CN101261288A - Load dump transient voltage generator - Google Patents

Abstract

The invention relates to a novel throw load voltage generator, belonging to the field of automotive electronics, which comprises a charging loop and a discharging loop, wherein, AD collecting signal amplifying circuits are connected with a Hall sensor I and a Hall sensor II respectively; the D collecting signal amplifying circuit is connected with a DSP controlling circuit which is connected with a digital-to-analog conversion circuit; the digital-to-analog conversion circuit is connected with an amplifier which is connected with an MOSFET pipe; the two ends of a resistance R4 are respectively connected with a Hall sensor III and the amplifier. The novel throw load voltage generator has the advantages of avoiding the difficulties of the circuit design caused by the extremely large volume of the needed inductance for good discharging effect to be achieved actually, and the novel throw load voltage generator can achieve the aim of controlling the size of the inductance by software by an adjustment parameter L.

Description

Load dump transient voltage generator

Technical field

The invention belongs to vehicle electric field, be specifically related to a kind of load dump transient voltage waveform generator, be that various electron devices for automobile carry out Unloading Voltage and impact a kind of device that designs, can provide in the world in the ISO7637 agreement 5a clause the desired Unloading Voltage surge waveform of electron device.Voltage waveform provided by the invention also has adjustable advantage flexibly simultaneously, the forceful electric power that can not only provide the ISO7637 agreement to be strict with is pressed surge waveform, can also provide strict more voltage waveform impulse test, with the impact resistance of further check auto electronic device.

Background technology

Automobile electronics use under harsh conditions at environmental facies, and the car electrics product will stand high temperature, high voltage, and sharp pounding and surge, therefore, the examination requirements of its quality is quite strict.At present, except that surge, other Interventions Requested have trended towards maturation.On the automobile, a lot of local electrical equipment all will bear the impact of Unloading Voltage, as: ignition module, regulator etc.For the security and the serviceable life of automobile, these key components all must carry out the impact experiment of Unloading Voltage.The 5a clause is done following requirement to the Unloading Voltage waveform among the ISO7637, and shown in the figure in the accompanying drawing-1, Fig. 1 is a test pulse 5a oscillogram, just the change in voltage shape figure that forms at its two ends during the engine throw load.U among the figure _sBe the pulse waveform maximum voltage value, t _rBe pulse waveform when rising from 0.1U _sArrive 0.9U _sThe time of Shi Suoxu, t _dVoltage is from 0.1U when being rising _sArrive 0.1U when descending _sThe time of Shi Suoxu.

The test pulse of this standard-required is that simulation is in the condition that disconnects battery (power shortage state), alternator is producing charging current, and the transient state that produces when still having other loads on the generator circuit, when the amplitude of throw load depends on that disconnecting battery connects, the size of the excitation field intensity of the rotating speed of generator and generator, throw load pulse width depend primarily on the time constant and the pulse height of field circuit.The possible cause that produces throw load is because cable corrosion, loose contact or engine, have a mind to disconnect just in the running and being connected of battery.And just can form as shown in Figure 1 momentary pulse behind the throw load at auto electronic device two ends, the effect of Unloading Voltage generator is to want simulating actual conditions that electron device is done detection.

In actual applications to figure-1 waveform parameters requirement such as following in table-1, the table-2 shown in:

Parameters when table-1 rated peak voltage is the 100V system in the oscillogram

Parameters when table-2 rated peak voltages are the 200V system in the oscillogram

The Unloading Voltage impulse detection must satisfy above-mentioned requirements.

The at present domestic voltage generator that impacts as the anti-instantaneous pressure of automobile electronics mainly is to form waveform that Fig. 1 describes according to the RCL discharge loop, shown in Figure 2 in discharge loop such as the accompanying drawing substantially, and Fig. 2 is the structural drawing of traditional Unloading Voltage generator.Resistance R 1 and resistance R 2 constitute the resistance of voltage generator self, the load that reception is impacted between C and the D, and the frame of broken lines between C and D is the automotive electronics device of accepting impact, and its internal resistance value is RL.Impact energy is provided by capacitor C.During beginning, switch closes the end to A, and by AC power, rectifier bridge to the electric capacity charging, provides energy.Treating that energy provides finishes, and switch closes to B and holds.Thereby electric capacity, inductance, resistance forms the RCL discharge loop.Electric current flow through R1 respectively when electric capacity released energy, two branch roads of R2.So will form waveform as shown in Figure 1 at device under test RL two ends.Tradition Unloading Voltage generator is realized easy, be convenient to operation, but it but has two bigger shortcomings:

Because the parameter of inductance L size is determined by hardware, so the L size promptly can not be changed in case circuit is determined, just causes the adaptability of this setting scheme poor, and different systems is needed different loops.In case the requirement to waveform changes, just need the change hardware circuit, this is pretty troublesome.

Because compole was short when Fig. 1 waveform pulse required to rise to ceiling voltage, the longest have only 10ms as table-1, shown in the table-2, so the inductance induction reactance in will realistic border circuit very little be 10 milihenries, and internal resistance reaches negligible degree (because the resistance of pull-up resistor has only 2 ohm) also for very little.So just require shapes of inductors to do very greatly, this just causes the Unloading Voltage generator shape of making very big in actual conditions, nor realizes easily.

More than two shortcomings difficult to traditional Unloading Voltage generator with what overcome, bring a lot of inconvenience to practical application.

Summary of the invention

The invention provides a kind of Unloading Voltage waveshape generating device of software-controllable,, Unloading Voltage generator shape very big problem poor with the adaptability that solves present setting scheme.The technical scheme that the present invention takes is: constitute charge circuit by AC power AC, rectifier bridge 6, switch and storage capacitor C, resistance R 1, R2, R3, Hall element 1, Hall element 22, Hall element 33, and MOSFET pipe formation discharge loop, wherein resistance R 2 is connected with MOSFET pipe and Hall element 33; Resistance R 1, R3, Hall element two series connection; Hall element one is connected on to be prepared to insert in the circuit of testing resistance RL, these three circuit are in parallel each other, AD acquired signal amplifying circuit is connected with Hall element 1, Hall element 22 respectively, this AD acquired signal amplifying circuit is connected with the DSP control circuit, this DSP control circuit is connected with D/A converting circuit, this D/A converting circuit is connected with amplifier, and this amplifier is connected with the MOSFET pipe, and resistance R 4 two ends are connected with amplifier with Hall element 33 respectively.

The present invention is concrete to adopt a MOSFET to replace discharge inductance in the major loop of Fig. 2, and the conducting degree by control MOSFET is in order to the performance of simulaed inductance.The conducting degree of MOSFET in real time calculated and controlled to size of current in the major loop to reach the purpose of control main circuit current and load both end voltage according to ISO7637 to the requirement of Unloading Voltage by DSP.

As shown in Figure 3, we will place the position of inductance originally and change MOSFET, adopt the piDSP30F6014A model DSP of Microchip company that it is controlled; Left part is by AC power AC, and rectifier bridge 6, switch and storage capacitor C constitute charge circuit, are responsible for storage capacitor C energy accumulation; Center section is by storage capacitor C, switch, and resistance R 1, R2, R3, RL and MOSFET pipe constitute discharge loop, are specifically responsible for needed pulse voltage waveform when producing throw load; The right side part is by AD acquired signal amplifying circuit, the DSP control section, and the digital-to-analog conversion part, amplifier and resistance R 4 constitute control loops, are specifically responsible for the control to MOSFET.

R1 among Fig. 3 and R2 are the internal resistance of this voltage generator, and the electron device that reception is surveyed in the frame of broken lines between C and the D is connected on C and D respectively with device under test in the time of promptly will detecting and holds.Switch during beginning among Fig. 3 closes the end to A earlier, gives storage capacitor C energy accumulation by AC network and rectifier bridge.Treating that energy is accumulated finishes, and switch closes the end to B, begins discharge and forms surge waveform.During discharge, the electric current that flows out from B is divided into three branch roads, one road R2 that flows through, one road flow through Hall current sensor 1 and electron device RL to be measured, one road flow through resistance R 3 and Hall element 2 is gathered together by MOSFET and Hall current sensor 3 at the Q4 point at last and gets back to storage capacitor C.Wherein the function of each several part is respectively: because in the process that throw load impacts, the internal resistance RL that accepts the electron device of impact may change constantly, we need know constantly that its internal resistance value is to calculate the magnitude of voltage that its each moment two ends should have.We cooperate a known resistance R 3 of size to obtain the value of RL by two Hall current sensors.Concrete principle is, because Hall current sensor 1, RL and Hall current sensor 2, R3 are relation in parallel, equate so be added in two voltages on the branch road, promptly put Q2, the voltage between Q3.If certain constantly the electric current that provides of Hall current sensor 1 be I1, the electric current that Hall current sensor 2 provides is I2, so this internal resistance RL=I2*R3/I1 of device under test constantly, wherein the R3 size is known, so the RL of this moment just can in the hope of.As shown in Figure 3, by Hall current sensor 1,2 current values that obtain are very little of the milliampere order of magnitude, this two paths of signals need be entered the DSP control module again by AD acquired signal amplifying circuit, DSP calculates the size of trying to achieve RL this moment according to these two values, and utilize RL to try to achieve should to flow through the current value I dum of MOSFET, the form that this current value is changed into voltage is defeated by D/A converter module.Through obtaining after the digital-to-analog conversion is exactly in-phase end and the resistance R 4 that an analog voltage outputs to operational amplifier, and Hall element 3 constitutes to be penetrated with circuit, is added to the grid of MOSFET at last from the output terminal of amplifier.This penetrates with circuit can guarantee the to flow through electric current I act of MOSFET and changes according to the value Idum of our calculation requirement, thereby plays the purpose of control MOSFET conducting degree.

The control algolithm that we take total system in the software program in the DSP is described below.

The front was mentioned, and was corresponding to effect when reaching with inductance existence discharge by the mode with MOSFET replacement inductance L among the present invention.So the present invention is still the RLC discharge loop of utilization in fact and produces the principle of transient voltage pulse.Only do not have real inductance herein, but replace a MOSFET by DSP control.The Theoretical Calculation of RLC discharge loop is:

According to Kirchhoff's second law, list

$L\frac{d_i}{d_t}+R*i+u_C=0$ Formula (1)

Will $i=C\frac{{\mathrm{du}}_c}{\mathrm{dt}}$ The substitution following formula can get

$L*C\frac{d^2{u}_{\mathrm{<figure-callout\; id="2"\; label="c\; dt"\; filenames="A20081005065400131.png"\; state="\{\{state\}\}">c</figure-callout>}}}{{\mathrm{dt}}^{}}+R*C\frac{{\mathrm{du}}_c}{\mathrm{dt}}+u_c=0$ Formula (2)

L in last two formulas is not the size of actual inductance, but the selectable parameter that the user provides in the dsp software program.Can determine the size of L according to given parameter value.As shown in Figure 3, u _CIt is the instantaneous voltage value at capacitor C two ends, R is a resistance R 1, R2, the total resistance after R3 and the RL parallel connection, the resistance sizes between promptly from Q1 to Q4, R1 wherein, R2, the R3 size is known, has illustrated that above the size of RL can be tried to achieve according to two-way AD collection, also be known quantity, so the size of R also is known in last two formulas.The size of capacitor C is that we just determine when design hardware, also is known quantity.

Actual following formula (2) is exactly the mathematical analysis formula of the desired waveform of ISO7637 standard, separates the instantaneous voltage that this equation can be tried to achieve the capacitor C two ends.So also just obtain electric capacity both end voltage rate of change, will try to achieve the current value of the MOSFET that flows through according to this rate of change, thereby finally also just obtain being added in the voltage pulse waveforms at electron device to be measured two ends.Formula (2) is a single order second differential equation, and this equation finding the solution on digital processing chip is that process of iteration realizes by discrete.If the stepping of time is T, then formula (2) becomes after dispersing:

$L*C\frac{u_C\left(k\right)-2u_C(k-1)+u_C(k-2)}{{\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="A20081005065400131.png"\; state="\{\{state\}\}">T</figure-callout>}}^2}+R*C\frac{u_C\left(k\right)-u_C(k-1)}{T}+u_C(k-1)=0$ Formula (3)

Can get the result at last:

$u_C\left(k\right)=\frac{2\mathrm{LC}+\mathrm{RCT}}{\mathrm{LC}+\mathrm{RCT}+T^2}{u}_C(k-1)-\frac{\mathrm{LC}}{\mathrm{LC}+\mathrm{RCT}+T}{u}_C(k-2)$ Formula (4)

Need when algorithm is realized in DSP to carry out iteration, above determined parameter L according to following formula, R, the size of C can be obtained the time dependent discrete data of voltage signal u then, the data u that T is preceding constantly _C(k-1) and the data u of T after constantly _C(k) subtract each other and can get electric capacity both end voltage rate du over time, wherein the time stepping is T.And voltage change ratio takes advantage of capacitance can get the electric quantity change rate, i.e. current value, with the load on duty of this electric current get final product the magnitude of voltage at load two ends, promptly be the desired voltage waveform of Unloading Voltage generator with this voltage output.

Be U _L=du _C* C*R U _LBe the instantaneous voltage value at load two ends.

By above calculating, we have finally reached the purpose that replaces inductance with MOSFET.

The invention has the advantages that and to avoid to reach the excessive difficulty that circuit design is brought of the required inductance volume of discharge effect preferably because of actual.Can reach the purpose of regulating and control the inductance size by software by the adjustment type parameter L again, promptly need not change hardware circuit and also can pass through the software alteration discharge waveform.By theoretical analysis as can be known, the voltage waveform among Fig. 1, voltage rise time t _rBe by the decision of the size of inductance in fact, inductance value is short more between more hour.And the requirement of ISO7637 standard time to this is short more good more, and scope is controlled at 5ms---between the 10ms.The MOSFET that uses software control instead replaces and just can control this time behind this inductance flexibly and reached according to the different device different waveforms of regulation and control and need not make any change on hardware.And can reach the inaccessible waveform effect of actual inductance.In fact merely the traditional Unloading Voltage generator by inductance can only be controlled at 10ms with this time.

Description of drawings

Fig. 1 is the oscillogram that test pulse 5a requires in the ISO7637 standard;

Fig. 2 is the structured flowchart of traditional Unloading Voltage generator;

Fig. 3 is a structured flowchart of the present invention;

Fig. 4 is the specific implementation figure of load dump transient voltage generator; Do not draw piDSP30F6014A model DSP pin part among the figure, wherein need to connect the part of DSP pin, the mode of the port that adopts among the figure is connected to DSP, and the corresponding ports mark is arranged.

Embodiment

Constitute charge circuit by AC power AC, rectifier bridge 6, switch and storage capacitor C, resistance R 1, R2, R3, Hall element 1, Hall element 22, Hall element 33, and MOSFET pipe formation discharge loop, wherein resistance R 2 is connected with MOSFET pipe and Hall element 33; Resistance R 1, R3, Hall element two series connection; Hall element one is connected on to be prepared to insert in the circuit of testing resistance RL, these three circuit are in parallel each other, AD acquired signal amplifying circuit is connected with Hall element 1, Hall element 22 respectively, this AD acquired signal amplifying circuit is connected with the DSP control circuit, this DSP control circuit is connected with D/A converting circuit, this D/A converting circuit is connected with amplifier, and this amplifier is connected with the MOSFET pipe, and resistance R 4 two ends are connected with amplifier with Hall element 33 respectively.

The present invention is made up of main charging and discharging circuit and governor circuit two large divisions.The physical circuit principle as shown in Figure 4.

1. main charging and discharging circuit be the forceful electric power loop by charging circuit, discharge circuit and unload current circuit and form:

A. charging circuit is by transformer T1, rectifier bridge D16, and relay K 1,50 Europe/200 watts of 26,5 bidirectional triode thyristors of resistance R (Q1-Q5), 10 high capacity storage capacitors (C31-C39) are formed.Close to the storage capacitor charging end by its switch of pilot relay K1, after the transformer transformation, accumulate electric charge, to store in order to form the energy of discharge waveform, in order to carry out the impact of throw load to electron device to storage capacitor by AC network.The loop that form this moment is charging circuit.

B. discharge circuit is by storage capacitor (C31-C39), bidirectional triode thyristor (Q1-Q5), relay K 1, Hall current sensor A (U1), Hall current sensor B (U2), Hall current sensor C (U3), MOSFET (Q6), Unloading Voltage generator internal resistance (according to the R27 of ISO7637 protocol requirement by 2 ohm, 4 ohm R28 constitutes) and electron device to be measured (R30) constitute discharge loop, and this loop forms the throw load shock pulse.Close to the storage capacitor discharge end by its switch of pilot relay K1, the electric current above-mentioned device of flowing through flows back to storage capacitor at last.The loop that form this moment is discharge circuit.

C. unload current circuit by storage capacitor (C31-C39), unidirectional conducting diode (D17-D21), relay K 1, high-power unload discharge resistance (R31, R32), resistance R 33, stabilivolt (D22) and LED lamp (D23) composition.This circuit is not discharge by unloading leakage resistance discharging the energy that finishes in the throw load discharge impact process.Make its switch be pointed to by the charging circuit end by pilot relay and unload the stream end this moment.The loop that the above-mentioned device of flowing through this moment forms is unloads current circuit.

Governor circuit be weak electrical loop by the AD sample circuit, digital-to-analog conversion control circuit, DSP peripheral module circuit are formed:

The a.AD sample circuit is by Hall element A and B (U1, U2) pair end and current amplification circuit (with operational amplifier IC1A, IC1B, IC2A cooperate peripheral resistance to constitute) and filtering circuit (capacitor C 23, the simple R C filtering that C24 forms filters the electromagnetic interference (EMI) of the simulating signal that enters DSP) form.The purpose that designs this sample circuit is to be used for calculating within the electron device of accepting to impact hindering, because impact along with big electric current, the internal resistance of device might change in the process of impacting to preventing because impact the infringement that causes device, the DSP program takes to carve knows its internal resistance value, and be added in the magnitude of voltage at two ends according to its instantaneous resistance adjustment, again because in formula (2), resistance R is that DSP is in order to calculate an important parameter of discharge pulse waveform, so when taking, program inside grasps the size of device internal resistance, and just the same when adjusting in size of current and the reality by major loop with MOSFET replacement inductance.This AD takes a sample by the two-way sampling, and one the tunnel gets the electric current of the device (R30) of the acceptance impact of flowing through, and one the tunnel gets the voltage that is added in its two ends, after the two-way sampling, can obtain its transient resistance value according to sampling value via Ohm law calculating.The main devices of circuit is that (U1 U2), is placed on the A and the B place of circuit respectively to two Hall current sensors, and why will use this sensor is for forceful electric power circuit and light current circuit are isolated.Hall current sensor at position B place can record the electric current of the electron device R30 that flows through, other goes out a branch road resistance R in parallel with electron device 29 its resistances is 1K, size has the poor of three orders of magnitude with the electron device internal resistance, so the pulse waveform can't discharge to throw load the time has a significant impact.Place the Hall current sensor at A place to record the current value of the R29 that flows through, because R29 is the standard electric resistance, can record the voltage at R30 two ends so electric current and resistance multiply each other, combine with the current value of B place Hall current sensor again and can try to achieve the instantaneous resistance of R30 in each moment.

Hall current sensor is a kind of sensor that utilizes Hall effect magnetic field sensor signal or electric signal.Its principle is when former limit lead during through over-current sensor, primary current ip can produce the magnetic line of force, the former limit magnetic line of force concentrates on the magnetic core air gap periphery, being built in Hall electricity sheet in the magnetic core air gap can produce with the former limit magnetic line of force and be directly proportional, size only is several millivolts a induced voltage, can become secondary current is to this small signal transition by follow-up electronic circuit, and have following relational expression:

is*ns＝ip*np

Wherein, is-secondary current;

The ip-primary current;

The np-primary coil number of turn;

The ns-secondary coil number of turn;

The np/ns-turn ratio.

The output signal of Hall current sensor is secondary current is, it is directly proportional with input signal (primary current ip), is is very little, the order of magnitude at milliampere, the AD conversion of dsp chip can not directly be gathered, so in application, also need this current signal is amplified, and carry out the conversion of current and voltage signals so that process chip can be carried out acquisition process to signal.

Current/voltage transforms link and the signal amplifying element passes through LM258 amplifier (IC1A, IC1B, IC2A) cooperate the current signal of resistance realization on every side to amplify to the conversion of voltage signal and with it, then by capacitor C 23, the simulating signal that C24 finishes to amplification is carried out simple hardware capacitor filtering, and by ADcollection1 and AD collection2 port input DSP.

B. digital-to-analog conversion control circuit

DSP obtains the momentary current value at each discrete main discharge circuit constantly after as calculated, need this value to be reflected in the major loop by the specific hardware circuit, because among the DSP be digital quantity, so need at first be converted into simulating signal, utilize this simulating signal to control the conducting degree of MOSFET again to reach the purpose of control main circuit current.What digital-to-analog conversion was selected for use is MAX5541 (U7) low cost ,+5V, and the serial input, the digital to analog converter of 16 precision is no matter all can meet design requirement at data transmission period and conversion accuracy.Be 40us the computing time of the DSP algorithm among the present invention, and the signal output gap of discrete time is set at 60us, and the data transmission period of the time of 20us as DSP and digital to analog converter arranged, and is enough to satisfy temporal requirement by the high speed SPI communication modes.U7 is by port CLK, and port DATA and port EN meet DSP, provide the SPI communication needed clock signal by DSP respectively, data-signal and enable control signal.

To set forth the voltage signal that how forms by MAX5541 below and control the conducting of MOSFET, at first explanation is that the present invention controls its conducting degree by the size that control is added in the voltage on the MOSFET grid.The making alive amplifying circuit amplifies the virtual voltage that just obtains on the MOSFET grid with voltage signal after MAX5541 earlier, and amplifying circuit still adopts LM258 (IC2B) composition amplifying circuit to realize.As for conducting degree how to control MOSFET, the present invention adopts be penetrate with mode, as shown in Figure 4, by operational amplifier IC3B, resistance R 37, Hall current sensor C (U3), and MOSFET (Q6) constitutes.If this moment, the Hall element primary current was ip, secondary current is is, because the magnitude of voltage of operational amplifier IC3B pin 5 and pin 6 equates, so this moment, the magnitude of voltage of MOSFET grid control end was u=ip*R37*ns/np (ns/np is a turn ratio), because voltage u is that DSP provides by digital-to-analog conversion, so the current i p of main discharge circuit just can determine according to the output voltage that control circuit provides.The control voltage u that the DSP waveform that impact requires according to throw load calculates and exports has also just played us and has substituted the effect of inductance by this MOSFET.

The c.DSP peripheral module is some accessory circuits that we can operate as normal provide for the assurance system in actual use.Comprise by what constitute and provide the feed circuit of 15V voltage for the LM258 operational amplifier by LM7815 and LM7915, the system's feed circuit that have LM7805 to constitute, with 82C250 is the main CAN of formation bus communication interface conversion circuit, is the main serial communication circuit that constitutes with MAX232.These all are basic circuit commonly used, are no longer marked and illustrate at this.

Claims (1)

1, a kind of load dump transient voltage generator, it is characterized in that: constitute charge circuit by AC power AC, rectifier bridge 6, switch and storage capacitor C, resistance R 1, R2, R3, Hall element one, Hall element two, Hall element three, and MOSFET pipe formation discharge loop, wherein resistance R 2 is connected with MOSFET pipe and Hall element three; Resistance R 1, R3, Hall element two series connection; Hall element one is connected on to be prepared to insert in the circuit of testing resistance RL, these three circuit are in parallel each other, AD acquired signal amplifying circuit is connected with Hall element one, Hall element two respectively, this D acquired signal amplifying circuit is connected with the DSP control circuit, this DSP control circuit is connected with D/A converting circuit, this D/A converting circuit is connected with amplifier, and this amplifier is connected with the MOSFET pipe, and resistance R 4 two ends are connected with amplifier with Hall element three respectively.

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