Large-scale photovoltaic DC collection and transmission three-port power router and control method thereof

Abstract

A large-scale photovoltaic DC collection and transmission three-port power router and its control method relate to the field of power electronics technology. This invention utilizes an MMC + integrated transformer + thyristor commutation circuit structure, enabling large-scale photovoltaic power stations to directly transmit power through a DC collection port-high-voltage DC transmission port path and providing an AC support port. This not only reduces the number of voltage conversion stages but also provides power and active support capabilities for the local AC power grid. The high-frequency voltage freedom of the MMC bridge arm is synchronized and coordinated with the thyristor trigger pulse to make the thyristor opening and closing fully controllable. The thyristors are sequentially controlled to carry the photovoltaic DC collection port current in turn, ensuring DC current smoothing without the need for a filter. Furthermore, the control method of the invention simplifies the photovoltaic DC collection structure and reduces device costs by approximately 70%. This invention addresses the current problems of multiple power conversion stages, a large number of devices, and high costs.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to a large-scale photovoltaic direct current collection and transmission three-port power router and a control method thereof. Background Art

[0002] Global photovoltaic power generation has experienced sustained and rapid growth in recent years. my country's solar energy resources are generally distributed more on plateaus than on plains, and more in the dry western regions than in the humid eastern regions. Gobi and desert regions are particularly rich in renewable energy, but their grid architecture is characterized by weak thermal power support, insufficient short-circuit capacity, and limited voltage regulation capabilities, making it a typical weak grid.

[0003] In existing technology, large-scale photovoltaic stations use small-capacity centralized inverters to aggregate AC power, which is then boosted through multiple stages to the grid and then transmitted via traditional DC transmission. However, in weak grid environments such as deserts and Gobi deserts, it is difficult to build supporting thermal power or hydroelectric generators near new energy sites to provide regulated power for the new energy stations. Furthermore, the multi-stage boosting increases the electrical distance from the main grid, resulting in insufficient support for frequency and voltage regulation, and highlighting the stability issues of weak grid-connected systems.

[0004] To this end, a new type of power router is currently needed. It is used to enable large-scale photovoltaic power stations to directly transmit power through the "DC collection port-high-voltage DC transmission port" path and provide an AC support port. This not only meets the needs of reducing the number of voltage conversion levels, but also has the ability to provide power and active support to the local AC power grid, providing a solution for the large-scale base transmission of new energy in the west. Summary of the Invention

[0005] In response to the above-mentioned problems, the present invention provides a large-scale photovoltaic DC collection and transmission three-port power router and its control method, thereby solving the problems of the large number of power conversion stages, large number of components and high cost in existing large-scale photovoltaic DC collection and transmission converters. It also meets the current demand for reducing the number of voltage conversion stages, providing power and active support capabilities to the local AC power grid, and providing solutions for large-scale base transmission of new energy in the western region.

[0006] The technical solution adopted in the present invention is:

[0007] A large-scale photovoltaic DC collection and transmission three-port power router, comprising a thyristor commutation circuit (1), a three-phase high-voltage MMC (2), a thyristor commutation control system (3) and an integrated transformer (4);

[0008] The thyristor commutation circuit (1) is a three-phase bridge composed of six thyristor valve groups (T1 to T6); each thyristor valve group consists of N ThyThe DC bus of the thyristor commutation circuit (1) leads to the photovoltaic DC collection port; N Thy is an integer greater than or equal to 1;

[0009] The three-phase high-voltage MMC (2) consists of phases A, B and C. The upper and lower bridge arms of each phase are composed of N submodules (SM1~SM N ) is composed; N is an integer greater than 1;

[0010] The two primary windings of the integrated transformer (4) are connected to the upper and lower bridge arms of the three-phase high-voltage MMC (2) as bridge arm inductors, and the secondary side of the integrated transformer (4) is connected to the three-phase bridge arms of the thyristor commutation circuit (1);

[0011] The DC bus of the three-phase high-voltage MMC (2) leads to a high-voltage DC output port, and the center tap of the primary winding of the integrated transformer (4) leads to a high-voltage AC support port;

[0012] The thyristor commutation control system (3) is used for controlling the commutation of the thyristor commutation circuit (1) and the three-phase high-voltage MMC (2).

[0013] Furthermore, the thyristor commutation control system (3) is composed of a thyristor trigger pulse generator (31), a synchronization signal generator (32), a thyristor turn-off voltage generator (33), a thyristor commutation control voltage generator (34), a high-frequency trapezoidal wave voltage generator (35), and a high-frequency injection voltage generator (36); the high-frequency injection voltage generator (36) is composed of a high-frequency voltage synthesis module (361) and a disturbance compensation signal generator (362);

[0014] The thyristor trigger pulse generator (31) is used to generate the trigger pulse (g T1 ~g T6 ), controls the opening of the thyristor;

[0015] A thyristor turn-off voltage generator (33) is used to generate a turn-off voltage u of the thyristor valve group (T1-T6) Tx,off , control the turn-off control of the thyristor;

[0016] A thyristor commutation control voltage generator (34) is used to generate a commutation control voltage u for the thyristor valve group (T1-T6) Tx,on , controls the commutation of the thyristor;

[0017] A high-frequency trapezoidal wave voltage generator (35) is used to generate a high-frequency voltage basic waveform u Tx,b , controlling the primary and secondary voltage matching of the integrated transformer (4);

[0018] The disturbance compensation signal generator (362) is used to generate a disturbance compensation signal according to the photovoltaic DC collection port current reference signal I M,ref 、Upper and lower bridge arm submodule voltage (u C,upx 、u C,lwx ) is calculated to obtain the disturbance compensation signal Δu Tx ;

[0019] A high-frequency voltage synthesis module (361) for receiving the disturbance compensation signal Δu Tx and thyristor turn-off voltage u Tx,off , thyristor commutation control voltage u Tx,on and high-frequency trapezoidal wave voltage u Tx,b , and after synthesis, the output is the MMC three-phase high-frequency injection voltage (u HFa 、u HFb and u HFc ), the high-frequency injection voltage of each phase is evenly divided (×0.5) and injected into the upper and lower bridge arms of the three-phase high-voltage MMC (2).

[0020] Furthermore, the three-phase bridge composed of the six thyristor valve groups (T1 to T6) is specifically connected as follows:

[0021] The anodes of the thyristor valve group T1, the thyristor valve group T3, and the thyristor valve group T5 are connected in parallel; the cathodes of the thyristor valve group T2, the thyristor valve group T4, and the thyristor valve group T6 are connected in parallel; the cathode of the thyristor valve group T5 is connected to the anode of the thyristor valve group T2; the cathode of the thyristor valve group T3 is connected to the anode of the thyristor T6; and the cathode of the thyristor valve group T1 is connected to the anode of the thyristor valve group T4.

[0022] Furthermore, the two primary windings of the integrated transformer (4) are connected to the upper and lower bridge arms of the three-phase high-voltage MMC (2) as bridge arm inductors, and the secondary side of the integrated transformer (4) is connected to the three-phase bridge arm of the thyristor commutation circuit (1). The specific connection method is:

[0023] One winding of the primary side of the integrated transformer (4) is connected to the upper bridge arms of the A-phase, B-phase, and C-phase of the three-phase high-voltage MMC (2); another winding of the primary side of the integrated transformer (4) is connected to the lower bridge arms of the A-phase, B-phase, and C-phase of the three-phase high-voltage MMC (2);

[0024] The secondary side of the integrated transformer (4) is connected to a three-phase bridge formed by the thyristor valve groups (T1 to T6) of the three-phase bridge arms of the thyristor commutation circuit (1).

[0025] A control method based on a large-scale photovoltaic DC collection and transmission three-port power router, the method comprising:

[0026] For generating the trigger pulse (g T1 ~gT6 ), a method for controlling the opening of a thyristor;

[0027] Used to generate the turn-off voltage u of the thyristor valve group (T1-T6) Tx,off , a method for controlling the turn-off control of a thyristor;

[0028] Used to generate the commutation control voltage u of the thyristor valve group (T1-T6) Tx,on , a method for controlling commutation of thyristors;

[0029] Used to generate high-frequency voltage basic waveform u Tx,b , a method for controlling the voltage matching between the primary and secondary sides of the integrated transformer (4);

[0030] Used to calculate the current reference signal I of the photovoltaic DC collection port M,ref 、Upper and lower bridge arm submodule voltage (u C,upx 、u C,lwx ) is calculated to obtain the disturbance compensation signal Δu Tx Methods;

[0031] Used to receive the disturbance compensation signal Δu Tx and thyristor turn-off voltage u Tx,off , thyristor commutation control voltage u Tx,on and high-frequency trapezoidal wave voltage u Tx,b , and after synthesis, the output is the MMC three-phase high-frequency injection voltage (u HFa 、u HFb and u HFc ), the high-frequency injection voltage of each phase is evenly divided (×0.5) and then injected into the upper and lower bridge arms of the three-phase high-voltage MMC (2).

[0032] Furthermore, the method for controlling the turning on, turning off and commutation of the thyristor is specifically as follows:

[0033] In the thyristor commutation control system (3), the synchronization signal generator (32) generates a synchronization signal and transmits it to the thyristor trigger pulse generator (31), the thyristor turn-off voltage generator (33), the thyristor commutation control voltage generator (34) and the high-frequency trapezoidal wave voltage generator (35). The thyristor commutation control system (3) uses the synchronization signal to make the thyristor trigger pulse (g T1 ~g T6 ) and thyristor turn-off voltage u Tx,off , thyristor commutation control voltage u Tx,on And the high frequency voltage basic waveform u Tx,b synchronous;

[0034] The thyristor turn-off voltage u Tx,off , thyristor commutation control voltage u Tx,onAnd the high frequency voltage basic waveform u Tx,b The high frequency injected voltage (u HFa 、u HFb and u HFc ) is injected into the upper and lower bridge arms of the three-phase high-voltage MMC (2), and the upper and lower bridge arms of the three-phase high-voltage MMC (2) are coupled to the secondary winding through the integrated transformer (4), and then act on the thyristor commutation circuit (1), and the thyristor trigger pulse (g T1 ~g T6 ) synchronized and coordinated to make the turning on and off of the thyristor fully controllable and complete the reliable commutation of the thyristor.

[0035] Furthermore, in the method for controlling the opening, closing and commutation of the thyristors, under the commutation control method, the thyristor valve groups T1 to T6 take turns to carry the photovoltaic DC sink port current I M , and a continuous DC current can be synthesized without the need for a filter capacitor.

[0036] Furthermore, the method is used to determine the current reference signal I of the photovoltaic DC collection port. M,ref 、Upper and lower bridge arm submodule voltage (u C,upx and u C,lwx ) is calculated to obtain the disturbance compensation signal Δu Tx The method, wherein the disturbance compensation signal Δu is obtained Tx The method is as follows:

[0037] The disturbance compensation signal generator (362) generates a disturbance compensation signal according to the photovoltaic DC collection port current reference signal I M,ref 、Upper and lower bridge arm submodule voltage (u C,upx and u C,lwx ), high frequency voltage reference signal u HFx,ref 、Upper and lower bridge arm reference voltage signal (u refx,up and u refx,lw ) calculates and generates the disturbance compensation signal Δu Tx .

[0038] The disturbance compensation signal Δu Tx The high frequency voltage synthesis module (361) synthesizes the high frequency injection voltage (u HFa 、u HFb and u HFc ).

[0039] Furthermore, the disturbance compensation signal generator (362) generates a disturbance compensation signal according to the photovoltaic DC collection port current reference signal I M,ref 、Upper and lower bridge arm submodule voltage (u C,upx and u C,lwx ), high-frequency voltage reference signal u HFx,ref 、Upper and lower bridge arm reference voltage signal (urefx,up and u refx,lw ) calculates and generates the disturbance compensation signal Δu Tx The method is as follows:

[0040] The signal of the disturbance compensation signal generator (362) includes a capacitor disturbance voltage compensation signal and a current error compensation signal. In order to obtain the capacitor voltage fluctuation compensation signal, the primary winding voltage of the integrated transformer (4) is written as follows according to the MMC DC loop voltage equation:

[0041]

[0042] in:

[0043] ——u pri,x is the transformer primary winding voltage, x=a,b,c;

[0044] ——U HVDC is the voltage of the high voltage DC output port;

[0045] ——u refx,up and u refx,lw They are the reference voltage signals of the upper and lower bridge arms respectively;

[0046] ——N is the number of bridge arm submodules;

[0047] ——u Cx,up and u Cx,lw are the upper and lower bridge arm submodule capacitor voltages respectively.

[0048] The upper and lower bridge arm reference voltage signals contain a DC component 1 / 2U HVDC , power frequency component u refx and high frequency component 1 / 2u HFx , which is expressed as follows:

[0049]

[0050] The capacitor voltage of the upper and lower bridge arm submodules can be expressed as the capacitor voltage rating (U HVDC / N) and ripple voltage (Δu Cx,up and Δu Cx,lw ), the expression is as follows:

[0051]

[0052] Substituting equations (2) and (3) into equation (1), the primary winding voltage of the integrated transformer (4) is obtained as:

[0053]

[0054] From formula (4), we can see that the sum of the capacitance fluctuation voltages of all the sub-modules in the upper and lower arms of the three-phase high-voltage MMC (2) generates a capacitance fluctuation voltage disturbance Δu on the primary winding of the transformer. C,x , and the high frequency voltage u HFx After superposition, they jointly affect the thyristor commutation circuit;

[0055] In order to eliminate its influence, a capacitor fluctuation voltage compensation signal is added to the high-frequency injection voltage of the upper and lower bridge arms of the three-phase high-voltage MMC (2).

[0056] The capacitor fluctuation voltage compensation signal is calculated by combining equations (1) and (4): as follows:

[0057]

[0058] Based on (5), in order to further improve the current control accuracy, the PI regulator is used to generate the current error compensation signal according to the error calculation of the high-frequency current. Compensation signal with capacitor fluctuation voltage After adding, we get the disturbance compensation signal Δu Tx .

[0059] The disturbance compensation signal Δu Tx The high frequency voltage synthesis module (361) synthesizes the high frequency injection voltage (u HFa 、u HFb and u HFc ) is as follows:

[0060] Step 1: In the high frequency voltage synthesis module (361), the thyristor turn-off voltage u Tx,off , thyristor commutation control voltage u Tx,on And the high frequency voltage basic waveform u Tx,b The high-frequency voltage reference signal u is synthesized HFx,ref , the synthesis method is:

[0061] u HFx,ref =u Tx,off +u Tx,on +u Tx,b ,(x=a,b,c)

[0062] Step 2: In the disturbance compensation signal generator (362), the upper and lower bridge arm submodule voltages (u C,upx and u C,lwx ), high-frequency voltage reference signal u HFx,ref 、Upper and lower bridge arm reference voltage signal (u refx,up and u refx,lw ) Calculate and generate capacitor fluctuation voltage compensation signal The calculation method is as follows:

[0063]

[0064] in:

[0065] ——U HVDC is the voltage of the high voltage DC output port;

[0066] ——u refx,up and u refx,lw They are the reference voltage signals of the upper and lower bridge arms respectively;

[0067] ——N is the number of bridge arm submodules;

[0068] ——u Cx,up and u Cx,lw are the upper and lower bridge arm submodule capacitor voltages respectively;

[0069] Step 3: In the disturbance compensation signal generator, the PV DC sink port current reference signal I M,ref Input the high frequency reference signal generation module and get the amplitude I M,ref The high-frequency current reference signal i HFx,ref , which is consistent with the actual value of high-frequency current i HFx The error signal obtained after subtraction is input into the PI regulator. The PI regulator outputs the current error compensation signal

[0070] Step 4: Figure 3 The capacitance fluctuation voltage compensation signal of step 2 is converted into the disturbance compensation signal generator (362). and the current error compensation signal generated in step 3 Add together to get the disturbance compensation signal Δu Tx , as the output of the disturbance compensation signal generator;

[0071] Step 5: In the high-frequency voltage synthesis module (361), the high-frequency voltage reference signal u HFx,ref and disturbance compensation signal Δu Tx Synthesize and obtain the high-frequency injection voltage u HFx , the synthesis method is as follows:

[0072] u HFx =u HFx,ref -u Tx ,(x=a,b,c)

[0073] Final high frequency injection voltage u HFx The signal is sent to the MMC bridge arm modulation module to control the thyristor commutation circuit.

[0074] Beneficial effects:

[0075] This invention proposes a novel, large-scale photovoltaic DC energy router with three ports for collection and transmission, employing an "MMC + integrated transformer + thyristor commutation circuit" (MMC: modular multilevel converter) structure. Large-scale photovoltaic power plants can directly transmit power through a "DC collection port - HVDC transmission port" path, while also providing an AC support port. This reduces the number of voltage conversion stages and provides the ability to provide power and actively support the local AC grid, offering a solution for large-scale, base-based transmission of new energy in western China.

[0076] The novel three-port power router proposed in this invention utilizes the high-frequency voltage freedom of the MMC bridge arm to synchronize and coordinate with the thyristor trigger pulse to achieve fully controllable thyristor opening and closing. This solves the problem that the thyristors of semi-controlled devices cannot achieve active opening and closing, and realizes reliable thyristor commutation. A large-scale photovoltaic DC collection port can be constructed by simply connecting a three-phase bridge thyristor circuit to the secondary side of the integrated transformer of the MMC bridge arm. Taking advantage of the large current capacity of thyristors (up to 5000A or more), low conduction loss, mature series voltage balancing technology, and low cost, the photovoltaic DC collection port of the present invention can achieve large-scale photovoltaic energy access at the 100-megawatt level, and has the advantages of low loss, high stability, and low cost.

[0077] Compared with the prior art, the present invention has the following advantages:

[0078] (1) The proposed new three-port power router utilizes the high-frequency voltage freedom of the MMC bridge arm in coordination with the thyristor trigger pulse, making the thyristor on and off fully controllable. This control sequentially controls the thyristors to carry the photovoltaic DC sink port current in turn, ensuring DC current smoothing without the need for a filter. The saved filter capacitors can reduce system costs and equipment size, while also preventing excessive short-circuit fault currents.

[0079] (2) By utilizing the high-frequency voltage freedom of the MMC bridge arm and the synchronous coordination of the thyristor trigger pulse, the high-frequency current is precisely controlled to make the three-phase operation symmetrical. The high-frequency current forms a circulation current inside the three-phase MMC and cancels each other out, eliminating the high-frequency current ripple at the high-voltage DC transmission port and improving the power quality and stability.

[0080] (3) The unique control method of the present invention allows the device of the present invention to construct a large-scale (hundreds of megawatts) photovoltaic DC collection system using only thyristors, semi-controlled devices with large current capacity and low cost. Compared with the existing technology, the present invention does not require the large-scale use of fully controlled devices (such as IGBTs, IGCTs, MOSFETs, etc.) with small current capacity and high cost, thus simplifying the photovoltaic DC collection structure and reducing device costs by approximately 70%. At the same time, thyristors have a lower conduction voltage drop, which means lower conduction losses.

[0081] (4) The present invention proposes a disturbance compensation signal generator solution to solve the problem of thyristor commutation failure caused by the fluctuating voltage of the MMC sub-module capacitor, thereby further improving the reliability and safety of the large-scale photovoltaic DC collection and transmission three-port power router. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] Figure 1 This is a schematic diagram of the structure of a three-port power router for large-scale photovoltaic DC collection and transmission;

[0083] Figure 2 It is a schematic diagram of the principle of synchronous coordination among thyristor trigger signal, high-frequency voltage and high-frequency current signal;

[0084] Figure 3 This is a schematic diagram of the principle of a high-frequency injection voltage generator;

[0085] Figure 4 1 is a schematic diagram of the working waveform of thyristor commutation failure when the control method of the present invention is not adopted;

[0086] Figure 5 The figure is a schematic diagram of the working waveforms of the thyristor for achieving reliable commutation when the control method of the present invention is adopted. DETAILED DESCRIPTION

[0087] The technical solution of the present invention is further described below with reference to the accompanying drawings, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention should be included in the scope of protection of the present invention.

[0088] The first embodiment of the present invention is Figure 1 As shown in FIG, the topology of the proposed large-scale photovoltaic DC collection and transmission three-port power router includes: a thyristor commutation circuit 1, a three-phase high-voltage MMC 2, an integrated transformer 4 and a thyristor commutation control system 3.

[0089] In this embodiment, the power and voltage levels of the three ports are: high-voltage DC transmission port 500MW / ±320kV, photovoltaic DC collection port 500MW / ±50kV, and high-voltage AC support port 500MW / 110kV.

[0090] The thyristor commutation circuit 1 is a three-phase bridge composed of six thyristor valve groups (T1 to T6). Each thyristor valve group consists of N Thy Thyristors are connected in series, N Thy is an integer greater than or equal to 1;

[0091] According to the power and voltage level of the photovoltaic DC collection port (500MW / ±50kV), 4kV / 5kA thyristors are preferred. Each thyristor has a withstand voltage of 2kV, so N is selected. Thy =50.

[0092] The three-phase high-voltage MMC2 consists of phases A, B, and C. The upper and lower bridge arms of each phase are composed of N submodules (SM1~SM N ) is constructed using the two primary windings of integrated transformer 4 as bridge arm inductors connecting the upper and lower bridge arms, while the secondary side of the integrated transformer is connected to the thyristor commutation circuit. The DC busbar of the three-phase high-voltage MMC 2 leads to the high-voltage DC transmission port, and the center tap of the primary winding of integrated transformer 4 leads to the high-voltage AC support port. Based on the power and voltage levels of the high-voltage DC transmission port (500MW / ±320kV) and the high-voltage AC support port (500MW / 110kV), the preferred submodule voltage is 2.24kV, resulting in the number of bridge arm submodules N = 286.

[0093] Thyristor commutation control system 3 generates thyristor valve group trigger pulse g T1 ~g T6 , and are connected to the trigger pins of the thyristor valve groups T1 to T6 respectively to realize the opening control of the thyristor. At the same time, the thyristor commutation control system generates a high-frequency injection voltage (u HFa 、u HFb and u HFc ), the high frequency injection voltage is evenly divided (×0.5) and then injected into the upper and lower bridge arm voltages, which is combined with the thyristor valve group trigger pulse g T1 ~g T6 Synchronous coordination and cooperation realize the commutation control of the thyristor circuit.

[0094] The second embodiment of the present invention is Figure 2 The synchronization signal generated by the synchronization signal generator 32 is a logic signal S with an amplitude of 1. T , the thyristor valve group (T1 ~ T6) trigger pulse (g T1 ~g T6 ) is a logic signal with an amplitude of 1. The thyristor turn-off voltage generator generates the turn-off voltage u of the thyristor valve group (T1 to T6). Tx,off , whose amplitude is U OFF (In this embodiment, select U OFF =70kV); the thyristor commutation control voltage generator generates the commutation control voltage u of the thyristor valve group (T1 ~ T6) Tx,on , whose amplitude is U T (In this embodiment, select U T =35kV); the high-frequency trapezoidal wave voltage generator is responsible for generating the high-frequency voltage basic waveform u Tx,b , whose amplitude is nU M (In this embodiment, the transformer ratio n = 3.5, the photovoltaic DC collection port voltage U M =100kV). The above thyristor trigger pulse (gT1 ~g T6 ) and thyristor turn-off voltage u Tx,off , thyristor commutation control voltage u Tx,on And the high frequency voltage basic waveform u Tx,b According to the synchronization signal S T Align and synthesize the synchronized high-frequency voltage reference signal (u HFa,ref 、u HFb,ref and u HFc,ref ). Further, with the high frequency voltage reference signal (u HFa,ref 、u HFb,ref and u HFc,ref ) and thyristor trigger pulse (g T1 ~g T6 ) The corresponding three-phase high-frequency current reference signal is u HFa,ref 、u HFb,ref and u HFc,ref .

[0095] The third embodiment of the present invention is Figure 3 As shown, it shows the principle of the high-frequency injection voltage generator of the present invention, which includes the following steps:

[0096] Step 1: In Figure 3 In the high-frequency voltage synthesis module 361, the thyristor turn-off voltage u Tx,off , thyristor commutation control voltage u Tx,on And the high frequency voltage basic waveform u Tx,b The high-frequency voltage reference signal u is synthesized HFx,ref , the synthesis method is

[0097] u HFx,ref =u Tx,off +u Tx,on +u Tx,b ,(x=a,b,c)

[0098] Step 2: Figure 3 In the disturbance compensation signal generator, the upper and lower bridge arm submodule voltages (u C,upx and u C,lwx ), high-frequency voltage reference signal u HFx,ref 、Upper and lower bridge arm reference voltage signal (u refx,up and u refx,lw ) Calculate and generate capacitor fluctuation voltage compensation signal The calculation method is as follows:

[0099]

[0100] in:

[0101] ——U HVDC is the voltage of the high voltage DC output port;

[0102] ——u refx,up and u refx,lw They are the reference voltage signals of the upper and lower bridge arms respectively;

[0103] ——N is the number of bridge arm submodules;

[0104] ——u Cx,up and u Cx,lw are the upper and lower bridge arm submodule capacitor voltages respectively.

[0105] Step 3: Figure 3 In the disturbance compensation signal generator, the photovoltaic DC sink port current reference signal I M,ref Input the high frequency reference signal generation module and get the amplitude I M,ref The high-frequency current reference signal i HFx,ref , which is consistent with the actual value of high-frequency current i HFx The error signal obtained after subtraction is input into the PI regulator. The PI regulator outputs the current error compensation signal

[0106] Step 4: Figure 3 In the disturbance compensation signal generator, the capacitor fluctuation voltage compensation signal of step 2 is converted to and the current error compensation signal generated in step 3 Add together to get the disturbance compensation signal Δu Tx , as the output of the disturbance compensation signal generator.

[0107] Step 5: Figure 3 In the high-frequency voltage synthesis module, the high-frequency voltage reference signal u HFx,ref and disturbance compensation signal Δu Tx Synthesize and obtain the high-frequency injection voltage u HFx , the synthesis method is as follows:

[0108] u HFx =u HFx,ref -u Tx ,(x=a,b,c)

[0109] Final high frequency injection voltage u HFx The signal is sent to the MMC bridge arm modulation module to realize the commutation control of the thyristor commutation circuit.

[0110] In order to illustrate the superiority of the control method of the present invention, two embodiments are compared below:

[0111] In one embodiment, the thyristor commutation control system does not adopt the control method of the present invention, that is, it does not have a disturbance compensation signal generator, and its operating waveform is as follows: Figure 4As shown in the figure, the high-frequency voltages of phases A, B, and C are superimposed on the capacitor fluctuation voltage, which in turn affects the high-frequency current waveform. As the fluctuation voltage increases, the high-frequency current is seriously out of control at 0.008s, and the thyristor commutation fails.

[0112] In order to improve the reliability of the three-port power router, the present invention proposes a disturbance compensation signal generator solution to solve the thyristor commutation failure problem caused by the fluctuation voltage of the MMC submodule capacitor. M,ref 、Upper and lower bridge arm submodule voltage (u C,upx and u C,lwx ), high-frequency voltage reference signal u HFx,ref 、Upper and lower bridge arm reference voltage signal (u refx,up and u refx,lw ) calculates and generates the disturbance compensation signal Δu Tx The compensation signal is synthesized into high frequency injection voltage (u HFa 、u HFb and u HFc ), eliminate the influence of the MMC submodule capacitor fluctuation voltage on the thyristor current and solve the thyristor commutation failure problem.

[0113] The key to the aforementioned advancements in the present invention lies in the fact that the proposed novel three-port power router utilizes the high-frequency voltage freedom of the MMC bridge arm in synchronization with the thyristor trigger pulse to make the thyristor switching on and off fully controllable. Specifically:

[0114] In the thyristor commutation control system (3), the synchronization signal generator (32) generates a synchronization signal and transmits it to the thyristor trigger pulse generator (31), the thyristor turn-off voltage generator (33), the thyristor commutation control voltage generator (34) and the high-frequency trapezoidal wave voltage generator (35). The thyristor commutation control system (3) uses the synchronization signal to make the thyristor trigger pulse (g T1 ~g T6 ) and thyristor turn-off voltage u Tx,off , thyristor commutation control voltage u Tx,on And the high frequency voltage basic waveform u Tx,b synchronous;

[0115] The thyristor turn-off voltage u Tx,off , thyristor commutation control voltage u Tx,on And the high frequency voltage basic waveform u Tx,b The high frequency injected voltage (u HFa 、u HFb and u HFc) is injected into the upper and lower bridge arms of the three-phase high-voltage MMC (2), and the upper and lower bridge arms of the three-phase high-voltage MMC (2) are coupled to the secondary winding through the integrated transformer (4), and then act on the thyristor commutation circuit (1), and the thyristor trigger pulse (g T1 ~g T6 ) synchronized and coordinated, making the thyristor opening and closing fully controllable and completing the thyristor reliable commutation. Under this commutation control method, the thyristor valve group (T1~T6) takes turns to carry the photovoltaic DC collection port current I M , a continuous DC current can be synthesized without the need for filter capacitors. The saved filter capacitors can reduce system cost and volume on the one hand, and avoid excessive short-circuit fault current on the other.

[0116] In another embodiment, the thyristor commutation control system adopts the control method of the present invention, and its working waveform is as follows: Figure 5 As shown, the capacitor voltage fluctuation has no effect on the high-frequency voltage, and the high-frequency current runs stably and symmetrically across the three phases. This demonstrates that the control method of the present invention solves the problem of thyristor commutation failure caused by capacitor voltage fluctuation, further improving the reliability and safety of the system. Furthermore, the three-phase symmetrical high-frequency current forms a circulating current within the three phases of the MMC, eliminating high-frequency current ripple at the high-voltage DC output port and improving the system's output power quality.

[0117] The present invention is described by way of several specific embodiments. It should be understood by those skilled in the art that various modifications and equivalent substitutions may be made to the present invention without departing from the scope of the present invention. In addition, various modifications may be made to the present invention for specific situations or circumstances without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed, but is intended to include all embodiments falling within the scope of the claims.

Claims

1. A three-port power router for large-scale photovoltaic DC collection and transmission, characterized by: It includes a thyristor commutation circuit (1), a three-phase high-voltage MMC (2), a thyristor commutation control system (3) and an integrated transformer (4); The thyristor commutation circuit (1) is a three-phase bridge composed of six thyristor valve groups (T1~T6); each thyristor valve group consists of N Thy The DC bus of the thyristor commutation circuit (1) leads to the photovoltaic DC collection port; N Thy is an integer greater than or equal to 1; The three-phase high-voltage MMC (2) consists of phases A, B, and C. The upper and lower bridge arms of each phase are composed of N submodules (SM1~SM N ) is composed; N is an integer greater than 1; The two primary windings of the integrated transformer (4) are connected to the upper and lower bridge arms of the three-phase high-voltage MMC (2) as bridge arm inductors, and the secondary side of the integrated transformer (4) is connected to the three-phase bridge arm of the thyristor commutation circuit (1); The DC bus of the three-phase high-voltage MMC (2) leads to a high-voltage DC output port, and the center tap of the primary winding of the integrated transformer (4) leads to a high-voltage AC support port; The thyristor commutation control system (3) is used to control the commutation of the thyristor commutation circuit (1) and the three-phase high-voltage MMC (2); The thyristor commutation control system (3) is composed of a thyristor trigger pulse generator (31), a synchronization signal generator (32), a thyristor turn-off voltage generator (33), a thyristor commutation control voltage generator (34), a high-frequency trapezoidal wave voltage generator (35), and a high-frequency injection voltage generator (36); the high-frequency injection voltage generator (36) is composed of a high-frequency voltage synthesis module (361) and a disturbance compensation signal generator (362); The thyristor trigger pulse generator (31) is used to generate the trigger pulse (g T1 ~g T6 ), controls the opening of the thyristor; A thyristor turn-off voltage generator (33) is used to generate a turn-off voltage u of the thyristor valve group (T1-T6). Tx,off , control the turn-off control of the thyristor; A thyristor commutation control voltage generator (34) is used to generate a commutation control voltage u for the thyristor valve group (T1-T6). Tx,on , controls the commutation of the thyristor; A high-frequency trapezoidal wave voltage generator (35) is used to generate a high-frequency voltage basic waveform u Tx,b , controlling the primary and secondary voltage matching of the integrated transformer (4); The disturbance compensation signal generator (362) is used to generate a disturbance compensation signal according to the photovoltaic DC collection port current reference signal I M,ref , upper and lower bridge arm submodule voltage (u C,upx 、u C,lwx ) operation to obtain the disturbance compensation signal Δu Tx ; A high-frequency voltage synthesis module (361) is used to receive the disturbance compensation signal Δu Tx and thyristor turn-off voltage u Tx,off , thyristor commutation control voltage u Tx,on and high-frequency trapezoidal wave voltage u Tx,b , and after synthesis, the output is the MMC three-phase high-frequency injection voltage (u HFa 、u HFb and u HFc ), the high-frequency injection voltage of each phase is evenly divided (×0.5) and then injected into the upper and lower bridge arms of the three-phase high-voltage MMC (2).

2. The large-scale photovoltaic DC collection and transmission three-port power router according to claim 1 is characterized in that: The three-phase bridge composed of the six thyristor valve groups (T1 to T6) is specifically connected as follows: The anodes of the thyristor valve group T1, the thyristor valve group T3, and the thyristor valve group T5 are connected in parallel; the cathodes of the thyristor valve group T2, the thyristor valve group T4, and the thyristor valve group T6 are connected in parallel; the cathode of the thyristor valve group T5 is connected to the anode of the thyristor valve group T2; the cathode of the thyristor valve group T3 is connected to the anode of the thyristor T6; and the cathode of the thyristor valve group T1 is connected to the anode of the thyristor valve group T4.

3. The large-scale photovoltaic DC collection and transmission three-port power router according to claim 1 is characterized in that: The two primary windings of the integrated transformer (4) are connected to the upper and lower bridge arms of the three-phase high-voltage MMC (2) as bridge arm inductors, and the secondary side of the integrated transformer (4) is connected to the three-phase bridge arms of the thyristor commutation circuit (1). The specific connection method is: One winding of the primary side of the integrated transformer (4) is connected to the upper bridge arms of the A phase, the B phase, and the C phase of the three-phase high-voltage MMC (2); another winding of the primary side of the integrated transformer (4) is connected to the lower bridge arms of the A phase, the B phase, and the C phase of the three-phase high-voltage MMC (2); The secondary side of the integrated transformer (4) is connected to a three-phase bridge formed by the thyristor valve groups (T1 to T6) of the three-phase bridge arms of the thyristor commutation circuit (1).

4. The control method of the large-scale photovoltaic DC collection and transmission three-port power router according to claim 1 is characterized in that: The method includes: For generating the trigger pulse (g T1 ~g T6 ), a method for controlling the opening of the thyristor; Used to generate the turn-off voltage u of the thyristor valve group (T1~T6) Tx,off , a method for controlling the turn-off control of a thyristor; Used to generate the commutation control voltage u of the thyristor valve group (T1~T6) Tx,on , a method for controlling commutation of thyristors; Used to generate high-frequency voltage basic waveform u Tx,b , a method for controlling the voltage matching between the primary and secondary sides of the integrated transformer (4); Used to calculate the current reference signal I of the photovoltaic DC collection port M,ref , upper and lower bridge arm submodule voltage (u C,upx 、u C,lwx ) operation to obtain the disturbance compensation signal Δu Tx Methods; Used to receive the disturbance compensation signal Δu Tx and thyristor turn-off voltage u Tx,off , thyristor commutation control voltage u Tx,on and high-frequency trapezoidal wave voltage u Tx,b , and after synthesis, the output is the MMC three-phase high-frequency injection voltage (u HFa 、u HFb and u HFc ), the high-frequency injection voltage of each phase is evenly divided (×0.5) and then injected into the upper and lower bridge arms of the three-phase high-voltage MMC (2).

5. The control method of the large-scale photovoltaic DC collection and transmission three-port power router according to claim 4 is characterized in that: The method for controlling the turning on, turning off and commutation of the thyristor is specifically as follows: In the thyristor commutation control system (3), the synchronization signal generator (32) generates a synchronization signal and transmits it to the thyristor trigger pulse generator (31), the thyristor turn-off voltage generator (33), the thyristor commutation control voltage generator (34) and the high-frequency trapezoidal wave voltage generator (35). The thyristor commutation control system (3) uses the synchronization signal to make the thyristor trigger pulse (g T1 ~g T6 ) and thyristor turn-off voltage u Tx,off , thyristor commutation control voltage u Tx,on And the high frequency voltage basic waveform u Tx,b synchronous; The thyristor turn-off voltage u Tx,off , thyristor commutation control voltage u Tx,on And the high frequency voltage basic waveform u Tx,b The high frequency injection voltage (u HFa 、u HFb and u HFc ) is injected into the upper and lower bridge arms of the three-phase high-voltage MMC (2), and is coupled to the secondary winding through the upper and lower bridge arms of the three-phase high-voltage MMC (2) via the integrated transformer (4), and then acts on the thyristor commutation circuit (1), and is combined with the thyristor trigger pulse (g T1 ~g T6 ) synchronized and coordinated to make the turning on and off of the thyristor fully controllable and complete the reliable thyristor commutation.

6. The control method of the large-scale photovoltaic DC collection and transmission three-port power router according to claim 5 is characterized in that: In the method for controlling the opening, closing and commutation of the thyristors, under the commutation control method, the thyristor valve group T1 to the thyristor valve group T6 take turns to carry the photovoltaic DC sink port current I M , and a continuous DC current can be synthesized without the need for a filter capacitor.

7. The control method of the large-scale photovoltaic DC collection and transmission three-port power router according to claim 5 is characterized in that: The method is used to determine the photovoltaic DC collection port current reference signal I M,ref , upper and lower bridge arm submodule voltage (u C,upx and u C,lwx ) operation to obtain the disturbance compensation signal Δu Tx The method, wherein the disturbance compensation signal Δu is obtained Tx The method is as follows: The disturbance compensation signal generator (362) generates a disturbance compensation signal according to the photovoltaic DC collection port current reference signal I M,ref , upper and lower bridge arm submodule voltage (u C,upx and u C,lwx )、high frequency voltage reference signal u HFx,ref 、Upper and lower bridge arm reference voltage signal(u refx,up and u refx,lw ) Calculate and generate the disturbance compensation signal Δu Tx ; The disturbance compensation signal Δu Tx The high frequency voltage synthesis module (361) synthesizes the high frequency injection voltage (u HFa 、u HFb and u HFc ).

8. The control method of the large-scale photovoltaic DC collection and transmission three-port power router according to claim 7 is characterized in that: The disturbance compensation signal generator (362) generates a disturbance compensation signal according to the photovoltaic DC collection port current reference signal I M,ref , upper and lower bridge arm submodule voltage (u C,upx and u C,lwx )、high frequency voltage reference signal u HFx,ref 、Upper and lower bridge arm reference voltage signal(u refx,up and u refx,lw ) Calculate and generate the disturbance compensation signal Δu Tx The method is as follows: The signal of the disturbance compensation signal generator (362) includes a capacitor disturbance voltage compensation signal and a current error compensation signal; in order to obtain the capacitor voltage fluctuation compensation signal, according to the MMC DC loop voltage equation, the primary winding voltage of the integrated transformer (4) is written as follows: （1） in: —— is the transformer primary winding voltage, x=a,b,c; —— is the voltage of the high voltage DC output port; —— and They are the reference voltage signals of the upper and lower bridge arms respectively; ——N is the number of bridge arm submodules; —— and are the upper and lower bridge arm submodule capacitor voltages respectively; The upper and lower bridge arm reference voltage signals contain a DC component ½U HVDC , power frequency component u refx and high frequency component ½u HFx , which is expressed as follows: （2） The capacitor voltage of the upper and lower bridge arm submodules can be expressed as the capacitor voltage rating (U HVDC / N) and ripple voltage (Δu Cx,up and Δu Cx,lw ), the expression is as follows: （3） Substituting equations (2) and (3) into equation (1), the primary winding voltage of the integrated transformer (4) is obtained as: （4） From formula (4), it can be seen that the sum of the capacitance fluctuation voltages of all the sub-modules in the upper and lower arms of the three-phase high-voltage MMC (2) generates a capacitance fluctuation voltage disturbance Δu on the primary winding of the transformer. C,x , and the high frequency voltage u HFx After superposition, they jointly affect the thyristor commutation circuit; In order to eliminate its influence, a capacitor fluctuation voltage compensation signal is added to the high-frequency injection voltage of the upper and lower bridge arms of the three-phase high-voltage MMC (2). ; The capacitor fluctuation voltage compensation signal is calculated by combining equations (1) and (4): as follows: （5） Based on (5), in order to further improve the current control accuracy, the PI regulator is used to generate the current error compensation signal according to the error calculation of the high-frequency current. , and capacitor fluctuation voltage compensation signal After adding, we get the disturbance compensation signal Δu Tx .

9. The control method of a large-scale photovoltaic DC collection and transmission three-port power router according to claim 7, characterized in that: The disturbance compensation signal Δu Tx The high frequency voltage synthesis module (361) synthesizes the high frequency injection voltage (u HFa 、u HFb and u HFc ) is as follows: Step 1: In the high-frequency voltage synthesis module (361), the thyristor turn-off voltage u Tx,off , thyristor commutation control voltage u Tx,on And the high frequency voltage basic waveform u Tx,b The high-frequency voltage reference signal u is synthesized HFx,ref , the synthesis method is: Step 2: In the disturbance compensation signal generator (362), the upper and lower bridge arm submodule voltages (u C,upx and u C,lwx )、high frequency voltage reference signal u HFx,ref 、Upper and lower bridge arm reference voltage signal(u refx,up and u refx,lw ) Calculate and generate capacitor fluctuation voltage compensation signal , which is calculated as follows: in: —— is the voltage of the high voltage DC output port; —— and They are the reference voltage signals of the upper and lower bridge arms respectively; ——N is the number of bridge arm submodules; —— and are the upper and lower bridge arm submodule capacitor voltages respectively; Step 3: In the disturbance compensation signal generator, the PV DC sink port current reference signal I M,ref Input the high frequency reference signal generation module and get the amplitude I M,ref The high-frequency current reference signal i HFx,ref , which is consistent with the actual value of high-frequency current i HFx The error signal obtained after subtraction is input into the PI regulator, and the PI regulator outputs the current error compensation signal ; Step 4: In the disturbance compensation signal generator (362) of FIG3, the capacitance fluctuation voltage compensation signal of step 2 is converted to and the current error compensation signal generated in step 3 Add together to get the disturbance compensation signal Δu Tx , as the output of the disturbance compensation signal generator; Step 5: In the high-frequency voltage synthesis module (361), the high-frequency voltage reference signal u HFx,ref and disturbance compensation signal Δu Tx Synthesize and obtain the high-frequency injection voltage u HFx , the synthesis method is as follows: Final high frequency injection voltage u HFx The signal is sent to the MMC bridge arm modulation module to control the thyristor commutation circuit.

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