1. Introduction
high-power ultrasonic device addition for industrial
cleaning, still in medical, military, oil transducer technology, as well as
ocean exploration and development of, noise abatement anti-vibration system,
intelligent robot has a broad application prospects, fluctuations in oil and
other high-tech fields [1]. The ultrasonic device by ultrasonic power inverter
and transducer. In recent years, due to the development and the successful
development of new rare earth functional materials, the manufacture of
high-power ultrasonic transducer as possible, but the accompanying
high-frequency sine wave inverter power supply products are still rare. At
present, the market of high-power sine power inverter are using products made in
low-frequency IGBT [2], while high-frequency inverter power supply most of the
power or duty cycle of the square wave pulse inverter power adjustable.
Therefore, the high-frequency high-power sine wave inverter power has become the
bottleneck of ultrasound applications, making the power development has become a
pressing problem. Here, the application of hybrid pulse width modulation (Hybrid
Pulse Width Modulation, HPWM) control technology, using MOSFET parallel
operation mode, the application MCU intelligent control systems,
high-performance, high-power sine the ultrasonic wave inverter power
development.
2. form
for high-performance, high-power the sine ultrasonic
inverter power frequency of 25kHz, the power of 4.5kW. The voltage is adjustable
between 0 ~ 200V adjustable frequency between 10 ~ 25kHz.
a. program design
the Figure 1 shows a
hardware configuration of the power inverter system diagram [3]. It is composed
of two parts by AC / DC and DC / AC. AC - DC - AC main circuit, driver circuit
includes the main aspects of the SCM control system, a low-pass filter, display
and protection.
main circuit directly from 220V mains supply.
ECONOMY the thyristor Constant-Current/Constant-Voltage control module phase AC
voltage of the AC is converted to DC inverter provides a constant DC
voltage.
order so that the inverter can get better
performance and waveform sinusoidal output, there needs to be greater than the
carrier. Therefore only chosen due to its carrier signal will reach 400 ~ 600kHz
MOSFET as a switching device. However, the output power of the MOSFET is
smaller, in order to increase the output power MOSFET in parallel can be used to
run the way to resolve the contradiction between high frequency and high
power.
power inverter the inverter parts of constant
frequency triangular carrier signal input sine wave with asynchronous
modulation. Control mode uses HPWM Technology. The inverse of the DC voltage
pulse signal into a series of amplitude. The amplitude and pulse width of the
pulse signal is always proportional to the modulating sine wave. These pulse
signals are filtered via low pass filter, a high-frequency carrier signal. Can
be obtained with the modulation wave with the frequency of the sine wave output.
Therefore, as long as the change in the input modulated wave can be easily
realized adjustable amplitude, variable frequency sine wave output.
b.SCM control system the power supply using the
control inverter design 80C196MC microcontroller as the the inverter control
core [4,5]. 80C196MC microcontroller internal waveform generator WFG, the CPU
time is very short. By P6 port directly output 4 PWM signals for the inverter
drive. By 80C196MC and EPROM2764 constitute minimum microcomputer system. The
completion of the ultrasonic frequency and the magnitude of the voltage given.
As well as the setting of the carrier frequency, and analog output unipolar sine
wave with constant amplitude pulse width modulation HPWM signal. The display of
the voltage amplitude and frequency can be realized. And the protective control
of the power supply.
c. the inverter main circuit and HPWM of control run
at high frequencies, the the great switching losses of the power tube. The
device is easy to damage, to limit the power increases. The key technical
problems of the power in the high frequency, and how to get the high-power
variable frequency sine wave output. That the inverter difficulty is how to
reduce the switching losses of the switch, the du / dt and di / dt stress
dropped significantly, in order to achieve the high-frequency inverter. In order
to achieve these objectives. The main circuit of the inverter uses a
soft-switching technology is easy to implement single-phase full-bridge
topology. In a controlled manner using the the HPWM control mode. Figure 2
illustrates the topology of the main circuit of the inverter. Figure 3
illustrates the output signal of the four switch control of the drive signal and
the inverter.
essence of the HPWM control mode is still a unipolar
SPWM control. The output of the inverter bridge is a tri-state output voltage
wave shape. The sinusoidal modulating wave and the triangular carrier wave in
the positive half cycle of the output voltage of the AC / sectional generated
pulse signal control VS1 and VS3 bridge Arm HF complementary off; control VS2
and VS4 the arm low frequency complementary to off, i.e. VS2 off, VS4 guide
through. In the negative half cycle of the output voltage, the working status of
the two bridge arm is interchangeable. VS1 has been turned off, VS3 has been
turned on, VS2, and VS4 high-frequency modulation work. HPWM control mode two
power tubes work in the low-frequency case, reducing the switching losses in
general, this is extremely beneficial to improve power at high frequencies. With
SPWM control way. HPWM way two bridge arm alternately work in the state of
low-frequency and high-frequency, so that the two bridge arm symmetry, power
transistors operating state equalizer, which will extend the life of the power
tube, so that the increased reliability of the entire circuit, with a voltage
utilization rate, harmonic content is small, low switching losses of the
advantages. As each switch in parallel with a capacitor, in appropriate
circumstances, the filter inductance parameter selection, the circuit is easy to
implement the switching tube of the zero voltage (ZVS) off, so that the du / dt
and di / dt stress greatly decreased, can be to achieve the high-frequency power
inverter.
d.The drive circuit switch tube drive circuit latest
LM5111 drives can be used. SOIC-8 pin package and provide separate ground and
reference voltage pin for the input and output stages, in order to support the
use of powered separately designed gate drive configuration. LM5111 chip peak
output currents up to 5A LM5111's two of 5A current drive channel independently,
can also be connected in parallel, the peak output drive current is increased to
10A, in order to be able to drive great power MOSFET high efficiency. LM5111's
operating frequency up to 1MHz, its open, off delay, respectively 12ns and 14ns.
Fully able to meet the requirements of the power supply.
3. software implementation
a. main program
Figure 4 shows the main program flow chart. It
contains the initialization subroutine HPWM signal of subroutines, keyboard
scanning and display routines. Initialization routine, 80C196MC initialize the
stack address and carrier frequency parameters, and microcontroller I / O ports,
interrupt and waveform generator set work. Keyboard given desired output sine
wave frequency is displayed by the display program. Subroutine of the voltage
signal timing sampling A / D conversion, dynamic, time-sharing the frequency and
amplitude of the sine wave value.
b. HPWM signal generator subroutine
HPWM sinusoidal modulation wave with constant
amplitude triangular carrier. Waveform generator in the center-aligning manner,
the counting process of the WG-Counter forming a virtual triangular wave
carrier. Sinusoidal modulation wave through a look-up table method. Have
symmetry Since the output HPWM wave, so just to create a 0 ° ~ 180 ° of the sine
function table. In order to achieve sufficient resolution, the sine function
table at 0.15 ° intervals to arrange a sample point, each data having a 15-bit
binary value, representing the two bytes, the half cycle of the sine wave output
of 1200 of data, stored the starting address SIGN storage area, Grid
tie inverter. Carrier frequency fc, the output frequency is fo, then N = fc
/ FO intersection value each half cycle of sine wave output, corresponding to
the intersection of the i-th sinusoidal modulation amplitude value can be
obtained through the look-up table, the address SIGN +1200 i / N.amplitude
values ??of the sinusoidal modulation of the the triangle carrier and at the
intersection compared to obtain the inverter HPWM switch mode. Whenever the peak
of the triangular wave carrier (WG-COUNTER = WG-RELOAD) or bottom when an
interrupt request to the microcontroller, data loading. So, each half cycle of
the exchange of two-phase, mixed unipolar modulation mode HPWM wave. Figure 5
illustrates HPWM signal generating subroutine flowchart.
4. experimental results
the main circuit structure, control method,
developed an output frequency of 25kHz; carrier frequency of 600kHz; principle
prototype output power of 4.5kW. Figure 6a, b shows when the full load of the
the inductive half load and inductive filter inductor current iL and output
voltage uo experimental waveforms. The figure shows that the half load and full
load, uo the small changes better load regulation. Figure 6c, d shows the
inverter bridge the same bridge arm two power tubes VS2 and VS4 drive voltage
ugsVS2 and ugsVS4 the enlarged ugsVS2 and ugsVS4 experimental waveforms. Seen,
taking into account the dead zone, the same bridge arm of the two power tubes
are complementary conduction. Power tube driving voltage waveforms of the rise
and fall delay time is very short, and can meet the requirements.
5. Conclusion
high-power ultrasonic power MCU intelligent control
system, artificial setting of the power frequency and output voltage. Simplifies
hardware circuit the the microcontroller analog outputs HPWM signal, greatly
improving the power factor and the efficiency of the system; simultaneously
applied the HPWM control mode with ZVS resonant soft-switching technology,
reduces the loss of the switch, and inhibit the high-order harmonics, reduced
transducer losses. The experiments show that the proposed power performance,
convenient adjustment, high reliability. For high-power ultrasonic transducer
provides excellent performance in various fields of application of ultrasonic
power. (Source: Power Electronics Technology)
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