Converter port voltage balancing method of full direct current system

Abstract

The invention discloses a converter port voltage balancing method of a full-direct-current system, the voltage balancing method is applied to the full-direct-current system, and the system comprises a fan, an AC / DC converter, a DC / DC converter, a DC / AC converter and an alternating-current power grid. The voltage balancing method comprises the following steps: carrying out VOC voltage stabilization control on the machine side DC voltage of the AC / DC converter based on a preset AC / DC converter model; performing voltage control on the DC / DC converter by adopting a control strategy of outer ring port voltage and inner ring output current, so that the output port voltage of the DC / DC converter is balanced; and carrying out system transmission power stable control on the DC / AC converter according to a preset inverter control strategy, wherein the preset inverter control strategy comprises a network following type control strategy and a network constructing type control strategy. The technical problems that an existing full-direct-current system is difficult to achieve voltage balance of a convergence network direct-current port, and the absorption pressure of an alternating-current grid-connected point cannot be relieved can be solved.

Description

Technical Field

[0001] The present application relates to the technical field of new energy power grids, and in particular to a method for voltage balancing of converter ports of a full DC system. Background Art

[0002] The new energy transmission system is a necessary way to ensure the reliable consumption of new energy and realize the remote transmission of new energy. Today, the forms of new energy transmission mainly include distributed transmission and centralized transmission. With the gradual increase in the penetration rate of new energy, the voltage level of distributed grid connection is gradually increasing, and the energy structure of the power system is undergoing extensive and profound changes. In addition, the existence of spatial inconsistency in the development and utilization of new energy makes centralized transmission a hot topic in current research.

[0003] Taking the offshore wind power transmission system as an example, the traditional method is to use high voltage AC transmission (HVAC) AC convergence, AC transmission and delivery system (referred to as full AC system). However, the capacitive effect of submarine cables hinders the development trend of deep sea and offshore, making the traditional full AC system dependent on additional static reactive power compensation devices. Therefore, the AC convergence and DC transmission and delivery system based on high voltage DC transmission (HVDC) has become a more reliable engineering project. However, this type of delivery system requires the construction of expensive offshore converter platforms, and the operating cost problem is prominent. Although some more economical and feasible wind power convergence systems have been proposed later, these technologies still have various limitations, making them difficult to apply to transmission systems. Therefore, a DC convergence and DC transmission and delivery system, that is, a full DC system, has been proposed.

[0004] However, it is difficult to achieve balanced control of the voltage at the DC port of the converged network in the existing full DC system. In addition, the increasing capacity of new energy power fields has put greater pressure on the AC grid connection points that are centrally transmitted. Therefore, the control strategy of the existing full DC system has a poor control effect and is difficult to meet actual application needs. Summary of the invention

[0005] The present application provides a method for voltage balancing of converter ports of a full DC system, which is used to solve the technical problem that the existing full DC system is difficult to achieve voltage balancing of the DC port of the aggregation network and cannot alleviate the absorption pressure of the AC grid connection point.

[0006] In view of this, the present application provides a converter port voltage balancing method for a full DC system, wherein the voltage balancing method is applied in a full DC system, wherein the full DC system includes: a fan, an AC / DC converter, a DC / DC converter, a DC / AC converter, and an AC power grid;

[0007] The fan and the AC / DC converter are electrically connected, and the AC / DC converters are connected in series;

[0008] The output end of the AC / DC converter is connected to the DC / DC converter;

[0009] The output end of the DC / DC converter is connected to the DC / AC converter;

[0010] The output end of the DC / AC converter is connected to the AC power grid;

[0011] The voltage balancing method is:

[0012] Based on a preset AC / DC converter model, VOC voltage stabilization control is performed on the DC voltage on the machine side of the AC / DC converter;

[0013] The DC / DC converter is voltage controlled by adopting a control strategy of an outer loop port voltage and an inner loop output current, so that the output port voltage of the DC / DC converter is balanced;

[0014] The DC / AC converter is subjected to system transmission power stability control according to a preset inverter control strategy, wherein the preset inverter control strategy includes a grid-following control strategy and a grid-building control strategy.

[0015] Preferably, the performing system transmission power stabilization control on the DC / AC converter according to a preset inverter control strategy comprises:

[0016] When the grid short-circuit ratio of the new power system is greater than the short-circuit threshold, the DC / AC converter is subjected to a PQ control-based system transmission power stability control according to a grid-following control strategy, and a target real-time dispatching instruction is generated based on a preset artificial intelligence algorithm;

[0017] When the grid short-circuit ratio of the new power system is less than the short-circuit threshold, the DC / AC converter is subjected to VF control-based system transmission power stability control according to the grid-forming control strategy, and the target real-time scheduling instruction is generated based on the preset artificial intelligence algorithm.

[0018] Preferably, when the grid short-circuit ratio of the novel power system is less than the short-circuit threshold, the DC / AC converter is subjected to a VF control-based system transmission power stability control according to a grid-forming control strategy, and the target real-time dispatching instruction is generated based on the preset artificial intelligence algorithm, further comprising:

[0019] A preset frequency synchronization control strategy is adopted to perform frequency synchronization control on the system frequency in the VF control process, and the preset frequency synchronization control strategy includes a droop control strategy and a virtual synchronization control strategy.

[0020] Preferably, when the grid short-circuit ratio of the novel power system is less than the short-circuit threshold, the DC / AC converter is subjected to a VF control-based system transmission power stability control according to a grid-forming control strategy, and the target real-time dispatching instruction is generated based on the preset artificial intelligence algorithm, further comprising:

[0021] If the output demand of each new energy unit under the target real-time dispatch instruction is not greater than the maximum power of the new energy electric field, the full DC system performs voltage balancing control according to the target real-time dispatch instruction;

[0022] If under the target real-time scheduling instruction, the output demand of a preset number of new energy units is greater than the maximum power of the new energy electric field, then the preset number of new energy units are controlled to be controlled at the maximum power of the new energy electric field, and the remaining number of new energy units are controlled for voltage balancing according to the balanced power.

[0023] Preferably, the AC / DC converter has a voltage boost function.

[0024] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0025] In the present application, a method for voltage balancing of converter ports of a full DC system is provided, and the voltage balancing method is applied in the full DC system, and the full DC system includes: a wind turbine, an AC / DC converter, a DC / DC converter, a DC / AC converter and an AC power grid; the wind turbine AC / DC converter is electrically connected, and the AC / DC converters are connected in series; the output end of the AC / DC converter is connected to the DC / DC converter; the output end of the DC / DC converter is connected to the DC / AC converter; the output end of the DC / AC converter is connected to the AC power grid; the voltage balancing method is: based on a preset AC / DC converter model, the machine-side DC voltage of the AC / DC converter is subjected to VOC voltage stabilization control; the DC / DC converter is voltage controlled by adopting a control strategy of an outer loop port voltage and an inner loop output current, so that the output port voltage of the DC / DC converter is balanced; the DC / AC converter is subjected to system transmission power stability control according to a preset inverter control strategy, and the preset inverter control strategy includes a grid-following control strategy and a grid-forming control strategy.

[0026] The converter port voltage balancing method of the full DC system provided in the present application replaces the grid-side inverter of the AC permanent magnet synchronous wind turbine with the grid-side DC / DC converter, and the voltage balancing of the DC port of the converged network refers to the voltage balancing of the output port of the DC / DC converter; by respectively performing VOC voltage stabilization control, port voltage control and system transmission power control on the AC / DC converter, DC / DC converter and DC / AC converter, the voltage balancing control of the full DC system and the stable AC grid connection point absorption regulation and control are realized; this process can provide a control strategy that is more in line with the actual situation for the full DC system and maintain the stable operation of the system. Therefore, the present application can solve the technical problem that the existing full DC system is difficult to achieve voltage balancing of the DC port of the converged network and cannot alleviate the absorption pressure of the AC grid connection point. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of the structure of a full DC system for applying the converter port voltage balancing method of the full DC system provided in an embodiment of the present application;

[0028] Figure 2 The AC / DC converter structure diagram and the corresponding VOC control strategy diagram provided in the embodiment of the present application;

[0029] Figure 3 A schematic diagram of a DC / DC converter and its control strategy provided in an embodiment of the present application;

[0030] Figure 4 A schematic diagram of a DC / AC converter and its control strategy provided in an embodiment of the present application;

[0031] Figure 5 A schematic diagram of a process for generating a power dispatch instruction under a DC / AC converter control strategy provided in an embodiment of the present application;

[0032] Figure 6 A schematic diagram of the process analysis of the impact of real-time power scheduling instructions on new energy electric fields provided in an embodiment of the present application. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0034] For easier understanding, see Figure 1, the present application provides an embodiment of a converter port voltage balancing method for a full DC system, the voltage balancing method is applied in a full DC system, the full DC system includes: a fan, an AC / DC converter, a DC / DC converter, a DC / AC converter and an AC power grid;

[0035] The AC / DC converters of the fans are electrically connected, and the AC / DC converters are connected in series;

[0036] The output end of the AC / DC converter is connected to the DC / DC converter;

[0037] The output end of the DC / DC converter is connected to the DC / AC converter;

[0038] The output end of the DC / AC converter is connected to the AC power grid.

[0039] Furthermore, the AC / DC converter has a voltage boost function.

[0040] It should be noted that in this embodiment, the grid-side inverter of the traditional AC permanent magnet synchronous wind turbine (PMSG) is replaced by a grid-side DC / DC converter on the new energy side, and the output port voltage of the DC / DC converter is the port voltage of the converter unit, which needs to be balanced. For the convenience of description, the new wind turbine and the converter unit are called DC wind turbines. Moreover, multiple DC wind turbines are connected in series at the output port to form a convergence network, which is connected to the AC power grid through the DC / AC converter on the shore of the transmission line.

[0041] Since different DC fans in the convergence network are connected in series, the output current of each fan unit remains consistent in steady state, and the port voltages of different DC fan units will be distributed in proportion to the transmitted active power. At this time, if each fan adopts Maximum Power Point Tracking (MPPT) control, the transmission power of different DC fans will be different, resulting in unbalanced port voltage. Therefore, the premise of port voltage balance control is to ensure the consistency of the transmission power of each fan unit.

[0042] The voltage balancing method is:

[0043] Based on the preset AC / DC converter model, VOC voltage stabilization control is performed on the DC voltage on the generator side of the AC / DC converter;

[0044] The voltage of the DC / DC converter is controlled by using the control strategy of the outer loop port voltage and the inner loop output current, so that the output port voltage of the DC / DC converter is balanced;

[0045] The DC / AC converter is controlled to stably transmit power according to a preset inverter control strategy, and the preset inverter control strategy includes a grid-following control strategy and a grid-forming control strategy.

[0046] Furthermore, the DC / AC converter is controlled to stabilize the system transmission power according to the preset inverter control strategy, including:

[0047] When the grid short-circuit ratio of the new power system is greater than the short-circuit threshold, the DC / AC converter is subjected to PQ control based on the grid-following control strategy to stabilize the system transmission power, and a target real-time dispatching instruction is generated based on a preset artificial intelligence algorithm;

[0048] When the grid short-circuit ratio of the new power system is less than the short-circuit threshold, the DC / AC converter is subjected to system transmission power stability control based on VF control according to the grid-forming control strategy, and the target real-time dispatching instructions are generated based on the preset artificial intelligence algorithm.

[0049] Furthermore, when the grid short-circuit ratio of the new power system is less than the short-circuit threshold, the DC / AC converter is subjected to a system transmission power stability control based on VF control according to the grid-forming control strategy, and a target real-time dispatching instruction is generated based on a preset artificial intelligence algorithm, which also includes:

[0050] The preset frequency synchronization control strategy is adopted to perform frequency synchronization control on the system frequency in the VF control process. The preset frequency synchronization control strategy includes a droop control strategy and a virtual synchronization control strategy.

[0051] It should be noted that this embodiment adopts voltage-oriented control (VOC) for the AC / DC converter on the machine side. At this time, the transmission power of the DC fan unit is controlled by the external circuit, that is, the subsequent converter. Therefore, as long as the output port voltage is controlled by the grid-side DC / DC converter unit to be consistent, the transmission power balance between different wind turbine units can be guaranteed. The total transmission power of the system will be controlled by the shore DC / AC converter (that is, the receiving-end converter). At this time, the power size of the new energy consumption can be determined according to the real-time dispatching instructions of the new power system, and the grid-following type and grid-forming type control strategies can be selected according to the strength of the shore AC power grid.

[0052] VOC control theory can be explained by the mathematical model of wind turbine, permanent magnet synchronous generator and machine-side converter. The wind turbine equation is expressed as:

[0053]

[0054] in, , , , , , , , , They respectively represent the wind energy captured by the wind turbine, air density, radius of the wind turbine blade, wind speed, wind energy utilization coefficient, pitch angle, tip speed ratio, electrical angular velocity of the wind turbine and pole pair number.

[0055] The voltage equation of the permanent magnet synchronous generator is expressed as:

[0056]

[0057] in, , , , , , , They represent the PMSG inductance, resistance, d-axis current, q-axis current, d-axis voltage, q-axis voltage and permanent magnet flux respectively.

[0058] The torque equation is expressed as:

[0059]

[0060] Among them, T e Represents the electromagnetic torque of PMSG.

[0061] The equation of motion is:

[0062]

[0063] in, , , They respectively represent the mechanical torque, rotor moment of inertia and rotational viscosity coefficient input from the wind turbine to the generator.

[0064] The preset AC / DC converter model on the machine side is expressed as:

[0065]

[0066] in, , , , , They respectively represent the d-axis switching function, q-axis switching function, DC side voltage, DC side capacitance and DC side output current of the machine-side AC / DC converter.

[0067] From the above equations, we can see that there are 10 equations for the wind turbine, permanent magnet synchronous generator and machine-side AC / DC converter, and 13 variables, which are: , , , , , , T e , , , , , , Therefore, if the system is to have a unique equilibrium point, three additional conditions are required. The VOC control strategy used in this embodiment can provide and The two values ​​will exhaust all the two control degrees of freedom of the AC / DC converter on the machine side, so an external output current i is required. o , that is to say, at this time, the active power output of PMSG is completely determined by the external circuit.

[0068] The DC voltage command value of the AC / DC converter on the fan side needs to be set in combination with the topology of the DC / DC converter; for example, if the DC / DC converter is a Boost converter, then the DC voltage command value of the AC / DC converter needs to meet , and it is necessary to consider that the AC fan port voltage is 690V or 3.3kV; therefore, the DC voltage command value set in this embodiment is .

[0069] For specific VOC control strategies, please refer to Figure 2 ,in, , Respectively represent the DC voltage set value and the rotor position angle, , They represent the voltage controller and current controller of the AC / DC converter on the fan side. The control command of the AC / DC converter on the fan side is the DC voltage command value. ; The machine-side AC / DC converter uses all two control degrees of freedom to allocate to the DC voltage And the direct axis current i of PMSG sd VOC adopts the control strategy of outer loop DC voltage and inner loop stator current. Instead of the traditional outer loop speed and inner loop current control, the advantage of this method is that the power output of PMSG can be decided by the external circuit, thereby improving the flexibility of the overall power transmission of the system.

[0070] The grid-side DC / DC converter control strategy of the DC fan unit is mainly to achieve port voltage balance. According to the VOC control theory, the power output of the fan depends on the external converter. At this time, if the port voltage of the grid-side DC / DC converter is directly controlled and the port voltage set values ​​of different DC fan units are set to the same value, the consistency of the power transmitted by different fans can be achieved, thereby ensuring the balance of port voltage.

[0071] For specific DC / DC converter port voltage balancing control strategies, please refer to Figure 3 ,in , , , , , , They represent the instantaneous value of the DC fan unit port voltage, the instantaneous value of the output current, the control signal, the inner loop current controller, the outer loop voltage controller, the HVDC bus voltage set value, and the number of series fans in the aggregation network. The grid-side DC / DC converter adopts the control strategy of the outer loop port voltage and the inner loop output current to improve the dynamic response performance of the converter. The grid-side DC / DC converters of different DC fan units all adopt the same control method, and the port voltage command value is set to V T / N. Under such a control strategy, if there is no power loss in the converter, the transmission power of different fan units will remain consistent; if there is power loss in the converter, the transmission power of different fan units will be different, but it will not affect the balance of the voltage at the aggregation network port.

[0072] In addition, since it is necessary to achieve port voltage balance between different DC fan units, the port voltage command value of the grid-side DC / DC converter is set to 1 / N of the HVDC voltage V T The utilization rate of the DC voltage is determined by the modulation method of the DC / AC converter on the shore, and the lower limit of the voltage may be different. Taking sinusoidal pulse width modulation as an example, the voltage needs to be greater than twice the phase voltage amplitude, that is, ,in Represents the effective value of the phase voltage of the shore AC power grid. For SVPWM, this voltage needs to be greater than the line voltage amplitude, that is, In this embodiment, the above-mentioned restrictions are taken into consideration. Set to Therefore, the DC / DC converter port voltage command value on the wind turbine grid side is set to .

[0073] There are two main control strategies for DC / AC converters on the transmission line shore: one is the grid-following control strategy, and the other is the grid-building control strategy. Regardless of which control strategy is used, the purpose is to ensure the stability of the system transmission power control and to generate reliable target real-time scheduling instructions, thereby alleviating the absorption pressure of the AC grid connection point.

[0074] Since the machine-side AC / DC converter uses all two control degrees of freedom to allocate to the DC voltage and the direct-axis current of the PMSG, there are no other control degrees of freedom that can be used to control the active power output of the wind turbine. In other words, when the VOC control strategy is adopted in this embodiment, the power output of the wind turbine is determined by the external circuit. Moreover, since one degree of freedom of the grid-side DC / DC converter has been used to control the port voltage, the transmission power needs to be controlled by the shore DC / AC converter, which can provide a scheduling interface for real-time optimization of the new power system.

[0075] For specific power control strategies, please refer to Figure 4 The whole control process is divided into two categories, namely, the grid-following control process and the grid-building control process. The grid-following PQ control strategy uses the outer loop active power and inner loop AC current to achieve stable power control; while the grid-building VF control strategy constructs a new AC voltage V and system frequency F. Figure 4 middle, , , , , , , , , , , , , They respectively represent the output active power set value, instantaneous value, d-axis output current, q-axis output current, d-axis PCC voltage instantaneous value, q-axis PCC voltage instantaneous value, set value, d-axis switching function, q-axis switching function, coordinate transformation phase angle, power controller, voltage controller and current controller of the onshore DC / AC converter.

[0076] The two strategies are not executed at the same time, but one of them is executed under certain conditions. Please refer to Figure 5First, PCC data can be collected, and the strength of the power grid can be analyzed based on the collected PCC data. If the short-circuit ratio exceeds the short-circuit threshold, the grid-following control strategy is selected, otherwise, the grid-building control strategy is selected; the short-circuit threshold of this embodiment is set to 5, and other values ​​can be selected according to actual conditions. Next, the preset artificial intelligence algorithm can be trained with the daily power curve and satellite cloud map, and the power prediction of the new energy field can be predicted by the trained preset artificial intelligence algorithm, so as to determine the target real-time dispatch instruction.

[0077] The power dispatch instruction of the onshore DC / AC converter determines the size of the system transmission power of the full DC system. This instruction is the dispatch interface of the power system and can allocate appropriate values ​​according to the actual needs of the power system.

[0078] An attention mechanism is set in the preset artificial intelligence algorithm of this embodiment. The algorithm realizes power prediction by constructing a prediction model. The training process uses the daily power curve and satellite cloud map to perform prediction training on the model; the generated target real-time scheduling instruction will be issued and act on the DC / AC converter on the shore as the real-time target real-time scheduling instruction P of the control link.

[0079] In addition, the grid-type control strategy of this embodiment needs to generate a signal AC voltage and system frequency. This embodiment chooses to adopt a droop control strategy or a virtual synchronization control strategy to achieve system frequency synchronization control. The power synchronization process can increase the frequency inertia of the system. Other frequency synchronization control strategies can also be set according to actual conditions. This is only an example and not a limitation.

[0080] Furthermore, when the grid short-circuit ratio of the new power system is less than the short-circuit threshold, the DC / AC converter is subjected to a system transmission power stability control based on VF control according to the grid-forming control strategy, and a target real-time dispatching instruction is generated based on a preset artificial intelligence algorithm, which also includes:

[0081] If the output demand of each new energy unit under the target real-time dispatch instruction is not greater than the maximum power of the new energy electric field, the entire DC system performs voltage balancing control according to the target real-time dispatch instruction;

[0082] If under the target real-time dispatch instruction, the output demand of a preset number of new energy units is greater than the maximum power of the new energy electric field, the preset number of new energy units are controlled at the maximum power of the new energy electric field, and the remaining number of new energy units are controlled for voltage balancing according to the balanced power.

[0083] It should be noted that since the real-time scheduling instruction training set used in this embodiment is the total power of the new energy power field, and a single-node scheduling scheme for the onshore DC / AC converter is adopted, the selection of real-time scheduling instructions does not take into account the difference in output of different new energy units. The DC / DC port voltage balance will make the power transmitted by all wind turbine units basically the same. If the power instruction required by the scheduling is too large, that is, the target real-time scheduling instruction P is too large, it may exceed the limit of wind energy capture of some wind turbines or even all wind turbines, resulting in a deterioration in the effect of port voltage balance control. That is, the output of different units in the new energy power field may not meet the requirements of voltage equalization control, resulting in a deviation in the port voltage. Therefore, this embodiment will also consider whether the target real-time scheduling instruction P meets the actual output of the new energy power field.

[0084] For details, please refer to Figure 6 , assuming the maximum output of the wind turbine in the new energy power plant, that is, the maximum power is , so that the power system's target real-time dispatch instructions ; In order to meet the needs of flexible scheduling, there is Assuming that the number of new energy units in the series aggregation network is N, the maximum power that a single unit can output is recorded as ,in, Without considering system loss or with small loss, if the port voltage is balanced, it can be considered that the output of each new energy unit is the same. .

[0085] If for all new energy units, , it means that the output of the new energy unit itself can meet the port voltage balance control requirements, that is, in steady state At this time, it means that the new energy unit itself can meet the voltage balancing control requirements, and the full DC system can directly perform voltage balancing control according to the target real-time scheduling instructions generated by the above control strategy.

[0086] The total DC system output power, that is, the system transmission power is , if there are a preset number l new energy units , it means that the output of this new energy unit itself cannot meet the pressure control demand, and the pressure stability control process may exist To achieve stable voltage control, these new energy units need to output at their maximum For transmission, these units can be recorded as ,in, ; The remaining new energy units The total output required is recorded as .

[0087] If the remaining new energy units Both , it means that the remaining number of new energy units can also meet the pressure control requirements, that is, to achieve steady-state control That is, when some units do not meet the voltage-balancing control requirements, the power difference will be evenly distributed to other new energy units, thereby ensuring that the output of the new energy power field as a whole can meet the voltage-balancing control requirements.

[0088] The converter port voltage balancing method of the full DC system provided in the embodiment of the present application replaces the grid-side inverter of the AC permanent magnet synchronous wind turbine with the grid-side DC / DC converter, and the voltage balancing of the DC port of the converged network refers to the voltage balancing of the output port of the DC / DC converter; by respectively performing VOC voltage stabilization control, port voltage control and system transmission power control on the AC / DC converter, DC / DC converter and DC / AC converter, the voltage balancing control of the full DC system and the stable AC grid connection point absorption regulation are realized; this process can provide a control strategy that is more in line with the actual situation for the full DC system and maintain the stable operation of the system. Therefore, the embodiment of the present application can solve the technical problems that the existing full DC system is difficult to achieve voltage balancing of the DC port of the converged network and cannot alleviate the absorption pressure of the AC grid connection point.

[0089] In the several embodiments provided in the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0090] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0091] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0092] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium, including a number of instructions for executing all or part of the steps of the method described in each embodiment of the present application through a computer device (which can be a personal computer, server, or network device, etc.). The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (full name in English: Read-Only Memory, English abbreviation: ROM), random access memory (full name in English: Random Access Memory, English abbreviation: RAM), disk or optical disk and other media that can store program codes.

[0093] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for equalizing converter port voltage in a full DC system, characterized in that: The voltage balancing method is applied in a full DC system, which includes: a fan, an AC / DC converter, a DC / DC converter, a DC / AC converter and an AC power grid; The fan and the AC / DC converter are electrically connected, and the AC / DC converters are connected in series; The output end of the AC / DC converter is connected to the DC / DC converter; The output end of the DC / DC converter is connected to the DC / AC converter; The output end of the DC / AC converter is connected to the AC power grid; The voltage balancing method is: Based on a preset AC / DC converter model, VOC voltage stabilization control is performed on the DC voltage on the machine side of the AC / DC converter; The DC / DC converter is voltage controlled by adopting a control strategy of an outer loop port voltage and an inner loop output current, so that the output port voltage of the DC / DC converter is balanced; The DC / AC converter is subjected to a system transmission power stability control according to a preset inverter control strategy, wherein the preset inverter control strategy includes a grid-following control strategy and a grid-building control strategy.

2. The converter port voltage equalization method of the full DC system according to claim 1, characterized in that: The step of performing system transmission power stabilization control on the DC / AC converter according to a preset inverter control strategy includes: When the grid short-circuit ratio of the new power system is greater than the short-circuit threshold, the DC / AC converter is subjected to a PQ control-based system transmission power stability control according to a grid-following control strategy, and a target real-time dispatching instruction is generated based on a preset artificial intelligence algorithm; When the grid short-circuit ratio of the new power system is less than the short-circuit threshold, the DC / AC converter is subjected to VF control-based system transmission power stability control according to the grid-forming control strategy, and the target real-time scheduling instruction is generated based on the preset artificial intelligence algorithm.

3. The converter port voltage equalization method of the full DC system according to claim 2, characterized in that: When the grid short-circuit ratio of the novel power system is less than the short-circuit threshold, the DC / AC converter is subjected to a system transmission power stability control based on VF control according to a grid-forming control strategy, and the target real-time dispatching instruction is generated based on the preset artificial intelligence algorithm, further comprising: A preset frequency synchronization control strategy is adopted to perform frequency synchronization control on the system frequency in the VF control process, and the preset frequency synchronization control strategy includes a droop control strategy and a virtual synchronization control strategy.

4. The converter port voltage equalization method of the full DC system according to claim 2, characterized in that: When the grid short-circuit ratio of the novel power system is less than the short-circuit threshold, the DC / AC converter is subjected to a system transmission power stability control based on VF control according to a grid-forming control strategy, and the target real-time dispatching instruction is generated based on the preset artificial intelligence algorithm, further comprising: If the output demand of each new energy unit under the target real-time dispatch instruction is not greater than the maximum power of the new energy electric field, the full DC system performs voltage balancing control according to the target real-time dispatch instruction; If under the target real-time scheduling instruction, the output demand of a preset number of new energy units is greater than the maximum power of the new energy electric field, then the preset number of new energy units are controlled to be controlled at the maximum power of the new energy electric field, and the remaining number of new energy units are controlled for voltage balancing according to the balanced power.

5. The converter port voltage balancing method of the full DC system according to claim 1, characterized in that: The AC / DC converter has a voltage boost function.

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