Voltage regulation and reactive power compensation device for power distribution network

Abstract

The invention provides a voltage regulation and reactive power compensation device for a power distribution network. The voltage regulation and reactive power compensation device comprises an autotransformer with a tap and a UPFC (Unified Power Flow Controller) regulation device, the primary side of the main transformer is adjusted by adopting a self-coupling transformer and a tap and is used for roughly compensating the voltage of the power grid; a secondary side low-voltage winding of the main transformer is connected into a three-phase rectifier of a UPFC structure, a split capacitor is arranged on the direct current side of the three-phase rectifier, a midpoint N is led out to be connected with a common point of the secondary side winding of the main transformer and grounded, and the output end of a three-phase inverter of the UPFC structure is filtered through an LC filter. The primary side of the auxiliary three-phase transformer is connected in a triangular connection mode, and the secondary side of the auxiliary three-phase transformer is connected in series with the power distribution network and is used for finely compensating the voltage of the power distribution network.

Description

Technical Field

[0001] The present invention relates to the technical field of electrical equipment, and in particular to a voltage regulation and reactive power compensation device for a distribution network. Background Art

[0002] The new distribution network has become a common carrier for the consumption of diversified loads and renewable energy, and there are significant differences in the power flow distribution and regulation methods of the traditional distribution network. Renewable energy and new loads represented by electric vehicles are intermittent and random, which will cause changes in the power flow distribution, voltage, phase, etc. of the distribution network, resulting in large differences between different distribution networks. The traditional solution is to use autotransformers and tap changers to compensate for voltage fluctuations through mechanical gear adjustment, but this regulation method is discrete, lacks precision, and cannot perform reactive power compensation. Summary of the invention

[0003] In order to solve the problem of voltage fluctuation and perform reactive power compensation, the present invention proposes a regulation device based on the combination of an autotransformer and a UPFC (unified power flow controller). Compared with discrete traditional autotransformer regulation, it can not only continuously regulate voltage, but also perform reactive power compensation and assist voltage regulation, so as to achieve the purpose of continuous voltage regulation and reactive power compensation.

[0004] The present invention combines a tapped autotransformer with a small-capacity UPFC regulating device, thereby solving the shortcoming of discrete voltage regulation of a traditional autotransformer, and can both continuously regulate voltage and realize reactive power compensation.

[0005] The primary side of the main transformer adopts auto-coupling and tapping regulation to roughly compensate the grid voltage, which is connected in star shape;

[0006] The secondary low-voltage winding of the main transformer is connected to a three-phase rectifier. A split capacitor is installed on the DC side of the rectifier and the midpoint is connected to the common point of the secondary winding of the main transformer and grounded.

[0007] The output of the three-phase inverter is filtered by an LC filter and connected to the primary side of the auxiliary three-phase transformer in a triangle connection. The secondary side is connected to the grid in series to perform fine compensation for the grid voltage.

[0008] The present invention specifically adopts the following technical solutions:

[0009] A distribution network voltage regulation and reactive power compensation device:

[0010] It includes an autotransformer with taps and a UPFC regulator;

[0011] The primary side of the main transformer adopts autotransformer plus tap adjustment to roughly compensate the grid voltage;

[0012] The secondary low-voltage winding of the main transformer is connected to the three-phase rectifier of the UPFC structure. The DC side of the three-phase rectifier is provided with a split capacitor and the midpoint N is connected to the common point of the secondary winding of the main transformer and grounded. The output end of the three-phase inverter of the UPFC structure is filtered by an LC filter and connected to the primary side of the auxiliary three-phase transformer in a triangle connection. The secondary side of the auxiliary three-phase transformer is connected to the distribution network in series to perform fine compensation for the grid voltage.

[0013] Furthermore, the primary side of the main transformer adopts an autotransformer plus tap adjustment structure and is star-connected.

[0014] Furthermore, the coarse adjustment gear of the autotransformer is provided with 5 positive and negative gears, corresponding to 0, ±1, ±2, ±3, ±4, and the amplitude of the phase voltage adjusted by each gear is the same.

[0015] And, a distribution network voltage regulation method, based on the distribution network voltage regulation and reactive power compensation device described above: when the phase voltage V of the three-phase distribution network at the front end of a given compensation point is a1 、V b1 and V c1 and the phase voltage rating of the three-phase distribution network V ar 、V br and V cr Finally, the device controls the position of the three-phase taps through the controller, thereby achieving continuous voltage regulation.

[0016] When only active power compensation is performed, the device emits or absorbs active power P, and reactive power Q=0.

[0017] When only reactive power compensation is performed, the device sends out a vertical voltage phasor to perform reactive power compensation on the distribution network, and at this time the active power P=0.

[0018] When performing reactive power compensation on the distribution network, the rectifier in the UPFC structure does not work, and only the inverter works.

[0019] And, a distribution network system is connected to a distributed power source and is connected to the distribution network voltage regulation and reactive power compensation device mentioned above.

[0020] Compared with the prior art, the present invention and its preferred embodiment combine the traditional autotransformer with the UPFC power electronic regulator, overcoming the disadvantage of the discrete voltage regulation of the autotransformer. At the same time, it can also compensate for reactive power for the system and improve system efficiency, so that within the same regulation range and capacity, the regulation is more precise (compared with the autotransformer), the equipment cost is lower, and the control and manufacturing are simpler (compared with UPFC). BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0022] Figure 1 A schematic diagram of the topological structure of the device according to an embodiment of the present invention;

[0023] Figure 2 is a control block diagram of a device according to an embodiment of the present invention;

[0024] Figure 3 The phasor diagram of the device according to the embodiment of the present invention when the active power or reactive power is compensated alone;

[0025] Figure 4 The phasor diagram of the device of the embodiment of the present invention performing active and reactive power compensation simultaneously;

[0026] Figure 5 A simple power supply line connected to DG;

[0027] Figure 6 It is the voltage phasor diagram of the connected DG. DETAILED DESCRIPTION

[0028] Hereinafter, the specific embodiments of the present application will be described in detail with reference to the accompanying drawings. According to these detailed descriptions, those skilled in the art can clearly understand the present application and can implement the present application. Without violating the principles of the present application, the features in the various embodiments can be combined to obtain new implementations, or certain features in certain embodiments can be replaced to obtain other preferred implementations.

[0029] In order to make the features and advantages of this patent more obvious and easy to understand, the following embodiments are specifically described in detail with the accompanying drawings as follows:

[0030] The present invention further introduces the topological structure of the device combining the proposed autotransformer and UPFC, the control strategy of the device, and the principle of voltage regulation and reactive power compensation through specific implementation. The present invention combines the traditional autotransformer with the UPFC power electronic regulator, overcomes the disadvantage of the discrete voltage regulation of the autotransformer, and can also compensate for reactive power for the system, improve system efficiency, and make the regulation more accurate (compared with the autotransformer) under the same regulation range and capacity, the equipment cost is lower, and the control and manufacturing are simpler (compared with UPFC).

[0031] like Figure 1As shown, the present invention first provides a circuit structure of a distribution network voltage regulation and reactive power compensation device, wherein the primary side of the main transformer adopts an autotransformer plus tap adjustment method to roughly compensate the grid voltage; the secondary low-voltage winding of the main transformer is connected to a three-phase rectifier, and the DC side of the rectifier is provided with split capacitors C1 and C2, and the midpoint N is connected to the common point of the secondary winding of the main transformer and grounded, the output end of the three-phase inverter is filtered by an LC filter, and connected to the primary side of the auxiliary three-phase transformer in a triangle connection, and its secondary side is connected to the grid in a series connection to finely compensate the grid voltage.

[0032] The calculation method of the above device related parameters is as follows. Assuming the rated voltage is 10kV, the efficiency is not less than 98%, the number of ports is not less than 2, the capacity is 2MW, and the required voltage regulation range is ±20%, then:

[0033] According to the capacity and rated voltage, the effective value of the rated current can be calculated to be 115.5A. Considering the extreme case of a 20% voltage drop, the rated current of the main transformer needs to be increased by 20%, which is 138.6A. The gear of the autotransformer is set to 5 gears (i.e. 0, ±1, ±2, ±3, ±4), and the amplitude of the phase voltage adjusted in each gear is:

[0034]

[0035] The corresponding phase voltage effective value is 288.7V, and the corresponding line voltage effective value is 500V. The voltage amplitude that the series transformer needs to compensate is about 205V (this is calculated based on compensating half of the gear, if it is calculated based on compensating the entire gear, it is 410V), and then the total capacity of the series transformer can be calculated as:

[0036]

[0037] If calculated based on the compensation of the entire gear, the total capacity of the series transformer is 100.4kW. When the ratio of the inverter side winding to the series side winding of the series transformer is 2:1, the rated current effective value of the inverter side winding becomes 57.7A. At this time, the phase voltage and current amplitudes of the inverter output are:

[0038]

[0039] If the entire gear is compensated, the amplitude of the phase voltage and current output by the inverter will be doubled. When the ratio of the inverter side winding of the series transformer to the series side winding is 3:1, the rated current effective value of the inverter side winding becomes 38.5A. At this time, the amplitude of the phase voltage and current output by the inverter are:

[0040]

[0041] exist Figure 2 In, D a ,D b and D c represents the position of the three-phase tap, and V ar 、V br and V cr Represents the phase voltage rating of the three-phase distribution network. The variable V a1 、V b1 and V c1 Represents the phase voltage of the three-phase distribution network in front of the compensation point, V a2 、V b2 and V c2 It represents the phase voltage at the rear end of the compensation point. a1 、i b1 and i c1 Represents the current in the three-phase distribution network before the compensation point.

[0042] Variable v d1 、v q1 、v 01 、i d1 、i q1 and i 01 Represents the components of the phase voltage and current on the d-axis, q-axis, and 0-axis at the front end of the compensation point after Park transformation. Voltage v dc1 、v dc2 and v dcr correspond Figure 1 The voltage of capacitors C1 and C2 and the DC bus reference voltage of the three-phase rectifier. a 、i b and i c represents the AC side current of the three-phase rectifier, and ω0t represents the phase of va1.

[0043] The transformation from abc to dq0 is Park transformation, while the transformation from dq0 to abc is inverse Park transformation. SPWM stands for sinusoidal pulse width modulation. When the phase voltage V of the three-phase distribution network at the front end of the compensation point is given a1 、V b1 and V c1 and the phase voltage rating of the three-phase distribution network V ar 、V br and V cr After that, the system can control the position of the tap through the four controllers G1, G2, G3, and G4, thereby achieving continuous voltage regulation.

[0044] Figure 3This is the phasor diagram when the device only performs active or reactive compensation. When only active compensation is performed, the device emits or absorbs active power P, at which time Q = 0; when only reactive compensation is performed, the device emits a vertical voltage phasor to perform reactive compensation on the system, at which time P = 0. When reactive compensation is performed on the line, the rectifier in the UPFC does not work, only the inverter works. Since there is only reactive exchange, only one side of the capacitor in the device works, which further improves efficiency. Figure 4 It is the phasor diagram when the device performs active and reactive compensation simultaneously, and the system absorbs or emits active power P and reactive power Q.

[0045] In particular, if Figure 5 , Figure 6 As shown in the figure, after the distribution network is connected to the distributed generation (DG), it will change from the original radial network to an active network that interconnects the power supply and the user. Since the distributed generation will output active power and reactive power after being connected, reducing the voltage drop on the line, the voltage offset can be further derived as:

[0046]

[0047] It can also be seen from the above formula that when the system is compensated for reactive power, Thereby further assisting in regulating the voltage.

[0048] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0049] The above is a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

[0050] This patent is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of distribution network voltage regulation and reactive power compensation devices under the inspiration of this patent. All equal changes and modifications made according to the scope of the patent application of the present invention should be covered by this patent.

Claims

1. A distribution network voltage regulation and reactive power compensation device, characterized in that: It includes an autotransformer with taps and a UPFC regulator; The primary side of the main transformer adopts autotransformer plus tap adjustment to roughly compensate the grid voltage; The secondary low-voltage winding of the main transformer is connected to the three-phase rectifier of the UPFC structure. The DC side of the three-phase rectifier is provided with a split capacitor and the midpoint N is connected to the common point of the secondary winding of the main transformer and grounded. The output end of the three-phase inverter of the UPFC structure is filtered by an LC filter and connected to the primary side of the auxiliary three-phase transformer in a triangle connection. The secondary side of the auxiliary three-phase transformer is connected to the distribution network in series to perform fine compensation for the grid voltage.

2. The distribution network voltage regulation and reactive power compensation device according to claim 1, characterized in that: The primary side of the main transformer adopts an autotransformer plus tap adjustment structure and is star-connected.

3. The distribution network voltage regulation and reactive power compensation device according to claim 1, characterized in that: The coarse adjustment gear of the autotransformer is provided with 5 positive and negative gears, corresponding to 0, ±1, ±2, ±3, ±4, and the amplitude of the phase voltage adjusted by each gear is the same.

4. A distribution network voltage regulation method, based on the distribution network voltage regulation and reactive power compensation device according to claim 1, characterized in that: When the phase voltage of the three-phase distribution network in front of the given compensation point is V a1 , V b1 and V c1 and phase voltage ratings of three-phase distribution networks V ar , V br and V cr Finally, the device controls the position of the three-phase taps through the controller, thereby achieving continuous voltage regulation.

5. A method for reactive power compensation in a distribution network, based on the distribution network voltage regulation and reactive power compensation device according to claim 1, characterized in that: When only active power compensation is performed, the device emits or absorbs active power. P , this time no work Q =0.

6. A method for reactive power compensation in a distribution network, based on the distribution network voltage regulation and reactive power compensation device according to claim 1, characterized in that: When only reactive power compensation is performed, the device sends vertical voltage phasors to compensate reactive power of the distribution network. P =0.

7. A method for reactive power compensation in a distribution network, based on the distribution network voltage regulation and reactive power compensation device according to claim 1, characterized in that: When performing reactive power compensation on the distribution network, the rectifier in the UPFC structure does not work, and only the inverter works.

8. A distribution network system, connected to a distributed power source, characterized in that: A distribution network voltage regulation and reactive power compensation device according to claim 1 is connected.

Images