Multi-functional hybrid emergency support device for online ice-melting and power management

Abstract

The application provides a multifunctional hybrid emergency support device for online ice melting and power management, comprising: the device is composed of a multifunctional active device connected to the first end of a line and a grounding transformer connected to the end of the line, the multifunctional active device comprises a first cascaded H-bridge module K 1, first midpoint clamping module D 1, second cascaded H-bridge module K 2, second midpoint clamping module D 2, third cascaded H-bridge module K 3, third midpoint clamping module D 3, fourth cascaded H-bridge module K 4, fourth midpoint clamping module D 4, first DC split capacitor C 1, second DC split capacitor C 2, first filter inductor L 1, second filter inductor L 2. The device is composed of a multifunctional active device and a grounding transformer to form a zero sequence ice melting circuit, which has the advantages of not affecting normal power use of users, high equipment utilization rate and low cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power distribution network online ice melting, in particular to a multifunctional hybrid emergency support device for online ice melting and power management and a line current determination method. BACKGROUND

[0002] With the intensification of global climate change, the power system is subjected to frequent extreme disasters, among which ice and snow disasters can cause a series of serious problems such as tower collapse, ice-covered insulator flashover, conductor dancing and breaking, and further cause tripping and large-area power outage accidents, reducing the reliability of power supply of the power distribution network. However, the current ice melting method of the power distribution network is still mainly manual ice melting, which has problems such as low ice melting efficiency and difficulty in ensuring personal safety. By actively intervening in the ice coating of the conductor, the ice melting technology can significantly improve the power supply reliability under extreme climate events and effectively prevent regional power outages caused by ice and snow disasters, which is a key measure to ensure the safe and stable operation of modern power grids.

[0003] According to whether the user can normally use electricity during ice melting, the ice melting scheme can be divided into online ice melting and offline ice melting. As a widely used ice melting technology, alternating current offline ice melting realizes ice melting by using the short-circuit current heat effect of overhead lines through short-circuit grounding at the end of the line. However, the reactive power demand increases dramatically during ice melting due to the non-negligible reactance of this scheme. In order to solve this problem, the direct current offline ice melting technology is widely used in high-voltage and large-reactance scenarios by using the on-off resistance characteristic of inductance. However, the proportion of ice coating time in the whole year is limited, and the ice melting device is in idle state for a long time, so the flexible regulation and control potential of power electronic equipment is not fully utilized, and the existing offline ice melting scheme cannot guarantee the normal use of electricity of the ice melting line.

[0004] With the unique advantage of parallel functions of line ice melting and power supply, online ice melting technology has attracted widespread attention from domestic and foreign scholars. Considering the zero sequence isolation effect of double-ended distribution transformers in the power distribution network, online ice melting of the power distribution line can be realized by flexibly regulating and controlling the zero sequence current without affecting the power supply of the power grid. The existing online ice melting scheme only works during the ice coating period of the power distribution network, and the utilization rate of the equipment is low. Therefore, online ice melting technology that takes into account equipment cost and utilization efficiency needs to be broken through. SUMMARY

[0005] In order to overcome the above technical defects, the present application provides a multifunctional hybrid emergency support device for online ice melting and power management.

[0006] To achieve the above purpose, the present application is realized according to the following technical scheme:

[0007] In a first aspect, the present application provides a multifunctional hybrid emergency support device for online ice melting and power management, comprising:

[0008] The device is composed of a multifunctional active device connected to the first end of the line and a grounding transformer connected to the last end of the line;

[0009] The multifunctional active device comprises a first cascaded H-bridge module K 1, a first midpoint clamping module D 1, a second cascaded H-bridge module K 2, a second midpoint clamping module D 2, a third cascaded H-bridge module K 3, a third midpoint clamping module D 3, a fourth cascaded H-bridge module K 4, a fourth midpoint clamping module D 4, a first DC split capacitor C 1, a second DC split capacitor C 2, a first filter inductor L 1, a second filter inductor L 2.

[0010] Optionally, the first cascaded H-bridge module K 1, the second cascaded H-bridge module K 2, the third cascaded H-bridge module K 3, and the fourth cascaded H-bridge module K 4 each comprise a plurality of sub-modules connected in series.

[0011] Optionally, the first midpoint clamping module D 1, the second midpoint clamping module D 2, the third midpoint clamping module D 3, and the fourth midpoint clamping module D 4 each have a DC bus positive port connected to the positive end of the first DC split capacitor C 1.

[0012] Optionally, the first midpoint clamping module D 1, the second midpoint clamping module D 2, the third midpoint clamping module D 3, and the fourth midpoint clamping module D 4 each have a DC bus negative port connected to the negative end of the second DC split capacitor C 2, and the negative end of the first DC split capacitor C 1 is connected to the positive end of the second DC split capacitor C 2.

[0013] Optionally, the first midpoint clamping module D 1, the second midpoint clamping module D 2, the third midpoint clamping module D3. the fourth midpoint clamping module D 4 is connected to the midpoint of the first DC split capacitor C 1 and the midpoint of the second DC split capacitor C 2.

[0014] Optionally, the output port of the first midpoint clamping module D 1 is connected to the first cascaded H-bridge module D 2 is connected to the second cascaded H-bridge module D 3, respectively. K 1, the output port of the second cascaded H-bridge module K 2, the output port of the third cascaded H-bridge module K 3.

[0015] Optionally, the output port of the fourth midpoint clamping module D 4 is connected to one end of the first filter inductor L 1, one end of the fourth cascaded H-bridge module K 4 is connected to the other end of the first filter inductor L 1, the other end of the fourth cascaded H-bridge module K 4 is connected to one end of the second filter inductor L 2, the other end of the second filter inductor L 2 is connected to the ground terminal.

[0016] The application has the following beneficial effects:

[0017] The device provided by the application has the advantages of not affecting normal power use of users, high equipment utilization rate, and low cost.

[0018] In addition to the purposes, features and advantages described above, the application has other purposes, features and advantages. The application will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0019] The accompanying drawings, which form a part of the present application, are provided to further understand the present application, and the illustrative embodiments of the present application and their descriptions are used to explain the present application, and do not constitute an improper limitation on the present application. In the drawings:

[0020] Figure 1 is a topological structure schematic diagram of a multifunctional hybrid emergency support device for online ice melting and power management provided by the embodiment of the present application;

[0021] Figure 2 is a reactive power compensation principle schematic diagram of the multifunctional hybrid emergency support device in a reactive power compensation mode.

[0022] Figure 3 This is a schematic diagram of the online ice melting principle of the multifunctional hybrid emergency support device provided by an embodiment of the present application in the online ice melting mode;

[0023] Figure 4 Schematic diagram of an equivalent circuit of the multifunctional hybrid emergency support device provided in an embodiment of the present application in an online ice melting mode. DETAILED DESCRIPTION

[0024] The embodiments of the present application are described in detail below with reference to the accompanying drawings, but the present application can be implemented in many different ways as defined and covered by the claims.

[0025] It should be noted that the terms "first", "second", "third", etc. in the claims, description and drawings of the present application are used to distinguish similar objects and are not used to describe a specific order or sequence. The data used in this way are interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "including", "having" and their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or modules is not necessarily limited to those steps or modules clearly listed, but may include other steps or modules that are not clearly listed or inherent to these processes, methods, products or devices.

[0026] In order to provide a more vivid explanation of the issues raised in the background technology, Figure 1 As shown, this application proposes a multifunctional hybrid emergency support device for online ice melting and power management, including:

[0027] The device consists of a multi-functional active ice-melting device (MAID) connected to the line headend and a grounding transformer (GT) connected to the line end.

[0028] The multifunctional active device includes a first cascaded H-bridge module K 1 (cascaded H-bridge, CHB), first midpoint clamp module D 1 (neutral point clamped, NPC), second cascade H-bridge module K 2. Second midpoint clamp module D 2. The third cascade H-bridge module K 3. Third midpoint clamp module D 3. The fourth cascade H-bridge moduleK 4, fourth midpoint clamping module D 4, first dc split capacitor C 1, second dc split capacitor C 2, first filter inductor L 1, second filter inductor L 2;

[0029] first cascaded h-bridge module K 1, second cascaded h-bridge module K 2, third cascaded h-bridge module K 3, fourth cascaded h-bridge module K 4 each comprise a plurality of sub-modules connected in series;

[0030] first midpoint clamping module D 1, second midpoint clamping module D 2, third midpoint clamping module D 3, fourth midpoint clamping module D 4 positive dc bus ports are connected to the first dc split capacitor C 1 positive end;

[0031] first midpoint clamping module D 1, second midpoint clamping module D 2, third midpoint clamping module D 3, fourth midpoint clamping module D 4 negative dc bus ports are connected to the second dc split capacitor C 2 negative end, the negative end of the first dc split capacitor is connected to the positive end of the second dc split capacitor C 2;

[0032] first midpoint clamping module D 1, second midpoint clamping module D 2, third midpoint clamping module D 3, fourth midpoint clamping module D 4 clamping points are connected to the midpoint of the first dc split capacitor C 1 and the second dc split capacitor C 2;

[0033] first midpoint clamping module D 1, second midpoint clamping module D 2, third midpoint clamping module D 3 output ports are connected to the first cascaded h-bridge module K 1, second cascaded h-bridge module K 2, third cascaded h-bridge module K 3;

[0034] fourth midpoint clamping moduleD The output port of 4 is connected to the first filter inductor L One end of 1, the fourth cascade H-bridge module K One end of 4 is connected to the first filter inductor L The other end of 1, the fourth cascade H-bridge module K The other end of 4 is connected to the second filter inductor L 2, one end of the second filter inductor L The other end of 2 is connected to the ground.

[0035] In order to facilitate Figure 1 To understand it more vividly, Figure 1 To explain in more detail, MAID is composed of a neutral point clamped (NPC) unit and a cascaded H-bridge (CHB) unit in series. The NPC unit is a three-phase four-bridge structure, and each bridge arm consists of a CHB unit. N It is composed of H-bridge units. E x ( x = a, b, c) are the grid phase voltages, U 0 is the neutral point voltage; U x is the bus voltage, U npc is the output voltage of the NPC unit, U chb is the output voltage of the CHB unit, U c is the submodule capacitor voltage of the CHB unit, U dc is the DC side voltage of the NPC unit. I zx is the output current of the three-phase bridge arm of MAID, I z0 is the output current of the fourth bridge arm of MAID. I cx is the line-to-ground leakage current, I lx is the line current, I Lx is the load current, I t0 is the ice-melting current received by the transformer. C N is the NPC unit DC splitting capacitor, C h is the submodule capacitance of the CHB unit, L is the filter inductor, C 0x is the line-to-ground capacitance,r 0x is the line-to-ground resistance, Z x is the line impedance, Z x = R x + jX x wherein R x is the line resistance, X x is the line reactance.

[0036] When the power grid is in normal operation, the MAID provides reactive power support for the power grid; when the distribution line is iced, the MAID cooperates with the GT to realize on-line ice melting by using the zero-sequence ice-melting current, effectively improving the equipment utilization rate of the ice-melting device and the power supply reliability.

[0037] The existing ice-melting scheme mainly generates enough heat according to the Joule theorem to melt the ice on the line. Related research shows that the Joule theorem ice-melting process of the power line should comprehensively consider the influence of many factors such as temperature, wind speed, convection and radiation heat transfer, etc. Therefore, the Burgos-Dorl ice-melting empirical model is generally used:

[0038] (1)

[0039] (2)

[0040] (3)

[0041] In the formula: is the critical ice-melting current (A); is the ice-melting time (h); is the ice thickness (cm); is the resistance of the conductor per unit length at 0℃ ; is the difference between the conductor temperature and the ambient temperature (℃); is the equivalent ice layer conduction thermal resistance (℃·cm / W); is the equivalent thermal resistance of convection and radiation (℃·cm / W); is the ice density, generally taken as 0.9 g / cm 3 ; is the outer diameter of the conductor after icing (cm); is the diameter of the conductor (cm); is the wind speed (m / s); is the thermal conductivity (W / (℃·cm)), in the wet growth icing scene, =2.27×10 -2 .

[0042] According to the above model, when the effective value of the line current is always maintained as the critical ice-melting current , the line ice can be melted.

[0043] Based on the above ice-melting principle and device, a line current determination method in an online ice-melting mode can be simply proposed, according to the foregoing device, comprising:

[0044] Step S201: obtaining a zero sequence equivalent loop corresponding to the device in the online ice-melting mode;

[0045] Firstly, when the device is in the reactive power compensation mode, the three-phase bridge arm of the MAID outputs reactive power, and the fourth bridge arm of the MAID and the GT are not put into operation. By monitoring the reactive power downstream of the grid grid-connected point in real time , the reactive power to be compensated can be calculated. The reactive power compensation principle is shown in Figure 2 .

[0046] When the device is in the online ice-melting mode, the three-phase bridge arm of the MAID provides energy support for the NPC unit DC bus, and the fourth bridge arm and the GT are put into operation. The online ice-melting principle of the device is shown in Figure 3 . Since the distribution transformer generally adopts connection mode, there is no zero sequence current flow path, so the load side line voltage still maintains a symmetrical state, and does not affect the normal power consumption of the load. Since the three-phase bridge arm and the fourth bridge arm current can be independently controlled, the MAID can be equivalent to a controlled current source. At this time, the zero sequence equivalent loop formed by the MAID and the GT in the device can be obtained, as shown in Figure 4 . The distribution network has a ground resistance of and a ground capacitance of .

[0047] Step S202: determining the ice-melting current injected by the multifunctional active device based on the zero sequence equivalent loop;

[0048] After the above zero sequence equivalent loop is determined, under the premise of ignoring the influence of the line on the ground branch, the KCL equation can be written for the connection point as follows:

[0049] (4)

[0050] In the formula, is the output current of the fourth bridge arm of the MAID, is the ice-melting current injected by the multifunctional active device.

[0051] At this time, the ice-melting current injected by the multifunctional active device can be further obtained as ​is expressed as:

[0052] (5)

[0053] The whole line is three-phase symmetrical, and the superposition theorem can be obtained;

[0054] (6)

[0055] Step S203: Obtain the load current of the distribution line;

[0056] At this time, when deicing is performed, the load current of the distribution line also needs to be obtained .

[0057] Step S204: Determine the line current based on the one-third of the injected deicing current and the load current.

[0058] After obtaining the load current of the MAID distribution line , the line current can be determined , which can be expressed as:

[0059] (7)

[0060] Assuming that the total deicing time is , the critical deicing current can be obtained from the Burgos-Dorfler deicing empirical model. When the line current effective value reaches the critical deicing current, the line ice melts within the specified time . During the line deicing mode, the deicing current injected by the MAID fourth bridge arm is assumed to be:

[0061] (8)

[0062] In the formula, is the grid angular frequency.

[0063] Combining formula (7) and formula (8), the line current can be expressed as:

[0064] (9)

[0065] In the formula, is the load current effective value, is the deicing current effective value injected by each phase. is the load power factor, is the phase of the deicing current.

[0066] Based on the above analysis, the device can achieve the effect of line deicing by accurately controlling the output current of the fourth bridge arm to make the line current reach the critical deicing current.

[0067] In summary, the device provided in the application forms a zero sequence ice melting loop by cooperating with the grounding transformer through the MAID, and has the advantages of not affecting normal power use of users, high equipment utilization, and low cost.

[0068] The above merely provides preferred embodiments of the application, but is not for limiting the application. For those skilled in the art, the application can have various modifications and changes. Any modified, equivalent replaced, improved, etc. within the spirit and principle of the application should be included in the protection scope of the application.

Claims

1. A multifunctional hybrid emergency support device for online ice melting and power management, characterized by: include: The device consists of a multifunctional active device connected to the head end of the line and a grounding transformer connected to the end of the line; The multifunctional active device includes a first cascaded H-bridge module K 1. First midpoint clamp module D 1. Second cascade H-bridge module K 2. Second midpoint clamp module D 2. The third cascade H-bridge module K 3. Third midpoint clamp module D 3. The fourth cascade H-bridge module K 4. Fourth midpoint clamp module D 4. First DC split capacitor C 1. Second DC splitting capacitor C 2. First filter inductor L 1. Second filter inductor L 2; The fourth midpoint clamp module D The output port of 4 is connected to the first filter inductor L 1, the fourth cascaded H-bridge module K One end of 4 is connected to the first filter inductor L 1, the other end of the fourth cascaded H-bridge module K The other end of 4 is connected to the second filter inductor L 2, the second filter inductor L The other end of 2 is connected to the ground.

2. The device according to claim 1, characterized in that The first cascaded H-bridge module K 1. The second cascade H-bridge module K 2. The third cascade H-bridge module K 3 and the fourth cascaded H-bridge module K 4 each includes a plurality of submodules connected in series.

3. The device according to claim 1, characterized in that The first midpoint clamp module D 1. The second midpoint clamp module D 2. The third midpoint clamping module D 3. The fourth midpoint clamping module D The DC bus positive terminals of 4 are connected to the first DC splitting capacitor C 1's positive terminal.

4. The device according to claim 1, characterized in that The first midpoint clamp module D 1. The second midpoint clamp module D 2. The third midpoint clamping module D 3. The fourth midpoint clamping module D The negative terminals of the DC busbars 4 are connected to the second DC splitting capacitors C 2, the negative terminal of the first DC splitting capacitor C 1 is connected to the negative terminal of the second DC splitting capacitor C 2's positive terminal.

5. The device according to claim 1, characterized in that The first midpoint clamp module D 1. The second midpoint clamp module D 2. The third midpoint clamping module D 3. The fourth midpoint clamping module D The clamp midpoints of 4 are connected to the first DC splitting capacitor C 1 and the second DC splitting capacitor C At the midpoint of 2.

6. The device according to claim 1, characterized in that The first midpoint clamp module D 1. The second midpoint clamp module D 2. The third midpoint clamping module D The output ports of 3 are respectively connected to the first cascade H-bridge module K 1. The second cascade H-bridge module K 2. The third cascade H-bridge module K 3.

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