A control method and system based on multi-terminal hybrid DC networking

Abstract

The application discloses a control method and system based on multi-terminal hybrid DC networking, and the method comprises the following steps: determining the multi-terminal hybrid DC networking, wherein the AC side of a sending terminal MMC and a sending terminal LCC is connected with a corresponding first new energy base and a second new energy base respectively, and the DC side of the sending terminal MMC and the sending terminal LCC is connected in parallel; the DC side of the sending terminal MMC and the sending terminal LCC connected in parallel is connected with the DC side of a receiving terminal LCC through a DC line, and the AC side of the receiving terminal LCC is connected with a receiving terminal AC power grid; based on the connection state of the first new energy base connected with the sending terminal MMC and the operation state of the sending terminal MMC and the sending terminal LCC, the operation mode of the DC networking is determined; based on the operation mode of the DC networking, the corresponding control method and starting method are determined, and the operation of the hybrid DC system is completed. The application provides a new DC networking mode suitable for some large-scale new energy sending scenarios, and improves the capacity of large-scale new energy through DC sending.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high-voltage direct current transmission technology in the field of power systems, and more particularly, to a control method and system based on multi-terminal hybrid direct current networking. BACKGROUND

[0002] Due to the fact that the western new energy base is far away from the sending end of the AC main grid, direct current transmission is one of the main forms of external transmission.

[0003] Considering the natural geographical and resource environmental restrictions, the new energy base collection forms are complex and diverse. In some cases, the entire source side system presents weak voltage support, and even part of the large-scale new energy station presents island transmission characteristics. If conventional direct current transmission based on line commutated converters (LCC) is used for large-scale new energy base power transmission, in the case of a new energy base connected to the grid or a low proportion of network-forming equipment in the new energy base, the source side and the direct current both need strong support power to operate stably. The operating conditions are relatively harsh, which severely limits the new energy transmission capacity. Flexible direct current transmission based on multilevel modular converters (MMC) can provide certain voltage support capability for the sending end new energy base, but is limited by voltage level and capacity, and still needs further technical improvement in the context of large-scale new energy consumption. New energy through single type direct current transmission technology has been unable to meet the demand for transmission of super large-scale, dispersed development of multiple types of large-scale new energy, and there is an urgent need to study the networking form of new multi-type converter hybrid direct current transmission system. SUMMARY

[0004] The technical scheme of the present application provides a control method and system based on multi-terminal hybrid direct current networking to solve the problem of how to network and control the multi-terminal hybrid direct current transmission of large-scale new energy.

[0005] To solve the above problems, the present application provides a control method based on multi-terminal hybrid direct current networking, which comprises the following steps:

[0006] determining the multi-terminal hybrid direct current networking, wherein the AC side of the sending end MMC and the AC side of the sending end LCC are connected to the corresponding first new energy base and second new energy base respectively, and the DC side of the sending end MMC and the DC side of the sending end LCC are connected in parallel;

[0007] the DC side of the sending end MMC and the DC side of the sending end LCC are connected in parallel and connected to the DC side of the receiving end LCC through a direct current line, and the AC side of the receiving end LCC is connected to the receiving end AC power grid;

[0008] determine a running mode of the DC network based on a connection state of the first new energy base connected with the sending-end MMC and a running state of the sending-end MMC and the sending-end LCC, wherein the connection state comprises access and disconnection, the running state comprises start and stop, and the running mode comprises a first running mode, a second running mode, a third running mode and a fourth running mode;

[0009] determine a corresponding control method and starting method based on the running mode of the DC network to complete the running of the hybrid DC system.

[0010] Preferably, the first running mode is that:

[0011] the first new energy base accesses the sending-end AC power grid, the sending-end MMC and the receiving-end LCC are in the running state, and the sending-end LCC is in the exit running state;

[0012] the second running mode is that:

[0013] the second new energy base accesses the sending-end AC power grid, the sending-end MMC is in the exit running state, and the sending-end LCC and the receiving-end LCC are in the running state;

[0014] the third running mode is that:

[0015] the first new energy base is in island operation, the second new energy base accesses the sending-end AC power grid, and the sending-end MMC, the sending-end LCC and the receiving-end LCC are in the running state;

[0016] the fourth running mode is that:

[0017] the first new energy base accesses the sending-end AC power grid, the second new energy base accesses the sending-end AC power grid, and the sending-end MMC, the sending-end LCC and the receiving-end LCC are in the running state.

[0018] Preferably, the first control method of the first running mode is that:

[0019] the sending-end MMC is controlled by using a virtual synchronous machine, a reactive power ring, a voltage ring and a current ring;

[0020] the receiving-end LCC is controlled by using a constant DC voltage control.

[0021] Preferably, the DC networking-based operation mode determines corresponding control methods and starting methods, wherein a third control method of the third operation mode is:

[0022] The sending-end MMC adopts a constant AC voltage and constant frequency control mode, which includes a voltage loop and a current loop;

[0023] The sending-end LCC adopts constant active power or constant DC current control;

[0024] The receiving-end LCC adopts constant DC voltage control.

[0025] Preferably, the DC networking-based operation mode determines corresponding control methods and starting methods, wherein a fourth control method of the fourth operation mode is:

[0026] The sending-end MMC adopts virtual synchronous machine, reactive power loop, voltage loop and current loop control;

[0027] The sending-end LCC adopts constant active power or constant DC current control;

[0028] The receiving-end LCC adopts constant DC voltage control.

[0029] Preferably, the DC networking-based operation mode determines corresponding control methods and starting methods, wherein a first starting method of the first operation mode is:

[0030] The sending-end MMC is uncontrolled charged;

[0031] The sending-end MMC is controlled charged;

[0032] The receiving-end LCC is unlocked;

[0033] The control strategy of the sending-end MMC is switched to virtual synchronous machine control.

[0034] Preferably, the DC networking-based operation mode determines corresponding control methods and starting methods, wherein a third starting method of the third operation mode is:

[0035] The sending-end LCC and the receiving-end LCC are started;

[0036] The sending-end MMC is uncontrolled charged;

[0037] The sending-end MMC is controlled charged;

[0038] The control strategy of the sending-end MMC is switched to constant AC voltage and constant frequency control;

[0039] The first new energy base is connected to the grid.

[0040] Preferably, the operation mode based on the DC network determines the corresponding control method and starting method, wherein the starting method of the fourth operation mode is:

[0041] The sending end LCC and the receiving end LCC are started;

[0042] The sending end MMC is uncontrolled charged;

[0043] The sending end MMC is controlled charged;

[0044] The sending end MMC is connected on the DC side;

[0045] The control strategy of the sending end MMC is switched to virtual synchronous machine control.

[0046] According to another aspect of the present application, the present application provides a multi-terminal hybrid DC network and control system, the system:

[0047] The first network unit is used for connecting the AC side of the sending end MMC and the sending end LCC to the corresponding first new energy base and the second new energy base respectively, and the DC side of the sending end MMC and the sending end LCC is connected in parallel;

[0048] The second network unit is used for connecting the DC side of the sending end MMC and the sending end LCC in parallel to the DC side of the receiving end LCC through a DC line, and the AC side of the receiving end LCC is connected to the receiving end AC power grid;

[0049] The determination unit is used for determining the operation mode of the DC network based on the connection state of the first new energy base connected to the sending end MMC and the operation state of the sending end MMC and the sending end LCC, wherein the connection state includes access and disconnection, the operation state includes start and stop, and the operation model includes the first operation mode, the second operation mode, the third operation mode and the fourth operation mode;

[0050] The result unit is used for determining the corresponding control method and starting method based on the operation mode of the DC network, and completing the operation of the hybrid DC system.

[0051] Preferably, the determination unit is used for determining the operation mode of the DC network based on the connection state of the first new energy base connected to the sending end MMC and the operation state of the sending end MMC and the sending end LCC, and is also used for:

[0052] The operation mode includes the first operation mode, and the first operation mode is:

[0053] The first new energy base accesses a sending-end AC power grid, the sending-end MMC and the receiving-end LCC are in an operating state, and the sending-end LCC is in an exiting operating state;

[0054] The operating mode includes a second operating mode, and the second operating mode is:

[0055] The second new energy base accesses a sending-end AC power grid, the sending-end MMC is in an exiting operating state, and the sending-end LCC and the receiving-end LCC are in an operating state;

[0056] The operating mode includes a third operating mode, and the third operating mode is:

[0057] The first new energy base is in an island operating state, the second new energy base accesses a sending-end AC power grid, and the sending-end MMC, the sending-end LCC and the receiving-end LCC are in an operating state;

[0058] The operating mode includes a fourth operating mode, and the fourth operating mode is:

[0059] The first new energy base accesses a sending-end AC power grid, the second new energy base accesses a sending-end AC power grid, and the sending-end MMC, the sending-end LCC and the receiving-end LCC are in an operating state.

[0060] Preferably, the result unit is configured to determine a corresponding control method and starting method based on an operating mode of the DC networking, wherein a first control method of the first operating mode is:

[0061] The sending-end MMC is controlled by using a virtual synchronous machine, a reactive power ring, a voltage ring and a current ring;

[0062] The receiving-end LCC is controlled by using a constant DC voltage control.

[0063] Preferably, the result unit is configured to determine a corresponding control method and starting method based on an operating mode of the DC networking, wherein a third control method of the third operating mode is:

[0064] The sending-end MMC is controlled by using a constant AC voltage and constant frequency control mode, and the constant AC voltage and constant frequency control mode includes a voltage ring and a current ring;

[0065] The sending-end LCC is controlled by using a constant active power or constant DC current control;

[0066] The receiving-end LCC is controlled by using a constant DC voltage control.

[0067] Preferably, the result unit is configured to determine a corresponding control method and starting method based on an operating mode of the DC networking, wherein a fourth control method of the fourth operating mode is:

[0068] The sending-end MMC is controlled by a virtual synchronous machine, a reactive power loop, a voltage loop and a current loop;

[0069] The sending-end LCC is controlled by a constant active power or a constant DC current;

[0070] The receiving-end LCC is controlled by a constant DC voltage.

[0071] Preferably, the result unit is configured to determine a corresponding control method and starting method based on an operation mode of the DC network, wherein the first starting method of the first operation mode is:

[0072] The sending-end MMC is uncontrolled charged;

[0073] The sending-end MMC is controlled charged;

[0074] The receiving-end LCC is unlocked;

[0075] The control strategy of the sending-end MMC is switched to the virtual synchronous machine control.

[0076] Preferably, the result unit is configured to determine a corresponding control method and starting method based on an operation mode of the DC network, wherein the starting method of the third operation mode is:

[0077] The sending-end LCC and the receiving-end LCC are started;

[0078] The sending-end MMC is uncontrolled charged;

[0079] The sending-end MMC is controlled charged;

[0080] The control strategy of the sending-end MMC is switched to the constant AC voltage and constant frequency control;

[0081] The first new energy base is connected to the grid.

[0082] Preferably, the result unit is configured to determine a corresponding control method and starting method based on an operation mode of the DC network, wherein the starting method of the fourth operation mode is:

[0083] The sending-end LCC and the receiving-end LCC are started;

[0084] The sending-end MMC is uncontrolled charged;

[0085] The sending-end MMC is controlled charged;

[0086] The sending-end MMC is connected to the DC side;

[0087] Switch the control strategy of the sending-end MMC to adopt a virtual synchronous machine control.

[0088] Based on another aspect of the present application, the present application provides a computer readable storage medium, which stores a computer program for executing a control method based on a multi-terminal hybrid DC network.

[0089] Based on another aspect of the present application, the present application provides an electronic device, comprising a processor and a memory; wherein,

[0090] The memory is configured to store the executable instructions of the processor.

[0091] The processor is configured to read the executable instructions from the memory and execute the instructions to implement a control method based on a multi-terminal hybrid DC network.

[0092] The present application provides a control method and system based on a multi-terminal hybrid DC network, wherein the method comprises determining a multi-terminal hybrid DC network, wherein the AC side of a sending-end MMC and a sending-end LCC is connected to a corresponding first new energy base and a second new energy base respectively, and the DC side of the sending-end MMC and the sending-end LCC is connected in parallel; the DC side of the sending-end MMC and the sending-end LCC connected in parallel is connected to the DC side of a receiving-end LCC through a DC line, and the AC side of the receiving-end LCC is connected to a receiving-end AC power grid; based on the connection state of the first new energy base connected to the sending-end MMC and the operating state of the sending-end MMC and the sending-end LCC, the operating mode of the DC network is determined; wherein the connection state includes access and disconnection; the operating state includes start and stop; the operating mode includes a first operating mode, a second operating mode, a third operating mode and a fourth operating mode; based on the operating mode of the DC network, the corresponding control method and starting method are determined to complete the operation of the hybrid DC system. The present application provides a new DC network mode suitable for some large-scale new energy sending scenarios, improves the capacity of large-scale new energy through DC sending, and reduces the operating cost and loss of the DC system. BRIEF DESCRIPTION OF DRAWINGS

[0093] The exemplary embodiments of the present application can be more completely understood in reference to the following drawings:

[0094] Figure 1 A flow chart of a control method based on a multi-terminal hybrid DC network according to a preferred embodiment of the present application;

[0095] Figure 2 A system structure diagram of a multi-terminal hybrid DC network mode according to a preferred embodiment of the present application.

[0096] Figure 3A sending-end MMC structure diagram according to a preferred embodiment of the present application;

[0097] Figure 4 A sending-end / receiving-end LCC bipolar single 12-pulse wiring mode structure diagram according to a preferred embodiment of the present application;

[0098] Figure 5 An operation mode 1 wiring diagram according to a preferred embodiment of the present application;

[0099] Figure 6 An operation mode 2 wiring diagram according to a preferred embodiment of the present application;

[0100] Figure 7 An operation mode 3 wiring diagram according to a preferred embodiment of the present application;

[0101] Figure 8 An operation mode 4 wiring diagram according to a preferred embodiment of the present application;

[0102] Figure 9 A sending-end MMC virtual synchronous machine control schematic diagram according to a preferred embodiment of the present application;

[0103] Figure 10 A receiving-end LCC constant DC voltage control schematic diagram according to a preferred embodiment of the present application;

[0104] Figure 11 A sending-end MMC constant AC voltage / frequency control schematic diagram according to a preferred embodiment of the present application;

[0105] Figure 12 A sending-end LCC constant active power control schematic diagram according to a preferred embodiment of the present application;

[0106] Figure 13 A mode 1 starting method flow chart according to a preferred embodiment of the present application;

[0107] Figure 14 A mode 3 starting method flow chart according to a preferred embodiment of the present application;

[0108] Figure 15 A mode 4 starting method flow chart according to a preferred embodiment of the present application;

[0109] Figure 16 A control system structure diagram based on a multi-terminal hybrid DC network according to a preferred embodiment of the present application. DETAILED DESCRIPTION

[0110] Reference will now be made to the drawings to describe the exemplary embodiments of the present application in greater detail. The present application can be variously embodied and is not limited to the embodiments described herein, which are provided for the purposes of disclosure and to fully and completely disclose the present application to those skilled in the art. The terms used in the exemplary embodiments of the present application shown in the drawings are terms that are used to describe the present application and are not intended to limit the present application. In the drawings, the same elements are denoted by the same reference numerals.

[0111] Unless otherwise defined, the terms (including technical terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. In addition, it is to be understood that the terms defined by dictionaries and otherwise common usage are to be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and are not to be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0112] Figure 1 A flow chart of a control method based on a multi-terminal hybrid DC networking according to a preferred embodiment of the present application.

[0113] The present application comprehensively utilizes the voltage support capability of flexible DC power transmission and the advantages of low cost and large capacity of conventional DC to form a new DC networking mode suitable for some large-scale new energy sending scenarios, the purpose being to improve the capacity of large-scale new energy sent through DC and reduce the operation cost and loss of the DC system.

[0114] As shown in Figure 1 The present application provides a control method based on a multi-terminal hybrid DC networking, the method comprising the steps of:

[0115] Step 101: determining a multi-terminal hybrid DC networking, wherein the AC side of a sending-end MMC and the AC side of a sending-end LCC are connected to a corresponding first new energy base and a second new energy base respectively, and the DC side of the sending-end MMC and the DC side of the sending-end LCC are connected in parallel; the DC side of the sending-end MMC and the DC side of the sending-end LCC are connected in parallel and connected to the DC side of a receiving-end LCC through a DC line, and the AC side of the receiving-end LCC is connected to a receiving-end AC power grid.

[0116] Figure 2 The multi-terminal hybrid DC networking structure for large-scale new energy sending provided by the present application is composed of a sending-end MMC, a sending-end LCC, a receiving-end LCC, a DC line, etc. The DC side of the sending-end MMC and the DC side of the sending-end LCC are connected in parallel, and the AC side of the sending-end MMC and the AC side of the sending-end LCC are connected to a new energy base 1 and a new energy base 2 respectively; the receiving-end LCC is connected to a receiving-end AC power grid; the sending-end DC and the receiving-end DC are connected through a DC line. In an actual power grid, the new energy base 1 connected to the sending-end MMC can be operated in island mode or connected to a sending-end AC power grid, and the new energy base 2 needs to be connected to the sending-end AC power grid.

[0117] The sending-end MMC adopts a bipolar connection mode, and includes a converter bus, a converter transformer, a half-bridge MMC converter, a pole line reactor, a neutral line reactor, an AC starting resistor, a DC starting resistor, and a grounding pole system, and has a structure as shown in Figure 3 The sending-end LCC and the receiving-end LCC have the same structure, adopt a bipolar connection mode, and include a converter bus, a converter transformer, an LCC converter, an AC filter, a DC filter, a smoothing reactor, and a grounding pole system, and the converter can adopt a bipolar single 12-pulse connection mode or a bipolar double 12-pulse connection mode according to different voltage levels, wherein the LCC structure of the bipolar single 12-pulse connection mode is as shown in Figure 4

[0118] The capacity of the receiving-end LCC is equal to the sum of the capacities of the sending-end MMC and the LCC, that is, the total capacity of the DC system. Meanwhile, the capacities of the sending-end MMC and the LCC need to match the capacity of the new energy to be sent out, so as to ensure that the new energy output reaches the maximum and can still be sent out to the receiving-end AC power grid through the DC system.

[0119] Step 102: determining an operation mode of the DC networking based on a connection state of a first new energy base connected with the sending-end MMC and operation states of the sending-end MMC and the sending-end LCC, wherein the connection state includes access and disconnection, the operation state includes start and stop, and the operation mode includes a first operation mode, a second operation mode, a third operation mode, and a fourth operation mode.

[0120] Step 103: determining a corresponding control method and starting method based on the operation mode of the DC networking, and completing the transmission of the DC.

[0121] Preferably, the operation mode of the DC networking is determined based on the connection state of the first new energy base connected with the sending-end MMC and the operation states of the sending-end MMC and the sending-end LCC, the first operation mode is that:

[0122] the first new energy base accesses the sending-end AC power grid, the sending-end MMC and the receiving-end LCC are in the operation state, and the sending-end LCC is in an exit operation state;

[0123] the second operation mode is that:

[0124] the second new energy base accesses the sending-end AC power grid, the sending-end MMC is in the exit operation state, and the sending-end LCC and the receiving-end LCC are in the operation state;

[0125] the third operation mode is that:

[0126] the first new energy base is in island operation, the second new energy base accesses the sending-end AC power grid, and the sending-end MMC, the sending-end LCC, and the receiving-end LCC are in the operation state;

[0127] ​The fourth operation mode is:

[0128] The first new energy base is connected to the sending end AC power grid, the second new energy base is connected to the sending end AC power grid, the sending end MMC, the sending end LCC and the receiving end LCC are in an operation state.

[0129] According to whether the sending end new energy base 1 is connected to the sending end AC power grid and whether the sending end MMC and the sending end LCC are put into operation, the DC networking mode of the application has four operation modes.

[0130] Figure 5 It is the wiring diagram of the first operation mode, the new energy base 1 is connected to the AC power grid, the sending end MMC and the receiving end LCC are operated, and the sending end LCC is out of operation. In this mode, the sending end new energy base 1 can be sent out through the sending end MMC and the receiving end LCC.

[0131] Figure 6 It is the wiring diagram of the second operation mode, the sending end MMC is out of operation, the sending end LCC and the receiving end LCC are operated. In this mode, the sending end new energy base 2 can be sent out through the sending end LCC and the receiving end LCC.

[0132] Figure 7 It is the wiring diagram of the third operation mode, the sending end new energy base 1 is operated in island mode, and the sending end and the receiving end DC are in an operation state. In this mode, the sending end new energy base 1 can be sent out through the sending end MMC, and the new energy base 2 can be sent out through the sending end LCC.

[0133] Figure 8 It is the wiring diagram of the fourth operation mode, the sending end new energy base 1 is connected to the sending end AC power grid, and the sending end and the receiving end DC are in an operation state. In this mode, the sending end new energy can be sent out through the hybrid DC system.

[0134] Preferably, based on the operation mode of the DC networking, the corresponding control method and starting method are determined, wherein the first control method of the first operation mode is:

[0135] The sending end MMC is controlled by using a virtual synchronous machine, a reactive power ring, a voltage ring and a current ring;

[0136] The receiving end LCC adopts a constant DC voltage control.

[0137] Preferably, based on the operation mode of the DC networking, the corresponding control method and starting method are determined, wherein the third control method of the third operation mode is:

[0138] The sending end MMC adopts a constant AC voltage and constant frequency control mode, and the constant AC voltage and constant frequency control includes a voltage ring and a current ring;

[0139] The sending end LCC adopts a constant active power or constant DC current control;

[0140] The receiving LCC adopts constant DC voltage control.

[0141] Preferably, based on the operation mode of the DC network, corresponding control methods and starting methods are determined, wherein the fourth control method of the fourth operation mode is:

[0142] The sending MMC adopts virtual synchronous machine, reactive power ring, voltage ring and current ring for control;

[0143] The sending LCC adopts constant active power or constant DC current control;

[0144] The receiving LCC adopts constant DC voltage control.

[0145] Preferably, based on the operation mode of the DC network, corresponding control methods and starting methods are determined, wherein the first starting method of the first operation mode is:

[0146] The sending MMC is uncontrolled charged;

[0147] The sending MMC is controlled charged;

[0148] The receiving LCC is unlocked;

[0149] The control strategy of the sending MMC is switched to adopt virtual synchronous machine control.

[0150] Preferably, based on the operation mode of the DC network, corresponding control methods and starting methods are determined, wherein the starting method of the third operation mode is:

[0151] The sending LCC and the receiving LCC are started;

[0152] The sending MMC is uncontrolled charged;

[0153] The sending MMC is controlled charged;

[0154] The control strategy of the sending MMC is switched to adopt constant AC voltage and constant frequency control;

[0155] The first new energy base is connected to the grid for operation.

[0156] Preferably, based on the operation mode of the DC network, corresponding control methods and starting methods are determined, wherein the starting method of the fourth operation mode is:

[0157] The sending LCC and the receiving LCC are started;

[0158] The sending MMC is uncontrolled charged;

[0159] The sending MMC is controlled charged;

[0160] The sending end MMC is connected at the DC side;

[0161] The control strategy of the sending end MMC is switched to virtual synchronous machine control.

[0162] The application performs steady-state control of DC networking mode, comprising:

[0163] 1) Mode 1 steady-state control method

[0164] In mode 1, the new energy base 1 is connected to the AC power grid, and the sending end MMC adopts virtual synchronous machine control to improve the inertia support and voltage support capability of the sending end power grid. The virtual synchronous machine control includes four parts, namely virtual synchronous machine, reactive power ring, voltage ring and current ring, and the control block is as shown in Figure 9 .

[0165] Among them, P ref and P are active power reference value and measured value, ω0, ω are angular frequency reference value and reference value, θ is phase reference value, J is rotational inertia, D is damping coefficient, Q ref and Q are reactive power reference value and measured value, U ref is the AC voltage amplitude reference value, u sdref , u sd are the d-axis voltage reference value and measured value of the power grid, u sqref , u sq are the q-axis voltage reference value and measured value of the power grid, i dref , i d are the d-axis current reference value and measured value, i qref , i q are the q-axis current reference value and measured value (the current is positive when flowing into the converter), u vdr , u vqr are the d-axis reference value and q-axis reference value of the converter output voltage, and L is the leakage inductance of the converter transformer.

[0166] Since the active power of the system is determined by the sending end, the receiving end LCC is mainly responsible for controlling the stability of the DC voltage, and adopts the typical constant DC voltage control, and the control block is as shown in Figure 10 .

[0167] Among them, U dc2 is the receiving end DC voltage measured value, U dcref is the sending end DC voltage reference value, I dc2 is the receiving end DC current measured value, R line is the DC line resistance, and γ is the reference value of the off angle.

[0168] 2) Mode 2 steady-state control method

[0169] Mode 2 is LCC end-to-end DC, which can use existing mature control methods without the need to design special control strategies.

[0170] 3) Mode 3 steady-state control method

[0171] In mode 3, new energy base 1 operates in island mode and needs AC voltage support, so the sending-end MMC needs to provide island new energy AC voltage. Here, a typical constant AC voltage / frequency (V / f) control method is used, and the control block is as shown in Figure 11 .

[0172] The sending-end MMC constant AC voltage / frequency control of the application includes a voltage loop and a current loop, which are the same as the voltage loop and the current loop of the virtual synchronous machine control. The angular frequency reference value here is ω = 2πf, and f is the power frequency of 50 Hz.

[0173] The sending-end LCC in mode 3 uses constant active power or constant DC current control, and the control block of constant active power is as shown in Figure 12 .

[0174] In the formula, P LCCref is the active power reference value of the sending-end LCC, U dc1 is the DC voltage measurement value of the sending-end LCC, I LCC and I LCCref are the LCC DC side current measurement value and reference value (with the sending-end flow to the receiving-end as positive), and α is the LCC trigger angle reference value.

[0175] The receiving-end LCC uses constant DC voltage control, which is the same as mode 1.

[0176] 4) Mode 4 steady-state control method

[0177] In mode 4, new energy base 1 is connected to the AC grid, and the sending-end MMC uses virtual synchronous machine control, which is the same as mode 1.

[0178] The sending-end LCC uses constant active power or constant DC current control, which is the same as mode 3.

[0179] The receiving-end LCC uses constant DC voltage control, which is the same as mode 1.

[0180] (3) Starting method of DC networking mode

[0181] The starting method of the new DC networking mode needs to be designed according to different operating modes. Mode 2 is LCC end-to-end DC, which can use existing mature starting methods without the need for special design.

[0182] For mode 1, new energy base 1 operates in networked mode. The sending-end MMC can be charged through the AC side first, and then the DC power transmission is started. The specific steps are as follows:

[0183] 1) Sending MMC uncontrollable charging: close the AC circuit breaker, the AC grid charges the submodule capacitor, the starting resistor suppresses the overcurrent during the charging process, and the submodule capacitor voltage rises to U p-p / N, where U p-p is the peak value of the sending AC line voltage, N is the total number of MMC single bridge arm submodules, and then bypass the AC starting resistor.

[0184] 2) Sending MMC controllable charging: unlock the converter, set the reference value of the MMC DC voltage control to the DC voltage reference value U dcref , the DC side voltage rises to U dcref , and the submodule capacitor voltage reaches U dcref / N.

[0185] 3) Receiving LCC unlocking: the receiving LCC is unlocked and uses fixed DC voltage control.

[0186] 4) Sending MMC control strategy switching: the sending MMC quickly switches the control strategy to virtual synchronous machine control, delivering minimum DC current, then the sending new energy base 1 starts and the DC power transmission is correspondingly increased, and the new energy output is sent to the receiving grid.

[0187] The mode 1 starting control method flow is shown in Figure 13 .

[0188] For mode 3, new energy base 1 island operation, it needs to start the LCC at both ends first, and then start the sending MMC, the specific steps are as follows:

[0189] 1) Sending and receiving LCC starting: the LCC starting method uses the LCC DC conventional starting method, the receiving end is unlocked after the sending end is unlocked, the DC voltage is established, and the minimum DC current is delivered. Then, according to the grid operation demand, the LCC sending new energy base 2 is started, and the LCC power transmission is correspondingly increased, and the power of new energy base 2 is sent out by the sending LCC-receiving LCC.

[0190] 2) Sending MMC uncontrollable charging: close the DC circuit breaker, the DC line charges the submodule capacitor, the DC starting resistor suppresses the overcurrent during the charging process, until the submodule capacitor voltage rises to U dc1 / 2N, where U dc1 is the sending DC voltage.

[0191] 3) Sending MMC controllable charging: the MMC submodule uses the active charging method to continue charging through the DC side to unlock the MMC by setting all submodules, adjust the number of submodules of each bridge arm to N / 2, and at the same time ensure the consistency of the single bridge arm submodule capacitor voltage through the voltage balancing strategy, until the capacitor voltage of each submodule reaches U dc1 / N, and then bypass the DC starting resistor.

[0192] 4) Send MMC control strategy switching: After the active charging is completed, the MMC control strategy is switched to V / f control, and the AC voltage on the new energy side is established.

[0193] 5) Island new energy grid-connected operation: Start the island new energy base 1 connected to the send MMC, and the island new energy will send out power through the send MMC-receive LCC.

[0194] The mode 3 start control method flow is shown in Figure 14 .

[0195] For mode 4, the new energy base 1 is in grid-connected operation, and the specific start steps are as follows:

[0196] 1) Send and receive LCC start: The LCC start method adopts the LCC DC conventional start method, the send end is unlocked after the receive end is unlocked, the DC voltage is established, and the minimum DC current is transmitted. Then, according to the grid operation demand, the send LCC new energy base 2 is started, and the LCC power transmission power is correspondingly increased, and the power of the new energy base 2 is sent out by the send LCC-receive LCC.

[0197] 2) Send MMC uncontrollable charging: Close the AC circuit breaker, and the AC grid charges the sub-module capacitor. The AC starting resistor suppresses the overcurrent in the charging process, until the sub-module capacitor voltage rises to U p-p / N, and then the AC starting resistor is bypassed.

[0198] 3) Send MMC controllable charging: Unlock the converter, and input the MMC constant DC voltage control. The DC voltage reference value is the send DC voltage measurement value U dc1 , the DC side voltage rises to U dc1 , and the sub-module capacitor voltage reaches U dc1 / N.

[0199] 4) Send MMC DC side connection: The DC circuit breaker at the outlet of the MMC DC side is closed, and the MMC DC side and the LCC are connected in parallel.

[0200] 5) Send MMC control strategy switching: The MMC constant DC voltage control is switched to the virtual synchronous machine control. Then, according to the grid operation demand, the send new energy base 1 is started, and the MMC DC power transmission power is correspondingly increased, and the power of the new energy base 1 is sent out by the send MMC-receive LCC.

[0201] The mode 4 start control method flow is shown in Figure 15 .

[0202] This invention provides a multi-terminal hybrid DC grid configuration for large-scale renewable energy transmission. The transmitting end consists of a parallel connection of an LCC and a MMC. The transmitting end LCC can transmit renewable energy with voltage support, while the MMC can transmit isolated renewable energy or improve the inertia and voltage support capability of the transmitting end grid. Both transmit renewable energy power to the receiving end through DC lines, and the receiving end LCC is used to control the DC voltage.

[0203] Meanwhile, this invention provides a control method for the proposed DC grid configuration. Its steady-state control method can ensure the stable output of new energy sources, while the system startup method can ensure the normal establishment of active power transmission of new energy sources and hybrid DC systems through the orderly startup of LCC, MMC and new energy units, and ultimately enable the system to enter stable operation.

[0204] The DC grid connection method of the present invention can make full use of the advantages of MMC and LCC, providing a feasible solution for large-scale new energy transmission scenarios, improving the DC system's ability to transmit large-scale new energy, and reducing investment costs and operating losses.

[0205] The multi-terminal hybrid DC grid method for large-scale new energy transmission proposed in this invention includes a sending-end MMC, a sending-end LCC, a receiving-end LCC, DC lines, and other equipment. Depending on the new energy connection method and whether the sending-end DC is in operation, there are four operating modes for the DC grid method.

[0206] The present invention proposes a control method for multi-terminal hybrid DC grid configuration for large-scale renewable energy transmission, which is designed for different operating modes, including steady-state control method and starting method.

[0207] Figure 16 This is a structural diagram of a control system based on a multi-terminal hybrid DC network according to a preferred embodiment of the present invention.

[0208] like Figure 16 As shown, this invention provides a control system based on a multi-terminal hybrid DC network. The system includes:

[0209] The first networking unit 1601 is used to connect the AC side of the sending-end MMC and the sending-end LCC to the corresponding first new energy base and the second new energy base respectively, and the DC side of the sending-end MMC and the sending-end LCC are connected in parallel.

[0210] The second networking unit 1602 is used to connect the DC sides of the sending-end MMC and the sending-end LCC in parallel and then connect them to the DC side of the receiving-end LCC through a DC line. The AC side of the receiving-end LCC is connected to the receiving-end AC power grid.

[0211] The determining unit 1603 is configured to determine an operation mode of the DC network based on a connection state of the first new energy base connected with the sending-end MMC and operation states of the sending-end MMC and the sending-end LCC, wherein the connection state comprises access and disconnection, the operation state comprises start and stop, and the operation mode comprises a first operation mode, a second operation mode, a third operation mode and a fourth operation mode.

[0212] Preferably, the determining unit 1603 is configured to determine the operation mode of the DC network based on the connection state of the first new energy base connected with the sending-end MMC and the operation states of the sending-end MMC and the sending-end LCC, and the first operation mode is that:

[0213] The first new energy base accesses the sending-end AC power grid, the sending-end MMC and the receiving-end LCC are in the operation state, and the sending-end LCC is in the exit operation state.

[0214] The second operation mode is that:

[0215] The second new energy base accesses the sending-end AC power grid, the sending-end MMC is in the exit operation state, and the sending-end LCC and the receiving-end LCC are in the operation state.

[0216] The third operation mode is that:

[0217] The first new energy base is in island operation, the second new energy base accesses the sending-end AC power grid, and the sending-end MMC, the sending-end LCC and the receiving-end LCC are in the operation state.

[0218] The fourth operation mode is that:

[0219] The first new energy base accesses the sending-end AC power grid, the second new energy base accesses the sending-end AC power grid, and the sending-end MMC, the sending-end LCC and the receiving-end LCC are in the operation state.

[0220] The result unit 1604 is configured to determine a corresponding control method and start method based on the operation mode of the DC network, and complete the transmission of the DC.

[0221] Preferably, the result unit 1604 is configured to determine the corresponding control method and start method based on the operation mode of the DC network, and the first control method of the first operation mode is that:

[0222] The sending-end MMC is controlled by using a virtual synchronous machine, a reactive power ring, a voltage ring and a current ring.

[0223] The receiving-end LCC is controlled by using a constant DC voltage control.

[0224] Preferably, the result unit 1604 is configured to determine the corresponding control method and start method based on the operation mode of the DC network, and the third control method of the third operation mode is that:

[0225] The sending-end MMC adopts a constant AC voltage and constant frequency control mode, and the constant AC voltage and constant frequency control includes a voltage loop and a current loop;

[0226] The sending-end LCC adopts constant active power or constant DC current control;

[0227] The receiving-end LCC adopts constant DC voltage control.

[0228] Preferably, the result unit 1604 is configured to determine a corresponding control method and starting method based on an operation mode of the DC network, wherein a fourth control method of a fourth operation mode is:

[0229] The sending-end MMC adopts virtual synchronous machine, reactive power loop, voltage loop and current loop for control;

[0230] The sending-end LCC adopts constant active power or constant DC current control;

[0231] The receiving-end LCC adopts constant DC voltage control.

[0232] Preferably, the result unit 1604 is configured to determine a corresponding control method and starting method based on an operation mode of the DC network, wherein a first starting method of a first operation mode is:

[0233] The sending-end MMC is subjected to uncontrolled charging;

[0234] The sending-end MMC is subjected to controllable charging;

[0235] The receiving-end LCC is subjected to unlocking;

[0236] The control strategy of the sending-end MMC is switched to virtual synchronous machine control.

[0237] Preferably, the result unit 1604 is configured to determine a corresponding control method and starting method based on an operation mode of the DC network, wherein a starting method of a third operation mode is:

[0238] The sending-end LCC and the receiving-end LCC are started;

[0239] The sending-end MMC is subjected to uncontrolled charging;

[0240] The sending-end MMC is subjected to controllable charging;

[0241] The control strategy of the sending-end MMC is switched to constant AC voltage and constant frequency control;

[0242] The first new energy base is subjected to grid-connected operation.

[0243] Preferably, the result unit 1604 is configured to determine a corresponding control method and starting method based on the operation mode of the direct current network, wherein the starting method of the fourth operation mode is:

[0244] starting the sending end LCC and the receiving end LCC;

[0245] uncontrollably charging the sending end MMC;

[0246] controllably charging the sending end MMC;

[0247] connecting the direct current side of the sending end MMC;

[0248] switching the control strategy of the sending end MMC to the virtual synchronous machine control.

[0249] The multi-terminal hybrid direct current network and control system of the preferred embodiment of the present application corresponds to the control method based on the multi-terminal hybrid direct current network of another preferred embodiment of the present application, which will not be described here.

[0250] The present application provides a computer readable storage medium, which stores a computer program, and the computer program is used to execute the control method based on the multi-terminal hybrid direct current network.

[0251] The present application provides an electronic device, which comprises a processor and a memory, wherein

[0252] The memory is configured to store the processor executable instructions.

[0253] The processor is configured to read the executable instructions from the memory and execute the instructions to implement the multi-terminal hybrid direct current network and control method.

[0254] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can be in the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can be in the form of a computer program product implemented on one or more computer usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer usable program code. The solutions in the embodiments of the present application can be implemented in various computer languages, such as object-oriented programming language Java and interpreted scripting language JavaScript.

[0255] The present application is described in reference to the flowchart and / or block diagram of the method, apparatus (system) and computer program product according to an embodiment of the present application. It is understood that each flow and / or block in the flowchart and / or block diagram, and a combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general purpose computer, a special purpose computer, an embedded processor or other programmable data processing device to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing device, create means for implementing the functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more flows and / or blocks. Figure 1 one or more blocks or a combination of one or more flows and / or blocks.

[0256] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including an instruction means that implements the function specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more flows and / or blocks. Figure 1 one or more blocks or a combination of one or more flows and / or blocks.

[0257] These computer program instructions can also be loaded onto a computer or other programmable data processing device to cause a series of operational steps to be performed on the computer or other programmable device to produce a computer implemented process such that the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more flows and / or blocks. Figure 1 one or more blocks or a combination of one or more flows and / or blocks.

[0258] While the preferred embodiments of the application have been described, additional variations and modifications can be made to the embodiments by those skilled in the art once they learn of the basic inventive concepts. Therefore, the appended claims are intended to cover all such modifications and variations as fall within the true spirit and scope of the application.

[0259] It is apparent that a person skilled in the art can make various changes and modifications to the application without departing from the spirit and scope thereof. Thus, if these modifications and variations fall within the scope of the patent claims and their equivalents, it is intended to include them in the application.

[0260] The application has been described with reference to a few embodiments. However, one skilled in the art will understand that the application is not limited to the embodiments described, but rather only by the claims and their equivalents.

[0261] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / an / the [device, component, etc.] are to be interpreted openly as referring to at least one instance of the device, component, etc., unless otherwise indicated. The steps of any methods disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

Claims

1. A control method based on a multi-terminal hybrid DC network, the method comprising: determining a multi-terminal hybrid DC network, wherein: AC sides of a sending MMC and a sending LCC are connected to corresponding first and second new energy bases respectively, DC sides of the sending MMC and the sending LCC are connected in parallel, DC sides of the sending MMC and the sending LCC connected in parallel are connected to a DC side of a receiving LCC through a DC line, and an AC side of the receiving LCC is connected to a receiving AC power grid; determining an operation mode of the DC network based on a connection state of the first new energy base connected to the sending MMC and operation states of the sending MMC and the sending LCC, wherein the connection state comprises: access and disconnection, the operation states comprise: start and stop, and the operation mode comprises: a first operation mode, a second operation mode, a third operation mode and a fourth operation mode; the first operation mode is: the first new energy base accesses a sending AC power grid, the sending MMC and the receiving LCC are in an operation state, and the sending LCC is in an exit operation state; the second operation mode is: the second new energy base accesses the sending AC power grid, the sending MMC is in an exit operation state, and the sending LCC and the receiving LCC are in an operation state; the third operation mode is: the first new energy base operates in an island mode, the second new energy base accesses the sending AC power grid, and the sending MMC, the sending LCC and the receiving LCC are in an operation state; and the fourth operation mode is: the first new energy base accesses the sending AC power grid, the second new energy base accesses the sending AC power grid, and the sending MMC, the sending LCC and the receiving LCC are in an operation state; and determining a corresponding control method and a starting method based on the operation mode of the DC network to complete operation of the hybrid DC system. 2.The method of claim 1, wherein the first control method of the first operation mode is: the sending MMC is controlled by a virtual synchronous machine, a reactive power ring, a voltage ring and a current ring; and the receiving LCC is controlled by a constant DC voltage control. 3.The method of claim 1, wherein the third control method of the third operation mode is: the sending MMC is controlled by a constant AC voltage and a constant frequency control mode, the constant AC voltage and the constant frequency control mode comprising a voltage ring and a current ring; the sending LCC is controlled by a constant active power or a constant DC current control; and the receiving LCC is controlled by a constant DC voltage control. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 4. The method of claim 1, wherein the fourth operation mode of the DC networking based operation mode determines a corresponding control method and starting method, wherein the fourth control method of the fourth operation mode is: the sending end MMC is controlled by a virtual synchronous machine, a reactive power ring, a voltage ring and a current ring; the sending end LCC is controlled by a constant active power or a constant DC current; the receiving end LCC is controlled by a constant DC voltage.

5. The method of claim 1, wherein the first starting method of the first operation mode of the DC networking based operation mode is: uncontrollable charging of the sending end MMC; controllable charging of the sending end MMC; unlocking of the receiving end LCC; switching the control strategy of the sending end MMC to virtual synchronous machine control.

6. The method of claim 1, wherein the starting method of the third operation mode of the DC networking based operation mode is: starting of the sending end LCC and the receiving end LCC; uncontrollable charging of the sending end MMC; controllable charging of the sending end MMC; switching the control strategy of the sending end MMC to constant AC voltage and constant frequency control; grid connection operation of the first new energy base.

7. The method of claim 1, wherein the starting method of the fourth operation mode of the DC networking based operation mode is: starting of the sending end LCC and the receiving end LCC; uncontrollable charging of the sending end MMC; controllable charging of the sending end MMC; DC side connection of the sending end MMC; switching the control strategy of the sending end MMC to virtual synchronous machine control.

8. A control system based on multi-terminal hybrid DC networking, the system comprising: a first networking unit for connecting AC sides of a sending end MMC and a sending end LCC to corresponding first and second new energy bases respectively, and connecting DC sides of the sending end MMC and the sending end LCC in parallel; a second networking unit for connecting DC sides of the sending end MMC and the sending end LCC in parallel to a DC side of a receiving end LCC through a DC line, and connecting an AC side of the receiving end LCC to a receiving end AC power grid; a determination unit for determining an operation mode of the DC networking based on a connection state of the first new energy base connected to the sending end MMC and operation states of the sending end MMC and the sending end LCC, wherein the connection state includes: access and disconnection; the operation state includes: starting and stopping; and the operation mode includes: a first operation mode, a second operation mode, a third operation mode and a fourth operation mode; and the determination unit is configured to determine the operation mode of the DC networking based on the connection state of the first new energy base connected to the sending end MMC and the operation states of the sending end MMC and the sending end LCC, and the first operation mode is: The first new energy base accesses a sending end alternating current power grid, the sending end MMC and the receiving end LCC are in an operating state, and the sending end LCC is in an exiting operating state; The second operating mode is: The second new energy base accesses the sending end alternating current power grid, the sending end MMC is in an exiting operating state, and the sending end LCC and the receiving end LCC are in an operating state; The third operating mode is: The first new energy base is in an island operating state, the second new energy base accesses the sending end alternating current power grid, and the sending end MMC, the sending end LCC and the receiving end LCC are in an operating state; The fourth operating mode is: The first new energy base accesses the sending end alternating current power grid, the second new energy base accesses the sending end alternating current power grid, and the sending end MMC, the sending end LCC and the receiving end LCC are in an operating state; A result unit is configured to determine a corresponding control method and starting method based on an operating mode of the DC networking, and complete operation of the hybrid DC system. 9.The system of claim 8, wherein the result unit is configured to determine a corresponding control method and starting method based on an operating mode of the DC networking, and the first control method of the first operating mode is: The sending end MMC is controlled by using a virtual synchronous machine, a reactive power ring, a voltage ring and a current ring; The receiving end LCC is controlled by using a constant DC voltage. 10.The system of claim 8, wherein the result unit is configured to determine a corresponding control method and starting method based on an operating mode of the DC networking, and the third control method of the third operating mode is: The sending end MMC is controlled by using a constant AC voltage and a constant frequency control mode, the constant AC voltage and constant frequency control mode comprises a voltage ring and a current ring; The sending end LCC is controlled by using a constant active power or a constant DC current; The receiving end LCC is controlled by using a constant DC voltage. 11.The system of claim 8, wherein the result unit is configured to determine a corresponding control method and starting method based on an operating mode of the DC networking, and the fourth control method of the fourth operating mode is: The sending end MMC is controlled by using a virtual synchronous machine, a reactive power ring, a voltage ring and a current ring; The sending end LCC is controlled by using a constant active power or a constant DC current; The receiving end LCC is controlled by using a constant DC voltage. 12.The system of claim 8, wherein the result unit is configured to determine a corresponding control method and starting method based on an operating mode of the DC networking, and the first starting method of the first operating mode is: The sending end MMC is uncontrolled charged; The sending end MMC is controlled charged; The receiving end LCC is unlocked; The control strategy of the sending end MMC is switched to using a virtual synchronous machine control. 13.The system of claim 8, wherein the result unit is configured to determine a corresponding control method and starting method based on an operating mode of the DC networking, and the starting method of the third operating mode is: The sending end LCC and the receiving end LCC are started; The sending end MMC is uncontrolled charged; The sending end MMC is controlled charged. switching a control strategy of the sending-end MMC to employ a constant AC voltage and a constant frequency control; performing grid-connected operation on the first new energy base. 14.The system of claim 8, wherein the result unit is configured to determine a corresponding control method and starting method based on an operation mode of the DC network, and wherein the starting method of the fourth operation mode is: starting the sending-end LCC and the receiving-end LCC; uncontrollably charging the sending-end MMC; controllably charging the sending-end MMC; connecting the sending-end MMC at a DC side; switching a control strategy of the sending-end MMC to employ a virtual synchronous machine control.

15. A computer-readable storage medium, characterized in that, The computer readable storage medium stores a computer program for executing the method of any one of claims 1-7.

16. An electronic device, comprising: The electronic device comprises a processor and a memory; wherein, The memory is configured to store the executable instructions of the processor. The processor is configured to read the executable instructions from the memory and execute the instructions to implement the method of any one of claims 1-7.

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