2
System structure and working principle
Figure
1 shows a block diagram of the high voltage series resonant power supply
system. The power supply for the material surface treatment equipment
developed. It includes: three-phase AC / DC converter, voltage-bridge series
resonant inverter, super audio step-up transformer and the load. Super audio
transformer for load impedance
power inverter with charger
IGBT modules used, the operating
frequency is about 20kHz. System work, showing little emotional, zero current
conduction. For inductive loads, in a work cycle, the order of the power device
is a diode conduction earlier, IGBT in the post, which ensures zero current
conditions in IGBT conduction (ZCSON), conduction velocity after being resonant
circuit current rise constraints, therefore, IGBT turn-on loss is small. Also
shown in Figure 2, IGBT snubber capacitor Cr1 and Cr2 access, limiting the IGBT
turn-off rate of voltage rise, reducing the turn-off losses.
High
series resonant power supply system diagram
The
use of load resonant RLC series resonant circuit whose resonant frequency is
The
use of load resonant RLC series resonant circuit whose resonant frequency is
Inverter
main circuit and the impedance characteristic shown in Figure 2. Inverter
output is high frequency square wave, the transformer leakage inductance and
capacitive load resonance, close to the ideal sinusoidal current waveform.
Shown
in Figure 2 for the resonant circuit, the quality factor
Resonant
circuit quality factor
| UL |
= | UC | = QUo (3)
The
voltage step-up transformer output after the resonance voltage reaches 10 ~
30kV, load discharge phenomenon occurs, or the treatment material for
generating ozone.
RLC
series resonant
(A) the inverter main circuit (b)
Impedance
Figure
2 RLC series resonance
3 Control
Circuit
The
method used to adjust the output power of a controlled rectifier voltage
regulation power, chopper power, phase transfer function or PWM function. This
design uses three-phase phase-controlled rectifier power supply technology to
achieve through the phase-controlled rectifier output power adjustment.
Although this method is under control in the deep disadvantage of low output
power factor, but its control methods mature, high reliability, for most of the
work at full power output (α = 0) case, after all, a good choice . A
half-bridge inverter circuit, which is in the full-bridge inverter output
voltage of the DC component contained in the high frequency high voltage
booster designed to take into account the
DC TO AC
magnetic flux may cause the
problem of saturation magnetic flux, and it will increased core loss,
increasing the difficulty of transformer design. Although you can output
blocking capacitors in series to avoid this problem, but adds cost and
complexity.
Inverter
control block diagram shown in Figure 3. Load equivalent to a nonlinear lossy
capacitor, in the case of high power output load of work in the vicinity of the
resonance, the experimental results, the load in the course of discharge spark
enhanced resonance frequency drops, never started discharging down to around
30kHz 15kHz. If you do not use frequency tracking, unable to meet the high
power output. Used in the inverter control circuit CD4046 PLL, the current
phase as measured by the transformer, the monostable circuit (interference) is
taken directly from the control circuit after the output voltage signal for the
edge of the phase. 4046 has two internal phase, a first phase is XOR phase
detector, it is only the duty cycle of 0.5 to two square wave phase, and phase
characteristic curve is not monotonic, the working must be the first one signal
phase-shifted by 90 ° in order to work properly. Therefore, using the edge of
the phase, it can not consider the pulse width, pulse rise concerned only,
shown in Figure 4, the end edge of the signal 1, the time difference is zero
pulse.
