CN104242720A - Modular multilevel converter (MMC) of alternating current side cascading H-bridge - Google Patents

Abstract

The present invention provides a mixed module combined multilevel converter of cascaded H bridges on the AC side, each phase circuit of which is composed of an upper bridge arm, a lower bridge arm, an AC side bridge arm, a first capacitor and a second capacitor; the upper bridge The circuit structure of the arm and the lower bridge arm is exactly the same. Both the upper bridge arm and the lower bridge arm are composed of N half-bridge sub-modules and 1 inductor connected in series, and the AC-side bridge arm is composed of M full-bridge sub-modules. The hybrid module combination multilevel converter of the invention can operate in the STATCOM state, and has the self-clearing capability of the DC side short-circuit fault. Compared with the existing MMC composed of only half-bridge sub-modules, it has the self-clearing capability of short-circuit faults on the DC side; compared with the existing MMC composed of only full-bridge sub-modules, it saves a lot of switching tubes and reduces the cost.

Description

A hybrid module multilevel converter with cascaded H-bridges on the AC side

technical field

The invention relates to the field of combined module multilevel converters, in particular to a hybrid module multilevel converter with cascaded H bridges on the AC side.

Background technique

With the continuous development of HVDC transmission, multilevel converters have been greatly developed. Among them, the modular multilevel converter (Modular Multilevel Converter, MMC) is a new type of multilevel topology. In addition to the advantages of the traditional multilevel converter, the modular multilevel converter adopts a modular structure design. It is convenient for system expansion and redundant work; it has unbalanced operation capability, fault ride-through and recovery capability, and high system reliability; due to the common DC bus, the module combined multilevel converter is especially suitable for high-voltage direct current transmission system applications.

Currently, MMC sub-modules mainly include half-bridge sub-modules and full-bridge sub-modules. The MMC composed of half-bridge sub-modules has a simple structure, but it does not have the ability to self-clear short-circuit faults on the DC side; the MMC composed of full-bridge sub-modules has the ability to self-clear short-circuit faults on the DC side, but it requires double the number of devices, and the cost is very high.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art, and propose a hybrid module multilevel converter with cascaded H bridges on the AC side.

The purpose of the present invention is achieved through the following technical solutions:

The hybrid module combination multilevel converter of cascaded H bridges on the AC side, each phase circuit of which is composed of an upper bridge arm, a lower bridge arm, an AC side bridge arm, a first capacitor and a second capacitor; the upper bridge arm and the lower bridge arm The circuit structure of the bridge arm is exactly the same. The positive pole of the first capacitor is connected to one end of the upper bridge arm, the other end of the upper bridge arm is connected to one end of the lower bridge arm and one end of the AC side bridge arm, and the other end of the lower bridge arm is connected to the negative pole of the second capacitor. The positive pole of the capacitor is connected to the negative pole of the first capacitor and the ground; the positive pole of the first capacitor is connected to the positive pole of the DC side of the DC power transmission system, the negative pole of the second capacitor is connected to the negative pole of the DC side of the DC power transmission system, and the other end of the bridge arm of the AC side It is connected to the AC side of the DC transmission system.

For further optimized implementation, the upper bridge arm is composed of N half-bridge sub-modules and inductors; the N half-bridge sub-modules are connected in series to form a half-bridge sub-module string, and one end of the half-bridge sub-module string is connected to one end of the inductor, The other end of the half-bridge sub-module string is used as one end of the upper bridge arm, and the other end of the inductor is used as the other end of the upper bridge arm. The AC-side bridge arm is sequentially connected in series by M full-bridge sub-modules to form a string of full-bridge sub-modules, and the two ends of the string of full-bridge sub-modules are used as. Both ends of the bridge arm on the AC side.

For further optimized implementation, the half-bridge sub-module is composed of a first switch tube, a second switch tube and a third capacitor; the collector of the first switch tube is connected to the positive pole of the third capacitor, and the negative pole of the third capacitor is connected to the second switch tube The emitter of the first switching tube is connected to the collector of the second switching tube; the collector and emitter of the second switching tube serve as two ends of the half-bridge sub-module. The full bridge sub-module is composed of the third switch tube, the fourth switch tube, the fifth switch tube, the sixth switch tube and the fourth capacitor; the collector of the third switch tube and the positive pole of the fourth capacitor, the collector of the fourth switch tube The electrodes are connected, the emitter of the third switching tube is connected to the collector of the fifth switching tube, the emitter of the fourth switching tube is connected to the collector of the sixth switching tube, the emitter of the fifth switching tube is connected to the negative pole of the fourth capacitor 1. The emitter of the sixth switching tube is connected; the collector of the fifth switching tube and the collector of the sixth switching tube serve as two ends of the full bridge sub-module.

Compared with the prior art, the present invention has the advantages of self-clearing capability of DC side short-circuit fault, and can operate in Static Synchronous Compensator (STATCOM) state. Compared with the existing MMC composed only of half-bridge sub-modules, the present invention has the self-clearing capability of DC side short-circuit faults; compared with the existing MMC composed only of full-bridge sub-modules, the present invention uses a large number of switch tubes Reduced, lowered costs.

Description of drawings

Fig. 1 is the circuit structural diagram of the hybrid module combination multilevel converter of AC side cascaded H bridge of the present invention;

Fig. 2 is the circuit structure diagram of the half-bridge sub-module combined with the hybrid module of the cascaded H-bridge on the AC side shown in Fig. 1;

Fig. 3 is the circuit structure diagram of the full-bridge sub-module of the mixed module combination multilevel converter of the AC side cascaded H-bridge shown in Fig. 1;

Fig. 4 is the modulation waveform diagram of the hybrid module combination multilevel converter of the AC side cascaded H-bridge shown in Fig. 1;

Fig. 5 is the equivalent circuit when a short-circuit fault occurs on the DC side of the three-phase hybrid module combined multilevel converter with cascaded H-bridges on the AC side;

Fig. 6 is an equivalent circuit of a three-phase hybrid module combined multilevel converter with cascaded H-bridges on the AC side working in STATCOM state.

Detailed ways

In order to further illustrate the content and characteristics of the present invention, the specific embodiments of the present invention will be described below in conjunction with the accompanying drawings, but the implementation of the present invention is not limited thereto. If there are any processes that are not specifically described in detail below, those skilled in the art can refer to the prior art for implementation.

With reference to Fig. 1, each phase circuit of the hybrid module combined multilevel converter of the AC side cascaded H-bridge of the present invention consists of an upper bridge arm 11, a lower bridge arm 12, an AC side bridge arm 13, a first capacitor C ₁ and a first capacitor C 1 . Composed of two capacitors C2 ; the circuit structures of the upper bridge arm 11 and the lower _bridge arm 12 are exactly the same. Wherein, the positive pole of the first capacitor C1 is connected to one end of the upper bridge arm 11, the other end of the upper bridge arm 11 is connected to one _end b of the lower bridge arm 12, and one end b of the AC side bridge arm 13, and the other end of the lower bridge arm 12 It is connected to the negative pole of the second capacitor C2 , and _the positive pole of the second capacitor C2 is connected to the negative pole of the first capacitor C1 and ground n ; the positive pole of _the first capacitor C1 is connected _to the positive pole ₁₅ of the DC side of the direct current transmission system, and the second The negative pole of the capacitor C2 is connected to the negative pole 16 of the DC side of the DC power transmission system, and the other _end a of the bridge arm 13 on the AC side is connected to the AC side 14 of the DC power transmission system.

The upper bridge arm 11 is composed of N half-bridge sub-modules HSM ₁ , HSM ₂ , . _. . , HSM _N and an inductor L ; N half-bridge sub-modules HSM ₁ , HSM ₂ , . In the half-bridge sub-module string, one end of the half-bridge sub-module string is connected to one end of the inductor L , the other end of the half-bridge sub-module string is used as one end of the upper bridge arm 11 , and the other end of the inductor L is used as the other end of the upper bridge arm 11 . The AC-side bridge arm 13 is connected in series by M full-bridge submodules FSM ₁ , FSM ₂ , ..., FSM _M sequentially to form a full-bridge sub-module string, and the two ends of the full-bridge sub-module string serve as the ends of the AC-side bridge arm 13. ends.

The half-bridge sub-module is shown in FIG. ₂ and is composed of _a first switching tube T1 , a second switching tube T2 and a third capacitor C3 ; the collector of the first switching tube T1 _and the _third capacitor _C3 The positive pole of the third capacitor C3 is connected to the emitter of the second switching tube T2 _, the emitter _{of the} first switching tube T1 is connected to the collector of the _second switching tube T2 ; the _second switching tube T2 The collector and emitter of the half-bridge sub-module are used as two ends; the switch tube is an IGBT.

The full-bridge sub-module is _shown in Figure ₃ and is composed of a third switching tube T3 , _a fourth switching tube T4 , a fifth switching tube T5 , _a sixth switching tube T6 and a fourth capacitor C4 _; The collector of _the third switching tube T3 is connected to the anode of _the fourth capacitor C4 _and the collector of the fourth switching tube T4 , the emitter of the third switching tube T3 is connected to the collector of the fifth switching tube _{T5 ,} and the third switching tube T5 is connected to the collector. The emitter _of the fourth switching tube T4 is connected to the collector of the sixth switching tube T6 , the emitter of the fifth switching tube T5 is connected to the negative pole of _the fourth capacitor C4 _, and the emitter of the _sixth switching tube T6 _{; The} collector of the fifth switching tube T5 and the collector _of the sixth switching tube T6 serve as two ends of the full bridge sub-module.

The modulation waveform diagram of the hybrid module combination multilevel converter of the AC side cascaded H bridge of the present invention is shown in Figure 4, the single-phase output voltage u _an is a sine waveform, and the voltage u _bn at point b is a ladder waveform approaching a sine wave, The output voltage u _ab of the bridge arm 13 on the AC side is the single-phase output voltage u _an minus the voltage u _bn at point b .

Take the three-phase ( u, v, w ) hybrid module combined multilevel converter with cascaded H bridges on the AC side as an example. When a short-circuit fault occurs on the DC side, all switching tubes are blocked, that is, when a short-circuit fault occurs on the DC side of the converter All switching tubes are controlled to be turned off. The equivalent circuit diagram is shown in Figure 5. The operation of a three-phase uncontrolled rectifier equivalent to a parallel capacitor on the DC side can quickly reduce the short-circuit current, thereby self-clearing the short-circuit fault on the DC side.

Taking the three-phase ( u, v, w ₎ hybrid module combination multilevel converter of cascaded H bridges on the AC side as an example, the first switching tube T1 of each half-bridge sub-module in the upper bridge arm 11 is controlled to be turned off, The second switching tube T2 is turned on to block all the switching tubes of the lower bridge arm 12. _Its equivalent circuit diagram is shown in FIG.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the embodiment, and any other changes, modifications, substitutions and combinations made without departing from the spirit and principle of the present invention , simplification, all should be equivalent replacement methods, and are all included in the protection scope of the present invention.

Claims (6)

1. the mixing module combination multi-level converter of AC cascaded H-bridges, is characterized in that: every circuitry phase of converter comprise brachium pontis (11), lower brachium pontis (12), AC brachium pontis (13), the first electric capacity ( c ₁) and the second electric capacity ( c ₂); The circuit structure of described upper brachium pontis (11) and lower brachium pontis (12) is completely the same.

2. the mixing module combination multi-level converter of AC cascaded H-bridges according to claim 1, is characterized in that: the first electric capacity ( c ₁) positive pole be connected with one end of upper brachium pontis (11), one end of the other end of upper brachium pontis (11) and one end of lower brachium pontis (12), AC brachium pontis (13) ( b) connect, the other end of lower brachium pontis (12) and the second electric capacity ( c ₂) negative pole connect, the second electric capacity ( c ₂) positive pole and the first electric capacity ( c ₁) negative pole, ( n) connect; First electric capacity ( c ₁) positive pole be connected with the positive pole (15) of DC transmission system DC side, the second electric capacity ( c ₂) negative pole be connected with the negative pole (16) of DC transmission system DC side, the other end of AC brachium pontis (13) ( a) be connected with DC transmission system AC (14).

3. the mixing module combination multi-level converter of AC cascaded H-bridges according to claim 1, is characterized in that: described upper brachium pontis (11) is by N number of half-bridge submodule (HSM ₁, HSM ₂..., HSM _n) and inductance ( l) form; N number of half-bridge submodule (HSM ₁, HSM ₂..., HSM _n) connect successively, form half-bridge submodule string, one end of half-bridge submodule string and inductance ( l) one end connect, the other end of half-bridge submodule string as one end of upper brachium pontis (11), inductance ( l) the other end as the other end of upper brachium pontis (11).

4. the mixing module combination multi-level converter of AC cascaded H-bridges according to claim 1, is characterized in that: described AC brachium pontis (13) is by M full-bridge submodule (FSM ₁, FSM ₂..., FSM _m) connect successively, form full-bridge submodule string, the two ends of full-bridge submodule string are as the two ends of AC brachium pontis (13).

5. AC cascaded H-bridges according to claim 3 mixing module combination multi-level converter, it is characterized in that: described half-bridge submodule by the first switching tube ( t ₁), second switch pipe ( t ₂) and the 3rd electric capacity ( c ₃) form; First switching tube ( t ₁) collector electrode and the 3rd electric capacity ( c ₃) positive pole connect, the 3rd electric capacity ( c ₃) negative pole and second switch pipe ( t ₂) emitter connect, the first switching tube ( t ₁) emitter and second switch pipe ( t ₂) collector electrode connect; Second switch pipe ( t ₂) collector electrode, emitter is as the two ends of half-bridge submodule; Described switching tube is IGBT.

6. AC cascaded H-bridges according to claim 4 mixing module combination multi-level converter, it is characterized in that: described full-bridge submodule by the 3rd switching tube ( t ₃), the 4th switching tube ( t ₄), the 5th switching tube ( t ₅), the 6th switching tube ( t ₆) and the 4th electric capacity ( c ₄) form; 3rd switching tube ( t ₃) collector electrode and the 4th electric capacity ( c ₄) positive pole, the 4th switching tube ( t ₄) collector electrode connect, the 3rd switching tube ( t ₃) emitter and the 5th switching tube ( t ₅) collector electrode connect, the 4th switching tube ( t ₄) emitter and the 6th switching tube ( t ₆) collector electrode connect, the 5th switching tube ( t ₅) emitter and the 4th electric capacity ( c ₄) negative pole, the 6th switching tube ( t ₆) emitter connect; 5th switching tube ( t ₅) collector electrode, the 6th switching tube ( t ₆) collector electrode as the two ends of full-bridge submodule.