CN115296521A - Soft start control method based on three-phase hybrid multi-level converter - Google Patents

Soft start control method based on three-phase hybrid multi-level converter Download PDF

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CN115296521A
CN115296521A CN202210910180.1A CN202210910180A CN115296521A CN 115296521 A CN115296521 A CN 115296521A CN 202210910180 A CN202210910180 A CN 202210910180A CN 115296521 A CN115296521 A CN 115296521A
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phase
state
flying capacitor
switch
charging
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CN115296521B (en
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赵一晖
潘建宇
唐海博
杜翊豪
罗尧
王庆林
王钰明
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Chongqing University
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Chongqing University
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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
    • H02M1/36—Means for starting or stopping converters
    • 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
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/4837—Flying capacitor converters
    • 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
    • H02M7/53875—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 with analogue control of three-phase output
    • 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
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inverter Devices (AREA)

Abstract

The invention discloses a soft start control method based on a three-phase hybrid multi-level converter, and belongs to the technical field of power electronics. The soft start control method is based on a three-phase HCC system, and forms a direct-current bus terminal capacitor charging circuit and a flying capacitor charging circuit by changing different switch combination states, wherein the flying capacitor charging circuit has three circuit states and can be switched among the three circuit states in a short period at the same time. The control method based on the three-phase hybrid multi-level converter soft start can quickly and reliably charge all capacitors in the three-phase HCC system to the rated working voltage, avoids large impact current generated in the starting process, fully ensures the working stability of the three-phase HCC system, and is beneficial to popularization and application of the three-phase HCC in the field of DC/AC electric energy conversion.

Description

Soft start control method based on three-phase hybrid multi-level converter
Technical Field
The invention belongs to the technical field of power electronics, and particularly relates to a soft start control method based on a three-phase hybrid multi-level converter.
Background
Research and development and innovation of the multi-level converter are keys for developing medium-high voltage variable frequency drivers, and the three-level, four-level and five-level converters are considered to be the most promising industrial application structures. Compared with a three-level converter, the output voltage of the four-level converter is closer to a sine wave, and compared with a five-level converter, the structure of the four-level converter reduces the control complexity and the number of switches. Therefore, the four-level converter is receiving more and more attention from students. A Hybrid Clamped Converter (HCC) is an emerging medium-high voltage multi-level converter, which has 8 switching state combinations and can output 4-level phase voltages, and the redundancy of the switching states provides additional control freedom. The HCC has a minimum number of devices compared to a conventional four-level converter. Thus, HCC is a very competitive multilevel converter topology.
Dc bus capacitance and flying capacitance are important elements in a three-phase HCC system. During normal operation, the voltage of each capacitor needs to be stabilized at one third of the voltage of the direct current bus. However, the initial values of the voltages of the dc bus capacitor and the flying capacitor are zero, and if no pre-charging operation is performed in the middle-high voltage application, the dc bus capacitor and the flying capacitor are directly controlled by the conventional phase-shift pulse width modulation method, so that a very large capacitor inrush current is generated inside the HCC, which may cause system damage and even burnout. The existing method cannot reliably and softly start the three-phase HCC system and can not well apply the three-phase HCC system to the actual industrial occasions.
Therefore, how to provide a simple and effective control method to suppress the impulse current generated when the three-phase HCC system is started, so that the capacitor voltage of the three-phase HCC system is boosted from zero to a rated value, and the method is a safe start and is a key practical scientific problem to apply the three-phase HCC system.
Disclosure of Invention
In view of this, the present invention provides a simple and effective control method for soft start of a three-phase hybrid multi-level converter. The invention aims to solve the problem that the traditional method generates large impact current in three-phase HCC when being directly started in practical application, and the system is easy to damage and burn.
In order to achieve the aim, the invention provides a soft start control method based on a three-phase hybrid multi-level converter, wherein a pre-charging circuit of the three-phase hybrid multi-level converter comprises a direct-current power supply V dc Switch S 0 、S l Current limiting resistor R l Three-phase load RL, DC bus terminal capacitance C d1 、C d2 And C d3 Flying capacitor C fa 、C fb And C fc And three bridge arms, comprising the steps of:
step 1: setting the capacitance C of the DC bus terminal d1 、C d2 And C d3 And a flying capacitor C fa 、C fb And C fc Rated operating voltage V of ref Turn off the switch S 0 、S l And switches in the three bridge arms;
step 2: closing switch S 0 Turn off the switch S 1 Connected to a current limiting resistor R l Form a charging loop 1 to the capacitor C at the DC bus terminal d1 、C d2 And C d3 The charging loop 1 is connected with a direct current power supply V dc Switch S 0 And a current limiting resistor R l And a DC bus terminal capacitance C d1 、C d2 And C d3 (ii) a The states of switches in three bridge arms are adjusted simultaneously, so that a charging circuit in the three-phase HCC can be rapidly switched among three circuit states in one period to form three different charging circuits 2 for the flying capacitor C fa 、C fb And C fc Charging, charging loop 2 is connected with DC power supply V dc Switch S 0 Current limiting resistor R l Flying capacitor C fa 、C fb And C fc And a three-phase load RL;
the three circuit states of the charging circuit 2 are as follows:
(1) State 1: flying capacitor C of B phase fb Flying capacitor C of C phase fc Flying capacitor C connected in parallel with phase A fa Are connected in series;
(2) State 2: flying capacitor C of A phase fa Flying capacitor C of C phase fc Flying capacitor C connected in parallel with phase B fb Are connected in series;
(3) State 3: flying capacitor C of A phase fa And flying capacitor C of phase B fb Flying capacitor C connected in parallel with C phase fc Are connected in series;
and step 3: detecting flying capacitor C fa 、C fb 、C fc As the flying capacitor C fa 、C fb 、C fc All reach k cf V ref When the direct current bus is started, the switches in the three bridge arms are turned off, and the capacitance C of the direct current bus terminal is accelerated d1 、C d2 、C d3 Charging of (a), said k cf Is a first preset variable coefficient;
and 4, step 4: detecting DC bus end capacitance C d1 、C d2 、C d3 When the voltage of the DC bus terminal capacitor C d1 、C d2 、C d3 All reach k cd V ref While closing switch S l I.e. to complete the soft start of the three-phase hybrid multilevel converter, said k cd Is a second predetermined variable coefficient.
Further, the capacitance C of the DC bus terminal d1 、C d2 And C d3 Flying capacitor C fa 、C fb And C fc Rated operating voltage V ref Are all DC supply voltage V dc 1/3 of (1).
Further, k is cf The value range of (A) is 0.5-3.
Further, k is cd The value range of (A) is 0.5-1.5.
Further, each circuit state of the charging circuit 2 corresponds to two switch combinations:
(1) In the state 1, connection and switching are realized in the following two switch combination modes:
(1-1) the on-off state of the A phase is V 1 The switching states of the B phase and the C phase are V 2 ；
(1-2) the on-off state of the A phase is V 2 The switching states of the B phase and the C phase are V 1 ；
(2) In the state 2, connection and switching are realized through the following two switch combination modes:
(2-1) the switching state of the B phase is V 1 The switching state of A phase and C phase is V 2 ；
(2-2) the switching state of the B phase is V 2 The switching state of A phase and C phase is V 1 ；
(3) The state 3 realizes connection and switching by the following two switch combination modes:
(3-1) the switching state of the C phase is V 1 The switching state of A phase and B phase is V 2 ；
(3-2) the switching state of the C phase is V 2 The switching state of A phase and B phase is V 1 ；
Wherein, the switch state V 1 Internal switch S representing the corresponding phase of a three-phase HCC 1x ，S 2x ，S’ 3x The three-phase hybrid multi-level converter is switched on, other internal switches are switched off, and x is a/B/C and corresponds to the A/B/C phase of the three-phase hybrid multi-level converter respectively; on-off state V 2 Internal switch S representing x-phase corresponding to three-phase HCC 3x ，S’ 2x ，S’ 4x And the rest of the internal switches are turned on and turned off.
Further, one period in the step 2 is 0.1ms to 1s, and the charging loop 2 can be switched between three circuit states and the like in one period.
The invention has the beneficial effects that:
1) According to the soft start control method based on the three-phase hybrid multi-level converter, different charging loops are formed through reasonable switching actions, all capacitors in the three-phase HCC system can be charged to the rated working voltage quickly and reliably, large impact current is prevented from being generated in the starting process, and the working stability of the three-phase HCC system is fully guaranteed.
2) According to the soft start control method based on the three-phase hybrid multi-level converter, the three circuit states of the pre-charging loop 2 are subjected to isochronous rotation, so that simultaneous charging of three-phase flying capacitors is guaranteed, and the control complexity is greatly reduced; meanwhile, each circuit state corresponds to two switch combinations in the three-phase HCC, the control freedom degree is improved, and the three-phase hybrid multi-level converter has a greater popularization and application value in the fields of medium-voltage high-capacity new energy grid connection, motor driving, power transmission and the like.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the means of the instrumentalities and combinations particularly pointed out hereinafter.
Drawings
Fig. 1 is a schematic circuit connection diagram of a three-phase hybrid multilevel converter according to the present invention;
fig. 2 is a schematic diagram of the three circuit states of the charging loop 2 in the pre-charging process of the three-phase hybrid multi-level converter according to the present invention;
fig. 3 is a simulation waveform diagram of the capacitance voltage at the end of the direct current bus and the switch Sl in the pre-charging process of the three-phase hybrid multi-level converter of the embodiment;
fig. 4 is a simulated waveform diagram of flying capacitor voltage during the pre-charging process of the three-phase hybrid multi-level converter of the embodiment.
Detailed Description
In order to make the technical solutions, advantages and objects of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention without inventive step, are within the scope of protection of the present application.
The invention is further illustrated by the following figures and examples.
The invention provides a soft start control method based on a three-phase hybrid multi-level converter, wherein a pre-charging circuit of the three-phase hybrid multi-level converter in the method is shown in figure 1 and comprises a direct-current power supply V dc Switch S 0 And S l Current limiting resistor R l Three-phase HCC and three-phase load RL;
DC power supply V dc For providing a DC supply voltage, the DC power supply V of this embodiment dc The voltage class of (2) is 6kV;
three-phase HCC includes a DC bus terminal capacitance C d1 、C d2 And C d3 Flying capacitor C fa 、C fb And C fc And three bridge arms, DC bus terminal capacitance C d1 、C d2 And C d3 The bridge arms are connected in series, and each bridge arm is provided with four groups of switches;
DC power supply V dc Positive pole of (2) and switch S 0 Is connected to a first terminal of a switch S 0 Through a current limiting resistor R l And a DC bus terminal capacitor C d1 Is connected with the positive pole of the power supply V dc The negative electrode of the capacitor C is connected with the capacitor C of the DC bus terminal d3 The negative electrodes are connected;
switch S l And a current limiting resistor R l Parallel connection;
three-phase HCC is divided into A phase, B phase and C phase, wherein A corresponds to flying capacitor C fa And bridge arm switch S 1a And S' 1a ，S 2a And S' 2a ，S 3a And S' 3a ，S 4a And S' 4a B corresponding to flying capacitor C fb And bridge arm switch S 1b And S' 1b ，S 2b And S' 2b ，S 3b And S' 3b ，S 4b And S' 4b C corresponds to flying capacitor C fc And bridge arm switch S 1c And S' 1c ，S 2c And S' 2c ，S 3c And S' 3c ，S 4c And S' 4c ；
S 1a First terminal and DC bus terminal capacitance C d1 Is connected to the positive pole of S 1a Is connected to S' 1a First end of (A) and S 2a A first end of (a); s' 1a The first terminal of (A) is also connected with S 2a Is connected to the first end of S' 1a The second end is connected with a capacitor C at the DC bus end d1 The negative electrode of (1); s 2a Second end of (2) is connected to S 3a The first end of (a); s is 4a Is connected with a capacitor C at the end of a direct current bus d3 The positive electrode of (1), S 4a Is connected to the second end of S' 2a And S' 4a A first end of (a); and S' 4a The second end of the capacitor is connected with a capacitor C at the end of the direct current bus d3 The negative electrode of (1); and S' 2a Is connected to the second end of S' 3a A first end of (a); said S 3a And S 'and a second end of' 3a The second ends of the two ends are connected with a load RL; said S 2a And S and a second terminal of 3a First ends of the first and second flying capacitors C fa Is connected to the positive electrode of (1), said S' 2a And S' 3a First ends of the first and second flying capacitors C fa Is connected with the negative pole of the anode;
s is 1b First terminal of (2) and DC bus terminal capacitance C d1 Is connected to the positive electrode of S 1b Is connected to S' 1b First end of (1) and S 2b The first end of (a); and S' 1b The first terminal of (A) is also connected with S 2b Is connected to the first end of (S)' 1b The second end is connected with a capacitor C at the end of the DC bus d1 The negative electrode of (1); s is 2b Second end of (2) is connected to S 3b The first end of (a); said S 4b The first end of the capacitor is connected with a DC bus end capacitor C d3 The positive electrode of (1), S 4b Is connected to S' 2b And S' 4b A first end of (a); s' 4b The second end of the capacitor is connected with a capacitor C at the end of the direct current bus d3 The negative electrode of (1); s' 2b Is connected to the second end of S' 3b A first end of (a); said S 3b And S 'and a second end of' 3b At the second end of eachA load RL is connected; said S 2b Second end of (S) and 3b first ends of the first and second flying capacitors C fb Is connected to the positive electrode of (1), said S' 2b And S' 3b First ends of the first and second flying capacitors C fb Is connected with the negative pole of the anode;
said S 1c First terminal and DC bus terminal capacitance C d1 Is connected to the positive electrode of S 1c Is connected to the second end of S' 1c First end of (1) and S 2c A first end of (a); s' 1c The first terminal of (A) is also connected with S 2c Is connected to the first end of S' 1c The second end is connected with a capacitor C at the end of the DC bus d1 The negative electrode of (1); said S 2c Is connected to the second end S 3c A first end of (a); s is 4c The first end of the capacitor is connected with a DC bus end capacitor C d3 The positive electrode of (1), S 4c Is connected to the second end of S' 2b And S' 2c The first end of (a); s' 4c The second end of the capacitor is connected with a capacitor C at the end of the direct current bus d3 The negative electrode of (1); and S' 2c Is connected to the second end of S' 3c The first end of (a); said S 3c And S 'and a second end of' 3c The second ends of the two ends are connected with a load RL; s is 2c Second end of (S) and 3c first ends of the first and second flying capacitors C fc S 'is connected to the positive electrode of' 2c And S' 3c First ends of the first and second flying capacitors C fc Is connected.
The three-phase load RL consists of three resistors and inductors which are connected in series, the resistance value of the resistor of the load RL is 20 omega, and the inductance is 1mH: the three-phase output terminals of the three-phase HCC are connected to a load RL, respectively.
The invention discloses a soft start control method based on a three-phase hybrid multi-level converter, which comprises the following steps of:
step 1: direct current bus terminal capacitance C in three-phase HCC d1 、C d2 And C d3 Flying capacitor C fa 、C fb And C fc Rated operating voltages of all the units are set to V ref ，V ref Is a DC supply voltage V dc 1/3 of (S), turn off the switch S 0 、S l And three areA switch in the bridge arm.
Step 2:
2-1) closing switch S 0 Turn off the switch S l Connected to a current limiting resistor R l Form a charging loop 1 to a DC bus capacitor C d1 、C d2 And C d3 Charging, charging loop 1 is connected with DC power supply V dc Switch S 0 Current limiting resistor R l And a DC bus terminal capacitance C d1 、C d2 And C d3 ；
2-2) simultaneously adjusting the states of the switches in the three bridge arms, so that the charging circuit in the three-phase HCC can be rapidly switched among three circuit states in one period to form three different charging circuits 2 for the flying capacitor C fa 、C fb And C fc Charging, one cycle of the embodiment is 0.06s, the charging loop 2 is connected with a direct current power supply V dc Switch S 0 And a current limiting resistor R l Three flying capacitors C fa 、C fb And C fc And a three-phase load RL.
Fig. 2 is a schematic diagram of a rotation of three circuit states of the charging circuit 2, where the three circuit states of the charging circuit 2 are as follows:
(1) State 1: flying capacitor C of B phase fb Flying capacitor C of C phase fc After parallel connection, the flying capacitor C is connected with the phase A fa Are connected in series;
(2) State 2: flying capacitor C of A phase fa Flying capacitor C of C phase fc Flying capacitor C connected in parallel with phase B fb Are connected in series;
(3) State 3: flying capacitor C of A phase fa And flying capacitor C of phase B fb Flying capacitor C connected in parallel with C phase fc Are connected in series.
And step 3: detecting flying capacitor C fa 、C fb 、C fc As the flying capacitor C fa 、C fb 、C fc All reach k cf V ref When the DC bus is in use, the switches of the three bridge arm groups are turned off, and the capacitor C at the end of the DC bus is accelerated d1 、C d2 、C d3 Charging of (k) cf Is the first stepLet coefficient of variation, k in this example cf Is chosen to be 1.
And 4, step 4: detecting DC bus end capacitance C d1 、C d2 、C d3 When the DC bus terminal capacitance C d1 、C d2 、C d3 All reach k cd V ref While closing switch S l Cutting off the current limiting resistor R l I.e. soft start of the three-phase hybrid multilevel converter is completed, k cd As coefficient of variation, k of this implementation cd The selection was 0.9999.
As a preference of this embodiment, each circuit state of the charging circuit 2 corresponds to two switch combinations:
(1) In the state 1, connection and switching are realized through the following two switch combination modes:
(1-1) the on-off state of the A phase is V 1 The switching state of B phase and C phase is V 2 ；
(1-2) the on-off state of the A phase is V 2 The switching state of B phase and C phase is V 1 ；
(2) In the state 2, connection and switching are realized through the following two switch combination modes:
(2-1) the switching state of the B phase is V 1 The switching state of A phase and C phase is V 2 ；
(2-2) the switching state of the B phase is V 2 The switching state of A phase and C phase is V 1 ；
(3) In the state 3, connection and switching are realized through the following two switch combination modes:
(3-1) the switching state of the C phase is V 1 The switching state of A phase and B phase is V 2 ；
(3-2) the switching state of the C phase is V 2 The switching state of A phase and B phase is V 1 ；
Wherein, the switch state V 1 Internal switch S representing x-phase corresponding to three-phase HCC 1x ，S 2x ，S’ 3x Conducting, and turning off the rest internal switches; on-off state V 2 Internal switch S representing x-phase corresponding to three-phase HCC 3x ，S’ 2x ，S’ 4x Is conducted to the restThe partial switch is turned off.
Under the control of the method of the invention, the whole soft start process of the three-phase HCC is divided into three stages: stage one, the capacitor C of the DC bus terminal d1 、C d2 、C d3 And flying capacitor C fa 、C fb 、C fc Charging at the same time; stage two, flying capacitor C fa 、C fb 、C fc The charging is completed and the DC bus terminal capacitance C is accelerated d1 、C d2 、C d3 Charging; and step three, finishing charging all the capacitors, and waiting for the whole system to enter a normal working state.
FIG. 3 shows the capacitor voltage and the switch S at the end of the DC bus during the pre-charging process of the three-phase hybrid multi-level converter of this embodiment l The simulated waveform of (2).
From the analysis in fig. 3, it can be seen that: when the soft start control method provided by the invention is used, the capacitor C of the DC bus end in the first stage d1 、C d2 And C d3 Starting charging, second stage DC bus terminal capacitance C d1 、C d2 And C d3 Charging acceleration, third stage, 3s time DC bus capacitor C d1 、C d2 And C d3 Charging to 99.99% of rated working voltage, judging that charging is finished, and then closing switch S l Cutting off the current limiting resistor R l And at the moment, the capacitor voltage at the end of the direct current bus is clamped at the rated working value, and the charging is finished.
Fig. 4 is a simulated waveform diagram of flying capacitor voltage during the pre-charging process of the three-phase hybrid multi-level converter of the embodiment.
From the analysis in fig. 4, it can be seen that: when the soft start control method provided by the invention is used, the flying capacitor C is in the first stage fa 、C fb And C fc Rapidly charging, and charging to a rated working value after 0.6 s; in the second stage, the charging circuit 2 is turned off, and the flying capacitor C is connected fa 、C fb And C fc Stopping charging, DC bus terminal capacitance C d1 、C d2 And C d3 Accelerating charging; third stage, flying capacitor C fa 、C fb And C fc And dynamically supplementing power, finishing charging and waiting for switching into a normal working state.
In summary, the soft start control method based on the three-phase hybrid multi-level converter provided by the invention forms different charging loops through reasonable switching actions, all capacitors in the three-phase HCC system can be quickly and reliably charged to the rated working voltage, large impact current generated in the starting process is avoided, and the working stability of the three-phase HCC system is fully ensured.
According to the three-phase HCC soft start control method, simultaneous charging of flying capacitors is guaranteed through isochronous rotation of three circuit states of the pre-charging loop 2, control complexity is reduced, meanwhile, each circuit state corresponds to two HCC internal switch combination states, control freedom is improved, and the three-phase HCC soft start control method has a larger popularization and application value in the fields of medium-voltage high-capacity new energy grid connection, motor driving, power transmission and the like.
Finally, the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all of them should be covered in the protection scope of the present invention.

Claims (6)

1. A soft start control method based on a three-phase hybrid multi-level converter is disclosed, wherein a pre-charging circuit of the three-phase hybrid multi-level converter comprises a direct current power supply V dc Switch S 0 、S l Current limiting resistor R l Three-phase load RL, DC bus terminal capacitance C d1 、C d2 And C d3 Flying capacitor C fa 、C fb And C fc And three bridge arms, wherein the control method comprises the following steps:
step 1: setting the capacitance C of the DC bus terminal d1 、C d2 And C d3 And a flying capacitor C fa 、C fb And C fc Rated operating voltage V ref Turning off the switch S 0 、S l And switches in the three bridge arms;
and 2, step: closing switch S 0 Turn off the switch S 1 Connected to a current limiting resistor R l Form a charging loop 1 to the capacitor C at the DC bus terminal d1 、C d2 And C d3 The charging loop 1 is connected with a direct current power supply V dc Switch S 0 Current limiting resistor R l And a DC bus terminal capacitance C d1 、C d2 And C d3 (ii) a The states of the switches in the three bridge arms are adjusted simultaneously, so that the charging circuit in the three-phase HCC can be rapidly switched among three circuit states in one period to form three different charging circuits 2 for the flying capacitor C fa 、C fb And C fc Charging, charging loop 2 is connected with DC power supply V dc Switch S 0 Current limiting resistor R l Flying capacitor C fa 、C fb And C fc And a three-phase load RL;
the three circuit states of the charging circuit 2 are as follows:
(1) State 1: flying capacitor C of B phase fb Flying capacitor C of C phase fc Flying capacitor C connected in parallel with phase A fa Are connected in series;
(2) State 2: flying capacitor C of A phase fa Flying capacitor C of C phase fc Flying capacitor C connected in parallel with phase B fb Are connected in series;
(3) State 3: flying capacitor C of A phase fa Flying capacitor C of phase B fb Flying capacitor C connected in parallel with C phase fc Are connected in series;
and step 3: detecting flying capacitor C fa 、C fb 、C fc As the flying capacitor C fa 、C fb 、C fc All reach k cf V ref When the DC bus is started, the switches in the three bridge arms are turned off, and the capacitance C of the DC bus terminal is accelerated d1 、C d2 、C d3 Charging of (a), said k cf Is a first preset variable coefficient;
and 4, step 4: detecting DC bus end capacitance C d1 、C d2 、C d3 When the voltage of the DC bus terminal capacitor C d1 、C d2 、C d3 All reach k cd V ref While closing switch S l I.e. to complete the soft start of the three-phase hybrid multilevel converter, said k cd Is a second predetermined variable coefficient.
2. The soft-start control method of the three-phase hybrid multilevel converter according to claim 1, wherein the DC bus end capacitor C d1 、C d2 And C d3 Flying capacitor C fa 、C fb And C fc Rated operating voltage V of ref Are all DC supply voltage V dc 1/3 of (1).
3. The method as claimed in claim 1, wherein the k is a soft start control of the three-phase hybrid multilevel converter cf The value range of (A) is 0.5-3.
4. The soft start control method of the three-phase hybrid multilevel converter according to claim 1, wherein k is cd The value range of (A) is 0.5-1.5.
5. The method as claimed in claim 1, wherein each circuit state of the charging circuit 2 corresponds to two switch combinations:
(1) In the state 1, connection and switching are realized in the following two switch combination modes:
(1-1) the on-off state of the A phase is V 1 The switching states of the B phase and the C phase are V 2 ；
(1-2) the on-off state of the A phase is V 2 The switching state of B phase and C phase is V 1 ；
(2) In the state 2, connection and switching are realized through the following two switch combination modes:
(2-1) the switching state of the B phase is V 1 The switching state of A phase and C phase is V 2 ；
(2-2) the switching state of the B phase is V 2 On-off state of A phase and C phaseState is V 1 ；
(3) The state 3 realizes connection and switching by the following two switch combination modes:
(3-1) the switching state of the C phase is V 1 The switching state of A phase and B phase is V 2 ；
(3-2) the switching state of the C phase is V 2 The switching state of A phase and B phase is V 1 ；
Wherein, the switch state V 1 Internal switch S representing the corresponding phase of a three-phase HCC 1x ，S 2x ，S’ 3x The three-phase hybrid multilevel converter is switched on, other internal switches are switched off, x is a/B/C and corresponds to the A/B/C phase of the three-phase hybrid multilevel converter respectively; on-off state V 2 Internal switch S representing the corresponding phase of a three-phase HCC 3x ，S’ 2x ，S’ 4x And the rest internal switches are turned off.
6. The method as claimed in claim 1, wherein a period of the step 2 is 0.1ms to 1s, and the charging loop 2 switches between three circuit states in one period.
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