CN114865935B - Carrier mixed pulse width modulation strategy control method of modularized multi-level converter - Google Patents
Carrier mixed pulse width modulation strategy control method of modularized multi-level converter Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
- H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/539—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency
- H02M7/5395—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency by pulse-width modulation
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
The invention discloses a carrier mixed pulse width modulation strategy control method of a modularized multi-level converter, which comprises the following steps of obtaining a modularized multi-level converter submodule trigger pulse signal through comparison with a reference signal; based on CCSC technology, adjusting the carrier signal; the reference signal acquisition method comprises the steps that a modular multilevel converter obtains reference voltages on all bridge arms through a power inner ring, a voltage outer ring and a circulation suppression ring; and then the reference voltage is multiplied by a proportion coefficient and then is compared with the novel carrier mixed pulse width carrier to obtain a pulse signal. According to the characteristics of the carrier wave, through the simulation of theory, under the condition that the modulation wave is an ideal sine wave, compared with the carrier wave lamination technology, the ripple wave of the capacitance voltage of the submodule of the modularized multi-level converter is smaller; compared with the carrier phase shifting technology, the modularized multi-level converter has smaller switching frequency and smaller switching loss.
Description
Technical Field
The invention relates to the technical field of power electronics, in particular to a carrier mixed pulse width modulation strategy control method of a modularized multi-level converter.
Background
With the rapid development of the economy in China, the consumption of electric energy is continuously increased, the energy problem is increasingly prominent, and the development of cleaner and more efficient renewable energy sources is promoted, but renewable energy sources such as wind energy, solar energy and the like are generally remote or occupy larger geographic space, and the development has larger limitation, so how to grid-connect the new energy sources to an electric transmission and distribution network through a stable and reliable circuit topology becomes an important subject of the current research. Among the converters, the modularized multi-level converter (modular multilevel converter) has the advantages of high modularization, low switching frequency, low output harmonic content and the like, and has been widely focused in the academic fields at home and abroad especially in the fields of high-voltage direct-current transmission, renewable energy grid connection and the like.
The modulation technology is used as the basis of the operation of the modularized multi-level converter, and takes on the task of converting a modulation signal into a switching signal of an IGBT on a sub-module, thereby directly influencing the running condition of the converter and the balance control of capacitor voltage. Currently, there are two main modulation schemes for modular multilevel converters in the existing literature, namely, the latest level approximation modulation (NEARESTLEVEL MODULATION, NLM) and the multicarrier-based pulse width modulation. In the multi-carrier-based pulse width modulation technology, carrier phase-shift pulse width modulation (CARRIER PHASE-shifted pulse width modulation, CPS-PWM) and carrier stacked pulse width modulation (CARRIER LEVEL-shifted pulse width modulation, CLS-PWM) are classified according to the form of carrier distribution. The latest level approximation modulation approximates the modulation wave by calculating the number of submodules required to be input at each moment, and is suitable for occasions with larger submodules. The pulse width modulation technology based on multi-carrier has advantages compared with the recent level approximation modulation under the scene of less submodules. When carrier phase-shifting modulation is used, trigger pulses of all sub-modules are close and switching frequencies are consistent, so that power distribution is more balanced compared with a pulse width modulation method based on multiple carriers, and capacitance voltage ripple amplitude of the sub-modules is smaller. However, since the carrier amplitude is always greater than or equal to the modulation wave amplitude, the switching frequency of carrier phase-shift modulation is greater and the switching loss is greater than in the multi-carrier-based pulse width modulation method. In the carrier wave lamination modulation technology, various improved methods are provided for the capacitance voltage ripple of the submodule, and the essence of the improved methods is that trigger pulses of different submodules are more uniformly redistributed on the premise of not changing the original duty ratio, so that the effect of equalizing the voltage of the submodule is achieved.
In the existing two main forms in the carrier form, the switching frequency and the capacitance voltage of the submodule have obvious difference, and the two main forms are in an opposite situation, so that a novel carrier form is provided, two factors are balanced by researching one of the two methods, and more references and choices are provided for the modulation method.
Disclosure of Invention
This section is intended to outline some aspects of embodiments of the application and to briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section as well as in the description of the application and in the title of the application, which may not be used to limit the scope of the application.
The present invention has been made in view of the problems occurring in the prior art.
Therefore, the technical problem to be solved by the invention is how to reduce the switching frequency of the submodule of the modularized multi-level converter and reduce the ripple wave of the capacitance voltage of the submodule.
In order to solve the technical problems, the invention provides the following technical scheme: a carrier mixed pulse width modulation strategy control method of a modularized multi-level converter comprises the following steps,
Obtaining a trigger pulse signal of a submodule of the modularized multi-level converter through comparison with a reference signal;
The carrier signal is adjusted based on CCSC techniques.
As the preferable scheme of the carrier mixed pulse width modulation strategy control method of the modularized multi-level converter, the invention comprises the following steps: the method for acquiring the reference signal comprises the steps of,
The modularized multi-level converter obtains the reference voltage on each bridge arm through the power inner ring, the voltage outer ring and the circulation suppression ring;
And then the reference voltage is multiplied by a proportion coefficient and then is compared with a carrier wave to obtain a pulse signal.
As the preferable scheme of the carrier mixed pulse width modulation strategy control method of the modularized multi-level converter, the invention comprises the following steps: performing periodic cyclic configuration on the obtained pulse signals;
and finally, respectively corresponding the obtained pulse signals to sub-modules in the modularized multi-level converter.
The system judges according to the active power and reactive power of the direct current side and the alternating current side, determines the energy amount to be inverted, determines the active power and the non-active power, measures the voltage of the alternating current end, obtains the reference currents Id and Iq of the alternating current end under a dq coordinate system through a dq conversion power calculation formula, collects the current of the alternating current side, obtains the actual currents Id and Iq through dq change, carries out PI regulation on the actual currents Id and Iq, carries out decoupling control on the actual currents Id and Iq, obtains bridge arm reference voltages Vd and Vq under the dq coordinate system, and obtains the voltage under the three-phase coordinate system through dq reverse conversion; meanwhile, because the circulation has a negative sequence frequency doubling component, the three-phase negative sequence circulation is adopted to carry out the dq conversion of frequency doubling, PI control with 0 is carried out on the frequency doubling quantity in the obtained circulation reference current, the reference voltage under the influence of the circulation is obtained by the same method, and the component is subtracted from the original Vd and Vq, so that the influence of frequency doubling in the current conversion is reduced. And finally, comparing the obtained reference voltage with a carrier wave after per unit to form N groups of PWM trigger pulse signals, and triggering trigger pulses to the sub-modules one by one in a power frequency period by using a pulse width modulation pulse sequence to realize voltage equalizing of the sub-modules so as to finally realize inversion of the modularized multi-level converter.
As the preferable scheme of the carrier mixed pulse width modulation strategy control method of the modularized multi-level converter, the invention comprises the following steps: according to the number N of the sub-modules in the modularized multi-level converter, the number of the required carriers is determined, the carriers are arranged in a group by group in an up-down stacking mode, and in-phase stacking is performed in a triangular wave mode.
N is the number of sub-modules of an upper bridge arm or a lower bridge arm of each phase in the modularized multi-level converter.
As the preferable scheme of the carrier mixed pulse width modulation strategy control method of the modularized multi-level converter, the invention comprises the following steps:
The carrier wave forming link comprises: designing a group of carriers, taking per unit value as an example, wherein the amplitude variation of one group of triangular carriers is [00.50] and the other group of amplitude variation is [0.510.5], and the frequency of the triangular carriers is set to be 1KHz;
And determining the carrier group number N/2 according to the submodule number N, enabling each group of carriers to sequentially move away from a 2/N triangular carrier period, namely a 4 pi/N phase angle, and then comparing the carrier periods with the modulated waves to generate N groups of PWM modulated signals.
As the preferable scheme of the carrier mixed pulse width modulation strategy control method of the modularized multi-level converter, the invention comprises the following steps: when the N groups of PWM pulse trigger signals are generated, the first period of the first sub-module uses pulse signals obtained by comparing the carrier signal 1 with the modulated wave, the second period uses pulse signals obtained by comparing the carrier signal 2 with the modulated wave, and the like, N different trigger pulse signals are given to the N sub-modules.
As the preferable scheme of the carrier mixed pulse width modulation strategy control method of the modularized multi-level converter, the invention comprises the following steps: the two groups of continuous pulse signals need to be pulse signals obtained by comparing carrier waves with modulation waves in a carrier wave lamination state.
As the preferable scheme of the carrier mixed pulse width modulation strategy control method of the modularized multi-level converter, the invention comprises the following steps:
the formation link of the modulated wave signal comprises:
by using direct power control of loop current inhibition, the current of the frequency doubling component in the loop current can be reduced, so that the ripple wave of the capacitor voltage in the submodule is inhibited, and the expression of the reference modulation signal is as follows:
Wherein, And/>The switching functions of the ith sub-module of the j-phase upper bridge arm and the j-phase lower bridge arm are respectively set;
Where j e { a, b, c }, i e {1,2, …, N }, U cap is the submodule capacitor voltage.
As the preferable scheme of the carrier mixed pulse width modulation strategy control method of the modularized multi-level converter, the invention comprises the following steps: the voltage equalizing control link of the capacitance and the voltage of the submodule comprises that the trigger signal on the submodule is circulated every time a power frequency period passes.
As the preferable scheme of the carrier mixed pulse width modulation strategy control method of the modularized multi-level converter, the invention comprises the following steps:
the control strategy is divided into the following steps:
giving reference active and reactive power, and obtaining reference voltages of upper and lower bridge arms of each phase through direct power control and circulation suppression control;
Dividing the reference voltage by the DC side voltage amplitude to obtain the per unit value of the modulated wave, comparing the modulated wave with a carrier wave, outputting 0 when the carrier wave is Yu Diaozhi wave amplitude, outputting 1 when the carrier wave amplitude is Yu Diaozhi wave amplitude, and obtaining the trigger pulse of the sub-module;
And distributing pulses to each sub-module through cyclic sequencing of the N groups of obtained signal pulses.
The invention has the beneficial effects that:
1. According to the characteristics of the carrier wave, through the simulation of theory, under the condition that the modulation wave is an ideal sine wave, compared with the carrier wave lamination technology, the ripple wave of the capacitance voltage of the submodule of the modularized multi-level converter is smaller; compared with the carrier phase shifting technology, the modularized multi-level converter has smaller switching frequency and smaller switching loss.
2. In order to reduce the loop current more preferably, loop current suppression control is generally used. Under CCSC working conditions, the modulation wave can have high-frequency oscillation due to the action of PI, the carrier wave lamination technology with the original advantages of the switching frequency can obviously rise due to small carrier wave amplitude, the switching frequency and the carrier wave phase shifting technology have a smaller gap compared with an ideal sinusoidal modulation wave due to larger amplitude when the carrier wave encounters the oscillation.
3. The carrier pulse sequence has a slow switching period, does not increase the complexity of a control circuit additionally, and is easy to realize.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the description of the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art. Wherein:
Fig. 1 is a waveform diagram of a capacitor voltage of upper and lower bridge arms controlled by carrier stack in a first embodiment.
Fig. 2 is a waveform diagram of a capacitor voltage of upper and lower bridge arms for carrier phase shift control in the first embodiment.
Fig. 3 is a waveform diagram of the capacitor voltage of the upper and lower bridge arms of the carrier mixed modulation control in the first embodiment.
Fig. 4 is a graph showing comparison between loop waveforms in carrier stacked control and loop waveforms in carrier mixed modulation control in the first embodiment.
Fig. 5 is a diagram of a carrier wave mixed modulation waveform and a modulation waveform in the first embodiment.
Fig. 6 is a schematic diagram of a direct power control strategy in a second embodiment.
Fig. 7 is a schematic diagram of a loop current suppression control strategy in the second embodiment.
Fig. 8 is a schematic diagram of a carrier signal and a modulated wave signal in a second embodiment.
Fig. 9 is a schematic diagram of a modular multilevel converter structure in a second embodiment.
Detailed Description
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways other than those described herein, and persons skilled in the art will readily appreciate that the present invention is not limited to the specific embodiments disclosed below.
Further, reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic can be included in at least one implementation of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments.
Example 1
Referring to fig. 1 to 5, a first embodiment of the present invention provides a carrier hybrid pulse width modulation strategy control method for a modular multilevel converter.
Obtaining a trigger pulse signal of a submodule of the modularized multi-level converter through comparison with a reference signal;
The carrier signal is adjusted based on CCSC techniques.
The method of acquiring the reference signal includes,
The modularized multi-level converter obtains the reference voltage on each bridge arm through the power inner ring, the voltage outer ring and the circulation suppression ring;
And then the reference voltage is multiplied by a proportion coefficient and then is compared with a carrier wave to obtain a pulse signal.
Performing periodic cyclic configuration on the obtained pulse signals;
and finally, respectively corresponding the obtained pulse signals to sub-modules in the modularized multi-level converter.
According to the number N of the sub-modules in the modularized multi-level converter, the number of the required carriers is determined, the carriers are arranged in a group by group in an up-down stacking mode, and in-phase stacking is performed in a triangular wave mode.
N is the number of sub-modules of an upper bridge arm or a lower bridge arm of each phase in the modularized multi-level converter.
The carrier wave forming link comprises: designing a group of carriers, taking per unit value as an example, wherein the amplitude variation of one group of triangular carriers is [00.50] and the other group of amplitude variation is [0.510.5], and the frequency of the triangular carriers is set to be 1KHz;
And determining the carrier group number N/2 according to the submodule number N, enabling each group of carriers to sequentially move away from a 2/N triangular carrier period, namely a 4 pi/N phase angle, and then comparing the carrier periods with the modulated waves to generate N groups of PWM modulated signals.
When N groups of PWM pulse trigger signals are generated, the first period of the first sub-module uses pulse signals obtained by comparing the carrier signal 1 with the modulated wave, the second period uses pulse signals obtained by comparing the carrier signal 2 with the modulated wave, and the like, N different trigger pulse signals are given to N sub-modules.
The two groups of continuous pulse signals need to be pulse signals obtained by comparing carrier waves with modulation waves in a carrier wave lamination state.
The formation link of the modulated wave signal includes:
by using direct power control of loop current inhibition, the current of the frequency doubling component in the loop current can be reduced, so that the ripple wave of the capacitor voltage in the submodule is inhibited, and the expression of the reference modulation signal is as follows:
wherein, And/>The switching functions of the ith submodule of the j-phase upper bridge arm and the j-phase lower bridge arm are respectively represented by ' j ' epsilon { a, b, c }, i ' epsilon {1,2, …, N }, and U cap is the capacitance voltage of the submodule.
The voltage equalizing control link of the capacitance and the voltage of the sub-module comprises that the trigger signal on the sub-module is circulated every time a power frequency period passes.
The control strategy is divided into the following steps:
giving reference active and reactive power, and obtaining reference voltages of upper and lower bridge arms of each phase through direct power control and circulation suppression control;
Dividing the reference voltage by the DC side voltage amplitude to obtain the per unit value of the modulated wave, comparing the modulated wave with a carrier wave, outputting 0 when the carrier wave is Yu Diaozhi wave amplitude, outputting 1 when the carrier wave amplitude is Yu Diaozhi wave amplitude, and obtaining the trigger pulse of the sub-module;
And distributing pulses to each sub-module through cyclic sequencing of the N groups of obtained signal pulses.
Taking a 4-submodule as an example, a pulse width modulation pulse sequence of the lower bridge arm five-level modularized multi-level converter is shown in the following table:
| SMs | cycle 1 | cycle 2 | cycle 3 | cycle 4 |
| SML1 | g′L1 | g′L2 | g′L3 | g′L4 |
| SML2 | g′L2 | g′L3 | g′L4 | g′L1 |
| SML3 | g′L3 | g′L4 | g′L1 | g′L2 |
| SML4 | g′L4 | g′L1 | g′L2 | g′L3 |
the specific implementation process comprises the following steps:
Firstly, the system judges according to the active power and reactive power of a direct current side and an alternating current side, determines the energy size to be inverted, determines the active power and the non-active power, measures the voltage of an alternating current end, obtains reference currents Id and Iq of the alternating current end under a dq coordinate system through a dq conversion power calculation formula, collects the current of the alternating current side, obtains actual currents Id and Iq through dq change, carries out PI regulation on the actual currents Id and Iq, carries out decoupling control on the actual currents Id and Iq, obtains bridge arm reference voltages Vd and Vq under the dq coordinate axis, and obtains the voltage under a three-phase coordinate system through dq reverse conversion; meanwhile, because the circulation has a negative sequence frequency doubling component, the three-phase negative sequence circulation is adopted to carry out the dq conversion of frequency doubling, PI control with 0 is carried out on the frequency doubling quantity in the obtained circulation reference current, the reference voltage under the influence of the circulation is obtained by the same method, and the component is subtracted from the original Vd and Vq, so that the influence of frequency doubling in the current conversion is reduced. And finally, comparing the obtained reference voltage with a carrier wave after per unit to form N groups of PWM trigger pulse signals, and triggering trigger pulses to the sub-modules one by one in a power frequency period by using a pulse width modulation pulse sequence in order to realize the voltage equalizing of the sub-modules, so that the inversion of the modularized multi-level converter is finally realized, the switching frequency of the sub-modules is effectively reduced, and compared with a carrier wave lamination modulation means, the capacitance voltage ripple of the sub-modules is remarkably inhibited.
Example 2
Referring to fig. 6 to 9, a second embodiment of the present invention is based on the previous embodiment.
The converter is a modularized multi-level converter, the internal control mode is realized by switching the IGBTs on the internal submodules, and the source of the IGBT switching signals is the control mode of the modularized multi-level converter. The inner ring and the outer ring are controlled by just forming a PI closed loop on a control structure, the inner ring is controlled by current, the outer ring is controlled by voltage, and the inner ring is controlled by signals. The modular multilevel converter is externally controlled by energy, the modular multilevel converter is internally controlled by an inner ring and an outer ring, and the inner ring and the outer ring are both internal control signals, so that the modular multilevel converter is controlled as a whole.
The direct power control strategy includes: the component of the alternating current side voltage on the dq axis is obtained through collecting the alternating current side voltage and through abc/dq conversion, the reference current component of the alternating current output side on the dq axis is obtained after calculation with the reference active and reactive components, the reference voltage of the alternating current output side is obtained through PI regulator and decoupling link and dq/abc conversion, and finally the reference voltage of the upper bridge arm and the lower bridge arm of the converter is obtained through subtracting the direct current side voltage, so that the distribution of electric quantity is realized.
As shown in fig. 6, id and Iq are the reference components on the current dq axis of the current inner loop reference, respectively; p and Q are the active and reactive power of the reference, respectively; vd and Vq are respectively corresponding values of three-phase voltage at the distribution network side under the dq coordinate axis, and v * is the reference voltage at the alternating current output side; v dc is the voltage on the internal dc side of the modular multilevel converter; and Vn and Vu are references corresponding to the voltages of the upper bridge arm and the lower bridge arm of each item on the inversion side of the corresponding converter.
Id real-time tracking Id, PI is a controller, ABC/dq is a three-phase coordinate system transformed to dq coordinate system, wLg is a decoupling part, dq/ABC is coordinate system reconverted back to obtain reference voltage v in the controller, and then voltage reference signals Vn and Vu are given to the inside of the modularized multi-level converter, and control signals such as switching or switching are given to the control signals according to the voltage reference signals.
In the modularized multi-level converter, circulation is inevitably generated, the generation of the circulation can lead to the increase of the current in the converter, so that the capacity of the converter can be influenced, and in order to make the invention more economical, a control strategy of circulation inhibition is added.
The loop suppression strategy includes: in the modularized multi-level converter device, a circulation flow of energy exchange exists between an upper bridge arm and a lower bridge arm, fundamental frequency components on direct current and alternating current sides are divided, the most main harmonic component in the circulation flow is a negative sequence frequency doubling component, and a circulation flow inhibition strategy is used for reducing circulation flow fluctuation.
The control process is as shown in fig. 7, firstly, the currents i pj and i nj in the upper bridge arm and the lower bridge arm of the modularized multi-level converter are measured, the loop current of the bridge arm of the modularized multi-level converter is obtained after the current is added, and the three-phase coordinate system is converted into the dq coordinate system through the dq coordinate transformation. I 2fd and i 2fq in the dq coordinate system are obtained, similar to the current inner loop control, in order to minimize the double loop current, the reference value is set to 0, i.e. i 2fd-ref＝0、i2fq-ref =0, and the reference bridge arm voltage for suppressing the loop current in the dq coordinate system, i.e. u diffd-ref、udiffq-ref, is obtained through PI (k p+ki/S) control and decoupling control again. Finally, the reference voltage u diffj-ref for inhibiting the circulation in the three-phase system is obtained through the inverse transformation of the dq coordinate.
The final reference voltage signal udiffj-ref corresponding to the voltage reference signal Vn, vu minus the loop current suppressed is obtained as the final modulated wave signal, i.e. the modulated wave signal of the curve shown in fig. 8 below.
As shown in fig. 9, since the three-phase and single-phase modular multilevel converters are similar, only a single phase is drawn for illustration, and n=4 is selected in the example of the present invention.
It is important to note that the construction and arrangement of the application as shown in the various exemplary embodiments is illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters (e.g., temperature, pressure, etc.), mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter described in this application. For example, elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. Accordingly, all such modifications are intended to be included within the scope of present application. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. In the claims, any means-plus-function clause is intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the present applications. Therefore, the application is not limited to the specific embodiments, but extends to various modifications that nevertheless fall within the scope of the appended claims.
Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not be described (i.e., those not associated with the best mode presently contemplated for carrying out the invention, or those not associated with practicing the invention).
It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
It should be noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solution of the present invention may be modified or substituted without departing from the spirit and scope of the technical solution of the present invention, which is intended to be covered in the scope of the claims of the present invention.
Claims (4)
1. The carrier mixed pulse width modulation strategy control method of the modularized multi-level converter is characterized by comprising the following steps of: comprises the steps of,
Obtaining a trigger pulse signal of a submodule of the modularized multi-level converter through comparison with a reference signal;
Based on CCSC technology, adjusting the carrier signal;
The method for acquiring the reference signal comprises the steps of,
The modularized multi-level converter obtains the reference voltage on each bridge arm through the power inner ring, the voltage outer ring and the circulation suppression ring;
secondly, multiplying the reference voltage by a proportion coefficient, and comparing the reference voltage with the carrier wave to obtain a pulse signal;
Performing periodic cyclic configuration on the obtained pulse signals;
finally, respectively corresponding the obtained pulse signals to sub-modules in the modularized multi-level converter;
The system judges according to the active power and reactive power of the direct current side and the alternating current side, determines the energy amount to be inverted, determines the active power and the non-active power, measures the voltage of the alternating current end, obtains the reference currents Id and Iq of the alternating current end under a dq coordinate system through a dq conversion power calculation formula, collects the current of the alternating current side, obtains the actual currents Id and Iq through dq change, carries out PI regulation on the actual currents Id and Iq, carries out decoupling control on the actual currents Id and Iq, obtains bridge arm reference voltages Vd and Vq under the dq coordinate system, and obtains the voltage under the three-phase coordinate system through dq reverse conversion; meanwhile, as a negative sequence frequency doubling component exists in the circulation, the three-phase negative sequence circulation is adopted to carry out the dq conversion of frequency doubling, the obtained frequency doubling quantity in the circulation reference current is subjected to PI control with 0, the reference voltage under the influence of the circulation is obtained by the same, the component is subtracted from the original Vd and Vq, so that the influence of frequency doubling in the current conversion is reduced, the finally obtained reference voltage is compared with a carrier wave after per unit to form N groups of PWM trigger pulse signals, in order to ensure that the submodules are in voltage equalizing, a pulse width modulation pulse sequence is used, the trigger pulses are triggered to the submodules one by one according to a power frequency period, and finally the inversion of the modularized multi-level converter is realized;
According to the number N of the sub-modules in the modularized multi-level converter, determining the number of the required carriers, wherein the carriers are arranged in a mode of stacking up and down in pairs, and the carriers are stacked in the same phase in a triangular wave mode;
n is the number of sub-modules of an upper bridge arm or a lower bridge arm of each phase in the modularized multi-level converter;
The carrier wave forming link comprises: designing a group of carriers, taking per unit value as an example, wherein the amplitude variation of one group of triangular carriers is [00.50] and the other group of amplitude variation is [0.510.5], and the frequency of the triangular carriers is set to be 1KHz;
According to the number N of the submodules, the number N/2 of carrier groups is determined, each group of carriers is sequentially moved away from a 2/N triangular carrier period, namely, a 4 pi/N phase angle, and then is compared with a modulating wave to generate N groups of PWM modulating signals;
When the N groups of PWM pulse trigger signals are generated, a first period of a first sub-module uses pulse signals obtained by comparing a carrier signal 1 with a modulation wave, a second period of the first sub-module uses pulse signals obtained by comparing a carrier signal 2 with the modulation wave, and N different trigger pulse signals are given to N sub-modules by the same way;
the two groups of continuous pulse signals need to be pulse signals obtained by comparing carrier waves with modulation waves in a carrier wave lamination state.
2. The carrier hybrid pulse width modulation strategy control method of the modular multilevel converter of claim 1, wherein:
the formation link of the modulated wave signal comprises:
by using direct power control of loop current inhibition, the current of the frequency doubling component in the loop current can be reduced, so that the ripple wave of the capacitor voltage in the submodule is inhibited, and the expression of the reference modulation signal is as follows:
Wherein, And/>The switching functions of the ith sub-module of the j-phase upper bridge arm and the j-phase lower bridge arm are respectively set;
Where j e { a, b, c }, i e {1,2, …, N }, U cap is the submodule capacitor voltage.
3. The carrier hybrid pulse width modulation strategy control method of the modular multilevel converter of claim 2, wherein: the voltage equalizing control link of the capacitance and the voltage of the submodule comprises that the trigger signal on the submodule is circulated every time a power frequency period passes.
4. A carrier hybrid pulse width modulation strategy control method for a modular multilevel converter according to claim 3, wherein:
the control strategy is divided into the following steps:
giving reference active and reactive power, and obtaining reference voltages of upper and lower bridge arms of each phase through direct power control and circulation suppression control;
Dividing the reference voltage by the DC side voltage amplitude to obtain the per unit value of the modulated wave, comparing the modulated wave with a carrier wave, outputting 0 when the carrier wave is Yu Diaozhi wave amplitude, outputting 1 when the carrier wave amplitude is Yu Diaozhi wave amplitude, and obtaining the trigger pulse of the sub-module;
And distributing pulses to each sub-module through cyclic sequencing of the N groups of obtained signal pulses.
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