CN105553304A - Novel modular multi-level solid-state transformer and internal model control method thereof - Google Patents

Abstract

The invention provides a novel modular multi-level solid-state transformer and an internal model control method thereof. The solid-state transformer comprises a modular multi-level converter, a DC-DC isolator and a DC-AC inverter, wherein the alternating current side of the modular multi-level converter is connected to a high-voltage AC network and the direct current side of the modular multi-level converter is connected to the input end of the DC-DC isolator; the direct current side of the DC-AC inverter is connected to the output end of the DC-DC isolator and the alternating current side of the DC-AC inverter is connected to a low-voltage AC network or load; through changing the number of power sub-modules connected to each bridge arm of the modular multi-level solid-state transformer in series, the voltage application range of the solid-state transformer is flexibly adjusted, and a problem of application of the solid-state transformer in middle-high voltage occasions is effectively solved. According to the characteristics of internal model control, an internal model current inner loop is combined with a PI voltage outer loop, and a new double closed loop control structure is constructed, so that the modular multi-level converter and the DC-AC inverter are controlled; and through the control method, the current has a quicker response speed and stronger anti-disturbance capability.

Description

A kind of novel modular multilevel type solid-state transformer and internal model control method thereof

Technical field

The present invention relates to a kind of solid-state transformer (SolidStateTransformer, SST), be specifically related to a kind of novel modular multilevel type solid-state transformer (MMC-SST) and internal model control method thereof.

Background technology

Solid-state transformer is a kind of novel intelligent power transformer realizing voltage transformation and energy transferring based on high-power electric and electronic converter technique.Along with proposition and the development of energy interconnected systems, solid-state transformer, as its key equipment electric energy router, receives more and more many concerns.

Up to now, on the topological structure implementation and control method of SST, certain achievement in research has been achieved both at home and abroad.At present, solid-state transformer mainly contains traditional two level or three level VSC (VoltageSourceConverter) type solid-state transformer and H bridge cascading multiple electrical level solid-state transformer.But, two level SST to be applied to mesohigh occasion, usually need by input stage all-controlling power electronics device string (and) connection uses, this just needs to solve all to press (current-sharing) problem, just at present, the challenge that this or are very large.H bridge cascade connection multi-level current transformer is applied to the needs that can meet mesohigh application scenario in solid-state transformer, but it needs a large amount of full-controlled switch devices and high frequency transformer, and high frequency transformer accounts for the passive device of very large proportion as volume and weight in SST, it uses the power density being unfavorable for improving solid-state transformer in a large number.In addition, control system is as the another core technology of solid-state transformer, and its quality will directly affect the service behaviour of whole system.The design of current solid-state transformer controller, mostly based on the Mathematical Modeling set up under dq rotating coordinate system, adopts the double circle controling mode based on PI controller, and the independence being realized active power and reactive power by dq uneoupled control is controlled.Although system has good response performance, due to needs cross decoupling, and feedback decoupling effect is responsive to Parameters variation, so be difficult to realize full decoupled control, the quality of control effects is overly dependent upon the Mathematical Modeling of controlled device, and controls relative complex.

Summary of the invention

In view of this, for the deficiency of existing solid-state transformer topological structure implementation and control method, the object of the present invention is to provide a kind of novel modular multilevel type solid-state transformer (MMC-SST) and internal model control method thereof.

For achieving the above object, technical scheme provided by the invention is as follows:

A novel modular multilevel type solid-state transformer, comprises modular multi-level converter, DC-DC isolator and DC-AC inverter;

The AC of described modular multi-level converter connects High-voltage AC Network, DC side connects the input of described DC-DC isolator, the DC side of described DC-AC inverter connects the output of described DC-DC isolator, and AC connects low-voltage alternating-current electrical network or load.

Further, described modular multi-level converter comprises the first unsteady flow bridge, second unsteady flow bridge and the 3rd unsteady flow bridge, the input of described unsteady flow bridge is as a phase of three-phase alternating current input, described unsteady flow bridge comprises positive convertor arm, negative convertor arm, first filter reactor and the second filter reactor, the anode of described positive convertor arm is connected to the direct current anode of described modular multi-level converter, and then be connected to the anode of described DC-DC isolator, the negative terminal of described positive convertor arm is connected with one of electrical network by described first filter reactor, the negative terminal of described negative convertor arm is connected to the direct current negative terminal of described modular multi-level converter, and then be connected to the negative terminal of described DC-DC isolator, the anode of described negative convertor arm is connected with one of electrical network by described second filter reactor, described positive convertor arm/negative convertor arm comprises the power modules of multiple positive-negative series successively, the DC side of described power modules is positive and negative to be connected with the positive and negative of high-voltage direct current power grid respectively.

Further, described power modules comprises direct current capacitor, the first switching device, second switch device, the first fly-wheel diode and the second fly-wheel diode, and described first switching device and second switch device are full-control type semiconductor switch device;

The collector electrode of described first switching device is connected with the negative electrode of described first fly-wheel diode, and the emitter of described first switching device is connected with the anode of described first fly-wheel diode; The collector electrode of described second switch device is connected with the negative electrode of described second fly-wheel diode, and the emitter of described second switch device is connected with the anode of described second fly-wheel diode; The anode of described direct current capacitor is connected with the collector electrode of described first switching device, and the negative terminal of described direct current capacitor is connected with the emitter of described second switch device; The emitter of described first switching device is as the anode of described power modules, and the emitter of described second switch device is as the negative terminal of described power modules.

Further, described DC-DC isolator comprises the first electric capacity, single-phase full-bridge inverter, high frequency transformer, single-phase full bridge rectifier and the second electric capacity, in parallel described first electric capacity of direct current input side of described DC-DC isolator forms direct-flow input end mouth, described first DC capacitor is connected with described single-phase full-bridge inverter, described single-phase full-bridge inverter and the series connection of described high frequency transformer, described high frequency transformer is connected with described single-phase full bridge rectifier, described single-phase full bridge rectifier and described second Capacitance parallel connection form DC output end mouth, described DC output end mouth is connected with low-voltage direct electrical network, described direct-flow input end mouth is connected with the DC output end of described power modules.

Further, described DC-AC inverter is three-phase voltage source type inverter (VSI), is directly connected with low-voltage alternating-current electrical network or load by LC filter branch.

To an internal model control method for above-mentioned novel modularized many level-types solid-state transformer, comprise the following steps:

The control of S1, modular multi-level converter:

MMC outer shroud adopts PI controller to control direct voltage, inner ring adopts internal mode controller to realize controlling alternating current DAZ gene, and adopt the capacitor voltage balance control strategy based on phase-shifting carrier wave technology, to realize the alternate Pressure and Control of MMC and submodule Pressure and Control.

The control of S2, DC-DC isolator:

The DC-DC converter unit that DC-DC isolator adopts N number of structure identical is formed by connecting by the mode of ISOP, first the high direct voltage that MMC exports is modulated into high frequency square wave by the single-phase full-bridge inverter that the N number of structure controlled by same synchronizing signal is identical, be coupled to pair side by high frequency transformer again, the single-phase full bridge rectifier that the N number of structure finally controlled by same synchronizing signal is identical is also made into low-voltage direct.

The control of S3, DC-AC inverter:

Inverter outer shroud adopts PI controller to control the power frequency ac voltage of stable output, inner ring adopts internal mode controller to carry out DAZ gene control to the feedback current of filter inductance and load-current feedforward offset current, and adopts space voltage vector modulation technology (SVPWM).

Further, in step S1, when model mates with control object MMC, DAZ gene can be carried out to input, order

$C_M\left(s\right)=G^{-1}\left(s\right)=\left(\begin{array}{cc}{R}^{\′}+sL& -{\mathrm{\ωL}}^{\′}\\ {\mathrm{\ωL}}^{\′}& R+{\mathrm{sL}}^{\′}\end{array}\right)$

In formula, C _ms () is internal mode controller, G ^-1s () is respectively the estimated value of input side resistance and inductance for the inverse matrix of control object model, R ', L ', ω is system angle frequency, and s is regarded as j ω by equivalence;

C _ms the form of () cannot realize in practice, must add low pass filter, introduces a low-pass first order filter

$L\left(s\right)=\frac{\mathrm{\λ}}{s+\mathrm{\λ}}I$

In formula, L (s) is low-pass first order filter, and λ is closed-loop bandwidth, and I is unit matrix;

After introducing low pass filter, inner membrance controller becomes:

$C_M\left(s\right)=G^{-1}\left(s\right)L\left(s\right)=\left(\begin{array}{cc}{R}^{\′}+sL& -{\mathrm{\ωL}}^{\′}\\ {\mathrm{\ωL}}^{\′}& R+{\mathrm{sL}}^{\′}\end{array}\right)L\left(s\right)$

Equivalent block diagram is controlled by inner membrance, then in conjunction with C _ms () can obtain:

$F\left(s\right)==\mathrm{\λ}\left(\begin{array}{cc}L+R^{\′}/s& -{\mathrm{\ωL}}^{\′}/s\\ {\mathrm{\ωL}}^{\′}/s& L+R^{\′}/s\end{array}\right)$

In formula, F (s) is inner membrance decoupling zero equivalence matrix, and on leading diagonal, element is current controller transfer function expression formula, and on back-diagonal, element is then the transfer function of Internal Model Decoupling network;

Decoupling zero implementation method based on internal model control is specially: AC network is surveyed voltage U _sabcthrough a phase-locked loop pll, obtain its system angle frequencies omega _s, converted by abc-dq simultaneously, obtain dq component: U _dand U _q; AC network surveys electric current I _sabcconverted by abc-dq, obtain dq component: i _dand i _q; DC bus-bar voltage U _dCwith voltage reference value U ^* _dCafter subtracting each other, obtain instruction current i through PI controller ^* _d; AC network surveys idle Q and reactive power reference qref Q ^*subtract each other rear same through PI controller, obtain instruction current i ^* _q, these signals realize the input of figure as the decoupling zero in the present embodiment shown in Fig. 8, can obtain command signal u ^* _dand u ^* _q; U _d, U _qrespectively with u ^* _d, u ^* _qsubtract each other, obtain U _rd, U _rq, abc three-phase command voltage can be obtained through dq-abc inverse transformation, as the input signal of phase-shifting carrier wave modulation, above-mentioned middle U _d, U _qand I _d, I _qbe respectively line voltage and the component of electric current on d axle and q axle.

Further, in step S2, wherein N number of inverter and rectifier all adopt PWM to control, and drive singal is the complementary trigger impulse of 50% duty ratio, and adopting active power balance control method, making full-controlled switch device be in Zero Current Switch state by rationally arranging series resonant circuit.

Further, in step S3, concrete control procedure is as follows:

Load side voltage U _lkload voltage angular frequency is obtained through a phase-locked loop pll _l, it is as the input of abc-dq and dq-abc conversion module, obtains dq axle component U through abc-dq conversion simultaneously _ld, U _lq, load-side electric current I _lkdq axle component I is obtained through abc-dq conversion _ld, I _lq, inverter output current I _ikdq axle component I is obtained through abc-dq conversion _id, I _iq, above-mentioned middle I _id, I _iq, U _id, U _iqfor d axle component under dq rotating coordinate system of three-phase DC/AC inverter output current, voltage and q axle component, U _ld, U _lq, I _ld, I _lqfor d axle component under dq rotating coordinate system of load voltage, electric current and q axle component.

Compared with prior art, beneficial effect of the present invention is:

(1) in topological structure, the input stage of this solid-state transformer adopts modular multi-level converter, by increasing and decreasing the number of each brachium pontis sub-series module, adjust the voltage scope of application of current transformer neatly, solid-state transformer can be made to apply to high voltage, high-power field according to application needs.Modular multi-level converter is compared with the Multilevel Inverters of other type, and have main circuit simple, device loss is little, and floor space is little, and cost is low, is convenient to modularized design, all brings facility for the design of solid-state transformer device, production, maintenance;

(2) in control method, a kind of novel double-closed-loop control method internal mold current inner loop be combined with PI outer voltage is proposed.This control mode can make electric current have response speed and stronger Ability of Resisting Disturbance faster.Meanwhile, this control method avoids the cross decoupling problem under two-phase rotating coordinate system, reduces the complexity of Control System Design to a certain extent.

Accompanying drawing explanation

Fig. 1 is the structural framing figure of a kind of modular multilevel type solid-state transformer that the present invention proposes;

Fig. 2 is the topological structure schematic diagram of a kind of modular multilevel type solid-state transformer that the present invention proposes;

Fig. 3 is the structural representation of the modular multi-level converter (MMC) in the present invention;

Fig. 4 is the electrical block diagram of the power modules in the present invention;

Fig. 5 is the electrical block diagram of the DC-DC isolator that the present invention uses;

Fig. 6 is the electrical block diagram of the voltage source inverter that the present invention uses;

Fig. 7 is internal model control block diagram provided by the invention;

Fig. 8 is internal model control block diagram isoboles provided by the invention;

Fig. 9 the invention provides the theory diagram that internal model control method realizes decoupling zero;

Figure 10 is high-pressure side provided by the invention MMC control principle drawing;

Figure 11 is low-pressure side inverter control schematic diagram provided by the invention;

Figure 12 is the current vs figure of IMC and the PI control MMC that the present invention realizes.

Embodiment

Below in conjunction with drawings and Examples, a kind of novel modular multilevel type solid-state transformer of the present invention and internal model control method thereof are described further.

Refer to Fig. 1 and Fig. 2, Fig. 1 is the structural framing figure of a kind of modular multilevel type solid-state transformer that the present invention proposes, Fig. 2 is the topological structure schematic diagram of a kind of modular multilevel type solid-state transformer that the present invention proposes, particularly, described novel modular multilevel type solid-state transformer, comprises modular multi-level converter, DC-DC isolator and DC-AC inverter; The AC of described modular multi-level converter connects High-voltage AC Network, DC side connects the input of described DC-DC isolator, the DC side of described DC-AC inverter connects the output of described DC-DC isolator, and AC connects low-voltage alternating-current electrical network or load; Described modular multi-level converter has direct current anode, direct current negative terminal and three-phase alternating current input.

In the present embodiment, described electrical network is High-Voltage Network, and described modular multi-level converter directly can be connected with electrical network, by changing the number energy flexible adaptation electric pressure of submodule, and effectively can reduce harmonic wave, improving the quality of power supply.

The structured flowchart of the modular multi-level converter in the present invention has been shown in Fig. 3, particularly, described modular multi-level converter comprises A phase unsteady flow bridge, B phase unsteady flow bridge and C phase unsteady flow bridge, the input of each unsteady flow bridge is respectively a phase of three-phase alternating current input, wherein, each unsteady flow bridge comprises a positive convertor arm, a negative convertor arm and two filter reactors; Each convertor arm comprises the power modules of multiple positive-negative series successively, namely the anode of a power modules is connected to the negative terminal of another power modules, multiple power modules connects successively, and the power modules being positioned at two ends forms anode and the negative terminal of convertor arm respectively.Positive convertor arm comprises the multiple power modules being numbered SM1 to SMN, and negative convertor arm also includes the multiple power modules being numbered SM1 to SMN, and the quantity namely comprising power modules in positive convertor arm and negative convertor arm is equal.

In each unsteady flow bridge, the anode of positive convertor arm is connected to the direct current anode of modular multi-level converter, and then is connected to the anode of DC-DC isolator, and the negative terminal of positive convertor arm is connected with one of electrical network by a filter reactor; The negative terminal of negative convertor arm is connected to the direct current negative terminal of modular multi-level converter, and then is connected to the negative terminal of DC-DC isolator, and the anode of negative convertor arm is connected with one of electrical network by another filter reactor.

Fig. 4 is the electrical block diagram of the power modules in the present invention, and each power modules comprises direct current capacitor Cd, the first switching device S1, second switch device S2, the first fly-wheel diode VD1 and the second fly-wheel diode VD2; Wherein, described first switching device S1 and second switch device S2 is full-control type semiconductor switch device.The collector electrode of the first switching device S1 is connected with the negative electrode of the first fly-wheel diode VD1, and the emitter of the first switching device S1 is connected with the anode of the first fly-wheel diode VD1; The collector electrode of second switch device S2 is connected with the negative electrode of the second fly-wheel diode VD2, and the emitter of second switch device S2 is connected with the anode of the second fly-wheel diode VD2; The anode of direct current capacitor C is connected with the collector electrode of the first switching device S1, and the negative terminal of direct current capacitor C is connected with the emitter of second switch device S2; The emitter of the first switching device S1 is as the anode of power modules, and the emitter of second switch device S2 is as the negative terminal of power modules.

Fig. 5 shows the structure chart of described DC-DC isolator, described DC-DC isolator has the identical DC-DC converter unit of each structure of N, and each DC-DC converter unit is composed in series by a single-phase full-bridge inverter, a high frequency transformer and a single-phase full bridge rectifier; High frequency transformer in DC-DC isolator realizes electric pressure conversion and electrical isolation, single-phase full bridge rectifier in described DC-DC isolator adopts the form of Parallel opertation, its input is connected with described high frequency transformer, the anode exported is connected with the anode of described DC-AC inverter, and the negative terminal of output is connected with the negative terminal of described DC-AC inverter.

Fig. 6 gives the structure chart of described DC-AC inverter, and described DC-AC inverter is the three-phase full-bridge inverter of voltage-source type, and its input is connected with the output of above-mentioned DC-DC isolator, exports and is directly connected with low-voltage alternating-current electrical network or load by LC filter branch.

A kind of modular multilevel type solid-state transformer that the present embodiment provides adopts modular multi-level converter, by increasing and decreasing the number of each brachium pontis sub-series module, solid-state transformer can be made to apply to different voltage domain.Compared with conventional solid-state transformer, the advantage of this novel solid-state transformer in High-Voltage Network is fairly obvious.

For solving the problem of dq cross decoupling in conventional solid-state transformer control method, simplifying the design of controller, reducing and calculate.The present embodiment provides a kind of control method of solid-state transformer of modularization level current transformer described above, the novel double-closed-loop control method be combined with PI outer voltage by internal mold current inner loop.

Internal model control (IMC) is the novel control mode that a kind of Kernel-based methods Mathematical Modeling carries out Controller gain variations, has the advantages such as structure is simple, tracking performance of control is good, strong robustness, is widely used in Control of Nonlinear Systems field.

Figure 7 shows that internal model control structure block diagram, wherein, R (s), Y (s) are respectively system input and output signal, C _ms () is internal mode controller, G (s) is control object, the internal mold that M (s) is control object, and D (s) is disturbance, and d (s) exports Y for system exports Y (s) with internal mold _mthe difference of (s).

Control method in the present embodiment comprises following step:

The control of S1, modular multi-level converter;

The control of S2, DC-DC isolator;

The control of S3, DC-AC inverter.

Concrete, in step S1, modular multi-level converter outer shroud adopts PI controller to control direct voltage, and inner ring adopts internal mode controller to realize controlling alternating current DAZ gene.The present embodiment also adopts the capacitor voltage balance control strategy based on phase-shifting carrier wave technology, to realize the alternate Pressure and Control of MMC and submodule Pressure and Control.

By the feature of internal model control, when model mates with control object (MMC), DAZ gene can be carried out to input, order

$C_M\left(s\right)=G^{-1}\left(s\right)=\left(\begin{array}{cc}{R}^{\′}+sL& -{\mathrm{\ωL}}^{\′}\\ {\mathrm{\ωL}}^{\′}& R+{\mathrm{sL}}^{\′}\end{array}\right)$

In formula, G ^-1s () is respectively the estimated value of input side resistance and inductance for the inverse matrix of control object model, R ', L ', ω is system angle frequency, and s is regarded as j ω by equivalence;

C _ms the form of () cannot realize in practice, must add low pass filter, makes system stability by regulating the structure and parameter of low pass filter.In the present embodiment, introduce a low-pass first order filter

$L\left(s\right)=\frac{\mathrm{\λ}}{s+\mathrm{\λ}}I$

In formula, L (s) is low-pass first order filter, and λ is closed-loop bandwidth, and I is unit matrix.

After introducing low pass filter, inner membrance controller becomes:

$C_M\left(s\right)=G^{-1}\left(s\right)L\left(s\right)=\left(\begin{array}{cc}{R}^{\′}+sL& -{\mathrm{\ωL}}^{\′}\\ {\mathrm{\ωL}}^{\′}& R+{\mathrm{sL}}^{\′}\end{array}\right)L\left(s\right)$

Figure 8 shows that the equivalent control block diagram of internal mode controller, control equivalent block diagram by inner membrance, then in conjunction with C _ms () can obtain:

$F\left(s\right)==\mathrm{\λ}\left(\begin{array}{cc}L+R^{\′}/s& -{\mathrm{\ωL}}^{\′}/s\\ {\mathrm{\ωL}}^{\′}/s& L+R^{\′}/s\end{array}\right)$

In formula, F (s) is inner membrance decoupling zero equivalence matrix, on leading diagonal, element is current controller transfer function expression formula, and on back-diagonal, element is then the transfer function of Internal Model Decoupling network, and the Internal Model Decoupling figure realized by internal model control method as shown in Figure 9.

As shown in Figure 10, in step S1 recited above, the decoupling zero implementation method based on internal model control is specially: AC network is surveyed voltage U _sabcthrough a phase-locked loop pll, obtain its system angle frequencies omega _s, converted by abc-dq simultaneously, obtain dq component: U _dand U _q.AC network surveys electric current I _sabcconverted by abc-dq, obtain dq component: i _dand i _q; DC bus-bar voltage U _dCwith voltage reference value U ^* _dCafter subtracting each other, obtain instruction current i through PI controller ^* _d; AC network surveys idle Q and reactive power reference qref Q ^*subtract each other rear same through PI controller, obtain instruction current i ^* _q, these signals realize the input of figure as the decoupling zero in the present embodiment shown in Fig. 9, can obtain command signal u ^* _dand u ^* _q.U _d, U _qrespectively with u ^* _d, u ^* _qsubtract each other, obtain U _rd, U _rq, abc three-phase command voltage can be obtained through dq-abc inverse transformation, as the input signal of phase-shifting carrier wave modulation, above-mentioned middle U _d, U _qand I _d, I _qbe respectively line voltage and the component of electric current on d axle and q axle.

In step S2, the control of DC-DC isolator is comprised: the DC-DC converter unit that DC-DC isolator adopts N number of structure identical is formed by connecting by the mode of ISOP.First the high direct voltage that MMC exports is modulated into high frequency square wave by the single-phase full-bridge inverter that the N number of structure controlled by same synchronizing signal is identical, pair side is coupled to again by high frequency transformer, the single-phase full bridge rectifier that the last N number of structure controlled by same synchronizing signal is identical is also made into low-voltage direct, N number of inverter wherein and rectifier all adopt PWM to control, and drive singal is the complementary trigger impulse of 50% duty ratio.The high frequency transformer parameter caused for solving ISOP connected mode does not mate the unequal problem with DC voltage, the present embodiment have employed a kind of active power Balance route strategy, in addition, in order to reduce system loss, by rationally arranging series resonant circuit (L _rand C _r) make full-controlled switch device be in Zero Current Switch state (ZCS).

As shown in figure 11, in step S3, the control of DC-AC inverter comprises: outer shroud adopts PI controller to control the power frequency ac voltage of stable output, inner ring adopts internal mode controller to carry out DAZ gene control to the feedback current of filter inductance and load-current feedforward offset current, makes it have larger current limiting capacity, preferably dynamic response performance and stronger anti-disturbance ability concurrently.It is substantially identical that inner membrance control method described herein and inner membrance control decoupling principle figure with MMC.Concrete control method and inner membrance control decoupling principle figure as shown in Figure 11 and Fig. 9.Meanwhile, in order to improve inverter direct-current voltage utilance, reduce switching loss, the present embodiment adopts space voltage vector modulation technology (SVPWM).

Load side voltage U _lkload voltage phase place ω is obtained through a phase-locked loop pll _l, it is as the input of abc-dq and dq-abc conversion module, obtains dq axle component U through abc-dq conversion simultaneously _ld, U _lq.Load-side electric current I _lkdq axle component I is obtained through abc-dq conversion _ld, I _lq.Inverter output current I _ikdq axle component I is obtained through abc-dq conversion _id, I _iq, above-mentioned middle I _id, I _iq, U _id, U _iqfor d axle component under dq rotating coordinate system of three-phase DC/AC inverter output current, voltage and q axle component, U _ld, U _lq, I _ld, I _lqfor d axle component under dq rotating coordinate system of load voltage, electric current and q axle component.In Figure 11, ω is power angle frequency, C _ffor filtering capacitance.

For the control method of above-mentioned proposition, the present embodiment is verified its control effects, and the concrete working condition considered is: grid side power factor change.Figure 12 shows that, the comparison of wave shape figure of the dq current component of modular multi-level converter when adopting IMC control and PI to control.

Concrete has, and the direct voltage set-point of modular multi-level converter 1 is always 18kV, output stage band three-phase balancing load.During initial condition, the idle set-point of input stage is 0.625Mvar, and namely netting side power factor is 0.95 (absorbing idle); During 0.3s, reactive power set-point becomes-0.65Mvar, and namely netting side power factor is 0.95 (sending idle); During 0.4s, idle set-point is 0, namely nets side unity power factor and runs.When Figure 12 adopts IMC to control to the modular multi-level converter 1 described in the present invention and adopts PI to control, the tracking effect of dq current component under above-mentioned operating mode contrasts: can find out from the dq shaft current waveform provided,, reactive power meritorious in increase and decrease gives timing, adopts IMC control mode faster than employing PI control mode current inner loop response speed.During 0.3s, the sudden change of rectification side reactive power given generation step, can find out that the d shaft current fluctuation that PI controls is obvious, and electric current under IMC control mode is very steady.IMC control mode can realize dq current decoupled control and performance of noiseproof is stronger than PI control mode as can be seen here, can find out that the present invention adopts the MMC-SST controller of IMC inner ring control method to have response speed and stronger antijamming capability faster compared with traditional PI inner ring controller significantly.

In the present invention, the input stage of solid-state transformer adopts modular multi-level converter (Modularmultilevelconverter, MMC), by increasing and decreasing the number of each brachium pontis sub-series module, makes solid-state transformer apply to different voltage domain.Run according to given power factor to enable MMC-SST, and there is the advantages such as voltage, electric current dynamic response is fast, anti-disturbance ability is strong, according to the characteristic of internal model control, propose a kind of novel double-closed-loop control method internal mold current inner loop be combined with PI outer voltage.This control mode can make electric current have response speed and stronger Ability of Resisting Disturbance faster.Meanwhile, this control method avoids the cross decoupling problem under two-phase rotating coordinate system, reduces the complexity of Control System Design to a certain extent.

The above embodiment only have expressed several execution mode of the present invention, and it describes comparatively concrete and detailed, but therefore can not be interpreted as the restriction to the scope of the claims of the present invention.It should be pointed out that for the person of ordinary skill of the art, without departing from the inventive concept of the premise, can also make some distortion and improvement, these all belong to protection scope of the present invention.Therefore, the protection range of patent of the present invention should be as the criterion with claims.

Claims (9)

1. a novel modular multilevel type solid-state transformer, is characterized in that, comprises modular multi-level converter, DC-DC isolator and DC-AC inverter;

The AC of described modular multi-level converter connects High-voltage AC Network, DC side connects the input of described DC-DC isolator, the DC side of described DC-AC inverter connects the output of described DC-DC isolator, and AC connects low-voltage alternating-current electrical network or load.

2. modular multilevel type solid-state transformer as claimed in claim 1, it is characterized in that, described modular multi-level converter comprises the first unsteady flow bridge, second unsteady flow bridge and the 3rd unsteady flow bridge, the input of described unsteady flow bridge is as a phase of three-phase alternating current input, described unsteady flow bridge comprises positive convertor arm, negative convertor arm, first filter reactor and the second filter reactor, the anode of described positive convertor arm is connected to the direct current anode of described modular multi-level converter, and then be connected to the anode of described DC-DC isolator, the negative terminal of described positive convertor arm is connected with one of electrical network by described first filter reactor, the negative terminal of described negative convertor arm is connected to the direct current negative terminal of described modular multi-level converter, and then be connected to the negative terminal of described DC-DC isolator, the anode of described negative convertor arm is connected with one of electrical network by described second filter reactor, described positive convertor arm/negative convertor arm comprises the power modules of multiple positive-negative series successively, the DC side of described power modules is positive and negative to be connected with the positive and negative of high-voltage direct current power grid respectively.

3. modular multilevel type solid-state transformer as claimed in claim 2, it is characterized in that, described power modules comprises direct current capacitor, the first switching device, second switch device, the first fly-wheel diode and the second fly-wheel diode, and described first switching device and second switch device are full-control type semiconductor switch device;

The collector electrode of described first switching device is connected with the negative electrode of described first fly-wheel diode, and the emitter of described first switching device is connected with the anode of described first fly-wheel diode; The collector electrode of described second switch device is connected with the negative electrode of described second fly-wheel diode, and the emitter of described second switch device is connected with the anode of described second fly-wheel diode; The anode of described direct current capacitor is connected with the collector electrode of described first switching device, and the negative terminal of described direct current capacitor is connected with the emitter of described second switch device; The emitter of described first switching device is as the anode of described power modules, and the emitter of described second switch device is as the negative terminal of described power modules.

4. modular multilevel type solid-state transformer as claimed in claim 1, it is characterized in that, described DC-DC isolator comprises the first electric capacity, single-phase full-bridge inverter, high frequency transformer, single-phase full bridge rectifier and the second electric capacity, in parallel described first electric capacity of direct current input side of described DC-DC isolator forms direct-flow input end mouth, described first DC capacitor is connected with described single-phase full-bridge inverter, described single-phase full-bridge inverter and the series connection of described high frequency transformer, described high frequency transformer is connected with described single-phase full bridge rectifier, described single-phase full bridge rectifier and described second Capacitance parallel connection form DC output end mouth, described DC output end mouth is connected with low-voltage direct electrical network, described direct-flow input end mouth is connected with the DC output end of described power modules.

5. modular multilevel type solid-state transformer as claimed in claim 1, it is characterized in that, described DC-AC inverter is three-phase voltage source type inverter, is directly connected with low-voltage alternating-current electrical network or load by LC filter branch.

6., to an internal model control method for the modular multilevel type solid-state transformer described in any one of aforementioned claim, it is characterized in that, comprise the following steps:

The control of S1, modular multi-level converter:

MMC outer shroud adopts PI controller to control direct voltage, inner ring adopts internal mode controller to realize controlling alternating current DAZ gene, and adopt the capacitor voltage balance control strategy based on phase-shifting carrier wave technology, to realize the alternate Pressure and Control of MMC and submodule Pressure and Control;

The control of S2, DC-DC isolator:

The DC-DC converter unit that DC-DC isolator adopts N number of structure identical is formed by connecting by the mode of ISOP, first the high direct voltage that MMC exports is modulated into high frequency square wave by the single-phase full-bridge inverter that the N number of structure controlled by same synchronizing signal is identical, be coupled to pair side by high frequency transformer again, the single-phase full bridge rectifier that the N number of structure finally controlled by same synchronizing signal is identical is also made into low-voltage direct;

The control of S3, DC-AC inverter:

Inverter outer shroud adopts PI controller to control the power frequency ac voltage of stable output, and inner ring adopts internal mode controller to carry out DAZ gene control to the feedback current of filter inductance and load-current feedforward offset current, and adopts space voltage vector modulation technology.

7. the internal model control method of modular multilevel type solid-state transformer as claimed in claim 6, is characterized in that, in step S1, when model mates with control object MMC, can carry out DAZ gene to input, order

$C_M\left(s\right)=G^{-1}\left(s\right)=\left(\begin{array}{cc}{R}^{\′}+sL& -{\mathrm{\ωL}}^{\′}\\ {\mathrm{\ωL}}^{\′}& R+{\mathrm{sL}}^{\′}\end{array}\right)$

In formula, C _ms () is internal mode controller, G ^-1s () is respectively the estimated value of input side resistance and inductance for the inverse matrix of control object model, R ', L ', ω is system angle frequency, and s is regarded as j ω by equivalence;

C _ms the form of () cannot realize in practice, must add low pass filter, introduces a low-pass first order filter

$L\left(s\right)=\frac{\mathrm{\λ}}{s+\mathrm{\λ}}I$

In formula, L (s) is low-pass first order filter, and λ is closed-loop bandwidth, and I is unit matrix;

After introducing low pass filter, inner membrance controller becomes:

$C_M\left(s\right)=G^{-1}\left(s\right)L\left(s\right)=\left(\begin{array}{cc}{R}^{\′}+sL& -{\mathrm{\ωL}}^{\′}\\ {\mathrm{\ωL}}^{\′}& R+{\mathrm{sL}}^{\′}\end{array}\right)L\left(s\right)$

Equivalent block diagram is controlled by inner membrance, then in conjunction with C _ms () can obtain:

$F\left(s\right)==\mathrm{\λ}\left(\begin{array}{cc}L+R^{\′}/s& -{\mathrm{\ωL}}^{\′}/s\\ {\mathrm{\ωL}}^{\′}/s& L+R^{\′}/s\end{array}\right)$

In formula, F (s) is feedback controller, and on leading diagonal, element is current controller transfer function expression formula, and on back-diagonal, element is then the transfer function of Internal Model Decoupling network;

Decoupling zero implementation method based on internal model control is specially: AC network is surveyed voltage U _sabcthrough a phase-locked loop pll, obtain its system angle frequencies omega _s, converted by abc-dq simultaneously, obtain dq component: U _dand U _q; AC network surveys electric current I _sabcconverted by abc-dq, obtain dq component: i _dand i _q; DC bus-bar voltage U _dCwith voltage reference value U ^* _dCafter subtracting each other, obtain instruction current i through PI controller ^* _d; AC network surveys idle Q and reactive power reference qref Q ^*subtract each other rear same through PI controller, obtain instruction current i ^* _q, these signals realize the input of figure as the decoupling zero in the present embodiment shown in Fig. 8, can obtain command signal u ^* _dand u ^* _q; U _d, U _qrespectively with u ^* _d, u ^* _qsubtract each other, obtain U _rd, U _rq, abc three-phase command voltage can be obtained through dq-abc inverse transformation, as the input signal of phase-shifting carrier wave modulation, above-mentioned middle U _d, U _qand I _d, I _qbe respectively line voltage and the component of electric current on d axle and q axle.

8. the internal model control method of modular multilevel type solid-state transformer as claimed in claim 6, it is characterized in that, in step S2, wherein N number of inverter and rectifier all adopt PWM to control, drive singal is the complementary trigger impulse of 50% duty ratio, and adopting active power balance control method, making full-controlled switch device be in Zero Current Switch state by rationally arranging series resonant circuit.

9. the internal model control method of modular multilevel type solid-state transformer as claimed in claim 6, it is characterized in that, in step S3, concrete control procedure is as follows:

Load side voltage U _lkload voltage angular frequency is obtained through a phase-locked loop pll _l, it is as the input of abc-dq and dq-abc conversion module, obtains dq axle component U through abc-dq conversion simultaneously _ld, U _lq, load-side electric current I _lkdq axle component I is obtained through abc-dq conversion _ld, I _lq, inverter output current I _ikdq axle component I is obtained through abc-dq conversion _id, I _iq, above-mentioned middle I _id, I _iq, U _id, U _iqfor d axle component under dq rotating coordinate system of three-phase DC/AC inverter output current, voltage and q axle component, U _ld, U _lq, I _ld, I _lqfor d axle component under dq rotating coordinate system of load voltage, electric current and q axle component.