CN105138799A - Method for designing parameter of direct current reactor suitable for modular multi-level converter - Google Patents

Abstract

The invention discloses a method for designing the parameter of a direct current reactor suitable for a modular multi-level converter. The method includes the steps that the maximal instantaneous current value Ilim allowed by a bridge arm is determined according to the parameter of a converter valve; the maximal current value Ifault of the bridge arm before a system is locked is calculated when a direct current polar line short-circuit fault happens; the maximal instantaneous current value Ilim allowed by the bridge arm is compared with the maximal current value Ifault of the bridge arm before the system is locked, and the lower limit value Llim of the inductance of the direct current reactor is calculated to serve as the final design value of the inductance of the direct current reactor. The method has the advantages that the inductance value of the direct current reactor is designed through the maximal failure current limiting value condition borne by the bridge arm, and meanwhile the influence on failure currents by alternating current feed-in and capacitor discharge is considered. The calculation method is simple, and calculation results are more accurate.

Description

Be applicable to the direct current reactor Parameters design of modularization multi-level converter

Technical field

The present invention relates to Power System Flexible power transmission and distribution technical field, be specifically related to a kind of direct current reactor Parameters design being applicable to modularization multi-level converter.

Background technology

Along with development and the application of Power Electronic Technique in electric system of all-controlling power electronics device, the Technology of HVDC based Voltage Source Converter based on modularization multi-level converter comes into one's own day by day.Direct current reactor is one of visual plant in modular multilevel current conversion station system, the fault current rejection ability of the direct influential system of its parameter.The factor of two aspects is mainly considered in the design of direct current reactor parameter:

One is that brachium pontis submodule limits the ability to bear of fault current final value.The harshest operating mode is system generation DC bipolar short trouble, now bridge arm current rises rapidly, when considering direct-current polar short trouble, if brachium pontis fault current does not reach the electric current final value that submodule can bear before system locking, then direct current reactor is not needed to carry out fault current limiting climbing speed; If brachium pontis fault current has reached the electric current final value that submodule can bear before system locking, now need design direct current reactor to suppress fault current escalating rate, with the safety of safeguards system.

Two is distributing rationally of direct current reactor and brachium pontis reactor.Direct current reactor is larger, and system time constant is larger, and transient response time is longer, add construction cost simultaneously, therefore, when meeting design conditions and the limit value condition to fault current of brachium pontis reactor, the inductance value of direct current reactor should be reduced as much as possible.

By the upper lower limit value of fault current escalating rate rejection condition, direct current dynamic responding speed condition determination direct current reactor inductance value in prior art, but the method have ignored interchange feed-in trouble spot to the impact of fault current, and result of calculation exists comparatively big error.

Summary of the invention

Object of the present invention solves the problem exactly, provide a kind of direct current reactor Parameters design being applicable to modularization multi-level converter, the method designs the parameter of direct current reactor by the maximum fault current limit value condition that brachium pontis can bear, consider simultaneously and exchange feed-in, capacitor discharge and on the impact of fault current, and finally calculated direct current reactor value.

For achieving the above object, the present invention adopts following technical proposals, comprising:

Be applicable to a direct current reactor Parameters design for modularization multi-level converter, comprise:

(1) according to the maximum instantaneous current value I that converter valve parameter determination brachium pontis allows _lim;

(2) when calculating generation direct-current polar short trouble, the bridge arm current maximal value I before current conversion station locking _fault;

(3) by the maximum instantaneous current value I of brachium pontis permission _limwith the bridge arm current maximal value I before system locking _faultcompare, if I _lim>I _fault, then direct current reactor is not set; If I _lim<I _fault, then the lower limit L of direct current reactor inductance is calculated _lim, and as the final design value of direct current reactor inductance.

The maximum instantaneous current value I that described step (1) bridge arm allows _limcurrent limit parameter according to components and parts each in converter valve sets.

In described step (2), brachium pontis current maxima I before system locking _faultcomputing method be:

After there is direct-current polar short trouble, brachium pontis fault current is made up of two parts: a part is submodule capacitance discharge current, the electric current that a part produces for AC system feed-in;

Branch road equivalent inductance L during direct-current polar short trouble _eqequal brachium pontis reactor inductance value L _arm;

The current-rising-rate of calculating sub module capacitance discharge current escalating rate and AC system feed-in generation respectively, according to above-mentioned current-rising-rate and brachium pontis overcurrent protection time setting value T _pro, obtain brachium pontis current maxima I before system locking _fault.

The defining method of described submodule capacitance discharge current escalating rate is:

$k_c=U_{dc}*\sqrt{\frac{C_{sm}}{N*L_{eq}}}*\frac{4}{T_c}=\frac{U_{dc}}{\mathrm{\&pi;}*L_{eq}};$

Wherein, L _eqfor loop equivalent inductance; R _eqfor loop equivalent resistance; C _smfor submodule electric capacity; N is brachium pontis submodule number; T _cfor the capacitor discharge cycle; U _dcfor DC bus-bar voltage.

The defining method of the current-rising-rate that described AC system feed-in produces is:

$k_g=\frac{U_s}{L_{eq}+2L_{\mathrm{\&sigma;}}};$

Wherein, U _sfor converter valve side ac phase voltage peak value; L _σfor Transformer Short Circuit Impedance.

Brachium pontis current maxima I before system locking _faultbe specially:

$I_{fault}=I_{pro}+\&lsqb;\frac{U_s}{(2L_{\mathrm{\&sigma;}}+L_{arm})}+\frac{U_{dc}}{{\mathrm{\&pi;L}}_{arm}}\&rsqb;\&CenterDot;T_{pro};$

Wherein, I _profor brachium pontis overcurrent protection setting valve; U _sfor converter valve side ac phase voltage peak value; U _dcfor DC bus-bar voltage; L _armfor brachium pontis reactor inductance value; L _σfor Transformer Short Circuit Impedance value; T _profor brachium pontis overcurrent protection time setting value.

The lower limit L of direct current reactor inductance is calculated in described step (3) _limmethod be specially:

$I_{pro}+\&lsqb;\frac{U_s}{\left(2L_{\mathrm{\&sigma;}}+L_{arm}+L_{\lim }\right)}+\frac{U_{dc}}{\mathrm{\&pi;}\left(L_{arm}+L_{\lim }\right)}\&rsqb;\&CenterDot;T_{pro}=I_{\lim };$

Wherein, I _profor brachium pontis overcurrent protection setting valve, U _sfor converter valve side ac phase voltage peak value; U _dcfor DC bus-bar voltage; L _armfor brachium pontis reactor inductance value; L _σfor Transformer Short Circuit Impedance; T _profor brachium pontis overcurrent protection time setting value.

The lower limit L of direct current reactor inductance value _limbe specially:

L _lim＝max(L _dc1,L _dc2)；

Wherein, $\left\{\begin{array}{c}{L}_{dc1}=\frac{-b+\sqrt{b^2-4ac}}{2a}\\ L_{dc2}=\frac{-b-\sqrt{b^2-4ac}}{2a}\\ a=\mathrm{\&pi;}\&CenterDot;\frac{I_{fault}-I_{pro}}{T_{pro}}\\ b=2\mathrm{\&pi;}(L_{\mathrm{\&sigma;}}+L_{arm})\&CenterDot;\frac{I_{fault}-I_{pro}}{T_{pro}}-U_{dc}-{\mathrm{\&pi;U}}_s\\ c=(2L_{\mathrm{\&sigma;}}+L_{arm})\&CenterDot;(\mathrm{\&pi;}\&CenterDot;\frac{I_{fault}-I_{pro}}{T_{pro}}\&CenterDot;L_{arm}-U_{dc})-\mathrm{\&pi;}\&CenterDot;U_s\&CenterDot;L_{arm}\end{array}\right.$

L _armfor brachium pontis reactor value; L _σfor Transformer Short Circuit Impedance, I _profor brachium pontis overcurrent protection setting valve, I _faultfor brachium pontis current maxima before system locking, U _sfor converter valve side ac phase voltage peak value; U _dcfor DC bus-bar voltage, T _profor brachium pontis overcurrent protection time setting value.

Beneficial effect of the present invention:

The maximum fault current limit value condition that direct current reactor Parameters design of the present invention be can bear by brachium pontis designs direct current reactor inductance value, consider and exchange feed-in, capacitor discharge to the impact of fault current, computing method are simple, do not contain capacitance parameter in result of calculation expression formula simultaneously, eliminate the impact that capacitance parameter error calculates direct current reactor parameter, result is more accurate.

Accompanying drawing explanation

Fig. 1 is direct current reactor parameter designing process flow diagram flow chart provided by the invention;

Fig. 2 is capacitor discharge equivalent circuit provided by the invention;

Fig. 3 is interchange feed-in fault current equivalent circuit provided by the invention.

Embodiment

Below in conjunction with accompanying drawing and embodiment, the present invention will be further described:

Direct current reactor method for designing design cycle block diagram of the present invention as shown in Figure 1.

First the maximum instantaneous current value I of brachium pontis permission will be obtained according to converter valve parameter _lim.In the design process of converter valve, need to carry out type selecting to major loop device, brachium pontis allows the maximum instantaneous current value that flows through by the limit value of the element such as switching device, electric capacity, can obtain by the databook or consulting producer consulting related elements the maximum instantaneous current value I that brachium pontis allows to flow through _lim.

Next is when calculating generation direct-current polar short trouble, the bridge arm current maximal value I before system locking _fault.

System transient modelling regulating time being caused elongated after adding direct current reactor, and increase the construction cost of current conversion station, therefore needing the necessity to adding direct current reactor to verify.When the present invention selects direct-current polar short trouble, the brachium pontis maximum current value I before system locking _faultwith I _limcompare, determine whether to need to design direct current reactor.

After there is direct-current polar short trouble, brachium pontis fault current is made up of two parts, and a part is submodule capacitance discharge current, the electric current that a part produces for AC system feed-in.Can think in short time that the two is linear change, then its rate of change may be calculated:

1. submodule capacitance discharge current rate of change calculates.

Submodule discharge loop equivalent electrical circuit as shown in Figure 2.Wherein L _eqfor loop equivalent inductance, R _eqfor loop equivalent resistance, C _smfor submodule electric capacity, N is brachium pontis submodule number.

Wherein R _eqrelatively little, negligible, therefore the capacitor discharge cycle may be calculated:

$T_c=2\mathrm{\&pi;}\sqrt{\frac{2\&CenterDot;C_{sm}\&CenterDot;2\&CenterDot;L_{eq}}{N}}---\left(3\right)$

Then submodule discharge current escalating rate may be calculated:

$k_c=U_{dc}*\sqrt{\frac{C_{sm}}{N*L_{eq}}}*\frac{4}{T_c}=\frac{U_{dc}}{\mathrm{\&pi;}*L_{eq}}---\left(4\right)$

2. exchange feed-in current-rising-rate to calculate.

Exchange feed-in current equivalence loop as shown in Figure 3.Wherein R _eq, R _strayfor loop equivalent resistance, L _σfor Transformer Short Circuit Impedance, u _sfor electrical network phase voltage, L _eqfor branch road equivalent inductance.

Due to R _eq, R _strayrelatively little, negligible, then bridge arm current may be calculated:

$\left\{\begin{array}{c}{i}_u=\frac{U_s}{{\mathrm{\&omega;}}_s\left(L_{eq}+2L_{\mathrm{\&sigma;}}\right)}\&lsqb;1-\cos \left({\mathrm{\&omega;}}_{s}t\right)\&rsqb;\\ i_d=\frac{U_s}{{\mathrm{\&omega;}}_s\left(L_{eq}+2L_{\mathrm{\&sigma;}}\right)}\&lsqb;1+\cos \left({\mathrm{\&omega;}}_{s}t\right)\&rsqb;\end{array}\right.---\left(5\right)$

Consider the most serious operating mode, then bridge arm current escalating rate maximal value may be calculated:

$k_g=\frac{U_s}{L_{eq}+2L_{\mathrm{\&sigma;}}}---\left(6\right)$

Brachium pontis maximum current before system protection action may be calculated (L during direct-current polar short trouble _eqequal L _arm):

$I_{fault}=I_{pro}+\&lsqb;\frac{U_s}{L_{arm}+2L_{\mathrm{\&sigma;}}}+\frac{U_{dc}}{\mathrm{\&pi;}\&CenterDot;L_{arm}}\&rsqb;\&CenterDot;T_{pro}---\left(7\right)$

In formula, I _profor brachium pontis overcurrent protection current setting; T _profor brachium pontis overcurrent protection time setting value, U _dcfor DC bus-bar voltage.

Finally compare I _limand I _faultmagnitude relationship, and determine the final design value of direct current reactor.

The defining method of direct current reactor final design value is:

Work as I _limbe greater than I _faulttime, in theory can not direct current reactor be set.

Work as I _limbe less than I _faulttime, needing to arrange direct current reactor to suppress fault current, now needing to calculate direct current reactor lower limit L by solving an equation _lim, following (the DC bipolar short trouble loop equivalent inductance L after access direct current reactor of equation _eqfor L _armwith direct current reactor and):

$I_{pro}+\&lsqb;\frac{U_s}{L_{arm}+2L_{\mathrm{\&sigma;}}+L_{\lim }}+\frac{U_{dc}}{\mathrm{\&pi;}\&CenterDot;(L_{arm}+L_{lim})}\&rsqb;\&CenterDot;T_{pro}=I_{fault}---\left(8\right)$

Solve an equation (8), the lower limit of direct current reactor value can be obtained:

L _lim＝max(L _dc1,L _dc2)(9)

In formula:

$\left\{\begin{array}{c}{L}_{dc1}=\frac{-b+\sqrt{b^2-4ac}}{2a}\\ L_{dc2}=\frac{-b-\sqrt{b^2-4ac}}{2a}\\ a=\mathrm{\&pi;}\&CenterDot;\frac{I_{fault}-I_{pro}}{T_s}\\ b=2\mathrm{\&pi;}(L_{\mathrm{\&sigma;}}+L_{arm})\&CenterDot;\frac{I_{fault}-I_{pro}}{T_s}-U_{dc}-{\mathrm{\&pi;U}}_s\\ c=(2L_{\mathrm{\&sigma;}}+L_{arm})\&CenterDot;(\mathrm{\&pi;}\&CenterDot;\frac{I_{fault}-I_{pro}}{T_s}\&CenterDot;L_{arm}-U_{dc})-\mathrm{\&pi;}\&CenterDot;U_s\&CenterDot;L_{arm}\end{array}\right.---\left(10\right)$

Consider the distributing rationally of direct current reactor, then the direct current reactor lower limit L that obtains of seletion calculation _limas the final design value of direct current reactor, i.e. L _dc=L _lim.

By reference to the accompanying drawings the specific embodiment of the present invention is described although above-mentioned; but not limiting the scope of the invention; one of ordinary skill in the art should be understood that; on the basis of technical scheme of the present invention, those skilled in the art do not need to pay various amendment or distortion that creative work can make still within protection scope of the present invention.

Claims (8)

1. be applicable to a direct current reactor Parameters design for modularization multi-level converter, it is characterized in that, comprising:

(1) according to the maximum instantaneous current value I that converter valve parameter determination brachium pontis allows _lim;

(2) when calculating generation direct-current polar short trouble, the bridge arm current maximal value I before current conversion station locking _fault;

(3) by the maximum instantaneous current value I of brachium pontis permission _limwith the bridge arm current maximal value I before system locking _faultcompare, if I _lim>I _fault, then direct current reactor is not set; If I _lim<I _fault, then the lower limit L of direct current reactor inductance is calculated _lim, and as the final design value of direct current reactor inductance.

2. a kind of direct current reactor Parameters design being applicable to modularization multi-level converter as claimed in claim 1, is characterized in that, the maximum instantaneous current value I that described step (1) bridge arm allows _limcurrent limit parameter according to components and parts each in converter valve sets.

3. a kind of direct current reactor Parameters design being applicable to modularization multi-level converter as claimed in claim 1, is characterized in that, in described step (2), and brachium pontis current maxima I before system locking _faultcomputing method be:

After there is direct-current polar short trouble, brachium pontis fault current is made up of two parts: a part is submodule capacitance discharge current, the electric current that a part produces for AC system feed-in;

Branch road equivalent inductance L during direct-current polar short trouble _eqequal brachium pontis reactor inductance value L _arm;

The current-rising-rate of calculating sub module capacitance discharge current escalating rate and AC system feed-in generation respectively, according to above-mentioned current-rising-rate and brachium pontis overcurrent protection time setting value T _pro, obtain brachium pontis current maxima I before system locking _fault.

4. a kind of direct current reactor Parameters design being applicable to modularization multi-level converter as claimed in claim 3, it is characterized in that, the defining method of described submodule capacitance discharge current escalating rate is:

$k_c=U_{dc}*\sqrt{\frac{C_{sm}}{N*L_{eq}}}*\frac{4}{T_c}=\frac{U_{dc}}{\mathrm{\&pi;}*L_{eq}};$

Wherein, L _eqfor loop equivalent inductance; R _eqfor loop equivalent resistance; C _smfor submodule electric capacity; N is brachium pontis submodule number; T _cfor the capacitor discharge cycle; U _dcfor DC bus-bar voltage.

5. a kind of direct current reactor Parameters design being applicable to modularization multi-level converter as claimed in claim 3, is characterized in that, the defining method of the current-rising-rate that described AC system feed-in produces is:

$k_g=\frac{U_s}{L_{eq}+2L_{\mathrm{\&sigma;}}};$

Wherein, U _sfor converter valve side ac phase voltage peak value; L _σfor Transformer Short Circuit Impedance.

6. a kind of direct current reactor Parameters design being applicable to modularization multi-level converter as claimed in claim 3, is characterized in that, brachium pontis current maxima I before system locking _faultbe specially:

$I_{fault}=I_{pro}+\&lsqb;\frac{U_s}{(2L_{\mathrm{\&sigma;}}+L_{arm})}+\frac{U_{dc}}{{\mathrm{\&pi;L}}_{arm}}\&rsqb;\&CenterDot;T_{pro};$

Wherein, I _profor brachium pontis overcurrent protection setting valve; U _sfor converter valve side ac phase voltage peak value; U _dcfor DC bus-bar voltage; L _armfor brachium pontis reactor inductance value; L _σfor Transformer Short Circuit Impedance value; T _profor brachium pontis overcurrent protection time setting value.

7. a kind of direct current reactor Parameters design being applicable to modularization multi-level converter as claimed in claim 1, is characterized in that, calculates the lower limit L of direct current reactor inductance in described step (3) _limmethod be specially:

$I_{pro}+\&lsqb;\frac{U_s}{(2L_{\mathrm{\&sigma;}}+L_{arm}+L_{\lim })}+\frac{U_{dc}}{\mathrm{\&pi;}(L_{arm}+L_{\lim })}\&rsqb;\&CenterDot;T_{pro}=I_{\lim };$

Wherein, I _profor brachium pontis overcurrent protection setting valve, U _sfor converter valve side ac phase voltage peak value; U _dcfor DC bus-bar voltage; L _armfor brachium pontis reactor inductance value; L _σfor Transformer Short Circuit Impedance; T _profor brachium pontis overcurrent protection time setting value.

8. a kind of direct current reactor Parameters design being applicable to modularization multi-level converter as claimed in claim 4, is characterized in that, the lower limit L of direct current reactor inductance value _limbe specially:

L _lim＝max(L _dc1,L _dc2)；

Wherein, $\left\{\begin{array}{c}{L}_{dc1}=\frac{-b+\sqrt{b^2-4ac}}{2a}\\ L_{dc2}=\frac{-b-\sqrt{b^2-4ac}}{2a}\\ a=\mathrm{\&pi;}\&CenterDot;\frac{I_{fault}-I_{pro}}{T_{pro}}\\ b=2\mathrm{\&pi;}(L_{\mathrm{\&sigma;}}+L_{arm})\&CenterDot;\frac{I_{fault}-I_{pro}}{T_{pro}}-U_{dc}-{\mathrm{\&pi;U}}_s\\ c=(2L_{\mathrm{\&sigma;}}+L_{arm})\&CenterDot;(\mathrm{\&pi;}\&CenterDot;\frac{I_{fault}-I_{pro}}{T_{pro}}\&CenterDot;L_{arm}-U_{dc})-\mathrm{\&pi;}\&CenterDot;U_s\&CenterDot;L_{arm}\end{array}\right.$

L _armfor brachium pontis reactor value; L _σfor Transformer Short Circuit Impedance, I _profor brachium pontis overcurrent protection setting valve, I _faultfor brachium pontis current maxima before system locking, U _sfor converter valve side ac phase voltage peak value; U _dcfor DC bus-bar voltage, T _profor brachium pontis overcurrent protection time setting value.