CN106374420A - DC micro grid converter - Google Patents

Abstract

The invention relates to a DC micro grid converter comprising a transformer, a filter unit, a converter unit, a DC flat-wave inductor and a mechanical switch, which are connected in sequence. The DC micro grid converter further comprises a short-circuit protection module, which is connected in series between the converter unit and the flat-wave inductor and includes at least two switching tubes. A DC-side short-circuit fault can be isolated quickly, impact current can be inhibited in the fault process, and the system stability is ensured.

Description

A kind of direct-current grid current transformer

Technical field

The invention belongs to technical field of photovoltaic power generation, more particularly to a kind of direct-current grid current transformer.

Technical background

With the development of social economy, spacecraft power supply system, offshore wind farm grid-connected system, energy-storage system etc. are a lot Distributed power grid increasingly tends to DC distribution.DC load increase and the development of DC distribution technology will effectively promote The development of DC distribution net, therefore DC transformer occupy increasingly consequence in the market.Have one in direct-current micro-grid Individual major issue is short-circuit protection.When DC load occurs positive-negative polarity short circuit, it is protection equipment safety, need to be very short Excision trouble point in time.But direct-current short circuit electric current is generally very big, it is difficult to disconnect；Simultaneously for AC system, directly Streaming system load short circuits impedance is low, does not have zero crossing, and this will make short circuit current rise to very high value within a short period of time, and then Damage network system.Due to common breaker actuation is relatively slow and direct-current short circuit electric current no zero crossing the features such as, by common Chopper cannot realize short-circuit protection.It is currently available that dc circuit breaker manufactures relatively difficult, cost intensive simultaneously, medium and small System cost is caused to increase in power.

Three phase full bridge circuit as shown in Figure 1 is a kind of common ac-dc converter topology, is connected including with AC network The transformator t connecing, the lc unit strobing, current transforming unit, direct current flat ripple inductance l1 and mechanical switch etc., but this change Stream device topological structure does not have output short-circuit current limiting capacity, in load short circuits, can produce very big short circuit current, may be right Equipment causes to damage.

Content of the invention

For solving three phase full bridge ac/dc current transformer of the prior art when there is direct-current short circuit fault, short circuit current mistake Greatly, easily cause the unstable problem of system, the invention provides a kind of direct-current grid current transformer.

A kind of direct-current grid current transformer, except be sequentially connected transformator t, filter unit, current transforming unit, the flat ripple of direct current Inductance l1 and mechanical switch, also include short circuit protection module, short circuit protection module be connected on current transforming unit and flat ripple inductance l1 it Between, including at least two switching tubes.

Further, described short circuit protection module is the switching tube of two differential concatenations, and each switching tube is all parallel with instead To diode.

Further, above-mentioned switching tube is igbt.

Further, above-mentioned short circuit protection module also includes one for electric with described flat ripple when described switching tube turns off Sense forms the fly-wheel diode in loop.

The invention has the beneficial effects as follows: the present invention can be suppressed it is ensured that system is steady to dc-side short-circuit fault electric current Fixed；And the present invention only increases the short circuit protection module of an inclusion switching tube, just realize short circuit current limitation ability, structure letter Single, low cost.

Setting fly-wheel diode, can play afterflow effect when switching tube turns off to the electric current on direct current flat ripple inductance l1.

Brief description

Fig. 1 is the topological circuit structure chart of three phase full bridge ac/dc current transformer in prior art；

The topological circuit structure chart of the three phase full bridge ac/dc current transformer that Fig. 2 provides for the present invention；

Fig. 3 is current transformer schematic diagram when rectification mode works；

Fig. 4 is current transformer schematic diagram when inverter mode works；

Fig. 5 is current transformer schematic diagram in direct-current short circuit；

Fig. 6 is schematic diagram when waiting direct-current short circuit to recover；

Schematic diagram when Fig. 7 charges for dc bus.

Specific embodiment

The invention provides a kind of direct-current grid current transformer, by the topological circuit in three phase full bridge ac/dc current transformer The middle igbt increasing by a pair reverse concatenation and fly-wheel diode, realize the protection of direct-current short circuit fault traversing, prevent failure propagation, really Insurance system normal table.

The present invention will be further described in detail below in conjunction with the accompanying drawings.

Fig. 1 be prior art in a kind of common three phase full bridge ac/dc converter topologies, including with AC network phase The transformator t connecting, the lc filter unit strobing, current transforming unit, direct current flat ripple inductance l1 and mechanical switch etc., but It is that this converter topologies do not have output short-circuit current limiting capacity, in DC side load short circuits, can produce very big Short circuit current, may cause to equipment to damage.

In DC micro power grid system as shown in Figure 2, using the direct-current grid current transformer of present invention offer.Shown in Fig. 2 Micro-grid system include equipment 1 and equipment 2, equipment 1 is identical with the structure of equipment 2, with reference to structure and the work of equipment 1 The present invention will be described in detail for flow process.

Compared to Figure 1, in equipment 1, the topological circuit of three phase full bridge ac/dc current transformer increased a short circuit protection module, The i.e. igbt of a pair reverse concatenation and fly-wheel diode.Wherein igbt1 and igbt2 reversely concatenates, when electrical switch direct-current short circuit During fault, directly turn off, prevent short circuit infringement device components and parts；In addition, fly-wheel diode is used for being had no progeny in igbt1,2 passes, it is Play afterflow effect in electric current present on inductance；DC side flat ripple inductance l1, in the prior art, can make multiple stage DC source it Between current energy smooth flow, and moreover it is possible to play when dc-side short-circuit in the present invention program, limit raising speed on electric current Degree it is ensured that igbt can safe shutdown it is ensured that the effect that is not compromised of electric components.

Opening, turning off and to realize normally running control, direct-current short circuit event of igbt1, igbt2 can be changed according to system mode Barrier protection controls, DC Line Fault passes through control.

Above-mentioned short circuit protection module is Two switches in series structure, as other embodiment, can also be using others The structure of structure, such as reverse parallel connection or bridge architecture etc..

Below with regard to the short circuit protection module structure shown in Fig. 2, in conjunction with current transformer different working modes schematic diagram pair The present invention is described further:

As shown in figure 3, during direct current network system worked well, opening igbt1, igbt2 and be always maintained at conducting state, unsteady flow Device is operated under rectification mode, igbt1, igbt2 series diode d1 and d2 respectively, and electric current can only be negative through igbt1, d2 flow direction Carry；

As shown in figure 4, during direct current network system worked well, opening igbt1, igbt2 and be always maintained at conducting state, trend Controller is operated under inverter mode, igbt1, igbt2 series diode d1 and d2 respectively, and electric current can only flow to through igbt1, d2 Load；

As shown in figure 5, when current Hall detector unit lem detect direct current or alternating current overshoot more than 1.3 times specified During electric current, when that is, direct-current short circuit fault occurs, block all igbt pulses, igbt1 and igbt2 is turned off, isolate AC network With direct current network, prevent dc/dc and dc/ac equipment room energy flux；

As shown in fig. 6, for blocking after all igbt pulse 5ms, igbt opens in three-phase half-bridge, carry out voltage stabilizing, igbt1 and Igbt2 keeps locking to wait direct-current short circuit fault recovery；

As shown in fig. 7, after for the excision of direct-current short circuit trouble point, system, by carrying out Pulse Width Control to igbt1, is realized to straight Stream busbar charging.

When selecting short circuit current limitation inductance, according to:

$l\frac{\mathrm{\δ}i}{\mathrm{\δ}t}=\mathrm{\δ}u$

$l=\frac{\mathrm{\δ}u*\mathrm{\δ}t}{\mathrm{\δ}i}$

Calculate inductance value l.

In the present invention, set DC current protection and be worth for 1.3in, with reference to current Hall detection response time, conditioning Plate hardware and fpga detection delay adjustmentses guard time, for ensureing reliability, the rapidity of protection, set guard time △ t= 30us；Meanwhile, the load voltage value of dc bus is 560v, change in voltage △ u ≈ 650v on short circuited inductance.

When selecting igbt, according to current changing rate it is considered to time delay situation DC Line Fault, calculating current overshoot value is it is ensured that High current, in igbt rated current working range, prevents igbt from damaging.

Claims (4)

1. a kind of direct-current grid current transformer, including the transformator (t) being sequentially connected, filter unit, current transforming unit, the flat ripple of direct current Inductance (l1) and mechanical switch, it is characterized by, also include short circuit protection module, described short circuit protection module includes at least two and opens Guan Guan, described short circuit protection module is connected between described current transforming unit and described flat ripple inductance (l1).

2. direct-current grid current transformer according to claim 1, it is characterized by, described short circuit protection module includes two instead To the switching tube of series connection, each switching tube is all parallel with backward diode.

3. direct-current grid current transformer according to claim 1, it is characterized by, described switching tube is igbt.

4. direct-current grid current transformer according to claim 1, it is characterized by, described short circuit protection module also includes one For forming the fly-wheel diode in loop with described flat ripple inductance when described switching tube turns off.