CN114720765A - A Harmonic Algorithm and Control System for Active Distribution Network Based on Situational Awareness - Google Patents

Abstract

The invention relates to the technical field of active power distribution, in particular to a situation perception-based harmonic algorithm of an active power distribution network and a control system thereof. The algorithm comprises the following steps: acquiring a current sampling value and a voltage sampling value by performing alternating current sampling from a power distribution network; respectively constructing a current sampling value and a voltage sampling value into complex sequences; performing discrete Fourier transform on the complex sequence, and obtaining an electrical parameter formula, a frequency spectrum formula of voltage and a frequency spectrum formula of current according to the complex conjugate property of the discrete Fourier transform; respectively calculating the harmonic content of the voltage and the harmonic content of the current through a frequency spectrum formula of the voltage and a frequency spectrum formula of the current; and calculating basic electrical parameters in the power distribution network through an electrical parameter formula. The invention aims to solve the problems that the waveform in a power distribution network is distorted due to the fact that the harmonic change in the power distribution network cannot be timely and accurately measured, and the problems of management evaluation, prediction planning, operation control and fault diagnosis in the power distribution network cannot be effectively solved.

Description

A Harmonic Algorithm and Control System for Active Distribution Network Based on Situational Awareness

technical field

The invention relates to the technical field of active power distribution, in particular to a harmonic algorithm of an active power distribution network based on situational awareness and a control system thereof.

Background technique

Active distribution network is a form of smart grid. The adoption of active distribution network technology helps to make full use of clean energy and renewable energy in various places. The situational awareness of active distribution network is obtained in the large-scale system environment of the power grid. A technology that processes, mines and analyzes the data that causes changes in the power grid operation situation, and presents the results in a visual way. Through situational awareness, the overall and accurate control of the operation situation of the active distribution network can be achieved, which provides a strong support for intelligent management and control based on situational awareness to improve the dispatching control level of complex active distribution networks.

With the continuous increase in the penetration rate of distributed generation (DG), energy storage system (ESS), capacitor banks (CB) and other equipment at the distribution network level, it has also caused Voltage fluctuations and bidirectional power flow.

At present, relying on training samples provided by big data technology, intelligent algorithms represented by genetic algorithms and artificial neural network algorithms have been widely used in the field of active power distribution systems.

However, with the development of the national economy, a large number of nonlinear and impact loads are connected to the power grid, and harmonics, voltage fluctuations and flicker are generated during operation, resulting in distortion of the grid voltage waveform, three-phase imbalance, and reduced power supply quality. Affect the safety and economic operation of the power grid and user equipment. The active distribution system is essentially a nonlinear dynamic system, it is difficult to establish an accurate mathematical model to solve quickly, and it cannot measure the changes of harmonics in the distribution system in a timely and accurate manner, so it cannot effectively solve the management evaluation in the distribution network. , predictive planning, operational control and troubleshooting problems.

SUMMARY OF THE INVENTION

Aiming at the shortcomings of the prior art, the present invention proposes a harmonic algorithm and a control system for an active distribution network based on situational awareness, so as to solve the problem that the changes of harmonics in the distribution network cannot be measured in a timely and accurate manner, causing the distribution of power distribution problems. The waveform in the network is distorted, which cannot effectively solve the problems of management evaluation, prediction planning, operation control and fault diagnosis in the distribution network.

In order to achieve the above object, the present invention adopts the following technical scheme: a harmonic algorithm of an active distribution network based on situational awareness, comprising the following steps:

Obtain the sampled value of current and the sampled value of voltage through AC sampling from the distribution network;

Constructing the sampled value of the current and the sampled value of the voltage as a complex sequence respectively;

The complex sequence is subjected to discrete Fourier transform, and according to the complex conjugate property of the discrete Fourier transform, an electrical parameter formula, a voltage spectrum formula and a current spectrum formula are obtained;

Calculate the harmonic content of voltage and the harmonic content of current through the spectral formula of voltage and the spectral formula of current respectively;

The basic electrical parameters in the distribution network are calculated through the electrical parameter formula.

When the above technical solution is adopted, a complex sequence is constructed by acquiring the current sampling value and the voltage sampling value from the distribution network, and then the discrete Fourier transform is performed and the complex sequence is obtained by acquiring the current sampling value and the voltage sampling value. Conjugate properties, so that the fundamental wave and harmonic content in the voltage and current can be obtained through the spectrum formula. At the same time, the basic electrical parameters such as voltage, current, active and reactive power of the equipment in the distribution network can be calculated according to the electrical parameter formula. , so that the changes of harmonics in the distribution network can be measured quickly and accurately.

Preferably, the calculation of the basic electrical parameter formula, the voltage spectrum formula and the current spectrum formula are all performed by a computer.

Preferably, the voltage spectrum formula and the current spectrum formula are:

Among them, K=0, 1, 2, ..., N-1 is the number of sampling times; N is the number of sampling per cycle.

Preferably, the electrical parameter formula is:

Preferably, the specific derivation steps of the discrete Fourier transform are:

The voltage and current with periodic signals collected in the distribution network can be expressed as the following formula:

Decompose equations (1) and (2) according to the Fourier series:

or

Among them, A ₀ is the DC component, which is the average value in one cycle of the periodic function f(t), and A _n and B _n are the coefficients of the Fourier series, which are the rectangular coordinate components of the n-th harmonic.

It is obtained that the nth harmonic vector is:

C_n∠φ_n＝A_n+jB_n；

C _n ∠φ _n =A _n +jB _n ;

After discretization, the following formula is obtained:

In the formula, n=0,1,2,...,N-1 is the harmonic order, K=0,1,2,...,N-1 is the sampling number;

f _k is the Kth sampling value, and N is the number of samples per cycle;

According to the digital signal processing formula:

From equations (5), (6) and (7), the discrete Fourier transform (DFT) can be expressed as:

The present invention also provides an intelligent management and control system according to the above harmonic algorithm of an active distribution network based on situational awareness, including an analog-digital circuit, a digital-analog circuit, an optoelectronic isolation circuit, a DSP chip and an FPGA chip;

The analog-to-digital circuit is used to convert the collected analog signal of voltage or current into a digital signal, and the digital-to-analog circuit converts the digital signal output by the DSP chip into an analog signal;

The optoelectronic isolation circuit is used for optoelectronic isolation of the received signal;

The output end of the digital-analog circuit is electrically connected to the input end of the DSP chip, and the DSP chip is provided with a harmonic algorithm of the active distribution network based on situational awareness, which is used for calculation and processing of AC sampling and power parameters, and Detection, control and communication of load equipment;

The output end of the FPGA chip is electrically connected to the input end of the DSP chip, the input end of the FPGA chip is electrically connected to the output end of the optoelectronic isolation circuit, and the FPGA chip is used for fusion processing of several received signals.

When the above technical solution is adopted, the input signal of the power line in the distribution network is sampled by the analog-to-digital circuit, the converted digital signal is sent to the DSP chip, and the calculation is realized by the harmonic algorithm of the active distribution network, and the distribution network is obtained. Data such as voltage, current, active and reactive power, and electrical energy of equipment operation. At the same time, the origin signal, the limit signal and the switch signal of the switch signal are separated by the photoelectric coupling of the photoelectric isolation circuit, and sent to the FPGA chip for fusion processing, and then sent to the DSP chip, so that the DSP chip can obtain the remote signal status of the distribution network. , displacement recording, pulse power measurement, etc., and through DSP chip remote control to automatically or manually realize fault segment isolation and network reconstruction, so as to reduce the scope of power outages and improve the reliability of power supply. Thereby improving the reliability and anti-interference ability of distribution network regulation.

Preferably, it also includes RAM, Flash, an encryption circuit and a voltage regulator circuit, and the RAM, Flash, encryption circuit and voltage regulator circuit are all electrically connected to the DSP chip, and the DSP chip is further provided with a communication interface, and the communication The interface includes Ethernet interface, CAN bus interface, RS-232 serial port, human-machine interface interface and PCI interface.

Preferably, it also includes a level conversion circuit and a pulse width modulation circuit. Both the level conversion circuit and the pulse width modulation circuit are electrically connected to the DSP chip. The level conversion circuit is used for level conversion of pulse signals. The modulation circuit is used for modulation of the PWM signal.

Preferably, the input end of the optoelectronic isolation circuit is electrically connected with an I/O device, and the output end of the optoelectronic isolation circuit is connected to the input end of the I/O device through an amplifying circuit.

Compared with the prior art, the beneficial effects of this solution are:

Through the settings of the DSP chip and the FPGA chip, the FPGA chip reduces the processing burden of the DSP chip by merging and processing various signals; thus, the DSP chip can realize the harmonic algorithm of the active distribution network based on situational awareness. The power line input signal in the power line is quickly processed, and the DSP chip is used to achieve fault segment isolation and network reconstruction, so as to reduce the scope of power outages and improve the reliability of power supply, so as to effectively solve the management evaluation, prediction planning, and operation control in the distribution network. and troubleshooting.

Description of drawings

In order to describe the specific embodiments of the present invention more clearly, the accompanying drawings required for the specific embodiments will be briefly introduced below. In all the drawings, elements or sections are not necessarily drawn to actual scale.

Fig. 1 is a flow chart of a control system of an active distribution network based on situational awareness of the present invention;

FIG. 2 is a flow chart of a DSP chip in an active distribution network control system based on situational awareness of the present invention.

Detailed ways

Embodiments of the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings. The following examples are only used to more clearly illustrate the technical solutions of the present invention, and are therefore only used as examples, and cannot be used to limit the protection scope of the present invention.

A harmonic algorithm for an active distribution network based on situational awareness includes the following steps:

Step 1: Obtain the sampled value of current and the sampled value of voltage by performing AC sampling from the distribution network.

Step 2: Construct the sampled value of the current and the sampled value of the voltage as complex sequences respectively.

In this embodiment, 32-point current {i(n)} sampled values and 32-point voltage {u(n)} sampled values collected from AC sampling in the distribution network construct a complex sequence respectively.

Step 3: Perform discrete Fourier transform on the complex sequence, and obtain basic electrical parameter formula, voltage spectrum formula and current spectrum formula according to the complex conjugate property of discrete Fourier transform.

The voltage harmonics and the current harmonics are respectively calculated by the voltage spectrum formula and the current spectrum formula.

The basic electrical parameters in the distribution network are calculated through the basic electrical parameter formula.

In this embodiment, the specific derivation steps of discrete Fourier transform (DFT) are:

The voltage and current with periodic signals collected in the distribution network can be expressed as the following formula:

Decompose equations (1) and (2) according to the Fourier series:

or

Among them, A ₀ is the DC component, which is the average value in one cycle of the periodic function f(t), and A _n and B _n are the coefficients of the Fourier series, which are the rectangular coordinate components of the n-th harmonic.

It is obtained that the nth harmonic vector is:

C_n∠φ_n＝A_n+jB_n；

C _n ∠φ _n =A _n +jB _n ;

After discretization, the following formula is obtained:

In the formula, n=0,1,2,...,N-1 is the harmonic order, K=0,1,2,...,N-1 is the sampling number;

f _k is the Kth sampling value, and N is the number of samples per cycle;

According to the digital signal processing formula:

From equations (5), (6) and (7), the discrete Fourier transform (DFT) can be expressed as:

In this step, the voltage spectrum formula and the current spectrum formula are:

The electrical parameter formula is:

Completing the calculation of various electric parameters through the electric parameter formula, the effective value and power factor of each item are obtained.

In the above technical solution, a complex sequence is constructed by acquiring the sampling value of current and the sampling value of voltage from the distribution network, and then performing discrete Fourier transform and according to the complex sequence. The fundamental wave and harmonic content in the voltage and current can be obtained through the spectrum formula. At the same time, the basic electrical parameters such as voltage, current, active and reactive power of the equipment in the distribution network can be calculated according to the electrical parameter formula. Thus, the change of harmonics in the distribution network can be measured quickly and accurately.

The present invention also provides the above intelligent management and control system based on the harmonic algorithm of the active distribution network based on situational awareness, including analog-digital circuit, digital-analog circuit, optoelectronic isolation circuit, DSP chip, FPGA chip, RAM, Flash, encryption circuit, voltage regulator circuit, level conversion circuit and pulse width modulation circuit.

In this embodiment, the DSP chip adopts TMS320F2812 of TI Company.

Specifically, the analog-to-digital circuit is used to convert the collected analog signal of voltage or current into a digital signal, and the digital-to-analog circuit converts the digital signal output by the DSP chip into an analog signal.

Optical isolation circuit is used to optically isolate the received signal.

The output end of the digital-analog circuit is electrically connected to the input end of the DSP chip. The DSP chip is equipped with a harmonic algorithm of the active distribution network based on situational awareness, which is used for AC sampling and calculation and processing of power parameters, and for load equipment. Detection, control and communication.

The output end of the FPGA chip is electrically connected to the input end of the DSP chip, the input end of the FPGA chip is electrically connected to the output end of the optoelectronic isolation circuit, and the FPGA chip is used for fusion processing of several received signals. In this embodiment, the FPGA chip is used to fuse the switch signal, the origin signal and the limit signal obtained in the power distribution network. The FPGA chip provides a real-time clock and saves important information of the system through memory, reducing the burden on the DSP chip.

Among them, RAM, Flash, encryption circuit and voltage stabilizer circuit are all electrically connected to the DSP chip. The DSP chip is connected to a communication interface, a human-machine interface interface and a PCI interface. The communication interface includes an Ethernet interface, a CAN bus interface, and an RS-232 serial port. . In order to facilitate the electrical connection with the power supply through the voltage stabilizing circuit, a stable power supply can be provided to the DSP chip. The interaction of the man-machine interface is carried out through the man-machine interface interface, and the communication connection with the PC is carried out through the PCI interface.

At the same time, the level conversion circuit and the pulse width modulation circuit are both electrically connected with the DSP chip, the level conversion circuit is used for level conversion of the pulse signal, and the pulse width modulation circuit is used for the modulation of the PWM signal.

The input end of the photoelectric isolation circuit is electrically connected with the I/O device, and the output end of the photoelectric isolation circuit is connected with the input end of the I/O device through the amplifier circuit.

The working principle is: input signal through the power line in the distribution network, through the voltage transformer PT, the current transformer CT becomes a lower voltage signal, after filtering and signal conditioning, it is sent to the analog-digital circuit of the DSP chip for AD sampling, After the DSP chip obtains the sampled digital signal, it uses the synchrophasor measurement (PMU) algorithm and the harmonic algorithm of the active distribution network to calculate, and obtains data such as voltage, current, active and reactive power, and electric quantity of equipment operation.

The switch state or the pulse output of the origin signal or limit signal generated by the electronic watt-hour meter through the position sensor enters the FPGA chip through the photoelectric isolation circuit, and then sends it to the DSP chip for collection (remote signal input), and the DSP chip obtains the remote signal status, Displacement recording, pulse electrical quantity, etc.

Human-computer interaction is carried out through the human-machine interface interface projection keyboard, LED display and light-emitting diode. The command after human-computer interaction can drive the opening and closing operation of the output relay control switch through the photoelectric isolation circuit, and execute remote control or local protection control at the same time.

Through the setting of the DSP chip and the FPGA chip, the invention has powerful fast signal processing ability, can improve reliability and anti-interference ability, and can realize various complex fast algorithms. It can realize the timely and accurate measurement of harmonic changes in order to monitor the quality of the power grid. At the same time, the use of DSP chips can reduce the scope of power outages and improve the reliability of power supply by realizing fault segment isolation and network reconstruction, thereby effectively solving the management evaluation, prediction planning, operation control and fault diagnosis in the distribution network.

The above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that the foregoing embodiments can still be used for The recorded technical solutions are modified, or some or all of the technical features thereof are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and should be included in the The invention is within the scope of the claims and description.

Claims (9)

1. A situation awareness-based harmonic algorithm of an active power distribution network is characterized by comprising the following steps:

acquiring a current sampling value and a voltage sampling value by performing alternating current sampling from a power distribution network;

respectively constructing the sampling values of the current and the voltage into complex sequences;

performing discrete Fourier transform on the complex sequence, and obtaining an electrical parameter formula, a frequency spectrum formula of voltage and a frequency spectrum formula of current according to the complex conjugation property of the discrete Fourier transform;

respectively calculating the harmonic content of the voltage and the harmonic content of the current through a frequency spectrum formula of the voltage and a frequency spectrum formula of the current;

and calculating basic electrical parameters in the power distribution network through an electrical parameter formula.

2. The situation awareness-based harmonic algorithm for the active power distribution network according to claim 1, wherein the basic electrical parameter formula, the voltage spectrum formula and the current spectrum formula are calculated by a computer.

3. The situation awareness-based harmonic algorithm for the active power distribution network according to claim 1, wherein the voltage spectrum formula and the current spectrum formula are as follows:

wherein, K is 0,1,2, …, N-1 is sampling times; n is the number of samples per cycle.

4. The situational awareness-based harmonic algorithm for an active power distribution network according to claim 1, wherein the electrical parameter formula is:

5. the situation awareness-based harmonic algorithm for the active power distribution network according to claim 4, wherein the discrete Fourier transform is derived by the following steps:

collecting voltage and current with periodic signals in a power distribution network can be expressed as follows:

decomposing the equations (1) and (2) according to a Fourier series:

or

Wherein A is₀Is a direct current component and is the average value of a periodic function f (t) in one period, A_nAnd B_nThe coefficients, which are fourier series, are rectangular components of the nth harmonic.

To obtain: the nth harmonic vector is:

C_n∠φ_n＝A_n+jB_n；

after dispersion, the following formula is obtained:

wherein N is 0,1,2, …, N-1 is the harmonic order, K is 0,1,2, …, N-1 is the sampling order; f. of_kThe value of the sample at the K-th time,n is the sampling number of each cycle;

according to the digital signal processing formula:

as can be seen from equations (5), (6) and (7), the Discrete Fourier Transform (DFT) is expressed as:

6. an intelligent management and control system for a situation awareness-based harmonic algorithm of an active power distribution network according to any one of claims 1 to 5, comprising an analog-digital circuit, a digital-analog circuit, a photoelectric isolation circuit, a DSP chip and an FPGA chip;

the analog-digital circuit is used for converting the analog signal of the acquired voltage or current into a digital signal, and the digital-analog circuit is used for converting the digital signal output by the DSP chip into an analog signal;

the photoelectric isolation circuit is used for carrying out photoelectric isolation on the received signals;

the output end of the digital-to-analog circuit is electrically connected with the input end of the DSP chip, and a harmonic algorithm and a synchronous phasor measurement algorithm of an active power distribution network are arranged in the DSP chip and are used for alternating current sampling, calculation and processing of power parameters and detection, control and communication of load equipment;

the output end of the FPGA chip is electrically connected with the input end of the DSP chip, the input end of the FPGA chip is electrically connected with the output end of the photoelectric isolation circuit, and the FPGA chip is used for fusing a plurality of received signals.

7. The situation awareness-based intelligent management and control system for the active power distribution network according to claim 6, further comprising a RAM, a Flash, an encryption circuit and a voltage stabilizing circuit, wherein the RAM, the Flash, the encryption circuit and the voltage stabilizing circuit are all electrically connected with the DSP chip, the DSP chip is in communication connection with a communication interface, a human-computer interface and a PCI interface, and the communication interface comprises an Ethernet interface, a CAN bus interface and an RS-232 serial port.

8. The situation awareness-based intelligent management and control system for the active power distribution network according to claim 7, further comprising a level conversion circuit and a pulse width modulation circuit, wherein the level conversion circuit and the pulse width modulation circuit are both electrically connected to the DSP chip, the level conversion circuit is used for level conversion of pulse signals, and the pulse width modulation circuit is used for modulation of PWM signals.

9. The situation awareness-based intelligent management and control system for the active power distribution network according to claim 6, wherein an input end of the photoelectric isolation circuit is electrically connected with an I/O device, and an output end of the photoelectric isolation circuit is connected with an input end of the I/O device through an amplification circuit.

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