, excessive power loss, low transmission efficiency, large device size, and high cost in existing current-source transmission systems. The transmission system includes:

[0006] The photovoltaic power module, boost module, high voltage DC transmission module, high voltage active phase commutation module and power grid connection module are connected in sequence. The boost module includes a low-voltage active commutation converter, a medium-frequency transformer, and a high-voltage uncontrolled rectifier bridge; the high-voltage active commutation converter module includes a first high-voltage active commutation converter, a second high-voltage active commutation converter, a first transformer, and a second transformer.

[0007] In some preferred embodiments, the photovoltaic power module includes a photovoltaic power source and a low-voltage DC capacitor. and low-voltage DC inductors ; Among them, the low-voltage DC capacitor Connected between the positive and negative output terminals of the photovoltaic power supply, with the positive output terminal of the photovoltaic power supply connected to the low-voltage DC inductor. The positive terminal of the photovoltaic power supply is used as the positive terminal of the photovoltaic power module, and the negative terminal of the photovoltaic power supply is used as the negative terminal of the photovoltaic power module.

[0008] In some preferred embodiments, the boost module specifically includes: A low-voltage active commutation converter is connected between the positive output terminal and the negative output terminal of the photovoltaic power module, and includes a first fully controlled power semiconductor device S31, a second fully controlled power semiconductor device S32, a third fully controlled power semiconductor device S33 and a fourth fully controlled power semiconductor device S34. The first common node Py3, which is the positive terminal of the output of the photovoltaic power module, is connected to the second common node Ny3 through the first and second low-voltage active commutation bridge arms in parallel. The second common node Ny3 is connected to the negative terminal of the output of the photovoltaic power module. The orientation of the fully controlled power semiconductor devices is such that the anode is closer to the first common node Py3 and the cathode is closer to the second common node Ny3. The first low-voltage active commutation bridge arm includes a first fully controlled power semiconductor device S31 and a second fully controlled power semiconductor device S32 connected in sequence, and a first low-voltage output terminal x1 is led out from between the first fully controlled power semiconductor device S31 and the second fully controlled power semiconductor device S32; The second low-voltage active commutation bridge arm includes a third fully controlled power semiconductor device S33 and a fourth fully controlled power semiconductor device S34 connected in sequence, and a second low-voltage output terminal x2 is led out from between the third fully controlled power semiconductor device S33 and the fourth fully controlled power semiconductor device S34. The input terminals of the intermediate frequency transformer are connected to the first low-voltage output terminal x1 and the second low-voltage output terminal x2, respectively. The output terminals of the intermediate frequency transformer are connected to the first input terminal and the second input terminal of the uncontrolled rectifier bridge, respectively. The third common node of the uncontrolled rectifier bridge The uncontrolled rectifier bridge is connected to the fourth common node via the first and second arms of the uncontrolled rectifier bridge connected in parallel. ; The first arm of the uncontrolled rectifier bridge includes a first diode group D1 and a second diode group D2. The midpoint of the first diode group D1 and the second diode group D2 is connected to the first input terminal of the uncontrolled rectifier bridge. The second arm of the uncontrolled rectifier bridge includes a third diode group D3 and a fourth diode group D4. The midpoint of the third diode group D3 and the fourth diode group D4 is connected to the second input terminal of the uncontrolled rectifier bridge. All diodes in the diode groups are connected towards the third common node. The cathode is located near the fourth common node. The anode is ; Third public node The positive terminal of the boost module output, the fourth common node It is the negative terminal of the boost module output.

[0009] In some preferred embodiments, the fully controlled power semiconductor device is a thyristor.

[0010] In some preferred embodiments, the high-voltage DC transmission module includes a high-voltage DC capacitor. First high-voltage DC inductor High-voltage DC cable, second high-voltage DC inductor ; The high voltage DC capacitor Connect between the positive and negative output terminals of the boost module; High voltage DC capacitor The positive terminal is connected to the first high-voltage DC inductor. Connected to the first terminal P1 of the in-phase input high-voltage DC cable, the high-voltage DC capacitor The negative terminal is connected to the first end N1 of the inverting input high-voltage DC cable; The second end P2 of the in-phase input high-voltage DC cable is connected to the second high-voltage DC inductor. The second end N2 of the high-voltage DC transmission cable, connected to the non-inverting output terminal of the high-voltage DC transmission module, serves as the inverting input terminal of the high-voltage DC transmission module.

[0011] In some preferred embodiments, the high-voltage active phase-commutation converter module includes a first high-voltage active phase-commutation converter, a second high-voltage active phase-commutation converter, a first transformer, and a second transformer.

[0012] In some preferred embodiments, the high-voltage active phase-commutation converter module specifically includes: The three-phase connection terminals on the secondary side of the first transformer are denoted as a1, b1, and c1, and the three-phase connection terminals on the primary side of the first transformer are denoted as A1, B1, and C1. The three-phase connection terminals on the secondary side of the second transformer are denoted as a2, b2, and c2, and the three-phase connection terminals on the primary side of the second transformer are denoted as A2, B2, and C2. The first terminal Py1 of the first high-voltage active phase-commutation converter is connected to the in-phase output terminal of the high-voltage DC transmission module, the second terminal Ny1 of the first high-voltage active phase-commutation converter is connected to the first terminal Py2 of the second high-voltage active phase-commutation converter, and the second terminal Ny2 of the second high-voltage active phase-commutation converter is connected to the in-phase output terminal of the high-voltage DC transmission module. The first terminal Py1 of the first high-voltage active commutator is connected to the second terminal Ny1 of the first high-voltage active commutator through the first high-voltage active commutator bridge arm, the second high-voltage active commutator bridge arm and the third high-voltage active commutator bridge arm connected in parallel. The first high-voltage active commutation converter arm includes a first high-voltage fully controlled power semiconductor device S11 and a fourth high-voltage fully controlled power semiconductor device S14 connected in sequence; the second high-voltage active commutation converter arm includes a third high-voltage fully controlled power semiconductor device S13 and a sixth high-voltage fully controlled power semiconductor device S16 connected in sequence; the third high-voltage active commutation converter arm includes a fifth high-voltage fully controlled power semiconductor device S15 and a second high-voltage fully controlled power semiconductor device S12 connected in sequence; the orientation of the high-voltage fully controlled power semiconductor devices is close to the first terminal Py1 of the first high-voltage active commutation converter, with Py1 being anode. The cathode is located at the second end Ny1, which is close to the first high-voltage active commutator. The first output phase u1 of the first high-voltage active commutator is led out between the first high-voltage fully controlled power semiconductor device S11 and the fourth high-voltage fully controlled power semiconductor device S14. The second output phase v1 of the first high-voltage active commutator is led out between the third high-voltage fully controlled power semiconductor device S13 and the sixth high-voltage fully controlled power semiconductor device S16. The third output phase w1 of the first high-voltage active commutator is led out between the fifth high-voltage fully controlled power semiconductor device S15 and the second high-voltage fully controlled power semiconductor device S12. The first terminal Py2 of the second high-voltage active commutator is connected to the second terminal Ny2 of the second high-voltage active commutator through the fourth, fifth and sixth high-voltage active commutator bridge arms connected in parallel. The fourth high-voltage active commutation converter arm includes the seventh high-voltage fully controlled power semiconductor device S21 and the tenth high-voltage fully controlled power semiconductor device S24 connected in sequence; the fifth high-voltage active commutation converter arm includes the ninth high-voltage fully controlled power semiconductor device S23 and the twelfth high-voltage fully controlled power semiconductor device S26 connected in sequence; the sixth high-voltage active commutation converter arm includes the eleventh high-voltage fully controlled power semiconductor device S25 and the eighth high-voltage fully controlled power semiconductor device S22 connected in sequence; the orientation of the high-voltage fully controlled power semiconductor devices is close to the first terminal of the second high-voltage active commutation converter, with Py2 being the anode. The cathode is located at the second end Ny2, which is close to the second high-voltage active commutator. The first output phase u2 of the second high-voltage active commutator is led out between the seventh high-voltage fully controlled power semiconductor device S21 and the tenth high-voltage fully controlled power semiconductor device S24. The second output phase v2 of the second high-voltage active commutator is led out between the ninth high-voltage fully controlled power semiconductor device S23 and the twelfth high-voltage fully controlled power semiconductor device S26. The third output phase w2 of the second high-voltage active commutator is led out between the eleventh high-voltage fully controlled power semiconductor device S25 and the eighth high-voltage fully controlled power semiconductor device S22. The first output phase u1, the second output phase v1, and the third output phase w1 of the first high-voltage active commutator are respectively connected to the three-phase connection terminals a1, b1, and c1 of the secondary side of the first transformer. The first output phase u2 of the second high-voltage active commutator, the second output phase v2 of the second high-voltage active commutator, and the third output phase w2 of the second high-voltage active commutator are respectively connected to the three-phase connection terminals a2, b2 and c2 of the secondary side of the second transformer. The primary three-phase connection terminals A1, B1 and C1 of the first transformer are connected to the primary three-phase connection terminals A2, B2 and C2 of the second transformer, respectively.

[0013] In some preferred embodiments, the power transmission and grid connection module specifically includes: The initial three-phase circuit after the primary three-phase connection terminals A1, B1 and C1 of the first transformer are connected to the primary three-phase connection terminals A2, B2 and C2 of the second transformer, respectively, is connected from the first filter node d, the second filter node e and the third filter node f, respectively, via the first filter capacitor Ca, the second filter capacitor Cb and the third filter capacitor Cc to the filter node Mc. The initial three-phase circuits are each connected to the A-phase terminal, B-phase terminal, and C-phase terminal of the three-phase AC power grid through the first filter inductor La, the second filter inductor Lb, and the third filter inductor Lc, respectively.

[0014] In another aspect, the present invention also proposes a photovoltaic high-voltage direct current transmission method using a current-source active commutation converter. The method is implemented based on the above-mentioned transmission system and includes the steps of controlling a boost module and controlling a high-voltage active commutation converter module. The steps for controlling the boost module specifically include: During the [0~Tad] phase of the switching cycle, the first fully controlled power semiconductor device S31, the second fully controlled power semiconductor device S32, the third fully controlled power semiconductor device S33, and the fourth fully controlled power semiconductor device S34 are all turned on; where Tad represents the superimposed current adjustment time. During the [Tad~1 / 2fsw] phase of the switching cycle, the first fully controlled power semiconductor device S31 and the fourth fully controlled power semiconductor device S34 are turned on, while the second fully controlled power semiconductor device S32 and the third fully controlled power semiconductor device S33 are turned off; where fsw represents the switching frequency of the fully controlled power semiconductor device. During the switching cycle [1 / 2fsw~1 / 2fsw+Tad] phase, the first fully controlled power semiconductor device S31, the second fully controlled power semiconductor device S32, the third fully controlled power semiconductor device S33, and the fourth fully controlled power semiconductor device S34 are all turned on; During the switching cycle [1 / 2fsw+Tad~1 / fsw] phase, the first fully controlled power semiconductor device S31 and the fourth fully controlled power semiconductor device S34 are turned off, and the second fully controlled power semiconductor device S32 and the third fully controlled power semiconductor device S33 are turned on. The superposition current regulation time Tad is calculated based on the change in the maximum photovoltaic power output as follows:

[0015] in, This represents the low-voltage capacitor voltage at the maximum power output of the photovoltaic power source. This indicates the switching frequency of a fully controlled power semiconductor device.

[0016] The method further includes a step of controlling the high-voltage active commutation module, specifically including: By controlling the on-time of high-voltage fully controlled power semiconductor devices S11, S12, S13, S14, S15, S16, S21, S22, S23, S24, S25, and S26, the second high-voltage DC inductor is... current To take control; Specifically: Within each grid fundamental frequency cycle 1 / F, the time when both Usa and Usc of the three-phase AC power supply voltages at the A-phase terminal, B-phase terminal, and C-phase terminal of the three-phase AC grid are positive, and Usa = Usc, is defined as follows: F represents the switching frequency of the high-voltage fully controlled power semiconductor device. Within each fundamental frequency cycle 1 / F of the power grid, the conduction angle is... The shut-off angles are all Adjustment time is ,and ; The turn-on time of the high-voltage fully controlled power semiconductor device S11 is T0-TR, and the turn-off time is T0~TR+. The turn-on time of the high-voltage fully controlled power semiconductor device S12 is from T0 to TR+. The shutdown time is from T0 to TR+. The turn-on time of the high-voltage fully controlled power semiconductor device S13 is from T0 to TR+. The shutdown time is from T0 to TR+. The turn-on time of the high-voltage fully controlled power semiconductor device S14 is from T0 to TR+. The shutdown time is from T0 to TR+. The turn-on time of the high-voltage fully controlled power semiconductor device S15 is from T0 to TR+. The turn-off time is T0~TR+1 / F; the turn-on time of the high-voltage fully controlled power semiconductor device S16 is T0~TR+1 / F. The shutdown time is from T0 to TR+. The turn-on time of the high-voltage fully controlled power semiconductor device S21 is T0+TR, and the turn-off time is T0+TR+ The turn-on time of the high-voltage fully controlled power semiconductor device S22 is T0+TR+ The turn-off time is T0+TR+ The turn-on time of the high-voltage fully controlled power semiconductor device S23 is T0+TR+ The turn-off time is T0+TR+ The turn-on time of the high-voltage fully controlled power semiconductor device S24 is T0+TR+ The turn-off time is T0+TR+ The turn-on time of the high-voltage fully controlled power semiconductor device S25 is T0+TR+ The turn-off time is T0+TR+1 / F; the turn-on time of the high-voltage fully controlled power semiconductor device S26 is T0+TR+1 / F. The turn-off time is T0+TR+ If any of the above-mentioned turn-on or turn-off times is greater than 1 / F, then subtract 1 / F from this turn-on or turn-off time and use it as the actual turn-on or turn-off time; if any of the above-mentioned turn-on or turn-off times is less than 0, then add 1 / F to this turn-on or turn-off time and use it as the actual turn-on or turn-off time.

[0017] In some preferred embodiments, controlling the high-voltage active commutation module further includes changing the adjustment time. Output voltage of high voltage DC cable The steps for implementing control include: High voltage DC cable output voltage The output voltage of the high-voltage DC cable is always positive. When the value is less than its reference value, the adjustment time TR is reduced by a preset step size until... The value should be equal to the reference value; otherwise, the adjustment time should be increased. .

[0018] The above-described at least one technical solution adopted in the embodiments of this specification can achieve the following beneficial effects: (1) The low-voltage side adopts a current source active commutation converter and a high-voltage uncontrolled rectifier bridge, which can realize the maximum power tracking of photovoltaic power generation without the need to add an additional DC / DC converter. At the same time, it reduces the first stage of power conversion and the system switching loss is low.

[0019] (2) An uncontrolled rectifier bridge is used on the high-voltage side of the sending end, which can realize unidirectional energy flow, reduce the use of fully controlled semiconductor devices, and thus reduce the system cost.

[0020] (3) The receiving end high voltage side adopts a combined current source active commutation converter, which does not require multiple module energy storage capacitors, reducing the converter footprint and improving the system power density. Attached Figure Description

[0021] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of a photovoltaic high-voltage direct current transmission system circuit using a current-source type active commutation converter, as provided in one embodiment of this specification. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] The technical solutions provided by the various embodiments of this application are described in detail below with reference to the accompanying drawings.

[0024] Figure 1 A schematic diagram of a photovoltaic high-voltage direct current transmission system circuit using a current-source type active commutator provided in one embodiment of this specification is shown below. Figure 1 The system includes: The photovoltaic power module, boost module, high voltage DC transmission module, high voltage active phase commutation module and power grid connection module are connected in sequence. In this embodiment, the photovoltaic power module includes a photovoltaic power source and a low-voltage DC capacitor. and low-voltage DC inductors ; Among them, the low-voltage DC capacitor Connected between the positive and negative output terminals of the photovoltaic power supply, with the positive output terminal of the photovoltaic power supply connected to the low-voltage DC inductor. The positive terminal of the photovoltaic power supply is used as the positive terminal of the photovoltaic power module, and the negative terminal of the photovoltaic power supply is used as the negative terminal of the photovoltaic power module.

[0025] The boost module includes a low-voltage active commutation converter, an intermediate frequency transformer, and a high-voltage uncontrolled rectifier bridge; the high-voltage active commutation converter module includes a first high-voltage active commutation converter, a second high-voltage active commutation converter, a first transformer, and a second transformer. Specifically, it includes: A low-voltage active commutation converter is connected between the positive output terminal and the negative output terminal of the photovoltaic power module, and includes a first fully controlled power semiconductor device S31, a second fully controlled power semiconductor device S32, a third fully controlled power semiconductor device S33, and a fourth fully controlled power semiconductor device S34; in this embodiment, the fully controlled power semiconductor device is a thyristor.

[0026] The first common node Py3, which is the positive terminal of the output of the photovoltaic power module, is connected to the second common node Ny3 through the first and second low-voltage active commutation bridge arms in parallel. The second common node Ny3 is connected to the negative terminal of the output of the photovoltaic power module. The orientation of the fully controlled power semiconductor devices is such that the anode is closer to the first common node Py3 and the cathode is closer to the second common node Ny3. The first low-voltage active commutation bridge arm includes a first fully controlled power semiconductor device S31 and a second fully controlled power semiconductor device S32 connected in sequence, and a first low-voltage output terminal x1 is led out from between the first fully controlled power semiconductor device S31 and the second fully controlled power semiconductor device S32; The second low-voltage active commutation bridge arm includes a third fully controlled power semiconductor device S33 and a fourth fully controlled power semiconductor device S34 connected in sequence, and a second low-voltage output terminal x2 is led out from between the third fully controlled power semiconductor device S33 and the fourth fully controlled power semiconductor device S34. The input terminals of the intermediate frequency transformer are connected to the first low-voltage output terminal x1 and the second low-voltage output terminal x2, respectively. The output terminals of the intermediate frequency transformer are connected to the first input terminal and the second input terminal of the uncontrolled rectifier bridge, respectively. Constant power control is adopted, and the current flowing into the intermediate frequency transformer from the low-voltage commutator is adjusted in real time according to the maximum photovoltaic power generation. ih ; The third common node of the uncontrolled rectifier bridge The uncontrolled rectifier bridge is connected to the fourth common node via the first and second arms of the uncontrolled rectifier bridge connected in parallel. ; The first arm of the uncontrolled rectifier bridge includes a first diode group D1 and a second diode group D2. The midpoint of the first diode group D1 and the second diode group D2 is connected to the first input terminal of the uncontrolled rectifier bridge. The second arm of the uncontrolled rectifier bridge includes a third diode group D3 and a fourth diode group D4. The midpoint of the third diode group D3 and the fourth diode group D4 is connected to the second input terminal of the uncontrolled rectifier bridge. All diodes in the diode groups are connected towards the third common node. The cathode is located near the fourth common node. The anode is ; Third public node The positive terminal of the boost module output, the fourth common node It is the negative terminal of the boost module output.

[0027] In this embodiment, the high-voltage DC transmission module includes a high-voltage DC capacitor. First high-voltage DC inductor High-voltage DC cable, second high-voltage DC inductor ; The high voltage DC capacitor Connect between the positive and negative output terminals of the boost module; High voltage DC capacitor The positive terminal is connected to the first high-voltage DC inductor. Connected to the first terminal P1 of the in-phase input high-voltage DC cable, the high-voltage DC capacitor The negative terminal is connected to the first end N1 of the inverting input high-voltage DC cable; The second end P2 of the in-phase input high-voltage DC cable is connected to the second high-voltage DC inductor. The second end N2 of the high-voltage DC transmission cable, connected to the non-inverting output terminal of the high-voltage DC transmission module, serves as the inverting input terminal of the high-voltage DC transmission module.

[0028] In this embodiment, the voltage difference between the first terminal P1 of the in-phase input high-voltage DC cable and the first terminal N1 of the out-of-phase input high-voltage DC cable is: The voltage difference between the second terminal P2 of the in-phase input high-voltage DC cable and the second terminal N2 of the out-of-phase input high-voltage DC cable is: .

[0029] In this embodiment, the high-voltage active phase-commutation converter module includes a first high-voltage active phase-commutation converter, a second high-voltage active phase-commutation converter, a first transformer, and a second transformer.

[0030] In this embodiment, the high-voltage active phase-commutation converter module specifically includes: The three-phase connection terminals on the secondary side of the first transformer are denoted as a1, b1, and c1, and the three-phase connection terminals on the primary side of the first transformer are denoted as A1, B1, and C1. The three-phase connection terminals on the secondary side of the second transformer are denoted as a2, b2 and c2, and the three-phase connection terminals on the primary side of the second transformer are denoted as A2, B2 and C2. The first terminal Py1 of the first high-voltage active phase-commutation converter is connected to the in-phase output terminal of the high-voltage DC transmission module, the second terminal Ny1 of the first high-voltage active phase-commutation converter is connected to the first terminal Py2 of the second high-voltage active phase-commutation converter, and the second terminal Ny2 of the second high-voltage active phase-commutation converter is connected to the in-phase output terminal of the high-voltage DC transmission module. The first terminal Py1 of the first high-voltage active commutator is connected to the second terminal Ny1 of the first high-voltage active commutator through the first high-voltage active commutator bridge arm, the second high-voltage active commutator bridge arm and the third high-voltage active commutator bridge arm connected in parallel. The first high-voltage active commutation converter arm includes a first high-voltage fully controlled power semiconductor device S11 and a fourth high-voltage fully controlled power semiconductor device S14 connected in sequence; the second high-voltage active commutation converter arm includes a third high-voltage fully controlled power semiconductor device S13 and a sixth high-voltage fully controlled power semiconductor device S16 connected in sequence; the third high-voltage active commutation converter arm includes a fifth high-voltage fully controlled power semiconductor device S15 and a second high-voltage fully controlled power semiconductor device S12 connected in sequence; the orientation of the high-voltage fully controlled power semiconductor devices is close to the first terminal Py1 of the first high-voltage active commutation converter, with Py1 being anode. The cathode is located at the second end Ny1, which is close to the first high-voltage active commutator. The first output phase u1 of the first high-voltage active commutator is led out between the first high-voltage fully controlled power semiconductor device S11 and the fourth high-voltage fully controlled power semiconductor device S14. The second output phase v1 of the first high-voltage active commutator is led out between the third high-voltage fully controlled power semiconductor device S13 and the sixth high-voltage fully controlled power semiconductor device S16. The third output phase w1 of the first high-voltage active commutator is led out between the fifth high-voltage fully controlled power semiconductor device S15 and the second high-voltage fully controlled power semiconductor device S12. The first terminal Py2 of the second high-voltage active commutator is connected to the second terminal Ny2 of the second high-voltage active commutator through the fourth, fifth and sixth high-voltage active commutator bridge arms connected in parallel. The fourth high-voltage active commutation converter arm includes the seventh high-voltage fully controlled power semiconductor device S21 and the tenth high-voltage fully controlled power semiconductor device S24 connected in sequence; the fifth high-voltage active commutation converter arm includes the ninth high-voltage fully controlled power semiconductor device S23 and the twelfth high-voltage fully controlled power semiconductor device S26 connected in sequence; the sixth high-voltage active commutation converter arm includes the eleventh high-voltage fully controlled power semiconductor device S25 and the eighth high-voltage fully controlled power semiconductor device S22 connected in sequence; the orientation of the high-voltage fully controlled power semiconductor devices is close to the first terminal of the second high-voltage active commutation converter, with Py2 being the anode. The cathode is located at the second end Ny2, which is close to the second high-voltage active commutator. The first output phase u2 of the second high-voltage active commutator is led out between the seventh high-voltage fully controlled power semiconductor device S21 and the tenth high-voltage fully controlled power semiconductor device S24. The second output phase v2 of the second high-voltage active commutator is led out between the ninth high-voltage fully controlled power semiconductor device S23 and the twelfth high-voltage fully controlled power semiconductor device S26. The third output phase w2 of the second high-voltage active commutator is led out between the eleventh high-voltage fully controlled power semiconductor device S25 and the eighth high-voltage fully controlled power semiconductor device S22. The first output phase u1, the second output phase v1, and the third output phase w1 of the first high-voltage active commutator are respectively connected to the three-phase connection terminals a1, b1, and c1 of the secondary side of the first transformer. The first output phase u2 of the second high-voltage active commutator, the second output phase v2 of the second high-voltage active commutator, and the third output phase w2 of the second high-voltage active commutator are respectively connected to the three-phase connection terminals a2, b2 and c2 of the secondary side of the second transformer. The primary three-phase connection terminals A1, B1 and C1 of the first transformer are connected to the primary three-phase connection terminals A2, B2 and C2 of the second transformer, respectively.

[0031] In this embodiment, the power transmission and grid connection module specifically includes: The initial three-phase circuit after the primary three-phase connection terminals A1, B1 and C1 of the first transformer are connected to the primary three-phase connection terminals A2, B2 and C2 of the second transformer, respectively, is connected from the first filter node d, the second filter node e and the third filter node f, respectively, via the first filter capacitor Ca, the second filter capacitor Cb and the third filter capacitor Cc to the filter node Mc. The initial three-phase circuits are each connected to the A-phase terminal, B-phase terminal, and C-phase terminal of the three-phase AC power grid through the first filter inductor La, the second filter inductor Lb, and the third filter inductor Lc, respectively.

[0032] In this embodiment, the currents output from the three-phase primary terminals A1, B1, and C1 of the first transformer are respectively , and ; The output currents of the primary three-phase connection terminals A2, B2, and C2 of the second transformer are respectively , and ; The initial three-phase circuit currents are respectively , and ; The currents of the input filter inductors in the initial three-phase circuit are respectively , and .

[0033] A second embodiment of the present invention provides a photovoltaic high-voltage direct current transmission method using a current-source active commutation converter, implemented based on the above-mentioned transmission system, including the steps of controlling the boost module and controlling the high-voltage active commutation converter module; The steps for controlling the boost module specifically include: During the [0~Tad] phase of the switching cycle, the first fully controlled power semiconductor device S31, the second fully controlled power semiconductor device S32, the third fully controlled power semiconductor device S33, and the fourth fully controlled power semiconductor device S34 are all turned on; where Tad represents the superimposed current adjustment time. In this embodiment, the superposition current regulation time Tad is calculated based on the change in the maximum photovoltaic power output, and the method is as follows:

[0034] in, This represents the low-voltage capacitor voltage at the maximum power output of the photovoltaic power source. This indicates the switching frequency of a fully controlled power semiconductor device.

[0035] During the [Tad~1 / 2fsw] phase of the switching cycle, the first fully controlled power semiconductor device S31 and the fourth fully controlled power semiconductor device S34 are turned on, while the second fully controlled power semiconductor device S32 and the third fully controlled power semiconductor device S33 are turned off; where fsw represents the switching frequency of the fully controlled power semiconductor device. During the switching cycle [1 / 2fsw~1 / 2fsw+Tad] phase, the first fully controlled power semiconductor device S31, the second fully controlled power semiconductor device S32, the third fully controlled power semiconductor device S33, and the fourth fully controlled power semiconductor device S34 are all turned on; During the switching cycle [1 / 2fsw+Tad~1 / fsw] phase, the first fully controlled power semiconductor device S31 and the fourth fully controlled power semiconductor device S34 are turned off, while the second fully controlled power semiconductor device S32 and the third fully controlled power semiconductor device S33 are turned on.

[0036] In this embodiment, the method further includes a step of controlling the high-voltage active commutation module, including: By controlling the on-time of high-voltage fully controlled power semiconductor devices S11, S12, S13, S14, S15, S16, S21, S22, S23, S24, S25, and S26, the second high-voltage DC inductor is... current To take control; Specifically: Within each grid fundamental frequency cycle 1 / F, the time when both Usa and Usc of the three-phase AC power supply voltages at the A-phase terminal, B-phase terminal, and C-phase terminal of the three-phase AC grid are positive, and Usa = Usc, is defined as follows: F represents the switching frequency of the high-voltage fully controlled power semiconductor device. Within each fundamental frequency cycle 1 / F of the power grid, the conduction angle is... The shut-off angles are all Adjustment time is ,and ; The turn-on time of the high-voltage fully controlled power semiconductor device S11 is T0-TR, and the turn-off time is T0~TR+. The turn-on time of the high-voltage fully controlled power semiconductor device S12 is from T0 to TR+. The shutdown time is from T0 to TR+. The turn-on time of the high-voltage fully controlled power semiconductor device S13 is from T0 to TR+. The shutdown time is from T0 to TR+. The turn-on time of the high-voltage fully controlled power semiconductor device S14 is from T0 to TR+. The shutdown time is from T0 to TR+. The turn-on time of the high-voltage fully controlled power semiconductor device S15 is from T0 to TR+. The turn-off time is T0~TR+1 / F; the turn-on time of the high-voltage fully controlled power semiconductor device S16 is T0~TR+1 / F. The shutdown time is from T0 to TR+. The turn-on time of the high-voltage fully controlled power semiconductor device S21 is T0+TR, and the turn-off time is T0+TR+ The turn-on time of the high-voltage fully controlled power semiconductor device S22 is T0+TR+ The turn-off time is T0+TR+ The turn-on time of the high-voltage fully controlled power semiconductor device S23 is T0+TR+ The turn-off time is T0+TR+ The turn-on time of the high-voltage fully controlled power semiconductor device S24 is T0+TR+ The turn-off time is T0+TR+ The turn-on time of the high-voltage fully controlled power semiconductor device S25 is T0+TR+ The turn-off time is T0+TR+1 / F; the turn-on time of the high-voltage fully controlled power semiconductor device S26 is T0+TR+1 / F. The turn-off time is T0+TR+ If any of the above-mentioned turn-on or turn-off times is greater than 1 / F, then subtract 1 / F from this turn-on or turn-off time and use it as the actual turn-on or turn-off time; if any of the above-mentioned turn-on or turn-off times is less than 0, then add 1 / F to this turn-on or turn-off time and use it as the actual turn-on or turn-off time.

[0037] In this embodiment, controlling the high-voltage active commutation module further includes changing the adjustment time. Output voltage of high voltage DC cable The steps for implementing control include: High voltage DC cable output voltage The output voltage of the high-voltage DC cable is always positive. When the value is less than its reference value, the adjustment time TR is reduced by a preset step size until... The value should be equal to the reference value; otherwise, the adjustment time should be increased. .

[0038] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A photovoltaic high-voltage direct current transmission method using a current-source type active commutation converter, characterized in that, include: The photovoltaic power module, boost module, high voltage DC transmission module, high voltage active commutation module and power grid connection module are connected in sequence. The boost module includes a low-voltage active commutation converter, an intermediate frequency transformer, and a high-voltage uncontrolled rectifier bridge; the high-voltage active commutation converter module includes a first high-voltage active commutation converter, a second high-voltage active commutation converter, a first transformer, and a second transformer. The boost module specifically includes: A low-voltage active commutation converter is connected between the positive output terminal and the negative output terminal of the photovoltaic power module, and includes a first fully controlled power semiconductor device S31, a second fully controlled power semiconductor device S32, a third fully controlled power semiconductor device S33 and a fourth fully controlled power semiconductor device S34. The first common node Py3, which is the positive terminal of the output of the photovoltaic power module, is connected to the second common node Ny3 through the first and second low-voltage active commutation bridge arms in parallel. The second common node Ny3 is connected to the negative terminal of the output of the photovoltaic power module. The orientation of the fully controlled power semiconductor devices is such that the anode is closer to the first common node Py3 and the cathode is closer to the second common node Ny3. The first low-voltage active commutation bridge arm includes a first fully controlled power semiconductor device S31 and a second fully controlled power semiconductor device S32 connected in sequence, and a first low-voltage output terminal x1 is led out from between the first fully controlled power semiconductor device S31 and the second fully controlled power semiconductor device S32; The second low-voltage active commutation bridge arm includes a third fully controlled power semiconductor device S33 and a fourth fully controlled power semiconductor device S34 connected in sequence, and a second low-voltage output terminal x2 is led out from between the third fully controlled power semiconductor device S33 and the fourth fully controlled power semiconductor device S34. The input terminals of the intermediate frequency transformer are connected to the first low-voltage output terminal x1 and the second low-voltage output terminal x2, respectively. The output terminals of the intermediate frequency transformer are connected to the first input terminal and the second input terminal of the uncontrolled rectifier bridge, respectively. The third common node of the uncontrolled rectifier bridge The uncontrolled rectifier bridge is connected to the fourth common node via the first and second arms of the uncontrolled rectifier bridge connected in parallel. ; The first arm of the uncontrolled rectifier bridge includes a first diode group D1 and a second diode group D2. The midpoint of the first diode group D1 and the second diode group D2 is connected to the first input terminal of the uncontrolled rectifier bridge. The second arm of the uncontrolled rectifier bridge includes a third diode group D3 and a fourth diode group D4. The midpoint of the third diode group D3 and the fourth diode group D4 is connected to the second input terminal of the uncontrolled rectifier bridge. All diodes in the diode groups are connected towards the third common node. The cathode is located near the fourth common node. The anode is ; Third public node The positive terminal of the boost module output, the fourth common node This is the negative terminal of the boost module output. The steps for controlling the boost module specifically include: During the [0~Tad] phase of the switching cycle, the first fully controlled power semiconductor device S31, the second fully controlled power semiconductor device S32, the third fully controlled power semiconductor device S33, and the fourth fully controlled power semiconductor device S34 are all turned on; where Tad represents the superimposed current adjustment time. During the [Tad~1 / 2fsw] phase of the switching cycle, the first fully controlled power semiconductor device S31 and the fourth fully controlled power semiconductor device S34 are turned on, while the second fully controlled power semiconductor device S32 and the third fully controlled power semiconductor device S33 are turned off; where fsw represents the switching frequency of the fully controlled power semiconductor device. During the switching cycle [1 / 2fsw~1 / 2fsw+Tad] phase, the first fully controlled power semiconductor device S31, the second fully controlled power semiconductor device S32, the third fully controlled power semiconductor device S33, and the fourth fully controlled power semiconductor device S34 are all turned on; During the switching cycle [1 / 2fsw+Tad~1 / fsw] phase, the first fully controlled power semiconductor device S31 and the fourth fully controlled power semiconductor device S34 are turned off, and the second fully controlled power semiconductor device S32 and the third fully controlled power semiconductor device S33 are turned on. The superposition current regulation time Tad is calculated based on the change in the maximum photovoltaic power output as follows: ； in, This represents the low-voltage capacitor voltage at the maximum power output of the photovoltaic power source. This indicates the switching frequency of a fully controlled power semiconductor device. This indicates the input voltage of the high-voltage DC cable.

2. The photovoltaic high-voltage direct current transmission method using a current-source type active commutation converter according to claim 1, characterized in that, The photovoltaic power module includes a photovoltaic power source and a low-voltage DC capacitor. and low-voltage DC inductors ; Among them, the low-voltage DC capacitor Connected between the positive and negative output terminals of the photovoltaic power supply, with the positive output terminal of the photovoltaic power supply connected to the low-voltage DC inductor. The positive terminal of the photovoltaic power supply is used as the positive terminal of the photovoltaic power module, and the negative terminal of the photovoltaic power supply is used as the negative terminal of the photovoltaic power module.

3. The photovoltaic high-voltage direct current transmission method using a current-source type active commutation converter according to claim 2, characterized in that, The high-voltage DC transmission module includes a high-voltage DC capacitor. First high-voltage DC inductor High-voltage DC cable, second high-voltage DC inductor ; The high voltage DC capacitor Connect between the positive and negative output terminals of the boost module; High voltage DC capacitor The positive terminal is connected to the first high-voltage DC inductor. Connected to the first terminal P1 of the in-phase input high-voltage DC cable, the high-voltage DC capacitor The negative terminal is connected to the first end N1 of the reverse-input high-voltage DC cable; The second end P2 of the in-phase input high-voltage DC cable is connected to the second high-voltage DC inductor. The second end N2 of the high-voltage DC transmission cable, connected to the non-inverting output terminal of the high-voltage DC transmission module, serves as the inverting input terminal of the high-voltage DC transmission module.

4. The photovoltaic high-voltage direct current transmission method using a current-source type active commutation converter according to claim 3, characterized in that, The high-voltage active commutation converter module includes a first high-voltage active commutation converter, a second high-voltage active commutation converter, a first transformer, and a second transformer; specifically, it includes: The three-phase connection terminals on the secondary side of the first transformer are denoted as a1, b1, and c1, and the three-phase connection terminals on the primary side of the first transformer are denoted as A1, B1, and C1. The three-phase connection terminals on the secondary side of the second transformer are denoted as a2, b2 and c2, and the three-phase connection terminals on the primary side of the second transformer are denoted as A2, B2 and C2. The first terminal Py1 of the first high-voltage active phase-commutation converter is connected to the in-phase output terminal of the high-voltage DC transmission module, the second terminal Ny1 of the first high-voltage active phase-commutation converter is connected to the first terminal Py2 of the second high-voltage active phase-commutation converter, and the second terminal Ny2 of the second high-voltage active phase-commutation converter is connected to the in-phase output terminal of the high-voltage DC transmission module. The first terminal Py1 of the first high-voltage active commutator is connected to the second terminal Ny1 of the first high-voltage active commutator through the first high-voltage active commutator bridge arm, the second high-voltage active commutator bridge arm and the third high-voltage active commutator bridge arm connected in parallel. The first high-voltage active commutation converter arm includes a first high-voltage fully controlled power semiconductor device S11 and a fourth high-voltage fully controlled power semiconductor device S14 connected in sequence; the second high-voltage active commutation converter arm includes a third high-voltage fully controlled power semiconductor device S13 and a sixth high-voltage fully controlled power semiconductor device S16 connected in sequence; the third high-voltage active commutation converter arm includes a fifth high-voltage fully controlled power semiconductor device S15 and a second high-voltage fully controlled power semiconductor device S12 connected in sequence; the orientation of the high-voltage fully controlled power semiconductor devices is close to the first terminal Py1 of the first high-voltage active commutation converter, with Py1 being anode. The cathode is located at the second end Ny1, which is close to the first high-voltage active commutator. The first output phase u1 of the first high-voltage active commutator is led out between the first high-voltage fully controlled power semiconductor device S11 and the fourth high-voltage fully controlled power semiconductor device S14. The second output phase v1 of the first high-voltage active commutator is led out between the third high-voltage fully controlled power semiconductor device S13 and the sixth high-voltage fully controlled power semiconductor device S16. The third output phase w1 of the first high-voltage active commutator is led out between the fifth high-voltage fully controlled power semiconductor device S15 and the second high-voltage fully controlled power semiconductor device S12. The first terminal Py2 of the second high-voltage active commutator is connected to the second terminal Ny2 of the second high-voltage active commutator through the fourth, fifth and sixth high-voltage active commutator bridge arms connected in parallel. The fourth high-voltage active commutation converter arm includes the seventh high-voltage fully controlled power semiconductor device S21 and the tenth high-voltage fully controlled power semiconductor device S24 connected in sequence; the fifth high-voltage active commutation converter arm includes the ninth high-voltage fully controlled power semiconductor device S23 and the twelfth high-voltage fully controlled power semiconductor device S26 connected in sequence; the sixth high-voltage active commutation converter arm includes the eleventh high-voltage fully controlled power semiconductor device S25 and the eighth high-voltage fully controlled power semiconductor device S22 connected in sequence; the orientation of the high-voltage fully controlled power semiconductor devices is close to the first terminal of the second high-voltage active commutation converter, with Py2 being the anode. The cathode is located at the second end Ny2, which is close to the second high-voltage active commutator. The first output phase u2 of the second high-voltage active commutator is led out between the seventh high-voltage fully controlled power semiconductor device S21 and the tenth high-voltage fully controlled power semiconductor device S24. The second output phase v2 of the second high-voltage active commutator is led out between the ninth high-voltage fully controlled power semiconductor device S23 and the twelfth high-voltage fully controlled power semiconductor device S26. The third output phase w2 of the second high-voltage active commutator is led out between the eleventh high-voltage fully controlled power semiconductor device S25 and the eighth high-voltage fully controlled power semiconductor device S22. The first output phase u1, the second output phase v1, and the third output phase w1 of the first high-voltage active commutator are respectively connected to the three-phase connection terminals a1, b1, and c1 of the secondary side of the first transformer. The first output phase u2 of the second high-voltage active commutator, the second output phase v2 of the second high-voltage active commutator, and the third output phase w2 of the second high-voltage active commutator are respectively connected to the three-phase connection terminals a2, b2 and c2 of the secondary side of the second transformer. The primary three-phase connection terminals A1, B1 and C1 of the first transformer are connected to the primary three-phase connection terminals A2, B2 and C2 of the second transformer, respectively.

5. The photovoltaic high-voltage direct current transmission method using a current-source type active commutation converter according to claim 4, characterized in that, The power transmission and grid connection module specifically includes: The initial three-phase circuit after the primary three-phase connection terminals A1, B1 and C1 of the first transformer are connected to the primary three-phase connection terminals A2, B2 and C2 of the second transformer, respectively, is connected from the first filter node d, the second filter node e and the third filter node f, respectively, via the first filter capacitor Ca, the second filter capacitor Cb and the third filter capacitor Cc to the filter node Mc. The initial three-phase circuits are each connected to the A-phase terminal, B-phase terminal, and C-phase terminal of the three-phase AC power grid through the first filter inductor La, the second filter inductor Lb, and the third filter inductor Lc, respectively.

6. The photovoltaic high-voltage direct current transmission method using a current-source type active commutation converter according to claim 5, characterized in that, The steps for controlling the high-voltage active commutation converter module specifically include: By controlling the on-time of high-voltage fully controlled power semiconductor devices S11, S12, S13, S14, S15, S16, S21, S22, S23, S24, S25, and S26, the second high-voltage DC inductor is... current To take control; Specifically: Within each grid fundamental frequency cycle 1 / F, the time when both Usa and Usc of the three-phase AC power supply voltages at the A-phase terminal, B-phase terminal, and C-phase terminal of the three-phase AC grid are positive, and Usa = Usc, is defined as follows: F represents the switching frequency of the high-voltage fully controlled power semiconductor device. Within each fundamental frequency cycle 1 / F of the power grid, the conduction angle is... The shut-off angles are all Adjustment time is ,and ; The turn-on time of the high-voltage fully controlled power semiconductor device S11 is T0-TR, and the turn-off time is T0~TR+. The turn-on time of the high-voltage fully controlled power semiconductor device S12 is from T0 to TR+. The shutdown time is from T0 to TR+ The turn-on time of the high-voltage fully controlled power semiconductor device S13 is from T0 to TR+. The shutdown time is from T0 to TR+ The turn-on time of the high-voltage fully controlled power semiconductor device S14 is from T0 to TR+. The shutdown time is from T0 to TR+ The turn-on time of the high-voltage fully controlled power semiconductor device S15 is from T0 to TR+. The turn-off time is T0~TR+1 / F; the turn-on time of the high-voltage fully controlled power semiconductor device S16 is T0~TR+1 / F. The shutdown time is from T0 to TR+ The turn-on time of the high-voltage fully controlled power semiconductor device S21 is T0+TR, and the turn-off time is T0+TR+ The turn-on time of the high-voltage fully controlled power semiconductor device S22 is T0+TR+ The turn-off time is T0+TR+ The turn-on time of the high-voltage fully controlled power semiconductor device S23 is T0+TR+ The turn-off time is T0+TR+ The turn-on time of the high-voltage fully controlled power semiconductor device S24 is T0+TR+ The turn-off time is T0+TR+ The turn-on time of the high-voltage fully controlled power semiconductor device S25 is T0+TR+ The turn-off time is T0+TR+1 / F; the turn-on time of the high-voltage fully controlled power semiconductor device S26 is T0+TR+1 / F. The turn-off time is T0+TR+ If any of the above-mentioned turn-on or turn-off times is greater than 1 / F, then subtract 1 / F from this turn-on or turn-off time and use it as the actual turn-on or turn-off time; if any of the above-mentioned turn-on or turn-off times is less than 0, then add 1 / F to this turn-on or turn-off time and use it as the actual turn-on or turn-off time.

7. The photovoltaic high-voltage direct current transmission method using a current-source type active commutation converter according to claim 6, characterized in that, Controlling the high-voltage active commutation module also includes changing the adjustment time. Output voltage of high voltage DC cable The steps for implementing control include: High voltage DC cable output voltage The output voltage of the high-voltage DC cable is always positive. When the value is less than the reference value, the adjustment time is reduced by a preset step size. until The value should be equal to the reference value; otherwise, the adjustment time should be increased. .

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