CN101847891A - Method for monitoring distributed power supply network incorporation in distribution network terminal - Google Patents

Abstract

The present invention relates to the technical field of power supply and distribution, and discloses a method for monitoring distributed power grid connection in a distribution network terminal, including the following steps: (a) the distribution network terminal collects distributed power grid connection feeder data; (b) ) The distribution network terminal processes the collected data to obtain the power quality status; (c) processes the grid-connected status of distributed power sources. The beneficial effects of the present invention are: the present invention can separate the distributed power grid-connected system and the power distribution network when the detection of the power quality of the distributed power system occurs, so as to avoid affecting the power distribution network normal operation; at the same time, the distributed power system can be notified of the status, so that the distributed power generation system can deal with it in time.

Description

Method for monitoring distributed power grid connection in distribution network terminal

technical field

The invention relates to the technical field of power supply and distribution, in particular to a method for monitoring distributed power grid connection in a distribution network terminal.

Background technique

The power industry standard DL/T 721-2000 "Distribution Network Automation System Remote Terminal" defines the distribution network automation system remote terminal as: the distribution network automation system remote terminal is used for various distribution network distribution circuits. The general term for equipment such as power remote terminals, distribution transformer remote terminals, and medium-voltage monitoring units (distribution automation and management system sub-stations). The communication channel is used to complete functions such as data collection and remote control. Distributed Generation (DG for short) refers to the economical, efficient and reliable power generation by using small and medium-sized power generation devices distributed near the load. The global energy crisis and environmental crisis make the development and utilization of new energy sources an urgent need. The distributed power generation technology based on the utilization of new energy has also attracted more and more attention. Many countries have introduced preferential policies to encourage the use of distributed power generation. At the same time, with the rapid development of science and technology, the advantages of distributed power generation have gradually emerged, resulting in more and more distributed power sources being integrated into the grid for operation. The impact of grid-connected operation on distribution network operation is becoming more and more serious.

The impact of distributed generation grid connection on the power quality of distribution network mainly includes:

a) Effect on voltage distribution

Although the IEEE 1547 standard clearly stipulates that the distributed power supply is not allowed to actively adjust the voltage of the access point, and stipulates that the voltage fluctuation of the public contact point caused by the DG grid connection should not exceed 5%, but the DG access will inevitably cause related lines and areas. The power flow changes, which affects the steady-state voltage distribution. The results of the simulation study on the load node voltage change after multiple DGs are connected show that the load node voltage change and the distance between the DG connection point and the busbar, the connection capacity, the active and reactive power ratio and the connection mode (centralized connection or Multi-point distributed access) are closely related.

b) Impact on trends

On the one hand, because the DG is controlled by the user, it may start and stop frequently due to its own needs. On the other hand, the wind power system and photovoltaic system may be affected by external weather changes, which may cause the DG output power in a large area to appear in clusters. All of these will cause the load flow of distribution lines to change greatly, making voltage adjustment very difficult and easily causing voltage to exceed the standard. In particular, the cluster phenomenon of DG in a large area will cause large-scale power flow changes, increase the difficulty of system control, and make it difficult to guarantee the quality of power supply. How to control the switching of DGs and avoid the impact of a large number of DGs on the system has become an important issue to ensure the quality of power supply of the system.

c) Influence on power factor

Because DG can control the output reactive power through excitation adjustment or phase shifting device, and the traditional distribution network will also use the method of capacitor switching to track the reactive power change of the system. The grid capacitor switching operation will cause competition for regulation. At the same time, distributed power generation devices such as photovoltaics, wind power generation, and fuel cells, which use power electronic devices as grid-connected interfaces, can quickly follow the load changes of the system and quickly and accurately adjust the reactive power output of the system, but the reactive power capacity is small; and The distribution network performs reactive power compensation through capacitor switching, and the reactive power capacity is large, but the adjustment accuracy is limited. There is a strong complementarity between the two types of reactive power adjustment. If the two types of compensation can be coordinated and controlled, the reactive power compensation effect of the system can be effectively improved and the power quality can be improved.

d) Voltage fluctuation and flicker:

Due to its small capacity and small inertia, DG units in distribution network are easily impacted by load changes. The results of the simulation test show that when the DG unit is forced to adjust the output of the unit following the load change, if the control system of the unit is not adjusted properly, the adjustment amount does not match the change of the actual load, and the amplitude of the voltage at the generator outlet will be very large. Periodic fluctuations are maintained for a long time, and the frequency is between 6 and 7 Hz.

e) Harmonic pollution problem

The DG system, which uses power electronic components such as inverters as the grid-connected interface, will inevitably bring harmonic pollution to the grid. When distributed power is integrated into the grid, distorted current will be injected into the common connection point. The solution to the harmonic problem mainly depends on the development of power electronics technology.

Due to the relatively small capacity of the DG unit, it is easily affected by load changes. Moreover, distributed power generation is an emerging technology, and some control and operation measures are not yet perfect, and are still under development. Therefore, the grid connection of DG units may bring some unstable factors to the power system, the main performance of which is in the power quality. When the DG unit is running in parallel with the power system, the quality of the unit’s power supply to the local AC load and power transmission to the grid should be controlled, and the voltage, fluctuation, frequency, harmonics and power factor should meet the practicability and meet the standards. When there is an over-limit situation that deviates from the standard (voltage sag, instantaneous interruption, etc.), the DG system should be separated from the grid. Due to the lack of detection of the power quality of the distributed power grid-connected operation in the current distribution network system, it will affect the power supply reliability of the distribution network when the distributed power grid-connected operation.

Contents of the invention

In order to solve the problems in the prior art, the present invention provides a method for monitoring the grid-connection of distributed power sources in the distribution network terminal. There is a lack of monitoring of power quality and lack of control over the operation of distributed power sources.

The technical solution adopted by the present invention to solve the existing technical problems is: to design and manufacture a method for monitoring distributed power grid connection in the distribution network terminal, including the following steps, (a) the distribution network terminal collects the distributed power supply grid connection feeder (b) The distribution network terminal processes the collected data to obtain the power quality status; (c) Processes the grid-connected status of distributed power sources.

A further improvement of the present invention is: the step (a) further includes the following steps: (a1) transforming the primary-side high voltage on the grid-connected feeder of the distributed power supply into a secondary-side low voltage through the voltage transformer TV and the current transformer TA Voltage; primary side large current is transformed into secondary side small current; (a2) TV and TA are used in distribution network terminal telemetry module to convert secondary side low voltage and secondary side small current into suitable A/D analog-to-digital conversion circuit The input analog quantity; (a3) A/D analog-to-digital conversion circuit converts the analog quantity into digital quantity, and sends it to the main processing chip of the distribution network terminal telemetry module.

A further improvement of the present invention is: said step (b) further includes: processing the sampling data obtained through A/D analog-to-digital conversion with a corresponding algorithm in the distribution network terminal to obtain parameters; Process to obtain distributed power grid-connected power quality parameters.

A further improvement of the present invention is that: the power quality parameters include at least voltage, fluctuation, frequency, harmonic and power factor; and the parameters include at least voltage and current.

The further improvement of the present invention is: in the step (c), the power quality parameters of the distributed power supply are compared with the standard parameters in the distribution network terminal, and when there is an over-limit situation that deviates from the standard, the distributed power supply is connected to the grid The system is separated from the distribution network.

The further improvement of the present invention is: the secondary side low voltage and secondary side small current can be connected to the distribution network terminal, and the secondary circuit is protected safely.

The further improvement of the present invention is: the A/D analog-to-digital conversion circuit converts the analog quantity into a digital quantity, and sends it to the main processing chip of the distribution network terminal telemetry module, and the A/D analog-to-digital conversion circuit uses the main processing chip to Controls the number of sampling points per cycle.

The further improvement of the present invention is: the main processing chip calculates the corresponding parameters with the corresponding algorithm for the sampled data, and after the algorithm processing, the power quality parameters of the distributed power supply can be obtained.

A further improvement of the present invention is: the distribution network terminal can set standard parameters of power quality by itself.

The beneficial effects of the present invention are: the present invention detects the power quality parameters of the distributed power supply in the distribution network terminal to monitor the method for the grid-connected operation of the distributed power supply system, which overcomes the problems in the existing distributed power supply grid-connected operation process. The network system lacks monitoring of the power quality of the distributed power supply, which affects the reliability of the distribution network operation; through the detection of the power quality of the distributed power system, it is possible to separate the distributed power supply and connect it to the grid when there is an out-of-limit situation that deviates from the standard System and distribution network to avoid affecting the normal operation of the distribution network; at the same time, the distributed power system can be notified of the status, so that the distributed power generation system can deal with it in a timely manner.

Description of drawings

Fig. 1 is a distribution network terminal monitoring distributed power grid connection process of the present invention.

Fig. 2 is a process of collecting power quality parameters of a distributed power supply according to the present invention.

Fig. 3 is a flow chart of processing power quality parameters of distributed power sources by the distribution network terminal of the present invention.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing.

As shown in Figure 1, a method for monitoring distributed power grid-connected in a distribution network terminal includes the following steps: a) The distribution network terminal collects distributed power grid-connected feeder data; b) The distribution network terminal processes the collected data to obtain Power quality status; c process the grid-connected state of distributed power generation. Through the detection of the power quality of the distributed power system, it is possible to separate the distributed power grid-connected system and the power distribution network when there is an out-of-limit situation that deviates from the standard, so as to avoid affecting the normal operation of the power distribution network. At the same time, the distributed power system can be notified of the status, so that the distributed power generation system can deal with it in time.

The step a further includes the following steps: a1 Transform the high voltage on the primary side on the grid-connected feeder of the distributed power supply into a low voltage on the secondary side through the voltage transformer TV and the current transformer TA; convert the high current on the primary side into a low voltage on the secondary side Small current; a2 Use TV and TA in the distribution network terminal telemetry module to convert the secondary side low voltage and secondary side small current into an analog quantity suitable for the input of the A/D analog-to-digital conversion circuit; a3A/D analog-to-digital conversion circuit will The analog quantity is converted into digital quantity and sent to the main processing chip of the distribution network terminal telemetry module.

The step b further includes: processing the sampled data obtained through A/D analog-to-digital conversion with corresponding algorithms in the distribution network terminal to obtain parameters; obtaining the distributed power grid-connected power quality by processing the sampled data in the distribution network terminal parameter.

The power quality parameters include at least voltage, fluctuation, frequency, harmonic and power factor; the parameters include at least voltage and current.

In the step c, the power quality parameters of the distributed power generation are compared with the standard parameters in the distribution network terminal, and when there is an out-of-limit situation deviating from the standard, the distributed power generation grid-connected system is separated from the power distribution network.

The secondary side low voltage and secondary side small current can be connected to the distribution network terminal, and the secondary circuit is protected safely.

The A/D analog-to-digital conversion circuit converts analog quantities into digital quantities and sends them to the main processing chip of the telemetry module of the distribution network terminal, and the A/D analog-to-digital conversion circuit controls the number of weekly wave sampling points through the main processing chip.

The main processing chip uses a corresponding algorithm to calculate corresponding parameters for the sampled data, and after algorithm processing, the power quality parameters of the distributed power supply can be obtained.

The distribution network terminal can set standard parameters of power quality by itself.

In one embodiment of the present invention, the distributed power supply is connected to the medium-voltage power distribution network, and communicates with the power distribution network through GPRS.

Fig. 1 shows a distribution network terminal monitoring method for grid-connected distributed power sources of the present invention; Fig. 2 also shows that the present invention needs to collect operation information of grid-connected feeders of distributed power sources.

Use voltage transformer (TV) and current transformer (TA) to transform the primary side high voltage and primary side high current of distributed power grid-connected feeder into secondary side low voltage and secondary side small current. The low voltage of the secondary side is 220V/100V, and the small current of the secondary side is 5A/1A. TV and TA played the role of isolation and reduce the amplitude. The low voltage on the secondary side and the small current on the secondary side can be connected to the distribution network terminal, and safety protection for the secondary circuit is required. The voltage input circuit adopts a fast-protected air switch, and the current input circuit adopts a special test terminal.

The distribution network terminal uses TV and TA in the telemetry module to transform the secondary-side low voltage and secondary-side small current into analog quantities suitable for A/D input, filter the input signal, and convert the level into 0-+5V The voltage signal is input to the A/D converter.

The main processing chip on the telemetry module determines the number of sampling points in an AC cycle according to the power quality parameters, such as sampling 64 points per cycle to analyze harmonics.

The A/D conversion circuit converts the analog quantity into a digital quantity, and sends it to the main processing chip of the telemetry module of the distribution network terminal, and at the same time controls the number of weekly wave sampling points through the main processing chip.

The main processing chip uses a corresponding algorithm to calculate the corresponding voltage, current and other parameters for the sampled data, and the Fourier algorithm can be used. After the sampling data is processed by the algorithm, the power quality parameters of the distributed power supply can be obtained, including voltage, fluctuation, frequency, harmonic and power factor.

The distribution network terminal must process the collected power quality parameters of the distributed power supply, as shown in Figure 3: the power quality parameters must be compared with the standard. At present, my country has not formulated the power quality standard for distributed power grid connection, so the standard can adopt the power quality standard of general power plant operation in my country, including GB12325-90 power quality power supply voltage allowable deviation; GB12326-2000 power quality voltage fluctuation and flash Change; GB/T14549-93 power quality public grid harmonics; GB/T15543-1995 power quality three-phase voltage allowable unbalance; GB/T15945-1995 power quality power system frequency allowable deviation, etc. The distribution network terminal can also be used as a comparison standard by setting parameters such as voltage, fluctuation, frequency, harmonics and power factor by itself. The distribution network terminal compares the collected power quality parameters of the distributed power supply with the standard. If there is an over-limit situation that deviates from the standard, the distributed power grid-connected system will be separated from the distribution network to ensure the power supply reliability of the distribution network. At the same time, the distributed power generation system is notified through GPRS communication, so that the distributed power generation system can deal with the situation of being separated from the power distribution network in time. By detecting the power quality parameters of the distributed power supply in the distribution network terminal to monitor the grid-connected operation of the distributed power supply system, it can monitor the operation of the distribution network in time and improve the reliability of the operation of the distribution network.

The distribution network terminal can transmit the collected power quality parameters to the main station, coordinate the distribution network capacitor switching compensation and the reactive power adjustment of the distributed power supply through GPRS communication, optimize the power factor control of the system, and improve the power supply quality of the system.

The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it cannot be assumed that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some simple deduction or replacement can be made, which should be regarded as belonging to the protection scope of the present invention.

Claims (9)

1. A method for monitoring distributed power grid-connected in distribution network terminal, is characterized in that, comprises the following steps, (a) distribution network terminal collects distributed power supply grid-connected feeder data; (b) distribution network terminal collects quantity Perform processing to obtain the power quality status; (c) process the grid-connected state of the distributed power generation. 2. The method for monitoring distributed power grid connection in a distribution network terminal according to claim 1, characterized in that: the step (a) further comprises the following steps: (a1) through the voltage transformer TV and the current transformer TA Transform the high voltage on the primary side on the grid-connected feeder of distributed power into low voltage on the secondary side; transform the high current on the primary side into small current on the secondary side; (a2) use TV and TA in the distribution network terminal telemetry module to convert the secondary The low voltage on the side and the small current on the secondary side are converted into an analog quantity suitable for the input of the A/D analog-to-digital conversion circuit; (a3) the A/D analog-to-digital conversion circuit converts the analog quantity into a digital quantity and sends it to the telemetry module of the distribution network terminal main processing chip. 3. The method for monitoring distributed power grid-connected in the distribution network terminal according to claim 1, characterized in that: said step (b) further comprises: processing through the A/D modulus in the distribution network terminal with a corresponding algorithm The converted sampling data is used to obtain parameters; in the distribution network terminal, the distributed power grid-connected power quality parameters are obtained by processing the sampling data. 4. The security protection method of the electric power prepayment system according to claim 3, characterized in that: said power quality parameters include at least voltage, fluctuation, frequency, harmonic and power factor; said parameters include at least voltage and current. 5. The method for monitoring distributed power grid-connected in the distribution network terminal according to claim 1, characterized in that: in the step (c), the power quality parameter and the standard parameter of the distributed power supply in the distribution network terminal For comparison, when there is an out-of-limit situation that deviates from the standard, the distributed generation grid-connected system is separated from the power distribution network. 6. The method for monitoring distributed power grid connection in a distribution network terminal according to claim 2, characterized in that: the secondary side low voltage and secondary side small current can be connected to the distribution network terminal, and The secondary circuit is used for safety protection. 7. The method for monitoring distributed power grid connection in the distribution network terminal according to claim 2, characterized in that: the A/D analog-to-digital conversion circuit converts the analog quantity into a digital quantity, and sends it to the distribution network terminal telemetry module A main processing chip, the A/D analog-to-digital conversion circuit controls the number of sampling points per cycle through the main processing chip. 8. The method for monitoring distributed power grid connection in a distribution network terminal according to claim 7, characterized in that: the main processing chip uses corresponding algorithms to calculate corresponding parameters for the sampled data and can obtain after algorithm processing Power quality parameters of distributed generation. 9. The method for monitoring distributed power grid connection in a distribution network terminal according to claim 1, characterized in that: the distribution network terminal can set standard parameters of power quality by itself.

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