CN103516221A - Bi-direction direct-current solid-state transformer with high-frequency alternating-current isolation link - Google Patents

Abstract

The invention discloses a bi-direction direct-current solid-state transformer with a high-frequency alternating-current isolation link, and belongs to the technical field of electric power. The transformer is formed by connecting n identical direct-current transformer units at a low-voltage port in parallel and at a high-voltage port in series, wherein n is a positive integer larger than or equal to 2. Each direct-current transformer unit comprises two full-bridge transformers (H1 and H2), an auxiliary inductor (L), an isolation transformer (T) and two direct-current filter capacitors (C1 and C2), wherein the direct-current filter capacitors (C1 and C2) are connected with the direct-current ends of the full-bridge transformers (H1 and H2) respectively in parallel, the primary side and the secondary side of the isolation transformer are in parallel connection with the alternating current ends of the full-bridge transformers (H1 and H2) respectively, and the auxiliary inductor (L) is connected between the alternating current end of the full-bridge transformer H1 and the isolation transformer. Voltage matching of high-voltage and low-voltage direct-current links can be achieved, bi-direction flowing of power and electric isolation can be achieved, and the transformer has a certain application prospect in a direct-current power distribution network and a direct-current micro-grid.

Description

A kind of bidirectional, dc solid-state transformer with high-frequency ac isolation link

Technical field

The invention belongs to power technology field, relate to solid-state transformer, particularly a kind of bidirectional, dc solid-state transformer with high-frequency ac isolation link.

Background technology

The dramatic benefits such as the degree of modularity is high, efficiency is high, power density is high, noise is low owing to having, intelligent degree height, there is at present more research to pay close attention to and adopted electric power electric transformer (also referred to as solid-state transformer SST) to replace conventional AC distribution transformer, especially along with the fast development of distribution type electric energy, energy storage etc. in intelligent grid, SST is as the integrated system of various distributed unit and realize the solution that voltage, trend etc. control flexibly and more and more come into one's own.

And at present, based on voltage source converter (Voltage Source Converter, VSC) direct current transportation (VSC-HVDC) can be controlled active power and the reactive power of transmitting independently, fast, therefore greatly strengthened the flexibility of transmission of electricity, become the electric power transfer mode of being potential most that latest developments are got up, be specially adapted to stable connection between wind power plant and major network, to application such as an isolated distant place little loading zone power supplies.Technology of HVDC based Voltage Source Converter has all obtained general attention at home and abroad in recent years, and flexible DC power transmission engineering is also increasing.Aspect distribution network, along with the development in city and the quick increase of power load, the requirement of distribution network transmission capacity is also increased day by day, need on limited power distribution network corridor, carry larger capacity.In the intensive urban distribution network of electricity consumption, adopt flexible direct current technology, can take transmission of electricity corridor still less, and can utilize its features such as quick controllability, solve the power supply difficulty that exists in urban electricity supply, cost is high and trend is difficult to the problems such as control, maintains the safe and reliable economical operation of urban distribution network.By the mode of direct current distribution, can also reduce the intermediate link of energy-storage system and grid-connected power generation system access electrical network, reduce cost of access, improve power conversion efficiency and the quality of power supply.

With respect to electric power transmission network, when being applied to power distribution network, flexible direct current technology will face more complicated technical problem.Owing to need to tackling the access of load, energy-storage system and the distributed power generation of various different direct voltage grades, the DC voltage conversion in direct current distribution will be inevitable.But in direct current distribution, be difficult to by magnetic-coupled mode, realize voltage transformation as AC transformer, therefore must by DC/DC converter, realize the conversion of direct voltage and the bi-directional of power based on power electronic technology, major way is to realize high frequency conversion by electronic power convertor, and by high frequency transformer, realizes conversion and the electrical isolation of voltage.

In low pressure low capacity field, DC/DC converter has obtained applying more widely, for high-frequency isolation type DC/DC converter, also has more document to inquire into.But due to the restriction of power electronics semiconductor device development degree, the high-frequency isolation DC/DC converter of the large capacitance grade of mesohigh seldom has document to relate to.Especially, due to the concept of flexible direct current distribution, to obtain time of paying attention to very short, at present wholely in the world the research of solid-state transformer all rested on alternating current solid-state transformer substantially, to the research of DC solid transformer, relates to less.Patent " based on full-bridge topologies input series and output parallel automatically equalizing voltage commutator transformer " has proposed a kind of high input voltage, low pressure output isolated DC transformer of being applied in, but because output adopts, do not control rectifier bridge, make this commutator transformer not there is bidirectional power transmittability.But along with the development of flexible direct current distribution, not only need DC solid transformer to import the power of DC distribution net into load, also need the power loopback that distributed power source is sent to DC distribution net, this just requires DC solid transformer to have bidirectional power transmittability.

Summary of the invention

The object of the invention is for solving above-mentioned technical problem, propose a kind of bidirectional, dc solid-state transformer with high-frequency ac isolation link, not only realize the voltage matches of high-low pressure DC link, and realize two-way flow and the electrical isolation of power.

The technical scheme that the present invention takes is as follows:

A kind of bidirectional, dc solid-state transformer with high-frequency ac isolation link, it is characterized in that, this bidirectional, dc solid-state transformer is mainly comprised of n identical DC converter unit, the low-pressure port of this n DC converter unit is connected in parallel, and the high pressure port of this n DC converter unit is connected successively; N is more than or equal to 2 positive integer; Each DC convertor unit comprises: two full-bridge converter (H ₁, H ₂), an auxiliary induction (L), an isolating transformer (T) and two DC filter capacitor (C ₁, C ₂), DC filter capacitor (C ₁, C ₂) respectively with full-bridge converter (H ₁, H ₂) DC terminal in parallel, the former limit of isolating transformer and secondary respectively with full-bridge converter (H ₁, H ₂) interchange end in parallel, auxiliary induction (L) is connected to full-bridge converter H ₁interchange end and isolating transformer between.

Described a kind of bidirectional, dc solid-state transformer with high-frequency ac isolation link, is characterized in that described full-bridge converter (H ₁, H ₂) be single-phase full bridge converter or three phase full bridge converter;

Described a kind of bidirectional, dc solid-state transformer with high-frequency ac isolation link, is characterized in that, described auxiliary induction and isolating transformer are high-gradient magnetism element, and frequency is more than or equal to 10kHz;

Described a kind of bidirectional, dc solid-state transformer with high-frequency ac isolation link, is characterized in that, described auxiliary induction can be thought independently element, can be also the leakage inductance of isolating transformer;

Adopt technique scheme, beneficial effect of the present invention is:

1) DC solid transformer can be used as the interface system between high voltage direct current power distribution network and the micro-electrical network of low-voltage direct, realizes the voltage matches of high-low pressure DC link, and realizes two-way flow and the electrical isolation of power.

2) scheme of DC solid transformer adopting high-frequency isolation, can effectively dwindle current transformer volume, improves power density.

3) the modular full-bridge converter structure of DC solid transformer adopting, capacity can pass through increase and decrease converter cell flexible, and can provide redundant module to improve system reliability.

Accompanying drawing explanation

Fig. 1 is a kind of composition structure chart with the bidirectional, dc solid-state transformer of high-frequency ac isolation link of the present invention.

Fig. 2 is the composition structure chart that another kind of the present invention has the bidirectional, dc solid-state transformer of high-frequency ac isolation link.

Fig. 3 is the averaging model equivalent electric circuit of bidirectional, dc solid-state transformer of the present invention.

Fig. 4 is the control method of bidirectional, dc solid-state transformer of the present invention.

Fig. 5 is the through-put power model of bidirectional, dc solid-state transformer of the present invention.

Fig. 6 (a) is the voltage and current waveform of bidirectional, dc solid-state transformer high-pressure side of the present invention;

Fig. 6 (b) is the voltage and current waveform of bidirectional, dc solid-state transformer low-pressure end of the present invention.

Fig. 7 (a) is the voltage waveform that in bidirectional, dc solid-state transformer of the present invention, each DC convertor unit is held in series connection;

Fig. 7 (b) be in bidirectional, dc solid-state transformer of the present invention each DC convertor unit at the current waveform of high-frequency ac isolation link.

When Fig. 8 (a) is the through-put power direction transformation of bidirectional, dc solid-state transformer of the present invention, the voltage and current waveform of high-pressure side;

When Fig. 8 (b) is the through-put power direction transformation of bidirectional, dc solid-state transformer of the present invention, the voltage and current waveform of low-pressure end.

Embodiment

Below in conjunction with technical scheme of the present invention and accompanying drawing, describe specific embodiments of the invention in detail.

The composition structure of a kind of bidirectional, dc solid-state transformer with high-frequency ac isolation link of the present invention as shown in Figure 1.This bidirectional, dc solid-state transformer is mainly comprised of n identical DC converter unit, and n is more than or equal to 2 positive integer; A port (low-pressure end) of each DC converter unit is parallel with one another, and another port (high-pressure side) of each DC converter unit is connected successively.

The topological structure of each DC convertor unit is phase structure, comprising: two full-bridge converter H ₁, H ₂, auxiliary induction L, an isolating transformer T and two DC filter capacitor C ₁, C ₂, DC filter capacitor C ₁, C ₂respectively with full-bridge converter H ₁, H ₂dC terminal in parallel, the former limit of isolating transformer and secondary respectively with full-bridge converter H ₁, H ₂interchange end in parallel, auxiliary induction L is connected to full-bridge converter H ₁interchange end and isolating transformer between.

The another kind that the present invention proposes have high-frequency ac isolation link bidirectional, dc solid-state transformer composition structure as shown in Figure 2, this bidirectional, dc solid-state transformer is mainly comprised of n identical DC converter unit, the low-pressure port of this n DC converter unit is connected in parallel, and the high pressure port of this n DC converter unit is connected successively; N is more than or equal to 2 positive integer;

The topological structure of each DC convertor unit comprises: two three phase full bridge converter (H ₁, H ₂), a three-phase isolation transformer (T) and two DC filter capacitor (C ₁, C ₂), DC filter capacitor (C ₁, C ₂) respectively with three phase full bridge converter (H ₁, H ₂) DC terminal in parallel, the former limit of three-phase isolation transformer and secondary respectively with full-bridge converter (H ₁, H ₂) interchange end in parallel; The leakage inductance of three-phase isolation transformer (T) is as auxiliary induction.

Auxiliary induction in Fig. 1 and 2 and isolating transformer are high-gradient magnetism element, get 20kHz in the present embodiment, also can get the value that other is more than or equal to 10kHz.

In Fig. 1, auxiliary induction is element independently, and auxiliary induction adopts the leakage inductance of isolating transformer in Fig. 2.

In embodiments of the invention, by three identical DC convertor unit in parallel, formed, in each unit, get two single-phase full bridge converter H ₁, H ₂switching frequency be that 20kHz, auxiliary induction L are that 0.1mH, isolating transformer T no-load voltage ratio are 200/200, two DC filter capacitor C ₁, C ₂be 3300uF.Low-voltage direct busbar voltage 200V, high voltage dc bus voltage 600V.According to different applicable cases, also desirable other value.

Operation principle of the present invention:

Fig. 3 has provided the averaging model equivalent electric circuit of bidirectional, dc solid-state transformer of the present invention.Wherein, V _hVand V _lVbe respectively bidirectional, dc solid-state transformer high-low pressure DC bus-bar voltage, I _hViand I _lVibe respectively each DC convertor unit at the average current of height pressure side, V _i1and V _i2be respectively each DC convertor unit at the average voltage of height pressure side, I _i1and I _i2be respectively each DC convertor unit at the average current of the full-bridge converter of height pressure side, P _imean value for each DC convertor unit through-put power; In above-mentioned variable, i=1,2,3 ... n.

Fig. 4 has provided the control method of bidirectional, dc solid-state transformer of the present invention.Except existing between each both sides, DC convertor unit full-bridge converter, D is compared in phase shift _i2in each full-bridge converter inside, also exist interior phase shift to compare D outward, _i1.In Figure 4 and 5, v _hi1, v _hi2be respectively each DC convertor unit full-bridge converter (H ₁, H ₂) interchange terminal voltage, i _lifor each DC convertor unit full-bridge converter (H ₁, H ₂) interchange end electric current, T _hsit is half switch periods.

For each DC convertor unit, through-put power P _ican be expressed as,

$P_i=\frac{n_T{V}_{i1}{V}_{i2}}{2f_{s}L}[D_{i2}(1-D_{i2})-\frac{1}{2}{D}_{i1}^2]---\left(1\right)$

Wherein, f _sfor switching frequency, n _tfor transformer voltage ratio, L is the leakage inductance sum of auxiliary induction and high frequency transformer.

For bidirectional, dc solid-state transformer, each DC convertor unit is equal at the electric current of series side, equal at the voltage of side in parallel, can obtain

$\left\{\begin{array}{c}{V}_{\mathrm{HV}}=V_{11}+V_{21}+\&CenterDot;\&CenterDot;\&CenterDot;+V_{n1}\\ I_{\mathrm{HV}}={\mathrm{<figure-callout\; id="1"\; label="I\; HV"\; filenames="HDA0000393447150000023.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{HV}}=I_{\mathrm{HV}2}=\&CenterDot;\&CenterDot;\&CenterDot;=I_{\mathrm{HVn}}\\ V_{\mathrm{LV}}=V_{12}=V_{22}=\&CenterDot;\&CenterDot;\&CenterDot;=V_{n2}\\ P_{\mathrm{DCSST}}={\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HDA0000393447150000023.png"\; state="\{\{state\}\}">P</figure-callout>}}_1+P_2+\&CenterDot;\&CenterDot;\&CenterDot;+P_n\end{array}\right.---\left(2\right)$

Wherein, P _dCSSTthrough-put power for bidirectional, dc solid-state transformer.In full accord when control method and the parameter of each DC convertor unit, have

$\left\{\begin{array}{c}{\mathrm{<figure-callout\; id="1"\; label="D"\; filenames="HDA0000393447150000023.png"\; state="\{\{state\}\}">D</figure-callout>}}_1=D_{11}=D_{21}=\&CenterDot;\&CenterDot;\&CenterDot;=D_{n1}\\ D_2=D_{12}=D_{22}=\&CenterDot;\&CenterDot;\&CenterDot;=D_{n2}\end{array}\right.---\left(3\right)$

According to formula (1)-(3), can obtain,

$P_{\mathrm{DCSST}}=\frac{n_T{V}_{\mathrm{HV}}{V}_{\mathrm{LV}}}{2f_{s}L}[D_2(1-D_2)-\frac{1}{2}{{\mathrm{<figure-callout\; id="1"\; label="D"\; filenames="HDA0000393447150000023.png"\; state="\{\{state\}\}">D</figure-callout>}}_1}^2]---\left(4\right)$

According to formula (4), can obtain the maximum transmission power P of bidirectional, dc solid-state transformer _{dCSST_max}at D ₁=0, D ₂=0.5 place obtains, and maximum is,

$P_{\mathrm{DCSST}\_\max }=\frac{n_T{V}_{\mathrm{HV}}{V}_{\mathrm{LV}}}{8f_{s}L}---\left(5\right)$

Fig. 5 has provided the through-put power model of bidirectional, dc solid-state transformer.As can be seen here, by regulating the inside and outside phase shift between each both sides, DC convertor unit full-bridge converter to compare D ₁and D ₁, just can regulate the size and Orientation of through-put power, and then also can regulate the output voltage of DC solid transformation.

As shown in Figure 6 (a), the voltage and current waveform of bidirectional, dc solid-state transformer low-pressure end as shown in Figure 6 (b) for the voltage and current waveform of the bidirectional, dc solid-state transformer high-pressure side of the present embodiment.As can be seen from the figure, high-low pressure terminal voltage is stabilized in respectively 600V and 200V, and the voltage and current conversion of DC solid transformer is all working properly.

In the bidirectional, dc solid-state transformer of the present embodiment each DC convertor unit at the voltage waveform of series connection end as shown in Fig. 7 (a), in bidirectional, dc solid-state transformer each DC convertor unit at the current waveform of high-frequency ac isolation link as shown in Fig. 7 (b).Therefrom can find out, the series voltage of each DC convertor unit all equates, has showed good balance of voltage effect; The electric current of each high-frequency ac isolation link also equates, has showed good power-balance effect.

During the through-put power direction transformation of the bidirectional, dc solid-state transformer of the present embodiment, the voltage and current waveform of high-pressure side as shown in Figure 8 (a), during the through-put power direction transformation of bidirectional, dc solid-state transformer, the voltage and current waveform of low-pressure end as shown in Figure 8 (b) shows.As can be seen from the figure,, before t0, the power of DC solid transformer flows to low-pressure end from high-pressure side; And after t0, power flows to high-pressure side from low-pressure end.When through-put power direction is switched, it is constant that high-pressure side voltage maintains substantially, and other voltage and currents are recovering very soon stable after one section of transient state, and keep fixing voltage and current conversion ratio.

Claims (4)

1. a bidirectional, dc solid-state transformer with high-frequency ac isolation link, it is characterized in that, this bidirectional, dc solid-state transformer is mainly comprised of n identical DC converter unit, the low-pressure port of this n DC converter unit is connected in parallel, and the high pressure port of this n DC converter unit is connected successively; N is more than or equal to 2 positive integer; Each DC convertor unit comprises: two full-bridge converter (H ₁, H ₂), an auxiliary induction (L), an isolating transformer (T) and two DC filter capacitor (C ₁, C ₂), DC filter capacitor (C ₁, C ₂) respectively with full-bridge converter (H ₁, H ₂) DC terminal in parallel, the former limit of isolating transformer and secondary respectively with full-bridge converter (H ₁, H ₂) interchange end in parallel, auxiliary induction (L) is connected to full-bridge converter H ₁interchange end and isolating transformer between.

2. a kind of bidirectional, dc solid-state transformer with high-frequency ac isolation link as claimed in claim 1, is characterized in that described full-bridge converter (H ₁, H ₂) be single-phase full bridge converter or three phase full bridge converter.

3. a kind of bidirectional, dc solid-state transformer with high-frequency ac isolation link as claimed in claim 1, is characterized in that, described auxiliary induction and isolating transformer are high-gradient magnetism element, and frequency is more than or equal to 10kHz.

4. a kind of bidirectional, dc solid-state transformer with high-frequency ac isolation link as claimed in claim 1, is characterized in that, described auxiliary induction is element or be the leakage inductance of isolating transformer independently.

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