CN115347781B - Design method of intrinsically safe single-inductor multi-output switch converter - Google Patents

Design method of intrinsically safe single-inductor multi-output switch converter Download PDF

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CN115347781B
CN115347781B CN202211060764.0A CN202211060764A CN115347781B CN 115347781 B CN115347781 B CN 115347781B CN 202211060764 A CN202211060764 A CN 202211060764A CN 115347781 B CN115347781 B CN 115347781B
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converter
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CN115347781A (en
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皇金锋
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Pingyuan Power Supply Co Of State Grid Shandong Electric Power Co
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Shaanxi University of Technology
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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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0083—Converters characterised by their input or output configuration
    • H02M1/009—Converters characterised by their input or output configuration having two or more independently controlled outputs
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

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

Abstract

The invention discloses a design method of an intrinsically safe single-inductor multi-output switch converter, which comprises the following steps: step 1: determining basic characteristics of an SIDO Buck converter; step 2: analyzing the output short-circuit energy of the SIDO Buck converter, and determining an output intrinsic safety criterion of the converter; step 3: an intrinsically safe inductor design of a SIDOBuck converter; step 4: intrinsically safe capacitive design of SIDO Buck converter. The SIDO Buck converter designed by the invention is suitable for dangerous environments such as mines, can provide theoretical guidance for development of the intrinsic safety SIDO Buck converter, and can also provide thinking for research of other intrinsic safety SIMO DC-DC converters.

Description

Design method of intrinsically safe single-inductor multi-output switch converter
Technical Field
The invention belongs to the technical field of converters, and particularly relates to a design method of an intrinsically safe single-inductor multi-output switching converter.
Background
Nowadays, coal mine industry is more and more important for production safety, underground environment is very complex and often accompanies inflammable and explosive gases such as gas, thus various electronic equipment is required to monitor underground conditions in real time, the power supply of the electronic equipment must meet the explosion-proof requirement, and intrinsic safety is the best explosion-proof form at present, so research on intrinsic safety power supplies suitable for underground has important significance.
Linear power supplies have the advantages of stability and small noise, most of today's intrinsically safe power supplies adopt the form, but the linear power supplies are large in size and high in cost, more and more expert scholars are devoted to researching the explosion-proof intrinsically safe switching power supplies applied to the underground, the switching power supplies have the advantages of wide input and wide output, small size, low cost and the like, research on intrinsically safe switching power supplies is the basis of researching the intrinsically safe switching power supplies, in recent years, research on intrinsically safe switching power supplies by researchers, particularly research on Single-output intrinsically safe switching power supplies, has more achievements, but due to the fact that the output form of the traditional Single-output switching power supplies is Single, the practical application of the Single-inductance multiple-output (Single-Inductor Multiple-output) power supplies is greatly limited, and in recent years, as shown in fig. 1, if the switch power supplies can be applied to the intrinsically safe power supplies, the switch power supplies have the advantages of being compared with the traditional Single-output intrinsically safe switching power supplies, the switch power supplies can not only realize multiple outputs, and under the same output quantity, particularly, the energy storage elements of the Single-inductance multiple-output power converters can release the energy when the output energy is reduced to the largest extent. Because of the existence of the branch switching tube, if the output of one branch of the converter is short-circuited, the system can switch off the switching tube of the branch in time without affecting the normal operation of other branches, and the short-circuit energy is only the energy released by a single capacitor. Even in the worst case (all outputs are shorted together), the energy released by the short circuit is only the sum of the energy released by all the capacitors and the energy released by one inductor, which is far smaller than the energy released by the parallel converter by the simultaneous short circuit, so that the single-inductor multi-output converter is easier to realize explosion protection effectively.
Disclosure of Invention
The invention aims to provide a design method of an intrinsically safe single-inductor multi-output switch converter, and the designed SIDO Buck converter can be used for explosion protection requirements of an underground intrinsically safe power supply.
The technical scheme adopted by the invention is that the design method of the intrinsically safe single-inductor multi-output switch converter is implemented according to the following steps:
step 1: determining basic characteristics of an SIDO Buck converter;
step 1.1: calculating the output voltage of the SIDO Buck converter;
step 1.2: calculating the output ripple voltage of the SIDO Buck converter;
step 1.3: determining the working area of an SIDO Buck converter;
step 2: analyzing the output short-circuit energy of the SIDO Buck converter, and determining an output intrinsic safety criterion of the converter;
step 3: an intrinsically safe inductor design of the SIDO Buck converter;
step 4: intrinsically safe capacitive design of SIDO Buck converter.
The present invention is also characterized in that,
the step 1.1 specifically comprises the following steps:
the SIDO Buck converter comprises a switching tube S i 、S a 、S b Diode VD, inductance L, capacitance C a 、C b Load resistor R a 、R b ，D i 、D a 、D b Is a switching tube S i 、S a 、S b And satisfies the following: d (D) i <D b ，D a +D b ＝1；
When the converter works in the continuous conduction mode CCM, the load resistance R in the converter is obtained according to a time average equivalent circuit method a 、R b The output voltages of the two branches are respectively:
in the formula (1), V i Representing the converter input voltage; v (V) oa Representing the output voltage of branch a; v (V) ob Representing the output voltage of branch b.
The step 1.2 specifically comprises the following steps:
peak inductor current I when the SIDO Buck converter is operating in CCM LP Turning inductor current I LT Valley inductor current I LV The calculation is as follows:
in the formula (2), I o Represents the average inductor current, anT represents a switching period;
when the converter operates in the critical state of CCM and DCM, I LV At a certain moment is exactly zero, and is eliminated by the formula (1)D is removed i Can obtain critical inductance L C The method comprises the following steps:
thus, when L>L C When the converter works in CCM; when L<L C When the converter is operating in DCM.
Critical inductance L C Respectively to R a And R is b The deviation derivative can be obtained:
therefore, if the critical load R of the converter C >R min ，R aC >R amin ，R bC >R bmin ，R min 、R aC 、R amin 、R bmin Representing minimum load, critical load of branch a, minimum load of branch a and minimum load of branch b respectively, when the load of the converter takes R a,min 、R b,min When the converter is in CCM operation;
load resistor R when SIDO Buck converter works in CCM a 、R b The output ripple voltages of the two branches are respectively:
in the formula (5), f represents a switching frequency;
thus, the converter load resistance R is obtained a 、R b The maximum output voltage at which is:
the step 1.3 specifically comprises the following steps:
let the input voltage range of SIDO Buck converter be V i,min ～V i,max The load ranges of the two branches are respectively as follows: r is R a,min ～R a,max And R is b,min ～R b,max In V i 、R a 、R b Establishing O-V for coordinate axes i R a R b In the space rectangular coordinate system, the working area of the SIDO Buck converter in the space rectangular coordinate system is a cube, and the vertexes and the coordinates of the cube are A (R b,min ，R a,max ，V i,min )、B(R b,max ，R a,max ，V i,min )、C(R b,max ，R a,min ，V i,min )、D(R b,min ，R a,min ，V i,min )、E(R b,min ，R a,max ，V i,max )、F(R b,max ，R a,max ，V i,max )、G(R b,max ，R a,min ，V i,max )、H(R b,min ，R a,min ，V i,max ) Different L's can be drawn according to the formula (3) and the formula (4) C A curve in which the critical inductances L corresponding to points D and F CD 、L CF The method comprises the following steps of:
when inductance l=l CD When the converter works in DCM in the full dynamic range; when inductance l=l CF When the converter is in the CCM, the converter works in the full dynamic range.
The step 2 is specifically as follows:
step 2.1: peak inductor current analysis of a converter
From formula (1), D is obtained i And substituting the peak inductance current I of the SIDO Buck converter into the CCM obtained in the step (2) LP The method comprises the following steps:
in the formula (9), the amino acid sequence of the compound,
will I LP Respectively to V i 、R a And R is b Obtaining the deviation guide:
in order to meet the requirements of both output ripple voltage and intrinsically safe output, the inductor is designed in L CD <L<L CF In this case, the converter is partially operated in CCM and partially operated in DCM, and as can be seen from equation (10), the peak inductor current of the converter is maximized when the input voltage is maximized and the load resistance is minimized, so that the peak inductor current of the SIDO Buck converter is maximized in the entire operating region:
step 2.2: output short-circuit energy analysis of converter
Load resistor R assuming circuit failure a 、R b One of the two branches is short-circuited, the other branch works normally, the circuit turns off a switching tube of the fault branch in time, the connection between the fault branch and the circuit is cut off, the short-circuit discharge model of the converter is single-capacitor discharge, and the maximum short-circuit energy released by the converter is as follows:
in this case, the short-circuit energy released by the converter is only the energy released by the faulty branch capacitance;
load resistor R assuming circuit failure a 、R b When two branches are short-circuited at the same time, the short-circuit discharge model of the converter is single-inductance double-capacitance discharge, if the main switching tube S i And the power supply is turned off in time, and the connection with the power supply is cut off, so that the sum of short-circuit energy released by the inductor and the capacitor is as follows:
the maximum short-circuit energy at which the converter output is short-circuited is thus:
W max ＝W max2 (14)
substituting the formula (6) and the formula (11) into the formula (13) to obtain the maximum output short-circuit energy of the converter as follows:
in the formula (15), the amino acid sequence of the compound,
the high frequency output ripple voltage of a normal switching power supply is small, so equation (15) approximates:
as can be seen from formulas (11) and (16), when V i ＝V i,max ，R a ＝R a,min ，R b ＝R b,min When the output short-circuit energy of the converter is maximum, and the output short-circuit energy is increased along with the increase of the inductance and the capacitance;
step 2.3: determining output intrinsic safety criteria for a converter
The output of the SIDO Buck converter can be equivalently a capacitive circuit, and thus when changedThe output voltages of the converters are V respectively oa 、V ob The corresponding filter capacitors are C respectively aB 、C bB The minimum energy of the circuit to ignite the gas is:
if the maximum output short circuit energy of the converter in the full dynamic working range is smaller than W B Then the converter is intrinsically safe and therefore the criterion for judging the output of the converter to be intrinsically safe is:
W max ＜W B (18)
since the transmission energy of the circuit is smaller at DCM than at CCM, if the CCM time converter meets the intrinsic safety requirement, the DCM also has to meet the intrinsic safety requirement.
The step 3 is specifically as follows:
when R is a ＝R a,min ，R b ＝R b,min When the converter is in CCM, the input voltage is V in order to maximize peak inductor current i ＝V i,max The minimum inductance that meets the intrinsic safety condition is therefore:
the maximum inductance is determined by intrinsic safety conditions, when the capacitance C a And C b After the selection, according to the intrinsic safety requirement, the value of the inductance must satisfy:
therefore, the inductance L satisfying the formula (20) max Is the maximum inductance that meets the intrinsically safe condition,
to sum up, the range of the value of the inductance L of the intrinsically safe SIDO Buck converter is:
L∈[L min ，L max ] (21)。
the step 4 is specifically as follows:
as can be seen from equation (5), the capacitance C satisfying the output ripple voltage of the converter a 、C b The minimum capacitance values are respectively as follows:
considering the influence of circuit parasitic parameters on the output ripple voltage of the converter, the actual capacitance selection needs to take allowance lambda, lambda=1-2, so that the capacitance C a 、C b Actually selecting the minimum value C of the capacitor min The method comprises the following steps of:
when the converter output is shorted, i.e. both branches are shorted simultaneously, it is assumed that the maximum energy released by the converter is exactly equal to the ignition energy, i.e. in the critical ignition state, and therefore there is:
W max ＝W B (24)
namely:
thus satisfying the formula (25) C a,max And C b,max Is the maximum capacitance that meets intrinsic safety requirements,
the capacitance value range meeting the intrinsic safety requirement of the SIDO Buck converter is as follows:
the beneficial effects of the invention are as follows:
the invention relates to a design method of an intrinsically safe single-inductor multi-output switch converter, which is characterized in that under the working condition of full dynamic input voltage-load, the working area of the converter, the possible short-circuit condition and maximum output short-circuit energy of the converter in the working area are determined, the output intrinsically safe criterion of the converter is obtained, and the design range of the inductor and the capacitor of the converter meeting the intrinsically safe requirement is obtained on the basis of meeting the basic output index of the converter; the designed SIDO Buck converter is suitable for dangerous environments such as mines, can provide theoretical guidance for development of the intrinsic safety SIDO Buck converter, and can also provide ideas for research of other intrinsic safety SIMO DC-DC converters.
Drawings
FIG. 1 is a block diagram of a single-inductor multiple-output intrinsically safe power supply;
FIG. 2 is a circuit topology of an SIDO Buck converter;
FIG. 3 is a waveform diagram of each branch when the SIDO Buck converter is operating in CCM;
FIG. 4 is a diagram of an operating region of the SIDO Buck converter;
FIG. 5 is a load resistor R in an SIDO Buck converter a 、R b One of the two branches is short-circuited, and the other branch is in a circuit state diagram when working normally;
FIG. 6 is a load resistor R in an SIDO Buck converter a 、R b A circuit state diagram in which two branches are simultaneously short-circuited;
FIG. 7 is an experimental waveform diagram of an example;
fig. 8 is an output short-circuit energy profile for different operating conditions of the example.
Detailed Description
The invention will be described in detail below with reference to the drawings and the detailed description.
The invention discloses a design method of an intrinsically safe single-inductor multi-output switch converter, which is implemented according to the following steps:
step 1: determining basic characteristics of an SIDO Buck converter;
step 1.1: calculating the output voltage of the SIDO Buck converter;
as shown in fig. 2, the SIDO Buck converter includes a switching tube S i 、S a 、S b Diode VD, inductance L, capacitance C a 、C b Load resistor R a 、R b ，D i 、D a 、D b Is a switching tube S i 、S a 、S b And satisfies the following: d (D) i <D b ，D a +D b ＝1；
When the converter works in the continuous conduction mode CCM, the load resistance R in the converter is obtained according to a time average equivalent circuit method a 、R b The output voltages of the two branches are respectively:
in the formula (1), V i Representing the converter input voltage; v (V) oa Representing the output voltage of branch a; v (V) ob Representing the output voltage of branch b.
Step 1.2: calculating the output ripple voltage of the SIDO Buck converter;
the waveforms of the branches of the SIDO Buck converter operating in CCM are shown in FIG. 3, and the peak inductor current I is shown in the case of the SIDO Buck converter operating in CCM LP Turning inductor current I LT Valley inductor current I LV The calculation is as follows:
in the formula (2), I o Represents the average inductor current, anT represents a switching period;
when the converter operates in the critical state of CCM and DCM, I LV At t 3 The moment is exactly zero, and D is eliminated by using the formula (1) i Can obtain critical inductance L C The method comprises the following steps:
thus, when L>L C When the converter works in CCM; when L<L C When the converter is operating in DCM.
Critical inductance L C Respectively to R a And R is b The deviation derivative can be obtained:
therefore, if the critical load R of the converter C >R min ，R aC >R amin ，R bC >R bmin ，R min 、R aC 、R amin 、R bmin Representing minimum load, critical load of branch a, minimum load of branch a and minimum load of branch b respectively, when the load of the converter takes R a,min 、R b,min When the converter is in CCM operation;
load resistor R when SIDO Buck converter works in CCM a 、R b The output ripple voltages of the two branches are respectively:
in the formula (5), f represents a switching frequency;
thus, the converter load resistance R is obtained a 、R b The maximum output voltage at which is:
step 1.3: determining the working area of an SIDO Buck converter;
let the input voltage range of SIDO Buck converter be V i,min ～V i,max The load ranges of the two branches are respectively as follows: r is R a,min ～R a,max And R is b,min ～R b,max As shown in FIG. 4, in V i 、R a 、R b Establishing O-V for coordinate axes i R a R b In the space rectangular coordinate system, the working area of the SIDO Buck converter in the space rectangular coordinate system is a cube, and the vertexes and the coordinates of the cube are A (R b,min ，R a,max ，V i,min )、B(R b,max ，R a,max ，V i,min )、C(R b,max ，R a,min ，V i,min )、D(R b,min ，R a,min ，V i,min )、E(R b,min ，R a,max ，V i,max )、F(R b,max ，R a,max ，V i,max )、G(R b,max ，R a,min ，V i,max )、H(R b,min ，R a,min ，V i,max ) Different L's can be drawn according to the formula (3) and the formula (4) C A curve in which the critical inductances L corresponding to points D and F CD 、L CF The method comprises the following steps of:
when inductance l=l CD When the converter works in DCM in the full dynamic range; when inductance l=l CF When the converter is in the CCM, the converter works in the full dynamic range.
Step 2: analyzing the output short-circuit energy of the SIDO Buck converter, and determining an output intrinsic safety criterion of the converter;
step 2.1: peak inductor current analysis of a converter
From formula (1), D is obtained i And substituting the peak inductance current I of the SIDO Buck converter into the CCM obtained in the step (2) LP The method comprises the following steps:
in the formula (9), the amino acid sequence of the compound,
will I LP Respectively to V i 、R a And R is b Obtaining the deviation guide:
in order to meet the requirements of both output ripple voltage and intrinsically safe output, the inductor is designed in L CD <L<L CF In this case, the converter is partially operated in CCM and partially operated in DCM, and as can be seen from equation (10), the peak inductor current of the converter is maximized when the input voltage is maximized and the load resistance is minimized, so that the peak inductor current of the SIDO Buck converter is maximized in the entire operating region:
step 2.2: output short-circuit energy analysis of converter
Assuming that the circuit fails, as shown in FIG. 5, the load resistor R a 、R b One of the two branches is short-circuited, the other branch works normally, the circuit turns off a switching tube of the fault branch in time, the connection between the fault branch and the circuit is cut off, the short-circuit discharge model of the converter is single-capacitor discharge, and the maximum short-circuit energy released by the converter is as follows:
in this case, the short-circuit energy released by the converter is only the energy released by the faulty branch capacitance;
assuming that the circuit fails, as shown in FIG. 6, the load resistor R a 、R b When two branches are short-circuited at the same time, the short-circuit discharge model of the converter is single-inductance double-capacitance discharge, if the main switching tube S i And the power supply is turned off in time, and the connection with the power supply is cut off, so that the sum of short-circuit energy released by the inductor and the capacitor is as follows:
the maximum short-circuit energy at which the converter output is short-circuited is thus:
W max ＝W max2 (14)
substituting the formula (6) and the formula (11) into the formula (13) to obtain the maximum output short-circuit energy of the converter as follows:
in the formula (15), the amino acid sequence of the compound,
the high frequency output ripple voltage of a normal switching power supply is small, so equation (15) approximates:
as can be seen from formulas (11) and (16), when V i ＝V i,max ，R a ＝R a,min ，R b ＝R b,min When the output short-circuit energy of the converter is maximum, and the output short-circuit energy is increased along with the increase of the inductance and the capacitance;
step 2.3: determining output intrinsic safety criteria for a converter
The output of the SIDO Buck converter can be equivalently a capacitive circuit, so when the output voltages of the converter are V oa 、V ob The corresponding filter capacitors are C respectively aB 、C bB The minimum energy of the circuit to ignite the gas is:
if the maximum output short circuit energy of the converter in the full dynamic working range is smaller than W B Then the converter is intrinsically safe and therefore the criterion for judging the output of the converter to be intrinsically safe is:
W max ＜W B (18)
since the transmission energy of the circuit is smaller at DCM than at CCM, if the CCM time converter meets the intrinsic safety requirement, the DCM also has to meet the intrinsic safety requirement.
Step 3: an intrinsically safe inductor design of the SIDO Buck converter;
when R is a ＝R a,min ，R b ＝R b,min When the converter is in CCM, the input voltage is V in order to maximize peak inductor current i ＝V i,max The minimum inductance that meets the intrinsic safety condition is therefore:
the maximum inductance is determined by intrinsic safety conditions, when the capacitance C a And C b After the selection, according to the intrinsic safety requirement, the value of the inductance must satisfy:
therefore, the inductance L satisfying the formula (20) max Is the maximum inductance that meets the intrinsically safe condition,
to sum up, the range of the value of the inductance L of the intrinsically safe SIDO Buck converter is:
L∈[L min ，L max ] (21)。
step 4: an intrinsically safe capacitive design of the SIDO Buck converter;
as can be seen from equation (5), the capacitance C satisfying the output ripple voltage of the converter a 、C b The minimum capacitance values are respectively as follows:
considering the influence of circuit parasitic parameters on the output ripple voltage of the converter, the actual capacitance selection needs to take allowance lambda, lambda=1-2, so that the capacitance C a 、C b Actually selecting the minimum value C of the capacitor min The method comprises the following steps of:
when the converter output is shorted, i.e. both branches are shorted simultaneously, it is assumed that the maximum energy released by the converter is exactly equal to the ignition energy, i.e. in the critical ignition state, and therefore there is:
W max ＝W B (24)
namely:
thus satisfying the formula (25) C a,max And C b,max Is the maximum capacitance that meets intrinsic safety requirements,
the capacitance value range meeting the intrinsic safety requirement of the SIDO Buck converter is as follows:
instance verification
To verify the correctness of theoretical analysis, a intrinsically safe SIDO Buck converter is designed, and the main parameters of the circuit are shown in table 1.
Table 1 converter circuit parameters
Select V i ＝20V，R a ＝R b =10Ω (the short-circuit energy is maximum at this time), and the duty ratio D can be obtained by substituting formula (1) i And D b The method comprises the following steps of: d (D) i ＝0.42，D b =0.67. Substituting the parameters into equation (19) yields a minimum inductance of: l (L) min =70 μh, so inductance l=500 μh is desirable. Substituting the parameters into the formula (22), taking λ=1.2, and obtaining the values of the capacitances as follows: c (C) a ＝81μF，C b ＝107μF。
Substituting the calculated inductance and capacitance values into the equation (16) to obtain the maximum output short-circuit energy W max = 7.092mJ, less than the given minimum ignition energy, thus meeting the set intrinsic safety requirements.
In the experimental circuit, the inductance takes 500 mu H, and the capacitance takes the following value: c (C) a ＝81μF，C b =107 μf, the experimental waveforms are shown in fig. 7.
As can be seen from an analysis of fig. 7, the output voltage V of the branch a oa =5v, output ripple voltage V PP-oa =168 mV; output voltage V of branch b ob =10v, output ripple voltage V PP-ob =182 mV; therefore, the output voltage and the output ripple voltage of the converter meet the design requirements. Further, as can be seen from the figure, peak inductor current I LP =1.8a, substituting into formula (16) to calculate W max = 7.173mJ, less than the given minimum ignition energy, so the converter meets the intrinsically safe design requirements, verifying the correctness of the theoretical analysis.
Further experiments were performed under different input voltages, load conditions, where the input voltage was taken V i =15v and V i The load range of branch a and branch b is 10 to 50Ω, and the distribution of the short-circuit release energy under the most dangerous condition is shown in fig. 8.
As can be seen from fig. 8, the outputShort-circuit energy follows the input voltage V i Increases with decreasing load resistance, and when the input voltage takes 20V, the load takes R a ＝10Ω、R b When the power is 10 omega, the short-circuit release energy of the converter is maximum, the experimental result is consistent with the theoretical analysis, and the correctness of the theoretical analysis is verified.

Claims (1)

1. The design method of the intrinsically safe single-inductor multi-output switching converter is characterized by comprising the following steps of:
step 1: determining basic characteristics of an SIDO Buck converter;
step 1.1: calculating the output voltage of the SIDO Buck converter;
the SIDO Buck converter comprises a switching tube S i 、S a 、S b Diode VD, inductance L, capacitance C a 、C b Load resistor R a 、R b ，D i 、D a 、D b Is a switching tube S i 、S a 、S b And satisfies the following: d (D) i <D b ，D a +D b ＝1；
When the converter works in the continuous conduction mode CCM, the load resistance R in the converter is obtained according to a time average equivalent circuit method a 、R b The output voltages of the two branches are respectively:
in the formula (1), V i Representing the converter input voltage; v (V) oa Representing the output voltage of branch a; v (V) ob Representing the output voltage of branch b;
step 1.2: calculating the output ripple voltage of the SIDO Buck converter;
peak inductor current I when the SIDO Buck converter is operating in CCM LP Turning inductor current I LT Valley inductor current I LV The calculation is as follows:
in the formula (2), I o Represents the average inductor current, anT represents a switching period;
when the converter operates in the critical state of CCM and DCM, I LV At a certain point in time, the value D is eliminated by the formula (1) i Can obtain critical inductance L C The method comprises the following steps:
thus, when L>L C When the converter works in CCM; when L<L C When the converter is operating in DCM;
critical inductance L C Respectively to R a And R is b The deviation derivative can be obtained:
therefore, if the critical load R of the converter C >R min ，R aC >R amin ，R bC >R bmin ，R min 、R aC 、R amin 、R bmin Representing minimum load, critical load of branch a, minimum load of branch a and minimum load of branch b respectively, when the load of the converter takes R a,min 、R b,min When the converter is in CCM operation;
load resistor R when SIDO Buck converter works in CCM a 、R b The output ripple voltages of the two branches are respectively:
in the formula (5), f represents a switching frequency;
thus, the converter load resistance R is obtained a 、R b The maximum output voltage at which is:
step 1.3: determining the working area of an SIDO Buck converter;
let the input voltage range of SIDO Buck converter be V i,min ～V i,max The load ranges of the two branches are respectively as follows: r is R a,min ～R a,max And R is b,min ～R b,max In V i 、R a 、R b Establishing O-V for coordinate axes i R a R b In the space rectangular coordinate system, the working area of the SIDO Buck converter in the space rectangular coordinate system is a cube, and the vertexes and the coordinates of the cube are A (R b,min ，R a,max ，V i,min )、B(R b,max ，R a,max ，V i,min )、C(R b,max ，R a,min ，V i,min )、D(R b,min ，R a,min ，V i,min )、E(R b,min ，R a,max ，V i,max )、F(R b,max ，R a,max ，V i,max )、G(R b,max ，R a,min ，V i,max )、H(R b,min ，R a,min ，V i,max ) Different L's are drawn according to the formula (3) and the formula (4) C A curve in which the critical inductances L corresponding to points D and F CD 、L CF The method comprises the following steps of:
when inductance l=l CD When the converter works in DCM in the full dynamic range; when inductance l=l CF When the converter works in CCM in the full dynamic range;
step 2: analyzing the output short-circuit energy of the SIDO Buck converter, and determining an output intrinsic safety criterion of the converter;
step 2.1: peak inductor current analysis of a converter
From formula (1), D is obtained i And substituting the peak inductance current I of the SIDO Buck converter into the CCM obtained in the step (2) LP The method comprises the following steps:
in the formula (9), the amino acid sequence of the compound,
will I LP Respectively to V i 、R a And R is b Obtaining the deviation guide:
in order to meet the requirements of both output ripple voltage and intrinsically safe output, the inductor is designed in L CD <L<L CF In this case, the converter is partially operated in CCM and partially operated in DCM, and as can be seen from equation (10), the peak inductor current of the converter is maximized when the input voltage is maximized and the load resistance is minimized, so that the peak inductor current of the SIDO Buck converter is maximized in the entire operating region:
step 2.2: output short-circuit energy analysis of converter
Load resistor R assuming circuit failure a 、R b One of the two branches is short-circuited, the other branch works normally, the circuit turns off a switching tube of the fault branch in time, the connection between the fault branch and the circuit is cut off, the short-circuit discharge model of the converter is single-capacitor discharge, and the maximum short-circuit energy released by the converter is as follows:
in this case, the short-circuit energy released by the converter is only the energy released by the faulty branch capacitance;
load resistor R assuming circuit failure a 、R b When two branches are short-circuited at the same time, the short-circuit discharge model of the converter is single-inductance double-capacitance discharge, if the main switching tube S i And the power supply is turned off in time, and the connection with the power supply is cut off, so that the sum of short-circuit energy released by the inductor and the capacitor is as follows:
the maximum short-circuit energy at which the converter output is short-circuited is thus:
W max ＝W max2 (14)
substituting the formula (6) and the formula (11) into the formula (13) to obtain the maximum output short-circuit energy of the converter as follows:
in the formula (15), the amino acid sequence of the compound,
the high frequency output ripple voltage of a normal switching power supply is small, so equation (15) approximates:
as can be seen from formulas (11) and (16), when V i ＝V i,max ，R a ＝R a,min ，R b ＝R b,min When the output short-circuit energy of the converter is maximum, and the output short-circuit energy is increased along with the increase of the inductance and the capacitance;
step 2.3: determining output intrinsic safety criteria for a converter
The output of the SIDO Buck converter is equivalent to a capacitive circuit, so when the output voltages of the converter are V oa 、V ob The corresponding filter capacitors are C respectively aB 、C bB The minimum energy of the circuit to ignite the gas is:
if the maximum output short circuit energy of the converter in the full dynamic working range is smaller than W B Then the converter is intrinsically safe and therefore the criterion for judging the output of the converter to be intrinsically safe is:
W max ＜W B (18)
because the transmission energy of the circuit is smaller than that of the CCM in the DCM, if the CCM time converter meets the intrinsic safety requirement, the DCM also needs to meet the intrinsic safety requirement;
step 3: an intrinsically safe inductor design of the SIDO Buck converter;
when R is a ＝R a,min ，R b ＝R b,min When the converter is in CCM, the input voltage is V in order to maximize peak inductor current i ＝V i,max The minimum inductance that meets the intrinsic safety condition is therefore:
the maximum inductance is determined by intrinsic safety conditions, when the capacitance C a And C b After the selection, according to the intrinsic safety requirement, the value of the inductance must satisfy:
therefore, the inductance L satisfying the formula (20) max Is the maximum inductance that meets the intrinsically safe condition,
to sum up, the range of the value of the inductance L of the intrinsically safe SIDO Buck converter is:
L∈[L min ，L max ] (21)；
step 4: an intrinsically safe capacitive design of the SIDO Buck converter;
as can be seen from equation (5), the capacitance C satisfying the output ripple voltage of the converter a 、C b The minimum capacitance values are respectively as follows:
considering the influence of circuit parasitic parameters on the output ripple voltage of the converter, the actual capacitance selection needs to take allowance lambda, lambda=1-2, so that the capacitance C a 、C b Actually selecting the minimum value C of the capacitor min The method comprises the following steps of:
when the converter output is shorted, i.e. both branches are shorted simultaneously, it is assumed that the maximum energy released by the converter is exactly equal to the ignition energy, i.e. in the critical ignition state, and therefore there is:
W max ＝W B (24)
namely:
thus satisfying the formula (25) C a,max And C b,max Is the maximum capacitance that meets intrinsic safety requirements,
the capacitance value range meeting the intrinsic safety requirement of the SIDO Buck converter is as follows:
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