Modularized multi-lever converter with direct-current fault ride-through capacity

A modular multi-level, DC fault ride-through technology, applied in electrical components, power transmission AC networks, emergency protection circuit devices, etc., can solve problems such as device damage, DC side current increase, system danger, etc. Strong, the same effect, the effect of reducing the production cost

Active Publication Date: 2014-10-01
SOUTHEAST UNIV
5 Cites 23 Cited by

AI-Extracted Technical Summary

Problems solved by technology

Both will lead to a sharp increase in the current on the DC side, and the semiconductor switch T1 and the freewheeling di...
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Abstract

The invention provides a modularized multi-level converter with the direct-current fault ride-through capacity, wherein modules are divided into the first module and the second module. The structure of the first module is the same as the structure of a module in a traditional modularized multi-level converter, and a few semiconductor switches, a few diodes and a few damping resistors are added to the second module on the basis of the first module. The first module and the second module both have the level superposition function, but only the second module has the direct-current fault ride-through capacity. The modularized multi-level converter with the direct-current fault ride-through capacity not only can achieve the functions of a traditional modularized multi-level converter, but also has the direct-current fault ride-through capacity. Compared with an existing modularized multi-level circuit with the direct-current fault ride-through capacity, the circuit of the modularized multi-level converter is provided with fewer devices and simple in structure. The modularized multi-level converter is applicable to modulation and control strategies of the traditional modularized multi-level converter, applicable to high-voltage high-power occasions and particularly suitable for the high-voltage direct-current power transmission field in which a modularized multi-level converter is applied and prone to direct-current faults.

Application Domain

Technology Topic

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  • Modularized multi-lever converter with direct-current fault ride-through capacity
  • Modularized multi-lever converter with direct-current fault ride-through capacity
  • Modularized multi-lever converter with direct-current fault ride-through capacity

Examples

  • Experimental program(1)

Example Embodiment

[0026] Such as Figure 4 As shown, a modular multilevel converter with DC fault ride-through capability, the converter includes A-phase upper and lower bridge arms, B-phase upper and lower bridge arms, and C-phase upper and lower bridge arms; sub-modules are divided into two types: The first module and the second module.
[0027] Among them, the first module includes a DC capacitor C1, a semiconductor switch T1, a semiconductor switch T2, a freewheeling diode D1, and a freewheeling diode D2. A freewheeling diode D1 is connected in series between the emitter and collector of the semiconductor switch T1, and a freewheeling diode D2 is connected in series between the emitter and the collector of the semiconductor switch T2. The emitter of the semiconductor switch T1 and the collector of the semiconductor switch T2 are connected as the positive terminal A of the first module, the emitter of the semiconductor switch T2 serves as the negative terminal B of the first module, and the collector of the semiconductor switch T1 is connected to the DC capacitor C1. The anode is connected, and the emitter of the semiconductor switch T2 is connected with the cathode of the DC capacitor C1. The structure of the first module is the same as that of the traditional modular multilevel converter module, such as figure 2 Shown.
[0028] Such as image 3 As shown, the second module includes DC capacitor C2, DC capacitor C3, semiconductor switch T3, semiconductor switch T4, semiconductor switch T5, semiconductor switch T6, semiconductor switch T7, freewheeling diode D3, freewheeling diode D4, freewheeling diode D5, Freewheeling diode D6, freewheeling diode D7, freewheeling diode D8 and damping resistor R. A freewheeling diode D3 is connected in series between the emitter and collector of the semiconductor switch T3, a freewheeling diode D4 is connected in series between the emitter and collector of the semiconductor switch T4, and a freewheeling diode D4 is connected in series between the emitter and collector of the semiconductor switch T5. A freewheeling diode D5 is connected in series in a forward direction, a freewheeling diode D6 is connected in series between the emitter and collector of the semiconductor switch T6, and a freewheeling diode D7 is connected in series between the emitter and collector of the semiconductor switch T7. The emitter of the semiconductor switch T3 and the collector of the semiconductor switch T4 are connected as the positive terminal C of the second module, the collector of the semiconductor switch T3 is connected with the anode of the DC capacitor C2, and the emitter of the semiconductor switch T4 is connected with the DC capacitor C2. The negative electrode is connected, and the emitter of the semiconductor switch T5 and the collector of the semiconductor switch T6 are connected as the negative terminal D of the second module. The collector of semiconductor switch T5 is connected to the anode of DC capacitor C3, the emitter of semiconductor switch T6 is connected to the cathode of DC capacitor C3, the emitter of semiconductor switch T7 is connected to the cathode of DC capacitor C2, and the collector of semiconductor switch T7 The electrode is connected to the positive electrode of the DC capacitor C3. The cathode of the freewheeling diode D8 is connected to the anode of the DC capacitor C2, the anode of the freewheeling diode D8 is connected to one end of the damping resistor R, and the other end of the damping resistor R is connected to the cathode of the DC capacitor C3.
[0029] The A-phase upper bridge arm is composed of X first modules, Y second modules, and inductance Lap in series, and the A-phase lower bridge arm is composed of inductance Lan, X first modules, and Y second modules in series. . The end of the inductor Lap not connected to the sub-module and the end of the inductor Lan not connected to the sub-module are connected and used as the AC side A-phase port a of the modular multilevel converter.
[0030] The B-phase upper bridge arm is composed of X first modules, Y second modules, and inductance Lbp in series, and the B-phase lower bridge arm is composed of inductance Lbn, X first modules, and Y second modules in series. . The end of the inductor Lbp that is not connected to the sub-module and the end of the inductor Lbn that is not connected to the sub-module are connected and serve as the AC-side B-phase port b of the modular multilevel converter.
[0031] The C-phase upper bridge arm is composed of X first modules, Y second modules, and inductors Lcp in series, and the C-phase lower bridge arm is composed of inductors Lcn, X first modules, and Y second modules in series. . The end of the inductor Lcp not connected to the sub-module and the end of the inductor Lcn not connected to the sub-module are connected and serve as the AC-side C-phase port b of the modular multilevel converter.
[0032] The combination of the serial number of the first module and the second module in the modular multilevel converter with DC fault ride-through capability should be determined according to the required multi-level number and DC fault ride-through capability. The number of first modules and the number of second modules included in all upper or lower bridge arms are respectively the same, so that the total number of DC capacitors included in all upper or lower bridge arms is the same. Assuming that X and Y respectively represent the number of first and second modules required in a bridge arm, and n represents the number of levels required by this bridge arm, that is, the number of DC capacitors contained in a bridge arm, it needs to meet 2Y+X=n relationship. Among them, the DC fault ride-through capability is required. When a DC short-circuit fault occurs, the number of capacitors that need to flow in the unidirectional current path is at least n, so 4Y> n relationship. The number of first modules and second modules required in each bridge arm can be obtained through the above two restriction conditions, so as to determine the structure of the modular multilevel converter with DC fault ride-through capability. In addition, the series sequence of the first module and the second module in each phase bridge arm can be changed.
[0033] The pre-charging method of the modular multi-level converter with DC fault ride-through capability is the same as that of the traditional modular multi-level converter.
[0034] The modulation and control strategy of the modular multilevel converter with DC fault ride-through capability can adopt the modulation and control strategy of the traditional modular multilevel converter. It is only necessary to ensure that the T7 in the second module is in the modular The multi-level converter keeps conducting during normal operation, and the modular multi-level converter can be blocked when a DC fault occurs.
[0035] This modular multilevel converter with DC fault ride-through capability needs to turn off all semiconductor switches in the converter topology after a DC fault occurs, the capacitor discharge circuit is cut off, and the fault point current is fed by the AC side AC current and the discharge current of the bridge arm inductance; for the AC current fed from the AC side, since the number of DC capacitors that need to flow in the path is at least n, the amplitude of the AC phase voltage is hardly larger than the series of these capacitors. Voltage value, so the AC current fed into the AC side is very small or no; and regardless of the direction of the current, it will flow through and charge all the DC capacitors of the second module, and a half-cycle current needs to flow through the damping resistor , The current is rapidly reduced. When all the energy in the inductor is converted into the energy of the module capacitor, the current is reduced to zero, the capacitor voltage in the second module reaches the maximum, and the converter enters a completely locked state, thus realizing no need to disconnect Open the AC circuit breaker and the converter can clear the DC fault current by itself. Although the capacitor of the second module is partially discharged before the semiconductor switch is turned off, after the semiconductor switch is turned off, the fault current charges it, and the capacitor voltage will not drop to a very low level. Restarting is very beneficial. Normally, the system will restart. If the DC voltage can be established, it is a temporary fault and the fault has been cleared. If the DC voltage cannot be established, you can try multiple restarts. If the number of starts is greater than the specified number of starts (such as one), It is determined as a permanent failure, and the system should be shut down for troubleshooting.
[0036] The present invention proposes a modular multilevel converter with DC fault ride-through capability. Although a small number of semiconductor switches, diodes and damping resistors are used, DC faults occur in high-voltage and high-power applications, especially in the HVDC field. At the same time, the DC fault can be quickly self-cleared, and the increased damping resistance dissipates part of the stored energy of the DC network, reduces the amplitude of the capacitor voltage rise, and shortens the arc extinguishing time. The proposed circuit structure is simple, and the modulation and control strategies of traditional modular multi-level converters can be used, which will inevitably enable it to be widely used in the high-voltage and high-power applications of modular multi-level converters.
[0037] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications are also It should be regarded as the protection scope of the present invention.
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Description & Claims & Application Information

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Classification and recommendation of technical efficacy words

  • Reduce manufacturing cost
  • Simple circuit structure
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