CN117294153A - Variable frequency control method for realizing low input current total harmonic content of SWISS rectifier - Google Patents

Variable frequency control method for realizing low input current total harmonic content of SWISS rectifier Download PDF

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Publication number
CN117294153A
CN117294153A CN202311220926.7A CN202311220926A CN117294153A CN 117294153 A CN117294153 A CN 117294153A CN 202311220926 A CN202311220926 A CN 202311220926A CN 117294153 A CN117294153 A CN 117294153A
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current
frequency
voltage
rectifier
modulation
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杨子文
曾博
谢少军
陈文明
许津铭
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Nanjing University of Aeronautics and Astronautics
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Nanjing University of Aeronautics and Astronautics
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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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
    • 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
    • H02M1/12—Arrangements for reducing harmonics from ac 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
    • 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
    • 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
    • H02M3/33573—Full-bridge at primary 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
    • H02M7/02—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
    • 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)
  • Ac-Ac Conversion (AREA)

Abstract

The invention discloses a variable frequency control method for realizing low input current total harmonic content of a SWISS rectifier, which comprises the following steps: step 1, at a high frequency switching cycle time T s In the SWISS rectifier, the first high-frequency bridge outputs the voltage u H Transferring energy, and outputting voltage u by second high-frequency bridge L Transferring energy and then entering into a follow current stage; step 2, when the leakage inductance current is reduced to 0, namely the follow current phase is ended, the positive magnetization of the transformer is ended, and the SWISS rectifier immediately enters the negative magnetization phase; step 3, in the negative magnetization stage, from the firstA high-frequency bridge output voltage u H Transferring energy, and outputting voltage u by second high-frequency bridge L Energy is transferred and then the follow current phase is entered, and when the leakage inductance current is reduced to 0, the rectifier starts to enter the next switching cycle to work. The invention can effectively reduce the THD of the input current, reduce the volume of magnetic components and improve the power density.

Description

Variable frequency control method for realizing low input current total harmonic content of SWISS rectifier
Technical Field
The invention relates to the technical field of three-phase alternating current/direct current converters, in particular to a variable frequency control method for realizing low input current total harmonic content of a SWISS rectifier.
Background
The three-phase Pulse Width Modulation (PWM) rectifier adopts a full-control power device, can well control the waveform and the phase of input current, can realize high power factor, and is widely studied and applied nowadays. The SWISS rectifier is a novel step-down three-phase PWM rectifier, has the characteristics of high efficiency, high power factor, no input current impact, single-stage isolation step-down conversion, wide output voltage range and the like, and has good application prospects in the wide fields of uninterruptible power supplies, variable-frequency speed regulation, electric automobile charging, high-power lighting lamps, aviation power supplies and the like.
In order to solve the problems of duty cycle loss, high input current THD, low power density and the like caused by the output dc filter inductance of the SWISS rectifier, there is proposed a dc filter inductance-free SWISS rectifier which operates in a leakage current discontinuous mode (DCM) in which the high frequency switching period needs to be longer than the modulation period of the high frequency switching tube of the rectifier in full load operation. Because the rectifier works at a constant switching frequency, the proportion of the modulation time length to the switching period is smaller when the rectifier operates at a medium power level and a low power level than when the rectifier operates at a full load, and particularly under the lower power level operation condition, the leakage inductance current of the transformer is narrow and sharp, the waveform quality of the input current is influenced, and the reduction of the THD of the input current of the rectifier is not facilitated.
Disclosure of Invention
The invention aims to solve the technical problem of providing a frequency conversion control method for realizing low input current total harmonic content of a SWISS rectifier, which can effectively reduce the THD of the input current, reduce the volume of magnetic components and improve the power density.
In order to solve the technical problems, the invention provides a variable frequency control method for realizing low input current total harmonic content of a SWISS rectifier, which comprises the following steps:
step 1, at a high frequency switching cycle time T s In the SWISS rectifier, the first high-frequency bridge outputs the voltage u H Transferring energy, and outputting voltage u by second high-frequency bridge L Transferring energy and then entering into a follow current stage;
step 2, when the leakage inductance current is reduced to 0, namely the follow current phase is ended, the positive magnetization of the transformer is ended, and the SWISS rectifier immediately enters the negative magnetization phase;
step 3, in the negative magnetization stage, the voltage u is outputted by the first high-frequency bridge H Transferring energy, and outputting voltage u by second high-frequency bridge L Energy is transferred and then the follow current phase is entered, and when the leakage inductance current is reduced to 0, the rectifier starts to enter the next switching cycle to work.
Preferably, in step 2, the SWISS rectifier operates in a critical intermittent state of leakage current, i.e. immediately starts the next magnetization phase when the leakage current drops to 0, and operates in a variable frequency control mode, with an ideal switching frequency f per switching cycle s_cal From the calculation, u is calculated in half a switching period H The time of energy transfer is t H ，u L The time of energy transfer is t L The time of the follow current phase is t D And satisfies: t is t H +t L +t D ＝T s_cal /2。
Preferably, in step 3, in order to implement frequency conversion control of the rectifier, the zero crossing state of the leakage inductance current is detected to assist in indicating the start of the high-frequency switching period, and specifically includes the following steps:
step 31, the control unit comprises a threshold comparator hardware circuit, an FPGA and an MCU, the leakage inductance current obtained by sampling passes through the threshold comparator to obtain a leakage inductance current zero crossing mark Zrieoc, and the zero crossing mark is connected into the FPGA; an up counter is arranged in the FPGA every 10ns, the output value of the counter is Cnt, and when a zero crossing mark Zreeoc is set high, the output value Cnt of the counter is set to be zero;
step 32, when the counter output value Cnt is 0, the MCU is enabled to perform sampling and countingCalculating, for the three-phase input voltages u of SWISS rectifier a 、u b 、u c Dc output voltage u o Sampling, and sampling the obtained voltage u a 、u b 、u c The phase-locked loop calculates to obtain the peak value U of the input voltage m And phase θ; according to the sampled DC output voltage u o With the transformation ratio N of the transformer, the voltage u of the direct current output voltage folded to the primary side of the transformer is calculated s ＝Nu o ；
Step 33, according to the input voltage peak value U m And phase theta, calculating to obtain the output voltage u of the first high-frequency bridge in the control period H With a second high-frequency bridge output voltage u L According to the peak value reference value I of the three-phase input current m * And the phase theta, calculating to obtain a first current modulation target i of the bus in the control period H With a second current modulation target i L ；
Step 34, according to the leakage inductance value L of the transformer r Switching period T s Output voltage u of the first high-frequency bridge H With a second high-frequency bridge output voltage u L A first current modulation target i H With a second current modulation target i L Calculating to obtain auxiliary variable temp H And temp L Further calculate the ideal switching frequency f of the period s_cal ；
Step 35, according to the auxiliary variable temp H 、temp L With the ideal switching frequency f s_cal The first modulation time t of the high-frequency power tube can be calculated H And a second modulation time t L ；
Step 36, the first modulation time t of the high-frequency power tube H And a second modulation time t L To respectively with 10 8 Multiplying to obtain a first modulation comparison value Cnt H Comparing with the second modulation comparison value Cnt L First modulation comparison value Cnt H Comparing with the second modulation comparison value Cnt L And the control signals are transmitted to the FPGA and compared with the counter output value Cnt to generate high-frequency power tube control signals, so as to control the work of the SWISS rectifier high-frequency power tube.
Preferably, in step 33, the control is calculatedFirst current modulation target i of bus in system period H With a second current modulation target i L The method comprises the following steps:
preferably, in step 34, an auxiliary variable temp is calculated H And temp L Further calculate the ideal switching frequency f of the period s_cal The method comprises the following steps:
preferably, in step 35, a first modulation time t of the high-frequency power tube is calculated H And a second modulation time t L The method comprises the following steps:
the beneficial effects of the invention are as follows: in the invention, the rectifier works in a leakage inductance current critical intermittent mode, the total modulation time length of the high-frequency switching tube accounts for 100% of the switching period, and the THD of the input current can be effectively reduced; compared with the current interruption mode, the leakage inductance current peak value working in the leakage inductance current critical interruption mode is smaller when the current average value is fixed; under variable frequency control, the switching frequency of the high-frequency switching tube is relatively high, the size of magnetic components can be reduced, and the power density is improved.
Drawings
Fig. 1 is a circuit configuration diagram of a SWISS rectifier of the present invention.
FIG. 2 (a) is a waveform diagram of the SWISS rectifier input voltage development circuit of the present invention.
FIG. 2 (b) is a graph of the ideal current waveform of the SWISS rectifier bus of the present invention.
Fig. 3 is a schematic diagram of the modulation method of the present invention.
FIG. 4 (a) shows the forward magnetization u of the transformer according to the present invention H Operation state in power transmission stageA state diagram.
FIG. 4 (b) shows the forward magnetization u of the transformer according to the present invention L Schematic diagram of the operating state of the transfer power stage.
Fig. 4 (c) is a schematic diagram of the working state of the forward magnetization freewheel phase of the transformer according to the present invention.
FIG. 4 (d) shows the negative magnetization u of the transformer according to the invention H Schematic diagram of the operating state of the transfer power stage.
FIG. 4 (e) shows the negative magnetization u of the transformer according to the invention L Schematic diagram of the operating state of the transfer power stage.
Fig. 4 (f) is a schematic diagram of the working state of the negative magnetization flywheel stage of the transformer according to the present invention.
Fig. 5 is a flowchart of the frequency conversion control method of the present invention.
Fig. 6 (a) is a 5kW run-time rectifier input-output simulation waveform diagram of the present invention.
Fig. 6 (b) is a waveform diagram of the voltage and current simulation of the transformer in 5kW operation of the present invention.
Fig. 7 (a) is a waveform diagram of the input/output simulation of the rectifier of the present invention at 2.5kW operation.
Fig. 7 (b) is a voltage-current simulation waveform of the transformer in 2.5kW operation of the present invention.
Detailed Description
A frequency conversion control method for realizing low input current total harmonic content of SWISS rectifier includes the following steps:
step 1, at a high frequency switching cycle time T s In the SWISS rectifier, the first high-frequency bridge outputs the voltage u H Transferring energy, and outputting voltage u by second high-frequency bridge L Transferring energy and then entering into a follow current stage;
step 2, when the leakage inductance current is reduced to 0, namely the follow current phase is ended, the positive magnetization of the transformer is ended, and the SWISS rectifier immediately enters the negative magnetization phase;
step 3, in the negative magnetization stage, the voltage u is outputted by the first high-frequency bridge H Transferring energy, and outputting voltage u by second high-frequency bridge L Transferring energy, then entering into follow current stage, when leakage current is reduced to 0, the rectifier starts to enter into next switching cycleAnd (3) doing so.
Fig. 1 is a topological structure diagram of a SWISS rectifier, which consists of a three-phase input filter, a voltage unfolding circuit and a high-frequency isolation conversion circuit. Corresponding nodes of three buses at the output end of the voltage unfolding circuit are respectively defined as x, y and z, and the current flowing through the corresponding nodes is i x 、i y 、i z . The invention sets proper high-frequency tube switch time sequence and on time to ensure the output voltage u of the high-frequency bridge at the alternating current power supply side of the SWISS rectifier ab The first high-frequency bridge output voltage u appears in sequence H Output voltage u of second high-frequency bridge L Three levels of 0 and alternating square waves with the secondary side amplitude of the high-frequency isolation transformer being a direct-current output voltage value are adopted to realize leakage inductance L of the transformer r The left end is high-low-zero three-level voltage, and the right end is transformer secondary side voltage u cd Converted to the primary voltage u s The pressure difference at two ends of the leakage inductance enables the leakage inductance current to rise or fall, thereby achieving the purpose of controlling the energy transmission.
As shown in fig. 2 (a), the bidirectional switching tube of the voltage spreading circuit is switched on according to the three-phase voltage phase θ, one power grid period can be divided into 12 sectors, and the voltage u xy And u is equal to yz Is a triangular wave-like structure. Three-phase input current flows into three buses of the unfolding circuit respectively through alternate conduction of the bidirectional switch tube, and the bus current i is taken as sector 1 as an example x 、i y 、i z Respectively corresponding to three-phase current i a 、i b 、i c Therefore, the bus current can be controlled by taking the three-phase input current as a modulation target, and the ideal current waveform diagram of the SWISS rectifier bus is shown in fig. 2 (b).
According to different conduction combinations of the power tube of the high-frequency isolation conversion circuit, the output voltage u of the high-frequency bridge ab There may be three sets of voltage combinations, respectively: (1) a and b are respectively connected with x and z, the transformer is magnetized positively, a and b are respectively connected with z and x, the transformer is magnetized negatively, and the voltages at the two ends of a and b under the combination are defined as a first high-frequency bridge output voltage u H The method comprises the steps of carrying out a first treatment on the surface of the (2) a and b are respectively connected with x and y, the transformer is magnetized positively, a and b are respectively connected with y and x, and the transformer is magnetized negatively; or a and b are respectively connected with y and z, the transformer is magnetized in the forward direction,a. b are respectively connected with z and y, the transformer is magnetized negatively, and the voltages at the two ends of a and b under the combination are defined as the output voltage u of the second high-frequency bridge L The method comprises the steps of carrying out a first treatment on the surface of the (3) a and b are connected, the leakage inductance current of the transformer is freewheeling, and the voltage at the two ends of a and b is 0. The secondary side voltage u of the transformer cd The voltage converted to the primary side is defined as u s ，u s Is of amplitude Nu o Is a square wave of (c).
FIG. 3 is a schematic diagram of the modulation method, at a high frequency switching cycle time T s In the SWISS rectifier, the first high-frequency bridge outputs the voltage u H Transferring energy, and outputting voltage u by second high-frequency bridge L Transferring energy, then entering into a follow current stage, and immediately entering into a negative magnetization stage by the SWISS rectifier when the leakage inductance current is reduced to 0, namely the follow current stage is finished, and the positive magnetization of the transformer is finished; in the negative magnetization phase, the first high-frequency bridge outputs a voltage u H Transferring energy, and outputting voltage u by second high-frequency bridge L Energy is transferred and then the follow current phase is entered, and when the leakage inductance current is reduced to 0, the rectifier starts to enter the next switching cycle to work. The first high-frequency bridge output voltage u H The average current flowing into the bus from the leakage inductance of the transformer during the energy transfer is the first modulation current i H The method comprises the steps of carrying out a first treatment on the surface of the Output voltage u of second high-frequency bridge L The average current flowing into the bus from the leakage inductance of the transformer during the energy transfer is the second modulation current i L 。
The SWISS rectifier operates in a critical intermittent state of the high frequency AC tank (primary side of the transformer) current (also the transformer leakage inductance current), i.e. immediately starts the next magnetization phase when the leakage inductance current drops to 0, and operates in a variable frequency control mode, with an ideal switching frequency f per switching cycle s_cal From the calculation, u is calculated in half a switching period H The time of energy transfer is t H ，u L The time of energy transfer is t L The time of the follow current phase is t D And satisfies: t is t H +t L +t D ＝T s_cal /2。
It is noted that due to the y bus current i y The direction is determined each time energy is transferred, so that u in a complete power transfer cycle L Energy transferVoltage during measuring u ab Only by the x and y bus or the y and z bus. The detailed operation of the SWISS rectifier with y bus current positive under the modulation method of the present invention is shown in fig. 4 (a) -4 (f).
The following takes three-phase voltage phase θ∈ [ pi/6, pi/3 ] and forward magnetization of the transformer (as shown in fig. 4 (a) - (c)) as an example, and analyzes the working process of the SWISS rectifier under the modulation method of the present invention:
(c1)u H energy transfer: as shown in fig. 4 (a), the power transfer time of this mode is the first modulation time t H The average current i flowing into the bus bar in this mode can be obtained H The method comprises the following steps:
(c2)u L energy transfer: as shown in fig. 4 (b), the power transfer time of this mode is the second modulation time t L The average current i flowing into the bus bar in this mode can be obtained L The method comprises the following steps:
(c3) And (3) a follow current stage: as shown in FIG. 4 (c), the power transfer time in this mode is t D The average current i of the leakage inductance of the transformer in the mode can be obtained D The method comprises the following steps:
for example, negative magnetization of the transformer (see fig. 4 (d) - (f)), the SWISS rectifier operation process under the modulation method of the present invention was analyzed:
(c4)u H energy transfer: as shown in fig. 4 (d), the power transfer time of this mode is the first modulation time t H The average current i flowing into the bus bar in this mode can be obtained H The method comprises the following steps:
(c5)u L energy transfer: as shown in fig. 4 (e), the power transfer time of this mode is the second modulation time t L The average current i flowing into the bus bar in this mode can be obtained L The method comprises the following steps:
(c6) And (3) a follow current stage: as shown in FIG. 4 (f), the power transfer time in this mode is t D The average current i of the leakage inductance of the transformer in the mode can be obtained D The method comprises the following steps:
the modulation method of the invention takes three-phase input current as a modulation target to control bus current, and theta is [ pi/6, pi/3 ]]At the time, current i L Flow into phase b, i through the y bus H Flowing into phase a through the x bus, i.e. modulating current i with reference to the ideal current of phase b L Modulating current i with reference to a-phase ideal current H . The ideal modulation target can be expressed as:
in the switching period T s Leakage inductance value L of transformer r Under certain conditions, the formulas (4) - (6) are combined, so that u in one control period can be obtained through calculation H And u is equal to L The modulation time of (2) is:
and the same applies to other intervals. Therefore, the modulation method only needs to obtain the three-phase input voltage peak value U m And phase theta, therebyBy calculation to obtain u in one control period H 、u L 、i H * And i L * Then combine with the known switching period T s With the leakage inductance value L of the transformer r The modulation time t in the control period can be obtained H And t L 。
Fig. 5 is a flowchart of the modulation method according to the present invention, which is described in detail below:
1) The control unit consists of a threshold comparator hardware circuit, an FPGA and an MCU, the leakage inductance current obtained by sampling passes through the threshold comparator to obtain a leakage inductance current zero crossing mark Zrieoc, and the zero crossing mark is connected into the FPGA; an up counter per 10ns is arranged in the FPGA and used for controlling a high-frequency switching period, the output value of the counter is Cnt, and when the zero crossing mark Zreeoc is set high, the output value Cnt of the counter can be set to be zero.
2) When the output value Cnt of the counter is 0, the MCU is enabled to sample and calculate the three-phase input voltage u of the SWISS rectifier a 、u b 、u c Dc output voltage u o Sampling, and sampling the obtained voltage u a 、u b 、u c The phase-locked loop calculates to obtain the peak value U of the input voltage m And phase θ; according to the sampled DC output voltage u o With the transformation ratio N of the transformer, the voltage u of the direct current output voltage folded to the primary side of the transformer is calculated s ＝Nu o ；
3) According to the peak value U of the input voltage m And phase theta, calculating to obtain the output voltage u of the first high-frequency bridge in the control period H With a second high-frequency bridge output voltage u L According to the peak value reference value I of the three-phase input current m * And the phase theta, calculating to obtain a first current modulation target i of the bus in the control period H With a second current modulation target i L ：
4) According to the leakage inductance value L of the transformer r Switching period T s First high-frequency bridge transmissionOutput voltage u H With a second high-frequency bridge output voltage u L A first current modulation target i H With a second current modulation target i L Calculating to obtain auxiliary variable temp H And temp L Further calculate the ideal switching frequency f of the period s_cal The method comprises the following steps:
5) According to the auxiliary variable temp H 、temp L With the ideal switching frequency f s_cal The first modulation time t of the high-frequency power tube can be calculated H And a second modulation time t L The method comprises the following steps:
6) The first modulation time t of the high-frequency power tube H And a second modulation time t L To respectively with 10 8 Multiplying to obtain a first modulation comparison value Cnt H Comparing with the second modulation comparison value Cnt L First modulation comparison value Cnt H Comparing with the second modulation comparison value Cnt L And the eight high-frequency power tube control signals are transmitted to the FPGA and compared with the counter output value Cnt to control the SWISS rectifier high-frequency power tube to work.
Switching period T required for calculating modulation duration of high-frequency switching tube s And T in the variable frequency control process s For the variation, the switching period length is obtained before the modulation time length is calculated, and the sum t of the working total time lengths in half switching periods of the SWISS rectifier without the direct current filter inductor is known in the formula (8) s Can be expressed as:
d in y Is the ratio of the operating time to the switching period. At the same time, by the modulation time t H And t L Calculation type canTo obtain:
in the formula, temp H And temp L Are all independent of the switching period and can be expressed as:
the combination of formulas (12) and (13) can be obtained:
will D y Substitution equal to 0.5 into the above formula to obtain the ideal switching frequency f when the rectifier is operated in the leakage inductance current critical intermittent mode s_cal Expressed as:
and then combining (13), the modulation duration of the high-frequency switching tube under the ideal switching period can be obtained:
under the condition that three-phase input voltage, three-phase input current reference and leakage inductance value are known through formulas (14) - (17), temp is obtained through calculation H And temp L Further calculating an ideal switching frequency f for operating the rectifier in the leakage inductance current critical intermittent mode s_cal Finally according to temp H 、temp L And f s_cal And calculating to obtain the modulation time length of the high-frequency switching tube.
As can be seen from FIG. 6 (a), the switching frequency varies between 43k and 60kHz during full load (5 kW) operationThe input current THD is 2.19%; as can be seen from fig. 7 (a), the switching frequency varies between 90k and 120kHz during half-load (2.5 kW) operation, with an input current THD of 0.80% during half-load operation. As can be seen from fig. 6 (b) and fig. 7 (b), the leakage inductance current is increased or decreased by the voltage difference across the leakage inductance, the voltage u ab And u is equal to s The rising edges are coincident, and the leakage inductance current works in a critical intermittent mode, so that the design requirement of a variable frequency control method is met.

Claims (6)

1. A frequency conversion control method for realizing low input current total harmonic content of SWISS rectifier is characterized by comprising the following steps:
step 1, at a high frequency switching cycle time T s In the SWISS rectifier, the first high-frequency bridge outputs the voltage u H Transferring energy, and outputting voltage u by second high-frequency bridge L Transferring energy and then entering into a follow current stage;
step 2, when the leakage inductance current is reduced to 0, namely the follow current phase is ended, the positive magnetization of the transformer is ended, and the SWISS rectifier immediately enters the negative magnetization phase;
step 3, in the negative magnetization stage, the voltage u is outputted by the first high-frequency bridge H Transferring energy, and outputting voltage u by second high-frequency bridge L Energy is transferred and then the follow current phase is entered, and when the leakage inductance current is reduced to 0, the rectifier starts to enter the next switching cycle to work.
2. The variable frequency control method for realizing low input current total harmonic content of SWISS rectifier as claimed in claim 1, wherein in step 2, SWISS rectifier is operated in a leakage current critical intermittent state, i.e. when leakage current drops to 0, immediately starting the next magnetization phase, and in variable frequency control mode, ideal switching frequency f is set for each switching cycle s_cal From the calculation, u is calculated in half a switching period H The time of energy transfer is t H ，u L The time of energy transfer is t L The time of the follow current phase is t D And satisfies: t is t H +t L +t D ＝T s_cal /2。
3. The method for controlling frequency conversion of low input current total harmonic content of SWISS rectifier according to claim 1, wherein in step 2 and step 3, to control frequency conversion of the rectifier, the method comprises the following steps:
step 31, the control unit comprises a threshold comparator hardware circuit, an FPGA and an MCU, the leakage inductance current obtained by sampling passes through the threshold comparator to obtain a leakage inductance current zero crossing mark Zrieoc, and the zero crossing mark is connected into the FPGA; an up counter is arranged in the FPGA every 10ns, the output value of the counter is Cnt, and when a zero crossing mark Zreeoc is set high, the output value Cnt of the counter is set to be zero;
step 32, when the counter output value Cnt is 0, the MCU is enabled to sample and calculate the three-phase input voltage u of the SWISS rectifier a 、u b 、u c Dc output voltage u o Sampling, and sampling the obtained voltage u a 、u b 、u c The phase-locked loop calculates to obtain the peak value U of the input voltage m And phase θ; according to the sampled DC output voltage u o With the transformation ratio N of the transformer, the voltage u of the direct current output voltage folded to the primary side of the transformer is calculated s ＝Nu o ；
Step 33, according to the input voltage peak value U m And phase theta, calculating to obtain the output voltage u of the first high-frequency bridge in the control period H With a second high-frequency bridge output voltage u L According to the peak value reference value I of the three-phase input current m * And the phase theta, calculating to obtain a first current modulation target i of the bus in the control period H With a second current modulation target i L ；
Step 34, according to the leakage inductance value L of the transformer r Switching period T s Output voltage u of the first high-frequency bridge H With a second high-frequency bridge output voltage u L A first current modulation target i H With a second current modulation target i L Calculating to obtain auxiliary variable temp H And temp L Further calculate the ideal switching frequency of the periodRate f s_cal ；
Step 35, according to the auxiliary variable temp H 、temp L With the ideal switching frequency f s_cal The first modulation time t of the high-frequency power tube can be calculated H And a second modulation time t L ；
Step 36, the first modulation time t of the high-frequency power tube H And a second modulation time t L To respectively with 10 8 Multiplying to obtain a first modulation comparison value Cnt H Comparing with the second modulation comparison value Cnt L First modulation comparison value Cnt H Comparing with the second modulation comparison value Cnt L And the control signals are transmitted to the FPGA and compared with the counter output value Cnt to generate high-frequency power tube control signals, so as to control the work of the SWISS rectifier high-frequency power tube.
4. The variable frequency control method for achieving low total harmonic content of input current of SWISS rectifier as claimed in claim 3, characterized in that in step 33, a first current modulation target i of the bus in the control period is calculated H With a second current modulation target i L The method comprises the following steps:
5. the variable frequency control method for realizing low input current total harmonic content of SWISS rectifier as claimed in claim 3, wherein in step 34, an auxiliary variable temp is calculated H And temp L Further calculate the ideal switching frequency f of the period s_cal The method comprises the following steps:
6. the variable frequency control method for achieving low input current total harmonic content of SWISS rectifier as claimed in claim 3, characterized in that in step 35, high input current total harmonic content is calculatedFirst modulation time t of frequency power tube H And a second modulation time t L The method comprises the following steps:
CN202311220926.7A 2023-09-20 2023-09-20 Variable frequency control method for realizing low input current total harmonic content of SWISS rectifier Pending CN117294153A (en)

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