CN113410979B - Carrier phase-shifting pulse width modulation method, controller and MMC cascade system - Google Patents
Carrier phase-shifting pulse width modulation method, controller and MMC cascade system 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
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
- H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
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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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Abstract
A carrier phase-shift pulse width modulation method, a controller and an MMC cascade system can simultaneously restrain internal circulation harmonic waves and output voltage harmonic waves. The method is applied to the topology of two MMC bridge arms, each MMC bridge arm comprises two half bridge arms, each half bridge arm comprises a plurality of sub-modules which are connected in sequence, and the method comprises the following steps: according to the parity of the number of the sub-modules corresponding to each half bridge arm, determining an interphase carrier phase difference meeting an output voltage harmonic suppression condition and a half bridge arm carrier phase difference meeting an internal circulation harmonic suppression condition, wherein the interphase carrier phase difference is used for representing corresponding carrier phase differences among different MMC bridge arms, and the half bridge arm carrier phase difference is used for representing corresponding carrier phase differences among different half bridge arms on the same MMC bridge arm. And then, determining the initial carrier phase corresponding to each submodule according to the inter-phase carrier phase difference and the half-bridge arm carrier phase difference, so as to generate a carrier signal of each submodule and control each submodule to operate, thereby driving each MMC bridge arm to output voltage.
Description
Technical Field
The application relates to the technical field of power transmission engineering, in particular to a carrier phase-shifting pulse width modulation method, a controller and an MMC cascade system.
Background
The Modular Multilevel Converter (MMC) has the characteristics of easiness in expansion, high reliability, good high-voltage access, flexible structure and the like, and is widely applied to various fields such as high-voltage direct-current power transmission, flexible multi-terminal networks, direct-current power distribution networks, ship power supply micro-networks and the like. The existing MMC usually adopts a carrier Pulse Width Modulation (PWM) method, but the conventional carrier pulse width modulation method cannot simultaneously suppress circulating current harmonics inside the MMC and switch sub-high frequency harmonics in output voltage, and needs to be additionally provided with a heat dissipation device to reduce heating loss or an output voltage filtering device to reduce the influence caused by the output voltage harmonics, thereby increasing the design difficulty of the MMC.
Disclosure of Invention
The present application is directed to solving at least one of the problems in the prior art. Therefore, the application provides a carrier phase-shift pulse width modulation method, a controller and an MMC cascade system, which can simultaneously inhibit internal circulating current harmonic waves and switch sub-high frequency harmonic waves in output voltage and reduce the design difficulty of the MMC.
According to a first aspect of the present application, a carrier phase shift pulse width modulation method is applied to a topology of two MMC bridge arms, each MMC bridge arm includes two half bridge arms, each half bridge arm includes a plurality of sequentially connected sub-modules, and the method includes:
acquiring the number of sub-modules corresponding to each half bridge arm;
according to the parity of the number of the sub-modules, determining an interphase carrier phase difference meeting an output voltage harmonic suppression condition and a half-bridge arm carrier phase difference meeting an internal circulation harmonic suppression condition, wherein the interphase carrier phase difference is used for representing corresponding carrier phase differences among different MMC bridge arms, and the half-bridge arm carrier phase difference is used for representing corresponding carrier phase differences among different half bridge arms on the same MMC bridge arm;
determining a carrier initial phase corresponding to each sub-module according to the inter-phase carrier phase difference and the half-bridge arm carrier phase difference;
generating a carrier signal of each sub-module according to the initial carrier phase corresponding to each sub-module;
and controlling each submodule to operate based on the carrier signal of each submodule so as to drive each MMC bridge arm to output voltage.
The carrier phase-shifting pulse width modulation method according to the embodiment of the application has at least the following beneficial effects:
in the embodiment of the application, the inter-phase carrier phase difference meeting the output voltage harmonic suppression condition and the half-bridge arm carrier phase difference meeting the internal circulating current harmonic suppression condition can be directly determined according to the parity of the number of the sub-modules on each half-bridge arm. The inter-phase carrier phase difference represents the corresponding carrier phase difference between different MMC bridge arms, and the half-bridge arm carrier phase difference is used for representing the corresponding carrier phase difference between different half bridge arms on the same MMC bridge arm. And the phase difference of the phase carriers between the phases is adjusted properly, so that the function of increasing the number of output levels between bridge arms can be achieved, and output voltage harmonics are restrained. Meanwhile, the appropriate half-bridge arm carrier phase difference is adjusted in a matched mode, so that the number of submodules, which are put into a single MMC bridge arm at any moment, is constant to N, and the suppression of circulation harmonics inside the MMC is further guaranteed. Therefore, the loss of the transformer, the switching device and the bridge arm inductance can be reduced, the vibration heating phenomenon caused by high output voltage harmonic waves is avoided, the high internal circulation harmonic waves are avoided, the available current capacity and the utilization rate of the inverter are reduced, the service life of the MMC is effectively prolonged, and the voltage stabilization control difficulty of the modular multilevel inverter is increased.
Based on the method, the initial phase of the carrier corresponding to the sub-modules on each half bridge arm is determined, online calculation is easy to realize, and the method can be applied to any engineering site. Furthermore, corresponding carrier signals are generated according to the initial carrier phases corresponding to the sub-modules to drive the sub-modules to operate, so that carrier phase shift pulse modulation for simultaneously restraining output voltage harmonics and internal circulation harmonics can be realized only by adjusting the initial carrier phases of the sub-modules, the design difficulty of the MMC is reduced, the MMC is directly suitable for the existing MMC, and additional control links, hardware cost and computing resource cost are not required to be added.
According to some embodiments of the invention, the determining the inter-phase carrier phase difference satisfying the output voltage harmonic suppression condition according to the parity of the number of the sub-modules comprises:
if the number N of the sub-modules is an odd number, determining that the phase difference of the interphase carrier meeting the output voltage harmonic suppression condition is zero, wherein N is a positive integer; if the number N of the sub-modules is an even number, determining that the phase difference of the interphase carrier meeting the output voltage harmonic suppression condition is
。
According to some embodiments of the invention, the determining a half-bridge arm carrier phase difference satisfying an internal circulating current harmonic suppression condition according to the parity of the number of the sub-modules comprises:
if the number N of the sub-modules is an odd number, the condition that the number of the sub-modules meets the requirement in the bridge arm is determinedThe half-bridge arm carrier phase difference under the condition of circulating current harmonic suppression is
N is a positive integer; and if the number N of the sub-modules is an even number, determining that the phase difference of the carrier wave of the half-bridge arm meeting the condition of restraining the circulating current harmonic wave in the bridge arm is zero.
According to some embodiments of the invention, the two MMC bridge legs are divided into a first bridge leg and a second bridge leg; the determining the initial carrier phase corresponding to each submodule according to the phase-to-phase carrier phase difference and the half-bridge arm carrier phase difference includes:
determining a target initial phase of a first sub-module in a first half bridge arm of the first bridge arm, and extending the initial phases of the carriers of the ith sub-module in the first half bridge arm forward relative to the initial phase of the carrier of the (i-1) th sub-module
，
；
Determining the initial carrier phase of a first submodule in a second half bridge arm of the first bridge arm according to the half bridge arm carrier phase difference and the initial target carrier phase, and extending the initial carrier phase of the ith submodule in the second half bridge arm relative to the initial carrier phase of the (i-1) th submodule
；
According to the inter-phase carrier phase difference and the target carrier initial phase, determining the carrier initial phase of a first submodule in a third half bridge arm of the second bridge arm, and extending the carrier initial phases of the ith submodule in the third half bridge arm to the carrier initial phases of the (i-1) th submodule
；
According to the half bridge arm loadDetermining the initial phase of the carrier of the first submodule in the fourth half bridge arm of the second half bridge arm according to the wave phase difference and the initial phase of the carrier of the first submodule in the third half bridge arm, and carrying out forward delay on the initial phase of the carrier of the ith submodule in the fourth half bridge arm relative to the initial phase of the carrier of the (i-1) th submodule
。
According to some embodiments of the invention, before controlling each sub-module to operate based on the carrier signal of each sub-module, the method further comprises:
acquiring a modulation signal of each submodule;
the carrier signal based on each submodule controls each submodule to operate so as to drive each MMC bridge arm to output voltage, and the method comprises the following steps:
comparing the modulation signal of each submodule with a carrier signal to generate a driving signal of each submodule; and controlling each submodule to operate according to the driving signal of each submodule so as to drive each MMC bridge arm to output voltage.
According to some embodiments of the present invention, the comparing the modulation signal of each sub-module with the carrier signal to generate the driving signal of each sub-module includes:
and carrying out waveform comparison on the modulation signal of each sub-module and the carrier signal, if the waveform amplitude of the modulation signal of the sub-module is greater than that of the carrier signal, generating a high-level driving signal, and if the waveform amplitude of the modulation signal of the sub-module is less than that of the carrier signal, generating a low-level driving signal.
According to some embodiments of the invention, the two MMC bridge legs are divided into a first bridge leg and a second bridge leg; the acquiring of the modulation signal of each sub-module includes:
acquiring an input initial modulation signal;
normalizing the initial modulation signal to obtain a normalized modulation signal;
taking the normalized modulation signals as modulation signals of each sub-module on a first half bridge arm of the first bridge arm and modulation signals of each sub-module on a fourth half bridge arm of the second bridge arm;
and carrying out negation processing on the normalized modulation signal to obtain a negated modulation signal, and taking the negated modulation signal as a modulation signal of each sub-module on the second half bridge arm of the first bridge arm and a modulation signal of each sub-module on the third half bridge arm of the second bridge arm.
A controller according to an embodiment of the second aspect of the invention comprises:
at least one processor;
at least one memory for storing at least one program;
when executed by the at least one processor, cause the at least one processor to implement a method for carrier phase shifting pulse width modulation as described in embodiments of the first aspect of the invention.
The MMC cascade system according to the third aspect of the present invention includes at least one MMC bridge arm group and at least one controller, each MMC bridge arm group includes two MMC bridge arms, each MMC bridge arm includes a plurality of sequentially connected sub-modules, and the controller is respectively connected to each sub-module to control the operation of each sub-module according to the carrier phase shift pulse width modulation method according to the first aspect of the present invention.
Additional aspects and advantages of the present application will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the present application.
Drawings
The above and/or additional aspects and advantages of the present application will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
fig. 1 is a schematic view of a topological structure of an MMC bridge-arm assembly in an embodiment of the present application;
fig. 2 is a schematic structural diagram of a half-bridge arm according to an embodiment of the present application;
FIG. 3 is a circuit diagram of a sub-module according to an embodiment of the present application;
FIG. 4 is a schematic diagram of an equivalent circuit of the MMC bridge-arm set shown in FIG. 1;
FIG. 5 is a schematic flow chart of a carrier phase shift pulse width modulation method according to an embodiment of the present application;
fig. 6 is a schematic flowchart illustrating a process of controlling operations of each sub-module based on a carrier signal of each sub-module in an embodiment of the present application;
FIG. 7 is a schematic diagram of an embodiment of another carrier phase-shifting pulse width modulation method disclosed in the embodiments of the present application;
FIG. 8 is a schematic diagram of harmonic components of the output voltage and internal circulating current when the carrier phase-shift PWM method of the embodiment of the present application is compared with a conventional carrier phase-shift PWM method;
FIG. 9 is a schematic diagram of waveforms of an output voltage and an internal circulating current when the carrier phase-shift PWM method of the embodiment of the present application is compared with a conventional carrier phase-shift PWM method;
fig. 10 is a schematic structural diagram of a controller disclosed in an embodiment of the present application.
Detailed Description
Reference will now be made in detail to embodiments of the present application, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are exemplary only for the purpose of explaining the present application and are not to be construed as limiting the present application.
In the description of the present application, the meaning of a plurality is one or more, the meaning of a plurality is two or more, and larger, smaller, larger, etc. are understood as excluding the present number, and larger, smaller, inner, etc. are understood as including the present number. If the first and second are described for the purpose of distinguishing technical features, they are not to be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated or implicitly indicating the precedence of the technical features indicated.
The embodiment of the application discloses a carrier phase-shifting pulse width modulation method, a controller and an MMC cascade system, which can play a role in inhibiting the high-frequency harmonic of a switch in output voltage and reduce the design difficulty of an MMC. The following detailed description is made with reference to the accompanying drawings.
In order to better understand the carrier phase shift pulse width modulation method disclosed in the embodiment of the present application, a system applied in the embodiment of the present application is described below.
In the embodiment of the application, the MMC cascade system comprises at least one MMC bridge arm group and at least one controller, each MMC bridge arm group comprises two MMC bridge arms, each MMC bridge arm comprises a plurality of sequentially connected sub-modules, and the number of the MMC bridge arm group, the sub-modules on each MMC bridge arm and the number of the controllers are not specifically limited. The controller can be respectively connected with each submodule to control the operation of each submodule according to the carrier phase-shifting pulse width modulation method.
Referring to fig. 1, fig. 1 is a schematic diagram of a topology structure of an MMC bridge-arm assembly according to an embodiment of the present disclosure. Taking fig. 1 as an example for illustration, the MMC bridge leg set includes two MMC bridge legs 100, i.e., a first bridge leg and a second bridge leg. Each MMC bridge leg 100 may specifically include two half-legs 110 connected in series, divided into an upper half-leg and a lower half-bridge leg, and thus fig. 1 includes, in total, a first half-leg PS1 and a second half-leg NS1 of the first bridge leg, and a third half-leg PS2 and a fourth half-leg NS2 of the second bridge leg. One end of the first half bridge arm PS1 is electrically connected to ac through a first self-coupled bridge arm inductance Lp1, the other end of the first half bridge arm PS1 is connected to the positive electrode of dc, one end of the second half bridge arm NS1 is electrically connected to ac through a second self-coupled bridge arm inductance Ln1, and the other end of the second half bridge arm NS1 is connected to the negative electrode of dc. One end of the third half bridge arm PS2 is connected to ac through a third self-coupled bridge arm inductance Lp2, the other end of the third half bridge arm PS2 is connected to the positive pole of dc, one end of the fourth half bridge arm NS2 is connected to ac through a fourth self-coupled bridge arm inductance Ln2, and the other end of the fourth half bridge arm NS2 is connected to the negative pole of dc. Vdc is the DC voltage value, and Vdc/2 is half of the DC voltage value.
The first and second self-coupled bridge arm inductors Lp1 and Ln1, and the third and fourth self-coupled bridge arm inductors Lp2 and Ln1 connected in series on the second bridge armLn2 may satisfy:
，
is the mutual inductance value of the adjacent bridge arm inductances.
Referring to fig. 2 and fig. 3, fig. 2 is a schematic structural diagram of a half bridge arm in an embodiment of the present application, and fig. 3 is a schematic circuit diagram of a sub-module in the embodiment of the present application. As shown in fig. 2 and 3, the half bridge arm 110 includes a plurality of sub-modules 111 connected in series, and the sub-modules 111 may be conventional half-bridge MMC sub-modules or full-bridge MMC sub-modules, for example, the half-bridge MMC sub-module is composed of two insulated-gate bipolar transistor (IGBT) power components and a parallel capacitor, each IGBT power component may also be connected with a diode component in parallel, and the on/off of the IGBT power components is controlled by a controller.
Therefore, the submodules on the bridge arms have alternate symmetry, voltage-sharing control over the submodules is easy to realize, and the operation stability of the MMC is facilitated. In addition, the equivalent conduction time of each submodule is consistent, so that the loss of each submodule is consistent, and later maintenance is facilitated.
Based on this, please refer to fig. 4, fig. 4 is an equivalent circuit diagram of the MMC bridge-arm set shown in fig. 1. As shown in fig. 4, the four half-bridge arms in the MMC bridge arm set can be equivalent to four ac voltage currents, i.e., vp1, vn1, vp2 and vn2, and the final output voltage of the MMC bridge arm set is then obtained
And Vo1 is the output voltage of the first bridge arm, and Vo2 is the output voltage of the second bridge arm.
The topology of the MMC bridge arm group is easy to expand, high in reliability, good in high-voltage access performance, flexible in structure, good in output characteristic and low in switching frequency. And based on the structure of the serial connection of the sub-modules, the structures of the single sub-modules are consistent, so that the mass production of the sub-modules is facilitated, the cost is reduced, and the structure scale of the MMC is expanded. In addition, the sub-modular structure is convenient for the design of redundant bypass, improves the reliability, further improves the capacity of accessing a high-voltage power grid through the series connection of a large number of sub-modules, and ensures good output characteristics through a plurality of output voltage levels.
It can be understood that the topology of the MMC arm set described above is suitable for the carrier phase shift pulse width modulation method disclosed in the embodiment of the present application. The carrier phase shift pulse width modulation method disclosed in the embodiments of the present application is described in detail below. Referring to fig. 5, fig. 5 is a schematic flow chart of a carrier phase shift pulse width modulation method according to an embodiment of the present application.
500. And acquiring the number of the submodules corresponding to each half bridge arm.
510. And determining the phase difference of the interphase carrier meeting the output voltage harmonic suppression condition and the phase difference of the half-bridge arm carrier meeting the internal circulating current harmonic suppression condition according to the parity of the number of the sub-modules.
In the embodiment of the present application, the inter-phase carrier phase difference is used to represent corresponding carrier phase differences between different MMC bridge arms. As an optional implementation manner, according to the parity of the number of sub-modules, determining the inter-phase carrier phase difference meeting the output voltage harmonic suppression condition may specifically be:
and if the number N of the sub-modules is an odd number, determining that the phase difference of the interphase carrier waves meeting the output voltage harmonic suppression condition is zero, wherein N is a positive integer. If the number N of the sub-modules is even, determining that the phase difference of the phase-to-phase carriers meeting the output voltage harmonic suppression condition is
。
Based on this, in a half switching period, at least one sub-module on one of the adjacent bridge arms executes a switching action (i.e., switching between on and off states), so that the output level number and the total equivalent switching frequency between the adjacent bridge arms are increased, and the suppression of output voltage harmonics, especially odd harmonics, is facilitated. And the effect is more obvious when the number of the sub-modules is less and the switching frequency is lower. Therefore, the problems that the MMC output performance is influenced by high output voltage, the quality of external electric energy is reduced, the service life of the transformer is shortened, and the malfunction of a protection device is caused by resonance with an external power network can be solved, the operation stability of the equipment is improved, a filter device does not need to be matched, and the design difficulty and the use cost are reduced.
In the embodiment of the present application, the half-bridge arm carrier phase difference is used to represent a corresponding carrier phase difference between different half-bridge arms on the same MMC bridge arm. As an optional implementation manner, the half-bridge arm carrier phase difference meeting the internal circulating current harmonic suppression condition is determined according to the parity of the number of the sub-modules, and specifically may be:
if the number N of the sub-modules is odd, determining that the phase difference of the carrier waves of the half-bridge arm meeting the condition of restraining the circulating current harmonic wave in the bridge arm is equal to
And N is a positive integer. And if the number N of the submodules is an even number, determining that the phase difference of the carrier waves of the half-bridge arms meeting the condition of restraining the circulating current harmonic waves in the bridge arms is zero.
Based on the method, the input number of the neutron modules of the single MMC bridge arm is N constantly at any moment, and the condition that the input number is N-1 and N +1 is avoided, so that voltage drop is not formed on the bridge arm self-coupling inductor, and internal circulation harmonics, particularly odd-numbered harmonics in the internal circulation, can be restrained. And the effect is more obvious when the number of the sub-modules is less and the switching frequency is lower. In addition, bridge arm current can be effectively reduced, and the current capacity and the loss of a switching device are reduced, so that the manufacturing cost and the maintenance cost of the MMC are reduced, and the voltage stabilization control difficulty of the MMC is improved.
It can be seen that, by implementing the step 510, the internal circulating current harmonic and the output voltage harmonic can be suppressed at the same time, and the operation stability of the MMC is further improved. Compared with the traditional carrier PWM circuit structure, the number of the sub-modules can be reduced by 50% to achieve the same output voltage level number, and the switching frequency of the sub-modules can be reduced by 50% to achieve the same overall equivalent switching frequency.
520. And determining the initial carrier phase corresponding to each submodule according to the inter-phase carrier phase difference and the half-bridge arm carrier phase difference.
530. And generating the carrier signal of each sub-module according to the initial carrier phase corresponding to each sub-module.
In this embodiment, specifically, the carrier amplitude, the frequency, and the signal type of each sub-module may be obtained first, and then the carrier signal of each sub-module may be generated according to the carrier amplitude, the frequency, the signal type, and the initial carrier phase. The carrier amplitude, frequency and signal type may be artificially set, and are not particularly limited. Illustratively, a regular isosceles triangle carrier signal having a carrier amplitude of 1V and a carrier frequency of a preset switching frequency may be generated. Therefore, the switching frequency of the MMC is consistent with the carrier frequency, and controllability of the switching frequency of the sub-module can be achieved.
540. And controlling each submodule to operate based on the carrier signal of each submodule so as to drive each MMC bridge arm to output voltage.
As an alternative embodiment, before step 540, the modulation signals of the sub-modules may also be obtained. Correspondingly, please refer to fig. 6, where fig. 6 is a schematic flow chart illustrating a process of controlling each sub-module to operate based on a carrier signal of each sub-module in the embodiment of the present application. As shown in fig. 6, step 540 may specifically include:
541. and comparing the modulation signal of each sub-module with the carrier signal to generate a driving signal of each sub-module.
Specifically, step 541 may be: and carrying out waveform comparison on the modulation signal of each sub-module and the carrier signal, if the waveform amplitude of the modulation signal of the sub-module is greater than that of the carrier signal, generating a high-level driving signal, and if the waveform amplitude of the modulation signal of the sub-module is less than that of the carrier signal, generating a low-level driving signal, thereby realizing carrier phase-shifting type pulse width modulation.
In some optional embodiments, the steps 510, 520, 530, and 541 may be performed by a Field Programmable Gate Array (FPGA) to implement the functions of setting the initial phase of the carrier, generating the carrier signal, and comparing the modulated signal with the carrier signal.
542. And controlling each submodule to operate according to the driving signal of each submodule so as to drive each MMC bridge arm to output voltage.
In the embodiment of the present application, the driving signal may be input to the driving circuit corresponding to each sub-module. Specifically, the sub-module includes an upper half IGBT power component and a lower half IGBT power component, and the driving signal generated in step 541 can be used as a driving gate signal of the upper half IGBT power component, for example, the driving signal is input to the a port shown in fig. 3. And inverting the driving signal to be used as a driving gate signal of the lower half IGBT power component, for example, inputting the inverted driving signal to a port b shown in fig. 3, thereby driving the sub-module to output a voltage.
Further, as an optional implementation manner, based on the MMC bridge-arm group shown in fig. 1, the obtaining of the modulation signal of each sub-module may specifically be further:
acquiring an input initial modulation signal, and normalizing the initial modulation signal to obtain a normalized modulation signal. The normalized modulation signals are used as the modulation signals of each submodule on the first half bridge arm PS1 and the modulation signals of each submodule on the fourth half bridge arm NS 2. And carrying out negation processing on the normalized modulation signals to obtain negated modulation signals, and taking the negated modulation signals as modulation signals of each submodule on the second half bridge arm NS1 and modulation signals of each submodule on the third half bridge arm PS 2.
Based on the voltage amplitude value of the output voltage of the first bridge arm and the output voltage of the second bridge arm are both 50% of the direct current voltage value Vdc, and the phases are opposite, so that the voltage output by the bridge arm group consisting of the first bridge arm and the second bridge arm is enabled to be opposite
Exactly equal to the dc voltage value Vdc.
Optionally, the normalization processing on the initial modulation signal may specifically adopt the following formula:
and S is the modulated signal after normalization,
is the initial modulation signal.
In some optional embodiments, step 520 may specifically be:
determining the initial phase of a target carrier of a first submodule in the first half bridge arm PS1, and extending the initial phases of the carriers of the ith submodule in the first half bridge arm PS1 forward relative to the initial phase of the carrier of the (i-1) th submodule
，
。
According to half-bridge arm carrier phase difference
And the initial phase of the target carrier
Determining the initial carrier phase of the first submodule in the second half bridge arm NS1
And the initial carrier phases of the ith sub-module in the second half bridge arm NS1 are all extended along with the initial carrier phases of the (i-1) th sub-module
. Specifically, the initial carrier phase of the first submodule in the second half-bridge arm NS1
Can satisfy
。
According to phase difference of carriers between phases
And the initial phase of the target carrier
Determining the initial phase of the carrier of the first submodule in the third half bridge arm PS2
And the initial phase of the carrier of the ith sub-module in the third half bridge arm PS2 is extended along with the initial phase of the carrier of the (i-1) th sub-module
. Specifically, the initial phase of the carrier of the first submodule in the third half-bridge arm PS2
Can satisfy
。
According to half-bridge arm carrier phase difference
And the initial phase of the carrier of the first submodule in the third half bridge arm PS2
Determining the initial carrier phase of the first submodule in the fourth half-bridge arm NS2
And the initial carrier phases of the ith sub-module in the fourth half bridge arm NS2 are all extended along with the initial carrier phases of the (i-1) th sub-module
. Specifically, the initial carrier phase of the first submodule in the fourth half-bridge arm NS2
Can satisfy
。
For example, taking the initial phase of the target carrier equal to 0 as an example, please refer to table 1, where table 1 is a table of initial phase calculation results of the carrier of the sub-module in the embodiment of the present application.
Table 1 submodule carrier initial phase calculation result table
For example, when N is 3, the initial carrier phases of the sub-modules of the first half-bridge arm PS1 are 0, and,
And
the initial carrier phases of all the submodules on the second half bridge arm NS1 are sequentially
、
And
the initial carrier phases of the submodules on the third half bridge arm PS2 are 0,
And
the initial carrier phases of all the submodules on the fourth half bridge arm NS2 are sequentially
、
And
。
for another example, when N is 4, the initial carrier phases of the sub-modules of the first half-bridge arm PS1 are 0,
、
And
the initial carrier phases of the submodules on the second half bridge arm NS1 are 0,
、
And
the initial carrier phases of all the sub-modules on the third half bridge arm PS2 are sequentially
、
、
And
the initial carrier phases of all the submodules on the fourth half bridge arm NS2 are sequentially
、
、
And
。
referring to fig. 7, fig. 7 is a schematic waveform diagram of a modulation signal and a carrier signal corresponding to each half bridge arm in the embodiment of the present application. As shown in fig. 7, the vertical axis Y of each coordinate system represents the normalized signal amplitude, and the horizontal axis ω t of the coordinate system represents the phase angle, where ω represents the angular frequency and t represents time. Taking the first half-bridge arm PS1 as an example, the carrier signal of the first sub-module in the first half-bridge arm PS1 can be generated
Carrier signal of the second submodule
Based on
Phase delay
Carrier signal of the third sub-module
Based on
Phase delay
. Based on this, the carrier signal of each sub-module is compared with the modulation signal of the first half bridge arm PS1 to obtain each sub-moduleThe driving signal of the module is used to drive the first half bridge arm PS1 to output voltage. The second half bridge arm PN1 and the first half bridge arm PS1 meet the requirement of half bridge arm carrier phase difference
The third half bridge arm PS2 and the first half bridge arm PS1 meet the requirement of phase-to-phase carrier phase difference
And the fourth half bridge arm PN2 and the third half bridge arm PS2 satisfy the half bridge arm carrier phase
Otherwise, reference may be made to the description of first half bridge leg PS 1.
In order to better understand the practical effect of the carrier phase shift pulse width modulation method applied to the two MMC bridge arm topologies in the embodiment of the present application, the following description is made in combination with experimental results.
Referring to fig. 8 and 9, fig. 8 is a schematic diagram of harmonic components of the output voltage and the internal circulating current when the carrier phase shift pwm method of the embodiment of the present application is compared with the conventional carrier phase shift pwm method, and fig. 9 is a schematic diagram of waveforms of the output voltage and the internal circulating current when the carrier phase shift pwm method of the embodiment of the present application is compared with the conventional carrier phase shift pwm method.
From the perspective of harmonic components, as shown in fig. 8, (a), (b), and (c) respectively show the output voltage of the MMC and the harmonic component of the internal circulating current when the conventional N +1 mode carrier phase-shift type pulse width modulation method (hereinafter, referred to as N +1 mode), the 2N +1 mode carrier phase-shift type pulse width modulation method (hereinafter, referred to as 2N +1 mode), and the carrier phase-shift type pulse width modulation method of the present application are used under the same operating conditions. It can be seen that there are more output voltage harmonic components in the N +1 mode and more internal circulating harmonic components in the 2N +1 mode. And the output voltage harmonic component and the internal loop current harmonic component of this application are all less, and through comparing total harmonic distortion value (THD), to output voltage THD: 7.07% (present application) < 7.24% (2N +1 mode) < 19.76% (N +1 mode), for internal circulating THD: 2.66% (the present application) < 2.67% (N +1 mode) < 28.39% (2N +1 mode), so the output voltage harmonic and the internal circulating current harmonic of the present application are both effectively suppressed.
As shown in fig. 9, (a), (b), and (c) respectively represent the output voltage and the internal circulating current waveform of the MMC when the N +1 mode, the 2N +1 mode, and the carrier phase-shift pulse width modulation method of the present application are used. It can be seen that the internal circulating current waveform of the N +1 mode is smooth but has a small number of output levels, and the internal circulating current waveform of the 2N +1 mode has a large number of output levels but contains too many switching order high frequency harmonics. By adopting the method and the device, more output level numbers can be realized and the smoothness of the internal circulation waveform can be ensured.
Therefore, by implementing the method embodiment, the appropriate interphase carrier phase difference and half-bridge arm carrier phase difference are adjusted in a matching manner, so that the loss of the transformer, the switching device and the bridge arm inductance can be reduced, the vibration heating phenomenon caused by high output voltage harmonic waves is avoided, the reduction of the available current capacity and the utilization rate of the inverter by high internal circulating current harmonic waves is avoided, the service life of the MMC is effectively prolonged, and the voltage stabilization control difficulty of the modular multilevel inverter is increased. In addition, still easily realize on-line computation, can be applied to arbitrary engineering scene, only need the carrier initial phase place of adjustment submodule piece can realize restraining output voltage harmonic and internal circulation harmonic's carrier phase shift pulse modulation simultaneously, can enough avoid generating heat and the vibrations phenomenon that high output voltage harmonic leads to, effectively prolong MMC's life, can reduce MMC's the design degree of difficulty again to directly be applicable to existing MMC, need not to increase extra control link, hardware cost and computational resource cost.
Referring to fig. 10, fig. 10 is a schematic structural diagram of a controller according to an embodiment of the present application, including:
at least one memory 1001;
at least one processor 1002 for executing at least one computer program stored in the memory 1001 to perform the methods described in the embodiments above.
It should be noted that, for the specific implementation process of the present embodiment, reference may be made to the specific implementation process described in the above method embodiment, and a description thereof is omitted here.
The present application provides a computer-readable storage medium, on which computer instructions are stored, and the computer instructions, when executed, make a computer execute the carrier phase shift pulse width modulation method described in the above method embodiments.
The embodiments of the present application also disclose a computer program product, wherein, when the computer program product runs on a computer, the computer is caused to execute part or all of the steps of the method as in the above method embodiments.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
While embodiments of the present application have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the application, the scope of which is defined by the claims and their equivalents.
Claims (8)
1. A carrier phase-shifting pulse width modulation method is applied to the topology of two MMC bridge arms, each MMC bridge arm comprises two half bridge arms, each half bridge arm comprises a plurality of sub-modules which are connected in sequence, and the method comprises the following steps:
acquiring the number of sub-modules corresponding to each half bridge arm;
according to the parity of the number of the sub-modules, determining an interphase carrier phase difference meeting an output voltage harmonic suppression condition and a half-bridge arm carrier phase difference meeting an internal circulation harmonic suppression condition, wherein the interphase carrier phase difference is used for representing corresponding carrier phase differences among different MMC bridge arms, and the half-bridge arm carrier phase difference is used for representing corresponding carrier phase differences among different half bridge arms on the same MMC bridge arm;
determining a carrier initial phase corresponding to each sub-module according to the inter-phase carrier phase difference and the half-bridge arm carrier phase difference;
generating a carrier signal of each sub-module according to the initial carrier phase corresponding to each sub-module;
controlling each submodule to operate based on the carrier signal of each submodule so as to drive each MMC bridge arm to output voltage;
the determining the phase difference of the interphase carrier meeting the output voltage harmonic suppression condition according to the parity of the number of the sub-modules comprises the following steps:
if the number N of the sub-modules is an odd number, determining that the phase difference of the interphase carrier meeting the output voltage harmonic suppression condition is zero, wherein N is a positive integer;
if the number N of the sub-modules is an even number, determining that the phase difference of the interphase carrier meeting the output voltage harmonic suppression condition is
。
2. The method of claim 1, wherein determining the half-bridge arm carrier phase difference satisfying the internal circulating current harmonic rejection condition according to the parity of the number of the sub-modules comprises:
if the number N of the sub-modules is odd, determining that the phase difference of the carrier waves of the half-bridge arm meeting the condition of restraining the circulating current harmonic wave in the bridge arm is equal to
N is a positive integer;
and if the number N of the sub-modules is an even number, determining that the phase difference of the carrier wave of the half-bridge arm meeting the condition of restraining the circulating current harmonic wave in the bridge arm is zero.
3. The method according to claim 1 or 2, wherein the two MMC bridge legs are divided into a first leg and a second leg; the determining the initial carrier phase corresponding to each submodule according to the phase-to-phase carrier phase difference and the half-bridge arm carrier phase difference includes:
determining a target initial phase of a first sub-module in a first half bridge arm of the first bridge arm, and extending the initial phases of the carriers of the ith sub-module in the first half bridge arm forward relative to the initial phase of the carrier of the (i-1) th sub-module
，
；
Determining the initial carrier phase of a first submodule in a second half bridge arm of the first bridge arm according to the half bridge arm carrier phase difference and the initial target carrier phase, and extending the initial carrier phase of the ith submodule in the second half bridge arm relative to the initial carrier phase of the (i-1) th submodule
；
According to the inter-phase carrier phase difference and the target carrier initial phase, determining the carrier initial phase of a first submodule in a third half bridge arm of the second bridge arm, and extending the carrier initial phases of the ith submodule in the third half bridge arm to the carrier initial phases of the (i-1) th submodule
；
Determining the initial carrier phase of the first submodule in the fourth half bridge arm of the second half bridge arm according to the half bridge arm carrier phase difference and the initial carrier phase of the first submodule in the third half bridge arm, and extending the initial carrier phases of the ith submodule in the fourth half bridge arm relative to the initial carrier phase of the (i-1) th submodule
。
4. The method according to claim 1 or 2, wherein before controlling each sub-module to operate based on the carrier signal of each sub-module, the method further comprises:
acquiring a modulation signal of each submodule;
the carrier signal based on each submodule controls each submodule to operate so as to drive each MMC bridge arm to output voltage, and the method comprises the following steps:
comparing the modulation signal of each submodule with a carrier signal to generate a driving signal of each submodule;
and controlling each submodule to operate according to the driving signal of each submodule so as to drive each MMC bridge arm to output voltage.
5. The method of claim 4, wherein comparing the modulation signal of each sub-module with the carrier signal to generate the driving signal of each sub-module comprises:
and carrying out waveform comparison on the modulation signal of each sub-module and the carrier signal, if the waveform amplitude of the modulation signal of the sub-module is greater than that of the carrier signal, generating a high-level driving signal, and if the waveform amplitude of the modulation signal of the sub-module is less than that of the carrier signal, generating a low-level driving signal.
6. The method of claim 4, wherein the two MMC legs are divided into a first leg and a second leg; the acquiring of the modulation signal of each sub-module includes:
acquiring an input initial modulation signal;
normalizing the initial modulation signal to obtain a normalized modulation signal;
taking the normalized modulation signals as modulation signals of each sub-module on a first half bridge arm of the first bridge arm and modulation signals of each sub-module on a fourth half bridge arm of the second bridge arm;
and carrying out negation processing on the normalized modulation signal to obtain a negated modulation signal, and taking the negated modulation signal as a modulation signal of each sub-module on the second half bridge arm of the first bridge arm and a modulation signal of each sub-module on the third half bridge arm of the second bridge arm.
7. A controller, comprising:
at least one processor;
at least one memory for storing at least one program;
when executed by the at least one processor, cause the at least one processor to implement a method of carrier phase shifting pulse width modulation as claimed in any one of claims 1-6.
8. An MMC cascade system, comprising at least one MMC bridge arm group and at least one controller, wherein each MMC bridge arm group comprises two MMC bridge arms, each MMC bridge arm comprises a plurality of sequentially connected sub-modules, and the controller is respectively connected with each sub-module to control the operation of each sub-module according to a carrier phase-shifting pulse width modulation method of any one of claims 1-6.
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