CN113131527B - Full seamless switching control method for passive off-line of energy storage converter - Google Patents
Full seamless switching control method for passive off-line of energy storage converter Download PDFInfo
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- CN113131527B CN113131527B CN202110403276.4A CN202110403276A CN113131527B CN 113131527 B CN113131527 B CN 113131527B CN 202110403276 A CN202110403276 A CN 202110403276A CN 113131527 B CN113131527 B CN 113131527B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/001—Methods to deal with contingencies, e.g. abnormalities, faults or failures
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/388—Islanding, i.e. disconnection of local power supply from the network
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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
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
Abstract
The invention discloses a full seamless switching control method for passive off-grid of an energy storage converter, belonging to the technical field of energy storage system research, comprising an additional current ring, a voltage ring and an inductive current ring which are used for controlling the energy storage converter, wherein the inductive current inner ring and the additional current outer ring are used for adjusting during grid-connected operation to realize the control of output current; when the island operates, the additional current loop exits, and is adjusted by the voltage outer loop and the inductive current inner loop to realize the control of the output voltage; during island detection, the output of the controller in the voltage loop and the output of the controller in the additional current loop are matched with each other, so that the inductor current loop is stably output, the rated voltage of the output of the inverter is maintained, and voltage support is provided for a load. The invention ensures the continuity of the whole process by adjusting the structure of the controller and ensures that the energy storage converter can be seamlessly switched to an island mode when the passive disconnection occurs.
Description
Technical Field
The invention relates to the technical field of energy storage system research, in particular to a full seamless switching control method for passive off-line of an energy storage converter, which is used for carrying out seamless switching control on the energy storage converter under the passive off-line condition.
Background
With the rapid and continuous development of society and economy, the demand for energy sources is increasing, and because new energy sources such as wind energy, solar energy and the like have the advantages of cleanness, renewability and the like, new energy source power generation projects such as wind power generation, photovoltaic power generation and the like represented by the new energy sources become important research. However, wind energy, solar energy and the like have the characteristics of obvious randomness and intermittence, and the large-scale grid-connected operation brings problems to the stable operation and load allocation of a power grid, and even causes major accidents due to the impact on a local power grid.
The energy storage system has the functions of inhibiting power fluctuation, clipping peaks and filling valleys and the like, so that the stability of a power grid can be improved; the energy storage converter is used as the core of the whole energy storage system, energy bidirectional transfer between a direct current side and an alternating current power grid can be realized, and control of power of the grid side, smooth switching between grid connection and an island mode and the like can be realized through a control strategy.
When the power grid breaks down, the energy storage converter is passively disconnected from the grid, the grid-connected operation is switched to the island operation after the island detection, and the traditional inverter in the process needs to be switched between voltage control and current control, so that serious transient impact and vibration can be generated, and serious damage can be caused to important loads in the system. Therefore, the concept of seamless switching (seamless transition) was first proposed by the scholart Tirumala and other scholars in 2002, and the single-phase grid-connected inverter based on the LC filtering proposes a smooth switching scheme for grid-connected operation and off-grid independent operation, which is important for ensuring the power supply reliability of sensitive and critical loads and the continuous stability of the uninterruptible ac power supply.
The research on seamless handover is largely divided into two types: one is active disconnection from the grid actively according to the specific conditions of the user, and the other is forced disconnection caused by grid faults, which is also called passive disconnection. In recent years, researches on seamless switching are going on, but most researches are on active disconnection without island detection, and few researches on passive disconnection seamless switching are made, so that researches on a seamless switching control strategy of passive disconnection of an energy storage converter are of great significance.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a full seamless switching control method for the passive off-line of the energy storage converter, which can realize that the energy storage converter can be smoothly and seamlessly switched to an island operation mode when the passive off-line occurs by changing the structure of a controller, so that the impact caused by uncontrollable voltage during island detection is not generated, and the stable and uninterrupted power supply of a user load is realized.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a full seamless switching control method for passive off-grid of an energy storage converter is characterized in that a controller with a three-ring structure formed by combining an additional current ring, a voltage ring and an inductive current ring is adopted to control the energy storage converter; the control of the output current is realized by the adjustment of an inductive current inner ring and an additional current outer ring during the grid-connected operation; when the island operates, the additional current loop exits, and the voltage outer loop and the inductive current inner loop are used for adjusting to realize the control of the output voltage; during island detection, the output of the controller in the voltage loop and the output of the controller in the additional current loop are matched with each other, so that the inductive current loop is stably output, the rated voltage output by the inverter is maintained, and voltage support is provided for a load; the energy storage converter can be seamlessly switched to an island mode when the passive off-grid occurs.
The technical scheme of the invention is further improved as follows: the energy storage converter comprises energy storage power supplies V connected in sequence dc Neutral point clamped three-level inverter, LC filter, and load R Load On/off network switch S u An alternating current side power grid protection switch STS and a power grid; the energy storage converter has three operating states: in island mode of operation, andunder the condition that the grid operation mode is changed into the island operation mode, the grid operation mode is changed into the island operation mode through the control switch S 1 And S 2 To select a control method; on-off switch S u When the grid protection switch STS is disconnected with an alternating-current side, the grid protection switch STS works in an island operation mode, and the energy storage converter provides electric energy for a load; on-off switch S u When the AC side power grid protection switch STS is closed, the energy storage converter works in a grid-connected operation mode and is connected with a power grid; the specific control takes d axis as an example and is as follows:
will output a reference value i of the current dref And an output current i od Via a control switch S 1 Then sending the current into the additional current loop; through the additional current loop controller G Ⅱ Rear output Δ I d With the current i of the grid gd Added and then connected to a control switch S 2 ；
Output value i of the voltage ring Rd 、ΔI d And the grid current i gd Adding and adding the capacitance current i Cd Form the reference value of the inductor current
And the current value i of the inductor at that time Ld Subtracting the phase and sending the phase difference into an induction current ring; through the inductor current loop controller G Ⅰ Then inputting the data into an SVPWM modulation module;
the voltage ring is matched with the additional current ring and the additional current ring, wherein the voltage ring is used as a voltage controller to participate in voltage regulation when Ctrl =0, and is used as a retainer to maintain an output value at the last moment when Ctrl =1, and the controller in the voltage ring keeps the current output quantity i Rd (t) is expressed as:
in the formula i Rd (t-1) represents the previous time output value of the controller in the voltage loop, u dref Is an output of an inverterD-axis component, u, of the voltage reference value od Is the d-axis component, G, of the inverter output voltage v Is a voltage controller, G v ＝k vp +k vi /s。
The technical scheme of the invention is further improved as follows: the full seamless switching control method for the passive off-line of the energy storage converter comprises the following steps:
in the formula i Cd 、i Cq For filtering the capacitor current i Cabc D-q axis component of (d 1) od 、u oq For an inverter output voltage u oabc The dq-axis component of (a), ω is the angular frequency of the inverter, C f Is a filter capacitor;
then d-axis inductor current reference value
Expressed as:
in the formula i Rd Is the output of the controller in the voltage loop, i Cd For filtering the capacitor current i Cabc D-axis component of (C), ω being the angular frequency of the inverter, C f Is a filter capacitor, u oq For an inverter output voltage u oabc Q-axis component of (a);
wherein part of the inductor current is referenced to i Rd The voltage ring controls the output voltage to a rated voltage u by regulation dref Rated voltage support is provided for the load, and matching with actual load current is realized; the other part is referred to as the steady-state value-omega C of the d-axis capacitance current f ·u oq This portion is output by the q-axis voltage u oq Determining, i.e. depending on, the q-axis output rated voltage u qref (ii) a Therefore, the inductor current reference value in the case of islanding
Influenced by a voltage loop and controlled by voltage;
in the formula i Rd Is the output of the controller in the voltage loop, ω is the angular frequency of the inverter, C f As filter capacitance, u oq For an inverter output voltage u oabc Q-axis component of (i) gd For grid current i gabc D-axis component of (1), Δ I d The output of the controller is the additional current loop;
wherein the first part of the inductor current is referenced to i Rd Keeping the same; the second part is referred to as the steady-state value-omega C of the d-axis capacitance current f ·u oq This portion outputs a voltage u from the q-axis oq Determining that the clamping is the power grid voltage during grid connection, so that the clamping is not influenced by a voltage loop; the third part is referred to as d-axis grid current feedforward i gd And d-axis output current i od (ii) related; last part reference Δ I d Adding the output quantity of the controller in the current loop to the d axis and also adding the output current i to the d axis od Therefore, under the condition of grid connection, the additional current loop can realize the control of the output current;
when the grid is connected, the inverter works in a current control mode and outputs given active and reactive power values P n +jQ n The current reference value is calculated as formula (5):
in the formula i dref 、i qref For dq component of inverter output current reference value, u od 、u oq For an inverter output voltage u oabc The dq axis component of (1);
step 4, when the power grid fails, the energy storage converter needs to be switched from a grid-connected operation mode to an island operation mode, and at the moment, the current i of the power grid gabc When the current is zero, the energy storage converter is forced to be disconnected; the power grid side protection switch STS in the energy storage converter is immediately disconnected, island detection is started according to an island detection algorithm, ctrl in the auxiliary voltage ring is controlled to be still kept at 1 in the period of time, and the output of the controller in the voltage ring is still kept at i Rd Without change, while controlling the switch S in the additional current loop 1 When the system is disconnected, the additional current loop is not regulated any more, and the output quantity of the additional current loop keeps delta I when the system is connected to the power grid d Keeping the reference value of the inductor current unchanged, and keeping the reference value of the inductor current of the d axis unchanged
Changed from formula (4):
in the formula i Rd Is the output of the controller in the voltage loop, ω is the angular frequency of the inverter, C f Is a filter capacitor, u oq For inverter output voltage u oabc Q-axis component of (1), Δ I d The output of the controller is the additional current loop;
if the load remains unchanged throughout the process,. DELTA.I d The controller output quantity delta I in the additional current loop is used for compensating the fluctuation of load current in actual operation, but the fluctuation is small in the steady-state operation process of grid connection d Almost zero, the influence on the system can be ignored, then equation (6) can be simplified to equation (3) in case of island, i is in the island detection time Rd The output quantity of the part is always matched with the actual load current control quantity, so that rated voltage support can be provided for the load, and the phenomenon of voltage runaway in an island detection period is avoided;
if the load changes in the grid-connected operation, the output quantity delta I of the additional current loop is increased in the grid-connected operation d Changes occur which are not only used to compensate for fluctuations in the load current during actual operation, but also primarily to compensate for changes in the grid current due to load changes, so that during islanding detection time, although i Rd No longer matched to the control quantity of the actual load current, but through the output quantity deltaI d After compensation, make i Rd And Δ I d The sum of the voltage and the current of the actual load is matched with the current control quantity of the actual load after the load changes, and the voltage support can still be provided for the load, so that the output of the rated voltage of the inverter in the island detection time is maintained;
and after the island detection is finished, ctrl =0 in the voltage loop is controlled, and meanwhile, the switch S is switched 2 And (4) switching off, changing the voltage into island operation again, readjusting by the controller in the voltage ring, generating a control quantity matched with the current of the load at the moment, and realizing the control of the voltage.
The technical scheme of the invention is further improved as follows:
due to the adoption of the technical scheme, the invention has the technical progress that:
1. the invention can realize seamless switching of the energy storage converter during passive off-line through the mutual matching control among the voltage loop, the additional current loop and the inductance current loop, wherein the additional current loop has the following functions: firstly, an additional current loop controls the output current to a current reference value, so that constant power control under the condition of grid connection can be realized; secondly, when the grid is connected, the controller output quantity in the voltage loop keeps a fixed value, but the control quantity corresponding to the load current in actual operation slightly fluctuates, and the d-axis grid current correspondingly changes when the load changes, and at the moment, the additional current loop compensates the variable quantity in real time, so that the anti-interference capacity of the system can be improved.
2. According to the invention, by changing the structure of the controller, when the power grid fails, the energy storage converter can be switched to a voltage control mode without being influenced by island detection time; the output of the controller in the voltage ring and the output of the controller in the additional current are mutually matched during island detection, so that the output of the inductance current ring is stable, the rated voltage of the inverter is maintained, and voltage support is provided for a load, thereby solving the problem of voltage runaway during island detection.
3. The whole control process of the invention has continuity, so that the control mode can be smoothly switched, the balance of power in the energy storage converter is ensured, seamless passive disconnection of the energy storage converter is realized, and a solution is provided for realizing uninterrupted power supply of a load.
Drawings
FIG. 1 is a block diagram of the overall strategy for seamless handover control according to the present invention;
FIG. 2 is a block diagram of a specific strategy for controlling d-axis full seamless switching in the invention;
FIG. 3 is a timing diagram for mode switching of the present invention;
FIG. 4 is a graph of the voltage waveform output by the inverter when the energy storage converter is in parallel connection with the grid disconnection and an enlarged graph of the voltage waveform before and after the grid disconnection;
FIG. 5 is a load current waveform diagram of current waveforms before and after passive disconnection of the energy storage converter in the present invention;
fig. 6 is a grid-connected current waveform diagram of current waveforms before and after the energy storage converter is passively disconnected.
Wherein, V dc Is a direct currentA side energy storage power supply; c 1 、C 2 Two filter capacitors at the direct current side; l is f 、C f Respectively a filter inductor and a filter capacitor; l is g 、R g Respectively the equivalent inductance and resistance of the power grid line; r Load Load for the user; i all right angle gabc Is passing through L g 、R g Grid-connected current flowing through the power grid; i.e. i Cabc Is the current flowing through the filter capacitor; i all right angle Load Is the current flowing into the load; i all right angle Labc For flowing through the filter inductance L f A current on the substrate; i.e. i oabc Is the output current of the inverter after passing through the LC filter; u. u oabc Is the output voltage of the inverter, and is also a filter capacitor C f A voltage of; u. of g Is the grid side voltage; PCC denotes a point of common attachment; STS is an AC side power grid protection switch; s. the u Is an on/off network switch. i all right angle Ld 、i Lq For passing filter inductor current i Labc The dq axis component of (c); i.e. i Cd 、i Cq For filtering the capacitor current i Cabc The dq axis component of (1); i.e. i od 、i oq Is the output current i of the inverter after passing through an LC filter oabc The dq axis component of (1); i all right angle gd 、i gq For grid current i gabc The dq axis component of (1);
is the dq axis component of the reference value of the current flowing through the filter inductor; i.e. i dref 、i qref A dq component of the current reference value is output for the inverter; u. of od 、u oq For inverter output voltage u oabc The dq axis component of (1); u. of dref 、u qref A dq axis component that is an inverter output voltage reference; theta is the grid phase obtained by the phase-locked loop PLL; i all right angle Rd Is the output of the controller in the voltage loop; delta I d The output of the controller is the additional current loop; s. the 1 And S 2 Is a control switch; g v As a PI controller in a voltage loop, G v ＝k vp +k vi /s；G I Is a PI controller in the inductor current loop, G I ＝k Ip +k Ii /s；G II Is a PI controller in the inductor current loop, G II ＝k IIp +k IIi /s。
Detailed Description
The invention is described in further detail below with reference to the following figures and examples:
as shown in fig. 1, a Power Conversion System (PCS) includes an energy storage power supply V dc Neutral Point Clamped (NPC) three-level inverter, LC filter, and load R Load On/off network switch S u The system comprises an alternating current side power grid protection switch STS and a power grid. On-off switch S u When the grid protection switch STS is disconnected with an alternating-current side, the grid protection switch STS works in an island operation mode, and the energy storage converter provides electric energy for a load; on-off switch S u When the AC side power grid protection switch STS is closed, the energy storage converter works in a grid-connected operation mode, and is connected with a power grid.
The d-axis specific control block diagram of the full seamless switching overall control strategy block diagram in fig. 1 is shown in fig. 2, and comprises an additional current loop for outputting a reference value i of the current ref And an output current i o Via a control switch S 1 Then sending into an additional current loop; via an additional current loop controller G Ⅱ Post-output delta I and grid current I g Adding and then switching in a control switch S 2 ；
Output value i of simultaneous voltage loop R Δ I and grid current I g Adding and adding the capacitance current i C Form the reference value of the inductor current
And the current value i of the inductor at this time L Subtracting the phase and sending the phase difference into an induction current ring; through the inductor current loop controller G Ⅰ Then inputting the pulse width modulation signal into an SVPWM module;
the voltage loop is used as a voltage controller to participate in voltage regulation when Ctrl =0, is used as a retainer when Ctrl =1, maintains an output value at the last moment, and controls the current output quantity i of the voltage loop controller Rd (t) is expressed as:
in the formula i Rd (t-1) represents the previous time output value of the controller in the voltage loop, u dref D-axis component, u, of the reference value of the output voltage of the inverter od Is the d-axis component, G, of the inverter output voltage v Is a voltage controller, G v ＝k vp +k vi /s。
The energy storage converter has three operating states: under the conditions of an island operation mode, a grid-connected operation mode and a conversion from the grid-connected operation mode to the island operation mode, the control switch S is used 1 And S 2 The control method is selected. The specific implementation mode of the full seamless switching control method for the passive off-line of the energy storage converter is as follows:
in the formula i Cd 、i Cq For filtering the capacitor current i Cabc Dq axis component of (u) od 、u oq For an inverter output voltage u oabc The dq-axis component of (a), ω is the angular frequency of the inverter, C f Is a filter capacitor;
reference value of d-axis inductance current
Expressed as:
in the formula i Rd Is the output of the controller in the voltage loop, i Cd For filtering the capacitor current i Cabc D-axis component of (a), ω being the angular frequency of the inverter, C f As filter capacitance, u oq For inverter output voltage u oabc Q-axis component of (a);
wherein part of the inductor current is referenced to i Rd The voltage ring controls the output voltage to a rated voltage u by regulation dref Rated voltage support is provided for the load, and matching with actual load current is realized; the other part is referred to as the steady-state value-omega C of the d-axis capacitance current f ·u oq This portion is output by the q-axis voltage u oq Determining, i.e. depending on, the q-axis output rated voltage u qref . Therefore, the inductor current reference value in the case of islanding
Influenced by the voltage loop, is voltage control.
And 2, under the condition of grid-connected operation, assuming that the output power of an inverter in the energy storage converter is greater than the load power during grid connection. The grid side protection switch STS in fig. 1 is automatically closed, and after synchronous grid connection control, the switch S in fig. 1 is closed u While Ctrl =1 is controlled in fig. 2, the original controller G in the voltage loop is used V Keeping the controller in the voltage loop to output i under islanding Rd Is not changed and controls the switch S 1 And S 2 Closing the switch, adjusting by the additional current loop and the inductive current loop to control the output current, and obtaining the d-axis inductive current reference value
Expressed as:
in the formula i Rd Is a voltageThe output of the controller in the loop, ω, is the angular frequency of the inverter, C f Is a filter capacitor, u oq For inverter output voltage u oabc Q-axis component of (i) gd For grid current i gabc D-axis component of (1), Δ I d Looping the controller output for additional current;
wherein the first part of the inductor current is referenced to i Rd Keeping the original shape; the second part is referred to as the steady-state value- ω C of the d-axis capacitance current f ·u oq This portion outputs a voltage u from the q-axis oq Determining that the clamping is the power grid voltage when the grid is connected, so that the clamping is not influenced by a voltage loop; the third part is referred to as d-axis grid current feedforward i gd And d-axis output current i od (ii) related; last part reference Δ I d Adding the output quantity of the controller in the current loop to the d axis and also adding the output current i to the d axis od Accordingly, the additional current loop can control the output current in the case of grid connection.
When the grid is connected, the inverter works in a current control mode and outputs given active and reactive power values P n +jQ n . The current reference value is calculated according to formula (5):
in the formula i dref 、i qref For dq component of inverter output current reference value, u od 、u oq For inverter output voltage u oabc The dq axis component of (c);
step 4, when the power grid fails, the energy storage converter needs to be switched from a grid-connected operation mode to an island operation mode, and at the moment, the current i of the power grid is gabc And when the current is zero, the energy storage converter is forced to be disconnected. In the attached figure 1, a power grid side protection switch STS is immediately disconnected, and island detection is started according to an island detection algorithm. Ctrl in FIG. 2 is controlled to remain at 1 during this time, and the controller output in the voltage loop remains at i Rd Without change, while controlling the switch S 1 When the system is disconnected, the additional current loop is not regulated any more, and the output quantity of the additional current loop keeps delta I when the system is connected to the power grid d Keeping the given reference value of the inductive current unchanged, wherein the reference value of the d-axis inductive current is kept unchanged
Changed from formula (4):
in the formula i Rd Is the output of the controller in the voltage loop, ω is the angular frequency of the inverter, C f As filter capacitance, u oq For inverter output voltage u oabc Q-axis component of (1), Δ I d The output of the controller is the additional current loop;
if the load remains unchanged throughout the process,. DELTA.I d The controller output quantity delta I in the additional current loop is used for compensating the fluctuation of load current in actual operation, but the fluctuation is small in the steady-state operation process of grid connection d Almost zero, the influence on the system can be ignored, then equation (6) can be simplified to equation (3) in the case of islanding, i is in islanding detection time Rd The output quantity of the part is always matched with the actual load current control quantity, rated voltage support can be provided for the load, and the phenomenon that the voltage is out of control in an island detection period is avoided.
If the load changes in the grid-connected operation, the output quantity delta I of the additional current loop is increased in the grid-connected operation d Changes occur which are used not only to compensate for fluctuations in the load current during actual operation, but also primarily to compensate for changes in the grid current due to load changes. Therefore, during the islanding detection time, although i Rd No longer matched to the control quantity of the actual load current, but through the output quantity deltaI d After compensation, make i Rd And Δ I d The sum of the voltage and the current control quantity of the actual load after the load changes is matched, voltage support can be still provided for the load, and the output of the rated voltage of the inverter in the island detection time is maintained.
After the island detection is finished, ctrl =0 is controlled, and meanwhile, a switch S is switched 2 Disconnecting, changing into island operation again, and generating electricityAnd the controller in the pressure ring readjusts to generate a control quantity matched with the load current at the moment, so that the voltage is controlled.
The timing diagram for the mode switching of the control method obtained from the above analysis is shown in FIG. 3, at t 1 ～t 2 In the island detection time, the output of the controller in the voltage ring and the output of the controller in the additional current are matched with each other, so that the output of the inductance current ring is stable, the rated voltage of the inverter is maintained, the voltage support is provided for the load, the energy storage converter is not influenced by the island detection time when in passive off-line, and the seamless switching of the passive off-line is realized.
In order to verify the correctness of the analysis control method in the steps, matlab/simulink simulation is carried out on the circuit. The specific parameters in the simulation circuit are as follows: DC voltage V dc =600V, rated active power P n =50kW, rated reactive power Q n =0kvar, output ac line voltage V ac =380V, output frequency f n =50Hz, filter inductance L f =3mH, filter capacitance C f =20uF, a load of 30kW was initially added.
In the whole simulation process, the energy storage converter is connected to the grid in 1s and then operates in a grid-connected mode, the power grid fails in 3.5s, and the energy storage converter operates in an island mode after 20ms of island detection.
The operation simulation results are shown in fig. 4, 5 and 6:
FIG. 4 is an enlarged diagram of the waveform of the output voltage of the energy storage converter before and after disconnection, FIG. 5 is a load current waveform diagram of the output current waveform of the energy storage converter before and after passive disconnection,
fig. 6 is a grid-connected current waveform diagram of current waveforms before and after the energy storage converter is passively off-grid.
As can be seen from fig. 4, 5, and 6, the energy storage converter does not generate a runaway phenomenon of voltage and current within an islanding detection time, and can smoothly and seamlessly switch from grid-connected operation to islanding operation without generating impact.
In conclusion, the invention can realize seamless switching of the energy storage converter during passive disconnection through the mutual matching control among the voltage loop, the additional current loop and the inductance current loop, has continuity in the whole control process, ensures smooth switching of control modes, ensures the balance of power in the energy storage converter, realizes seamless passive disconnection of the energy storage converter and provides a solution for realizing uninterrupted power supply of a load.
Claims (2)
1. A full seamless switching control method for passive off-line of an energy storage converter is characterized by comprising the following steps: the energy storage converter is controlled by a controller with a three-ring structure formed by combining an additional current ring, a voltage ring and an inductive current ring; the control of the output current is realized by the adjustment of an inductive current inner ring and an additional current outer ring during grid-connected operation; when the island operates, the additional current loop exits, and is adjusted by the voltage outer loop and the inductive current inner loop to realize the control of the output voltage; during island detection, the output of the controller in the voltage loop and the output of the controller in the additional current loop are matched with each other, so that the inductive current loop is stably output, the rated voltage output by the inverter is maintained, and voltage support is provided for a load; the energy storage converter can be seamlessly switched to an island mode when passive off-grid occurs;
the energy storage converter comprises an energy storage power supply V which are connected in sequence dc Neutral point clamped three-level inverter, LC filter, and load R Load On/off network switch S u An alternating current side power grid protection switch STS and a power grid; the energy storage converter has three operating states: under the conditions of an island operation mode, a grid-connected operation mode and a conversion from the grid-connected operation mode to the island operation mode, the control switch S is used 1 And S 2 To select a control method; on-off switch S u When the alternating-current side power grid protection switch STS is disconnected, the device works in an island operation mode, and the energy storage converter provides electric energy for a load; on-off switch S u When the AC side power grid protection switch STS is closed, the energy storage converter works in a grid-connected operation mode and is connected with a power grid; the specific control takes d axis as an example and is as follows:
will output a reference value i of the current dref And an output current i od Via a control switch S 1 Then sending the current into the additional current loop; throughController G in the additional current loop Ⅱ Rear output Δ I d With the current i of the grid gd Adding and then switching in a control switch S 2 ；
The output value i of the voltage loop Rd 、ΔI d And the grid current i gd Adding and adding the capacitance current i Cd Form the reference value of the inductor current
And the current value i of the inductor at this time Ld Subtracting and sending the difference into an inductance current loop; through the inductor current loop controller G Ⅰ Then inputting the signal into an SVPWM modulation module;
the voltage ring is matched with the additional current ring and the additional current ring, wherein the voltage ring is used as a voltage controller to participate in voltage regulation when Ctrl =0, and is used as a retainer to maintain an output value at the last moment when Ctrl =1, and the controller in the voltage ring keeps the current output quantity i Rd (t) is expressed as:
in the formula i Rd (t-1) represents the previous-time output value of the controller in the voltage loop, u dref For the d-axis component, u, of the inverter output voltage reference od Is the d-axis component, G, of the inverter output voltage v Is a voltage controller, G v ＝k vp +k vi /s。
2. The full seamless switching control method for the passive off-grid of the energy storage converter according to claim 1, characterized in that: the full seamless switching control method for the passive off-line of the energy storage converter specifically comprises the following steps:
step 1, under the condition of island operation, a power grid side protection switch STS and a switch S of an energy storage converter u Are all disconnected, at the moment, controlCtrl =0 in the voltage loop and switch S in the additional current loop 1 And S 2 The additional current loop is disconnected, the additional current loop quits running and is regulated by the voltage outer loop and the inductive current inner loop together, and the control of the output voltage is realized; in steady state, the filter capacitor C f The relationship between voltage and current is represented on the d-q axis as:
in the formula i Cd 、i Cq For filtering the capacitor current i Cabc D-q axis component of (d 1) od 、u oq For inverter output voltage u oabc The dq-axis component of (a), ω is the angular frequency of the inverter, C f Is a filter capacitor;
reference value of d-axis inductance current
Expressed as:
in the formula i Rd Is the output of the controller in the voltage loop, i Cd For filtering the capacitor current i Cabc D-axis component of (a), ω being the angular frequency of the inverter, C f As filter capacitance, u oq For inverter output voltage u oabc Q-axis component of (a);
wherein part of the inductor current is referenced to i Rd The voltage ring controls the output voltage to a rated voltage u by regulation dref Rated voltage support is provided for the load, and matching with actual load current is realized; the other part is referred to as the steady-state value-omega C of the d-axis capacitance current f ·u oq This portion is output by the q-axis voltage u oq Determining, i.e. depending on, the q-axis output rated voltage u qref (ii) a Therefore, the reference value of the inductor current in case of islanding
Influenced by a voltage loop and controlled by voltage;
step 2, under the condition of grid-connected operation, assuming that the output power of an inverter in the energy storage converter is greater than the load power during grid connection, a power grid side protection switch STS in the energy storage converter is automatically closed, and a switch S is closed after synchronous grid connection control u While Ctrl =1 is controlled in the voltage loop, using the original controller G in the voltage loop V Keeping the controller in the voltage loop to output i under islanding Rd Does not change and controls the switch S in the additional current loop 1 And S 2 Closing the switch, adjusting by the additional current loop and the inductive current loop to control the output current, and obtaining the d-axis inductive current reference value
Expressed as:
in the formula i Rd Is the output of the controller in the voltage loop, ω is the angular frequency of the inverter, C f As filter capacitance, u oq For an inverter output voltage u oabc Q-axis component of (i) gd For grid current i gabc D-axis component of (1), Δ I d The output of the controller is the additional current loop;
wherein the first part of the inductor current is referenced to i Rd Keeping the original shape; the second part is referred to as the steady-state value-omega C of the d-axis capacitance current f ·u oq This portion outputs a voltage u from the q-axis oq Determining that the clamping is the power grid voltage during grid connection, so that the clamping is not influenced by a voltage loop; the third part is referred to as d-axis grid current feedforward i gd And d-axis output current i od Related to; last part reference Δ I d Adding the output quantity of the controller in the current loop to the d axis and also adding the output current i to the d axis od In connection with this, the additional current loop can thus be implemented for the output in the case of a grid connectionControlling the current;
when the grid is connected, the inverter works in a current control mode and outputs given active and reactive power values P n +jQ n The current reference value is calculated as formula (5):
in the formula i dref 、i qref For dq component of inverter output current reference value, u od 、u oq For an inverter output voltage u oabc The dq axis component of (1);
step 3, when the power grid fails, the energy storage converter needs to be switched from a grid-connected operation mode to an island operation mode, and at the moment, the current i of the power grid gabc When the current is zero, the energy storage converter is forced to be disconnected; the power grid side protection switch STS in the energy storage converter is immediately disconnected, island detection is started according to an island detection algorithm, ctrl in a control voltage ring is still kept to be 1 in the period of time, and the output of a controller in the voltage ring is still kept to be i Rd Without change, while controlling the switch S in the additional current loop 1 When the system is disconnected, the additional current loop is not regulated any more, and the output quantity of the additional current loop keeps delta I when the system is connected to the power grid d Keeping the given reference value of the inductive current unchanged, wherein the reference value of the d-axis inductive current is kept unchanged
Changed from formula (4):
in the formula i Rd Is the output of the controller in the voltage loop, ω is the angular frequency of the inverter, C f As filter capacitance, u oq For an inverter output voltage u oabc Q-axis component of (1), Δ I d The output of the controller is the additional current loop;
if the load remains unchanged throughout the process,. DELTA.I d The controller output quantity delta I in the additional current loop is used for compensating the fluctuation of load current in actual operation, but the fluctuation is small in the steady-state operation process of grid connection d Almost zero, the influence on the system can be ignored, then equation (6) is simplified to equation (3) in case of islanding, i during islanding detection time Rd The output quantity of the part is always matched with the actual load current control quantity, so that rated voltage support can be provided for the load, and the phenomenon of voltage runaway in an island detection period is avoided;
if the load changes in the grid-connected operation, the output quantity delta I of the additional current loop is increased in the grid-connected operation d Changes occur which are not only used to compensate for fluctuations in load current during actual operation, but also primarily used to compensate for changes in grid current due to load changes, so that during islanding detection time, although i Rd No longer matched to the control quantity of the actual load current, but through the output quantity deltaI d After compensation, make i Rd And Δ I d The sum of the voltage and the current of the actual load is matched with the current control quantity of the actual load after the load changes, and the voltage support can still be provided for the load, so that the output of the rated voltage of the inverter in the island detection time is maintained;
and after the island detection is finished, ctrl =0 in the voltage loop is controlled, and the switch S is switched simultaneously 2 And (4) switching off, changing the voltage into island operation again, readjusting by the controller in the voltage ring, generating a control quantity matched with the current of the load at the moment, and realizing the control of the voltage.
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