CN109149939B - Lightweight design method for auxiliary converter of low-floor tramcar - Google Patents

Lightweight design method for auxiliary converter of low-floor tramcar Download PDF

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CN109149939B
CN109149939B CN201811108360.8A CN201811108360A CN109149939B CN 109149939 B CN109149939 B CN 109149939B CN 201811108360 A CN201811108360 A CN 201811108360A CN 109149939 B CN109149939 B CN 109149939B
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capacitor
resonant
converter
inductance
current
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CN109149939A (en
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李骄松
夏猛
马法运
毕京斌
田以涛
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CRRC Qingdao Sifang Rolling Stock Research Institute Co Ltd
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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
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac 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
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac 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
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac 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 with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac 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 with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H02M3/1584—Conversion of dc power input into dc power output without intermediate conversion into ac 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 with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load with a plurality of power processing stages connected in parallel
    • 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
    • H02M3/33507—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 with automatic control of the output voltage or current, e.g. flyback converters
    • H02M3/33523—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 with automatic control of the output voltage or current, e.g. flyback converters with galvanic isolation between input and output of both the power stage and the feedback loop
    • 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
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M7/23—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only arranged for operation in parallel
    • 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
    • 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
    • H02M1/0048—Circuits or arrangements for reducing losses
    • H02M1/0054—Transistor switching losses
    • H02M1/0058—Transistor switching losses by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero
    • 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)
  • Dc-Dc Converters (AREA)

Abstract

The invention relates to a lightweight design method for an auxiliary converter of a low-floor tramcar, which comprises the following steps: the method comprises the following steps that a minimum voltage stress Buck converter provided with a minimum voltage stress resonance unit, an LLC fixed frequency resonance converter and a split capacitor three-phase inverter are sequentially connected in series to serve as an auxiliary inverter, and a charger is provided with a DC/DC current-multiplying rectification converter connected with the output end of the minimum voltage stress Buck converter; resonant inductance L for determining minimum voltage stress Buck converter2Resonant capacitor CrResonant capacitor CsAnd a minimum output current Io,min(ii) a Defining the limit condition of LLC fixed frequency resonant converter design, selecting excitation inductance LmCalculating the blocking capacitance CbPrimary side leakage inductance L of transformerkResonant frequency f of resonant cavityrVerifying whether the LLC fixed-frequency resonant converter meets a verification condition; neutral line inductor L is introduced into split capacitor three-phase inverternWhen three-phase load is unbalanced, by introducing central inductance LnEliminating neutral point potential uNIs applied to the surface of the material. The auxiliary converter designed by the invention has high power density and small volume and weight.

Description

Lightweight design method for auxiliary converter of low-floor tramcar
Technical Field
The invention belongs to the technical field of railway vehicle converters, relates to a tramcar converter, and particularly relates to a lightweight design method for an auxiliary converter of a low-floor tramcar and the auxiliary converter based on the lightweight design method.
Background
With the continuous development of urban rail transit, the low-floor tramcars have the advantages of low operation cost, energy conservation, environmental protection, simple line laying and the like, and are greatly popularized and developed in recent years. The auxiliary converter is used as an important component of the low-floor tramcar, and can convert high-voltage power supply on a direct current side into AC output and DC output which are respectively supplied to alternating current and direct current loads for a car so as to ensure safe and stable operation of the tramcar.
The low-floor tramcar auxiliary converter is generally arranged on the roof of a car, and compared with the subway car auxiliary converter, the low-floor tramcar auxiliary converter is more compact in internal component equipment and higher in required power density; meanwhile, the auxiliary converter of the low-floor tramcar has complex load, and the output voltage is distorted due to the responsiveness output voltage quality of the passenger room heat tracing load and the cab single-phase load.
Referring to fig. 1, a conventional auxiliary inverter is isolated by using a power frequency transformer (power: 50Hz), which has the advantage of stable operation, and provides a loop for zero-sequence current under unbalanced load, thereby having an effect of suppressing unbalanced voltage. However, the power frequency transformer has the disadvantages of large volume, heavy weight, high cost, low efficiency and the like, and is contrary to the concept of 'green trip' advocated by tramcars.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a lightweight design method for an auxiliary converter of a low-floor tramcar and the auxiliary converter based on the method, which can reduce the volume and weight of the auxiliary converter and reduce the unbalance degree of output voltage.
In order to achieve the aim, the invention provides a lightweight design method for an auxiliary converter of a low-floor tramcar, which comprises the following steps:
sequentially connecting a minimum voltage stress Buck converter provided with a minimum voltage stress resonance unit, an LLC fixed frequency resonance converter and a split capacitor three-phase inverter in series to serve as an auxiliary inverter, wherein a charger is provided with a DC/DC current-doubling rectifying converter which is connected with the output end of the minimum voltage stress Buck converter;
resonant inductance L for determining minimum voltage stress Buck converter2Resonant capacitor CrResonant capacitor CsAnd a minimum output current Io,min；
Defining the limit condition of LLC fixed frequency resonant converter design, selecting excitation inductance LmCalculating the DC blocking capacitor C in the LLC constant frequency resonant converterbPrimary side leakage inductance L of transformerkAnd resonant cavity resonant frequency frAnd verifying whether the LLC fixed-frequency resonant converter meets the following verification conditions: (1) whether zero voltage conduction realization condition of transformer primary side switch tube is met
Figure GDA0002338986580000021
In the formula, ZinIs an input impedance, CresIs IGBT parallel parasitic capacitance, TrIs the resonant period of the resonant cavity, i.e.
Figure GDA0002338986580000022
Uin_minIs the minimum value of the input voltage, Pin_maxIs the maximum input power; (2) whether quality factor Q of LLC fixed frequency resonance converter satisfies condition
Figure GDA0002338986580000023
In the formula, LrsFor exciting inductance LmAnd primary side leakage inductance LkRatio of (i) to (ii)
Figure GDA0002338986580000024
frsIs resonant frequency f of resonant cavityrAnd the switching frequency fsA ratio; (3) whether the primary side current of the transformer is reverse in the dead time or not; (4) whether the input impedance is inductive or not and an angle allowance is reserved; if the above four verification conditions cannot be satisfied simultaneously, the excitation inductance value L needs to be reselectedmPerforming accounting until the four verification conditions are met simultaneously;
neutral line inductor L is introduced into split capacitor three-phase inverternNeutral line inductance LnNegative pole and three-phase output filter capacitorAre connected to a common terminal of a neutral line inductor LnIs connected with the middle point between the two input split capacitors, and when the three-phase load is unbalanced, the central inductor L is introducednEliminating neutral point potential uNIs applied to the surface of the material.
Preferably, the resonant inductance L of the Buck converter with the minimum voltage stress is determined2Resonant capacitor CrResonant capacitor CsAnd a minimum output current Io,minThe method comprises the following specific steps:
resonant inductor L2The inductance value of (a) is selected to satisfy the following conditions:
Figure GDA0002338986580000031
in the formula, trIs a switch tube S1Current rise time of trrIs a freewheeling diode D4Reverse recovery time of io,peakFor output current peak, UiIs the input voltage;
resonant capacitor CrAnd a resonance capacitor CsThe selection comprises the following steps:
(a) arbitrarily fetch
Figure GDA0002338986580000032
Substituting into formula (2), obtaining the minimum output current I under the conditiono,minEquation (2) is expressed as:
Figure GDA0002338986580000033
in the formula, tr-off,maxThe maximum resonance turn-off time under the condition of meeting the soft chopping operation is given by a designer;
(b) comparing the value of step (a) with the minimum output current Io,minSubstituting formula (3) to obtain resonant capacitance CrEquation (3) is expressed as:
Figure GDA0002338986580000034
in the formula, omega is
Figure GDA0002338986580000035
(c) Verifying the resonance capacitance C obtained in step (b) by equation (4)rEquation (4) is expressed as:
Figure GDA0002338986580000036
in the formula, tfIs a switch tube S1Current fall time of (d);
(d) if the condition in step (C) is not satisfied, repeating steps (a) - (C) until the condition in step (C) is satisfied, and if the condition in step (C) is satisfied, selecting a resonant capacitor CrShould be greater than the theoretical value when selected, resonant capacitor CsThe capacitance value of (2) is obtained by equation (5), where equation (5) is expressed as:
Figure GDA0002338986580000041
Figure GDA0002338986580000046
preferably, the design constraints of the LLC fixed-frequency resonant converter are:
the LLC resonant cavity input impedance must exhibit an inductance, Angle (Z)in)>0；
The quality factor Q of the LLC fixed-frequency resonant converter is smaller than 0.005 so as to ensure that the LLC fixed-frequency resonant converter works in an inductive II area;
the dead time of the LLC fixed-frequency resonant converter is greater than the junction capacitor discharge time and is smaller than the sum of the junction capacitor discharge time and the time of the excitation current resonant to zero.
Preferably, the excitation inductance L is selectedmCalculating the DC blocking capacitor C in the LLC constant frequency resonant converterbPrimary side leakage inductance L of transformerkAnd resonant cavity resonant frequency frThe method comprises the following specific steps:
defining the excitation inductance LmHas a value range of not more than 0.7mH and not more than LmLess than or equal to 2mH, initially selecting excitation inductance LmTaking the value of (A);
the junction capacitance discharge time T is calculated by the following equations (6) and (7) respectively1And exciting current resonance to zero time Tm：
Figure GDA0002338986580000042
Figure GDA0002338986580000043
In the formula, n is the turn ratio of the transformer, and R is the equivalent impedance of the primary side of the transformer;
dead time tdead≥T1The current angle is calculated according to the following formula (8)
Figure GDA0002338986580000045
Figure GDA0002338986580000044
In the formula of UoFor LLC fixed-frequency resonant converter output voltage, IoOutputting current for the LLC fixed-frequency resonant converter;
ensuring that the LLC fixed-frequency resonant converter works in an inductive II area, the following limitations should be met:
Figure GDA0002338986580000051
calculating a blocking capacitor C in the LLC constant frequency resonant converterbPrimary side leakage inductance L of transformerkAnd resonant cavity resonant frequency fr。
Preferably, the neutral point potential u is balanced when the three phases are loadedNComprises the following steps:
Figure GDA0002338986580000052
in the formula udcThe output voltage of the LLC fixed-frequency resonant converter;
neutral point potential u when unbalanced load is connectedNIs offset, i.e.
Figure GDA0002338986580000053
Lead-in neutral inductance LnThe neutral point potential expression is as follows:
Figure GDA0002338986580000054
in the formula umIs the maximum value of the three-phase output voltage, Z is the load impedance, CinThe three-phase output filter capacitor is provided, and theta is an offset angle;
when three-phase load is unbalanced, the neutral point potential has sinusoidal disturbance by introducing central inductance
Figure GDA0002338986580000055
The disturbance is eliminated to restore the neutral point potential to
Figure GDA0002338986580000056
In order to achieve the aim, the invention also provides a low-floor tramcar auxiliary inverter, which comprises an auxiliary inverter and a charger based on the design method, wherein the auxiliary inverter comprises a minimum voltage stress Buck converter, an LLC fixed-frequency resonant converter and a split capacitor three-phase inverter, the minimum voltage stress Buck converter, the LLC fixed-frequency resonant converter and the split capacitor three-phase inverter are sequentially connected in series, the minimum voltage stress Buck converter is provided with a minimum voltage stress resonance unit, and the minimum voltage stress resonance unit is formed by a resonance inductor L2Resonant capacitor CrAnd a resonance capacitor CsAnd four freewheeling diodes, freewheeling diode D1Respectively with a freewheeling diode D3Anode and resonant capacitor CrIs connected to the negative electrode of a freewheeling diode D1Respectively with a freewheeling diode D2Cathode and resonant capacitor CsThe positive electrodes of the two electrodes are connected; freewheeling diode D2Anode and follow current twoPolar tube D4Is connected to the anode of a freewheeling diode D3Respectively with a resonant capacitor CsNegative electrode of (1), resonance inductor L2Negative electrode of (D), freewheel diode (D)4The cathodes of the two electrodes are connected; the charger is provided with a DC/DC current-multiplying rectifying converter, and the DC/DC current-multiplying rectifying converter is connected with the output end of the minimum voltage stress Buck converter.
Preferably, the minimum voltage stress Buck converter further comprises an input filter inductor L1Switch tube S1An input filter capacitor C1Follow current inductor L3The two output filter capacitors are connected in series, and the two voltage-sharing resistors are connected in series; input filter capacitor C1Respectively with the input filter inductance L1Negative electrode of (2), switching tube S1C pole and resonant capacitor CrIs connected with the anode of the input filter capacitor C1, and the cathode of the input filter capacitor C1 is respectively connected with the freewheel diode D2Anode of (2), freewheel diode D4The anode of the output filter capacitor C3 is connected with the cathode of the output filter capacitor C3, and the switching tube S1M pole and resonant inductor L2Is connected with the positive pole of the switching tube S1Respectively with a resonant capacitor CrNegative electrode of (D), freewheel diode (D)1Cathode of (D), freewheel diode (D)3The anodes of the anode groups are connected; the positive electrodes of the freewheeling inductors L3 and the resonant inductors L2Negative electrode of (D), freewheel diode (D)3Cathode and resonant capacitor CsNegative electrode of (D), freewheel diode (D)4Is connected with the cathode of the secondary current inductor L3Negative pole and output filter capacitor C2Is connected with the anode of the voltage-sharing resistor RC1Connected in parallel to an output filter capacitor C2At both ends of (2), a voltage-sharing resistor RC2Connected in parallel to an output filter capacitor C3At both ends of the same.
Preferably, the DC/DC current-doubling rectifying converter comprises a switching tube S2DC blocking capacitor CcTransformer T2Follow current inductor LaFollow current inductor LbAn output filter capacitor C6Anti-reflection diode D9And two diodes; switch tube S2M pole and DC blocking capacitor CcIs connected with the positive electrode of the capacitor CcAnd a negative electrode ofPressure device T2V of the primary sideaEnd connection; transformer T2V of the primary sidebTerminal and output filter capacitor C2And an output filter capacitor C3Are connected with each other; transformer T2V of minor edgecTerminals of which are respectively connected with follow current inductors LaCathode of (2), diode D8The anodes of the anode groups are connected; transformer T2V of minor edgedTerminals of which are respectively connected with follow current inductors LbCathode of (2), diode D7Is connected to the anode of a diode D7And a diode D8The cathode of the capacitor is connected with an output filter capacitor C6The negative electrodes are connected; follow current inductance LaAnd a follow current inductor LbRespectively with the output filter capacitor C6Positive and anti-reverse diode D9Are connected with each other.
Preferably, the LLC constant-frequency resonant converter includes two parallel-connected switching tubes and a dc blocking capacitor CbTransformer T1And two secondary rectifier diodes, transformer T1And a DC blocking capacitor CbForming an LLC resonant cavity; switch tube S3And a switching tube S4The bus is bridged between the positive output bus and the negative output bus of the minimum voltage stress Buck converter; switch tube S3M pole and DC blocking capacitor CbIs connected with the positive pole of the switching tube S4M pole and transformer T1V of the primary sidebEnd-connected, DC blocking capacitor CbAnd the transformer T1V of the primary sideaEnd connection; transformer T1V of minor edgecEnd and secondary side rectifier diode D5Is connected to the intermediate point of the transformer T1V of minor edgedEnd and secondary side rectifier diode D6Are connected.
Preferably, the split capacitor three-phase inverter comprises two input split capacitors connected in series, three switching tubes connected in parallel, three output filter inductors, three output filter capacitors connected in star, and an intermediate inductor LnAnd neutral capacitance Cn(ii) a Input split capacitor C4Positive and secondary rectifier diode D6Is connected to the anode of the input split capacitor C5Negative and secondary rectifier diode D6Cathode connection of(ii) a Switch tube S5Switch tube S6And a switching tube S7Split capacitors C respectively connected with the input4And an input split capacitor C5The constituent series circuits being connected in parallel, the switching tubes S5M pole and output filter inductance LuIs connected with the positive pole of the switching tube S6M pole and output filter inductance LvIs connected with the positive pole of the switching tube S7M pole and output filter inductance LwIs connected with the positive pole of the output filter capacitor CuAn output filter capacitor CvAnd an output filter capacitor CwCommon terminal and neutral line capacitor CnIs connected with the anode of a neutral line capacitor CnNegative pole and neutral line inductance LnIs connected with the negative pole of the neutral line inductor LnAnode and input split capacitor C4And an input split capacitor C5Connected at an intermediate point therebetween.
Compared with the prior art, the invention has the advantages and positive effects that:
(1) the design method of the invention is used for carrying out light weight design on the low-floor tramcar auxiliary converter, and compared with the traditional power frequency auxiliary converter, the low-floor tramcar auxiliary converter after light weight design has high power density and small volume and weight.
(2) The invention designs the preceding-stage Buck converter, the preceding-stage Buck converter is a minimum voltage stress Buck converter provided with a minimum voltage stress resonance unit, zero voltage conduction and zero voltage disconnection of a switching tube are realized by using a passive soft switch, no additional voltage stress is introduced in the process of realizing the soft switch, and the voltage stress at the moment of switching-off of the switching tube is relieved.
(3) Aiming at the defect that the LLC converter needs frequency conversion, the Buck voltage regulation link is introduced into the front stage to realize fixed-frequency modulation of the LLC converter, so that the design of a magnetic element is facilitated, and when the input voltage or the load changes, the output voltage of the front stage Buck converter is adjusted to adapt to the change; the LLC converter is designed as an LLC fixed-frequency resonant converter, can realize zero-voltage conduction (ZVS) and low-current turn-off of a primary power device and zero-voltage turn-off (ZCS) of a secondary rectifier diode, greatly improves the power density of an auxiliary inverter and reduces interference (namely EMI).
(4) According to the split capacitor three-phase inverter, the neutral line inductor is introduced into the three-phase inverter bridge, zero sequence current is inhibited, the unbalance degree of output voltage is reduced, the adaptability of the system to unbalanced load is improved, and the robustness of the system is enhanced.
(5) The auxiliary inverter of the auxiliary converter of the low-floor tramcar adopts a Buck + LLC + INV three-stage series connection structure, the charger is connected to the output side of the Buck converter, and when the rear-stage inverter fails (or the charger fails), the charger (or the inverter) can normally work and is not influenced by the failed inverter (or the charger).
Drawings
Fig. 1 is a circuit diagram of an existing power frequency isolation auxiliary converter of a low-floor tramcar.
Fig. 2 is a circuit diagram of the low-floor tramcar auxiliary converter of the present invention.
Fig. 3 is a state diagram of the main components of the minimum voltage stress Buck converter according to the present invention.
Fig. 4 is a waveform diagram of the working principle of the LLC fixed-frequency resonant converter of the invention.
In the figure, 1 is a minimum voltage stress Buck converter, 2 is an LLC fixed frequency resonance converter, 3 is a split capacitor three-phase inverter, and 4 is a DC/DC current-doubling rectifying converter.
Detailed Description
The invention is described in detail below by way of exemplary embodiments. It should be understood, however, that elements, structures and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.
The invention discloses a lightweight design method for an auxiliary converter of a low-floor tramcar, which comprises the following steps of:
and S1, sequentially connecting the minimum voltage stress Buck converter provided with the minimum voltage stress resonance unit, the LLC fixed frequency resonance converter and the split capacitor three-phase inverter in series to serve as an auxiliary inverter, wherein the charger is provided with a DC/DC current-multiplying rectification converter, and the DC/DC current-multiplying rectification converter is connected with the output end of the minimum voltage stress Buck converter.
S2, determining the resonant inductance L of the minimum voltage stress Buck converter2Resonant capacitor CrResonant capacitor CsAnd a minimum output current Io,min(ii) a The method comprises the following specific steps:
(1) resonant inductor L2The inductance value of (a) is selected to satisfy the following conditions:
Figure GDA0002338986580000091
in the formula, trIs a switch tube S1Current rise time of trrIs a freewheeling diode D4Reverse recovery time of io,peakFor output current peak, UiIs the input voltage;
(2) resonant capacitor CrAnd a resonance capacitor CsThe selection comprises the following steps:
(a) arbitrarily fetch
Figure GDA0002338986580000092
Substituting into formula (2), obtaining the minimum output current I under the conditiono,minEquation (2) is expressed as:
Figure GDA0002338986580000093
in the formula, tr-off,maxThe maximum resonance turn-off time under the condition of meeting the soft chopping operation is given by a designer;
(b) comparing the value of step (a) with the minimum output current Io,minSubstituting formula (3) to obtain resonant capacitance CrEquation (3) is expressed as:
Figure GDA0002338986580000101
in the formula, omega is
Figure GDA0002338986580000102
(c) Verifying the resonance capacitance C obtained in step (b) by equation (4)rEquation (4) is expressed as:
Figure GDA0002338986580000103
in the formula, tfIs a switch tube S1Current fall time of (d);
(d) if the condition in step (C) is not satisfied, repeating steps (a) - (C) until the condition in step (C) is satisfied, and if the condition in step (C) is satisfied, selecting a resonant capacitor CrShould be greater than the theoretical value when selected, resonant capacitor CsThe capacitance value of (2) is obtained by equation (5), where equation (5) is expressed as:
Figure GDA0002338986580000104
the operation state diagram of the above elements of the minimum voltage stress Buck converter is shown in FIG. 3.
S3, defining the limit conditions of LLC fixed frequency resonant converter design, and selecting excitation inductance LmCalculating the DC blocking capacitor C in the LLC constant frequency resonant converterbPrimary side leakage inductance L of transformerkAnd resonant cavity resonant frequency frAnd verifying whether the LLC fixed-frequency resonant converter meets the following verification conditions: (1) whether zero voltage conduction realization condition of transformer primary side switch tube is met
Figure GDA0002338986580000105
In the formula, ZinIs an input impedance, CresIs IGBT parallel parasitic capacitance, TrIs the resonant period of the resonant cavity, i.e.
Figure GDA0002338986580000106
Uin_minIs the minimum value of the input voltage, Pin_maxIs the maximum input power; (2) whether quality factor Q of LLC fixed frequency resonance converter satisfies condition
Figure GDA0002338986580000107
In the formula, LrsFor exciting inductance LmAnd primary side leakage inductance LkRatio of (i) to (ii)
Figure GDA0002338986580000111
frsIs resonant frequency f of resonant cavityrAnd the switching frequency fsA ratio; (3) whether the primary side current of the transformer is reverse in the dead time or not; (4) whether the input impedance is inductive or not and an angle allowance is reserved; if the above four verification conditions cannot be satisfied simultaneously, the excitation inductance value L needs to be reselectedmPerforming accounting until the four verification conditions are met simultaneously;
s4, introducing neutral line inductor L into split capacitor three-phase inverternNeutral line inductance LnIs connected with the common end of the three-phase output filter capacitor, and the neutral line inductor LnIs connected with the middle point between the two input split capacitors, and when the three-phase load is unbalanced, the central inductor L is introducednEliminating neutral point potential uNIs applied to the surface of the material.
In step S3, the design limiting conditions of the LLC fixed-frequency resonant converter are:
the LLC resonant cavity input impedance must exhibit an inductance, Angle (Z)in)>0；
The quality factor Q of the LLC fixed-frequency resonant converter is smaller than 0.005 so as to ensure that the LLC fixed-frequency resonant converter works in an inductive II area; in practical application, the value range of the excitation inductance of the transformer is 1mH, the primary side leakage inductance is several muH, and the ratio L of the primary side leakage inductance and the primary side leakage inductance is LrsIn the order of a few hundred, this leads to Mgain ═ f (f)rs) In the curve (where Mgain represents the resonator gain), the frequency change is large and the boundary between the inductive and capacitive impedances is shifted to the left in the same gain conversion range, so that the quality factor Q required in the design must be small to ensure the operation and the inductive II region.
The dead time of the LLC fixed-frequency resonant converter is longer than the discharge time of the junction capacitor and is simultaneously shorter than the sum of the discharge time of the junction capacitor and the time of the excitation current from resonance to zero, so that the condition for realizing zero voltage conduction (namely ZVS) of a primary side switching tube of a transformer in the LLC fixed-frequency resonant converter is ensured.
In step S3, the excitation inductance L is selectedmCalculating the DC blocking capacitor C in the LLC constant frequency resonant converterbPrimary side leakage inductance L of transformerkAnd resonant cavity resonant frequency frThe method comprises the following specific steps:
(1) defining the excitation inductance LmHas a value range of not more than 0.7mH and not more than LmLess than or equal to 2mH, initially selecting excitation inductance LmTaking the value of (A);
(2) the junction capacitance discharge time T is calculated by the following equations (6) and (7) respectively1And exciting current resonance to zero time Tm：
Figure GDA0002338986580000121
Figure GDA0002338986580000122
In the formula, n is the turn ratio of the transformer, and R is the equivalent impedance of the primary side of the transformer;
(3) dead time tdead≥T1The current angle is calculated according to the following formula (8)
Figure GDA0002338986580000123
Figure GDA0002338986580000124
In the formula of UoFor LLC fixed-frequency resonant converter output voltage, IoOutputting current for the LLC fixed-frequency resonant converter;
(4) ensuring that the LLC fixed-frequency resonant converter works in an inductive II area, the following limitations should be met:
Figure GDA0002338986580000125
(5) calculating a blocking capacitor C in the LLC constant frequency resonant converterbPrimary side leakage inductance L of transformerkAnd resonant cavity resonant frequency fr。
In step S4, neutral point potential u is set in the three-phase load balanceNComprises the following steps:
Figure GDA0002338986580000126
in the formula udcThe output voltage of the LLC fixed-frequency resonant converter;
neutral point potential u when unbalanced load is connectedNIs offset, i.e.
Figure GDA0002338986580000127
Lead-in neutral inductance LnPotential u of neutral pointNThe expression is as follows:
Figure GDA0002338986580000128
in the formula umIs the maximum value of the three-phase output voltage, Z is the load impedance, CinThe three-phase output filter capacitor is provided, and theta is an offset angle;
neutral point potential u when three-phase load is unbalancedNWith sinusoidal disturbance by introducing central inductance
Figure GDA0002338986580000131
Eliminating the disturbance to make the neutral point potential uNIs restored to
Figure GDA0002338986580000132
Thereby reducing the unbalance degree of the three-phase voltage.
The Buck converter, the LLC fixed-frequency resonant converter and the split capacitor three-phase inverter are designed without any sequence. Therefore, the order of the above steps S2, S3, S4 may be interchanged.
Referring to fig. 2, the invention also provides a low-floor tramcar auxiliary inverter, which comprises an auxiliary inverter and a charger based on the design method, wherein the auxiliary inverter comprises a minimum voltage stress Buck converter 1, an LLC fixed frequency resonance converter 2 and a split capacitor three-phase inverter3, a minimum voltage stress Buck converter 1, an LLC fixed frequency resonance converter 2 and a split capacitor three-phase inverter 3 are sequentially connected in series, wherein the minimum voltage stress Buck converter 1 is provided with a minimum voltage stress resonance unit, and the minimum voltage stress resonance unit is composed of a resonance inductor L2Resonant capacitor CrAnd a resonance capacitor CsAnd four freewheeling diodes, freewheeling diode D1Respectively with a freewheeling diode D3Is connected with the negative electrode of the resonant capacitor Cr, and a freewheeling diode D1Respectively with a freewheeling diode D2Cathode and resonant capacitor CsThe positive electrodes of the two electrodes are connected; freewheeling diode D2Anode and freewheeling diode D4Is connected to the anode of a freewheeling diode D3Respectively with a resonant capacitor CsNegative electrode of (1), resonance inductor L2Negative electrode of (D), freewheel diode (D)4The cathodes of the two electrodes are connected; the charger is provided with a DC/DC current-multiplying rectifying converter 4, and the DC/DC current-multiplying rectifying converter 4 is connected with the output end of the minimum voltage stress Buck converter 1.
With continued reference to fig. 2, the minimum voltage stress Buck converter further includes an input filter inductor L1Switch tube S1An input filter capacitor C1Follow current inductor L3The two output filter capacitors are connected in series, and the two voltage-sharing resistors are connected in series; input filter capacitor C1Respectively with the input filter inductance L1Negative electrode of (2), switching tube S1C pole and resonant capacitor CrIs connected to the positive pole of the input filter capacitor C1Respectively with a freewheeling diode D2Anode of (2), freewheel diode D4Anode and output filter capacitor C3Is connected with the negative pole of the switching tube S1M pole and resonant inductor L2Is connected with the positive pole of the switching tube S1Respectively with a resonant capacitor CrNegative electrode of (D), freewheel diode (D)1Cathode of (D), freewheel diode (D)3The anodes of the anode groups are connected; freewheeling diode D1Respectively with a freewheeling diode D3Anode and resonant capacitor CrIs connected to the negative electrode of a freewheeling diode D1Respectively with follow current twoPolar tube D2Cathode and resonant capacitor CsThe positive electrodes of the two electrodes are connected; freewheeling diode D2Anode and freewheeling diode D4Is connected to the anode of a freewheeling diode D3Respectively with a resonant capacitor CsNegative electrode of (1), resonance inductor L2Negative electrode of (D), freewheel diode (D)4The cathodes of the two electrodes are connected; follow current inductance L3Respectively with the resonant inductor L2Negative electrode of (D), freewheel diode (D)3Cathode and resonant capacitor CsNegative electrode of (D), freewheel diode (D)4Is connected with the cathode of the secondary current inductor L3Negative pole and output filter capacitor C2Is connected with the anode of the voltage-sharing resistor RC1Connected in parallel to an output filter capacitor C2At both ends of (2), a voltage-sharing resistor RC2Connected in parallel to an output filter capacitor C3At both ends of the same. Using resonant inductance L2Resonant capacitor CrAnd a resonance capacitor CsTo the switch tube S1The voltage and current waveforms are shaped and softened, so that the purpose of soft switching is achieved. Voltage-sharing resistor RC1Connected in parallel to an output filter capacitor C2At both ends of (2), a voltage-sharing resistor RC2Connected in parallel to an output filter capacitor C3The two ends of the pressure equalizing device play a role in equalizing pressure.
With continued reference to fig. 2, the DC/DC current doubler rectifier converter includes a switching tube S2DC blocking capacitor CcTransformer T2Follow current inductor LaFollow current inductor LbAn output filter capacitor C6Anti-reflection diode D9And two diodes; switch tube S2M pole and DC blocking capacitor CcIs connected with the positive electrode of the capacitor CcAnd the transformer T2V of the primary sideaEnd connection; transformer T2V of the primary sidebTerminal and output filter capacitor C2And an output filter capacitor C3Are connected with each other; transformer T2V of minor edgecTerminals of which are respectively connected with follow current inductors LaCathode of (2), diode D8The anodes of the anode groups are connected; transformer T2V of minor edgedTerminals of which are respectively connected with follow current inductors LbCathode of (2), diode D7Is connected to the anode of a diode D7And dipolarPipe D8The cathode of the capacitor is connected with an output filter capacitor C6The negative electrodes are connected; follow current inductance LaAnd a follow current inductor LbRespectively with the output filter capacitor C6Positive and anti-reverse diode D9Are connected with each other.
With continued reference to fig. 2, the LLC constant-frequency resonant converter includes two parallel-connected switching tubes and a dc blocking capacitor CbTransformer T1And two secondary rectifier diodes, transformer T1And a DC blocking capacitor CbForm an LLC resonant cavity, G1、G2、G3、G4Is a driving signal of the switching tube; switch tube S3And a switching tube S4The bus is bridged between the positive output bus and the negative output bus of the minimum voltage stress Buck converter; switch tube S3M pole and DC blocking capacitor CbIs connected with the positive pole of the switching tube S4M pole and transformer T1V of the primary sidebEnd-connected, DC blocking capacitor CbAnd the transformer T1V of the primary sideaEnd-to-end transformer integrated leakage inductance LkBelongs to a transformer T1A body; transformer T1V of minor edgecEnd and secondary side rectifier diode D5Is connected to the intermediate point of the transformer T1V of minor edgedEnd and secondary side rectifier diode D6Are connected. Referring to FIG. 4, the driving signal G1And a drive signal G4Same, drive signal G2And a drive signal G3Similarly, the switching frequency of the resonant cavity is higher than that of the LLC fixed-frequency resonant converter, so that the resonant period is ensured to be smaller than the switching period, and a condition is created for zero-current turn-off of the secondary side diode; will output a voltage UoConverted to transformer T1Primary side and using the voltage to the transformer T1The zero voltage conduction and the low current turn-off of the primary side switching tube are realized through the excitation and demagnetization functions.
With continued reference to fig. 2, the split-capacitor three-phase inverter includes two input split capacitors connected in series, three switching tubes connected in parallel, three output filter inductors, three star-connected output filter capacitors, and an intermediate inductor LnAnd neutral capacitance Cn(ii) a Input split capacitor C4Positive and secondary rectifier diode D6Is connected to the anode of the input split capacitor C5Negative and secondary rectifier diode D6The cathode of (a) is connected; switch tube S5Switch tube S6And a switching tube S7Split capacitors C respectively connected with the input4And an input split capacitor C5The constituent series circuits being connected in parallel, the switching tubes S5M pole and output filter inductance LuIs connected with the positive pole of the switching tube S6M pole and output filter inductance LvIs connected with the positive pole of the switching tube S7M pole and output filter inductance LwIs connected with the positive pole of the output filter capacitor CuAn output filter capacitor CvAnd an output filter capacitor CwCommon terminal and neutral line capacitor CnIs connected with the anode of a neutral line capacitor CnNegative pole and neutral line inductance LnIs connected with the negative pole of the neutral line inductor LnAnode and input split capacitor C4And an input split capacitor C5Connected at an intermediate point therebetween.
The above-described embodiments are intended to illustrate rather than to limit the invention, and any modifications and variations of the present invention are possible within the spirit and scope of the claims.

Claims (10)

1. A lightweight design method for an auxiliary converter of a low-floor tramcar is characterized by comprising the following steps:
sequentially connecting a minimum voltage stress Buck converter provided with a minimum voltage stress resonance unit, an LLC fixed frequency resonance converter and a split capacitor three-phase inverter in series to serve as an auxiliary inverter, wherein a charger is provided with a DC/DC current-doubling rectifying converter which is connected with the output end of the minimum voltage stress Buck converter; the minimum voltage stress resonance unit consists of a resonance inductor L2Resonant capacitor CrAnd a resonance capacitor CsAnd four freewheeling diodes, freewheeling diode D1Respectively with a freewheeling diode D3Anode and resonant capacitor CrOf the negative electrodeConnected, freewheeling diode D1Respectively with a freewheeling diode D2Cathode and resonant capacitor CsThe positive electrodes of the two electrodes are connected; freewheeling diode D2Anode and freewheeling diode D4Is connected to the anode of a freewheeling diode D3Respectively with a resonant capacitor CsNegative electrode of (1), resonance inductor L2Negative electrode of (D), freewheel diode (D)4The cathodes of the two electrodes are connected;
resonant inductance L for determining minimum voltage stress Buck converter2Resonant capacitor CrResonant capacitor CsAnd a minimum output current Io,min；
Defining the limit condition of LLC fixed frequency resonant converter design, selecting excitation inductance LmCalculating the DC blocking capacitor C in the LLC constant frequency resonant converterbPrimary side leakage inductance L of transformerkAnd resonant cavity resonant frequency frAnd verifying whether the LLC fixed-frequency resonant converter meets the following verification conditions: (1) whether zero voltage conduction realization condition of transformer primary side switch tube is met
Figure FDA0002338986570000011
In the formula, ZinIs an input impedance, CresIs IGBT parallel parasitic capacitance, TrIs the resonant period of the resonant cavity, i.e.
Figure FDA0002338986570000012
Uin_minIs the minimum value of the input voltage, Pin_maxIs the maximum input power; (2) whether quality factor Q of LLC fixed frequency resonance converter satisfies condition
Figure FDA0002338986570000013
In the formula, LrsFor exciting inductance LmAnd primary side leakage inductance LkRatio of (i) to (ii)
Figure FDA0002338986570000014
frsIs resonant frequency f of resonant cavityrAnd the switching frequency fsA ratio; (3) dead timeWhether the primary side current of the inner transformer is reverse or not; (4) whether the input impedance is inductive or not and an angle allowance is reserved; if the above four verification conditions cannot be satisfied simultaneously, the excitation inductance value L needs to be reselectedmPerforming accounting until the four verification conditions are met simultaneously;
neutral line inductor L is introduced into split capacitor three-phase inverternNeutral line inductance LnIs connected with the common end of the three-phase output filter capacitor, and the neutral line inductor LnIs connected with the middle point between the two input split capacitors, and when the three-phase load is unbalanced, the central inductor L is introducednEliminating neutral point potential uNIs applied to the surface of the material.
2. The method for designing the low-floor tramcar auxiliary converter in light weight according to claim 1, characterized by determining the resonant inductance L of the minimum voltage stress Buck converter2Resonant capacitor CrResonant capacitor CsAnd a minimum output current Io,minThe method comprises the following specific steps:
resonant inductor L2The inductance value of (a) is selected to satisfy the following conditions:
Figure FDA0002338986570000021
in the formula, trIs a switch tube S1Current rise time of trrIs a freewheeling diode D4Reverse recovery time of io,peakFor output current peak, UiIs the input voltage;
resonant capacitor CrAnd a resonance capacitor CsThe selection comprises the following steps:
(a) arbitrarily fetch
Figure FDA0002338986570000022
Substituting into formula (2), obtaining the minimum output current I under the conditiono,minEquation (2) is expressed as:
Figure FDA0002338986570000023
in the formula, tr-off,maxThe maximum resonance turn-off time under the condition of meeting the soft chopping operation is given by a designer;
(b) comparing the value of step (a) with the minimum output current Io,minSubstituting formula (3) to obtain resonant capacitance CrEquation (3) is expressed as:
Figure FDA0002338986570000031
in the formula, omega is
Figure FDA0002338986570000032
(c) Verifying the resonance capacitance C obtained in step (b) by equation (4)rEquation (4) is expressed as:
Figure FDA0002338986570000033
in the formula, tfIs a switch tube S1Current fall time of (d);
(d) if the condition in step (C) is not satisfied, repeating steps (a) - (C) until the condition in step (C) is satisfied, and if the condition in step (C) is satisfied, selecting a resonant capacitor CrShould be greater than the theoretical value when selected, resonant capacitor CsThe capacitance value of (2) is obtained by equation (5), where equation (5) is expressed as:
Figure FDA0002338986570000034
3. the method for designing the low-floor tramcar auxiliary converter in a light weight mode according to claim 2, wherein the design limiting conditions of the LLC fixed-frequency resonant converter are as follows:
the LLC resonant cavity input impedance must exhibit an inductance, Angle (Z)in)>0；
The quality factor Q of the LLC fixed-frequency resonant converter is smaller than 0.005 so as to ensure that the LLC fixed-frequency resonant converter works in an inductive II area;
the dead time of the LLC fixed-frequency resonant converter is greater than the junction capacitor discharge time and is smaller than the sum of the junction capacitor discharge time and the time of the excitation current resonant to zero.
4. The method as claimed in claim 3, wherein the excitation inductance L is selectedmCalculating the DC blocking capacitor C in the LLC constant frequency resonant converterbPrimary side leakage inductance L of transformerkAnd resonant cavity resonant frequency frThe method comprises the following specific steps:
defining the excitation inductance LmHas a value range of not more than 0.7mH and not more than LmLess than or equal to 2mH, initially selecting excitation inductance LmTaking the value of (A);
the junction capacitance discharge time T is calculated by the following equations (6) and (7) respectively1And exciting current resonance to zero time Tm：
Figure FDA0002338986570000041
Tm＝tan-1(n2×R/2πfrfrsLm)/π×Tr/2 (7)
In the formula, n is the turn ratio of the transformer, and R is the equivalent impedance of the primary side of the transformer;
dead time tdead≥T1The current angle is calculated according to the following formula (8)
Figure FDA0002338986570000045
Figure FDA0002338986570000042
In the formula of UoFor LLC fixed-frequency resonant converter output voltage, IoFixed-frequency resonant converter for LLCOutputting current;
ensuring that the LLC fixed-frequency resonant converter works in an inductive II area, the following limitations should be met:
Figure FDA0002338986570000043
calculating a blocking capacitor C in the LLC constant frequency resonant converterbPrimary side leakage inductance L of transformerkAnd resonant cavity resonant frequency fr。
5. The method of claim 4, wherein the neutral point potential u is set to be a neutral point potential u when the three-phase load is balancedNComprises the following steps:
Figure FDA0002338986570000044
in the formula udcThe output voltage of the LLC fixed-frequency resonant converter;
neutral point potential u when unbalanced load is connectedNIs offset, i.e.
Figure FDA0002338986570000051
Lead-in neutral inductance LnThe neutral point potential expression is as follows:
Figure FDA0002338986570000052
in the formula umIs the maximum value of the three-phase output voltage, Z is the load impedance, CinThe three-phase output filter capacitor is provided, and theta is an offset angle;
when three-phase load is unbalanced, the neutral point potential has sinusoidal disturbance by introducing central inductance
Figure FDA0002338986570000053
The disturbance is eliminated to restore the neutral point potential to
Figure FDA0002338986570000054
6. The low-floor tram auxiliary converter is based on the method for designing the low-floor tram auxiliary converter in a light weight mode according to claim 1 and comprises an auxiliary inverter and a charger, wherein the auxiliary inverter comprises a minimum voltage stress Buck converter, an LLC fixed-frequency resonance converter and a split capacitor three-phase inverter, the minimum voltage stress Buck converter, the LLC fixed-frequency resonance converter and the split capacitor three-phase inverter are sequentially connected in series, a minimum voltage stress resonant unit is arranged on the minimum voltage stress Buck converter, and the minimum voltage stress resonant unit is composed of a resonant inductor L2Resonant capacitor CrAnd a resonance capacitor CsAnd four freewheeling diodes, freewheeling diode D1Respectively with a freewheeling diode D3Anode and resonant capacitor CrIs connected to the negative electrode of a freewheeling diode D1Respectively with a freewheeling diode D2Cathode and resonant capacitor CsThe positive electrodes of the two electrodes are connected; freewheeling diode D2Anode and freewheeling diode D4Is connected to the anode of a freewheeling diode D3Respectively with a resonant capacitor CsNegative electrode of (1), resonance inductor L2Negative electrode of (D), freewheel diode (D)4The cathodes of the two electrodes are connected; the charger is provided with a DC/DC current-multiplying rectifying converter, and the DC/DC current-multiplying rectifying converter is connected with the output end of the minimum voltage stress Buck converter.
7. The low-floor tramcar auxiliary converter according to claim 6, characterized in that said minimum voltage stress Buck converter further comprises an input filter inductance L1Switch tube S1An input filter capacitor C1Follow current inductor L3The two output filter capacitors are connected in series, and the two voltage-sharing resistors are connected in series; input filter capacitor C1Respectively with the input filter inductance L1Negative electrode of (2), switching tube S1C pole and resonant capacitor CrIs connected to the positive pole of the input filter capacitor C1Respectively with a freewheeling diode D2Anode of (2), freewheel diode D4Anode and output filter capacitor C3Is connected with the negative pole of the switching tube S1M pole and resonant inductor L2Is connected with the positive pole of the switching tube S1Respectively with a resonant capacitor CrNegative electrode of (D), freewheel diode (D)1Cathode of (D), freewheel diode (D)3The anodes of the anode groups are connected; follow current inductance L3Respectively with the resonant inductor L2Negative electrode of (D), freewheel diode (D)3Cathode and resonant capacitor CsNegative electrode of (D), freewheel diode (D)4Is connected with the cathode of the secondary current inductor L3Negative pole and output filter capacitor C2Is connected with the anode of the voltage-sharing resistor RC1Connected in parallel to an output filter capacitor C2At both ends of (2), a voltage-sharing resistor RC2Connected in parallel to an output filter capacitor C3At both ends of the same.
8. The low-floor tramcar auxiliary converter according to claim 7, characterized in that the DC/DC double current rectifier converter comprises a switching tube S2DC blocking capacitor CcTransformer T2Follow current inductor LaFollow current inductor LbAn output filter capacitor C6Anti-reflection diode D9And two diodes; switch tube S2M pole and DC blocking capacitor CcIs connected with the positive electrode of the capacitor CcAnd the transformer T2V of the primary sideaEnd connection; transformer T2V of the primary sidebTerminal and output filter capacitor C2And an output filter capacitor C3Are connected with each other; transformer T2V of minor edgecTerminals of which are respectively connected with follow current inductors LaCathode of (2), diode D8The anodes of the anode groups are connected; transformer T2V of minor edgedTerminals of which are respectively connected with follow current inductors LbCathode of (2), diode D7Is connected to the anode of a diode D7And a diode D8The cathode of the capacitor is connected with an output filter capacitor C6The negative electrodes are connected; follow current inductance LaAnd a follow current inductor LbRespectively positive electrode ofAnd output filter capacitor C6Positive and anti-reverse diode D9Are connected with each other.
9. The low-floor tramcar auxiliary converter according to claim 6, characterized in that the LLC fixed-frequency resonant converter comprises two parallel-connected switching tubes, a DC blocking capacitor CbTransformer T1And two secondary rectifier diodes, transformer T1And a DC blocking capacitor CbForming an LLC resonant cavity; switch tube S3And a switching tube S4The bus is bridged between the positive output bus and the negative output bus of the minimum voltage stress Buck converter; switch tube S3M pole and DC blocking capacitor CbIs connected with the positive pole of the switching tube S4M pole and transformer T1V of the primary sidebEnd-connected, DC blocking capacitor CbAnd the transformer T1V of the primary sideaEnd connection; transformer T1V of minor edgecEnd and secondary side rectifier diode D5Is connected to the intermediate point of the transformer T1V of minor edgedEnd and secondary side rectifier diode D6Are connected.
10. The low-floor tram auxiliary converter according to claim 9, characterized in that the split-capacitor three-phase inverter comprises two series-connected input split capacitors, three parallel-connected switching tubes, three output filter inductors, three star-connected output filter capacitors, an intermediate inductor LnAnd neutral capacitance Cn(ii) a Input split capacitor C4Positive and secondary rectifier diode D6Is connected to the anode of the input split capacitor C5Negative and secondary rectifier diode D6The cathode of (a) is connected; switch tube S5Switch tube S6And a switching tube S7Split capacitors C respectively connected with the input4And an input split capacitor C5The constituent series circuits being connected in parallel, the switching tubes S5M pole and output filter inductance LuIs connected with the positive pole of the switching tube S6M pole and output filter inductance LvIs connected with the positive pole of the switching tube S7M pole and output filterWave inductor LwIs connected with the positive pole of the output filter capacitor CuAn output filter capacitor CvAnd an output filter capacitor CwCommon terminal and neutral line capacitor CnIs connected with the anode of a neutral line capacitor CnNegative pole and neutral line inductance LnIs connected with the negative pole of the neutral line inductor LnAnode and input split capacitor C4And an input split capacitor C5Connected at an intermediate point therebetween.
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