CN116430109B - Positive and negative sequence component detection method based on reduced order resonator in unbalanced state of power grid - Google Patents
Positive and negative sequence component detection method based on reduced order resonator in unbalanced state of power grid Download PDFInfo
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- G—PHYSICS
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
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- G01R25/00—Arrangements for measuring phase angle between a voltage and a current or between voltages or currents
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
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- H—ELECTRICITY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- H—ELECTRICITY
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- 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
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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- 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
- H02M7/219—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 in a bridge configuration
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
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Abstract
The invention relates to the technical field of power electronics, and discloses a method for detecting positive and negative sequence components of power measurement of a three-phase PWM converter network based on a reduced-order resonator in an unbalanced state of a power grid. Under an alpha beta coordinate system, the function of detecting positive and negative sequence components of the three-phase PWM converter network voltage measurement is realized by utilizing the frequency selection characteristic of a Reduced Order Resonator (ROR) and the characteristic of the ROR as a first-order integrator, so that no static difference detection can be realized, and the stability of the system is not reduced. The control part adopts PR unbalanced control strategy, designs the reference current by utilizing the power equation of the three-phase PWM converter, and the adopted unbalanced control can realize high power factor and reduce THD of the three-phase PWM converter system, and has particularly obvious effect of inhibiting the double frequency alternating current component of active power.
Description
Technical Field
The invention relates to the technical field of power electronics, in particular to a positive and negative sequence component detection method based on a reduced-order resonator in an unbalanced state of a power grid.
Background
The power supply system in actual production and life is complex, and relates to power supply of common users, small factory power supply, large factory power supply and the like, so that the three-phase power grid is easy to generate unbalanced power supply of the power grid. And the use of a large number of nonlinear electric equipment causes serious power quality problems of a power supply system, such as: unbalance of voltage and current, voltage distortion, harmonic pollution, low power factor and other power grid pollution. This requires power conversion by a power device to ensure the power quality, and PWM converters are commonly used power conversion devices. The control of the three-phase PWM converter is to control the on-off state of the power switch tube through PWM modulation, so that under the condition of ensuring the stable output voltage of the direct current side, the input current is close to a sine wave to eliminate current harmonic waves, the sine of the current of the alternating current side of the power grid is realized, the current and the voltage phase are controllable, and the high power factor is realized.
However, the common control strategies of the three-phase PWM converter such as PI control and PR control belong to vector control under the unbalanced state of the grid voltage, which requires to detect the positive and negative sequence components of the grid-side voltage of the three-phase PWM converter, and the current common methods for detecting the positive and negative sequence components of the voltage are a double frequency trap method and a T/4 delay method. However, the frequency doubling trap method is suitable for a synchronous rotation coordinate system, the frequency doubling trap belongs to a non-causal system, no static difference detection cannot be realized, and the frequency doubling trap can reduce the stability of the system; the T/4 time delay method is suitable for a two-phase static coordinate system, can realize the separation of positive and negative sequence components without static difference and can not influence the stability of a control system, but the T/4 time delay method is designed for the condition of voltage single-phase drop, and has lower universal applicability in actual production and life.
Many control strategies are currently applied to three-phase PWM converter systems in grid imbalance conditions, but the general control design is too complex. For example, the conventional current double-closed-loop PI control involves four control variables, so four controllers are needed for control, and a phase-locked loop is needed to be additionally designed for acquiring the rotation angular velocity in the synchronous rotation coordinate system; the input current of the traditional PR control is to take the current obtained by PI control of the direct-current output voltage of the three-phase PWM converter as the reference current, and the middle of the current needs to be subjected to coordinate inverse transformation, so that the problem that static difference cannot be eliminated is also solved.
Disclosure of Invention
The invention aims to: aiming at the problems in the prior art, the invention provides a positive and negative sequence component detection method based on a reduced-order resonator in an unbalanced state of a power grid, which is simple and easy to realize, solves the problem of static difference, improves the practicability and eliminates harmonic interference.
The technical scheme is as follows: the invention provides a positive and negative sequence component detection method based on a reduced order resonator in an unbalanced state of a power grid, which comprises a three-phase PWM converter, a voltage positive and negative sequence component detection module, a voltage outer loop control module and a PR unbalanced control module;
step 1: under a two-phase static coordinate, constructing a three-phase PWM converter mathematical model in the unbalanced state of the power grid according to kirchhoff voltage and current law and combining the power supply characteristic in the unbalanced state of the power grid, wherein positive and negative sequence components of the grid side voltage of the three-phase PWM converter are related in control variables of the three-phase PWM converter mathematical model;
Step 2: the detection of positive and negative sequence components of the network side voltage of the three-phase PWM converter in the step 1 is detected through a Reduced Order Resonator (ROR); firstly, establishing a ROR transfer function, and obtaining an expression of positive and negative sequence components of the network side voltage of the three-phase PWM converter by analyzing and calculating to eliminate unit imaginary number j in the transfer function;
Step 3: PI control is carried out on the voltage at the direct current side, the input of a voltage outer ring of the three-phase PWM converter is the difference value between the reference value V 0 of the output voltage at the direct current side and the actual output voltage V 0 at the direct current side, after PI control, the output current i dc * is multiplied by V 0 to obtain the reference value P 0 of the direct current component of active power, and the reference value P α * and i β * are obtained by substituting the reference value P 0 of the direct current component of active power and the detected positive and negative sequence component of the voltage into a reference current calculation formula determined by a power equation set of the three-phase PWM converter;
step 4: the PR unbalanced control module is provided with a quasi PR controller, and takes the difference value between a reference current i α * and a network side current i α of the three-phase PWM converter and the difference value between a reference current i β * and a network side current i β of the three-phase PWM converter as input through a transfer function of the quasi PR controller to obtain reference voltages e α * and e β *;
Step 5: and taking the reference voltages e α * and e β * as SVPWM input to obtain a switch control signal of a switch in the three-phase PWM converter.
Further, the mathematical model of the three-phase PWM converter when the power grid under the two-phase static coordinates is unbalanced is as follows:
L is the inductance of the alternating current side filter, and the equivalent resistance of the corresponding inductance is r L; c is a direct current bus filter capacitor, R is a parallel load equivalent resistor; v 0 is the dc output voltage; e α P、eα N is the positive sequence and negative sequence components of the alpha-axis voltage at the network side; e β P、eβ N is the positive sequence and negative sequence components of the network side beta-axis voltage; i α P,iα N is a positive sequence and a negative sequence component of the grid-side alpha-axis current, and i β P,iβ N is a positive sequence and a negative sequence component of the grid-side beta-axis current; s α P、Sα N is an alpha-axis positive sequence and negative sequence logic switching function; s β P、Sβ N is a beta-axis positive sequence and negative sequence logic switching function.
Further, the transfer function of ROR in step 2 is:
Wherein s is a complex parameter; j is the unit imaginary number; k r is the resonance coefficient; omega 0 is the resonance angular frequency of the reduced-order resonator, namely the power frequency angular frequency of the three-phase power grid; g ROR-P(s) is a transfer function for positive sequence component extraction; g ROR-N(s) is a transfer function for negative sequence component extraction; introducing a bandwidth omega c, and establishing a new ROR transfer function as follows:
Wherein, take the resonance coefficient k r =1.
Further, when positive sequence components of the three-phase PWM converter network side voltages on the α -axis and the β -axis are detected, the corresponding input signal G ROR-P(s) is a difference value between the positive sequence components of the three-phase PWM converter network side voltages on the α -axis and the β -axis and the negative sequence components on the α -axis and the β -axis, and the output signal is a positive sequence component of the three-phase PWM converter network side voltages on the α -axis and the β -axis, and is obtained by substituting the positive sequence components into the transfer function G ROR-P(s):
further, when detecting negative sequence components of the three-phase PWM converter network side voltages on the α -axis and the β -axis, the corresponding input signal G ROR-N(s) is a difference value between the three-phase PWM converter network side voltages on the α -axis and the β -axis and the positive sequence components on the α -axis and the β -axis, the output signal is a negative sequence component of the three-phase PWM converter network side voltages on the α -axis and the β -axis, and the output signal is obtained by substituting the negative sequence components into the transfer function G ROR-N(s):
Further, the spatial vector relation between the positive sequence component of the three-phase PWM converter network side voltage on the alpha axis and the positive sequence component on the beta axis is e α P＝jeβ P; the space vector relation between the negative sequence component of the three-phase PWM converter network side voltage on the alpha axis and the negative sequence component on the beta axis is e β N＝jeα N; the ROR detects the positive and negative sequence components as:
further, the reference value of the net side instantaneous active power direct current component of the three-phase PWM converter is:
Wherein k p is the proportional gain coefficient of the PI controller; k i is the integral gain factor of the PI controller.
Further, the three-phase PWM converter power equation set is:
Wherein p 0 is the active power direct current component at the network side of the three-phase PWM converter; p 2ω is the active power doubling alternating current component of the three-phase PWM converter network side; q 0 is the reactive power direct current component at the network side of the three-phase PWM converter; q 2ω is the reactive power doubling alternating current component at the network side of the three-phase PWM converter; e α P、eα N is the positive sequence and negative sequence components of the alpha-axis voltage at the network side; e β P、eβ N is the positive and negative sequence components of the net side beta-axis voltage.
Further, the reference current in the step 3 is:
Further, the transfer function of the quasi-PR controller set by the PR unbalanced control module is as follows:
Wherein k PR is a proportional term coefficient of the quasi PR controller, k pr is a resonant term coefficient of the quasi PR controller, ω PR is a resonant angular frequency of the quasi PR controller, and ω pr is a bandwidth of the quasi PR controller.
The beneficial effects are that:
1. The degradation resonator selected by the invention belongs to a first-order integrator, does not need to detect the amplitude and the phase of a signal step by step, and can independently and directly realize the function of detecting positive and negative sequence components.
2. The degradation resonator selected by the invention has the frequency selection characteristic, and the corresponding angular frequency can be set according to the detection requirement, so that the anti-interference capability of the degradation resonator on frequency change is strong, and the performance of the degradation resonator is not affected when the detected signal has harmonic waves, so that the frequency selection characteristic can eliminate the harmonic wave interference in the detection process, and the practicability of the method for detecting the positive and negative sequence components is improved.
3. The method for detecting the positive and negative sequence components is designed in the invention, and the values of the positive sequence component and the negative sequence component are mutually updated in the detection process, so that the method can realize zero static difference detection, improve the accuracy of detection results and solve the problem of static difference of the detection results in the prior art.
Drawings
Fig. 1 is a main circuit configuration diagram of a three-phase PWM converter according to the present invention;
FIG. 2 is a block diagram of a three-phase PWM converter imbalance control system according to the present invention;
FIG. 3 is a block diagram of a voltage positive-negative sequence component detection module based on a reduced-order resonator according to the present invention, wherein (a) is a block diagram of a design for detecting a voltage positive-sequence component, and (b) is a block diagram of a design for detecting a voltage negative-sequence component;
FIG. 4 is a block diagram of a PI voltage outer loop control system for a three-phase PWM converter according to the present invention;
FIG. 5 is a waveform of unbalanced network side voltage and distortion current of a three-phase PWM converter according to the present invention;
FIG. 6 is a waveform of positive and negative sequence components of the network side voltage of the three-phase PWM converter of the present invention;
FIG. 7 is a waveform of the DC side output voltage V0 of the three-phase PWM converter of the present invention;
FIG. 8 is a graph showing the waveform of the grid-side current of a three-phase PWM converter according to the present invention and the FFT analysis of the A-phase current;
Fig. 9 is a waveform of instantaneous active power p and instantaneous reactive power q of the three-phase PWM converter of the present invention;
fig. 10 is a waveform of a phase a voltage and current of the three-phase PWM converter according to the present invention.
Detailed Description
The invention is further described below with reference to the accompanying drawings. The following examples are only for more clearly illustrating the technical aspects of the present invention, and are not intended to limit the scope of the present invention.
Referring to a main circuit structure diagram of the three-phase PWM converter shown in fig. 1, wherein L is an ac side filter inductance, and a corresponding inductance equivalent resistance is denoted by r L;Sa,Sb,Sc and represents an upper bridge arm switching tube of the rectifier bridge; s' a,S'b,S'c represents a bridge arm switching tube under the rectifier bridge; c is a direct current bus filter capacitor, R is a parallel load equivalent resistor; i dc is direct-current side current, i 0 is direct-current side equivalent load current, and V 0 is direct-current output voltage; o is a neutral point of the power grid, and N is a ground wire node.
Referring to fig. 2, the method for detecting voltage positive and negative sequence components based on a reduced order resonator provided by the invention comprises a voltage positive and negative sequence component detection design based on ROR, a voltage outer loop control design and a quasi-PR control strategy design, and the implementation of the invention comprises the following steps:
Step 1: establishing a mathematical model of the three-phase PWM converter when the power grid is unbalanced under the two-phase static coordinates;
step 1.1: collecting network side voltage and current of a three-phase PWM converter;
The network side voltage e a、eb、ec and the direct current side output voltage V 0 of the three-phase PWM converter are collected through a Hall voltage sensor, and the network side current i a、ib、ic of the three-phase PWM converter is collected through the Hall voltage sensor.
Step 1.2: in a three-phase stationary coordinate system, the voltages and currents of the three-phase PWM converter are as follows:
wherein E, I is the amplitude of the voltage and current of the three-phase PWM converter.
The instantaneous value relationship between the voltage and current of a three-phase PWM converter is:
Step 1.2.1: according to kirchhoff's voltage law and three-phase PWM converter network side and alternating current side power conservation law, a mathematical model of the three-phase PWM converter under a three-phase static coordinate system is as follows:
wherein S k is a logic switching function, defined as:
step 1.3: constructing a mathematical model of the three-phase PWM converter in a two-phase static coordinate system under the balance state of the power grid:
step 1.3.1: clark coordinate transformation from a three-phase static coordinate system to a two-phase static coordinate system is carried out on the voltage and the current at the network side, and the voltage and the current after transformation are obtained as follows:
step 1.3.2: clark coordinate transformation from a three-phase static coordinate system to a two-phase static coordinate system is carried out on the logic switch function, and the obtained transformed logic switch function is as follows:
Step 1.3.3: substituting the formula (4) and the formula (5) into the formula (3), and calculating to obtain a mathematical model of the three-phase PWM converter in a power grid balance state under a two-phase static coordinate, wherein the mathematical model is as follows:
Step 1.4: constructing a mathematical model of the three-phase PWM converter in a two-phase static coordinate system when the power grid voltage is unbalanced:
Step 1.4.1: the network side voltage and current of the three-phase PWM converter are as follows:
Wherein P represents a positive sequence and N represents a negative sequence; e a P、ea N is the positive sequence and negative sequence component of the A phase voltage; e b P、eb N is the positive sequence and negative sequence components of the B phase voltage; e c P、ec N is the positive sequence and negative sequence components of the C-phase voltage; i a P、ia N is the positive sequence and negative sequence components of the A-phase current; i b P、ib N is the positive sequence and negative sequence components of the B-phase current; i c P、ic N is the positive sequence and negative sequence components of the C-phase current; is the initial phase of the positive sequence and negative sequence components.
When the voltage of the power grid is unbalanced, the voltage, current and logic switching function of the grid side of the three-phase PWM converter of the two-phase static coordinate system are as follows:
Step 1.4.2: substituting the formula (8) into the formula (6), and calculating to obtain a mathematical model of the three-phase PWM converter when the power grid voltage is unbalanced under the two-phase static coordinates, wherein the mathematical model is as follows:
L is the inductance of the alternating current side filter, and the equivalent resistance of the corresponding inductance is r L; c is a direct current bus filter capacitor, R is a parallel load equivalent resistor; v 0 is the dc output voltage; e α P、eα N is the positive sequence and negative sequence components of the alpha-axis voltage at the network side; e β P、eβ N is the positive sequence and negative sequence components of the network side beta-axis voltage; s α P、Sα N is an alpha-axis positive sequence and negative sequence logic switching function; s β P、Sβ N is a beta-axis positive sequence and negative sequence logic switching function.
Step 2: referring to fig. 3, a ROR-based detection voltage positive and negative sequence component module is designed:
Step 2.1: establishing a transfer function of the ROR;
Step 2.1.1: the transfer function of the ROR obtained after factoring the SOGI is:
wherein s is a complex parameter; j is the unit imaginary number; k r is the resonance coefficient; omega 0 is the resonance angular frequency of the reduced-order resonator, here the three-phase grid power frequency angular frequency; g ROR-P(s) is a transfer function for positive sequence component extraction; g ROR-N(s) is a transfer function for negative sequence component extraction.
Step 2.1.2: introducing a bandwidth omega c, and establishing a new ROR transfer function;
The ROR corresponding to equation (10), while having infinite gain at the resonant frequency, can easily cause instability of the system. And when the frequency shifts from the resonance frequency, the gain drops rapidly, and the robustness is poor. When the power grid fluctuates, the ideal control effect is difficult to achieve. It is therefore necessary to introduce a bandwidth omega c for improved robustness.
The value of the bandwidth omega c influences the rapidity of the current output response and the stability degree of the system, the response time of the current is faster along with the increase of the bandwidth omega c, and the current can be stably output in a short time, but the stability of the system is influenced by the overlarge value of the omega c, and the value is generally 10-30rad/s.
After introducing the bandwidth omega c, the transfer functions of detecting positive and negative sequence components based on the ROR design are respectively as follows:
step 2.1.3: confirming the value of a resonance coefficient k r;
The amplitude gain of G ROR-P/N(s) at the resonant frequency is affected by the resonant coefficient k r, the larger the k r, the larger the gain. In order to separate positive and negative sequence components with equal amplitude and no phase difference, taking a resonance coefficient k r =1, so that the gain of the output quantity of the resonance controller is 1, then the transfer functions of detecting positive and negative sequence components based on the ROR design are respectively as follows:
step 2.2: eliminating the unit imaginary number j in the ROR transfer function;
Taking the detection of the network side voltage of the three-phase PWM converter as an example, the principle of ROR for positive and negative sequence component detection is analyzed and introduced. Analysis finds that there is a unit imaginary number j in the ROR's transfer function, which makes the ROR's transfer function unrealizable directly during control, and therefore requires elimination of the unit imaginary number j.
Step 2.2.1: eliminating the unit imaginary number j in the transfer function G ROR-P(s);
when positive sequence components of the three-phase PWM converter network side voltage in the alpha axis and the beta axis are detected, G ROR-P(s) corresponding input signals are differences between the three-phase PWM converter network side voltage in the alpha axis and the beta axis and negative sequence components of the three-phase PWM converter network side voltage in the alpha axis and the beta axis, output signals are positive sequence components of the three-phase PWM converter network side voltage in the alpha axis and the beta axis, and the positive sequence components are substituted into transfer functions G ROR-P(s) to obtain:
Je α P and je β P exist in the formula (13), and the space vector relation between the positive sequence component of the alpha axis and the positive sequence component of the beta axis of the three-phase PWM converter network side voltage is e α P＝jeβ P, and the space vector relation is calculated by substituting the space vector relation into the three-phase PWM converter network side voltage:
step 2.2.2: eliminating the unit imaginary number j in the transfer function G ROR-N(s);
When detecting negative sequence components of the three-phase PWM converter network side voltage in the alpha axis and the beta axis, G ROR-N(s) corresponds to an input signal which is a difference value between the three-phase PWM converter network side voltage in the alpha axis and the beta axis and positive sequence components of the three-phase PWM converter network side voltage in the alpha axis and the beta axis, and an output signal which is the negative sequence components of the three-phase PWM converter network side voltage in the alpha axis and the beta axis is substituted into a transfer function G ROR-N(s) to obtain:
The above formulas exist je α N and je β N, and the spatial vector relation between the negative sequence component of the alpha axis and the negative sequence component of the beta axis of the three-phase PWM converter net side voltage is e β N＝jeα N, and the three-phase PWM converter net side voltage is calculated by substituting the spatial vector relation into the three-phase PWM converter net side voltage:
step 2.3: confirming a calculation formula of ROR detection of positive and negative sequence components;
equations (14) and (16) with the unit imaginary number j eliminated, the positive and negative sequence components of the deformed voltage are:
Step 3: calculating reference currents i α * and i β * of an input signal of the quasi-PR controller;
Step 3.1: referring to fig. 4, voltage outer loop control is designed; when PI control is performed on the voltage at the dc side, the input of the voltage outer loop of the three-phase PWM converter is the difference between the reference value V 0 of the output voltage at the dc side and the actual output voltage V 0 at the dc side, and the output current is i dc *, and then the reference value of the dc component of the net active power of the three-phase PWM converter is:
Wherein k p is the proportional gain coefficient; k i is the integral gain coefficient.
Step 3.2: establishing a power equation set of the three-phase PWM converter;
Step 3.2.1: the calculation formula of the instantaneous active power p and the instantaneous reactive power q of the three-phase PWM converter is as follows:
Step 3.2.2: under the unbalanced state of the three-phase power grid, according to the spatial vector relation between the three-phase static coordinate system and the two-phase static coordinate system and by combining the formula (19), in the two-phase static coordinate system, the grid-side voltage and the current of the three-phase PWM converter are cosine in the alpha axis and sine in the beta axis, and positive sequence components and negative sequence components exist in the grid-side voltage and the current of the three-phase PWM converter, and then the power equation of the three-phase PWM converter in the two-phase static coordinate system is as follows:
Wherein p 0 is the instantaneous active power dc component; p 2ω is the instantaneous active power doubling ac component; q 0 is the instantaneous reactive power dc component; q 2ω is the instantaneous reactive power doubled ac component.
Step 3.3: according to the power equation set, obtaining the reference current, in order to realize unit power factor, sinusoidal current of the alternating current side of the three-phase PWM converter, inhibit negative sequence current, inhibit active power and double frequency alternating current component of reactive power, the condition to be satisfied is P 0 *＝idc *V0 *, the direct current component of reactive power and the double frequency alternating current component of active power and reactive power are zero, and the following can be obtained:
wherein the method comprises the steps of ,[(eα P)2+(eβ P)2]+[(eα N)2+(eβ N)2]≠0;
The reference current is:
Step 4: calculating reference voltages e α * and e β * of the quasi-PR unbalanced control module;
step 4.1: let the transfer function of the PR controller be:
Wherein k PR is a proportional term coefficient of the quasi PR controller, k pr is a resonant term coefficient of the quasi PR controller, ω PR is a resonant angular frequency of the quasi PR controller, and ω pr is a bandwidth.
Step 4.2: the voltage obtained by performing quasi PR control on the difference value between the reference current i α * and the current i α subjected to coordinate transformation on the network side of the three-phase PWM converter is used as the input reference voltage e α * of SVPWM; and taking the voltage obtained by performing quasi PR control on the difference value between the reference current i β * and the current i β subjected to coordinate transformation on the network side of the three-phase PWM converter as an input reference voltage e β * of the SVPWM.
Step 5: and taking the reference voltages e α * and e β * as SVPWM inputs to obtain switch control signals of switches in the three-phase PWM converter.
Referring to fig. 5 to 10, the simulation effect verification analysis of the detection method of the present invention is:
Referring to fig. 5, fig. 5 (a) is a voltage waveform of a three-phase PWM converter when the power grid is unbalanced; fig. 5 (b) shows the net side distortion current of the three-phase PWM converter.
Referring to fig. 6, the grid equilibrium state is before 0.15s, and the grid imbalance state is after 0.15 s. FIG. 6 (a) is a positive sequence component of the three-phase PWM converter grid-side voltage based on ROR detection; fig. 6 (b) is a negative sequence component of the network side voltage of the three-phase PWM converter based on ROR detection. It can be found that when the grid voltage drops suddenly, no negative sequence component is positive sequence voltage when the grid is in a balanced state. The frequency of the detected positive and negative sequence components is 50Hz as the same as the network side voltage frequency of the three-phase PWM converter, and the result proves that the method for detecting the positive and negative sequence components based on ROR design is effective.
Referring to fig. 7, the dc side output voltage V 0 of the three-phase PWM converter is in an unbalanced state of the grid. FIG. 7 (a) is a V 0 waveform when the three-phase PWM converter does not employ an imbalance control strategy; FIG. 7 (b) is a V 0 waveform when the three-phase PWM converter employs an imbalance control strategy; it can be found that the secondary ripple of V 0 is significantly suppressed, substantially without ripple, after the imbalance control strategy is employed.
Referring to fig. 8, FFT analysis of the grid side current and the a-phase current of the three-phase PWM converter in the grid imbalance state. FIG. 8 (a) is an FFT analysis of the grid side current and the A-phase current when the three-phase PWM converter does not employ an imbalance control strategy; FIG. 8 (b) is an FFT analysis of the grid side current and the A phase current when the three-phase PWM converter adopts an unbalanced control strategy; it can be found that when no imbalance control strategy is adopted, the network side current of the three-phase PWM converter is severely distorted and THD is as high as 21.14%; with the unbalanced control strategy, the grid-side current of the three-phase PWM converter is sinusoidal and THD is reduced to 2.29%.
Referring to fig. 9, waveforms of instantaneous active power p and instantaneous reactive power q of the three-phase PWM converter in an unbalanced state of the grid. Fig. 9 (a) shows waveforms of p and q when the three-phase PWM converter does not adopt the unbalance control strategy; fig. 9 (b) shows waveforms of p and q when the unbalanced control strategy is applied to the three-phase PWM converter. It can be seen that when the unbalanced control strategy is adopted, the instantaneous active power p of the three-phase PWM converter has no secondary ripple basically, and the secondary ripple of the instantaneous reactive power q is also obviously reduced compared with that when the unbalanced control strategy is not adopted.
Referring to fig. 10, waveforms of a-phase voltage and current of the three-phase PWM converter in an unbalanced state of the power grid. FIG. 10 (a) is a waveform of the A-phase voltage and current when the three-phase PWM converter does not employ an unbalanced control strategy; FIG. 10 (a) is a waveform of the A-phase voltage and current when the three-phase PWM converter adopts an unbalanced control strategy; it can be calculated that the a-phase voltage is in phase with the current when the imbalance control strategy is adopted, and the power factor of the three-phase PWM converter is 0.9985 near unity while the power factor of the three-phase PWM converter is only 0.4782 when the imbalance control strategy is adopted.
The foregoing embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the present invention and to implement the same, not to limit the scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of the present invention.
Claims (6)
1. The positive and negative sequence component detection method based on the reduced order resonator in the unbalanced state of the power grid is characterized by comprising a three-phase PWM converter, a voltage positive and negative sequence component detection module, a voltage outer ring control module and a PR unbalanced control module;
step 1: under a two-phase static coordinate, constructing a three-phase PWM converter mathematical model in the unbalanced state of the power grid according to kirchhoff voltage and current law and combining the power supply characteristic in the unbalanced state of the power grid, wherein positive and negative sequence components of the grid side voltage of the three-phase PWM converter are related in control variables of the three-phase PWM converter mathematical model;
the mathematical model of the three-phase PWM converter when the power grid under the two-phase static coordinates is unbalanced is as follows:
l is the inductance of the alternating current side filter, and the equivalent resistance of the corresponding inductance is r L; c is a direct current bus filter capacitor, R is a parallel load equivalent resistor; v 0 is the dc output voltage; e α P、eα N is the positive sequence and negative sequence components of the alpha-axis voltage at the network side; e β P、eβ N is the positive sequence and negative sequence components of the network side beta-axis voltage; i α P,iα N is a positive sequence and a negative sequence component of the grid-side alpha-axis current, and i β P,iβ N is a positive sequence and a negative sequence component of the grid-side beta-axis current; s α P、Sα N is an alpha-axis positive sequence and negative sequence logic switching function; s β P、Sβ N is a beta-axis positive sequence and negative sequence logic switching function;
Step 2: the detection of positive and negative sequence components of the network side voltage of the three-phase PWM converter in the step 1 is detected through a reduced order resonator ROR; firstly, establishing a ROR transfer function, and obtaining an expression of positive and negative sequence components of the network side voltage of the three-phase PWM converter by analyzing and calculating to eliminate unit imaginary number j in the transfer function;
Step 3: PI control is carried out on the voltage at the direct current side, the input of a voltage outer ring of the three-phase PWM converter is the difference value between a reference value V 0 * of the output voltage at the direct current side and the actual output voltage V 0 at the direct current side, after PI control, the output current i dc * is multiplied by V 0 * to obtain a reference value P 0 * of the direct current component of active power, and the reference value P 0 * and the detected positive and negative sequence component of the voltage are substituted into a reference current calculation formula determined by a power equation set of the three-phase PWM converter to obtain reference currents i α * and i β *;
the reference value of the net side instantaneous active power direct current component of the three-phase PWM converter is as follows:
Wherein s is a complex parameter; k p is the proportional gain coefficient of the PI controller; k i is the integral gain coefficient of the PI controller;
The three-phase PWM converter power equation set is:
Wherein p 0 is the active power direct current component at the network side of the three-phase PWM converter; p 2ω is the active power doubling alternating current component of the three-phase PWM converter network side; q 0 is the reactive power direct current component at the network side of the three-phase PWM converter; q 2ω is the reactive power doubling alternating current component at the network side of the three-phase PWM converter; e α P、eα N is the positive sequence and negative sequence components of the alpha-axis voltage at the network side; e β P、eβ N is the positive sequence and negative sequence components of the network side beta-axis voltage;
The reference current is:
step 4: the PR unbalanced control module is provided with a quasi PR controller, and takes the difference value between a reference current i α * and a network side current i α of the three-phase PWM converter and the difference value between a reference current i β * and a network side current i β of the three-phase PWM converter as input through a transfer function of the quasi PR controller to obtain reference voltages e α * and e β *;
Step 5: and taking the reference voltages e α * and e β * as SVPWM input to obtain a switch control signal of a switch in the three-phase PWM converter.
2. The method for detecting positive and negative sequence components based on a reduced order resonator in an unbalanced state of a power grid according to claim 1, wherein the transfer function of ROR in step2 is:
Wherein j is the unit imaginary number; k r is the resonance coefficient; omega 0 is the resonance angular frequency of the reduced-order resonator, namely the power frequency angular frequency of the three-phase power grid; g ROR-P(s) is a transfer function for positive sequence component extraction; g ROR-N(s) is a transfer function for negative sequence component extraction; introducing a bandwidth omega c, and establishing a new ROR transfer function as follows:
Wherein, take the resonance coefficient k r =1.
3. The method for detecting positive and negative sequence components based on a reduced order resonator in a power grid unbalanced state according to claim 2, wherein when positive sequence components of the three-phase PWM converter grid-side voltage in an alpha axis and a beta axis are detected, G ROR-P(s) corresponding input signals are differences between the three-phase PWM converter grid-side voltage in the alpha axis and the beta axis and negative sequence components thereof in the alpha axis and the beta axis, output signals are positive sequence components of the three-phase PWM converter grid-side voltage in the alpha axis and the beta axis, and the positive sequence components are substituted into a transfer function G ROR-P(s) to obtain:
4. The method for detecting positive and negative sequence components based on a reduced order resonator in a power grid unbalanced state according to claim 3, wherein when negative sequence components of the three-phase PWM converter grid-side voltage on the alpha axis and the beta axis are detected, the G ROR-N(s) corresponding input signal is a difference value between the three-phase PWM converter grid-side voltage on the alpha axis and the beta axis and positive sequence components thereof on the alpha axis and the beta axis, the output signal is a negative sequence component of the three-phase PWM converter grid-side voltage on the alpha axis and the beta axis, and the output signal is obtained by substituting the negative sequence components into a transfer function G ROR-N(s):
5. The positive and negative sequence component detection method based on a reduced order resonator in a power grid unbalanced state of claim 4, wherein a spatial vector relation between a positive sequence component of a three-phase PWM converter grid-side voltage on an alpha axis and a positive sequence component on a beta axis is e α P＝jeβ P; the space vector relation between the negative sequence component of the three-phase PWM converter network side voltage on the alpha axis and the negative sequence component on the beta axis is e β N＝jeα N; the ROR detects the positive and negative sequence components as:
6. The method for detecting positive and negative sequence components based on a reduced order resonator in a power grid unbalanced state according to claim 1, wherein a transfer function of a quasi-PR controller set by the PR unbalanced control module is as follows:
Where k PR is the proportional term coefficient of the quasi PR controller, k pr is the resonant term coefficient of the quasi PR controller, and ω pr is the bandwidth of the quasi PR controller.
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| CN103956919A (en) * | 2014-04-15 | 2014-07-30 | 中国矿业大学 | Simplified model forecasting control method of network voltage unbalance three-level rectifier |
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| CN103956919A (en) * | 2014-04-15 | 2014-07-30 | 中国矿业大学 | Simplified model forecasting control method of network voltage unbalance three-level rectifier |
| CN106786780A (en) * | 2017-03-02 | 2017-05-31 | 江苏大学 | A kind of grid-connected control method and system based on virtual synchronous generator |
| CN107276117A (en) * | 2017-05-27 | 2017-10-20 | 上海电力学院 | LCL type three-phase grid-connected inverter double loop control with frequency locking |
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