CN113644641B - Multi-direct-current power spring voltage stable control method - Google Patents
Multi-direct-current power spring voltage stable control method 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
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Abstract
The invention relates to a method for stably controlling voltage of a multi-direct-current power spring, which comprises the following steps: constructing an outer loop power control law which considers communication time delay to obtain expected voltage tracks of all direct current buses; constructing a differential smoothing control law of dynamic reversible characteristics, and solving and obtaining a DCES filter inductance current expected track by combining each DC bus voltage expected track; based on the current inner loop design of model predictive control, a DCES filter inductance current expected track is taken as a tracking control target, and a corresponding DCES working mode is obtained; and correspondingly changing the working state of the switch in each DCES according to the working mode of the DCES. Compared with the prior art, the control method provided by the invention is based on the nonlinear nature of the DC micro-grid multi-DCES system with communication time delay, can rapidly compensate the multi-DCES distributed voltage control deviation caused by unknown time-varying communication time delay, and has the advantages of small calculated amount, good stability and strong robustness.
Description
Technical Field
The invention relates to the technical field of direct-current power spring control, in particular to a voltage stabilizing control method for a multi-direct-current power spring.
Background
When the renewable energy source is connected into the direct-current micro-grid with high permeability, because photovoltaic and wind power generation have intermittence and randomness, direct-current bus voltage fluctuation is easy to be caused, and the direct-current micro-grid can have obvious influence on the electric energy quality of a user side. The direct current power spring (DC electric spring, DCES) is used as a new demand side management technology, aims at smooth control of Critical Load (CL) voltage, and forms an intelligent load by connecting a non-critical load (NCL) in series, so that partial direct current bus voltage fluctuation is transferred to the NCL, and therefore stable direct current bus voltage under the condition of renewable energy output fluctuation is realized, the power quality of a user side is improved, meanwhile, the demand on the capacity of a storage battery is reduced as much as possible, the economic application value is high, the DCES is widely applied in a direct current micro-grid at present, and a plurality of DCES are usually arranged in the direct current micro-grid to ensure stable direct current bus voltage.
In order to realize the distributed coordinated operation of multiple DCES of the direct-current micro-grid, the prior art applies a consistency theory, and can asymptotically agree through local information interaction between adjacent control nodes, so that the functions of coordinated level and stability control of each bus voltage and plug and play of the DCES can be realized, the problems of low bus voltage precision and high communication cost of a centralized control method in the traditional distributed control method are effectively solved, and the application form is flexible, so that most of current researches are based on the consistency theory to perform the distributed control of the multiple DCES.
However, the reasons of communication distance, channel noise, etc. easily cause communication delay between network nodes, which is also a key influencing factor in the design of the consistency control method. Research shows that under the condition of communication time delay, a consistency control method is applied, a larger deviation exists between a convergence value and a true value, the control performance is obviously influenced by the communication time delay, and in practical application, the larger communication time delay can cause busbar voltage oscillation and even cause instability of a micro-grid system.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a method for stably controlling the voltage of a multi-DC power spring so as to solve the adverse effect of communication time delay on multi-DCES consistency control.
The aim of the invention can be achieved by the following technical scheme: a voltage stable control method of a multi-DC power spring comprises the following steps:
s1, constructing an outer loop power control law which considers communication time delay to obtain expected voltage tracks of all direct current buses;
s2, constructing a differential smoothing control law of dynamic reversible characteristics, and solving and obtaining a DCES filter inductance current expected track by combining each DC bus voltage expected track;
s3, designing a current inner loop based on model predictive control, and obtaining a corresponding DCES working mode by taking a DCES filter inductance current expected track as a tracking control target;
s4, correspondingly changing the working states of the switches in each DCES according to the DCES working modes.
Further, the step S1 specifically includes the following steps:
s11, calculating to obtain voltage error signals of all buses by considering communication time delay based on global average voltage target constraint of the direct-current micro-grid;
and S12, taking the voltage error signals of all the buses as compensation, and combining the ideal working voltage of the key load to obtain the expected value of the voltage of all the direct current buses.
Further, the global average voltage target constraint of the direct current micro-grid is specifically:
wherein V is i For the voltage of the DC bus i, V ref N is the total number of dc buses, which is the ideal operating voltage for the critical load.
Further, the bus voltage error signal is specifically:
wherein ε i Is the voltage error signal of bus i, x is the coupling parameter between active power and voltage regulator, c ij To the extent of communication between the DCES located on DC bus i and the DCES located on DC bus j, p es,i For active power at the i-th bus DCES,for the active power of the busbar DCES located in the ith section, +.>For consistency control of the hold-down items +.>Is a weighted average of the maximum power of a plurality of DCES, f i Control gain, p, of a hold-down coherence controller for delay compensation term es,i,ref For DCES at dc bus i, the desired output power, τ, is the communication delay.
Further, the expected value of the dc bus voltage is specifically:
V bus,i ＝V ref +ε i
wherein V is bus,i Is the voltage expected value of the direct current bus i.
Further, in the differential smoothing control law in step S2, a current i= [ I ] flowing through each dc bus is defined 1 ,i 2 ,…,i n ] T To smooth the output variable y, each DCES outputs a voltage V es ＝[V es1 ,V es2 ,…,V esn ] T Reference value i of the inductor current flowing through each DCES filter is the state variable x L,ref ＝[I L1,ref ,I L2,ref ,…,I Ln,ref ] T To control the variable u.
Further, the differential smoothing control law is specifically:
I nc ＝[I nc1 ,I nc2 ,…,I ncn ] T
V＝[V G ,V bus，1 ,V bus，2 ,…V bus,n ] T
R＝[R 1 ,R 2 ,…,R n ] T
L＝[L 1 ,L 2 ,…,L n ] T
V nc ＝[V nc1 ,V nc2 ,…,V ncn ] T
wherein I is nc Is non-critical load current, C is filter inductance capacitance, V is source side and DC bus voltage, R is critical load, L is filter inductance, V nc Is the voltage of the non-critical load,for differentiating operator +.>For smoothing the first order differential variable of the output variable y, is->Is a second order differential variable that smoothes the output variable y.
Further, the step S3 specifically includes the following steps:
s31, according to the switching state of a single DCES, measuring to obtain corresponding filter inductance current and DCES output voltage, so as to obtain the filter inductance current of the DCES in the next preset sampling time of the four switching states;
s32, inputting the filter inductance current and the filter inductance current reference value in the next preset sampling time into a set evaluation function to obtain a corresponding evaluation value;
s33, selecting a switch state combination corresponding to the minimum evaluation value as a DCES working mode.
Further, the filter inductor current in the next preset sampling time in step S31 is specifically:
in the first switching state of the DCES, i.e. when only the first switch and the fourth switch are turned on:
in the second switching state of the DCES, i.e. when only the first switch and the second switch are conducting:
in the third switching state of the DCES, i.e. only the second switch and the third switch are conducting:
in the fourth switching state of DCES, i.e. when only the third switch and the fourth switch are turned on:
the two ends of the first switch are respectively connected with one end of the second switch and one end of the third switch, the other end of the second switch is connected with one end of the fourth switch, and the other end of the fourth switch is connected with the other end of the third switch;
i L (k+1) is the filter inductance current at the time k+1, T S For a preset sampling time, V ES (k) For the output voltage of DCES at time k, V DC (k) For the energy storage battery voltage at time k, i L (k) The inductor current is filtered for time k.
Further, the evaluation function is specifically:
J＝|i L,ref (k+1)-i L (k+1)|
wherein J is an evaluation value, i L,ref (k+1) is the reference value, i, of the filter inductor current corresponding to the next sampling time L (k+1) is the filter inductor current in the next sampling time.
Compared with the prior art, the invention has the following advantages:
1. the invention can combine the active power information of the local DCES and the adjacent DCES by constructing the control law of the outer loop power drag-and-drop consistency, realize the on-line dynamic adjustment of the voltage expected track of each DC bus, therefore, the DCES input voltage deviation caused by communication time delay is effectively compensated, and the adverse effect of the communication time delay on the control of the consistency of multiple DCES is solved.
2. The invention designs a differential smooth control law with dynamic reversible characteristics, thereby realizing the linearization conversion of the output characteristics of a nonlinear system and realizing the situation that uncertainty disturbance exists and dynamic errors are not modeled.
3. According to the invention, by designing a model prediction method based on a DCES switching mode, the expected track of the DCES filtering inductive current is quickly tracked as a target, so that a corresponding DCES switching mode is obtained, and stable control on the DC bus voltage can be realized.
4. The differential smooth hold-down consistency control method has the advantages of small calculated amount, wide stability domain and strong robustness, and can quickly compensate the influence of unknown time-varying communication delay on the stable control of the DC bus voltage of the micro-grid when the external disturbance and the internal parameter perturbation conditions of uncertainty exist.
Drawings
FIG. 1 is a schematic flow chart of the method of the present invention;
FIG. 2 is a schematic diagram of a DC micro-grid with multiple DCES in an embodiment;
FIG. 3 is a control block diagram of an embodiment;
FIG. 4 is a block diagram of a DCES model predictive control in an embodiment;
FIG. 5 (a) is a source side voltage fluctuation waveform in an embodiment;
FIG. 5 (b) shows waveforms of DC bus voltages according to the embodiment;
fig. 5 (c) shows the voltage waveforms of each DCES in the embodiment.
Detailed Description
The invention will now be described in detail with reference to the drawings and specific examples.
Examples
As shown in fig. 1, a method for controlling voltage stability of a multi-dc power spring includes the following steps:
s1, constructing an outer loop power control law which considers communication time delay to obtain expected voltage tracks of all direct current buses, and specifically:
s11, calculating to obtain voltage error signals of all buses by considering communication time delay based on global average voltage target constraint of the direct-current micro-grid;
s12, taking the voltage error signals of all the buses as compensation, and combining the ideal working voltage of the key load to obtain expected values of all the DC bus voltages;
the global average voltage target constraint of the direct current micro-grid is as follows:
wherein V is i For the voltage of the DC bus i, V ref The ideal working voltage of the key load is that n is the total number of the direct current buses;
the bus voltage error signal is specifically:
wherein ε i Is the voltage error signal of bus i, x is the coupling parameter between active power and voltage regulator, c ij To the extent of communication between the DCES located on DC bus i and the DCES located on DC bus j, p es,i For active power at the i-th bus DCES,active power for DCES located in the ith section of bus， />For consistency control of the hold-down items +.>Is a weighted average of the maximum power of a plurality of DCES, f i Control gain, p, of a hold-down coherence controller for delay compensation term es,i,ref Expected output power of DCES positioned on the direct current bus i, and tau is communication time delay;
the final DC bus voltage expected value is specifically:
V bus,i ＝V ref +ε i
wherein V is bus,i The voltage expected value of the direct current bus i;
s2, constructing a differential smoothing control law of dynamic reversible characteristics, combining the expected track of the voltage of each direct current bus, and obtaining the expected track of the current of the DCES filter inductor, wherein in the differential smoothing control law, firstly, the current I= [ I ] flowing through each direct current bus is defined 1 ,i 2 ,…,i n ] T Is a smoothed output variable y;
each DCES output voltage V es ＝[V es1 ,V es2 ,…,V esn ] T Is a state variable x;
reference value i of current flowing through each DCES filter inductor L,ref ＝[I L1,ref ,I L2,ref ,…,I Ln,ref ] T Is the control variable u; then, designing a differential smoothing control law as follows:
I nc ＝[I nc1 ,I nc2 ,…,I ncn ] T
V＝[V G ,V bus，1 ,V bus，2 ,…V bus,n ] T
R＝[R 1 ,R 2 ,…,R n ] T
L＝[L 1 ,L 2 ,…,L n ] T
V nc ＝[V nc1 ,V nc2 ,…,V ncn ] T
wherein I is nc Is non-critical load current, C is filter inductance capacitance, V is source side and DC bus voltage, R is critical load, L is filter inductance, V nc Is the voltage of the non-critical load,for differentiating operator +.>For smoothing the first order differential variable of the output variable y, is->A second order differential variable that is a smoothed output variable y;
s3, designing a current inner loop based on model predictive control, taking a DCES filter inductance current expected track as a tracking control target, and solving to obtain a corresponding DCES working mode, specifically:
s31, according to the switching state of a single DCES, measuring to obtain corresponding filter inductance current and DCES output voltage, so as to obtain the filter inductance current of the DCES in the next preset sampling time in the four switching states, wherein in the first switching state of the DCES, namely, only the first switch and the fourth switch are turned on:
in the second switching state of the DCES, i.e. when only the first switch and the second switch are conducting:
in the third switching state of the DCES, i.e. only the second switch and the third switch are conducting:
in the fourth switching state of DCES, i.e. when only the third switch and the fourth switch are turned on:
wherein, two ends of the first switch are respectively connected with one end of the second switch and one end of the third switch, the other end of the second switch is connected with one end of the fourth switch, and the other end of the fourth switch is connected with the other end of the third switch;
i L (k+1) is the filter inductance current at the time k+1, T S For a preset sampling time, V ES (k) For the output voltage of DCES at time k, V DC (k) For the energy storage battery voltage at time k, i L (k) Filtering the inductance current for the moment k;
s32, inputting the filter inductance current and the filter inductance current reference value in the next preset sampling time into a set evaluation function to obtain a corresponding evaluation value, wherein the evaluation function specifically comprises:
J＝|i L,ref (k+1)-i L (k+1)|
wherein J is an evaluation value, i L,ref (k+1) is the reference value, i, of the filter inductor current corresponding to the next sampling time L (k+1) is the filter inductor current in the next sampling time;
s33, selecting a switch state combination corresponding to the minimum evaluation value as a DCES working mode.
In this embodiment, as shown in fig. 2, four DCES are provided in the dc micro grid, each including four switches (S 1 、S 2 、S 3 And S is 4 ) Thus, there are four switching states (switching variable S) for each DCES i The value of (i=1, 2,3, 4) represents the switching tube stateS, i.e i =1 indicates that the switching tube is turned on, S i =0 indicates that the switching tube is off):
first switching state: s is S 1 ＝1，S 4 ＝1；
Second switching state: s is S 1 ＝1，S 2 ＝1；
Third switching state: s is S 2 ＝1，S 3 ＝1；
Fourth switching state: s is S 3 ＝1，S 4 ＝1。
The embodiment applies the above method, and the specific control process is shown in fig. 3:
firstly, designing an outer loop power control law which considers communication time delay so as to dynamically adjust expected voltage tracks of all direct current buses;
based on the expected track of the DC bus voltage, the DCES filtering inductance current is obtained by constructing a differential smoothing control law of dynamic reversible characteristics;
and finally, tracking a DCES filter inductance current reference track based on a current inner loop design of model prediction, so as to obtain a DCES working mode.
In this embodiment, considering the consistency control target, the global average voltage of the dc micro-grid including multiple DCES should satisfy:
wherein V is i For the voltage of bus i, V ref Is the ideal operating voltage for CL.
The control law of the hold-down consistency taking the formula (1) as the target design and considering the communication delay is as follows:
wherein ε i Is the voltage error signal of bus i, x is the coupling parameter between active power and voltage regulator, c ij DCES and DC bus iDegree of communication between DCES located on DC bus j, p es,i For active power at the i-th bus DCES,for the active power of the busbar DCES located in the ith section, +.>For consistency control of the hold-down items +.>Is a weighted average of the maximum power of a plurality of DCES, f i Control gain, p, of a hold-down coherence controller for delay compensation term es,i,ref For DCES at dc bus i, the desired output power, τ, is the communication delay.
Adding each busbar voltage error signal as compensation into CL ideal working voltage to obtain each DC busbar voltage expected track:
V bus,i ＝V ref +ε i (3)
defining the current I= [ I ] flowing through each DC bus 1 ,i 2 ,…,i n ] T Is a smoothed output variable y; each DCES outputs a voltage V es ＝[V es1 ,V es2 ,…,V esn ] T Is a state variable x; reference value i of current flowing through each DCES filter inductor L , ref ＝[I L1,ref ,I L2,ref ,…,I Ln,ref ] T Is the control variable u;
then, designing a differential smoothing control law as follows:
wherein I is nc ＝[I nc1 ,I nc2 ,…,I ncn ] T Is non-critical load current, C is filter inductance capacitance, V= [ V ] G ,V bus，1 ,V bus，2 ,…V bus,n ] T For source side and dc bus voltage, r= [ R ] 1 ,R 2 ,…,R n ] T As a critical load, l= [ L ] 1 ,L 2 ,…,L n ] T For filtering inductance, V nc ＝[V nc1 ,V nc2 ,…,V ncn ] T Is the voltage of the non-critical load,for differentiating operator +.>For smoothing the first order differential variable of the output variable y, is->Is a second order differential variable that smoothes the output variable y.
As shown in fig. 4, the current inner loop design based on model predictive control uses DCES inductor current expected track fast tracking as a control target, and establishes a model predictive control evaluation function J as follows:
J＝|i L,ref (k+1)-i L (k+1)| (5)
according to the working mode of a single DCES, the filter inductance current i is measured L (k) And DCES output voltage V ES Solving four switching modes of DCES at next sampling time T s Filter inductor current i in L (k+1)：
First switching state: s is S 1 ＝1，S 4 ＝1
From KVL law:
wherein: l is a filter inductance, i L To filter the inductor current, V DC For storing the battery voltage, V ES The voltage is output for DCES.
Discretizing and finishing the formula (6) to obtain:
wherein: i.e L (k+1) is the filter inductance current at the time k+1, T s For sampling time, V ES (k) For the output voltage of DCES at time k, V DC (k) For the energy storage battery voltage at time k, i L (k) The inductor current is filtered for time k.
Similarly, the second switching state: s is S 1 ＝1，S 2 ＝1
From the KVL law, the discretization process is followed by:
third switching state: s is S 2 ＝1，S 3 ＝1
From the KVL law, the discretization process is followed by:
fourth switching state: s is S 3 ＝1，S 4 ＝1
From the KVL law, the discretization process is followed by:
will filter the inductance current reference value i L,ref (k+1) and a filter inductor current i L (k+1) substituting the evaluation function J to evaluate the next sampling time T S And selecting a switch combination with minimized error and applying the switch combination to DCES to realize quick tracking of the DCES filter inductor current reference value.
In the embodiment, a DC micro-grid simulation model of a plurality of DCES (direct current micro-grid) taking communication delay into consideration is built in MATLAB/Simulink, the effectiveness of circulation suppression of the invention is verified, and simulation parameters of the embodiment are shown in a table 1.
TABLE 1
| Parameters (parameters) | Numerical value |
| Line resistance R from power supply to bus 1 1 /Ω | 0.4 |
| Line inductance L from power supply to bus 1 1 /mH | 1.07 |
| Bus 2 to bus 4 line resistance R 2 -R 4 /Ω | 0.1 |
| CL resistor R located at bus 1 and bus 2 c1 -R c2 /Ω | 100 |
| CL resistor R located at bus 3 and bus 4 c3 -R c4 /Ω | 120 |
| NCL resistor R located on bus 1 and bus 2 n1 -R n2 /Ω | 40 |
| NCL resistor R located on bus 3 and bus 4 n3 -R n4 /Ω | 50 |
| Inductance value L/mH of LC filter | 6.6 |
| LC filter capacitance C/uF | 21 |
| DCES battery voltage V dc /V | 60 |
And carrying out simulation test by adopting a control method of drag consistency based on differential smoothing theory in a multi-DCES direct current micro-grid model considering communication time delay. Setting the simulation time to be 0.6s, wherein the communication short time delay is 0.2s, and the voltage of each direct current bus is along with the voltage V of a power supply G The waveform of the change is shown in fig. 5 (a), and the simulation results are shown in fig. 5 (b) and 5 (c). Fig. 5 (b) shows the dc bus voltage waveforms; fig. 5 (c) shows the respective DCES voltage waveforms. As shown by the graph results, the control method has the advantages of quick dynamic response, no static difference in steady state, and the voltage of each direct current bus is 48+/-1V in an expected value interval, and can keep the voltage of the direct current micro-grid bus stable when source voltage fluctuation and 0.2s communication short time delay coexist.
In summary, the invention can dynamically adjust the expected track of each DC bus voltage by designing the outer ring drag consistency control law; the linear conversion of the output characteristic of the nonlinear system can be realized by constructing a differential smoothing control law with dynamic reversible characteristic, and then the expected track of the DCES filtering inductance current is obtained by designing a simple output feedback controller; and finally, designing a current inner loop based on model prediction to obtain an optimal switching mode of the DCES so as to realize stable control of the voltage of the direct current bus. According to the invention, a differential smoothing control method is adopted, and the desired track of the DCES filter inductance current is quickly adjusted according to the reference value of each DC bus voltage obtained by the control of the drag consistency; in the invention, the model predictive control selects the DCES optimal working mode according to the evaluation function, so as to realize the rapid tracking of the DCES output voltage on the expected track. The control method has the advantages of small calculated amount, rapid dynamic response and small overshoot, has the advantage of no static difference in steady state, and can effectively inhibit the influence of communication time delay on the coordinated operation of multiple DCES.
Claims (7)
1. The method for stably controlling the voltage of the multi-direct-current power spring is characterized by comprising the following steps of:
s1, constructing an outer loop power control law which considers communication time delay to obtain expected voltage tracks of all direct current buses;
s2, constructing a differential smoothing control law of dynamic reversible characteristics, and solving and obtaining a DCES filter inductance current expected track by combining each DC bus voltage expected track;
s3, designing a current inner loop based on model predictive control, and obtaining a corresponding DCES working mode by taking a DCES filter inductance current expected track as a tracking control target;
s4, correspondingly changing the working state of a switch in each DCES according to the DCES working mode;
the step S1 specifically comprises the following steps:
s11, calculating to obtain voltage error signals of all buses by considering communication time delay based on global average voltage target constraint of the direct-current micro-grid;
s12, taking the voltage error signals of all the buses as compensation, and combining the ideal working voltage of the key load to obtain the expected voltage value of all the direct current buses;
the global average voltage target constraint of the direct current micro-grid is specifically as follows:
wherein V is i For the voltage of the DC bus i, V ref The ideal working voltage of the key load is that n is the total number of the direct current buses;
the bus voltage error signal specifically comprises:
wherein ε i Is the voltage error signal of bus i, x is the coupling parameter between active power and voltage regulator, c ij To the extent of communication between the DCES located on DC bus i and the DCES located on DC bus j, p es,i For active power at the i-th bus DCES,for the active power of the busbar DCES located in the ith section, +.>For consistency control of the hold-down items +.>Is a weighted average of the maximum powers of a plurality of DCES, f i Control gain, p, of a hold-down coherence controller for delay compensation term es,i,ref For DCES at dc bus i, the desired output power, τ, is the communication delay.
2. The method for controlling voltage stability of a multi-dc power spring according to claim 1, wherein the expected value of the dc bus voltage is specifically:
V bus,i ＝V ref +ε i
wherein V is bus,i Is the voltage expected value of the direct current bus i.
3. The method according to claim 2, wherein in the differential smoothing control law in the step S2, a current i= [ I ] flowing through each dc bus is defined 1 ,i 2 ,…,i n ] T To smooth the output variable y, each DCES outputs a voltage V es ＝[V es1 ,V es2 ,…,V esn ] T Reference value i of the inductor current flowing through each DCES filter is the state variable x L,ref ＝[I L1,ref ,I L2,ref ,…,I Ln,ref ] T Is the control variable u.
4. The method for controlling voltage stability of a multi-dc power spring according to claim 3, wherein the differential smoothing control law is specifically:
I nc ＝[I nc1 ,I nc2 ,…,I ncn ] T
V＝[V G ,V bus，1 ,V bus，2 ,…V bus,n ] T
R＝[R 1 ,R 2 ,…,R n ] T
L＝[L 1 ,L 2 ,…,L n ] T
V nc ＝[V nc1 ,V nc2 ,…,V ncn ] T
wherein I is nc Is non-critical load current, C is filter inductance capacitance, V is source side and DC bus voltage, R is critical load, L is filter inductance, V nc Is the voltage of the non-critical load,for differentiating operator +.>For smoothing the first order differential variable of the output variable y, is->Is flatSecond order differential variable of the sliding output variable y.
5. The method for controlling voltage stability of a multi-dc power spring according to claim 1, wherein the step S3 specifically comprises the steps of:
s31, according to the switching state of a single DCES, measuring to obtain corresponding filter inductance current and DCES output voltage, so as to obtain filter inductance current of the DCES in the next preset sampling time of the four switching states;
s32, inputting the filter inductance current and the filter inductance current reference value in the next preset sampling time into a set evaluation function to obtain a corresponding evaluation value;
s33, selecting a switch state combination corresponding to the minimum evaluation value as a DCES working mode.
6. The method for stabilizing and controlling the voltage of the multi-dc power spring according to claim 5, wherein the filter inductor current in the next preset sampling time in step S31 is specifically:
in the first switching state of the DCES, i.e. when only the first switch and the fourth switch are turned on:
in the second switching state of the DCES, i.e. when only the first switch and the second switch are conducting:
in the third switching state of the DCES, i.e. only the second switch and the third switch are conducting:
in the fourth switching state of DCES, i.e. when only the third switch and the fourth switch are turned on:
the two ends of the first switch are respectively connected with one end of the second switch and one end of the third switch, the other end of the second switch is connected with one end of the fourth switch, and the other end of the fourth switch is connected with the other end of the third switch;
i L (k+1) is the filter inductance current at the time k+1, T S For a preset sampling time, V ES (k) For the output voltage of DCES at time k, V DC (k) For the energy storage battery voltage at time k, i L (k) The inductor current is filtered for time k.
7. The method for controlling voltage stability of a multi-dc power spring according to claim 6, wherein the evaluation function is specifically:
J＝|i L,ref (k+1)-i L (k+1)|
wherein J is an evaluation value, i L,ref (k+1) is the reference value, i, of the filter inductor current corresponding to the next sampling time L (k+1) is the filter inductor current in the next sampling time.
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