Inverter adaptive control system suitable for low voltage ride through and frequency disturbance

Abstract

The invention relates to the technical field of inverter control, in particular to an inverter adaptive control system suitable for low voltage ride through and frequency disturbance, which comprises a detection module, a processing module, an adaptive module and a control module, the detection module collects power data at a grid-connected point of a renewable energy unit in the power system according to a period T, and transmits the power data to the processing module; the processing module is used for processing the electric power data acquired by the detection module and transmitting a result to the adaptive module; the adaptive module sends a control switching command; and the control module adjusts the inverter according to the judgment result of the self-adaptive module to realize the control of the inverter. According to the invention, stable operation of the access power grid under the condition of low voltage ride through frequency disturbance is realized; the over-current protection of the inverter is not easy to cause, and the continuous operation of the photovoltaic inverter is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of inverter control, and in particular to an inverter adaptive control system suitable for low voltage ride-through and frequency disturbance. Background Art

[0002] Photovoltaic power generation occupies a very important position in today's electricity production. After years of exploration and research, the number of constructions has continued to increase and the scale has continued to expand. It has received much attention and support for its advantages such as renewable nature, high conversion efficiency and environmental protection.

[0003] In the actual power generation process, due to the indirectness and volatility of renewable energy power generation, the output voltage and frequency of the power system change drastically. A sharp drop in voltage will cause a rapid overcurrent. Long-term overcurrent will cause components to break down and explode, ultimately affecting the stability of the power system. Due to changes in system frequency caused by the environment, the adjustable capacity may not be able to meet the active power and reactive power regulation requirements at the same time.

[0004] In the power system, the inverter is a key power conversion device used to convert direct current into alternating current. When the voltage drops significantly during the grid connection process, the inverter can ensure that a certain amount of reactive power is provided to maintain the normal operation of the power grid.

[0005] As the proportion of photovoltaic power generation increases, the inverter control system that maintains the stability of the power system becomes more important. In the case of low voltage ride-through and frequency disturbance, how to control the inverter to make the system more stable and reliable is a problem that needs to be solved. Summary of the invention

[0006] Based on the above objectives, the present invention provides an inverter adaptive control system suitable for low voltage ride-through and frequency disturbance.

[0007] An inverter adaptive control system suitable for low voltage ride-through and frequency disturbance, comprising a detection module, a processing module, an adaptive module and a control module, wherein; The detection module collects power data at a grid connection point of a renewable energy unit in the power system according to a period T, and transmits the power data to the processing module; The processing module processes the power data collected by the detection module and transmits the result to the adaptive module; The adaptive module issues a control switching command; The control module adjusts the inverter according to the judgment result of the adaptive module to realize the control of the inverter.

[0008] Furthermore, the power data includes the inverter grid connection point voltage, AC bus current and grid frequency.

[0009] Furthermore, the processing module includes: Low voltage judgment: monitor the operating status of the grid connection point voltage. If the grid connection point voltage is lower than the preset voltage value, it is judged that the renewable energy unit is in a low voltage situation; Frequency disturbance judgment: monitor the operating status of the grid connection point frequency. If the grid connection point frequency is within the preset dead zone, it is judged that the renewable energy unit is in a frequency disturbance.

[0010] Furthermore, the preset voltage value is 0.9 pu.

[0011] Furthermore, the adaptive module includes: Low voltage ride-through control: When in low voltage ride-through, the adaptive control rate will be selected according to the grid equivalent inductance value and the phase-locked loop bandwidth parameter; Frequency disturbance control: When the renewable energy unit is in a frequency disturbance state, the active and reactive current proportional distribution is implemented to solve the disturbance problem.

[0012] Furthermore, the low voltage ride through control includes: Three-value periodic signal superposition: superimpose the three-value periodic signal in the acquisition period on the first d-axis current reference signal of the current loop of the phase-locked loop inverter, and then obtain the second d-axis current reference signal, so that the phase-locked loop inverter switches to work at three steady-state operating points within one period T; Voltage-current transformation: transform the voltage and current at the grid connection point to obtain the d-axis voltage and current in the dq coordinate system; Equivalent impedance calculation: Calculate the resistance value of the grid equivalent impedance and the grid equivalent inductance value through the average value of the d-axis voltage and current; Adaptive control rate feedback: By feeding back the equivalent inductance value of the power grid to the adaptive control rate in real time, the phase-locked loop inverter can be adaptively and stably controlled.

[0013] Furthermore, the frequency disturbance control includes: Frequency disturbance detection: After receiving the processed power data of the grid-connected point of the renewable energy unit, it is determined that the inverter adaptive control system is in a frequency disturbance state; Reactive current calculation: When the renewable energy unit is in frequency disturbance, the reactive current value is calculated based on the dynamic active current value of the power data collected at the grid connection point of the renewable energy unit; Transmit reactive current value: transmit the calculated reactive current value to the control module to adjust the inverter; Current threshold judgment: judge whether the grid-connected point current adjusted by the original active current adjustment value meets the current threshold limit of the inverter; Reactive current adjustment: If the adjusted grid-connected point current does not meet the current threshold limit of the inverter, the reactive current is adjusted while maintaining the original active current adjustment value so that the grid-connected point current meets the current threshold limit of the inverter, and the reactive current value is gradually reduced based on the actual reactive current.

[0014] Furthermore, the reactive current calculation includes: Active current priority distribution: In order to realize the priority distribution of active current under frequency disturbance, only the frequency control link is used to adjust the active current to obtain the original active current value; Reactive current adjustment calculation: Based on the original active current adjustment value, the reactive current adjustment value after dynamic allocation is calculated.

[0015] Furthermore, the current threshold determination includes: Root mean square value calculation: Calculate whether the root mean square value of the actual reactive current value and the active current reference value is within the current threshold limit range of the inverter; Active current reference value calculation: The active current reference value is the sum of the actual active current value and the original active current adjustment value.

[0016] Furthermore, the calculation formula of the root mean square value is: ; in, is the actual active current value, is the actual reactive current value, It is the original active current adjustment value.

[0017] Beneficial effects of the present invention: The present invention ensures stable operation of access to a power grid under low voltage ride-through and frequency disturbance conditions by adding an adaptive module to an inverter adaptive control system.

[0018] The present invention establishes an adaptive control rate for selecting the equivalent inductance value of the power grid and the bandwidth parameter of the phase-locked loop, and feeds back the real-time equivalent inductance value of the power grid to the adaptive control rate. During low voltage ride-through, the current impact is smaller, the current is more stable, and the overcurrent protection of the inverter is not easily triggered, thereby ensuring the continuous operation of the photovoltaic inverter.

[0019] The present invention performs dynamic distribution control on the basis of frequency control output, adjusts the inverter of the new energy unit according to the reactive current adjustment value after dynamic distribution and the original active current adjustment value, and re-collects the power data of the grid connection point of the new energy unit to obtain the optimal active and reactive current distribution plan within the current range that the inverter can withstand. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 Schematic diagram of system function modules according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0023] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0024] like Figure 1 As shown, an inverter adaptive control system suitable for low voltage ride-through and frequency disturbance includes a detection module, a processing module, an adaptive module and a control module, wherein; The detection module collects power data at the grid connection point of the renewable energy unit in the power system according to a period T, and transmits the power data to the processing module.

[0025] Power data includes inverter grid connection point voltage, AC bus current, and grid frequency.

[0026] The processing module processes the power data collected by the detection module and transmits the result to the adaptive module; By monitoring the operating status of the grid connection point voltage, if the grid voltage is lower than 0.9pu, it is judged that the renewable energy unit is in a low voltage state; By monitoring the operating status of the frequency at the grid connection point and whether it is within the preset dead zone, it is determined whether the renewable energy unit is in a frequency disturbance.

[0027] The adaptive module issues a control switching command; When in low voltage ride-through, the adaptive control rate will be selected according to the grid equivalent inductance value and the phase-locked loop bandwidth parameter: The three-value periodic signal in the acquisition period is superimposed on the first d-axis current reference signal of the current loop of the phase-locked loop inverter, thereby obtaining a second d-axis current reference signal, so that the phase-locked loop inverter can switch to work at three steady-state operating points within a period T; the voltage and current at the grid connection point are transformed to obtain the d-axis voltage and current in the dq coordinate system; the resistance value of the grid equivalent impedance and the grid equivalent inductance value are calculated through the average value of the d-axis voltage and current; the grid equivalent inductance value is fed back to the adaptive control rate in real time, so that the phase-locked loop inverter is adaptively and stably controlled; When the renewable energy unit is in the condition of frequency disturbance, the active and reactive current proportional distribution is implemented to solve the disturbance problem. The adaptive control under frequency disturbance is as follows: Step S1, receiving a signal from a processing module after the processing and collection module obtains the power data of the grid connection point of the renewable energy unit, that is, the grid connection point voltage is not within the dead zone and the grid frequency is within the dead zone, and judging that the system is in a frequency disturbance state; Step S2, when the renewable energy unit is in frequency disturbance, the reactive current value is calculated according to the dynamic active current value of the power data collected at the grid connection point of the renewable energy unit; In order to realize the priority distribution of active current under frequency disturbance, only the frequency control link is used to adjust the active current to obtain the original active current value; according to the original active current adjustment value, the reactive current adjustment value after dynamic distribution is calculated; Step S3, transmitting the calculated reactive current value to the control module to adjust the inverter; Step S4, determining whether the grid connection point current adjusted by the original active current adjustment value meets the current threshold limit of the inverter; Calculate whether the root mean square value of the actual reactive current value and the active current reference value is within the current threshold limit range of the inverter; the active current reference value is the sum of the actual active current value and the original active current adjustment value; the root mean square value is calculated as follows: ; in, is the actual active current value, is the actual reactive current value, is the original active current adjustment value; Step S5: If not, the reactive current is adjusted while maintaining the original active current adjustment value, so that the grid-connected point current meets the current threshold limit of the inverter, and the reactive current value is gradually reduced based on the actual reactive current.

[0028] The control module adjusts the inverter according to the judgment result of the adaptive module, thereby realizing the control of the inverter.

[0029] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Under the concept of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

[0030] The present invention is intended to cover all such substitutions, modifications and variations that fall within the broad scope of the claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An inverter adaptive control system suitable for low voltage ride-through and frequency disturbance, characterized in that: It includes a detection module, a processing module, an adaptive module and a control module, wherein; The detection module collects power data at a grid connection point of a renewable energy unit in the power system according to a period T, and transmits the power data to the processing module; The processing module processes the power data collected by the detection module and transmits the result to the adaptive module; The adaptive module issues a control switching command; The control module adjusts the inverter according to the judgment result of the adaptive module to realize the control of the inverter.

2. The inverter adaptive control system suitable for low voltage ride through and frequency disturbance according to claim 1, characterized in that: The power data includes the inverter grid connection point voltage, AC bus current and grid frequency.

3. The inverter adaptive control system suitable for low voltage ride through and frequency disturbance according to claim 2, characterized in that: The processing module comprises: Low voltage judgment: monitor the operating status of the grid connection point voltage. If the grid connection point voltage is lower than the preset voltage value, it is judged that the renewable energy unit is in a low voltage situation; Frequency disturbance judgment: monitor the operating status of the grid connection point frequency. If the grid connection point frequency is within the preset dead zone, it is judged that the renewable energy unit is in a frequency disturbance.

4. The inverter adaptive control system suitable for low voltage ride through and frequency disturbance according to claim 3, characterized in that: The preset voltage value is 0.9 pu.

5. The inverter adaptive control system suitable for low voltage ride through and frequency disturbance according to claim 3, characterized in that: The adaptive module comprises: Low voltage ride-through control: When in low voltage ride-through, the adaptive control rate will be selected according to the grid equivalent inductance value and the phase-locked loop bandwidth parameter; Frequency disturbance control: When the renewable energy unit is in a frequency disturbance state, the active and reactive current proportional distribution is implemented to solve the disturbance problem.

6. The inverter adaptive control system suitable for low voltage ride through and frequency disturbance according to claim 5, characterized in that: The low voltage ride through control comprises: Three-value periodic signal superposition: superimpose the three-value periodic signal in the acquisition period on the first d-axis current reference signal of the current loop of the phase-locked loop inverter, and then obtain the second d-axis current reference signal, so that the phase-locked loop inverter switches to work at three steady-state operating points within one period T; Voltage-current transformation: transform the voltage and current at the grid connection point to obtain the d-axis voltage and current in the dq coordinate system; Equivalent impedance calculation: Calculate the resistance value of the grid equivalent impedance and the grid equivalent inductance value through the average value of the d-axis voltage and current; Adaptive control rate feedback: By feeding back the equivalent inductance value of the power grid to the adaptive control rate in real time, the phase-locked loop inverter can be adaptively and stably controlled.

7. The inverter adaptive control system suitable for low voltage ride through and frequency disturbance according to claim 6, characterized in that: The frequency disturbance control comprises: Frequency disturbance detection: After receiving the processed power data of the grid-connected point of the renewable energy unit, it is determined that the inverter adaptive control system is in a frequency disturbance state; Reactive current calculation: When the renewable energy unit is in frequency disturbance, the reactive current value is calculated based on the dynamic active current value of the power data collected at the grid connection point of the renewable energy unit; Transmit reactive current value: transmit the calculated reactive current value to the control module to adjust the inverter; Current threshold judgment: judge whether the grid-connected point current adjusted by the original active current adjustment value meets the current threshold limit of the inverter; Reactive current adjustment: If the adjusted grid-connected point current does not meet the current threshold limit of the inverter, the reactive current is adjusted while maintaining the original active current adjustment value so that the grid-connected point current meets the current threshold limit of the inverter, and the reactive current value is gradually reduced based on the actual reactive current.

8. The inverter adaptive control system suitable for low voltage ride through and frequency disturbance according to claim 7, characterized in that: The reactive current calculation includes: Active current priority distribution: In order to realize the priority distribution of active current under frequency disturbance, only the frequency control link is used to adjust the active current to obtain the original active current value; Reactive current adjustment calculation: Based on the original active current adjustment value, the reactive current adjustment value after dynamic allocation is calculated.

9. The inverter adaptive control system suitable for low voltage ride through and frequency disturbance according to claim 8, characterized in that: The current threshold determination includes: Root mean square value calculation: Calculate whether the root mean square value of the actual reactive current value and the active current reference value is within the current threshold limit range of the inverter; Active current reference value calculation: The active current reference value is the sum of the actual active current value and the original active current adjustment value.

10. The inverter adaptive control system suitable for low voltage ride through and frequency disturbance according to claim 9, characterized in that: The calculation formula of the root mean square value is: ； in, is the actual active current value, is the actual reactive current value, It is the original active current adjustment value.

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