WO2019075703A1

WO2019075703A1 - Mixed power flow control device

Info

Publication number: WO2019075703A1
Application number: PCT/CN2017/106937
Authority: WO
Inventors: 赵国亮; 邓占锋; 陆振纲; 宋洁莹; 尉志勇; 蔡林海; 汤广福; 戴朝波; 于弘洋; 刘海军
Original assignee: 全球能源互联网研究院有限公司; 国家电网公司
Priority date: 2017-10-19
Filing date: 2017-10-19
Publication date: 2019-04-25

Abstract

A mixed power flow control device comprises a reactor unit (101), a capacitor unit (102), a converter (103), and a coupling transformer (104). The reactor unit (101) is serially connected to a first switch and when is connected to the capacitor unit (102) in parallel. The reactor unit (101), the first switch and the converter (103) are sequentially connected and then are connected to a winding on one side of the coupling transformer (104) in parallel, and a winding on the other side of the coupling transformer (104) is connected to an electric transmission line, and a second switch is connected to the winding on the other side in parallel.

Description

Hybrid flow control device

Technical field

The present invention relates to the field of power electronics, and in particular to a hybrid power flow control device.

Background technique

With the vigorous development of power systems, the scale access of new energy sources, the increasingly complex grid structure, and the uneven distribution of power flow have brought new challenges to the safe and stable operation of the power grid. Power supply bottlenecks have appeared in some areas and cannot meet the needs of load development. From the actual situation of the power grid, the uneven distribution of power flow is an important factor that restricts the transmission capacity of the power grid. The method of line compensation through series capacitors is called fixed series compensation, which has the characteristics of simple control and good economy, but the compensation capacity cannot be flexibly adjusted, and the parameter mismatch may cause system oscillation. The conventional controllable series compensator is composed of a reactor, a capacitor and a half-controlled switching device, and can realize the control of the serial-in capacitive reactance, but has the problems of high insulation requirement, high cost, and slow adjustment speed.

It is a realistic and ideal choice to improve the operating conditions of the system and improve the transmission capacity of the grid by adopting the new Flexible AC Current System (FACTS) device. The Unified Power Flow Controller (UPFC) and the Static Synchronous Series Compensator (SSSC) are equivalent to a synchronous AC power supply in the line. When the injected controllable voltage is opposite or the same as the voltage drop on the line reactance, it can function like a series capacitor. Or the role of an inductor. In capacitive compensation, the active power of the line increases with the increase of the injection voltage amplitude; when the inductive compensation, the active power decreases as the injection voltage amplitude increases. Therefore, UPFC and SSSC can be equivalent to capacitive and inductive bidirectional variable impedance capable of quickly controlling line power in the line, and have excellent control performance.

Conventional UPFC and SSSC control functions are flexible and superior, but their use in power systems does not have capacity and price advantages. Conventional capacitors and reactors can be compensated in series as a line, but the flexibility and speed of action cannot meet the requirements of precise adjustment. Need more flexible functional configuration, The fixed series compensation is combined with the converter valve to meet the power flow regulation requirements of the grid.

Summary of the invention

In order to meet the needs of the prior art, the present invention provides a hybrid flow control device.

An embodiment of the present invention provides a hybrid power flow control device, where the hybrid power flow control device includes a reactor unit, a capacitor unit, an inverter, and a coupling transformer;

The reactor unit is connected in series with the first switch and is connected in parallel with the capacitor unit;

The reactor unit, the first switch and the inverter are sequentially connected in parallel with a first side winding of the coupling transformer, and a second side winding of the coupling transformer is connected to a power transmission line, the first A second switch is connected in parallel on the two side windings.

In a first aspect, in the hybrid power flow control device provided by the present invention, the reactance can be continuously adjusted by the thyristor bidirectional switch connected in series with the reactor unit, thereby achieving continuous adjustment of the equivalent capacitive reactance, focusing on steady state control; and the inverter Continuous and fast bi-directional adjustment capability is provided, with a focus on dynamic control. Through the cooperation of the active part and the passive part, the problem that the existing power flow adjusting device cannot be continuously and widely adjusted in a wide range is solved.

In a second aspect, in the hybrid power flow control device provided by the present invention, it can be used in a transmission line or a distribution line to perform capacitive or inductive adjustment, control line current, improve line transmission capacity and system stability level, and reduce The capacity of the voltage source converter reduces the cost of the device.

In a third aspect, in the hybrid power flow control device provided by the present invention, the reactor and the capacitor are connected to the valve side of the coupling transformer to reduce the insulation level of the reactor and the capacitor.

DRAWINGS

1 is a schematic structural view of a hybrid power flow control device according to an embodiment of the present invention;

2 is a schematic structural view of another hybrid type power flow control device according to an embodiment of the present invention;

3 is a schematic structural view of another hybrid type power flow control device according to an embodiment of the present invention;

4 is a schematic structural view of another hybrid type power flow control device according to an embodiment of the present invention;

Wherein: 101: reactor unit; 102: capacitor unit; 103: inverter; 104: coupling transformer.

Detailed ways

In the following, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. It is a partial embodiment of the invention, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts are within the scope of the present invention.

A hybrid power flow control device according to an embodiment of the present invention will be described below with reference to the accompanying drawings.

1 is a schematic structural diagram of a hybrid power flow control device according to an embodiment of the present invention. As shown in the figure, the hybrid power flow control device in this embodiment includes:

Reactor unit 101, capacitor unit 102, inverter unit 103, and coupling transformer 104. among them,

The reactor unit 101 is connected in series with the first switch and in parallel with the capacitor unit 102.

The reactor unit 101, the first switch and the inverter unit 103 are sequentially connected in parallel with one side winding of the coupling transformer 104, and the other side winding of the coupling transformer 104 is connected to the power transmission line, and the other side winding is connected in parallel. Two switches.

In the present embodiment, the reactor unit 101 includes one or more reactors connected to each other. The capacitor unit 102 includes one or more interconnected capacitors. The inverter unit 103 includes one or more inverters connected to each other.

The one side winding may also be referred to as a first side winding, which may be referred to as a second side winding; wherein the first side winding and the second side winding are located on different sides of the coupling transformer The windings are usually the windings on the opposite side. For example, when the first side winding is on the primary side The winding, then the second winding is a winding on the secondary side. Of course, this is only an example, and the specific implementation is not limited to this.

The capacitor unit 102 in the embodiment of the invention comprises a capacitor or a plurality of connected capacitors. At the same time, each capacitor includes an automatic switching switch for disconnecting when the transmission line needs to be connected to the capacitor, and is closed when the capacitor is not required to be connected. When the capacitor unit 102 includes a plurality of capacitors, the capacitors may be connected in series, or may be connected in parallel, or may be a hybrid connection in series and in parallel.

In the embodiment of the invention, the first switch comprises any one of a circuit breaker, an isolating switch and a power electronic switch, and the first switch is used for controlling the input and exit of the reactor unit. When the power electronic switch is a thyristor bidirectional switch, which includes an anti-parallel thyristor, the equivalent impedance of the reactor unit 101 can be adjusted by changing the firing angle of the thyristor, thereby performing capacitive compensation or inductive compensation on the transmission line.

When the firing angle of the thyristor in the thyristor bidirectional switch is changed, the equivalent reactance of the reactor unit 101 is smaller than the equivalent capacitive reactance of the capacitor unit 102, and the unified power flow controller operates in the capacitive compensation mode to capacitively compensate the transmission line.

After changing the firing angle of the thyristor in the thyristor bidirectional switch, the equivalent reactance of the reactor unit 101 is greater than the equivalent capacitive reactance of the capacitor unit 102, and the unified power flow controller operates in an inductive compensation mode to inductively compensate the transmission line.

In the embodiment of the invention, the second switch comprises any one of a circuit breaker, an isolating switch and a power electronic switch or two switches in parallel, and the second switch is used for controlling the input and exit of the coupling transformer. Among them, the two switches in parallel may be a circuit breaker and an isolating switch in parallel, the circuit breaker is connected in parallel with the power electronic switch, and the isolating switch is connected in parallel with the power electronic switch.

In the embodiment of the present invention, the inverter unit 103 includes a two-level inverter, a three-level inverter, a diode clamp type inverter, a flying capacitor type inverter, a modular multi-level converter, and Any one or more of the H-bridge cascaded multilevel converters.

2 is a schematic structural diagram of a preferred hybrid power flow control device according to an embodiment of the present invention. As shown in the figure, in this embodiment, the reactor unit 101 includes a reactor L, and the capacitor unit 102 includes a capacitor C and an inverter. Unit 103 is an inverter VSC and coupling transformer 104 is a coupling transformer Tse. The reactor L is connected in series with the first switch, the capacitor C is connected in parallel across the branch composed of the reactor L and the first switch, and the hybrid branch composed of the reactor L, the first switch and the capacitor C is connected in series with the inverter VSC. Parallel to both ends of one side winding of the coupling transformer Tse, the other side winding of the coupling transformer Tse is connected to the transmission line between the system 1 and the system 2, and a second switch is connected in parallel across the winding.

The hybrid power flow control device includes a capacitive compensation mode and an inductive compensation mode to compensate for different impedances:

First, the capacitive compensation mode

In this embodiment, the capacitive reactance of the capacitor unit 102 is set to Xc, and the equivalent impedance range of the inverter unit 103 is [0 to Zinv], and the compensation range of the hybrid power flow control device in the capacitive compensation mode is capacitive reactance. The vector sum of Xc and the converter impedance Zinv.

In this embodiment, the thyristor firing angle of the first switch can be continuously adjusted, and the impedance of the inverter unit 103 can be adjusted. The inverter unit 103 has a faster response speed, which can be used to enhance system damping and further improve the system. Dynamic response capability. By inputting different capacitor capacities, the capacitive reactance Xc can be obtained, so that the hybrid type flow control device realizes dynamic adjustment while stepwise adjustment, and has a larger dynamic adjustment range.

Second, the inductive compensation mode

In this embodiment, the reactance of the reactor is XL, and the equivalent impedance range of the inverter unit 103 is [0 to Zinv], and the compensation range of the hybrid power flow control device in the inductive compensation mode is the reactance XL and the inverter. The sum of the vectors of the impedance Zinv.

In this embodiment, if the transmission line is faulty, in order to reduce the short-circuit current of the transmission line and reduce the energy absorbed by the arrester, the thyristor in the first switch is controlled to be fully turned on, and at the same time, it can be fast. The impedance value of the inverter unit 103 is adjusted in speed to improve the dynamic response capability of the system. When the dynamic compensation mode is dynamically adjusted to the inductive compensation mode, the maximum inductive compensation of the hybrid power flow control device is -XL-Zinv, and the maximum capacitive compensation is Xc+Zinv.

3 is a schematic structural view of another hybrid power flow control device according to an embodiment of the present invention. As shown in the figure, the reactor unit, the capacitor unit and the inverter unit are in a parallel connection relationship. The unified power flow controller shown in FIG. 3 introduces a third switch above the power flow controller shown in FIG. 2. Wherein the third switch is connected in series with the capacitor unit. In this embodiment, the capacitor unit and the third switch are connected in series to form a first branch; the reactor unit and the first switch form a second branch; the first branch and the second branch Parallel connections.

4 is a schematic structural view of another hybrid power flow control device according to an embodiment of the present invention. As shown in the figure, a reactor unit and a capacitor unit are connected in series to a line, and the inverter unit is connected in series to the line via a coupling transformer.

The working process of the preferred hybrid power flow control device according to the embodiment of the present invention is described below:

1. Hybrid power flow control device is not connected to the system

Before the hybrid power flow control device is connected to the system, the second switch is closed, the inverter unit 103 and the thyristor of the first switch are bidirectionally opened and closed, and the hybrid power flow control device is in a bypass state without any influence on the operating state of the system.

2. Hybrid power flow control device access system

The hybrid power flow control device determines the impedance value to be compensated according to the upper layer scheduling command and the actual operating condition. When the reactance of the long-distance transmission line is large, it is required to operate in the capacitive compensation mode to compensate the reactance of the transmission line and reduce the transmission loss. When the transmission line is overloaded due to short-circuit fault or load increase, parallel line trip, etc., it is necessary to operate in the inductive impedance compensation mode to limit the current amplitude. By adjusting the thyristor firing angle of the thyristor bidirectional switch in the first switch, the hybrid power flow control device operates in a capacitive compensation mode or an inductive compensation mode, and The need for system damping control controls the operation of the inverter unit 103 to improve the dynamic response of the system.

In the embodiment of the present invention, the protection measures of the hybrid power flow control device in the event of system failure or device failure mainly include:

1. When a fault occurs on the system side, for example, when a single-phase ground fault occurs in the line or the line is over-current, in order to protect the hybrid power flow control device, the second switch needs to be closed to exit the operation of the inverter unit 103.

2. When a fault occurs inside the inverter unit 103, it is necessary to lock the switching device trigger pulse of the inverter unit 103, and close the second switch to exit the operation of the inverter unit 103, at this time, the reactor unit 101 and Capacitor unit 102 can still perform capacitive or inductive compensation.

One of ordinary skill in the art can understand that all or part of the process of implementing the foregoing embodiments can be completed by a computer program to instruct related hardware, and the program can be stored in a computer readable storage medium. When executed, the flow of an embodiment of the methods as described above may be included. The storage medium may be a magnetic disk, an optical disk, a read-only memory (Read-Only, ROM), or a random access memory (RAM). At the same time, the present invention does not indicate equipment such as lightning arresters, gaps, etc. for protecting capacitors, coupling transformers, inverters and their switching devices, and does not indicate that these devices are not present when the device is designed and manufactured and the engineering is actually implemented. When the actual project is implemented, there will be many isolation knife gates, circuit breakers, current measuring devices, and voltage measuring devices not shown in the drawings of the present embodiment, and does not indicate that these devices do not exist when the actual implementation of the project.

The hybrid power flow control device in the embodiment of the present invention can be used in a transmission line or a distribution line to perform capacitive or inductive adjustment, improve line transmission capacity, improve system stability level, control line current, and enhance system damping, and solve the problem. The existing unified power flow controller or the static synchronous series compensator can not continuously and extensively adjust the problem in a large range, thereby reducing the device cost.

Another embodiment of the present invention is shown in FIG. 3. The reactor unit, the capacitor unit and the inverter unit are connected in parallel and then connected to one side of the coupling transformer. By adjusting the thyristor in the first switch to open in both directions The off thyristor firing angle adjusts the reactance value of the reactor unit. The automatic switching of the capacitor bank can adjust the capacitance of the capacitor, and the inverter unit can dynamically adjust the impedance. The impedance injected into the system side can be controlled by the equivalent impedance adjustment of the reactor unit, the capacitor unit, and the inverter, thereby achieving dynamic adjustment of a wide range of impedances.

According to another embodiment of the present invention, as shown in FIG. 4, the reactor unit and the capacitor unit are connected in series to the coupling transformer after being connected in series on the system side, and the inverter unit is connected to the line via the coupling transformer. The reactor unit is also connected in parallel with the first switching device, and the capacitor unit is connected in parallel with the second switching device. When the first switching device is turned on and the second switching device is closed, the device operates in an inductive bias state. When the first switching device is closed and the second switching device is open, the device operates in a capacitively biased state. The third switching device and the fourth switching device are used to control whether the coupling transformer and the converter valve are put into operation. The reactor device and the capacitor device are fixedly compensated, and the converter valve is dynamically adjusted to achieve dynamic adjustment of a wide range of impedances. In this embodiment, the fourth switching device includes: a second switch connected to the winding of the other side of the coupling transformer.

In some embodiments, both the reactor unit and the capacitor unit are accessed from the mesh side of the coupling transformer.

In other embodiments, the reactor unit and the capacitor unit are each accessed from a valve side of the coupling transformer.

The coupling transformer is divided into a mesh side and a valve side, the mesh side - one side connected to the grid, and the valve side - connected to one side of the converter valve.

In still other embodiments, the reactor unit is on the mesh side, the capacitor unit is on the valve side, or the reactor unit is on the valve side, and the capacitor unit is on the mesh side.

In some embodiments, when the reactor unit is coupled to the coupling transformer and the capacitor unit is disconnected from the coupling transformer, an inductive offset configuration is formed to inductively compensate the circuit.

In other embodiments, when the reactor unit is disconnected from the coupling transformer and the When the coupling unit of the capacitor unit is connected, a capacitive offset structure is formed to capacitively compensate the circuit.

It should be noted that the case where the inductor and the capacitor are connected in series or in parallel with the inverter is not limited to the structure shown in the embodiment, and any case where a large-scale compensation is realized by increasing or decreasing the inductance and the capacitance is within the scope of the present invention. Inside. It is also within the scope of the invention that the inverter can also be connected to other inverters or energy storage devices.

It is apparent that those skilled in the art can make various modifications and variations to the invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and modifications of the invention

Claims

A hybrid power flow control device, the hybrid power flow control device comprising: a reactor unit, a capacitor unit, an inverter unit, and a coupling transformer;

The reactor unit is connected in series with the first switch and is connected in parallel with the capacitor unit;

The reactor unit, the first switch and the inverter unit are sequentially connected in parallel with a first side winding of the coupling transformer, and a second side winding of the coupling transformer is connected to a power transmission line, A second switch is connected in parallel on the second side winding.
The hybrid flow control device according to claim 1, wherein

The capacitor unit includes: one capacitor or a plurality of connected capacitors;

The capacitor includes: an automatic switching switch;

The automatic switching switch is configured to be turned off when the power transmission line needs to access the capacitor, and is closed when the power transmission line does not need to access the capacitor.
The hybrid flow control device according to claim 1, wherein

The first switch includes: one of a circuit breaker, an isolating switch, and a power electronic switch;

The first switch is configured to control input and exit of the reactor unit;

The second switch includes: one of a circuit breaker, an isolating switch, and a power electronic switch, or any two switches in parallel;

The second switch is configured to control input and exit of the coupling transformer.
The hybrid flow control device according to claim 3, wherein

When the first switch and the second switch comprise the power electronic switch, the power electronic switch is a thyristor bidirectional switch;

The thyristor bidirectional switch includes a thyristor connected in anti-parallel;

The thyristor bidirectional switch of the first switch is further configured to adjust an equivalent impedance of the reactor unit by changing a firing angle of the thyristor.
The hybrid power flow control device according to any one of claims 1 to 4, wherein when the first switch includes a power electronic switch that is a thyristor bidirectional switch, the second switch is turned off, and the thyristor in the thyristor bidirectional switch is changed. The firing angle, thereby capacitively compensating or inductively compensating the transmission line:

After changing the firing angle of the thyristor in the thyristor bidirectional switch, the equivalent reactance of the reactor unit is less than the equivalent capacitive reactance of the capacitor unit, and the hybrid power flow control device operates in a capacitive compensation mode, The transmission line performs capacitive compensation;

After changing the firing angle of the thyristor in the thyristor bidirectional switch, the equivalent reactance of the reactor unit is greater than the equivalent capacitive reactance of the capacitor unit, and the hybrid power flow control device operates in an inductive compensation mode. The transmission line is inductively compensated.
A hybrid power flow control device according to claim 1, wherein said inverter unit comprises: a two-level inverter, a three-level inverter, a diode clamp type inverter, and a fly. Any one or more of a transcapacitive inverter, a modular multilevel converter, and an H-bridge cascaded multilevel converter.
The hybrid flow control device according to claim 1, wherein

Both the reactor unit and the capacitor unit are connected from the mesh side of the coupling transformer.
A hybrid line flow control device according to claim 1;

The reactor unit and the capacitor unit are each connected from a valve side of the coupling transformer.
The hybrid flow control device according to any one of claims 1 to 4 and 6 to 8,

Forming an inductive offset type structure when the reactor unit is connected to the coupling transformer and the capacitor unit is disconnected from the coupling transformer;

A capacitive offset structure is formed when the reactor unit is disconnected from the coupling transformer and the capacitor unit is coupled to the coupling transformer.
The hybrid power flow control device according to any one of claims 1 to 4 and 6 to 8, wherein the capacitor unit and the third switch are connected in series to form a first branch;

The reactor unit forms a second branch with the first switch;

The first branch is connected in parallel with the second branch.