New energy direct current collecting and sending-out system and control method thereof

Abstract

The invention relates to the technical field of direct current collecting and sending out, and particularly provides a new energy direct current collecting and sending out system and a control method thereof, and the system comprises a new energy station, a network construction type energy storage device, a distributed diode rectifier, a direct current circuit breaker, a direct current power transmission line, and a controllable commutation current converter. The alternating current of the new energy station is rectified by a distributed diode rectifier, then is subjected to direct current collection, and is sent to a receiving end alternating current power grid through a direct current power transmission line; a direct-current circuit breaker is arranged between the direct-current output end of the distributed diode rectifier and the direct-current power transmission line; and the receiving-end alternating-current power grid adopts a controllable commutation current converter to invert direct current of the direct-current power transmission line into alternating current. The technical scheme provided by the invention is flexible in design, easy to maintain, high in capacity and voltage grade expansibility, good in economical efficiency, good in networking flexibility, suitable for island or weak network new energy collection grid connection and long-distance transmission scenes, wide in application scene and outstanding in advantage effect.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current collection and transmission, and in particular to a new energy direct current collection and transmission system and a control method thereof. Background Art

[0002] Under the current grid structure and development model, the AC grid connection in new energy-intensive areas leads to serious reverse overload problems in the power grid. In addition, the shortage of transmission corridors leads to high investment costs and construction difficulties in power grid facilities. At the same time, the gradual increase in the proportion of wind and solar power and other new energy installed capacity has led to increasingly prominent low inertia and hollowing characteristics of the system. The safe and stable operation of the power grid will face huge challenges, and a safer and more efficient new energy collection and transmission solution is urgently needed.

[0003] In response to the above problems, the current solutions for the collection and transmission of new energy include AC solutions and flexible DC solutions. (1) AC solution: New energy is collected through AC and gradually stepped up for transmission, relying on strong grid support; this solution is mature in technology and suitable for local consumption of new energy, especially for scenarios with short transmission distances and small transmission capacities; however, with the large-scale access of new energy, this solution may lead to reduced system strength and stability; and this solution has no support capacity for the receiving grid; in addition, large-scale access to new energy may cause overload of the main transformer and line, while long-distance and large-capacity power transmission requires additional equipment to maintain grid stability, thereby increasing costs. (2) Flexible DC solution: New energy is collected through AC and then transmitted through flexible DC rectification, which does not rely on the AC grid and can operate in an island; this solution has high technical maturity, flexible control, and the ability to build a grid, can provide frequency and voltage support for the grid, and has the ability to support the receiving grid; however, the control of this solution is relatively complex, and there is a risk of coupled oscillation caused by the control system. The converter station is large in size and weight, expensive, and the collection of new energy AC may cause voltage stability problems. In order to reduce the cost of the DC transmission system, a DC transmission system for a new energy power generation base based on grid-type energy storage (CN116316787B) proposes a DC transmission system for a new energy power generation base based on grid-type energy storage, a diode rectifier valve and a VSC converter valve. The grid-type energy storage device is used to provide grid-connected voltage support for a new energy power generation base without conventional power supply support, and the power transmission from the new energy power generation base to the receiving power grid is realized through the interaction between the control protection device and the grid-type energy storage device, thereby reducing the cost. However, the receiving end of the system still uses a flexible DC converter valve, which is relatively expensive, and when a fault occurs at the receiving end, it will affect the power transmission of the DC transmission system. At this time, the DC transmission system cannot be guaranteed to be in a stable operating state.

[0004] Compared with the AC solution and the flexible DC solution, the new energy DC collection solution has greater comprehensive advantages in terms of technology and economy. Typical solutions proposed so far include: a new energy base DC collection hub system and its corresponding joint system (CN116316787B), which proposes a DC collection system including diode rectifier converters and DCDC converters, which can collect large-scale new energy through the DC system, interconnect it over a wide area, and complement it in time and space. The system is suitable for scenarios where large-scale new energy bases collect and then boost DC voltage for long-distance transmission; however, the solution is not economically effective in small-capacity DC collection scenarios, and does not give full play to the technical potential of energy storage configured in new energy sites. It has little technical and economic advantages for new energy collection and transmission scenarios in local new energy-intensive areas in the central and eastern regions. Summary of the invention

[0005] In order to overcome the above-mentioned defects, the present invention proposes a new energy DC collection and transmission system and a control method thereof.

[0006] In a first aspect, a new energy direct current collection and transmission system is provided, the new energy direct current collection and transmission system comprising:

[0007] New energy stations, grid-type energy storage, distributed diode rectifiers, DC circuit breakers, DC transmission lines and controllable commutation converters;

[0008] The AC power of the new energy station is rectified by a distributed diode rectifier and then collected into DC power, and then sent to the receiving AC power grid via a DC transmission line;

[0009] A DC circuit breaker is provided between the DC output end of the distributed diode rectifier and the DC transmission line;

[0010] The receiving-end AC power grid uses a controllable phase-commutation converter to invert the DC power of the DC transmission line into AC power.

[0011] Preferably, the new energy stations include: network-building type new energy and network-following type new energy.

[0012] Furthermore, the grid-type converters corresponding to the grid-type energy storage and grid-type new energy are controlled by a droop control strategy, the grid-side converters of the grid-type new energy are controlled by a voltage loop control strategy, and the controllable commutation converters are controlled by a constant DC voltage control strategy.

[0013] Furthermore, in the process of controlling the grid-type converter corresponding to the grid-type energy storage and the grid-type new energy by adopting the droop control strategy, the AC system frequency ω and phase angle θ at the collection point of the new energy station are adjusted according to the following formula:

[0014]

[0015] Adjust the AC voltage d-axis component V at the collection point of the new energy station according to the following formula d and the q-axis component V q :

[0016]

[0017] In the above formula, P is the active power output by the grid-type converter, Q is the reactive power output by the grid-type converter, v d is the d-axis component of the output voltage of the grid-connected converter, i d is the d-axis component of the output current of the grid-connected converter, v q is the q-axis component of the output voltage of the grid-connected converter, i q is the q-axis component of the output current of the grid-type converter, ω ref is the frequency reference value, D f is the active power droop coefficient of grid-connected energy storage or grid-connected new energy, P * is the active power reference value of grid-connected energy storage or grid-connected new energy, s is the Laplace operator, V ref is the voltage reference value of the AC system, D q is the reactive power droop coefficient of grid-connected energy storage or grid-connected new energy, Q * It is the reactive power reference value of grid-building energy storage or grid-building new energy.

[0018] Further, when the frequency deviation of the AC system at the sending end exceeds 0.5 Hz, the active power reference value is adjusted within the maximum active power output range of the grid-forming energy storage until the frequency deviation of the AC system at the sending end is less than 0.5 Hz or the active power of the grid-forming energy storage reaches the rated power;

[0019] When the frequency deviation of the sending-end AC system exceeds 0.5Hz and the active power of the grid-forming energy storage reaches the rated power, the active power reference value is adjusted within the maximum active power output range of the grid-forming new energy until the frequency deviation of the sending-end AC system is less than 0.5Hz or the active power of the grid-forming new energy reaches the rated power.

[0020] Furthermore, in the process of controlling the grid-side converter of the grid-following renewable energy by adopting the voltage loop control strategy, the voltage reference value of the grid-following renewable energy is determined by the following formula:

[0021]

[0022] In the above formula, k p is the proportional link control parameter, k i is the integral link control parameter, s is the Laplace operator, P druis the actual value of active power at the inlet of the distributed diode rectifier, is the given distributed diode rectifier active power command value, V 0 is the design value of the AC network voltage.

[0023] Furthermore, when a voltage drop fault occurs in the receiving-end AC, the trigger angle of the controllable commutation converter is increased until the voltage drop fault disappears;

[0024] When an AC fault occurs in the receiving-end power grid, the operating mode of the controllable phase-commutating converter is switched to an energy consumption mode until the AC fault disappears.

[0025] Furthermore, the startup process of the system is as follows:

[0026] Step a. Start the new energy station and distributed diode rectifier;

[0027] Step b. unlocking the controllable commutated converter until the DC voltage of the DC transmission line increases to the operating setting value;

[0028] Step c. Close the DC circuit breaker.

[0029] Further, the step a comprises:

[0030] Unlock the grid-type energy storage converter corresponding to the grid-type energy storage, and use a ramp to increase the voltage reference value of the AC system in the droop control strategy until the AC voltage is established in the sending-end AC system;

[0031] Unlock the distributed diode rectifier and control the input of the new energy unit until the new energy unit achieves maximum power tracking.

[0032] In a second aspect, a control method based on the new energy DC collection and transmission system is provided, the method comprising:

[0033] Start-up of new energy stations and distributed diode rectifiers;

[0034] unlocking the controllable commutated converter until the DC voltage of the DC transmission line increases to the operating setting value;

[0035] Close the DC circuit breaker.

[0036] Preferably, the starting of the new energy station and the distributed diode rectifier includes:

[0037] Unlock the grid-type energy storage converter corresponding to the grid-type energy storage, and use a ramp to increase the voltage reference value of the AC system in the droop control strategy until the AC voltage is established in the sending-end AC system;

[0038] Unlock the distributed diode rectifier and control the input of the new energy unit until the new energy unit achieves maximum power tracking.

[0039] In a third aspect, a computer device is provided, comprising: one or more processors;

[0040] The processor is configured to execute one or more programs;

[0041] When the one or more programs are executed by the one or more processors, the control method of the new energy DC collection and transmission system is implemented.

[0042] In a fourth aspect, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed, the control method of the new energy DC collection and transmission system is implemented.

[0043] The above one or more technical solutions of the present invention have at least one or more of the following beneficial effects:

[0044] The present invention provides a new energy DC collection and transmission system and its control method, including: a new energy station, a grid-type energy storage, a distributed diode rectifier, a DC circuit breaker, a DC transmission line and a controllable phase-commutating converter; the AC power of the new energy station is rectified by a distributed diode rectifier and then DC collected, and then sent to the receiving AC power grid via the DC transmission line; a DC circuit breaker is provided between the DC output end of the distributed diode rectifier and the DC transmission line; the receiving AC power grid uses a controllable phase-commutating converter to invert the DC power of the DC transmission line into AC power. The technical solution provided by the present invention is flexible in design and easy to maintain, has strong scalability in capacity and voltage levels, good economy, and good network construction flexibility. It is suitable for isolated or weak network new energy collection and grid connection and long-distance transmission scenarios, has a wide range of usage scenarios, and has outstanding advantages and effects, specifically:

[0045] (1) The technical solution proposed in the present invention can realize the DC collection of distributed multi-type renewable energy after rectification by medium- and high-voltage multi-terminal diode converters, and coordinate with the controllable phase-commutated converter at the receiving end to jointly maintain the stability of the DC system. The distributed topology structure is convenient for project expansion, and can realize long-term DC collection and transmission circuit expansion without power outage, multi-terminal DC networking, and batch planning access on the power supply side. It is a new power system architecture different from the multi-terminal ring mesh DC power grid.

[0046] (2) The technical solution proposed in the present invention has large DC transmission capacity, wide collection range and good overall economic efficiency. The present invention proposes DC collection instead of AC collection, which can save transmission corridors and floor space, and reduce line investment; the diode rectifier has large capacity, low cost and no need for control, which is efficient and reliable, and improves the economic efficiency of the system; the controllable commutation converter is used at the receiving end, which is lower in cost than the modular multi-level converter used in other DC system topologies, further improving the economic efficiency of the system.

[0047] (3) The technical solution proposed by the present invention does not rely on strong network support, thus avoiding the voltage stability problem of new energy AC aggregation and grid connection. The grid-type energy storage and grid-type new energy units simulate synchronous generators and cooperate to provide voltage and frequency support for new energy stations, realize the island operation of new energy stations, and avoid the safety and stability problems caused by the decrease of short-circuit ratio after large-scale new energy is connected to the system.

[0048] (4) The receiving end of the technical solution of the present invention adopts a controllable commutation converter, which can improve the receiving end power grid fault resistance and reactive power support capabilities. Compared with the topology of the receiving end using LCC converters, it can resist commutation failures and has fault ride-through and reactive power support capabilities. Compared with the topology of the receiving end using VSC converters, it can also provide flexible active / reactive support according to system needs during faults, and the support capacity can reach or even exceed the level of VSC of the same capacity.

[0049] (5) Compared with the AC solution, the technical solution proposed in the present invention uses distributed diode rectifier collection instead of step-by-step voltage boost collection, giving full play to the technical and economic advantages of DC transmission, avoiding the voltage stability problem of AC transmission, eliminating the construction of booster stations, and reducing line investment and land occupation; the combination of grid-type energy storage and diode rectifiers does not rely on the AC grid, is suitable for different types of new energy sites, and eliminates the synchronous phase regulator required by the AC solution and the reactive compensation and filtering equipment required by the diode rectifier; it realizes the transmission of new energy islands without connecting to the sending-end AC power grid, avoiding the problem of heavy overload of AC equipment such as main transformers or lines.

[0050] (6) Compared with the flexible direct current solution, the technical solution proposed in the present invention has low cost, strong current carrying capacity, and no control link, thus avoiding the high-frequency oscillation problem caused by the control link. Compared with the proposed direct current collection solution, the receiving end adopts a more economical converter with reactive power support capability, further saving the cost of the converter station, thereby improving the overall economy of the system; and when an AC fault occurs at the receiving end, the transmission power in the direct current transmission system where the converter is located can be maintained, avoiding the impact of the AC fault at the receiving end on the direct current transmission system, and ensuring that the direct current transmission system is in a stable operating state. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1This is a main structural block diagram of a new energy DC collection and transmission system according to an embodiment of the present invention;

[0052] Figure 2 It is the waveform of the active power output of the distributed diode rectifier, the active power output of the new energy, and the active and reactive power output of the grid-type energy storage when the output of the new energy fluctuates;

[0053] Figure 3 It is the active power output by the distributed diode rectifier, the active power output by the new energy, the effective value of the AC voltage at the grid connection point, and the active power waveform output by the grid-connected energy storage when a three-phase short circuit occurs at the grid connection point;

[0054] Figure 4 It is the waveform of the active power of the DC line, the active power and reactive power of the DC side of the controllable commutation converter at the receiving end when a three-phase short circuit fault occurs at the grid connection point;

[0055] Figure 5 It is a comparison diagram of the simulated waveforms of the VSC converter station and the controllable commutation converter station when the AC system fault voltage at the receiving end drops to 0.5pu;

[0056] Figure 6 This is a comparison diagram of the simulated waveforms of the VSC converter station and the controllable commutation converter station when the AC system fault voltage at the receiving end drops to 0.2pu;

[0057] Figure 7 It is a schematic diagram of the energy consumption mode started by a fault in the receiving-end AC system. DETAILED DESCRIPTION

[0058] The specific implementation modes of the present invention will be further described in detail below in conjunction with the accompanying drawings.

[0059] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0060] As disclosed in the background technology, under the current grid and development model, the AC grid connection in the new energy-intensive areas leads to serious reverse overload problems in the power grid. In addition, the shortage of transmission corridors leads to high investment costs and construction difficulties in power grid facilities. At the same time, the gradual increase in the proportion of wind and solar power and other new energy installed capacity has led to increasingly prominent low inertia and hollowing characteristics of the system. The safe and stable operation of the power grid will face huge challenges, and a safer and more efficient new energy collection and transmission solution is urgently needed.

[0061] In response to the above problems, the current solutions for the collection and transmission of new energy include AC solutions and flexible DC solutions. (1) AC solution: New energy is collected through AC and gradually stepped up for transmission, relying on strong grid support; this solution is mature in technology and suitable for local consumption of new energy, especially for scenarios with short transmission distances and small transmission capacities; however, with the large-scale access of new energy, this solution may lead to reduced system strength and stability; and this solution has no support capacity for the receiving grid; in addition, large-scale access to new energy may cause overload of the main transformer and line, while long-distance and large-capacity power transmission requires additional equipment to maintain grid stability, thereby increasing costs. (2) Flexible DC solution: New energy is collected through AC and then transmitted through flexible DC rectification, which does not rely on the AC grid and can operate in an island; this solution has high technical maturity, flexible control, and the ability to build a grid, can provide frequency and voltage support for the grid, and has the ability to support the receiving grid; however, the control of this solution is relatively complex, and there is a risk of coupled oscillation caused by the control system. The converter station is large in size and weight, expensive, and the collection of new energy AC may cause voltage stability problems. In order to reduce the cost of the DC transmission system, a DC transmission system for a new energy power generation base based on grid-type energy storage (CN116316787B) proposes a DC transmission system for a new energy power generation base based on grid-type energy storage, a diode rectifier valve and a VSC converter valve. The grid-type energy storage device is used to provide grid-connected voltage support for a new energy power generation base without conventional power supply support, and the power transmission from the new energy power generation base to the receiving power grid is realized through the interaction between the control protection device and the grid-type energy storage device, thereby reducing the cost. However, the receiving end of the system still uses a flexible DC converter valve, which is relatively expensive, and when a fault occurs at the receiving end, it will affect the power transmission of the DC transmission system. At this time, the DC transmission system cannot be guaranteed to be in a stable operating state.

[0062] Compared with the AC solution and the flexible DC solution, the new energy DC collection solution has greater comprehensive advantages in terms of technology and economy. Typical solutions proposed so far include: a new energy base DC collection hub system and its corresponding joint system (CN116316787B), which proposes a DC collection system including diode rectifier converters and DCDC converters, which can collect large-scale new energy through the DC system, interconnect it over a wide area, and complement it in time and space. The system is suitable for scenarios where large-scale new energy bases collect and then boost DC voltage for long-distance transmission; however, the solution is not economically effective in small-capacity DC collection scenarios, and does not give full play to the technical potential of energy storage configured in new energy sites. It has little technical and economic advantages for new energy collection and transmission scenarios in local new energy-intensive areas in the central and eastern regions.

[0063] In order to improve the above problems, the present invention provides a new energy DC collection and transmission system and its control method, including: a new energy station, a grid-type energy storage, a distributed diode rectifier, a DC circuit breaker, a DC transmission line and a controllable phase-commutating converter; the AC power of the new energy station is rectified by a distributed diode rectifier and then DC collected, and then sent to the receiving AC power grid via the DC transmission line; a DC circuit breaker is provided between the DC output end of the distributed diode rectifier and the DC transmission line; the receiving AC power grid uses a controllable phase-commutating converter to invert the DC power of the DC transmission line into AC power. The technical solution provided by the present invention is flexible in design and easy to maintain, has strong scalability in capacity and voltage levels, good economy, and good network construction flexibility. It is suitable for isolated or weak grid new energy collection and grid connection and long-distance transmission scenarios, has a wide range of usage scenarios, and has outstanding advantages and effects. Specifically:

[0064] (1) The technical solution proposed in the present invention can realize the DC collection of distributed multi-type renewable energy after rectification by medium- and high-voltage multi-terminal diode converters, and coordinate with the controllable phase-commutated converter at the receiving end to jointly maintain the stability of the DC system. The distributed topology structure is convenient for project expansion, and can realize long-term DC collection and transmission circuit expansion without power outage, multi-terminal DC networking, and batch planning access on the power supply side. It is a new power system architecture different from the multi-terminal ring mesh DC power grid.

[0065] (2) The technical solution proposed in the present invention has large DC transmission capacity, wide collection range and good overall economic efficiency. The present invention proposes DC collection instead of AC collection, which can save transmission corridors and floor space, and reduce line investment; the diode rectifier has large capacity, low cost and no need for control, which is efficient and reliable, and improves the economic efficiency of the system; the controllable commutation converter is used at the receiving end, which is lower in cost than the modular multi-level converter used in other DC system topologies, further improving the economic efficiency of the system.

[0066] (3) The technical solution proposed by the present invention does not rely on strong network support, thus avoiding the voltage stability problem of new energy AC aggregation and grid connection. The grid-type energy storage and grid-type new energy units simulate synchronous generators and cooperate to provide voltage and frequency support for new energy stations, realize the island operation of new energy stations, and avoid the safety and stability problems caused by the decrease of short-circuit ratio after large-scale new energy is connected to the system.

[0067] (4) The receiving end of the technical solution of the present invention adopts a controllable commutation converter, which can improve the receiving end power grid fault resistance and reactive power support capabilities. Compared with the topology of the receiving end using LCC converters, it can resist commutation failures and has fault ride-through and reactive power support capabilities. Compared with the topology of the receiving end using VSC converters, it can also provide flexible active / reactive support according to system needs during faults, and the support capacity can reach or even exceed the level of VSC of the same capacity.

[0068] (5) Compared with the AC solution, the technical solution proposed in the present invention uses distributed diode rectifier collection instead of step-by-step voltage boost collection, giving full play to the technical and economic advantages of DC transmission, avoiding the voltage stability problem of AC transmission, eliminating the construction of booster stations, and reducing line investment and land occupation; the combination of grid-type energy storage and diode rectifiers does not rely on the AC grid, is suitable for different types of new energy sites, and eliminates the synchronous phase regulator required by the AC solution and the reactive compensation and filtering equipment required by the diode rectifier; it realizes the transmission of new energy islands without connecting to the sending-end AC power grid, avoiding the problem of heavy overload of AC equipment such as main transformers or lines.

[0069] (6) Compared with the flexible direct current solution, the technical solution proposed in the present invention has low cost, strong current carrying capacity, and no control link, thus avoiding the high-frequency oscillation problem caused by the control link. Compared with the proposed direct current collection solution, the receiving end adopts a more economical converter with reactive power support capability, further saving the cost of the converter station, thereby improving the overall economy of the system; and when an AC fault occurs at the receiving end, the transmission power in the direct current transmission system where the converter is located can be maintained, avoiding the impact of the AC fault at the receiving end on the direct current transmission system, and ensuring that the direct current transmission system is in a stable operating state.

[0070] The above scheme is described in detail below.

[0071] Example 1

[0072] See attached Figure 1 , Figure 1 This is a main structural block diagram of a new energy DC collection and transmission system according to an embodiment of the present invention. Figure 1 As shown, the new energy DC collection and transmission system in the embodiment of the present invention mainly includes: a new energy station, a grid-type energy storage, a distributed diode rectifier (DR converter station), a DC circuit breaker, a DC transmission line and a controllable commutation converter;

[0073] The AC power of the new energy station is rectified by a distributed diode rectifier and then collected into DC power, and then sent to the receiving AC power grid via a DC transmission line;

[0074] A DC circuit breaker is provided between the DC output end of the distributed diode rectifier and the DC transmission line;

[0075] The receiving-end AC power grid uses a controllable phase-commutation converter to invert the DC power of the DC transmission line into AC power.

[0076] Among them, the new energy stations include: grid-building new energy and grid-following new energy.

[0077] In one embodiment, the grid-type converters corresponding to the grid-type energy storage and the grid-type new energy are controlled by a droop control strategy, the grid-side converters of the grid-type new energy are controlled by a voltage loop control strategy, and the controllable commutation converters are controlled by a constant DC voltage control strategy.

[0078] In one embodiment, in the process of controlling the grid-type converter corresponding to the grid-type energy storage and the grid-type new energy by adopting the droop control strategy, the AC system frequency ω and phase angle θ at the collection point of the new energy station are adjusted as follows:

[0079]

[0080] Adjust the AC voltage d-axis component V at the collection point of the new energy station according to the following formula d and the q-axis component V q :

[0081]

[0082] In the above formula, P is the active power output by the grid-type converter, Q is the reactive power output by the grid-type converter, v d is the d-axis component of the output voltage of the grid-connected converter, i d is the d-axis component of the output current of the grid-connected converter, v q is the q-axis component of the output voltage of the grid-connected converter, i q is the q-axis component of the output current of the grid-type converter, ω ref is the frequency reference value, D f is the active power droop coefficient of grid-connected energy storage or grid-connected new energy, P * is the active power reference value of grid-connected energy storage or grid-connected new energy, s is the Laplace operator, V ref is the voltage reference value of the AC system, D q is the reactive power droop coefficient of grid-connected energy storage or grid-connected new energy, Q * It is the reactive power reference value of grid-building energy storage or grid-building new energy.

[0083] The above formula controls the q-axis component of the AC voltage to zero, so that the AC voltage vector coincides with the d-axis of the synchronous rotating coordinate system, that is, the d-axis voltage orientation. In this case, the d-axis voltage amplitude is the amplitude of the AC voltage.

[0084] The inner loop adopts voltage and current dual closed-loop control to obtain the output voltage reference value of the bridge arm of the grid-side converter of the new energy power generation base, and finally generates the bridge arm drive signal through modulation.

[0085] In one embodiment, when the frequency deviation of the sending-end AC system exceeds 0.5 Hz, the active power reference value is adjusted within the maximum active power output range of the grid-forming energy storage until the frequency deviation of the sending-end AC system is less than 0.5 Hz or the active power of the grid-forming energy storage reaches the rated power;

[0086] When the frequency deviation of the sending-end AC system exceeds 0.5Hz and the active power of the grid-forming energy storage reaches the rated power, the active power reference value is adjusted within the maximum active power output range of the grid-forming new energy until the frequency deviation of the sending-end AC system is less than 0.5Hz or the active power of the grid-forming new energy reaches the rated power.

[0087] In one embodiment, in the process of controlling the grid-side converter of the grid-following new energy by adopting the voltage loop control strategy, the voltage reference value of the grid-following new energy is determined by the following formula:

[0088]

[0089] In the above formula, k p is the proportional link control parameter, k i is the integral link control parameter, s is the Laplace operator, P dru is the actual value of active power at the inlet of the distributed diode rectifier, is the given distributed diode rectifier active power command value, V 0 is the design value of the AC network voltage.

[0090] In one embodiment, when a voltage drop fault occurs in the receiving-end AC, the trigger angle of the controllable commutation converter is increased until the voltage drop fault disappears; specifically, the DC voltage is increased by adjusting the trigger angle of the controllable commutation converter, the reactive power consumed by the inverter-side converter valve is reduced, and the AC filter group injects reactive power into the power grid to support the recovery of the power grid voltage; in addition, the reactive power absorbed by the controllable commutation converter decreases as the trigger angle of the inverter increases, and the trigger angle is increased so that the current phase lags behind the AC voltage phase by more than 180°, the reactive component of the current changes from negative to positive, and reactive power begins to be emitted to the AC system, thereby achieving transient reactive support. Specifically as follows: the trigger angle of the controllable commutation converter is adjusted according to the measured reactive power value of the controllable commutation converter in the converter station or the measured voltage value of the AC bus in the converter station, wherein the upper limit of the trigger angle can be greater than 180°; the reactive power of the controllable commutation converter is controlled according to the trigger angle.

[0091] When an AC fault occurs in the receiving-end power grid, the working mode of the controllable commutation converter is switched to the energy consumption mode until the AC fault disappears. On the basis of ensuring the successful commutation from the main branch of the controllable commutation converter to the auxiliary branch, the surplus energy can be discharged through the energy consumption branch of the converter to maintain the transmission power in the DC power transmission system where the converter is located, avoid the impact of the AC fault at the receiving end on the DC power transmission system, and ensure that the DC power transmission system is in a stable operating state.

[0092] In one embodiment, the system startup process is as follows:

[0093] Step a. Start the new energy station and distributed diode rectifier;

[0094] Step b. unlocking the controllable commutated converter until the DC voltage of the DC transmission line increases to the operating setting value;

[0095] Step c. Close the DC circuit breaker.

[0096] In one embodiment, step a comprises:

[0097] Unlock the grid-type energy storage converter corresponding to the grid-type energy storage, and use a ramp to increase the voltage reference value of the AC system in the droop control strategy until the AC voltage is established in the sending-end AC system;

[0098] Unlock the distributed diode rectifier and control the input of the new energy unit until the new energy unit achieves maximum power tracking.

[0099] In a specific embodiment, Figure 2 When the output of renewable energy fluctuates, the waveforms of the active power output of the distributed diode rectifier, the active power output of renewable energy, and the active and reactive power output of the grid-type energy storage are given by Figure 2 It can be seen that when the output of renewable energy fluctuates, grid-connected energy storage can smooth out the active power fluctuations and the system PCC point voltage can remain stable. Figure 3 It is the active power output by the distributed diode rectifier, the active power output by the new energy, the effective value of the AC voltage at the grid connection point, and the active power waveform output by the grid-connected energy storage when a three-phase short circuit occurs at the grid connection point; Figure 4 It is the waveform of the active power of the DC line, the active power and reactive power of the DC side of the controllable commutation converter at the receiving end when a three-phase short circuit occurs at the grid connection point. Figure 3 , Figure 4 It can be seen that the fault is cleared after 0.15s, and the system can return to the steady-state operation state after the fault is cleared. Figure 5 This is a comparison diagram of the simulated waveforms of the VSC converter station and the controllable commutation converter station when the AC system fault voltage at the receiving end drops to 0.5pu. Figure 6This is a comparison diagram of the simulated waveforms of the VSC converter station and the controllable commutation converter station when the AC system fault voltage at the receiving end drops to 0.2pu. It can be seen that under AC faults of different severity and the same reactive power output conditions, the active power transmission capacity of the controllable commutation converter station (including the AC filter group) is higher than that of the VSC. Figure 7 It is a schematic diagram of the energy consumption mode started by a fault in the receiving-end AC system.

[0100] Example 2

[0101] The present invention provides a control method based on the new energy DC collection and transmission system, the method comprising:

[0102] Step a. Start the new energy station and distributed diode rectifier;

[0103] Step b. unlocking the controllable commutated converter until the DC voltage of the DC transmission line increases to the operating setting value;

[0104] Step c. Close the DC circuit breaker.

[0105] Preferably, step a comprises:

[0106] Unlock the grid-type energy storage converter corresponding to the grid-type energy storage, and use a ramp to increase the voltage reference value of the AC system in the droop control strategy until the AC voltage is established in the sending-end AC system;

[0107] Unlock the distributed diode rectifier and control the input of the new energy unit until the new energy unit achieves maximum power tracking.

[0108] Example 3

[0109] Based on the same inventive concept, the present invention also provides a computer device, which includes a processor and a memory, wherein the memory is used to store a computer program, the computer program includes program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, and is specifically suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding function, so as to implement the steps of the control method of a new energy DC collection and transmission system in the above embodiment.

[0110] Example 4

[0111] Based on the same inventive concept, the present invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device for storing programs and data. It can be understood that the computer-readable storage medium here can include both built-in storage media in a computer device and, of course, extended storage media supported by the computer device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by a processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the steps of a control method of a new energy DC collection and transmission system in the above embodiment.

[0112] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take 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.

[0113] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes 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, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0114] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0115] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0116] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A new energy DC collection and transmission system, characterized in that: The system includes: a new energy station, a grid-type energy storage, a distributed diode rectifier, a DC circuit breaker, a DC transmission line and a controllable phase-commutation converter; The AC power of the new energy station is rectified by a distributed diode rectifier and then collected into DC power, and then sent to the receiving AC power grid via a DC transmission line; A DC circuit breaker is provided between the DC output end of the distributed diode rectifier and the DC transmission line; The receiving-end AC power grid uses a controllable phase-commutation converter to invert the DC power of the DC transmission line into AC power.

2. The system according to claim 1, characterized in that The new energy stations include: grid-building new energy and grid-following new energy.

3. The system according to claim 2, characterized in that The grid-type converters corresponding to the grid-type energy storage and grid-type new energy are controlled by a droop control strategy, the grid-side converters of the grid-following new energy are controlled by a voltage loop control strategy, and the controllable commutation converters are controlled by a constant DC voltage control strategy.

4. The system according to claim 3, characterized in that In the process of controlling the grid-type converter corresponding to the grid-type energy storage and the grid-type new energy by adopting the droop control strategy, the AC system frequency ω and phase angle θ at the collection point of the new energy station are adjusted as follows: Adjust the AC voltage d-axis component V at the collection point of the new energy station according to the following formula d and the q-axis component V q : In the above formula, P is the active power output by the grid-type converter, Q is the reactive power output by the grid-type converter, v d is the d-axis component of the output voltage of the grid-connected converter, i d is the d-axis component of the output current of the grid-connected converter, v q is the q-axis component of the output voltage of the grid-connected converter, i q is the q-axis component of the output current of the grid-type converter, ω ref is the frequency reference value, D f is the active power droop coefficient of grid-connected energy storage or grid-connected new energy, P * is the active power reference value of grid-connected energy storage or grid-connected new energy, s is the Laplace operator, V ref is the voltage reference value of the AC system, D q is the reactive power droop coefficient of grid-connected energy storage or grid-connected new energy, Q * It is the reactive power reference value of grid-building energy storage or grid-building new energy.

5. The system according to claim 4, characterized in that When the frequency deviation of the AC system at the sending end exceeds 0.5Hz, the active power reference value is adjusted within the maximum active power output range of the grid-forming energy storage until the frequency deviation of the AC system at the sending end is less than 0.5Hz or the active power of the grid-forming energy storage reaches the rated power; When the frequency deviation of the sending-end AC system exceeds 0.5Hz and the active power of the grid-forming energy storage reaches the rated power, the active power reference value is adjusted within the maximum active power output range of the grid-forming new energy until the frequency deviation of the sending-end AC system is less than 0.5Hz or the active power of the grid-forming new energy reaches the rated power.

6. The system according to claim 3, characterized in that In the process of controlling the grid-side converter of the grid-following renewable energy by adopting the voltage loop control strategy, the voltage reference value of the grid-following renewable energy is determined according to the following formula: In the above formula, k p is the proportional link control parameter, k i is the integral link control parameter, s is the Laplace operator, P dru is the actual value of active power at the inlet of the distributed diode rectifier, is the given distributed diode rectifier active power command value, and V0 is the design value of the AC network voltage.

7. The system according to claim 3, characterized in that When a voltage drop fault occurs in the receiving-end AC, the trigger angle of the controllable commutation converter is increased until the voltage drop fault disappears; When an AC fault occurs in the receiving-end power grid, the operating mode of the controllable phase-commutating converter is switched to an energy consumption mode until the AC fault disappears.

8. The system according to claim 3, characterized in that The system startup process is as follows: Step a. Start the new energy station and distributed diode rectifier; Step b. unlocking the controllable commutated converter until the DC voltage of the DC transmission line increases to the operating setting value; Step c. Close the DC circuit breaker.

9. The system according to claim 8, characterized in that The step a comprises: Unlock the grid-type energy storage converter corresponding to the grid-type energy storage, and use a ramp to increase the voltage reference value of the AC system in the droop control strategy until the AC voltage is established in the sending-end AC system; Unlock the distributed diode rectifier and control the input of the new energy unit until the new energy unit achieves maximum power tracking.

10. A control method for the new energy DC collection and transmission system according to any one of claims 1 to 9, characterized in that: The method comprises: Start-up of new energy stations and distributed diode rectifiers; unlocking the controllable commutated converter until the DC voltage of the DC transmission line increases to the operating setting value; Close the DC circuit breaker.

11. The method according to claim 10, characterized in that The starting of the new energy station and the distributed diode rectifier includes: Unlock the grid-type energy storage converter corresponding to the grid-type energy storage, and use a ramp to increase the voltage reference value of the AC system in the droop control strategy until the AC voltage is established in the sending-end AC system; Unlock the distributed diode rectifier and control the input of the new energy unit until the new energy unit achieves maximum power tracking.

12. A computer device, characterized in that: include: one or more processors; The processor is configured to execute one or more programs; When the one or more programs are executed by the one or more processors, the control method of the new energy direct current collection and transmission system as described in any one of claims 10 to 11 is implemented.

13. A computer-readable storage medium, characterized in that: A computer program is stored thereon, and when the computer program is executed, the control method of the new energy direct current collection and transmission system as described in any one of claims 10 to 11 is implemented.

Images