Abstract: In view of high-power ultrasonies power source high accuracy, high power output characteristic. Has made the improvement to the ultrasonic wave power source control policy. Proposed that one kind the cyclical partition phase shifting control policy which unifies based on the 56F803 DSP frequency track and the power regulation. Has studied based on this control method ultrasonic wave power source.
Key word: Ultrasonic wave power source; Frequency track and power coordination control; Ultrasonic generator; Digital signal processor; 56F803
1 introduction
Along with science development and technical progress. The ultrasonic wave in the ultrasonic welding, the supersonic clean, dry, domain and so on atomization, guidance, range finder, breeding applications is day by day widespread. Present’s high-power ultrasonies power source uses the frequency follow-up control or the power control mostly. This unicontrol method will not only cut the ultrasonic wave power source efficiency, will affect the output precision and the intensity. How to cause the ultrasonic wave power source basis net load real-time, the dynamic regulation output resonance frequency and the power, thus operation and so on guarantee ultrasonic machining requests have the important fundamental research and the practical application value.
2 ultrasonic wave electrical power system’s composition
The ultrasonic wave electrical power system mainly by the 220V power source, the rectification filter, the high frequency contravariant unit, the matching network, examines the electric circuit, PWM to produce the electric circuit and the driving circuit is composed, as shown in Figure 1.
the 220V single-phase alternating current obtains the DC voltage after the diode uncontrolled leveling circuit, then passes through the high frequency contravariant electric circuit which is composed of MOSFET to obtain satisfies the transducer request the voltage. For the reduction high frequency working condition under the MOSFET switching loss, the high frequency contravariant electric circuit uses the belt auxiliary network the entire bridge structure, as shown in Figure 2. This circuit structure solved the traditional zero potential switch (ZVS)PWM electric circuit transformer leakage inductance to be small, and the lag bridge arm difficulty with realized the ZVS question. At the same time, according to the electric current enhancement principle, this circuit structure may realizes the zero potential switch in the random load and in the input voltage scope, reduced the dutyfactor loss greatly. The ultrasonic wave power source and the transducer match the quality will decide the entire electric circuit’s control effect. Therefore, should to matching network each parameter (high-frequency transformer ratio-turn K, output match inductance Lf) carry on the strict computation. The match mainly refers to cause the generator output fixed electric power, carries on the impedance conversion match. As well as to cause the generator output peak efficiency to carry on the harmonious match.
Uses 56F803 DSP to take control circuit’s core processor. Its built-in 2 KB SRAM,31.5 KB FLASH, simultaneously, its 40 MHz CPU clock rate has the stronger handling ability compared to other monolithic integrated circuits. 6 group PWM signals may realize the high frequency contravariant electric circuit switching valve MOSFET phase shifting control. 12 A/D switch gathering may realize the voltage and the electric current sampling and satisfies the sampled data precision the request. Timer’s capture function may calculate the phase difference size precisely using 56F803 DSP, realizes system’s frequency follow-up control. Serial peripheral device connection SPI and the MCl4489 coordination use may realize to 5-and-a-half nixietube controls. Thus realizes the system frequency and the power demonstration. Moreover, 56F803 also supports the C language and the assembly language mix programming SDK software development package. May realize the online debugging.
The driving circuit uses the IR21lO actuation module. It has the integration rate to be high, speed of response quick (tar/taff=120 ns/94 ns), bias voltage high (<600 V), driving force, the cost low and easy to debug and so on merits. IR2110 is based on from lifts the actuation principle the power MOSFET driving circuit. The driving signal time delay for a nanosecond level, the turn-on frequency may from dozens of hertz to several hundred kilohertzes. At the same time, IR2110 also has the quite perfect protection function (for example undervoltage examination, antijamming, the exterior protection block system and so on). IR2110 may simultaneously actuate single bridge arm’s about two MOSFET, therefore, the use few discrete component and a group control supply may realize a bridge arm MOSFET actuation control, reduced driving circuit’s volume and the cost like this greatly.
3 system’s control policies
The ultrasonic wave electrical power system uses the control policy which the frequency track and the power regulation unify, thus causes the generator at the output maximum work rate time may achieve the peak efficiency. This kind of control policy mainly through controls PWM the cycle (is also controlling switch frequency) and the PWM control profile phase shifting angle realizes.
3.1 frequency follow-up control realization
Uses the phase-lock law to realize the frequency follow-up control. Uses the KT20A/P electric current sensor and the KV20A/P voltage pick-up examines the transducer two ends separately the voltages and the electric current, the process stagnates the link control to obtain the voltage and the electric current square-wave signal, as shown in Figure 3. Should stagnate the link to return to the difference is lV. Then, passes through the different or gate and the D trigger to two group square-wave signals obtains the phase difference profile and the phase difference mark. The phase difference profile sends in DSP the capture mouth, computation showing off potential difference size T, the phase difference mark sends in the GPIOA7 mouth. Obtains the sign flag to measure flag. When T≠O, flag=o, expression voltage leading current. This time, should reduce switching valve’s frequency f; When T≠O, flag=l, indicated that the voltage lagging current, this time, should increase switching valve’s frequency f, then transforms the frequency quantity the time quantity to attach for the DSP mold value register, thus changes outputs the PWM signal the cycle.
3.2 power control realization
In order to cause the high frequency contravariant electric circuit’s output to satisfy the rated power which the transducer needs, must use the power control electric circuit, namely the gathering cocurrent side’s electric current signal with the magnitude of current which assigns carries on the comparison, and carries on the digital PI adjustment to the deviation, thus change phase shifting control profile phase shifting angle. Then change high frequency inversion electric circuit’s output voltage.
The gathering cocurrent side’s electric current realizes the power control primary cause is through transducer’s voltage and the electric current is the exchange, needs to detect, treating processes and so on filter to be able to examine, is like this quite difficult. But directs current the side voltage is the direct-current quantity, based on this kind of consideration, has used the examination cocurrent side electric current method. Uses the increase type digit PI operation to reduce the displacement quantity, thus achieves not static difference control. The direct-current side electric current real-time track assigns the electric current, changes the soft on-off control signal the phase shifting angle, thus changes the high frequency contravariant electric circuit’s output voltage, when the phase shifting angle increases the output voltage also increases, therefore the high frequency contravariant electric circuit will output the power which finally the transducer will request.
3.3 cyclical partition realize the phase shifting control
This system’s switch uses the dutyfactor is 50% PWM signal phase shifting control. The traditional phase shifting control method has two kinds: One kind is uses UC3875 to have the phase shifting control profile. But the electric circuit is complex, is not advantageous for the debugging. The precision is low: Another kind uses the monolithic integrated circuit, this method uses the sine table to have the phase shifting profile long majority, the procedure, complex, the readability is bad. This system uses the cycle piggy-back control method to realize the phase shifting control profile. Divides into each PWM cycle switching valve’s control profile 4 sections. In each section of profiles DSP the mold value register PWMCM value is equal to counter PWMVAL the value. What variable Count represents the output is the several section of profile, when Count=l or Count=3. Profile I orⅢMold value MODUL01 (I sumⅢThe mold value same) bestows on for the mold value register. When Count=l, the PWM module’s 0 channels and 3 channels output the high level and the low level separately. When Count=3 the .PWM module’s 0 channels and 2 channels output the low level and the high level separately; When Count=2 or Count=4. ProfileⅡOr IV mold value MODULO 2 (ⅡWith IV mold value same) bestows on for the mold value register. When Count=2, PWM the module O channel and 3 channels output the high level. When Count=4 the .PWM module’s 0 channels and 2 channels output the low level. Then, according to the above way circulation output wave shape, as shown in Figure 4 the flow chart.
Figure 5 primarily flow chart. When the procedure, the frequency track part presents the phase difference, first to the frequency bestows on great length of stride (m=100). then along with phase difference reduction. Reduces the length of stride gradually. Until the phase difference is zero.
4 experimental result analysis
The above ultrasonic wave power source’s main parameter is the direct-current side voltage 270 V; Turn-on frequency fS=20 kHz; High-frequency transformer ratio-turn K=38:15; Resonant inductance Lf=3 mH; The transducer uses the operating frequency is 20 kHz. interface resistances for 10Ω, the electric capacity is 12 000pF, the peak power output is l 500 W.
Figure 6(a) gives the contravariant bridge output voltage and the electric current experiment profile.
Figure 6(b) is the Q1 tube control profile and leaks between a source the voltage experiment profile. Obviously, when the control signal causes time the switching valve breakover. Between its drain electrode and the source voltage was already zero, has realized the switching valve zero potential breakover
Figure 6(c) is the transducer two terminal voltage experiment profile. The transducer is at when the natural frequency resonance condition for pure resistive load, therefore two terminal voltages are the sines.
5 concluding remark
Uses the frequency track and the power coordination control numerical control type new ultrasonic wave power source has the following characteristic:
(1) uses the belt auxiliary circuit, the electric current enlargement mode ZVS entire bridge converter. Has realized all switching valve’s ZVS; (2) has realized the frequency track and the power control coordination control strategy, the tracking accuracy may reach 4Hz. to be able to satisfy control and so on ultrasonic welding, supersonic clean requests; (3) uses the cycle piggy-back control strategy to realize the ZVS phase shifting control, causes the procedure simplification; (4) uses the IR2110 integration actuation, the actuation is simple. Reduced system’s volume, reduced the cost.
