CN111245029B - Cooperative processing method for micro power source fault control and micro power grid protection - Google Patents

Cooperative processing method for micro power source fault control and micro power grid protection Download PDF

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CN111245029B
CN111245029B CN202010043729.2A CN202010043729A CN111245029B CN 111245029 B CN111245029 B CN 111245029B CN 202010043729 A CN202010043729 A CN 202010043729A CN 111245029 B CN111245029 B CN 111245029B
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牟龙华
张鑫
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Tongji University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/48—Controlling the sharing of the in-phase component
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/50—Controlling the sharing of the out-of-phase component

Abstract

The invention relates to a cooperative processing method for micro-power source fault control and micro-grid protection, wherein a micro-power source comprises a prime motor, an inverter and a filter, the filter is connected with a micro-grid, the micro-power source is divided into a main micro-power source and a slave micro-power source, the method carries out fault control by stages by constructing a main micro-power source control system and a slave micro-power source control system, and the main micro-power source control system and the slave micro-power source control system are respectively connected with corresponding inverters, and the method comprises the following steps: first phase of fault control: keeping the network access current of the micro power supply consistent with the current before the fault, and completing fault positioning through the micro power grid protection device; second phase of fault control: and a low voltage ride through fault control strategy is adopted to realize the support of the voltage and the power of the microgrid. Compared with the prior art, the method and the device realize the cooperative processing of the micro-power source fault control and the micro-grid protection, can identify the micro-grid fault lines with different topologies and different operation modes, and have the advantages of stability, reliability and the like.

Description

Cooperative processing method for micro power source fault control and micro power grid protection
Technical Field
The invention relates to the technical field of micro-grids, in particular to a micro-power source fault control and micro-grid protection cooperative processing method.
Background
The microgrid is an effective utilization form of distributed energy, is a future development trend of a power system, and has an important position in aspects of sustainable development, comprehensive utilization of energy and the like. The development of the micro-grid technology provides a wide prospect for the application of distributed power generation, a small power network integrating regional power generation, transmission, distribution and transmission is formed by a distributed power source and a load, and the problem of long-distance transmission energy loss of a large power grid is effectively solved.
With the continuous and deep research of micro-grids, related protection and control technologies have become major barriers limiting the development of micro-grids. Compared with the traditional large power grid, the micro power grid has new requirements for protection configuration due to the characteristics of a more flexible operation mode, a lower voltage level, a smaller power distribution network and the like. Under the influence of factors such as a micro-grid operation mode, a topological structure, inverter type micro-power failure characteristics and the like, the traditional protection method for the power distribution network cannot be completely adapted, the failure region cannot be quickly and selectively cut off from the micro-grid, and the failure-free region is ensured to recover to normal operation. Therefore, the research on the micro-grid protection and control technology has important theoretical value and practical significance.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a cooperative processing method for micro-power source fault control and micro-grid protection.
The purpose of the invention can be realized by the following technical scheme:
a cooperative processing method of micro-power source fault control and micro-grid protection, wherein the micro-power source comprises a prime mover, an inverter and a filter, the filter is connected with the micro-grid, the micro-power source is divided into a master micro-power source and a slave micro-power source, the method carries out fault control in stages by constructing a master micro-power source control system and a slave micro-power source control system, and the master micro-power source control system and the slave micro-power source control system are respectively connected with the corresponding inverters, and the method comprises the following steps:
first phase of fault control: keeping the network access current of the micro power supply consistent with the current before the fault, and completing fault positioning through a micro power grid protection device;
second phase of fault control: the voltage and power of the microgrid are supported by a low-voltage ride-through fault control strategy;
the network access current is the current accessed to the microgrid.
Furthermore, the filter is connected with a capacitance branch, the main micro-power control system comprises a current controller and a compensation capacitance current calculation circuit, the compensation capacitance current calculation circuit is connected with the current controller, the current controller is connected with the inverter, and the compensation capacitance current calculation circuit is used for compensating branch currents of the capacitance branch.
Further, the low voltage ride through fault control strategy specifically includes:
switching a main micro power control system to a voltage control mode for limiting the output current of the inverter and supporting the voltage of a grid-connected point;
and switching the micro power source control system to a current control mode for maintaining the active power and the reactive power output by the inverter constant.
For a micro-power source with a booster station, a grid-connected point is a high-voltage side bus or node of the micro-power source booster station; for a micro power supply without a booster station, a grid-connected point is an output summary point of the micro power supply.
Further, the main micro-power source control system comprises a voltage reference signal calculation circuit and a voltage controller which are sequentially connected, and the voltage control mode of the main micro-power source control system is specifically that a grid-connected point voltage reference required in a low voltage ride-through period is generated through the voltage reference signal calculation circuit, so that a reference value of the voltage controller is set, and voltage control is realized.
Further, the current control mode of the slave micro-power control system is specifically that the slave micro-power control system performs current reference signal calculation by extracting positive and negative sequence components of the grid-connected point voltage, so as to perform current control and provide power support for a power grid.
Further, the main micro power source control system comprises a voltage controller, a current controller, a switching control circuit, a current holding circuit before fault and a voltage reference signal calculation circuit, wherein the switching control circuit is respectively connected with the voltage controller and the current controller.
Further, in order to avoid the inverter output voltage oscillation caused by the drastic change of the output current at the switching moment, the main micro power source control system adopts a controller state following method to realize the transition from the first stage of fault control to the second stage of fault control.
Further, the master micro-power source control system and the slave micro-power source control system perform fault control by changing the modulation factor of pulse width modulation.
Further, the expression of the fault current output from the micro power source is as follows:
Figure BDA0002368640950000031
in the formula iref.dIs a d-axis component, i, of a reference current output from a micro-power source control systemref.qTo be driven from microQ-axis component of reference current output from the source control system, theta is phase angle of fault current output from the micro power source, PrefFor active power reference output from micro-power source, QrefFor reference value of reactive power output from micro-power source, u+For positive sequence component of grid-connected point voltage, k is 1 to output active power first, k is 0 to output reactive power first, PoutIs the average value of active power output from a micro power supply, QoutIs the average value of reactive power output from a micro power source, IlimFor maximum allowable current value of inverter, iq.fReactive current, i, output from a micro-power source in the event of a faultd.fIs the active current output from the micro power supply in the fault.
Compared with the prior art, the invention has the following advantages:
(1) according to the invention, by adjusting the fault control strategy of the micro power supply, the fault equivalent model of the micro power supply is changed, the micro grid fault equivalent additional network is simplified, and the micro grid fault lines with different topologies and different operation modes can be identified by the protection device without complex fault calculation.
(2) According to the micro-power source fault control method, a staged fault control strategy is adopted, a fault line can be accurately positioned in the first stage, a low-voltage ride-through strategy can be flexibly selected in the second stage, micro-grid protection and voltage frequency support are considered, and cooperative processing of micro-power source fault control and micro-grid protection is achieved.
(3) The main micro power control system adopts a controller state following method, can avoid the output voltage oscillation of the inverter caused by the violent change of the output current at the switching moment, and improves the reliability of the method.
(4) According to the invention, the amplitude part of the fault current is limited to exceed the maximum allowable current value of the inverter, so that the power device of the inverter is protected from being damaged, and the reliability of the method is improved.
Drawings
FIG. 1 is a schematic diagram of a general configuration of a micro power supply;
FIG. 2 is a schematic structural diagram of a primary micro-power control system according to the present invention;
FIG. 3 is a schematic diagram of a phased fault control strategy of the present invention;
FIG. 4 is a schematic diagram of a switching control circuit in the primary micro-power control system according to the present invention;
FIG. 5 is a schematic diagram of a slave micro-power control system according to the present invention.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.
Example 1
As shown in fig. 3, the present embodiment provides a cooperative processing method for micro-power source fault control and micro-grid protection, which takes a master micro-power source and a slave micro-power source in a micro-grid as control objects, and performs fault control in stages by constructing a master micro-power source control system and a slave micro-power source control system, where the cooperative processing method of the present embodiment includes the following steps:
(1) when the micro-grid fails, the micro-power source adopts a staged fault control strategy, a fault line is accurately positioned in the first stage, and a low-voltage ride-through control strategy is flexibly selected in the second stage.
(2) In the first stage of fault control, the network access current of the micro power supply is kept consistent with the current before the fault, and the control system works in a current control mode for 2 periods. At this stage, the micro power source generates a specific fault characteristic, and the micro grid protection device completes fault location.
(3) And in the second stage of fault control, the micro power source adopts a fault control strategy of low voltage ride through, wherein:
the U/f-DG (main micro power supply) control system works in a voltage control mode. At this stage, the control targets of the U/f-DG are the limitation of the output current of the inverter and the support of the grid-connected point voltage; the voltage reference signal calculation module generates a grid-connected point voltage reference required in a low voltage ride-through period, and realizes the stable control of the grid-connected point voltage by setting the reference value of the voltage controller;
the PQ-DG (from the micro-power supply) control system operates in a current control mode. In this phase, the control goal of the PQ-DG is to ensure that the active power and the reactive power output by the inverter are constant; and current reference signal calculation is carried out by extracting positive and negative sequence components of the voltage of the grid-connected point, so that power support is provided for a power grid.
Each part is described in detail below.
1. Micro-grid
The micro-grid related to the embodiment can work in an island operation mode and a grid connection operation mode. When the micro-grid isolated island operates, the micro-grid adopts a master-slave control strategy, wherein a main micro-power source adopts a constant-voltage constant-frequency control strategy (U/f control), and the micro-power source is called as U/f-DG for short and mainly provides voltage and frequency support for the micro-grid; a constant power control strategy (PQ control) is adopted from a micro power source, and the micro power source is called PQ-DG for short and is used as a main power source of a micro power grid. When the micro-grid is connected to the power grid, all micro-power supplies are controlled by PQ and supply power to loads together with an external power grid.
As shown in fig. 1, the general structure of the micro power supply to which the method of the present embodiment is applied mainly includes a prime mover, an inverter, a filter, and the like. The U/f-DG and PQ-DG micro-power sources are connected with a micro-grid through an internal LCL filter, and are connected with a grid side inductor L through a filter capacitor CoThe high-frequency component of the output current i of the inverter is shunted, and the high-frequency switching harmonic generated by the inverter is attenuated. To suppress LCL resonance, a resistor r is connected in series with the filter capacitor branchd. I in FIG. 1oRepresenting the network access current of the micro power supply; i. u represents the inverter output current and the grid-connected point voltage; u. ofcRepresenting the node voltage of the filter capacitive branch. The control system of the micro power supply can realize a corresponding control strategy according to the measurement of the signals.
2. Main micro power source control system and fault control method thereof
The U/f-DG control system is shown in FIG. 2. When the micro-grid operates normally, the voltage reference signal urefControlling the node voltage of the capacitor branch of the filter, adopting PI double closed loop control of an inductive current inner loop and a capacitor voltage outer loop to change the modulation coefficient p of Pulse Width Modulation (PWM)mIs realized byAnd adjusting the voltage of the mesh point.
Since the current controller uses the inverter side inductance current i as the control quantity, the network access current i cannot be directly controlledoIn this embodiment, a method of capacitance current compensation is adopted, and branch current of a capacitance branch is compensated in a control quantity, so that a current reference signal i is directly tracked by network access currentref. The compensation capacitance current is calculated by detecting the node voltage of the capacitance branch, divided by the total impedance of the filter capacitance branch:
Figure BDA0002368640950000051
where ω is the angular frequency of the inverter output.
When the micro-grid fails, the U/f-DG adopts a staged fault control strategy, as shown in FIG. 3. In the first stage of fault control, the network-in current of U/f-DG is kept and the current i before faultholdIn agreement, the control system operates in current control mode for 2 cycles. In the stage, the U/f-DG micro power supply generates specific fault characteristics, and the micro grid protection device finishes fault positioning. And in the second stage of fault control, the U/f-DG adopts a fault control strategy of low voltage ride through, and the control system works in a voltage control mode. In this stage, the control targets of the U/f-DG mainly comprise the limitation of the output current of the inverter and the support of the grid-connected point voltage. The voltage reference signal calculation module generates a grid-connected point voltage reference required in a low voltage ride-through period, and the stable control of the grid-connected point voltage is realized by setting a reference value of the voltage controller.
Because the control modes of the U/f-DG control system in the two stages are different, in order to avoid the output voltage oscillation of the inverter caused by the violent change of the output current at the switching moment, the U/f-DG adopts a controller state following method to realize the smooth transition of the control modes in the two stages.
As shown in FIG. 4, which is a block diagram of the switching controller, when the U/f-DG operates normally, the switch K is turned on1 Connecting contact 2, switch K2The contact 4 is connected, and the control system works in a voltage source mode of double closed-loop control. Fault ofFirst stage of control, switch K1 Connecting contact 1, switch K2 Connecting contact 3, the control system works in a single current loop current source mode, and the output signal of the voltage controller tracks irefAnd the reference signal of the current controller at the switching moment is ensured to have no jump phenomenon. Second stage of fault control, switch K1 Connecting contact 2, switch K2The contact 4, U/f-DG, is connected for low voltage ride through control.
3. Slave micro power source control system and fault control method thereof
When the micro-grid operates normally, the PQ-DG only outputs positive sequence active power and reactive power. When a fault occurs in the microgrid, the PQ-DG control system also employs a staged fault control strategy as shown in fig. 3, with a switching control system as shown in fig. 5. In FIG. 5, u+Representing the positive-sequence component, u, of the voltage of the grid-connection point-A negative sequence component of the dot-connected point voltage is represented. In the first phase of the fault control, the switch K is connected to the contact 2, and the network-in current of PQ-DG is kept equal to the current i before the faultholdThe consistency is achieved; in the second stage of fault control, the PQ-DG control system continues to work in a current control mode, and in the stage, the PQ-DG control aim is to ensure that the active power and the reactive power output by the inverter are kept constant; the switch K is connected with the contact 1, and current reference signal calculation is carried out by extracting positive and negative sequence components of the voltage of the grid-connected point, so that power support is provided for a power grid.
According to the instantaneous power theory, under a synchronous rotating coordinate system, the d axis is oriented to a grid-connected voltage positive sequence component rotating vector. Average value P of active and reactive power output by PQ-DGout、QoutCan be expressed as:
Figure BDA0002368640950000061
in the formula iref.d、iref.qRepresenting the d and q-axis components of the current reference signal, respectively. To improve the output characteristics of PQ-DG, which outputs only positive sequence power during low voltage ride through, the fault current it outputs can be expressed as:
Figure BDA0002368640950000062
in the formula, Pref、QrefRespectively representing the reference values of active power and reactive power output by the PQ-DG; k is 1 to indicate active power priority output, and k is 0 to indicate reactive power priority output; θ represents the phase angle of the output fault current. In order to ensure that the inverter power device is not damaged, the amplitude of the fault current must not exceed the maximum allowable current value I of the inverterlim(typically 2-3 times the rated value).
According to the method, the fault equivalent model of the micro power supply is changed by adjusting the fault control strategy of the U/f-DG and PQ-DG micro power supplies, the fault equivalent additional network of the micro power supply is simplified, and fault lines of any fault type of the micro power supply with different topologies and different operation modes can be identified by the protection device without complex fault calculation. Because the micro power supply adopts a staged fault control strategy, a fault line can be accurately positioned in the first stage, and a low-voltage ride-through strategy can be flexibly selected in the second stage. The micro-grid protection and voltage frequency support are considered, and linkage processing of micro-power failure control and micro-grid protection can be achieved.
The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.

Claims (6)

1. A cooperative processing method of micro-power source fault control and micro-grid protection, wherein the micro-power source comprises a prime mover, an inverter and a filter, the filter is connected with the micro-grid, the micro-power source is divided into a master micro-power source and a slave micro-power source, and the method carries out fault control in stages by constructing a master micro-power source control system and a slave micro-power source control system, and the master micro-power source control system and the slave micro-power source control system are respectively connected with the corresponding inverter, and the method comprises the following steps:
first phase of fault control: keeping the network access current of the micro power supply consistent with the current before the fault, and completing fault positioning through a micro power grid protection device;
second phase of fault control: the voltage and power of the microgrid are supported by a low-voltage ride-through fault control strategy;
the low voltage ride through fault control strategy specifically comprises the following steps:
switching a main micro power control system to a voltage control mode for limiting the output current of the inverter and supporting the voltage of a grid-connected point;
switching a slave micro-power control system to a current control mode for maintaining the active power and the reactive power output by the inverter constant;
the current control mode is specifically that the slave micro-power control system performs current reference signal calculation by extracting positive and negative sequence components of the voltage of the grid-connected point, so as to perform current control and provide power support for a power grid;
the computational expression of the current reference signal is as follows:
Figure FDA0002959843310000011
in the formula iref.dIs the d-axis component, i, of the current reference signalref.qIs the q-axis component of the current reference signal, theta is the phase angle of the fault current output from the micro-power supply, PrefFor active power reference output from micro-power source, QrefFor reference value of reactive power output from micro-power source, u+For positive sequence component of grid-connected point voltage, k is 1 to output active power first, k is 0 to output reactive power first, PoutIs the average value of active power output from a micro power supply, QoutIs the average value of reactive power output from a micro power source, IlimFor maximum allowable current value of inverter, iq.fReactive current, i, output from a micro-power source in the event of a faultd.fIs the active current output from the micro power supply in the fault.
2. The cooperative processing method for micro power supply fault control and micro grid protection as claimed in claim 1, wherein the filter is connected to a capacitive branch, the main micro power supply control system comprises a current controller and a compensation capacitive current calculation circuit, the compensation capacitive current calculation circuit is connected to the current controller, the current controller is connected to the inverter, and the compensation capacitive current calculation circuit is used for compensating branch currents of the capacitive branch.
3. The cooperative processing method for micro-power source fault control and micro-grid protection as claimed in claim 1, wherein the main micro-power source control system comprises a voltage reference signal calculation circuit and a voltage controller connected in sequence, and the voltage control mode of the main micro-power source control system is specifically that the voltage reference signal calculation circuit generates a grid-connected point voltage reference required during a low voltage ride through period, so as to set a reference value of the voltage controller, thereby realizing voltage control.
4. The cooperative processing method for micro-power source fault control and micro-grid protection as claimed in claim 1, wherein the main micro-power source control system comprises a voltage controller, a current controller, a switching control circuit, a pre-fault current holding circuit and a voltage reference signal calculation circuit, and the switching control circuit is respectively connected with the voltage controller and the current controller.
5. The cooperative processing method for micro-power source fault control and micro-grid protection as claimed in claim 4, wherein the primary micro-power source control system adopts a controller state following method to implement the transition from the first stage of fault control to the second stage of fault control.
6. The cooperative processing method for micro-power source fault control and micro-grid protection as claimed in claim 1, wherein the master micro-power source control system and the slave micro-power source control system perform fault control by changing modulation factor of pulse width modulation.
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