CN115296521B - 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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CN115296521B
CN115296521B CN202210910180.1A CN202210910180A CN115296521B CN 115296521 B CN115296521 B CN 115296521B CN 202210910180 A CN202210910180 A CN 202210910180A CN 115296521 B CN115296521 B CN 115296521B
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phase
capacitor
switch
current bus
flying
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CN115296521A (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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    • 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, forms a direct-current bus end capacitor charging loop and a flying capacitor charging loop by changing different switch combination states, and the flying capacitor charging loop has three circuit states and can be switched among the three circuit states in a short period. The control method based on the soft start of the three-phase hybrid multi-level converter can charge all the capacitors in the three-phase HCC system to rated working voltage quickly and reliably, avoids large impact current 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
The research and development and innovation of the multi-level converter are key in developing a medium-high voltage variable frequency driver, and three-level, four-level and five-level converters are considered as 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 four-level converter reduces the control complexity and the number of switches. Therefore, four-level converters are receiving more and more attention from students. The hybrid multilevel converter (HybridClampedConverter, HCC) is an emerging medium-high voltage multilevel converter with 8 switch state combinations that can output 4-level phase voltages, the redundancy of the switch states providing additional control freedom. HCC has a minimum device count compared to conventional four-level converters. HCC is therefore a very competitive multilevel converter topology.
Dc bus capacitance and flying capacitance are important components in a three-phase HCC system. In normal operation, each capacitor voltage needs to be stabilized at one third of the dc bus voltage. However, if the voltage of the dc bus capacitor and the flying capacitor is zero, and the dc bus capacitor and the flying capacitor are directly controlled by the conventional phase-shift pulse width modulation method without any precharge operation in the middle-high voltage application, a very large capacitor surge current is generated in the HCC, which causes damage or even burnout of the system. The existing method cannot reliably and softly start the three-phase HCC system, and cannot well apply the three-phase HCC system to actual industrial occasions.
Therefore, how to propose a simple and effective control method to suppress the rush current generated when the three-phase HCC system is started, to make the capacitor voltage of the three-phase HCC system reach the rated value from zero boost, is a safe start, and applies the three-phase HCC system to practical key scientific problems.
Disclosure of Invention
In view of the above, the present invention aims to provide 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 in practical application, large impact current is generated in three-phase HCC (liquid Crystal display) when the traditional method is directly started, and the system is extremely easy to damage and burn.
In order to achieve the above objective, the present invention provides a soft start control method based on a three-phase hybrid multi-level converter, wherein a precharge circuit of the three-phase hybrid multi-level converter includes a dc power V dc, a switch S 0、Sl, a current limiting resistor R l, a three-phase load RL, dc bus end capacitors C d1、Cd2 and C d3, flying capacitors C fa、Cfb and C fc, and three bridge arms, and the method comprises the following steps:
Step 1: setting rated working voltages V ref of direct-current bus-end capacitors C d1、Cd2 and C d3 and flying capacitors C fa、Cfb and C fc, turning off a switch S 0、Sl and switches in three bridge arms;
Step 2: closing the switch S 0, closing the switch S 1, and connecting the current-limiting resistor R l to form a charging loop 1 to charge the direct-current bus end capacitors C d1、Cd2 and C d3, wherein the charging loop 1 is connected with a direct-current power supply V dc, the switch S 0, the current-limiting resistor R l and the direct-current bus end capacitors C d1、Cd2 and C d3; simultaneously, the states of the switches in the three bridge arms are adjusted, so that a charging loop in the three-phase HCC can be rapidly switched among three circuit states in one period, three different charging loops 2 are formed to charge flying capacitors C fa、Cfb and C fc, and the charging loop 2 is connected with a direct-current power supply V dc, a switch S 0, a current-limiting resistor R l, flying capacitors C fa、Cfb and C fc and a three-phase load RL;
The three circuit states of the charging loop 2 are as follows:
(1) State 1: the flying capacitor C fb of the phase B and the flying capacitor C fc of the phase C are connected in parallel and then connected in series with the flying capacitor C fa of the phase A;
(2) State 2: the flying capacitor C fa of the phase A and the flying capacitor C fc of the phase C are connected in parallel and then connected in series with the flying capacitor C fb of the phase B;
(3) State 3: the flying capacitor C fa of the phase A and the flying capacitor C fb of the phase B are connected in parallel and then connected in series with the flying capacitor C fc of the phase C;
Step 3: detecting the voltage of a flying capacitor C fa、Cfb、Cfc, when the voltage of the flying capacitor C fa、Cfb、Cfc reaches k cfVref, turning off switches in three bridge arms to accelerate the charging of a direct current bus end capacitor C d1、Cd2、Cd3, wherein k cf is a first preset variable coefficient;
Step 4: and detecting the voltage of the direct-current bus end capacitor C d1、Cd2、Cd3, closing the switch S l when the voltage of the direct-current bus end capacitor C d1、Cd2、Cd3 reaches k cdVref, namely finishing the soft start of the three-phase hybrid multi-level converter, wherein k cd is a second preset variable coefficient.
Further, the rated operating voltages V ref of the dc bus terminal capacitors C d1、Cd2 and C d3 and the flying capacitors C fa、Cfb and C fc are 1/3 of the dc power supply voltage V dc.
Further, the value range of k cf is 0.5-3.
Further, the value range of k cd is 0.5-1.5.
Further, each circuit state of the charging loop 2 corresponds to two switch combinations:
(1) The state 1 realizes connection and switching in the following two switch combination modes:
(1-1) the switching state of phase A is V 1, and the switching state of phase B and phase C is V 2;
(1-2) the switching state of phase A is V 2, and the switching state of phase B and phase C is V 1;
(2) The state 2 realizes connection and switching in the following two switch combination modes:
(2-1) the switching state of phase B is V 1, and the switching state of phase A and phase C is V 2;
(2-2) the switching state of phase B is V 2, and the switching state of phase a and phase C is V 1;
(3) The state 3 realizes connection and switching in the following two switch combination modes:
(3-1) the switching state of the C phase is V 1, and the switching state of the A phase and the B phase is V 2;
(3-2) the switching state of the C phase is V 2, and the switching state of the A phase and the B phase is V 1;
Wherein, the switch state V 1 indicates that the internal switch S 1x,S2x,S'3x of the phase corresponding to the three-phase HCC is turned on, the other internal switches are turned off, x is a/B/C, and the three-phase hybrid multi-level converter A/B/C phases respectively correspond to the three-phase hybrid multi-level converter; switch state V 2 indicates that the x-phase internal switch S 3x,S'2x,S'4x corresponding to the three-phase HCC is on, and the remaining internal switches are off.
Further, in the step 2, one cycle is 0.1ms to 1s, and the charging circuit 2 can be switched between three circuit states and the like in one cycle.
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 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, provided by the invention, the three-phase flying capacitor is ensured to be charged simultaneously through the three circuit states of the precharge circuit 2 and the equal time rotation, so that the control complexity is greatly reduced; meanwhile, each circuit state corresponds to two switch combinations in the three-phase HCC, so that the control degree of freedom is improved, and the three-phase hybrid multi-level converter has higher popularization and application values 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 objects and other advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the specification.
Drawings
Fig. 1 is a schematic diagram of circuit connections of a three-phase hybrid multilevel converter according to the present invention;
fig. 2 is a schematic diagram illustrating the rotation of three circuit states of the charging loop 2 during the precharge process of the three-phase hybrid multilevel converter according to the present invention;
fig. 3 is a simulation waveform diagram of a capacitor voltage and a switch Sl at a dc bus end in a precharge process of the three-phase hybrid multilevel converter according to the embodiment;
fig. 4 is a simulated waveform diagram of the flying capacitor voltage during the precharge process of the three-phase hybrid multilevel converter according to the present embodiment.
Detailed Description
In order to make the technical scheme, advantages and objects of the present application more clear, the technical scheme of the embodiment of the present application will be clearly and completely described below with reference to the accompanying drawings of the embodiment of the present application. It will be apparent that the described embodiments are some, but not all, embodiments of the application. All other embodiments, which can be obtained by a person skilled in the art without creative efforts, based on the described embodiments of the present application belong to the protection scope of the present application.
The invention is further described below with reference to the drawings and examples.
The invention provides a soft start control method based on a three-phase hybrid multi-level converter, wherein a precharge circuit of the three-phase hybrid multi-level converter in the method is shown in a figure 1, and comprises a direct current power supply V dc, switches S 0 and S l, a current limiting resistor R l, a three-phase HCC and a three-phase load RL;
The direct current power supply V dc is used for providing direct current power supply voltage, and the voltage class of the direct current power supply V dc is 6kV;
The three-phase HCC comprises direct-current bus end capacitors C d1、Cd2 and C d3, flying capacitors C fa、Cfb and C fc and three bridge arms, wherein the direct-current bus end capacitors C d1、Cd2 and C d3 are mutually connected in series, and each bridge arm is provided with four groups of switches;
The positive electrode of the direct current power supply V dc is connected with the first end of the switch S 0, the second end of the switch S 0 is connected with the positive electrode of the direct current bus end capacitor C d1 through the current limiting resistor R l, and the negative electrode of the power supply V dc is connected with the negative electrode of the direct current bus end capacitor C d3;
the switch S l is connected with the current limiting resistor R l in parallel;
Three-phase HCC is divided into A, B, C phases, a corresponds to flying capacitor C fa and leg switches S 1a and S '1a,S2a and S' 2a,S3a and S '3a,S4a and S' 4a, B corresponds to flying capacitor C fb and leg switches S 1b and S '1b,S2b and S' 2b,S3b and S '3b,S4b and S' 4b, C corresponds to flying capacitor C fc and leg switches S 1c and S '1c,S2c and S' 2c,S3c and S '3c,S4c and S' 4c;
The first end of S 1a is connected with the positive electrode of the direct current bus end capacitor C d1, and the second end of S 1a is connected with the first end of S' 1a and the first end of S 2a; the first end of S '1a is also connected with the first end of S 2a, and the second end of S' 1a is connected with the negative electrode of the direct current bus end capacitor C d1; the second end of S 2a is connected with the first end of S 3a; the first end of the S 4a is connected with the positive electrode of the direct current bus end capacitor C d3, and the second end of the S 4a is connected with the first end of the S '2a and the first end of the S' 4a; the second end of the S' 4a is connected with the negative electrode of the direct-current bus end capacitor C d3; the second end of the S '2a is connected with the first end of the S' 3a; the second end of S 3a and the second end of S' 3a are both connected with a load RL; the second end of S 2a and the first end of S 3a are both connected with the anode of flying capacitor C fa, and the second end of S '2a and the first end of S' 3a are both connected with the cathode of flying capacitor C fa;
The first end of the S 1b is connected with the positive electrode of the direct current bus end capacitor C d1, and the second end of the S 1b is connected with the first end of the S' 1b and the first end of the S 2b; the first end of the S '1b is also connected with the first end of the S 2b, and the second end of the S' 1b is connected with the negative electrode of the direct current bus end capacitor C d1; the second end of the S 2b is connected with the first end of the S 3b; the first end of the S 4b is connected with the positive electrode of the direct current bus end capacitor C d3, and the second end of the S 4b is connected with the first end of the S '2b and the first end of the S' 4b; the second end of the S' 4b is connected with the negative electrode of the direct-current bus end capacitor C d3; the second end of the S '2b is connected with the first end of the S' 3b; the second end of S 3b and the second end of S' 3b are both connected with a load RL; the second end of S 2b and the first end of S 3b are both connected with the anode of flying capacitor C fb, and the second end of S '2b and the first end of S' 3b are both connected with the cathode of flying capacitor C fb;
the first end of the S 1c is connected with the positive electrode of the direct current bus end capacitor C d1, and the second end of the S 1c is connected with the first end of the S' 1c and the first end of the S 2c; the first end of the S '1c is also connected with the first end of the S 2c, and the second end of the S' 1c is connected with the negative electrode of the direct current bus end capacitor C d1; the second end of the S 2c is connected with the first end of the S 3c; the first end of the S 4c is connected with the positive electrode of the direct current bus end capacitor C d3, and the second end of the S 4c is connected with the first end of the S '2b and the first end of the S' 2c; the second end of the S' 4c is connected with the negative electrode of the direct-current bus end capacitor C d3; the second end of the S '2c is connected with the first end of the S' 3c; the second end of S 3c and the second end of S' 3c are both connected with a load RL; the second end of S 2c and the first end of S 3c are both connected to the positive pole of flying capacitor C fc, and the second end of S '2c and the first end of S' 3c are both connected to the negative pole of flying capacitor C fc.
The three-phase load RL consists of three resistors and inductors which are connected in series, the resistance value of the load RL resistor is 20Ω, and the inductance is 1mH: the three-phase outputs 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:
Step 1: the rated operating voltages of the dc bus-end capacitances C d1、Cd2 and C d3, flying capacitances C fa、Cfb and C fc in the three-phase HCC are each set to 1/3 of the dc supply voltage V dc for V ref,Vref, and the switch S 0、Sl, and the switches in the three legs, are turned off.
Step 2:
2-1) closing the switch S 0, closing the switch S l, and connecting the current-limiting resistor R l to form a charging loop 1 for charging the direct-current bus capacitors C d1、Cd2 and C d3, wherein the charging loop 1 is connected with a direct-current power supply V dc, the switch S 0, the current-limiting resistor R l, and the direct-current bus end capacitors C d1、Cd2 and C d3;
2-2) simultaneously adjusts the states of the switches in the three bridge arms, so that the charging loop in the three-phase HCC can be rapidly switched between three circuit states in one period, three different charging loops 2 are formed to charge flying capacitors C fa、Cfb and C fc, one period of the embodiment is 0.06S, and the charging loop 2 is connected with a direct current power supply V dc, a switch S 0, a current limiting resistor R l, three flying capacitors C fa、Cfb and C fc and a three-phase load RL.
Fig. 2 is a schematic diagram illustrating 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: the flying capacitor C fb of the phase B and the flying capacitor C fc of the phase C are connected in parallel and then connected in series with the flying capacitor C fa of the phase A;
(2) State 2: the flying capacitor C fa of the phase A and the flying capacitor C fc of the phase C are connected in parallel and then connected in series with the flying capacitor C fb of the phase B;
(3) State 3: the phase a flying capacitor C fa and the phase B flying capacitor C fb are connected in parallel and then connected in series with the phase C flying capacitor C fc.
Step 3: when the voltage of the flying capacitor C fa、Cfb、Cfc is detected and the voltages of the flying capacitor C fa、Cfb、Cfc reach k cfVref, the switches of the three bridge arm groups are turned off, the charging of the direct current bus end capacitor C d1、Cd2、Cd3 is accelerated, k cf is a first preset variable coefficient, and k cf in this embodiment is selected to be 1.
Step 4: when the voltage of the direct current bus end capacitor C d1、Cd2、Cd3 is detected and the voltage of the direct current bus end capacitor C d1、Cd2、Cd3 reaches k cdVref, the switch S l is closed, the current limiting resistor R l is cut off, and then the soft start of the three-phase hybrid multi-level converter is completed, k cd is the variable coefficient, and k cd in the implementation is selected to be 0.9999.
As one preferable example of the present embodiment, each circuit state of the charging circuit 2 corresponds to two kinds of switch combinations:
(1) The state 1 realizes connection and switching in the following two switch combination modes:
(1-1) the switching state of phase A is V 1, and the switching state of phase B and phase C is V 2;
(1-2) the switching state of phase A is V 2, and the switching state of phase B and phase C is V 1;
(2) The state 2 realizes connection and switching in the following two switch combination modes:
(2-1) the switching state of phase B is V 1, and the switching state of phase A and phase C is V 2;
(2-2) the switching state of phase B is V 2, and the switching state of phase a and phase C is V 1;
(3) The state 3 realizes connection and switching in the following two switch combination modes:
(3-1) the switching state of the C phase is V 1, and the switching state of the A phase and the B phase is V 2;
(3-2) the switching state of the C phase is V 2, and the switching state of the A phase and the B phase is V 1;
Wherein, the switch state V 1 indicates that the x-phase internal switch S 1x,S2x,S'3x corresponding to the three-phase HCC is turned on, and the other internal switches are turned off; switch state V 2 indicates that the x-phase internal switch S 3x,S'2x,S'4x corresponding to the three-phase HCC is on, and the remaining internal switches are off.
Under the control of the method of the invention, the soft start process of the whole three-phase HCC is divided into three phases: in the first stage, the direct current bus end capacitor C d1、Cd2、Cd3 and the flying capacitor C fa、Cfb、Cfc are charged simultaneously; step two, the flying capacitor C fa、Cfb、Cfc finishes charging, and the charging of the capacitor C d1、Cd2、Cd3 at the DC bus end is accelerated; and step three, charging all the capacitors is completed, and the whole system waits to enter a normal working state.
Fig. 3 is a simulation waveform diagram of the dc bus end capacitor voltage and the switch S l during the precharge process of the three-phase hybrid multilevel converter according to this embodiment.
From the analysis in fig. 3, it can be seen that: when the soft start control method provided by the invention is used, the first-stage direct current bus terminal capacitors C d1、Cd2 and C d3 start to charge, the second-stage direct current bus terminal capacitors C d1、Cd2 and C d3 accelerate to charge, the third-stage direct current bus terminal capacitors C d1、Cd2 and C d3 charge to 99.99% of rated working voltage at 3S, the charging is judged to be completed, then the switch S l is closed, the current-limiting resistor R l is cut off, and at the moment, the direct current bus terminal capacitor voltage is clamped at the rated working value, and the charging is completed.
Fig. 4 is a simulated waveform diagram of the flying capacitor voltage during the precharge process of the three-phase hybrid multilevel converter according to the present 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 capacitors C fa、Cfb and C fc in the first stage are rapidly charged, and the capacitor is charged to a rated working value after 0.6 s; in the second stage, the charging loop 2 is turned off, the flying capacitors C fa、Cfb and C fc stop charging, and the charging of the capacitors C d1、Cd2 and C d3 at the direct current bus end is accelerated; and in the third stage, the flying capacitors C fa、Cfb and C fc are dynamically charged, and the charging is completed and the normal working state is waited for switching in.
In summary, according to the soft start control method based on the three-phase hybrid multi-level converter provided by the invention, different charging loops are formed through reasonable switching actions, so that all capacitors in the three-phase HCC system can be charged to 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 ensured.
According to the three-phase HCC soft start control method provided by the invention, through the equal rotation of three circuit states of the precharge circuit 2, the simultaneous charging of the flying capacitor is ensured, the control complexity is reduced, and each circuit state corresponds to two HCC internal switch combination states, so that the control freedom degree is improved, and the control method has greater popularization and application values in the fields of medium-voltage high-capacity new energy grid connection, motor driving, power transmission and the like.
Finally, it is noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and 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 the technical solution of the present invention may be modified or substituted without departing from the spirit and scope of the technical solution, and the present invention is intended to be covered in the scope of the present invention.

Claims (6)

1. A soft start control method based on a three-phase hybrid multi-level converter, wherein a pre-charge circuit of the three-phase hybrid multi-level converter comprises a direct current power supply V dc, a switch S 0、Sl, a current limiting resistor R l, a three-phase load RL, direct current bus end capacitors C d1、Cd2 and C d3, flying capacitors C fa、Cfb and C fc and three bridge arms, the three-phase hybrid multi-level converter is divided into A, B, C phases, A corresponds to the flying capacitor C fa and bridge arm switches S 1a and S '1a,S2a and S' 2a,S3a and S '3a,S4a and S' 4a, B corresponds to the flying capacitor C fb and bridge arm switches S 1b and S '1b,S2b and S' 2b,S3b and S '3b,S4b and S' 4b, and C corresponds to the flying capacitors C fc and bridge arm switches S 1c and S '1c,S2c and S' 2c,S3c and S '3c,S4c and S' 4c;
The positive electrode of the direct current power supply V d C is connected with the first end of the switch S 0, the second end of the switch S 0 is connected with the positive electrode of the direct current bus end capacitor C d1 through the current limiting resistor R l, the negative electrode of the direct current bus end capacitor C d1 is connected with the positive electrode of the direct current bus end capacitor C d2, the negative electrode of the direct current bus end capacitor C d2 is connected with the positive electrode of the direct current bus end capacitor C d3, the negative electrode of the power supply V dc is connected with the negative electrode of the direct current bus end capacitor C d3, and the switch S l is connected with the current limiting resistor R l in parallel; the first end of S 1a is connected with the positive electrode of the direct current bus end capacitor C d1, and the second end of S 1a is connected with the first end of S' 1a and the first end of S 2a; the first end of S '1a is also connected with the first end of S 2a, and the second end of S' 1a is connected with the negative electrode of the direct current bus end capacitor C d1; the second end of S 2a is connected with the first end of S 3a; the first end of the S 4a is connected with the positive electrode of the direct current bus end capacitor C d3, and the second end of the S 4a is connected with the first end of the S '2a and the first end of the S' 4a; the second end of the S' 4a is connected with the negative electrode of the direct-current bus end capacitor C d3; the second end of the S '2a is connected with the first end of the S' 3a; the second end of S 3a and the second end of S' 3a are both connected with a load RL; the second end of S 2a and the first end of S 3a are both connected with the anode of flying capacitor C fa, and the second end of S '2a and the first end of S' 3a are both connected with the cathode of flying capacitor C fa;
the control method is characterized by comprising the following steps:
Step 1: setting rated working voltages V ref of direct-current bus-end capacitors C d1、Cd2 and C d3 and flying capacitors C fa、Cfb and C fc, turning off a switch S 0、Sl and switches in three bridge arms;
Step 2: closing the switch S 0, turning off the switch S 1, and connecting the current-limiting resistor R l to form a charging loop 1 to charge the direct-current bus end capacitors C d1、Cd2 and C d3, wherein the charging loop 1 is connected with a direct-current power supply Vdc, the switch S 0, the current-limiting resistor R l and the direct-current bus end capacitors C d1、Cd2 and C d3; simultaneously, the states of the switches in the three bridge arms are adjusted, so that a charging loop in the three-phase HCC can be rapidly switched among three circuit states in one period, three different charging loops 2 are formed to charge flying capacitors C fa、Cfb and C fc, and the charging loop 2 is connected with a direct-current power supply V dc, a switch S 0, a current-limiting resistor R l, flying capacitors C fa、Cfb and C fc and a three-phase load RL;
The three circuit states of the charging loop 2 are as follows:
(1) State 1: the flying capacitor C fb of the phase B and the flying capacitor C fc of the phase C are connected in parallel and then connected in series with the flying capacitor C fa of the phase A;
(2) State 2: the flying capacitor C fa of the phase A and the flying capacitor C fc of the phase C are connected in parallel and then connected in series with the flying capacitor C fb of the phase B;
(3) State 3: the flying capacitor C fa of the phase A and the flying capacitor C f B of the phase B are connected in parallel and then connected in series with the flying capacitor C fc of the phase C;
step 3: detecting the voltage of a flying capacitor C fa、Cfb、Cfc, when the voltage of the flying capacitor C fa、Cfb、Cfc reaches k cfVref, turning off switches in three bridge arms to accelerate the charging of a direct current bus end capacitor C d1、Cd2、Cd3, wherein kcf is a first preset variable coefficient;
Step 4: and detecting the voltage of the direct-current bus end capacitor C d1、Cd2、Cd3, closing the switch S l when the voltage of the direct-current bus end capacitor C d1、Cd2、Cd3 reaches k cdVref, namely finishing the soft start of the three-phase hybrid multi-level converter, wherein k cd is a second preset variable coefficient.
2. The soft start control method based on the three-phase hybrid multilevel converter according to claim 1, wherein the rated operating voltage Vref of the dc bus terminal capacitors C d1、Cd2 and C d3 and the flying capacitors C fa、Cfb and C fc is 1/3 of the dc power supply voltage V dc.
3. The soft start control method based on the three-phase hybrid multi-level converter according to claim 1, wherein the value range of k cf is 0.5-3.
4. The soft start control method based on the three-phase hybrid multi-level converter according to claim 1, wherein the value range of k cd is 0.5-1.5.
5. The soft start control method based on the three-phase hybrid multi-level converter according to claim 1, wherein each circuit state of the charging loop 2 corresponds to two switch combinations:
(1) The state 1 realizes connection and switching in the following two switch combination modes:
(1-1) the switching state of phase A is V 1, and the switching state of phase B and phase C is V 2;
(1-2) the switching state of phase A is V 2, and the switching state of phase B and phase C is V 1;
(2) The state 2 realizes connection and switching in the following two switch combination modes:
(2-1) the switching state of phase B is V 1, and the switching state of phase A and phase C is V 2;
(2-2) the switching state of phase B is V 2, and the switching state of phase a and phase C is V 1;
(3) The state 3 realizes connection and switching in the following two switch combination modes:
(3-1) the switching state of the C phase is V 1, and the switching state of the A phase and the B phase is V 2;
(3-2) the switching state of the C phase is V 2, and the switching state of the A phase and the B phase is V 1;
wherein, the switch state V 1 indicates that the internal switch S 1x,S2x,S'3x of the phase corresponding to the three-phase HCC is turned on, the other internal switches are turned off, x is a/B/C, and the three-phase hybrid multi-level converter A/B/C phases respectively correspond to the three-phase hybrid multi-level converter; switch state V 2 indicates that internal switch S 3x,S'2x,S'4x of the phase corresponding to the three-phase HCC is on, and the remaining internal switches are off.
6. The soft start control method based on a three-phase hybrid multilevel converter according to claim 1, wherein one period in the step 2 is 0.1 ms-1 s, and the charging circuit 2 is switched in three circuit states or the like in one period.
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