CN112532025B - Method for optimizing Vienna rectifier input current when power grid is disturbed - Google Patents

Method for optimizing Vienna rectifier input current when power grid is disturbed Download PDF

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CN112532025B
CN112532025B CN202011396769.1A CN202011396769A CN112532025B CN 112532025 B CN112532025 B CN 112532025B CN 202011396769 A CN202011396769 A CN 202011396769A CN 112532025 B CN112532025 B CN 112532025B
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current
reference voltage
voltage
grid
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CN112532025A (en
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吕建国
吕勋
史兆成
孙状
蔡卫峰
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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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • 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
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/084—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters using a control circuit common to several phases of a multi-phase system
    • 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
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
    • 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

Abstract

The invention discloses a method for optimizing input current of a Vienna rectifier when a power grid is interfered, and belongs to the field of power electronic conversion devices. The method comprises the following steps: when a power grid is interfered, three-phase reference voltage is established by taking the suppression of active power fluctuation as a control target to generate basic modulation waves; respectively calculating the phase difference between each phase of current and each phase of reference voltage, and determining a distortion area and a compensation range corresponding to each phase of current by judging the current advance or lag reference voltage; and in the three-phase current distortion interval, adding compensation voltage to the original reference voltage of each phase to obtain a new modulation wave, intersecting the new modulation wave with a triangular carrier wave with the same upper and lower amplitudes and phases, and finally obtaining a pulse width modulation wave for controlling the switch of the Vienna rectifier when the power grid is interfered. The method can effectively inhibit the current distortion of the Vienna rectifier caused by the inconsistency of the phases of the grid 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 grid side current, and improve the efficiency of the Vienna rectifier.

Description

Method for optimizing Vienna rectifier input current when power grid is disturbed
Technical Field
The invention belongs to the technical field of power electronic conversion devices, and particularly relates to a method for optimizing input current of a Vienna rectifier when a power grid is interfered.
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 rectifier, 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 without setting dead time. 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 an incorrect voltage vector 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 voltage and the current of the power grid are in the same phase under the condition of the balanced unit power factor of the power grid, but actually, the power grid is often in an unbalanced state due to the fact that the phase and the amplitude of the voltage of the power grid have offset situations, and in this situation, the problem of secondary fluctuation of the active power occurs, so that when the suppression of the fluctuation of the active power is taken as a control target, a phase difference exists between the voltage on the grid side and the current on the grid side, which makes the analysis of the distortion problem of the current on the grid side more complicated. Therefore, the problem of three-phase current distortion of the Vienna rectifier when the power grid is interfered 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 input current of a Vienna rectifier when a power grid is interfered, which can effectively inhibit current distortion of the Vienna rectifier caused by inconsistent phase of grid-side current and reference voltage when the power grid is interfered, improve the power factor of a system, reduce the harmonic distortion 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 when a grid is disturbed, comprising the steps of:
step 1, establishing three-phase reference voltage by using active power fluctuation suppression as a control target when a power grid is interfered, and generating basic modulation waves;
step 2, respectively calculating the phase difference between each phase of current and each phase of reference voltage, and determining a distortion area and a compensation range corresponding to each phase of current by judging whether the current leads or lags the reference voltage;
and 3, in a three-phase current distortion interval, adding compensation voltage to the original reference voltage of each phase to obtain a new modulation wave, intercepting the new modulation wave with a triangular carrier wave with the same upper and lower amplitude values and phases, and finally obtaining a pulse width modulation wave for controlling a switch of the Vienna rectifier when the power grid is interfered.
Further, the step 1 of establishing a three-phase reference voltage with active power fluctuation suppression as a control target to generate a basic modulation wave when the power grid is interfered includes the following steps:
(1) extracting positive and negative sequence components of the voltage of the power grid and Phase-locking the positive sequence component of the voltage of the power grid through a Decoupling Double Synchronous coordinate system Phase-Locked Loop (DDSRF-PLL) unit;
(2) with the suppression of active power fluctuation as a control target, obtaining a network side current instruction through a current instruction calculation unit, and realizing the tracking control of network side current through a PI controller;
(3) and carrying out dq/abc conversion on the obtained positive and negative sequence components of the modulated wave to obtain a basic modulated wave.
Further, the step 2 calculates the phase difference between each phase of current and each phase of reference voltage, and determines the distortion area and the compensation range corresponding to each phase of current by determining whether the current is leading or lagging the reference voltage, specifically as follows:
under the condition of balancing the unit power factor of the power grid, the grid side current and the grid side voltage are in the same phase, and the grid side current generates phase offset through a filter, so that the phases of the grid side current and the three-phase reference voltage at the rectifier side are inconsistent, and the phenomenon of zero crossing point distortion of the grid side current occurs;
the power grid is interfered in an unbalanced state, a double-current control strategy based on positive and negative sequence double control is adopted to restrain active power fluctuation as a control target, a phase difference exists between grid side voltage and grid side current due to the fact that the negative sequence component of the grid side current is opposite to the negative sequence component of the grid side voltage, meanwhile, due to the fact that inductance voltage drop is generated by a filter, the phase of the grid side current is finally inconsistent with the phase of three-phase reference voltage on the rectifier side, and the fact that the polarity of the grid side current is opposite to that of the reference voltage is a main reason for current distortion. Therefore, it is important to find the phase difference between each phase current and each phase reference voltage and the initial time of current distortion;
the method comprises the following steps:
(1) sampling three-phase voltage e at AC sidea、eb、ecThe symmetrical component method is utilized to carry out positive and negative sequence decomposition on the alternating-current side voltage, and because the Vienna rectifier in the embodiment adopts a three-phase three-wire system connection method, no zero-sequence current path exists, the zero-sequence component of the network side voltage is not considered, and only the positive and negative sequence components are considered;
(2) calculating current set by taking the suppression of active power fluctuation as a control target, and calculating a grid-side three-phase current expression through dq/abc conversion;
(3) establishing a KVL equation, and calculating a three-phase reference voltage expression;
(4) and comparing the phase difference between each phase of current and each phase of reference voltage, and determining the corresponding distortion area and compensation range of each phase of current by judging whether the current leads or lags the reference voltage.
Further, in the three-phase current distortion interval, in step 3, a compensation voltage is added to the original reference voltage of each phase at the same time to obtain a new modulation wave, the new modulation wave intersects with a triangular carrier wave with the same upper and lower amplitudes and phases, and finally a pulse width modulation wave for controlling the switch of the Vienna rectifier when the power grid is interfered is obtained, specifically:
in a three-phase current distortion interval, adding a compensation voltage to the original reference voltage of each phase at the same time, compensating the original modulation wave to 0 in the distortion area to obtain a compensated modulation wave, and improving the current distortion problem;
and respectively intersecting the compensated new modulated wave with a triangular carrier wave with the upper and lower amplitudes and phases consistent with each other at the positive and negative half shafts to obtain a pulse width modulated wave capable of controlling switching tubes of the Vienna rectifier, namely respectively controlling the upper and lower switching tubes of the same bridge arm of the six-switching-tube Vienna rectifier by two pulse width modulated waves on each phase, or controlling the switching tubes on each bridge arm of the three-switching-tube Vienna rectifier after the phase of the two pulse width modulated waves on each phase is intersected with the phase of the two pulse width modulated waves on each phase.
Compared with the prior art, the invention has the remarkable advantages that: (1) the phase difference between each phase of current and each phase of reference voltage is calculated by sampling the three-phase voltage at the AC side, the range of distortion compensation is determined by comparing the initial phase and the phase difference of the current at the network side and the reference voltage, the current distortion of the Vienna rectifier caused by the inconsistency of the phases of the current at the network side and the reference voltage when the power grid is interfered is effectively inhibited, the harmonic distortion rate of the current at the network side is reduced, and the efficiency of the Vienna rectifier is improved; (2) the Vienna rectifier alternating current side non-unit power factor operates, a corresponding distortion interval is found out by analyzing current lead or lag reference voltage, and compensation voltage is added in a distortion area to effectively inhibit the zero-crossing distortion problem of the network side current; (3) the method is suitable for the operation condition of the Vienna rectifier when the power grid is interfered, and has the advantages of reliable operation, low hardware cost, accurate control, good flexibility and easy realization.
Drawings
Fig. 1 is a topological structure diagram of a three-phase three-level Vienna rectifier in the invention.
FIG. 2 is a structural diagram of the overall control under the two-coordinate transformation of a Vienna topology dq rotating coordinate system when a power grid is interfered.
Fig. 3 is a phase diagram of each phase current and each phase reference voltage in the present invention.
Fig. 4 is a flow chart of the current distortion suppression process of the Vienna rectifier when the power grid is disturbed in the invention.
Fig. 5 is a graph of input imbalance voltage waveform when the power grid is disturbed according to the invention.
Fig. 6 is a diagram of three-phase network side current waveforms before and after the method for optimizing input current according to the present invention, wherein (a) is a simulation waveform before adding a compensation voltage according to the present invention, and (b) is a simulation waveform after adding a compensation voltage according to the present invention.
Fig. 7 is a comparison graph of the harmonic distribution of C-phase current before and after the method of the present invention, in which (a) is the harmonic distribution of C-phase current before the method of the present invention, and (b) is the harmonic distribution of C-phase current after the method of the present invention.
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 the two-coordinate transformation of the Vienna topology dq rotating coordinate system when the power grid is disturbed. The three-phase voltage at the AC side is subjected to phase-locked loop unit of a decoupling double-synchronous coordinate system to extract the positive and negative sequence components of the grid voltage under the dq axis and phase-lock the positive sequence component of the grid voltage, and the output voltage is given by Vdc_refAnd measuring the output voltage V of the DC sidedcObtaining output current given I through PI regulator after difference makingo_refGiven signal P multiplied by the output voltage as the DC component of the active power0Obtaining a network side current instruction through a current instruction calculation unit, realizing the tracking control of the network side current through a PI controller, and converting the obtained positive and negative sequence components of the modulation wave through dq/abc to obtain a basic three-phase reference voltage Ua_ref、Ub_ref、Uc_ref. And finally generating a pulse width modulation wave for controlling the on-off of a switching tube of the Vienna rectifier by designing the compensation voltage of the input current of the optimized Vienna rectifier aiming at the interference of the power grid.
The invention relates to a method for optimizing Vienna rectifier input current when a power grid is interfered, which specifically comprises the following steps:
step 1, when a power grid is interfered, three-phase reference voltage is established by taking active power fluctuation suppression as a control target to generate basic modulation waves, and the method comprises the following steps;
(1) extracting positive and negative sequence components of the voltage of the power grid and Phase-locking the positive sequence component of the voltage of the power grid through a Decoupling Double Synchronous coordinate system Phase-Locked Loop (DDSRF-PLL) unit;
(2) with the suppression of active power fluctuation as a control target, a network side current instruction is obtained through a current instruction calculation unit, and the tracking control of the network side current is realized through a PI controller;
(3) and carrying out dq/abc conversion on the positive sequence component and the negative sequence component of the obtained modulation wave to obtain a basic modulation wave.
Step 2, respectively calculating the phase difference between each phase of current and each phase of reference voltage, and determining a distortion area and a compensation range corresponding to each phase of current by judging whether the current leads or lags the reference voltage, wherein the method comprises the following steps:
(1) sampling three-phase voltage e at AC sidea、eb、ecThe alternating-current side voltage is subjected to positive and negative sequence decomposition by using a symmetrical component method, and because the Vienna rectifier in the embodiment adopts a three-phase three-wire system connection method, no zero-sequence current path exists, the zero-sequence component of the network side voltage is not considered, only the positive and negative sequence components are considered, and the three-phase voltage is represented as follows:
eabc(t)＝eabcp(t)+eabcn(t) (1)
in the formula, eabcp(t)、eabcn(t) positive and negative sequence components of grid voltage respectively:
Figure BSA0000226738010000051
in the formula, Ap、AnAmplitude of positive and negative sequence components of the grid voltage, θnIs an initial phase angle, omega, of the negative sequence component of the grid voltage0The frequency is the fundamental frequency of the positive sequence component of the power grid voltage.
(2) With the suppression of active power fluctuation as a control target, calculating current setting, and calculating a grid-side three-phase current expression through dq/abc conversion:
to suppress secondary fluctuations in active power and to make the average reactive power 0Let instantaneous reactive power Q0And (3) calculating a current given quantity which accords with a control target, and calculating a grid-side three-phase current expression through dq/abc conversion, wherein the given quantity is 0:
Figure BSA0000226738010000052
N＝1.5(Ap 2-An 2) (4)
(3) establishing a KVL equation, and calculating a three-phase reference voltage expression:
as shown in the topology of the three-phase three-level Vienna rectifier in fig. 1, the three-phase reference voltage can be represented as:
uabc_ref(t)＝uabcp_ref(t)+uabcn_ref(t) (5)
wherein u isabcp_ref(t)、uabcn_ref(t) respectively adopting positive and negative sequence components of the three-phase reference voltage, and adopting a column KVL equation, wherein L is assumed to be equal to inductance components of the filter, R is assumed to be equal to resistance components of the filter:
Figure BSA0000226738010000053
expressed in phasor form:
Figure BSA0000226738010000054
and (3) combining the voltage and current relationship obtained in the step (2), and expressing the phasor expression form of the three-phase current:
Figure BSA0000226738010000055
the three-phase reference voltage is:
Figure BSA0000226738010000061
for convenience and simplicity, order:
Figure BSA0000226738010000062
the positive and negative order decomposition relationship is simplified to obtain:
Figure BSA0000226738010000063
introducing Euler's formula, the above variables can be expressed as:
Figure BSA0000226738010000064
all conversion to real and imaginary representation, let:
Figure BSA0000226738010000065
calculated, wherein:
Figure BSA0000226738010000066
Figure BSA0000226738010000067
Figure BSA0000226738010000068
Figure BSA0000226738010000071
Figure BSA0000226738010000072
Figure BSA0000226738010000073
(4) and comparing the phase difference between each phase of current and each phase of reference voltage, and determining the corresponding distortion area and compensation range of each phase of current by judging whether the current leads or lags the reference voltage.
To find the phase angle of the three-phase reference voltage, let:
Figure BSA0000226738010000074
and (3) combining the (2) to obtain an amperometric expression, a three-phase current phase angle:
Figure BSA0000226738010000075
the phase difference between the two is as follows:
Figure BSA0000226738010000076
the polarity of the phase difference between each phase of current and each phase of reference voltage is judged according to the formula, and the current is judged to lead or lag the reference voltage.
According to the phase diagram of each phase current and each phase reference voltage shown in fig. 3, (a) a certain phase current is shown to lead the phase reference voltage, and the current distortion is mainly caused by the inconsistency of the polarities of the current and the reference voltage, so that the initial time of the current distortion is the current zero-crossing time, and the distortion range can be determined by combining the phase difference of the two phases, such as the shaded area shown in (a); (b) displaying that a certain phase current lags the reference voltage of the phase, wherein the initial time of current distortion is the zero crossing time of the reference voltage, and combining the phase difference of the two, the distortion range of the current under the condition can be determined, as shown in the shaded area in (b).
FIG. 4 is a flow chart of a Vienna rectifier current distortion suppression process when a power grid is interfered, and three-phase voltage e is sampleda、eb、ecObtaining related variables through positive and negative sequence decomposition calculation, and further calculating each phase current and corresponding phase angle thetaIxReference voltage of each phase and corresponding phase angle thetaUxThe phase difference polarity of the two signals determines whether the current leads or lags the reference voltage, thereby determining a distortion interval 1 and a distortion interval 2. The distortion interval 1 is determined to be (-theta) due to symmetry when the current leads the reference voltage, the current zero-crossing time is the current distortion initial time, and the reference voltage zero-crossing time is the current distortion end timeIx～-θUx)∪(180°-θIx～180°-θUx). The distortion interval 2 is determined to be the distortion interval and is (-theta) due to symmetry under the condition that the current lags behind the reference voltage, the zero-crossing time of the reference voltage is the initial current distortion time, and the zero-crossing time of the current is the end current distortion timeUx～-θIx)∪(180°-θUx～180°-θIx). And determining final compensation voltage in the distortion interval, and superposing the final compensation voltage on the original modulation wave to realize the suppression of current distortion.
Step 3, in a three-phase current distortion interval, adding compensation voltage to the original reference voltage of each phase to obtain a new modulation wave, intercepting the new modulation wave with a triangular carrier wave with the same upper and lower amplitude values and phases, and finally obtaining a pulse width modulation wave for controlling a switch of a Vienna rectifier when a power grid is interfered, wherein the method specifically comprises the following steps:
in the three-phase current distortion interval, each original phase modulated wave is compensated to 0, outside the distortion area, each phase modulated wave is consistent with the original modulated wave, no compensation is needed, taking phase a as an example, in the distortion interval (-theta)Ia～-θUa)∪(180°-θIa～180°-θUa) And the compensation voltage satisfies the following conditions:
ucoma＝-ua_ref (18)
outside the distortion interval, need not the compensation, the compensation voltage zero can, this moment:
ucoma＝0 (19)
the b and c phase compensation voltage u can be determined in the same waycomb、ucomcAnd the final compensation voltage is the sum of three-phase compensation voltages, and meets the following requirements:
ucom＝ucoma+ucomb+ucomc (20)
in the three-phase current distortion interval, the final compensation voltage u is added to the original reference voltage of each phasecomAnd the original modulation wave is compensated to 0 in the distortion area to obtain a compensated new modulation wave, the current distortion problem is improved, and the new modulation wave meets the following requirements:
Figure BSA0000226738010000081
and respectively intercepting the compensated new modulation wave with a triangular carrier with the upper and lower amplitudes and phases consistent with each other at the positive half shaft and the negative half shaft to obtain a pulse width modulation wave capable of controlling the switching tubes of the Vienna rectifier, namely, respectively controlling the upper and lower switching tubes of the same bridge arm of the six-switching-tube Vienna rectifier by two pulse width modulation waves on each phase, or controlling the switching tubes on each bridge arm of the three-switching-tube Vienna rectifier after the phase of the two pulse width modulation waves on each phase is matched with the phase of the two pulse width modulation waves on each phase.
Example 1
In this embodiment, a three-phase Vienna rectifying circuit is built by using a Simulink tool in MATLAB, and direct current is obtained after the input voltage is rectified by the three-phase Vienna rectifying circuit. The electrical parameter settings during the simulation are as in table 1:
TABLE 1
Figure BSA0000226738010000091
Table 1 shows Simulink simulation parameters, when a power grid is disturbed, an input voltage is unbalanced, the amplitude of the phase of the input voltage B, C is reduced by 23%, a phase shift occurs, the phase of B, C phase leads the phase of a phase by 230 ° and 100 °, and fig. 7 is a voltage waveform diagram of the input unbalance when the power grid is disturbed.
Fig. 6 is a diagram of current waveforms of the front and rear grid sides before and after the method for optimizing input current according to the present invention is used under the above electrical parameters, wherein (a) is a diagram of a simulation waveform before compensation voltage is added according to the present invention, and (b) is a diagram of a simulation waveform after compensation voltage is added according to the present invention. Fig. 7 is a comparison graph of the harmonic distribution of the C-phase current before and after the method of the present invention, wherein (a) is the harmonic distribution of the C-phase current before the method of the present invention, and (b) is the harmonic distribution of the C-phase current after the method of the present invention.
In summary, the method for optimizing the input current of the Vienna rectifier when the power grid is interfered, 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 initial time of distortion compensation by comparing the phase of each phase of current with each phase of reference voltage, determining the range of distortion compensation by combining the phase difference of the current on the network side and the reference voltage, adding compensation voltage to each phase of reference voltage in the distortion interval of the three-phase current to enable the modulation wave in the distortion area to be 0, and finally obtaining the pulse width modulation wave for controlling the switch of the Vienna rectifier when the power grid is interfered. The Vienna rectifier can effectively inhibit current distortion of the Vienna rectifier caused by inconsistent phases of grid side current and reference voltage when a power grid is interfered, improves the power factor of a system, reduces the harmonic distortion rate of the grid side current, improves the efficiency of the Vienna rectifier, and meets the strict requirements of the power grid and electric equipment on harmonic standards.

Claims (3)

1. A method for optimizing Vienna rectifier input current in case of grid disturbances, comprising the steps of:
step 1, generating a basic modulation wave by taking active power fluctuation suppression as a control target when a power grid is interfered;
step 2, phase differences of each phase of current and each phase of reference voltage are respectively calculated, and a distortion area and a compensation range corresponding to each phase of current are determined by judging whether the current is advanced or lagged by the reference voltage;
step 3, in a three-phase current distortion interval, determining a compensation voltage based on a basic modulation wave, adding the compensation voltage to the original reference voltage of each phase to obtain a new modulation wave, intersecting the new modulation wave with a triangular carrier wave with the same upper and lower amplitude values and phase positions, and finally obtaining a pulse width modulation wave for controlling a switch of the Vienna rectifier when a power grid is interfered;
the method is characterized in that the phase difference between each phase of current and each phase of reference voltage is calculated respectively in the step 2, and the corresponding distortion area and compensation range of each phase of current are determined by judging whether the current is advanced or delayed by the reference voltage, and the method specifically comprises the following steps:
under the condition of balancing the unit power factor of the power grid, the grid side current and the grid side voltage are in the same phase, and the grid side current generates phase offset through a filter, so that the phases of the grid side current and the three-phase reference voltage at the rectifier side are inconsistent, and the phenomenon of zero crossing point distortion of the grid side current occurs;
when a power grid is interfered, a double-current control strategy based on positive and negative sequence double control is adopted to restrain active power fluctuation as a control target, a phase difference exists between grid side voltage and grid side current due to the fact that a grid side current negative sequence component and a grid side voltage negative sequence component are in opposite phase, and the phase of the grid side current is finally inconsistent with a rectifier side three-phase reference voltage due to inductance voltage drop generated by a filter, the grid side current is opposite to the reference voltage in polarity and is a main reason for current distortion, and therefore, the determination of the phase difference between each phase of current and each phase of reference voltage and the initial moment of current distortion are vital;
the method comprises the following steps:
(1) sampling three-phase voltage e at AC sidea、eb、ecThe symmetrical component method is utilized to carry out positive and negative sequence decomposition on the alternating-current side voltage, and because the Vienna rectifier adopts a three-phase three-wire system connection method, no zero-sequence current path exists, the zero-sequence component of the network side voltage is not considered, and only the positive and negative sequence components are considered;
(2) calculating a network side three-phase current expression based on positive and negative sequence components by taking active power fluctuation inhibition as a control target;
(3) establishing a KVL equation, and calculating a three-phase reference voltage expression;
(4) and comparing the phase difference between each phase of current and each phase of reference voltage, and determining the corresponding distortion area and compensation range of each phase of current by judging whether the current leads or lags the reference voltage.
2. The method for optimizing the input current of the Vienna rectifier in the case of power grid disturbance according to claim 1, wherein the step 1 of establishing a three-phase reference voltage with the objective of suppressing active power fluctuation as a control target and generating a basic modulation wave in the case of power grid disturbance comprises the following steps:
(1) extracting positive and negative sequence components of the power grid voltage and locking the phase of the positive sequence component of the power grid voltage by a decoupling double-synchronous coordinate system phase-locked loop unit;
(2) with the suppression of active power fluctuation as a control target, a network side current instruction is obtained through a current instruction calculation unit, and the tracking control of the network side current is realized through a PI controller;
(3) and carrying out dq/abc conversion on the obtained positive and negative sequence components of the modulated wave to obtain a basic modulated wave.
3. The method according to claim 1, wherein in the three-phase current distortion interval, the compensation voltage is added to the original reference voltage of each phase to obtain a new modulation wave, the new modulation wave intersects with a triangular carrier wave with the same upper and lower amplitudes and phases, and finally obtains a pulse width modulation wave for controlling the switch of the Vienna rectifier when the power grid is disturbed, specifically:
in a three-phase current distortion interval, adding a compensation voltage to the original reference voltage of each phase at the same time, compensating the original reference voltage of each phase to 0 in a distortion area to obtain a compensated new modulation wave, and improving the current distortion problem;
and respectively intersecting the compensated new modulated wave with a triangular carrier wave with the upper and lower amplitudes and phases consistent with each other at the positive and negative half shafts to obtain a pulse width modulated wave capable of controlling switching tubes of the Vienna rectifier, namely respectively controlling the upper and lower switching tubes of the same bridge arm of the six-switching-tube Vienna rectifier by two pulse width modulated waves on each phase, or controlling the switching tubes on each bridge arm of the three-switching-tube Vienna rectifier after the phase of the two pulse width modulated waves on each phase is intersected with the phase of the two pulse width modulated waves on each phase.
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