CN105021241B - The electromagnetic flow meter excitation control system of PWM based on current error control - Google Patents
The electromagnetic flow meter excitation control system of PWM based on current error control Download PDFInfo
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Abstract
The present invention relates to a kind of electromagnetic flow meter excitation control system of the PWM based on current error control.It is made up of high voltage power supply, energy feedback circuit, exciting coil drive circuit, galvanometer circuit, logic circuit, PWM controller and excitation con-trol timing sequence generating circuit.Using the inductive load characteristic of magnet exciting coil, the error amount of exciting current is controlled, exports the turn-on and turn-off of the PWM waveform controlling switch pipe of upper frequency, realizes the stabilization of exciting current.The voltage of the power supply of exciter control system is high, and exciting current can be made to have faster response speed, be favorably improved the excitation frequency of electromagnetic flowmeter；High voltage power supply is applied directly on magnet exciting coil by switching tube, considerably reduces the power of electromagnetic flow meter excitation control system consumption；Exciter control system based on PWM is the control system of a closed loop, can encourage the primary instrument with different DC resistance magnet exciting coils, strong adaptability.
Description
Technical field
The present invention relates to field of flow detection, and in particular to a kind of electromagnetic current of the PWM based on current error control
Gauge exciter control system, the electromagnetic flow meter excitation control system of more low-power consumption and higher frequency can be realized.
Background technology
Electromagnetic flowmeter is to measure conducting liquid volume flow according to the operation principle of Faraday's electromagnetic induction law
Instrument, response speed, antijamming capability and zero stability when its exciting method directly determines electromagnetic flowmeter work.Excitation
Circuit provides stable exciting current to the magnet exciting coil in primary instrument, to produce constant magnetic field, quilt in pipeline is measured
Fluid measured motional induction in magnetic field goes out induced electromotive force, and rate of flow of fluid can be obtained by detecting and handling the electromotive force signal, from
And realize the measurement of flow.
HeFei University of Technology (Xu Kejun, Zhang Zhen, Yang Shuanlong, waits to have the Electromagnetic Flow of bypass and energy feedback circuit
Count high/low voltage switching excitation system, application number：201110350132.3 the applying date：That 2011.11.08) develops has quick ring
The electromagnetic flowmeter high-low voltage power source switched energization control system answered drastically increases excitation frequency, has electromagnetic flowmeter
Faster response speed；Meanwhile the stabilization of electromagnetic flowmeter electric current in measurement process is ensure that, measurement result is accurate.But
High-low voltage power source switched energization control system there may be following three problems：(1) power consumption and heating problem.Due in high-low pressure
In power supply switched energization control system, the stabilization of exciting current is realized by constant-current control circuit, and constant-current control circuit needs
Larger voltage is undertaken to maintain the stabilization of exciting current, and exciting current value is big, therefore, constant-current control circuit can consume compared with
Big power, and produce heating problem.(2) high voltage power supply is switched to after low-tension supply, and exciting current stills need longer tune
The whole time could enter stable state, and which limits the further raising of electromagnetic flowmeter excitation frequency.Because high voltage power supply switches
To low-tension supply, exciting current is stilled need just eventually enter into stable state under the regulation of constant-current control circuit, and this is adjusted
The process of section is carried out under the excitation of low-tension supply, and therefore, regulation process is longer, the coil inductance particularly when sensor
Value is bigger, and the required time is longer, and this is unfavorable for the raising of excitation frequency.(3) high-low voltage power source switched energization control system
System can only encourage the magnet exciting coil of physical parameter within the specified range.Because in high-low voltage power source switched energization control system,
Constant-current control circuit is to maintain to flow through the constant of electric current in magnet exciting coil by undertaking the pressure drop in addition to magnet exciting coil, without
DC resistance with magnet exciting coil is unequal, and for the magnet exciting coil of a preset parameter, it is stable in exciting current
When, the stabilization of exciting current can be always maintained on constant-current control circuit in the presence of a most rational pressure drop, constant current control will not be made again
Excessive pressure drop is undertaken on circuit processed so as to cause serious heating problem.But when encouraging the different excitation of another parameter
During coil, the pressure drop on constant-current control circuit can deviate from this optimum value, particularly the DC resistance phase when magnet exciting coil
When difference is larger, constant-current control circuit cisco unity malfunction may be made, or constant-current control circuit is seriously generated heat.
Chen quintessences etc. (Chen quintessences, Hu Guoqing, Zou Chong, wait a kind of excitation systems for capacitive electromagnetic flow meter of to grind
Make [J] Chinese journal of scientific instrument, 2013,34 (7)：1660-1666) to the field circuit based on current source and based on current-mode
The power of the field circuit consumption of PWM full-bridge inverters compares, and analysis shows are based on current mode PWM full-bridge inverter
The power consumption of field circuit be far smaller than the field circuit based on current source, and have developed based on current mode PWM full-bridge inverting
The exciter control system of device.But following two problems be present：(1) when excitation system works, exciting current fluctuation is big.Using
Hysteresis comparator circuit sets two threshold values up and down, makes the amplitude stability of exciting current between two thresholds, the difference of upper lower threshold value
Value directly determines the size of exciting current fluctuation.When upper and lower threshold difference is smaller, the fluctuation of exciting current will be smaller, but
It is easily to be influenceed by noise and interference voltage, causes output control signal unstable, frequently switch on switching tube, increase switch
The switching loss of pipe.When upper and lower threshold difference is larger, output control signal is relatively stable, still, may cause exciting current ripple
It is dynamic big, larger differential interference is produced, influences to measure.(2) switching tube driving problems.The switching tube of bridge arm is using bootstrapping electricity thereon
The type of drive of appearance, i.e. bootstrap capacitor, which once charge, will realize multiple driving, with the increase of driving number, on bootstrap capacitor
Voltage can decline, last it is possible that the problem of bootstrap capacitor makes switching tube conducting impacted because of driving voltage deficiency.
Japanese Yokogawa Electric Corporation (Tamotsu Kobayashi, Kenichi Kuromori, Shigeru Goto,
Et al. Electromagnetic flow meter [P] United States, 4773274,1988-9-27) disclose
The dual-frequency excitation scheme of electromagnetic flowmeter, the Excitation Control Scheme are by setting constant current transistor to carry out perseverance in H bridges low side
Flow control, this constant current control method can cause the fluctuation of H bridges lower terminal voltage larger, be unfavorable for the control of H bridge switch, while can also deposit
In heating problem.Japanese Yokogawa Electric Corporation (Ishikawa Yu Guang electromagnetic flowmeters [P] China, CN1734240,2006-
2-15) and disclose using on-off modulated electromagnetic flowmeter, still, do not introduce key technology details.
The content of the invention
In order to improve the excitation frequency of electromagnetic flowmeter, reduce the power of field circuit consumption, the present invention provides a kind of base
In the PWM excitation system of current error control, there is the characteristics of excitation frequency height and field circuit low in energy consumption.
PWM excitation system based on current error control is driven by high voltage power supply, energy feedback circuit, magnet exciting coil
Circuit, galvanometer circuit, logic circuit, PWM controller and excitation con-trol timing sequence generating circuit composition；
High voltage power supply provides DC voltage, and its value is 60-80V.It is to reduce exciting current using higher voltage
Rise time, realize the quick response of exciting current, effectively improve the excitation frequency of electromagnetic flowmeter；
Energy feedback circuit absorbs the energy in magnet exciting coil at the end of each excitation half period, and in next half cycle
When phase starts, by the energy feedback being absorbed to magnet exciting coil, the recycling of energy is realized；
Exciting coil drive circuit includes H bridge switch circuit and H-bridge drive circuit, and exciting current is realized in an effect
Stable, another effect is to change the direction of exciting current in magnet exciting coil, realizes square-wave excitation, avoids electrode polarization；
Current value in galvanometer circuit detection stream overexcitation coil, fed-back current signals are provided for PWM controller；
PWM controller detects exciting current value in real time, and according to the big of exciting current value and exciting current setting value difference
Small output frequency is fixed, dutycycle from adjustable PWM waveform, to produce stable current value in magnet exciting coil；
Excitation con-trol timing sequence generating circuit exports the relatively low complementary PWM square waves with dead band of two-way frequency, is magnet exciting coil
Drive circuit provides control signal, directly determines the excitation frequency of electromagnetic flowmeter；
Logic circuit is controlled by PWM controller output signal and excitation con-trol timing sequence generating circuit output signal, to encourage
Magnetic coil drive circuit provides control signal, for maintaining the stabilization of exciting current；
In the incipient stage of each excitation half period, the exciting current value of galvanometer circuit detection is less than the setting of exciting current
Value, current error is larger, and therefore, PWM controller output duty cycle is 1 PWM ripples, and now high voltage power supply is driven by magnet exciting coil
Voltage is all added on magnet exciting coil by dynamic circuit, and the electric current in magnet exciting coil rises rapidly.Connect when exciting current value rises to
During nearly setting value, current error value also begins to enter in the range of setting, and PWM controller output frequency is higher and dutycycle is less than
1 PWM ripples, and the electric current value stabilization for making to flow through magnet exciting coil is in setting value.Exciting current is stable to excitation half period knot
Beam, excitation con-trol sequential enter dead band state, and now, exciting coil drive circuit is stopped, the energy quilt in magnet exciting coil
Energy feedback circuit absorbs.After state terminates in dead band, next excitation half period is entered, energy feedback circuit is by absorption
Energy feedback can not only improve the efficiency of energy utilization, but also can accelerate the response speed of exciting current to magnet exciting coil
Degree.
The excitation con-trol sequential is the complementary PWM ripples for carrying dead band of two-way, the dead band that excitation con-trol sequential specially provides
Time is used for the energy that the storage in magnet exciting coil is absorbed in every half of excitation end cycle, improves energy utilization efficiency.
The advantageous effects of the present invention embody in the following areas：
1. in excitation system of the present invention, the voltage of excitation power supply is 60-80V, greatly accelerates exciting current
Response speed, it is possible to achieve higher excitation frequency.
2. the present invention is the stabilization for using the PWM modulation technology based on current error control to realize exciting current, Ke Yi great
It is big to reduce the power consumption of field circuit, while the heating of electromagnetic flowmeter is reduced, to ensure electromagnetic flowmeter for a long time, stably, reliably
Work.
3. exciter control system of the present invention and the flexibility that magnet exciting coil is used cooperatively are more preferable.
Brief description of the drawings
Fig. 1 is the composition frame chart of the PWM excitation system based on current error control；
Fig. 2 is partial circuit schematic diagram, i.e. high voltage power supply, energy in the PWM excitation system based on current error control
Measure feedback circuit, exciting coil drive circuit and galvanometer circuit schematic diagram；
Fig. 3 is PWM controller circuit diagram；
Fig. 4 is logic circuit schematic diagram；
Fig. 5 is excitation con-trol timing sequence generating circuit schematic diagram；
Fig. 6 is the control signal oscillogram of the PWM excitation system based on current error control；
Fig. 7 is that exciting current flows to schematic diagram.
Embodiment
The present invention is further illustrated below in conjunction with the accompanying drawings.
The present invention design philosophy be：In high-low voltage power source switched energization control system, although high voltage power supply can make to encourage
Magnetoelectricity stream rapidly increases to the current value of setting, but after high voltage power supply switches to low-tension supply, exciting current needs
Stable state can be just eventually entered under the regulation of constant-current control circuit.This regulation process is carried out under low-tension supply, and low pressure
Power supply only has more than ten volts, and therefore, governing speed is slow, and particularly when the inductance value of magnet exciting coil is larger, this is particularly problematic,
The serious raising for constraining electromagnetic flowmeter excitation frequency.Constant-current control circuit undertakes very for the constant needs of guarantee exciting current
Big pressure drop, and exciting current value is larger, this can cause the heating problem of electromagnetic flowmeter.High/low voltage switching excitation control system
Low tension source value depend on the physical parameter of magnet exciting coil, therefore, after low tension source value determines, only physical parameter
Magnet exciting coil within the specified range could be used, this just limit high-low pressure excitation system coordinate primary instrument use it is flexible
Property.For problem above, the electromagnetic flow meter excitation control system of the PWM based on current error control is developed, using encouraging
Magnetic coil is the characteristic that inductive load its electric current can not be mutated, and using single high-voltage DC power supply, passes through PWM, i.e. arteries and veins
Width adjusting is rushed, in the ascent stage of exciting current, forms big dutycycle, whole excitation voltages are applied to magnet exciting coil
On, accelerate the rising of exciting current, it is quickly entered stable state, so as to improve excitation frequency；After exciting current enters stable state,
By PWM, small dutycycle is formed, exciting current is fluctuated a little with fixed frequency, so both ensures excitation
Electric current it is basicly stable, be advantageous to signal transacting；Magnet exciting coil is set to continue to undertake most excitation voltage again, not because of excitation electricity
After flowing complete stability, magnet exciting coil just turns into pure resistance (i.e. D.C. resistance), the pressure drop very little undertaken thereon, causes field power supply
Voltage just most of drop on field circuit, produces very big heating.Field circuit is encapsulated in the watchcase of electromagnetic flowmeter,
Radiating is difficult, and magnet exciting coil is arranged on pipeline, rapid heat dissipation.So the present invention can be greatly enhanced excitation frequency, and
Reduce the heating of electromagnetic flowmeter, increase the service life.
It is characteristic of the invention that：（1）Only by driving voltage of the high voltage power supply as magnet exciting coil in exciter control system, i.e.,
The rising of exciting current and stably maintained by high voltage power supply, this is it is avoided that the long regulating time brought by handoff procedure.
（2）Only connected between high voltage power supply and magnet exciting coil by switching tube, and the pressure drop very little on switching tube, it can greatly reduce and encourage
The caloric value of magnetic control system.（3）According to the current value flowed through in magnet exciting coil and the size of setting value error, PWM controller
The PWM waveform that output frequency is fixed, with the turn-on and turn-off of controlling switch pipe, so as to form the control loop of a closed loop, increase
The adaptability that strong exciter control system is used cooperatively from the primary instrument of different DC resistance magnet exciting coils.
The composition frame chart of present system including high voltage power supply 1, energy feedback circuit 2, magnet exciting coil as shown in figure 1, drive
Dynamic circuit 3, galvanometer circuit 4, logic circuit 5, PWM controller 6 and excitation con-trol timing sequence generating circuit 7.
The course of work of present system is：In the incipient stage of each excitation half period, galvanometer circuit 4, which detects, to be based on
The exciting current value of the PWM excitation system of current error control is less than the exciting current value of setting, and current error is larger, because
This, the output duty cycle of PWM controller 6 is 1 PWM ripples, and now high voltage power supply 1 is electric by excitation by exciting coil drive circuit 3
Pressure is all added on magnet exciting coil, and the electric current in magnet exciting coil rises rapidly.When exciting current value rises towards encouraging for setting
During magnetoelectricity flow valuve, in the range of current error value initially enters setting, the output frequency of PWM controller 6 is higher and dutycycle is less than 1
PWM ripples, and make the electric current value stabilization that magnet exciting coil flows through in the current value of setting.Exciting current is stable to the excitation half period
Terminate, excitation con-trol sequential enters dead band state, and now, exciting coil drive circuit 3 is stopped, the energy in magnet exciting coil
Absorbed by energy feedback circuit 2.After state terminates in dead band, next excitation half period is entered, energy feedback circuit 2 will be inhaled
The magnet exciting coil that the energy feedback of receipts is given, this not only increases energy utilization efficiency, and accelerates the response speed of exciting current
Degree.
Fig. 2 is the schematic diagram of partial circuit in present system, specifically includes high voltage power supply 1, energy feedback circuit 2, encourages
Magnetic coil drive circuit 3 and galvanometer circuit 4.
High voltage power supply 1 is 60-80V high-voltage DC power supply, can accelerate the rate of climb of exciting current, reduces exciting current
Transit time.
Energy feedback circuit 2 is made up of electric capacity C1, voltage-stabiliser tube Z1 and resistance R3.Wherein, electric capacity C1 is storage capacitor, is used
To absorb the energy in every half of excitation end cycle in magnet exciting coil, and in the beginning in back to back lower half of excitation cycle
Stage is the energy feedback of absorption to magnet exciting coil.Electric capacity C1 value is small, so that electric capacity C1 is after energy is absorbed, thereon
Magnitude of voltage rises rapidly, can soon be higher than the value of high voltage power supply.This is advantageous to the energy feedback by the overwhelming majority to excitation
Coil, improve the utilization ratio to recover energy, it helps improve the response speed of exciting current.Voltage-stabiliser tube Z1 prevents electric capacity C1
On magnitude of voltage it is too high, circuit is shielded.Resistance R3 is used for the slow release electricity when exciter control system is stopped
Hold the electric energy in C1, prevent the residual voltage on electric capacity C1 from being damaged to human body.
Exciting coil drive circuit 3 includes H bridge switch circuit and H-bridge drive circuit.H bridge switch circuit is by first switch pipe
Q1, second switch pipe Q2, the 3rd switching tube Q3 and the 4th switching tube Q4 compositions.Wherein, the 3rd switching tube Q3 drive circuit and
The power supply of the 4th switching tube Q4 drive circuit isolated from power with exciter control system respectively, it is possible to achieve higher opens
Frequency is closed, while reduces the switching loss of switching tube；When first switch pipe Q1 works, the 3rd switching tube Q3 could work, and second
When switching tube Q2 works, the 4th switching tube Q4 could work.First switch pipe Q1 switching frequency and opening for second switch pipe Q2
Pass frequency is identical, and the two is used for the direction for changing exciting current, and the switching frequency of the two determines the excitation frequency of electromagnetic flowmeter
Rate；3rd switching tube Q3 switching frequency and the 4th switching tube Q4 switching frequency are identical, for maintaining the stabilization of exciting current.
First switch pipe Q1 and second switch pipe Q2 switching frequency are less than the 3rd switching tube Q3 and the 4th switching tube Q4 switching frequency,
First switch pipe Q1 switching frequency and second switch pipe Q2 switching frequency can be 12.5,25,75,160 hertz, and the 3rd opens
It is 20 KHzs to close pipe Q3 switching frequency and the 4th switching tube Q4 switching frequency.First switch pipe Q1 and the 3rd switching tube Q3
Cooperating, when first switch pipe Q1 is turned on, the 3rd switching tube Q3 carries out switch control.Second switch pipe Q2 and the 4th switching tube
Q4 cooperatings, when second switch pipe Q2 is turned on, the 4th switching tube Q4 carries out switch control.H-bridge drive circuit is by the first optocoupler
Element P1, the second optic coupling element P2, the first level shifting circuit T1 and second electrical level change-over circuit T2 are formed.First optic coupling element
P1 amplifies control signal CT_3, for driving the 3rd switching tube Q3, the isolated from power of its power supply Vex1 and system.Second
Optic coupling element P2 amplifies control signal CT_4, for driving the 4th switching tube Q4, the power supply of its power supply Vex2 and system
Isolation.First level shifting circuit T1 amplifies control signal CT_1, for driving first switch pipe Q1, the ground of its power supply
Ground with excitation system is samely.Second electrical level change-over circuit T2 amplifies control signal CT_2, for driving second to open
Pipe Q2, the ground of its power supply and the ground of excitation system are closed as samely.
Galvanometer circuit 4 is made up of the first inspection leakage resistance R1, the second inspection leakage resistance R2 and single-pole double-throw switch (SPDT) S1.First inspection stream
Resistance R1 detections are that the electricity in magnet exciting coil is flowed through when first switch pipe Q1 and the 3rd switching tube the Q3 work of H bridge switch circuits
Flow valuve.Flowed through when what the second inspection leakage resistance R2 was detected is second switch pipe Q2 and the 4th switching tube the Q4 work of H bridge switch circuits
Current value in magnet exciting coil.Single-pole double-throw switch (SPDT) S1 suspension control signals CT_1 control, the electric current for flowing through magnet exciting coil is defeated
Go out to PWM controller 6, the current signal for ensureing to feed back to PWM controller 6 is always just.
Fig. 3 is the circuit diagram of PWM controller 6.PWM controller 6 by the first amplifier U1, the second amplifier U2, resistance R4,
R5, R6, R7, R8, electric capacity C2, a reference source Vref and triangular wave eT compositions.Wherein, a reference source Vref is used to set exciting current
Stationary value.Triangular wave eT is error reference signal, compared with error amount, for producing the pwm waveform with it with frequency.First
Amplifier U1 and resistance R4, R5, R6, R7 composition error amplifying circuit, for amplifying the value of feedback of exciting current and the difference of a reference source
Value, its multiplication factor are determined that multiplication factor can not be too big by R4, R5, R6 and R7, and too conference makes the waveform that PWM controller exports
Irregular, the too small fluctuation that can make exciting current becomes big；Wherein the feedback signal of exciting current is connected to the first fortune by resistance R4
U1 inverting input is put, a reference source Vref is connected to the first amplifier U1 normal phase input end by resistance R6.Second amplifier U2, electricity
R8 and electric capacity C2 composition square wave output circuits are hindered, the positive that the output signal of error amplifier delivers to the second amplifier U2 by R8 is defeated
Enter end；Triangular wave eT is connected to the second amplifier U2 inverting input, for controlling the output frequency of PWM controller, the second amplifier
U2 passes through the output signal of relative error amplifier and the switching tube Q3 and the 4th switching tube Q4 of triangular wave eT signal outputs the 3rd
Control signal C_PWM；Electric capacity C2 is attempted by the second amplifier U2 normal phase input end and output end, and shaping electricity is formed with resistance R8
Road, because when the current value and the setting value of exciting current that flow through magnet exciting coil are equal, square wave output circuit may export height
Level may also export low level, so, shaping circuit can be formed by electric capacity C2 and resistance R8, PWM controller 6 is exported
C_PWM waveforms carry out shaping.Electric capacity C2 and resistance the R8 course of work is：It is for square wave output circuit output voltage amplitude
0V low level, when the current value and the setting value of exciting current that flow through magnet exciting coil are equal, due to the voltage on C2 electric capacity
It can not be mutated, so, square wave output circuit continues to output low level；When the current value for flowing through magnet exciting coil is less than exciting current
During setting value, the second amplifier U2 output high level, and electric capacity C2 is charged by resistance R8, because electric capacity C2 capacitance is smaller,
So the output of square wave output circuit is turned negative number to positive number quickly.Height for square wave output circuit output voltage amplitude close to power rail
Level, when the current value and the setting value of exciting current that flow through magnet exciting coil are equal, because the voltage on C2 electric capacity can not dash forward
Become, so, square wave output circuit continues to output high level；When the current value for flowing through magnet exciting coil is more than the setting value of exciting current
When, the second amplifier U2 output low levels, electric capacity C2 is discharged by resistance R8, because electric capacity C2 capacitance is smaller, so square wave is defeated
The output for going out circuit is negative by rotating forward quickly.
The course of work of PWM controller circuit：In exciting current ascent stage, the current value for flowing through magnet exciting coil is less than and encouraged
The setting value of magnetoelectricity stream, the error amplifying circuit with larger multiplication factor amplify to both differences, the close fortune of output amplitude
The high level signal of discharge source rail, now, the output valve of error amplifying circuit are consistently greater than triangular wave eT maximums, square wave output
Circuit output dutycycle is 1 PWM waveform.In the exciting current stabilization sub stage, the current value and exciting current of magnet exciting coil are flowed through
Setting value between difference after error amplifying circuit amplifies, just fall triangular wave eT maximum and minimum value it
Between.When error amplification signal rises to the value more than triangular signal in the same time, the output of square wave output circuit is turned by negative
For just；When error amplification signal deteriorates to less than the value of triangular signal in the same time, the output of square wave output circuit is by just
Switch to bear.Repeat the reverse turn operation within the eT of triangular signal each cycle, to export pwm waveform.
Fig. 4 is the schematic diagram of logic circuit 5.Logic circuit is made up of the first logical device U3 and the second logical device U4.
Control signal CT_1 and control signal C_PWM delivers to the first logical device U3 two inputs, the first logical device U3 respectively
Output signal CT_3 be used for control the 3rd switching tube Q3 turn-on and turn-off.C_PWM points of control signal CT_2 and control signal
The second logical device U4 two inputs are not delivered to, and the second logical device U4 output signal CT_4 is used to control the 4th switch
Pipe Q4 turn-on and turn-off.
Fig. 5 is the circuit diagram of excitation con-trol timing sequence generating circuit 7.Control signal CT_1 and control signal CT_2 be by
Excitation con-trol timing sequence generating circuit dsp chip U5（TMS320F28335）In ePWM modules produce, be complementary to occur and carry
The two-way PWM waveform in dead band.It determines the excitation frequency of electromagnetic flowmeter.TMS320F28335DSP is electromagnetic flowmeter
Computing and control core, arithmetic speed 150MHz, single command cycle 6.67ns, abundant peripheral hardware is integrated with, for extension
Instrument function, its exterior device is reduced, reduce printed circuit board (PCB) cloth version scale, reduce cost and improve system reliability etc. and rise
Important effect is arrived.TMS320F28335DSP has 6 independent ePWM modules, each with oneself independent when base, and not
With module between can be synchronous, according to when base pattern can be flexibly configured to a variety of interrupt modes and ask interrupt thing
Part, and the control to dead band is convenient to, and is suitable for producing the excitation drive control of two-way mutual symmetry in the present invention
Signal；It is internally integrated the SRAM of FLASH, 34K word of 256K words, you can as the program space but also as data space, be
Electromagnetic Flow meter systems provide the program and data space of abundance；A variety of serial communication interfaces such as McBSP, SCI, SPI, I2C
Deng flexibly realizing the requirement of a variety of different pieces of information transformats.In addition, also independent eCAP, eQEP, 16 general timings
Device, 32 bit CPU timers, house dog etc..
Fig. 6 is control signal oscillogram in PWM exciter control system.Wherein, S1 is first switch pipe Q1 control
Signal, S2 are second switch pipe Q2 control signal, and SW is the signal of PWM controller output, and S3 is the 3rd switching tube Q3 control
Signal processed, S4 are the 4th switching tube Q4 control signal.When control signal is high level, switching tube conducting；Work as control signal
For low level when, switching tube close.For regulation when first switch pipe Q1 and the 3rd switching tube Q3 works, exciting current is just, to claim
For positive excitation；When second switch pipe Q2 and the 4th switching tube Q4 work, exciting current is negative, referred to as negative sense excitation.One is encouraged
The magnetic cycle phase includes a positive excitation process, a negative sense excitation process and two dead band processes.
Fig. 7 is that exciting current flows to schematic diagram.Illustrate the course of work of positive excitation, negative sense excitation mistake with reference to Fig. 6 and Fig. 7
Cheng Yuqi is similar.T represents the time in an excitation cycle in Fig. 6, and Tp represents the time of positive excitation, and Tn represents negative sense excitation
Time, Td represent dead time.In the incipient stage of positive excitation, first switch pipe Q1 conductings, second switch pipe Q2 is closed, inspection
Current circuit 4 flows through current feedback on the first inspection leakage resistance R1 to PWM controller 6, due to flowing through on the first inspection leakage resistance R1
Current value be much smaller than the setting value of exciting current, the output duty cycle of PWM controller 6 is 1 square wave, control signal S1 and signal
SW exports high level by logic circuit 5, and the 3rd switching tube Q3 conductings, control signal S2 and signal SW are defeated by logic circuit 5
Go out low level, the 4th switching tube Q4 is closed, and now, high voltage power supply 1 is all added on magnet exciting coil by the 3rd switching tube Q3, is made
Exciting current rapid increase, its rise time are Tr, and its actuation path is the switching tube Q3 of high voltage power supply → the 3rd → magnet exciting coil
→ first switch pipe Q1 → first examines leakage resistance R1, such as the path I in Fig. 7.The excitation of setting was risen in exciting current value
After current value, when exciting current exceedes the exciting current value of setting, PWM control output low levels, the 3rd switching tube Q3 shut-offs,
High voltage power supply 1 is cut off, and now, magnet exciting coil carries out afterflow by the energy itself stored, and its free wheeling path is magnet exciting coil
→ first switch pipe Q1 → first examines leakage resistance R1 → second and examines diode parasitic on leakage resistance R2 → second switch pipe Q2, such as
Path II in Fig. 7.During afterflow, flowing through the electric current in magnet exciting coil can reduce, and when detecting, the electric current in magnet exciting coil is small
When the setting value of exciting current, PWM controller 6 exports high level again, and the 3rd switching tube Q3 conductings, high voltage power supply 1 is again
Excitation coil.The 3rd switching tube Q3 turn-on and turn-off are controlled by PWM controller 6, make the electric current in magnet exciting coil steady
Setting value is scheduled on, the electric current stable time is Tc.Because in PWM controller 6, the difference of exciting current value and a reference source is passed through
It is compared after amplification with triangular wave eT, to realize the output of PWM ripples, therefore its frequency is identical with triangular wave eT frequency.
At the end of positive excitation, excitation enters dead time, now, first switch pipe Q1, second switch pipe Q2, the 3rd switching tube Q3
All off with the 4th switching tube Q4, the energy in magnet exciting coil is switched by second switch pipe Q2 parasitic diode and the 4th
Diode parasitic pipe Q4 to the electric capacity C1 in energy feedback circuit, accelerates energy feedback exergonic in magnet exciting coil
Process, its feedback path are the switching tube of the second inspection leakage resistance R2 → second switch pipe Q2 parasitic diodes → magnet exciting coil → the 4th
Q4 parasitic diodes → electric capacity C1, such as path III in Fig. 7.The energy of feedback can make electric capacity C1 value rise above high voltage power supply 1
Value, energy can be fed back to magnet exciting coil again when negative sense excitation starts, not only increase the utilization rate of energy, also have
Help accelerate the response speed of exciting current.
Claims (4)
1. the electromagnetic flow meter excitation control system of the PWM based on current error control, it is characterised in that：By high voltage power supply
（1）, energy feedback circuit（2）, exciting coil drive circuit（3）, galvanometer circuit（4）, logic circuit（5）, PWM controller（6）
With excitation con-trol timing sequence generating circuit（7）Composition；
High voltage power supply（1）For high-voltage DC power supply, it is possible to reduce the transition of exciting current inverse change after excitation direction switching
Time, the quick response of exciting current is realized, the excitation frequency of electromagnetic flowmeter can be effectively improved；
Energy feedback circuit（2）At the end of each excitation half period, the energy in magnet exciting coil is absorbed, and in the next half period
During beginning, by the energy feedback being absorbed to magnet exciting coil, it is possible to achieve the recycling of energy；
Exciting coil drive circuit（3）Including H bridge switch circuit and H-bridge drive circuit；Exciting current is realized in one effect
Stable, another effect is to change the direction of exciting current in magnet exciting coil, realizes square-wave excitation, avoids electrode polarization；
Galvanometer circuit（4）Current value in detection stream overexcitation coil, fed-back current signals are provided for PWM controller；
PWM controller（6）Detection exciting current value in real time, and according to flowing through the big of the current value of magnet exciting coil and setting value error
Small output frequency is fixed, dutycycle from adjustable PWM waveform, to produce stable current value in magnet exciting coil；
Excitation con-trol timing sequence generating circuit（7）The relatively low PWM square waves with dead band of two-way frequency are exported, for magnet exciting coil driving electricity
Road provides control signal, directly determines the excitation frequency of electromagnetic flowmeter；
Logic circuit（5）Controlled by PWM controller output signal and excitation con-trol timing sequence generating circuit output signal, be excitation
Coil driver（3）Control signal is provided, for maintaining the stabilization of exciting current；
In the incipient stage of each excitation half period, galvanometer circuit（4）The exciting current value of detection is less than the setting of exciting current
Value, current error is larger, therefore, PWM controller（6）Output duty cycle is 1 PWM ripples, now high voltage power supply（1）Pass through excitation
Coil driver（3）All it is added on magnet exciting coil, the electric current in magnet exciting coil rises rapidly；When exciting current value rises to
During close to the exciting current value set, in the range of current error value initially enters setting, PWM controller（6）Stably export
Frequency is higher and dutycycle is less than 1 PWM ripples, and makes the electric current value stabilization that magnet exciting coil flows through in the current value of setting；Excitation
Electric current stabilization to the excitation half period terminates, and excitation con-trol sequential enters dead band state, now, exciting coil drive circuit（3）
It is stopped, the energy in magnet exciting coil is by energy feedback circuit（2）Absorb；After in dead band, state terminates, enter next
Excitation half period, energy feedback circuit（2）By the energy feedback of absorption to exciting coil drive circuit（3）Magnet exciting coil, no
But the efficiency of energy utilization can be improved, but also the response speed of exciting current can be accelerated；
The excitation con-trol sequential is the complementary PWM ripples for carrying dead band of two-way, and the dead time specially provided is used at every half
The energy of the storage in magnet exciting coil is absorbed during excitation end cycle, improves energy utilization efficiency.
2. the electromagnetic flow meter excitation control system of the PWM according to claim 1 based on current error control, its
It is characterised by：The high voltage power supply（1）Voltage be 60-80V, can accelerate the response speed of exciting current, improve Electromagnetic Flow
The excitation frequency of meter.
3. the electromagnetic flow meter excitation control system of the PWM as claimed in claim 1 based on current error control, it is special
Sign is：The exciting coil drive circuit（3）H bridge switch circuit opened by first switch pipe Q1, second switch pipe Q2, the 3rd
Close pipe Q3 and the 4th switching tube Q4 compositions；Wherein, the 3rd switching tube Q3 drive circuit and the 4th switching tube Q4 drive circuit
The power supply isolated from power with exciter control system respectively, it is possible to achieve higher switching frequency, while reduce switching tube
Switching loss；When first switch pipe Q1 works, the 3rd switching tube Q3 could work, and when second switch pipe Q2 works, the 4th opens
Closing pipe Q4 could work.
4. the electromagnetic flow meter excitation control system of the PWM as claimed in claim 1 based on current error control, it is special
Sign is：The PWM controller is by the first amplifier U1, the second amplifier U2, a reference source Vref, triangular wave eT, resistance R4, R5, R6,
R7, R8 and electric capacity C2 compositions；A reference source Vref is used to set the size for flowing through current value in magnet exciting coil；Triangular wave eT is error
Reference signal, compared with error amount, for producing the pwm waveform with it with frequency；First amplifier U1 and resistance R4, R5, R6,
R7 forms error amplifier, for amplifying the value of feedback of exciting current and a reference source Vref difference, its multiplication factor by R4,
R5, R6 and R7 are determined；Second amplifier U2 by comparing triangular wave eT and error amplifier output signal, and with resistance R8 and electricity
Hold C2 and collectively constitute square wave output circuit；Wherein, resistance R8 and electric capacity C2 carries out shaping to the square wave of output.
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| CN105939159A (en) * | 2015-12-27 | 2016-09-14 | 天津市品通电力科技有限公司 | PWM analog DA output circuit for excitation speed-adjusting system |
| CN106969806A (en) * | 2017-03-22 | 2017-07-21 | 重庆川仪自动化股份有限公司 | A kind of two-wire system series system high-efficiency energy-storage circuit |
| DE102018102145B4 (en) * | 2018-01-31 | 2019-10-02 | Infineon Technologies Ag | Circuit, system and method for polarizing magnetic material to discharge exciting coils |
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| CN114355765B (en) * | 2022-01-19 | 2024-05-14 | 致瞻科技(上海)有限公司 | Full-bridge excitation source with multiple excitation outputs and control method |
| CN117111520B (en) * | 2023-09-12 | 2024-02-20 | 中航试金石检测科技(大厂)有限公司 | Laboratory environment monitoring system |
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