CN116054186B - Hybrid multifunctional grid-connected converter system under complex scene and control method - Google Patents

Hybrid multifunctional grid-connected converter system under complex scene and control method Download PDF

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CN116054186B
CN116054186B CN202310335102.8A CN202310335102A CN116054186B CN 116054186 B CN116054186 B CN 116054186B CN 202310335102 A CN202310335102 A CN 202310335102A CN 116054186 B CN116054186 B CN 116054186B
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current
grid
voltage
value
npc
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CN116054186A (en
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涂春鸣
黄泽钧
郭祺
侯玉超
肖凡
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Hunan University
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Hunan University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
    • H02J3/1835—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control
    • H02J3/1842—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
    • H02J3/1857—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters wherein such bridge converter is a multilevel converter
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
    • H02H9/08—Limitation or suppression of earth fault currents, e.g. Petersen coil
    • 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
    • H02M7/487—Neutral point clamped inverters

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  • Power Engineering (AREA)
  • Control Of Electrical Variables (AREA)
  • Inverter Devices (AREA)

Abstract

The invention discloses a hybrid multifunctional grid-connected converter system and a control method under a complex scene. The grid-connected converter direct-current side capacitor voltage stability can be maintained, additional direct-current side power supply equipment is not needed, the device cost is reduced, and the economy of the equipment is enhanced.

Description

Hybrid multifunctional grid-connected converter system under complex scene and control method
Technical Field
The invention relates to the field of arc extinction of power distribution networks, in particular to a hybrid multifunctional grid-connected converter system under a complex scene and a control method.
Background
The operation mode of the power distribution network is complex, faults are frequently caused by the influence of factors such as environment, and the fault state is difficult to predict. Among various faults of the power distribution network, single-phase earth faults account for the largest proportion. With the massive access of new energy, the power electronization degree of the power distribution network is increased, the proportion of an active component and a harmonic component in single-phase earth fault current is increased continuously, and the electric arc is difficult to self-extinguish. If not suppressed in time, permanent single-phase earth faults are liable to occur, and system overvoltage can be caused, so that insulation breakdown is caused, and interphase short circuit is caused.
According to whether different arc extinction technologies can realize full compensation of fault current, the existing arc extinction technologies can be divided into a passive arc extinction technology and an active arc extinction technology. The passive arc suppression device mainly comprises a fixed compensation type arc suppression coil and an automatic tuning type arc suppression coil. Because the passive arc extinguishing device only contains passive elements, reactive components in fault current can be compensated, and with the development of modern power grids, the passive arc extinguishing method cannot meet the arc extinguishing requirement of a power distribution network. To achieve full compensation of fault currents, active arc extinction techniques have been proposed, the characteristic feature of which is the use of active inverters. The active arc extinction technology injects full compensation current into a power distribution network system through an inverter circuit formed by power electronic devices, so that reactive components in fault current can be compensated, active and harmonic components can be compensated, and the aim of effectively inhibiting arc current is fulfilled. At present, the active arc extinction technology of the domestic power distribution network mainly comprises the following steps: active arc suppression coil method based on master-slave inverter, active arc suppression method based on flexible grounding control, fault arc suppression method based on cascade H-bridge converter, and the like.
A schematic diagram of a grid-connected converter (Grid connected Inverter, GCI) with simultaneous single-phase ground fault regulation and reactive compensation is shown in fig. 1. The scheme consists of a cascade H-bridge part and a neutral point clamped (Neutral Point Clamped, NPC) three-phase four-bridge arm part. After the single-phase earth fault occurs, the earth fault point and the earth parameter of the distribution network form a loop, and the distribution network earth current flows through the fault point to form fault current. The grid-connected current transformer is respectively injected with arc suppression current and reactive compensation current, so that fault point current is effectively restrained, and meanwhile, the power grid is ensured to still operate in a unit power factor during a single-phase grounding fault period. The switching loss of the grid-connected converter and the active component of the arc suppression current can lead to the voltage drop of the direct current side of the grid-connected converter in the arc suppression period, so that an additional energy supply device is needed to be added to the direct current side of the grid-connected converter, and the cost is high.
Disclosure of Invention
The present invention aims to solve at least one of the technical problems existing in the prior art. Therefore, the invention provides a hybrid multifunctional grid-connected converter system under a complex scene and a control method. The grid-connected converter direct-current side capacitor voltage stability can be maintained, additional direct-current side power supply equipment is not needed, the device cost is reduced, and the economy of the equipment is enhanced.
According to an embodiment of the first aspect of the invention, a control method of a hybrid multifunctional grid-connected converter in a complex scene comprises the following steps:
acquiring three-phase load current, and passing the three-phase load current through
Figure SMS_1
Obtaining a reactive compensation current reference value after transformation;
calculating additional total current flowing through the three-phase power grid, and passing the additional total current flowing through the three-phase power grid
Figure SMS_2
After transformation get +.>
Figure SMS_3
Shaft current reference value->
Figure SMS_4
and />
Figure SMS_5
Shaft current reference value->
Figure SMS_6
；
Obtaining reference value of NPC DC side capacitor voltage
Figure SMS_8
And reference value of direct-current side capacitor voltage of CHB
Figure SMS_10
Obtaining the actual value of NPC DC side capacitor voltage +.>
Figure SMS_13
And the actual value of the direct-side capacitor voltage of CHB +.>
Figure SMS_9
Reference value of NPC DC side capacitor voltage +.>
Figure SMS_11
And reference value of direct-current side capacitor voltage of CHB +.>
Figure SMS_14
Actual value of capacitor voltage on the DC side of NPC +.>
Figure SMS_16
And the actual value of the direct-side capacitor voltage of CHB +.>
Figure SMS_7
After making the difference, obtaining +.f through a voltage ring PI controller>
Figure SMS_12
Shaft current reference value->
Figure SMS_15
；
Obtaining actual measurement values of the output current and the direct-current side voltage of the grid-connected converter and given values of the output current and the direct-current side voltage of the grid-connected converter; the actual measurement values of the output current and the direct current side voltage of the grid-connected converter are used as feedback quantities, the deviation quantity is obtained by calculating the difference value between the actual measurement values and the given value of the output current and the direct current side voltage of the grid-connected converter, the deviation quantity is used as the input of a current loop PI controller, the modulation signal is generated after the voltage difference value between the grid-connected point and the power grid is added to the output of the current loop PI controller, and the voltage signal output by the current loop control is obtained after comprehensive control
Figure SMS_17
；
Obtaining reference value of NPC DC side capacitor voltage
Figure SMS_18
And the actual value of the NPC DC side capacitance voltage value
Figure SMS_19
Reference value of NPC DC side capacitor voltage +.>
Figure SMS_20
And the actual value of the NPC DC side capacitance voltage value +.>
Figure SMS_21
After the difference is made, and a voltage signal which is output by controlling the voltage loop PI controller and the current loop +.>
Figure SMS_22
After superposition, obtaining a switching signal of NPC through carrier lamination modulation;
obtaining reference value of capacitor voltage at direct current side of CHB
Figure SMS_23
And the actual value of the capacitor voltage value at the direct current side of CHB
Figure SMS_24
Reference value of capacitor voltage on direct current side of CHB +.>
Figure SMS_25
And the actual value of the capacitor voltage value at the direct current side of CHB +.>
Figure SMS_26
After the difference is made, the voltage signal output by the voltage loop PI controller and the current loop control is +.>
Figure SMS_27
After superposition, obtaining a switching signal of CHB through carrier phase-shifting modulation;
calculating arc suppression current to be output by the grid-connected converter during single-phase grounding fault as a reference value of a fourth bridge arm current, and combining the reference value of the fourth bridge arm current with an actual value of the fourth bridge arm currenti o Obtaining a modulation signal of a fourth bridge arm of the grid-connected converter by making a difference and passing through a current loop PIAnd (3) modulating the modulation signal of the fourth bridge arm of the grid-connected converter by PWM to obtain the switching signal of the fourth bridge arm of the grid-connected converter.
Further, it also includes constructing filter inductance
Figure SMS_28
The following formula is satisfied
Figure SMS_29
；
wherein ,
Figure SMS_30
for the capacitor voltage at the direct current side of the grid-connected converter, < + >>
Figure SMS_31
For the switching frequency +.>
Figure SMS_32
And injecting current for the maximum ripple allowed by the grid-connected current transformer.
Further, the method also comprises the construction of zero sequence inductance
Figure SMS_33
Step (a) ， Said zero sequence inductance->
Figure SMS_34
The following formula is satisfied
Figure SMS_35
；
wherein
Figure SMS_36
,/>
Figure SMS_37
For angular frequency +.>
Figure SMS_38
For the capacitance value of the three-phase line to ground capacitance, < >>
Figure SMS_39
For the resistance value of the three-phase line to ground resistance, < >>
Figure SMS_40
For the effective value of the fourth bridge arm output current, is->
Figure SMS_41
Is an effective value of the grid voltage. />
Further, in the step of calculating the additional total current flowing through the three-phase power grid, a calculation formula of the additional total current flowing through the three-phase power grid is as follows
Figure SMS_42
；
wherein ,
Figure SMS_45
、/>
Figure SMS_46
、/>
Figure SMS_48
additional total current, respectively three-phase current, ">
Figure SMS_43
、/>
Figure SMS_47
、/>
Figure SMS_49
A, B, C three-phase mains voltage, +.>
Figure SMS_50
For the capacitance value of the three-phase line to ground capacitance, < >>
Figure SMS_44
Is the resistance value of the three-phase line to ground resistance,θis the included angle between the power grid voltage and the zero sequence current.
Further, what is said isIn the step of calculating the arc suppression current required to be output by the grid-connected converter during single-phase grounding fault as the reference value of the fourth bridge arm current, the arc suppression current required to be output by the grid-connected converter
Figure SMS_51
The calculation formula of (2) is
Figure SMS_52
；
wherein ,
Figure SMS_53
grid voltage for phase line for single-phase earth fault occurrence,/->
Figure SMS_54
For the capacitance value of the three-phase line to ground capacitance, < >>
Figure SMS_55
For the resistance value of the three-phase line to ground resistance, < >>
Figure SMS_56
Is imaginary unit, ++>
Figure SMS_57
Is the angular frequency.
According to a second aspect of the present invention, a hybrid multifunctional grid-connected converter control system in a complex scenario includes:
the reactive current detection unit is used for acquiring three-phase load current and passing the three-phase load current through
Figure SMS_58
Obtaining a reactive compensation current reference value after transformation;
an additional current calculation unit for calculating an additional total current flowing through the three-phase power grid and passing the additional total current flowing through the three-phase power grid
Figure SMS_59
After transformation get +.>
Figure SMS_60
Shaft current reference value->
Figure SMS_61
and />
Figure SMS_62
Shaft current reference value->
Figure SMS_63
；
The overall voltage control unit is used for obtaining the reference value and the actual value of the NPC DC side voltage, the reference value and the actual value of the CHB DC side voltage, and obtaining the reference value and the actual value of the NPC and the CHB DC side voltage through the voltage ring PI after differencing
Figure SMS_64
Shaft current reference value->
Figure SMS_65
；
The comprehensive control unit is used for obtaining actual measurement values of the output current and the direct-current side voltage of the grid-connected converter and given values of the output current and the direct-current side voltage of the grid-connected converter; the actual measurement values of the output current and the direct current side voltage of the grid-connected converter are used as feedback quantities, the deviation values are obtained by calculating the difference values with the given values of the output current and the direct current side voltage of the grid-connected converter, the deviation values are used as the input of a current loop PI controller, the modulation signals are generated after the voltage difference values of the grid-connected point and the power grid are added to the output of the current loop PI controller, and the modulation signals are obtained after comprehensive control
Figure SMS_66
；
NPC control unit for obtaining reference value of NPC DC side capacitor voltage
Figure SMS_67
And the actual value of the NPC DC side capacitance voltage value +.>
Figure SMS_68
Reference value of NPC DC side capacitor voltage +.>
Figure SMS_69
And the actual value of the NPC DC side capacitance voltage value +.>
Figure SMS_70
After making the difference, the difference is controlled by a voltage loop PI controller and +.>
Figure SMS_71
After superposition, obtaining a switching signal of NPC through carrier lamination modulation;
the CHB control unit is used for acquiring a reference value of the capacitor voltage at the direct current side of the CHB
Figure SMS_72
And the actual value of the capacitor voltage value at the direct current side of CHB +.>
Figure SMS_73
Reference value of capacitor voltage on direct current side of CHB +.>
Figure SMS_74
And the actual value of the capacitor voltage value at the direct current side of CHB +.>
Figure SMS_75
After making the difference, the difference is controlled by a voltage ring PI controller and +.>
Figure SMS_76
After superposition, obtaining a switching signal of CHB through carrier phase-shifting modulation;
the fourth bridge arm control unit is used for calculating arc suppression current required to be output by the grid-connected converter during single-phase grounding fault as a reference value of fourth bridge arm current, and comparing the reference value of the fourth bridge arm current with the reference value of the fourth bridge arm current
Figure SMS_77
The difference is processed through a current loop PI to obtain a modulation signal of a fourth bridge arm of the grid-connected converter, and the modulation signal of the fourth bridge arm of the grid-connected converter is modulated through PWM to obtain a switching signal of the fourth bridge arm of the grid-connected converter.
Further, filtering inductance in grid-connected converter
Figure SMS_78
The following formula is satisfied
Figure SMS_79
；
wherein ,
Figure SMS_80
for the capacitor voltage at the direct current side of the grid-connected converter, < + >>
Figure SMS_81
For the switching frequency +.>
Figure SMS_82
And injecting current for the maximum ripple allowed by the grid-connected current transformer.
Further, zero sequence inductance in grid-connected converter
Figure SMS_83
The following formula is satisfied
Figure SMS_84
；
wherein
Figure SMS_85
，/>
Figure SMS_86
For angular frequency +.>
Figure SMS_87
For the capacitance value of the three-phase line to ground capacitance, < >>
Figure SMS_88
For the resistance value of the three-phase line to ground resistance, < >>
Figure SMS_89
For the effective value of the fourth bridge arm output current, is->
Figure SMS_90
Is an effective value of the grid voltage.
According to the hybrid multifunctional grid-connected converter system and the control method under the complex scene, the hybrid multifunctional grid-connected converter system at least has the following beneficial effects:
the invention obtains three-phase load current and passes the three-phase load current
Figure SMS_99
Obtaining a reactive compensation current reference value after transformation; calculating an additional total current flowing through the three-phase network, and passing the additional total current flowing through the three-phase network through +.>
Figure SMS_93
After transformation get +.>
Figure SMS_95
Shaft current reference value->
Figure SMS_102
and />
Figure SMS_107
Shaft current reference value->
Figure SMS_109
The method comprises the steps of carrying out a first treatment on the surface of the Obtaining a reference value and an actual value of the NPC direct current side voltage, a reference value and an actual value of the CHB direct current side voltage, and obtaining +.>
Figure SMS_110
Shaft current reference value->
Figure SMS_101
The method comprises the steps of carrying out a first treatment on the surface of the Obtaining actual measurement values of the output current and the direct-current side voltage of the grid-connected converter and given values of the output current and the direct-current side voltage of the grid-connected converter; the actual measurement values of the output current and the direct current side voltage of the grid-connected converter are used as feedback quantities, the deviation values are obtained by calculating the difference values between the actual measurement values and the given values of the output current and the direct current side voltage of the grid-connected converter, the deviation values are used as the input of a current loop PI controller, and the output of the current loop PI controller is added with the grid-connected point sumThe voltage difference of the power grid is used for generating a modulation signal, and the modulation signal is obtained after comprehensive control>
Figure SMS_105
The method comprises the steps of carrying out a first treatment on the surface of the Obtaining a reference value +.>
Figure SMS_91
And the actual value of the NPC DC side capacitance voltage value +.>
Figure SMS_97
Reference value of NPC DC side capacitor voltage +.>
Figure SMS_92
And the actual value of the NPC DC side capacitance voltage value +.>
Figure SMS_98
After making the difference, the difference is controlled by a voltage loop PI controller and +.>
Figure SMS_103
After superposition, obtaining a switching signal of NPC through carrier lamination modulation; obtaining reference value +.>
Figure SMS_106
And the actual value of the capacitor voltage value at the direct current side of CHB +.>
Figure SMS_96
Reference value of capacitor voltage on direct current side of CHB +.>
Figure SMS_100
And the actual value of the capacitor voltage value at the direct current side of CHB +.>
Figure SMS_104
After making the difference, the difference is controlled by a voltage ring PI controller and +.>
Figure SMS_108
After superposition, obtaining a switching signal of CHB through carrier phase-shifting modulation; calculating arc suppression current to be output by the grid-connected converter during single-phase grounding fault as a reference value of a fourth bridge arm current, and taking the fourth bridge arm current as a reference value of the fourth bridge arm currentReference value and ∈r of bridge arm current>
Figure SMS_94
The difference is processed through a current loop PI to obtain a modulation signal of a fourth bridge arm of the grid-connected converter, and the modulation signal of the fourth bridge arm of the grid-connected converter is modulated through PWM to obtain a switching signal of the fourth bridge arm of the grid-connected converter. The grid-connected converter direct-current side capacitor voltage stability can be maintained, additional direct-current side power supply equipment is not needed, the device cost is reduced, and the economy of the equipment is enhanced.
Additional aspects and advantages of the invention 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 invention.
Drawings
The invention is further described with reference to the accompanying drawings and examples, in which:
fig. 1 is a circuit structure diagram of a hybrid multifunctional grid-connected converter system in a complex scene;
fig. 2 is an equivalent circuit diagram of a power distribution network comprising a grid-connected converter topology device;
FIGS. 3a-3d are NPC output current phasors;
FIG. 4a is a current flow diagram of the crowbar current loop;
FIG. 4b is a current flow diagram of an additional current loop;
FIGS. 5a-5c are additional current phasors;
fig. 6 is a schematic diagram of a hybrid multifunctional grid-connected inverter control method under a complex scene in an embodiment of the invention;
fig. 7 is a fourth leg phasor diagram;
FIG. 8 is a diagram of
Figure SMS_111
Phasor diagram at minimum;
FIG. 9a shows an embodiment of the present invention
Figure SMS_112
、/>
Figure SMS_113
、/>
Figure SMS_114
Is a simulation waveform diagram of (1);
FIG. 9b shows an embodiment of the present invention
Figure SMS_115
Is a simulation waveform diagram of (1);
FIG. 9c shows an embodiment of the present invention
Figure SMS_116
、/>
Figure SMS_117
Is a simulation waveform diagram of (1);
FIG. 9d shows an embodiment of the present invention
Figure SMS_118
、/>
Figure SMS_119
Is a simulation waveform diagram of (1);
FIG. 9e shows an embodiment of the present invention
Figure SMS_120
、/>
Figure SMS_121
Is a simulation waveform diagram of (1);
FIG. 9f shows an embodiment of the present invention
Figure SMS_122
、/>
Figure SMS_123
、/>
Figure SMS_124
Is a simulation waveform diagram of (1);
FIG. 9g is a diagram of an embodiment of the present invention
Figure SMS_125
、/>
Figure SMS_126
Is a simulation waveform diagram of (1).
Detailed Description
Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are illustrative only and are not to be construed as limiting the invention.
In the description of the present invention, it should be understood that the direction or positional relationship indicated with respect to the description of the orientation, such as up, down, etc., is based on the direction or positional relationship shown in the drawings, is merely for convenience of describing the present invention and simplifying the description, and does not indicate or imply that the apparatus or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention.
In the description of the present invention, plural means two or more. The description of the first and second is for the purpose of distinguishing between technical features only and should not be construed 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.
In the description of the present invention, unless explicitly defined otherwise, terms such as arrangement, installation, connection, etc. should be construed broadly and the specific meaning of the terms in the present invention can be reasonably determined by a person skilled in the art in combination with the specific contents of the technical scheme.
Firstly, introducing the working principle of a hybrid multifunctional grid-connected converter (Grid connected Inverter, GCI) system in a complex scene, wherein the grid-connected converter comprises a three-phase cascade H-bridge converter unit (CHB) and a neutral point clamped (Neutral Point Clamped, NPC) three-phase four-bridge arm unit, three-phase output ends of the three-phase cascade H-bridge converter unit are respectively connected with three phase lines of a three-phase power distribution network, and the neutral point clamped three-phase four-bridge arm unit is connected to a common point of the three-phase cascade H-bridge converter unit in series as shown in fig. 1;
in particular, the method comprises the steps of,the three-phase cascade H-bridge converter unit comprises six cascade H-bridge modules and three filter inductors
Figure SMS_127
The structure is that every two cascade H-bridge modules are connected in series and are connected in series through a filter inductor>
Figure SMS_128
The cascade H-bridge module comprises a PWM inverter formed by full-control devices and a third direct-current side energy storage capacitor +.>
Figure SMS_129
. The PWM inverter is formed by a fifth IGBT module S 5 Sixth IGBT module S 6 Seventh IGBT Module S 7 Eighth IGBT module S 8 And 4 freewheeling diodes, one end of which is connected with the sixth IGBT module S 6 Emitter and eighth IGBT module S of (v) 8 The node of the collector electrode of the (B) is connected to another PWM inverter or neutral point clamped three-phase four-bridge arm unit, and the other end of the three-phase four-bridge arm unit passes through a fifth IGBT module S 5 Emitter of (c) and seventh IGBT module S 7 The node of the collector of (c) is connected to a filter inductance +.>
Figure SMS_130
. Third DC side energy storage capacitor->
Figure SMS_131
The energy storage capacitor is arranged on the direct current side of the PWM inverter and on the third direct current side>
Figure SMS_132
Positive electrode of (a) and fifth IGBT module S 5 The collector of which is connected to a third DC-side energy storage capacitor->
Figure SMS_133
Anode of (c) and seventh IGBT module S 7 Is connected to the node emitter of (c).
The neutral point clamped three-phase four-bridge arm unit comprises a first NPC module, a second NPC module, a third NPC module and a fourth NPC module which are identical in structure, wherein the first NPC module, the second NPC module and the third NPThe C module corresponds to A, B, C three phases respectively, and the fourth NPC module is used as a fourth bridge arm and further comprises a first direct current side energy storage capacitor
Figure SMS_134
And a second DC-side energy storage capacitor->
Figure SMS_138
First DC side energy storage capacitor->
Figure SMS_140
Is connected to the negative pole of (a) and the second DC side energy storage capacitor->
Figure SMS_135
The positive electrode of the first direct current side energy storage capacitor is connected with
Figure SMS_139
The positive pole of the first NPC module, the second NPC module, the third NPC module and the fourth NPC module are respectively connected with one end of the first NPC (Neutral Point Clamped) module, the second NPC module, the third NPC module and the fourth NPC module, and the second direct current side energy storage capacitor is->
Figure SMS_141
The negative electrodes of the first NPC module, the second NPC module, the third NPC module and the fourth NPC module are respectively connected with the other ends of the first NPC module, the second NPC module, the third NPC module and the fourth NPC module, and the first direct current side energy storage capacitor is->
Figure SMS_142
And a second DC-side energy storage capacitor->
Figure SMS_136
The common end of the first NPC module, the second NPC module, the third NPC module and the direct current side midpoint of the fourth NPC module are connected, the alternating current side terminals of the first NPC module, the second NPC module and the third NPC module are respectively connected with one corresponding cascade H bridge module in the three-phase cascade H bridge converter unit, and the alternating current side terminal of the fourth NPC module is added with the direct current side midpoint of the fourth NPC module through an inductor>
Figure SMS_137
And (5) grounding.
Specifically, a first NPC module and a second NPC moduleThe block, the third NPC module and the fourth NPC module have the same structure and all comprise first IGBT modules S connected in series 1 Second IGBT module S 2 Third IGBT module S 3 Fourth IGBT Module S 4 First flywheel diode D 1 And a second flywheel diode D 2 First IGBT module S 1 Is connected with the first direct current side energy storage capacitor
Figure SMS_143
Positive electrode of the first IGBT module S 1 Is connected with a second IGBT module S 2 Collector of the second IGBT module S 2 Is connected with a third IGBT module S 3 Collector of third IGBT module S 3 The emitter of (a) is connected with a fourth IGBT module S 4 Collector of the fourth IGBT module S 4 The emitter of (2) is connected with a second direct-current side energy storage capacitor->
Figure SMS_144
A cathode of the first flywheel diode D 1 Is connected with the first IGBT module S 1 And a second IGBT module S 2 A first freewheeling diode D 1 The anode of the first flywheel diode D is connected with 2 A cathode of a second flywheel diode D 2 Is connected with a third IGBT module S 3 And a fourth IGBT module S 4 A first freewheeling diode D 1 And a second flywheel diode D 2 The common end of the second IGBT module S is used as the midpoint of the direct current side of the first NPC module, the second NPC module, the third NPC module and the fourth NPC module 2 And a third IGBT module S 3 Is used as the ac side terminal of the first NPC module, the second NPC module, the third NPC module, and the fourth NPC module.
Figure SMS_153
、/>
Figure SMS_145
、/>
Figure SMS_150
A, B, C three-phase network voltages respectively; />
Figure SMS_148
、/>
Figure SMS_149
、/>
Figure SMS_154
A, B, C three-phase network currents respectively
Figure SMS_159
、/>
Figure SMS_155
、/>
Figure SMS_157
A, B, C three-phase output currents of grid-connected converters respectively, < >>
Figure SMS_147
For the output current of the fourth bridge arm of the grid-connected converter, < >>
Figure SMS_151
、/>
Figure SMS_158
、/>
Figure SMS_161
The resistances to ground of the three-phase lines are A, B, C respectively; />
Figure SMS_162
、/>
Figure SMS_164
、/>
Figure SMS_152
A, B, C three-phase line-to-ground capacitors; />
Figure SMS_156
A transition resistance for ground fault; />
Figure SMS_160
Is a direct current side capacitor; />
Figure SMS_163
Is a filter inductance; />
Figure SMS_146
Is zero sequence inductance. To simplify the analysis, one of the phases is described below as an example.
As shown in fig. 2, an equivalent circuit diagram of a power distribution network with a grid-connected converter is shown, when a single-phase grounding fault occurs, a grounding fault point forms a loop with the ground and the parameters of the power distribution network to the ground, and the power distribution network to the ground current flows through the fault point to form a fault current. The grid-connected converter can be equivalently a differential mode voltage source and a common mode voltage source, and arc suppression current and reactive compensation current are respectively injected at the moment, so that fault point current is effectively restrained, and meanwhile, the power grid is ensured to still operate in a unit power factor during a single-phase grounding fault period.
When the C phase has single-phase ground fault, writing KCL equation to the D point column, and carrying in voltage and network parameters to obtain:
Figure SMS_165
(1)
is provided with
Figure SMS_166
，/>
Figure SMS_167
，/>
Figure SMS_168
Then the value of the injected arc extinction current is as follows:
Figure SMS_169
(2)
at this time, the A, B, C three-phase output current of the grid-connected converter is the vector sum of arc suppression current and reactive current, namely:
Figure SMS_170
(3)
the current phasor relationship of the grid-connected converter is shown in fig. 3a-3 c, in which
Figure SMS_174
、/>
Figure SMS_177
、/>
Figure SMS_180
Load reactive current of grid-connected converter, < +.>
Figure SMS_172
、/>
Figure SMS_175
、/>
Figure SMS_178
The current is the zero sequence current flowing through A, B, C three phases of grid-connected converters respectively, and the ultraviolet is A, B, C three-phase output current +.>
Figure SMS_181
、/>
Figure SMS_171
、/>
Figure SMS_176
，/>
Figure SMS_179
Is->
Figure SMS_182
And->
Figure SMS_173
Included angle of (a)θThe specific expression related to the capacitance to ground and the resistance is as follows:
Figure SMS_183
(4)
at this time, the active power of A, B, C three-phase transmission of the grid-connected converter is as follows:
Figure SMS_184
(5)
as can be seen from fig. 3a, the angle between the a-phase voltage and the zero sequence current is always acute during extinction, so that the a-phase consumes active power during extinction. As can be seen from FIG. 3b, when 0.ltoreq.θWhen the angle is less than 30 degrees, the included angle between the B-phase voltage and the zero sequence current is an acute angle, and the B-phase consumes active power in the arc extinction period; when (when)θWhen the phase-B voltage is equal to 30 degrees, the phase-B voltage is perpendicular to the zero sequence current, and the phase-B only transmits reactive power in the arc extinction period; 30 degrees < "θWhen the temperature is less than or equal to 60 degrees, the included angle between the B phase voltage and the zero sequence current is an obtuse angle, and the B phase absorbs active power in the arc extinction period. In fig. 3C, the C-phase only outputs load reactive power, since the fault phase voltage is zero. Three lines in FIG. 3d
Figure SMS_185
、/>
Figure SMS_186
、/>
Figure SMS_187
As can be seen from the figure, the output currents of the grid-connected converters are not symmetrical due to the overlapping of the zero-sequence current components, wherein the output current phasors are A, B, C three-phase output current phasors of the NPCs respectively.
Fig. 4a is a circuit of arc suppression current, when the grid-connected converter performs arc suppression, the arc suppression current flows from the a-phase and B-phase of the grid-connected converter to the ground capacitor and the resistor, and the active power is required to be consumed by the grid-connected converter during the arc suppression period because the arc suppression current contains the active component. Fig. 4b shows an additional current loop, in which additional current flows between the grid and the grid-connected converter. By adding an additional current loop, the grid-connected converter can absorb active power from a power grid, so that energy loss in an arc extinction process is compensated, stability of direct-current side capacitor voltage is further maintained, and operation reliability of the device is improved.
In order to further verify that the capacitor voltage on the direct current side of the grid-connected converter can be stable at the same time, the following specific analysis is performed, and as can be seen from the formula (5), the additional active current flowing through the three-phase power grid is as follows:
Figure SMS_188
(6)
as can be seen from the formula (6),
Figure SMS_190
the method comprises the following steps: if the grid-connected converter only exchanges active power with the power grid, the neutral point of the power grid does not meet the current balance equation. Thus, the grid-connected converter must also have reactive power exchange with the grid. As shown in FIGS. 5a-5c, an additional current phasor diagram is shown, wherein +.>
Figure SMS_194
、/>
Figure SMS_197
、/>
Figure SMS_191
Additional active current flowing for the three-phase network, +.>
Figure SMS_192
、/>
Figure SMS_195
、/>
Figure SMS_198
For the additional reactive current flowing in the three-phase network, +.>
Figure SMS_189
、/>
Figure SMS_193
、/>
Figure SMS_196
An additional total current flowing for three phases of current. />
As can be seen from fig. 5a-5c, the additional reactive current flowing through the three-phase network is:
Figure SMS_199
(7)
the additional total current flowing through the three-phase network is:
Figure SMS_200
(8)
in summary, due to the existence of the additional loop, the grid-connected converter can absorb the energy required by arc extinction from the power grid, and the direct-current side capacitor voltage of the grid-connected converter can be stabilized at the same time in the arc extinction period.
According to the above analysis, referring to fig. 6, the method for controlling a hybrid multifunctional grid-connected converter in a complex scenario according to the embodiment of the present invention includes several parts including reactive current detection, additional current calculation, overall voltage control, comprehensive control, NPC control, CHB control, and fourth bridge arm control:
reactive current detection: acquiring three-phase load current, and passing the three-phase load current through
Figure SMS_201
Obtaining a reactive compensation current reference value after transformation;
additional current calculation: calculating additional total current flowing through the three-phase power grid through the method (8), and passing the additional total current flowing through the three-phase power grid through
Figure SMS_202
After transformation get +.>
Figure SMS_203
Shaft current reference value->
Figure SMS_204
and />
Figure SMS_205
Shaft current reference value->
Figure SMS_206
；
Overall voltage control: obtaining reference value of NPC DC side capacitor voltage
Figure SMS_208
And reference value of direct-current side capacitor voltage of CHB +.>
Figure SMS_212
Obtaining the actual value of NPC DC side capacitor voltage +.>
Figure SMS_215
And the actual value of the direct-side capacitor voltage of CHB +.>
Figure SMS_207
Reference value of NPC DC side capacitor voltage +.>
Figure SMS_210
And reference value of direct-current side capacitor voltage of CHB +.>
Figure SMS_214
Actual value of capacitor voltage on the DC side of NPC +.>
Figure SMS_216
And the actual value of the DC side capacitor voltage of CHB
Figure SMS_209
After making the difference, obtaining +.f through a voltage ring PI controller>
Figure SMS_211
Shaft current reference value->
Figure SMS_213
；
And (3) comprehensive control: obtaining actual measurement values of the output current and the direct-current side voltage of the grid-connected converter and given values of the output current and the direct-current side voltage of the grid-connected converter; the actual measurement values of the output current and the direct current side voltage of the grid-connected converter are taken as feedback values to be matched with the given values of the output current and the direct current side voltage of the grid-connected converterThe difference value is calculated to obtain the deviation value, the deviation value is used as the input of a current loop PI controller, the output of the current loop PI controller is added with the voltage difference value between the grid connection point and the power grid to generate a modulation signal, and the voltage signal of the current loop control output is obtained after comprehensive control
Figure SMS_217
The step adopts +.>
Figure SMS_218
The decoupling control algorithm can realize active and reactive decoupling control; />
NPC control: obtaining reference value of NPC DC side capacitor voltage
Figure SMS_219
And the actual value of the NPC DC side capacitance voltage value +.>
Figure SMS_220
Reference value of NPC DC side capacitor voltage +.>
Figure SMS_221
And the actual value of the NPC DC side capacitance voltage value
Figure SMS_222
After making the difference, the difference is controlled by a voltage loop PI controller and +.>
Figure SMS_223
After superposition, obtaining a switching signal of NPC through carrier lamination modulation;
CHB control: obtaining reference value of capacitor voltage at direct current side of CHB
Figure SMS_224
And the actual value of the capacitor voltage value at the direct current side of CHB +.>
Figure SMS_225
Reference value of capacitor voltage on direct current side of CHB +.>
Figure SMS_226
And CHB dc sideActual value of the capacitance voltage value +.>
Figure SMS_227
After making the difference, the difference is controlled by a voltage ring PI controller and +.>
Figure SMS_228
After superposition, obtaining a switching signal of CHB through carrier phase-shifting modulation;
fourth bridge arm control: calculating arc suppression current to be output by the grid-connected converter during single-phase earth fault through the method (2) as a reference value of a fourth bridge arm current, and combining the reference value of the fourth bridge arm current with an actual value of the fourth bridge arm current
Figure SMS_229
The difference is processed through a current loop PI to obtain a modulation signal of a fourth bridge arm of the grid-connected converter, and the modulation signal of the fourth bridge arm of the grid-connected converter is modulated through PWM to obtain a switching signal of the fourth bridge arm of the grid-connected converter.
It should be noted that, in order to ensure stable operation of the grid-connected converter, the embodiment further includes constructing a filter inductor
Figure SMS_230
Zero sequence inductance->
Figure SMS_231
The method is characterized by comprising the following steps:
filtering inductance
Figure SMS_232
：
Filtering inductance
Figure SMS_233
The function of the grid-connected converter is to reduce the current ripple output by the grid-connected converter, and the value of the current ripple meets the following formula:
Figure SMS_234
(9)
wherein ,
Figure SMS_235
for the capacitor voltage at the direct current side of the grid-connected converter, < + >>
Figure SMS_236
For the switching frequency +.>
Figure SMS_237
And injecting current for the maximum ripple allowed by the grid-connected current transformer.
Zero sequence inductance
Figure SMS_238
：
The zero sequence inductor of the fourth bridge arm has the functions of suppressing the subharmonic of the switching frequency and bearing most of the voltage during arc extinction, and a voltage equation is written for the fourth bridge arm column:
Figure SMS_239
(10)
wherein ,
Figure SMS_240
is imaginary unit, ++>
Figure SMS_241
The fourth bridge arm phasor relationship is shown in FIG. 7, which shows the angular frequencyαIs->
Figure SMS_242
And (3) with
Figure SMS_243
The specific expression is as follows:
Figure SMS_244
(11)
the fourth arm output voltage can be obtained according to FIG. 7
Figure SMS_245
The method comprises the following steps:
Figure SMS_246
(12)
wherein the fourth bridge arm outputs an effective value of current
Figure SMS_247
The expression of (2) is:
Figure SMS_248
(13)/>
from equation (13), it is found that the corresponding phasor relationship in order to minimize the output voltage of the fourth arm is shown in FIG. 8
Figure SMS_249
The optimal values of (2) are:
Figure SMS_250
(14)
wherein E is the effective value of the grid voltage.
The invention also relates to a mixed type multifunctional grid-connected converter control system in a complex scene, which comprises the following components:
the reactive current detection unit is used for obtaining three-phase load current, and obtaining a reactive compensation current reference value after the three-phase load current is subjected to dq conversion;
an additional current calculation unit for calculating additional total current flowing through the three-phase power grid, and obtaining a q-axis current reference value after dq conversion of the additional total current flowing through the three-phase power grid
Figure SMS_251
And d-axis current reference value->
Figure SMS_252
；
The overall voltage control unit is used for obtaining the reference value and the actual value of the NPC DC side voltage, the reference value and the actual value of the CHB DC side voltage, and obtaining the d-axis current reference value through the voltage ring PI after the reference value and the actual value of the NPC and the CHB DC side voltage are differenced
Figure SMS_253
；
The comprehensive control unit is used for obtaining actual measurement values of the output current and the direct-current side voltage of the grid-connected converter and given values of the output current and the direct-current side voltage of the grid-connected converter; the actual measurement values of the output current and the direct current side voltage of the grid-connected converter are used as feedback quantities, the deviation values are obtained by calculating the difference values with the given values of the output current and the direct current side voltage of the grid-connected converter, the deviation values are used as the input of a current loop PI controller, the modulation signals are generated after the voltage difference values of the grid-connected point and the power grid are added to the output of the current loop PI controller, and the modulation signals are obtained after comprehensive control
Figure SMS_254
；
NPC control unit for obtaining reference value of NPC DC side capacitor voltage
Figure SMS_255
And the actual value of the NPC DC side capacitance voltage value +.>
Figure SMS_256
Reference value of NPC DC side capacitor voltage +.>
Figure SMS_257
And the actual value of the NPC DC side capacitance voltage value +.>
Figure SMS_258
After making the difference, the difference is controlled by a voltage loop PI controller and +.>
Figure SMS_259
After superposition, obtaining a switching signal of NPC through carrier lamination modulation;
the CHB control unit is used for acquiring a reference value of the capacitor voltage at the direct current side of the CHB
Figure SMS_260
And the actual value of the capacitor voltage value at the direct current side of CHB +.>
Figure SMS_261
Reference value of capacitor voltage on direct current side of CHB +.>
Figure SMS_262
And the actual value of the capacitor voltage value at the direct current side of CHB +.>
Figure SMS_263
After making the difference, the difference is controlled by a voltage ring PI controller and +.>
Figure SMS_264
After superposition, obtaining a switching signal of CHB through carrier phase-shifting modulation;
the fourth bridge arm control unit is used for calculating arc suppression current required to be output by the grid-connected converter during single-phase grounding fault as a reference value of fourth bridge arm current, and comparing the reference value of the fourth bridge arm current with the reference value of the fourth bridge arm current
Figure SMS_265
The difference is processed through a current loop PI to obtain a modulation signal of a fourth bridge arm of the grid-connected converter, and the modulation signal of the fourth bridge arm of the grid-connected converter is modulated through PWM to obtain a switching signal of the fourth bridge arm of the grid-connected converter.
Filtering inductor in grid-connected converter
Figure SMS_266
The following formula is satisfied
Figure SMS_267
；
wherein ,
Figure SMS_268
for the capacitor voltage at the direct current side of the grid-connected converter, < + >>
Figure SMS_269
For the switching frequency +.>
Figure SMS_270
And injecting current for the maximum ripple allowed by the grid-connected current transformer.
Zero sequence inductance in grid-connected converter
Figure SMS_271
The following formula is satisfied
Figure SMS_272
；
wherein ,
Figure SMS_273
，/>
Figure SMS_274
for angular frequency +.>
Figure SMS_275
For the capacitance value of the three-phase line to ground capacitance, < >>
Figure SMS_276
For the resistance value of the three-phase line to ground resistance, < >>
Figure SMS_277
For the effective value of the fourth bridge arm output current, is->
Figure SMS_278
Is an effective value of the grid voltage.
In order to verify the effectiveness and feasibility of the invention, a simulation model is built in a MATLAB/Simulink simulation platform for simulation analysis, and simulation parameters are shown in Table 1. The power grid of 0.8 to 0.9s normally operates, and the grid-connected converter outputs reactive compensation current; 0.9s A phase is subjected to single-phase grounding fault, and the grid-connected converter outputs reactive compensation current and arc suppression current simultaneously; and 1.3s of faults are eliminated, at the moment, the current of the fourth bridge arm is zero, and the grid-connected converter outputs reactive compensation current.
Figure SMS_279
As can be seen from fig. 9a and 9b, the grid-connected converter injects an arc suppression current, and the ground fault current is suppressed to 1.8A. Fig. 9C-9 e are graphs of the grid voltage and current, and it can be seen from the graph that the a-phase grid current leads the voltage by 10.8 ° and the B-phase grid voltage is substantially in phase with the current and the C-phase grid voltage leads the current by 4.8 ° due to the additional current loop. Fig. 9 f-9 g are dc side capacitor voltage waveforms of CHB and NPC, respectively, in which the dc side voltages of NPC and CHB are maintained stable due to the addition of the voltage stabilizing control during the arc extinction, the voltage fluctuation of CHB is about 20V, and the voltage fluctuation of NPC is about 40V.
The embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of one of ordinary skill in the art without departing from the spirit of the present invention.

Claims (8)

1. The control method of the hybrid multifunctional grid-connected converter in the complex scene is characterized by comprising the following steps of:
three-phase load current is obtained, and reactive compensation current reference values are obtained after dq conversion of the three-phase load current;
calculating additional total current flowing through the three-phase power grid, and obtaining a q-axis current reference value after dq conversion of the additional total current flowing through the three-phase power grid
Figure QLYQS_1
And d-axis current reference value->
Figure QLYQS_2
；
Obtaining reference value of NPC DC side capacitor voltage
Figure QLYQS_5
And reference value of direct-current side capacitor voltage of CHB +.>
Figure QLYQS_8
Obtaining the actual value of NPC DC side capacitor voltage +.>
Figure QLYQS_10
And the actual value of the direct-side capacitor voltage of CHB +.>
Figure QLYQS_3
Reference value of NPC DC side capacitor voltage +.>
Figure QLYQS_7
And reference value of direct-current side capacitor voltage of CHB +.>
Figure QLYQS_9
Actual value of capacitor voltage on the DC side of NPC +.>
Figure QLYQS_11
And the actual value of the direct-side capacitor voltage of CHB +.>
Figure QLYQS_4
After the difference is made, a d-axis current reference value is obtained through a voltage ring PI controller>
Figure QLYQS_6
；
Obtaining actual measurement values of the output current and the direct-current side voltage of the grid-connected converter and given values of the output current and the direct-current side voltage of the grid-connected converter; the actual measurement values of the output current and the direct current side voltage of the grid-connected converter are used as feedback quantities, the deviation quantity is obtained by calculating the difference value between the actual measurement values and the given value of the output current and the direct current side voltage of the grid-connected converter, the deviation quantity is used as the input of a current loop PI controller, the modulation signal is generated after the voltage difference value between the grid-connected point and the power grid is added to the output of the current loop PI controller, and the voltage signal output by the current loop control is obtained after comprehensive control
Figure QLYQS_12
；
Obtaining reference value of NPC DC side capacitor voltage
Figure QLYQS_13
And the actual value of the NPC DC side capacitance voltage value +.>
Figure QLYQS_14
Reference value of NPC DC side capacitor voltage +.>
Figure QLYQS_15
And the actual value of the NPC DC side capacitance voltage value +.>
Figure QLYQS_16
After the difference is made, and a voltage signal which is output by controlling the voltage loop PI controller and the current loop +.>
Figure QLYQS_17
After superposition, obtaining a switching signal of NPC through carrier lamination modulation;
obtaining reference value of capacitor voltage at direct current side of CHB
Figure QLYQS_18
And the actual value of the capacitor voltage value at the direct current side of CHB +.>
Figure QLYQS_19
Reference value of capacitor voltage on direct current side of CHB +.>
Figure QLYQS_20
And the actual value of the capacitor voltage value at the direct current side of CHB +.>
Figure QLYQS_21
After the difference is made, the voltage signal output by the voltage loop PI controller and the current loop control is +.>
Figure QLYQS_22
After superposition, obtaining a switching signal of CHB through carrier phase-shifting modulation;
calculating arc suppression current to be output by the grid-connected converter during single-phase grounding fault as a reference value of a fourth bridge arm current, and combining the reference value of the fourth bridge arm current with an actual value of the fourth bridge arm currenti o And obtaining a modulation signal of a fourth bridge arm of the grid-connected converter by the difference through a current loop PI, and obtaining a switching signal of the fourth bridge arm of the grid-connected converter by PWM modulation of the modulation signal of the fourth bridge arm of the grid-connected converter.
2. The method for controlling a hybrid multifunctional grid-connected converter in a complex scenario according to claim 1, further comprising constructing a filter inductor
Figure QLYQS_23
Step, the filter inductance->
Figure QLYQS_24
The following formula is satisfied
Figure QLYQS_25
;
wherein ,
Figure QLYQS_26
for the capacitor voltage at the direct current side of the grid-connected converter, < + >>
Figure QLYQS_27
For the switching frequency +.>
Figure QLYQS_28
And injecting current for the maximum ripple allowed by the grid-connected current transformer.
3. The method for controlling a hybrid multifunctional grid-connected converter in a complex scenario according to claim 1, further comprising constructing a zero sequence inductance
Figure QLYQS_29
Step (a) ， Said zero sequence inductance->
Figure QLYQS_30
The following formula is satisfied
Figure QLYQS_31
;
wherein
Figure QLYQS_32
,/>
Figure QLYQS_33
For angular frequency +.>
Figure QLYQS_34
For the capacitance value of the three-phase line to ground capacitance, < >>
Figure QLYQS_35
For the resistance value of the three-phase line to ground resistance, < >>
Figure QLYQS_36
For the effective value of the fourth bridge arm output current, is->
Figure QLYQS_37
Is an effective value of the grid voltage.
4. The method for controlling a hybrid multifunctional grid-connected inverter in a complex scenario according to claim 1, wherein in the step of calculating the additional total current flowing through the three-phase power grid, a calculation formula of the additional total current flowing through the three-phase power grid is as follows
Figure QLYQS_38
;
wherein ,
Figure QLYQS_40
、/>
Figure QLYQS_42
、/>
Figure QLYQS_44
additional total current, respectively three-phase current, ">
Figure QLYQS_41
、/>
Figure QLYQS_43
、/>
Figure QLYQS_45
A, B, C three-phase mains voltage, +.>
Figure QLYQS_46
For the capacitance value of the three-phase line to ground capacitance, < >>
Figure QLYQS_39
Is the resistance value of the three-phase line to ground resistance,θis the included angle between the power grid voltage and the zero sequence current.
5. The method for controlling a hybrid multifunctional grid-connected converter in a complex scenario according to claim 1, wherein in the step of calculating the arc suppression current to be output by the grid-connected converter during a single-phase earth fault as the reference value of the fourth bridge arm current, the arc suppression current to be output by the grid-connected converter
Figure QLYQS_47
The calculation formula of (2) is
Figure QLYQS_48
;
wherein ,
Figure QLYQS_49
grid voltage for phase line for single-phase earth fault occurrence,/->
Figure QLYQS_50
For the capacitance value of the three-phase line to ground capacitance, < >>
Figure QLYQS_51
For the resistance value of the three-phase line to ground resistance, < >>
Figure QLYQS_52
Is imaginary unit, ++>
Figure QLYQS_53
Is the angular frequency.
6. The utility model provides a mixed type multifunctional grid-connected inverter control system under complicated scene which characterized in that includes:
the reactive current detection unit is used for acquiring three-phase load current and passing the three-phase load current through
Figure QLYQS_54
Obtaining a reactive compensation current reference value after transformation;
an additional current calculation unit for calculating additional total current flowing through the three-phase power grid, and obtaining a q-axis current reference value after dq conversion of the additional total current flowing through the three-phase power grid
Figure QLYQS_55
And d-axis current reference value->
Figure QLYQS_56
；
The overall voltage control unit is used for obtaining a reference value of NPC direct-current side capacitor voltage
Figure QLYQS_57
And reference value of direct-current side capacitor voltage of CHB +.>
Figure QLYQS_61
Obtaining the actual value of NPC DC side capacitor voltage +.>
Figure QLYQS_63
And the actual value of the direct-side capacitor voltage of CHB +.>
Figure QLYQS_58
Reference value of NPC DC side capacitor voltage +.>
Figure QLYQS_60
And reference value of direct-current side capacitor voltage of CHB +.>
Figure QLYQS_64
Actual value of capacitor voltage on the DC side of NPC +.>
Figure QLYQS_65
And the actual value of the direct-side capacitor voltage of CHB +.>
Figure QLYQS_59
After the difference is made, a d-axis current reference value is obtained through a voltage ring PI controller>
Figure QLYQS_62
；
The comprehensive control unit is used for obtaining actual measurement values of the output current and the direct-current side voltage of the grid-connected converter and given values of the output current and the direct-current side voltage of the grid-connected converter; the actual measurement values of the output current and the direct current side voltage of the grid-connected converter are used as feedback quantities, the deviation quantity is obtained by calculating the difference value between the actual measurement values and the given value of the output current and the direct current side voltage of the grid-connected converter, the deviation quantity is used as the input of a current loop PI controller, the modulation signal is generated after the voltage difference value between the grid-connected point and the power grid is added to the output of the current loop PI controller, and the voltage signal output by the current loop control is obtained after comprehensive control
Figure QLYQS_66
；
NPC control unit for obtaining reference value of NPC DC side capacitor voltage
Figure QLYQS_67
And the actual value of the NPC DC side capacitance voltage value +.>
Figure QLYQS_68
Reference value of NPC DC side capacitor voltage +.>
Figure QLYQS_69
And the actual value of the NPC DC side capacitance voltage value +.>
Figure QLYQS_70
After the difference is made, and a voltage signal which is output by controlling the voltage loop PI controller and the current loop +.>
Figure QLYQS_71
After superposition, obtaining a switching signal of NPC through carrier lamination modulation;
the CHB control unit is used for acquiring a reference value of the capacitor voltage at the direct current side of the CHB
Figure QLYQS_72
And the actual value of the capacitor voltage value at the direct current side of CHB +.>
Figure QLYQS_73
Reference value of capacitor voltage on direct current side of CHB +.>
Figure QLYQS_74
And the actual value of the capacitor voltage value at the direct current side of CHB +.>
Figure QLYQS_75
After the difference is made, the voltage signal output by the voltage loop PI controller and the current loop control is +.>
Figure QLYQS_76
After superposition, obtaining a switching signal of CHB through carrier phase-shifting modulation;
the fourth bridge arm control unit is used for calculating arc suppression current required to be output by the grid-connected converter during single-phase grounding fault as a reference value of fourth bridge arm current, and combining the reference value of the fourth bridge arm current with the actual value of the fourth bridge arm currenti o And obtaining a modulation signal of a fourth bridge arm of the grid-connected converter by the difference through a current loop PI, and obtaining a switching signal of the fourth bridge arm of the grid-connected converter by PWM modulation of the modulation signal of the fourth bridge arm of the grid-connected converter.
7. The hybrid multifunctional grid-connected inverter control system in complex scenarios according to claim 6, characterized in that the filter inductance in the grid-connected inverter
Figure QLYQS_77
The following formula is satisfied
Figure QLYQS_78
;
wherein ,
Figure QLYQS_79
for the capacitor voltage at the direct current side of the grid-connected converter, < + >>
Figure QLYQS_80
For the switching frequency +.>
Figure QLYQS_81
And injecting current for the maximum ripple allowed by the grid-connected current transformer.
8. The hybrid multifunctional grid-connected converter control system under complex scenarios according to claim 6, characterized in that the zero sequence inductance in the grid-connected converter
Figure QLYQS_82
The following formula is satisfied
Figure QLYQS_83
;
wherein
Figure QLYQS_84
,/>
Figure QLYQS_85
For angular frequency +.>
Figure QLYQS_86
Is three-phaseCapacitance value of line-to-ground capacitance, +.>
Figure QLYQS_87
For the resistance value of the three-phase line to ground resistance, < >>
Figure QLYQS_88
For the effective value of the fourth bridge arm output current, is->
Figure QLYQS_89
Is an effective value of the grid voltage. />
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