A flexible loop closing topology device applied to a low-voltage distribution network and a control method thereof

Abstract

The application discloses a flexible loop closing topological device applied to a low-voltage power distribution network and a control method thereof, relates to the technical field of power generation, power transformation or power distribution, and comprises a common module and a non-common module. In a 380V low-voltage power distribution network, 24 switch tubes with a voltage resistance value of 800V are needed for a BTB-VSC, and 18 switch tubes with a voltage resistance value of 600V and 6 switch tubes with a voltage resistance value of 450V are needed for the proposed topology, so that the equipment cost is effectively reduced, special control technology is not needed to ensure that the switch tubes on the same side are turned on and turned off at the same time, and the carrier phase-shifted PWM modulation technology is used, so that the equivalent switching frequency is higher, the system harmonic content is less, the filter inductance is smaller, the number of switch tubes through which the current flows is less, and therefore the power transmission efficiency is improved to a certain extent. The common module and the non-common module have multiple schemes and have great development space.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power generation, power transformation or power distribution, in particular to a flexible loop closing topology device applied to a low-voltage power distribution network and a control method thereof. BACKGROUND

[0002] With the transformation of global energy structure, the power system is facing great changes, and more and more distributed power generation units and energy storage devices are equipped in the power system. The structure of the power distribution network system becomes more and more complex, and problems such as voltage crossing, complex power flow, high peak demand, and large feeder voltage drop cause the reduction of power supply reliability and power quality. In order to solve this problem, mechanical switches can be installed between different nodes of the power distribution network to adjust the power flow between the nodes. However, the traditional mechanical switch will produce a large impact current in the moment of closing and opening operation, and cannot flexibly adjust the power flow between different nodes according to the actual working state of the power distribution network, so it is increasingly difficult to meet the intelligent demand of the power distribution network.

[0003] As a flexible power electronic device to replace the traditional mechanical switch, the flexible loop closing device not only can realize and replace the basic functions of the traditional mechanical switch, but also will not produce a large impact current in the loop closing moment, and has auxiliary functions such as continuous power flow adjustment, load balancing, error isolation and fault recovery. Therefore, the flexible loop closing device has gradually become a research hotspot in the field of power distribution network in recent years.

[0004] In the topology of the flexible loop closing device of the low-voltage power distribution network, the Back To Back Voltage Source Converter (BTB-VSC) is currently mostly used. The traditional BTB-VSC topology adopts two converters VSC1 and VSC2 connected back to back through a common DC capacitor, and two switch tubes in series are used on the same side of each phase bridge arm to bear higher voltage stress. This topology has simple control and mature theory, but has the following disadvantages: special control technology is needed to ensure that the switch tubes in series on the same side are turned on and turned off at the same time; the voltage stress borne by the switch tubes is still large, and switch tubes with high voltage resistance value are needed; the number of switch tubes through which the current flows is large, thereby reducing the power transmission efficiency; therefore, the present application provides a flexible loop closing topology device applied to a low-voltage power distribution network and a control method thereof. SUMMARY

[0005] In order to solve the above-mentioned deficiencies in the background art, the purpose of the present application is to provide a flexible loop closing topology device applied to a low-voltage power distribution network and a control method thereof.

[0006] The purpose of the application can be realized by the following technical solutions: A flexible loop topology device applied to a low-voltage distribution network, the flexible loop topology device is respectively connected in star with a first power grid and a second power grid, the flexible loop topology device comprises a common module and a non-common module, the common module is composed of three bridge arms and a direct-current capacitor, the non-common module is composed of two grid-side bridge arms, a multiplex bridge arm and a direct-current capacitor, and the common module and the non-common module together require 24 switching tubes, 4 direct-current capacitors and 2 sets of three-phase filters.

[0007] Further, the midpoints of the two grid-side bridge arms of the non-common module are connected with two distribution network nodes through filters, the AC input line and the AC output line of the three-phase topology are connected in star to the AC power grid, and the midpoint of each phase multiplex bridge arm of the non-common module is connected with the midpoint of the corresponding bridge arm of the common module.

[0008] Further, the first power grid side port of the non-common module and the AC port of the common module jointly support the AC voltage of the first power grid, and the second power grid side port of the non-common module and the AC port of the common module jointly support the AC voltage of the second power grid.

[0009] Further, the common module is responsible for controlling the stability of the direct-current voltage and providing the AC voltage at the AC port thereof, and jointly supports the power grid voltage with the non-common module, and the direct-current voltage of the common module is not equal to the direct-current voltage of the non-common module.

[0010] Further, the non-common module transmits active power to the distribution network node on the other side, and the direct-current side of the common module does not have a load, so only reactive power flows.

[0011] Further, a control method of the flexible loop topology device applied to the low-voltage distribution network, the method comprises:

[0012] The first power grid side bridge arm of the non-common module adopts a voltage-current double closed loop control strategy, the whole control is based on a dq rotating coordinate system, the voltage outer ring controls the stability of the direct-current voltage of the non-common module, the current inner ring controls the sinusoidalization of the first power grid side current, and the generated modulation wave is subtracted from the modulation wave of the common module to serve as the modulation wave of the first grid side bridge arm;

[0013] The second power grid side bridge arm of the non-common module adopts a power-current double closed loop control strategy, the whole control is based on a dq rotating coordinate system, the power outer ring controls the transmission of active and reactive power of the whole device to be constant, and the current inner ring ensures the sinusoidalization of the second power grid side current. The generated modulation wave is subtracted from the modulation wave of the common module to serve as the modulation wave of the second grid side bridge arm;

[0014] The multiplex bridge arm of the non-shared module adopts open-loop control, the modulation amplitude value of the multiplex bridge arm takes the average of the modulation amplitude values of the two grid-side bridge arms, and the phase takes the negative direction of the bisector of the grid voltage vector angle;

[0015] The shared module adopts single voltage loop control.

[0016] The PS-PWM modulation strategy is adopted between the non-shared module and the shared module.

[0017] The present application has the following advantages:

[0018] In the process of use, in the 380V low-voltage power distribution network, the BTB-VSC needs 24 switch tubes with a withstand voltage of 800V, while the topology needs 18 switch tubes with a withstand voltage of 600V and 6 switch tubes with a withstand voltage of 450V, thereby effectively reducing the equipment cost, without the need to use special control technology to ensure that the switch tubes on the same side are turned on and turned off at the same time, and the carrier phase-shifted PWM modulation technology is used, so that the equivalent switching frequency is higher, the system harmonic content is less, the filter inductance is smaller, the number of switch tubes through which the current flows is less, and therefore the power transmission efficiency is improved to a certain extent, the shared module and the non-shared module have multiple schemes, and there is a large development space. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows, and obviously, other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings;

[0020] Figure 1 is a three-phase topology structure diagram of the flexible loop closing device of the shared module of the present application;

[0021] Figure 2 is a three-phase topology structure diagram of the flexible loop closing device of the shared module of the present application;

[0022] Figure 3 is a single-phase topology structure diagram of the flexible loop closing device of the shared module of the present application;

[0023] Figure 4 is a single-phase topology structure diagram of the flexible loop closing device of the shared module of the present application;

[0024] Figure 5 is a control strategy block diagram of the first grid-side bridge arm of the non-shared module of the device of the present application;

[0025] Figure 6 is a control strategy block diagram of the second grid-side bridge arm of the non-shared module of the device of the present application;

[0026] Figure 7The control strategy block diagram of the non-shared module of the device of the application;

[0027] Figure 8 The control strategy block diagram of the shared module of the device of the application;

[0028] Figure 9 The voltage and current waveform diagram of the first grid side of the device of the application;

[0029] Figure 10 The voltage and current waveform diagram of the second grid side of the device of the application;

[0030] Figure 11 The DC voltage waveform diagram of the device of the application;

[0031] Figure 12 The active power and reactive power waveform diagram of the device of the application. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the application.

[0033] As shown in Figure 1 a flexible loop topology device applied to a low-voltage distribution network, comprising a shared module and a non-shared module, the shared module is composed of three bridge arms and a DC capacitor, the non-shared module is composed of two grid-side bridge arms, a multiplexing bridge arm and a DC capacitor, and it needs to be further explained that in the specific implementation process, the shared module and the non-shared module need 24 switching tubes, 4 DC capacitors and 2 sets of three-phase filters in total.

[0034] The midpoints of the two grid-side bridge arms of the non-shared module are connected to two distribution network nodes through filters, and the AC input and output lines of the three-phase topology are connected to the AC power grid in a star connection mode. The midpoint of each phase multiplexing bridge arm of the non-shared module is connected to the midpoint of the corresponding bridge arm of the shared module, and it needs to be further explained that in the specific implementation process, this design is used to share the voltage stress borne by each switching tube.

[0035] It needs to be further explained that in the specific implementation process, the first grid-side port of the non-shared module and the AC port of the shared module jointly support the first grid AC voltage, and the second grid-side port of the non-shared module and the AC port of the shared module jointly support the second grid AC voltage.

[0036] It needs to be further explained that in the specific implementation process, the common module is responsible for controlling the direct current voltage stability, and provides alternating current voltage at its alternating current port, which supports the power grid voltage together with the non-common module, and the direct current voltage of the common module is not equal to that of the non-common module.

[0037] It needs to be further explained that in the specific implementation process, the non-common module transmits active power to the power distribution network node on the other side, and the direct current side of the common module is not loaded, so only reactive power flows through, and the benefit of such design is to improve the operation efficiency of the entire flexible loop device.

[0038] It needs to be further explained that in the specific implementation process, a control method of a flexible loop topology device applied to a low-voltage power distribution network, the method comprises:

[0039] The first grid-side bridge arm of the non-common module adopts a voltage-current double-loop control strategy, and the entire control is based on a dq rotating coordinate system, the voltage outer loop controls the direct current voltage stability of the non-common module, and the current inner loop controls the first grid-side current to be sinusoidal, and the generated modulation wave is subtracted from the modulation wave of the common module to serve as the modulation wave of the first grid-side bridge arm;

[0040] The second grid-side bridge arm of the non-common module adopts a power-current double-loop control strategy, and the entire control is based on a dq rotating coordinate system, the power outer loop controls the transmission of active and reactive power of the entire device to be constant, and the current inner loop ensures the second grid-side current to be sinusoidal. The generated modulation wave is subtracted from the modulation wave of the common module to serve as the modulation wave of the second grid-side bridge arm;

[0041] The multiplexing bridge arm of the non-common module adopts open-loop control, the amplitude of the multiplexing bridge arm modulation wave is the average of the amplitudes of the two grid-side bridge arm modulation waves, and the phase is the negative direction of the bisector of the two grid voltage vector angles;

[0042] The common module adopts single voltage loop control, and the common module is responsible for controlling the current voltage stability thereof;

[0043] The PS-PWM modulation strategy is adopted between the non-common module and the common module, and it needs to be further explained that in the specific implementation process, the benefit of such design is to improve the equivalent switching frequency.

[0044] The following table is the module common flexible loop device parameters under the present example

[0045] Parameter Value Parameter Value First grid voltage u g1 / V]] 380∠0° Non-shared module DC capacitor C dc / mF]]> 20 Second grid voltage u g2 / V]]> 380∠30° Common module DC capacitor C dc / mF]]> 20 Non-shared module DC voltage u dc / V]]> 300 Filter inductance L / mH 0.5 Non-shared module DC voltage u dc / V]]> 200 Transmission power P / kW 250

[0046] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above-mentioned embodiments, and the above-mentioned embodiments and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application.

Claims

1. A flexible loop closing topology device applied to a low voltage distribution network, characterized in that, The flexible closed-loop topology device is respectively connected in star with a first power grid and a second power grid, the flexible closed-loop topology device comprises a common module and a non-common module, the non-common module and the common module are connected in series, the common module is composed of three bridge arms and a direct-current capacitor, the non-common module is composed of two grid-side bridge arms, a multiplex bridge arm and a direct-current capacitor, and 24 switch tubes, 4 direct-current capacitors and 2 sets of three-phase filters are needed in total for the common module and the non-common module; The midpoints of the two grid-side bridge arms of the non-common module are connected with two power grid nodes through filters, the AC input line and the AC output line of the three-phase topology are connected in star mode to the AC power grid, and the midpoint of each phase multiplex bridge arm of the non-common module is connected with the midpoint of the corresponding bridge arm of the common module.

2. The flexible looped topology device for low voltage distribution network according to claim 1, characterized in that, The first power grid side port of the non-common module and the AC port of the common module jointly support the AC voltage of the first power grid, and the second power grid side port of the non-common module and the AC port of the common module jointly support the AC voltage of the second power grid.

3. The flexible looped topology device for low voltage distribution network according to claim 2, characterized in that, The common module is responsible for controlling the stability of the direct-current voltage and providing an AC voltage at the AC port thereof, and supports the grid voltage together with the non-common module, and the direct-current voltage of the common module is not equal to the direct-current voltage of the non-common module.

4. The flexible closed-loop topology device for low voltage distribution network according to claim 3, characterized in that, The non-common module transmits active power to the power grid node on the other side, and the direct-current side of the common module does not have a load, so only reactive power flows.

5. A control method of the flexible loop closing topology device applied to a low-voltage distribution network, using the flexible loop closing topology device applied to a low-voltage distribution network according to any one of claims 1 to 4, characterized in that, The method comprises the following steps: The first power grid side bridge arm of the non-common module adopts a voltage-current double closed-loop control strategy, the entire control is based on a dq rotating coordinate system, the voltage outer ring controls the stability of the direct-current voltage of the non-common module, the current inner ring controls the sinusoidalization of the first power grid side current, and the generated modulation wave is subtracted from the modulation wave of the common module to serve as the modulation wave of the first grid side bridge arm; The second power grid side bridge arm of the non-common module adopts a power-current double closed-loop control strategy, the entire control is based on a dq rotating coordinate system, the power outer ring controls the transmission of active and reactive power of the entire device to be constant, and the current inner ring ensures the sinusoidalization of the second power grid side current; the generated modulation wave is subtracted from the modulation wave of the common module to serve as the modulation wave of the second grid side bridge arm; The multiplex bridge arm of the non-common module adopts open-loop control, the amplitude of the multiplex bridge arm modulation wave is the average of the amplitudes of the modulation waves of the two grid-side bridge arms, and the phase is the negative direction of the bisector of the grid voltage vector angle; The common module adopts single voltage loop control; The non-common module and the common module adopt PS-PWM modulation strategy.

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