CN103894590B - Cast by digital ultrasonic-frequency power supply control system - Google Patents

Abstract

The invention discloses the design of a digital ultrasonic power control system for casting, including the following aspects: (1) The invention proposes a digital ultrasonic power control system for casting based on DSP2808. The main circuit of the ultrasonic generator includes: rectifier Transformer, diode rectifier circuit, MOSFET single-phase full-bridge inverter circuit, analog input unit, waveform conversion circuit and matching circuit; (2) The existing self-excited ultrasonic power supply is prone to detuning, this system is designed There are two working modes, manual and automatic, and the real-time tracking of the frequency is realized through software control. The real-time tracking of frequency realized by software is controlled based on the maximum effective value of the current, according to the characteristic that the current effective value is the largest at resonance; (3) The test proves that the ultrasonic power supply designed in this scheme has a large tracking frequency range and long working time And other advantages, compared with the original self-excited ultrasonic power supply has been significantly improved.

Description

Digital Ultrasonic Power Supply Control System for Foundry

technical field

This patent relates to the technical field of aluminum alloy casting technology control, in particular, it provides a digital ultrasonic power control system.

Background technique

At present, the method of applying an external physical field before or during the solidification of the metal is generally used, that is, the interaction between the metal and the physical field is used to improve its solidification structure. Applying ultrasound in the solidification process of aluminum alloy is an effective method to improve its microstructure and mechanical properties, which is beneficial to the process optimization and microstructure regulation of aluminum alloy casting forming, and to obtain high-performance casting products. When the ultrasonic waves propagate in the melt, the melt is subjected to the periodic alternating sound field, which produces a series of nonlinear effects such as cavitation and acoustic flow, which increases the nucleation rate of the metal and can produce obvious grain refinement effects. Homogenize the overall temperature and chemical composition of the alloy, thereby fundamentally improving the mechanical properties of the aluminum alloy.

In terms of ultrasonic generators, high-power high-frequency switching transistors began to be used in the mid-1980s. Most of the amplifiers were self-excited class D half-bridges or full-bridges. After that, separately-excited high-power module amplifiers also appeared. The self-excited ultrasonic power supply integrates the signal generator, power amplifier, output transformer and transducer into one body to form a closed loop, so that the entire generator can generate enough power through amplitude and phase feedback, so that the transducer is always Keep at the resonant frequency, and the externally excited ultrasonic power supply includes two parts, the front stage is a signal generator, the rear stage is a power amplifier, and finally it is coupled to the transducer through an output transformer.

In the ultrasonic casting experiment, the ultrasonic transducer system is in contact with the high-temperature aluminum alloy melt, and its resonance frequency and impedance will change significantly. At present, the ordinary domestic ultrasonic power supply adopts a self-excited circuit, and the frequency tracking range is narrow. The longer the working time of the transduction system, the greater the deviation of its resonant frequency from the output frequency (frequency deviation) of the generator, and the greater the vibration amplitude of the tool head. When the frequency deviation reaches a certain level, the ultrasonic power supply will take a protective action to stop the system, and the energy conversion system must be cooled before continuing to work, resulting in interruption of casting. Because the energy conversion system is greatly affected by the high-temperature aluminum alloy melt, the domestic conventional self-excited analog ultrasonic power supply cannot work normally, and detuning often occurs, resulting in the disappearance of the tool head end face amplitude reduction setting, and ultrasonic processing cannot be carried out effectively. Therefore, it is necessary to design a digital ultrasonic power supply that can automatically follow the resonance frequency. Perform frequency tracking on it, and increase the frequency output range to adapt to the working conditions of aluminum alloy casting.

Contents of the invention

The technical problem to be solved by the present invention is to provide a safe, reliable, real-time and highly targeted power control system that can meet the requirements of special aluminum alloy casting.

In order to solve the above technical problems, the special aluminum alloy casting power supply control system provided by the present invention,

The ultrasonic power supply converts the power frequency 220V voltage into a high-frequency voltage output through AC-DC-AC, and drives the vibration of the piezoelectric transducer system to obtain ultrasonic waves;

The current flowing through the transducer and the voltage at both ends of the transducer are detected by the Hall sensor, and the DSP collects the current and voltage signals, and sends out a square wave with frequency and dead zone to the drive circuit to form two driving signals to drive Switching on and off of the inverter;

Foundry ultrasonic generator system includes: TMS320F2808DSP circuit main controller, rectifier transformer, diode rectifier circuit, MOSFET single-phase full-bridge inverter circuit, analog input unit, waveform conversion and matching circuit;

The main controller of the control circuit is TMS320F2808DSP. Its main function is to receive various setting information and instructions, generate a certain frequency PWM signal to control the on-off of the MOSFET, and output the voltage signal of the required voltage amplitude and frequency, so that the transducer always works at Resonant frequency point, at the same time, there are human-computer interaction, signal sampling and fault self-diagnosis functions;

The main circuit is mainly composed of a diode controllable rectifier and a PWM inverter, and the PWM signal of a certain frequency is output through the DSP to control the MOSFET inverter to adjust the output voltage and frequency;

The waveform conversion and matching circuit includes a high-frequency power transformer, which is used for boosting and isolating, so as to avoid the instantaneous high voltage of the inductance at the load end under the action of high frequency and damage the power device;

The DSP adjusts the output voltage frequency of the MOSFET in time by sampling the phase of the output voltage and current, and tracks the resonant frequency of the transducer in real time. At the same time, the DSP detects the fault signal in real time to protect the main circuit to achieve the maintenance-free performance of the system.

Optionally, the software implementation of frequency tracking includes two modes: one is to change the frequency by manual keys, if the frequency changes a lot, directly input the number to change the frequency; the other is to change the frequency by automatic tracking;

According to the characteristic that the effective value of the current is the largest at resonance, under the condition of resonance, the impedance of the ultrasonic transducer system is the smallest, so the maximum current will be output, and the method of sweeping frequency is used to search for the resonance frequency of the ultrasonic transducer system. Values are defined as:

In actual operation, through programming, the current ix of multiple discrete points is collected according to the time interval t within several cycles, and then two adjacent points iA and iB are searched for among these points, so that iA<0, iB>0, we get There is a zero-crossing point between point iA and point iB, and then look for N-2 points later, N=T/t, T=1/f, so that these N points fall within one cycle, by Approximate its rms value.

The power supply control system adopting the above-mentioned technical scheme adopts the principle of AC-DC-AC frequency conversion to realize continuous adjustable output frequency. At the same time, the output power can be adjusted through the rectifier transformer, and the voltage, current and frequency parameters can be displayed in real time on LCD.

The invention makes up for the shortcomings of the previous ultrasonic power supply control system, increases the nucleation rate of metal, can produce obvious grain refinement effect, and at the same time makes the overall temperature and chemical composition of the alloy uniform, and the performance of the aluminum alloy is improved. The invention has high reliability, high flexibility, high EMC, can work stably for a long time, is easy to maintain, and can realize standardization and serialization.

To sum up, the present invention is a reliable and stable power control system based on TMS320F2808 microprocessor, which is designed for special aluminum alloy casting and has high real-time performance and strong pertinence.

Description of drawings

Fig. 1 is the overall block diagram of the hardware of the ultrasonic power supply device;

Figure 2 is a flow chart of the frequency automatic search and tracking program.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

See Figure 1. The main controller of the control circuit is TMS320F2808. The inverter bridge uses the MOSFET of STMicroelectronics to control the frequency of the output voltage signal. The analog input unit is composed of a Hall sensor and a pre-signal processing circuit to obtain current , voltage real-time signal, the thermocouple obtains the temperature signal of the load, and then sends the data to the control board for processing through AD sampling; the display unit adopts a high-quality liquid crystal display module LCD128645ZK, and each screen can display 8×4 Chinese characters (16×16 ) or graphics with 128×64 pixels. At the same time, this system also has functions such as fault self-diagnosis.

After the equipment is powered on and preheated and checked to be normal, the main program completes the initialization and enters the automatic search for the resonant frequency. After the resonant frequency is found, it enters the frequency tracking stage. The automatic search frequency and tracking procedure flow chart 2 is shown.

The advantages of the present invention are:

(1) The power supply unit is designed for special aluminum casting, which has strong pertinence and practical value;

(2) Adopt all-digital direct control technology to replace the original analog control technology. Realize control and signal processing functions through DSP technology;

(3) Compared with the phase monitoring of current and voltage through devices used in the past, the present invention adopts a frequency search algorithm based on the maximum effective value of current to realize real-time tracking of frequency. Under the condition of resonance, the impedance of the ultrasonic transducer system is the smallest, so the maximum current will be output, and the resonance frequency of the ultrasonic transducer system will be searched by the method of sweeping frequency;

(4) The ultrasonic power supply designed in this scheme has the advantages of large tracking frequency range and long working time, which are obviously improved compared with the original self-excited ultrasonic power supply.

Claims (2)

1. a digital type ultrasound wave power control system based on aluminum alloy casting technique, it is characterised in that:

Ultrasonic power is by AC-DC-AC, power frequency 220V voltage to be converted into high frequency voltage export, and promotes pressure Electricity energy converting system vibration, obtains ultrasonic wave；

Obtaining flowing through electric current and the voltage at transducer two ends of transducer by Hall element detection, DSP adopts Colleeting comb and voltage signal, send the square wave with frequency, dead band through computing and form two-way to drive circuit Signal is driven to promote opening and closing of inverter；

Casting resonant ultrasonic tool generator system includes: rectifier transformer, diode rectifier circuit, MOSFET The conversion of single-phase full bridge inverter circuit, analog input unit, waveform and match circuit；

Control circuit main controller is TMS320F2808 DSP, and major function is to receive various set informations and refer to Order, the pwm signal producing certain frequency controls break-make output required voltage amplitude and the frequency of MOSFET Voltage signal, make transducer always work in resonant frequency point, meanwhile, also man-machine interaction, signal are adopted Sample and fault self-diagnosis function；

Main circuit is mainly made up of diode controlled rectifier and PWM inverter, certain by DSP output The pwm signal of frequency controls MOSFET inverter regulation output voltage and frequency；

Waveform conversion comprises high-frequency power transformer with match circuit, is used for boosting and isolating, it is to avoid load end Inductance produces instantaneous pressure under high frequency effect and damages power device；

DSP adjusts the output voltage frequency of MOSFET in time by the phase place of sampling and outputting voltage and electric current, The resonant frequency of real-time tracking transducer, meanwhile, DSP detects fault-signal in real time and protects main circuit Protect, the performance that the system that reaches is non-maintaining.

Digital type ultrasound wave power supply based on aluminum alloy casting technique the most according to claim 1 controls system

System, it is characterised in that:

The software of frequency-tracking realizes comprising both of which: a kind of is that the mode of manually button changes frequency Rate, if frequency shift is a lot, directly inputs numeral and changes frequency；One is that autotrack mode changes frequency Rate；

It is maximum feature, at a resonant condition, the resistance of ultrasonic transducer system according to current effective value during resonance Anti-minimum, therefore will export maximum current, use the method for frequency sweep to search for the resonance frequency of ultrasonic transducer system Rate, the virtual value of described electric current is defined as:

First within several cycles, multiple discrete points are gathered according to time interval t by programming when of practical operation Electric current ix, then finds two adjacent some iA, iB in these are put so that iA<0, iB>0, obtains IA point and iB point there is a zero crossing, then finds N-2 point, N=T/t, T=1/f so that this N backward Individual point falls in a cycle, byApproximation draws its virtual value.