Method for monitoring voltage out-of-limit and harmonic interference problems of photovoltaic transformer area based on inductance-calculation-communication integrated technology

Abstract

The invention provides a photovoltaic transformer area voltage out-of-limit and harmonic interference problem monitoring method based on an inductance-computing-communication integrated technology, and the method specifically comprises the following steps: 1, constructing an inductance-computing-communication integrated monitoring platform, for the lower part, carrying out the interaction with a distributed power supply through an RS485 / USB / CAN bus, and for the upper part, carrying out the interaction with a transformer area terminal through a carrier dual mode; step 2, acquiring original cycle data output by the inverter at a high frequency of 12800 points per second by the sensing, computing and communication integrated monitoring platform; 3, monitoring the reverse power of the transformer area in real time by the transformer area terminal side; 4, improving the quality of electric energy by adjusting the power of a photovoltaic grid-connected point or disconnecting the connection and the like; 5, when the platform is authorized to a local automatic control function and a voltage out-of-limit event is monitored, a control command is directly issued locally to the inverter for flexible adjustment, and the adjustment period is in a minute level; and when events such as frequency and voltage simultaneous swing occur, a rigid control command is issued to a grid-connected switch to cut off a grid-connected loop. The technical scheme can be used for improving the grid-connected electric energy quality.

Description

Technical Field

[0001] The present invention relates to the field of distributed power supply access monitoring technology, and in particular to a method for monitoring voltage over-limit and harmonic interference problems in photovoltaic areas based on sensing, computing and communication integration technology. Background Art

[0002] With the advancement of the national dual-carbon policy, the installed capacity of distributed photovoltaics has expanded rapidly. New energy power generation is volatile and intermittent. Large-scale access to the grid will affect the power quality of the distribution network, such as voltage level, harmonic content, and degree of fluctuation. The high penetration rate of distributed photovoltaics has changed the power flow distribution of the distribution network and affected the voltage level of the distribution network. When distributed photovoltaics inject power into the grid in reverse, it will cause the voltage of the distribution network node to rise. If it does not operate at a unity power factor, it will inject reactive power into the grid, which will also cause the voltage deviation to change. When the access capacity exceeds the maximum limit, it will cause the voltage to exceed the limit. The IGBT devices of the photovoltaic inverter are frequently in operation, which is easy to generate harmonic components with similar frequencies. The larger the capacity of distributed photovoltaics and the closer the access location is to the end of the distribution network, the greater the impact of the generated harmonics.

[0003] The access of distributed photovoltaic power sources gradually changes the original grid structure. When high-penetration photovoltaic power sources are connected to the distribution network in an disorderly manner, it will cause serious harm. The power peak they provide may exceed the absorption capacity of the distribution network, breaking the active and reactive balance of the power system, and thus affecting the stability of the grid voltage and frequency.

[0004] For the problem of over-limit voltage in photovoltaic power stations, 1) install voltage regulators to control the grid voltage and alleviate overvoltage by adjusting the output voltage of the grid connection point; 2) adjust the active and reactive output of the photovoltaic power generation system to match the power station and reduce the probability of overvoltage; 3) deploy distributed energy storage systems to mitigate the impact of overvoltage and achieve distributed photovoltaic smooth output. For harmonic detection in photovoltaic stations, online power quality monitoring devices can be deployed at the grid connection point to record power quality events and assist management personnel in timely discovering and handling power quality problems.

[0005] As mentioned above, common solutions all require dedicated equipment, which increases investment costs and also requires consideration of the timeliness of the collaborative work of multiple devices. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a monitoring method for photovoltaic area voltage over-limit and harmonic interference problems based on integrated sensing, computing and communication technology, so as to improve the quality of grid-connected power.

[0007] To achieve the above purpose, the present invention adopts the following technical solution: a monitoring method for the voltage over-limit and harmonic interference problems in photovoltaic areas based on the integrated sensing and computing technology, which is as follows:

[0008] Step 1: Build an integrated monitoring platform for sensing and computing. To the bottom: interact with the distributed power supply through RS485 / USB / CAN bus, and to the top: interact with the substation terminal through carrier dual-mode;

[0009] Step 2: The integrated monitoring platform collects the original frequency data output by the inverter at a high frequency of 12,800 points per second, separates the harmonic components through the hardware FFT module and calculates the corresponding harmonic content; at the same time, voltage swells, sags and fluctuations are monitored and analyzed based on the original frequency data; when harmonics, voltage swells, sags and fluctuations are detected that exceed the error limit, an alarm event is generated, and the event is reported to the substation terminal through the dual-mode communication unit;

[0010] Step 3: The terminal side of the substation monitors the reverse power of the substation in real time. When the reverse load rate is ≥80%, a fair distribution or step-by-step adjustment strategy is adopted to adjust the active output of the photovoltaic inverter; the fair distribution reduces the active output in proportion to the inverter capacity and the current power output; the step-by-step adjustment strategy is adjusted step by step according to the capacity of the inverter and the current power output; when the photovoltaic grid-connected voltage is high enough that the reactive power regulation reaches the upper limit and the voltage is still over the limit, the terminal selects the photovoltaic grid-connected node PV curve that is similar to the weather on that day, and calculates the active power △Pv to be adjusted according to the current voltage over-limit value until the voltage does not exceed the limit;

[0011] Step 4: When the substation terminal receives an abnormal power quality event, it reads the event details recorded by the platform and improves the power quality by adjusting the power of the photovoltaic grid-connected point or disconnecting it;

[0012] Step 5: When the platform is authorized with the local self-control function, when a voltage over-limit event is detected, the local control command is directly issued to the inverter for flexible adjustment, with an adjustment cycle of minutes. When events such as simultaneous frequency and voltage swings occur, a rigid control command is issued to the grid-connected switch to cut off the grid-connected circuit.

[0013] In a preferred embodiment, in step 1, the core processing unit SoC chip of the integrated monitoring platform of sensing and computing adopts a dual-core architecture; the sampling front end selects an external open-type transformer or a fixed transformer of the corresponding level according to the capacity of the distributed power supply, reduces the large current to a current that can be accurately measured by the metering unit according to the transformation ratio, and converts the large voltage into a certain proportion of weak voltage through a voltage transformer to make it meet the input voltage requirement of the metering unit.

[0014] In a preferred embodiment, in step 1, the current and voltage signals are converted into differential voltage signals of corresponding channels through load resistors so that the collection and measurement unit can perform analog-to-digital conversion to obtain current and voltage digital instantaneous signals, instantaneous power p(t)=v(t)×i(t), and the active power component is obtained by low-pass filtering; the electric energy E=∫P(t)dt is calculated by integrating the instantaneous power, where E is electric energy, P(t) is instantaneous power, and t is time.

[0015] In a preferred embodiment, the step 2 includes a harmonic analysis module and a flicker monitoring module; the harmonic analysis module includes performing discrete sampling point approximate integration of the voltage and current sampling values ​​to calculate the voltage effective Current RMS Frequency domain analysis and extraction by fast Fourier transform of voltage and current sampling values as well as The flicker monitoring module captures flicker signals through a 0.05Hz-35Hz bandpass filter and a visual sensitivity weighted filter, and then outputs flicker visual sensitivity S(t) through squaring and low-pass filtering to simulate the human eye's perception of voltage fluctuation flicker.

[0016] In a preferred embodiment, step 3 specifically includes:

[0017] Step 31: Data collection and prediction: collect the capacity, output power and load power of the distributed power source in the current area in a 5-minute cycle, predict the output curve based on the meteorological information and the installed capacity of the distributed power source in the area, and modify the predicted curve according to the collected output power;

[0018] Step 32: Data analysis and determination: determine whether there is a reverse heavy overload based on the current operating data, and execute the current control plan if there is; determine whether there is a reverse heavy overload in the future period based on the predicted data, and formulate a pre-control plan;

[0019] Step 33: Formulate a control plan, calculate the current load rate based on the transformer capacity of the substation and the current grid-connected power, and issue a control command when the load rate exceeds 80%. A control cycle is performed every 5 minutes to adjust the active output of the distributed power source to achieve the downward adjustment target and suspend control after eliminating the reverse heavy overload. According to the predicted photovoltaic output power and the substation's demand, the control target is corrected in time to reduce the impact of control lag.

[0020] In a preferred embodiment, the step 5 specifically includes the following steps:

[0021] Step 51: Acquisition task response, the platform collects the electrical parameter information of the distributed power source in real time, responds to the reading task of the substation terminal at a fixed time, and uploads data such as voltage, current, power, and power factor;

[0022] Step 52: Control task response: the platform receives the power control command issued by the substation terminal, sends it to the distributed power supply device, and responds to the substation terminal at the same time;

[0023] Step 53: Local automatic control scheme. According to the photovoltaic capacity and consumption demand of the substation, the terminal dynamically sets the control parameters for each grid-connected point and authorizes the platform to enable the local automatic control function. Generally, when the platform detects that the voltage exceeds the limit by 7% for 30 minutes, exceeds the limit by 10% for 15 minutes, and exceeds the limit by 15% for 15 seconds, it directly issues a control command for flexible adjustment with an adjustment cycle of 1 minute. When the frequency swings by 0.2Hz~1Hz and the voltage swings by 0.1Un~025Un, a rigid control command is issued to the grid-connected switch to cut off the grid-connected circuit.

[0024] Compared with the prior art, the present invention has the following beneficial effects: the integrated photovoltaic monitoring solution designed by the present invention solves the problems of complicated equipment deployment, high cost, and difficult coordination in the prior art solutions. Through functional integration and business collaboration, it improves the accuracy, timeliness and reliability of the manageability of low-voltage distributed photovoltaic stations. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is an overall flow chart of a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0027] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0028] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0029] A monitoring method for voltage over-limit and harmonic interference in photovoltaic areas based on integrated sensing and computing technology, reference Figure 1 , as follows:

[0030] Design a sensor-computing integrated monitoring platform, which can interact with distributed power sources through RS485 / USB / CAN bus, and interact with substation terminals through carrier dual-mode. The platform has rich interfaces and protocols, is compatible with multi-source heterogeneous equipment access, and has three-phase metering, power quality analysis, protocol conversion, dual-mode communication and other functions, effectively reducing equipment deployment and implementation costs. The metering unit of the platform has a high-precision, wide-bandwidth ADC converter, which performs high-speed real-time sampling and analog-to-digital conversion of voltage and current. The wide passband reduces the influence of ADC on harmonic signal attenuation and phase shift.

[0031] The platform collects the original frequency data output by the inverter at a high frequency of 12,800 points per second, separates the harmonic components through the hardware FFT module and calculates the corresponding harmonic content; at the same time, it monitors and analyzes voltage swells, sags and fluctuations based on the original frequency data. When harmonics, voltage swells, sags and fluctuations are detected that exceed the error limit, an alarm event is generated and the event is reported to the substation terminal through the dual-mode communication unit.

[0032] The terminal side of the substation monitors the reverse power of the substation in real time. When the reverse load rate is ≥80%, a fair distribution or step-by-step adjustment strategy can be adopted to adjust the active output of the photovoltaic inverter. The former reduces the active output in proportion to the inverter capacity and the current power output; the latter adjusts step by step according to the inverter capacity and the current power output. When the photovoltaic grid-connected voltage is too high, the reactive power regulation reaches the upper limit and the voltage is still over the limit, the terminal selects the photovoltaic grid-connected node PV curve similar to the weather on that day, and calculates the active power △Pv to be adjusted according to the current voltage over-limit value until the voltage does not exceed the limit.

[0033] When the substation terminal receives an abnormal power quality event, it reads the event details recorded by the reading platform and improves the power quality by adjusting the power of the photovoltaic grid-connected point or disconnecting it.

[0034] When the platform is authorized with the local self-control function, when a voltage over-limit event is detected, a control command can be directly issued locally to the inverter for flexible adjustment with an adjustment cycle in minutes. When events such as simultaneous frequency and voltage swings occur, a rigid control command can be issued to the grid-connected switch to cut off the grid-connected circuit.

[0035] The integrated photovoltaic monitoring solution designed by the present invention improves the accuracy, timeliness and reliability of the management of low-voltage distributed photovoltaic stations through functional integration and business collaboration.

[0036] Step 1: Sampling Processing Unit

[0037] Platform architecture: The core processing unit SoC chip of the platform adopts a dual-core architecture, with IP cores such as measurement, communication, and algorithms. The dynamic range of the acquisition and measurement unit is 8000:1, and it supports hardware FFT, up to 256 points of sampling per cycle, and ADC data cache, which can effectively capture high-order harmonic information.

[0038] At the sampling front end, according to the capacity of the distributed power source, an external open-type transformer or fixed transformer of the corresponding level is selected to reduce the large current to a current that can be accurately measured by the metering unit according to the transformation ratio, and the large voltage is converted into a certain proportion of weak voltage through the voltage transformer to meet the input voltage requirements of the metering unit;

[0039] For electric energy measurement, the current and voltage signals are converted into differential voltage signals of the corresponding channels through load resistors so that the measurement unit can perform analog-to-digital conversion to obtain current and voltage digital instantaneous signals. The instantaneous power p(t)=v(t)×i(t) is obtained by low-pass filtering, and the active power component is obtained. The electric energy E=∫P(t)dt is calculated by integrating the instantaneous power, where E is electric energy, P(t) is instantaneous power, and t is time.

[0040] Note: For the self-generation and self-use, and surplus power grid-connected mode, when the power generation and surplus power consumption are close to balance or the power grid fluctuates or the load changes suddenly, the current direction will change rapidly, which will affect the accuracy of the bidirectional metering device. In the general metering scheme, there is only one channel for the accumulation of positive and negative power. When 1 pulse is output in 2s, the pulse counter in the previous 1s has accumulated half. At this moment, switching to reverse current requires first offsetting half of the pulse accumulated in the forward direction, that is, the next pulse will not be issued until 3s after switching, which is the main reason for the error. In the general metering scheme, if the current direction is switched once every 5S, there is generally one pulse in about 2 seconds, and the error is more than -20%. If the switch is performed once every minute, the error is more than 3%; for example, if the power consumption is 10kwh and the power generation is 1kwh, it may become 9kwh of power consumption and 0kwh of power generation. For photovoltaic scenarios, the error is unacceptable. In the present invention, the metering unit accumulates the positive and negative power respectively, and outputs pulses respectively to solve the metering error problem caused by single pulse offset.

[0041] Step 2: Power Quality Analysis

[0042] The harmonic analysis module calculates the effective voltage by performing approximate integration of discrete sampling points on the voltage and current sampling values. Current RMS By performing fast Fourier transform (calling FFT module) on the voltage and current sampling values, the harmonic content is extracted through frequency domain analysis.

[0043] The flicker monitoring module draws on the principle of IEC flicker meter and designs a 0.05Hz~35Hz bandpass filter and a visual sensitivity weighted filter (whose amplitude characteristic curve is close to the visual sensitivity coefficient curve) to capture flicker signals, and then outputs the flicker visual sensitivity S(t) through square summing and low-pass filtering to simulate the human eye's perception of voltage fluctuation flicker.

[0044] Note: The FFT module decomposes the original DFT into multiple small-scale DFTs, uses pipeline technology to perform butterfly operations in parallel, and combines algorithm accelerator units (floating-point unit FPU, trigonometric function accelerator TMU) to improve the processing efficiency of each DFT.

[0045] Step 3: Edge Control Solution

[0046] Data collection and prediction: collect the capacity, output power and load power of the current distributed power generation area in a 5-minute cycle, combine meteorological information and the installed capacity of distributed power generation in the area to predict the output curve, and modify the predicted curve according to the collected output power;

[0047] Data analysis and judgment: determine whether there is a reverse heavy overload based on the current operating data, and execute the current control plan if it exists; determine whether there is a reverse heavy overload in the future period based on the predicted data, and formulate a pre-control plan;

[0048] Formulate a control plan, calculate the current load rate based on the transformer capacity of the substation and the current grid-connected power, and issue a control command when the load rate exceeds 80%. A control cycle is set every 5 minutes to adjust the active output of the distributed power source to achieve the downward adjustment target and suspend control after eliminating reverse heavy overload. According to the predicted photovoltaic output power and the substation's demand, timely revise the control target to reduce the impact of control lag.

[0049] Step 4: Local Control Plan

[0050] Collection task response: the platform collects the electrical parameter information of distributed power sources in real time, responds to the reading tasks of the substation terminals at regular intervals, and uploads data such as voltage, current, power, and power factor;

[0051] Control task response: the platform receives the power control command issued by the substation terminal, sends it to the distributed power supply equipment, and responds to the substation terminal at the same time;

[0052] For the local automatic control solution, according to the photovoltaic capacity and consumption demand of the substation, the terminal dynamically sets the control parameters for each grid-connected point and authorizes the platform to enable the local automatic control function. Generally, when the platform detects that the voltage exceeds the limit by 7% for 30 minutes, exceeds the limit by 10% for 15 minutes, and exceeds the limit by 15% for 15 seconds, it directly issues a control command for flexible adjustment with an adjustment cycle of 1 minute. When the frequency swings by 0.2Hz~1Hz and the voltage swings by 0.1Un~025Un, a rigid control command is issued to the grid-connected switch to cut off the grid-connected circuit.

Claims

1. A monitoring method for the voltage over-limit and harmonic interference problems in photovoltaic areas based on the integrated sensing and computing technology, characterized in that: The details are as follows: Step 1: Build an integrated monitoring platform for sensing and computing. To the bottom: interact with the distributed power supply through RS485 / USB / CAN bus, and to the top: interact with the substation terminal through carrier dual-mode; Step 2: The integrated monitoring platform collects the original frequency data output by the inverter at a high frequency of 12,800 points per second, separates the harmonic components through the hardware FFT module and calculates the corresponding harmonic content; at the same time, voltage swells, sags and fluctuations are monitored and analyzed based on the original frequency data; when harmonics, voltage swells, sags and fluctuations are detected that exceed the error limit, an alarm event is generated, and the event is reported to the substation terminal through the dual-mode communication unit; Step 3: The terminal side of the substation monitors the reverse power of the substation in real time. When the reverse load rate is ≥80%, a fair distribution or step-by-step adjustment strategy is adopted to adjust the active output of the photovoltaic inverter; the fair distribution reduces the active output in proportion to the inverter capacity and the current power output; the step-by-step adjustment strategy is adjusted step by step according to the capacity of the inverter and the current power output; when the photovoltaic grid-connected voltage is high enough that the reactive power regulation reaches the upper limit and the voltage is still over the limit, the terminal selects the photovoltaic grid-connected node PV curve that is similar to the weather on that day, and calculates the active power △Pv to be adjusted according to the current voltage over-limit value until the voltage does not exceed the limit; Step 4: When the substation terminal receives an abnormal power quality event, it reads the event details recorded by the platform and improves the power quality by adjusting the power of the photovoltaic grid-connected point or disconnecting it; Step 5: When the platform is authorized with the local self-control function, when a voltage over-limit event is detected, the local control command is directly issued to the inverter for flexible adjustment, with an adjustment cycle of minutes. When events such as simultaneous frequency and voltage swings occur, a rigid control command is issued to the grid-connected switch to cut off the grid-connected circuit.

2. According to claim 1, a monitoring method for photovoltaic area voltage over-limit and harmonic interference problems based on sensing and computing integrated technology is characterized in that: In the step 1, the core processing unit SoC chip of the sensor-computing integrated monitoring platform adopts a dual-core architecture; The sampling front end selects an external open-type transformer or fixed transformer of the corresponding level according to the capacity of the distributed power supply, reduces the large current to a current that can be accurately measured by the metering unit according to the transformation ratio, and converts the large voltage into a certain proportion of weak voltage through the voltage transformer to meet the input voltage requirement of the metering unit.

3. According to claim 2, a monitoring method for photovoltaic area voltage over-limit and harmonic interference problems based on sensing and computing integrated technology is characterized in that: In step 1, the current and voltage signals are converted into differential voltage signals of the corresponding channels through load resistors so that the measurement unit can perform analog-to-digital conversion to obtain current and voltage digital instantaneous signals, instantaneous power p(t)=v(t)×i(t), and the active power component is obtained by low-pass filtering; the electric energy E=∫P(t)dt is calculated by integrating the instantaneous power, where E is the electric energy, P(t) is the instantaneous power, and t is the time.

4. According to claim 1, a monitoring method for photovoltaic area voltage over-limit and harmonic interference problems based on sensing and computing integrated technology is characterized in that: The step 2 includes a harmonic analysis module and a flicker monitoring module; the harmonic analysis module includes performing discrete sampling point approximate integration of the voltage and current sampling values ​​to calculate the voltage effective Current RMS Frequency domain analysis and extraction by fast Fourier transform of voltage and current sampling values as well as The flicker monitoring module captures flicker signals through a 0.05Hz-35Hz bandpass filter and a visual sensitivity weighted filter, and then outputs flicker visual sensitivity S(t) through squaring and low-pass filtering to simulate the human eye's perception of voltage fluctuation flicker.

5. According to claim 1, a monitoring method for photovoltaic area voltage over-limit and harmonic interference problems based on sensing and computing integrated technology is characterized in that: Step 3 specifically includes: Step 31: Data collection and prediction: collect the capacity, output power and load power of the distributed power source in the current area in a 5-minute cycle, predict the output curve based on the meteorological information and the installed capacity of the distributed power source in the area, and modify the predicted curve according to the collected output power; Step 32: Data analysis and determination: determine whether there is a reverse heavy overload based on the current operating data, and execute the current control plan if there is; determine whether there is a reverse heavy overload in the future period based on the predicted data, and formulate a pre-control plan; Step 33: Formulate a control plan, calculate the current load rate based on the transformer capacity of the substation and the current grid-connected power, and issue a control command when the load rate exceeds 80%. A control cycle is performed every 5 minutes to adjust the active output of the distributed power source to achieve the downward adjustment target and suspend control after eliminating the reverse heavy overload. According to the predicted photovoltaic output power and the substation's demand, the control target is corrected in time to reduce the impact of control lag.

6. The method for monitoring the voltage over-limit and harmonic interference problems in photovoltaic areas based on the integrated sensing and computing technology according to claim 1 is characterized in that: The step 5 specifically comprises the following steps: Step 51: Acquisition task response, the platform collects the electrical parameter information of the distributed power source in real time, responds to the reading task of the substation terminal at a fixed time, and uploads data such as voltage, current, power, and power factor; Step 52: Control task response: the platform receives the power control command issued by the substation terminal, sends it to the distributed power supply device, and responds to the substation terminal at the same time; Step 53: Local automatic control scheme. When the platform is authorized with the local automatic control function, when it is detected that the voltage exceeds the limit by 15% for 30 minutes, exceeds the limit by 20% for 15 minutes, and exceeds the limit by 25% for 15 seconds, a control command is directly issued for flexible adjustment. The adjustment cycle is 1 minute. When the frequency swing is 0.2Hz~1Hz and the voltage swing is 0.1Un~025Un, a rigid control command is issued to the grid-connected switch to cut off the grid-connected circuit.

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