CN111030174B - Grid-connected inverter VSG mode and current source mode undisturbed switching control method - Google Patents
Grid-connected inverter VSG mode and current source mode undisturbed switching control method Download PDFInfo
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- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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Abstract
The invention discloses a method for controlling undisturbed switching between a grid-connected inverter VSG mode and a current source mode, which is applied toThe inverter topology structure using the control method comprises a direct current voltage source and a direct current side filter capacitor C in The three-phase inverter, the LC filter and the power grid; the DC voltage source and the DC side filter capacitor C in The grid-connected inverter is connected with a direct-current voltage source in series, and the output of the grid-connected inverter is filtered by an LC filter and then passes through a power grid impedance L g And accessing to a power grid. When the inverter works in a current source mode, tracking current source mode output by a VSG mode algorithm; when the inverter works in the VSG mode, the current source mode algorithm tracks the voltage source mode output, so that the double-mode undisturbed switching of the inverter is ensured, and the grid-connected stability of the inverter is improved.
Description
Technical Field
The invention belongs to the technical field of distributed power generation and power electronics, and particularly relates to a grid-connected inverter VSG mode and current source mode undisturbed switching control method.
Background
With the worsening of the environment and the worsening of the energy crisis, new energy plays an increasingly important role in economic development and social progress. Compared with the traditional synchronous generator, the power accessed into the power grid through the current source control type inverter has the advantages of high control speed, capability of better tracking the maximum power point, good economic benefit and the like, but also has the defects of insufficient inertia and damping. When the new energy power generation permeability is improved, the instability problems such as harmonic resonance and the like are easily caused.
In order to ensure the safety and the friendliness of the electric power transmitted to the power grid by the new energy power generation equipment, many researchers at home and abroad propose a VSG (virtual synchronous generator) control strategy. The existing research shows that VSG control can simulate the inertia and damping characteristics of the traditional synchronous generator, and has better power grid friendliness and safety than current source control in a weak power grid state. However, the grid state changes from moment to moment, and it is desirable that the new energy power generation equipment can select a corresponding control mode according to the grid state, so as to deliver safe electric power to the grid to serve thousands of households.
Therefore, the switching between the inverter voltage control type strategy and the current control type strategy is a problem to be researched. Regarding the problem, the existing research schemes at home and abroad mainly focus on the undisturbed switching aspect of grid-connected and off-grid inverters.
At present, for a disturbance-free switching scheme of multiple control modes of an inverter, a plurality of academic papers have been analyzed and proposed to solve the problem, for example:
1. the subject is a research on a microgrid on-line/off-line smooth switching control strategy based on an energy storage generalized control algorithm, the Chinese Motor engineering project, and an article on 2840-2853 of No. 10 in 2019. The paper provides a generalized control algorithm suitable for an energy storage grid-connected inverter, and microgrid on-grid/off-grid smooth switching is achieved. However, the method aims at the grid-connected and grid-disconnected scene, and the inverter is disconnected when working in the voltage source mode, so that the method is not suitable for the scene that the inverter is always connected to the grid.
2. The invention discloses a grid-connected and grid-disconnected switching device and system which are disclosed in the patent document of China (publication number CN 108899935B) in 2019, 10 and 18.A grid-connected and grid-disconnected switching device and system are provided by the invention, wherein the grid-connected and grid-disconnected switching device comprises a grid-connected point switch, a bidirectional tide inverter, an island detection device and an energy storage device, but the grid-connected and grid-disconnected switching device needs the energy storage device and a communication device, so that the complexity of the system is increased, and the coordination control is not facilitated.
3. In the invention patent document of china (publication No. CN 110021959A) in "a grid-connected inverter dual-mode control method based on short-circuit ratio under weak grid" published in 2019, 7, 16, the invention provides a switching method of droop mode control and current source control, but the voltage source control method of the invention is droop control, and does not relate to a switching method of VSG control and current source control. Compared with droop control, VSG control has inertia and damping effects, and can better simulate the characteristics of a synchronous generator.
In view of the above documents, the dual-mode undisturbed switching of the existing inverter has the following disadvantages:
1. the existing research on the undisturbed switching of the inverter mainly focuses on grid-connected and off-grid switching, and the grid-connected and off-grid undisturbed switching mode is not suitable for the application scene of grid-connected power generation all the time;
2. the existing grid-connected inverter undisturbed switching mode mainly focuses on undisturbed switching between current source control and droop control, and VSG control has more damping and inertia than droop control, so that the voltage and frequency of a synchronous generator supporting grid can be better simulated.
Disclosure of Invention
The invention provides a grid-connected inverter VSG mode and current source mode undisturbed switching control method, an inverter applying the control method can complete switching from VSG control to current source control or from current source control to VSG control, and the output voltage and current of the inverter are smooth and undisturbed in the switching process.
The object of the invention is thus achieved. The invention provides a method for controlling undisturbed switching of a VSG mode and a current source mode of a grid-connected inverter, which can realize switching of inverter control modes under different power grid states. Inverter control includes voltage source control and current source control. When the inverter operates in a voltage source mode, the current source control algorithm tracks the voltage source control output; when the inverter is operating in a current source mode, the voltage source control algorithm tracks the current source output, thereby ensuring undisturbed switching between the voltage source and current source modes. The modulation signal passes through the dsp and the switching device to obtain the inverter side voltage, and passes through the filter inductor L of the LC filter f And filter capacitor C of LC filter f Through the network impedance L g And accessing to a power grid.
In particular to a grid-connected inverterThe inverter topology structure applying the control method comprises a direct current voltage source V dc DC side filter capacitor C in Grid-connected inverter, LC filter and grid impedance L g And Grid; the DC voltage source V dc And a DC side filter capacitor C in In parallel, the grid-connected inverter and the DC side filter capacitor C in In parallel connection, the output of the inverter is filtered by an LC filter and then passes through a power grid impedance L g Accessing to a power grid;
the control method comprises the following steps:
step 1, sampling output phase voltage U of inverter oa ,U ob ,U oc Sampling inverter side filter inductor phase current I of inverter inva ,I invb ,I invc Sampling of the output phase current I of the inverter oa ,I ob ,I oc And setting an inverter operation mode and setting: 0 is the current source mode, 1 is the VSG mode, all voltage source modes in the text represent VSG mode;
the transformation formula from the three-phase voltage to the two-phase rotating coordinate system is as follows:
the phase locking formula of the single synchronous coordinate system is as follows:
ω csm ＝V csm_q ×(K spll_p +K spll_i /s)+100π
wherein K spll_p Is the spll PLL proportioner coefficient, K spll_i The coefficient of a phase-locked loop integral regulator of a single synchronous coordinate system is obtained, s is a Laplace operator, and theta' is the output voltage angle of the three-phase inverter in the previous period;
step 3, according to the angular frequency omega of the current source obtained in the step 2 csm Obtaining the output voltage angle theta of the three-phase inverter through a mode selection integral formula 1;
the mode selection integral formula 1 is:
step 4, according to the inverter output voltage angle theta obtained in the step 3, the inverter side filter inductance phase current I obtained in the step 1 through the current source mode inverter side phase current rotating coordinate transformation equation 1 inva ,I invb ,I invc Coordinate transformation is carried out to obtain d-axis feedback I of filter inductance current at the inverter side in the current source mode of the inverter csm_dfeedback And current source mode inverter side filter inductor current q-axis feedback I csm_qfeedback ；
The current source mode inverter side phase current rotation coordinate transformation equation 1 is as follows:
step 5, according to the filtered inductive current d-axis feedback I obtained in the step 4, on the inverter side of the inverter in the current source mode csm_dfeedback Current source mode inverter side filter inductance current q axis feedback I csm_qfeedback And externally given electricityStream source d-axis reference I csm_dref Current source q-axis reference I csm_qref Obtaining the current source mode modulation d-axis reference e through a current source mode current loop equation csm_dref And current source mode modulation q-axis reference e csm_qref ；
The current loop equation of the current source mode is as follows:
wherein, K csm_ip Is the current source mode current loop proportional regulator coefficient, K csm_ii Current source mode current loop integral regulator coefficients;
step 6, modulating d-axis reference e according to the current source mode obtained in the step 5 csm_dref And current source mode modulation q-axis reference e csm_qref Selecting equation 1 through a modulation mode to obtain a modulation wave e under a dq coordinate system d And e q Then modulating the wave to make the inverter pass through the grid impedance L g Outputting electric energy to a power grid;
the modulation mode selection equation 1 is:
e d ＝e csm_dref
e q ＝e csm_qref
and 7, converting the three-phase inverter output phase voltage U obtained by sampling in the step 1 according to a conversion formula 1 from the output three-phase voltage to a two-phase static coordinate system oa ,U ob ,U oc Converting to obtain two-phase static coordinate system component U of inverter output phase voltage oα ,U oβ Converting the inverter output phase current I obtained by sampling in the step 1 according to the conversion formula 1 from the output three-phase current to the two-phase static coordinate system oa ,I ob ,I oc Converting to obtain the two-phase static coordinate system component I of the inverter output phase current oα ,I oβ (ii) a Then, the inverse is obtained by the power calculation formula 1The inverter outputs active power P and the inverter outputs reactive power Q; then the VSG angular frequency omega is obtained through a VSG reactive power control formula 1 vsm Obtaining d-axis voltage amplitude reference U through VSG active power control formula 1 dref ；
The conversion formula 1 from the output three-phase voltage to the two-phase static coordinate system is as follows:
the conversion formula 1 from the output three-phase current to the two-phase static coordinate system is as follows:
the power calculation formula 1 is:
P＝U oα I oα +U oβ I oβ
Q＝U oβ I oα -U oα I oβ
the VSG active power control formula 1 is:
wherein, P ref To rated active power, omega 0 At the fundamental angular frequency, ω csm The current source angular frequency is adopted, m is an active droop coefficient, J is a virtual moment of inertia, and D is a virtual damping coefficient;
the VSG reactive power control formula 1 is as follows:
wherein: q ref Rated reactive power, V grms Is the effective value of the fundamental wave of the power grid, n is the reactive droop coefficient, I d_ref_vsm "is a given value of a period on d-axis current of a current loop in VSG mode, and I is set when a current source mode is started d_ref_vsm "has an initialization value of 0;
step 8, according to the filtered inductive current d-axis feedback I obtained in the step 4 at the side of the inverter in the current source mode of the inverter csm_dfeedback And current source mode inverter side filter inductor current q-axis feedback I csm_qfeedback Obtaining the d-axis feedback I of the filter inductance current at the inverter side in the VSG mode through a voltage source mode inverter side phase current rotation coordinate transformation equation 1 vsm_dfeedback And VSG mode inverter side filter inductor current q-axis feedback I vsm_qfeedback And (3) converting the inverter output phase voltage U sampled in the step (1) through a voltage source mode inverter side phase voltage rotating coordinate transformation equation 1 oa ,U ob ,U oc Coordinate transformation is carried out to obtain d-axis feedback U of voltage source mode output voltage of the inverter vsm_dfeedback And inverter voltage source mode output voltage q-axis feedback U vsm_qfeedback ；
The voltage source mode inverter side phase current rotation coordinate transformation equation 1 is as follows:
I vsm_dfeedback ＝I csm_dfeedback
I vsm_qfeedback ＝I csm_qfeedback
the voltage source mode inverter side phase voltage rotating coordinate transformation equation 1 is as follows:
step 9, d-axis feedback U is carried out according to the output voltage of the inverter voltage source mode obtained in the step 8 vsm_dfeedback Inverter voltage source mode output voltage q-axis feedback U vsm_qfeedback And U obtained in step 7 drefv Obtaining d-axis reference I of voltage source mode current loop through voltage source mode voltage loop equation 1 vsm_dref And voltage source mode current loop q-axis reference I vsm_qref ；
Equation 1 for the voltage source mode voltage ring is:
I vsm_dref ＝(U drefv -U vsm_dfeedback )×(K vsm_vp +K vsm_vi /s)
I vsm_qref ＝(0-U vsm_qfeedback )×(K vsm_vp +K vsm_vi /s)
wherein K vsm_vp Is the VSG mode voltage loop proportional regulator coefficient, K vsm_vi Is the VSG mode voltage loop integral regulator coefficient;
The voltage source mode current loop equation 1 is:
e vsm_dref ＝(I vsm_dref -I vsm_dfeedback )×K vsm_ip +e csm_dref
e vsm_qref ＝(I vsm_qref -I vsm_qfeedback )×K vsm_ip +e csm_qref
wherein K vsm_ip Is the VSG mode current loop proportioner coefficient;
step 11, switching into a VSG mode, namely setting the operation mode as 1, and recording the operation of an inverter in the mode as a new period;
sampling output phase voltage U of new cycle of inverter oa ',U ob ',U oc ', sampling the inverter side filter inductance phase current I of the new cycle of the inverter inva ',I invb ',I invc ', sampling the output phase current I of the new cycle of the inverter oa ',I ob ',I oc '；
Step 12, according to the conversion formula 2 from the output three-phase voltage to the two-phase static coordinate system, the output phase voltage U of the new period of the inverter sampled in the step 11 is obtained oa ',U ob ',U oc ' conversion to obtain two-phase stationary coordinate system component U of output phase voltage in new cycle of inverter oα ',U oβ '; converting the output three-phase current to a two-phase static coordinate system according to a conversion formula 2, and outputting the output phase current I of the inverter in the new period sampled in the step 11 oa ',I ob ',I oc ' conversion to obtain the output phase current two-phase stationary coordinate system component I of the new cycle of the inverter oα ',I oβ '; secondly, obtaining the output active power P 'of the inverter in the new period and the output reactive power Q' of the inverter in the new period through a power calculation formula 2; then, a VSG angular frequency omega of a new period is obtained through a VSG reactive power control formula 2 vsm ', VSG active power control formula 2 obtains d-axis voltage amplitude reference U of a new period dref '；
The conversion formula 2 from the output three-phase voltage to the two-phase static coordinate system is as follows:
the conversion formula 2 from the output three-phase current to the two-phase stationary coordinate system is as follows:
the power calculation formula 2 is:
P＝U oα 'I oα '+U oβ 'I oβ '
Q'＝U oβ 'I oα '-U oα 'I oβ '
the active power control formula 2 is:
the reactive power control formula 2 is:
step 13, obtaining a new periodic angular frequency ω of the voltage source according to the step 12 csm ', obtaining an output voltage angle theta' of a new period of the inverter through a mode selection integral formula 2;
the mode selection integral equation 2 is:
step 14, according to the output voltage angle θ' of the inverter in the new period obtained in step 13, the inverter side filter inductor phase current I of the inverter in the new period obtained in step 11 is sampled by the voltage source mode inverter side phase current rotating coordinate transformation equation 2 inva ',I invb ',I invc ' coordinate transformation is carried out to obtain the feedback I of the side filter inductive current d axis of the voltage source mode inverter of a new period of the inverter vsm_dfeedback ' and voltage source module of new cycleFormula dc-to-ac converter side filter inductive current q axle feedback I vsm_qfeedback ' the output phase voltage U of the new cycle of the inverter sampled in the step 11 is converted by the voltage source mode inverter side phase voltage rotating coordinate transformation equation 2 oa ',U ob ',U oc ' coordinate transformation is carried out to obtain d-axis feedback U of output voltage of the voltage source mode inverter in a new period of the inverter vsm_dfeedback ' and new period of q-axis feedback U of output voltage of voltage source mode inverter vsm_qfeedback '；
The voltage source mode inverter side phase current rotation coordinate transformation equation 2 is as follows:
the voltage source mode inverter side phase voltage rotating coordinate transformation equation 2 is as follows:
step 15, according to the filter inductance current d-axis feedback I of the voltage source mode inverter side of the new cycle of the inverter obtained in the step 14 vsm_dfeedback ' with new period of the voltage source mode inverter side filter inductor current q-axis feedback I vsm_qfeedback ', the current source mode inverter side filter inductance current d-axis feedback I of the new cycle of the inverter is obtained through the current source mode inverter side phase current rotation coordinate transformation equation 2 csm_dfeedback ' and new periodic current source mode inverter side filter inductor current q-axis feedback I csm_qfeedback '；
The current source mode inverter side phase current rotation coordinate transformation equation 2 is:
I csm_dfeedback '＝I vsm_dfeedback '
I csm_qfeedback '＝I vsm_qfeedback '
step 16, according to the d-axis feedback U of the output voltage of the voltage source mode inverter of the new period of the inverter obtained in the step 14 vsm_dfeedback ' and new period of q-axis feedback U of output voltage of voltage source mode inverter vsm_qfeedback ' and step 12. The new cycle of U drefv ' obtaining a new cycle of d-axis reference I of the voltage source mode current loop through the voltage source mode voltage loop equation 2 vsm_dref ' and new periodic Voltage Source mode Current Loop q-axis reference I vsm_qref '；
The voltage source mode voltage loop equation 2 is:
I vsm_dref '＝(U drefv '-U vsm_dfeedback ')×(K vsm_vp +K vsm_vi /s)
I vsm_qref '＝(0-U vsm_qfeedback ')×(K vsm_vp +K vsm_vi /s)
step 17, referring to I according to the d-axis of the new periodic voltage source mode current loop obtained in step 16 vsm_dref ', new periodic voltage source mode current loop q-axis reference I vsm_qref ', new cycle voltage source mode inverter side filter inductor current d-axis feedback I of new cycle obtained in step 14 vsm_dfeedback ' with new period of the voltage source mode inverter side filter inductor current q-axis feedback I vsm_qfeedback ' and current source mode modulation d-axis reference e obtained in step 5 csm_dref Current source mode modulated q-axis reference e csm_qref Obtaining a new period of voltage source mode modulation d-axis reference e through a voltage source mode current loop equation 2 vsm_dref ' modulating the q-axis reference e with the new periodic voltage source pattern vsm_qref '；
The voltage source mode current loop equation 2 is:
e vsm_dref '＝(I vsm_dref '-I vsm_dfeedback ')×K vsm_ip +e csm_dref
e vsm_qref '＝(I vsm_qref '-I vsm_qfeedback ')×K vsm_ip +e csm_qref
step 18, obtaining a new period of voltage source mode modulation d-axis reference e according to step 17 vsm_dref ' modulating the q-axis reference e with the new periodic voltage source pattern vsm_qrefv ' obtaining a modulation wave e of a new period in the dq coordinate system by selecting equation 2 through the modulation mode d ' and e q ', then modulating the wave to pass the inverter through the grid impedance L g Outputting electric energy to a power grid;
the modulation mode selection equation 2 is:
e d '＝e vsm_dref '
e q '＝e vsm_qref '
step 19, according to the new period obtained in step 15, the d-axis feedback I of the current source mode inverter side filter inductor current csm_dfeedback ', new period current source mode inverter side filter inductance current q axis feedback I csm_qfeedback ', externally given current source d-axis reference I csm_dref Current source q-axis reference I csm_qref And current source mode modulated d-axis reference e obtained in step 5 csm_dref And current source mode modulation q-axis reference e csm_qref Obtaining a new cycle of current source mode modulation d-axis reference e through a current source mode current loop equation 2 csm_dref ' modulating the q-axis reference e with a new periodic current source pattern csm_qref '；
The current loop equation 2 for the current source mode is:
preferably, the three-phase inverter output voltage angle θ ″ of the previous cycle in step 2 is initialized to 0 in the first cycle of the operation of the present control method.
Compared with the prior art, the invention has the beneficial effects that:
1. the method for controlling the undisturbed switching between the VSG mode and the current source mode of the grid-connected inverter has the advantages of simple structure, economy and effectiveness, and no need of adding other equipment;
2. the undisturbed switching realized by the invention can transmit green electric energy friendly to the power grid, and the environment is protected and the sustainable development is realized;
3. the VSG control of the invention has inertia and damping, can better simulate the performance of the synchronous generator, and plays a role in supporting the voltage and frequency of a power grid.
Drawings
Fig. 1 is a grid-connected topological diagram of a grid-connected inverter VSG mode and current source mode undisturbed switching control method.
Fig. 2 is a control block diagram of a method for controlling undisturbed switching between a grid-connected inverter VSG mode and a current source mode according to the invention.
Fig. 3 is a voltage waveform diagram of the VSG mode and current source mode undisturbed switching control grid connection when the short circuit ratio is 10.
Fig. 4 is a waveform diagram of the VSG mode and current source mode undisturbed switching control grid-connected current when the short-circuit ratio is 10.
Fig. 5 is a voltage waveform diagram of the VSG mode and current source mode undisturbed switching control grid when the short circuit ratio is 5.
Fig. 6 is a waveform diagram of the VSG mode and current source mode undisturbed switching control grid-connected current when the short-circuit ratio is 5.
Detailed Description
The present embodiment will be described in detail below with reference to the accompanying drawings.
Fig. 1 is a topological diagram of a method for controlling the undisturbed switching between a grid-connected inverter VSG mode and a current source mode. As can be seen from the figure, the topology includes a DC voltage source V dc DC side filter capacitor C in Grid-connected inverter, LC filter and grid impedance L g And a Grid; the DC voltage source V dc And a DC side filter capacitor C in In parallel, the grid-connected inverter and the DC side filter capacitor C in In parallel, the output of the inverter passes through an LC filterFiltered through the grid impedance L g And accessing to a power grid. In addition, in FIG. 1, L f Is the filter inductance of an LC filter, C f Is the filter capacitance of the LC filter, L g Is the grid impedance.
The specific parameters are as follows: the rated output line voltage of the inverter is 380V/50Hz, and the filter capacitor C at the direct current side in Filter inductance L of =15mf, lc filter f =0.56mh, filter capacitance C of lc filter f =270uF, rated inverter capacity of 100kVA, and grid impedance L when the short-circuit ratio is 5 g =0.56mH; when the short circuit ratio is 10, the network impedance L g ＝0.56mH。
Fig. 2 is a control block diagram of the method for controlling the switching between the grid-connected inverter in the VSG mode and the current source mode without disturbance. As can be seen from the figure, the steps of the invention are as follows:
step 1, sampling inverter output phase voltage U oa ,U ob ,U oc Sampling inverter side filter inductor phase current I inva ,I invb ,I invc Sampling inverter output phase current I oa ,I ob ,I oc Setting an inverter operation mode and setting: the voltage source mode is represented by the voltage source mode, i.e., VSG mode, where 0 is the current source mode and 1 is the VSG mode.
the transformation formula from the three-phase voltage to the two-phase rotating coordinate system is as follows:
the phase locking formula of the single synchronous coordinate system is as follows:
ω csm ＝V csm_q ×(K spll_p +K spll_i /s)+100π
wherein K spll_p Is the spll PLL proportioner coefficient, K spll_i The method is characterized in that the method is a single synchronous coordinate system phase-locked loop integral regulator coefficient, s is a Laplace operator, and theta' is the output voltage angle of the three-phase inverter in the previous period. The three-phase inverter output voltage angle θ ″ of the previous cycle is initialized to 0 in the first cycle of the operation of the control method.
Step 3, according to the angular frequency omega of the current source obtained in the step 2 csm And obtaining the output voltage angle theta of the three-phase inverter through the mode selection integral formula 1.
The mode selection integral formula 1 is:
step 4, according to the inverter output voltage angle theta obtained in the step 3, the inverter side filter inductance phase current I obtained in the step 1 through the current source mode inverter side phase current rotating coordinate transformation equation 1 inva ,I invb ,I invc Coordinate transformation is carried out to obtain d-axis feedback I of filter inductance current at the inverter side in the current source mode of the inverter csm_dfeedback And current source mode inverter side filter inductor current q-axis feedback I csm_qfeedback 。
The current source mode inverter side phase current rotation coordinate transformation equation 1 is as follows:
step 5, according to the filtered inductive current d-axis feedback I obtained in the step 4, on the inverter side of the inverter in the current source mode csm_dfeedback Current source mode inverter side filter inductor current q-axis feedback I csm_qfeedback And an externally given current source d-axis reference I csm_dref Current source q-axis reference I csm_qref Obtaining the current source mode modulation d-axis reference e through a current source mode current loop equation csm_dref And current source mode modulation q-axis reference e csm_qref 。
The current loop equation of the current source mode is as follows:
wherein, K csm_ip Is the current source mode current loop proportional regulator coefficient, K csm_ii The current source mode current loop integrates the regulator coefficients. In this embodiment, K csm_ip ＝1.8，K csm_ii ＝5000。
Step 6, modulating the d-axis reference e according to the current source mode obtained in the step 5 csm_dref And current source mode modulation q-axis reference e csm_qref Selecting equation 1 through a modulation mode to obtain a modulation wave e under a dq coordinate system d And e q Then modulating the wave to make the inverter pass through the line inductance L g And outputting the electric energy to a power grid.
The modulation mode selection equation 1 is:
e d ＝e csm_dref
e q ＝e csm_qref
step 7, converting the inverter output phase voltage U obtained by sampling in the step 1 according to the conversion formula 1 from the output three-phase voltage to the two-phase static coordinate system oa ,U ob ,U oc Converting to obtain two-phase static coordinate system component U of inverter output phase voltage oα ,U oβ And (3) converting the three-phase inverter output phase current I obtained by sampling in the step (1) according to a conversion formula 1 for outputting the three-phase current to a two-phase static coordinate system oa ,I ob ,I oc Converting to obtain the two-phase static coordinate system component I of the inverter output phase current oα ,I oβ (ii) a Secondly, obtaining the output active power P of the inverter and the output reactive power Q of the inverter through a power calculation formula 1; then the VSG angular frequency omega is obtained through a VSG reactive power control formula 1 vsm Obtaining d-axis voltage amplitude reference U through VSG active power control formula 1 dref 。
The conversion formula 1 from the output three-phase voltage to the two-phase static coordinate system is as follows:
the conversion formula 1 from the output three-phase current to the two-phase static coordinate system is as follows:
the power calculation formula 1 is:
P＝U oα I oα +U oβ I oβ
Q＝U oβ I oα -U oα I oβ
the VSG active power control formula 1 is:
wherein, P ref To rated active power, omega 0 At the fundamental angular frequency, ω csm The current source angular frequency is shown, m is an active droop coefficient, J is a virtual moment of inertia, and D is a virtual damping coefficient. In this example P ref ＝100000,ω 0 ＝100×π,m＝3.1415×10 -5 ,J＝5,D＝2。
The VSG reactive power control formula 1 is as follows:
wherein: q ref Rated reactive power, V grms Is the effective value of the fundamental wave of the power grid, n is the reactive droop coefficient, I d_ref_vsm "is a given value of a period on d-axis current of a current loop in VSG mode, and I is set when a current source mode is started d_ref_vsm "has an initialization value of 0. In this example Q ref ＝0,V grms ＝220,n＝7×10 -5 。
Step 8, according to the filtered inductor current d-axis feedback I obtained in the step 4 on the inverter side of the current source mode of the inverter csm_dfeedback And current source mode inverter side filter inductor current q-axis feedback I csm_qfeedback Obtaining the d-axis feedback I of the filter inductance current at the inverter side in the VSG mode through a voltage source mode inverter side phase current rotation coordinate transformation equation 1 vsm_dfeedback And VSG mode inverter side filter inductor current q-axis feedback I vsm_qfeedback (ii) a Converting equation 1 through the side phase voltage rotating coordinate of the voltage source mode inverter to obtain inverter output voltage U of the inverter sampled in step 1 oa ,U ob ,U oc Coordinate transformation is carried out to obtain d-axis feedback U of voltage source mode output voltage of the inverter vsm_dfeedback And inverter voltage source mode output voltage q-axis feedback U vsm_qfeedback ；
The voltage source mode inverter side phase current rotation coordinate transformation equation 1 is as follows:
I vsm_dfeedback ＝I csm_dfeedback
I vsm_qfeedback ＝I csm_qfeedback
the voltage source mode inverter side phase voltage rotating coordinate transformation equation 1 is as follows:
step 9, d-axis feedback U is output according to the voltage source mode output voltage of the inverter obtained in the step 8 vsm_dfeedback Inverter voltage source mode output voltage q-axis feedback U vsm_qfeedback And U obtained in step 7 drefv Obtaining d-axis reference I of voltage source mode current loop through voltage source mode voltage loop equation 1 vsm_dref And voltage source mode current loop q-axis reference I vsm_qref 。
Equation 1 for the voltage source mode voltage ring is:
I vsm_dref ＝(U drefv -U vsm_dfeedback )×(K vsm_vp +K vsm_vi /s)
I vsm_qref ＝(0-U vsm_qfeedback )×(K vsm_vp +K vsm_vi /s)
wherein K vsm_vp Is the VSG mode voltage loop proportional regulator coefficient, K vsm_vi Is the VSG mode voltage loop integral regulator coefficient. In this example K vsm_vp ＝1，K vsm_vi ＝400。
The voltage source mode current loop equation 1 is:
e vsm_dref ＝(I vsm_dref -I vsm_dfeedback )×K vsm_ip +e csm_dref
e vsm_qref ＝(I vsm_qref -I vsm_qfeedback )×K vsm_ip +e csm_qref
wherein K vsm_ip Is the VSG mode current loop proportioner coefficient.
And step 11, finishing the current source mode operation, switching into the VSG mode, namely setting the operation mode as 1, and recording the operation of the inverter in the mode as a new period.
Sampling output phase voltage U of new cycle of inverter oa ',U ob ',U oc ', sampling the inverter side filter inductance phase current I of the new cycle of the inverter inva ',I invb ',I invc ', sampling the output phase current I of the new cycle of the inverter oa ',I ob ',I oc '。
Step 12, according to the conversion formula 2 from the output three-phase voltage to the two-phase static coordinate system, the output phase voltage U of the new period of the inverter sampled in the step 11 is obtained oa ',U ob ',U oc ' conversion to obtain two-phase stationary coordinate system component U of output phase voltage in new cycle of inverter oα ',U oβ '; converting the output three-phase current to a two-phase static coordinate system according to a conversion formula 2, and outputting the output phase current I of the inverter in the new period sampled in the step 11 oa ',I ob ',I oc ' conversion to obtain the output phase current two-phase stationary coordinate system component I of the new cycle of the inverter oα ',I oβ '; secondly, obtaining the output active power P 'of the inverter in the new period and the output reactive power Q' of the inverter in the new period through a power calculation formula 2; then, the VSG angular frequency omega of a new period is obtained through a VSG reactive power control formula 2 vsm ', VSG active power control formula 2 obtains d-axis voltage amplitude reference U of new period dref '。
The formula 2 for converting the output three-phase voltage into the two-phase static coordinate system is as follows:
the conversion formula 2 from the output three-phase current to the two-phase stationary coordinate system is as follows:
the power calculation formula 2 is:
P'＝U oα 'I oα '+U oβ 'I oβ '
Q'＝U oβ 'I oα '-U oα 'I oβ '
the active power control formula 2 is:
the reactive power control formula 2 is:
step 13, obtaining the angular frequency omega of the voltage source in the new period according to the step 12 csm 'the output voltage angle theta' of the new cycle of the inverter is obtained through the mode selection integral formula 2.
The mode selection integral formula 2 is:
step 14, according to the output voltage angle θ' of the inverter in the new period obtained in step 13, the inverter side filter inductor phase current I of the inverter in the new period obtained in step 11 is sampled by the voltage source mode inverter side phase current rotating coordinate transformation equation 2 inva ',I invb ',I invc ' coordinate transformation is carried out to obtain the feedback I of the side filter inductive current d axis of the voltage source mode inverter of a new period of the inverter vsm_dfeedback ' with new period of the voltage source mode inverter side filter inductor current q-axis feedback I vsm_qfeedback ' the output phase voltage U of the new cycle of the inverter sampled in the step 11 is converted into the output phase voltage U of the new cycle of the inverter by the voltage source mode inverter side phase voltage rotating coordinate transformation equation 2 oa ',U ob ',U oc ' coordinate transformation is carried out to obtain the new period of d-axis feedback U of the filter inductive current at the side of the voltage source mode inverter vsm_dfeedback ' and new period of the q-axis feedback U of the filter inductor current on the side of the voltage source mode inverter vsm_qfeedback '。
The voltage source mode inverter side phase current rotation coordinate transformation equation 2 is as follows:
the voltage source mode inverter side phase voltage rotation coordinate transformation equation 2 is as follows:
step 15, according to the filtered inductive current d-axis feedback I of the inverter side of the voltage source mode of the new period of the inverter obtained in the step 14 vsm_dfeedback ' with new period of the voltage source mode inverter side filter inductor current q-axis feedback I vsm_qfeedback ', the current source mode inverter side filter inductance current d-axis feedback I of the new cycle of the inverter is obtained through the current source mode inverter side phase current rotation coordinate transformation equation 2 csm_dfeedback ' and new periodic current source mode inverter side filter inductor current q-axis feedback I csm_qfeedback '；
The current source mode inverter side phase current rotation coordinate transformation equation 2 is:
I csm_dfeedback '＝I vsm_dfeedback '
I csm_qfeedback '＝I vsm_qfeedback '
step 16, according to the d-axis feedback U of the output voltage of the voltage source mode inverter of the new period of the inverter obtained in the step 14 vsm_dfeedback ' New period voltage source mode inverter output voltage q-axis feedback U vsm_qfeedback ' and step 12 the new periodic d-axis voltage magnitude reference U drefv ' obtaining a new cycle of d-axis reference I of the voltage source mode current loop through the voltage source mode voltage loop equation 2 vsm_dref ' and new periodic voltage source mode current loop q-axis reference I vsm_qref '。
The voltage source mode voltage loop equation 2 is:
I vsm_dref '＝(U drefv '-U vsm_dfeedback ')×(K vsm_vp +K vsm_vi /s)
I vsm_qref '＝(0-U vsm_qfeedback ')×(K vsm_vp +K vsm_vi /s)
step 17, referring to I according to the d-axis of the new periodic voltage source mode current loop obtained in step 16 vsm_dref ', new periodic voltage source mode current loop q-axis referenceI vsm_qref ', new cycle voltage source mode inverter side filter inductor current d-axis feedback I obtained in step 14 vsm_dfeedback ', new period of filter inductor current q-axis feedback I at side of voltage source mode inverter vsm_qfeedback ' and current source mode modulation d-axis reference e obtained in step 5 csm_dref Current source mode modulation q-axis reference e csm_qref Obtaining a new period of voltage source mode modulation d-axis reference e through a voltage source mode current loop equation 2 vsm_dref ' modulating the q-axis reference e with the new periodic voltage source pattern vsm_qref '。
The voltage source mode current loop equation 2 is:
e vsm_dref '＝(I vsm_dref '-I vsm_dfeedback ')×K vsm_ip +e csm_dref
e vsm_qref '＝(I vsm_qref '-I vsm_qfeedback ')×K vsm_ip +e csm_qref
step 18, obtaining a new period of voltage source mode modulation d-axis reference e according to step 17 vsm_dref ' modulating the q-axis reference e with the new periodic voltage source pattern vsm_qrefv ' obtaining a modulation wave e of a new period in the dq coordinate system by selecting equation 2 through the modulation mode d ' and e q ' then modulating the wave to make the inverter pass through the network impedance L g And outputting the electric energy to a power grid.
The modulation mode selection equation 2 is:
e d '＝e vsm_dref '
e q '＝e vsm_qref '
step 19, according to the new period obtained in step 15, the d-axis feedback I of the current source mode inverter side filter inductor current csm_dfeedback ', new period current source mode inverter side filter inductance current q axis feedback I csm_qfeedback ', externally given current source d-axis reference I csm_dref Current source q-axis reference I csm_qref And current source mode modulated d-axis reference e obtained in step 5 csm_dref And current source mode modulated q-axis referencee csm_qref Obtaining a new cycle of current source mode modulation d-axis reference e through a current source mode current loop equation 2 csm_dref ' modulating the q-axis reference e with a new periodic current source pattern csm_qref '。
The current loop equation 2 for the current source mode is:
fig. 3 and 4 are a grid-connected voltage change waveform diagram and a grid-connected current waveform diagram respectively when the inverter with VSG control and current source control undisturbed switching control is connected to a power grid with short-circuit ratios of 10 and 5, the grid-connected current waveform diagram is that the grid-connected current ratio is 10 when 0-0.5s, the working mode signal input is 0, the grid-connected inverter works in the current source mode, the grid-connected current ratio is changed to 5 when 0.5s, at this time, the operation mode switching is required, the working mode signal input is 1 when 0.5-1s, and the grid-connected inverter works in the VSG mode; the grid short-circuit ratio is 10 when 1-1.5s, the working mode signal input is 0, the grid-connected inverter works in the current source mode, the grid short-circuit ratio is 5 when 1.5-2s, the working mode signal input is 1, the grid-connected inverter works in the VSG mode, and the operation is finished when 2 s. It can be seen that the voltage and current waveforms are undisturbed at the three switching moments of 0.5s, 1s and 1.5s, which illustrates the effectiveness of the scheme provided by the invention.
Fig. 5 and fig. 6 are a grid-connected voltage variation waveform diagram and a grid-connected current waveform diagram respectively when the inverter with VSG control and current source control undisturbed switching control is connected to a power grid with short-circuit ratios of 8 and 3, the grid-connected short-circuit ratio is 8 at 0-0.5s, the working mode signal input is 0, the grid-connected inverter works in the current source mode, the grid-connected short-circuit ratio is 3 at 0.5s, at this time, the operation mode switching is required, the working mode signal input is 1 at 0.5-1s, and the grid-connected inverter works in the VSG mode; the grid short-circuit ratio is 8 when 1-1.5s, the working mode signal input is 0, the grid-connected inverter works in the current source mode, the grid short-circuit ratio is changed into 3 when 1.5-2s, the working mode signal input is 1, the grid-connected inverter works in the VSG mode, and the operation is finished when 2 s. It can be seen that the voltage and current waveforms are undisturbed at the three switching moments of 0.5s, 1s and 1.5s, which illustrates the effectiveness of the scheme provided by the invention.
It can be seen from the figure that, under the weak grid, by adopting the VSG mode and current source mode undisturbed switching method provided by the patent, grid-connected voltage and current can be switched undisturbed well.
Claims (2)
1. A control method for undisturbed switching between VSG mode and current source mode of a virtual synchronous machine of a grid-connected inverter is disclosed, wherein the topological structure of the inverter applying the control method comprises a direct-current voltage source V dc DC side filter capacitor C in Grid-connected inverter, LC filter and grid impedance L g And a Grid; the DC voltage source V dc And a DC side filter capacitor C in Connected in parallel, the grid-connected inverter and a DC side filter capacitor C in In parallel connection, the output of the inverter is filtered by an LC filter and then passes through a power grid impedance L g Accessing a power grid;
the control method is characterized by comprising the following steps:
step 1, sampling output phase voltage U of an inverter oa ,U ob ,U oc Sampling inverter side filter inductor phase current I of inverter inva ,I invb ,I invc Sampling the output phase current I of the inverter oa ,I ob ,I oc Setting an inverter operation mode and setting: 0 is a current source mode, 1 is a VSG mode, and all voltage source modes represent the VSG mode;
step 2, firstly setting the operation mode of the inverter to be 0, and obtaining the output phase voltage U of the three-phase inverter according to the sampling in the step 1 oa ,U ob ,U oc Obtaining q-axis voltage V of output phase voltage of the three-phase inverter through a conversion formula from three-phase voltage to a two-phase rotating coordinate system csm_q And d-axis voltage V csm_d Then obtaining the angular frequency omega of the current source through a single synchronous coordinate system phase-locking formula csm Wherein the d axis is an active axis and the q axis is a reactive axis;
the transformation formula from the three-phase voltage to the two-phase rotating coordinate system is as follows:
the phase locking formula of the single synchronous coordinate system is as follows:
ω csm ＝V csm_q ×(K spll_p +K spll_i /s)+100π
wherein K spll_p For the spll PLL proportioner coefficient, K spll_i The coefficient of a phase-locked loop integral regulator of a single synchronous coordinate system is obtained, s is a Laplace operator, and theta' is the output voltage angle of the three-phase inverter in the previous period;
step 3, according to the angular frequency omega of the current source obtained in the step 2 csm Obtaining the output voltage angle theta of the three-phase inverter through a mode selection integral formula 1;
the mode selection integral formula 1 is:
step 4, according to the inverter output voltage angle theta obtained in the step 3, the inverter side filter inductance phase current I obtained in the step 1 through the current source mode inverter side phase current rotating coordinate transformation equation 1 inva ,I invb ,I invc Coordinate transformation is carried out to obtain the d-axis feedback I of the filter inductance current at the inverter side of the inverter in the current source mode of the inverter csm_dfeedback And current source mode inverter side filter inductor current q-axis feedback I csm_qfeedback ；
The current source mode inverter side phase current rotation coordinate transformation equation 1 is as follows:
step 5, according to the filtered inductive current d-axis feedback I obtained in the step 4, on the inverter side of the inverter in the current source mode csm_dfeedback Current source mode inverter side filter inductor current q-axis feedback I csm_qfeedback And an externally given current source d-axis reference I csm_dref Current source q-axis reference I csm_qref Obtaining the current source mode modulation d-axis reference e through a current source mode current loop equation csm_dref And current source mode modulation q-axis reference e csm_qref ；
The current loop equation of the current source mode is as follows:
wherein, K csm_ip Is the current source mode current loop proportional regulator coefficient, K csm_ii Current source mode current loop integral regulator coefficients;
step 6, modulating d-axis reference e according to the current source mode obtained in the step 5 csm_dref And current source mode modulation q-axis reference e csm_qref Selecting equation 1 through a modulation mode to obtain a modulation wave e under a dq coordinate system d And e q Then modulating the wave to make the inverter pass through the network impedance L g Outputting electric energy to a power grid;
the modulation mode selection equation 1 is:
e d ＝e csm_dref
e q ＝e csm_qref
step 7, converting the three-phase voltage to a two-phase static coordinate system according to the output three-phase voltageFormula 1 is that the three-phase inverter output phase voltage U obtained by sampling in the step 1 oa ,U ob ,U oc Converting to obtain two-phase static coordinate system component U of inverter output phase voltage oα ,U oβ Converting the inverter output phase current I obtained by sampling in the step 1 according to the conversion formula 1 from the output three-phase current to the two-phase static coordinate system oa ,I ob ,I oc Converting to obtain the two-phase static coordinate system component I of the inverter output phase current oα ,I oβ (ii) a Secondly, obtaining the output active power P of the inverter and the output reactive power Q of the inverter through a power calculation formula 1; then obtaining the VSG angular frequency omega through a VSG reactive power control formula 1 vsm Obtaining d-axis voltage amplitude reference U through VSG active power control formula 1 dref ；
The conversion formula 1 from the output three-phase voltage to the two-phase static coordinate system is as follows:
the conversion formula 1 from the output three-phase current to the two-phase static coordinate system is as follows:
the power calculation formula 1 is:
P＝U oα I oα +U oβ I oβ
Q＝U oβ I oα -U oα I oβ
the VSG active power control formula 1 is:
wherein, P ref To rated active power, omega 0 At the fundamental angular frequency, ω csm The current source angular frequency is adopted, m is an active droop coefficient, J is a virtual moment of inertia, and D is a virtual damping coefficient;
the VSG reactive power control formula 1 is as follows:
wherein: q ref Rated reactive power, V grms Is the effective value of the fundamental wave of the power grid, n is the reactive droop coefficient, I d_ref_vsm "is a given value of a period on d-axis current of a current loop in VSG mode, and I is set when a current source mode is started d_ref_vsm "has an initialization value of 0;
step 8, according to the filtered inductive current d-axis feedback I obtained in the step 4 at the side of the inverter in the current source mode of the inverter csm_dfeedback And current source mode inverter side filter inductor current q-axis feedback I csm_qfeedback Obtaining the d-axis feedback I of the filter inductance current at the inverter side in the VSG mode through a voltage source mode inverter side phase current rotation coordinate transformation equation 1 vsm_dfeedback And VSG mode inverter side filter inductor current q-axis feedback I vsm_qfeedback And (3) converting the inverter output phase voltage U sampled in the step (1) through a voltage source mode inverter side phase voltage rotating coordinate transformation equation 1 oa ,U ob ,U oc Coordinate transformation is carried out to obtain d-axis feedback U of voltage source mode output voltage of the inverter vsm_dfeedback And inverter voltage source mode output voltage q-axis feedback U vsm_qfeedback ；
The voltage source mode inverter side phase current rotation coordinate transformation equation 1 is as follows:
I vsm_dfeedback ＝I csm_dfeedback
I vsm_qfeedback ＝I csm_qfeedback
the voltage source mode inverter side phase voltage rotating coordinate transformation equation 1 is as follows:
step 9, d-axis feedback U is output according to the voltage source mode output voltage of the inverter obtained in the step 8 vsm_dfeedback Inverter voltage source mode output voltage q-axis feedback U vsm_qfeedback And U obtained in step 7 drefv Obtaining d-axis reference I of voltage source mode current loop through voltage source mode voltage loop equation 1 vsm_dref And voltage source mode current loop q-axis reference I vsm_qref ；
Equation 1 for the voltage source mode voltage ring is:
I vsm_dref ＝(U drefv -U vsm_dfeedback )×(K vsm_vp +K vsm_vi /s)
I vsm_qref ＝(0-U vsm_qfeedback )×(K vsm_vp +K vsm_vi /s)
wherein K vsm_vp Is the VSG mode voltage loop proportional regulator coefficient, K vsm_vi Is the VSG mode voltage loop integral regulator coefficient;
step 10, according to the d-axis reference I of the voltage source mode current loop obtained in the step 9 vsm_dref Voltage source mode current loop q-axis reference I vsm_qref And d-axis feedback I of inverter VSG mode inverter side filter inductor current obtained in step 8 vsm_dfeedback And VSG mode inverter side filter inductor current q-axis feedback I vsm_qfeedback Obtaining a voltage source mode modulation d-axis reference e through a voltage source mode current loop equation 1 vsm_drefv And voltage source modeModulating q-axis reference e vsm_qrefv ；
The voltage source mode current loop equation 1 is:
e vsm_dref ＝(I vsm_dref -I vsm_dfeedback )×K vsm_ip +e csm_dref
e vsm_qref ＝(I vsm_qref -I vsm_qfeedback )×K vsm_ip +e csm_qref
wherein K vsm_ip Is the VSG mode current loop proportioner coefficient;
step 11, switching into a VSG mode, namely setting the operation mode as 1, and recording the operation of an inverter in the mode as a new period;
sampling output phase voltage U of new cycle of inverter oa ',U ob ',U oc ', sampling the inverter side filter inductance phase current I of the new cycle of the inverter inva ',I invb ',I invc ', sampling the output phase current I of the new cycle of the inverter oa ′,I ob ′,I oc ′；
Step 12, according to the conversion formula 2 from the output three-phase voltage to the two-phase static coordinate system, the output phase voltage U of the new cycle of the inverter sampled in the step 11 is obtained oa ',U ob ',U oc ' converting to obtain the output phase voltage two-phase stationary coordinate system component U of the new cycle of the inverter oα ',U oβ '; converting the output three-phase current to a two-phase static coordinate system according to a conversion formula 2, and outputting the output phase current I of the inverter in the new period sampled in the step 11 oa ',I ob ',I oc ' conversion to obtain the output phase current two-phase stationary coordinate system component I of the new cycle of the inverter oα ',I oβ '; secondly, obtaining the output active power P 'of the inverter in a new period and the output reactive power Q' of the inverter in the new period through a power calculation formula 2; then, the VSG angular frequency omega of a new period is obtained through a VSG reactive power control formula 2 vsm ', VSG active power control formula 2 obtains d-axis voltage amplitude reference U of new period dref '；
The conversion formula 2 from the output three-phase voltage to the two-phase static coordinate system is as follows:
the conversion formula 2 from the output three-phase current to the two-phase stationary coordinate system is as follows:
the power calculation formula 2 is:
P′＝U oα ′I oα ′+U oβ ′I oβ ′
Q'＝U oβ 'I oα '-U oα 'I oβ '
the active power control formula 2 is:
the reactive power control formula 2 is:
step 13, obtaining the angular frequency omega of the voltage source in the new period according to the step 12 csm ', obtaining an output voltage angle theta' of a new period of the inverter through a mode selection integral formula 2;
the mode selection integral equation 2 is:
step 14, according to the output voltage angle θ' of the inverter in the new period obtained in step 13, the inverter side filter inductor phase current I of the inverter in the new period obtained in step 11 is sampled by the voltage source mode inverter side phase current rotating coordinate transformation equation 2 inva ',I invb ',I invc ' coordinate transformation is carried out to obtain the feedback I of the side filter inductive current d axis of the voltage source mode inverter of a new period of the inverter vsm_dfeedback ' with new period of the voltage source mode inverter side filter inductor current q-axis feedback I vsm_qfeedback ' the output phase voltage U of the new cycle of the inverter sampled in the step 11 is converted into the output phase voltage U of the new cycle of the inverter by the voltage source mode inverter side phase voltage rotating coordinate transformation equation 2 oa ',U ob ',U oc ' coordinate transformation is carried out to obtain d-axis feedback U of output voltage of the voltage source mode inverter in a new period of the inverter vsm_dfeedback ' and new period of q-axis feedback U of output voltage of voltage source mode inverter vsm_qfeedback '；
The voltage source mode inverter side phase current rotation coordinate transformation equation 2 is as follows:
the voltage source mode inverter side phase voltage rotating coordinate transformation equation 2 is as follows:
step 15, according to the filter inductance current d-axis feedback I of the voltage source mode inverter side of the new cycle of the inverter obtained in the step 14 vsm_dfeedback ' and new cycle voltage source mode inverter side filter inductor current q-axis feedback I vsm_qfeedback ' obtaining the filter inductance current d-axis feedback I at the side of the current source mode inverter of a new period of the inverter through a current source mode inverter side phase current rotation coordinate transformation equation 2 csm_dfeedback ' and new periodic current source mode inverter side filter inductor current q-axis feedback I csm_qfeedback '；
The current source mode inverter side phase current rotation coordinate transformation equation 2 is:
I csm_dfeedback ′＝I vsm_dfeedback ′
I csm_qfeedback ′＝I vsm_qfeedback ′
step 16, according to the d-axis feedback U of the output voltage of the voltage source mode inverter of the new period of the inverter obtained in the step 14 vsm_dfeedback ' and new period of q-axis feedback U of output voltage of voltage source mode inverter vsm_qfeedback ' and step 12. The new cycle of U drefv ' obtaining a new cycle of d-axis reference I of the voltage source mode current loop through the voltage source mode voltage loop equation 2 vsm_dref ' and new periodic Voltage Source mode Current Loop q-axis reference I vsm_qref '；
The voltage source mode voltage loop equation 2 is:
I vsm_dref '＝(U drefv '-U vsm_dfeedback ')×(K vsm_vp +K vsm_vi /s)
I vsm_qref '＝(0-U vsm_qfeedback ')×(K vsm_vp +K vsm_vi /s)
step 17, referring to I according to the d-axis of the new periodic voltage source mode current loop obtained in step 16 vsm_dref ', new cycle voltage source mode electricityFlow ring q-axis reference I vsm_qref ', new cycle voltage source mode inverter side filter inductor current d-axis feedback I for the new cycle obtained in step 14 vsm_dfeedback ' and new cycle voltage source mode inverter side filter inductor current q-axis feedback I vsm_qfeedback ' and current source mode modulation d-axis reference e obtained in step 5 csm_dref Current source mode modulated q-axis reference e csm_qref Obtaining a new period of voltage source mode modulation d-axis reference e through a voltage source mode current loop equation 2 vsm_dref ' modulating the q-axis reference e with the new periodic voltage source pattern vsm_qref '；
The voltage source mode current loop equation 2 is:
e vsm_dref '＝(I vsm_dref '-I vsm_dfeedback ')×K vsm_ip +e csm_dref
e vsm_qref '＝(I vsm_qref '-I vsm_qfeedback ')×K vsm_ip +e csm_qref
step 18, obtaining a new period of voltage source mode modulation d-axis reference e according to step 17 vsm_dref ' modulating the q-axis reference e with the new periodic voltage source pattern vsm_qrefv ' obtaining a modulation wave e of a new period in the dq coordinate system by selecting equation 2 through the modulation mode d ' and e q ', then modulating the wave to pass the inverter through the grid impedance L g Outputting electric energy to a power grid;
the modulation mode selection equation 2 is:
e d ′＝e vsm_dref ′
e q ′＝e vsm_qref ′
step 19, according to the current source mode inverter side filter inductor current d-axis feedback I of the new period obtained in the step 15 csm_dfeedback ', new period current source mode inverter side filter inductance current q axis feedback I csm_qfeedback ', externally given current source d-axis reference I csm_dref Current source q-axis reference I csm_qref And current source mode modulation d-axis reference e obtained in step 5 csm_dref And a current sourceMode-modulated q-axis reference e csm_qref Obtaining a new cycle of current source mode modulation d-axis reference e through a current source mode current loop equation 2 csm_dref ' modulating the q-axis reference e with a new periodic current source pattern csm_qref '；
The current loop equation 2 for the current source mode is:
2. the method according to claim 1, wherein the three-phase inverter output voltage angle θ ″ of the previous cycle in step 2 is initialized to 0 in the first cycle of the operation of the control method.
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