CN114826008A - Control system and method for reducing bridge arm current peak value of MMC (Modular multilevel converter) - Google Patents
Control system and method for reducing bridge arm current peak value of MMC (Modular multilevel converter) Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
- H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- 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
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
- H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/32—Means for protecting converters other than automatic disconnection
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Abstract
The invention relates to the technical field of electrical control, in particular to a control system and a control method for reducing a bridge arm current peak value of an MMC (modular multilevel converter). The invention comprises a voltage/power and current control module, a frequency doubling loop control module and a frequency quadrupling loop control module; the voltage/power and current control module is used for generating a three-phase modulation voltage reference value e aref 、e bref 、e cref (ii) a The double-frequency circulation control module is used for generating a reference value e of a three-phase double-frequency circulation modulation voltage ciraref2 、e cirbref2 、e circref2 (ii) a The quadruple frequency circulation control module is used for generating a quadruple frequency circulation modulation voltage reference value e of three phases ciraref4 、e cirbref4 、e circref4 (ii) a The three-phase modulation voltage reference value e aref 、e bref 、e cref Respectively superpose the voltage reference e of the double frequency circulation modulation ciraref2 、e cirbref2 、e circref2 And a quadruple frequency circulating current modulation voltage reference e ciraref4 、e cirbref4 、e circref4 And then, generating pulse signals of each bridge arm submodule of the MMC through bridge arm voltage synthesis and a bottom layer modulation module.
Description
Technical Field
The invention relates to the technical field of electrical control, in particular to a control system and a control method for reducing a bridge arm current peak value of an MMC (modular multilevel converter).
Background
Modular Multilevel Converters (MMC), as shown in fig. 1, have the characteristics of modular structure, low harmonic and low switching frequency, and have become one of the most attractive high-power and high-voltage converter topologies. An MMC-based high-voltage direct current transmission system (MMC-HVDC) is an effective solution for large-scale new energy source friendly grid connection and reliable transmission, and development is still underway.
The MMC converter station grid-connected system, as shown in fig. 2, has a steady-state operation range limited mainly by the following factors: bridge arm current peak value, submodule capacitor voltage ripple, modulation ratio, bridge arm voltage output capacity and the like. The peak value of the bridge arm current limits the peak current of the power devices such as the IGBT in the Safe Operating Area (SOA) of the power devices, and when the peak current exceeds the current threshold value, the possibility that the IGBT module fails due to overcurrent is increased. It is a more economical practice to reduce the maximum current value through the power devices in a controlled manner, so that the converter station has a higher power handling capability without reducing the current margin or exceeding the maximum collector current.
The presence of circulating currents in the phase cells of an MMC is its intrinsic property, and the second and fourth harmonic components are the main components of the circulating currents. The peak value of bridge arm current can be reduced by controlling double-frequency circulating current and quadruple-frequency circulating current of the MMC in the existing research, but the ripple of sub-module capacitor voltage is reduced by additionally increasing the capacitance value of sub-module capacitors. Therefore, the control of double-frequency and quadruple-frequency circulating currents of the MMC needs to be researched, and the bridge arm current peak value of the MMC is reduced under the condition that the capacitance value of the sub-module is not increased.
Disclosure of Invention
The invention aims to solve the problems and provides a control system and a control method for reducing the bridge arm current peak value of an MMC (modular multilevel converter), which realize the reduction of the bridge arm current peak value of the MMC under the condition of not increasing the capacitance value of a sub-module by controlling double-frequency and quadruple-frequency circulating currents of the MMC.
In order to achieve the purpose, the invention adopts the following technical scheme:
a control system for reducing the peak value of bridge arm current of MMC comprises a voltage/power and current control module, a double-frequency loop control module and a quadruple-frequency loop control module; the voltage/power and current control module is used for generating a three-phase modulation voltage reference value e aref 、e bref 、e cref (ii) a The double-frequency circulation control module is used for generating a reference value e of a three-phase double-frequency circulation modulation voltage ciraref2 、e cirbref2 、e circref2 (ii) a The quadruple frequency circulation control module is used for generating a quadruple frequency circulation modulation voltage reference value e of three phases ciraref4 、e cirbref4 、e circref4 (ii) a The three-phase modulation voltage reference value e aref 、e bref 、e cref Respectively superpose the voltage reference e of the double frequency circulation modulation ciraref2 、e cirbref2 、e circref2 And a quadruple frequency circulating current modulation voltage reference e ciraref4 、e cirbref4 、e circref4 And then, generating pulse signals of each bridge arm submodule of the MMC through bridge arm voltage synthesis and a bottom layer modulation module.
A control method of a control system for reducing the peak value of bridge arm current of an MMC (modular multilevel converter) is characterized in that the voltage/power and current control module adopts the following control method:
reference value U of DC voltage dcref With a direct voltage feedback value U dc The difference after subtraction is delta U, and the MMC outputs an active power reference value P ref The difference obtained by subtracting the MMC output active power feedback value P is delta P, and the output of delta U or delta P after entering a PI regulator is a reference value i of a grid-connected current d-axis component sdref MMC output idle workPower reference value Q ref The difference obtained by subtracting the MMC output reactive power feedback value Q is delta Q, and the output of the delta Q after entering a PI regulator is the reference value i of the grid-connected current Q-axis component sqref (ii) a Feedback value i of grid-connected current d-axis component sd Multiplying by the synchronous angular frequency omega and the bridge arm inductance L by u 1cd Feedback value i of q-axis component of grid-connected current sq Multiplying by the synchronous angular frequency omega and the bridge arm inductance L by u 1cq ，i sdref And i sd The difference enters a PI regulator, and the output of the PI regulator is superposed with a grid-connected point voltage d-axis component u sd Then subtract u 1cd Followed by the reference value e of the d-axis component of the modulation voltage dref ；i sqref And i sq The difference enters a PI regulator, and the output of the PI regulator is superposed with a q-axis component u of the grid-connected point voltage sq Re-stacking u 1cq Followed by the reference value e of the q-axis component of the modulated voltage qref (ii) a Reference value e of d-axis component of modulation voltage dref Reference value e of q-axis component of modulation voltage qref Entering a rotation conversion link from a two-phase rotation coordinate system to a three-phase static coordinate system to generate a three-phase modulation voltage reference value e aref 、e bref 、e cref The phase for rotation transformation is the phase theta of the MMC grid-connected point observed by the phase-locked loop p ；
The double-frequency loop control module adopts the following control method: three-phase double frequency circulating current i cira2 、i cirb2 、i circ2 Entering a rotation transformation link from a three-phase static coordinate system to a two-phase rotating coordinate system to generate a double-frequency circulation i under the two-phase rotating coordinate system cird2 、i cirq2 The phase for the rotation transformation is-2 theta p ；i cird2 U after multiplying by 2 ω L 2cd ，i cirq2 U after multiplying by 2 ω L 2cq (ii) a Reference value i of d-axis component of double frequency circulation cirdref2 And i cird2 The difference enters a PI regulator, and the output of the PI regulator is superposed with u 2cq After is e cirdref2 (ii) a Reference value i of q-axis component of double frequency circulating current cirqref2 And i cirq2 The difference is fed to a PI regulator, the output of which subtracts u 2cd After is e cirqref2 ；e cirdref2 、e cirqref2 Entering a rotation conversion link from a two-phase rotation coordinate system to a three-phase static coordinate system to generate a three-phase dual-frequency circulating current modulation voltage reference value e ciraref2 、e cirbref2 、e circref2 The phase for the rotation transformation is-2 theta p ；
The quadruple frequency circulation control module adopts the following control method: three-phase quadruple frequency circulation i cira4 、i cirb4 、i circ4 Entering a rotation conversion link from a three-phase static coordinate system to a two-phase rotating coordinate system to generate quadruple frequency circulation i under the two-phase rotating coordinate system cird4 、i cirq4 Phase for rotational transformation of 4 theta p ；i cird4 U after multiplying by 4 ω L 4cd ，i cirq4 U after multiplying by 4 ω L 4cq (ii) a Reference value i of d-axis component of quadrupled frequency circulation cirdref4 And i cird4 The difference is fed to a PI regulator, the output of which subtracts u 4cq After is e cirdref4 (ii) a Reference value i of q-axis component of quadrupled frequency circulation cirqref4 And i cirq4 The difference enters a PI regulator, and the output of the PI regulator is superposed with u 4cd After is e cirqref4 ；e cirdref4 、e cirqref4 Entering a rotation conversion link from a two-phase rotation coordinate system to a three-phase static coordinate system to generate a three-phase quadruple frequency circulation modulation voltage reference value e ciraref4 、e cirbref4 、e circref4 Phase for rotational transformation of 4 theta p ；
The three-phase modulation voltage reference value e aref 、e bref 、e cref Respectively superpose the voltage reference e of the double frequency circulation modulation ciraref2 、e cirbref2 、e circref2 And a quadruple frequency circulating current modulation voltage reference e ciraref4 、e cirbref4 、e circref4 And then, generating pulse signals of each bridge arm submodule of the MMC through bridge arm voltage synthesis and a bottom layer modulation module.
As a preferred technical scheme of the invention: reference value i of d-axis and q-axis components of the double frequency circulation cirdref2 、i cirqref2 Calculated according to the following formula,
wherein i sd 、i sq Respectively a d-axis component, a q-axis component, theta of the grid-connected current p Phase of MMC grid-connected point for phase-locked loop observation sm Amplitude, k, of the MMC grid-connected current T For coupling the transformation ratio of the transformer, k 2 Control coefficient, i, for double frequency circulating current ciraref2 Is a double frequency circulating current reference value of a phase cirbref2 Is a double frequency circulating current reference value of b phase circref2 Is the double frequency circulating current reference value of the c phase.
As a preferred technical scheme of the invention: reference value i of components of d axis and q axis of quadruple frequency circulation cirdref4 、i cirqref4 Calculated according to the following formula,
wherein i sd 、i sq Respectively a d-axis component, a q-axis component, theta of the grid-connected current p Phase of MMC grid-connected point for phase-locked loop observation sm Amplitude, k, of the MMC grid-connected current T For coupling the transformation ratio of the transformer, k 4 Control coefficient for quadruple frequency circulation i ciraref4 Quadruple frequency circulating current reference value of a phase i cirbref4 Quadruple frequency circulation reference value of b phase, i circref4 Is the quadruple frequency circulating current reference value of the c phase.
As a preferred technical scheme of the invention: double frequency circulating current i of the three phases cira2 、i cirb2 、i circ2 Calculated according to the following formula,
wherein i ap Upper arm current of phase a, i an Lower arm current of phase a, i bp Upper arm current of phase b, i bn Lower arm current of phase b, i cp Upper arm current of c phase, i cn Lower arm current of c phase, i ciraref4 Quadruple frequency circulating current reference value of a phase i cirbref4 Quadruple frequency circulation reference value of b phase, i circref4 Is the quadruple frequency circulating current reference value of the c phase.
As a preferred technical scheme of the invention: the quadruple frequency circulation i of the three phases cira4 、i cirb4 、i circ4 Calculated according to the following formula,
wherein i ap Upper arm current of phase a, i an Lower arm current of phase a, i bp Upper arm current of phase b, i bn Lower arm current of phase b, i cp Upper arm current of c phase, i cn Lower arm current of c phase, i ciraref2 Is a double frequency circulating current reference value of a phase cirbref2 Is a double frequency circulating current reference value of b phase circref2 Is the double frequency circulating current reference value of the c phase.
Compared with the prior art, the control system and the control method for reducing the peak value of the bridge arm current of the MMC provided by the invention have the beneficial effects that:
the invention provides a control system and a control method for reducing the peak value of bridge arm current of an MMC, which utilize double-frequency and quadruple-frequency circulating current injection to reduce the peak value of bridge arm current of the MMC; the peak value of the bridge arm current is reduced and the increase amplitude of the capacitor voltage ripple is considered, and the peak value of the bridge arm current can be reduced under the condition that the capacitance value of the sub-module is not increased.
Drawings
FIG. 1 is a prior art topological structure diagram of an MMC converter station;
FIG. 2 is an equivalent structure diagram of a prior art MMC converter station grid-connected system;
FIG. 3 is a block diagram of a control system and method for reducing peak bridge arm current of an MMC according to an embodiment of the present invention;
FIG. 4 is a simulation waveform of a control system and method for reducing peak current value of an MMC bridge arm according to a simulation embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. Of course, the examples described by referring to the drawings are only for explaining the present invention and are not to be construed as limiting the present invention.
Referring to fig. 3, a control system for reducing a peak value of a bridge arm current of an MMC comprises a voltage/power and current control module, a frequency doubling loop control module and a frequency quadrupling loop control module; the voltage/power and current control module is used for generating a three-phase modulation voltage reference value e aref 、e bref 、e cref (ii) a The double-frequency circulation control module is used for generating a reference value e of a three-phase double-frequency circulation modulation voltage ciraref2 、e cirbref2 、e circref2 (ii) a The quadruple frequency circulation control module is used for generating a quadruple frequency circulation modulation voltage reference value e of three phases ciraref4 、e cirbref4 、e circref4 (ii) a The three-phase modulation voltage reference value e aref 、e bref 、e cref Respectively superpose the voltage reference e of the double frequency circulation modulation ciraref2 、e cirbref2 、e circref2 And a quadruple frequency circulating current modulation voltage reference e ciraref4 、e cirbref4 、e circref4 And then, generating pulse signals of each bridge arm submodule of the MMC through bridge arm voltage synthesis and a bottom layer modulation module.
A control method of a control system for reducing the peak value of bridge arm current of an MMC (modular multilevel converter) is characterized in that the voltage/power and current control module adopts the following control method:
reference value U of DC voltage dcref With a direct voltage feedback value U dc The difference after subtraction is delta U, and the MMC outputs an active power reference value P ref The difference obtained by subtracting the MMC output active power feedback value P is delta P, and the output of delta U or delta P after entering a PI regulator is a reference value i of a grid-connected current d-axis component sdref MMC output reactive power reference value Q ref The difference obtained by subtracting the MMC output reactive power feedback value Q is delta Q, and the output of the delta Q after entering a PI regulator is the reference value i of the grid-connected current Q-axis component sqref (ii) a Feedback value i of grid-connected current d-axis component sd Multiplying by the synchronous angular frequency omega and the bridge arm inductance L by u 1cd Feedback value i of q-axis component of grid-connected current sq Multiplying by the synchronous angular frequency omega and the bridge arm inductance L by u 1cq ，i sdref And i sd The difference enters a PI regulator, and the output of the PI regulator is superposed with a grid-connected point voltage d-axis component u sd Then subtract u 1cd Followed by the reference value e of the d-axis component of the modulation voltage dref ；i sqref And i sq The difference enters a PI regulator, and the output of the PI regulator is superposed with a q-axis component u of the grid-connected point voltage sq Re-stacking u 1cq Followed by the reference value e of the q-axis component of the modulated voltage qref (ii) a Reference value e of d-axis component of modulation voltage dref Reference value e of q-axis component of modulation voltage qref Entering a rotation conversion link from a two-phase rotation coordinate system to a three-phase static coordinate system to generate a three-phase modulation voltage reference value e aref 、e bref 、e cref The phase for rotation transformation is the phase theta of the MMC grid-connected point observed by the phase-locked loop p ；
The double-frequency loop control module adopts the following control method: three-phase double frequency circulating current i cira2 、i cirb2 、i circ2 Entering a rotation transformation link from a three-phase static coordinate system to a two-phase rotating coordinate system to generate a double-frequency circulation i under the two-phase rotating coordinate system cird2 、i cirq2 The phase for the rotation transformation is-2 theta p ；i cird2 U after multiplying by 2 ω L 2cd ，i cirq2 U after multiplying by 2 ω L 2cq (ii) a Reference value i of d-axis component of double frequency circulation cirdref2 And i cird2 The difference enters a PI regulator, and the output of the PI regulator is superposed with u 2cq After is e cirdref2 (ii) a Reference value i of q-axis component of double frequency circulating current cirqref2 And i cirq2 The difference is fed to a PI regulator, the output of which subtracts u 2cd After is e cirqref2 ；e cirdref2 、e cirqref2 Entering a rotation conversion link from a two-phase rotation coordinate system to a three-phase static coordinate system to generate a three-phase dual-frequency circulating current modulation voltage reference value e ciraref2 、e cirbref2 、e circref2 The phase for the rotation transformation is-2 theta p ；
The quadruple frequency circulation control module adopts the following control method: three-phase quadruple frequency circulation i cira4 、i cirb4 、i circ4 Entering a rotation conversion link from a three-phase static coordinate system to a two-phase rotating coordinate system to generate quadruple frequency circulation i under the two-phase rotating coordinate system cird4 、i cirq4 Phase for rotational transformation of 4 theta p ；i cird4 U after multiplying by 4 ω L 4cd ，i cirq4 U after multiplying by 4 ω L 4cq (ii) a Reference value i of d-axis component of quadrupled frequency circulation cirdref4 And i cird4 The difference is fed to a PI regulator, the output of which subtracts u 4cq After is e cirdref4 (ii) a Reference value i of q-axis component of quadrupled frequency circulation cirqref4 And i cirq4 The difference enters a PI regulator, and the output of the PI regulator is superposed with u 4cd After is e cirqref4 ；e cirdref4 、e cirqref4 Entering a rotation conversion link from a two-phase rotation coordinate system to a three-phase static coordinate system to generate a three-phase quadruple frequency circulation modulation voltage reference value e ciraref4 、e cirbref4 、e circref4 Phase for rotational transformation of 4 theta p ；
The three-phase modulation voltage reference value e aref 、e bref 、e cref Respectively superpose the voltage reference e of the double frequency circulation modulation ciraref2 、e cirbref2 、e circref2 And frequency quadruplingReference value e of circulating current modulation voltage ciraref4 、e cirbref4 、e circref4 And then, generating pulse signals of each bridge arm submodule of the MMC through bridge arm voltage synthesis and a bottom layer modulation module.
Reference value i of d-axis and q-axis components of the double frequency ring current cirdref2 、i cirqref2 Calculated according to the following formula,
wherein i sd 、i sq Respectively a d-axis component, a q-axis component, theta of the grid-connected current p Phase of MMC grid-connected point for phase-locked loop observation sm Amplitude, k, of the MMC grid-connected current T For coupling the transformation ratio of the transformer, k 2 Control coefficient, i, for double frequency circulating current ciraref2 Is a double frequency circulating current reference value of a phase cirbref2 Is a double frequency circulating current reference value of b phase circref2 Is the double frequency circulating current reference value of the c phase.
Reference value i of components of d axis and q axis of quadruple frequency circulation cirdref4 、i cirqref4 Calculated according to the following formula,
wherein i sd 、i sq Respectively a d-axis component, a q-axis component, theta of the grid-connected current p Phase of MMC grid-connected point for phase-locked loop observation sm Amplitude, k, of the MMC grid-connected current T For coupling the transformation ratio of the transformer, k 4 Is quadrupledControl coefficient of circulating current, i ciraref4 Quadruple frequency circulating current reference value of a phase i cirbref4 Quadruple frequency circulation reference value of b phase, i circref4 Is the quadruple frequency circulating current reference value of the c phase.
Double frequency circulating current i of the three phases cira2 、i cirb2 、i circ2 Calculated according to the following formula,
wherein i ap Upper arm current of phase a, i an Lower arm current of phase a, i bp Upper arm current of phase b, i bn Lower arm current of phase b, i cp Upper arm current of c phase, i cn Lower arm current of c phase, i ciraref4 Quadruple frequency circulating current reference value of a phase i cirbref4 Quadruple frequency circulation reference value of b phase, i circref4 Is the quadruple frequency circulating current reference value of the c phase.
The quadruple frequency circulation i of the three phases cira4 、i cirb4 、i circ4 Calculated according to the following formula,
wherein i ap Upper arm current of phase a, i an Lower arm current of phase a, i bp Upper arm current of phase b, i bn Lower arm current of phase b, i cp Upper arm current of c phase, i cn Lower arm current of c phase, i ciraref2 Is a double frequency circulating current reference value of a phase cirbref2 Is a double frequency circulating current reference value of b phase circref2 Is the double frequency circulating current reference value of the c phase.
Referring to fig. 4, a simulation waveform of a control system and method for reducing a peak value of a bridge arm current of an MMC according to a simulation embodiment of the present invention, wherein the control method for reducing the peak value of the bridge arm current provided by the present application is not added in an MMC control loop before 1s, and the control method for reducing the peak value of the bridge arm current provided by the present application is added after 1 s; as can be seen from FIG. 4, after the control method for reducing the peak value of the bridge arm current of the MMC provided by the application is added, the peak value of the bridge arm current is reduced from 3.69 to 2.95, and the amplitude reduction of the peak value of the bridge arm current is close to 20%; under the condition of not increasing the capacitance value of the sub-module, the ripple of the sub-module capacitor voltage is still lower than 10 percent, and the engineering requirement is met; the simulation result shown in fig. 4 illustrates that the peak value of the bridge arm current can be reduced without increasing the capacitance of the sub-module by using the control system and the method for reducing the peak value of the bridge arm current provided by the present application.
The peak value of the bridge arm current of the modular multilevel converter limits the peak current of safe and reliable operation of power devices such as IGBT in a safe working area, and the possibility of the IGBT module breaking down due to overcurrent is increased when the current threshold value is exceeded. Therefore, it is important to reduce the maximum current value flowing through the power device in a controlled manner.
The invention provides a control system and a control method for reducing the peak value of bridge arm current of an MMC, which utilize double-frequency and quadruple-frequency circulating current injection to reduce the peak value of bridge arm current of the MMC; the reduction of the peak value of the bridge arm current and the increase amplitude of the capacitor voltage ripple are considered, and the peak value of the bridge arm current can be reduced under the condition that the capacitance value of the sub-module is not increased.
The above-mentioned embodiments, objects, technical solutions and advantages of the present invention are further described in detail, it should be understood that the above-mentioned embodiments are only illustrative of the present invention, and are not intended to limit the scope of the present invention, and any person skilled in the art should understand that equivalent changes and modifications made without departing from the concept and principle of the present invention should fall within the protection scope of the present invention.
Claims (6)
1. A control system for reducing the peak value of bridge arm current of MMC (modular multilevel converter) is characterized by comprising a voltage/power and current control module, a frequency doubling loop control module and a frequency quadrupling loop control module; the voltage/power and current control module is used for generating three-phase modulation voltage parameterReference value e aref 、e bref 、e cref (ii) a The double-frequency circulation control module is used for generating a reference value e of a three-phase double-frequency circulation modulation voltage ciraref2 、e cirbref2 、e circref2 (ii) a The quadruple frequency circulation control module is used for generating a quadruple frequency circulation modulation voltage reference value e of three phases ciraref4 、e cirbref4 、e circref4 (ii) a The three-phase modulation voltage reference value e aref 、e bref 、e cref Respectively superpose the voltage reference e of the double frequency circulation modulation ciraref2 、e cirbref2 、e circref2 And a quadruple frequency circulating current modulation voltage reference e ciraref4 、e cirbref4 、e circref4 And then, generating pulse signals of each bridge arm submodule of the MMC through bridge arm voltage synthesis and a bottom layer modulation module.
2. The control method of the control system for reducing the peak value of the bridge arm current of the MMC according to claim 1, wherein the voltage/power and current control module adopts the following control method:
reference value U of DC voltage dcref With a direct voltage feedback value U dc The difference after subtraction is delta U, and the MMC outputs an active power reference value P ref The difference obtained by subtracting the MMC output active power feedback value P is delta P, and the output of delta U or delta P after entering a PI regulator is a reference value i of a grid-connected current d-axis component sdref MMC outputs reactive power reference value Q ref The difference after subtracting with MMC output reactive power feedback value Q is delta Q, the output of delta Q entering a PI regulator is the reference value i of grid-connected current Q-axis component sqref (ii) a Feedback value i of grid-connected current d-axis component sd Multiplying by the synchronous angular frequency omega and the bridge arm inductance L by u 1cd Feedback value i of q-axis component of grid-connected current sq Multiplying by the synchronous angular frequency omega and the bridge arm inductance L by u 1cq ，i sdref And i sd The difference enters a PI regulator, and the output of the PI regulator is superposed with a grid-connected point voltage d-axis component u sd Then subtract u 1cd Followed by the reference value e of the d-axis component of the modulation voltage dref ；i sqref And i sq The difference enters a PI regulator, and the output of the PI regulator is superposed with a q-axis component u of the grid-connected point voltage sq Re-stacking u 1cq Followed by the reference value e of the q-axis component of the modulated voltage qref (ii) a Reference value e of d-axis component of modulation voltage dref Reference value e of q-axis component of modulation voltage qref Entering a rotation conversion link from a two-phase rotation coordinate system to a three-phase static coordinate system to generate a three-phase modulation voltage reference value e aref 、e bref 、e cref The phase for rotation transformation is the phase theta of the MMC grid-connected point observed by the phase-locked loop p ；
The double-frequency loop control module adopts the following control method: three-phase double frequency circulating current i cira2 、i cirb2 、i circ2 Entering a rotation transformation link from a three-phase static coordinate system to a two-phase rotating coordinate system to generate a double-frequency circulation i under the two-phase rotating coordinate system cird2 、i cirq2 The phase for the rotation transformation is-2 theta p ；i cird2 U after multiplying by 2 ω L 2cd ，i cirq2 U after multiplying by 2 ω L 2cq (ii) a Reference value i of d-axis component of double frequency circulation cirdref2 And i cird2 The difference enters a PI regulator, and the output of the PI regulator is superposed with u 2cq After is e cirdref2 (ii) a Reference value i of q-axis component of double frequency circulating current cirqref2 And i cirq2 The difference is fed to a PI regulator, the output of which subtracts u 2cd After is e cirqref2 ；e cirdref2 、e cirqref2 Entering a rotation conversion link from a two-phase rotation coordinate system to a three-phase static coordinate system to generate a three-phase dual-frequency circulating current modulation voltage reference value e ciraref2 、e cirbref2 、e circref2 The phase for the rotation transformation is-2 theta p ；
The quadruple frequency circulation control module adopts the following control method: three-phase quadruple frequency circulation i cira4 、i cirb4 、i circ4 Entering a rotation conversion link from a three-phase static coordinate system to a two-phase rotating coordinate system to generate quadruple frequency circulation i under the two-phase rotating coordinate system cird4 、i cirq4 Phase for rotational transformation of 4 theta p ；i cird4 U after multiplying by 4 ω L 4cd ，i cirq4 U after multiplying by 4 ω L 4cq (ii) a Reference value i of d-axis component of quadrupled frequency circulation cirdref4 And i cird4 The difference is fed to a PI regulator, the output of which subtracts u 4cq After is e cirdref4 (ii) a Reference value i of q-axis component of quadrupled frequency circulation cirqref4 And i cirq4 The difference enters a PI regulator, and the output of the PI regulator is superposed with u 4cd After is e cirqref4 ；e cirdref4 、e cirqref4 Entering a rotation conversion link from a two-phase rotation coordinate system to a three-phase static coordinate system to generate a three-phase quadruple frequency circulation modulation voltage reference value e ciraref4 、e cirbref4 、e circref4 Phase for rotational transformation of 4 theta p ；
The three-phase modulation voltage reference value e aref 、e bref 、e cref Respectively superpose the voltage reference e of the double frequency circulation modulation ciraref2 、e cirbref2 、e circref2 And a quadruple frequency circulating current modulation voltage reference e ciraref4 、e cirbref4 、e circref4 And then, generating pulse signals of each bridge arm submodule of the MMC through bridge arm voltage synthesis and a bottom layer modulation module.
3. The control method for reducing the peak value of the bridge arm current of the MMC bridge arm according to claim 2, characterized in that the reference values i of the components of the d-axis and the q-axis of the frequency doubling circulating current are cirdref2 、i cirqref2 Calculated according to the following formula,
wherein i sd 、i sq Respectively a d-axis component, a q-axis component, theta of the grid-connected current p Phase of MMC grid-connected point for phase-locked loop observation sm Amplitude, k, of the MMC grid-connected current T For coupling the transformation ratio of the transformer, k 2 Control coefficient, i, for double frequency circulating current ciraref2 Is a double frequency circulating current reference value of a phase cirbref2 Is a double frequency circulating current reference value of b phase circref2 Is the double frequency circulating current reference value of the c phase.
4. The control method for the control system for reducing the peak value of the bridge arm current of the MMC according to claim 2, characterized in that the reference values i of the components of d and q axes of the quadruple frequency circulating current cirdref4 、i cirqref4 Calculated according to the following formula,
wherein i sd 、i sq Respectively a d-axis component, a q-axis component, theta of the grid-connected current p Phase of MMC grid-connected point for phase-locked loop observation sm Amplitude, k, of the MMC grid-connected current T For coupling the transformation ratio of the transformer, k 4 Control coefficient for quadruple frequency circulation i ciraref4 Quadruple frequency circulating current reference value of a phase i cirbref4 Quadruple frequency circulation reference value of b phase, i circref4 Is the quadruple circulating current reference value of the c phase.
5. The control method of the control system for reducing the peak value of the bridge arm current of the MMC according to claim 2, characterized in that the frequency doubling circulating current i of the three phases cira2 、i cirb2 、i circ2 Calculated according to the following formula,
wherein i ap Upper arm current of phase a, i an Lower arm current of phase a, i bp Upper arm current of phase b, i bn Lower arm current of phase b, i cp Upper arm current of c phase, i cn Lower arm current of c phase, i ciraref4 Quadruple frequency circulating current reference value of a phase i cirbref4 Quadruple frequency circulation reference value of b phase, i circref4 Is the quadruple frequency circulating current reference value of the c phase.
6. The control method of the control system for reducing the peak value of the bridge arm current of the MMC according to claim 2, characterized in that the quadruple frequency circulating current i of the three phases cira4 、i cirb4 、i circ4 Calculated according to the following formula,
wherein i ap Upper arm current of a phase, i an Lower arm current of phase a, i bp Upper arm current of phase b, i bn Lower arm current of phase b, i cp Upper arm current of c phase, i cn Lower arm current of c-phase, i ciraref2 Is a double frequency circulating current reference value of a phase cirbref2 Is a double frequency circulating current reference value of b phase circref2 Is a double circulating current reference value of the c phase.
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