A grid-connected topology for new energy power generation.

Abstract

This invention discloses a grid-connected topology for new energy power generation, comprising: a new energy power generation side for generating electrical energy; a converter for converting the electrical energy into target electrical energy to be fed into the DC bus; a DC / AC converter for converting the target electrical energy into AC power with adjustable frequency, magnitude, and phase; and a synchronous motor-synchronous generator set: the variable frequency AC power output from the DC / AC converter drives the synchronous motor and the synchronous generator coaxially connected to it to rotate, completing the variable frequency start-up of the synchronous motor-synchronous generator set from standstill to rated speed. After the synchronous motor-synchronous generator set has started, the constant frequency output of the DC / AC converter drives the synchronous motor-synchronous generator set to rotate synchronously at a constant speed, and the synchronous generator outputs constant frequency AC power to be connected to the AC grid. The grid-connected topology disclosed in this invention solves the power system stability problem and has active and hard-support functions.

Description

Technical Field

[0001] This invention belongs to the field of wind and solar new energy power generation grid connection and power equipment technology, and more specifically, relates to a grid connection topology for new energy power generation to access the power grid. Background Technology

[0002] As the installed capacity and power generation of new energy sources such as wind power and photovoltaics continue to increase in my country's power system, a new power system with wind and solar new energy power generation as the main body is gradually being built.

[0003] Currently, wind and solar power generation both domestically and internationally generally adopts a power electronic converter grid-connected topology, requiring wind and solar equipment to connect to the grid via power electronic converters. In replacing traditional synchronous generator sets for grid connection, this type of new energy equipment and grid-connected converters suffer from problems such as insufficient system inertia, increased equipment failure rates, and a higher probability of protection activation. Crucially, new energy power systems significantly lack the synchronous inertia support, fault transient stability support, and system oscillation suppression capabilities provided by synchronous generators driven by constant-speed control prime movers in traditional AC grids. This leads to a substantial decrease in system stability, making them prone to grid failures and system oscillations, and in severe cases, even inducing large-scale power outages. This seriously restricts the safe and stable operation of new energy power systems, consequently causing significant impacts on society and the economy. Therefore, solving the problem of safe and stable operation of new energy power systems, primarily wind and solar power, has become a major technical challenge that urgently needs to be overcome both domestically and internationally.

[0004] To improve the stability of new energy power systems and prevent the risk of large-scale power outages, existing technical approaches mainly include adding active / reactive power compensation and support equipment and implementing grid-based modifications to wind and solar power generation equipment. However, none of these solutions can equivalently achieve the active, hard-supported system stabilization function of traditional synchronous generators, and they cannot fundamentally solve the structural and fundamental stability problems faced by new energy power systems. Therefore, it is particularly necessary to develop a grid-connected topology for new energy power generation to solve the problem of power system safety and stability while possessing active, hard-supported functions. Summary of the Invention

[0005] In response to the shortcomings and improvement needs of existing technologies, this invention provides a grid connection topology for new energy power generation to access the power grid, which aims to solve the problems of system instability and poor security in the existing new energy grid connection process.

[0006] To achieve the above objectives, according to one aspect of the present invention, a grid-connected topology for connecting new energy power generation to the power grid is provided, comprising: New energy generation side: used to generate electricity; Converter: Connected between the power generation side and the DC bus, it is used to convert the electrical energy generated by the new energy power generation side into the target electrical energy and feed it into the DC bus. The target electrical energy is DC. DC / AC converter: Connected to the DC bus, used to convert target electrical energy into AC power with adjustable frequency, magnitude, and phase; Synchronous motor-generator set: This includes a synchronous motor and a synchronous generator coaxially connected to it. The synchronous motor is connected between a DC / AC converter and the synchronous generator. The AC power output from the DC / AC converter is connected to the stator side of the synchronous motor. The AC power output from the DC / AC converter drives the synchronous motor and the synchronous generator coaxially connected to it to rotate. The DC / AC converter drives the synchronous motor-generator set to start from rest to rated speed via frequency conversion. After the synchronous motor-generator set has started, the constant frequency output of the DC / AC converter drives the synchronous motor-generator set to rotate synchronously at a constant speed. The constant frequency AC power generated by the synchronous generator is connected to the AC power grid. The magnitude of the DC voltage of the target electrical energy is matched with the magnitude of the operating voltage of the synchronous motor.

[0007] In summary, the core and key aspect of the technical solution conceived in this invention lies in the electrical energy generated by wind and solar renewable energy. Wind power is converted from AC to DC, and solar power is converted from DC to DC to the DC bus, or optionally via a DC / DC converter with a matching voltage level. The subsequent connection to the AC grid must and can only occur through: DC / AC converter → synchronous motor → synchronous generator coaxially connected to the synchronous grid → AC grid. This ensures that the wind and solar power ultimately connected to the AC grid is driven by a DC / AC converter with constant frequency output control, which drives the synchronous motor to operate at a constant speed, thereby driving the synchronous generator to rotate synchronously at a constant speed. The synchronous generator then generates constant frequency AC power that is connected to the AC grid.

[0008] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects: (1) Constructing a new grid-connected topology to significantly improve system inertia: The AC power that is finally connected to the grid in this invention is achieved by using a "DC / AC converter + synchronous motor - synchronous generator coaxial unit" to realize constant frequency grid connection of wind and solar new energy power generation, which fundamentally eliminates the prominent problems such as reduced inertia, insufficient transient support, and easy oscillation caused by the grid connection of large-scale power electronic converters; the coaxially connected synchronous motor unit structure can provide nearly twice the synchronous inertia of synchronous motors of the same capacity, and the inertia level is better than that of traditional thermal power and hydropower units.

[0009] (2) Active hard support for grid stability and faster response speed: Under the condition of new energy fluctuations or faults, the unit can maintain constant speed and frequency operation, ensure the stability of output voltage and frequency, and realize active hard support for grid frequency; through excitation regulation to compensate reactive power and stabilize voltage, the system stability is significantly improved. The synchronous motor's synchronous power angle characteristic can adapt to the characteristics of wind and solar power fluctuations within its static stable range, and can automatically maintain the speed stability of the synchronous motor. It is particularly suitable for adapting to the fluctuations of wind and solar power while still maintaining the speed stability of the synchronous motor. Moreover, the dynamic response of the synchronous motor to wind and solar power fluctuations is an electromagnetic dynamic response process, which is much faster than the dynamic response speed of traditional thermal power units and hydropower units to changes in prime mover drive power. Similarly, the adaptive characteristics of the synchronous generator's synchronous power angle to changes in active power can also adaptively cope with fluctuations in active power within the range of the synchronous generator's static stability, thereby maintaining the stability of the synchronous generator's speed and thus the stability of the synchronous generator's power generation frequency. Furthermore, by reasonably controlling the magnitude of the synchronous generator's rotor excitation current, it can also prioritize and maintain the stability of the system voltage. Therefore, the system topology of this invention has stronger transient, frequency stabilization, and voltage stabilization support capabilities, and can fundamentally solve the problem of stable operation of new energy power generation grid connection.

[0010] (3) Simplify system architecture and eliminate the risk of large-scale power outages: The system does not require or reduces the configuration of inertia and stability support equipment such as flywheel energy storage, SVG, and synchronous condensers, reconstructing and simplifying the theoretical and technical system of new energy power systems, so that the system structure and stability return to the level of traditional synchronous power grids, fundamentally avoiding large-scale power outage accidents. The power fluctuation of wind and solar power generation and the transient stability problem of the system are independent of each other. This invention focuses on solving the problems of insufficient synchronous inertia, fault stability and oscillation suppression, realizing stable frequency and voltage of the system, and ensuring the inherent safety of the system.

[0011] (4) Mature, reliable, low-cost, easy to promote, and with significant industrial value: Relying on mature synchronous motor and power electronics technologies, synchronous motor equipment has a long lifespan (generally more than 30 years), high reliability, and lower cost than power electronic equipment of the same capacity; this invention can be directly applied to newly built wind and solar power plants and the renovation of existing plants, with low implementation difficulty and strong promotion. With reasonable measures to smooth out wind and solar power fluctuations, the problem of wind and solar curtailment can be completely solved, promoting large-scale and efficient grid connection of wind and solar power, and realizing a disruptive transformation of the new energy power system.

[0012] (5) Flexible application scenarios: It can be applied independently to wind farms and photovoltaic power stations, and is also suitable for wind-solar hybrid power stations.

[0013] (6) Applicable to multiple types of new energy sources: In addition to wind and solar power, it is also applicable to non-constant speed driven synchronous generator grid connection systems such as wave power generation and tidal power generation.

[0014] (7) Compatible with multiple types of synchronous motors: Applicable to various types of synchronous motors such as electrically excited and permanent magnet synchronous motors, synchronous generators and various unit combinations.

[0015] (8) Adaptable to AC / DC power transmission, with a variety of grid construction schemes: Applied to AC power transmission: forming a high-inertia, strong-support, robust AC power grid with the entire source-grid-load system connected, maximizing the stability benefits of the system topology of this invention; Applied to DC power transmission: improving the inertia and stability of the sending end, suppressing the oscillation of DC converter stations; providing five preferred grid construction schemes, configured according to the principle of AC transmission priority and AC / DC integrated transmission, to meet different grid requirements; each scheme needs to be equipped with adjustment and compensation measures to deal with and compensate for the fluctuation of wind and solar power generation, so as to achieve the unity of safety, stability and efficient utilization. Attached Figure Description

[0016] Figure 1 The diagram shown is a grid-connected topology diagram of wind power generation based on existing permanent magnet synchronous wind turbine generators according to an embodiment of the present invention. Figure 2 The diagram shown is a grid-connected topology diagram of wind power generation based on an electrically excited synchronous wind turbine generator set according to an embodiment of the present invention. Figure 3 The diagram shown is a grid-connected topology diagram of wind power generation based on existing permanent magnet synchronous wind turbine generators according to an embodiment of the present invention. Figure 4 The diagram shown is an alternative grid-connected topology for wind power generation based on an electrically excited synchronous wind turbine generator set, according to an embodiment of the present invention. Figure 5 The diagram shown is a grid-connected topology diagram of a photovoltaic power generation system based on a photovoltaic power generation array, according to an embodiment of the present invention. Figure 6 The diagram shown is an alternative grid-connected topology for photovoltaic power generation based on a photovoltaic power generation array, according to an embodiment of the present invention. Figure 7 The diagram shown is a grid-connected topology diagram of wind power generation based on a newly proposed doubly fed wind turbine generator set modified into an electrically excited synchronous wind turbine generator set, according to an embodiment of the present invention. Figure 8 The diagram shown is a grid-connected topology diagram of wind power generation based on a newly proposed doubly fed wind turbine generator set modified into an electrically excited synchronous wind turbine generator set, according to an embodiment of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0018] In this invention, the terms "first," "second," etc. (if present) in the invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0019] This invention discloses a grid-connected topology for new energy power generation, including: New energy power generation side: used to generate electricity, including but not limited to: wind power generation, photovoltaic power generation, wave power generation, tidal power generation, electricity generated by non-constant speed driven synchronous generator sets, and other new energy power generation; Converter: Connected between the power generation side and the DC bus, it is used to convert the electrical energy generated by the new energy power generation side into the target electrical energy and feed it into the DC bus. The target electrical energy is DC. DC / AC converter: Connected to the DC bus, used to convert target electrical energy into AC power with adjustable frequency, magnitude, and phase; Synchronous motor-generator set: This includes a synchronous motor and a synchronous generator coaxially connected to it. The synchronous motor is connected between a DC / AC converter and the synchronous generator via a coaxial mechanical connection. The output of the DC / AC converter is connected to the stator side of the synchronous motor. The AC power output from the DC / AC converter drives the synchronous motor and the coaxially connected synchronous generator to rotate. The DC / AC converter drives the synchronous motor-generator set to start from rest at rated speed via frequency conversion. After the synchronous motor-generator set has started, the constant frequency output of the DC / AC converter drives the synchronous motor-generator set to rotate synchronously at a constant speed. The synchronous generator outputs constant frequency AC power which is connected to the AC power grid. The magnitude of the DC voltage of the target electrical energy matches the magnitude of the operating voltage of the synchronous motor. This invention utilizes the adaptive characteristic of the synchronous motor's synchronous power angle to changes in active power. Within its static stability range, it can adapt to fluctuations in wind and solar power generation while maintaining a constant rotational speed, thereby ensuring the stability of the synchronous generator's power generation frequency.

[0020] It should be noted that when the new energy power generation side is wind power generation, the converter includes an AC / DC converter. The electrical energy generated by wind power generation is AC, and the AC / DC converter converts the AC output of wind power generation into DC power before feeding it into the DC bus.

[0021] In one implementation, when the DC voltage output of the AC / DC converter does not match the target electrical energy, the converter further includes a DC / DC converter connected to the AC / DC converter. The DC / DC converter converts the DC voltage to the level required for the target electrical energy. The input or output side of the DC / DC converter is connected to a DC bus. Furthermore, the wind turbine generator in this invention includes: a permanent magnet synchronous generator, an electrically excited synchronous generator, and a doubly-fed wind turbine generator used as an electrically excited synchronous generator.

[0022] It should be noted that when the wind turbine is an electrically excited synchronous generator or a doubly fed wind turbine used as an electrically excited synchronous generator, the grid-connected topology also includes a DC excitation controller and a DC energy storage device. The input side of the DC excitation controller and the DC energy storage device are both connected to the DC bus. The output side of the DC excitation controller is connected to the rotor winding of the electrically excited synchronous generator. The DC excitation controller provides the rotor DC excitation current to the electrically excited synchronous generator. The DC energy storage device is used to store DC electricity and provide the initial DC excitation energy to the DC excitation controller.

[0023] In one optional embodiment, when the new energy power generation side is photovoltaic power generation, the converter includes a first DC / DC converter connected between the photovoltaic power generation and the DC bus. The first DC / DC converter is used to convert the DC power generated by the photovoltaic power generation into the target electrical energy. When the DC voltage output of the first DC / DC converter does not match the target electrical energy, the converter also includes a second DC / DC converter connected to the first DC / DC converter. The second DC / DC converter converts the DC voltage to the DC voltage level required for the target electrical energy. The input or output side of the second DC / DC converter is connected to the DC bus.

[0024] Furthermore, the grid-connected topology for new energy power generation to access the grid disclosed in this invention also includes a synchronous motor auxiliary braking device, such as a braking resistor, for assisting in braking the synchronous motor-synchronous generator set, accelerating the braking or deceleration of the synchronous motor-synchronous generator set. The synchronous motor auxiliary braking device is connected to the stator side of the synchronous motor or the synchronous motor auxiliary braking device is connected to the stator side of the synchronous generator.

[0025] To further understand the grid connection topology of new energy power generation disclosed in this invention, the following will describe the grid connection topology with specific embodiments. In this invention, the same type and function of individual units or components with the same name are the same.

[0026] Example 1: like Figure 1The diagram shown illustrates a grid-connected topology for wind power generation based on existing permanent magnet synchronous wind turbine generators, as provided by this invention. Figure 1 As shown, this grid-connected topology includes: a permanent magnet synchronous wind turbine generator set, specifically including a wind turbine, gearbox, permanent magnet synchronous generator, etc.; an AC / DC converter; a DC bus; a DC / DC converter; a DC / AC converter; a synchronous motor, such as an electrically excited synchronous motor with an externally applied DC excitation current to the rotor, or a permanent magnet synchronous motor (either is acceptable). If it is an electrically excited synchronous motor, it also includes a matching DC excitation controller; and a synchronous generator coaxially connected to the synchronous motor, such as an electrically excited synchronous generator with an externally applied DC excitation current to the rotor, or a permanent magnet synchronous generator (generally an electrically excited synchronous generator). If it is an electrically excited synchronous generator, it also includes a matching DC excitation controller. The output of the synchronous generator is connected to the AC grid. It should be noted that the location of the DC bus is not unique, such as... Figure 1 As shown in the diagram, the dashed lines indicate the optional positions of the DC bus, meaning the DC bus can be connected to... Figure 1 The DC / DC converter can be connected to either the input or output side. When the grid-connected system does not include a DC / DC converter, the DC bus connects the output side of the AC / DC converter and the input side of the DC / AC converter. The DC / DC converter represented by the dashed box in the figure is optional. In the following embodiments, the meaning of the DC / DC converter represented by the dashed box is the same, and it will not be described in detail again to avoid redundancy.

[0027] In an embodiment of the present invention, the grid-connected topology operates as follows: Alternating current (AC) generated by the permanent magnet synchronous wind turbine generator is converted into direct current (DC) by an AC / DC converter and fed into the DC bus. The AC / DC converter converts the AC current into the target electrical energy before feeding it into the DC bus. When the DC voltage output by the AC / DC converter does not match the target electrical energy, the grid-connected topology also includes a DC / DC converter connected to the AC / DC converter. The DC / DC converter converts the DC voltage to the required DC voltage level for the target electrical energy. The input or output side of the DC / DC converter is connected to the DC bus. Furthermore, the DC bus feeds... DC power is converted into AC power with adjustable frequency and magnitude by a DC / AC converter, which is then connected to the stator winding of a synchronous motor to drive the synchronous motor and the synchronous generator connected to it on the same axis. This not only maintains the constant frequency output of the converter and drives the synchronous motor unit to rotate at a constant speed, but also meets the requirements for frequency conversion starting of the synchronous motor-synchronous generator unit from standstill to rated speed. The AC power generated by the synchronous motor-synchronous generator unit is connected to the AC power grid. The AC / DC converter or a combination of AC / DC converter and DC / DC converter is called a converter, and its function is to convert the AC power generated by the permanent magnet synchronous wind turbine into the target electrical energy and then feed it into the DC bus.

[0028] It should be noted that, because the grid-connected topology uses a synchronous motor-synchronous generator set driven by a DC / AC converter capable of constant frequency output, it can achieve constant-speed synchronous rotation of the synchronous motor-synchronous generator set, ensuring that the synchronous generator outputs constant-frequency AC power. Due to the adaptive characteristics of the synchronous motor and synchronous generator's inherent synchronous power angle to power changes, within its static stability range, it can adapt to the fluctuations in wind and solar power generation while still maintaining a constant synchronous motor speed and a stable AC output frequency from the synchronous generator. Furthermore, by controlling the rotor excitation current of the synchronous motor and synchronous generator (for electrically excited synchronous motors), it not only ensures the operational stability of the synchronous motor-synchronous generator set but also guarantees the appropriate overload capacity of the synchronous motor and the reliable frequency and voltage stabilization output capability of the synchronous generator. Due to the large inertia of the synchronous motor-synchronous generator set (nearly twice the rotational inertia of a synchronous generator of the same capacity), the electromagnetic dynamic rapid response characteristics of the synchronous motor as the prime mover of the synchronous generator, and the strong transient stability support capability and the ability to suppress and dampen system oscillations of the synchronous generator, the system topology of this wind power grid connection has many outstanding advantages in terms of system stability support capability as described above. It can fundamentally overcome a series of prominent problems brought about by the existing wind and solar power grid connection system topologies, that is, solve the problem of insufficient stability in traditional grid-connected systems.

[0029] Example 2: Figure 2 The diagram shown is a grid-connected topology diagram of wind power generation based on the proposed electrically excited synchronous wind turbine generator set provided by the present invention.

[0030] like Figure 2 As shown, this grid-connected topology includes: an electrically excited synchronous wind turbine generator set with external DC excitation on the rotor, comprising: a wind turbine, a gearbox, an electrically excited synchronous generator and its DC excitation controller, an AC / DC converter, a DC energy storage device, a DC bus, a DC / AC converter, and a synchronous motor, such as an electrically excited synchronous motor with external DC excitation current on the rotor, or a permanent magnet synchronous motor; either is acceptable. If it is an electrically excited synchronous motor, a matching DC excitation controller is also required, as well as a synchronous generator coaxially connected to the synchronous motor, such as an electrically excited synchronous generator with external DC excitation current on the rotor, or a permanent magnet synchronous generator, generally an electrically excited synchronous generator. If it is an electrically excited synchronous generator, a matching DC excitation controller is also required, and the synchronous generator output is connected to the AC grid, etc. Figure 2 The dashed box in the middle indicates the use of DC / DC converters and Figure 1 Similar to the previous one, I will not describe it in detail to avoid being redundant.

[0031] like Figure 2The grid-connected topology operates as follows: A DC energy storage device connected to the DC bus provides initial DC excitation power to the DC bus. This power is then supplied to the rotor excitation winding of the electrically excited synchronous wind turbine by a DC excitation controller connected to both ends of the DC bus and to the rotor winding of the synchronous wind turbine. The electrically excited synchronous wind turbine generates AC power, which is converted to DC power by an AC / DC converter and fed into the DC bus. The AC / DC converter converts the AC power into the target electrical energy before feeding it into the DC bus. When the DC voltage output of the AC / DC converter does not match the target electrical energy, the grid-connected topology also includes a DC / DC converter. The DC / DC converter and... An AC / DC converter is connected, which converts DC voltage to the DC voltage level required for the target electrical energy. The input or output side of the DC / DC converter is connected to the DC bus. Furthermore, the DC power output from the DC bus is converted into AC power with adjustable frequency and magnitude by the DC / AC converter, which is connected to the stator winding of the synchronous motor to drive the synchronous motor and the synchronous generator connected to it on the same axis. It can not only maintain the constant frequency output of the converter and the constant frequency drive of the synchronous motor unit to rotate at a constant speed, but also meet the requirements for frequency conversion starting of the synchronous motor-synchronous generator set from standstill to rated speed. The AC power generated by the synchronous motor-synchronous generator set is connected to the AC power grid.

[0032] The DC energy storage device is connected to the DC bus and is a bidirectional DC energy storage device that can be used for both storage and output. Its basic function is to provide initial DC power to the DC excitation controller of the electrically excited synchronous wind turbine connected to the DC bus. The DC excitation controller then provides DC excitation current to the rotor of the electrically excited synchronous wind turbine, establishing the rotor magnetic field and enabling the wind turbine to generate AC power. When the electrically excited synchronous wind turbine is operating normally, the AC power it generates is connected to the DC bus after passing through an AC / DC converter. This power can provide DC excitation power to the DC excitation controller of the electrically excited synchronous wind turbine connected to the DC bus, and simultaneously charge the DC energy storage device for use in the next excitation of the electrically excited synchronous wind turbine. If the capacity of the DC energy storage device is relatively large, in addition to serving as the initial DC excitation power supply for the DC excitation controller of the electrically excited synchronous wind turbine, it can also compensate for power fluctuations in the wind and solar new energy power system. The specific function depends on the capacity of the DC energy storage device, but priority should be given to its use as the initial excitation power supply for the electrically excited synchronous wind turbine to ensure that the electrically excited synchronous wind turbine can start generating electricity normally.

[0033] The key feature of this embodiment 2 compared to embodiment 1 is that it replaces the permanent magnet synchronous wind turbine with an electrically excited synchronous wind turbine, which saves a large amount of permanent magnet material required for the manufacture of permanent magnet synchronous wind turbines and fundamentally eliminates problems such as demagnetization during the use of permanent magnet motors. The working process and operating characteristics of wind power grid connection after the AC / DC converter in this embodiment are the same as in embodiment 1.

[0034] Example 3: Figure 3 The diagram shown is a grid-connected topology diagram of wind power generation based on existing permanent magnet synchronous wind turbine generator sets provided by the present invention.

[0035] The difference between Example 3 and Example 1 is that, optionally, a synchronous motor auxiliary braking device, such as a braking resistor or other braking device, can be connected via a transfer switch on the stator side of the synchronous motor in the synchronous motor-synchronous generator set or on the stator side of the synchronous generator. This allows for auxiliary braking of the synchronous motor-synchronous generator set when necessary, accelerating the braking or deceleration of the synchronous motor set. Apart from this, the other working processes and operating characteristics are the same as in Example 1.

[0036] Example 4: Figure 4 The diagram shows a grid-connected topology for wind power generation based on a newly proposed electrically excited synchronous wind turbine generator set, as provided by this invention.

[0037] The difference between Example 4 and Example 2 is that, optionally, a synchronous motor auxiliary braking device, such as a braking resistor or other braking device, can be connected via a transfer switch on the stator side of the synchronous motor in the synchronous motor-synchronous generator set or on the stator side of the synchronous generator. This allows for auxiliary braking of the synchronous motor-synchronous generator set when necessary, accelerating the braking or deceleration of the synchronous motor set. Apart from this, the other working processes and operating characteristics are the same as in Example 2.

[0038] Example 5: Figure 5 The diagram shown is a grid-connected topology diagram of a photovoltaic power generation system based on a photovoltaic power generation array, provided by the present invention.

[0039] like Figure 5As shown, this grid-connected topology includes: a photovoltaic power generation array, a DC / DC converter, a DC bus, a DC / AC converter, and a synchronous motor. This can be an electrically excited synchronous motor with an externally applied DC excitation current to the rotor, or a permanent magnet synchronous motor (either is acceptable). If it's an electrically excited synchronous motor, a matching DC excitation controller and a synchronous generator coaxially connected to the synchronous motor are also required. This could be an electrically excited synchronous generator with an externally applied DC excitation current to the rotor, or a permanent magnet synchronous generator. Generally, an electrically excited synchronous generator is preferred. If it's an electrically excited synchronous generator, a matching DC excitation controller is also required, and it needs to be connected to the AC power grid. Figure 3 The dashed box in the middle indicates the use of DC / DC converters and Figure 1 Similar to the previous one, I will not describe it in detail to avoid being redundant.

[0040] The basic working process of this grid-connected topology is as follows: The DC power generated by the photovoltaic array is converted into voltage by a first DC / DC converter before being fed into the DC bus. The first DC / DC converter converts the DC power into the target electrical energy before feeding it into the DC bus. When the DC voltage output of the first DC / DC converter does not match the target electrical energy, the grid-connected topology also includes a second DC / DC converter. The second DC / DC converter is connected to the first DC / DC converter and converts the DC voltage to the required DC voltage level for the target electrical energy. The input or output side of the DC converter is connected to the DC bus. Furthermore, the DC power collected by the DC bus is converted into AC power with adjustable frequency and magnitude by the DC / AC converter, which is then connected to the stator winding of the synchronous motor to drive the synchronous motor and the synchronous generator coaxially connected to it to rotate. The grid-connected topology of this invention can not only maintain the constant frequency output of the converter and the constant frequency drive of the synchronous motor unit to rotate at a constant speed, but also meet the requirements for frequency conversion starting of the synchronous motor-synchronous generator unit from standstill to rated speed. The AC power generated by the synchronous motor-synchronous generator unit is connected to the AC power grid.

[0041] Example 5 shows the same working process and operating characteristics of photovoltaic power generation connected to the grid after the DC / AC converter as Example 1.

[0042] Example 6: Figure 6 The diagram shown is a grid-connected topology diagram of a photovoltaic power generation system based on a photovoltaic power generation array, provided by the present invention.

[0043] The difference between Example 6 and Example 5 is that, optionally, a synchronous motor auxiliary braking device, such as a braking resistor or other braking device, can be connected via a transfer switch on the stator side of the synchronous motor in the synchronous motor-synchronous generator set or on the stator side of the synchronous generator. This allows for auxiliary braking of the synchronous motor-synchronous generator set when necessary, accelerating the braking or deceleration of the synchronous motor set. Apart from this, the other working processes and operating characteristics are the same as in Example 5.

[0044] Example 7: Figure 7 The diagram shows a grid-connected topology for wind power generation based on a newly proposed doubly fed wind turbine generator set modified into an electrically excited synchronous wind turbine generator set, as provided by the present invention.

[0045] like Figure 7 As shown, the grid-connected topology includes: a doubly-fed wind turbine generator set that is modified for use as an electrically excited synchronous wind turbine generator set. For example, the three-phase stator windings of the doubly-fed motor are still used as the three-phase stator windings of the electrically excited synchronous wind turbine generator set, while the three-phase AC windings of the doubly-fed motor rotor are modified to be used as DC windings that can operate with an externally applied DC excitation current. The specific modification scheme is as follows: Reconnection Option 1: Use any one of the three sets of slip ring brush leads of the rotor three-phase winding as one electrode terminal of the single-phase DC winding, and connect the other two sets of slip ring brush leads in parallel as the other electrode terminal of the single-phase DC winding.

[0046] Reconnection Option 2: If the three-phase AC windings of the rotor can be independently reconnected, the three-phase windings A-X, B-Y, and C-Z of the rotor can be connected in series in a one-positive-two-negative relationship to form a single-phase DC winding, such as A-XY-BZ-C three-phase series connection.

[0047] Modification Solution 3: The three electrodes AYZ are connected in parallel to form a single-phase DC circuit, and the three electrodes XBC are connected in parallel to form a single-phase DC circuit. The combined magnetomotive force amplitude of the three-phase winding DC excitation in modification scheme 1 is 1.5 times the maximum excitation magnetomotive force amplitude of a single-phase winding. In contrast, the combined magnetomotive force amplitude of the three-phase winding DC excitation in modification schemes 2 and 3 is twice that of a single-phase winding. Therefore, modification schemes 2 and 3 have a higher effective utilization rate of excitation magnetomotive force than modification scheme 1. However, their modification methods are relatively complex, requiring a reconfiguration of the rotor's three-phase windings, while modification scheme 1 is relatively simple to implement. This embodiment 7 also includes a wind turbine, gearbox, and a DC excitation controller for the rotor windings. Except for converting the doubly-fed wind turbine into an electrically excited synchronous wind turbine, the other components of this embodiment 7 are the same as those in embodiment 2.

[0048] The basic working process of Example 7 is as follows: except that the system composition is changed from a doubly fed wind turbine to an electrically excited synchronous wind turbine, its basic working process, operating characteristics and features are the same as those of Example 2.

[0049] Example 8: Figure 8 The diagram shows a grid-connected topology for wind power generation based on a newly proposed doubly fed wind turbine generator set modified into an electrically excited synchronous wind turbine generator set, as provided by the present invention.

[0050] The difference between Example 8 and Example 7 is that, optionally, a synchronous motor auxiliary braking device, such as a braking resistor or other braking device, can be connected via a transfer switch on the stator side of the synchronous motor in the synchronous motor-synchronous generator set or on the stator side of the synchronous generator. This allows for auxiliary braking of the synchronous motor-synchronous generator set when necessary, accelerating the braking or deceleration of the synchronous motor set. Apart from this, the other working processes and operating characteristics are the same as in Example 7.

[0051] In the various diagrams of this invention, which describe a novel system topology for grid connection of wind and solar power generation, the AC / DC converter, optional DC / DC converter, and DC / AC converter corresponding to the wind power generation system represent the topological functions within the block diagrams. In actual manufacturing and application, each block diagram can be an independent unit, or they can be combined into one unit or two units. Similarly, the first DC / DC converter, optional second DC / DC converter, and DC / AC converter corresponding to the photovoltaic power generation system represent the topological functions within the block diagrams. In actual manufacturing and application, each block diagram can be an independent unit, or they can be combined into one unit or two units.

[0052] This invention applies to a new system topology embodiment of wind and solar new energy power generation connected to the grid, which is a set of unit systems formed by "DC / AC converter → synchronous motor - synchronous generator set" in the diagram. Depending on the installed capacity of the specific wind and solar power plant, it can be flexibly configured into one or several sets of such unit systems in parallel. The capacity of each set of unit systems in parallel can be the same or different.

[0053] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A grid-connected topology for new energy power generation, characterized in that, include: New energy generation side: used to generate electricity; Converter: Connected between the power generation side and the DC bus, it is used to convert the electrical energy generated by the new energy power generation side into the target electrical energy and feed it into the DC bus. The target electrical energy is DC. DC / AC converter: Connected to the DC bus, used to convert target electrical energy into AC power with adjustable frequency, magnitude, and phase; Synchronous motor-generator set: This includes a synchronous motor and a synchronous generator coaxially connected to it. The synchronous motor is connected between a DC / AC converter and the synchronous generator. The AC power output from the DC / AC converter is connected to the stator side of the synchronous motor. The AC power drives the synchronous motor and the synchronous generator coaxially connected to it to rotate. The DC / AC converter drives the synchronous motor set to rotate. The DC / AC converter drives the synchronous motor-generator set to start from rest to rated speed via frequency conversion. After the synchronous motor-generator set has started, the constant frequency output of the DC / AC converter drives the synchronous motor-generator set to rotate synchronously at a constant speed. The synchronous generator outputs constant frequency AC power and connects to the AC power grid. The magnitude of the DC voltage of the target electrical energy is matched with the magnitude of the operating voltage of the synchronous motor.

2. The grid connection topology for new energy power generation according to claim 1, characterized in that, The new energy power generation side includes wind power, photovoltaic power, wave power, tidal power, and electricity generated by non-constant speed driven synchronous generator sets.

3. The grid connection topology for new energy power generation according to claim 2, characterized in that, When the new energy power generation side is wind power generation, the converter includes an AC / DC converter. The electrical energy generated by wind power generation is AC, and the AC / DC converter converts the AC output of wind power generation into DC and then feeds it into the DC bus.

4. The grid connection topology for new energy power generation according to claim 3, characterized in that, The converter also includes a DC / DC converter, which is connected to the output of the AC / DC converter. When the DC voltage output of the AC / DC converter does not match the target power, the DC / DC converter converts the DC voltage to the DC voltage level required for the target power. The input or output side of the DC / DC converter is connected to the DC bus.

5. The grid connection topology for new energy power generation according to claim 3, characterized in that, Wind turbines include: permanent magnet synchronous generators, electrically excited synchronous generators, and doubly fed wind turbines that have been modified for use as electrically excited synchronous generators.

6. The grid connection topology for new energy power generation according to claim 4, characterized in that, When the wind turbine is an electrically excited synchronous generator or a doubly fed wind turbine that is converted for use as an electrically excited synchronous generator, the grid-connected topology also includes a DC excitation controller and a DC energy storage device. The input side of the DC excitation controller and the DC energy storage device are both connected to the DC bus. The output side of the DC excitation controller is connected to the rotor winding of the wind turbine. The DC excitation controller provides the rotor DC excitation current to the electrically excited synchronous generator. The DC energy storage device is used to store DC electricity and provide the initial DC excitation energy to the DC excitation controller.

7. The grid connection topology for new energy power generation according to claim 2, characterized in that, When the new energy power generation side is photovoltaic power generation, the converter includes a first DC / DC converter, which is connected between the photovoltaic power generation and the DC bus. The first DC / DC converter is used to convert the DC power generated by the photovoltaic power generation into the target electrical energy.

8. The grid connection topology for new energy power generation according to claim 7, characterized in that, The converter also includes a second DC / DC converter, which is connected to the first DC / DC converter. When the DC voltage output by the first DC / DC converter does not match the target power, the second DC / DC converter converts the DC voltage to the DC voltage level required for the target power. The input or output side of the second DC / DC converter is connected to the DC bus.

9. The grid connection topology for new energy power generation according to claim 1, characterized in that, It also includes a synchronous motor auxiliary braking device, which includes a braking resistor for assisting in braking the synchronous motor-synchronous generator set, accelerating the braking or deceleration of the synchronous motor-synchronous generator set. The synchronous motor auxiliary braking device is connected to the stator side of the synchronous motor or the synchronous motor auxiliary braking device is connected to the stator side of the synchronous generator.

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