CN114094847A - Method for optimizing VIENNA rectifier input current under wide-range unbalanced power grid - Google Patents

Method for optimizing VIENNA rectifier input current under wide-range unbalanced power grid Download PDF

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CN114094847A
CN114094847A CN202111479585.6A CN202111479585A CN114094847A CN 114094847 A CN114094847 A CN 114094847A CN 202111479585 A CN202111479585 A CN 202111479585A CN 114094847 A CN114094847 A CN 114094847A
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current
vienna rectifier
reference voltage
phase
interval
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CN114094847B (en
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吕建国
史兆成
李志洲
李高宁
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Nanjing University of Science and Technology
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/06—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes without control electrode or semiconductor devices without control electrode
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only

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Abstract

The invention discloses a method for optimizing VIENNA rectifier input current under a wide-range unbalanced power grid, and belongs to the field of power electronic conversion devices. The method comprises the following steps: through analyzing the static working range of the VIENNA rectifier, the distortion of the input current is inhibited through a method of modulating wave interval clamping in the static working range; outside a static working range, a negative sequence current control coefficient k is introduced on the basis of three current control targets when a power grid is unbalanced, k is defined in a continuous interval, a reference voltage is restricted in the static working range by adjusting the value of k, and the distortion of an input current is restrained by clamping in a modulation wave interval. And finally, performing Sinusoidal Pulse Width Modulation (SPWM) on the generated modulation wave to obtain a pulse width modulation wave for controlling a VIENNA rectifier switch when the power grid is unbalanced. The method can effectively inhibit the current distortion of the VIENNA rectifier caused by the inconsistent phase of the network side current and the reference voltage when the power grid is unbalanced, improve the power factor of the system, reduce the harmonic distortion rate of the network side current, and simultaneously improve the efficiency of the VIENNA rectifier.

Description

Method for optimizing VIENNA rectifier input current under wide-range unbalanced power grid
Technical Field
The invention belongs to the technical field of power electronic conversion devices, and particularly relates to a method for optimizing VIENNA rectifier input current under a wide-range unbalanced power grid.
Background
With the rapid development of semiconductor technology and micro-processing technology, power electronic technology has changed greatly in the last three decades and is more and more widely applied to various fields of national economy, including various High-quality power supplies, Flexible AC Transmission systems (FACTS), High Voltage Direct Current (High Voltage Direct Current) Transmission, aerospace and other application fields. Meanwhile, the nonlinearity, the impulse and the imbalance of the equipment and the system can cause the distortion of voltage waveforms and current waveforms in the power grid, so that the quality of input current is reduced, and the efficiency of the equipment and the system is greatly reduced.
In the annual meeting of IEEE industrial application (ISA) in 1980, a.nabae in japan proposes a three-level midpoint clamp structure; subsequently, j.w.kolar et al, 1994 proposed a VIENNA rectifier structure that has attracted scientific attention and research due to the advantages of input current sinusoidization and low distortion rate, being able to operate at unity power factor, and the like. The three-phase three-level VIENNA rectifier has the advantages of high power density, high system reliability and the like and is widely applied to an aviation alternating current power supply system. Compared with the traditional diode clamping type and flying capacitor clamping type three-level rectifiers, the three-level rectifier has the advantages that the topological structure is simpler, the required power devices are fewer, and no bridge arm direct connection risk is caused, and no dead time is required. Therefore, the VIENNA rectifier is a very ideal topology in some high power, high power density applications.
However, the topology structure of the three-level VIENNA rectifier has certain particularity, voltage drop on the filter inductor causes a certain phase difference between a current vector and a reference voltage vector, and the VIENNA rectifier outputs wrong voltage when the current crosses zero, so that the waveform of the three-phase current is distorted, certain harmonic pollution is caused to a power grid, and the power factor is reduced. In fact, the research on the distortion of the input current of the VIENNA rectifier basically assumes that the grid voltage and the current are in the same phase under the condition of the balanced unit power factor of the grid, but actually, the grid voltage is often in an unbalanced state due to the fact that the phase and the amplitude of the grid voltage have offset situations, and the control targets in this situation are: and inhibiting active power secondary fluctuation, inhibiting negative sequence current and inhibiting reactive power secondary fluctuation. The three control modes have the problem that the voltage and the current on the network side have phase difference. Because of the constraints of the VIENNA rectifier topology, the limitations of the VIENNA rectifier in a stable operating state are as follows: the rectifier three-phase reference voltage polarity must be consistent with the corresponding ac side input current polarity. The phase difference between the grid voltage and the current may cause distortion of the rectifier grid current, and in severe cases, may even cause the system to fail. Therefore, the problem of three-phase current distortion of the VIENNA rectifier when the power grid is unbalanced is solved, and harmonic current injected into the power grid by the system can be reduced.
Disclosure of Invention
The invention aims to provide a method for optimizing the input current of a VIENNA rectifier under a wide-range unbalanced power grid, which can effectively inhibit the current distortion of the VIENNA rectifier caused by the inconsistent phase of the grid-side current and the reference voltage when the power grid is unbalanced, reduce the harmonic distortion rate of the grid-side current and improve the efficiency of the VIENNA rectifier.
The technical solution for realizing the purpose of the invention is as follows: a method for optimizing VIENNA rectifier input current under a wide-range unbalanced power grid is characterized by comprising a VIENNA rectifier, a digital processing control module and a driving circuit, wherein the digital processing control module comprises a sampling unit, a voltage control unit, a reference current calculation unit, a quasi-PR current control unit and a sine pulse width modulation unit; wherein:
(1) the sampling unit respectively collects voltage signals of upper and lower capacitors at the direct current side of the VIENNA rectifier, three-phase voltage signals at the alternating current side of the VIENNA rectifier and three-phase current signals at the alternating current side of the VIENNA rectifier;
(2) the voltage control unit processes the voltage signals of the upper capacitor and the lower capacitor on the direct current side into active power reference signals;
(3) the reference current calculation unit processes the active power reference signal and the voltage and current signals obtained after coordinate transformation into a current reference signal under a static coordinate system;
(4) the quasi-PR current control unit processes the current reference signal to obtain a modulation wave signal and sends the modulation wave signal to the sine pulse width modulation unit;
(5) the output end of the sine pulse width modulation unit is connected to each switching tube of each phase bridge arm in the three-level VIENNA rectifier through the driving circuit.
2. The method for optimizing VIENNA rectifier input current in a wide-range unbalanced network of claim 1, wherein the digital processing control modules are chips TMS320F28377D and EPM 1270T.
3. The method of claim 1 for optimizing VIENNA rectifier input current over a wide range of imbalanced power networks, comprising the steps of:
step 1, calculating the static working range of the VIENNA rectifier according to the inherent topological characteristic of the VIENNA rectifier.
(1) Establishing a three-phase reference voltage and three-phase switching tube duty ratio equation;
(2) the constraint on the reference voltage at the moment can be obtained by solving the duty ratio within the range of the interval [0, 1], namely the static working range of the VIENNA rectifier;
step 2, calculating a phase difference between a VIENNA rectifier reference current instruction and a reference voltage, and suppressing the distortion of the input current by injecting a zero-sequence component to enable a modulation wave to be clamped to zero in a distortion interval in a static working range; introducing a negative sequence current regulation coefficient k outside a static working range, restraining a reference voltage within the static working range by adjusting the value of k, and inhibiting the distortion of an input current by an interval clamping method, wherein the method comprises the following steps:
(1) extracting positive and negative sequence components of the voltage of the power grid and an initial Phase angle of the negative sequence component through a Double Second Order Generalized Integrator Phase-Locked Loop (DSOGI-PLL);
(2) calculating current reference under a control strategy for inhibiting active power secondary fluctuation and calculating reference voltage at the moment;
(3) judging whether the reference voltage is in a static working range, and when the reference voltage is in the static working range, providing a method for clamping a modulation wave interval, judging an interval in which the polarities of the reference voltage and the reference current are inconsistent, wherein the interval is a current distortion interval, and superposing a zero-sequence component in the distortion interval to clamp the original modulation wave to zero in the distortion interval so as to inhibit the distortion of the input current;
(4) when the reference voltage is out of the static working range, an interval clamping method based on negative sequence current regulation is provided, a negative sequence current regulation coefficient k is introduced, the reference current and the reference voltage are recalculated, the reference voltage is restricted in the static working range by adjusting the value of k, and then the distortion of the input current is restrained by the interval clamping method.
And 3, performing sinusoidal pulse width modulation on the obtained modulation wave to obtain a pulse width modulation wave of a VIENNA rectifier switch under the wide-range unbalanced power grid.
Compared with the prior art, the invention has the remarkable advantages that: (1) the method comprises the steps of respectively calculating a positive sequence component, a negative sequence component and a negative sequence component initial phase angle of the voltage of the power grid by sampling three-phase voltage at an alternating current side, calculating a static working interval of the power grid by combining topological constraint of the VIENNA rectifier, effectively inhibiting current distortion of the VIENNA rectifier caused by inconsistent phases of current at the power grid side and reference voltage when the power grid is seriously unbalanced by adopting an interval clamping method and an interval clamping method of current instruction regulation aiming at different power grid conditions, reducing harmonic distortion rate of the current at the power grid side, and simultaneously improving the efficiency of the VIENNA rectifier; (2) the method is suitable for the operation condition of the VIENNA rectifier under the wide-range unbalanced power grid, and has the advantages of reliable operation, low hardware cost, accurate control, good flexibility and easy realization.
Drawings
Fig. 1 is a topology structure diagram of a three-phase three-level VIENNA rectifier according to the present invention.
FIG. 2 is an overall control structure diagram under a VIENNA topology alpha-beta static coordinate system when a power grid is interfered.
Fig. 3 is an equivalent circuit diagram of the VIENNA rectifier of the present invention.
Fig. 4 is a schematic diagram of waveforms of modulation interval clamp and zero sequence voltage in the present invention.
Fig. 5 is a waveform diagram of three-phase voltage under unbalanced grid condition 1 in the present invention.
Fig. 6 is a waveform diagram of three-phase voltage under unbalanced grid condition 2 in the present invention.
Fig. 7 is a waveform diagram of current at the three-phase grid side before and after the method for optimizing input current under unbalanced grid condition 1 in the present invention, where (a) is a simulated waveform of current under conventional control, and (b) is a simulated waveform of current under a modulation wave interval clamping method.
Fig. 8 is a comparison graph of harmonic distribution of a current before and after an input current optimization method under unbalanced grid condition 1 in the present invention, where (a) is a harmonic distribution graph of a current under conventional control, and (b) is a harmonic distribution graph of a current under a modulated wave interval clamping method.
Fig. 9 is graphs of current waveforms of the three-phase grid side before and after the method for optimizing the input current under unbalanced grid condition 2, where (a) is a simulated waveform of modulated wave interval clamping, and (b) is a simulated waveform of current under the modulated wave interval clamping method based on current instruction adjustment.
Fig. 10 is a comparison graph of harmonic distributions of a-phase current before and after the method of optimizing the input current under unbalanced grid condition 2 in the present invention, where (a) is a harmonic distribution graph of a current under a modulated wave interval clamp and (b) is a harmonic distribution graph of a current under a modulated wave interval clamp method using current command-based adjustment.
Detailed Description
The invention is further described in detail below with reference to the following figures and detailed description.
As shown in fig. 1, fig. 1 is a topology structure diagram of a three-phase three-level VIENNA rectifier.
As shown in FIG. 2, FIG. 2 is a structural diagram of the overall control under a VIENNA topology alpha-beta static coordinate system when a power grid is unbalanced.
In each switching period, the sampling unit of the digital control module respectively collects three-phase voltage e at the alternating current sidea、eb、ecAlternating side three-phase current ia、ib、icCapacitor voltage U on the DC sideC1And the capacitor voltage U under the DC sideC2；
The three-phase voltage on the alternating current side is used for extracting the positive sequence component e of the power grid voltage through a double-second order generalized integrator phase-locked loop unitα p、eβ pNegative sequence component eα n、eβ nDegree of unbalance λ, initial phase angle of negative sequence component θn；
Output voltage given Udc_refAnd measuring the output voltage U of the DC sidedcAfter the difference is made, an output direct current given I is obtained through a PI regulatordc_refGiven signal P multiplied by the output voltage as the DC component of the active power0。
Will P0、eα p、eβ p、eα n、eβ n、λ、θnAnd the input current negative sequence component adjusting coefficient calculating unit obtains a current negative sequence component adjusting coefficient k, further obtains improved current setting, and realizes tracking control of the network side current through the quasi-PR controller.
And the output of the quasi-PR controller is subjected to power grid voltage feedforward decoupling to obtain a modulation wave of the system.
The modulation wave is overlapped with a zero-sequence component based on a modulation wave interval clamping method so as to achieve the purpose of inhibiting the distortion of the input current.
Finally, a pulse width modulation wave capable of controlling a VIENNA rectifier switching tube is obtained through Sinusoidal Pulse Width Modulation (SPWM), and input current distortion suppression of the VIENNA rectifier is finally achieved.
Further, step 1 calculates the static working range of the VIENNA rectifier according to the inherent topological characteristic of the VIENNA rectifier. The method comprises the following steps:
(1) establishing a three-phase reference voltage and three-phase switching tube duty ratio equation; let the instantaneous value of three-phase reference voltage be Va_ref、Vb_refAnd Vc_ref(ii) a The duty ratio of each phase of switching tube is da、dbAnd dc(ii) a For the VIENNA rectifier, the following equation applies:
Figure BSA0000259868100000041
the general interpretation of formula (1) can be expressed as:
Figure BSA0000259868100000042
wherein d is0Is an arbitrary constant.
(2) The constraint on the reference voltage at the moment can be obtained by solving the duty ratio within the range of the interval [0, 1], namely the static working range of the VIENNA rectifier;
d in the above matrix equation when the VIENNA rectifier can work normallya、dbAnd dcShould be in the range [0, 1]]There is a solution in between. With ia＞0，ib＜0，ic< 0 as an example, the reference voltage for three phases in the analytical formula (2) is Va_ref、Vb_refAnd Vc_refThe constraint of VIENNA rectifier, i.e., the static operating range of the VIENNA rectifier. Under this current condition, equation (2) can be simplified as:
Figure BSA0000259868100000051
(1) when V isa_ref＜0、Vb_ref< 0 and Vc_refWhen > 0, d0If not, the VIENNA rectifier cannot work normally;
(2) when V isa_ref＜0、Vb_ref> 0 and Vc_refWhen > 0, d0If not, the VIENNA rectifier cannot work normally;
(3) when V isa_ref＜0、Vb_ref> 0 and Vc_refWhen < 0, d0If not, the VIENNA rectifier cannot work normally;
(4) when V isa_ref＞0、Vb_ref< 0 and Vc_refWhen < 0, d0The VIENNA rectifier can work normally only if the voltage is 0;
(5) when V isa_ref＞0、Vb_ref< 0 and Vc_refWhen the polarity of the reference voltage of the c phase is not consistent with that of the reference current when the polarity is more than 0, in order to ensure that the inequality is true, the following steps are carried out:
Figure BSA0000259868100000052
for d0To ensure that the other two phases meet the inequality requirement, the value of | d can be taken0|minFor inequality (4), taking the right side of inequality at this time, and substituting into equation (4), the simplification can be:
Figure BSA0000259868100000053
therefore, when Va_ref＞0、Vb_ref＜0、Vc_refWhen the voltage is more than 0, the VIENNA rectifier needs to meet the formula (5) when working normally.
(6) When V isa_ref＞0、Vb_ref> 0 and Vc_refWhen < 0, similar to the above method, the constraint equation at this time can be obtained as:
Figure BSA0000259868100000054
therefore, when Va_ref＞0、Vb_ref＞0、Vc_refWhen the voltage is less than 0, the VIENNA rectifier needs to meet the formula (6) when working normally. In the same way, the working interval of the VIENNA rectifier under the conditions of different current polarities and reference voltage polarities can be deduced.
Table 1 lists the VIENNA rectifier reference voltage constraints. The constraint equations in the table are as follows:
Figure BSA0000259868100000055
Figure BSA0000259868100000061
Figure BSA0000259868100000062
Figure BSA0000259868100000063
it has been found that when the reference voltage polarity is different from the current polarity, the VIENNA rectifier cannot operate.
TABLE 1 VIENNA rectifier static operating Range
Figure BSA0000259868100000064
Further, step 2, calculating a phase difference between a VIENNA rectifier reference current instruction and a reference voltage, and suppressing input current distortion by injecting a zero-sequence component to enable a modulation wave to be clamped to zero in a distortion interval in a static working range; introducing a negative sequence current regulation coefficient k outside a static working range, restraining a reference voltage within the static working range by adjusting the value of k, and inhibiting the distortion of an input current by an interval clamping method, wherein the method comprises the following steps:
(1) extracting positive and negative sequence components of the voltage of the power grid and an initial Phase angle of the negative sequence component through a Double Second Order Generalized Integrator Phase-Locked Loop (DSOGI-PLL);
three-phase grid voltage can be decomposed into positive sequence, negative sequence and zero sequence components based on a symmetrical component method under an unbalanced grid, and for a three-phase three-wire system VIENNA rectifier, zero sequence current access does not exist, so that zero sequence voltage does not influence power, and influence of the zero sequence voltage is not considered, and under the condition, an expression of the grid voltage can be written as follows:
Figure BSA0000259868100000065
wherein A isp、AnPositive sequence and negative sequence fundamental voltage peak values; the initial phase angle of the positive sequence component of the grid voltage is assumed to be 0, and the initial phase angle of the negative sequence component of the grid voltage is assumed to be thetan。
(2) Calculating current reference under a control strategy for inhibiting active power secondary fluctuation and calculating reference voltage at the moment;
three current control strategies exist in the VIENNA rectifier under the unbalanced power grid, generally, a current control strategy for inhibiting active power as a control target is selected, and a reference current expression of the active secondary wave control strategy of the VIENNA rectifier under an abc coordinate system is as follows:
Figure BSA0000259868100000071
fig. 3 is a single-phase equivalent circuit between the VIENNA rectifier and the grid, from which the following equation can be established:
Figure BSA0000259868100000072
the calculation is simplified by introducing an Euler formula, and a power grid voltage formula (11) and an input current instruction formula (12) are expressed in a real and imaginary form as follows:
Figure BSA0000259868100000073
Figure BSA0000259868100000074
simultaneous equations (13), (14) and (15) are given by λ ═ an/Ap；M＝ωLP0(ii) a Neglecting the inductance equivalent resistance R, let:
Figure BSA0000259868100000075
from the above, the phase difference between the reference current and the reference voltage is:
Δθx＝θix-θvx(x＝a，b，c) (17)
then thetavx、θixCan be expressed as:
Figure BSA0000259868100000081
Figure BSA0000259868100000082
wherein s isx、tx、mx、nxThe specific expression of (A) is as follows:
Figure BSA0000259868100000083
Figure BSA0000259868100000084
Figure BSA0000259868100000085
Figure BSA0000259868100000091
(3) judging whether the reference voltage is in a static working range, and when the reference voltage is in the static working range, providing a method for clamping a modulation wave interval, judging an interval in which the polarities of the reference voltage and the reference current are inconsistent, wherein the interval is a current distortion interval, and superposing a zero-sequence component in the distortion interval to clamp the original modulation wave to zero in the distortion interval so as to inhibit the distortion of the input current;
as can be seen from the calculations of equations (20) - (23), the reference current and the reference voltage can be expressed as:
Figure BSA0000259868100000092
wherein:
Figure BSA0000259868100000093
based on the topological limitation of the VIENNA rectifier, even if the reference voltage is in the static working range of the VIENNA rectifier, the input current still can be distorted by using a conventional carrier modulation method, the main reason is that the reference voltage is caused by inconsistent polarity with the reference current, and the distorted current is a region with inconsistent polarity, namely a region with inconsistent polarity of the reference voltage and the reference current, and the formula (2) shows that the three-phase reference voltage and the three-phase current can keep consistent polarity by injecting zero-sequence components into the distorted region, so that the distortion of the input current can be inhibited in a mode of clamping the corresponding phase modulation wave to zero in the distorted region.
In the above-described modulated wave interval clamping method, first, a clamped interval, which is a distorted interval of a current, needs to be determined. Solving the phases of the reference voltage and the reference current according to the expressions (19) to (23), and determining the phase difference between the two, wherein the phase difference between the two is a distortion interval, namely: between the zero crossings of both the reference voltage and the reference current. According to the formula (17), when Δ θxWhen the reference current is higher than 0 and the reference voltage is higher than the reference voltage, the starting point of the clamping interval is-thetaixEnd point is-thetavx(ii) a When Δ θx< 0, when the reference current lags behind the reference voltage, the start point of the clamping interval is-thetavxEnd point is-thetaix. In a power frequency period, each phase of reference voltage and reference current has two zero-crossing points, 6 clamping intervals exist, and the distribution of the three-phase reference voltage clamping intervals is shown in table 2.
TABLE 2 three-phase reference voltage clamping interval
Figure BSA0000259868100000094
And in combination with the VIENNA rectifier static working range, the zero sequence voltage based on the modulation wave interval clamping method is as follows:
Figure BSA0000259868100000101
taking phase a as an example, in the sector A interval, first, it is determined whether the current time is in the static working range, i.e. | Vb，ref-Va，ref|≤Udc/2，|Vc，ref-Va，ref|≤Udc/2. When the voltage is in a static working range, clamping the a-phase reference voltage; when the static working range is exceeded, clamping is not carried out, and the reference current needs to be recalculated. Fig. 4 shows a schematic diagram of the clamp based on the modulation wave interval.
(4) When the reference voltage is out of the static working range, an interval clamping method based on negative sequence current regulation is provided, a negative sequence current regulation coefficient k is introduced, the reference current and the reference voltage are recalculated, the reference voltage is restricted in the static working range by adjusting the value of k, and then the distortion of the input current is restrained by the interval clamping method.
When the formula (26) determines that the reference voltage is outside the static operating range, the distortion of the VIENNA rectifier input current cannot be effectively suppressed only by the interval clamping method. The patent provides a new current control strategy based on three current control strategies under the traditional unbalanced power grid, a negative sequence current control coefficient k is introduced into a current instruction, k is defined between continuous intervals (-1, 1), and D (k) is 1.5 (A)p 2+kAn 2) (ii) a Then, the expression of the three-phase current on the grid side under the abc coordinate system is as follows:
Figure BSA0000259868100000102
for the above formula, when k is-1, the active secondary wave suppression control strategy is adopted; when k is 0, the control strategy is a control strategy for inhibiting the current negative sequence component; and when k is 1, the reactive secondary fluctuation control strategy is restrained.
Similar to the above method, the phase difference between the input current reference command after k is introduced and the reference voltage needs to be calculated. Order:
Figure BSA0000259868100000103
the phase difference between the reference current and the reference voltage is:
Δθx(k)＝θix(k)-θvx(k)(x＝a，b，c) (29)
θvx、θixcan be expressed as:
Figure BSA0000259868100000111
Figure BSA0000259868100000112
in the formula mx(k)、nx(k)、sx(k)、tx(k) The specific expression of (a) is as follows:
Figure BSA0000259868100000113
Figure BSA0000259868100000114
Figure BSA0000259868100000115
Figure BSA0000259868100000121
the introduction of equation (26) into parameter k can be simplified as:
Figure BSA0000259868100000122
for the formula (36), the VIENNA rectifier can be ensured to operate in a static working range by adjusting the value of k to satisfy the inequality, that is, the three-phase modulation wave and the current polarity after interval clamping are ensured to be inhibited, and the overmodulation phenomenon is avoided. Taking phase b as an example, if phase a is positive and phase a does not overmodulation in the b-phase distortion interval, the following steps are performed:
Figure BSA0000259868100000123
and solving the equation to obtain the value of the target k. Considering that the inductance voltage drop is small, the influence of adjusting the value of k on the reference voltage is small, so that the influence of the change of the value of k on the reference voltage can be ignored, the calculation is simplified, and the reference voltage amplitude V in the formula (37)a(k)、Vb(k) And phase thetava(k)、θvb(k) The parameter k in (1).
Substituting equations (28) - (35) into the above equations, we can simplify:
Figure BSA0000259868100000124
order:
Figure BSA0000259868100000125
taking into account the solving function fb(k) Is too complex, so that f can be equivalently replaced by a function fitting modeb(k) Take fb(k) And the slope of the line connecting the two end points of (1) and passing through the point (0, f)b(0) Is equivalent to a function f)b(k) The specific expression is as follows:
Figure BSA0000259868100000126
will f isb(k) Equivalent substitution is yb(k) Simultaneous equations (38) and (40) can be solved in the b-phase clamp regionWhen phase a shows overmodulation and Va_refK value when k is greater than 0baComprises the following steps:
Figure BSA0000259868100000131
similarly, the same equivalent is used when computing the other two phases, so fa(k)，fc(k)，ya(k)，yc(k) The expression of (a) is as follows:
Figure BSA0000259868100000132
Figure BSA0000259868100000133
to distinguish the values of k under different grid conditions conveniently, k is usedbaFor example, it represents that the a-phase overmodulation occurs when the b-phase interval is clamped, and so on, the values of k are as follows:
Figure BSA0000259868100000134
Figure BSA0000259868100000135
Figure BSA0000259868100000136
Figure BSA0000259868100000137
Figure BSA0000259868100000141
the above formula shows that when the clamping is carried out in the clamping interval, the value of k is greater than 0 when overmodulation occurs to a certain phase reference voltage, and when the reference voltage is less than zero, only U in the formula needs to be addeddcReplacement of 2 into-Udc/2. Namely:
Figure BSA0000259868100000142
Figure BSA0000259868100000143
Figure BSA0000259868100000144
Figure BSA0000259868100000145
Figure BSA0000259868100000146
Figure BSA0000259868100000147
when the k value is determined, the clamping interval Δ θ at that time can be known from equations (29) to (35)xAt this time, the reference voltage may be clamped in the clamping interval described in table 3.2. In summary, the values of k under different grid conditions can be obtained as follows:
Figure BSA0000259868100000151
wherein k is-1, which means that the distortion of the input current can be restrained only by clamping the distortion interval, and the reference voltage does not exceed the static working range of the VIENNA rectifier. Further, step 3, the obtained modulation wave is subjected to sine pulse width modulation to obtain a pulse width modulation wave of a VIENNA rectifier switch under the wide-range unbalanced power grid.
Example 1
In this embodiment, a three-phase VIENNA rectifier circuit is built by using a Simulink tool in MATLAB, and the input voltage is rectified by the three-phase VIENNA rectifier circuit to obtain direct current. The electrical parameter settings during the simulation are as in table 3:
TABLE 3
Figure BSA0000259868100000152
Two power grid conditions are selected in the simulation:
(1) setting the initial phase of the a-phase power grid to be 0; compared with the phase a, the amplitude of the phase b power grid voltage is increased by 20%, the phase lags by 120 degrees, namely the initial phase of the phase b power grid voltage is-120 degrees; compared with the phase a, the amplitude of the phase c power grid voltage is increased by 40%, the phase is advanced by 120 degrees, namely the initial phase of the phase c power grid voltage is 120 degrees;
(2) setting the initial phase of the a-phase power grid to be 0; compared with the phase a, the amplitude of the phase b power grid voltage is increased by 10%, the phase lags by 100 degrees, namely the initial phase of the phase b power grid voltage is-100 degrees; compared with the phase a, the amplitude of the c-phase grid voltage is increased by 30%, the phase is advanced by 140 degrees, namely the initial phase of the c-phase grid voltage is 140 degrees.
Fig. 5 is a waveform diagram of three-phase voltage under unbalanced grid condition 1 in the present invention.
Fig. 6 is a waveform diagram of three-phase voltage under unbalanced grid condition 2 in the present invention.
Fig. 7 is a waveform diagram of current at the three-phase grid side before and after the method for optimizing input current under unbalanced grid condition 1 in the present invention, where (a) is a simulated waveform of current under conventional control, and (b) is a simulated waveform of current under a modulation wave interval clamping method.
Fig. 8 is a comparison graph of harmonic distribution of a current before and after an input current optimization method under unbalanced grid condition 1 in the present invention, where (a) is a harmonic distribution graph of a current under conventional control, and (b) is a harmonic distribution graph of a current under a modulated wave interval clamping method.
At the moment, the VIENNA rectifier which takes the control strategy of inhibiting the active secondary wave as a control target operates in a static working interval, and the distortion problem of the alternating current side current can be effectively inhibited by using the modulated wave interval clamping.
Fig. 9 is a waveform diagram of current at the three-phase grid side before and after adjustment with negative-sequence current under unbalanced grid condition 2 in the present invention, where (a) is a simulated waveform of modulated-wave-interval clamping and (b) is a simulated waveform of current under the modulated-wave-interval clamping method with negative-sequence current adjustment.
Fig. 10 is a comparison graph of the harmonic distribution of C-phase current before and after adjustment with negative-sequence current under unbalanced grid condition 2 in the present invention, where (a) is the harmonic distribution of current under modulated wave interval clamping and (b) is the harmonic distribution of current under modulated wave interval clamping method based on current command adjustment.
At the moment, the VIENNA rectifier which takes the active secondary wave suppression control strategy as a control target operates outside a static working interval, the distortion problem of alternating current side current cannot be effectively suppressed by using modulated wave interval clamping, and the distortion of the alternating current side current can be effectively suppressed only by using a modulated wave interval clamping method based on current instruction regulation.
In summary, the method for optimizing the input current of the VIENNA rectifier under the wide-range unbalanced power grid, which is set forth by the invention, includes the steps of calculating three-phase current and three-phase reference voltage by sampling three-phase power grid voltage, determining the static working range of the VIENNA rectifier by combining with the topology constraint of the VIENNA rectifier, restraining input current distortion by a method based on modulated wave interval clamping in the static working range, and restraining input current distortion by a method based on modulated wave interval clamping adjusted by a current instruction outside the static working range. The invention can effectively inhibit the current distortion of the VIENNA rectifier caused by the inconsistency of the phases of the network side current and the reference voltage when the power grid is interfered, improve the power factor of the system, reduce the harmonic distortion rate of the network side current, improve the efficiency of the VIENNA rectifier and meet the strict requirements of the power grid and electric equipment on the harmonic standard.

Claims (3)

1. A method for optimizing VIENNA rectifier input current under a wide-range unbalanced power grid is characterized by comprising a VIENNA rectifier, a digital processing control module and a driving circuit, wherein the digital processing control module comprises a sampling unit, a voltage control unit, a reference current calculation unit, a quasi-PR current control unit and a sine pulse width modulation unit; wherein:
(1) the sampling unit respectively collects voltage signals of upper and lower capacitors at the direct current side of the VIENNA rectifier, three-phase voltage signals at the alternating current side of the VIENNA rectifier and three-phase current signals at the alternating current side of the VIENNA rectifier;
(2) the voltage control unit processes the voltage signals of the upper capacitor and the lower capacitor on the direct current side into active power reference signals;
(3) the reference current calculation unit processes the active power reference signal and the voltage and current signals obtained after coordinate transformation into a current reference signal under a static coordinate system;
(4) the quasi-PR current control unit processes the current reference signal to obtain a modulation wave signal and sends the modulation wave signal to the sine pulse width modulation unit;
(5) the output end of the sine pulse width modulation unit is connected to each switching tube of each phase bridge arm in the three-level VIENNA rectifier through the driving circuit.
2. The method for optimizing VIENNA rectifier input current in a wide-range unbalanced network of claim 1, wherein the digital processing control modules are chips TMS320F28377D and EPM 1270T.
3. The method of claim 1 for optimizing VIENNA rectifier input current over a wide range of imbalanced power networks, comprising the steps of:
step 1, calculating the static working range of the VIENNA rectifier according to the inherent topological characteristic of the VIENNA rectifier.
(1) Establishing a three-phase reference voltage and three-phase switching tube duty ratio equation;
for the VIENNA rectifier, the following equation applies:
Figure FSA0000259868090000011
the general interpretation of the above formula can be expressed as:
Figure FSA0000259868090000012
wherein d is0Is an arbitrary constant.
(2) The constraint on the reference voltage at the moment can be obtained by solving the duty ratio within the range of the interval [0, 1], namely the static working range of the VIENNA rectifier; the constraints on the VIENNA rectifier reference voltage are shown in the table below.
VIENNA rectifier static operating range
Figure FSA0000259868090000021
The constraint equations in the table are as follows:
Figure FSA0000259868090000022
Figure FSA0000259868090000023
Figure FSA0000259868090000024
step 2, calculating a phase difference between a VIENNA rectifier reference current instruction and a reference voltage, and suppressing the distortion of the input current by injecting a zero-sequence component to enable a modulation wave to be clamped to zero in a distortion interval in a static working range; introducing a negative sequence current regulation coefficient k outside a static working range, restraining a reference voltage within the static working range by adjusting the value of k, and inhibiting the distortion of an input current by an interval clamping method, wherein the method comprises the following steps:
(1) extracting positive and negative sequence components of the voltage of the power grid and an initial Phase angle of the negative sequence component through a Double Second Order Generalized Integrator Phase-Locked Loop (DSOGI-PLL);
the expression for the grid voltage can be written as:
Figure FSA0000259868090000025
(2) calculating current reference under a control strategy for inhibiting active power secondary fluctuation and calculating reference voltage at the moment;
the reference current expression of the active secondary wave control strategy of the VIENNA rectifier under the abc coordinate system is as follows:
Figure FSA0000259868090000031
the power grid voltage formula and the input current instruction formula are expressed in an actual and imaginary number form as follows:
Figure FSA0000259868090000032
Figure FSA0000259868090000033
Figure FSA0000259868090000034
ea∠θea＝Ap∠0+An∠θn＝Ap+An(cos(θn)+jsin(θn))
Figure FSA0000259868090000035
Figure FSA0000259868090000036
let λ be An/Ap；M＝ωLP0(ii) a Solving the phase difference between the reference current and the reference voltage as follows:
Δθx＝θix-θvx(x＝a，b，c)
(3) judging whether the reference voltage is in a static working range, and when the reference voltage is in the static working range, providing a method for clamping a modulation wave interval, judging an interval in which the polarities of the reference voltage and the reference current are inconsistent, wherein the interval is a current distortion interval, and superposing a zero-sequence component in the distortion interval to clamp the original modulation wave to zero in the distortion interval so as to inhibit the distortion of the input current;
the VIENNA rectifier operates in a static operating range when Δ θxWhen the reference current is higher than 0 and the reference voltage is higher than the reference voltage, the starting point of the clamping interval is-thetaixEnd point is-thetavx(ii) a When Δ θx< 0, when the reference current lags behind the reference voltage, the start point of the clamping interval is-thetavxEnd point is-thetaix. In a power frequency period, each phase of reference voltage and reference current has two zero-crossing points, 6 clamping intervals exist, and the distribution of the three-phase reference voltage clamping intervals is shown in table 2.
TABLE 2 three-phase reference voltage clamping interval
Figure FSA0000259868090000037
(4) When the reference voltage is out of the static working range, an interval clamping method based on negative sequence current regulation is provided, a negative sequence current regulation coefficient k is introduced, the reference current and the reference voltage are recalculated, the reference voltage is restricted in the static working range by adjusting the value of k, and then the distortion of the input current is restrained by the interval clamping method.
Based on three current control side rates under the traditional unbalanced power grid, a new current control strategy is provided, a negative sequence current control coefficient k is introduced into a current instruction, k is defined between continuous intervals (-1, 1), and D (k) is made to be 1.5 (A)p 2+kAn 2) (ii) a Then, the expression of the three-phase current on the grid side under the abc coordinate system is as follows:
Figure FSA0000259868090000041
for the above formula, when k is-1, the active secondary wave suppression control strategy is adopted; when k is 0, the control strategy is a control strategy for inhibiting the current negative sequence component; and when k is 1, the reactive secondary fluctuation control strategy is restrained.
Similar to the above method, the phase difference between the reference current and the reference voltage is:
Δθx(k)＝θix(k)-θvx(k)(x＝a，b，c)
with the static working interval as a limiting condition, the value of k under different power grid conditions can be obtained as follows:
Figure FSA0000259868090000042
and 3, performing sinusoidal pulse width modulation on the obtained modulation wave to obtain a pulse width modulation wave of a VIENNA rectifier switch under the wide-range unbalanced power grid.
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CN112532025A (en) * 2020-12-03 2021-03-19 南京理工大学 Method for optimizing Vienna rectifier input current when power grid is disturbed
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CN112532025A (en) * 2020-12-03 2021-03-19 南京理工大学 Method for optimizing Vienna rectifier input current when power grid is disturbed
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