CN116565944A - Synchronous frequency adaptive resonance-based negative sequence voltage compensation method for grid-structured converter - Google Patents
Synchronous frequency adaptive resonance-based negative sequence voltage compensation method for grid-structured converter Download PDFInfo
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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
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
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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
- H02J3/002—Flicker reduction, e.g. compensation of flicker introduced by non-linear load
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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
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
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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
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/493—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode the static converters being arranged for operation in parallel
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- Supply And Distribution Of Alternating Current (AREA)
Abstract
The invention discloses a synchronous frequency self-adaptive resonance-based negative sequence voltage compensation method for a grid-connected converter, which eliminates a phase acquisition link of negative sequence voltage, avoids using a complex positive and negative sequence coordinate system, does not need to extract a negative sequence voltage component of a grid-connected point, does not introduce decomposition delay, and improves control rapidity; meanwhile, the direct resonance control is carried out based on the voltage error, the output voltage is directly supplied to the modulation voltage, the configuration of a negative sequence instruction is avoided, a control structure is simplified, the influence of the negative sequence voltage control on positive sequence voltage control is reduced, a quicker negative sequence voltage compensation dynamic effect is achieved, and the effect of the grid-connected converter on the negative sequence voltage compensation is achieved; therefore, the method can achieve the aim of compensating the voltage unbalance under the unbalanced computer network condition, effectively improve the negative sequence voltage compensation capability of the network converter and expand the voltage supporting capability of the network converter.
Description
Technical Field
The invention belongs to the technical field of converter control, and particularly relates to a synchronous frequency self-adaptive resonance-based negative sequence voltage compensation method for a grid-connected converter.
Background
Along with the wide access of wind-solar new energy, the power system gradually evolves into a novel power system dominated by a converter. Unlike traditional synchronous machine power generation technology, the existing converters all adopt power decoupling control based on voltage orientation, and have no supporting effect on the voltage and frequency of a power grid. With the gradual increase of the permeability of new energy, a series of voltage frequency instability problems can occur. In order to improve the stability of a novel power system which is dominant by the converter, a grid-structured converter with voltage and frequency supporting performance is widely paid attention to and researched. Different from the conventional grid-connected converter, the grid-connected converter adopts a power synchronization mode and a voltage control mode, can independently establish voltage, can operate in an island, can support the voltage and frequency of a power grid in a grid-connected mode, and is a key technology for future power system development. However, the current grid-structured current transformer is mainly aimed at the control and optimization of positive sequence fundamental wave, and the compensation of unbalanced negative sequence voltage is rarely discussed. According to the latest performance test standard of the grid-connected converter, the grid-connected converter not only has a supporting function on positive-sequence fundamental waves, but also has certain compensation energy on unbalanced harmonic waves.
Patent document CN115714426a discloses a control method and system of negative sequence voltage and harmonic voltage of a grid-built converter, by collecting three-phase voltage signals and three-phase current signals of an ac side of the grid-built converter; coordinate transformation and positive and negative sequence separation are carried out on the three-phase voltage signals and the three-phase current signals, so that positive and negative sequence components respectively corresponding to fundamental frequency voltage, fundamental frequency current, harmonic voltage and harmonic current are generated; positive and negative sequence components corresponding to the fundamental frequency voltage and the fundamental frequency current respectively pass through a positive and negative sequence fundamental frequency control loop to generate positive and negative sequence components corresponding to the valve side fundamental frequency reference voltage; positive and negative sequence components corresponding to the harmonic voltage and the harmonic current respectively pass through a positive and negative sequence harmonic control loop to generate positive and negative sequence components corresponding to the valve side harmonic reference voltage; performing coordinate inverse transformation and PWM (pulse-Width modulation) on positive and negative sequence components corresponding to the valve side frequency reference voltage and the valve side harmonic reference voltage respectively, generating a trigger pulse signal and outputting the trigger pulse signal to a grid-structured converter; and responding to the received trigger pulse signal through the network-structured converter, and controlling the negative sequence voltage and the harmonic voltage according to valve side reference voltage information carried by the trigger pulse signal. The method solves the technical problem that the stability of the power grid is reduced because the voltage quality of the grid-connected point is affected by the control of the power electronic equipment more deeply under the condition of weak power grid in the prior art, can realize independent control of negative sequence voltage and harmonic voltage, improves the alternating current voltage control capability of the grid-built converter, reduces the unbalance degree and harmonic voltage content of the three-phase voltage at the alternating current side, and improves the voltage quality. However, the above scheme needs to adopt a plurality of positive and negative sequence rotating coordinate systems, and needs a negative sequence voltage and current extraction link, the extraction of the negative sequence voltage and current and the inversion coordinate system are both dependent on a delay link extraction, and the delay link corresponds to the fundamental wave period, if the power grid frequency changes, the negative sequence extraction and the inversion coordinate system of the scheme deviate, and then the negative sequence voltage cannot be accurately controlled.
Disclosure of Invention
Aiming at the problem of insufficient negative sequence voltage control capability in the prior art, the invention provides a synchronous frequency adaptive resonance-based grid-constructed converter negative sequence voltage compensation method, which does not need positive and negative sequence separation and detection, enhances the rapidity and stability of negative sequence voltage control, can make up for the defect of the negative sequence voltage control capability of the current-constructed converter, ensures that the grid-constructed converter can provide sine balanced high-quality alternating current under the scene of an unbalanced power grid, and provides reliable equipment for constructing a novel power system with new energy as a main body.
The technical scheme of the invention is as follows:
a synchronous frequency self-adaptive resonance-based negative sequence voltage compensation method for a grid-connected converter comprises the following steps:
(1) Collecting three-phase capacitor voltage and inverter side three-phase current of a grid-structured converter, determining components of the three-phase capacitor voltage and the three-phase current in a static alpha-beta coordinate system through Clark conversion, and calculating active power and reactive power;
(2) The active control loop is configured with inertia and damping coefficients of the grid-constructed converter, and synchronous frequency is generated according to the active control loop, and a synchronous angle is generated by integrating the synchronous frequency;
(3) The reactive control loop configures a sagging coefficient of the grid-connected converter, and generates an internal potential amplitude of the grid-connected converter according to the reactive control loop;
(4) Performing park transformation on the three-phase voltage, the three-phase capacitor voltage and the three-phase current of the public coupling point according to the synchronous angle in the step (2) to obtain a dq axis component in a synchronous coordinate system;
(5) Generating a dq axis command of the current through the virtual impedance according to the internal potential amplitude and the capacitance voltage;
(6) And generating the modulation voltage of the grid-connected converter by combining PI control, feedforward control and direct resonance control of negative sequence compensation of the current.
In the step (1), calculating power according to the following formula;
wherein: v (V) cα V cβ Alpha and beta components of three-phase voltage respectively, I α I β The alpha beta component of the three-phase currents, respectively.
In the step (2), the synchronization frequency and the synchronization angle are obtained according to the following formula:
wherein: p (P) ref Is an active power given value, J is inertia of the grid-formed converter, and D is a damping coefficient of the grid-formed converter; omega n Is the rated angular frequency of the grid-connected inverter, ω is the angular frequency actually output by the grid-connected inverter, and θ is the synchronous angle of the grid-connected inverter.
In the step (3), the internal potential dq axis component reference value of the grid-connected inverter is generated according to the following calculation expression:
V dref ＝V n +k q (Q ref -Q)
V qref ＝0
wherein: v (V) dref And V qref Respectively the internal potential dq axis component reference value of the network converter, V n For peak voltage of rated phase of inverter, Q ref K for a given reactive power reference q Is the sag coefficient of the reactive ring;
in the step (4), dq axis components of the three-phase voltage, the three-phase capacitor voltage and the three-phase current of the public coupling point under a synchronous rotation coordinate system are obtained according to the following formula;
wherein V is pcca V pccb V pccc Three-phase voltages, V, respectively, of the point of common coupling ca V cb V cc Three-phase voltages of the capacitances of the grid-connected converter, I a I b I c Three-phase currents of the grid-connected converter are respectively;
in the step (5), a dq axis instruction of the current of the grid-connected converter is obtained according to the following formula;
wherein: v (V) cd And V cq Respectively the dq-axis component of the capacitance voltage, L v Is virtual inductance, R v For virtual admittance, I dref And I qref Respectively the dq axis reference value of the inverter current.
In the step (6), the modulation voltage of the grid-connected converter is obtained according to the following expression:
wherein: k (k) p And k i Proportional and integral coefficients, ω, of the current loop PI controller, respectively c Is the bandwidth, k, of the resonant controller r Is the gain, ω of the resonant controller ff Is the cut-off angular frequency of the feed-forward low-pass filter.
Compared with the prior art, the invention has the following beneficial effects:
1) The phase estimation of the three-phase voltage of the public coupling point is not required by adopting a positive and negative sequence phase-locked loop technology, and the extraction of complex negative sequence voltage components is not required, so that the control delay can be greatly reduced, and the rapidity and the stability of the system are enhanced.
2) The voltage and current control is only carried out under the synchronous rotation coordinate system of the grid-structured converter, and an additional negative sequence coordinate system is not needed to be built, so that the complexity of a control system is greatly reduced, the control code of the grid-structured converter is simplified, and the calculation time is shortened.
3) Compared with the traditional negative sequence voltage control method constructed by negative sequence current under the double synchronous rotation coordinate system, the method does not need to introduce an additional negative sequence instruction current configuration link, greatly simplifies the control structure, has a faster dynamic control effect due to the fact that the additional negative sequence current control link is not introduced, and has a simplified control structure and an accurate and rapid negative sequence voltage control effect, and is superior to the traditional negative sequence voltage control strategy at present.
4) Compared with CN115714426A, the invention adopts a direct self-adaptive resonance control technology based on synchronous frequency, does not need to extract negative sequence components and construct a negative sequence coordinate system, and can reduce the complexity of a control structure. The method has the characteristic of self-adaption of the frequency of the power grid, can well overcome the defects of complex control structure, large operand and no frequency self-adaption of the patent document CN115714426A, and achieves the effect of effectively controlling the negative sequence voltage when the frequency of the power grid changes.
5) The method is suitable for various grid-structured converters adopting different positive sequence fundamental wave control structures.
Drawings
Fig. 1 is a control block diagram of a grid-tied converter with negative sequence voltage compensation according to the present invention.
Fig. 2 is a simulated waveform diagram of the input direct resonance control under a balanced power grid.
FIG. 3 is a dynamic negative sequence voltage compensation waveform diagram for input direct resonance control under an unbalanced grid
FIG. 4 is a negative sequence voltage compensation waveform diagram of an unbalanced grid with a pair of grid impedance changes.
FIG. 5 is a negative sequence voltage compensation waveform diagram when grid frequency changes under an unbalanced network
Detailed Description
In order to more specifically describe the present invention, the following describes the negative sequence voltage compensation method of the grid-connected converter according to the present invention in detail with reference to the accompanying drawings and the detailed description.
As shown in fig. 1, a synchronous frequency adaptive resonance-based negative sequence voltage control method for a grid-connected inverter comprises the following steps:
(1) Collecting three-phase voltage V at a point of common coupling using a voltage hall sensor pcca ～V pccc And three-phase voltage V on the grid converter capacitor ca ～V cc Three-phase current I at the switching side of the grid-connected converter is collected by using a current Hall sensor 3 a ～I c ；
For three-phase capacitor voltage V by Clark transformation ca ～V cc And three-phase current I a ～I c Clark transformation is carried out to obtain an alpha-axis component V of the three-phase capacitor voltage in a static alpha-beta coordinate system cα And beta-axis component V cβ And an alpha-axis component I of the three-phase current in a stationary alpha-beta coordinate system α And beta-axis component I β The method comprises the steps of carrying out a first treatment on the surface of the The transformation formula for the Clark transformation is as follows:
the active and reactive power expressions of the grid-structured converter can be obtained according to the alpha-beta components of the three-phase voltage and the three-phase current in a static coordinate system as follows:
(2) The key characteristics of the grid-structured converter are that the grid-structured converter can provide support for the frequency and the voltage of a power grid, the support mode is realized mainly by controlling the power, a control strategy of active power control and power grid frequency coupling is established, the frequency of the grid-structured converter is formed by active power through inertia and damping, the grid-structured converter is different from the power non-static difference control of the grid-structured converter, the active power of the grid-structured converter is controlled in a difference manner when the power grid frequency changes, and the relation between the active power of the grid-structured converter and the synchronous angular frequency can be expressed as follows;
wherein: p (P) ref Is an active power given value, J is inertia of the grid-formed converter, and D is a damping coefficient of the grid-formed converter; omega n Is the rated angular frequency of the grid-connected inverter, ω is the angular frequency actually output by the grid-connected inverter, and θ is the synchronous angle of the grid-connected inverter.
(3) The reactive power control of the grid-structured converter needs to have a certain supporting function when the voltage amplitude of the power grid changes, so that the relation between the internal potential of the grid-structured converter and the reactive power is as follows:
V dref ＝V n +k q (Q ref -Q)
V qref ＝0
wherein: v (V) dref And V qref Respectively the internal potential dq axis component reference value of the network converter, V n For peak voltage of rated phase of inverter, Q ref For a given purposeReference quantity of reactive power, k q Is the sag coefficient of the reactive ring; the reason why the q-axis component of the internal potential is directly given to zero is to realize that the control coordinate system is oriented in accordance with the internal potential vector.
(4) In order to realize the control of the grid-connected converter in the synchronous coordinate system, the voltage and current involved in the control need to be Park-converted to the synchronous rotation coordinate system. Acquiring dq axis components of the three-phase voltage, the three-phase capacitance voltage and the three-phase current of the public coupling point under a synchronous rotation coordinate system according to the following formula;
wherein V is pcca V pccb V pccc Three-phase voltages, V, respectively, of the point of common coupling ca V cb V cc Three-phase voltages of the capacitances of the grid-connected converter, I a I b I c Three-phase currents of the grid-structured current transformer respectively.
(5) After having the potential dq-axis component in the grid-connected converter in the synchronous rotation coordinate system, it also has
After the dq axis component of the three-phase capacitor voltage, the next step is how to obtain the current dq axis instruction of the switching side of the grid-connected converter. According to the standard specification of the grid-connected converter, the grid-connected converter externally presents the characteristic of series impedance of a voltage source, so that a current dq-axis instruction at the switching side of the grid-connected converter can be obtained according to the dq-axis component of the internal potential and the dq-axis component of the capacitor voltage as follows;
wherein: v (V) cd And V cq Respectively the dq-axis component of the capacitance voltage, L v Is virtual inductance, R v For virtual admittance, I dref And I qref Respectively the dq axis reference value of the inverter current.
(6) After having the dq-axis current command of the grid-connected inverter and the dq-axis component of the actual three-phase current, the modulation voltage of the grid-connected inverter is obtained according to the following expression:
wherein: k (k) p And k i Proportional and integral coefficients, ω, of the current loop PI controller, respectively c Is the bandwidth, k, of the resonant controller r Is the gain, ω of the resonant controller ff Is the cut-off angular frequency of the feed-forward low-pass filter. The modulating voltage consists of three items, PI control of current is to realize no static difference control of current, feedforward is to realize fast response of fundamental wave, and the resonance controller is to realize accurate control of negative sequence voltage.
Finally, the component V in the stationary alpha-beta coordinate system is obtained by inverse park transformation according to the dq voltage command of the synchronous rotation coordinate system α And V β A group of PWM signals are obtained through SVPWM technology construction to carry out switch control on power switching devices in the network converter.
The network converter under the control method of the embodiment is simulated; as shown in fig. 2, scr=2, p ref The effect of direct feed forward addition on balanced net pressure when =0.5 p.u.. With the embodiment, in an ideal power gridThe voltage has better steady-state performance, and the voltage and the current are symmetrical sine waveforms. As shown in fig. 3, when the grid voltage has 20% of unbalance, and SCR is equal to 2, direct resonance control is not adopted before, it can be found that the voltage of the point of common coupling is unbalanced, and the output current is unbalanced; however, after the direct resonance negative sequence inhibition strategy provided by the invention is adopted, the voltage unbalance degree of the public coupling point is obviously inhibited, and the voltage of the public coupling point has the characteristic of balance.
As shown in fig. 4, when the SCR is changed from 2 to 4, the control strategy still has better unbalanced voltage compensation capability and better dynamic performance, and the method has better adaptability to the impedance change of the power grid.
As shown in fig. 5, pref=0.1p.u., when the grid frequency jumps from 1.0p.u. to 1.05p.u., the compensation effect for the negative sequence voltage (0.2p.u.), after the implementation mode is adopted, the phase estimation of the negative sequence voltage of the public coupling point is not needed, and a complex negative sequence voltage component extraction link is not needed, so that the software complexity of the control system is reduced, and the calculation time is saved. The voltage error of the common coupling point is directly transmitted to the modulation voltage by adopting the resonance controller, so that the dynamic characteristic of negative sequence voltage compensation is improved.
Claims (6)
1. A synchronous frequency self-adaptive resonance-based negative sequence voltage compensation method for a grid-connected converter is characterized by comprising the following steps:
s1, collecting three-phase capacitor voltage and inverter-side three-phase current of a grid-structured converter;
s2, determining the component V of the three-phase capacitor voltage in a static alpha-beta coordinate system through Clark transformation cα、 V cβ And component I of the three-phase current in a stationary alpha-beta coordinate system α、 I β ；
S3, calculating active power P and reactive power Q, wherein the formula is as follows:
s4, the active control loop configures inertia and damping coefficient of the grid-constructed converter, and a synchronous frequency is generated according to the active control loop, and a synchronous angle is generated by integrating the synchronous frequency;
s5, configuring a sagging coefficient of the grid-connected converter by the reactive power control loop, and generating an internal potential amplitude of the grid-connected converter according to the reactive power control loop;
s6, performing park transformation on the three-phase voltage, the three-phase capacitor voltage and the three-phase current of the public coupling point according to the synchronous angle of the grid construction transformation obtained in the step S4, and obtaining a dq axis component in a synchronous coordinate system;
s7, obtaining an internal potential amplitude value and a capacitor voltage obtained in the step S6 according to the step S5, and generating a dq axis instruction of the current of the grid-connected converter through virtual impedance;
s8, combining PI control, feedforward control and direct resonance control of negative sequence compensation of the current to generate modulation voltage of the grid-connected converter.
2. The method for compensating negative sequence voltage of a grid-tied converter according to claim 1, wherein: step 4, obtaining the synchronous frequency and the synchronous angle according to the following formula:
wherein: p (P) ref Is an active power given value, J is inertia of the grid-formed converter, and D is a damping coefficient of the grid-formed converter; omega n Is the rated angular frequency of the grid-connected inverter, ω is the angular frequency actually output by the grid-connected inverter, θ is the synchronization angle of the grid-connected inverter, and s represents the integrator.
3. The method for compensating negative sequence voltage of a grid-tied converter according to claim 1, wherein: step S5 generates an internal potential dq axis component reference value of the grid-connected converter, and the formula is as follows:
V dref ＝V n +k q (Q ref -Q)
V qref ＝0
wherein: v (V) dref And V qref Respectively the internal potential dq axis component reference value of the network converter, V n For peak voltage of rated phase of inverter, Q ref K for a given reactive power reference q Is the sag coefficient of the reactive ring.
4. The method for compensating negative sequence voltage of a grid-tied converter according to claim 1, wherein: in the step S6, dq axis components of the three-phase voltage, the three-phase capacitor voltage and the three-phase current in the synchronous coordinate system of the common coupling point are obtained according to the following formula;
wherein V is pcca V pccb V pccc Three-phase voltages, V, respectively, of the point of common coupling ca V cb V cc Three-phase voltages of the capacitances of the grid-connected converter, I a I b I c Three-phase currents of the grid-structured current transformer respectively.
5. The method for compensating negative sequence voltage of a grid-tied converter according to claim 1, wherein: in the step S7, a dq axis command of the current of the grid-connected inverter is obtained, and the formula is as follows:
wherein: v (V) cd And V cq Respectively the dq-axis component of the capacitance voltage, L v Is virtual inductance, R v For virtual admittance, I dref And I qref Respectively the dq axis reference value of the inverter current.
6. The method for compensating negative sequence voltage of a grid-tied converter according to claim 1, wherein: the modulating voltage of the grid-connected converter is obtained in the step/8, and the formula is as follows:
wherein: k (k) p And k i Proportional and integral coefficients, ω, of the current loop PI controller, respectively c Is the bandwidth, k, of the resonant controller r Is the gain of the resonant controller, ω is the synchronization frequency acquired by the active control loop, ω ff Is the cut-off angular frequency of the feed-forward low-pass filter.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117650529A (en) * | 2024-01-30 | 2024-03-05 | 武汉理工大学 | Method and device for suppressing subsynchronous oscillation of grid-structured converter based on voltage compensation |
| CN117713085A (en) * | 2024-02-05 | 2024-03-15 | 武汉理工大学 | Virtual admittance-based method and device for suppressing power oscillation of grid-structured converter |
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2023
- 2023-04-25 CN CN202310455209.6A patent/CN116565944A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117650529A (en) * | 2024-01-30 | 2024-03-05 | 武汉理工大学 | Method and device for suppressing subsynchronous oscillation of grid-structured converter based on voltage compensation |
| CN117713085A (en) * | 2024-02-05 | 2024-03-15 | 武汉理工大学 | Virtual admittance-based method and device for suppressing power oscillation of grid-structured converter |
| CN117713085B (en) * | 2024-02-05 | 2024-07-09 | 武汉理工大学 | Virtual admittance-based method and device for suppressing power oscillation of grid-structured converter |
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