Abstract: Introduced the power component actuates module TLP250 the structure and the application method, has given its and power MOSFET and the DSP controller connection hardware circuit diagram. In elaborated that IRF840 in the power MOSFET switch characteristic foundation, has designed the absorbing circuit. Finally the union cocurrent cuts the wave velocity modulation technology, has designed based on the TMS320LF2407 DSP direct current motor entire digit closed loop velocity modulation system, and has given the experimental result.
Key word: TLP250; IRF840 MOSFET; Absorbing circuit; The cocurrent cuts the wave; DSP
Introduction
—The power integrated circuit actuates the module is the product which the microelectronic technology and the electric power electronic technology unifies, its basic function is causes the power and the information unites, becomes machine and the electricity essential connection. The fast electric power electronic device MOSFET appearance, to cut the wave frequency the enhancement to create the condition, enhanced cuts the wave frequency to be possible to reduce the low frequency harmonic component, reduced to the filter primary device’s request, reduced the volume and the weight. Uses from shuts off the component, omitted has traded the class return route, might also enhance the chopper the frequency.
—Direct current motor’s excitation return route and the armature loop current’s automatic control uses power MOSFET frequently. Power MOSFET is more than one kind of child electric conduction single pole voltage control component, has the shutter speed quickly, the high-frequency response to be good, the thermostability is fine, the driving circuit is simple, the driver power small, the clear working place wide, does not have two puncture questions and so on remarkable merit. At present, the power MOSFET target achieves pressure resistance 600V, electric current 70A, the operating frequency 100kHz level, in the switching power supply, the office equipment, in the low power electrical machinery velocity modulation obtains the widespread application, causes the power transducer to realize the high efficiency and the miniaturization.
—Because the main circuit voltage is the high voltage, the big electric current situation, but control unit for weak electricity electric circuit, therefore between them must take the electro-optic quarantine measures, enhances the system antijamming measure, may use the belt electro-optic isolation MOSFET actuation chip TLP250. Light pair TLP250 is one kind may direct drive low power MOSFET and the IGBT power light pair, produces by Japanese Toshiba Corporation, its biggest driving force reaches 1.5A. Selected the TLP250 light pair both to guarantee the power driving circuit and the PWM pulse-duration modulation electric circuit’s reliable isolation, and has had the direct drive MOSFET ability, made the driving circuit to be specially simple.
TLP250 structure and driving circuit’s design
—The power MOSFET actuation’s difficulty mainly manifests in power aspects and so on component’s characteristic, absorbing circuit and electronics grid actuation, below first introduced that above TLP250 the structure and the pin application method, then introduce each item separately.
* TLP250 power component
—Toshiba Corporation’s special-purpose integrated power actuation module TLP250 contains a GaA1As photoemission diode and an integrated light detector, is 8 foot double row seal, suits in IGBT or the power MOSFET electronics grid driving circuit. TLP250 base pin as shown in Figure 1, base pin wiring method as shown in Table 1.
—The TLP250 actuation mainly has the following characteristic: Input threshold current IF=5mA(max); Supply current ICC=11mA(max); Supply voltage (VCC)=10~35V; Output current IO=±0.5A(min); Switching time tpLH/tpHL=0.5μs (max).
—Based on TMS320LF2407 DSP, TLP250, IRF840 MOSFET electronics grid driving circuit’s direct-current velocity modulation system’s basic structure as shown in Figure 1, how carries on the actuation to power component IRF840 is very important, must first solve to this question, then can based on this carry on the design to the controller.
* power MOSFET switch characteristic
—IRF840 MOSFET electric power field effect transistor when breakover has one kind of polar current carrier (majority carriers) to participate in the electric conduction, is the single pole transistor. The electric power field effect transistor is controls the drain electrode electric current with the grid bias, therefore its outstanding feature is the driving circuit is simple, the driver power is small. Its second outstanding feature is the shutter speed is quick, the operating frequency is high, electric power MOSFET operating frequency in fall time mainly by input circuit time-constant decision.
—The MOSFET shutter speed and its input capacity’s charging and discharging have the very big relations. Although the user is unable to reduce Cin the value, but may reduce the electronics grid to actuate return route supply oscillator interface resistance Rs the value, thus reduces grid return’s charging and discharging time-constant, speeds up the shutter speed.
—IRF 840 for the single pole component, do not have the minority carrier memory effect, the input impedance to be high, thus the shutter speed may enhance, the driver power is small, the electric circuit is simple. But, the power MOSFET inter-electrode capacity is big, thus the working speed and the actuation source internal resistance concerns. Is similar with GTR, the power MOSFET electronics grid actuates also to need to consider questions and so on protection, isolation.
* absorbing circuit’s design
—The electronics grid driving circuit is between the excitation return route and control circuit’s connection, is the excitation return route control device important link, has the very tremendous influence to the entire control performance. Uses the performance good absorbing circuit, may cause the power MOSFET work at the ideal on-off state, reduces the switching time, reduces the switching loss, to the installment operating efficiency, the reliability, the security has the vital significance. Moreover, many protect the link to be located in the driving circuit or realizes through the driving circuit, also causes driving circuit’s design to be more important.
—Electric power MOSFET is the voltage control component, when the static state does not need the input current nearly, but as a result of electronics grid input capacity Cin existence, in cleared and in the shutdown process still needed certain drive current to give the input capacity charging and discharging. Grid bias UG rising time tr and uses the electric discharge impediment cushion circuit, its cushion circuit electric capacity CS may obtain by type (1).
(1)
—In the formula, L primarily return route stray inductance; I0 is time the IGBT shutdown drain electrode electric current; VCEP is the cushion electric capacity CS voltage stable state value; Ed is the direct-current power supply voltage. The cushion circuit resistance RS choice is according to hoped MOSFET before shutdown signal arrival, accumulates the electric charge the cushion electric capacity to put only. May estimate by type (2).
(2)
—In the formula, f is the turn-on frequency.
—If the cushion circuit resistance is too small, will cause the current fluctuation, time the MOSFET clear drain electrode electric current starting value to increase, therefore, hoped that the selection big resistance, in the cushion resistance’s power loss will have nothing to do with as far as possible with its resistance number, may extract by type (3).
(3)
—In the formula, LS is cushion circuit’s inductance.
—After the computation, the match, the cushion circuit which and the parameter selection shown in Figure 2.
Controller’s design
—Controller’s design mainly includes the hardware control system’s design and software’s realization, below elaborated from these two aspects.
—* rotational speed closed loop controller’s hardware design
—(1) rectification return route’s design
—The direct current motor obtains the direct-current power supply is realizes through the leveling circuit, this system uses the RS507 single-phase bridge-type integration leveling circuit. Because the bridge-type leveling circuit has realized the full-wave rectification electric circuit, it also uses keying waveform’s negative half period, therefore in the transformer vice-side voltage effective value same situation, output voltage’s mean value is half-wave rectification electric circuit’s two times, sees type (4).
(4)
(2) hardware overall return route’s design
—Control system’s hardware overall structure drawing as shown in Figure 3, obviously the strong electricity and the weak electricity’s separation is realizes through TLP250, its PWM control signal after rotational speed regulating control algorithm resolving, outputs by the TMS320LF2407 PWM mouth. After TLP250 light pair, after enlargement, reshaping, driver power MOSFET(IRF840). The input armature coil’s DC voltage cuts the wave modulation after PWM, forms control DC voltage which needs. Is precisely through the TLP250 driver power component’s make-and-break, comes designer’s control thought through the power component’s make-and-break to realize.
—The NR24 manostat is TLP250 provides 24V the voltage-stabilized source, guaranteed that its work is normal. Certainly, the PWM signal is outputs through the software operation through the TMS320LF2407 component, because here the length limits, the reader may refer to the corresponding books.
—* rotational speed closed loop controller’s design
—(1) directs current the PWM pulse-duration modulation technology
—Compares with the traditional direct-current velocity modulation technology, PWM (pulse-duration modulation technology) directs current the velocity modulation system to have the big superiority: The main circuit line is simple, the power part which needs are few; The turn-on frequency is high, electric current easy continuously, the overtone are few, the loss of machine and gives off heat is small; The low-speed performance is good, the steady fast precision is high, thus the governor deflection is wide; The system band width, the fast response performance is good, dynamic antijamming ability; The main circuit part work in on-off state, the breakover loss is small, the unit efficiency is high.
—This system direct current motor return route uses the gate to be possible to shut off the power extremely to control type electric power electronic device MOSFET, changes its load both sides the direct-current average voltage modulator approach to use the pulse to adjust the wide way, namely main switch make-and-break’s cyclical T maintains invariable, but each time electrifies time t to variable. In fact is the use from shuts off the component to realize on-off control, the direct-current power supply voltage off and on will add to the load, through passes the time variation which, breaks to change the load voltage mean value, also calls the cocurrent - direct-current converter.
—(2) digital controller’s design
—Figure 4 has given the rotational speed digit controller’s structure. In order to realize the rotational speed and the electric current two kind of negative feedbacks has an effect separately, has established two regulators in the system, the distinction governed speed and the electric current, between the two implements the series connection. That is, treats as RPM control’s output current regulator’s input, uses the current regulator to lose again controls IRF840 MOSFET the trigger, namely TLP250 input PWM dutyfactor.
—In order to obtain the good static state, the dynamic property, the double closed loop velocity modulation system’s two regulators use the digital PI regulator. Computation like type (5) shows.
—u(k)=Kpe(k) KlTsame(k) ul(k-l) (5)
—And, Tsam is the sampling period.
Experiment conclusion
—This experiment establishes the electric motor rotational speed the control value is 1500 revolution of/minutes, armature coil’s resistance for 3.3Ω. Oscilloscope observation as shown in Figure 5 to the stable state dynamic profile after Gould Data SYS 944A. Obviously namely establishes the stable state after 600ms, the stable state precision is 0.5% rapidly, the static error is only 1~2 revolution of/minutes. In order to prevent time the start the rotational speed over modulation, obtains scale-up factor P is small. Obtained the good application from the experimental result obvious power MOSFET component in the direct current machine rotational speed adjustment.
—Meanwhile through the observation armature return route after flow diode both sides’ voltage, may discover that the absorbing circuit work is normal, after flow diode both sides profile as shown in Figure 6.
—The experiment debugs in the process, must pay attention to the below item: In the main circuit, must to cut the wave chip to take the radiation measure, enhances the electric circuit operational reliability, should install the radiator fin; In order to reduce cuts in the wave electric circuit the output voltage ripple, must take the output filter measure, may adopt the LC filter; Must aim at the controlled variable to carry on the installation, found corresponding the reasonable output magnitude of current, increased the control precision.
