CN115995813B - Grid-connected inverter oscillation suppression strategy based on hybrid damping - Google Patents
Grid-connected inverter oscillation suppression strategy based on hybrid damping Download PDFInfo
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Abstract
The invention discloses a grid-connected inverter oscillation suppression strategy based on mixed damping, which mainly comprises a passive damping circuit module and a voltage-current double-closed-loop control module introducing active damping control, wherein the passive damping circuit comprises a parallel capacitor and a damping resistor, the damping resistor is connected with the parallel capacitor in parallel after being connected with a filter capacitor in series, the active damping control is introduced into the voltage-current double-closed-loop module, the passive damping circuit and the voltage-current double-closed-loop control introducing the active damping control jointly form the mixed damping control, the damping of the circuit is improved, and the grid-connected inverter oscillation is suppressed, so that the stability of a system is ensured.
Description
Technical Field
The invention relates to the field of new energy grid-connected inverters, in particular to a grid-connected inverter oscillation suppression strategy based on hybrid damping.
Background
Under the dual-carbon background, a large amount of new energy is connected to a power grid through a grid-connected inverter, and the power grid impedance in the running process of the system is not negligible due to the existence of line impedance, so that the system is in weak susceptibility. But the impedance of the power grid often varies with the leakage reactance of the transformer and the length of the transmission line. At this time, due to the dynamic interaction between the inverter and the power distribution network, a series of harmonic and oscillation problems may occur in the system, which jeopardizes the stability of the system. When the number of the grid-connected inverters connected in parallel to the public coupling point is increased, the control loop of each inverter is overlapped and then acts on the impedance phase of the power grid, so that the oscillation between the grid-connected inverter and the power grid is more serious, and the running stability of the power grid is possibly damaged.
Disclosure of Invention
In order to achieve the above purpose, the technical scheme provided by the invention is as follows:
the grid-connected inverter oscillation suppression strategy based on the hybrid damping is characterized by comprising the following steps of:
in passive resistanceIn the damping control module, oscillation of the grid-connected inverter is restrained in a mode of introducing actual damping to the filter circuit, wherein the actual damping is a filter capacitor C f Series damping resistor R d Rear and parallel capacitance C d In parallel, wherein the damping resistor R d The value range of (2) is 220<R d <300, parallel capacitor C d The range of the value of (2) is 5 multiplied by 10 -8 <C d <5×10 -6 ；
In the droop control module, detecting abc three-phase output voltage u of the grid-connected inverter after adding the passive damping control module oa 、u ob And u oc Abc three-phase output current i oa 、i ob And i oc Obtaining an output voltage u corresponding to the dq coordinate system through park transformation od And u oq Output current i od And i oq The expression is:
wherein ω is an angular frequency;
and then the active power P and the reactive power Q are obtained through a power calculation unit, wherein the expression of the power calculation unit is as follows:
wherein p is instantaneous active power, q is instantaneous reactive power, and s is Laplacian;
multiplying the active power P by the active/voltage droop control coefficient n to obtain an output voltage transition value u n Reference output voltage u * And an output voltage transition value u n The output voltage amplitude u is obtained by subtraction, and the reactive power Q and the reactive power/frequency droop control coefficient m are multiplied to obtain the angular frequency transition value omega m Angular frequency reference ω * And angular frequency transition value omega m Adding to obtain angular frequency omega, multiplying the angular frequency omega by 1/s of the integral link to obtain phase angle
Output voltage amplitude u and phase angle +.>
Obtaining abc three-phase voltage reference value u through a voltage synthesis unit refa 、u refb And u refc Wherein the expression of the voltage synthesis unit is:
and then the obtained abc three-phase voltage reference value u refa 、u refb And u refc Performing park transformation to obtain a voltage reference value u corresponding to the dq coordinate system refd And u refq The expression is:
in the voltage-current double closed-loop control module with active damping control, the d-axis and q-axis control modes are the same, so the invention takes the d-axis as an example to take the d-axis voltage reference value u refd Output voltage u with d-axis od Is input into a voltage ring PI controller G u (s) comparing the output result with the d-axis output current i od The product of the feedforward gain H and the q-axis voltage coupling term u are added oq ωC f Subtracting to obtain d-axis current reference value i refd The d-axis inductance current i passing through the active damping feedback coefficient K is compared with the d-axis inductance current i fd Subtracting from d-axis inductance current i fd The result obtained by subtraction passes through a current loop P controller G i (s) obtaining d-axis control voltage u td D-axis control voltage u td Coupling term i with q-axis current oq ωL f Subtracting from d-axis output voltage u od Adding to obtain d-axis driving voltage u sd D-axis driving voltage u sd Comparing with triangular carrier wave to obtain modulation signal, generating voltage by main circuit under the action of modulation signal, filteringWave inductance L f Filter resistor R f Filter capacitor C f Damping resistor R d Parallel capacitor C d Then, the d-axis output voltage u is obtained od Wherein the value range of the active damping feedback coefficient K is 30<K<60。
Compared with the prior art, the principle and the advantages of the scheme are as follows:
the invention discloses a grid-connected inverter oscillation suppression strategy based on mixed damping, which mainly comprises a passive damping circuit module and a voltage-current double-closed-loop control module introducing active damping control, wherein the passive damping circuit comprises a parallel capacitor and a damping resistor, the damping resistor is connected with the parallel capacitor in parallel after being connected with a filter capacitor in series, the active damping control is introduced into the voltage-current double-closed-loop module, the passive damping circuit and the voltage-current double-closed-loop control introducing the active damping control jointly form the mixed damping control, the damping of the circuit is improved, and the grid-connected inverter oscillation is suppressed, so that the stability of a system is ensured.
Drawings
FIG. 1 is a schematic diagram of a grid-connected inverter topology and a hybrid damping control strategy in an embodiment of the present invention;
FIG. 2 is a diagram of an active power waveform of a conventional control strategy according to an embodiment of the present invention;
FIG. 3 is a graph of reactive power waveforms for a conventional control strategy in an embodiment of the present invention;
fig. 4 is a voltage waveform diagram of the point of common coupling in the conventional control strategy according to the embodiment of the present invention;
fig. 5 is a FFT analysis of the pcc voltage in a conventional control strategy in an embodiment of the present invention;
FIG. 6 is a graph of the active power waveforms of the hybrid damping control strategy according to an embodiment of the present invention;
FIG. 7 is a reactive power waveform diagram of a hybrid damping control strategy in an embodiment of the present invention;
FIG. 8 is a graph of a CPC voltage waveform in a hybrid damping control strategy according to an embodiment of the present invention;
fig. 9 is an FFT analysis of the pcc voltage in a hybrid damping control strategy in accordance with an embodiment of the present invention.
Detailed Description
The invention is further illustrated by the following examples:
fig. 1 is a schematic diagram of a grid-connected inverter topology and hybrid damping control strategy, including the steps of:
in the passive damping control module, oscillation of the grid-connected inverter is restrained in a mode of introducing actual damping to a filter circuit, wherein the actual damping is a filter capacitor C f Series damping resistor R d Rear and parallel capacitance C d In parallel, wherein the damping resistor R d The value range of (2) is 220<R d <300, parallel capacitor C d The range of the value of (2) is 5 multiplied by 10 -8 <C d <5×10 -6 ；
In the droop control module, detecting abc three-phase output voltage u of the grid-connected inverter after adding the passive damping control module oa 、u ob And u oc Abc three-phase output current i oa 、i ob And i oc Obtaining an output voltage u corresponding to the dq coordinate system through park transformation od And u oq Output current i od And i oq The expression is:
wherein ω is an angular frequency;
and then the active power P and the reactive power Q are obtained through a power calculation unit, wherein the expression of the power calculation unit is as follows:
wherein p is instantaneous active power, q is instantaneous reactive power, and s is Laplacian;
multiplying the active power P by the active/voltage droop control coefficient n to obtain an output voltage transition value u n Reference output voltage u * And an output voltage transition value u n The output voltage amplitude u is obtained by subtraction, and the reactive power Q and the reactive power/frequency droop control coefficient m are multiplied to obtain the angular frequency transition value omega m Angular frequency reference ω * And angular frequency transition value omega m Adding to obtain angular frequency omega, multiplying the angular frequency omega by 1/s of the integral link to obtain phase angle
Output voltage amplitude u and phase angle->
Obtaining abc three-phase voltage reference value u through a voltage synthesis unit refa 、u refb And u refc Wherein the expression of the voltage synthesis unit is:
and then the obtained abc three-phase voltage reference value u refa 、u refb And u refc Performing park transformation to obtain a voltage reference value u corresponding to the dq coordinate system refd And u refq The expression is:
in the voltage-current double closed-loop control module with active damping control, the d-axis and q-axis control modes are the same, so the invention takes the d-axis as an example to take the d-axis voltage reference value u refd Output voltage u with d-axis od Is input into a voltage ring PI controller G u (s) comparing the output result with the d-axis output current i od The product of the feedforward gain H and the q-axis voltage coupling term u are added oq ωC f Subtracting to obtain d-axis current reference value i refd The d-axis inductance current i passing through the active damping feedback coefficient K is compared with the d-axis inductance current i fd Subtracting from d-axis inductance current i fd The result obtained by subtraction passes through a current loop P controller G i (s) obtaining d-axis control voltage u td D-axis control voltage u td Coupling term i with q-axis current oq ωL f Subtracting from d-axis output voltage u od Adding to obtain d-axis driving voltage u sd D-axis driving voltage u sd Comparing with the triangular carrier wave to obtain a modulation signal, generating voltage by the main circuit under the action of the modulation signal, and passing through a filter inductance L f Filter resistor R f Filter capacitor C f Damping resistor R d Parallel capacitor C d Then, the d-axis output voltage u is obtained od Wherein the value range of the active damping feedback coefficient K is 30<K<60。
Fig. 2, 3 and 4 are graphs of the active power, reactive power, voltage waveforms at the point of common coupling of the system under a conventional control strategy, respectively, the reactive/frequency droop factor m=1×10 -3 Active power/voltage droop factor n=2×10 -4 Line impedance Z l1 Line impedance z=0.18Ω l2 ＝0.18Ω+8×10 -4 H, grid impedance Z g ＝0.00001Ω+8×10 -4 H, load resistance R p =2Ω. In the simulation process, the active power, the reactive power and the public coupling point voltage waveform diagram can be found to be serious in oscillation and serious in instability of the system. Fig. 5 is a graph of voltage U at the point of common coupling to the system pcc As a result of FFT analysis, thd= 2683.48% was far higher than the distortion rate by 5%, which was not expected.
Fig. 6, 7 and 8 are graphs of the active power, reactive power and voltage waveforms at the point of common coupling of the system under a hybrid damping control strategy, respectively, the grid impedance Z g Active power p=3.46×10 when the remaining parameters remain unchanged =3Ω+0.03h 4 W gradually tends to be equally divided and keeps stable; reactive power q=0var, is divided equally and kept stable; point of common coupling voltage U pcc =292V, frequency f=50 Hz, satisfies the condition and remains stable. Fig. 9 shows the FFT analysis result of the pcc voltage in the hybrid damping control strategy, and it can be seen from fig. 9 that thd=1.27%, which is lower than 5% of distortion rate, and meets the expectation.
The above embodiments are only preferred embodiments of the present invention, and are not intended to limit the scope of the present invention, so variations in shape and principles of the present invention should be covered.
Claims (4)
1. The grid-connected inverter oscillation suppression strategy based on the hybrid damping is characterized by comprising the following steps of:
1) In the passive damping control module, oscillation of the grid-connected inverter is restrained in a mode of introducing actual damping to a filter circuit, wherein the actual damping is a filter capacitor C f Series damping resistor R d Rear and parallel capacitance C d Parallel connection;
2) In the droop control module, detecting abc three-phase output voltage u of the grid-connected inverter after adding the passive damping control module oa 、u ob And u oc Abc three-phase output current i oa 、i ob And i oc Obtaining an output voltage u corresponding to the dq coordinate system through park transformation od And u oq Output current i od And i oq The expression is:
wherein ω is an angular frequency;
3) And then the active power P and the reactive power Q are obtained through a power calculation unit, wherein the expression of the power calculation unit is as follows:
wherein p is instantaneous active power, q is instantaneous reactive power, and s is Laplacian;
4) Multiplying the active power P by the active/voltage droop control coefficient n to obtain an output voltage transition value u n Reference output voltage u * And an output voltage transition value u n The output voltage amplitude u is obtained by subtraction, and the reactive power Q and the reactive power/frequency droop control coefficient m are multiplied to obtain the angular frequency transition value omega m Angular frequency reference ω * And angular frequency transition value omega m Adding to obtain angular frequency omega, multiplying the angular frequency omega by 1/s of the integral link to obtain phase angle
Output voltage amplitude u and phase angle->
Obtaining abc three-phase voltage reference value u through a voltage synthesis unit refa 、u refb And u refc Wherein the expression of the voltage synthesis unit is:
5) And then the obtained abc three-phase voltage reference value u refa 、u refb And u refc Performing park transformation to obtain a voltage reference value u corresponding to the dq coordinate system refd And u refq The expression is:
6) In a voltage-current double closed-loop control module introducing active damping control, d-axis voltage reference value u refd Output voltage u with d-axis od Is input into a voltage ring PI controller G u (s) comparing the output result with the d-axis output current i od The product of the feedforward gain H and the q-axis voltage coupling term u are added oq ωC f Subtracting to obtain d-axis current reference value i refd The d-axis inductance current i passing through the active damping feedback coefficient K is compared with the d-axis inductance current i fd Subtracting from d-axis inductance current i fd The result obtained by subtraction passes through a current loop P controller G i (s) obtaining d-axis control voltage u td D-axis control voltage u td Coupling term i with q-axis current oq ωL f Subtracting from d-axis output voltage u od Adding to obtain d-axis driving voltage u sd D-axis driving voltage u sd Comparing with the triangular carrier wave to obtain a modulation signal, generating voltage by the main circuit under the action of the modulation signal, and passing through a filter inductance L f Filter resistor R f Filter capacitor C f Damping resistor R d Parallel capacitor C d Then, the d-axis output voltage u is obtained od 。
2. The hybrid damping-based grid-connected inverter oscillation suppression strategy according to claim 1, wherein in step 1), the damping resistor R d The value range of (2) is 220<R d <300。
3. The hybrid damping-based grid-connected inverter oscillation suppression strategy of claim 1, wherein in step 1), the parallel capacitance C d The range of the value of (2) is 5 multiplied by 10 -8 <C d <5×10 -6 。
4. The hybrid damping-based grid-connected inverter oscillation suppression strategy according to claim 1, wherein in step 6), the value range of the active damping feedback coefficient K is 30< K <60.
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