Photovoltaic electric field intermediate frequency boosting device and method

Abstract

The invention discloses an intermediate-frequency boosting device and method for a photovoltaic electric field, and relates to the technical field of photovoltaic power generation confluence inversion boosting power transmission, and the device comprises a photovoltaic power generation system which is used for generating direct current; the intermediate-frequency boosting system comprises an inverter system, a first-stage boosting system, a second-stage boosting system and a commutation system; the inverter system comprises a plurality of inverters and is used for converting the direct current generated by the photovoltaic power generation system into intermediate-frequency low-voltage alternating current; the first-stage boosting system converts the medium-frequency low-voltage alternating current into medium-frequency medium-voltage alternating current; the secondary boosting system converts the intermediate-frequency medium-voltage alternating current into intermediate-frequency high-voltage alternating current; the converter system is used for converting the intermediate-frequency high-voltage alternating current into power-frequency high-voltage alternating current or high-voltage direct current, the power-frequency high-voltage alternating current is transmitted to a power-frequency large power grid, and the high-voltage direct current is transmitted to a direct-current large power grid. And the power generation installed capacity of the photovoltaic electric field is effectively improved.

Description

Technical Field

[0001] The present application relates to the technical field of photovoltaic power generation, converging, inverting and boosting power transmission, and in particular to a photovoltaic electric field medium frequency boosting device and method. Background Art

[0002] By the end of 2023, the installed capacity of solar power generation in China will be about 609.49GW. While the newly installed capacity of photovoltaic power generation is growing rapidly, photovoltaic power generation technology has also developed synchronously. For example, the power generation efficiency of photovoltaic modules has continued to improve. Ten years ago, the power generation efficiency of photovoltaic modules was about 17-18%. Today, the efficiency of commercialized modules is 23-24% (commodity sold on the market), an increase of 6 percentage points. In terms of the proportion of technological progress, the efficiency has increased by more than 30% year-on-year. The technological progress of photovoltaic modules has brought customers an additional 30% of benefits.

[0003] In order to improve the efficiency of photovoltaic power generation, photovoltaic fields need to increase their power generation capacity on the existing basis through technical means including increasing the number of photovoltaic modules, replacing high-efficiency photovoltaic modules, optimizing the layout of photovoltaic modules, adding energy storage systems, upgrading inverters, adding tracking systems, optimizing operation and maintenance management, adding photovoltaic module cleaning equipment, adding photovoltaic module cooling systems, and adding distributed power generation systems.

[0004] After the power generation capacity is improved, the existing technology needs to increase the installed capacity of the boost system at the same time. One is to increase the number of transformers or the capacity of a single unit; the other is to increase the busbar cables. However, the above transformation methods all require a large amount of direct or indirect cost increase without exception, and the economic efficiency is poor; sometimes the number of transformers cannot be increased due to space constraints. Summary of the invention

[0005] The purpose of the present application is to provide a photovoltaic electric field medium frequency boost device and method, which can increase the operating frequency of the boost system and effectively increase the photovoltaic electric field power generation installed capacity without almost increasing the cost.

[0006] To achieve the above objectives, this application provides the following solutions:

[0007] In a first aspect, the present application provides a photovoltaic electric field medium frequency boost device, including: a photovoltaic power generation system, a medium frequency boost system, a large industrial frequency power grid and a large DC power grid.

[0008] Photovoltaic power generation system for generating direct current electricity;

[0009] The medium frequency boost system includes an inverter system, a primary boost system, a secondary boost system and a commutation system; wherein the inverter system includes a plurality of inverters for converting the direct current generated by the photovoltaic power generation system into a medium frequency low voltage alternating current; the primary boost system is used to convert the medium frequency low voltage alternating current into a medium frequency medium voltage alternating current; the secondary boost system is used to convert the medium frequency medium voltage alternating current into a medium frequency high voltage alternating current; the commutation system is used to convert the medium frequency high voltage alternating current into industrial frequency high voltage alternating current and high voltage direct current, and transmit the industrial frequency high voltage alternating current to the industrial frequency large power grid, and transmit the high voltage direct current to the direct current large power grid.

[0010] Optionally, the output frequency of the inverter has a value range of greater than 50 Hz and not greater than 60 Hz.

[0011] Optionally, the number of the inverters is greater than one.

[0012] Optionally, the primary boost system includes at least two first transformers.

[0013] Optionally, the two-stage boost system includes a second transformer.

[0014] Optionally, the commutation system includes a commutation device and a rectifier device;

[0015] The converter device is connected to the large industrial frequency power grid and is used to convert the medium frequency high voltage AC power into the industrial frequency high voltage AC power and transmit the industrial frequency high voltage AC power to the large industrial frequency power grid;

[0016] The rectifier device is connected to the DC power grid and is used to convert medium-frequency high-voltage AC power into high-voltage DC power and transmit the high-voltage DC power to the DC power grid.

[0017] Optionally, the photovoltaic power generation system, the medium frequency boost system, the industrial frequency large power grid and the DC large power grid are connected via transmission cables.

[0018] Optionally, the photovoltaic electric field medium frequency boost device further includes a protection system; the protection system is connected to the medium frequency boost system and is used to protect the medium frequency boost system.

[0019] In a second aspect, the present application provides a photovoltaic electric field medium frequency boosting method based on the photovoltaic electric field medium frequency boosting device described above, comprising:

[0020] Get the output parameters of the inverter;

[0021] The output parameter of the inverter is regulated so that the output parameter of the inverter reaches a target value; the output parameter is an output frequency or an output voltage.

[0022] Optionally, when the output parameter is an output frequency, regulating the output parameter of the inverter so that the output parameter of the inverter reaches a target value specifically includes:

[0023] The control parameters of the inverter are adjusted so that the output frequency of the inverter reaches the target frequency; the control parameters include modulation ratio, frequency setting, pulse width modulation frequency or control algorithm parameters.

[0024] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0025] The present application provides a photovoltaic electric field medium-frequency boost device and method, including a photovoltaic power generation system, a medium-frequency boost system, a large industrial frequency power grid and a large DC power grid. Through an inverter system, a primary boost system, a secondary boost system and a commutation system, a medium-frequency boost device after capacity expansion and transformation of a photovoltaic electric field power generation installed capacity is provided. By adjusting the output frequency or output voltage of the inverter, the operating frequency of the boost system is increased, and the installed capacity of the photovoltaic electric field power generation is effectively increased without almost increasing the cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 A schematic diagram of the growth rate of solar power generation installed capacity provided for this application;

[0028] Figure 2 A structural diagram of a photovoltaic electric field system in the related technology provided by this application;

[0029] Figure 3 A schematic diagram of the structure of a photovoltaic electric field medium frequency boost device provided in one embodiment of the present application;

[0030] Figure 4 A schematic diagram of a photovoltaic electric field medium frequency boost device provided in one embodiment of the present application;

[0031] Figure 5 A schematic diagram of a curve showing the relationship between the total cost of main materials and frequency provided in an embodiment of the present application;

[0032] Figure 6 A schematic diagram of a curve showing the relationship between no-load loss and frequency provided in an embodiment of the present application;

[0033] Figure 7A schematic diagram of a curve showing the relationship between load loss and frequency provided in an embodiment of the present application;

[0034] Figure 8 A schematic diagram of a curve showing the relationship between total loss and frequency provided in an embodiment of the present application;

[0035] Fig. 9 A schematic diagram of a curve showing the relationship between the core magnetic flux density and the frequency provided in an embodiment of the present application;

[0036] Fig.10 A schematic flow chart of a photovoltaic electric field medium frequency boosting method provided in one embodiment of the present application. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions 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.

[0038] China's newly installed photovoltaic power generation capacity and growth rate (GW, %) from 2011 to 2023 Figure 1 shown. Figure 2 The photovoltaic electric field system diagram in the related art, the power generated by the photovoltaic electric field is generally output through two paths, one is the high-voltage industrial frequency AC power grid, and the other is the high-voltage DC power grid. The operating frequency of the inverter INV1 in the photovoltaic electric field system is 50Hz.

[0039] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0040] In an exemplary embodiment, Figure 3 As shown, a photovoltaic electric field medium frequency boost device is provided, which includes a photovoltaic power generation system, a medium frequency boost system, and a large power frequency grid (i.e. Figure 4 The photovoltaic power generation system, medium frequency boost system, industrial frequency power grid and DC power grid are connected through transmission cables.

[0041] The photovoltaic power generation system includes a plurality of photovoltaic power generation submodules for generating direct current.

[0042] The medium frequency boost system includes an inverter system, a primary boost system, a secondary boost system and a commutation system. The inverter system includes a plurality of inverters INV1, which are used to convert the DC power generated by the photovoltaic power generation system into medium frequency low voltage AC power and adjust the output voltage and frequency. The output frequency of the inverter INV1 is in the range of greater than 50Hz and less than 60Hz, preferably 60Hz. The number of inverters INV1 is greater than 1. Figure 4 This is a device connection diagram when the number of inverters INV1 and is 4.

[0043] The primary boost system is used to convert the medium-frequency low-voltage AC power generated by the inverter system into medium-frequency medium-voltage AC power. The primary boost system includes more than one first transformer T1.

[0044] The secondary boost system is used to convert the medium-frequency medium-voltage AC power generated by the primary boost system into medium-frequency high-voltage AC power. The secondary boost system includes a second transformer T2.

[0045] The commutation system is used to convert the medium-frequency high-voltage AC power generated by the secondary boost system into industrial-frequency high-voltage AC power and high-voltage DC power, and transmit the industrial-frequency high-voltage AC power to the industrial-frequency large power grid, and transmit the high-voltage DC power to the DC large power grid.

[0046] The commutation system includes a commutation device CON and a rectifier SCR.

[0047] The converter CON is connected to the industrial frequency large power grid and is used to convert medium frequency high voltage AC power into industrial frequency high voltage AC power, convert medium frequency electric energy into industrial frequency electric energy, and transmit the industrial frequency high voltage AC power to the industrial frequency large power grid.

[0048] The rectifier SCR is connected to the DC grid and is used to convert medium-frequency high-voltage AC power into high-voltage DC power, convert medium-frequency electrical energy into DC electrical energy, and transmit high-voltage DC power to the DC grid.

[0049] In another exemplary embodiment of the present application, the photovoltaic electric field medium frequency boost device also includes a protection system; the protection system includes a protection device and software. It is connected to each module in the medium frequency boost system (including the inverter INV1, the first transformer T1, the second transformer T2, the commutation device CON, and the rectifier SCR) to protect the medium frequency boost system so that the medium frequency boost system can operate normally.

[0050] The embodiment of the present application also provides a photovoltaic electric field medium frequency boosting method based on the photovoltaic electric field medium frequency boosting device involved above. The specific limitations in the provided one or more photovoltaic electric field medium frequency boosting method embodiments can be referred to the above limitations on the photovoltaic electric field medium frequency boosting device, which will not be repeated here.

[0051] In an exemplary embodiment, Fig.10 As shown, a photovoltaic electric field medium frequency boost method is provided, comprising:

[0052] S1: Get the output parameters of inverter INV1.

[0053] S2: regulating an output parameter of the inverter INV1 so that the output parameter of the inverter INV1 reaches a target value; the output parameter is an output frequency or an output voltage.

[0054] As an optional implementation, when the output parameter is the output voltage, the switching parameter of the switching element of the inverter INV1 or the input voltage of the inverter INV1 is regulated so that the output voltage of the inverter INV1 reaches the voltage target value; the switching parameter includes the conduction time and the phase;

[0055] When the output parameter is the output frequency, the output parameter of the inverter is regulated so that the output parameter of the inverter reaches a target value, specifically including: regulating the control parameters of the inverter so that the output frequency of the inverter reaches a target frequency; the control parameters include modulation ratio, frequency setting, pulse width modulation frequency or control algorithm parameters.

[0056] The photovoltaic inverter INV1 can adjust the output frequency and voltage. The present application increases the output frequency of the inverter INV1 and the operating frequency of the medium frequency boost system from the original frequency F1 (50 Hz) to the target frequency F2. The target frequency F2 is in the range of greater than 50 Hz and not greater than 60 Hz, preferably 60 Hz.

[0057] The present application increases the output voltage U5 of the inverter INV1 and the operating voltage of the medium frequency boost system, and increases the original output voltage U1 to the voltage target value U5. The voltage target value U5 is the input voltage of the first transformer T1, and U0 is the input voltage of the inverter INV1. The preferred voltage target value U5 can be calculated by the original output voltage of the inverter INV1. The relationship between the original output voltage U1 of the inverter INV1 and the voltage target value U5 is: U5=1.1-1.15U1.

[0058] First, adjust the output frequency:

[0059] Fixed frequency: Generally, the output frequency of the photovoltaic inverter INV1 is fixed, usually 50 Hz, and cannot be changed at will. This is because the inverter INV1 has been set at the factory to adapt to the standard grid frequency.

[0060] Adjustment in special cases: When adjusting the frequency of the inverter INV1, you can turn on the machine and find the variable frequency resistor around the oscillation integrated tube to adjust it. However, this is not recommended to do it yourself, because improper frequency adjustment will have a bad effect on the load electrical appliances, or even damage the appliances.

[0061] Professional advice: If the frequency needs to be adjusted, it is recommended to contact the technicians of the inverter INV1 manufacturer to operate to ensure safety and effectiveness.

[0062] To change the output frequency of the inverter, you can adjust the inverter control parameters, including:

[0063] 1. Modulation Index: By changing the modulation index, the frequency and amplitude of the inverter output can be affected.

[0064] 2. Frequency setting: Many inverters allow the user to set the output frequency directly, usually on the control panel or through software adjustment.

[0065] 3. PWM (Pulse Width Modulation) Frequency: In some inverters, adjustment of the PWM frequency can also affect the output frequency.

[0066] 4. Control algorithm parameters: Parameter adjustments such as PID controller may affect the dynamic response and output frequency of the inverter.

[0067] It should be noted that when adjusting these parameters, it is necessary to ensure that the other operating conditions and load characteristics of the inverter can support the new output frequency to avoid equipment damage or performance degradation.

[0068] Second, adjust the output voltage:

[0069] Voltage regulation: According to the output voltage and the grid voltage, the output voltage of the inverter INV1 is adjusted to match the grid voltage.

[0070] Frequency regulation: According to the grid frequency, adjust the frequency output by the inverter INV1 to make it the same as the grid frequency.

[0071] Specific adjustment method:

[0072] Pulse Width Modulation (PWM): The output voltage is regulated by varying the on-time of the switching element.

[0073] Phase-shift voltage regulation: The output voltage is adjusted by changing the phase of the internal switching elements of the inverter INV1.

[0074] Adjust the DC side voltage: adjust the output AC voltage by changing the input DC voltage.

[0075] Actual operation: The actual grid voltage is high: If the actual grid voltage is high, the AC voltage can be reduced by adjusting the transformer.

[0076] Adjust protection parameters: If the inverter INV1 frequently experiences overvoltage protection, the overvoltage protection value can be appropriately increased so that the inverter INV1 can still work normally under a higher voltage.

[0077] Professional advice: If you encounter voltage regulation problems, it is recommended to contact the customer service personnel or engineering project service personnel of the inverter INV1 manufacturer for maintenance and adjustments.

[0078] The inverter INV1 can adjust the output voltage, but the output frequency is usually fixed and it is not recommended to adjust it yourself. If you need to adjust the frequency or voltage, it is recommended to contact a professional technician to ensure safety and normal operation of the system.

[0079] The output voltage U6 of the first transformer T1 is U2 / U1*U5, where U2 / U1 is the transformation ratio of the first transformer T1 before the capacity increase and transformation. The transformation ratio range of the first transformer T1 can be expanded or reduced by adjusting the gear position of the tap switch of the first transformer T1 to reduce or increase the value of U6. The sixth voltage U6 is the input voltage of the second transformer T2, and the output voltage U7 of the second transformer T2 is U4 / U3*U6, where U4 / U3 is the transformation ratio of the second transformer T2 before the transformation and transformation. The gear position of the tap switch of the second transformer T2 can be adjusted to reduce or increase the value of U6. The second transformer T2 is set to expand or reduce the ratio range of the second transformer T2 to reduce or increase the value of U7; U7 is the input voltage of the converter, and the converter converts the AC power with voltage U7 and frequency F2 into AC power with voltage U8 and frequency F1 for output; the voltage U8 value matches the voltage value of the industrial frequency AC power grid; U7 is also the input voltage of the rectifier, and the rectifier converts the AC power with voltage U7 and frequency F2 into DC power with voltage U9 for output; the voltage U9 value matches the voltage value of the DC power grid. Among them, U6 and U7 do not exceed the maximum voltage of the equipment.

[0080] The following is an experimental verification of the impact of distribution transformer frequency on cost and its main performance:

[0081] Taking S20-2000 / 10 (level 2 energy efficiency) as an example, the performance parameters of distribution transformers at different frequencies were calculated and analyzed using computer optimization software. The calculation results are summarized as follows:

[0082] 1. Basic parameters of transformer:

[0083] 1) Product model: S20-2000 / 10 (Level 2 energy efficiency)

[0084] 2) Silicon steel sheet grade used: B20R60

[0085] 3) Lamination coefficient 0.94, P0 process coefficient 1.2

[0086] 4) Calculate the frequency: 50Hz, 60Hz, 80Hz, 100Hz, 120Hz, 140Hz, 150Hz, 160Hz, 180Hz, 200Hz, 250Hz, 300Hz, 350Hz, 400Hz, 450Hz.

[0087] 2. The comparison results of the main performance parameters of the transformer are shown in Table 1.

[0088] 3. The comparison results of transformer weight and cost are shown in Table 2. Weight unit: kg, cost unit: 10,000 yuan.

[0089] Table 1 Comparison results of main performance parameters of transformers

[0090]

[0091]

[0092] Table 2 Transformer weight and cost comparison results

[0093]

[0094]

[0095] The relationship curves of the total cost of main materials and frequency, the relationship curves of no-load loss and frequency, the relationship curves of load loss and frequency, the relationship curves of total loss and frequency, and the relationship curves of core column magnetic flux density (core column magnetic density) and frequency are shown as follows: Figure 5-Figure 9 shown.

[0096] This application has the following advantages:

[0097] 1) The present application does not need to increase the number of the first transformer T1 and the second transformer T2 of the boost system;

[0098] 2) This application does not increase the boost voltage or slightly increase the operating current of each part of the system, provided that the safe operation of the system is ensured;

[0099] 3) This application does not increase or only slightly increases the transmission cables in various parts of the boost system, provided that the safe operation of the system is ensured;

[0100] 4) This application can increase the installed capacity of photovoltaic power generation by 10-15% (because the system capacity is When the system voltage increases by 10%-15%, the capacity increases by 10%-15%).

[0101] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0102] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A photovoltaic electric field medium frequency boost device, characterized in that: The photovoltaic electric field medium frequency boost device comprises a photovoltaic power generation system, a medium frequency boost system, a large industrial frequency power grid and a large DC power grid; Photovoltaic power generation system for generating direct current electricity; The medium frequency boost system includes an inverter system, a primary boost system, a secondary boost system and a commutation system; wherein the inverter system includes a plurality of inverters for converting the direct current generated by the photovoltaic power generation system into a medium frequency low voltage alternating current; the primary boost system is used to convert the medium frequency low voltage alternating current into a medium frequency medium voltage alternating current; the secondary boost system is used to convert the medium frequency medium voltage alternating current into a medium frequency high voltage alternating current; the commutation system is used to convert the medium frequency high voltage alternating current into industrial frequency high voltage alternating current or high voltage direct current, and transmit the industrial frequency high voltage alternating current to the industrial frequency large power grid, and transmit the high voltage direct current to the direct current large power grid.

2. The photovoltaic electric field medium frequency boost device according to claim 1, characterized in that: The output frequency of the inverter has a value range of greater than 50 Hz and not greater than 60 Hz.

3. The photovoltaic electric field medium frequency boost device according to claim 1, characterized in that: The number of the inverters is greater than one.

4. The photovoltaic electric field medium frequency boost device according to claim 1, characterized in that: The primary boost system includes at least two first transformers.

5. The photovoltaic electric field medium frequency boost device according to claim 1, characterized in that: The two-stage boost system includes a second transformer.

6. The photovoltaic electric field medium frequency boost device according to claim 1, characterized in that: The commutation system comprises a commutation device and a rectifier device; The converter device is connected to the large industrial frequency power grid and is used to convert the medium frequency high voltage AC power into the industrial frequency high voltage AC power and transmit the industrial frequency high voltage AC power to the large industrial frequency power grid; The rectifier device is connected to the DC power grid and is used to convert medium-frequency high-voltage AC power into high-voltage DC power and transmit the high-voltage DC power to the DC power grid.

7. The photovoltaic electric field medium frequency boost device according to claim 1, characterized in that: The photovoltaic power generation system, the medium frequency boost system, the industrial frequency large power grid and the DC large power grid are connected via transmission cables.

8. The photovoltaic electric field medium frequency boost device according to claim 1, characterized in that: The photovoltaic electric field medium frequency boost device also includes a protection system; the protection system is connected to the medium frequency boost system and is used to protect the medium frequency boost system.

9. A photovoltaic electric field medium frequency boosting method based on the photovoltaic electric field medium frequency boosting device according to any one of claims 1 to 8, characterized in that: The photovoltaic electric field medium frequency boosting method comprises: Get the output parameters of the inverter; The output parameter of the inverter is regulated so that the output parameter of the inverter reaches a target value; the output parameter is an output frequency or an output voltage.

10. The photovoltaic electric field medium frequency boosting method according to claim 9, characterized in that: When the output parameter is the output frequency, regulating the output parameter of the inverter so that the output parameter of the inverter reaches a target value specifically includes: The control parameters of the inverter are adjusted so that the output frequency of the inverter reaches the target frequency; the control parameters include modulation ratio, frequency setting, pulse width modulation frequency or control algorithm parameters.

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