CN112311238A - Novel direct-current power electronic transformer with direct-current short-circuit fault protection capability - Google Patents

Novel direct-current power electronic transformer with direct-current short-circuit fault protection capability Download PDF

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Publication number
CN112311238A
CN112311238A CN201910686304.0A CN201910686304A CN112311238A CN 112311238 A CN112311238 A CN 112311238A CN 201910686304 A CN201910686304 A CN 201910686304A CN 112311238 A CN112311238 A CN 112311238A
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China
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direct
current
circuit
power electronic
electronic transformer
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付超
武承杰
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North China Electric Power University
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North China Electric Power University
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Priority to CN201910686304.0A priority Critical patent/CN112311238A/en
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention discloses a novel direct current power electronic transformer with direct current short-circuit fault protection capability, which is mainly applied to voltage conversion and power management between a medium-voltage direct current bus and a low-voltage direct current bus. The power electronic transformer comprises a cascade type isolation DC/DC converter, a switch circuit and an energy consumption circuit, wherein the cascade type isolation DC/DC converter adopts a connection mode of input, series connection and output in parallel connection so as to meet the use requirement of high voltage and high power in a power grid. The switching circuit is connected in series with the cascade direct-current converter and is used for realizing the connection and disconnection of the power electronic transformer; the energy consumption circuit is connected with the cascade direct current converter in parallel and used for realizing the consumption and transfer of the energy at the network side. The power electronic transformer provided by the invention is simple to control, can realize active fault isolation and self-protection when a direct current fault occurs in the lines at the input/output sides, reduces the dependence on a direct current breaker, and reduces the cost of power grid construction.

Description

Novel direct-current power electronic transformer with direct-current short-circuit fault protection capability
Technical Field
The invention relates to a novel direct-current power electronic transformer topology with direct-current short-circuit fault protection capability, which is suitable for the fields of medium and high voltage direct current conversion, such as a flexible direct-current power grid, a direct-current micro-power grid, a new energy grid connection and the like.
Background
In recent years, flexible direct-current transmission technology and application thereof in a direct-current power grid gradually become research hotspots and receive wide attention. As a key link in a flexible direct-current distribution network, a Power Electronic Transformer (PET) or a Solid State Transformer (SST) can realize flexible control and rapid management of voltage and Power in a high-low voltage direct-current distribution network or a microgrid, and has important theoretical value and engineering significance.
The flexible direct current system has low inertia and weak damping characteristics, so that the direct current power grid has poor capability of tolerating serious direct current short circuit faults. The direct current power electronic transformer can play the roles of fault area isolation and non-fault area power rapid recovery during direct current fault, so domestic and foreign scholars propose a series of direct current power electronic transformers to realize fault isolation of a direct current power grid so as to improve the safety and reliability of the system.
At present, the dc power electronic transformers with dc fault protection capability have the following two types: one is a Half-Bridge type Modular Multilevel Converter (HB-MMC), the topology realizes fault isolation by using a method of directly locking a control trigger signal of the MMC, but the topology has the defects of large transformer core loss and higher equivalent switching frequency; the other is a direct current power electronic transformer composed of a direct current autotransformer and a half-bridge full-bridge mixed MMC. However, when the voltage transformation ratio is too large, the topology is lack of electrical isolation inside, cannot block fault current, and is not suitable for high-power occasions. Meanwhile, the manufacturing process of the high-voltage high-capacity direct-current circuit breaker is not mature, and the realization of the fault protection strategy based on the direct-current circuit breaker is still difficult.
Therefore, the research on the power electronic transformer with the direct-current short-circuit fault protection capability has certain practical value.
Disclosure of Invention
The invention aims to solve the problem of how to provide a novel direct-current power electronic transformer topology with direct-current short-circuit fault protection capability so as to enhance the fault protection capability of a system and reduce the dependence of the system on a direct-current circuit breaker.
In order to solve the problems, the technical scheme adopted by the invention is as follows: the utility model provides a novel direct current power electronic transformer that possesses direct current short-circuit fault protection ability which characterized in that: the bidirectional full-bridge direct-current converter comprises N cascaded isolated bidirectional full-bridge direct-current converters, a switch circuit and an energy consumption circuit, wherein direct-current input sides of the bidirectional full-bridge direct-current converters are connected in series and used for adapting to the higher voltage grade of a high-voltage direct-current side, and direct-current output sides of the bidirectional full-bridge direct-current converters are connected in parallel and used for outputting larger power to a low-voltage direct-current side.
The further technical scheme is as follows: the isolated bidirectional full-bridge direct-current converter comprises: the high-voltage side H bridge, high frequency transformer and low pressure side H bridge, the input of high-voltage side H bridge does the input of two-way full-bridge DC converter of isolated form, the output of high-voltage side with the side that once inclines of high frequency transformer connects, the secondary side of high frequency transformer with the input side of low pressure side H bridge is connected, the output of low pressure side H bridge does the output of two-way full-bridge DC converter of isolated form connects.
The further technical scheme is that the number of modules of the cascade type direct current converter is determined according to the voltage-resistant grade and the current-resistant grade of a switching tube adopted in the isolation type bidirectional full-bridge direct current converter.
The further technical scheme is that the turn ratio of the primary side winding and the secondary side winding of the high-frequency transformer is determined according to the module number of the cascade type direct current converter and the voltage levels of the high direct current bus and the low direct current bus.
The technical scheme is that the switching circuit consists of a circuit change-over switch, a metal oxide arrester, an arc suppression circuit and a quick mechanical switch; the circuit switch is composed of a plurality of IGBTs which are connected in series in an opposite direction, and the number of the IGBTs is determined by the voltage resistance and current resistance values of the switch tubes.
The further technical scheme is that the energy consumption circuit consists of a plurality of thyristors, power resistors and current-limiting inductors which are connected in series in a pairwise reverse direction; the number of the thyristors is determined by the voltage and current resistance values of the thyristor tubes.
The further technical scheme is that the power electronic transformer is specifically controlled as follows: when the system is in a normal working state, the power electronic transformer adopts a constant output voltage control mode. Specifically, the isolated bidirectional full-bridge direct-current converter adopts phase-shift control, and when the voltage of a low-voltage direct-current bus at the output end is reduced, the isolated bidirectional full-bridge direct-current converter adopts phase-shift control, so that the phase-shift ratio is increased, and the output direct-current voltage is increased; when the voltage of the low-voltage direct-current bus at the output end rises, the phase shift ratio is reduced, so that the output direct-current voltage is reduced.
The further technical proposal is that the phase shift control adopts single phase shift control or other multiple phase shift control; the phase shift control adopts a PI controller, the input of the controller is a voltage or power difference value, and the output of the controller is a phase shift ratio in the phase shift control.
The further technical scheme is that the power electronic transformer is specifically controlled as follows: when the input end or the output end of the power electronic transformer has a direct current short circuit fault, the power electronic transformer executes a fault working mode. Specifically, through fault detection and diagnosis, the system starts a control command in a fault state, locks the trigger signal of each isolated bidirectional full-bridge direct-current converter, switches on a thyristor on the energy consumption circuit, locks a circuit change-over switch of the switch circuit, and opens the quick mechanical switch.
The further technical scheme is that 2 milliseconds of delay exists between a trigger signal for locking each isolated bidirectional full-bridge direct-current converter and a conducting signal on an energy consumption circuit.
Adopt the produced beneficial effect of above-mentioned technical scheme to lie in: the barrier protection control strategy used by the direct current power electronic transformer is simple, the reaction is rapid, the characteristic under stable work cannot be influenced, meanwhile, the proposed topological structure can be applied to a high-voltage high-power scene, the dependence on a direct current breaker is reduced, and the cost is low.
Drawings
The drawings of the invention are as follows:
FIG. 1 is a schematic circuit diagram of the novel DC power electronic transformer of the present invention;
FIG. 2 is a schematic diagram illustrating the overall control of the novel DC power electronic transformer in an embodiment of the present invention;
FIG. 3 is a schematic diagram of constant voltage control of the novel DC power electronic transformer in an embodiment of the present invention;
FIG. 4 is a timing diagram illustrating DC fault operation of the novel DC power electronic transformer in accordance with an embodiment of the present invention;
FIG. 5 is a system block diagram of a simulation embodiment;
FIGS. 6(a) - (d) are equivalent circuit diagrams of the novel DC power electronic transformer in the embodiment of the present invention at various stages of the DC fault operation period;
fig. 7(a) - (d) are simulated waveforms of voltage and current of each part of the novel dc power electronic transformer during dc fault operation period in the embodiment of the present invention.
Wherein: 1. a high-voltage side H bridge 2, a high-frequency transformer 3, a low-voltage side H bridge 4, a switch circuit 5, a capacity consumption circuit 6, a high-voltage direct current bus 7 and a low-voltage direct current bus
Detailed Description
The present invention provides a novel dc power electronic transformer with dc short-circuit fault protection capability, which is described in detail with reference to fig. 1-6.
FIG. 1 is a diagram of a novel DC power electronic transformer topology with DC short-circuit fault protection capability according to the present invention, in which the input and output sides of the topology are respectively connected to two high and low levels of DC buses, the basic DC/DC converter unit is an isolated bidirectional full-bridge DC converter, and the C converter unit is an isolated bidirectional full-bridge DC converterin、CoRespectively a series (high voltage) side and a parallel (low voltage) side filter capacitor.
FIG. 2 is a schematic diagram illustrating the overall control of the novel DC power electronic transformer in an embodiment of the present invention; in the figure, Vo_refIs the output voltage reference value; vin、VoThe total input and output voltage; i isin、IoFor input and output of voltage, I1Is primary side current of high frequency transformer, Vin(i)(i ═ 1, 2.., n) is the input voltage of the i-th sub-module.
When the system is in a normal working state, the power electronic transformer adopts a control instruction in the normal working state, namely constant output voltage control; when the system is in a fault state, the system starts a control instruction in the fault state through fault detection and diagnosis. Firstly, the respective DC/DC converter is blocked, secondly all thyristors on the energy consuming circuit are switched on, and secondly the switching circuit is blocked. In order to simplify the control, reduce the number of trigger pulses and increase the quick response capability of the system, the latching signal of the power electronic transformer and the conduction control signal of the energy consumption circuit are opposite signals. To ensure that the energy consuming circuit is already conducting, a small delay is added between the energy consuming circuit trigger signal and the switching circuit latch signal. And after the quick mechanical switch is completely disconnected, the fault line is cut off, and the DCSST is recovered to a trigger signal in a normal working state.
FIG. 3 is a schematic diagram of constant voltage control of the novel DC power electronic transformer in an embodiment of the present invention; the isolated bidirectional full-bridge direct-current converter adopts phase-shift control, the phase-shift control adopts a PI controller, the input of the controller is voltage or power difference, and the output of the controller is phase-shift ratio in the phase-shift control. When the voltage of the low-voltage direct-current bus at the output end is reduced, the isolated bidirectional full-bridge direct-current converter adopts phase-shifting control, and the phase-shifting ratio is increased, so that the output direct-current voltage is increased; when the voltage of the low-voltage direct-current bus at the output end rises, the phase shift ratio is reduced, so that the output direct-current voltage is reduced.
Fig. 4 is a timing diagram of dc fault operation of the novel dc power electronic transformer in the embodiment of the present invention, which is divided into: (I) a fault occurrence stage; (II) a fault detection stage; (III) initiating a failed operation phase; (IV) opening operation stage of the mechanical switch; (V) opening the mechanical switch;
FIG. 5 is a diagram of a simulation system, which is a typical 1MW/10kV/400V double-ended DC power distribution system.
Fig. 6(a) - (d) are equivalent circuit diagrams of the novel dc power electronic transformer in the embodiment of the present invention at each stage of the dc fault operation period, and the detailed description is as follows:
(1)t0time: at this point, a short-circuit fault of the dc line occurs, and the phase I is entered, and the equivalent circuit is as shown in fig. 6 (a). At the moment, the voltage on the fault side of the DC/DC converter suddenly drops, the current on the non-fault side feeds short-circuit current to the fault point through the high-frequency transformer and the H-bridge follow current path,and the fault side capacitor also starts to discharge to the fault point, and the fault current at the moment is the superposition of the short-circuit current and the capacitor discharge current.
(2)t1Time: the fault is detected at this moment, and the existing fast fault detection method for research can be 10-4short circuit faults are detected within s time steps.
(3)t2Time: after the occurrence of the fault is detected, the fault protection action is started at time t2 in consideration of the communication delay, and the equivalent circuit of this stage is as shown in fig. 6 (b). And the fault side switch tube is locked, a thyristor on the fault side circuit B is triggered, and all switch tubes in the fault side switch circuit are locked.
(4)t3Time: at t3The mechanical switch is started to open at the moment, and the equivalent circuit is shown in fig. 6 (c). To ensure that the circuit switch has been latched and that the energy consuming circuit has been switched into the circuit, t2Time and t3The moment needs to experience a small delay. Due to the connection of the lightning arrester and the energy consumption circuit, the impedance in a capacitor discharge loop is increased, the discharge current of the capacitor is reduced, and the current stress when the quick mechanical switch is turned off is reduced.
(5)t4Time: considering the opening time of the mechanical switch, the IV stage is passed, and the t is4At the moment, the mechanical switch is completely opened, and meanwhile, the direct current circuit breaker close to the line starts to work, and the fault line is cut off. The fault-side energy dissipation circuit, the line resistance, the smoothing reactor, and the fault point form a discharge circuit, so that the fault current gradually decays to zero, and the equivalent circuit at this time is as shown in fig. 6 (d).
(6)t5Time: through the V stage, at t5And the normal triggering of each sub-module of the DCSST is recovered at any moment, a circuit change-over switch in a switch circuit is switched on, the energy consumption circuit at the fault side is locked, after the current at the fault side is attenuated to zero, the energy consumption circuit is naturally switched off, so that the energy consumption circuit is recovered to a normal working mode, and the rest lines except the fault line are recovered to operate normally.
FIGS. 7(a) - (d) are simulated waveforms of voltage and current of each part of the novel DC power electronic transformer during the operation period of DC fault according to the embodiment of the present invention; suppose that the high-voltage direct-current bus of the system is short-circuited at 0.2s, and the fault is cleared at 0.22s, the voltage waveform of the high-voltage direct-current bus is as shown in fig. 7(a), the bus voltage falls at 0.2s, and the high-voltage direct-current bus returns to normal at 0.22 s. The waveform of the dc voltage at the low voltage side is as shown in fig. 7(b), and the voltage at the output side does not drop significantly due to the voltage supporting effect of the output side capacitor. Fig. 7(c) and 7(d) show waveforms of primary-side voltage and current of the high-frequency transformer, respectively. As can be seen, during a fault, no over-voltage and over-current conditions occur.

Claims (9)

1. A novel direct-current power electronic transformer with direct-current short-circuit fault protection capability is characterized by comprising N isolation type bidirectional full-bridge direct-current converters, a switch circuit and an energy consumption circuit.
2. The direct-current input sides of the bidirectional full-bridge direct-current converters are connected in series and are used for adapting to the higher voltage level of the high-voltage direct-current side; the direct current output sides of the bidirectional full-bridge direct current converters are connected in parallel and used for outputting larger power to the low-voltage direct current side.
3. The novel dc power electronic transformer with dc short-circuit fault protection capability of claim 1, wherein: when the system is in a normal working state, the power electronic transformer adopts a constant output voltage control mode; when the system is in a fault state, the power electronic transformer adopts a fault protection control mode.
4. The novel dc power electronic transformer with dc short-circuit fault protection capability of claim 1, wherein: when the power electronic transformer is in a normal working state, the bidirectional full-bridge direct-current converter executes a normal working mode, and realizes stable and active regulation on output voltage or output power by utilizing phase-shifting control. The phase shift control adopts single phase shift control or other multiple phase shift control; the phase shift control adopts a PI controller, the input of the controller is a voltage or power difference value, and the output of the controller is a phase shift ratio in the phase shift control.
5. The novel dc power electronic transformer with dc short-circuit fault protection capability of claim 1, wherein: when the input end or the output end of the power electronic transformer has a direct-current short-circuit fault, the power electronic transformer can be directly locked, and the fault isolation effect is achieved.
6. The novel dc power electronic transformer with dc short-circuit fault protection capability of claim 1, wherein: when the input end or the output end of the power electronic transformer has a direct-current short-circuit fault, the power electronic transformer executes a fault working mode, a circuit change-over switch in a switch circuit is closed, and a quick mechanical switch is closed. The thyristor in the energy consumption circuit is connected to the line.
7. A novel direct-current power electronic transformer with direct-current short-circuit fault protection capability is characterized in that a switch circuit is connected in series at an input/output port, the switch circuit comprises a circuit switching switch formed by connecting a plurality of IGBTs in series, an arc suppression circuit, an arrester and a quick mechanical switch, and the switch circuit is used for cutting off connection between a cascaded direct-current converter and a circuit when a direct-current short-circuit fault occurs at the input/output side.
8. A novel direct-current power electronic transformer with direct-current short-circuit fault protection capability is characterized in that an input/output port is connected with an energy consumption circuit in parallel, the energy consumption circuit comprises a plurality of thyristors, a current-limiting resistor and a current inductor which are connected in series, and the energy consumption circuit is used for being connected into a circuit to play a role in energy transfer when a direct-current short-circuit fault occurs on the input/output side.
9. The novel dc power electronic transformer with dc short-circuit fault protection capability of claim 1, wherein: the isolated bidirectional full-bridge direct-current converter can be any type of isolated direct-current converter.
CN201910686304.0A 2019-07-29 2019-07-29 Novel direct-current power electronic transformer with direct-current short-circuit fault protection capability Pending CN112311238A (en)

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Application Number Priority Date Filing Date Title
CN201910686304.0A CN112311238A (en) 2019-07-29 2019-07-29 Novel direct-current power electronic transformer with direct-current short-circuit fault protection capability

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113014086A (en) * 2021-03-08 2021-06-22 东南大学 Direct-current transformer topological structure with high voltage transmission ratio and control method thereof

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113014086A (en) * 2021-03-08 2021-06-22 东南大学 Direct-current transformer topological structure with high voltage transmission ratio and control method thereof
CN113014086B (en) * 2021-03-08 2022-02-01 东南大学 Direct-current transformer topological structure with high voltage transmission ratio and control method thereof

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