Novel alternating-current and direct-current complementary hybrid power electronic transformer

Abstract

The invention discloses a novel alternating current and direct current mutual aid hybrid power electronic transformer which comprises a transformer box body, a power module box body and an auxiliary circuit box body, and a transformer winding, a current transformer and a BCT terminal box are arranged in the transformer box body; the auxiliary circuit box body comprises a power distribution unit, a lightning protection unit, a bypass protection unit and a maintenance assembly unit. The power module box body comprises an AC / DC module and a DC / AC module. The transformer is compact in overall design and is more suitable for a double-pole cross arm installation mode in a transformer area, and the construction difficulty is reduced; and in the alternating current and direct current mutual assistance mode, flexible power mutual assistance between an alternating current power grid and a direct current power grid is achieved, meanwhile, the output voltage qualification rate under different input voltage conditions can be met, and continuous online adjustment is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of smart grids, and in particular to a novel AC / DC hybrid power electronic transformer. Background Art

[0002] Traditional distribution substations generally include 10kV / 0.4kV distribution transformers and JP cabinets or branch boxes. Distribution transformers are generally equipped with taps to meet the low-voltage output voltage under different input voltage conditions to meet the substation usage requirements, but the adjustment between different taps requires power outages for adjustment, and the full-caliber voltage qualification rate cannot be met for different substation load types, affecting the user's electricity experience. The JP cabinet or branch box contains substation metering, branch switches, and reactive power compensation configurations. The JP cabinet or branch box is placed and installed separately from the distribution transformer, which requires a large installation space and is difficult to construct.

[0003] At the same time, the power of the traditional low-voltage AC distribution network can only flow in one direction, and the output from the transformer is a radial power supply mode. The power transmission line of this power supply mode is generally within 2km, and the line impedance cannot be ignored. The active and reactive power changes all the time, affecting the voltage amplitude at various points of the line. The impedance at the end of the distribution network line is the largest. When the end is overloaded during peak power consumption, it is easy to cause the low voltage at the end of the line to exceed the limit. When there are a large number of distributed power sources at the end, it is easy to cause the high voltage at the end of the line to exceed the limit. At the same time, due to the rise of the new energy industry, the coverage rate of distributed power sources has increased year by year, and the randomness of distributed power generation has increased, causing the line voltage to fluctuate violently, affecting the stability and reliability of the power supply system.

[0004] In view of the above problems, the existing technical solutions generally include: 1) Add a voltage regulator separately in the distribution area (at the head end or in the middle and back end of the line), including a traditional on-load voltage regulator or a power electronic voltage regulator, to solve the problem that the existing distribution transformer cannot be energized for gear adjustment. This solution may have problems such as lack of installation space and difficulty in installation at the head end of the area, and can only be used as a transitional solution; 2) Adopt cross-station flexible DC interconnection system, which installs bidirectional converters on the transformer side of two stations and connects their DC busbars, through which port interconnection can be realized to achieve power control, and corresponding DC loads can be connected to DC-LINK. This system is a full-power topology with large system capacity and high loss.

[0005] Therefore, how to solve the above technical problems is the research direction that technicians in this field are committed to. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a new AC / DC hybrid power electronic transformer to solve the problem that the current distribution station area does not have online voltage regulation to meet the full-caliber voltage qualification rate and to meet the access of the DC microgrid system under the new power system, thereby realizing AC / DC power mutual assistance and increasing the utilization rate of new energy.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a new AC / DC hybrid power electronic transformer, including a transformer box, a power module box and an auxiliary line box, The transformer box is provided with a transformer winding, a current transformer and a BCT terminal box. The transformer winding is divided into a low-voltage winding and a high-voltage winding. The low-voltage winding includes a first winding and a second winding. The first winding interface is connected to the power supply line; the second winding is an adjustable winding connected to the auxiliary line box; the current transformer is used to sample the current of the low-voltage winding in real time, and is connected to the outside through the BCT terminal box; The auxiliary line box includes a power distribution unit, a lightning protection unit, a bypass protection unit and a maintenance component unit, wherein: The power distribution unit includes a power module box input side circuit breaker QF1 and a DC side circuit breaker QF3, and the power distribution unit is used to provide a DC port to the outside; The lightning protection unit includes a miniature circuit breaker QF2 and a surge protector FB1. The lightning protection unit is used for input surge protection. One end of the surge protector FB1 is connected to one end of the miniature circuit breaker QF2, and the other end is grounded. The other end of the miniature circuit breaker QF2 is connected to one end of the circuit breaker QF1 on the input side of the power module box. The bypass protection unit includes a miniature circuit breaker QF4, an anti-parallel thyristor assembly SCR and an AC contactor KM1. The miniature circuit breaker QF4 is connected in series with the anti-parallel thyristor assembly SCR, and the miniature circuit breaker QF4 is connected in parallel with the AC contactor KM1. The bypass protection unit is used for transient switching and protection when the main circuit in the power module box is running and the shutdown transformer is bypassing. The maintenance component unit includes a double-cut isolating switch QS1, which is used to short-circuit the second winding and form a maintenance breakpoint when the power module box is overhauled; The power module box includes an AC / DC module and a DC / AC module; The DC side circuit breaker QF3 is a 2P circuit breaker. The positive and negative poles of the AC / DC module and the DC / AC module are connected respectively and then connected in parallel to one end of the DC side circuit breaker QF3. The other end of the DC side circuit breaker QF3 provides an external DC interface. The DC interface is set on the auxiliary line box and is used to connect to external devices. The input A / B / C / N terminals of the AC / DC module are connected to the circuit breaker QF1 on the input side of the power module box and then connected to the output side of the first winding; The output A / B / C terminal of the DC / AC module is connected to one end of the second winding.

[0008] As a specific implementation, the second winding is a series coupled winding.

[0009] As a specific implementation manner, the power module box and the auxiliary line box are respectively arranged on the left and right sides of the transformer box.

[0010] As a specific implementation, the transformer has the following working modes: 1) AC / DC mutual assistance mode: the circuit breaker QF1, miniature circuit breaker QF2, DC side circuit breaker QF3, miniature circuit breaker QF4, and double-cut disconnector QS1 on the input side of the power module box are all in the closed state, and the AC contactor KM1 is in the open state. At this time, the power module box receives the dispatching instruction to work, the AC / DC module works normally for voltage regulation, and the DC / AC module outputs according to the received power instruction signal, adjusts the amplitude and phase of its output voltage, and realizes continuous and precise power regulation. At this time, the DC side circuit breaker QF3 is connected to an external device at the external DC port; 2) Bypass operation mode: The circuit breaker QF1, miniature circuit breaker QF2, miniature circuit breaker QF4, double-cut disconnector QS1 and AC contactor KM1 on the input side of the power module box are all in the closed state, and the DC side circuit breaker QF3 is in the open state. At this time, the AC / DC module is working normally, and the DC / AC module is in the shutdown state; 3) Main circuit voltage regulation operation mode: The circuit breaker QF1, miniature circuit breaker QF2, miniature circuit breaker QF4, and double-cut isolating switch QS1 on the input side of the power module box are all in the closed state, and the AC contactor KM1 and the DC side circuit breaker QF3 are in the open state. At this time, the AC / DC module works normally, and the DC / AC module makes real-time judgments by detecting the grid voltage data and adjusts the overall port output voltage to meet the output voltage qualification rate under different input voltage conditions, realizing continuous online adjustment; 4) Maintenance mode: The circuit breaker QF1, miniature circuit breaker QF2, double-cut isolating switch QS1, and AC contactor KM1 on the input side of the power module box are all in the disconnected state, and the DC side circuit breaker QF3 and miniature circuit breaker QF4 are in the closed state. At this time, the power module box is powered off, and the AC / DC module, DC / AC module, AC contactor KM1 and anti-parallel thyristor assembly SCR are inspected and maintained.

[0011] As a specific implementation method, among the multiple transformer sections, transformers in each two adjacent transformer sections are interconnected via a DC interface.

[0012] As a specific implementation method, among multiple transformer sections, the AC sides of the transformers in every two adjacent transformer sections are interconnected.

[0013] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art: 1) The transformer in the present invention adopts a transformer box and a power module box and an auxiliary line box on the left and right sides thereof. The overall design is compact and more suitable for the double-pole cross-arm installation mode in the station area, reducing the difficulty of construction; 2) The transformer structure of the present invention can be connected to a DC load or photovoltaic MMPT / energy storage device through the DC side circuit breaker QF3 in the AC / DC mutual assistance mode to achieve flexible power mutual assistance between the AC grid and the DC grid; in the main line operation mode, the DC / AC module makes a real-time judgment based on the detected grid voltage data and adjusts the overall port output voltage to meet the output voltage qualification rate under different input voltage conditions, thereby achieving continuous online adjustment; 3) The transformer structure of the present invention is equipped with a DC port to realize AC / DC mixed supply, meet various application scenarios of current new energy microgrids, solve the problem of unstable DC side voltage during peak and valley periods of new energy power generation, and solve the problem of short-term power outages during line maintenance and supply transfer. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A topological diagram of the novel AC / DC hybrid power electronic transformer described in the present invention; Figure 2 A top view of the appearance design of the novel AC / DC hybrid power electronic transformer described in the present invention; Figure 3 It is a topological diagram of AC-DC-AC power mutual assistance among multiple intervals; Figure 4 It is a topological diagram of AC and DC power mutual assistance among multiple intervals; Among them: 1. Transformer box; 2. Power module box; 3. Auxiliary line box. DETAILED DESCRIPTION

[0015] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0016] The present invention provides a novel AC / DC hybrid power electronic transformer, including a transformer box, a power module box and an auxiliary circuit box. Figure 2 As shown, the transformer box is centered, and the power module box and the auxiliary line box are respectively arranged on the left and right sides of the transformer box. This arrangement makes the overall structural design of the transformer compact. At the same time, this design is more suitable for the double-pole cross-arm installation method in the substation area, reducing the construction difficulty.

[0017] See also Figure 1 As shown, the transformer box is provided with transformer windings, current transformers and BCT terminal boxes, and the transformer windings are divided into low-voltage windings and high-voltage windings. The low-voltage windings further include a first winding and a second winding, the first winding interface is connected to the power supply line, that is, connected to the AC load; the second winding is an adjustable winding, specifically a series coupling winding, connected to the auxiliary line box; the current transformer is used to sample the current of the low-voltage winding in real time, and is connected to the outside through the BCT terminal box.

[0018] The auxiliary line box includes a power distribution unit, a lightning protection unit, a bypass protection unit and a maintenance component unit. Specifically, the power distribution unit includes a power module box input side circuit breaker QF1 and a DC side circuit breaker QF3, and the power distribution unit is used to provide a DC port to the outside.

[0019] The lightning protection unit includes a miniature circuit breaker QF2 and a surge protector FB1. The lightning protection unit is used for input surge protection. One end of the surge protector FB1 is connected to one end of the miniature circuit breaker QF2, and the other end is grounded; the other end of the miniature circuit breaker QF2 is connected to one end of the circuit breaker QF1 on the input side of the power module box.

[0020] The bypass protection unit includes a miniature circuit breaker QF4, an anti-parallel thyristor assembly SCR and an AC contactor KM1. The miniature circuit breaker QF4 is connected in series with the anti-parallel thyristor assembly SCR, and the miniature circuit breaker QF4 is connected in parallel with the AC contactor KM1. The bypass protection unit is used for transient switching and protection when the main circuit in the power module box is running and the shutdown transformer is bypassing.

[0021] The maintenance component unit includes a double-cut isolating switch QS1, which is used to short-circuit the second winding and form a maintenance breakpoint when the power module box is overhauled, so as to facilitate product maintenance.

[0022] The power module box includes AC / DC module and DC / AC module. The power module box mainly realizes the comprehensive management of the power quality at the outlet of the distribution transformer. The AC / DC module manages the current quality issues, and the DC / AC module manages the voltage quality issues to ensure the qualified rate of the outlet voltage of the substation.

[0023] Here, the DC side circuit breaker QF3 is a 2P circuit breaker. The positive and negative poles of the AC / DC module and the DC / AC module are connected respectively and then connected in parallel to one end of the DC side circuit breaker QF3. The other end of the DC side circuit breaker QF3 provides an external DC interface. The DC interface is arranged on the auxiliary line box for connecting to external devices. The input A / B / C / N terminals of the AC / DC module are connected to the circuit breaker QF1 on the input side of the power module box and then connected to the output side of the first winding. The output A / B / C terminals of the DC / AC module are connected to one end of the second winding.

[0024] Here, the transformer has the following working modes: 1) AC / DC mutual assistance mode: The circuit breaker QF1, miniature circuit breaker QF2, DC side circuit breaker QF3, miniature circuit breaker QF4, and double-cut disconnector QS1 on the input side of the power module box are all in the closed state, and the AC contactor KM1 is in the open state. At this time, the power module box receives the dispatch instruction to work, the AC / DC module works normally for voltage regulation, and the DC / AC module outputs according to the received power instruction signal, adjusts the amplitude and phase of its output voltage, and realizes continuous and precise power regulation. At this time, the DC side circuit breaker QF3 connects the external DC port to the DC load or photovoltaic MMPT / energy storage device to realize flexible power mutual assistance between the AC grid and the DC grid; 2) Bypass operation mode: The circuit breaker QF1, miniature circuit breaker QF2, miniature circuit breaker QF4, double-cut isolating switch QS1 and AC contactor KM1 on the input side of the power module box are all in the closed state, and the DC side circuit breaker QF3 is in the open state. At this time, the AC / DC module works normally and the grid current quality problem is being managed. The DC / AC module is in the shutdown state; 3) Main circuit voltage regulation operation mode: The circuit breaker QF1, miniature circuit breaker QF2, miniature circuit breaker QF4, and double-cut isolating switch QS1 on the input side of the power module box are all in the closed state, and the AC contactor KM1 and the DC side circuit breaker QF3 are in the open state. At this time, the AC / DC module works normally, and the DC / AC module makes real-time judgments by detecting the grid voltage data and adjusts the overall port output voltage to meet the output voltage qualification rate under different input voltage conditions, realizing continuous online adjustment; 4) Maintenance mode: The circuit breaker QF1, miniature circuit breaker QF2, double-cut isolating switch QS1, and AC contactor KM1 on the input side of the power module box are all in the disconnected state, and the DC side circuit breaker QF3 and miniature circuit breaker QF4 are in the closed state. At this time, the power module box is powered off, and the AC / DC module, DC / AC module, AC contactor KM1 and anti-parallel thyristor assembly SCR are inspected and maintained.

[0025] When this new AC / DC hybrid power electronic transformer is used in multiple areas at the same time, see Figure 3 As shown, the transformers in two adjacent substations can be interconnected through a DC interface to achieve two-way power mutual assistance in the AC-DC-AC mode, flexibly mobilize the distribution resources of adjacent substations, and combine with DC-side photovoltaic and energy storage devices to maximize economic benefits. This technical solution solves the problem that traditional distribution substations cannot be continuously regulated online, and at the same time integrates the solution of comprehensive voltage and current management of multiple devices in traditional substations, realizing a truly integrated design of distribution transformers, with intelligent and multifunctional characteristics, equipped with a DC port, and realizing AC-DC mixed supply, meeting various application scenarios of current new energy microgrids, solving the problem of unstable DC side voltage during peak and valley periods of new energy power generation, and solving the problem of short-term power outages during line maintenance and transfer.

[0026] When the second winding is added to the transformer box as a series coupling winding, the power part capacity can be only the adjustment power during the regulation process, that is, the system high power is mobilized with a small power. Based on this feature, the AC side can also be interconnected, such as Figure 4 The block diagram shown can realize direct resource sharing between adjacent substations on the AC side, and resource sharing between the DC side and the AC sides on both sides, forming a hand-in-hand ring-shaped power grid, increasing the reliability of power grid operation. Based on this solution, uninterrupted power supply can also be achieved between multiple substations, improving users' power consumption experience.

[0027] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A novel AC / DC hybrid power electronic transformer, characterized in that: Including transformer box, power module box and auxiliary line box, The transformer box is provided with a transformer winding, a current transformer and a BCT terminal box, the transformer winding is divided into a low voltage winding and a high voltage winding, the low voltage winding includes a first winding and a second winding, and the first winding interface is connected to a power supply line; The second winding is an adjustable winding, connected to the auxiliary line box; the current transformer is used to sample the current of the low-voltage winding in real time, and is connected to the outside through the BCT terminal box; The auxiliary line box includes a power distribution unit, a lightning protection unit, a bypass protection unit and a maintenance component unit, wherein: The power distribution unit includes a power module box input side circuit breaker QF1 and a DC side circuit breaker QF3, and the power distribution unit is used to provide a DC port to the outside; The lightning protection unit includes a miniature circuit breaker QF2 and a surge protector FB1. The lightning protection unit is used for input surge protection. One end of the surge protector FB1 is connected to one end of the miniature circuit breaker QF2, and the other end is grounded. The other end of the miniature circuit breaker QF2 is connected to one end of the circuit breaker QF1 on the input side of the power module box. The bypass protection unit includes a miniature circuit breaker QF4, an anti-parallel thyristor assembly SCR and an AC contactor KM1. The miniature circuit breaker QF4 is connected in series with the anti-parallel thyristor assembly SCR, and the miniature circuit breaker QF4 is connected in parallel with the AC contactor KM1. The bypass protection unit is used for transient switching and protection when the main circuit in the power module box is running and the shutdown transformer is bypassing. The maintenance component unit includes a double-cut isolating switch QS1, which is used to short-circuit the second winding and form a maintenance breakpoint when the power module box is overhauled; The power module box includes an AC / DC module and a DC / AC module; The DC side circuit breaker QF3 is a 2P circuit breaker. The positive and negative poles of the AC / DC module and the DC / AC module are connected respectively and then connected in parallel to one end of the DC side circuit breaker QF3. The other end of the DC side circuit breaker QF3 provides an external DC interface. The DC interface is set on the auxiliary line box and is used to connect to external devices. The input A / B / C / N terminals of the AC / DC module are connected to the circuit breaker QF1 on the input side of the power module box and then connected to the output side of the first winding; The output A / B / C terminal of the DC / AC module is connected to one end of the second winding.

2. A novel AC / DC hybrid power electronic transformer according to claim 1, characterized in that: The second winding is a series coupled winding.

3. A novel AC / DC hybrid power electronic transformer according to claim 1, characterized in that: The power module box and the auxiliary line box are respectively arranged on the left and right sides of the transformer box.

4. A novel AC / DC hybrid power electronic transformer according to any one of claims 1 to 3, characterized in that: The transformer has the following working modes: 1) AC / DC mutual assistance mode: the circuit breaker QF1, miniature circuit breaker QF2, DC side circuit breaker QF3, miniature circuit breaker QF4, and double-cut disconnector QS1 on the input side of the power module box are all in the closed state, and the AC contactor KM1 is in the open state. At this time, the power module box receives the dispatching instruction to work, the AC / DC module works normally for voltage regulation, and the DC / AC module outputs according to the received power instruction signal, adjusts the amplitude and phase of its output voltage, and realizes continuous and precise power regulation. At this time, the DC side circuit breaker QF3 is connected to an external device at the external DC port; 2) Bypass operation mode: The circuit breaker QF1, miniature circuit breaker QF2, miniature circuit breaker QF4, double-cut disconnector QS1 and AC contactor KM1 on the input side of the power module box are all in the closed state, and the DC side circuit breaker QF3 is in the open state. At this time, the AC / DC module is working normally, and the DC / AC module is in the shutdown state; 3) Main circuit voltage regulation operation mode: The circuit breaker QF1, miniature circuit breaker QF2, miniature circuit breaker QF4, and double-cut isolating switch QS1 on the input side of the power module box are all in the closed state, and the AC contactor KM1 and the DC side circuit breaker QF3 are in the open state. At this time, the AC / DC module works normally, and the DC / AC module makes real-time judgments by detecting the grid voltage data and adjusts the overall port output voltage to meet the output voltage qualification rate under different input voltage conditions, realizing continuous online adjustment; 4) Maintenance mode: The circuit breaker QF1, miniature circuit breaker QF2, double-cut isolating switch QS1, and AC contactor KM1 on the input side of the power module box are all in the disconnected state, and the DC side circuit breaker QF3 and miniature circuit breaker QF4 are in the closed state. At this time, the power module box is powered off, and the AC / DC module, DC / AC module, AC contactor KM1 and anti-parallel thyristor assembly SCR are inspected and maintained.

5. A novel AC / DC hybrid power electronic transformer according to claim 4, characterized in that: In multiple sections, the transformers in each two adjacent sections are interconnected through a DC interface.

6. A novel AC / DC hybrid power electronic transformer according to claim 5, characterized in that: In multiple sections, the AC sides of the transformers in every two adjacent sections are interconnected.

Images