Large-scale new energy power generation direct current collecting and sending-out system

Abstract

The invention relates to a large-scale new energy power generation direct current collecting and sending-out system which comprises a photovoltaic power station, a wind power plant, an energy storage battery pack, a super capacitor bank, a non-isolated DC-DC converter, a non-isolated AC-DC converter, a low-voltage direct current bus, a high-frequency isolated DC-DC converter, a high-voltage direct current bus, a high-voltage power transmission line, an MMC-based DC-AC converter and a load center. According to the system, electric energy generated by wind energy or solar energy can be converted into direct current with the same voltage level through an AC-DC converter or a DC-DC converter and then is converged into a low-voltage direct-current bus, energy storage is configured on the low-voltage direct-current bus, and the electric energy generated by the wind energy or the solar energy can be flexibly combined and then flows into the low-voltage direct-current bus through the converter; the high-frequency isolation type DC-DC converter boosts the voltage level in a parallel input and series output mode, high-voltage direct-current electric energy is transmitted to a load center and inverted into alternating current through an MMC to be connected into a power grid, and a corresponding number of high-voltage direct-current collection systems are connected in parallel according to a capacity high-voltage power transmission line.

Description

Technical Field

[0001] The present invention relates to the field of renewable energy power generation technology, and in particular to a large-scale renewable energy power generation DC collection and transmission system. Background Art

[0002] As the global energy mix shifts toward a low-carbon future, large-scale renewable energy bases, represented by wind power and photovoltaics, are becoming the core power sources of the new power system. However, the randomness, volatility, and geographical distribution of renewable energy generation pose significant challenges to its efficient aggregation and long-distance transmission. While the current mainstream AC aggregation and flexible DC transmission technology is widely used, it faces the following bottlenecks:

[0003] ① Reactive power loss and overvoltage issues. Large-scale new energy bases cover a wide area and have long AC collection lines, which lead to a significant increase in reactive power loss and easily cause overvoltage risks.

[0004] ② Multi-stage power transformation is costly. Traditional AC power generation requires multiple stages of voltage boosting (e.g., photovoltaic inverter → AC step-up transformer → converter station). This results in bulky equipment and high investment costs. Offshore platforms, in particular, require the integration of large transformers, which limits power density.

[0005] ③ Multi-energy coordinated control is complex. The dynamic characteristics of wind power, photovoltaic power, and energy storage vary greatly, and existing hierarchical control strategies make it difficult to achieve dynamic power balance and rapid fault isolation.

[0006] ④ Cable and equipment costs account for a high proportion. AC collection cables can be hundreds of kilometers long, and investments in reactive power compensation devices and converter stations account for more than 30% of the total project cost.

[0007] The present invention standardizes the voltage levels and capacities of non-isolated DC-DC converters, AC-DC converters, and PCS converters connected in parallel to the low-voltage DC bus by unifying the voltage levels of the low-voltage DC bus. Since increasing the capacity of the DC collection system will lead to increased system losses and equipment investment, the present invention proposes connecting multiple collection systems in parallel to meet capacity requirements and is economical. High voltage is achieved through parallel input and series output. This topology control method is mature and easy to implement. Summary of the Invention

[0008] Therefore, the technical problem to be solved by the present invention is to solve the problems of the low-voltage DC-DC converter and AC-DC converter in the high-voltage DC collection and transmission system in the existing technology being not unified, the large capacity of the DC collection system resulting in large equipment investment, and the increased reactive power loss leading to the risk of excessive voltage.

[0009] In view of this, the present application provides a large-scale new energy power generation DC collection and transmission system, including a photovoltaic power station, a wind farm, an energy storage battery group, a supercapacitor group, a non-isolated DC-DC converter, a non-isolated AC-DC converter, a non-isolated bidirectional DC-DC converter, a low-voltage DC bus, a high-frequency isolated DC-DC converter, a high-voltage DC bus, a high-voltage transmission line, a DC-AC converter based on MMC and a load center; the photovoltaic power station is electrically connected to the non-isolated DC-DC converter, and the non-isolated DC-DC converter is electrically connected to the low-voltage DC bus. The wind farm is electrically connected to the non-isolated AC-DC converter, the non-isolated AC-DC converter is electrically connected to the low-voltage DC bus, the energy storage battery pack and the supercapacitor pack are electrically connected to the low-voltage DC bus, the low-voltage DC bus is electrically connected to the high-frequency isolated DC-DC converter, the high-voltage DC bus is electrically connected to the high-frequency isolated DC-DC converter and the high-voltage transmission line, and the MMC-based DC-AC converter is electrically connected to the high-voltage transmission line and the load center.

[0010] Optionally, the photovoltaic power station is composed of N photovoltaic arrays, the N photovoltaic arrays are electrically connected to the station-level DC collection subsystem, the station-level DC collection subsystem is electrically connected to the input end of the non-isolated DC-DC converter, the output end of the non-isolated DC-DC converter is electrically connected to one end of the low-voltage DC bus, and the electric energy of the non-isolated DC-DC converter can only flow in one direction, and the specific flow direction is from the photovoltaic power station into the low-voltage DC bus.

[0011] Optionally, the wind farm is composed of N wind turbines, and the N wind turbines are electrically connected to a field-level AC collection subsystem, and the field-level AC collection subsystem is electrically connected to the input end of the non-isolated AC-DC converter, and the output end of the non-isolated AC-DC converter is electrically connected to one end of the low-voltage DC bus. The electric energy of the non-isolated AC-DC converter can only flow in one direction, and the specific flow direction is from the wind farm into the low-voltage DC bus. The electricity generated by the N wind turbines is collected by the field-level AC collection subsystem and then transmitted to the non-isolated AC-DC converter.

[0012] Optionally, the energy storage battery group and the supercapacitor group are connected in parallel after passing through their respective PCSs, and then electrically connected to the input end of the non-isolated bidirectional DC-DC converter, and the output end of the non-isolated bidirectional DC-DC converter is electrically connected to one end of the low-voltage DC bus.

[0013] Optionally, the photovoltaic power station is connected to a station-level DC collection subsystem, the station-level DC collection subsystem is electrically connected to the input end of the non-isolated DC-DC converter, the input end of the non-isolated DC-DC converter is electrically connected to the DC end of the non-isolated AC-DC converter, the AC end of the non-isolated AC-DC converter is electrically connected to the wind farm, and the output end of the non-isolated DC-DC converter is electrically connected to the low-voltage DC bus.

[0014] Optionally, N of the high-frequency isolated DC-DC converters are connected in a parallel input and series output manner, the low-voltage end of each of the high-frequency isolated DC-DC converters is connected in parallel to the low-voltage DC bus, and the high-voltage ends of the high-frequency isolated DC-DC converters are connected in series in sequence.

[0015] Optionally, the number of high-frequency isolated DC-DC converters used is determined according to the voltage level of the high-voltage DC bus and the withstand voltage level of the power switching device.

[0016] Optionally, the high-voltage transmission line transmits electric energy to the load center, and the electric energy is inverted into high-voltage alternating current through an MMC-based DC-AC converter and then connected to the distribution network.

[0017] Optionally, the transmission end of the high-voltage transmission line is connected in parallel with a high-voltage direct current collection subsystem of corresponding number and capacity.

[0018] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0019] The present application provides a large-scale new energy power generation DC collection and transmission system, which includes a photovoltaic power station, a wind farm, an energy storage battery group, a supercapacitor group, a non-isolated DC-DC converter, a non-isolated AC-DC converter, a non-isolated bidirectional DC-DC converter, a low-voltage DC bus, a high-frequency isolated DC-DC converter, a high-voltage DC bus, a high-voltage transmission line, an MMC-based DC-AC converter and a load center; the photovoltaic power station is electrically connected to the non-isolated DC-DC converter, the non-isolated DC-DC converter is electrically connected to the low-voltage DC bus, the wind farm is electrically connected to the non-isolated AC-DC converter, the non-isolated AC-DC converter is electrically connected to the low-voltage DC bus, the energy storage battery group and the supercapacitor group are respectively electrically connected to the low-voltage DC bus, and the low-voltage DC bus is electrically connected to the The high-frequency isolated DC-DC converter is electrically connected, the high-voltage DC bus is electrically connected to the high-frequency isolated DC-DC converter and the high-voltage transmission line respectively, and the MMC-based DC-AC converter is electrically connected to the high-voltage transmission line and the load center respectively, so as to unify the voltage level of the low-voltage DC bus, and then standardize the voltage level and capacity of the non-isolated DC-DC converter, AC-DC converter and PCS converter connected in parallel to the low-voltage DC bus. Since the increase in the capacity of the DC collection system will lead to increased system losses and increased equipment investment, multiple collection subsystems are connected in parallel to meet the capacity requirements, which is economical and saves investment costs, and reduces reactive losses, and is not prone to overvoltage risks. At high voltage, the parallel input and series output method is adopted. This topology control method is mature and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly express the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0021] Figure 1 A schematic diagram of the system structure of a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application;

[0022] Figure 2 A schematic diagram of the structure of a non-isolated DC-DC converter for a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application;

[0023] Figure 3 A control strategy diagram for a non-isolated DC-DC converter of a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application;

[0024] Figure 3-1 This is a PI dual-loop control block diagram of a non-isolated DC-DC converter for a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application;

[0025] Figure 3-2 The triangular carrier between two adjacent BOOST boost circuits of a large-scale new energy power generation DC collection and transmission system provided by the embodiment of the present application has a phase shift angle of θ

[0026] Figure 3-3 The duty cycle of each BOOST boost circuit in a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application is obtained according to the voltage outer loop and current inner loop PI control;

[0027] Figure 4 A structural diagram of a non-isolated bidirectional DC-DC converter for a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application;

[0028] Figure 5 A control strategy diagram for a non-isolated bidirectional DC-DC converter operating in boost mode for a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application;

[0029] Figure 5-1 This is a PI dual-loop control block diagram of a bidirectional DC-DC converter operating in boost mode in a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application;

[0030] Figure 5-2 In a bidirectional DC-DC circuit of a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application, a phase shift angle of θ exists in the triangular carrier between the two BOOST boost circuits in the phase-leading manner;

[0031] Figure 5-3 The duty cycle of each BOOST circuit of a bidirectional DC-DC converter of a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application is obtained according to the voltage outer loop and current inner loop PI control;

[0032] Figure 6 A control strategy diagram for a non-isolated bidirectional DC-DC converter operating in buck mode for a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application;

[0033] Figure 6-1 This is a PI dual-loop control block diagram of a bidirectional DC-DC converter operating in buck mode in a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application;

[0034] Figure 6-2 In a bidirectional DC-DC circuit of a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application, a triangular carrier between two BUCK step-down circuits in a phase-leading manner has a phase shift angle of θ;

[0035] Figure 6-3 The duty cycle of each buck circuit of a bidirectional DC-DC converter of a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application is obtained according to the voltage outer loop and current inner loop PI control;

[0036] Figure 7 A structural diagram of a non-isolated AC-DC converter for a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application;

[0037] Figure 8 A control strategy diagram for a non-isolated AC-DC converter of a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application;

[0038] Figure 9 A structural diagram of a high-frequency isolated DC-DC converter for a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application;

[0039] Figure 10 A control strategy diagram for a high-frequency isolated DC-DC converter of a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application;

[0040] Figure 10-1 A phase-shift angle control PI double loop for a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application;

[0041] Figure 10-2 The present invention provides a large-scale renewable energy power generation DC collection and transmission system in a phase-shift control mode, including a method for generating a high-frequency inverter drive signal for a primary power switching device, a method for generating a high-frequency synchronous rectification drive signal for a secondary power switching device, and voltage waveforms at the input and output of the primary and secondary transformers.

[0042] Figure 11 A structural diagram of N high-frequency isolated DC-DC converters with parallel input and series output in a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application;

[0043] Figure 12 A control strategy diagram for a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application, wherein N high-frequency isolated DC-DC converters adopt parallel input and series output;

[0044] Figure 13This is a structural diagram of a MMC-based DC-AC converter for a large-scale renewable energy power generation DC collection and transmission system provided in an embodiment of the present application. DETAILED DESCRIPTION

[0045] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other unless they conflict.

[0046] It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention. Therefore, the drawings only show the layers related to the present invention and are not drawn according to the number, shape and size ratio of the layers in actual implementation. In actual implementation, the type and number of each layer can be changed at will, and the layer layout may also be more complicated.

[0047] In the following description, numerous details are set forth to provide a more thorough explanation of the embodiments of the present invention; however, it is apparent to one skilled in the art that the embodiments of the present invention may be practiced without these specific details.

[0048] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0049] The present invention provides a large-scale new energy power generation DC collection and transmission system, the specific structure of which is as follows: Figure 1As shown, it includes a photovoltaic power station, a wind farm, an energy storage battery group, a supercapacitor group, a non-isolated DC-DC converter, a non-isolated AC-DC converter, a non-isolated bidirectional DC-DC converter, a low-voltage DC bus, a high-frequency isolated DC-DC converter, a high-voltage DC bus, a high-voltage transmission line, an MMC-based DC-AC converter and a load center; the photovoltaic power station is electrically connected to the non-isolated DC-DC converter, the non-isolated DC-DC converter is electrically connected to the low-voltage DC bus, the wind farm is electrically connected to the non-isolated AC-DC converter, the non-isolated AC-DC converter is electrically connected to the low-voltage DC bus, the energy storage battery group and the supercapacitor group are respectively electrically connected to the low-voltage DC bus, the low-voltage DC bus is electrically connected to the high-frequency isolated DC-DC The converter is electrically connected, the high-voltage DC bus is electrically connected to the high-frequency isolated DC-DC converter and the high-voltage transmission line respectively, and the MMC-based DC-AC converter is electrically connected to the high-voltage transmission line and the load center respectively, so as to unify the voltage level of the low-voltage DC bus, and then standardize the voltage level and capacity of the non-isolated DC-DC converter, AC-DC converter and PCS converter connected in parallel to the low-voltage DC bus. Since the increase in the capacity of the DC collection system will lead to increased system losses and increased equipment investment, multiple collection subsystems are connected in parallel to meet the capacity requirements, which is also economical and saves investment costs, and reduces reactive losses, and is not prone to overvoltage risks. At high voltage, the parallel input and series output method is adopted. This topology control method is mature and easy to implement.

[0050] Furthermore, the photovoltaic power station is composed of N photovoltaic arrays, which are electrically connected to the station-level DC collection subsystem, which is electrically connected to the input end of the non-isolated DC-DC converter, and the output end of the non-isolated DC-DC converter is electrically connected to one end of the low-voltage DC bus. The electric energy of the non-isolated DC-DC converter can only flow in one direction, and the specific flow direction is from the photovoltaic power station into the low-voltage DC bus. Specifically, the electricity generated by the N photovoltaic arrays is collected by the station-level DC collection subsystem and then transmitted to the non-isolated DC-DC converter.

[0051] Furthermore, the wind farm is composed of N wind turbines, and the N wind turbines are electrically connected to a field-level AC collection subsystem, and the field-level AC collection subsystem is electrically connected to the input end of the non-isolated AC-DC converter, and the output end of the non-isolated AC-DC converter is electrically connected to one end of the low-voltage DC bus. The electric energy of the non-isolated AC-DC converter can only flow in one direction, and the specific flow direction is from the wind farm into the low-voltage DC bus. The electricity generated by the N wind turbines is collected by the field-level AC collection subsystem and then transmitted to the non-isolated AC-DC converter.

[0052] Furthermore, the energy storage battery pack and the supercapacitor pack are connected in parallel after passing through their respective PCSs, and then electrically connected to the input end of the non-isolated bidirectional DC-DC converter. The output end of the non-isolated bidirectional DC-DC converter is electrically connected to one end of the low-voltage DC bus. The PCS has the function of controlling the bidirectional flow of electric energy.

[0053] Furthermore, the photovoltaic power station is connected to a station-level DC collection subsystem, the station-level DC collection subsystem is electrically connected to the input end of the non-isolated DC-DC converter, the input end of the non-isolated DC-DC converter is electrically connected to the DC end of the non-isolated AC-DC converter, the AC end of the non-isolated AC-DC converter is electrically connected to the wind farm, and the output end of the non-isolated DC-DC converter is electrically connected to the low-voltage DC bus. Specifically, the electricity generated by the photovoltaic power station is collected by the station-level DC collection subsystem and then transmitted to the non-isolated DC-DC converter.

[0054] Furthermore, N of the high-frequency isolated DC-DC converters are connected in a parallel input and series output manner, the low-voltage end of each high-frequency isolated DC-DC converter is connected in parallel with the low-voltage DC bus, and the high-voltage ends of the high-frequency isolated DC-DC converters are connected in series in sequence.

[0055] Furthermore, the number of high-frequency isolated DC-DC converters used is determined according to the voltage level of the high-voltage DC bus and the withstand voltage level of the power switching device.

[0056] Furthermore, the high-voltage transmission line transmits electric energy to the load center, and after the electric energy is inverted into high-voltage alternating current through the MMC-based DC-AC converter, it is connected to the distribution network, thereby realizing large-scale DC collection and transmission of renewable energy power generation, saving investment costs, reducing reactive power losses, and not easily causing overvoltage risks.

[0057] Furthermore, the transmission end of the high-voltage transmission line is connected in parallel with a corresponding number and capacity of high-voltage direct current collection subsystems.

[0058] Specifically, such as Figure 2 The figure shows the circuit topology of the non-isolated DC-DC converter, which is composed of N BOOST circuits connected in parallel in an interleaved manner, where N represents the number of photovoltaic arrays connected to the photovoltaic power station. The photovoltaic power station contains 1, 2, ..., N photovoltaic arrays, and the input end of the non-isolated DC-DC converter has a total of #1PV_INPUT, #2PV_INPUT, ..., #N PV_INPUT input ports. The N photovoltaic arrays of the photovoltaic power station are sequentially connected to the N input ports of the non-isolated DC-DC converter. Figure 3 The control strategy diagram is shown below. Each BOOST circuit controls the duty cycle of the power switch device Qi_1 to Di_1 (where i is 1, 2, ..., N) based on the reference voltage and actual voltage of the low-voltage DC bus. The control relationship is:

[0059]

[0060] Where K p1 and K i1 The voltage P I Proportional and integral coefficients of the control loop, K p2 and K i2 The current P I The proportional coefficient and integral coefficient of the control loop, iLVDC_FB_i is the actual current flowing to the low-voltage DC bus (where i is 1, 2, ..., N).

[0061] like Figure 3-3 The figure shows the duty cycle Di_1 of each BOOST boost circuit according to the voltage outer loop and current inner loop PI control. The duty cycle Di_1 is compared with the triangular carrier to obtain the drive signal of the corresponding power switch device Qi_1. The triangular carrier between two adjacent BOOST boost circuits has a phase shift angle of θ, θ = T / N, as shown in Figure 1. Figure 3-2 shown.

[0062] like Figure 4 The figure shows the circuit topology of a non-isolated bidirectional DC-DC converter, which consists of N buck-boost bidirectional DC-DC circuits connected in parallel and interleaved. N depends on the rated capacity of the energy storage battery pack and supercapacitor pack.

[0063] like Figure 5 The figure shows the control strategy diagram of a non-isolated bidirectional DC-DC converter operating in boost mode. Figure 5-1 Figure 1 is the PI dual-loop control block diagram of a bidirectional DC-DC converter operating in boost mode. The specific control relationship is:

[0064]

[0065] Where K p3 and K i3 are the proportional coefficient and integral coefficient of the voltage PI control loop, K p4 and K i4 are the proportional coefficient and integral coefficient of the current PI control loop respectively, iLVDC_BAT_i is the actual current flowing to the low-voltage DC bus (where i is 1, 2, ..., N), and the triangular carrier between the two BOOST boost circuits in the bidirectional DC-DC circuit has a phase shift of θ, θ = T / N, as shown in Figure 5-2 shown.

[0066] like Figure 5-3 The figure shows the duty cycle Di_1 obtained by the PI control of the voltage outer loop and current inner loop of each boost circuit of the non-isolated bidirectional DC-DC converter. The duty cycle Di_1 is compared with the triangular carrier to obtain the drive signal of the corresponding power switching devices Qi_1 and Qi_2 after considering the dead zone.

[0067] like Figure 6 The figure shows the control strategy diagram of a non-isolated bidirectional DC-DC converter operating in buck mode. Figure 6-1 The PI dual-loop control block diagram of a non-isolated bidirectional DC-DC converter operating in buck mode is shown in Figure 1. The specific control relationship is:

[0068]

[0069] Where K p5 and K i5 are the proportional coefficient and integral coefficient of the voltage PI control loop, K p6 and K i6 are the proportional coefficient and integral coefficient of the current PI control loop, respectively, and iBAT_FB_i is the actual current flowing to the energy storage battery pack (where i is 1, 2, ..., N). In a non-isolated bidirectional DC-DC circuit, the triangular carrier between the two BUCK step-down circuits has a phase shift of θ, where θ = T / N. Figure 6-2 shown.

[0070] like Figure 6-3 The figure shows the duty cycle Di_2 obtained by the PI control of the voltage outer loop and current inner loop of each buck circuit of the non-isolated bidirectional DC-DC converter. The duty cycle Di_2 is compared with the triangular carrier to obtain the drive signal of the corresponding power switching devices Qi_2 and Qi_1 after considering the dead zone.

[0071] like Figure 7The figure shows the circuit topology of a non-isolated AC-DC converter, which is a three-phase full-bridge rectifier topology. It consists of the upper and lower bridge arms of phases A, B, and C, respectively. The upper and lower bridge arms of each phase are composed of N IGBT power switching devices connected in parallel, where N depends on the rated capacity of the connected wind farm.

[0072] like Figure 8 The figure shows the control strategy block diagram of a non-isolated AC-DC converter. The control relationship is:

[0073]

[0074] Where K p7 and K i7 They are respectively the low voltage DC bus voltage P I Proportional and integral coefficients of the control loop, K p8 and K i8 The current P I Proportional and integral coefficients of the control loop.

[0075] The uU_ref, uV_ref and uW_ref obtained by formula (4) are given to the SVPWM generation module to generate the power switch device drive signal PWMREC.

[0076] like Figure 9 The figure shows the circuit topology of a high-frequency isolated DC-DC converter, including a high-frequency transformer with a transformation ratio of k:1, a primary-side high-frequency full-bridge inverter, and a secondary-side high-frequency full-bridge rectifier. Each bridge arm of the inverter and rectifier is composed of N IGBT power switching devices connected in parallel, where N depends on the capacity of the high-voltage DC transmission line.

[0077] like Figure 10 The figure shows the control strategy of a high-frequency isolated DC-DC converter. The relationship between the primary and secondary voltages is:

[0078]

[0079] Where uDC_ISO is the high-side voltage of the isolation submodule, f is the operating frequency, and δ / (2πf) is the time taken for the phase shift angle.

[0080] like Figure 10-1 The figure shows the phase shift angle control PI double loop, and the mathematical relationship is:

[0081]

[0082] Where K p9 and K i9 are the proportional coefficient and integral coefficient of the voltage PI control loop, K p10 and K i10They are the proportional coefficient and integral coefficient of the current PI control loop respectively.

[0083] like Figure 10-2 The figure shows how the high-frequency inverter drive signal of the primary power switching device is generated, how the high-frequency synchronous rectification drive signal of the secondary power switching device is generated, and the voltage waveforms of the primary and secondary transformer inputs and outputs in the phase-shift control mode.

[0084] like Figure 11 The figure shows a circuit topology in which N high-frequency isolated DC-DC converters are connected in parallel and output in series, where N depends on the voltage level of the high-voltage DC bus.

[0085] like Figure 12 The figure shows a control strategy block diagram of N high-frequency isolated DC-DC converters with parallel input and series output. The triangular carriers between adjacent high-frequency isolated DC-DC converters have phase shift angles θ, θ = T / N, where T is the period and N is the number of isolated DC-DC converters. The control method of a single isolated DC-DC converter is as follows: Figure 10 shown.

[0086] like Figure 13 The figure shows the circuit topology of the MMC-based DC-AC converter. The MMC adopts a three-phase six-bridge-arm topology. Each bridge arm consists of N half-bridge sub-modules, where N depends on the voltage level of the high-voltage DC bus.

[0087] The terms "first", "second", "third", "fourth", etc. (if any) in the specification of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can, for example, be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0088] 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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above 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 large-scale new energy power generation DC collection and transmission system, characterized by: The invention comprises a photovoltaic power station, a wind farm, an energy storage battery group, a supercapacitor group, a non-isolated DC-DC converter, a non-isolated AC-DC converter, a non-isolated bidirectional DC-DC converter, a low-voltage DC bus, a high-frequency isolated DC-DC converter, a high-voltage DC bus, a high-voltage transmission line, an MMC-based DC-AC converter and a load center; the photovoltaic power station is electrically connected to the non-isolated DC-DC converter, the non-isolated DC-DC converter is electrically connected to the low-voltage DC bus, the wind farm is electrically connected to the non-isolated AC-DC converter, the non-isolated AC-DC converter is electrically connected to the low-voltage DC bus, the energy storage battery group and the supercapacitor group are respectively electrically connected to the low-voltage DC bus, the low-voltage DC bus is electrically connected to the high-frequency isolated DC-DC converter, the high-voltage DC bus is respectively electrically connected to the high-frequency isolated DC-DC converter and the high-voltage transmission line, and the MMC-based DC-AC converter is respectively electrically connected to the high-voltage transmission line and the load center.

2. A large-scale new energy power generation DC collection and transmission system according to claim 1, characterized in that: The photovoltaic power station is composed of N photovoltaic arrays. The electricity generated by the N photovoltaic arrays is electrically connected to the input end of the non-isolated DC-DC converter through a station-level DC collector, and the output end of the non-isolated DC-DC converter is electrically connected to one end of the low-voltage DC bus.

3. A large-scale new energy power generation DC collection and transmission system according to claim 1, characterized in that: The wind farm is composed of N wind turbines. The electricity generated by the N wind turbines is collected through field-level AC and electrically connected to the input end of the non-isolated AC-DC converter. The output end of the non-isolated AC-DC converter is electrically connected to one end of the low-voltage DC bus.

4. A large-scale new energy power generation DC collection and transmission system according to claim 1, characterized in that: The energy storage battery group and the supercapacitor group are connected in parallel after passing through their respective PCSs, and then electrically connected to the input end of the non-isolated bidirectional DC-DC converter, and the output end of the non-isolated bidirectional DC-DC converter is electrically connected to one end of the low-voltage DC bus.

5. A large-scale new energy power generation DC collection and transmission system according to claim 1, characterized in that: The electricity generated by the photovoltaic power station is electrically connected to the input end of the non-isolated DC-DC converter through the station-level DC collector, the input end of the non-isolated DC-DC converter is electrically connected to the DC end of the non-isolated AC-DC converter, the AC end of the non-isolated AC-DC converter is electrically connected to the wind farm, and the output end of the non-isolated DC-DC converter is electrically connected to the low-voltage DC bus.

6. A large-scale new energy power generation DC collection and transmission system according to claim 1, characterized in that: The N high-frequency isolated DC-DC converters are connected in a parallel input and series output manner, the low-voltage end of each high-frequency isolated DC-DC converter is connected in parallel with the low-voltage DC bus, and the high-voltage ends of the high-frequency isolated DC-DC converters are connected in series in sequence.

7. A large-scale new energy power generation DC collection and transmission system according to claim 6, characterized in that: The number of high-frequency isolated DC-DC converters used is determined according to the voltage level of the high-voltage DC bus and the withstand voltage level of the power switching device.

8. The large-scale new energy power generation DC collection and transmission system according to claim 1 is characterized in that: The high-voltage transmission line transmits electric energy to the load center, and the electric energy is inverted into high-voltage alternating current through the MMC-based DC-AC converter and then connected to the distribution network.

9. A large-scale renewable energy power generation DC collection and transmission system according to claim 1, characterized in that: The transmission end of the high-voltage transmission line is connected in parallel with a high-voltage direct current collection subsystem of corresponding quantity and capacity.

Images