CN112165257A - Isolated DC converter and fault-tolerant control method - Google Patents

Isolated DC converter and fault-tolerant control method Download PDF

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CN112165257A
CN112165257A CN202010910708.6A CN202010910708A CN112165257A CN 112165257 A CN112165257 A CN 112165257A CN 202010910708 A CN202010910708 A CN 202010910708A CN 112165257 A CN112165257 A CN 112165257A
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fault
isolated
converter
current
direct current
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CN112165257B (en
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张建文
施刚
周剑桥
王晗
蔡旭
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Shanghai Zhonglv New Energy Technology Co ltd
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Shanghai Jiaotong University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • H02M3/33584—Bidirectional converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H02M1/325—Means for protecting converters other than automatic disconnection with means for allowing continuous operation despite a fault, i.e. fault tolerant converters

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)
  • Inverter Devices (AREA)

Abstract

The invention discloses an isolated DC converter and a fault tolerance control method, wherein the converter comprises: the high-frequency transformer comprises a high-frequency transformer and bridge structures on two sides of the high-frequency transformer, wherein one side of the bridge structure is an inversion side, and the other side of the bridge structure is a rectification side; when the inverter side has a fault, the rectifier side injects a first preset compensation direct current; when the rectifying side has a fault, the inverting side injects a second preset compensation direct current. The method comprises the following steps: positioning the fault according to the fault characteristics, and judging whether the fault occurs on the inversion side or the rectification side; when a fault occurs on an inversion side, injecting a first preset compensation direct current on a rectification side; when the fault occurs on the rectifying side, a second preset compensation direct current is injected on the inverting side. The invention can realize DC bias magnetic flux compensation, avoid saturation of high-frequency transformer, and improve the safe and reliable operation capability of the converter.

Description

Isolated DC converter and fault-tolerant control method
Technical Field
The invention relates to the technical field of power electronics, in particular to an isolated direct current converter and a fault tolerance control method.
Background
In recent years, high-frequency isolated bidirectional direct current converters are gradually becoming research hotspots in the field of power electronics due to large-scale application of the high-frequency isolated bidirectional direct current converters in new energy power generation systems, energy internet grid-connected applications and energy storage systems. Among such converters, a dual active bridge DC-DC converter (DAB) has attracted much attention in various fields because of its advantages such as electrical isolation, bidirectional energy transfer, buck-boost conversion, and high power density.
Compared with the traditional equipment, the high-power electronic converter based on the semiconductor switching device is more easily influenced by abnormal working conditions, and the reliability and the robustness of the high-power electronic converter are reduced. In DAB, short-circuit faults, open-circuit faults and corresponding driver circuit faults of the IGBT account for 46% of all abnormal operating conditions. Wherein short-circuit faults are often handled in a shutdown manner due to large overcurrents. Unlike short circuit faults, when a single IGBT open circuit fault occurs, DAB can maintain certain power transmission capability in a fault state because the equipment overcurrent and overvoltage is not obvious at the moment.
Through a fault-tolerant operation scheme in a certain mode, the reliability, robustness and equipment utilization rate of DAB can be effectively improved, and the method has important significance for different applications of equipment. At present, there are two fault-tolerant operation schemes for the open circuit fault of the IGBT in DAB:
(1) redundant design of the used devices of DAB; (2) DAB itself fault-tolerant operation control method.
Method (1) while improving the reliability and robustness of the system, requires additional investment while reducing the power density of the power electronic transformer. The method (2) introduces extra control freedom by adjusting the DAB switch signal, and realizes fault-tolerant operation without using extra redundant equipment. However, the fault-tolerant operation control method only considers an ideal transformer model, and in the ideal transformer, because parasitic resistance is ignored, magnetic fluxes generated by primary and secondary direct current exciting currents caused by faults can be mutually offset in a high-frequency transformer; in the actual transformer model, due to the existence of the parasitic resistance of the transformer, the direct current bias current caused by the fault is gradually consumed at the non-fault side of the DAB, so that the primary and secondary magnetic fluxes are unbalanced, and the high-frequency transformer core is saturated. In addition, the DAB fault-tolerant operation control scheme proposed by the scholars only considers unidirectional power transmission, and when the power is transmitted reversely in a fault state, the proposed method cannot realize fault-tolerant operation.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides an isolated direct current converter and a fault-tolerant control method, which maintain the bidirectional power transfer capability of DAB in the state of IGBT open circuit fault and improve the availability of DAB; meanwhile, direct current bias current compensation can be realized, so that the saturation of the high-frequency transformer is avoided.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
the invention provides an isolated DC converter, which comprises: a high frequency transformer and bridge structures on both sides thereof; wherein the content of the first and second substances,
one side bridge structure is an inversion side, and the other side bridge structure is a rectification side;
when the inversion side has a fault, the rectification side injects a first preset compensation direct current;
when the rectifying side has a fault, the inverting side injects a second preset compensation direct current.
Preferably, the primary and secondary side currents of the inversion side are i1The primary and secondary side current of the rectifying side is i2(ii) a Wherein the content of the first and second substances,
when the inverter side fails, i1Not exceeding rated current value i1ratedThen, the phase shifting angle keeps the original parameter value; otherwise the phase shift angle is decreased to achieve reduced power operation;
when the rectifying side fails, i2Not exceeding rated current value i2ratedThen, the phase shifting angle keeps the original parameter value; otherwise the phase shift angle is decreased to achieve reduced power operation.
Preferably, the phase shift angle reduction to achieve power down operation is further: the phase shift angle is reduced to half of the original parameter value to realize reduced power operation.
Preferably, the front end voltage of the isolated dc converter is U1The back end voltage is U2；
The bridge structure positioned at the front end of the isolated DC converter is an inversion side, and the bridge structure positioned at the rear end of the isolated DC converter is a rectification side;
when T on the inverting sideiWhen an open-circuit fault occurs, the first preset compensation direct current IDC2Comprises the following steps:
Figure BDA0002663153600000031
when T of the rectifying sidejWhen an open-circuit fault occurs, the second preset compensation direct current IDC1Comprises the following steps:
Figure BDA0002663153600000032
wherein n is the primary and secondary side turn ratio of the high-frequency transformer,
Figure BDA0002663153600000033
is i1The current of the direct current bias is used,
Figure BDA0002663153600000034
is i2A direct current bias current.
Preferably, the bridge structures on both sides are double-sided active H-bridges, or double-sided midpoint clamped active bridges, or one-side midpoint clamped active bridge and the other-side active H-bridge.
The invention also provides a fault tolerance control method for the isolated DC converter, which comprises the following steps:
s61: positioning the fault according to the fault characteristics, and judging whether the fault occurs on the inversion side or the rectification side;
s62: when a fault occurs on the inversion side, injecting a first preset compensation direct current on the rectification side;
and when the fault occurs on the rectifying side, injecting a second preset compensation direct current on the inverting side.
Preferably, the S62 further includes:
s71: when a fault occurs on the inversion side, the primary and secondary side current i1 of the inversion side does not exceed the rated current value i1ratedThen, the phase shifting angle keeps the original parameter value; otherwise, reducing the phase shifting angle to realize reduced power operation;
when a fault occurs on the rectifying side, the primary side current i2 and the secondary side current i2 on the rectifying side do not exceed the rated current value i2ratedThen, the phase shifting angle keeps the original parameter value; otherwise, the phase shift angle is reduced to achieve reduced power operation.
Preferably, the reducing the phase shift angle to achieve the power reduction operation in S71 is further: and reducing the phase shifting angle to half of the original parameter value to realize reduced power operation.
Preferably, the front end voltage of the isolated dc converter is U1The back end voltage is U2；
The bridge structure positioned at the front end of the isolated DC converter is an inversion side, and the bridge structure positioned at the rear end of the isolated DC converter is a rectification side;
when T on the inverting sideiWhen an open-circuit fault occurs, the first preset compensation direct current IDC2Comprises the following steps:
Figure BDA0002663153600000041
when T of the rectifying sidejWhen an open-circuit fault occurs, the second preset compensation direct current IDC1Comprises the following steps:
Figure BDA0002663153600000042
wherein n is the primary and secondary side turn ratio of the high-frequency transformer,
Figure BDA0002663153600000043
is a dc bias current of i1,
Figure BDA0002663153600000044
is i2 dc bias current.
Preferably, the bridge structures on both sides of the isolated dc converter are double-sided active H-bridges, or double-sided midpoint clamped active bridges, or one-side midpoint clamped active bridge and the other-side active H-bridge.
Compared with the prior art, the invention has the following advantages:
(1) according to the isolated direct current converter and the fault-tolerant control method, the compensation direct current is injected into the non-fault side, so that two magnetic fluxes caused by the direct current bias current can be mutually offset, and the magnetic core of the high-frequency transformer is prevented from being saturated;
(2) the isolated DC converter and the fault-tolerant control method provided by the invention ensure the bidirectional power transfer capability of the system which always operates in a rated current range in a fault state by changing the phase shift angle of the DAB converter, and maintain the maximum equipment availability of the DAB.
Of course, it is not necessary for any product in which the invention is practiced to achieve all of the above-described advantages at the same time.
Drawings
Embodiments of the invention are further described below with reference to the accompanying drawings:
FIG. 1a is a topology diagram of a dual active H-bridge type DC-DC converter according to an embodiment of the present invention;
FIG. 1b is a topology diagram of a dual midpoint clamped active bridge type DC-DC converter according to another embodiment of the present invention
FIG. 1c is a schematic diagram of a single-sided active H-bridge, single-sided midpoint clamped active bridge type DC-DC converter according to another embodiment of the present invention;
fig. 2 is a voltage-current waveform of the isolated dc converter according to an embodiment of the present invention under a normal operating condition;
FIG. 3 shows an isolated DC converter at T according to an embodiment of the present invention1Open circuit thereforeVoltage, current and power waveforms under the barrier;
FIG. 4 shows an isolated DC converter at T according to an embodiment of the present invention5Voltage, current and power waveforms under open circuit fault;
FIG. 5 is a flow chart of a fault tolerance control method according to an embodiment of the present invention;
FIG. 6 is a control block diagram of a fault tolerance control method according to an embodiment of the present invention;
FIG. 7 shows an inverter side T according to an embodiment of the present invention1A fault high frequency transformer excitation current curve;
FIG. 8a shows an inverter side T according to an embodiment of the present invention1The alternating voltage of the fault inversion side and the original secondary side alternating current curve;
FIG. 8b shows the inversion side T according to an embodiment of the present invention1The AC voltage of the fault inversion side and the AC current of the primary side and the secondary side are expanded to form a curve in a normal state;
FIG. 8c shows an inverter side T according to an embodiment of the present invention1The curve is developed under the fault state of the alternating voltage of the fault inversion side and the alternating current of the primary side and the secondary side (fault-tolerant operation control is not started);
FIG. 8d shows an inverter side T according to an embodiment of the present invention1The AC voltage of the fault inversion side and the AC current of the primary side and the secondary side are developed into curves in a fault state (starting fault-tolerant operation control);
FIG. 9 shows a rectifying side T according to an embodiment of the present invention5A fault high frequency transformer excitation current curve;
FIG. 10a shows a rectifying side T according to an embodiment of the present invention5The alternating voltage of the fault inversion side and the original secondary side alternating current curve;
FIG. 10b shows a rectifying side T according to an embodiment of the present invention5The AC voltage of the fault inversion side and the AC current of the primary side and the secondary side are expanded to form a curve in a normal state;
FIG. 10c is a view of a rectifying side T according to an embodiment of the present invention5The curve is developed under the fault state of the alternating voltage of the fault inversion side and the alternating current of the primary side and the secondary side (fault-tolerant operation control is not started);
FIG. 10d shows a rectifying side T according to an embodiment of the present invention5Fault contravariant side ac voltage and primary and secondary side acAnd (4) unfolding the curve in the flow fault state (starting fault-tolerant operation control).
Detailed Description
The following examples are given for the detailed implementation and specific operation of the present invention, but the scope of the present invention is not limited to the following examples.
In one embodiment, the topology of the isolated dc converter (DAB) can be a double-sided active H-bridge (fig. 1a), a double-sided midpoint clamped active bridge (fig. 1b), or a one-sided midpoint clamped active bridge and the other-sided active H-bridge (fig. 1 c). Taking a double-sided active H-bridge as an example, the DC-DC converter comprises eight IGBT switches, four IGBTs per side, as shown in fig. 1 a. The inverting side includes T1-T4Wherein T is1And T4Using the same switching signal, T2And T3The same switching signal is used. The rectification side IGBT comprises T5-T8Wherein T is5And T8Using the same switching signal, T6And T7The same switching signal is used. D1-D8And the reverse freewheeling diodes are respectively correspondingly numbered IGBTs. Open circuit faults can be classified into two categories according to position, 1) inversion side; 2) rectifying the flow. When a single IGBT open-circuit fault occurs on either side, a branch bias current is generated simultaneously on both sides at the moment of the fault. The generated magnetic fluxes are mutually offset in the high-frequency transformer, so that the direct-current magnetic biasing phenomenon cannot be generated, and the magnetic core of the high-frequency transformer is not saturated at the moment. However, due to the parasitic resistance, the non-fault side dc bias current is gradually consumed, and the generated magnetic flux cannot completely compensate the magnetic flux generated by the fault side dc bias current, resulting in saturation of the high frequency transformer core.
In order to solve the problems, the specific analysis process of the open-circuit fault of the IGBT of the DAB comprises the following steps,
under normal working conditions, the magnetic fluxes generated by the primary side and the secondary side of the high-frequency transformer in the DAB are respectively as follows:
Figure BDA0002663153600000071
wherein the leakage inductances of the primary and secondary sides are respectively L1And L2，LMFor transformer mutual inductance, i1And i2Is primary and secondary side current of high frequency transformer, N1And N2Respectively showing the turns of the primary side and the secondary side of the high-frequency transformer.
Under normal working conditions, the peak power of the inversion side is,
Figure BDA0002663153600000072
under normal working conditions, the peak current of the inversion side is,
Figure BDA0002663153600000073
wherein, U1And U2Respectively the front and rear end voltages of DAB, n is the turn ratio of the primary side and the secondary side of the high-frequency transformer, fsFor switching frequency of DAB, LrThe sum of the leakage inductances converted from the primary side to the secondary side of the transformer.
The corresponding voltage and current waveforms of DAB under normal operating condition can be divided into six switch states as shown in fig. 2. The current flow paths corresponding to the respective switch states are shown in the following table,
Figure BDA0002663153600000074
due to the symmetrical circuit structure of the active bridge in the DAB, open-circuit faults can be divided into four categories:
1) inverter side H1 bridge T1(T4) Open circuit failure; 2) inverter side H1 bridge T2(T3) Open circuit failure; 3) rectifying side H2 bridge T5(T8) Open circuit failure; 4) rectifying side H2 bridge T6(T7) Open circuit failure.
The inverter-side faults have similar fault characteristics. In the case of fault 1), with T1Open circuit failure, as an example, i1Forward directionCan not flow through T1Switches but via D2And then follow current. At this time, the primary side voltage of the high-frequency transformer is zero. And in the reverse direction, i1And power is still transmitted according to a path under a normal working condition, so that negative direct current bias current on a fault side is caused. In addition, the direct current bias current is introduced to the rectification side through single phase shift modulation control, so that corresponding negative direct current bias current is generated. This dc bias will be gradually dissipated to zero by the parasitic resistance of the secondary side of the high frequency transformer, at which point the DAB-converter enters a new steady state. The primary and secondary magnetic fluxes in the formula (1) become
Figure BDA0002663153600000081
In the formula i1acAnd i2acAre respectively i1And i2Of the ac component. I isbiasT1Is i1A dc bias component of (1). This unbalanced flux will cause the high frequency transformer core to saturate. Meanwhile, in this fault state, the corresponding i1The peak current and the dc bias current are respectively:
Figure BDA0002663153600000082
Figure BDA0002663153600000083
wherein D is the phase shift angle of the original secondary side, and k is U1And nU2The ratio of (2) is used to define the primary and secondary voltage matching degree. When the primary and secondary side voltages are completely matched, k is 1. New steady state after fault, i1The peak current becomes 2 times of the normal working condition, and the safety of other non-fault components on the inversion side is threatened. DAB at T1The corresponding voltage, current and power waveforms at open circuit fault are shown in fig. 3. The current flow paths in the respective switching states are shown in the following table.
Figure BDA0002663153600000084
In the same way, when T4The same results can be obtained when an open circuit fault occurs.
Similarly, when T is2Or T3When open-circuit fault occurs, the fault is in i1Introducing forward DC bias current, other fault characteristics and T1The open circuit fault characteristics are consistent.
When the IGBT open-circuit fault occurs on the rectification side, T is used5Open circuit failure, as an example, i2Reverse direction can not flow through T5Switches but via D6And then follow current. At this time, the secondary side voltage of the high-frequency transformer is zero. While in the forward direction, i2And power is still transmitted according to a path under a normal working condition, so that negative direct current bias current on a fault side is caused. In addition, the direct current bias current can also be introduced to the inversion side through single phase shift modulation control, so that corresponding negative direct current bias current is caused. The dc bias will be gradually consumed to zero by the parasitic resistance of the primary side of the high frequency transformer, at which time the DAB converter enters a new steady state. The primary and secondary magnetic fluxes in the formula (1) become
Figure BDA0002663153600000091
In the formula i1acAnd i2ac are each i1And i2Of the ac component. I isbiasT5Is i2A dc bias component of (1). This unbalanced flux will cause the high frequency transformer to magnetically saturate. Meanwhile, in this fault state, the corresponding i2The peak current and the dc bias current are respectively:
Figure BDA0002663153600000092
Figure BDA0002663153600000093
new steady state after fault, i1The peak current becomes 2 times of the normal working condition, and the safety of other non-fault components on the inversion side is threatened.
DAB at T5The corresponding voltage, current and power waveforms at open circuit fault are shown in fig. 4. The current flow paths in the respective switching states are shown in the following table.
Figure BDA0002663153600000094
Figure BDA0002663153600000101
When T is8The same results can be obtained when an open circuit fault occurs.
Similarly, when T is6Or T7When open-circuit fault occurs, the fault is in i2Introducing forward DC bias current, other fault characteristics and T5The open circuit fault characteristics are consistent.
Fig. 5 is a flowchart of a fault-tolerant control method according to an embodiment of the present invention, and fig. 6 is a control block diagram of the fault-tolerant control method according to an embodiment of the present invention.
In this embodiment, in order to compensate for the dc bias current caused by the IGBT open-circuit fault, the proposed fault-tolerant operation control scheme needs to collect the dc bias current on the fault side, and inject the preset compensation dc current on the non-fault side in a closed-loop control manner, so as to ensure that the magnetic flux in the isolation transformer has no dc component. Preferably, in order to ensure that the power device and the transformer operate within the rated current stress range, the actual current i of the primary side and the secondary side of the high-frequency transformer is acquired in real time1And i2To rated current i1ratedAnd i2ratedAnd determining whether the original secondary side phase shift angle of the DAB needs to be adjusted or not.
In the preferred embodiment, when the double-active-bridge DC-DC converter has an IGBT open-circuit fault on the inversion side, after the fault diagnosis and positioning process, the straight line of the inversion side after the phase shift angle D is changed is extractedFlowing a bias current I'biasT1Calculating the compensation DC current I to be injected at the rectifying sideDC2，
Figure BDA0002663153600000102
When open-circuit fault occurs at T1Or T4When the switch is switched on or off,
if i1<i1ratedThe phase shift angle D does not need to be changed, and only the compensating direct current needs to be injected into i2In the method, the magnetic fluxes generated by the direct current in the primary side and the secondary side of the compensated high-frequency transformer are respectively as follows:
Figure BDA0002663153600000103
in the formula (11), after compensation, the magnetic fluxes generated by the dc bias currents on the two sides can be cancelled out, thereby preventing the magnetic core of the high-frequency transformer from being saturated.
If i1>i1ratedThe phase shift angle D is reduced to half of the initial value, and the required compensation direct current is injected into the i2The same compensation result can be obtained, and the saturation of the high-frequency transformer magnetic core and the overcurrent of system elements are avoided.
Similarly, when an open-circuit fault occurs at T2Or T3When switching, firstly according to i1And i1ratedMagnitude, determining if the phase shift angle needs to be changed, and then injecting a reverse compensating DC current into i according to (10)2The same compensation result can be obtained, and the saturation of the high-frequency transformer magnetic core and the overcurrent of system elements are avoided.
Further, when the double-active-bridge DC-DC converter has an IGBT open-circuit fault on the rectifying side, after fault diagnosis and positioning processes, extracting the direct current bias current I 'of the rectifying side after the phase shift angle D is changed'biasT5Calculating the compensation DC current I to be injected at the inversion sideDC1，
Figure BDA0002663153600000111
When open-circuit fault occurs at T5Or T8When the switch is switched on or off,
if i2<i2ratedThe phase shift angle D does not need to be changed, and only the compensating direct current needs to be injected into i1In the middle, the magnetic fluxes generated by the DC current in the primary side and the secondary side of the compensated high-frequency transformer are respectively,
Figure BDA0002663153600000112
in the formula (13), the magnetic fluxes generated by the dc bias current on both sides can be cancelled out, thereby preventing the magnetic core of the high-frequency transformer from being saturated.
If i2>i2ratedThe phase shift angle D is reduced to half of the initial value, and a compensating direct current is injected into the phase shift angle I1The same compensation result can be obtained, and the saturation of the high-frequency transformer magnetic core and the overcurrent of system elements are avoided.
Similarly, when an open-circuit fault occurs at T6Or T7When switching, firstly according to i2And i2ratedMagnitude, determining if the phase shift angle needs to be changed, and then injecting a compensating DC current into i according to (12)1The same compensation result can be obtained, and the saturation of the high-frequency transformer magnetic core and the overcurrent of system elements are avoided.
Next, MATLAB/Simulink software is adopted to carry out simulation verification on the control strategy, and an inversion side U1And a rectification side U2A40V direct current voltage source is connected, and the parameters are shown in the following table.
Parameter(s) Numerical value
Capacity of the device 430W
DC voltage U at inverter side1 40V
DC voltage U at rectifying side2 40V
High-frequency transformer turn ratio n 1:1
Leakage inductance L of high-frequency transformerr 77.54μH
Rectifying side DC capacitor CL 10mF
The simulation process is as follows:
when T is 0s, starting the DAB converter, and adopting a traditional single phase-shift modulation control strategy;
when T is 0.1s, the DAB converter reaches a steady-state operation working state, and the phase shift angle D is 0.212;
scene 1 (inversion side T)1Open circuit fault):
when T is 0.2s, T is activated1A failure;
when T is 1.401s, the fault-tolerant operation control of the inverter side is put into operation;
when T is 2.75s, the simulation ends.
The simulation results are shown in fig. 7 and 8.
Scene 2 (rectifying side T)5Open circuit fault):
when T is 0.2s, T is activated5A failure;
when T is 1.401s, switching into the fault-tolerant operation control of the rectification side;
when T is 2.75s, the simulation ends.
The simulation results are shown in fig. 9 and 10.
FIG. 7 is a graph of the high frequency transformer field current at inverter side fault, as seen at T, in one embodiment1In the open fault condition (after 0.2 s), the excitation current in the embodiment is dc biased. After an inverter-side fault-tolerant operation control strategy is put into operation, the direct current bias in the exciting current is eliminated, and the magnetic saturation of the high-frequency transformer is avoided;
FIG. 8a shows an embodiment of an inverter side T1According to the curve of alternating current voltage at the rectifying side and alternating current at the primary side and the secondary side under the fault, after the fault occurs and the fault-tolerant operation control condition of the inversion side is not started, the peak value of the alternating current at the fault side is increased to 2 times under the normal working condition, after the fault-tolerant operation control at the inversion side is started in 1.401s, by reducing half phase shift angle and injecting compensation direct current at the non-fault side, magnetic fluxes generated by direct currents at two sides are mutually offset, the saturation of a magnetic core of a high-frequency transformer is avoided, the peak value of the alternating current at the fault side can be controlled within a rated range, and the safety of devices at the fault side is;
FIG. 8b shows an embodiment of the inverter side T1Under the fault, the AC voltage at the rectifying side and the AC current at the primary side and the secondary side are expanded to form a curve under the normal state, and the current at the primary side and the secondary side has no DC component;
FIG. 8c shows an embodiment of an inverter side T1Under the fault, the alternating voltage at the rectifying side and the alternating current at the primary side and the secondary side are expanded to form curves under the fault state (a fault-tolerant operation control scheme is not started), the alternating current at the fault side is subjected to direct current bias, the peak value of the alternating current is increased to 2 times under the normal working condition, and the alternating current at the non-fault side is unchanged and conforms to the theory;
FIG. 8d shows an embodiment of the inverter side T1The curve is developed under the fault state of alternating voltage at the rectifying side and alternating current at the primary side and the secondary side under the fault (starting fault-tolerant operation control scheme), so that the magnetic fluxes generated by the direct currents at the two sides are mutually offset by reducing half phase shift angle and injecting compensation direct current at the non-fault side, and the high-frequency transformation is avoidedThe transformer core is saturated, consistent with theory.
FIG. 9 shows an embodiment of a rectifying side T5The exciting current curve of the fault high-frequency transformer can be seen in T5In the open fault condition (after 0.2 s), the excitation current in the embodiment is dc biased. After a fault-tolerant operation control strategy at the rectifying side is put into operation, the direct current bias in the exciting current is eliminated, and the magnetic saturation of the high-frequency transformer is avoided.
FIG. 10a shows an embodiment of a rectifying side T5According to the curve of the alternating current at the inverse side and the alternating current at the primary side and the secondary side under the fault, after the fault occurs and the fault-tolerant operation control condition at the rectification side is not started, the peak value of the alternating current at the fault side is increased to 2 times under the normal working condition, after the fault-tolerant operation control at the inverse side is started at 1.401s, the magnetic fluxes generated by the direct currents at the two sides are mutually offset by reducing half phase shift angle and injecting compensation direct current at the non-fault side, the saturation of the magnetic core of the high-frequency transformer is avoided, the peak value of the alternating current at the fault side can be controlled within a rated range, and the safety of devices at the fault;
FIG. 10b shows an embodiment of a rectifying side T5Under the fault, the AC voltage at the inverse side and the AC current at the primary side and the secondary side are expanded to form a curve under the normal state, and the current at the primary side and the secondary side has no DC component;
FIG. 10c shows an embodiment of a rectifying side T5Under the fault, the alternating voltage at the inverse side and the alternating current at the primary side and the secondary side are expanded to form a curve under the fault state (a fault-tolerant operation control scheme is not started), the direct current bias is generated on the fault detection alternating current, the peak value of the direct current is increased to 2 times under the normal working condition, and the alternating current at the non-fault side is unchanged and conforms to the theory;
FIG. 10d shows an embodiment of a rectifying side T5Under the fault, the curve is developed under the fault state of the alternating voltage at the inverse transformation side and the alternating current at the primary side and the secondary side (starting the fault-tolerant operation control scheme), and it can be seen that by reducing half phase shift angle and injecting compensation direct current at the non-fault side, the magnetic fluxes generated by the direct currents at the two sides are mutually offset, so that the magnetic core saturation of the high-frequency transformer is avoided, and the theory is consistent. The fault tolerant control method described above is still applicable when the power is reversed.
In the isolated dc converter of the above embodiment, when the active bridge power device on one side fails: (1) if the power device and the transformer continuously operate at the moment, due to the working mode and the operating characteristics of the power device and the transformer, a direct current component appears at a port of the transformer at the fault side, in order to ensure that the power device and the transformer operate within a rated current stress range, rated transmission power is reduced according to rated limiting conditions, and the current of the transformer and the power device is ensured to be limited within the rated range by changing a phase shifting angle; (2) in addition, the fault side transformer winding introduces a direct current component to cause the saturation of the magnetic core of the transformer, and the reverse direct current component is actively injected through the non-fault side transformer port to offset the direct current flux caused by the introduction of the direct current component at the fault side, so that the magnetic core of the high-frequency transformer is prevented from being saturated.
The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, and not to limit the invention. Any modifications and variations within the scope of the description, which may occur to those skilled in the art, are intended to be within the scope of the invention.

Claims (10)

1. An isolated dc converter, comprising: a high frequency transformer and bridge structures on both sides thereof; wherein the content of the first and second substances,
one side bridge structure is an inversion side, and the other side bridge structure is a rectification side;
when the inversion side has a fault, the rectification side injects a first preset compensation direct current;
when the rectifying side has a fault, the inverting side injects a second preset compensation direct current.
2. The isolated DC converter according to claim 1, wherein the primary and secondary side currents of the inverting side are i1The primary and secondary side current of the rectifying side is i2(ii) a Wherein the content of the first and second substances,
when the inverter side fails, i1Not exceeding rated current value i1ratedTime, phase shift angle holdOriginal parameter values; otherwise the phase shift angle is decreased to achieve reduced power operation;
when the rectifying side fails, i2Not exceeding rated current value i2ratedThen, the phase shifting angle keeps the original parameter value; otherwise the phase shift angle is decreased to achieve reduced power operation.
3. The isolated dc converter of claim 2, wherein said phase shift angle reduction to achieve reduced power operation is further: the phase shift angle is reduced to half of the original parameter value to realize reduced power operation.
4. The isolated DC converter according to any one of claims 1 to 3, wherein the isolated DC converter has a front end voltage of U1The back end voltage is U2；
The bridge structure positioned at the front end of the isolated DC converter is an inversion side, and the bridge structure positioned at the rear end of the isolated DC converter is a rectification side;
when T on the inverting sideiWhen an open-circuit fault occurs, the first preset compensation direct current IDC2Comprises the following steps:
Figure FDA0002663153590000011
when T of the rectifying sidejWhen an open-circuit fault occurs, the second preset compensation direct current IDC1Comprises the following steps:
Figure FDA0002663153590000012
wherein n is the primary and secondary side turn ratio of the high-frequency transformer,
Figure FDA0002663153590000013
is i1The current of the direct current bias is used,
Figure FDA0002663153590000014
is i2A direct current bias current.
5. The isolated DC converter according to claim 4, wherein the bridge structure on both sides is a double-sided active H-bridge, or a double-sided midpoint clamped active bridge, or a one-side midpoint clamped active bridge and another-side active H-bridge.
6. A fault tolerance control method for an isolated DC converter is characterized by comprising the following steps:
s61: positioning the fault according to the fault characteristics, and judging whether the fault occurs on the inversion side or the rectification side;
s62: when a fault occurs on the inversion side, injecting a first preset compensation direct current on the rectification side;
and when the fault occurs on the rectifying side, injecting a second preset compensation direct current on the inverting side.
7. The fault-tolerant control method for the isolated DC converter according to claim 6, wherein the step S62 is preceded by:
s71: when a fault occurs on the inversion side, the primary and secondary side current i1 of the inversion side does not exceed the rated current value i1ratedThen, the phase shifting angle keeps the original parameter value; otherwise, reducing the phase shifting angle to realize reduced power operation;
when a fault occurs on the rectifying side, the primary side current i2 and the secondary side current i2 on the rectifying side do not exceed the rated current value i2ratedThen, the phase shifting angle keeps the original parameter value; otherwise, the phase shift angle is reduced to achieve reduced power operation.
8. The isolated dc converter fault tolerant control method of claim 7, wherein said reducing said phase shift angle to achieve reduced power operation in S71 is further comprising: and reducing the phase shifting angle to half of the original parameter value to realize reduced power operation.
9. The fault-tolerant control method for the isolated DC converter according to any one of claims 6 to 8, wherein the voltage at the front end of the isolated DC converter is U1The back end voltage is U2；
The bridge structure positioned at the front end of the isolated DC converter is an inversion side, and the bridge structure positioned at the rear end of the isolated DC converter is a rectification side;
when T on the inverting sideiWhen an open-circuit fault occurs, the first preset compensation direct current IDC2Comprises the following steps:
Figure FDA0002663153590000021
when T of the rectifying sidejWhen an open-circuit fault occurs, the second preset compensation direct current IDC1Comprises the following steps:
Figure FDA0002663153590000031
wherein n is the primary and secondary side turn ratio of the high-frequency transformer,
Figure FDA0002663153590000032
is a dc bias current of i1,
Figure FDA0002663153590000033
is i2 dc bias current.
10. The fault-tolerant control method for the isolated DC converter according to claim 9, wherein the bridge structures on both sides of the isolated DC converter are double-sided active H-bridges, or double-sided midpoint clamped active bridges, or one-side midpoint clamped active bridge and the other-side active H-bridge.
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