CN113114171B - Current source pulse control method for micro-arc oxidation - Google Patents
Current source pulse control method for micro-arc oxidation Download PDFInfo
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- 229910052751 metal Inorganic materials 0.000 description 2
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- 238000007254 oxidation reaction Methods 0.000 description 2
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- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K3/00—Circuits for generating electric pulses; Monostable, bistable or multistable circuits
- H03K3/01—Details
- H03K3/017—Adjustment of width or dutycycle of pulses
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- 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
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- 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
Abstract
The invention discloses a current source pulse control method for micro-arc oxidation, which controls a phase-shifting full-bridge DC-DC converter to directly output unipolar current pulses through a pulse shape control unit based on an output current prediction model, and comprises the following specific processes: giving information i about pulse amplitude in a given curve of current source pulses oref Average value of output current at k timek moment phase-shifting full-bridge DC-DC converter output voltage average valueAverage value of bus input voltage at k momentAnd (3) inputting the pulse current into a prediction model based on the output current to obtain the optimal duty ratio of the action at the moment k+1, and rapidly regulating the pulse current.
Description
Technical Field
The invention belongs to the technical field of power electronics, and relates to a current source pulse control method for micro-arc oxidation.
Background
In recent years, aluminum, magnesium, titanium metals and alloys thereof have been increasingly used in production and living, but their wear resistance, corrosion resistance and the like have been poor due to their own inherent defects. The micro-arc oxidation treatment technology can effectively improve the protective performance by generating a ceramic layer on the metal surface through pulse discharge.
In order to meet the requirements of different film processes, the micro-arc oxidation power supply often needs different pulse output types and output forms, wherein the pulse output types comprise voltage source type and current source type, and the pulse output forms comprise various high-power pulse waveforms such as unidirectional pulse, bidirectional symmetrical pulse, bidirectional asymmetrical pulse, direct current superposition pulse and the like. In particular, the pulse requirements for special forms such as bidirectional asymmetry and direct current superposition are increasing increasingly, and parameters such as pulse duty ratio, frequency and the like of the special forms are required to be freely adjustable.
For voltage source type pulse, the patent number is: CN103475256, authorized day: 2016.04.06, the invention name is: although the defect of single output form of the existing pulse converter is overcome to a certain extent, the direct current input side of the voltage source type asymmetric pulse converter is powered by a double power supply, the pulse amplitude of the voltage source is not adjustable, and the application range is limited; the document 'research on bidirectional asymmetric pulse type micro-arc oxidation power supply' proposes a bipolar pulse generation method, the bidirectional asymmetric pulse amplitude of which is adjustable, and the input side is powered by a single power supply, but the positive and negative pulse generation circuits are independent, so that the complexity of circuit structure and control is increased. In general, the existing micro-arc oxidation power supply is mainly realized by a voltage source with adjustable amplitude and a chopper circuit. Thus, to enable a wide range of adjustable outputs in the form of relatively complex pulses, it requires multiple adjustable voltage sources in combination with complex pulse circuits. The scheme has high cost and complex circuit structure, and the difficulty of pulse implementation is obviously increased.
Compared with the voltage source type pulse, the oxidation time of the current source type pulse is shorter than the time required by the voltage source type pulse, the oxidation time is easy to control, the calculation and the control of energy consumption are more convenient, the reliability of a circuit can be improved, and the load discharge state can be adjusted by adopting the positive and negative bidirectional current source pulse, so that the growth effect of a ceramic layer is better improved. The patent publication number is: CN107302321, publication date: 2017.10.27, the invention name is: a pulse current source based on a combination method is designed to output unidirectional current source pulses with different amplitudes and pulse widths based on superposition of a plurality of constant current modules. However, the amplitude of the constant current module is fixed, the amplitude of the output current pulse is limited to be freely regulated, and the number of the modules is increased, so that the circuit structure is more complex, and the control difficulty is increased. The literature 'study of micro-arc oxidation current pulse power supply and load electrical characteristics thereof' proposes a micro-arc oxidation square wave current pulse power supply scheme of a parallel combination structure, and the basic idea is that the implementation mode of 'constant current source + chopper circuit' can only realize unidirectional current pulse. The document 'variable polarity micro-arc oxidation current pulse power supply topology research' realizes the output of asymmetric bipolar triangular waves through the combination of two double-tube flyback circuits, the pulse of the circuit is limited by the conducting duty ratio of the flyback circuits, the pulse output parameter range is narrow, the problem of circulation exists between positive and negative pulse circuits, and a complex circulation suppression circuit is required to be additionally added. Therefore, the implementation of the current source pulse is based on the mode of 'constant current source + chopper circuit (shape and polarity control)', on one hand, the parallel circuit structure can increase the complexity of the system when implementing the bidirectional pulse, and new problems can be possibly introduced; on the other hand, the realization difficulty of the pulse form of direct current superposition is obviously increased.
In summary, the current micro-arc oxidation pulse power supply mainly has the following disadvantages, and specifically includes:
1) Whether a voltage source pulse or a current source pulse, if multiple output forms, such as bidirectional asymmetric pulses, are to be realized, the difficulty of a power supply system, a circuit structure and control is greatly increased.
2) Based on the basic idea of current source pulse realization, namely a constant current source and chopper circuit (shape and polarity control) mode, the special form of direct current superposition pulse is not easy to realize, and increasingly abundant processing requirements cannot be met.
Disclosure of Invention
The invention aims to provide a current source pulse control method for micro-arc oxidation, which can realize free output of various forms of current source pulses under the condition of single power supply, solves the problems of the prior art that the complexity of a power supply system, a circuit structure and a control system is increased and the like caused by the current source pulses in various output forms, and greatly expands the application range of the current source pulses.
The technical scheme adopted by the invention is that the current source pulse control method for micro-arc oxidation specifically comprises the following steps:
step 1, establishing a discretized output current prediction model according to a state space average model of a phase-shifting full-bridge DC-DC converter, correcting the output current prediction model aiming at the condition that the duty ratio of the secondary side is lost, and further deducing a prediction model expression of the output current at the moment k+2;
step 2, based on the result obtained in the step 1, establishing an evaluation function J (k), and obtaining the duty ratio D of the actual action of the phase-shifting full-bridge DC-DC converter c (k+1)；
Step 3, introducing an integral compensation link, compensating steady-state errors caused by differences between an actual circuit and a control model, obtaining a compensation quantity delta I, and substituting delta I into the duty ratio D obtained in the step 2 c In the expression (k+1), the duty ratio D after compensation is calculated cp (k+1)；
Step 4, based on a phase-shifting full-bridge DC-DC converter state space average model, writing a primary side resonance inductance peak current expression at k+2 time in columnsObtaining the current peak value limit as i Lmaxref The maximum duty cycle at the time is D max (k+1)；
Step 5, the duty ratio D obtained in the step 3 is calculated cp (k+1) and the maximum duty ratio D obtained in step 4 max (k+1) comparing, and selecting the duty ratio with smaller value as the actual effect.
The invention is also characterized in that:
the specific process of the step 1 is as follows:
step 1.1, according to a state space average model of filter inductance current at the output side of the phase-shifting full-bridge DC-DC converter, establishing a state equation of the filter inductance current, as shown in the following formula (1):
in the method, in the process of the invention,the average value of the filter inductance current in one control period is output for the phase-shifting full-bridge DC-DC converter,<V in >for the average value of the input voltage of the phase-shifted full-bridge DC-DC converter in one control period,<V o >for the average value of the output voltage of the phase-shifting full-bridge DC-DC converter in a control period, D is the equivalent duty ratio of a primary side switching tube of the phase-shifting full-bridge DC-DC converter under ideal conditions, n is the ratio of the number of turns of a coil on the secondary side to the primary side of the high-frequency transformer, L is the sum of the inductance value of the primary side of the transformer and the filter inductance of the secondary side of the transformer, and the calculation process of L is shown in the following formula (2):
L＝L f +n 2 L r (2)；
step 1.2, discretizing a state differential equation of the filter inductor current at the output side of the step 1.1 by adopting an Euler forward method, wherein the discretization is shown in the following formula (3):
in the method, in the process of the invention,for k+1 time, the average value of the inductor current is filtered,/->For the average value of the filter inductor current at time k +.>For the average value of the input voltage at time k, +.>For the average value of the output voltage at time k, T s The sampling period is represented, and D (k) is the equivalent duty ratio of k moment acting on a primary side switching tube of the phase-shifting full-bridge DC-DC converter under ideal conditions;
step 1.3, the k moment is acted on the wholeThe equivalent duty ratio of the primary side switching tube of the bridge converter is corrected, and the corrected duty ratio D actually acts on the converter c (k) The method comprises the following steps:
D c (k)＝D(k)+D loss (k) (4)；
wherein D is loss (k) The lost duty ratio of the secondary side of the transformer of the phase-shifting full-bridge DC-DC converter at the moment k compared with the primary side;
substituting the formula (4) into the formula (3) to obtain a prediction expression of the filter inductance current at the time k+1 after correction, wherein the prediction expression is as follows:
in the method, in the process of the invention,
due to the output capacitance C in steady state o The average current value in one switching period is zero, so that the average current value of the secondary side filter inductor is equal to the average current value of the output current, i.eSo the output current prediction model expression of the phase-shifting full-bridge DC-DC converter is,
wherein,for the average value of the output current of the full-bridge converter at time k+1,/v>Full bridge converter for k momentAn average value of the output current;
step 1.4, deducing a full-bridge converter output current prediction model expression at the moment k+2 according to a formula (7):
in the method, in the process of the invention,is the average value D of the output current of the converter at the time k+2 c (k+1) is the equivalent duty ratio, D, of the primary side switching tube actually acted on after the k+1 moment is corrected loss And (k+1) is the duty cycle lost on the secondary side of the transformer compared with the primary side of the transformer at time k+1.
The specific process of the step 2 is as follows:
establishing an evaluation function J (k) as the absolute value of the difference between the predicted value of the output current and the given value of the current source pulse:
wherein i is oref Representing a given amplitude of a current source pulse for micro-arc oxidation;
let J (k) =0, calculated,
the specific process of the step 3 is as follows:
based on the deviation between the output pulse current at the moment k and the given pulse current, carrying out integral operation on the deviation to obtain a compensation quantity delta I of the output pulse current at the next moment, and adding the compensation quantity delta I to a current source pulse given value at the next moment, thereby realizing the compensation of the duty ratio of the next switching cycle on the converter, wherein the expression of the compensation quantity is as follows:
wherein K is i Coefficients for the integral compensator;
substituting the formula (11) into the formula (10) can obtain the duty ratio expression which is actually acted on the primary side switching tube after integral compensation,
the specific process of the step 4 is as follows:
step 4.1, deriving from the operating waveform of the phase-shifted full-bridge DC-DC converter during one switching period, at t, when the resonant inductor current is operating under continuous conditions 2 At the moment, the state equation that the resonant inductor current reaches the peak value is that,
in the method, in the process of the invention,for the average value of the input voltage of the full bridge converter, < >>An average value of output voltages of the full-bridge converter;
step 4.2, deriving a peak current prediction expression at the time of k+2 based on the state equation of step 4.1, wherein the peak current prediction expression is as follows:
step 4.3, assuming that at time k+2 the resonant inductor current peak is limited to i Lmaxref Then, the value of the duty ratio at time k+1, that is, the maximum value of the duty ratio is obtained by substituting the value into equation (14):
the beneficial effects of the invention are as follows:
(1) The system can realize the output form of various current source pulses under the condition of single power supply and no additional circuit, thereby not only reducing the complexity of the system, but also greatly increasing the diversity of the pulses and expanding the application range of the system.
(2) Different from the traditional concept of 'constant current source+chopper circuit' adopted by current source pulse, the invention adopts the concept of 'current pulse shape control based on output current prediction model+polarity control', is easy to realize special form pulse such as DC superposition pulse, and has simple control.
(3) The method based on the output current prediction model is used for controlling the pulse shape of the current source, so that the dynamic response speed of the system can be effectively improved, the anti-interference performance under the load abrupt change working condition can be improved, and the healthy and stable operation of the system is facilitated.
Drawings
FIG. 1 is a schematic diagram of the overall topology of a current source pulse control method for micro-arc oxidation according to the present invention;
FIGS. 2 (a) and (b) are equivalent circuit diagrams of a phase-shifted full-bridge DC-DC converter of the present invention operating in half-cycles in a current source pulse control method for micro-arc oxidation;
FIG. 3 is a flow chart of primary side resonant inductor current peak limiting of the 1 phase shifted full bridge DC-DC converter of FIG. 1;
FIGS. 4 (a) and (b) are schematic diagrams of the output of a bi-directional asymmetric current source pulse in one cycle employed in a current source pulse control method for micro-arc oxidation according to the present invention;
fig. 5 is a schematic diagram of the output of a bi-directional superimposed current source pulse in one cycle employed in a current source pulse control method for micro-arc oxidation according to the present invention.
Detailed Description
The invention will be described in detail below with reference to the drawings and the detailed description.
The invention discloses a current source pulse control method for micro-arc oxidation, which is used for rapidly controlling current source pulses on a load in the micro-arc oxidation processing process, and as shown in figure 1, a main circuit topology structure for generating the current source pulses for micro-arc oxidation comprises a 1-phase-shifting full-bridge DC-DC converter and a 2-bridge inverter circuit. The phase-shifting full-bridge DC-DC converter comprises an H-bridge converter, a diode uncontrolled rectifier bridge and a high-frequency transformer, wherein the high-frequency transformer can effectively realize electric isolation and energy transmission of a primary side and a secondary side. The input end of the primary side H-bridge converter of the high-frequency transformer is connected with a direct current bus and is connected with a direct current bus supporting capacitor C in In parallel with one output of the H-bridge converter connected to an external resonant inductor L r Resonant inductance L r The other end of the primary side coil of the high-frequency transformer is connected with one end of the primary side coil of the high-frequency transformer, and the other end of the primary side coil of the high-frequency transformer is connected with a blocking capacitor C b The other end of the blocking capacitor is connected to the other output end of the H-bridge converter. Two terminals of a secondary side coil of the high-frequency transformer are respectively connected with the middle points of two bridge arms of the uncontrolled rectifier bridge, one output end of the uncontrolled rectifier bridge is connected with an inductance-capacitance (L-C) circuit, and then is connected with the input end of an upper bridge arm of the 2-bridge inverter unit; the output end of the lower bridge arm of the 2-bridge type inversion unit is connected with the other output end of the uncontrolled rectifier bridge. The load which needs micro-arc oxidation processing is connected between the middle points of the two bridge arms of the bridge type inverter circuit. In FIG. 1, V in Representing the input direct current bus voltage of the phase-shifted full-bridge DC-DC converter; c (C) in Representing bus bar support capacitance; s1 and S2 represent upper and lower power switching tubes of a first bridge arm of the primary side H-bridge converter, and D1 and D2 are anti-parallel diodes of S1 and S2 respectively; s3 and S4 represent upper and lower power switching tubes of a second bridge arm of the primary side H-bridge converter, and D3 and D4 are respectively anti-parallel diodes of S3 and S4; t represents a high-frequency transformer; v (V) ab Representing a primary side H-bridge converter output voltage; l (L) r Representing the primary side resonant inductance; c (C) b Representing the primary side blocking capacitance; n is the ratio of the number of turns of the coil on the secondary side to the primary side of the high frequency transformer; d5 and D6 represent the first bridge arm of the secondary side uncontrolled rectifier bridgeUpper and lower power diodes; d7 and D8 represent upper and lower power diodes of the second bridge arm of the secondary side uncontrolled rectifier bridge; l (L) f Representing the filter inductance; c (C) o Representing a filter capacitance; i.e Lf Is the current flowing through the filter inductor; v (V) o The voltage on the filter capacitor at the output side; s5 and S6 represent upper and lower power switching tubes of a first bridge arm of the bridge type inversion unit; s7 and S8 represent upper and lower power switch tubes of a second bridge arm of the bridge type inversion unit, i o Is the current through the load.
The invention can realize various current source pulses under the condition of not increasing the complexity of the system so as to meet different processing requirements. As shown in fig. 1, the main circuit topology for implementing current source pulse selects a combination of a phase-shifting full-bridge DC-DC converter and a bridge inverter circuit, the phase-shifting full-bridge DC-DC converter includes an H-bridge converter, a high-frequency transformer and a diode uncontrolled rectifier bridge; the specific process of the current source pulse control method is as follows: firstly, setting a current source pulse setting curve comprising parameter information such as pulse amplitude, frequency, duty ratio and the like of each stage to a pulse controller, then controlling a phase-shifting full-bridge DC-DC converter to directly output a set current pulse shape (positive direction at the moment) through a pulse shape control unit based on an output current prediction model, simultaneously controlling power switching tubes S5, S6, S7 and S8 contained in a bridge inverter circuit in a coordinated manner by a pulse polarity control unit according to polarity change of the current source pulse setting curve, sending out corresponding driving signals, and finally realizing the set current source pulse output form on a processing load.
The specific process for controlling the phase-shifting full-bridge DC-DC converter to directly output unipolar current pulses through the pulse shape control unit based on the output current prediction model comprises the following steps of: giving information i about pulse amplitude in a given curve of current source pulses oref Average value of output current at k timek moment phase-shifting full-bridge DC-DC converter output voltage average value +.>Bus input voltage average value at time k->And (3) inputting the pulse current into a prediction model based on the output current to obtain the optimal duty ratio of the action at the moment k+1, and rapidly regulating the pulse current.
The invention discloses a current source pulse control method for micro-arc oxidation, which comprises the following specific steps:
step 1, according to the topological structure of the 1 phase-shifting full-bridge DC-DC converter shown in fig. 1, a state space average model of output inductance current is established, and then a prediction model expression of discretized output current is deducedModel correction is carried out for the condition of secondary side duty ratio loss, and then a prediction model expression of the output current at the moment k+2 is deduced
The step 1 is specifically implemented according to the following steps:
step 1.1, firstly, according to the working process of the phase-shifting full-bridge DC-DC converter topology shown in fig. 2 in one switching period, an equivalent circuit is obtained, and a state space average model of filter inductance current is established; wherein FIG. 2 (a) is at [ t ] 0 ,t 2 ]FIG. 2 (b) is an equivalent circuit diagram during operation in time period [ t ] 2 ,t 3 ]And an equivalent circuit diagram when the device works in a time period. : since the working process of the converter in one control period is symmetrical, for simplifying the analysis, the equivalent circuit for only analyzing half period of the converter is shown in fig. 3, and mainly comprises two stages, and the corresponding state equations of the output voltage and the inductance current are respectively:
wherein L is the sum of the primary side resonant inductance of the transformer, the secondary side inductance value of the transformer and the secondary side filter inductance, and is specifically l=l f +n 2 L r 。
And combining the state equation of the output voltage and the filter inductance current in a half period, and calculating to obtain a differential equation of a state space average model of the output filter inductance current, wherein the differential equation is as follows:
in the method, in the process of the invention,the average value of the filter inductance current in one control period is output for the phase-shifting full-bridge DC-DC converter,<V in >for the average value of the input voltage of the phase-shifted full-bridge DC-DC converter in one control period,<V o >the average value of the output voltage of the phase-shifting full-bridge DC-DC converter in one control period is obtained, and D is the equivalent duty ratio of a primary side switching tube acting on the phase-shifting full-bridge DC-DC converter under ideal conditions.
Step 1.2, discretizing a state differential equation of the filter inductor current at the output side of step 1.1 by adopting an Euler forward method, and obtaining:
in the method, in the process of the invention,for k+1 time, the average value of the inductor current is filtered,/->Filtering the average value of the inductance current at the moment k，/>For the average value of the input voltage at time k, +.>For the average value of the output voltage at time k, T s And D (k) is an equivalent duty ratio of the k moment acting on a primary side switching tube of the phase-shifting full-bridge DC-DC converter under ideal conditions.
Step 1.3, in this embodiment, considering that the secondary side of the transformer has a loss phenomenon of equivalent duty ratio compared with the primary side in the primary side resonant inductor current continuous operation mode of the phase-shifted full-bridge DC-DC converter, in order to reduce the influence on the accuracy of the control model, the equivalent duty ratio of the k moment acting on the primary side switching tube of the full-bridge converter is corrected, and the duty ratio D actually acting on the converter after correction c (k) The method comprises the following steps:
D c (k)＝D(k)+D loss (k) (5)；
wherein D is loss (k) The secondary side of the transformer of the full-bridge DC-DC converter is phase-shifted for k time, compared with the primary side, by the lost duty ratio.
Substituting the formula (5) into the formula (4) to obtain a prediction expression of the filter inductance current at the time k+1 after correction, wherein the prediction expression is as follows:
in the method, in the process of the invention,
due to the output capacitance C in steady state o The average current value in one switching cycle is zero, so the average secondary side filter inductor current value and the average output current value can be considered to be equal,i.e.Therefore, the output current prediction model expression of the phase-shifting full-bridge DC-DC converter is as follows:
wherein,for the average value of the output current of the full-bridge converter at time k+1,/v>The average value of the output current of the full-bridge converter at the moment k.
And step 1.4, in order to eliminate the one-beat delay of the control system caused by the sampling time of the digital controller and the execution time of the control program in the actual control process, adopting two-step prediction to carry out delay compensation. First, a full-bridge converter output current prediction model expression at time k+2 can be derived from equation (9):
in the method, in the process of the invention,is the average value D of the output current of the converter at the time k+2 c (k+1) is the equivalent duty ratio, D, of the primary side switching tube actually acted on after the k+1 moment is corrected loss And (k+1) is the duty cycle lost on the secondary side of the transformer compared with the primary side of the transformer at time k+1.
Step 2, based on the predictive model expression of the output current at the time k+2 obtained in the step 1, establishing an evaluation function J (k) to obtain the duty ratio D of the actual action of the phase-shifting full-bridge DC-DC converter c (k+1)；
The method comprises the following steps: establishing an evaluation function J (k) as the absolute value of the difference between the predicted value of the output current and the given value of the current source pulse:
wherein i is oref Representing a given amplitude of a current source pulse for micro-arc oxidation.
The control objective of this embodiment is to always minimize the evaluation function, i.e. the deviation of the amplitude of the pulse current output by the converter from the given amplitude of the current source pulse, i.e. let J (k) =0. And (3) calculating to obtain:
step 3, introducing an integral compensation link, compensating steady-state errors caused by differences between an actual circuit and a control model, obtaining a compensation quantity delta I, and substituting the compensation quantity delta I into the duty ratio D obtained in the step 2 c In the expression (k+1), the duty ratio D after compensation is calculated cp (k+1)；
In the practical application process, certain deviation exists between the control model and the actual circuit model due to the existence of non-ideal switching devices, line impedance, inductance parameter changes and the like. To eliminate steady state errors between the output pulse current and a given pulse current, an integral compensator is introduced. Firstly, based on the deviation between the output pulse current at the moment k and the given pulse current, the deviation is integrated to obtain the compensation quantity delta I of the output pulse current at the next moment, and the compensation quantity is added with the given value of the current source pulse at the next moment, so that the compensation of the duty ratio of the next switching cycle to the converter is realized. The expression of the compensation amount is as follows:
wherein K is i Is the coefficient of the integral compensator.
The duty ratio expression actually applied to the primary side switching tube after integral compensation can be obtained by substituting the expression (12) into the expression (11):
and step 4, considering that if the primary side resonant inductor current of the transformer is too large, the resonant inductor, the transformer and the switching device can be adversely affected in safe and healthy operation, and the stability of the system is reduced. Therefore, the peak value is limited to a certain extent, and the specific process is as follows:
step 4.1, when the resonant inductor current is operated under continuous conditions, the operating waveform of the phase-shifted full-bridge DC-DC converter in one switching period can be seen at t 2 At moment, the resonant inductor current reaches a peak value, and the state equation is as follows:
in the method, in the process of the invention,for the average value of the input voltage of the full bridge converter, < >>Is the average value of the output voltage of the full-bridge converter.
Step 4.2, deriving a peak current prediction expression at the time of k+2 based on the state equation of step 4.1, wherein the peak current prediction expression is as follows:
step 4.3, assuming that at time k+2 the resonant inductor current peak is limited to i Lmaxref Then, the value of the duty ratio at time k+1, that is, the maximum value of the duty ratio is obtained by substituting the value into equation (15):
step 5, as shown in FIG. 3, the duty ratio D at time k+1 obtained in step 3 is calculated cp (k+1) and maximum duty ratio D under peak current limit conditions obtained in step 4 max Comparing (k+1), and judging the sizes of the two: if D cp (k+1) is less than D max (k+1), then select D cp (k+1) as a full bridge converter actually acts on the duty cycle of the primary side switching tube to meet the load pulse current amplitude requirement; if D cp (k+1) is greater than D max (k+1), then select D max The (k+1) is used as a duty ratio of the phase-shifting full-bridge DC-DC converter actually acting on the primary side switching tube, so that the primary side resonance inductance current peak value is limited in a safe range, and the safety of the system is ensured. The finally selected duty ratio is acted on the phase-shifting modulator to generate switching signals of switching tubes of the phase-shifting full-bridge DC-DC converters S1-S4, so that the control of the pulse shape of the current source is realized.
The pulse polarity control unit coordinates and controls power switching tubes S5, S6, S7 and S8 contained in the bridge inverter circuit in FIG. 1 according to the polarity change of a given pulse curve, and sends out corresponding driving signals, and the specific process for realizing polarity inversion of current pulses is as follows:
the pulse polarity control unit coordinates and controls power switching tubes S5, S6, S7 and S8 of the bridge inverter circuit according to the polarity change of a given curve of the micro-arc oxidation current source pulse, and sends out corresponding driving signals. Two conditions need to be satisfied: (1) When the current source pulse is given as a forward pulse, the inversion side switching tube S5 and the switching tube S8 are required to be controlled to be in an overlapped on state, and the switching tube S6 and the switching tube S7 are required to be in an off state, so that current can flow through a micro-arc oxidation processing load in the forward direction, namely, the pulse current passes through a positive bus output by the phase-shifting full-bridge DC-DC converter, the switching tube S5, the load and the switching tube S8 and is subjected to a negative bus output by the phase-shifting full-bridge DC-DC converter; when the current source pulse is given as a negative pulse, the switching tube S6 and the switching tube S7 of the bridge inverter circuit are required to be controlled to be in an overlapped conduction state, and the switching tube S5 and the switching tube S8 are required to be in an off state, so that current can reversely flow through a micro-arc oxidation processing load, namely, pulse current passes through the phase-shifting full-bridge DC-DC converter to output a positive bus, the switching tube S7, the load and the switching tube S6 to the phase-shifting full-bridge DC-DC converter to output a negative bus. (2) Because the phase-shifting full-bridge DC-DC converter works in the current source mode, when the amplitude of a given curve of a current source pulse is reduced to zero, no energy is provided for a load at the moment, although a pulse shape control unit based on an output current prediction model can control the pulse current to be reduced to zero rapidly, in order to ensure the safety of a system, a flowing passage is still required to be provided for the existing pulse current to be consumed, namely, the pulse polarity control unit controls the switching tube S5 and the switching tube S6 of the bridge inverter circuit to be conducted in an overlapping mode or controls the switching tube S7 and the switching tube S8 of the bridge inverter circuit to be conducted in an overlapping mode. Therefore, the pulse polarity control unit needs to cooperate with the pulse shape control unit based on the output current prediction model to control in a cooperation way under the same time sequence, so that the realization of the micro-arc oxidation current source pulse can be rapidly and accurately controlled, and a plurality of different pulse output forms can be realized.
Wherein FIG. 4 (a) shows the pulse shape of the forward current source output by the phase-shifted full-bridge DC-DC converter, and the solid line shows the given amplitude i of the current source pulse oref The dashed line is the pulse current on the output inductor based on the output current prediction model method, and fig. 4 (b) is the bidirectional superposition current source pulse actually applied to the load after passing through the bridge inverter circuit.
Fig. 5 is a schematic diagram of the output of a bi-directional superimposed current source pulse in one cycle employed in a current source pulse control method for micro-arc oxidation according to the present invention.
The invention provides a current source pulse control method for micro-arc oxidation, which is different from the concept of 'constant current source + chopper circuit (shape, polarity control)' adopted in the current source pulse realization. And the method based on the output current prediction model is adopted, so that the response speed of the power supply system and the anti-interference performance under the sudden load change are improved, and the reliable operation of the system is ensured.
Claims (4)
1. A current source pulse control method for micro-arc oxidation is characterized in that: the method specifically comprises the following steps:
step 1, establishing a discretized output current prediction model according to a state space average model of a phase-shifting full-bridge DC-DC converter, correcting the output current prediction model aiming at the condition that the duty ratio of the secondary side is lost, and further deducing a prediction model expression of the output current at the moment k+2;
the specific process of the step 1 is as follows:
step 1.1, according to a state space average model of filter inductance current at the output side of the phase-shifting full-bridge DC-DC converter, establishing a state equation of the filter inductance current, as shown in the following formula (1):
in the method, in the process of the invention,for the phase-shifting full-bridge DC-DC converter to output the average value of the filter inductance current in one control period, V in For the average value of the input voltage of the phase-shifting full-bridge DC-DC converter in one control period, V o For the average value of the output voltage of the phase-shifting full-bridge DC-DC converter in one control period, D is the equivalent duty ratio acting on a primary side switching tube of the phase-shifting full-bridge DC-DC converter under ideal conditions, n is the coil turn ratio of the secondary side to the primary side of the high-frequency transformer, L is the sum of the primary side resonant inductance of the transformer to the secondary side inductance value of the transformer and the secondary side filter inductance, and the calculation process of L is as follows2) The following is shown:
L＝L f +n 2 L r (2)；
step 1.2, discretizing a state differential equation of the filter inductor current at the output side of the step 1.1 by adopting an Euler forward method, wherein the discretization is shown in the following formula (3):
in the method, in the process of the invention,for k+1 time, the average value of the inductor current is filtered,/->For the average value of the filter inductor current at time k +.>For the average value of the input voltage at time k, +.>For the average value of the output voltage at time k, T s The sampling period is represented, and D (k) is the equivalent duty ratio of k moment acting on a primary side switching tube of the phase-shifting full-bridge DC-DC converter under ideal conditions;
step 1.3, correcting the equivalent duty ratio of the k moment acting on the primary side switching tube of the full-bridge converter, and actually acting on the duty ratio D of the converter after correction c (k) The method comprises the following steps:
D c (k)＝D(k)+D loss (k)(4)；
wherein D is loss (k) The secondary side of the transformer of the full-bridge DC-DC converter is lost compared with the primary side for k moment phase shiftDuty cycle of (2);
substituting the formula (4) into the formula (3) to obtain a prediction expression of the filter inductance current at the time k+1 after correction, wherein the prediction expression is as follows:
in the method, in the process of the invention,
due to the output capacitance C in steady state o The average current value in one switching period is zero, so that the average current value of the secondary side filter inductor is equal to the average current value of the output current, i.eTherefore, the output current prediction model expression of the phase-shifting full-bridge DC-DC converter is as follows:
wherein,for the average value of the output current of the full-bridge converter at time k+1,/v>The average value of the output current of the full-bridge converter at the moment k;
step 1.4, deducing a full-bridge converter output current prediction model expression at the moment k+2 according to a formula (7):
in the method, in the process of the invention,is the average value D of the output current of the converter at the time k+2 c (k+1) is the equivalent duty ratio, D, of the primary side switching tube actually acted on after the k+1 moment is corrected loss (k+1) is the lost duty cycle of the secondary side of the transformer of the converter compared to the primary side at time k+1;
step 2, based on the result obtained in the step 1, establishing an evaluation function J (k), and obtaining the duty ratio D of the actual action of the phase-shifting full-bridge DC-DC converter c (k+1)；
Step 3, introducing an integral compensation link, compensating steady-state errors caused by differences between an actual circuit and a control model, obtaining a compensation quantity delta I, and substituting delta I into the duty ratio D obtained in the step 2 c In the expression (k+1), the duty ratio D after compensation is calculated cp (k+1)；
Step 4, based on a phase-shifting full-bridge DC-DC converter state space average model, writing a primary side resonance inductance peak current expression at k+2 time in columnsObtaining the current peak value limit as i Lmaxref The maximum duty cycle at the time is D max (k+1)；
Step 5, the duty ratio D obtained in the step 3 is calculated cp (k+1) and the maximum duty ratio D obtained in step 4 max (k+1) comparing, and selecting the duty ratio with smaller value as the actual effect.
2. A current source pulse control method for micro-arc oxidation according to claim 1, wherein: the specific process of the step 2 is as follows:
establishing an evaluation function J (k) as the absolute value of the difference between the predicted value of the output current and the given value of the current source pulse:
in the method, in the process of the invention,i oref representing a given amplitude of a current source pulse for micro-arc oxidation;
let J (k) =0, calculated,
3. a current source pulse control method for micro-arc oxidation according to claim 2, wherein: the specific process of the step 3 is as follows:
based on the deviation between the output pulse current at the moment k and the given pulse current, carrying out integral operation on the deviation to obtain a compensation quantity delta I of the output pulse current at the next moment, and adding the compensation quantity delta I to a current source pulse given value at the next moment, thereby realizing the compensation of the duty ratio of the next switching cycle on the converter, wherein the expression of the compensation quantity is as follows:
wherein K is i Coefficients for the integral compensator;
substituting the formula (11) into the formula (10) can obtain the duty ratio expression which is actually acted on the primary side switching tube after integral compensation,
4. a current source pulse control method for micro-arc oxidation according to claim 3, wherein: the specific process of the step 4 is as follows:
step 4.1, deriving from the operating waveform of the phase-shifted full-bridge DC-DC converter during one switching period, at t, when the resonant inductor current is operating under continuous conditions 2 At the moment, the resonant inductor current reaches a peak valueThe equation of state is that,
in the method, in the process of the invention,for the average value of the input voltage of the full bridge converter, < >>An average value of output voltages of the full-bridge converter;
step 4.2, deriving a peak current prediction expression at the time of k+2 based on the state equation of step 4.1, wherein the peak current prediction expression is as follows:
step 4.3, assuming that at time k+2 the resonant inductor current peak is limited to i Lmaxref Then, the value of the duty ratio at time k+1, that is, the maximum value of the duty ratio is obtained by substituting the value into equation (14):
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