CN117240121A - Fault-tolerant control method for input-series-output parallel-type current source inverter - Google Patents
Fault-tolerant control method for input-series-output parallel-type current source inverter Download PDFInfo
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Abstract
The invention discloses a fault-tolerant control method for an input-series-output parallel-connection type current source inverter, which ensures the stable operation of the inverter under the single-tube open-circuit fault condition of the input-series-output parallel-connection type PWM current source inverter by actively shifting a reference current vector neutral point, and is based on the feedback control of the harmonic current of a power grid so as to inhibit the ferromagnetic resonance of a transformer and ensure the good waveform quality of grid-connected current.
Description
Technical Field
The invention relates to a fault-tolerant control method for an input-series-output parallel-connection type current source inverter, in particular to a control method for ensuring stable operation of the inverter under the single-tube fault condition of the input-series-output parallel-connection type PWM current source inverter, inhibiting ferromagnetic resonance of a transformer and ensuring good waveform quality of grid-connected current.
Background
The PWM current source type grid-connected inverter has the advantages of simple structure and control, good short circuit characteristic, high output waveform quality and the like, and is paid more attention to the fields of novel distributed power generation, energy storage, power grid trend regulation and control and the like. With the continuous increase of voltage and power levels, a single converter cannot meet the requirement of system capacity, and a modularized PWM current source inverter topology is gradually used for expanding the capacity of the system.
Compared with a single current source device, the modularized current source converter uses more power switching devices and has more potential fault points. The fault of the switching device not only can cause serious distortion of the waveform of the output current, but also can have adverse effect on the running stability of the power grid. In actual operation, open-circuit faults are more common due to the fact that a switching device is damaged, trigger pulses are lost, wiring looseness and the like. In addition, researches on current source type converters are focused on optimizing modulation methods, power distribution, common-mode voltage suppression and the like, and researches on fault-tolerant control of current sources are still few. Therefore, there is a need to propose fault tolerant control techniques for open circuit faults of the switching devices of the modular current source converter.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides a fault-tolerant control method for an input-series-output parallel PWM current source inverter, which is used for ensuring the stable operation of the inverter under the single-tube open-circuit fault condition of the input-series-output parallel PWM current source inverter by actively shifting a neutral point of a reference current vector and is based on the feedback control of the harmonic current of a power grid so as to inhibit the ferromagnetic resonance of the transformer and ensure the good waveform quality of the grid-connected current.
The invention aims at realizing the following technical scheme:
the fault-tolerant control method for the input-series-output parallel-type current source inverter comprises the following steps of:
(1) Actively shifting a neutral point of a reference current vector to ensure sine output of grid-connected current of the current source grid-connected inverter under a single-tube open-circuit fault condition;
(2) And extracting harmonic components in the power grid current, multiplying the harmonic components by a feedback coefficient, adding the feedback coefficient into the reference current, and realizing the inhibition of the ferromagnetic resonance of the transformer by using a harmonic current active damping method.
Further, the step (1) includes the following steps:
a) According to the level difference of the three-phase total PWM current, all the switch states of the input series output parallel PWM current source inverter are divided into 19 PWM current vectors (I 0 ～I 18 ) After the single-tube open-circuit fault of the inverter occurs, selecting an effective PWM current vector which can still be used for synthesizing a reference current vector according to a switching tube of an actual fault, and further determining an effective operation range of the reference current vector;
b) In order to only adopt the effective PWM current vector, the neutral point of the original reference current vector is actively shifted so that the reference current vector operates in the effective operation range;
c) Superimposing the active offset vector in the modulator to the offset reference current vector:
wherein,for active offset vector, +.>For the active offset current reference vector, +.>Is the actual current reference vector for fault tolerant modulation;
d) Determining an active offset vector from an actual failed switching tubeAnd selecting an effective PWM current vector to generate a corresponding gate-level driving signal on the basis of meeting the ampere-second balance principle, thereby controlling the action of the power switch device.
Further, the step (2) includes the steps of:
a) Current i of three-phase power grid g Transforming the three-phase abc coordinate system into two-phase alpha beta coordinate system to obtain i gα And i gβ And is connected with a reference currentAnd->Comparing, realizing fundamental current control by PR controller, adding reference current feedforward and PR controller output to obtain fundamental current modulation input i α_ref1 And i β_ref1 ：
Wherein k is p 、k r And omega r Proportional parameter, resonance parameter and frequency bandwidth, omega of PR controller 0 Is the fundamental angular frequency of the current;
b) Current i of the power grid gα And i gβ Cut-off frequency of omega c The high-pass filter of (2) filters the fundamental wave and multiplies the fundamental wave by a feedback coefficient k to obtain a harmonic current modulation input i α_ref2 And i β_ref2 ：
The suppression of the ferromagnetic resonance of the transformer is realized by utilizing the active damping of harmonic current;
c) Adding the two modulated currents to obtain the final reference current i α_ref And i β_ref And transforming the two-phase alpha beta coordinate system back to the three-phase abc coordinate system to obtain a reference current
d) Space vector modulation is carried out according to the running condition of the current source inverter: during normal operation, reference currentCan be directly used for modulation; in case of a single tube fault, the reference current is +_in accordance with the description in step (1)>Middle-superimposed active offset vectorAnd then modulating.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
the fault-tolerant control method for the input-series output-parallel PWM current source inverter is adopted, the stable operation of the inverter is ensured under the single-tube fault condition of the inverter, the ferromagnetic resonance of the transformer is restrained, and the good waveform quality of the grid-connected current is ensured.
Drawings
Fig. 1 is a schematic diagram of an input-series-output parallel PWM current source inverter according to an embodiment of the present invention.
Fig. 2a and 2b are current space vector diagrams of the input-series output-parallel PWM current source inverter in normal operation and under single-tube open-circuit fault conditions, respectively.
Fig. 3 is a schematic diagram of an input-series-output-parallel current source topology and fault-tolerant control method.
Fig. 4a and 4b are respectively simulation waveforms of grid-connected current without adding harmonic current active damping control and with adding harmonic current active damping control when switching from normal operation to single-tube open-circuit fault.
Fig. 4c and fig. 4d are respectively the harmonic spectra of the steady-state grid-connected current without adding the harmonic current active damping control and with adding the harmonic current active damping control when the single-tube open circuit fault occurs.
Detailed Description
The fault-tolerant control method for the input-series-output-parallel current source inverter of the present invention is described in further detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Fig. 1 is a circuit diagram of a specific embodiment of the present invention, wherein CSC1 and CSC2 are two three-phase inverter full bridges composed of SGCT (symmetric gate commutated thyristor), and the two inverter bridges are connected in series on the dc side, and connected in parallel on the grid side after passing through respective LC filters and a three-winding transformer on the ac side.
The fault-tolerant control method for the input-series output-parallel current source inverter comprises the following basic steps:
step 1: according to the constraint condition of the current source converter: at any time, each full bridge has and only two devices are conducted, one is located in the upper half bridge, and the other is located in the lower half bridge. Under the constraint condition, the switching state of the input-series-output parallel PWM current source inverter can be divided into 19 PWM current vectors (I 0 ～I 18 ) The three-phase total PWM current level and the switching state corresponding to each current vector are shown in table 1, and the current space vector diagram is shown in fig. 2 a.
Table 1 current vector and corresponding switching state for input series output parallel PWM current source inverter
( And (3) injection: the switch states are represented by four digits separated by a colon, the first two digits representing the two on-switch device numbers in CSC1 and the second two digits representing the two on-switch device numbers in CSC2 )
When the single tube of the current source converter fails, taking an S1 open circuit failure in CSC1 as an example, since S1 cannot trigger conduction, part of the current vector cannot be used for synthesizing the reference current vector. All current vectors which cannot be used for synthesizing the reference current vector are indicated in table 1 in bold font, in which case the current vector I 1 、I 2 、I 7 Cannot be used for synthesizing reference vectors, I 8 、I 12 、I 13 ～I 18 I 0 The constant current vector also loses part of the switching state. The current space vector diagram is now shown in fig. 2b, the reference current vector can only run in the light gray area. The midpoint of the reference current vector is actively shifted, so that the circle center of the reference current vector is shifted from the original O point to the O' point and runs in the circle in the graph 2b, and the sinusoidal output of the network side current can be still maintained after the single tube fails. Wherein,for active offset vector, +.>For the current reference vector centered on O' after the active deflection, ">For the current reference vector which is actually synthesized in the modulation process and still takes the O point as the center of a circle, the three components meet (1-1)
And (3) superposing the active offset vector into the offset reference current vector in the modulator, namely switching from a normal modulation mode to a fault-tolerant modulation mode after S1 faults. Active offset vectorAccording to the actual faulty switching tube, table 2 gives the +.>Is an expression of (2).
TABLE 2 open circuit failure of different switching devices
And selecting an effective PWM current vector to generate a corresponding gate-level driving signal on the basis of meeting the ampere-second balance principle, thereby controlling the action of the power switch device.
Step 2: the topology structure of the input-series-output-parallel current source and the fault-tolerant control block diagram are shown in fig. 3. First, three-phase grid current i g Transforming the three-phase abc coordinate system into two-phase alpha beta coordinate system to obtain i gα And i gβ And is connected with a reference currentAndcomparing, realizing fundamental current control by PR controller, adding reference current feedforward and PR controller output to obtain fundamental current modulation input i α_ref1 And i β_ref1 ：
Wherein k is p 、k r And omega r Proportional parameter, resonance parameter and frequency bandwidth, omega of PR controller 0 Is the fundamental angular frequency of the current;
secondly, the grid current i gα And i gβ Cut-off frequency of omega c The high-pass filter of (2) filters the fundamental wave and multiplies the fundamental wave by a feedback coefficient k to obtain a harmonic current modulation input i α_ref2 And i β_ref2 ：
And the suppression of the ferromagnetic resonance of the transformer is realized by utilizing the active damping of harmonic current.
Then, the two modulated currents are added to obtain the final reference current i α_ref And i β_ref And transforming the two-phase alpha beta coordinate system back to the three-phase abc coordinate system to obtain a reference current
Finally, space vector modulation is carried out according to the running condition of the current source inverter: during normal operation, reference currentCan be directly used for modulation; in case of a single tube fault, the reference current is +_in accordance with the description in step (1)>Middle superimposed active offset vector +.>And then modulating.
Step 3: and constructing a 48kW input-series output-parallel current source inverter simulation model, and verifying the control method.
Fig. 4 (a) is a waveform diagram of an active damping three-phase grid-connected current without adding harmonic current in the process of switching the system from normal operation to single-tube fault tolerance control, and it can be seen that after switching to fault tolerance mode, the grid-connected current generates a large number of harmonic waves due to ferromagnetic resonance of the transformer, and the peak value of the grid-connected current is reduced. Fig. 4 (b) is a waveform diagram of three-phase grid-connected current when harmonic current active damping is added in the process of switching the system from normal operation to single-tube fault tolerance control, the grid-connected current is subjected to transient oscillation after the fault occurs, and the system quickly enters a steady state under the damping effect, and the whole process is only 30ms. After the transformer enters a steady state, the current waveform has good quality, and the ferromagnetic resonance of the transformer is obviously inhibited. Fig. 4 (c) and fig. 4 (d) are steady-state grid-connected current spectra for two cases, respectively. It can be seen that the grid current THD is reduced from 28.86% to 4.22% with harmonic current active damping.
In conclusion, the method can ensure that the input-series-output parallel PWM current source inverter stably operates under the single-tube fault condition, inhibit the ferromagnetic resonance of the transformer and ensure the good waveform quality of the grid-connected current.
The invention is not limited to the embodiments described above. The above description of specific embodiments is intended to describe and illustrate the technical aspects of the present invention, and is intended to be illustrative only and not limiting. Numerous specific modifications can be made by those skilled in the art without departing from the spirit of the invention and scope of the claims, which are within the scope of the invention.
Claims (3)
1. The fault-tolerant control method for the input-series-output parallel-type current source inverter is characterized by comprising the following steps of:
(1) Actively shifting a neutral point of a reference current vector to ensure sine output of grid-connected current of the current source grid-connected inverter under a single-tube open-circuit fault condition;
(2) And extracting harmonic components in the power grid current, multiplying the harmonic components by a feedback coefficient, adding the feedback coefficient into the reference current, and realizing the inhibition of the ferromagnetic resonance of the transformer by using a harmonic current active damping method.
2. The fault-tolerant control method for an input-series-output-parallel current source inverter according to claim 1, wherein the step (1) comprises the steps of:
a) According to the level difference of the three-phase total PWM current, all the switch states of the input series output parallel PWM current source inverter are divided into 19 PWM current vectors (I 0 ～I 18 ) After the single-tube open-circuit fault of the inverter occurs, selecting an effective PWM current vector which can still be used for synthesizing a reference current vector according to a switching tube of an actual fault, and further determining an effective operation range of the reference current vector;
b) In order to only adopt the effective PWM current vector, the neutral point of the original reference current vector is actively shifted so that the reference current vector operates in the effective operation range;
c) Superimposing the active offset vector in the modulator to the offset reference current vector:
wherein,for active offset vector, +.>For the active offset current reference vector, +.>Is the actual current reference vector for fault tolerant modulation;
d) Determining an active offset vector from an actually faulty switching tubeAnd selecting an effective PWM current vector to generate a corresponding gate-level driving signal on the basis of meeting the ampere-second balance principle, thereby controlling the action of the power switch device.
3. The fault-tolerant control method for an input-series-output-parallel current source inverter according to claim 1, wherein the step (2) comprises the steps of:
a) Current i of three-phase power grid g Transforming the three-phase abc coordinate system into two-phase alpha beta coordinate system to obtain i gα And i gβ And is connected with a reference currentAnd->Comparing, realizing fundamental current control by PR controller, adding reference current feedforward and PR controller output to obtain fundamental current modulation input i α_ref1 And i β_ref1 ：
Wherein k is p 、k r And omega r Proportional parameter, resonance parameter and frequency bandwidth, omega of PR controller 0 Is the fundamental angular frequency of the current;
b) Current i of the power grid gα And i gβ Cut-off frequency of omega c The high-pass filter of (2) filters the fundamental wave and multiplies the fundamental wave by a feedback coefficient k to obtain a harmonic current modulation input i α_ref2 And i β_ref2 ：
The suppression of the ferromagnetic resonance of the transformer is realized by utilizing the active damping of harmonic current;
c) Adding the two modulated currents to obtain the final reference current i α_ref And i β_ref And transforming the two-phase alpha beta coordinate system back to the three-phase abc coordinate system to obtain reference electricity
d) Space vector modulation is carried out according to the running condition of the current source inverter: during normal operation, reference currentCan be directly used for modulation; in case of a single tube failure, the reference current is +_according to the description in step (1)>Middle superimposed active offset vector->And then modulating.
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