CN105245087A - Modular multilevel converter capacitor voltage balance control method based on classification - Google Patents

Abstract

The invention belongs to the technical field of electrical power system model simulation and control and especially relates to a modular multilevel converter capacitor voltage balance control method based on classification. The method is characterized by carrying out classification on all capacitors in a bridge arm through submodule capacitor voltage rated fluctuation range, and summarizing the number of the capacitors included in each class; carrying out priority ranking on the classes according to the direction of the current in the bridge arm; determining ranking class according to the number of the capacitors needing to be input and the ranking sequence; and inputting all the capacitors in the class prior to the ranking class, and selecting residue number of capacitors needing to be input in the ranking class and inputting the capacitors. The method reduces switching frequency of a switch device and calculation quantity of the control method under the condition of guaranteeing the capacitor voltage fluctuation range, and the response speed of a control system is improved.

Description

Based on the modularization multi-level converter capacitor voltage-sharing control method of classification

Technical field

The invention belongs to operation and control of electric power system technical field, relate to a kind of modularization multi-level converter capacitance voltage balance control method.

Background technology

Modularization multi-level converter (ModularMultilevelConverter, MMC) is a kind of voltage source converter (VoltageSourcebasedConverter, VSC) adopting modularized design.Modularization multi-level converter not only has the feature that traditional electrical Source Con-verters independently controls active reactive, and the feature such as it is low to have switching frequency, and output voltage ripple harmonic content is low.

Capacitance energy storage element in modularization multi-level converter is distributed in submodule, causes capacitance voltage Balance route difficulty.Traditional modularization multi-level converter needs to sort to all submodule capacitor voltage to capacitance voltage Balance route, and the input number then exported according to nearest level modulation and bridge arm current determine the submodule dropped into.When bridge arm current is greater than 0, trigger from voltage is low; And bridge arm current is when being less than 0, then trigger from voltage is high.The submodule electric discharge making capacitance voltage high like this, the submodule charging that capacitance voltage is low, ensure that the equilibrium of submodule capacitor voltage.

Existing method causes the rising of switching frequency on the one hand, and on the other hand along with the lifting of transmission line capability and electric pressure, the level number of modularization multi-level converter also improves thereupon, needs to sort to all submodules, causes the rising of amount of calculation.

Summary of the invention

In order to solve the problem, the present invention proposes a kind of modularization multi-level converter capacitor voltage-sharing control method based on classification.

Technical scheme of the present invention is:

Based on the modularization multi-level converter capacitor voltage-sharing control method of classification, it is characterized in that, comprise the steps:

Step 1, according to submodule capacitor voltage specified fluctuation range Δ U _crefwith the last switching state FP of electric capacity _pre, electric capacity all in brachium pontis is classified, and adds up the electric capacity number comprised in each classification;

Step 2, direction according to bridge arm current, carry out preferential ordering in launching arrangement to the classification that step 1 obtains;

Step 3, foundation need to drop into electric capacity number N _firewith put in order, determine sort class;

Step 4, all electric capacity in preferential classification in sequence class are dropped into after, in sequence class, select residue to need the electric capacity dropping into number to drop into.

Rated voltage fluctuation range Δ U in described step 1 _crefgiven in advance according to system cloud gray model, and non-vanishing, U _creffor electric capacity rated voltage, the upper threshold value U of its fluctuation range _up, the lower threshold value U of fluctuation range _downexpression formula be:

Described is categorized as electric capacity all in brachium pontis: the electric capacity in traversal brachium pontis in all submodules, as capacitance voltage U _cbe more than or equal to U _uptime, this submodule is UP class; As capacitance voltage U _cbe less than or equal to U _downtime, this submodule is DOWN class; As capacitance voltage U _cbe less than U _upbe greater than U _downand the last switching state FP of electric capacity _prefor dropping into state, then this submodule is ON class; As capacitance voltage U _cbe less than U _upbe greater than U _downand the last switching state FP of electric capacity _prefor excision state, then this submodule is OFF class; According to the classification results obtained, the number N of statistics DOWN class submodule _dOWN, ON class submodule number N _oN, OFF class submodule number N _oFF, UP class submodule number N _uP.

In described step 2, the detailed process of preferential ordering in launching arrangement is: as bridge arm current I _armbe more than or equal to 0, the electric capacity preecedence requirement that capacitance voltage is low is charged, thus priority is followed successively by DOWN class, ON class, OFF class, UP class; As bridge arm current I _armwhen being less than 0, the electric capacity that capacitance voltage is high preferentially discharges, and priority is followed successively by UP class, ON class, OFF class, DOWN class; According to priority, be defined as the 1st class, the 2nd class, the 3rd class, the 4th class successively.

Described step 3 determines that the concrete steps of sequence class are: when needs drop into electric capacity number N _firebe more than or equal to 0 and be less than the 1st class electric capacity number, then the 1st class is sequence class; Work as N _firebe more than or equal to the 1st class electric capacity number and be less than front 2 class electric capacity numbers, then the 2nd class is sequence class; Work as N _firebe more than or equal to front 2 class electric capacity numbers and be less than the 3rd class electric capacity number, then the 3rd class is sequence class; Work as N _firebe more than or equal to front 3 class electric capacity numbers and be less than or equal to the 4th class electric capacity number, then the 4th class is sequence class.

In described step 4 by have precedence over sequence class classification in after all electric capacity all drops into, calculate the submodule number N that residue needs to drop into _left

In formula, j represents the numbering of sequence class, N _kfor the electric capacity number of kth class;

When bridge arm current is greater than 0, then select the N that capacitance voltage is minimum _leftindividual submodule drops into; When bridge arm current is less than 0, then select the N that capacitance voltage is maximum _leftindividual submodule drops into; According to the difference of classification, different to sequence class Neutron module capacitance voltage carry out the sorting sort method that adopts, be UP class when sequence class or be DOWN class, then adopt quick sorting algorithm to sort to sequence class Neutron module capacitance voltage; When sequence class is ON class or OFF class, adopt a kind of pseudo-sort method.

Described pseudo-sort method is: first, the minimum M in of the maximum Max obtaining the capacitance voltage participating in sequence and the capacitance voltage participating in sequence, by the interval [Min of capacitance voltage, Max] be divided into M minizone at equal intervals, then span Delta=(the Max-Min)/M in each interval, 1 to M minizone is followed successively by [Min, Min+Delta), [Min+Delta, Min+2Delta) ... [Max-Delta, Max], according to capacitance voltage size judge successively electric capacity fall into the position of minizone, use vectorial V _istore the electric capacity numbering falling into minizone, thus the ordering vector V={V of entirety ₁, V ₂..., V _m.

Beneficial effect

The present invention proposes the modularization multi-level converter capacitance voltage balance control method based on Classified optimization.In assorting process, introduce lower threshold value on voltage, effectively can control the fluctuation range of the capacitance voltage of submodule.Submodule between the upper and lower thresholds, the switching state according to the last time is classified, and greatly reduces the switching frequency of submodule.The present invention only needs to sort to a class wherein, and adopts a kind of pseudo-sequence to the classification between upper lower threshold value, reduces the computing time of control algolithm.

Accompanying drawing explanation

Fig. 1 is capacitance voltage balance control method flow chart of the present invention;

Fig. 2 is electric capacity classification schematic diagram;

Fig. 3 is classification priority ordering figure;

Fig. 4 is sequence class determination flow chart;

Fig. 5 is the module of the present invention realized in PSCAD;

Embodiment

Below in conjunction with specific embodiment, set forth the present invention further.

Show that namely triggering number needs to drop into electric capacity number N in modularization multi-level converter control system _fireafter, electric capacity rated voltage U _creffor set point, the submodule of capacitance voltage Balance route algorithms selection response number drops into.Its concrete implementing procedure as shown in Figure 1.

Step 1, electric capacity are classified: by the specified fluctuation range of submodule capacitor voltage, to electric capacity classification all in brachium pontis, and add up the electric capacity number comprised in each classification.The classification of electric capacity as shown in Figure 2,

Step 2, classification prioritization: according to the direction of bridge arm current, prioritizing is carried out to the classification that step 1 obtains.Put in order as shown in Figure 3.

Step 3, determine the class that sorts: electric capacity number and step 2 obtain puts in order according to needing to drop into, and determines the class that sorts.Sequence class determination computational process as shown in Figure 4.Wherein N _jrepresent the number of electric capacity in jth class.Such as, now bridge arm current is greater than 0, N _dOWN=3, N _oN=56, N _oFF=30, N _uP=1.If needing to drop into number is 1, then the class that sorts is DOWN class; If needing to drop into number is 80, then the class that sorts is OFF class.

Step 4, selection electric capacity drop into: all electric capacity that will have precedence in the classification of sequence class drop into, and need the electric capacity dropping into number to drop in sequence class selection residue.

PSCAD/EMTDC has write the custom block realizing said method, custom block as shown in Figure 5, left port is input as higher level and controls given input submodule number, upper port input now obtains bridge arm current size, capacitance voltage in lower port input brachium pontis, right output port output capacitance switching signal.In implementation process, the number M value of minizone at equal intervals of pseudo-sequence is 3.Simulation comparison has been carried out in the modular multilevel converter system of single-ended 101 level and conventional method.

Adopt the method in the present invention, the capacitance voltage of each submodule is controlled within certain limit, meets the demands.

As shown in table 1, conventional method makes switching device have very high switching frequency, and the present invention has lower switching frequency.

	Switching frequency	Calculate consuming time
			Conventional method	7735	3.6875s
Based on Classified optimization method	120	0.34375s

In table 1, the control time is in 1s simulation time, and the CPU of the capacitance voltage Balance route algorithm of single brachium pontis calculates consuming time, uses the present invention to only have 1/10th of conventional method.

Above-mentioned contrast, fully demonstrates the superiority of the present invention in the capacitance voltage Balance route of modularization multi-level converter.Lower threshold value in classification, ensure that the fluctuation range of submodule capacitor voltage; The submodule number participating in sequence is decreased by classification; Improve last input submodule priority level, effectively decrease the switching frequency of switching device; Electric capacity puppet sequence in classification between lower threshold value reduces the computing time of control mode further.

The above; be only the present invention's preferably embodiment, but protection scope of the present invention is not limited thereto, is anyly familiar with those skilled in the art in the technical scope that the present invention discloses; the change that can expect easily or replacement, all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of claim.

Claims (5)

1., based on the modularization multi-level converter capacitor voltage-sharing control method of classification, it is characterized in that, comprise the steps:

Step 1, according to submodule capacitor voltage specified fluctuation range Δ U _crefwith the last switching state FP of electric capacity _pre, electric capacity all in brachium pontis is classified, and adds up the electric capacity number comprised in each classification;

Step 2, direction according to bridge arm current, carry out preferential ordering in launching arrangement to the classification that step 1 obtains;

Step 3, foundation need to drop into electric capacity number N _firewith put in order, determine sort class;

Step 4, all electric capacity in preferential classification in sequence class are dropped into after, in sequence class, select residue to need the electric capacity dropping into number to drop into.

2., according to claim 1 based on the modularization multi-level converter capacitor voltage-sharing control method of classification, it is characterized in that, rated voltage fluctuation range Δ U in described step 1 _crefgiven in advance according to system cloud gray model, and non-vanishing, U _creffor electric capacity rated voltage, the upper threshold value U of its fluctuation range _up, the lower threshold value U of fluctuation range _downexpression formula be:

$\left\{\begin{array}{c}{U}_{up}=U_{cref}(1+{\mathrm{\ΔU}}_{cref})\\ U_{down}=U_{cref}(1-{\mathrm{\ΔU}}_{cref})\end{array}\right.---\left(1\right)$

Described is categorized as electric capacity all in brachium pontis: the electric capacity in traversal brachium pontis in all submodules, as capacitance voltage U _cbe more than or equal to U _uptime, this submodule is UP class; As capacitance voltage U _cbe less than or equal to U _downtime, this submodule is DOWN class; As capacitance voltage U _cbe less than U _upbe greater than U _downand the last switching state FP of electric capacity _prefor dropping into state, then this submodule is ON class; As capacitance voltage U _cbe less than U _upbe greater than U _downand the last switching state FP of electric capacity _prefor excision state, then this submodule is OFF class; According to the classification results obtained, the number N of statistics DOWN class submodule _dOWN, ON class submodule number N _oN, OFF class submodule number N _oFF, UP class submodule number N _uP.

3. according to claim 1 based on the modularization multi-level converter capacitance voltage balance control method of Classified optimization, it is characterized in that, in described step 2, the detailed process of preferential ordering in launching arrangement is: as bridge arm current I _armbe more than or equal to 0, the electric capacity preecedence requirement that capacitance voltage is low is charged, thus priority is followed successively by DOWN class, ON class, OFF class, UP class; As bridge arm current I _armwhen being less than 0, the electric capacity that capacitance voltage is high preferentially discharges, and priority is followed successively by UP class, ON class, OFF class, DOWN class; According to priority, be defined as the 1st class, the 2nd class, the 3rd class, the 4th class successively.

4. according to claim 1 based on the modularization multi-level converter capacitor voltage-sharing control method of classification, it is characterized in that, described step 3 determines that the concrete steps of sequence class are: when needs drop into electric capacity number N _firebe more than or equal to 0 and be less than the 1st class electric capacity number, then the 1st class is sequence class; Work as N _firebe more than or equal to the 1st class electric capacity number and be less than front 2 class electric capacity numbers, then the 2nd class is sequence class; Work as N _firebe more than or equal to front 2 class electric capacity numbers and be less than the 3rd class electric capacity number, then the 3rd class is sequence class; Work as N _firebe more than or equal to front 3 class electric capacity numbers and be less than or equal to the 4th class electric capacity number, then the 4th class is sequence class.

5., according to claim 1 based on the modularization multi-level converter capacitor voltage-sharing control method of classification, it is characterized in that, in described step 4 by have precedence over sequence class classification in after all electric capacity all drops into, calculate the submodule number N that residue needs to drop into _left

$N_{left}=N_{fire}-\underset{k=1}{\overset{j-1}{\Σ}}{N}_k---\left(2\right)$

In formula, j represents the numbering of sequence class, N _kfor the electric capacity number of kth class;

When bridge arm current is greater than 0, then select the N that capacitance voltage is minimum _leftindividual submodule drops into; When bridge arm current is less than 0, then select the N that capacitance voltage is maximum _leftindividual submodule drops into; According to the difference of classification, different to sequence class Neutron module capacitance voltage carry out the sorting sort method that adopts, be UP class when sequence class or be DOWN class, then adopt quick sorting algorithm to sort to sequence class Neutron module capacitance voltage; When sequence class is ON class or OFF class, adopt a kind of pseudo-sort method;

Described pseudo-sort method is: first, the minimum M in of the maximum Max obtaining the capacitance voltage participating in sequence and the capacitance voltage participating in sequence, by the interval [Min of capacitance voltage, Max] be divided into M minizone at equal intervals, then span Delta=(the Max-Min)/M in each interval, 1 to M minizone is followed successively by [Min, Min+Delta), [Min+Delta, Min+2Delta) ... [Max-Delta, Max], according to capacitance voltage size judge successively electric capacity fall into the position of minizone, use vectorial V _istore the electric capacity numbering falling into minizone, thus the ordering vector V={V of entirety ₁, V ₂..., V _m.