CN115549477A - ISOP type medium-voltage direct-current converter and DC-link capacitor state monitoring method thereof - Google Patents

ISOP type medium-voltage direct-current converter and DC-link capacitor state monitoring method thereof Download PDF

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CN115549477A
CN115549477A CN202211276011.3A CN202211276011A CN115549477A CN 115549477 A CN115549477 A CN 115549477A CN 202211276011 A CN202211276011 A CN 202211276011A CN 115549477 A CN115549477 A CN 115549477A
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link capacitor
circuit
voltage
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帅智康
王泉洁
彭英舟
王伟
李杨
赵崇宇
陈浩杰
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Hunan 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
    • H02M3/01—Resonant DC/DC converters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
    • G01R27/2605—Measuring capacitance
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/64—Testing of capacitors
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
    • H02M1/0074—Plural converter units whose inputs are connected in series
    • 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
    • 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
    • H02M3/285—Single converters with a plurality of output 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
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33573—Full-bridge at primary side of an isolation transformer
    • 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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  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Dc-Dc Converters (AREA)

Abstract

An ISOP type medium-voltage direct-current converter and a DC-link capacitor state monitoring method thereof are disclosed, the ISOP type medium-voltage direct-current converter comprises N full-bridge LLC resonant converters with input sides sequentially connected in series and output sides connected in parallel, the input side of one full-bridge LLC resonant converter is connected in parallel with a switching tube Q and an RC circuit to form a fault tolerance control redundant module, the input sides of the rest N-1 full-bridge LLC resonant converters are respectively connected in parallel with a switching tube Q and an RC circuit to form N-1 normally working sub-modules, and the RC circuit is a DC-link capacitor C in And a bleeder resistor R in A circuit connected in parallel. When the system works normally, all the sub-modules are put into use, and the redundant module is cut out; during fault tolerance control, the redundant module is put into use, all the sub-modules are sequentially replaced and cut out, when each sub-module is cut out, the RC circuit of the sub-module is isolated from the main circuit, and the DC-link capacitor C in the discharging process of the RC circuit is obtained in Processing the voltage measurement data to estimate the DC-link capacitor C in The capacitance value of (2).

Description

ISOP type medium-voltage direct-current converter and DC-link capacitor state monitoring method thereof
Technical Field
The invention relates to the technical field of state monitoring of direct current converters, in particular to an ISOP (input-side-coupled-output) type medium-voltage direct current converter and a DC-link capacitor state monitoring method thereof.
Background
A subsea observation network power conversion system generally comprises: shore-based medium-voltage direct-current conversion DC/DC, photoelectric composite submarine cables and underwater medium-voltage direct-current conversion DC/DC. The traditional DC/DC conversion technology has developed well, and is limited by the manufacturing technology of power electronic devices, these DC converters cannot be directly applied to medium voltage DC occasions, but the basic DC/DC is used as a power module, and the conversion between medium and high voltage and low voltage can be realized through series-parallel combination, wherein, the LLC resonant converter with input series-output parallel (ISOP) is a reliable medium voltage DC converter structure.
There is a large amount of capacitance in the modular DC-DC converter and its high failure rate is a serious threat to the reliable operation of the converter. If the DC-Link at the input side of the module fails, the system cannot suppress the ripple voltage within a required range, and meanwhile, the system serving as an energy storage Link cannot provide ideal power decoupling and power failure protection performance. If the filter capacitor on the output side of the module fails, the quality of the output voltage waveform cannot be ensured, the ripple amplitude is large, and the system efficiency is low. Therefore, accurate real-time monitoring of the capacitor running state is of great significance to reliable running of the system.
At present, the state monitoring research of the direct-current side capacitor is mainly developed aiming at various single converters, the research facing a modular system is started soon, and the research object is single. In the traditional monitoring method, the method can be divided into a periodic small signal ripple-based method, an aperiodic large signal charge-discharge curve-based method and a black box model-based method according to the principle. In recent years, a neural network method based on a black box model has just emerged, but the application of the neural network method is limited by a large amount of training and uncertainty of actual working conditions. The specific method based on the periodic small signal ripple principle mainly comprises a circuit model analysis method and a signal injection method, but in practical application, the circuit model analysis method is difficult in voltage ripple signal extraction and complex in modeling, more interference exists in practical working conditions, the precision is difficult to guarantee, and meanwhile once topology and working conditions change, modeling needs to be carried out again, and calculation is complex; the signal injection method influences the normal operation of the system to a certain extent, and the introduction of a large number of digital filters undoubtedly increases the burden of a control system. The process after the system is shut down needs to be modeled based on the non-periodic large-signal charge-discharge curve, ripple voltage information is not needed, the operation state of the converter is changed, and monitoring is carried out in the start-stop process, which is usually not allowed.
Disclosure of Invention
The technical problem to be solved by the invention is to provide an ISOP type medium-voltage direct-current converter and a DC-link capacitor state monitoring method thereof, wherein the method is simple and effective, and can be used for monitoring the state of the DC-link capacitor of each submodule on the premise of not interrupting the integral operation of the converter.
In order to solve the technical problems, the invention adopts the following technical scheme.
The input sides of the N full-bridge LLC resonant converters are sequentially connected in series and the output sides of the N full-bridge LLC resonant converters are connected in parallel, the input side of one full-bridge LLC resonant converter is connected with a switching tube Q and an RC circuit in parallel to form a fault tolerance control redundant module, the input sides of the rest N-1 full-bridge LLC resonant converters are respectively connected with a switching tube Q and an RC circuit in parallel to form N-1 normally-working sub-modules, and the RC circuit is a DC-link capacitor C in And a bleeder resistor R in A circuit connected in parallel.
Preferably, the DC-link capacitor C in Is a metal film capacitor.
In order to solve the above technical problem, the present invention adopts another technical solution as follows.
A method for monitoring the state of a DC-link capacitor of an ISOP type medium-voltage direct-current converter comprises the following steps:
s1, sequentially replacing sub-modules in the work of the redundant module, cutting out one sub-module each time, isolating an RC circuit of the sub-module from a main circuit, and acquiring a DC-link capacitor C in the discharging process of the RC circuit in Voltage measurement data of (a);
step S2, the DC-link capacitor C obtained in the step S1 is processed in Processing the voltage measurement data to estimate the DC-link capacitance C in The capacitance value of (c).
Further, in step S1, the process of sequentially replacing the sub-modules in operation by the redundant module is as follows: firstly, a switch tube Q at the input side of a redundancy module is turned off, the redundancy module is put into use, meanwhile, a switch tube Q at the input side of a first submodule is conducted, a power switch tube of a full-bridge LLC resonant converter in the first submodule is turned off, and the first submodule is cut out; and then switching off a switching tube Q at the input side of a first submodule, switching in the first submodule, simultaneously switching on a switching tube Q at the input side of a second submodule, switching off a power switching tube of a full-bridge LLC resonant converter in the second broken submodule, switching out the second submodule, and so on until an N-1 th submodule is switched in, switching out a redundant module, and restoring the LLC resonant converter to normal operation.
Further, in step S1, after each sub-module is put into use, the full-bridge LLC resonant converter will keep the switching frequency unchanged, and adjust the output voltage by adjusting the phase shift angle between the diagonal switching tubes.
Furthermore, in step S1, the obtained voltage measurement data is n DC-link capacitors C of the RC circuit of the sub-module in one discharge cycle in Voltage data.
Further, in step S2, the DC-link capacitor C is subjected to in Processing the voltage measurement data to estimate the DC-link capacitance C in Electricity (D) fromThe process of capacity is as follows:
step S201, extracting a voltage amplitude data sequence and a time data sequence based on n voltage data of an RC circuit of a submodule in a discharge period, and filtering and cleaning abnormal points of the data;
step S202, carrying out logarithmic conversion on the voltage amplitude data sequence, so as to convert the voltage amplitude data sequence from an exponential model to a linear model;
step S203, according to a least square method, representing the form of an analytic solution by a most-valued condition, and substituting the analytic solution into a voltage amplitude data sequence converted into a linear model to solve to obtain a capacitance estimation value;
further, in step S203, the least square method is any one of a minimum mean value two-product algorithm, a recursive least square algorithm, and an iterative least square algorithm.
Still further, for the DC-link capacitor C in Processing the voltage measurement data to estimate the DC-link capacitance C in The process of capacitance value of (a) further comprises: step S204, the capacitance estimated value is corrected according to the influence of the environment temperature.
Preferably, in step S204, the formula for correcting the capacitance estimation value is as follows:
Figure BDA0003896680650000031
wherein alpha is M 、β M 、γ M The three temperature characteristic parameters can be measured through experiments for the capacitors with specific types; t is a unit of a 、T a，min 、T a,max Respectively representing the actual operating temperature, the minimum operating temperature and the maximum operating temperature of the capacitor.
The invention provides an ISOP (inter-integrated Circuit) -type medium-voltage direct-current converter and a DC-link capacitor state monitoring method thereof, which are mainly applied to a medium-voltage high-frequency DC/DC converter, are deployed and implemented once every month or half month, do not need to interrupt the overall operation of the converter, mainly utilize a redundancy module to traverse sub-modules in switching work, monitor the states of DC-link capacitors of the switched sub-modules, and estimate capacitance values by acquiring voltage data of the DC-link capacitors during discharging. The method is based on the low sampling frequency and the charge-discharge curve of the data, avoids high-frequency sampling of ripples, does not need additional hardware circuits and sensors, is low in cost and high in reliability, and is based on the data algorithm of a filter and least square to carry out parameter estimation, so that the estimation accuracy is high. In conclusion, the method provided by the invention is simple and effective, and can be used for monitoring the state of the DC-link capacitor of each submodule on the premise of not interrupting the overall operation of the converter.
Drawings
Fig. 1 is a topology diagram of an iso p type medium voltage dc converter according to the present embodiment;
FIG. 2 is a time distribution diagram of the switching mode in the present embodiment (v in the figure) gs Representing the gate-source voltage of the power switch tube);
FIG. 3 is a flow chart of a traversal switching process of sub-modules of the present invention;
FIG. 4 is an equivalent circuit diagram of the DC-link capacitor of the present invention when discharging;
FIG. 5 is a graph showing the discharge of the DC-link capacitor in this embodiment under different aging conditions;
fig. 6 is an experimental waveform diagram of a prototype in the present embodiment.
Detailed Description
In order to facilitate understanding of those skilled in the art, the present invention is further described below with reference to the following examples and the accompanying drawings, which are not intended to limit the present invention.
In a high-power medium-voltage direct-current scene, in order to reduce the voltage stress of a switching tube, an ISOP type medium-voltage direct-current transformer is formed by connecting a plurality of converters with the same structure in series at the input side and in parallel at the output side. Furthermore, the output power of each module is only 1/n of the total output power of the system, which is beneficial to reducing the design difficulty of each module. The input voltage of each module is 1/n of the input bus voltage, and the voltage borne by the switch tube in the module is also reduced to the original 1/n, so that a proper switch tube is convenient to select. Based on the structural characteristics, the invention provides an ISOP type medium-voltage direct-current converter which is convenient for monitoring the state of a DC-link capacitor, and the ISOP type medium-voltage direct-current converter is as follows.
Taking N =4 as an example, the present embodiment provides an iso p type medium voltage dc converter, which includes three normally operating sub-modules and a redundant module for implementing fault tolerant control, where the three sub-modules are connected in series with an input side and in parallel with an output side of the redundant module. When the system works normally, all the three sub-modules are put into use, and the redundant module is switched out; during fault tolerance control, the redundant module is put into use, the three sub-modules are sequentially replaced and switched out, and when each sub-module is switched out, the DC-link capacitor state of the sub-module is monitored. The three sub-modules and one redundant module have the following specific structure.
As shown in fig. 1, the sub-modules and the redundant module each include a full-bridge LLC resonant converter, and each full-bridge LLC resonant converter includes four parts, i.e., a switch network, a resonant network, a transformer, and a rectifier filter network. In FIG. 1, V in 、R L The input voltage and the load resistance of each full-bridge LLC resonant converter are respectively.
A first sub-module: the input side of the full-bridge LLC resonant converter is connected in parallel with a switching tube Q 1 And a DC-link capacitor C connected in parallel in1 And a bleeder resistor R in1 And forming an RC circuit. The switching network of the full-bridge LLC resonant converter comprises a power switch tube S 11 ～S 41 And a body diode D 11 ～D 41 The resonant network comprising a resonant capacitor C r1 Resonant inductor L r1 And an excitation inductance L m1 The transformer is T 1 (the turn ratio of the primary side to the secondary side is m: 1), the rectification filter network comprises a rectifier diode D 51 ～D 81 Composed rectifier bridge and filter output capacitor C connected with the rectifier bridge in parallel f1 。
A second sub-module: the input side of the full-bridge LLC resonant converter is connected in parallel with a switching tube Q 2 And a DC-link capacitor C connected in parallel in2 And a bleeder resistor R in2 And forming an RC circuit. The switching network of the full-bridge LLC resonant converter comprises a power switch tube S 12 ～S 42 And a body diode D 12 ～D 42 The resonant network comprising a resonant capacitor C r2 Resonant inductor L r2 And an excitation inductance L m2 The transformer is T 2 (the turn ratio of the primary side to the secondary side is m: 1), the rectifying filter network comprises a rectifying diode D 52 ～D 82 Composed rectifier bridge and filter output capacitor C connected with the rectifier bridge in parallel f2 。
A third submodule: the input side of the full-bridge LLC resonant converter is connected in parallel with a switching tube Q 3 And a DC-link capacitor C connected in parallel in3 And a bleeder resistor R in3 And forming an RC circuit. The switch network of the full-bridge LLC resonant converter comprises a power switch tube S 13 ～S 43 And a body diode D 13 ～D 43 The resonant network comprising a resonant capacitor C r3 Resonant inductor L r3 And an excitation inductance L m3 The transformer is T 3 (the turn ratio of the primary side to the secondary side is m: 1), the rectifying filter network comprises a rectifying diode D 53 ～D 83 Composed rectifier bridge and filter output capacitor C connected with the rectifier bridge in parallel f3 。
A redundancy module: the input side of the full-bridge LLC resonant converter is connected in parallel with a switching tube Q 4 And a DC-link capacitor C connected in parallel in4 And a bleeder resistor R in4 And forming an RC circuit. The switch network of the full-bridge LLC resonant converter comprises a power switch tube S 14 ～S 44 And a body diode D 14 ～D 44 The resonant network comprising a resonant capacitor C r4 Resonant inductor L r4 And an excitation inductance L m4 The transformer is T 4 (the turn ratio of the primary side to the secondary side is m: 1), the rectifying filter network comprises a rectifying diode D 54 ～D 84 Composed rectifier bridge and filter output capacitor C connected with the rectifier bridge in parallel f4 。
The aforementioned DC-link capacitor C in1 ～C in4 Are all metalThe film capacitor can provide good balance performance for the application of high-voltage direct current occasions in the full-bridge LLC resonant converter. In general, when analyzing the degradation index of a metal film capacitor, a capacitance value C is often defined as the most critical electrical parameter, and typical end-of-life criteria defined by the capacitance value C are: the capacitance value C decays to 95% of the initial value, so an accurate estimate of the capacitance value is crucial for the state monitoring of the DC-link capacitor.
In this embodiment, the full-bridge LLC resonant converters of each sub-module and the redundant module keep the switching frequency unchanged during operation, and adjust the output voltage (i.e. phase shift control) by adjusting the phase shift angle between the diagonal power switch tubes, in this operating mode, as shown in fig. 2, the full-bridge LLC resonant converter has ten switching modes in one switching period, taking the full-bridge LLC resonant converter of the first sub-module as an example, and these are respectively:
switching mode 1,t 0 ～t 1 : at t 0 Time of day, switching power tube S 21 Zero voltage on, transformer T 1 The primary side bears forward voltage, the body diode D 11 And D 41 Conduction, the excitation inductance L m1 The voltages at both ends are clamped by the output voltage and do not participate in resonance, and the exciting current i m1 And (4) increasing linearly. Resonant current i at this stage r1 And an excitation current i m1 Is passed through a transformer T 1 Energy is transferred to the output side.
Switching mode 2,t 1 ～t 2 : at t 1 Time of day, switching power tube S 31 Zero voltage turn-off, resonant current i r1 For switching power tube S 31 Junction capacitance C 31 Charging and simultaneously providing the switching power tube S 41 Junction capacitance C of 41 And (4) discharging. To t 2 At that time, due to the body diode D 41 Has been turned on and can then be turned on at zero voltage. At this stage due to v ab (representing the bridge arm midpoint voltage) is decreasing, so the resonant current i r1 And decreases rapidly.
Switching mode 3,t 2 ～t 3 : from t 2 Time v ab Reduced to 0 and maintained unchangedSo that the input source does not supply energy, but the cavity still transfers energy to the secondary side, rectifying diode D 51 And D 81 The energy transferred is completely provided by the resonant cavity, so that the resonant current i r1 And decreases rapidly.
Switching mode 4,t 3 ～t 4 : at t 3 Time of day, resonant current i r1 Down to and with the excitation current i m1 Equal transformer T 1 No longer transmitting energy to the secondary side, body diode D 11 And D 41 Current natural zero-crossing turn-off, resonant capacitor C r1 Resonant inductor L r1 And an excitation inductance L m1 -play a part in resonance.
Switching mode 5,t 4 ～t 5 : at t 4 Time of day, switching power tube S 21 Zero voltage turn-off, resonant current i r1 For switching power tube S 21 Junction capacitance C 21 Charging and simultaneously providing the switching power tube S 11 Junction capacitance C 11 Discharging; to t 5 Time of day, switching power tube S 11 Junction capacitance C 11 Falling to 0, body diode D 21 And D 31 And starting to conduct, and switching on at zero voltage.
t 5 After the moment the full bridge LLC resonant converter enters another half cycle, the operation is similar to the half cycle described above.
The invention provides an ISOP type medium-voltage direct-current converter with the structure, which aims to facilitate monitoring of the state of a DC-link capacitor, therefore, based on the ISOP type medium-voltage direct-current converter comprising a redundancy module, the invention further deploys a DC-link capacitor state monitoring method of the ISOP type medium-voltage direct-current converter, and the core of the method is as follows: the redundant module can sequentially replace the sub-modules in work, after the sub-modules are cut out, the DC-link capacitor is in a discharge state, and during the discharge period, the voltage V of the DC-link capacitor is shown in the following formula (2) mppf In exponential form, based on the DC-link capacitor voltage V mppf And (5) carrying out parameter identification on the model by the data to obtain the DC-link capacitance C. In connection with this, the equivalent circuit of the DC-link capacitor when discharging is shown in FIG. 4, where R is ESR Representing the equivalent series resistance of a capacitorCan be obtained by parameter identification, R eq The equivalent resistance of the discharge circuit can be obtained by the resistance value of the discharge circuit resistor, V dc Representing the input side dc bus voltage.
Figure BDA0003896680650000071
It is worth mentioning that capacitor state monitoring is a technology for detecting the state of health of a capacitor in a direct current converter, and the low fault cost and long-time reliable operation of a system can be guaranteed by adopting preventive maintenance before a fault of a DC-link capacitor occurs. For the medium-high voltage direct current converter without frequent interruption, the utilization rate of the redundancy module in the normal operation period is improved, and the discharge process of the sub-module is constructed to carry out electric DC-link container monitoring on the premise of not interrupting the overall operation of the converter.
According to the method for monitoring the DC-link capacitor state of the ISOP type medium-voltage direct-current converter, the implementation frequency of capacitor state monitoring is one month or half month, and the implementation process of the method is shown in figure 3 and mainly comprises two steps, specifically as follows.
S1, switching submodules to obtain DC-link capacitor voltage measurement data.
S101, switching off the parallel switch tubes Q at the input side of the redundant module 4 Switching in the redundant module and simultaneously conducting the switching tube Q at the input side of the first submodule 1 And turning off the power switch tube S of the full-bridge LLC resonant converter in the first sub-module 11 ～S 41 Cutting out a first sub-module, wherein an RC circuit of the first sub-module is isolated from a main circuit, and obtaining n DC-link capacitors C of the RC circuit in one discharge cycle in1 Voltage data.
S102, turning off a switching tube Q at the input side of the first submodule 1 And starting the phase shift control of the full-bridge LLC resonant converter, inputting the first sub-module, and simultaneously conducting a switching tube Q at the input side of the second sub-module 2 And turning off a power switch tube S of a full-bridge LLC resonant converter in the second sub-module 12 ～S 42 Cutting intoAnd (4) a second sub-module is arranged, the RC circuit of the second sub-module is isolated from the main circuit, and n DC-link capacitors C of the RC circuit in one discharge cycle are obtained in2 Voltage data.
S103, turning off a switching tube Q at the input side of the second submodule 2 And starting the full-bridge LLC resonant converter phase shift control thereof, inputting the second submodule and simultaneously conducting a switching tube Q at the input side of the third submodule 3 And turning off the power switch tube S of the full-bridge LLC resonant converter in the third sub-module 13 ～S 43 Cutting out a third sub-module, isolating an RC (resistor-capacitor) circuit of the third sub-module from a main circuit, and acquiring n DC-link capacitors C of the RC circuit in one discharge cycle in3 Voltage data.
S104, switching off a switching tube Q at the input side of the third submodule 3 And starting the full-bridge LLC resonant converter to perform phase shift control, inputting a third sub-module, and simultaneously conducting a switching tube Q at the input side of the redundancy module 4 And turning off the power switch tube S of the full-bridge LLC resonant converter in the redundant module 14 ～S 44 And switching out the redundancy module, and restoring the LLC resonant converter to work normally.
It is worth mentioning that in each independent stage of the foregoing S101 to S103, the redundant module replaces a sub-module, an RC discharge circuit is created for the DC-link capacitor in the switching-out process of the sub-module, for the independent RC circuit, the energy stored in the capacitor is dissipated through the resistor, and the discharge curve includes the capacitance information sampled by the existing voltage sensor.
Step S2, processing the DC-link capacitor C in Voltage measurement data, estimating DC-link capacitance C in The capacitance value of (the first submodule is explained as an example in the following).
Step S201, n DC-link capacitors C in one discharge period based on RC circuit of first submodule in1 Voltage data, extracting voltage amplitude data sequence [ V ] 1 V 2 ...V n ]And time data series t 1 t 2 ...t n ]And filtering and cleaning abnormal points of the data.
Step S202, checking the original sourceVoltage amplitude data sequence [ V ] of exponential model 1 V 2 ...V n ]Carry out logarithmic transformation, V i 1 ＝ln(V i ) I =1, \ 8230;, n, resulting in a voltage amplitude data sequence [ V ] of the linear model 1 1 V 2 1 ...V n 1 ]。
Step S203, according to the least square method, the form of the analytic solution is expressed by the most value condition, and the voltage amplitude data sequence [ V ] converted into the linear model is brought in 1 1 V 2 1 ...V n 1 ]And solving to obtain a capacitance estimated value C. Here, the least square method is any one of a minimum mean value two-times algorithm, a recursive least square algorithm, and an iterative least square algorithm.
Step S204, correcting the capacitance estimation value C: since the operating frequency of the DC-link capacitor in the full-bridge LLC resonant converter is determined according to the known switching frequency, the correction can be made without considering the influence of the switching frequency change, but only considering the influence of the ambient temperature, and the estimated capacitance value C obtained in step S203 is corrected as shown in the following equation (1):
Figure BDA0003896680650000081
wherein alpha is M 、β M 、γ M The three temperature characteristic parameters can be measured through experiments for the capacitors with specific types; t is a 、T a，min 、T a,max Respectively representing the actual operating temperature, the minimum operating temperature and the maximum operating temperature of the capacitor.
In order to illustrate the effectiveness of the present invention, the method involved in the present invention is used to monitor the state of the DC-link capacitor of the iso p type medium voltage DC converter.
For a full-bridge LLC resonant converter, a DC-link capacitor is taken as an aging simulation object, different capacitors are connected in parallel on the input side to simulate an aging process, specifically, the DC-link capacitor of a redundant module is 1p.u. (1p.u. =220 uF), the DC-link capacitor of a third sub-module is 0.982p.u., the DC-link capacitor of a second sub-module is 0.964p.u., and the DC-link capacitor of a first sub-module is 0.945p.u. In practical application, accurate initial values of the capacitors do not need to be known in advance, a first bypass test result after operation can be taken as an initial reference, or the test result of the redundant module is taken as a reference. In the foregoing, the aging failure standard of the metal thin-film capacitor is that the capacitance value is attenuated by 5%, specifically, the judgment is performed by using the RC discharge trajectory information of the discharge bypass, and fig. 5 shows the discharge test results of the DC-link capacitor under different aging degrees, where the discharge curves under different aging degrees show significant differences, and the more serious the aging degree, the faster the capacitor discharges. Accurate capacitance value degradation information can be obtained through parameter estimation of an RC discharge curve, namely, a capacitance estimation value can be accurately obtained, and when the sampling frequency is 1k, the error of capacitance estimation is within 0.5%; when the sampling frequency is 10k, the error of capacitance estimation is within 0.2%; the error in capacitance estimation is within 0.1% at a sampling frequency of 100 k.
Fig. 6 is an experimental waveform of the prototype, wherein the waveform of the channel 2 is a voltage waveform of a middle point of a bridge arm, the waveform of the channel 4 is a resonant cavity current waveform, and the waveform of the channel 3 is an output voltage waveform. The full-bridge LLC resonant converter can effectively set a dead zone so as to realize zero-voltage conduction of the switching tube, and can effectively stabilize output voltage through phase-shifting control.
The above embodiments are preferred implementations of the present invention, and the present invention can be implemented in other ways without departing from the spirit of the present invention.
Some of the drawings and descriptions of the present invention have been simplified to facilitate the understanding of the improvements over the prior art by those skilled in the art, and other elements have been omitted from this document for the sake of clarity, and it should be appreciated by those skilled in the art that such omitted elements may also constitute the subject matter of the present invention.

Claims (10)

1. An ISOP type medium voltage DC converter comprises N full-bridge LLC resonant converters, and N full-bridges LLThe input side of the C resonant converter is connected in series in sequence, and the output side is connected in parallel, and the C resonant converter is characterized in that: the input side of one full-bridge LLC resonant converter is connected with a switching tube Q and an RC circuit in parallel to form a fault-tolerant control redundant module, the input sides of the rest N-1 full-bridge LLC resonant converters are connected with a switching tube Q and an RC circuit in parallel to form N-1 normally-working sub-modules respectively, and the RC circuit is a DC-link capacitor C in And a bleeder resistor R in A circuit connected in parallel.
2. An ISOP type medium voltage direct current converter according to claim 1, characterized in that: the DC-link capacitor C in Is a metal film capacitor.
3. The method for monitoring the state of the DC-link capacitor of an iso p type medium voltage DC converter as claimed in claim 2, comprising:
s1, sequentially replacing sub-modules in the work of the redundant module, cutting out one sub-module each time, isolating an RC circuit of the sub-module from a main circuit, and acquiring a DC-link capacitor C in the discharging process of the RC circuit in Voltage measurement data of (a);
step S2, the DC-link capacitor C obtained in the step S1 is subjected to in The voltage measurement data is processed to estimate the DC-link capacitance C in The capacitance value of (2).
4. The method for monitoring the state of the DC-link capacitor of the ISOP type medium voltage direct current converter according to claim 3, wherein: in step S1, the process of sequentially replacing the sub-modules in operation by the redundant module is as follows:
firstly, a switch tube Q at the input side of a redundancy module is turned off, the redundancy module is put into use, meanwhile, the switch tube Q at the input side of a first submodule is conducted, a power switch tube of a full-bridge LLC resonant converter in the first submodule is turned off, and the first submodule is cut out; and then switching off a switching tube Q at the input side of a first submodule, switching in the first submodule, simultaneously switching on a switching tube Q at the input side of a second submodule, switching off a power switching tube of a full-bridge LLC resonant converter in the second broken submodule, switching out the second submodule, and so on until an N-1 th submodule is switched in, switching out a redundant module, and restoring the LLC resonant converter to normal operation.
5. The method for monitoring the state of the DC-link capacitor of the ISOP type medium voltage direct current converter according to claim 4, wherein: in step S1, after each sub-module is put into use, the full-bridge LLC resonant converter keeps the switching frequency unchanged, and adjusts the output voltage by adjusting the phase shift angle between the diagonal switching tubes.
6. The method for monitoring the state of the DC-link capacitor of the ISOP type medium voltage direct current converter according to claim 5, wherein: in step S1, the obtained voltage measurement data are n DC-link capacitors C of the RC circuit of the submodule in one discharge period in Voltage data.
7. The method for monitoring the state of the DC-link capacitor of the ISOP type medium voltage direct current converter according to claim 6, wherein: in step S2, the DC-link capacitor C is subjected to in Processing the voltage measurement data to estimate the DC-link capacitance C in The process of capacitance value of (a) is as follows:
step S201, extracting a voltage amplitude data sequence and a time data sequence based on n voltage data of an RC circuit of a submodule in a discharge period, and filtering and cleaning abnormal points of the data;
step S202, carrying out logarithmic transformation on the voltage amplitude data sequence, so as to convert the voltage amplitude data sequence from an exponential model to a linear model;
and step S203, according to a least square method, representing the form of an analytic solution by a most-valued condition, and substituting the analytic solution into a voltage amplitude data sequence converted into a linear model to solve to obtain a capacitance estimation value.
8. The method for monitoring the state of the DC-link capacitor of the ISOP type medium voltage direct current converter according to claim 7, wherein: in step S203, the least square method is any one of a least mean squares algorithm, a recursive least square algorithm, and an iterative least square algorithm.
9. The method for monitoring the state of the DC-link capacitor of the ISOP type medium voltage DC converter according to claim 8, wherein: for DC-link capacitor C in The voltage measurement data is processed to estimate the DC-link capacitance C in The process of capacitance value of (a) further comprises: step S204, the capacitance estimated value is corrected according to the influence of the environment temperature.
10. The method for monitoring the state of the DC-link capacitor of the ISOP type medium voltage DC converter according to claim 9, wherein: in step S204, the formula for correcting the capacitance estimation value is as follows:
Figure FDA0003896680640000021
wherein alpha is M 、β M 、γ M The three temperature characteristic parameters can be measured through experiments for the capacitors with specific types; t is a unit of a 、T a，min 、T a,max Respectively representing the actual operating temperature, the minimum operating temperature and the maximum operating temperature of the capacitor.
CN202211276011.3A 2022-10-18 2022-10-18 ISOP type medium-voltage direct-current converter and DC-link capacitor state monitoring method thereof Pending CN115549477A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116879636A (en) * 2023-09-08 2023-10-13 湖南大学 LLC converter output side DC-link capacitance online monitoring system and method

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116879636A (en) * 2023-09-08 2023-10-13 湖南大学 LLC converter output side DC-link capacitance online monitoring system and method
CN116879636B (en) * 2023-09-08 2023-12-08 湖南大学 LLC converter output side DC-link capacitance online monitoring system and method

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