CN1913321A - DC voltage balance control method of three-level inverter - Google Patents

Abstract

A DC voltage balance control method for three-level current transformers including: measuring voltage and current of a current transformer and voltage signals of up and down DC capacitors Vdc1 and Vdc2 timely, getting pulse regulation signals S based on the applied formula of the tested signals to carry out pulse conversion based on the control pulse generated by the current transformer of the control system to judge the zero passage of the function of S and regulate the flow of the active current to influence the charge and discharge process of DC capacitors.

Description

DC voltage balance control method of three-level inverter

Technical field

Present technique belongs to the flexible power transmission and distribution of electric power system, power electronics and custom power technology field.

Background technology

Three-level current transformer is a kind of main circuit structure that power electronic equipment adopts, and with respect to simple two level current transformers, its advantage is that the current transformer voltage withstand class improves, device voltage utilance height, and the output harmonic wave characteristic is good etc.

But its DC side has two capacitor groups, in actual applications, because following various reasons:

(1) trueness error of device parameters;

(2) asymmetry of circuit structure (parameter);

(3) trueness error of sampling element and time-delay;

(4) theoretical error of discretization;

(5) trueness error and the time-delay of calculating link;

Shi Changhui causes the imbalance of two groups of direct current capacitor group voltages, causes the device withstand voltage inequality, when serious with critical device security of operation.

General way is to adopt the unbalance protection strategy of direct voltage at present, but does not intervene the imbalance of direct voltage by active adjustment.

Summary of the invention

The present invention is used to solve the direct voltage imbalance problem that three-level current transformer often occurs, and by trigger impulse is carried out active adjustment, makes the amplitude of two voltages reach balance, makes the device can safer, stable operation.

According to the present invention, a kind of three-level AC stream device DC voltage balance control method is disclosed, comprise step:

(1) measures current transformer voltage u (t) and current i (t) and dc capacitor V up and down in real time _Dc1And V _Dc2Voltage signal;

(2) calculate the acquisition pulse according to detection signal application of formula (1) and adjust signal S;

S＝(V _dc1-V _dc2)·i(t)·u(t) (1)

(3) adjust signal S according to the pulse that obtains, pulses switch is carried out in the converter control pulse that control system generates, judge, adjust active current and flow to, influence the impulse electricity process of dc capacitor by zero passage to the S function.

According to an aspect of the present invention, wherein above-mentioned step (3) application of formula (2) is changed:

Wherein, I1 and I2 are respectively the switching device control signal of two brachium pontis of main circuit, and left brachium pontis exchanges and is output as positive direction.

According to the present invention, comprise that further behind step (1)-(3), the voltage of single-phase three-level current transformer output satisfies formula (3):

u _out＝(I ₁+I ₂)u _origin (3)

U wherein _OutCurrent transformer output voltage after the pulses switch, u _OriginBe current transformer output voltage before the pulses switch.

According to another aspect of the present invention, wherein replace the zero passage of S function to judge with hysteresis comparator.

Description of drawings

Fig. 1 is a three-level current transformer typical case main circuit structure schematic diagram

Fig. 2 is a principle of the invention schematic diagram

Fig. 3 (a)-(b) is the direct voltage contrast effect figure that three-level current transformer practical application device uses algorithm of the present invention front and back.

Embodiment

Fig. 1 is a three-level current transformer typical case main circuit structure schematic diagram, and wherein u (t) and i (t) are the left brachium pontis voltage and current that exchanges port (directions with left brachium pontis for just), can obtain power signal value, V by the voltage u (t) and the current i (t) of measurement converter _Dc1And V _Dc2Be respectively the voltage signal of dc capacitor up and down.

Fig. 2 is a principle of the invention block diagram.

The invention belongs to a kind of method, the implementation step of concrete technical scheme is as follows:

(1) measures the power signal (current transformer voltage and current) and the voltage signal of dc capacitor up and down in real time.

(2) calculate pulse according to detection signal and adjust signal S (referring to Fig. 2).

Definition pulses switch signal such as formula (1):

S＝(V _dc1-V _dc2)·i(t)·u(t) (1)

(3) adjust signal S according to the pulse that obtains, pulses switch is carried out in the converter control pulse that control system generates, judge, adjust active current and flow to, influence the impulse electricity process of dc capacitor by zero passage to the S function.

Wherein: I1 and I2 are respectively the switching device control signal (switching signal) of two brachium pontis of main circuit; Left side brachium pontis exchanges and is output as positive direction; Wherein:

(a) when I1=1, T11 and T12 conducting, perhaps its antiparallel fly-wheel diode conducting; When I2=1, T21 and T22 conducting, perhaps its antiparallel fly-wheel diode conducting; Output phase voltage+u _C

(b) when I1=0, T12 or T13 are by the catching diode conducting; When I2=0, T22 or T23 are by the catching diode conducting; Output phase voltage 0;

(c) when I1=-1, T13 and T14 conducting, perhaps its antiparallel fly-wheel diode conducting; When I2=-1, T23 and T24 conducting, perhaps its antiparallel fly-wheel diode conducting; Output phase voltage-u _C

For single-phase three-level current transformer, have only that (I1, when I2) being taken as one of (1,0), (0 ,-1), (0,1) or (1,0) four kinds of patterns, its midpoint potential just can produce fluctuation, thereby causes the imbalance of direct voltage when switching signal.

Calculate the pulse that obtains according to step (2) and adjust signal S, control impuls is carried out small vector rotation conversion, conversion regime is according to formula (2):

By formula (2) as can be known, one of main Rule of judgment of formula is S＞0 or S＜0, and by the generation of S as can be known, S is an instantaneous of ac, judges by the zero passage to the S function, adjusts active current to flow to, and influences the impulse electricity process of dc capacitor.Through after the above-mentioned steps, the voltage of single-phase three-level current transformer output satisfies formula (3):

u _out＝(I ₁+I ₂)u _origin (3)

U wherein _OutCurrent transformer output voltage after the pulses switch, u _OriginBe current transformer output voltage before the pulses switch;

According to formula (2) as can be known, by the small vector rotation of control impuls, the output voltage of current transformer can not change.By above-mentioned conversion, adjust the direction of active current, thereby interfered the charge and discharge process of capacitance voltage, reach the purpose of balance of voltage control.

When practical application, adopted hysteresis comparator to replace the zero passage of S function to judge, effectively prevented the frequent switching of small vector, avoided the unusual adjustment of IGBT switching frequency.

Advantage and effect

The present invention is according to the problem that occurs in the actual commercial Application, the control skill with very strong practical significance that creates The art scheme can solve the ubiquitous DC voltage imbalance problem of three level current transformers, and in practical application In obtained good effect, use the present invention by Fig. 3 (a)-(b) three level current transformer practical application devices DC voltage contrast effect figure before and after the described algorithm can find out, after control method of the present invention, and two groups of direct currents The amplitude of the voltage of capacitor group reaches balance, makes the device can safer, stable operation.

Claims (4)

1, a kind of three-level AC stream device DC voltage balance control method comprises step:

(1) measures current transformer voltage u (t) and current i (t) and dc capacitor V up and down in real time _Dc1And V _Dc2Voltage signal;

(2) calculate the acquisition pulse according to detection signal application of formula (1) and adjust signal S;

S＝(V _dc1-V _dc2)·i(t)·u(t) (1)

(3) adjust signal S according to the pulse that obtains, pulses switch is carried out in the converter control pulse that control system generates, judge, adjust active current and flow to, influence the impulse electricity process of dc capacitor by zero passage to the S function.

2, control method as claimed in claim 1, wherein step (3) application of formula (2) is changed:

Wherein, I1 and I2 are respectively the switching device control signal of two brachium pontis of main circuit, and left brachium pontis exchanges and is output as positive direction.

3, control method as claimed in claim 1 further comprises, behind step (1)-(3), the voltage of single-phase three-level current transformer output satisfies formula (3):

u _out＝(I ₁+I ₂)u _origin (3)

U wherein _OutCurrent transformer output voltage after the pulses switch, u _OriginBe current transformer output voltage before the pulses switch.

4, as the control method of claim 1-3, wherein replace the zero passage of S function to judge with hysteresis comparator.

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