CN112600448B - Method for designing parameters of low-voltage side rectifier of modular multi-level flat-straight-flow transformer - Google Patents

Method for designing parameters of low-voltage side rectifier of modular multi-level flat-straight-flow transformer Download PDF

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CN112600448B
CN112600448B CN202011412162.8A CN202011412162A CN112600448B CN 112600448 B CN112600448 B CN 112600448B CN 202011412162 A CN202011412162 A CN 202011412162A CN 112600448 B CN112600448 B CN 112600448B
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CN112600448A (en
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徐扬
张紫涛
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Hohai University HHU
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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
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc 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
    • H02M7/217—Conversion of ac power input into dc 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
    • H02M7/219—Conversion of ac power input into dc 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 in a bridge configuration
    • 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
    • H02M1/14—Arrangements for reducing ripples from dc input or output
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • 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
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels

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Abstract

The invention discloses a method for designing parameters of a low-voltage side rectifier of a modular multi-level-to-level converter, which comprises the steps of establishing a low-voltage side rectifying circuit of the modular multi-level-to-level converter, and measuring the output voltage and the output current of the direct-current side of the rectifier by utilizing a magnetoelectric system voltmeter and an ammeter; and (4) designing an IGBT threshold value, a capacitance value of a support capacitor at the direct current side of the rectifier and an inductance value of an isolation inductor at the alternating current side of the rectifier according to the circuit principle and mathematical formula derivation. The invention comprehensively considers the problems of obtaining stable direct current bus voltage at a direct current output side and obtaining unit power factor at an alternating current input side, and aims to provide theoretical basis and technical support for parameter design of low-voltage side rectification of the modular multi-level flat-current transformer.

Description

Method for designing parameters of low-voltage side rectifier of modular multi-level flat-straight-flow transformer
Technical Field
The invention belongs to the technical field of power electronics, and particularly relates to a method for designing parameters of a low-voltage side rectifier of a modular multi-level straight-level transformer.
Background
The traditional alternating current distribution network is difficult to meet the further popularization of the new power generation technology. With the rapid development of power electronic technology in power systems, direct current power distribution networks have come up, and the defects of alternating current power distribution networks are made up by the appearance of the direct current power distribution networks. The direct current distribution network is divided into a medium-voltage direct current distribution network and a low-voltage direct current distribution network: the medium-voltage direct-current power distribution network distributes electric energy from the high-voltage transmission network to the low-voltage direct-current power distribution network; the low-voltage direct-current power distribution network distributes electric energy to various power loads and is mainly provided with a modular multilevel topological direct-current transformer. And the low-voltage side rectifier part is a core device of the modular multi-level direct current transformer, and the development and design level of the low-voltage side rectifier part directly influences the reliability of the modular multi-level direct current transformer.
The modular multi-level flat-current transformer low-voltage side rectifier has two main objectives: firstly, obtaining stable direct current bus voltage; and secondly, a unit power factor is obtained at an alternating current input side, and the low harmonic content of the alternating current input current is ensured. The output direct current can be controlled by controlling the input current, and further the output voltage of the direct current side can be controlled. Therefore, the control core part of the modular multi-level flat-current transformer low-voltage side rectifier is the control of the alternating input current.
Through retrieval, chinese patent application publication No. CN 111130364 a discloses a parameter design of a three-phase rectifier, which includes a three-phase rectifier circuit design and a capacitor voltage balance circuit design, where each phase rectifier circuit includes an input filter and a rectifier unit connected in series, and the rectifier unit includes five branches.
However, the technical scheme has the problem that the output side direct current bus voltage is unstable, the structure is simple, and the modular multi-level direct current transformer is not suitable for use.
Disclosure of Invention
The invention comprehensively considers the problems of obtaining stable direct current bus voltage at a direct current output side and obtaining unit power factor at an alternating current input side, and aims to provide theoretical basis and technical support for parameter design of a low-voltage side rectifier of a modular multi-level flat-current transformer.
In order to achieve the purpose, the invention provides the following technical scheme:
a method for designing parameters of a low-voltage side rectifier of a modular multi-level-to-level converter comprises the steps of firstly, establishing a low-voltage side rectifying circuit of the modular multi-level-to-level converter, and measuring output voltage and output current of a direct-current side of the rectifier by utilizing a magnetoelectric system voltmeter and an ammeter; and secondly, designing an IGBT threshold value, a capacitance value of a support capacitor at the direct current side of the rectifier and an inductance value of an isolation inductor at the alternating current side of the rectifier according to the circuit principle and mathematical formula derivation.
Specifically, the steps and specific calculation process for designing the IGBT threshold are as follows:
step 1: establishing a low-voltage side rectifying circuit of a modular multi-level-to-level converter, wherein the low-voltage side rectifying circuit of the modular multi-level-to-level converter comprises four IGBTs, an alternating current side isolating inductor and a direct current sideThe side supports the capacitor. The method is characterized in that: the sub-modules comprise IGBTs1、IGBT2、IGBT3、IGBT4A DC side support capacitor; positive pole of direct current side support capacitor and IGBT1Collector electrode, IGBT3The collector is connected; negative electrode of direct-current side support capacitor and IGBT2Emitter electrode of (1), IGBT4Connecting an emitter; IGBT (insulated Gate Bipolar translator)1And IGBT2Form a series circuit one, IGBT3And IGBT4Forming a second series circuit; the first series circuit and the second series circuit are connected with the DC side supporting capacitor in parallel to form a full-bridge circuit, and an isolation inductor is connected in series at the AC input side; each IGBT in the sub-module is formed by connecting an insulated gate field effect transistor in anti-parallel with a bipolar freewheeling diode.
Step 2: and measuring the output voltage of the low-voltage side rectifier of the modular multi-level flat-current transformer by using a magnetoelectric system voltmeter.
And step 3: according to Uac＝UdcAnd determining the input voltage peak value of the alternating current side of the rectifier. In the formula of UacThe input voltage peak value of the AC side of the rectifier; u shapedcThe voltage is output by the direct current side of the rectifier.
And 4, step 4: the output current of the rectifier on the DC side is measured by a magnetoelectric system ammeter.
And 5: according to the kirchhoff principle, Iac＝Idc(ii)/2, calculating the input current peak value at the AC side of the rectifier, wherein IacThe peak value of the input current at the AC side of the rectifier; i isdcAnd outputting current for the direct current side of the rectifier.
Step 6: and determining the IGBT threshold value by considering a certain margin according to the input voltage peak value and the input current peak value of the alternating current side of the rectifier. Rated voltage UDSGenerally 2 to 3 times of the peak voltage during normal operation,
Figure BDA0002815834510000031
rated current IDSThe peak current is generally 1.5-2 times of the peak current during normal operation,
IDS≥1.5Iac
further, the design steps and the specific calculation process of the capacitance value of the support capacitor on the direct current side of the rectifier are as follows.
Step 1: the voltage-current expression is written according to the full-bridge rectifier circuit column,
uac(t)＝Uacsin wt
Figure BDA0002815834510000032
in the formula uac、iacRespectively inputting voltage and current at the AC side of the rectifier; u shapeac、IacRespectively, the peak values thereof; ω represents the switching frequency;
Figure BDA0002815834510000041
for the phase shift angle, when the power factor is 1,
Figure BDA0002815834510000042
step 2: according to the voltage expression, the instantaneous input power p on the AC side of the rectifier can be obtainedacIn order to realize the purpose,
Figure BDA0002815834510000043
it can be seen that the instantaneous power on the ac side of the rectifier is divided into a dc component and an ac component. Similarly, the instantaneous power on the dc side is composed of two parts, one is the average power consumed by the load, and the other is the ripple power of the ripple current flowing through the capacitor. So that the instantaneous power p on the DC sidedcThe expression is as follows,
Figure BDA0002815834510000044
in the formula of UdcTo output a direct current voltage;
Figure BDA0002815834510000045
the dc-side ripple voltage and C is the dc-side support capacitance.
Instantaneous input power p at AC side without considering IGBT lossacAnd instantaneous output power p of the DC sidedcShould be equal, thereby obtaining a ripple voltage expression,
Figure BDA0002815834510000046
so as to obtain the composite material,
Figure BDA0002815834510000047
in the formula,. DELTA.Udc maxThe maximum allowable ripple of the direct-current voltage;
the lower limit of the dc-side support capacitance C is,
Figure BDA0002815834510000051
in the formula of UsIs the effective value of the alternating voltage at the input side; i issThe effective value of the alternating current on the input side.
Specifically, the specific design steps and the calculation process of the inductance value of the isolation inductor on the alternating current side of the rectifier are as follows:
step 1: according to the full-bridge rectifier circuit, the influence of the AC side isolation inductor on the tracking performance of the input current is considered, and an upper limit formula of the AC side isolation inductor of the rectifier is deduced.
According to kirchhoff's voltage law, the alternating-current side voltage equation is as follows:
Figure BDA0002815834510000052
in the formula uabIs the port voltage between the points a and b, and L is the inductance value of the isolation inductor at the AC side.
When the system operates at a high switching frequency, the AC side voltage equation becomes the same in one switching cycle
Figure BDA0002815834510000053
In the formula,. DELTA.iacIs the change of the alternating current side current in one period.
The actual input current being only during the switching period TsChanges in time, so that the maximum controllable change of the actual input current is
Figure BDA0002815834510000054
Namely, it is
Figure BDA0002815834510000055
And the input current reference value delta iac *The variation in one switching period is Δ iac *≈IacwTs
Namely, the isolation inductor at the alternating current side needs to meet the condition:
Figure BDA0002815834510000061
step 2: according to the full-bridge rectifier circuit, considering the suppression of the input current ripple by the AC side isolation inductor, the synchronous step 1 can be obtained,
Figure BDA0002815834510000062
Figure BDA0002815834510000063
in the formula,. DELTA.iac1Is t0Time t1The amount of current change at that time; Δ iac2Is t1Time t2The amount of change in current at a time.
Since the current change rate is minimum at the peak, which can be considered as zero, the rising value of the actual input current is equal to the falling value of the current in one switching period, i.e. the current changes in the peak
Δiac1＝Δiac2＝Δiac
If the allowable input current ripple range of the system is delta iac maxThen, it can be:
Figure BDA0002815834510000064
according to the requirement, a proper maximum ripple range of the input current is selected, the lower limit value of the isolation inductance at the alternating current side of the rectifier is determined,
Figure BDA0002815834510000065
and step 3: the steps 1 and 2 are integrated to obtain the range of the alternating current side isolation inductance of the rectifier
Figure BDA0002815834510000066
The invention has the beneficial effects that:
the invention comprehensively considers the problems of obtaining stable direct current bus voltage at a direct current output side and obtaining unit power factor at an alternating current input side, and aims to provide theoretical basis and technical support for parameter design of low-voltage side rectification of the modular multi-level flat-current transformer.
Drawings
Fig. 1 is a flow chart of modular multi-level flat-current transformer low-voltage side rectifier parameter design.
Figure 2 is a circuit topology diagram of a modular multi-level buck converter.
Fig. 3 is a low side rectifier circuit diagram of a modular multi-level flat-current transformer.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, a method for designing parameters of a low-voltage side rectifier of a modular multi-level-to-level converter includes the steps of firstly, establishing a low-voltage side rectifying circuit of the modular multi-level-to-level converter, and measuring output voltage and output current of the direct-current side of the rectifier by using a magnetoelectric system voltmeter and an ammeter; and secondly, designing an IGBT threshold value, a capacitance value of a support capacitor at the direct current side of the rectifier and an inductance value of an isolation inductor at the alternating current side of the rectifier according to the circuit principle and mathematical formula derivation.
The specific parameter calculation method for the step of designing the IGBT threshold value comprises the following steps:
step 1: a modular multi-level-to-flat-current transformer low-voltage side rectifying circuit is established, as shown in figure 2, a group of rectifying circuits are selected for parameter design due to the symmetry of the rectifying circuits, and a specific circuit is shown in figure 3. The method is characterized in that: the sub-modules comprise IGBTs1、IGBT2、IGBT3、IGBT4A DC side support capacitor; positive pole of direct current side support capacitor and IGBT1Collector electrode of (1), IGBT3The collector is connected; negative electrode of direct-current side support capacitor and IGBT2Emitter electrode of (1), IGBT4Connecting an emitter; IGBT (insulated Gate Bipolar translator)1And IGBT2Form a series circuit one, IGBT3And IGBT4Forming a second series circuit; the first series circuit and the second series circuit are connected with the DC side supporting capacitor in parallel to form a full-bridge circuit, and an isolation inductor is connected in series at the AC input side; each IGBT in the sub-module is formed by connecting an insulated gate field effect transistor in anti-parallel with a bipolar freewheeling diode.
Step 2: and measuring the output voltage of the low-voltage side rectifier of the modular multi-level flat-current transformer by using a magnetoelectric system voltmeter.
And step 3: according to Uac＝UdcAnd determining the input voltage peak value of the alternating current side of the rectifier. In the formula of UacThe input voltage peak value of the AC side of the rectifier; u shapedcThe voltage is output by the direct current side of the rectifier.
And 4, step 4: the output current of the rectifier on the DC side is measured by a magnetoelectric system ammeter.
And 5: according to the kirchhoff principle, Iac＝Idc(ii)/2, calculating the input current peak value at the AC side of the rectifier, wherein IacThe peak value of the input current at the AC side of the rectifier; i isdcAnd outputting current for the direct current side of the rectifier.
Step 6: and determining the IGBT threshold value by considering a certain margin according to the input voltage peak value and the input current peak value of the alternating current side of the rectifier. Rated voltage UDSGenerally 2 to 3 times of the peak voltage during normal operation,
Figure BDA0002815834510000081
rated current IDSThe peak current is generally 1.5-2 times of the peak current during normal operation,
IDS≥1.5Iac
specifically, the steps and the specific calculation process for designing the capacitance value of the support capacitor on the direct current side of the rectifier are as follows.
Step 1: the voltage-current expression is written according to the full-bridge rectifier circuit column,
uac(t)＝Uacsin wt
Figure BDA0002815834510000091
in the formula uac、iacRespectively inputting voltage and current at the AC side of the rectifier; u shapeac、IacRespectively, the peak values thereof; ω represents the switching frequency;
Figure BDA0002815834510000092
for the phase shift angle, when the power factor is 1,
Figure BDA0002815834510000093
step 2: according to the voltage expression, the instantaneous input power p on the AC side of the rectifier can be obtainedacIn order to realize the purpose,
Figure BDA0002815834510000094
it can be seen that the instantaneous power on the ac side of the rectifier is divided into a dc component and an ac component. Similarly, the instantaneous power on the dc side is composed of two parts, one is the average power consumed by the load, and the other is the ripple power of the ripple current flowing through the capacitor. So that the instantaneous power p on the DC sidedcThe expression is as follows,
Figure BDA0002815834510000095
in the formula of UdcTo output a direct current voltage;
Figure BDA0002815834510000096
the dc-side ripple voltage and C is the dc-side support capacitance.
Instantaneous input power p at AC side without considering IGBT lossacAnd instantaneous output power p of the DC sidedcShould be equal, thereby obtaining a ripple voltage expression,
Figure BDA0002815834510000101
so as to obtain the composite material,
Figure BDA0002815834510000102
in the formula,. DELTA.Udc maxThe maximum allowable ripple of the direct-current voltage;
the lower limit of the dc-side support capacitance C is,
Figure BDA0002815834510000103
in the formula of UsIs the effective value of the alternating voltage at the input side; i issThe effective value of the alternating current on the input side.
Specifically, the specific steps and calculation process for designing the inductance value of the isolation inductor on the alternating current side of the rectifier are as follows.
Step 1: according to the full-bridge rectifier circuit, the influence of the AC side isolation inductor on the tracking performance of the input current is considered, and an upper limit formula of the AC side isolation inductor of the rectifier is deduced.
According to kirchhoff's voltage law, the alternating-current side voltage equation is as follows:
Figure BDA0002815834510000104
in the formula uabIs the port voltage between the points a and b, and L is the inductance value of the isolation inductor at the AC side.
When the system operates at a high switching frequency, the AC side voltage equation becomes the same in one switching cycle
Figure BDA0002815834510000105
In the formula,. DELTA.iacIs the change of the alternating current side current in one period.
The actual input current being only during the switching period TsChanges in time, so that the maximum controllable change of the actual input current is
Figure BDA0002815834510000111
Namely, it is
Figure BDA0002815834510000112
And the input current reference value delta iac *The variation in one switching period is Δ iac *≈IacwTs
Namely, the isolation inductor at the alternating current side needs to meet the condition:
Figure BDA0002815834510000113
step 2: according to the full-bridge rectifier circuit, considering the suppression of the input current ripple by the AC side isolation inductor, the synchronous step 1 can be obtained,
Figure BDA0002815834510000114
Figure BDA0002815834510000115
in the formula,. DELTA.iac1Is t0Time t1The amount of current change at that time; Δ iac2Is t1Time t2The amount of change in current at a time.
Since the current change rate is minimum at the peak, which can be considered as zero, the rising value of the actual input current is equal to the falling value of the current in one switching period, i.e. the current changes in the peak
Δiac1＝Δiac2＝Δiac
If the allowable input current ripple range of the system is delta iac maxThen, it can be:
Figure BDA0002815834510000116
according to the requirement, a proper maximum ripple range of the input current is selected, the lower limit value of the isolation inductance at the alternating current side of the rectifier is determined,
Figure BDA0002815834510000121
and step 3: the steps 1 and 2 are integrated to obtain the range of the alternating current side isolation inductance of the rectifier
Figure BDA0002815834510000122
The above description is of the preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.

Claims (1)

1. A method for designing parameters of a low-voltage side rectifier of a modular multi-level flat-straight-flow transformer is characterized by comprising the following steps: firstly, establishing a low-voltage side rectifying circuit of a modular multi-level flat-level current transformer, and measuring the output voltage and the output current of the direct current side of a rectifier by using a magnetoelectric system voltmeter and an ammeter; secondly, designing an IGBT threshold value, a capacitance value of a support capacitor at the direct current side of the rectifier and an isolation inductance value at the alternating current side of the rectifier according to the circuit principle and mathematical formula derivation;
the steps and the specific calculation process for designing the IGBT threshold are as follows:
step 1: establishing a low-voltage side rectifying circuit of a modular multi-level flat-straight transformer, wherein the rectifying circuit comprises four IGBTs, an alternating current side isolation inductor and a direct current side support capacitor; the four IGBTs are respectively IGBT1、IGBT2、IGBT3And IGBT4Positive pole of DC side support capacitor and IGBT1Collector electrode of (1), IGBT3Is connected with the collector of the collector; negative electrode of direct-current side support capacitor and IGBT2Emitter electrode of (1), IGBT4The emitter of (3) is connected; IGBT (insulated Gate Bipolar translator)1And IGBT2Form a series circuit one, IGBT3And IGBT4Forming a second series circuit; the first series circuit and the second series circuit are connected with the DC side supporting capacitor in parallel to form a full-bridge circuit, and an isolation inductor is connected in series at the AC input side; each IGBT is formed by connecting an insulated gate field effect transistor in anti-parallel and a pairA polar freewheeling diode;
step 2: measuring the output voltage of a rectifier at the direct current side of the modular multilevel direct current transformer by using a magnetoelectric system voltmeter;
and step 3: according to Uac＝UdcDetermining the input voltage peak value of the alternating current side of the rectifier;
in the formula of UacThe input voltage peak value of the AC side of the rectifier; u shapedcOutputting voltage for the direct current side of the rectifier;
and 4, step 4: measuring the output current of the direct current side of the rectifier by using a magnetoelectric system ammeter;
and 5: according to the kirchhoff principle, Iac＝Idc(ii)/2, calculating the input current peak value at the AC side of the rectifier, wherein IacThe peak value of the input current at the AC side of the rectifier; i isdcOutputting current for the direct current side of the rectifier;
step 6: determining an IGBT threshold value according to the input voltage peak value and the input current peak value of the alternating current side of the rectifier; rated voltage UDSGenerally 2 to 3 times of the peak voltage during normal operation,
Figure FDA0003296554200000021
rated current IDSThe peak current is generally 1.5-2 times of the peak current during normal operation,
IDS≥1.5Iac；
the steps and the specific calculation process for designing the capacitance value of the support capacitor on the direct current side of the rectifier are as follows:
step 1: the voltage-current expression is written according to the full-bridge rectifier circuit column,
uac(t)＝Uacsinwt
Figure FDA0003296554200000022
in the formula uac、iacRespectively, the input voltage at the AC side of the rectifierAnd an input current; u shapeacFor the input voltage peak at the AC side of the rectifier, IacThe peak value of the input current at the AC side of the rectifier; ω represents the switching frequency;
Figure FDA0003296554200000023
for the phase shift angle, when the power factor is 1,
Figure FDA0003296554200000024
step 2: according to the voltage expression, the instantaneous input power p on the AC side of the rectifier can be obtainedacIn order to realize the purpose,
Figure FDA0003296554200000025
the instantaneous power at the AC side of the rectifier is divided into a DC part and an AC part, the instantaneous power at the DC side is also composed of two parts, one part is the average power consumed by the load, the other part is the ripple power of ripple current flowing through the capacitor, so the instantaneous power p at the DC side isdcThe expression is as follows:
Figure FDA0003296554200000031
in the formula of UdcTo output a direct current voltage;
Figure FDA0003296554200000032
the ripple voltage on the DC side, and C is the support capacitance value on the DC side;
instantaneous input power p at AC side without considering IGBT lossacAnd instantaneous output power p of the DC sidedcShould be equal, thereby obtaining a ripple voltage expression,
Figure FDA0003296554200000033
so as to obtain the composite material,
Figure FDA0003296554200000034
in the formula, Δ UdcmaxThe maximum allowable ripple of the direct-current voltage;
the lower limit of the dc-side support capacitance C is,
Figure FDA0003296554200000035
in the formula of UsIs the effective value of the alternating voltage at the input side; i issThe effective value of the alternating current at the input side;
the specific steps and calculation process for designing the inductance value of the isolation inductor at the alternating current side of the rectifier are as follows:
step 1: according to the full-bridge rectifier circuit, the influence of the AC side isolation inductor on the tracking performance of the input current is considered, and an upper limit formula of the AC side isolation inductor of the rectifier is deduced;
according to kirchhoff's voltage law, the alternating-current side voltage equation is as follows:
Figure FDA0003296554200000036
in the formula uabThe port voltage between the points a and b is obtained, and L is the inductance value of the isolation inductor at the alternating current side;
when the system operates at a high switching frequency, the alternating-current side voltage equation becomes:
Figure FDA0003296554200000041
in the formula,. DELTA.iacThe current variation of the alternating current side in one period;
the actual input current being only during the switching period TsChanges in time, so it is practicalThe maximum controllable variable quantity of the input current is
Figure FDA0003296554200000042
Namely, it is
Figure FDA0003296554200000043
And the input current reference value delta iac *The variation in one switching cycle is:
Δiac *≈IacwTs
namely, the isolation inductor at the alternating current side needs to satisfy the conditions:
Figure FDA0003296554200000044
step 2: according to the full-bridge rectifier circuit, considering the suppression of the input current ripple by the AC side isolation inductor, the synchronous step 1 can be obtained,
Figure FDA0003296554200000045
Figure FDA0003296554200000046
in the formula,. DELTA.iac1Is t0Time t1The amount of current change at that time; Δ iac2Is t1Time t2The amount of current change at that time;
since the current change rate is minimum at the peak, which can be considered as zero, the rising value of the actual input current is equal to the falling value of the current in one switching period, i.e. the current changes in the peak
Δiac1＝Δiac2＝Δiac
If the allowable input current ripple range of the system is delta iacmaxThen, it can be:
Figure FDA0003296554200000051
according to the requirement, a proper maximum ripple range of the input current is selected, the lower limit value of the isolation inductance at the alternating current side of the rectifier is determined,
Figure FDA0003296554200000052
and step 3: the steps 1 and 2 are integrated to obtain the range of the alternating current side isolation inductance of the rectifier
Figure FDA0003296554200000053
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