CN114977859B - Three-phase N-module cascading type unidirectional energy flow multi-level frequency converter and control method - Google Patents

Three-phase N-module cascading type unidirectional energy flow multi-level frequency converter and control method Download PDF

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CN114977859B
CN114977859B CN202210745487.0A CN202210745487A CN114977859B CN 114977859 B CN114977859 B CN 114977859B CN 202210745487 A CN202210745487 A CN 202210745487A CN 114977859 B CN114977859 B CN 114977859B
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module
phase
level
stage
energy flow
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CN114977859A (en
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王聪
程红
袁巍
赵志浩
丁冠华
苏雄
宋浩楠
郝俊豪
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China University of Mining and Technology Beijing CUMTB
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/487—Neutral point clamped inverters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
    • H02M1/007—Plural converter units in cascade
    • 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
    • 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
    • H02M7/493—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 the static converters being arranged for operation in parallel
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

Abstract

The invention discloses a three-phase N-module cascading type unidirectional energy flow multi-level frequency converter and a control method, the frequency converter does not need any isolation transformer, each phase is formed by cascading N unidirectional energy flow M-level single-phase frequency converters with the same structure, N is more than or equal to 2,M is more than or equal to 2, the total level number is (N x M-1) level, the alternating current input side of the three-phase N-module cascading type unidirectional energy flow multi-level frequency converter adopts star connection, and the inversion output side adopts an open winding connection mode; the rectification stage of the unidirectional energy flow M-level frequency converter consists of a diode rectification bridge and a flying capacitor type M-level Boost converter, and the inversion stage of the unidirectional energy flow M-level frequency converter consists of a diode clamping type M-level inverter. The control method comprises the following steps: the rectification stage adopts a carrier phase shift method to realize the control of multiple level current levels, and the inverter stage generates a PWM pulse signal of each full-control device through a carrier lamination modulation method.

Description

Three-phase N-module cascading type unidirectional energy flow multi-level frequency converter and control method
Technical Field
The invention belongs to the field of power electronics, and particularly relates to a three-phase N-module cascading type unidirectional energy flow multi-level frequency converter and a control method.
Background
In recent years, multilevel converters (Multilevel converters) have been successfully applied in the fields of high-voltage high-power frequency conversion speed regulation, active power filtering, high-voltage direct current (HVDC) transmission, reactive power compensation of power systems and the like. The basic circuit topologies of multilevel converters can be roughly classified into a clamping type and a cell cascade type. Diode-clamped three-level medium-high voltage inverters manufactured by siemens corporation or ABB corporation, which are widely used in the industry at present, and cascaded H-bridge medium-high voltage inverters manufactured by Luo Binkang corporation or Li Dehua ford corporation are typical representatives of the two types of products. In any of the two types of medium-high voltage frequency converters, in order to implement high-voltage power conversion by using low-voltage-resistant power electronic devices, an industrial frequency phase-shifting transformer with large volume, complex wiring and high price is required to be used at the input side of the rectifier to realize electrical isolation. This limits their use in many industrial applications.
The cascading multilevel converter without the power frequency transformer has attracted wide attention in the technical field of power electronics in recent years, and is considered to be an ideal implementation scheme of an intelligent power grid interface or a new generation medium-high voltage frequency converter which is suitable for a new energy power generation system to access and meets the distributed power generation requirement. The converter uses a high-frequency transformer to replace a power frequency phase-shifting transformer in the traditional cascade converter to realize electrical isolation, and when the converter is used for bidirectional power transmission, a cascade full-control H bridge multi-level power converter structure is adopted on a rectifying side. When the converter is used for unidirectional power transmission, a unidirectional cascade multilevel power converter structure (comprising a cascade diode + Boost rectifying circuit, a cascade bridgeless rectifying circuit, a cascade VIENNA rectifying circuit and the like) is adopted at the rectifying side. Compared with the traditional rectifier stage of a medium-high voltage frequency converter, the implementation scheme of the rectifier stage of the converter cancels a power frequency phase-shifting transformer which is large in size, complex in wiring and high in price, so that the size, the weight and the manufacturing cost of a system are effectively reduced. However, such converters also have significant drawbacks, mainly represented by: the N groups of direct current output ends of the rectification modules cannot be directly connected in series to form a pair of public high-voltage direct current output buses, cannot be directly connected with a multi-level inverter circuit and is used for medium-high voltage frequency conversion speed regulation. In order to realize a common high-voltage direct-current output bus or realize flexible control of N groups of rectified output direct-current voltages, N groups of cascaded rectification modules are necessarily connected with N high-frequency isolation DC-DC conversion modules in sequence, so that the complexity of the topological structure and the control mode of the whole system is increased, and the working efficiency is reduced.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a three-phase N-module cascading type unidirectional energy flow multi-level frequency converter and a control method thereof, and aims to solve the problems of complex system, large volume and high cost of the traditional medium-high voltage frequency converter with an isolation transformer.
In order to achieve the purpose, the invention provides a three-phase N-module cascading type unidirectional energy flow multi-level frequency converter which is composed of three single-phase N-module cascading type unidirectional energy flow multi-level frequency converters, wherein the single-phase N-module cascading type unidirectional energy flow multi-level frequency converter is composed of N unidirectional energy flow M level frequency converters with the same structure in a cascading mode, N is greater than or equal to 2,M and is greater than or equal to 2, and the total level number of the three-phase N-module cascading type unidirectional energy flow multi-level frequency converter is (N is M-1) level.
The three-phase N-module cascade type unidirectional energy flow M level frequency converter comprises a rectification stage and an inversion stage;
the rectifying stage of the unidirectional energy flow M level frequency converter comprises a diode rectifying bridge, a Boost inductor L1, a current-sharing inductor L2, a circulating current suppression diode D and a flying capacitor type M level Boost converter;
one end of the Boost inductor L1 is connected with the positive output end of the diode rectifier bridge, and the other end of the Boost inductor L1 is connected with the positive input end d of the flying capacitor type M level Boost converter;
one end of the current-sharing inductor L2 is connected with the negative output end of the diode rectifier bridge, and the other end of the current-sharing inductor L2 is connected with the negative input end e of the flying capacitor type M level Boost converter;
the anode of the circulation suppression diode D is connected with the negative electrode of the direct current output side of the flying capacitor type M level Boost converter, and the cathode of the circulation suppression diode D is connected with the negative input end e of the flying capacitor type M level Boost converter and used for suppressing circulation among modules;
the positive electrode and the negative electrode of the output side of the flying capacitor type M level Boost converter are the direct current output positive end and the direct current output negative end of a rectifier stage, and the two direct current output ends of the rectifier stage are respectively connected with the direct current input positive end and the direct current input negative end of an inverter stage;
the inverter stage of the unidirectional energy flow M-level frequency converter is a diode-clamped M-level inverter, and M is more than or equal to 2.
The three-phase N-module cascading type unidirectional energy flow multi-level frequency converter is characterized in that a diode rectifier bridge of each unidirectional energy flow M level frequency converter module rectifier stage is provided with two input ends, the second input end of a first module rectifier stage diode rectifier bridge of each phase is connected with the first input end of a second module rectifier stage diode rectifier bridge, the second input end of the second module rectifier stage diode rectifier bridge is connected with the first input end of a third module rectifier stage diode rectifier bridge, the second input end of the second module rectifier stage diode rectifier bridge is alternately connected with the first input end of the third module rectifier stage diode rectifier bridge, the second input end of the N-1 module rectifier stage diode rectifier bridge is connected with the first input end of the N-module rectifier stage diode rectifier bridge, the N-module cascading type unidirectional energy flow multi-level frequency converter rectifier stage has two residual free ends, namely the first module rectifier stage diode rectifier bridge has the first input end and the second input end of the N-module rectifier stage diode rectifier bridge, the three-phase rectifier stage has six residual alternating current input ends, the first module rectifier bridge of each phase has three input ends, the second rectifier bridge has one-phase rectifier stage three-phase rectifier bridge input ends, the three-phase rectifier bridge terminals constitute a group of three-phase rectifier bridge, and the high-frequency rectifier bridge is connected with another three-phase rectifier bridge.
The three-phase N-module cascading type unidirectional energy flow multi-level frequency converter is characterized in that each unidirectional energy flow multi-level frequency converter module inverter stage is provided with two output ends, the second output end of the first module inverter stage of each phase is connected with the first output end of the second module inverter stage, the second output end of the second module inverter stage is connected with the first output end of the third module inverter stage so as to be alternately connected, the second output end of the N-1 module inverter stage is connected with the first output end of the Nth module inverter stage, the two residual free ends of each phase N-module cascading type unidirectional energy flow multi-level frequency converter stage are cascaded, namely the first output end of the first module inverter stage is connected with the second output end of the Nth module inverter stage, the three phase inverter stages have six residual output ends, and the two residual output ends of each phase inverter stage are respectively connected with the two input ends of three stator windings of a motor to form open winding connection.
Based on the three-phase N-module cascading type unidirectional energy flow multi-level frequency converter provided by the invention, the invention provides a corresponding control method, which comprises rectification stage control and inverter stage control:
controlling a rectification stage:
step 1: sampling all the direct current side capacitor voltages of each module to obtain a direct current side voltage signal of each module, summing the direct current side voltages of each module to obtain a total direct current side voltage of all the modules, averaging the total direct current side voltage to obtain a total direct current side voltage average value of each module, and sending the difference between the total direct current side voltage average value of each module and a direct current side voltage expected value to a PI (proportional integral) regulator to obtain a current expected value required by each phase to maintain the voltage stability of the direct current side;
step 2: the difference between the direct current side voltage of each module and the expected direct current side voltage value is sent to a PI regulator, and the expected current value required for keeping the direct current side voltage of each module stable is obtained;
and step 3: sampling the flying capacitor voltage in each module, and feeding the difference between the flying capacitor voltage in each module and the expected voltage into a PI regulator to obtain an extra current expectation required for stabilizing the flying capacitor voltage;
and 4, step 4: adding the current expectation obtained in the step 1 and the current expectation obtained in the steps 2 and 3, and dividing the current expectation by the effective value of the grid current at the phase grid side to obtain a modulation wave corresponding to each fully-controlled device;
and 5: phase shifting the carrier signal of the full-control devices, and comparing the modulation wave of each full-control device with the carrier to obtain a PWM pulse signal;
and 6: the turn-off and the turn-on of all full-control devices in the rectifier are controlled through the PWM pulse signals, and then the modulation of the rectification stage of the three-phase N-module cascade type unidirectional energy flow multi-level frequency converter is realized;
and (3) inverter stage control:
the inverter stage generates PWM pulse signals of all fully-controlled devices through a carrier lamination modulation method, the difference between two bridge arm modulation waves of the inverter stage of each unidirectional energy flow M level frequency converter is 180 degrees, the modulation waves of different modules in the same phase are the same, and the carrier signals between different modules in the same phase are sequentially shifted by 180/N degrees from a module 1 to a module N.
Compared with the prior art, the technical scheme of the invention has the following remarkable advantages: on one hand, the invention provides a three-phase N-module cascade type unidirectional energy flow multi-level frequency converter, and by adding an inter-module balance inductor and a circulating current suppression diode, an isolation transformer in the traditional frequency converter is cancelled, so that the volume and the cost of the frequency converter are further reduced; on the other hand, the invention provides a control method for the three-phase N-module cascade type unidirectional energy flow multi-level frequency converter, the control structure is simple and easy to realize, and the control on a complex system can be effectively realized.
Reference will now be made in detail to the accompanying drawings, examples of which are illustrated in the accompanying drawings.
Drawings
Fig. 1 is a schematic structural diagram of a three-phase N-module cascaded unidirectional energy flow multi-level frequency converter provided by the invention;
FIG. 2 is a schematic diagram of a rectifying stage of a unidirectional energy flow M-level frequency converter provided by the present invention;
fig. 3 is a schematic structural diagram of a three-phase two-module cascade type unidirectional energy flow multi-level frequency converter provided by the invention;
FIG. 4 is a method of controlling a rectifier stage based on the topology shown in FIG. 3;
fig. 5 is a schematic diagram of an inverter stage a-phase two-leg modulation wave based on the topology shown in fig. 3;
FIG. 6 is a schematic diagram of a two-module carrier based on the topology shown in FIG. 3;
FIG. 7 is a schematic diagram of the three-phase input side current of the topology shown in FIG. 3 according to the present invention based on the proposed control method;
FIG. 8 is a schematic diagram of the three-phase output side phase voltage provided by the present invention based on the topology shown in FIG. 3 under the proposed control method;
fig. 9 is a schematic diagram of three-phase output side phase currents based on the topology shown in fig. 3 under the proposed control method provided by 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 described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention.
The invention provides a three-phase N-module cascading type unidirectional energy flow multi-level frequency converter which is composed of three single-phase N-module cascading type unidirectional energy flow multi-level frequency converters, wherein the single-phase N-module cascading type unidirectional energy flow multi-level frequency converter is composed of N unidirectional energy flow M level frequency converters with the same structure in a cascading mode, N is greater than or equal to 2,M and is greater than or equal to 2, and the total level number of the three-phase N-module cascading type unidirectional energy flow multi-level frequency converter is (N is the M-1) level.
The three-phase N-module cascade type unidirectional energy flow M level frequency converter comprises a rectification stage and an inversion stage;
the rectifying stage of the unidirectional energy flow M-level frequency converter comprises a diode rectifying bridge, a boosting inductor L1, a current-sharing inductor L2, a circulating current suppression diode D and a flying capacitor type M-level Boost converter;
one end of the Boost inductor L1 is connected with the positive output end of the diode rectifier bridge, and the other end of the Boost inductor L1 is connected with the positive input end d of the flying capacitor type M level Boost converter;
one end of the current-sharing inductor L2 is connected with the negative output end of the diode rectifier bridge, and the other end of the current-sharing inductor L2 is connected with the negative input end e of the flying capacitor type M level Boost converter;
the anode of the circulating current suppression diode D is connected with the negative electrode of the direct current output side of the flying capacitor type M level Boost converter, and the cathode of the circulating current suppression diode D is connected with the negative input end e of the flying capacitor type M level Boost converter and used for suppressing circulating current between modules;
the positive electrode and the negative electrode of the output side of the flying capacitor type M level Boost converter are the direct current output positive end and the direct current output negative end of a rectifier stage, and the two direct current output ends of the rectifier stage are respectively connected with the direct current input positive end and the direct current input negative end of an inverter stage;
the inverter stage of the unidirectional energy flow M-level frequency converter is a diode-clamped M-level inverter, and M is more than or equal to 2.
The three-phase N-module cascading type unidirectional energy flow multi-level frequency converter is characterized in that a diode rectifier bridge of each unidirectional energy flow M level frequency converter module rectifier stage is provided with two input ends, the second input end of a first module rectifier stage diode rectifier bridge of each phase is connected with the first input end of a second module rectifier stage diode rectifier bridge, the second input end of the second module rectifier stage diode rectifier bridge is connected with the first input end of a third module rectifier stage diode rectifier bridge, the second input end of the second module rectifier stage diode rectifier bridge is alternately connected with the first input end of the third module rectifier stage diode rectifier bridge, the second input end of the N-1 module rectifier stage diode rectifier bridge is connected with the first input end of the N-module rectifier stage diode rectifier bridge, the N-module cascading type unidirectional energy flow multi-level frequency converter rectifier stage has two residual free ends, namely the first module rectifier stage diode rectifier bridge has the first input end and the second input end of the N-module rectifier stage diode rectifier bridge, the three-phase rectifier stage has six residual alternating current input ends, the first module rectifier bridge of each phase has three input ends, the second rectifier bridge has one-phase rectifier stage three-phase rectifier bridge input ends, the three-phase rectifier bridge terminals constitute a group of three-phase rectifier bridge, and the high-frequency rectifier bridge is connected with another three-phase rectifier bridge.
The three-phase N-module cascading type unidirectional energy flow multi-level frequency converter is characterized in that each unidirectional energy flow multi-level frequency converter module inverter stage is provided with two output ends, the second output end of the first module inverter stage of each phase is connected with the first output end of the second module inverter stage, the second output end of the second module inverter stage is connected with the first output end of the third module inverter stage so as to be alternately connected, the second output end of the N-1 module inverter stage is connected with the first output end of the Nth module inverter stage, the two residual free ends of each phase N-module cascading type unidirectional energy flow multi-level frequency converter stage are cascaded, namely the first output end of the first module inverter stage is connected with the second output end of the Nth module inverter stage, the three phase inverter stages have six residual output ends, and the two residual output ends of each phase inverter stage are respectively connected with the two input ends of three stator windings of a motor to form open winding connection.
As shown in fig. 1, the embodiment provides a schematic structural diagram of a three-phase N-module cascade type unidirectional energy flow multi-level frequency converter, wherein a rectification input side is star-connected, and an inversion output side adopts an open-winding connection mode.
As shown in fig. 2, the embodiment provides a structural manner of a rectification stage of a unidirectional energy flow M-level frequency converter in a three-phase N-module cascade unidirectional energy flow multi-level frequency converter, and the rectification stage is composed of a diode rectification bridge, a flying capacitor type M-level Boost converter, and an inductor L 1 For step-up conversion, inductor L 2 For equalizing the current between the modules and diodes D for suppressing the circulating current between the modules.
Fig. 3 shows a structural schematic diagram of a three-phase two-module cascaded unidirectional energy flow multi-level frequency converter, each phase is formed by cascading two identical unidirectional energy flow three-level frequency converters, a diode-clamped three-level inverter is adopted in an inverter stage, the total level number is five levels (2*3-1), the rectification input sides of the three-phase two-module cascaded unidirectional energy flow multi-level frequency converter are connected in a star shape, and the inversion output side adopts an open winding connection mode.
Based on the three-phase N-module cascading type unidirectional energy flow multi-level frequency converter provided by the invention, the invention provides a corresponding control method, which comprises rectification stage control and inverter stage control:
controlling a rectification stage:
step 1: sampling all the direct current side capacitor voltages of each module to obtain a direct current side voltage signal of each module, summing the direct current side voltages of each module to obtain total direct current side voltages of all the modules, averaging the total direct current side voltages to obtain a total direct current side voltage average value of each module, and sending a difference between the total direct current side voltage average value of each module and a direct current side voltage expected value to a PI (proportional integral) regulator to obtain a current expected value required by maintaining the voltage stability of each phase at the direct current side;
and 2, step: the difference between the direct current side voltage of each module and the expected direct current side voltage value is sent to a PI regulator, and the expected current value required for keeping the direct current side voltage of each module stable is obtained;
and step 3: sampling the flying capacitor voltage in each module, and feeding the difference between the flying capacitor voltage in each module and the expected voltage into a PI regulator to obtain an extra current expectation required for stabilizing the flying capacitor voltage;
and 4, step 4: adding the current expectation obtained in the step 1 and the current expectation obtained in the steps 2 and 3, and dividing the current expectation by the effective value of the grid current at the phase grid side to obtain a modulation wave corresponding to each fully-controlled device;
and 5: phase shifting the carrier signal of the full-control devices, and comparing the modulation wave of each full-control device with the carrier to obtain a PWM pulse signal;
and 6: the turn-off and the turn-on of all full-control devices in the rectifier are controlled through PWM pulse signals, and then the modulation of rectification stages of the three-phase N-module cascade type unidirectional energy flow multi-level frequency converter is achieved;
and (3) inverter stage control:
the inverter stage generates PWM pulse signals of all fully-controlled devices through a carrier lamination modulation method, the difference between two bridge arm modulation waves of the inverter stage of each unidirectional energy flow M level frequency converter is 180 degrees, the modulation waves of different modules in the same phase are the same, and the carrier signals between different modules in the same phase are sequentially shifted by 180/N degrees from a module 1 to a module N.
FIG. 4 shows a control block diagram of a three-phase two-module cascaded unidirectional multi-level converter rectification stage, where U * dc For the desired value of the total voltage on the DC side of each module, U * fc For the desired value of the flying capacitor voltage, U dca Is the sum of DC side voltages of two A-phase modules, U dcb Is the sum of the voltages of two B-phase modules, U dcc Is the sum of the voltages of two C-phase modules, U dca1 Is the total DC side voltage, U, of the A-phase module 1 dca2 Is the total DC side voltage, U, of the A-phase module 2 fca1 For flying capacitor voltage, U, of A-phase module 1 fca2 Is flying capacitor voltage of A-phase module 2, U dcb1 Is a phase BDC side total voltage, U, of module 1 dcb2 Is the total DC side voltage, U, of the B-phase module 2 fcb1 Is flying capacitor voltage of B-phase module 1, U fcb2 Is the flying capacitor voltage of the B-phase module 2, U dcc1 Is the total DC side voltage, U, of the C-phase module 1 dcc2 Is the total DC side voltage, U, of the C-phase module 2 fcc1 Is flying capacitor voltage of C-phase module 1, U fcc2 For the flying capacitor voltage of the C-phase module 2, the average value of the DC side voltage of each module is subtracted from the expected DC side voltage, and the expected current magnitude i required by each phase is obtained through a PI regulator * dc Dc side voltage U of phase a module 1 dca1 And DC side voltage expectation U * dc The difference is made to obtain the current expectation i of the A-phase module 1 through a PI regulator * dca1 ，i * dc And i * dca1 Adding to obtain a fully-controlled device S a1 Average current expectation of switching period i * sa1 ，i * sa1 And i a Is divided by the absolute value of the voltage to obtain a fully-controlled device S a1 The modulation wave is compared with the triangular carrier wave to obtain a fully-controlled device S a1 PWM drive signal G of sa1 (ii) a Voltage U at two ends of flying capacitor of A-phase module 1 fca1 Voltage expectation U with flying capacitor * fc Obtaining the current expectation i required by the voltage stabilization of the flying capacitor through a PI regulator * fca1 ，i * fca1 And i * sa1 Adding to obtain a fully-controlled device S a2 Average current expectation of switching cycle i * sa2 ,i * sa2 And i a Is divided by the absolute value to obtain the fully-controlled device S a2 The modulation wave is compared with the triangular carrier wave to obtain a fully-controlled device S a2 PWM drive signal G sa2 Fully-controlled device S a2 The carrier signal of S is controlled by a fully-controlled device S a1 The carrier signal is obtained by delaying 90 degrees; DC side voltage U of A phase module 2 dca2 And DC side voltage expectation U * dc Obtaining the current expectation i of the A-phase module 2 by a PI regulator * dca2 ，i * dc And i * dca2 AddingObtaining a fully-controlled device S a3 Average current expectation of switching period i * sa3 ，i * sa3 And i a Is divided by the absolute value of the voltage to obtain a fully-controlled device S a3 The modulation wave is compared with the triangular carrier wave to obtain a fully-controlled device S a3 PWM drive signal G of sa3 Fully-controlled device S a3 The carrier signal of S is controlled by the full-controlled device S a1 The carrier signal is obtained by delaying 180 degrees; voltage U at two ends of flying capacitor of A-phase module 2 fca2 Voltage expectation U with flying capacitor * fc Obtaining the current expectation i required by the voltage stabilization of the flying capacitor through a PI regulator * fca2 ，i * fca2 And i * sa3 Adding to obtain a fully-controlled device S a4 Average current expectation of switching period i * sa4 ,i * sa4 And i a Is divided by the absolute value to obtain the fully-controlled device S a4 The modulating wave is compared with a triangular carrier wave to obtain a fully-controlled device S a4 PWM drive signal G of sa4 Fully-controlled device S a4 The carrier signal of S is controlled by the full-controlled device S a1 The carrier signal is delayed by 270 degrees; DC side voltage U of B phase module 1 dcb1 And DC side voltage expectation U * dc The difference is made to obtain the current expectation i of the B-phase module 1 through a PI regulator * dcb1 ，i * dc And i * dcb1 Adding to obtain a fully-controlled device S b1 Average current expectation of switching period i * sb1 ，i * sb1 And i b Is divided by the absolute value to obtain the fully-controlled device S b1 The modulating wave is compared with a triangular carrier wave to obtain a fully-controlled device S b1 PWM drive signal G sb1 (ii) a Voltage U at two ends of flying capacitor of B-phase module 1 fcb1 Voltage expectation U with flying capacitor * fc Obtaining the current expectation i required by the voltage stabilization of the flying capacitor through a PI regulator * fcb1 ，i * fcb1 And i * sb1 Adding to obtain a fully-controlled device S b2 Average current expectation of switching period i * sb2 ,i * sb2 And i b Is divided by the absolute value of the voltage to obtain a fully-controlled device S b2 The modulation wave is compared with the triangular carrier wave to obtain a fully-controlled device S b2 PWM drive signal G of sb2 Fully-controlled device S b2 The carrier signal of S is controlled by the full-controlled device S b1 The carrier signal is obtained by delaying 90 degrees; DC side voltage U of B phase module 2 dcb2 And DC side voltage expectation U * dc The difference is made to obtain the current expectation i of the B-phase module 2 through a PI regulator * dcb2 ，i * dc And i * dcb2 Adding to obtain the fully-controlled device S b3 Average current expectation of switching period i * sb3 ，i * sb3 And i b Is divided by the absolute value to obtain the fully-controlled device S b3 The modulation wave is compared with the triangular carrier wave to obtain a fully-controlled device S b3 PWM drive signal G sb3 Fully-controlled device S b3 The carrier signal of S is controlled by the full-controlled device S b1 The carrier signal is obtained by delaying 180 degrees; voltage U at two ends of flying capacitor of B-phase module 2 fcb2 Voltage expectation U with flying capacitor * fc Obtaining the current expectation i required by the voltage stabilization of the flying capacitor through a PI regulator * fcb2 ，i * fcb2 And i * sb3 Adding to obtain the fully-controlled device S b4 Average current expectation of switching period i * sb4 ,i * sb4 And i b Is divided by the absolute value to obtain the fully-controlled device S b4 The modulation wave is compared with the triangular carrier wave to obtain a fully-controlled device S b4 PWM drive signal G sb4 Fully-controlled device S b4 The carrier signal of S is controlled by the full-controlled device S b1 The carrier signal is delayed by 270 degrees; DC side voltage U of C phase module 1 dcc1 And DC side voltage expectation U * dc Obtaining the current expectation i of the C-phase module 1 by a PI regulator * dcc1 ，i * dc And i * dcc1 Adding to obtain a fully-controlled device S c1 Average current expectation of switching period i * sc1 ，i * sc1 And i c Is divided by the absolute value to obtain the fully-controlled device S c1 The modulation wave is compared with the triangular carrier wave to obtain a fully-controlled device S c1 PWM drive signal G sc1 (ii) a Voltage U at two ends of flying capacitor of C-phase module 1 fcc1 Voltage expectation U with flying capacitor * fc Obtaining the current expectation i required by the voltage stabilization of the flying capacitor through a PI regulator * fcc1 ，i * fcc1 And i * sc1 Adding to obtain a fully-controlled device S c2 Average current expectation of switching period i * sc2 ,i * sc2 And i c Is divided by the absolute value to obtain the fully-controlled device S c2 The modulation wave is compared with the triangular carrier wave to obtain a fully-controlled device S c2 PWM drive signal G of sc2 Fully-controlled device S c2 The carrier signal of S is controlled by the full-controlled device S c1 The carrier signal is obtained by delaying 90 degrees; DC side voltage U of C phase module 2 dcc2 And DC side voltage expectation U * dc The difference is made to obtain the current expectation i of the C-phase module 2 through a PI regulator * dcc2 ，i * dc And i * dcc2 Adding to obtain the fully-controlled device S c3 Average current expectation of switching period i * sc3 ，i * sc3 And i c Is divided by the absolute value to obtain the fully-controlled device S c3 The modulation wave is compared with the triangular carrier wave to obtain a fully-controlled device S c3 PWM drive signal G sc3 Fully-controlled device S c3 The carrier signal of S is controlled by the full-controlled device S c1 The carrier signal is obtained by delaying 180 degrees; voltage U at two ends of flying capacitor of C-phase module 2 fcc2 Voltage expectation U with flying capacitor * fc Obtaining the current expectation i required by the voltage stabilization of the flying capacitor through a PI regulator * fcc2 ，i * fcc2 And i * sc3 Adding to obtain a fully-controlled device S c4 Average current expectation of switching cycle i * sc4 ,i * sc4 And i c Is divided by the absolute value of the voltage to obtain a fully-controlled device S c4 The modulation wave is compared with the triangular carrier wave to obtain a fully-controlled device S c4 PWM drive signal G of sc4 Fully-controlled device S c4 The carrier signal of S is controlled by the full-controlled device S c1 Is delayed by 270 deg..
Fig. 5 shows a schematic diagram of an inverter stage a-phase two-leg modulation wave based on the topology shown in fig. 3, wherein the modulation wave of leg 1 is 180 ° different from the modulation wave of leg 2.
Fig. 6 shows a schematic diagram of two module carriers for each phase inversion stage based on the topology shown in fig. 3, the carrier of each phase module 2 lagging the carrier of module 1 by 180 °/2=90 °.
Fig. 7 shows the three-phase input side currents of the embodiment under the control mode, and the three-phase currents are approximately sinusoidal.
Fig. 8 is a voltage waveform of the three-phase inverter output side phase of the embodiment in the proposed control manner, and it can be seen that the phase voltage is five levels, and the three-phase voltages are symmetrical to each other.
Fig. 9 shows the waveform of the phase current at the output side of the three-phase inverter according to the embodiment under the control mode, and it can be seen that the phase current of the three-phase inverter is approximately sinusoidal, and satisfies the three-phase balance relationship, and can ensure the stable operation of the load.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (4)

1. The three-phase N-module cascading type unidirectional energy flow multi-level frequency converter is characterized by consisting of three single-phase N-module cascading type unidirectional energy flow multi-level frequency converters, each single-phase N-module cascading type unidirectional energy flow multi-level frequency converter is formed by cascading N unidirectional energy flow M level frequency converters with the same structure, N is greater than or equal to 2,M and is greater than or equal to 2, a rectification stage of each unidirectional energy flow M level frequency converter is formed by a diode rectification bridge and a flying capacitor type M level Boost converter, an inversion stage is formed by a diode clamping type M level inverter, the output side and the input side of the rectification stage share the same set of direct current side capacitors, and the total level number of the three-phase N-module cascading type unidirectional energy flow multi-level frequency converters is (N is M-1) level;
the control method based on the three-phase N-module cascading type unidirectional energy flow multi-level frequency converter is characterized by comprising rectification stage control and inverter stage control:
controlling a rectification stage:
step 1: sampling all the direct current side capacitor voltages of each module to obtain a direct current side voltage signal of each module, summing the direct current side voltages of each module to obtain a total direct current side voltage of all the modules, averaging the total direct current side voltage to obtain a total direct current side voltage average value of each module, and sending the difference between the total direct current side voltage average value of each module and a direct current side voltage expected value to a PI (proportional integral) regulator to obtain a current expected value required by each phase to maintain the voltage stability of the direct current side;
and 2, step: the difference between the direct-current side voltage of each module and the expected direct-current side voltage value is sent to a PI regulator, and a current expected value required by the stable direct-current side voltage of each module is obtained;
and 3, step 3: sampling the flying capacitor voltage in each module, and feeding the difference between the flying capacitor voltage in each module and the expected voltage into a PI regulator to obtain an extra current expectation required for stabilizing the flying capacitor voltage;
and 4, step 4: adding the current expectation obtained in the step 1 and the current expectation obtained in the steps 2 and 3 respectively and dividing the added current expectation by the effective value of the grid current at the phase grid side to obtain a modulation wave corresponding to each fully-controlled device;
and 5: phase shifting the carrier signal of the full-control devices, and comparing the modulation wave of each full-control device with the carrier to obtain a PWM pulse signal;
step 6: the turn-off and the turn-on of all full-control devices in the rectifier are controlled through the PWM pulse signals, and then the modulation of the rectification stage of the three-phase N-module cascade type unidirectional energy flow multi-level frequency converter is realized;
and (3) inverter stage control:
the inverter stage generates PWM pulse signals of all-control devices through a carrier lamination modulation method, the difference between two bridge arm modulation waves of the inverter stage of each unidirectional energy flow M level frequency converter is 180 degrees, the modulation waves of different in-phase modules are the same, and carrier signals between different in-phase modules are sequentially shifted in phase by 180/N degrees from the module 1 to the module N.
2. The three-phase N-module cascading type unidirectional energy flow multi-level frequency converter as claimed in claim 1, wherein each unidirectional energy flow M-level frequency converter is composed of a rectification stage and an inversion stage;
the rectifying stage of the unidirectional energy flow M-level frequency converter comprises a diode rectifying bridge and a boost inductor L 1 And a current-sharing inductor L 2 A circulating current suppression diode D and a flying capacitor type M level Boost converter;
the boost inductor L 1 One end of the voltage boosting inductor is connected with the positive output end of the diode rectifier bridge 1 The other end of the flying capacitor type M level Boost converter is connected with the positive input end d of the flying capacitor type M level Boost converter;
the current equalizing inductor L 2 One end of the current-sharing inductor is connected with the negative output end of the diode rectifier bridge 2 The other end of the flying capacitor type M level Boost converter is connected with a negative input end e of the flying capacitor type M level Boost converter;
the anode of the circulating current suppression diode D is connected with the negative electrode of the direct current output side of the flying capacitor type M level Boost converter, and the cathode of the circulating current suppression diode D is connected with the negative input end e of the flying capacitor type M level Boost converter and used for suppressing circulating current between modules;
the positive electrode and the negative electrode of the output side of the flying capacitor type M level Boost converter are the direct current output positive end and the direct current output negative end of a rectifier stage, and the two direct current output ends of the rectifier stage are respectively connected with the direct current input positive end and the direct current input negative end of an inverter stage;
the inverter stage of the unidirectional energy flow M-level frequency converter is a diode-clamped M-level inverter, and M is more than or equal to 2.
3. The three-phase N-module cascaded one-way power flow multi-level converter as claimed in claim 1, wherein the diode rectifier bridge of each one-way power flow M-level converter module rectifier stage has two inputs, the second input of the first module rectifier diode rectifier bridge of each phase is connected to the first input of the second module rectifier diode rectifier bridge, the second input of the second module rectifier diode rectifier bridge is connected to the first input of the third module rectifier diode rectifier bridge, and the second input of the N-1 module rectifier diode rectifier bridge is connected to the first input of the nth module rectifier diode rectifier bridge, and the cascaded N-module cascaded one-way power flow multi-level converter rectifier stages have two free ends, i.e. the first input of the diode rectifier bridge of the first module rectifier stage is connected to the second input of the N-module rectifier stage diode rectifier bridge, and the three-phase rectifier stages have six ac inputs, wherein the first input of the diode rectifier bridge of each phase constitutes a group of three-phase rectifier bridge terminals, and the second input of the N-module rectifier stage rectifier bridge constitutes a group of three-phase rectifier bridge, and the three-phase rectifier bridge terminals of the high frequency rectifier bridge is connected to the high frequency network.
4. The three-phase N-module cascaded unidirectional power flow multilevel converter according to claim 1, wherein each unidirectional power flow multilevel converter module inverter stage has two output terminals, the second output terminal of the first module inverter stage of each phase is connected to the first output terminal of the second module inverter stage, the second output terminal of the second module inverter stage is connected to the first output terminal of the third module inverter stage, so as to be alternately connected, the second output terminal of the N-1 th module inverter stage is connected to the first output terminal of the nth module inverter stage, and the cascaded N-phase cascaded unidirectional power flow multilevel converter inverter stages have two remaining free terminals, i.e., the first output terminal of the first module inverter stage is connected to the second output terminal of the nth module inverter stage, and the three-phase inverter stages have six remaining output terminals, wherein the two remaining output terminals of each phase inverter stage are respectively connected to the two input terminals of the three stator windings of the motor to form an open winding connection.
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