New energy grid-connected harmonic suppression power supply equipment

Abstract

The invention relates to the technical field of power supply equipment, in particular to new energy grid-connected harmonic suppression power supply equipment, which comprises a new energy power generation unit and a multi-level power electronic conversion unit, and adopts a modular multi-level converter MMC or a cascaded H-bridge topological structure. The harmonic detection and analysis unit is used for monitoring the voltage harmonic distortion rate THD and each harmonic content of the PCC in real time; and the adaptive multi-mode control unit integrates an SVPWM (Space Vector Pulse Width Modulation) strategy and a virtual impedance control algorithm. According to the invention, the multi-level power electronic conversion unit is configured at the new energy power generation side and the SVPWM optimization modulation strategy is applied, so that the technical target of reducing harmonic generation from the source is completed; by establishing a hierarchical control strategy based on THD real-time monitoring and an adaptive virtual impedance algorithm, real-time tracking of power grid impedance change and accurate matching of a harmonic suppression strategy are completed.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of power supply equipment, in particular to a new energy grid-connected harmonic suppression power supply equipment. BACKGROUND

[0002] With the increasing proportion of intermittent new energy such as wind power and photovoltaic in the power grid, the wide application of power electronic equipment such as grid-connected inverters leads to the increasingly prominent problem of harmonic pollution. A harmonic suppression photovoltaic grid-connected system is disclosed in a patent with the application number CN202322599306.0, which comprises a photovoltaic assembly and a public power grid. The input and output ends of the photovoltaic assembly are connected with a controller. The output end of the photovoltaic assembly comprises two ends, which are respectively connected with the direct current input end and the direct current load of the grid-connected inverter. The public power grid is connected with the alternating current output end and the alternating current input end of the grid-connected inverter, and the public power grid is connected with an alternating current load, and the alternating current load is grounded. The grid-connected inverter comprises a harmonic detection module, a current operation module, a harmonic suppression module, a driving circuit and an IGBT module which are connected in sequence. The input end of the harmonic detection module is connected with the public power grid with the alternating current load. The input end of the harmonic suppression module is also connected with the current output end of the grid-connected inverter. The output end of the IGBT module is connected with the public power grid. By means of the comparison processing of the current with harmonics and the output current of the grid-connected inverter, the IGBT module can be controlled by the driving circuit module to make compensation, thereby avoiding the influence of harmonics on the grid-connected inverter.

[0003] Harmonics not only have an influence on inverters, but also cause the decline of power quality, and can have a serious influence on power distribution equipment.

[0004] Influence on transformers: harmonic current causes skin effect and proximity effect, increases copper loss and iron loss, causes transformer overheating, insulation aging acceleration and service life shortening. The actual measurement shows that when the current harmonic distortion rate reaches 10%, the additional temperature rise of the transformer can reach 15-20%.

[0005] Influence on capacitors: harmonic voltage causes capacitor current to increase sharply, generates overload heating. More seriously, the capacitor and the system inductance can form parallel resonance, amplify specific harmonics, cause capacitor bulging, explosion and other faults.

[0006] Influence on switching equipment: harmonic current can increase the contact resistance of switching contacts, cause local overheating, reduce the switching analysis ability, and even cause the switching equipment to burn out.

[0007] Although the traditional governance measures such as improving the PWM modulation strategy and adopting the multi-level topology can reduce harmonic emission, they lack targeted protection for power distribution equipment and are difficult to adapt to the change of power grid impedance. The existing virtual impedance technology has fixed parameters, and in complex working conditions, the harmonic suppression effect is poor or the system is unstable. SUMMARY

[0008] In order to overcome the defects in the prior art, the purpose of the present application is to provide a new energy grid-connected harmonic suppression power supply device, which solves the problems in the background art through a three-level protection system of source suppression-process management-device protection.

[0009] In order to achieve the above-mentioned purpose, the present application provides a new energy grid-connected harmonic suppression power supply device, which comprises a new energy power generation unit containing a photovoltaic array or a wind turbine generator set; A multi-level power electronic conversion unit adopts a modular multi-level converter (MMC) or a cascaded H-bridge topology structure and is connected to the new energy power generation unit. A harmonic detection and analysis unit monitors the voltage harmonic distortion rate THD and the harmonic content of each order of the point of common coupling (PCC) in real time. An adaptive multi-mode control unit integrates SVPWM modulation strategy and virtual impedance control algorithm. A filtering execution unit contains an active filter module and a passive filter module. A power distribution equipment protection monitoring unit evaluates the harmonic tolerance state of transformers, capacitors and switching devices in real time.

[0010] The core of the above-mentioned arrangement is to build a three-level protection system of "source suppression-process management-device protection"; First level: source optimization Multi-level conversion technology (MMC or cascaded H-bridge) is adopted to reduce the voltage change rate dv / dt by increasing the number of output levels, thereby reducing the generation of harmonics from the source; SVPWM optimization modulation strategy is applied to improve the utilization rate of DC voltage and improve the output waveform quality. Second level: process management A hierarchical control strategy based on harmonic distortion rate THD is established to balance the management accuracy and energy consumption. Adaptive virtual impedance technology is adopted to track the impedance changes of the power grid in real time and avoid harmonic amplification. An active and passive collaborative filtering architecture is built to ensure effective harmonic suppression under various operating conditions. Third level: device protection A power distribution equipment harmonic tolerance model is established to evaluate the device operating state in real time. Multiple early warning thresholds are set to detect potential fault risks in advance. The device life is predicted by intelligent algorithm to optimize the maintenance cycle.

[0011] As a further improvement of the present technical solution, the multi-level power electronic conversion unit generates 5 or more levels at the output end to approximate the sine wave, which is used to control the total harmonic distortion rate of the output waveform.

[0012] As a further improvement of the technical solution, the adaptive multi-mode control unit is divided into three levels according to the harmonic severity: First level: THD < 5%, only SVPWM optimization modulation is enabled; Second level: 5% ≤ THD < 8%, virtual impedance control is enabled; Third level: THD ≥ 8%, active filter compensation is enabled.

[0013] As a further improvement of the technical solution, the virtual impedance control algorithm adopts an adaptive adjustment mechanism based on harmonic power feedback, and the virtual impedance value satisfies: wherein , is an adaptive adjustment coefficient, is a harmonic distortion rate deviation, refers to the cumulative amount of harmonic distortion rate deviation over time.

[0014] As a further improvement of the technical solution, the active filter module adopts a harmonic detection method based on instantaneous reactive power theory, and the compensation current response time is less than 100 μs.

[0015] As a further improvement of the technical solution, the passive filter module designs a tuning frequency for a specific harmonic and connects a capacitor in series with a harmonic resistance reactor, so that the parallel resonance frequency is lower than 90% of the lowest harmonic frequency.

[0016] As a further improvement of the technical solution, the power distribution equipment protection monitoring unit establishes a transformer hotspot temperature rise model: wherein is the effective value of harmonic current, is the rated current, is the winding resistance, is the harmonic loss coefficient.

[0017] As a further improvement of the technical solution, the device further comprises an intelligent early warning module, which issues a maintenance warning in advance when it is predicted that the transformer insulation life decay is accelerated, the capacitor is overloaded, or the switch device contact temperature rise exceeds the standard.

[0018] As a further improvement of the technical solution, the device supports a remote operation and maintenance interface, and can upload operation data to a cloud platform to realize collaborative harmonic control of multiple sites.

[0019] As a further improvement of the technical solution, the new energy power generation unit comprises an energy storage buffer module for smoothing power fluctuations caused by intermittent power generation and reducing harmonic generation from the source.

[0020] Compared with the prior art, the present application has the following beneficial effects: 1. The new energy grid-connected harmonic suppression power supply equipment, by configuring a multi-level power electronic conversion unit on the new energy power generation side and applying an SVPWM optimization modulation strategy, achieves the technical goal of reducing harmonic generation from the source, thereby achieving the basic technical effect of controlling the total harmonic distortion rate of the output waveform to be stable.

[0021] 2. The new energy grid-connected harmonic suppression power supply equipment, by establishing a hierarchical control strategy based on real-time THD monitoring and an adaptive virtual impedance algorithm, achieves real-time tracking of grid impedance changes and precise matching of harmonic suppression strategies, thereby achieving the governance effect of stable system operation within a range of ±50% of the grid impedance and reduction of PCC point voltage THD.

[0022] 3. The new energy grid-connected harmonic suppression power supply equipment, by constructing an active and passive collaborative filtering architecture and a three-level mode switching mechanism, achieves optimal governance scheme selection under different harmonic severity, thereby achieving the reliability technical effect of compensating current response time less than 100μs and effectively suppressing harmonics under various operating conditions.

[0023] 4. The new energy grid-connected harmonic suppression power supply equipment, by establishing a power distribution equipment harmonic tolerance model and an intelligent early warning module, achieves real-time state assessment and life prediction of transformers, capacitors, and switching devices, thereby achieving the equipment protection effect of increasing transformer life expectancy, reducing capacitor failure rate, and extending switching device maintenance cycle. BRIEF DESCRIPTION OF DRAWINGS

[0024] The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present disclosure in any way. In addition, the shapes and scale of the components in the figures are only illustrative and are used to help understand the present application, and are not specific limitations on the shapes and scale of the components. Those skilled in the art can select various possible shapes and scale sizes according to specific circumstances to implement the present application under the guidance of the present application.

[0025] Figure 1 is a power supply equipment system overall architecture diagram of the present application; Figure 2 is a multi-level converter topology structure diagram of the present application; Figure 3 is a self-adaptive control strategy flowchart of the present application; Figure 4 is a device tolerance characteristic protection strategy diagram of the present application; DETAILED DESCRIPTION

[0026] The details of the application can be more clearly understood in conjunction with the accompanying drawings and the description of the embodiments of the application. However, the embodiments of the application described herein are only intended to explain the application and should not be understood as limiting the application in any way. Any possible variations of the application conceived by the skilled person based on the teachings of the application should be considered as falling within the scope of the application. The terms “mounting” and “connection” should be interpreted broadly as direct connection or indirect connection through an intermediate medium. In addition, in the description of the application, “several” means two or more, unless specifically limited.

[0027] Referring to Figures 1-4 As shown in the drawings, the application provides a new energy grid-connected harmonic suppression power supply device, which comprises a new energy power generation unit, a multi-level power electronic conversion unit, a harmonic detection and analysis unit, an adaptive multi-mode control unit, a same filtering execution unit and a power distribution equipment protection monitoring unit. The power generation unit relies on new energy (photovoltaic / wind power) input, the multi-level topology conversion unit realizes core power conversion, the control unit is the brain, processes and analyzes and issues instructions, the filtering unit is the execution mechanism, and the active and passive units work together, and the monitoring unit is used for protecting the safe operation of the power distribution equipment. The new energy power generation unit comprises a photovoltaic array or a wind turbine generator set and an energy storage buffer module, which is used for suppressing the power fluctuation caused by intermittent power generation and reducing the harmonic generation from the source.

[0028] Specifically, the multi-level power electronic conversion unit adopts a modular multi-level converter (MMC) or a cascade H-bridge topology structure and is connected with the new energy power generation unit. Figure 2 As shown in the drawings, the sub-module SM is a basic component unit and comprises IGBT, capacitor and diode; the bridge arm structure comprises N SMs connected in series in the upper and lower bridge arms; and the output characteristic is that a multi-level output waveform is generated through the combination of SMs. The multi-level power electronic conversion unit generates 5 or more levels at the output end to approximate a sine wave, which is used for controlling the total harmonic distortion rate of the output waveform.

[0029] The multi-level conversion technology (MMC or cascade H-bridge) is adopted to reduce the voltage change rate dv / dt by increasing the number of output levels, thereby reducing the harmonic generation from the source; the SVPWM optimization modulation strategy is applied to improve the utilization rate of direct current voltage and improve the output waveform quality.

[0030] Specifically, the harmonic detection and analysis unit is used for monitoring the voltage harmonic distortion rate THD and the harmonic content of each order of the public coupling point PCC in real time; a hierarchical control strategy based on the harmonic distortion rate THD is established to realize the balance between the treatment accuracy and the energy consumption.

[0031] Specifically, the adaptive multi-mode control unit integrates the SVPWM modulation strategy and the virtual impedance control algorithm; the adaptive multi-mode control unit is divided into three levels according to the severity of the harmonic: Level 1 mode: THD < 5%, only SVPWM optimized modulation is enabled; Secondary mode: 5%≤THD<8%, virtual impedance control is enabled; Level 3 mode: THD≥8%, active filter compensation is enabled.

[0032] like Figure 3 As shown, the three-level modes are: automatic switching of control strategies based on THD values; closed-loop control: real-time monitoring-analysis-control-feedback; and adaptive adjustment: dynamic optimization of parameters based on equipment status. The virtual impedance control algorithm employs an adaptive adjustment mechanism based on harmonic power feedback, with virtual impedance values... satisfy: in , For adaptive adjustment coefficient, For harmonic distortion rate deviation, This refers to the cumulative amount of harmonic distortion rate deviation over time. Adaptive virtual impedance technology is used to track changes in grid impedance in real time, preventing harmonic amplification.

[0033] Specifically, the filtering execution unit includes an active filtering module and a passive filtering module. The active filtering module employs a harmonic detection method based on instantaneous reactive power theory, with a compensation current response time of less than 100μs. The passive filtering module designs a tuning frequency for specific harmonics and connects an anti-resonant reactor in series with the capacitor, ensuring that the parallel resonant frequency is below 90% of the lowest harmonic frequency. This active-passive collaborative filtering architecture ensures effective harmonic suppression under various operating conditions.

[0034] Specifically, the power distribution equipment protection monitoring unit is used to assess the harmonic tolerance status of transformers, capacitors, and switchgear in real time. For example... Figure 4 As shown, the tolerance ranking is: switching equipment > transformer > capacitor; the main limiting factors are different for each, requiring targeted protection; protection measures: corresponding strategies should be developed based on the equipment characteristics. The power distribution equipment protection monitoring unit establishes a transformer hotspot temperature rise model. in This is the effective value of the harmonic current. Rated current, For winding resistance, The harmonic loss coefficient is used. A harmonic tolerance model for power distribution equipment is established to evaluate the equipment's operating status in real time.

[0035] It is worth mentioning that the device also contains an intelligent early warning module, which gives a maintenance early warning when predicting that the transformer insulation life attenuation is accelerated, the capacitor is overloaded or the switch device contact temperature rise exceeds the standard; the device supports a remote operation and maintenance interface, and can upload operation data to a cloud platform to realize collaborative harmonic management of multiple sites. By setting multiple early warning thresholds, potential fault risks are found in advance, and the device life is predicted by an intelligent algorithm to optimize the maintenance cycle.

[0036] The implementation of the present application is illustrated by taking a 10MW photovoltaic power station as an example: Hardware configuration: New energy power generation unit: single crystal silicon photovoltaic module is adopted, and the total capacity is 12MWp; Multi-level conversion unit: modular multi-level converter MMC is adopted, there are 16 sub-modules per phase, and the number of output levels is 31; Harmonic detection unit: 0.2S grade power quality analyzer is adopted, and the sampling frequency is 25600Hz; Active filtering module: the capacity is 2MVA, and three-level NPC topology is adopted; Passive filtering module: four groups of tuning filters are designed for 5th, 7th, 11th and 13th harmonics; Control parameter setting: SVPWM switching frequency: 2kHz, three harmonic injection method is adopted to improve the utilization rate of DC voltage; Virtual impedance initial value: Rvir=0.5Ω, Lvir=3mH, Cvir=50μF; Protection threshold: transformer temperature rise alarm value 75℃, capacitor overcurrent alarm value 1.3In; Operation effect: The one-year data of grid-connected operation shows that the PCC point voltage THD is stabilized at 3.8-4.5%, the maximum operating temperature of the transformer is reduced by 12℃, the capacitor group does not need to be additionally expanded, and the maintenance cost in the whole life cycle is expected to be reduced by more than 35%.

[0037] The above implementation mode proves the effectiveness and practicability of the present application, which can realize effective harmonic management and reliable protection of distribution equipment in a complex power grid environment.

[0038] In summary, the core of the present application is to build a three-level protection system of "source suppression-process management-equipment protection".

[0039] First level: source optimization; Multi-level conversion technology (MMC or cascaded H-bridge) is adopted, the number of output levels is increased to reduce the voltage change rate dv / dt, and the harmonic generation is reduced from the source; SVPWM optimization modulation strategy is applied to improve the utilization rate of DC voltage and improve the output waveform quality; Second level: process governance; Establish a hierarchical control strategy based on THD to balance the precision of governance and energy consumption; Adopt adaptive virtual impedance technology to track the change of grid impedance in real time and avoid harmonic amplification; Build an active and passive collaborative filtering architecture to ensure effective harmonic suppression under various operating conditions; Third level: device protection; Establish a harmonic tolerance model of power distribution equipment to assess the operating state of the equipment in real time; Set multiple early warning thresholds to discover potential fault risks in advance; Predict the service life of the equipment through intelligent algorithms to optimize the maintenance cycle.

[0040] Through the three-level protection system, the PCC point voltage THD is reduced from 8-15% in the traditional scheme to below 5%, and the harmonic content of each order meets the requirements of IEEE Std 519 standard.

[0041] Perfect device protection function: through real-time monitoring and early warning, the expected life of the transformer can be increased by 20-30%, the failure rate of the capacitor can be reduced by 40-60%, and the maintenance cycle of the switch device can be extended by 1.5-2 times.

[0042] Strong adaptability: the virtual impedance parameters can be automatically adjusted according to the grid operating conditions, and stable operation can be maintained within a range of ±50% of the grid impedance.

[0043] Outstanding economy: make full use of existing grid-connected equipment to achieve harmonic governance, avoid additional investment in special filter devices, and shorten the investment recovery period to 2-3 years.

[0044] The above embodiments are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made in accordance with the spirit and essence of the present application shall be covered within the protection scope of the present application.

Claims

1. A new energy grid-connected harmonic suppression power supply device, characterized in that, Includes new energy power generation units, including photovoltaic arrays or wind turbine generators; The multilevel power electronic conversion unit adopts a modular multilevel converter (MMC) or cascaded H-bridge topology and is connected to the new energy power generation unit. The harmonic detection and analysis unit monitors the voltage harmonic distortion rate (THD) and the content of each harmonic at the common coupling point (PCC) in real time. Adaptive multi-mode control unit, integrating SVPWM modulation strategy and virtual impedance control algorithm; The same filtering execution unit includes an active filtering module and a passive filtering module; The power distribution equipment protection and monitoring unit assesses the harmonic tolerance status of transformers, capacitors, and switchgear in real time.

2. The new energy grid-connected harmonic suppression power supply equipment according to claim 1, characterized in that: The multi-level power electronic converter unit approximates a sine wave by generating five or more levels at the output terminal, which is used to control the total harmonic distortion rate of the output waveform.

3. The new energy grid-connected harmonic suppression power supply equipment according to claim 2, characterized in that: The adaptive multi-mode control unit operates in three levels according to the severity of harmonics: Level 1 mode: THD < 5%, only SVPWM optimized modulation is enabled; Secondary mode: 5%≤THD<8%, virtual impedance control is enabled; Level 3 mode: THD≥8%, active filter compensation is enabled.

4. The new energy grid-connected harmonic suppression power supply equipment according to claim 3, characterized in that: The virtual impedance control algorithm employs an adaptive adjustment mechanism based on harmonic power feedback, with the virtual impedance value... satisfy: in , For adaptive adjustment coefficient, For harmonic distortion rate deviation, This refers to the cumulative amount of harmonic distortion rate deviation over time.

5. The new energy grid-connected harmonic suppression power supply equipment according to claim 4, characterized in that: The active filter module employs a harmonic detection method based on instantaneous reactive power theory, with a compensation current response time of less than 100μs.

6. The new energy grid-connected harmonic suppression power supply equipment according to claim 5, characterized in that: The passive filter module is designed with a tuning frequency for specific subharmonics, and an anti-resonance reactor is connected in series with the capacitor to make the parallel resonant frequency lower than 90% of the lowest subharmonic frequency.

7. The new energy grid-connected harmonic suppression power supply equipment according to claim 6, characterized in that: The power distribution equipment protection and monitoring unit establishes a transformer hot spot temperature rise model: in This is the effective value of the harmonic current. Rated current, For winding resistance, This is the harmonic loss coefficient.

8. The new energy grid-connected harmonic suppression power supply equipment according to claim 7, characterized in that: The device also includes an intelligent early warning module that issues a maintenance warning in advance when it predicts that the transformer insulation life will deteriorate rapidly, the capacitor will be overloaded, or the temperature rise of the switchgear contacts will exceed the standard.

9. The new energy grid-connected harmonic suppression power supply equipment according to claim 8, characterized in that: The device supports a remote operation and maintenance interface, which can upload operational data to the cloud platform to achieve collaborative harmonic management across multiple sites.

10. The new energy grid-connected harmonic suppression power supply equipment according to claim 9, characterized in that: The new energy power generation unit includes an energy storage buffer module, which is used to smooth out power fluctuations caused by intermittent power generation.

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