CN108429476B - Control method and controller of cascaded H-bridge inverter - Google Patents

Control method and controller of cascaded H-bridge inverter Download PDF

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CN108429476B
CN108429476B CN201810265670.4A CN201810265670A CN108429476B CN 108429476 B CN108429476 B CN 108429476B CN 201810265670 A CN201810265670 A CN 201810265670A CN 108429476 B CN108429476 B CN 108429476B
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module
modulation
wave
amplitude
overmodulation
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CN108429476A (en
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赵涛
徐君
王新宇
顾亦磊
张兴
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Sungrow Power Supply Co Ltd
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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
    • 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
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • 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
    • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
    • H02M1/007—Plural converter units in cascade

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Abstract

The invention provides a control method of a cascade H-bridge inverter, which is used for compensating a second harmonic wave of a modulation wave of a normal module and a first harmonic wave of a limiting modulation wave of an overmodulation module, wherein the second harmonic wave and the first harmonic wave are of the same order, have the same amplitude and are opposite in phase, so that the total alternating current output voltage of the cascade H-bridge module does not contain the compensated harmonic wave, the compensation range can be expanded, and the operation range of a system can be further expanded. The invention also provides a controller of the cascade H-bridge inverter, and the same technical means is adopted to enlarge the operation range of the system.

Description

Control method and controller of cascaded H-bridge inverter
Technical Field
The invention relates to the technical field of photovoltaic power generation, in particular to a control method and a controller of a cascade H-bridge inverter.
Background
In the field of photovoltaic power generation, a system structure of a cascaded H-bridge inverter is shown in fig. 1, and an input end of each H-bridge module may be connected to a photovoltaic module (shown in fig. 1) or at least one photovoltaic string, or other dc conversion devices may be added. When the power received by the input end of one or even a plurality of H-bridge modules is seriously reduced due to uneven illumination or other conditions, the grid-connected current is greatly reduced; since the input power of other H-bridge modules is almost constant, the modulation degree thereof increases. Over-modulation can increase the harmonic content of the power grid current and even cause unstable operation of the system. Therefore, when the input power between the H-bridge modules is unbalanced, it is necessary to take certain measures to avoid the overmodulation of the H-bridge modules, thereby expanding the operating range of the system.
In the prior art, a third harmonic compensation strategy exists, which can enlarge the modulation degree of an H-bridge module to 1.155 and avoid overmodulation of the H-bridge module within a certain range. Meanwhile, the method can also ensure that the system operates under the unit power factor and the voltage fluctuation of the direct-current side capacitor is small. However, when the imbalance degree of the input power among the H-bridge modules is large, the modulation degree of the part of the H-bridge modules in the method may be larger than 1.155, and even if the third harmonic is compensated, some H-bridge modules cannot be prevented from overmodulation.
Disclosure of Invention
The invention provides a control method and a controller of a cascade H-bridge inverter, which are used for expanding the operation range of a system.
In order to achieve the purpose, the technical scheme provided by the application is as follows:
a control method of a cascade H-bridge inverter is applied to a controller of the cascade H-bridge inverter, wherein a main circuit of the cascade H-bridge inverter comprises a plurality of cascade H-bridge modules; the control method of the cascade H-bridge inverter comprises the following steps:
calculating to obtain the modulation degree of each H-bridge module;
obtaining a limiting modulation wave of an overmodulation module according to an overmodulation preset corresponding relation between a modulation degree and a modulation wave amplitude and the modulation degree;
calculating to obtain a first harmonic wave required to be compensated by the amplitude-limiting modulation wave of the overmodulation module according to the amplitude-limiting modulation wave of the overmodulation module and the modulation degree;
calculating to obtain a modulation wave of a normal module and a second harmonic wave required to be compensated according to the first harmonic wave and the modulation degree; the second harmonic and the first harmonic have the same order, the same amplitude and opposite phase;
and generating the driving signals corresponding to the H-bridge modules according to the amplitude limiting modulation wave of the overmodulation module, the modulation wave of the normal module and the carrier phase-shifting modulation strategy.
Preferably, the modulation degree of each H-bridge module is obtained by calculation, and an adopted formula is as follows:
Figure BDA0001611318320000021
wherein S isiIs the modulation degree, P, of the ith H-bridge moduleiIs the power of the ith H-bridge module, PTTotal power of all H-bridge modules, VrFor the amplitude of the total modulation voltage, VdciThe voltage of a direct current side capacitor of the ith H-bridge module is shown, and n is the number of the H-bridge modules.
Preferably, the obtaining of the amplitude-limited modulated wave of the overmodulation module according to the preset overmodulation correspondence between the modulation degree and the amplitude of the modulated wave and the modulation degree includes:
obtaining a modulation wave amplitude of an overmodulation module according to the overmodulation preset corresponding relation and the modulation degree; the over-modulation preset corresponding relation is
Figure BDA0001611318320000022
S is the modulation degree and the fundamental wave amplitude of the H-bridge module, and M is the modulation wave amplitude of the overmodulation module;
according to the amplitude of the modulation wave of the overmodulation module, adopting a formula
Figure BDA0001611318320000023
Calculating to obtain an amplitude-limiting modulation wave of the overmodulation module; wherein the content of the first and second substances,
Figure BDA0001611318320000024
l represents the positive and negative 1 amplitude limiting operation for the amplitude limiting modulation wave of the ith overmodulation module,
Figure BDA0001611318320000025
is the phase angle of the voltage of the power grid,
Figure BDA0001611318320000026
and x is the number of the overmodulation modules, and is the included angle between the total modulation voltage and the power grid voltage.
Preferably, the first harmonic to be compensated by the amplitude-limited modulated wave of the overmodulation module is calculated according to the amplitude-limited modulated wave of the overmodulation module and the modulation degree, and the formula is as follows:
Figure BDA0001611318320000027
wherein the content of the first and second substances,
Figure BDA0001611318320000028
the first harmonic to be compensated for by the amplitude-limited modulated wave of the ith overmodulation block,
Figure BDA0001611318320000029
is the ithAmplitude-limited modulated wave of overmodulation module, SiFor the modulation and fundamental amplitude of the ith overmodulation block,
Figure BDA0001611318320000031
for the phase angle of the voltage of the power network,
Figure BDA0001611318320000032
and x is the number of the over-modulation modules, and is the included angle between the total modulation voltage and the power grid voltage.
Preferably, the calculating to obtain the modulation wave of the normal module and the second harmonic to be compensated according to the first harmonic and the modulation degree includes:
according to the first harmonic wave, adopting a formula
Figure BDA0001611318320000033
Calculating to obtain the total harmonic voltage to be compensated of the normal module
Figure BDA0001611318320000034
Wherein the content of the first and second substances,
Figure BDA0001611318320000035
the first harmonic to be compensated for the amplitude-limited modulated wave of the ith overmodulation block, x is the number of overmodulation blocks, VdciThe voltage of a direct current side capacitor of the ith overmodulation module;
total harmonic voltage to be compensated according to normal module requirements
Figure BDA0001611318320000036
Using a formula
Figure BDA0001611318320000037
Calculating to obtain a second harmonic to be compensated for the modulation wave of the normal module, wherein Vdci(max)＝(1-Si)Vdci,i＝1,…,n-x，Vdci(max)Maximum positive voltage amplitude, V, allowed to compensate for the ith normal moduledciIs the DC side capacitor voltage of the ith normal module, SiAs the ith normal moduleModulation degree and fundamental amplitude; vdcj(max)＝(1-Sj)Vdcj,j＝1,…,n-x， Vdcj(max)Maximum positive voltage amplitude, V, allowed to compensate for the jth normal moduledcjIs the DC side capacitor voltage of the j normal module, SjThe modulation degree and the fundamental wave amplitude of the jth normal module are obtained; n-x is the number of normal modules,
Figure BDA0001611318320000038
a second harmonic to be compensated for the modulated wave of the ith normal module;
according to the second harmonic wave to be compensated of the modulation wave of the normal module and the modulation degree, adopting a formula
Figure BDA0001611318320000039
Calculating to obtain a modulation wave of a normal module; wherein the content of the first and second substances,
Figure BDA00016113183200000310
modulated wave of i-th normal module, SiThe modulation degree and the fundamental wave amplitude of the ith normal module,
Figure BDA00016113183200000311
for the phase angle of the voltage of the power network,
Figure BDA00016113183200000312
the included angle between the total modulation voltage and the power grid voltage is obtained.
A controller of a cascaded H-bridge inverter is connected with each cascaded H-bridge module in a main circuit of the cascaded H-bridge inverter; the controller of the cascaded H-bridge inverter includes:
the first calculation unit is used for calculating and obtaining the modulation degree of each H-bridge module;
the second calculation unit is used for obtaining a limiting modulation wave of the overmodulation module according to an overmodulation preset corresponding relation between the modulation degree and the modulation wave amplitude and the modulation degree;
the third calculation unit is used for calculating and obtaining a first harmonic wave required to be compensated by the amplitude-limiting modulation wave of the overmodulation module according to the amplitude-limiting modulation wave of the overmodulation module and the modulation degree;
the fourth calculation unit is used for calculating and obtaining the modulation wave of the normal module and the second harmonic wave needing to be compensated according to the first harmonic wave and the modulation degree; the second harmonic and the first harmonic have the same order, the same amplitude and opposite phase;
and the signal generation unit is used for generating driving signals corresponding to the H-bridge modules according to the amplitude limiting modulation wave of the overmodulation module, the modulation wave of the normal module and a carrier phase-shifting modulation strategy.
Preferably, when the first calculating unit calculates the modulation degree of each H-bridge module, an adopted formula is as follows:
Figure BDA0001611318320000041
wherein S isiIs the modulation degree, P, of the ith H-bridge moduleiIs the power of the ith H-bridge module, PTTotal power of all H-bridge modules, VrFor the amplitude of the total modulation voltage, VdciThe voltage of a direct current side capacitor of the ith H-bridge module is shown, and n is the number of the H-bridge modules.
Preferably, the second calculation unit includes:
the first module is used for obtaining the modulation wave amplitude of the overmodulation module according to the overmodulation preset corresponding relation and the modulation degree; the over-modulation preset corresponding relation is
Figure BDA0001611318320000042
S is the modulation degree and the fundamental wave amplitude of the H-bridge module, and M is the modulation wave amplitude of the overmodulation module;
a second module for applying a formula based on the modulation wave amplitude of the overmodulation module
Figure RE-GDA0001637179130000043
Calculating to obtain a amplitude-limited modulation wave of the overmodulation module, wherein i is 1,2, … and x; wherein the content of the first and second substances,
Figure RE-GDA0001637179130000044
l represents the positive and negative 1 amplitude limiting operation for the amplitude limiting modulation wave of the ith overmodulation module,
Figure RE-GDA0001637179130000045
for the phase angle of the voltage of the power network,
Figure RE-GDA0001637179130000046
and x is the number of the overmodulation modules, and is the included angle between the total modulation voltage and the power grid voltage.
Preferably, the third calculating unit calculates a first harmonic to be compensated by the amplitude-limited modulated wave of the overmodulation module according to the amplitude-limited modulated wave of the overmodulation module and the modulation degree, and an adopted formula is as follows:
Figure BDA0001611318320000051
wherein the content of the first and second substances,
Figure BDA0001611318320000052
the first harmonic to be compensated for by the amplitude-limited modulated wave of the ith overmodulation block,
Figure BDA0001611318320000053
for amplitude-limited modulated waves of the ith overmodulation block, SiFor the modulation and fundamental amplitude of the ith overmodulation block,
Figure BDA0001611318320000054
for the phase angle of the voltage of the power network,
Figure BDA0001611318320000055
and x is the number of the over-modulation modules, and is the included angle between the total modulation voltage and the power grid voltage.
Preferably, the fourth calculation unit includes:
a third module for applying a formula based on the first harmonic
Figure BDA0001611318320000056
Calculating to obtain the total harmonic voltage to be compensated of the normal module
Figure BDA0001611318320000057
Wherein the content of the first and second substances,
Figure BDA0001611318320000058
the first harmonic to be compensated for the amplitude-limited modulated wave of the ith overmodulation block, x is the number of overmodulation blocks, VdciThe voltage of a direct current side capacitor of the ith over-modulation module;
a fourth module for compensating the total harmonic voltage according to the normal module
Figure BDA0001611318320000059
Using a formula
Figure BDA00016113183200000510
Calculating to obtain a second harmonic to be compensated for the modulation wave of the normal module, wherein Vdci(max)＝(1-Si)Vdci,i＝1,…,n-x，Vdci(max)Maximum positive voltage amplitude, V, allowed to compensate for the ith normal moduledciIs the DC side capacitor voltage of the ith normal module, SiThe modulation degree and the fundamental wave amplitude of the ith normal module are obtained; vdcj(max)＝(1-Sj)Vdcj,j＝1,…,n-x， Vdcj(max)Maximum positive voltage amplitude, V, allowed to compensate for the jth normal moduledcjIs the DC side capacitor voltage of the j normal module, SjThe modulation degree and the fundamental wave amplitude of the jth normal module are obtained; n-x is the number of normal modules,
Figure BDA00016113183200000511
a second harmonic to be compensated for the modulated wave of the ith normal module;
a fifth module for adopting a formula according to the second harmonic wave to be compensated of the modulation wave of the normal module and the modulation degree
Figure BDA00016113183200000512
Calculating to obtain a modulation wave of a normal module; wherein the content of the first and second substances,
Figure BDA0001611318320000061
modulated wave of i-th normal module, SiThe modulation degree and the fundamental wave amplitude of the ith normal module,
Figure BDA0001611318320000062
for the phase angle of the voltage of the power network,
Figure BDA0001611318320000063
the included angle between the total modulation voltage and the power grid voltage is obtained.
The control method of the cascade H-bridge inverter provided by the invention comprises the following steps of firstly calculating the modulation degree of each H-bridge module; then, obtaining a limiting modulation wave of an overmodulation module according to an overmodulation preset corresponding relation between the modulation degree and the modulation wave amplitude and the modulation degree; then according to the amplitude-limiting modulation wave of the overmodulation module and the modulation degree, calculating to obtain a first harmonic wave which needs to be compensated by the amplitude-limiting modulation wave of the overmodulation module; calculating to obtain a second harmonic wave which needs to be compensated by the modulation wave of the normal module according to the first harmonic wave and the modulation degree, and further calculating to obtain the modulation wave of the normal module; and finally, according to the amplitude-limiting modulation wave of the overmodulation module, the modulation wave of the normal module and a carrier phase-shifting modulation strategy, the driving signals of all the H-bridge modules can be generated. The second harmonic of the modulation wave of the normal module and the first harmonic of the amplitude-limiting modulation wave of the overmodulation module are compensated by the first harmonic compensation circuit, the second harmonic and the first harmonic are the same in order, same in amplitude and opposite in phase, so that the AC total output voltage of the cascaded H-bridge module does not contain the compensated harmonic, the compensation range can be expanded, and the operation range of the system can be expanded.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without any creative work.
Fig. 1 is a system configuration diagram of a cascade H-bridge inverter provided in the prior art;
fig. 2 is a flowchart of a control method of a cascaded H-bridge inverter according to an embodiment of the present invention;
FIG. 3a is a waveform diagram of a normal modulation wave of an H-bridge module according to an embodiment of the present invention;
FIG. 3b is a waveform diagram of a clipped modulated wave of an overmodulation module according to an embodiment of the present invention;
fig. 3c is a graph illustrating an overmodulation preset correspondence between a modulation degree and a modulation wave amplitude according to an embodiment of the present invention;
fig. 4 is a partial flowchart of a control method of a cascaded H-bridge inverter according to an embodiment of the present invention;
FIG. 5a is a waveform of the input power of four H-bridge modules provided in accordance with another embodiment of the present invention;
FIG. 5b is a waveform diagram of modulation degrees of four H-bridge modules according to another embodiment of the present invention;
FIG. 5c is a waveform diagram of modulated waves of four H-bridge modules according to another embodiment of the present invention;
FIG. 5d is a graph of grid voltage and grid current waveforms provided by another embodiment of the present invention;
FIG. 5e is a diagram illustrating a DC-side capacitor voltage waveform of a first H-bridge module, according to another embodiment of the present invention;
FIG. 5f is a prior art provided grid voltage and grid current waveform diagram;
fig. 6 is a schematic structural diagram of a controller of a cascaded H-bridge inverter according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present application will be described below clearly and completely with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
The invention provides a control method of a cascade H-bridge inverter, which is used for expanding the operation range of a system.
The control method of the cascade H bridge inverter is applied to a controller of the cascade H bridge inverter; as shown in fig. 1, the main circuit of the cascaded H-bridge inverter includes a plurality of cascaded H-bridge modules; referring to fig. 2, the method for controlling the cascaded H-bridge inverter includes:
s101, calculating to obtain the modulation degree of each H-bridge module;
and calculating the modulation degree of each H-bridge module by using a formula which specifically comprises the following steps:
Figure BDA0001611318320000071
wherein S isiIs the modulation degree, P, of the ith H-bridge moduleiIs the power of the ith H-bridge module, PTTotal power of all H-bridge modules, VrFor the amplitude of the total modulation voltage, VdciThe voltage of a direct current side capacitor of the ith H-bridge module is shown, and n is the number of the H-bridge modules.
According to the modulation degree calculation result of each H-bridge module, each H-bridge module may be divided into an overmodulation module and a normal module, wherein: the H-bridge module with the modulation degree less than or equal to 1 is a normal module, and the H-bridge module with the modulation degree greater than 1 and less than or equal to 4/pi is an overmodulation module.
In the overmodulation module, it is assumed that the modulation wave is a sine wave as shown in fig. 3a, where the expression of the sine wave is f (x) msin (x), M >, and 1M is the modulation wave amplitude.
In order to make the amplitude of the modulated wave of the overmodulation module not greater than 1, it is necessary to perform a clipping operation on the amplitude of the modulated wave, so as to obtain a clipped modulated wave as shown in fig. 3b, where the expression of the clipped modulated wave is
Figure BDA0001611318320000081
That is to say
Figure BDA0001611318320000082
Wherein θ is arcsin (1/M).
Then, a Fourier series expansion is performed on the function g (x), and the expression is as follows:
Figure BDA0001611318320000083
wherein the content of the first and second substances,
Figure BDA0001611318320000084
Figure BDA0001611318320000085
Figure BDA0001611318320000086
therefore, the fundamental wave h (x) of the function g (x) is expressed as h (x) a1cosx+b1sinx＝Ssin(x)；
Wherein the content of the first and second substances,
Figure BDA0001611318320000087
the formula is also the over-modulation preset corresponding relation between the modulation degree and the modulation wave amplitude value;
can be obtained from the above formula
Figure BDA0001611318320000088
That is, for a fundamental frequency sine wave with amplitude M, after the nonlinear amplitude-limiting operation is performed on the fundamental frequency sine wave, the fundamental wave amplitude is reduced to S, and the relation curve of S and M is shown in fig. 3 c.
S102, obtaining a limiting modulation wave of an overmodulation module according to an overmodulation preset corresponding relation between a modulation degree and a modulation wave amplitude and the modulation degree;
preferably, the amplitude of the modulation wave of the overmodulation module can be obtained according to the preset corresponding relation of overmodulation and the modulation degree; and then, calculating to obtain a amplitude-limiting modulation wave of the overmodulation module according to the modulation wave amplitude of the overmodulation module.
Specifically, the over-modulation preset corresponding relation is as described above, and in a specific practical application, the preset corresponding relation can be directly determined according to
Figure BDA0001611318320000091
Calculating, or drawing a one-to-one table of S and M according to the relation curve shown in FIG. 3c, and looking up the table to obtain the corresponding M; without limitation, and depending on the specific application, are within the scope of the present application.
The amplitude limiting modulation wave of the overmodulation module is obtained by calculating according to the modulation wave amplitude of the overmodulation module by adopting a formula
Figure BDA0001611318320000092
As can be seen from the above-mentioned description,
Figure BDA0001611318320000093
is equal to the modulation degree Si(ii) a Wherein the content of the first and second substances,
Figure BDA0001611318320000094
l represents the positive and negative 1 amplitude limiting operation for the amplitude limiting modulation wave of the ith overmodulation module,
Figure BDA0001611318320000095
for the phase angle of the voltage of the power network,
Figure BDA0001611318320000096
and x is the number of the overmodulation modules, and is the included angle between the total modulation voltage and the power grid voltage.
S103, calculating to obtain a first harmonic wave to be compensated by the amplitude-limited modulation wave of the overmodulation module according to the amplitude-limited modulation wave and the modulation degree of the overmodulation module;
the formula used is:
Figure BDA0001611318320000097
wherein the content of the first and second substances,
Figure BDA0001611318320000098
the first harmonic to be compensated for by the amplitude-limited modulated wave of the ith overmodulation block,
Figure BDA0001611318320000099
for amplitude-limited modulated waves of the ith overmodulation block, SiFor the modulation and fundamental amplitude of the ith overmodulation block,
Figure BDA00016113183200000910
for the phase angle of the voltage of the power network,
Figure BDA00016113183200000911
and x is the number of the over-modulation modules, and is the included angle between the total modulation voltage and the power grid voltage.
S104, calculating to obtain a modulation wave of a normal module and a second harmonic wave needing to be compensated according to the first harmonic wave and the modulation degree;
specifically, step S104 includes the steps shown in fig. 4:
s201, calculating and obtaining total harmonic voltage needing to be compensated by a normal module according to the first harmonic
Figure BDA00016113183200000912
Total harmonic voltage compensated by overmodulation module
Figure BDA0001611318320000101
Comprises the following steps:
Figure BDA0001611318320000102
in order to ensure that the total output voltage of the cascade alternating current side of each H-bridge module does not contain the compensated harmonic voltage, the normal module needs the compensated total harmonic voltage
Figure BDA0001611318320000103
Comprises the following steps:
Figure BDA0001611318320000104
that is to say
Figure BDA0001611318320000105
Wherein the content of the first and second substances,
Figure BDA0001611318320000106
the first harmonic to be compensated for the amplitude-limited modulated wave of the ith overmodulation block, x is the number of overmodulation blocks, VdciThe voltage of a direct current side capacitor of the ith overmodulation module;
s202, compensating the total harmonic voltage according to the normal module requirement
Figure BDA0001611318320000107
Calculating to obtain a second harmonic wave to be compensated by the modulation wave of the normal module;
the formula used is:
Figure BDA0001611318320000108
wherein, Vdci(max)The maximum positive voltage amplitude allowed to be compensated by the ith normal module is calculated by the formula Vdci(max)＝(1-Si)Vdci,i＝1,…,n-x，VdciIs the direct current side capacitor voltage of the ith normal module, SiThe modulation degree and the fundamental wave amplitude of the ith normal module are obtained; vdcj(max)The maximum positive voltage amplitude allowed to be compensated by the jth normal module is calculated as Vdcj(max)＝(1-Sj)Vdcj,j＝1，…，n-x，VdcjIs the DC side capacitor voltage of the jth normal module, SjThe modulation degree and the fundamental wave amplitude of the jth normal module are obtained; n-x is the number of normal modules,
Figure RE-GDA0001637179130000109
a second harmonic to be compensated for the modulated wave of the ith normal module;
through the calculation process, the obtained second harmonic is identical to the first harmonic in order, identical in amplitude and opposite in phase.
S203, calculating to obtain the modulation wave of the normal module according to the second harmonic and the modulation degree which need to be compensated by the modulation wave of the normal module;
the formula used is:
Figure BDA0001611318320000111
wherein the content of the first and second substances,
Figure BDA0001611318320000112
modulated wave of i-th normal module, SiThe modulation degree and the fundamental wave amplitude of the ith normal module,
Figure BDA0001611318320000113
for the phase angle of the voltage of the power network,
Figure BDA0001611318320000114
the included angle between the total modulation voltage and the power grid voltage is obtained.
And S105, generating driving signals of each H-bridge module according to the amplitude limiting modulation wave of the overmodulation module, the modulation wave of the normal module and the carrier phase shift modulation strategy.
From the above, the modulation degree S of the H-bridge moduleiWhen the amplitude is 1-4/pi, the corresponding compensation coefficient, namely the amplitude M of the modulation wave can be always foundiAll can make its modulated wave amplitude MiNot greater than 1. Therefore, the method can expand the linear modulation range of the H-bridge module to 4/pi.
In the control method of the cascaded H-bridge inverter provided by this embodiment, since the second harmonic of the modulation wave for compensating the normal module and the first harmonic of the amplitude-limited modulation wave for compensating the overmodulation module are the same in order, the same in amplitude, and opposite in phase, it can be ensured that the total ac output voltage of the cascaded H-bridge module does not contain the compensated harmonic, and the compensation range can be expanded, thereby expanding the operating range of the system.
Taking a system with four H-bridge modules cascaded as an example for explanation, assuming that the peak value of the grid point voltage is 100V and the maximum output power of the photovoltaic module at the front stage of the four H-bridge modules is 260W, then:
when the system is initially operated, the illumination intensities of the four photovoltaic modules are respectively as follows: 1000W/m2, 1000W/m2, 850W/m2, and 700W/m 2; when t is 0.5s, the light intensities of the third and fourth photovoltaic modules become 350W/m2 and 400W/m2 respectively, and the input powers (P1 to P4) of the four H-bridges are shown in fig. 5 a.
The input power of the system is unbalanced, the first and second H-bridge modules will be over-modulated due to the larger input power, and the modulation degrees (S1-S4) of the four H-bridge modules are shown in fig. 5 b.
If the control method of the cascaded H-bridge inverter proposed in the above embodiment is adopted, the modulated waves (m 1-m 4) of the four H-bridge modules will be as shown in fig. 5c, and the grid voltage v isgAnd the grid current igAs shown in fig. 5d, the DC side capacitor voltage VdclAs shown in FIG. 5e, the difference Δ u between the upper and lower amplitudes thereof is changed from 1V to 0.8V.
It can be seen that the waveform of the grid current is better, and the power factor PF is 1, although the waveform synthesized by the carrier phase shift modulation strategy is not ideal as the module unbalance degree increases, and the Harmonic component of the double switching frequency increases, which results in the increase of the THD (Total Harmonic Distortion), compared with the third Harmonic compensation strategy adopted in the prior art, referring to the waveform diagram of the grid voltage and the grid current shown in fig. 5f, it can be found that since the modulation degree of the first and second H-bridges is about 1.2 (greater than 1.155), the THD of the grid current reaches 8.36%, which is much greater than 3.49% that can be realized by the control method of the cascade H-bridge inverter.
Therefore, compared with a third harmonic compensation strategy in the prior art, the control method of the cascade H-bridge inverter can enlarge the maximum linear modulation range of each H-bridge module to 4/pi under the condition of non-derating operation; and when the power of the H-bridge module is not balanced within a certain range (namely the modulation degree is between 1 and 4/pi), the THD is low, the voltage fluctuation of the direct current side is small, the unit power factor can be realized, and the normal operation of the system can be further ensured.
It is worth to be noted that, in the prior art, there are also a hybrid control strategy combining low-frequency square wave modulation and high-frequency sine wave pulse width modulation, an improved MPPT (Maximum Power Point Tracking) control strategy, and a reactive Power compensation control strategy; specifically, the method comprises the following steps:
the hybrid control strategy is characterized in that the voltage utilization rate of the direct current side of the H bridge is improved by utilizing the characteristic that the maximum modulation degree of square waves is 4/pi. However, the strategy allocates each H-bridge module to charge or discharge according to the system operating state, and does not precisely control the dc-side capacitor voltage, thereby causing large fluctuation of the dc-side capacitor voltage; the fluctuation of the voltage on the direct current side enables the photovoltaic assembly to deviate from the maximum power point to operate, and the average power generation amount of the photovoltaic assembly is reduced. In addition, the MPPT efficiency is low because the dc-side capacitor voltage control of the hybrid modulation strategy is a static difference.
According to the improved MPPT control strategy, when the power among the modules is unbalanced, the H module with larger output power is enabled to exit the maximum power point operation and operate in a voltage source region of an I-V characteristic curve, so that the input power among the modules is balanced. However, this strategy reduces the power production of the system.
According to the reactive compensation control strategy, by compensating certain reactive power, all H-bridge modules can still be ensured not to be overmodulatied when the output power of each H-bridge module is seriously unbalanced. However, this strategy may reduce the power factor of the inverter.
By summarizing the advantages and disadvantages of the prior art, the contents shown in table 1 can be obtained:
TABLE 1 summary of advantages and disadvantages of the prior art
Figure BDA0001611318320000131
According to the above, the voltage of the capacitor on the direct current side of the hybrid modulation strategy fluctuates irregularly, which affects the system power generation amount and the MPPT efficiency, so that the hybrid modulation strategy is not suitable for being applied to the field of photovoltaic power generation. Although the improved MPPT control strategy can balance the input power of the H-bridge module to a great extent, derating operation is required, and the power generation capacity of the system is reduced. The reactive compensation control strategy can avoid the H-bridge module overmodulation to a large extent, but the power factor of the system is reduced, and the application of the system can be limited. Although the third harmonic compensation strategy compromises the advantages and disadvantages of the algorithms, the method can expand the operation range of the system to a certain extent, simultaneously ensures that the voltage fluctuation of the direct current side is small and the system operates in a unit power factor, and only expands the maximum linear modulation range from 1 to 1.155, so that the method is limited in the unbalanced scene which can be responded to.
In the control method of the cascade H-bridge inverter provided in this embodiment, the voltage fluctuation of the dc side capacitor is small and the MPPT efficiency is relatively high because of PWM (Pulse width modulation). Moreover, a certain amount of harmonic waves are injected into the overmodulation module, so that the amplitude of a modulation wave of the overmodulation module can be reduced, and overmodulation is avoided; in addition, the method also compensates the harmonic waves which are in the same order, have the same amplitude and are opposite in phase with the normal module, so that the maximum linear modulation range of each H-bridge module is expanded to 4/pi under the condition of non-derating operation, and the unit power factor operation of the system can be ensured, and the method is favorable for application.
Another embodiment of the present invention further provides a controller of a cascaded H-bridge inverter, connected to each cascaded H-bridge module in a main circuit of the cascaded H-bridge inverter; referring to fig. 6, the controller of the cascaded H-bridge inverter includes:
the first calculating unit 101 is used for calculating and obtaining the modulation degree of each H-bridge module;
the second calculating unit 102 is configured to obtain a clipping modulation wave of the overmodulation module according to an overmodulation preset corresponding relationship between the modulation degree and the modulation wave amplitude and the modulation degree;
a third calculating unit 103, configured to calculate, according to the amplitude-limited modulated wave and the modulation degree of the overmodulation module, a first harmonic that needs to be compensated for the amplitude-limited modulated wave of the overmodulation module;
a fourth calculating unit 104, configured to calculate, according to the first harmonic and the modulation degree, a modulation wave of the normal module and a second harmonic that needs to be compensated; the second harmonic and the first harmonic have the same order, the same amplitude and opposite phase;
and a signal generating unit 105, configured to generate a driving signal of each H-bridge module according to the amplitude-limited modulation wave of the overmodulation module, the modulation wave of the normal module, and the carrier phase shift modulation strategy.
Preferably, when the first calculating unit 101 calculates the modulation degree of each H-bridge module, the formula used is as follows:
Figure BDA0001611318320000141
wherein S isiIs the modulation degree, P, of the ith H-bridge moduleiIs the power of the ith H-bridge module, PTTotal power of all H-bridge modules, VrFor the amplitude of the total modulation voltage, VdciThe voltage of a direct current side capacitor of the ith H-bridge module is shown, and n is the number of the H-bridge modules.
Preferably, the second calculation unit 102 includes:
the first module is used for obtaining the amplitude limiting modulation wave amplitude of the overmodulation module according to the overmodulation preset corresponding relation and the modulation degree; the over-modulation preset corresponding relation is
Figure BDA0001611318320000151
Wherein S is the modulation degree and the fundamental wave amplitude of the H-bridge module, and M is the modulation wave amplitude of the H-bridge module;
a second module for modulating the amplitude of the wave using a formula based on the amplitude limit of the overmodulation module
Figure RE-GDA0001637179130000152
Calculating to obtain a amplitude-limited modulation wave of the overmodulation module, wherein i is 1,2, … and x; wherein the content of the first and second substances,
Figure RE-GDA0001637179130000153
l represents the positive and negative 1 amplitude limiting operation for the amplitude limiting modulation wave of the ith overmodulation module,
Figure RE-GDA0001637179130000154
for the phase angle of the voltage of the power network,
Figure RE-GDA0001637179130000155
and x is the number of the overmodulation modules, and is the included angle between the total modulation voltage and the power grid voltage.
Preferably, third calculating unit 103 calculates a first harmonic to be compensated by the clipping-modulated wave of the overmodulation module according to the clipping-modulated wave and the modulation degree of the overmodulation module, and the formula used is as follows:
Figure BDA0001611318320000156
wherein the content of the first and second substances,
Figure BDA0001611318320000157
the first harmonic to be compensated for by the amplitude-limited modulated wave of the ith overmodulation block,
Figure BDA0001611318320000158
for amplitude-limited modulated waves of the ith overmodulation block, SiFor the modulation and fundamental amplitude of the ith overmodulation block,
Figure BDA0001611318320000159
for the phase angle of the voltage of the power network,
Figure BDA00016113183200001510
and x is the number of the over-modulation modules, and is the included angle between the total modulation voltage and the power grid voltage.
Preferably, the fourth calculation unit 104 includes:
a third module for applying a formula based on the first harmonic
Figure BDA00016113183200001511
Calculating to obtain the total harmonic voltage to be compensated of the normal module
Figure BDA00016113183200001512
Wherein the content of the first and second substances,
Figure BDA00016113183200001513
the first harmonic to be compensated for the amplitude-limited modulated wave of the ith overmodulation module, x is the number of overmodulation modules, VdciThe voltage of a direct current side capacitor of the ith overmodulation module;
a fourth module for compensating the total harmonic voltage according to the normal module
Figure BDA00016113183200001514
Using a formula
Figure BDA00016113183200001515
Calculating to obtain a second harmonic to be compensated for the modulation wave of the normal module, wherein Vdci(max)＝(1-Si)Vdci,i＝1,…,n-x， Vdcj(max)＝(1-Sj)Vdcj,j＝1,…,n-x，Vdci(max)Maximum positive voltage amplitude, V, allowed for compensation by the ith normal moduledciIs the DC side capacitor voltage of the ith normal module, SiIs the modulation degree and the fundamental amplitude, V, of the ith normal moduledcj(max)Maximum positive voltage amplitude, V, allowed to compensate for the jth normal moduledcjIs the DC side capacitor voltage of the jth normal module, SjIs the modulation degree and the fundamental wave amplitude of the jth normal module, n-x is the number of the normal modules,
Figure BDA0001611318320000161
a second harmonic to be compensated for the modulated wave of the ith normal module;
a fifth module for adopting a formula according to the second harmonic and the modulation degree required to be compensated by the modulation wave of the normal module
Figure BDA0001611318320000162
Calculating to obtain a modulation wave of a normal module; wherein the content of the first and second substances is controlled,
Figure BDA0001611318320000163
modulated wave of i-th normal module, SiThe modulation degree and the fundamental wave amplitude of the ith normal module,
Figure BDA0001611318320000164
for the phase angle of the voltage of the power network,
Figure BDA0001611318320000165
the included angle between the total modulation voltage and the power grid voltage is obtained.
The rest of the principle is the same as the above embodiments, and is not described in detail here.
The embodiments of the invention are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is simple, and the relevant points can be referred to the description of the method part.
The foregoing is merely a preferred embodiment of the invention and is not intended to limit the invention in any manner. Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make numerous possible variations and modifications to the present teachings, or modify it to equivalent embodiments, using the methods and techniques disclosed above, without departing from the scope of the present teachings. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention, unless the contents of the technical solution of the present invention are departed.

Claims (10)

1. A control method of a cascade H-bridge inverter is characterized in that the control method is applied to a controller of the cascade H-bridge inverter, and a main circuit of the cascade H-bridge inverter comprises a plurality of cascade H-bridge modules; the control method of the cascade H-bridge inverter comprises the following steps:
calculating to obtain the modulation degree of each H-bridge module;
obtaining a limiting modulation wave of an overmodulation module according to an overmodulation preset corresponding relation between a modulation degree and a modulation wave amplitude and the modulation degree;
calculating to obtain a first harmonic wave required to be compensated by the amplitude-limiting modulation wave of the overmodulation module according to the amplitude-limiting modulation wave of the overmodulation module and the modulation degree;
calculating to obtain a modulation wave of a normal module and a second harmonic wave required to be compensated according to the first harmonic wave and the modulation degree; the second harmonic and the first harmonic have the same order, the same amplitude and opposite phase;
and generating the driving signals corresponding to the H-bridge modules according to the amplitude limiting modulation wave of the overmodulation module, the modulation wave of the normal module and the carrier phase-shifting modulation strategy.
2. The method of claim 1, wherein the calculating obtains the modulation degree of each H-bridge module by using the formula:
Figure FDA0002239211600000011
wherein S isiIs the modulation degree, P, of the ith H-bridge moduleiIs the power of the ith H-bridge module, PTTotal power of all H-bridge modules, VrFor the amplitude of the total modulation voltage, VdciThe voltage of a direct current side capacitor of the ith H-bridge module is shown, and n is the number of the H-bridge modules.
3. The method according to claim 1, wherein obtaining the clipped modulated wave of the overmodulation module according to the overmodulation preset correspondence between the modulation degree and the amplitude of the modulated wave and the modulation degree comprises:
obtaining a modulation wave amplitude of an overmodulation module according to the overmodulation preset corresponding relation and the modulation degree; the over-modulation preset corresponding relation is
Figure FDA0002239211600000012
Wherein S is the modulation degree and the fundamental wave amplitude of the H-bridge module, and M is overmodulationThe amplitude of the modulation wave of the module;
according to the amplitude of the modulation wave of the overmodulation module, adopting a formula
Figure FDA0002239211600000013
Calculating to obtain an amplitude-limiting modulation wave of the overmodulation module; wherein the content of the first and second substances,
Figure FDA0002239211600000014
l represents the positive and negative 1 amplitude limiting operation for the amplitude limiting modulation wave of the ith overmodulation module,
Figure FDA0002239211600000015
for the phase angle of the voltage of the power network,
Figure FDA0002239211600000021
is the included angle between the total modulation voltage and the power grid voltage, x is the number of over-modulation modules, MiThe amplitude of the modulated wave for the ith overmodulation block.
4. The method according to claim 1, wherein the first harmonic to be compensated for by the clipping modulation wave of the overmodulation block is calculated based on the clipping modulation wave of the overmodulation block and the modulation degree by using the following formula:
Figure FDA0002239211600000022
wherein the content of the first and second substances,
Figure FDA0002239211600000023
the first harmonic to be compensated for by the amplitude-limited modulated wave of the ith overmodulation block,
Figure FDA0002239211600000024
for amplitude-limited modulated waves of the ith overmodulation block, SiThe modulation degree and the fundamental wave amplitude of the ith overmodulation block,
Figure FDA0002239211600000025
for the phase angle of the voltage of the power network,
Figure FDA0002239211600000026
and x is the number of the overmodulation modules, and is the included angle between the total modulation voltage and the power grid voltage.
5. The method for controlling a cascaded H-bridge inverter according to claim 1, wherein the calculating a modulation wave of a normal module and a second harmonic to be compensated according to the first harmonic and the modulation degree comprises:
according to the first harmonic wave, adopting a formula
Figure FDA0002239211600000027
Calculating to obtain the total harmonic voltage to be compensated of the normal module
Figure FDA0002239211600000028
Wherein the content of the first and second substances,
Figure FDA0002239211600000029
the first harmonic to be compensated for the amplitude-limited modulated wave of the ith overmodulation block, x is the number of overmodulation blocks, VdciThe voltage of a direct current side capacitor of the ith overmodulation module;
total harmonic voltage to be compensated according to normal module requirements
Figure FDA00022392116000000210
Using a formula
Figure FDA00022392116000000211
Calculating to obtain a second harmonic to be compensated for the modulation wave of the normal module, wherein Vdci(max)＝(1-Si)Vdci,i＝1,…,n-x，Vdci(max)Maximum positive voltage amplitude, V, allowed to compensate for the ith normal moduledciIs the ith normal modeDC side capacitor voltage of block, SiThe modulation degree and the fundamental wave amplitude of the ith normal module are obtained; vdcj(max)＝(1-Sj)Vdcj,j＝1,…,n-x，Vdcj(max)Maximum positive voltage amplitude, V, allowed to compensate for the jth normal moduledcjIs the DC side capacitor voltage of the jth normal module, SjThe modulation degree and the fundamental wave amplitude of the jth normal module are obtained; n-x is the number of normal modules,
Figure FDA0002239211600000031
a second harmonic to be compensated for the modulated wave of the ith normal module;
according to the second harmonic wave to be compensated of the modulation wave of the normal module and the modulation degree, adopting a formula
Figure FDA0002239211600000032
Calculating to obtain a modulation wave of a normal module; wherein the content of the first and second substances,
Figure FDA0002239211600000033
modulated wave of i-th normal module, SiThe modulation degree and the fundamental wave amplitude of the ith normal module,
Figure FDA0002239211600000034
for the phase angle of the voltage of the power network,
Figure FDA0002239211600000035
the included angle between the total modulation voltage and the power grid voltage is obtained.
6. A controller of a cascade H-bridge inverter is characterized in that the controller is connected with each cascade H-bridge module in a main circuit of the cascade H-bridge inverter; the controller of the cascaded H-bridge inverter includes:
the first calculation unit is used for calculating and obtaining the modulation degree of each H-bridge module;
the second calculation unit is used for obtaining a limiting modulation wave of the overmodulation module according to an overmodulation preset corresponding relation between the modulation degree and the modulation wave amplitude and the modulation degree;
the third calculation unit is used for calculating and obtaining a first harmonic wave required to be compensated by the amplitude-limiting modulation wave of the overmodulation module according to the amplitude-limiting modulation wave of the overmodulation module and the modulation degree;
the fourth calculation unit is used for calculating and obtaining the modulation wave of the normal module and the second harmonic wave needing to be compensated according to the first harmonic wave and the modulation degree; the second harmonic and the first harmonic have the same order, the same amplitude and opposite phase;
and the signal generation unit is used for generating the driving signals corresponding to the H-bridge modules according to the amplitude limiting modulation wave of the overmodulation module, the modulation wave of the normal module and the carrier phase-shifting modulation strategy.
7. The controller of a cascaded H-bridge inverter according to claim 6, wherein when the first calculating unit calculates the modulation degree of each H-bridge module, the formula used is:
Figure FDA0002239211600000036
wherein S isiIs the modulation degree, P, of the ith H-bridge moduleiIs the power of the ith H-bridge module, PTTotal power of all H-bridge modules, VrFor the amplitude of the total modulation voltage, VdciThe voltage of a direct current side capacitor of the ith H-bridge module is shown, and n is the number of the H-bridge modules.
8. The controller of a cascaded H-bridge inverter according to claim 6, wherein the second calculation unit comprises:
the first module is used for obtaining the modulation wave amplitude of the overmodulation module according to the overmodulation preset corresponding relation and the modulation degree; the over-modulation preset corresponding relation is
Figure FDA0002239211600000041
Wherein S is modulation of an H-bridge moduleThe amplitude of the modulation wave of the overmodulation module is M;
a second module for applying a formula based on the modulation wave amplitude of the overmodulation module
Figure FDA0002239211600000042
Calculating to obtain an amplitude-limiting modulation wave of the overmodulation module; wherein the content of the first and second substances,
Figure FDA0002239211600000043
l represents the positive and negative 1 amplitude limiting operation for the amplitude limiting modulation wave of the ith overmodulation module,
Figure FDA0002239211600000044
for the phase angle of the voltage of the power network,
Figure FDA0002239211600000045
is the included angle between the total modulation voltage and the power grid voltage, x is the number of over-modulation modules, MiThe amplitude of the modulated wave for the ith overmodulation block.
9. The controller of a cascaded H-bridge inverter according to claim 6, wherein the third calculating unit calculates a first harmonic to be compensated for obtaining the clipping-modulated wave of the overmodulation block according to the clipping-modulated wave of the overmodulation block and the modulation degree, and the formula is as follows:
Figure FDA0002239211600000046
wherein the content of the first and second substances,
Figure FDA0002239211600000047
the first harmonic to be compensated for by the amplitude-limited modulated wave of the ith overmodulation block,
Figure FDA0002239211600000048
for amplitude-limited modulated waves of the ith overmodulation block, SiFor the ith overmodulationThe modulation degree and the amplitude of the fundamental wave of the module,
Figure FDA0002239211600000049
for the phase angle of the voltage of the power network,
Figure FDA00022392116000000410
and x is the number of the overmodulation modules, and is the included angle between the total modulation voltage and the power grid voltage.
10. The controller of a cascaded H-bridge inverter according to claim 6, wherein the fourth calculation unit comprises:
a third module for applying a formula based on the first harmonic
Figure FDA00022392116000000411
Calculating to obtain the total harmonic voltage to be compensated of the normal module
Figure FDA00022392116000000412
Wherein the content of the first and second substances,
Figure FDA00022392116000000413
the first harmonic to be compensated for the amplitude-limited modulated wave of the ith overmodulation block, x is the number of overmodulation blocks, VdciThe voltage of a direct current side capacitor of the ith overmodulation module;
a fourth module for compensating the total harmonic voltage according to the normal module
Figure FDA00022392116000000414
Using a formula
Figure FDA0002239211600000051
Calculating to obtain a second harmonic to be compensated for the modulation wave of the normal module, wherein Vdci(max)＝(1-Si)Vdci,i＝1,…,n-x，Vdci(max)Maximum positive voltage amplitude, V, allowed to compensate for the ith normal moduledciIs as followsThe direct current side capacitor voltage of the i normal modules, and Si is the modulation degree and the fundamental wave amplitude of the ith normal module; vdcj(max)＝(1-Sj)Vdcj,j＝1,…,n-x，Vdcj(max)Maximum positive voltage amplitude, V, allowed to compensate for the jth normal moduledcjIs the DC side capacitor voltage of the jth normal module, SjThe modulation degree and the fundamental wave amplitude of the jth normal module are obtained; n-x is the number of normal modules,
Figure FDA0002239211600000052
a second harmonic to be compensated for the modulated wave of the ith normal module;
a fifth module for adopting a formula according to the second harmonic wave to be compensated of the modulation wave of the normal module and the modulation degree
Figure FDA0002239211600000053
Calculating to obtain a modulation wave of a normal module; wherein the content of the first and second substances,
Figure FDA0002239211600000054
modulated wave of i-th normal module, SiThe modulation degree and the fundamental wave amplitude of the ith normal module,
Figure FDA0002239211600000055
for the phase angle of the voltage of the power network,
Figure FDA0002239211600000056
the included angle between the total modulation voltage and the power grid voltage is obtained.
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