CN117318163B - Grid-connected converter operation control method based on symmetrical phase-locked loop structure - Google Patents
Grid-connected converter operation control method based on symmetrical phase-locked loop structure 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
- 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
- H02M1/0003—Details of control, feedback or regulation circuits
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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
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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
- 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
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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
- 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
- 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
-
- 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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Abstract
The invention discloses a grid-connected converter operation control method based on a symmetrical phase-locked loop structure, which comprises the steps of carrying out phase-locked tracking on the common point voltage of a power grid according to the symmetrical phase-locked loop structure to obtain a common voltage phase; performing first coordinate transformation on the grid-connected current to obtain a dq-axis current component of the grid-connected current; performing difference operation on the dq-axis current component of the grid-connected current and the dq-axis current reference value to obtain the dq-axis current deviation value, inputting the dq-axis current deviation value into a corresponding PI controller to obtain a dq-axis modulation signal, and performing second coordinate transformation on the dq-axis modulation signal according to the common voltage phase to obtain a three-phase modulation signal; and comparing and modulating the three-phase modulation signals and the carrier wave according to the pulse width modulation coefficient to obtain driving signals of the inverter bridge switching device, and controlling the operation of the grid-connected converter. The embodiment realizes the control of the tracking of the phase and amplitude between the grid-connected inverter and the power grid during grid connection, and improves the stability of the grid-connected inverter and the grid-connected system.
Description
Technical Field
The invention relates to the field of grid-connected converters, in particular to a grid-connected converter operation control method based on a symmetrical phase-locked loop structure.
Background
With the continuous innovation of new energy power generation technology, power electronic equipment with a power semiconductor device as a switch unit is widely applied to a power generation side, a power transmission side and a power utilization side of a power system, so that the power electronization degree of a source-net-charge is gradually improved, and the rapid development of new energy power generation to high permeability is further promoted. New features of the power system also lead to the grid gradually exhibiting weak grid characteristics, i.e. the grid impedance is not negligible. Meanwhile, in the aspect of power generation, a new energy power generation system mainly comprising a centralized fan, a distributed fan and photovoltaic is rapidly developed. The development of a multi-type new energy power generation system has the problems that the control targets of the power electronic converter are diversified, the complexity of a control structure, the difference of control time scales and the like are caused, and the interaction influence is generated between the converter and a power grid. In addition, because of the intermittence, randomness and fluctuation of wind power and photovoltaic output, the source-charge supply and demand unbalance is caused, and the system voltage and frequency stability are damaged.
The prior art improves the structure of the conventional SRF-PLL according to different applied scenes to meet the requirements under specific working conditions, for example, a filtering link is added in the front stage of the conventional PLL to inhibit the influence of the background harmonic wave of the power grid on the output performance of the PLL. Although the improved phase-locked structure based on the traditional SRF-PLL has various forms, the control structure is complex. Meanwhile, the existing improved phase-locked loop is not researched on the applicability of a weak current network, and the problem of fluctuation amplitude of the output frequency of the phase-locked loop when the running state of an inverter is suddenly changed under the weak current network cannot be solved. With the massive access of new energy photovoltaics and wind power generation and the access of random loads such as energy electric vehicles, the safe and stable operation of the power grid is likely to be more challenging.
Disclosure of Invention
The invention provides a grid-connected converter operation control method based on a symmetrical phase-locked loop structure, which realizes the tracking of the phase and amplitude between a grid-connected inverter and a power grid during grid connection and improves the stability of the grid-connected inverter and a grid-connected system.
In order to solve the above technical problems, an embodiment of the present invention provides a grid-connected converter operation control method based on a symmetrical phase-locked loop structure, including:
according to the symmetrical phase-locked loop structure, phase-locked tracking is carried out on the common point voltage of the power grid, and a common voltage phase is obtained; the public voltage phase comprises a voltage true amplitude value and a voltage true phase estimation value;
according to the common voltage phase, carrying out first coordinate transformation on the grid-connected current to obtain the dq-axis current component of the grid-connected current; wherein the dq-axis current component includes a d-axis current component and a q-axis current component;
performing difference operation on the dq-axis current component of the grid-connected current and the dq-axis current reference value to obtain the dq-axis current deviation value, inputting the dq-axis current deviation value into a corresponding PI controller, obtaining a dq-axis modulation signal at the output end of the PI controller, and performing second coordinate transformation on the dq-axis modulation signal according to the common voltage phase to obtain a three-phase modulation signal; wherein the dq-axis current reference value includes a d-axis current reference value and a q-axis current reference value;
and comparing and modulating the three-phase modulation signals and the carrier wave according to the pulse width modulation coefficient to obtain driving signals of the inverter bridge switching devices, and controlling the grid-connected converter to operate according to the driving signals of the inverter bridge switching devices.
According to the embodiment of the invention, according to the symmetrical phase-locked loop structure, phase-locked tracking is carried out on the common point voltage of the power grid to obtain a common voltage phase; the public voltage phase comprises a voltage true amplitude value and a voltage true phase estimation value; according to the common voltage phase, carrying out first coordinate transformation on the grid-connected current to obtain the dq-axis current component of the grid-connected current; wherein the dq-axis current component includes a d-axis current component and a q-axis current component; performing difference operation on the dq-axis current component of the grid-connected current and the dq-axis current reference value to obtain the dq-axis current deviation value, inputting the dq-axis current deviation value into a corresponding PI controller, obtaining a dq-axis modulation signal at the output end of the PI controller, and performing second coordinate transformation on the dq-axis modulation signal according to the common voltage phase to obtain a three-phase modulation signal; wherein the dq-axis current reference value includes a d-axis current reference value and a q-axis current reference value; and comparing and modulating the three-phase modulation signals and the carrier wave according to the pulse width modulation coefficient to obtain driving signals of the inverter bridge switching devices, and controlling the grid-connected converter to operate according to the driving signals of the inverter bridge switching devices. Based on the symmetrical phase-locked loop structure, the running stability of the grid-connected converter is improved, and frequency coupling components brought by the traditional SRF-PLL phase-locked loop can be restrained, so that the stability of the grid-connected system is improved. Meanwhile, by introducing additional damping and inertia, the additional damping and inertia characteristics ensure that the phase-locked loop output frequency has better robustness when the running state of the grid-connected converter changes.
As a preferred scheme, according to a symmetrical phase-locked loop structure, phase-locked tracking is performed on the common point voltage of the power grid to obtain a common voltage phase, which is specifically as follows:
the symmetrical phase-locked loop structure comprises a coordinate transformation link, an amplitude tracking link and a phase tracking link;
according to the current dq axis phase estimation value, performing park transformation on the power grid common point voltage through a coordinate transformation link to obtain the current d axis voltage and the current q axis voltage; the current dq-axis phase estimation value is obtained according to the current d-axis phase estimation value and the current q-axis phase estimation value;
judging whether the current d-axis voltage and the current q-axis voltage meet preset voltage conditions or not; the preset voltage condition is that the current d-axis voltage is the same as the amplitude of the common point voltage of the power grid, and the current q-axis voltage is 0;
if yes, taking the current d-axis voltage as a voltage real amplitude value, and taking the current d-axis phase estimation value as a voltage real phase estimation value;
if the current d-axis voltage and the current q-axis voltage do not meet the preset voltage condition, obtaining an updated dq-axis phase estimation value, taking the updated dq-axis phase estimation value as the current dq-axis phase estimation value through negative feedback, performing park transformation on the common point voltage of the power grid according to the current dq-axis phase estimation value through a coordinate transformation link to obtain the current d-axis voltage and the current q-axis voltage, judging whether the current d-axis voltage and the current q-axis voltage meet the preset voltage condition or not, and obtaining the voltage real amplitude and the voltage real phase estimation value through continuous feedback correction until the current d-axis voltage and the current q-axis voltage meet the preset voltage condition.
As a preferred scheme, the current d-axis voltage and the current q-axis voltage are subjected to amplitude phase tracking to obtain updated dq-axis phase estimation values, which specifically include:
wherein the updated dq-axis phase estimate comprises an updated d-axis phase estimate and an updated q-axis phase estimate;
the current d-axis voltage is used as the controlled quantity of the amplitude tracking link to carry out amplitude tracking according to the amplitude of the power grid common point voltage through the amplitude tracking link, and an updated d-axis phase estimated value is obtained;
and through a phase tracking link, obtaining output angular frequency according to the grid angular frequency, the damping coefficient of the symmetrical phase-locked loop structure and the amplitude of the grid common point voltage, and carrying out phase tracking by taking the current q-axis voltage as the controlled quantity of the phase tracking link according to the output angular frequency to obtain an updated q-axis phase estimated value.
Preferably, the current dq-axis phase estimation value is obtained according to the current d-axis phase estimation value and the current q-axis phase estimation value, specifically:
θ dq =θ d +jθ q
wherein θ dq For the current dq-axis phaseEstimate, θ d θ is the current d-axis phase estimate q Is the current q-axis phase estimate.
As a preferred scheme, according to the grid angular frequency, the damping coefficient of the symmetrical phase-locked loop structure and the amplitude of the grid common point voltage, the output angular frequency is obtained, specifically:
wherein,to output angular frequency omega g For the angular frequency of the electric network, U m Is the amplitude, k of the common point voltage of the power grid f Is the damping coefficient of a symmetrical phase-locked loop structure, T f Is an inertial time constant.
As a preferred solution, the transfer function of the symmetrical phase-locked loop structure is specifically:
wherein,is a transfer function of a symmetrical phase-locked loop structure, U m Is the amplitude of the voltage at the common point of the power grid, and xi is the damping ratio and omega n To be undamped in natural oscillation angular frequency, k f Is the damping coefficient of a symmetrical phase-locked loop structure, T f Is an inertial time constant.
As a preferred scheme, according to the common voltage phase, carrying out first coordinate transformation on the grid-connected current to obtain the dq-axis current component of the grid-connected current, which specifically comprises:
and according to the common voltage phase, converting the grid-connected current from a three-phase static coordinate system to a two-phase rotating coordinate system to obtain the dq-axis current component of the grid-connected current.
As a preferred scheme, according to the common voltage phase, the dq-axis modulation signal is subjected to second coordinate transformation to obtain a three-phase modulation signal, specifically:
transforming the modulation signal of the dq axis from a two-phase rotation coordinate system to a three-phase stationary coordinate system according to the common voltage phase to obtain a modulation signal under the three-phase stationary coordinate system, and obtaining a three-phase modulation signal;
wherein the modulation signal of the dq axis includes a modulation signal of the d axis and a modulation signal of the q axis.
In order to solve the same technical problems, the embodiment of the invention also provides a grid-connected converter operation control device based on a symmetrical phase-locked loop structure, which comprises: the phase-locked tracking module is used for carrying out phase-locked tracking on the common point voltage of the power grid according to the symmetrical phase-locked loop structure to obtain a common voltage phase; the public voltage phase comprises a voltage true amplitude value and a voltage true phase estimation value;
the coordinate transformation module is used for carrying out first coordinate transformation on the grid-connected current according to the public voltage phase to obtain the dq-axis current component of the grid-connected current; wherein the dq-axis current component includes a d-axis current component and a q-axis current component;
the deviation modulation module is used for carrying out difference operation on the dq-axis current component of the grid-connected current and the dq-axis current reference value to obtain the dq-axis current deviation value, inputting the dq-axis current deviation value into a corresponding PI controller, obtaining a dq-axis modulation signal at the output end of the PI controller, and carrying out second coordinate transformation on the dq-axis modulation signal according to the common voltage phase to obtain a three-phase modulation signal; wherein the dq-axis current reference value includes a d-axis current reference value and a q-axis current reference value;
the operation control module is used for comparing and modulating the three-phase modulation signals and the carrier waves according to the pulse width modulation coefficients to obtain driving signals of the inverter bridge switching devices, and controlling the grid-connected converter to operate according to the driving signals of the inverter bridge switching devices.
In order to solve the same technical problems, the embodiment of the invention also provides a computer device, which comprises a processor and a memory, wherein the memory is used for storing a computer program, and the computer program is executed by the processor to realize a grid-connected converter operation control method based on a symmetrical phase-locked loop structure.
Drawings
Fig. 1: the flow diagram of one embodiment of the grid-connected converter operation control method based on the symmetrical phase-locked loop structure is provided by the invention;
fig. 2: the control structure diagram of the grid-connected inverter under the dq domain of the grid-connected inverter operation control method based on the symmetrical phase-locked loop structure is provided by the invention;
fig. 3: the control structure diagram of the symmetrical phase-locked loop structure of one embodiment of the grid-connected converter operation control method based on the symmetrical phase-locked loop structure is provided by the invention;
fig. 4: the invention provides a unit step response diagram of an NS-PLL structure of one embodiment of a grid-connected converter operation control method based on a symmetrical phase-locked loop structure;
fig. 5: the stability analysis result graph of the traditional SRF-PLL structure of one embodiment of the grid-connected converter operation control method based on the symmetrical phase-locked loop structure is provided by the invention; wherein, (a) is grid impedance lg=8mh and (b) is grid impedance lg=9mh;
fig. 6: the stability analysis result graph of the NS-PLL structure of one embodiment of the grid-connected converter operation control method based on the symmetrical phase-locked loop structure is provided by the invention; wherein, (a) is grid impedance lg=10.5 mH and (b) is grid impedance lg=11.8 mH;
fig. 7: the grid system output electric result diagram under the traditional SRF-PLL structure of one embodiment of the grid-connected converter operation control method based on the symmetrical phase-locked loop structure is provided by the invention; wherein, (a) is the output current of a grid-connected converter with a traditional SRF-PLL structure, and (b) is the output frequency and phase of a phase-locked loop with a traditional SRF-PLL structure;
fig. 8: the grid system output electric result diagram under the NS-PLL structure of one embodiment of the grid-connected converter operation control method based on the symmetrical phase-locked loop structure is provided by the invention; wherein, (a) is the grid-connected converter output current of the NS-PLL structure, and (b) is the phase-locked loop output frequency and phase of the NS-PLL structure;
fig. 9: the invention provides a structure schematic diagram of an embodiment of a grid-connected converter operation control device based on a symmetrical phase-locked loop structure.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
Referring to fig. 1, a flow chart of a grid-connected converter operation control method based on a symmetrical phase-locked loop structure according to an embodiment of the present invention is shown. The grid-connected converter operation control method is suitable for grid-connected conversion of a grid-connected system, and the grid-connected converter operation stability is improved and the grid-connected system stability is improved through a symmetrical phase-locked loop structure. The grid-connected converter operation control method comprises steps 101 to 104, wherein the steps are as follows:
step 101: according to the symmetrical phase-locked loop structure, phase-locked tracking is carried out on the common point voltage of the power grid, and a common voltage phase is obtained; wherein the common voltage phase comprises a voltage true amplitude and a voltage true phase estimate.
In the embodiment, the symmetrical phase-locked loop structure NS-PLL is adopted for the common point voltage u of the power grid PCC And performing phase-locked tracking to obtain a common voltage phase. As shown in fig. 1, a main circuit and a control circuit of a 14kW three-phase LCL type grid-connected inverter under the control of unit power factor grid-connected current, in fig. 1, PCC represents grid-connected point of a converter, dq/abc represents transformation from a two-phase rotating coordinate system (dq coordinate system) to a three-phase stationary coordinate system (abc coordinate system), and abc/dq represents transformation from the three-phase stationary coordinate system (abc coordinate system) to a two-phase rotating coordinate system (dq coordinate system); θ dq Is phase-lockedThe phase angle of the ring in the dq coordinate system; u (u) dc Is the voltage of a direct current bus; inverter-side filter inductance L 1 Filter capacitor C f And net side filter inductance L 2 Constructing an LCL filter; r is R d Is a damping resistor; u (u) inv Outputting voltage for a bridge arm of the inverter; i.e 2 For grid-connected current, i 2d 、i 2q The current components of the grid-connected current in the dq axes are respectively the current components of the component dq axes of the grid-connected current in the d axis and the q axis; u (u) PCC Is grid-connected point voltage (grid common point voltage); u (u) g Is the grid voltage; z is Z g Is the impedance of the power grid; the current inner loop adopts a PI controller, and the transfer function is G i (s)=k ip +k ii /s，k ip Is proportional coefficient, k of PI controller ii Integrating the coefficients for the PI controller; i 2dref 、I 2qref Respectively a dq-axis current reference value of a reference value of the grid-connected current on a d-axis and a q-axis; v Md 、v Mq The current loop PI controller outputs three-phase modulation signals of the modulation signals on the d axis and the q axis respectively; k (k) PWM Is a pulse width modulation factor.
A converter is an electrical device that changes the voltage, frequency, phase number, and other electric quantity or characteristics of a power supply system. Including rectifiers (alternating current to direct current), inverters (direct current to alternating current), ac inverters and dc inverters. Besides the main circuit (a rectifying circuit, an inverter circuit, an alternating current conversion circuit and a direct current conversion circuit respectively), the converter also needs a trigger circuit for controlling the on-off of a power switch element and a control circuit for realizing the regulation and control of electric energy. An inverter (inverter) is an electronic device that converts direct current (battery, accumulator) into alternating current (typically 220v50HZ sinusoidal or square wave) and converts low voltage (12 or 24 or 48 volts) direct current into 220 volts alternating current.
In this embodiment, the symmetrical phase-locked loop (New Synchronous Phase Locked Loop, NS-PLL) structure includes a coordinate transformation link, an amplitude tracking link and a phase tracking link, and for simplicity of description, the symmetrical phase-locked loop structure is represented by the NS-PLL structure, and the control structure of the symmetrical phase-locked loop structure, as shown in fig. 2, implements inversion by the symmetrical phase-locked loop structureTracking of phase and amplitude between the device and the grid. By fixed d-axis control, i.e. when the voltage U is at the common point of the network pcc Is completely coincident with the d axis, at this time U pccd =U m 、U pccq =0，U m U is the amplitude of the common point voltage of the power grid pccd D-axis voltage, U, which is the voltage of the common point of the power grid pccq Q-axis voltage, which is the grid common point voltage. Thus, for an NS-PLL configuration, the d-axis voltage U can be utilized pccd (d-axis voltage of grid common point voltage) as controlled quantity of amplitude tracking link, and q-axis voltage U pccq The q-axis voltage of the grid common point voltage is used as the controlled quantity of the phase tracking link; then estimating value theta by d-axis phase d And q-axis phase estimation value θ q For three-phase voltage (common point voltage U of electric network) PCC ) Performing Park conversion, and continuously correcting theta by negative feedback d、 θ q Up to U pccd =U m 、U pccq =0; finally, stable U is obtained pccd And theta d I.e. an estimate of the true amplitude and phase of the PCC voltage.
Optionally, step 101 specifically includes steps 1011 to 1014, each of which specifically includes:
step 1011: according to the current dq axis phase estimation value, performing park transformation on the power grid common point voltage through a coordinate transformation link to obtain the current d axis voltage and the current q axis voltage; wherein the current dq-axis phase estimate is obtained from the current d-axis phase estimate and the current q-axis phase estimate.
The Park transform (Park transform) is to convert i a、 i b、 i c The projection of the current on the alpha and beta axes is equivalent to the d and q axes, and the current on the stator is equivalent to the direct axis and the quadrature axis.
Step 1012: judging whether the current d-axis voltage and the current q-axis voltage meet preset voltage conditions or not; the preset voltage condition is that the current d-axis voltage is the same as the amplitude of the common point voltage of the power grid, and the current q-axis voltage is 0.
Step 1013: if the current d-axis voltage is satisfied, the current d-axis voltage is taken as the voltage real amplitude value, and the current d-axis phase estimated value is taken as the voltage real phase estimated value.
Step 1014: if the current d-axis voltage and the current q-axis voltage do not meet the preset voltage condition, obtaining an updated dq-axis phase estimation value, taking the updated dq-axis phase estimation value as the current dq-axis phase estimation value through negative feedback, performing park transformation on the common point voltage of the power grid according to the current dq-axis phase estimation value through a coordinate transformation link to obtain the current d-axis voltage and the current q-axis voltage, judging whether the current d-axis voltage and the current q-axis voltage meet the preset voltage condition or not, and obtaining the voltage real amplitude and the voltage real phase estimation value through continuous feedback correction until the current d-axis voltage and the current q-axis voltage meet the preset voltage condition.
Optionally, the current dq-axis phase estimation value is obtained according to the current d-axis phase estimation value and the current q-axis phase estimation value, specifically:
θ dq =θ d +jθ q
wherein θ dq For the current dq axis phase estimate, θ d θ is the current d-axis phase estimate q Is the current q-axis phase estimate.
In the present embodiment, θ dq =θ d +jθ q To track the phase angle and magnitude of the grid common point (PCC point) voltage.
Optionally, the current d-axis voltage and the current q-axis voltage are subjected to amplitude phase tracking to obtain updated dq-axis phase estimation values, which specifically include:
wherein the updated dq-axis phase estimate comprises an updated d-axis phase estimate and an updated q-axis phase estimate;
the current d-axis voltage is used as the controlled quantity of the amplitude tracking link to carry out amplitude tracking according to the amplitude of the power grid common point voltage through the amplitude tracking link, and an updated d-axis phase estimated value is obtained; and through a phase tracking link, obtaining output angular frequency according to the grid angular frequency, the damping coefficient of the symmetrical phase-locked loop structure and the amplitude of the grid common point voltage, and carrying out phase tracking by taking the current q-axis voltage as the controlled quantity of the phase tracking link according to the output angular frequency to obtain an updated q-axis phase estimated value.
Optionally, the output angular frequency is obtained according to the grid angular frequency, the damping coefficient of the symmetrical phase-locked loop structure and the amplitude of the grid common point voltage, specifically:
wherein,to output angular frequency omega g For the angular frequency of the electric network, U m Is the amplitude, k of the common point voltage of the power grid f Is the damping coefficient of a symmetrical phase-locked loop structure, T f Is an inertial time constant.
In this embodiment, the output angular frequency of the NS-PLL structure is:
wherein U is m Is the amplitude of the common point voltage (PCC point voltage amplitude) of the power grid, k f Damping coefficient, T, of NS-PLL structure f Is inertial time constant omega g Is the grid angular frequency.
Optionally, the transfer function of the symmetrical phase-locked loop structure is specifically:
wherein,is a transfer function of a symmetrical phase-locked loop structure, U m Is the amplitude of the voltage at the common point of the power grid, and xi is dampingRatio omega n To be undamped in natural oscillation angular frequency, k f Is the damping coefficient of a symmetrical phase-locked loop structure, T f Is an inertial time constant.
In this embodiment, the transfer function of the pll structure is a typical second-order oscillation link, and for a typical second-order oscillation system, the damping ratio is generally set to be. Meanwhile, the invention selects the bandwidth of the phase-locked loop to be 70Hz, and calculates the bandwidth to be +.>、/>From this, a unit step response curve for a conventional SRF-PLL structure and an NS-PLL structure of the present invention can be obtained, as shown in FIG. 4. As can be seen from fig. 4, the NS-PLL structure provides a certain damping and inertia during tracking of the grid frequency. Thus, it is envisioned that the component U of the PCC point voltage in dq coordinate system when the grid-connected converter jumps from half-load to full-load PCCd 、U PCCq Mutations also occur; and at this time U PCCd 、U PCCq Deviation from the steady state value before abrupt change exists, and fluctuation of the frequency amplitude is restrained through a regulator with additional damping.
Step 102: according to the common voltage phase, carrying out first coordinate transformation on the grid-connected current to obtain the dq-axis current component of the grid-connected current; wherein the dq-axis current component includes a d-axis current component and a q-axis current component.
Optionally, step 102 specifically includes performing a first coordinate transformation on the grid-connected current according to the common voltage phase to obtain a dq-axis current component of the grid-connected current, where the dq-axis current component specifically includes: and according to the common voltage phase, converting the grid-connected current from a three-phase static coordinate system to a two-phase rotating coordinate system to obtain the dq-axis current component of the grid-connected current.
In the present embodiment, the grid-connected current i is based on the common voltage phase 2 Through the coordinate transformation (first coordinate transformation) of abc/dq, the components in d and q axes, namely the current component i of d axis, are obtained 2d And current component i of q-axis 2q . abc/dq represents the transformation from a three-phase stationary coordinate system (abc coordinate system) to a two-phase rotating coordinate system (dq coordinate system).
Step 103: performing difference operation on the dq-axis current component of the grid-connected current and the dq-axis current reference value to obtain the dq-axis current deviation value, inputting the dq-axis current deviation value into a corresponding PI controller, obtaining a dq-axis modulation signal at the output end of the PI controller, and performing second coordinate transformation on the dq-axis modulation signal according to the common voltage phase to obtain a three-phase modulation signal; wherein the dq-axis current reference value includes a d-axis current reference value and a q-axis current reference value.
In this embodiment, the dq-axis current component and the dq-axis current reference value (the current given value under the dq-axis) are respectively differenced to obtain the dq-axis current deviation amount including the d-axis current deviation amount and the q-axis current deviation amount, that is, the d-axis current deviation amount is obtained by differencing the d-axis current component and the d-axis current reference value (the current given value under the d-axis), and the q-axis current deviation amount is obtained by differencing the q-axis current component and the q-axis current reference value (the current given value under the q-axis). The dq-axis current deviation is passed through the corresponding PI controller to obtain the components of the modulation signal in d and q axes (dq-axis modulation signal), i.e. the current loop PI controller outputs the modulation signal v in d axis Md (d-axis modulation signal) and q-axis modulation signal v Mq (q-axis modulation signal). Then the dq axis modulation signal is transformed through a second coordinate to obtain a modulation signal v under an abc three-phase coordinate system Mabc I.e. a three-phase modulated signal.
Optionally, according to the phase of the common voltage, performing a second coordinate transformation on the dq-axis modulation signal to obtain a three-phase modulation signal, specifically: transforming the modulation signal of the dq axis from a two-phase rotation coordinate system to a three-phase stationary coordinate system according to the common voltage phase to obtain a modulation signal under the three-phase stationary coordinate system, and obtaining a three-phase modulation signal; wherein the modulation signal of the dq axis includes a modulation signal of the d axis and a modulation signal of the q axis.
In the present embodiment, the dq-axis modulation signal is subjected to dq/abc coordinate transformation (second coordinate transformation) according to the common voltage phase to obtain a modulation signal v in the abc three-phase coordinate system Mabc I.e. a three-phase modulated signal. dq/abc represents the transformation from a two-phase rotating coordinate system (dq coordinate system) to a three-phase stationary coordinate system (abc coordinate system).
Step 104: and comparing and modulating the three-phase modulation signals and the carrier wave according to the pulse width modulation coefficient to obtain driving signals of the inverter bridge switching devices, and controlling the grid-connected converter to operate according to the driving signals of the inverter bridge switching devices.
In the present embodiment, the pulse width modulation factor k is used PWM Modulating the three-phase modulation signal v Mabc And comparing the driving signals with the carrier waves to obtain driving signals of the inverter bridge switching devices, and realizing the operation control of the grid-connected converter according to the driving signals of the inverter bridge switching devices.
In this embodiment, in order to verify the validity and feasibility of the NS-PLL structure of the present invention, a comparison is made between the conventional SRF-PLL structure and the NS-PLL structure of the present invention, where the grid-connected converter system uses the conventional SRF-PLL structure to perform stability analysis under different grid impedance conditions, as shown in fig. 5, and the grid-connected converter system uses the NS-PLL structure of the present invention to perform stability analysis under different grid impedance conditions, as shown in fig. 6. As can be seen from fig. 5, when the conventional SRF-PLL structure is adopted, the grid-connected converter can stably operate when the grid impedance lg=8mh, and when the grid impedance increases to 9mH, the grid-connected converter is unstable. However, as can be seen from fig. 6, with the symmetrical phase-locked loop structure (NS-PLL) with additional damping and inertia according to the present invention, the grid-connected converter can keep running stably at the grid resistance lg=10.5mh, and the grid-connected converter is not unstable until the grid resistance increases further to 11.8 mH. According to the stability analysis result of the grid-connected converter adopting two different phase-locked loop structures, the NS-PLL structure provided by the invention can improve the adaptability of the grid impedance of the grid-connected converter, and the stability of the grid-connected converter can be improved.
In this embodiment, in order to explain the additional damping and inertia characteristics of the NS-PLL structure of the present invention, when the grid impedance lg=5mh, the output frequency and phase of the phase-locked loop after the grid-connected converter operation condition is suddenly changed in the conventional SRF-PLL structure and the NS-PLL structure are compared. When the operation condition changes, the power grid system outputs an electrical result under the traditional SRF-PLL structure, as shown in FIG. 7, when the traditional SRF-PLL structure is adopted, the system outputs current and phase, FIG. 7 (a) is the grid-connected converter output current of the traditional SRF-PLL structure, and FIG. 7 (b) is the phase-locked loop output frequency and phase of the traditional SRF-PLL structure. When the operation condition changes, the grid system outputs an electrical result under the NS-PLL structure, as shown in FIG. 8, and the system outputs current and phase when the NS-PLL structure is adopted, wherein FIG. 8 (a) is the grid-connected converter output current of the NS-PLL structure, and FIG. 8 (b) is the phase-locked loop output frequency and phase of the NS-PLL structure. As can be seen from fig. 7 (a): when the traditional SRF-PLL structure is adopted, the converter jumps from full load to half load, and the transient fluctuation of the output current is serious. Meanwhile, as can be known from the output frequency and phase angle of the phase-locked loop under the SRF-PLL structure, when the operation condition of the grid-connected converter changes, the up-and-down fluctuation amplitude of the output frequency of the system is about 15Hz, so that the fluctuation amplitude is larger, and the safe and stable operation of the grid-connected converter is not facilitated. Comparing fig. 7 and fig. 8, it can be known that the symmetrical phase-locked loop structure (NS-PLL structure) with additional damping and inertia according to the present invention has smooth transient process of the grid-connected current under the same working condition as the conventional SRF-PLL, and the up-and-down fluctuation of the frequency of the phase-locked loop output is only 1.7Hz and 5.2Hz, the fluctuation amplitude is greatly suppressed, which is far smaller than that of the conventional SRF-PLL phase-locked loop.
Through the theory and simulation, the symmetrical phase-locked loop structure with the additional damping and inertia provided by the invention can effectively inhibit the problem of large fluctuation of the system output frequency caused by abrupt change of the system in the operation working condition while improving the stability of the grid-connected converter.
According to the embodiment of the invention, according to the symmetrical phase-locked loop structure, phase-locked tracking is carried out on the common point voltage of the power grid to obtain a common voltage phase; the public voltage phase comprises a voltage true amplitude value and a voltage true phase estimation value; according to the common voltage phase, carrying out first coordinate transformation on the grid-connected current to obtain the dq-axis current component of the grid-connected current; wherein the dq-axis current component includes a d-axis current component and a q-axis current component; performing difference operation on the dq-axis current component of the grid-connected current and the dq-axis current reference value to obtain the dq-axis current deviation value, inputting the dq-axis current deviation value into a corresponding PI controller, obtaining a dq-axis modulation signal at the output end of the PI controller, and performing second coordinate transformation on the dq-axis modulation signal according to the common voltage phase to obtain a three-phase modulation signal; wherein the dq-axis current reference value includes a d-axis current reference value and a q-axis current reference value; and comparing and modulating the three-phase modulation signals and the carrier wave according to the pulse width modulation coefficient to obtain driving signals of the inverter bridge switching devices, and controlling the grid-connected converter to operate according to the driving signals of the inverter bridge switching devices. Based on the symmetrical phase-locked loop structure, the running stability of the grid-connected converter is improved, and frequency coupling components brought by the traditional SRF-PLL phase-locked loop can be restrained, so that the stability of the grid-connected system is improved. Meanwhile, by introducing additional damping and inertia, the additional damping and inertia characteristics ensure that the phase-locked loop output frequency has better robustness when the running state of the grid-connected converter changes.
Example two
Correspondingly, referring to fig. 9, fig. 9 is a schematic structural diagram of a second embodiment of a grid-connected inverter operation control device based on a symmetrical phase-locked loop structure provided by the invention. As shown in fig. 9, the grid-connected converter operation control device based on the symmetrical phase-locked loop structure includes a phase-locked tracking module 901, a coordinate transformation module 902, a deviation modulation module 903 and an operation control module 904;
the phase-locked tracking module 901 is used for phase-locked tracking of the common point voltage of the power grid according to the symmetrical phase-locked loop structure to obtain a common voltage phase; the public voltage phase comprises a voltage true amplitude value and a voltage true phase estimation value;
the coordinate transformation module 902 is configured to perform a first coordinate transformation on the grid-connected current according to the common voltage phase, so as to obtain a dq-axis current component of the grid-connected current; wherein the dq-axis current component includes a d-axis current component and a q-axis current component;
the deviation modulation module 903 is configured to perform a difference operation on a dq-axis current component of the grid-connected current and a dq-axis current reference value to obtain a dq-axis current deviation, input the dq-axis current deviation into a corresponding PI controller, obtain a dq-axis modulation signal at an output end of the PI controller, and perform a second coordinate transformation on the dq-axis modulation signal according to a common voltage phase to obtain a three-phase modulation signal; wherein the dq-axis current reference value includes a d-axis current reference value and a q-axis current reference value;
the operation control module 904 is configured to compare and modulate the three-phase modulation signal with the carrier according to the pulse width modulation factor, obtain a driving signal of the inverter bridge switching device, and perform operation control on the grid-connected converter according to the driving signal of the inverter bridge switching device.
The grid-connected converter operation control device based on the symmetrical phase-locked loop structure can implement the grid-connected converter operation control method based on the symmetrical phase-locked loop structure in the method embodiment. The options in the method embodiments described above are also applicable to this embodiment and will not be described in detail here. The rest of the embodiments of the present application may refer to the content of the method embodiments described above, and in this embodiment, no further description is given.
By implementing the embodiment of the invention, the symmetrical phase-locked loop structure inhibits the frequency coupling phenomenon of the grid-connected converter caused by the asymmetry of the phase-locked loop under the dq coordinate system, improves the stability of the grid-connected system, and improves the robustness of the grid-connected system by inhibiting the frequency coupling component of the traditional SRF-PLL phase-locked loop so as to enhance the stability of the grid-connected system and introducing additional damping and inertia to ensure the stable output frequency of the phase-locked loop when the running state of the grid-connected converter changes, and inhibit the frequency fluctuation caused by the abrupt change of the working condition of the converter.
In addition, the embodiment of the application further provides a computer device, which comprises a processor and a memory, wherein the memory is used for storing a computer program, and the computer program is executed by the processor to realize the steps in any of the method embodiments.
The foregoing embodiments have been provided for the purpose of illustrating the general principles of the present invention, and are not to be construed as limiting the scope of the invention. It should be noted that any modifications, equivalent substitutions, improvements, etc. made by those skilled in the art without departing from the spirit and principles of the present invention are intended to be included in the scope of the present invention.
Claims (7)
1. A grid-connected converter operation control method based on a symmetrical phase-locked loop structure is characterized by comprising the following steps:
according to the symmetrical phase-locked loop structure, phase-locked tracking is carried out on the common point voltage of the power grid, and a common voltage phase is obtained; wherein the common voltage phase comprises a voltage true amplitude value and a voltage true phase estimation value;
according to the symmetrical phase-locked loop structure, the phase-locked tracking is carried out on the common point voltage of the power grid to obtain a common voltage phase, which is specifically as follows:
the symmetrical phase-locked loop structure comprises a coordinate transformation link, an amplitude tracking link and a phase tracking link;
according to the current dq axis phase estimation value, performing park transformation on the power grid common point voltage through the coordinate transformation link to obtain the current d axis voltage and the current q axis voltage; the current dq-axis phase estimation value is obtained according to the current d-axis phase estimation value and the current q-axis phase estimation value;
judging whether the current d-axis voltage and the current q-axis voltage meet a preset voltage condition or not; the preset voltage condition is that the current d-axis voltage is the same as the amplitude of the power grid common point voltage, and the current q-axis voltage is 0;
if yes, taking the current d-axis voltage as the voltage real amplitude value, and taking the current d-axis phase estimation value as the voltage real phase estimation value;
if the current d-axis voltage and the current q-axis voltage do not meet the preset voltage condition, amplitude phase tracking is carried out on the current d-axis voltage and the current q-axis voltage to obtain an updated dq-axis phase estimated value, the updated dq-axis phase estimated value is used as the current dq-axis phase estimated value through negative feedback, park transformation is carried out on the power grid common point voltage according to the current dq-axis phase estimated value through the coordinate transformation link to obtain the current d-axis voltage and the current q-axis voltage, whether the current d-axis voltage and the current q-axis voltage meet the preset voltage condition is judged, and the current d-axis voltage and the current q-axis voltage meet the preset voltage condition through continuous feedback correction until the current d-axis voltage and the current q-axis voltage meet the preset voltage condition to obtain the voltage real amplitude and the voltage real phase estimated value;
and carrying out amplitude phase tracking on the current d-axis voltage and the current q-axis voltage to obtain an updated dq-axis phase estimated value, wherein the method specifically comprises the following steps of:
wherein the updated dq-axis phase estimate comprises an updated d-axis phase estimate and an updated q-axis phase estimate;
performing amplitude tracking by taking the current d-axis voltage as a controlled quantity of the amplitude tracking link according to the amplitude of the power grid common point voltage to obtain the updated d-axis phase estimated value;
obtaining output angular frequency according to the angular frequency of the power grid, the damping coefficient of the symmetrical phase-locked loop structure and the amplitude of the power grid common point voltage through the phase tracking link, and carrying out phase tracking by taking the current q-axis voltage as the controlled quantity of the phase tracking link according to the output angular frequency to obtain the updated q-axis phase estimation value;
the output angular frequency is obtained according to the angular frequency of the power grid, the damping coefficient of the symmetrical phase-locked loop structure and the amplitude of the voltage of the common point of the power grid, and is specifically:
wherein,for the output angular frequency ω g For the grid angular frequency, U m K is the amplitude of the grid common point voltage f Is the damping coefficient, T, of the symmetrical phase-locked loop structure f Is an inertial time constant;
according to the public voltage phase, carrying out first coordinate transformation on the grid-connected current to obtain the dq axis current component of the grid-connected current; wherein the dq-axis current component includes a d-axis current component and a q-axis current component;
performing difference operation on the dq-axis current component of the grid-connected current and a dq-axis current reference value to obtain a dq-axis current deviation value, inputting the dq-axis current deviation value into a corresponding PI controller, obtaining a dq-axis modulation signal at the output end of the PI controller, and performing second coordinate transformation on the dq-axis modulation signal according to the common voltage phase to obtain a three-phase modulation signal; wherein the dq-axis current reference value includes a d-axis current reference value and a q-axis current reference value;
and comparing and modulating the three-phase modulation signal and the carrier wave according to the pulse width modulation coefficient to obtain a driving signal of an inversion bridge switching device, and controlling the operation of the grid-connected converter according to the driving signal of the inversion bridge switching device.
2. The grid-connected inverter operation control method based on the symmetrical phase-locked loop structure according to claim 1, wherein the current dq-axis phase estimation value is obtained according to a current d-axis phase estimation value and a current q-axis phase estimation value, specifically:
θ dq =θ d +jθ q
wherein θ dq θ is the current dq-axis phase estimate d θ is the current d-axis phase estimate q Is the current q-axis phase estimate.
3. The grid-connected converter operation control method based on the symmetrical phase-locked loop structure as claimed in claim 2, wherein the transfer function of the symmetrical phase-locked loop structure is specifically:
wherein,u is the transfer function of the symmetrical phase-locked loop structure m For the amplitude value of the voltage at the common point of the power grid, xi is the damping ratio, omega n To be undamped in natural oscillation angular frequency, k f Is the damping coefficient, T, of the symmetrical phase-locked loop structure f Is the inertial time constant.
4. The grid-connected converter operation control method based on the symmetrical phase-locked loop structure according to claim 1, wherein the first coordinate transformation is performed on the grid-connected current according to the common voltage phase to obtain the dq-axis current component of the grid-connected current, specifically:
and according to the common voltage phase, transforming the grid-connected current from a three-phase static coordinate system to a two-phase rotating coordinate system to obtain the dq-axis current component of the grid-connected current.
5. The grid-connected inverter operation control method based on the symmetrical phase-locked loop structure according to claim 4, wherein the second coordinate transformation is performed on the dq-axis modulation signal according to the common voltage phase to obtain a three-phase modulation signal, specifically:
transforming the modulation signal of the dq axis from the two-phase rotation coordinate system to the three-phase stationary coordinate system according to the common voltage phase to obtain a modulation signal under the three-phase stationary coordinate system, and obtaining a three-phase modulation signal;
wherein the dq-axis modulation signal includes a d-axis modulation signal and a q-axis modulation signal.
6. The grid-connected converter operation control device based on the symmetrical phase-locked loop structure is characterized in that the grid-connected converter operation control device is used for realizing the grid-connected converter operation control method based on the symmetrical phase-locked loop structure as claimed in any one of claims 1 to 5, and comprises the following steps: the system comprises a phase-locked tracking module, a coordinate transformation module, a deviation modulation module and an operation control module;
the phase-locked tracking module is used for carrying out phase-locked tracking on the common point voltage of the power grid according to the symmetrical phase-locked loop structure to obtain a common voltage phase; wherein the common voltage phase comprises a voltage true amplitude value and a voltage true phase estimation value;
the coordinate transformation module is used for carrying out first coordinate transformation on the grid-connected current according to the public voltage phase to obtain a dq axis current component of the grid-connected current; wherein the dq-axis current component includes a d-axis current component and a q-axis current component;
the deviation modulation module is used for carrying out difference operation on the dq-axis current component of the grid-connected current and the dq-axis current reference value to obtain the dq-axis current deviation value, inputting the dq-axis current deviation value into a corresponding PI controller, obtaining a dq-axis modulation signal at the output end of the PI controller, and carrying out second coordinate transformation on the dq-axis modulation signal according to the public voltage phase to obtain a three-phase modulation signal; wherein the dq-axis current reference value includes a d-axis current reference value and a q-axis current reference value;
the operation control module is used for comparing and modulating the three-phase modulation signals and the carrier wave according to the pulse width modulation coefficient to obtain driving signals of the inverter bridge switching device, and controlling the grid-connected converter to operate according to the driving signals of the inverter bridge switching device.
7. A computer device comprising a processor and a memory for storing a computer program which when executed by the processor implements the grid-connected inverter operation control method based on a symmetrical phase-locked loop structure as claimed in any one of claims 1 to 5.
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