Download phase shift pwm with double two-switch bridge for high

PHASE SHIFT PWM WITH DOUBLE TWO-SWITCH BRIDGE
FOR HIGH POWER CAPACITOR CHARGING
U.S.Karandikar#, Yashpal Singh, A.C. Thakurta
Power Supply and Industrial Accelerator Division (PSIAD),
Raja Ramanna Center for Advanced Technology (RRCAT), Indore, India 452013.
Design Parameter
Maximum Output Voltage
Load Capacitance
Pulse Repetition Rate
Charging Time
Average Charging Current
Charging Rate
Peak Charging Rate
Primary DC Bus Voltage
Inverter Switching Frequency
Value
2500
50
25
35
3.57
4464
8928
500
33
Units
Volts
µF
Hz
ms
A
J/sec
J/sec
V
kHz
D
2
PROPOSED SCHEME
The proposed converter has fallowing features.
1Double two-switchPower Bridge
The tow-switch converters have proved their
reliability for low power forward and fly-back
converters. Full bridge is commonly used for high
power but suffers from shoot-through problem.
Driver modules are used to address shoot-through
problem but they have their own limitations.
In the proposed scheme a full bridge is
realized using double two-switch power bridges in
push pull to enhance reliability with two identical
primary windingsas shown in fig-2. This
configuration was used for high voltage [3]. We
propose to use it for capacitor charging with LC filter
at output.
2
INTRODUCTION
A high voltage pulse charger is required to charge a
60 nF capacitor bank up to 60 kV at 25 Hz for pulse
generation. The pulse charger is commonly used for
charging h.v. capacitor bank in short duration [1-2]. It
utilizes resonance for transfer of energy from a low
voltage capacitor to high voltage capacitor by means
of a step-up transformer. The proposed charger is
designed to charge the low voltage capacitance in the
given time for repeated charge transfer. [fig-1]
DESIGN PARAMETERS
D
Abstract: Pulse power supply systems working at
higher voltage and high repetition rate demands for
higher power from capacitor chargers. Capacitor
charging requirement become more challenging in
such cases. In pulse power circuits, energy storage
capacitor should be charged to its desired voltage
before the next switching occurs. It is discharged
within a small time, delivering large pulse power. A
capacitor charger has to work with wide load
variation repeatedly. Many schemes are used for this
purpose. The proposed scheme aims at reducing
stresses on switches by reducing peak current and
their evils.
A high voltage power supply is designed for
capacitor charging. The proposed scheme is based on
a Phase-Shifted PWM without using any extra
component to achieve soft switching. Indirect
constant average current capacitor charging is
achieved with a simple control scheme. A double
two-switch bridge is proposed to enhance reliability.
Power supply has been developedto charge a
capacitor of 50uF to 2.5 kV at25Hz.
2
1
2
S
1
S
1
3
T1
1
7
2
D
2
1
2
9
5
2
2
4
1
Vin
D
TRNSFMR
CHAGING PERIOD
S
1
S
1
Vi
1
Tc
1
OUTPUT VOLTAGE Vf
REFRESH PERIOD
2
Q1
DISCHAGING PERIOD
TIME
Fig1: Charge discharge cycles of a CCPS
# [email protected]
Fig2: Double two-switch converter circuit
LOAD
2 Phase shift PWM
Phase shift PWM for power conversion is popular to
provide soft switching with loss less snubber. The
output inductor current and magnetizing current is
utilized to achieve soft switching with capacitors
across switches as loss less snubber.No extra
component is required so complexity is
avoided.Phase shift PWM technique has been used
and reported with double two-switch power bridges
for high power application with soft switching [4].
We have used a phase shift PWM IC UCC3895 to
generate phase shifted drive signals for switches and
have demonstrated the use of this scheme for
capacitor charging applications [5].
3ConstantCurrent Charging without current
sense
A simple control scheme is adopted for a constant
average current capacitor charging. A reference ramp
is generated by using straight line equitation:
𝑣 = 𝑉𝑖 +
(𝑉𝐹 − 𝑉𝑖 ) × 𝑡
𝑇𝑐
+ADD
+
S/H
Vi
PHASE
SHIFT
PWM
SD
+
SENSE
+
ADD
_
A prototype power supply was assembled around
step- up transformer with turn ratio 1:8 (Np:Ns).
Ferrite cores U94 four pairs are used and litz wire
was used for primary winding. The transformer was
placed in oil tank for cooling and insulation. Output
inductor used was a 3mH made with EE65 4 pairs
also used litz wire.
IXYS make diodes DS40-18A (1800V/40A/100ns)
are used for high voltage rectification and DSEI2 x
31 (1000V/30A/35ns) are used for free wheeling. For
initial testing an SCR HF80TB10 Hirect make
(1kV/80A) was used for discharging capacitor and
MOSFETs IRFP460 (500V/20A) was used in
switching bridge.
Power supply was tested to charge a 50 µF capacitor
up to ~1kV in 35ms. Tektronics make DSO TPS
2024 was used foracquiring traces. Tektronics probe
P5100 (100:1) is used for high voltage measurement.
Pearson CT P6600 (10:1) used for primary current of
both the windings in common and a 1Ω shunt was
used for measuring secondary current.
E/A
.
-
REFERANCE
+INT
.
-
Vf
EXPERIMENTAL RESULTS
SWITCH DRIVE
where v & t are variables. Vi is capacitor voltage
present before start of charging VF is final output
voltage and TCis time available for charging for each
cycle. This ramp is continuously tracked and
indirectly a constant average current is achieved
without using current signals.
reference and Vi.An error is used to modify the
signal given to PSPWM controller. The synchronism
is maintained by a timing circuit.
TIMING CIRCUIT
SCR
TRIGGER
O/C & O/V
Fig3:Block schematic of control scheme
As shown in the Fig-3above a sample and hold circuit
is used to store the information (Vi). A sample and
hold signal is given by timing circuit before starting
of each charging cycle. A ramp is generated using
Fig 4: Capacitor charging voltage: Green,Secondary
current: Red, Primary current: Blue.
Figure-4 shows test results. Trace-3 shows capacitor
was charged to 960V in 35 ms. A linear capacitor
charging shows that average charging current was
constant. It can be confirmed by trace-2 for
secondary current. For capacitor charging average
current Iav can be given by equation:
𝐼𝑎𝑣 =
𝐶 × ∆𝑉
𝑇𝑐
For our test it is 1.4A. The average of trace-2 in
figure-4 gives the same. Primary current is also seen
nearly constant for the cycle.
Fig
5:
Primary
current:
Blue
correspondingSwitch drives for 0.4 duty.
with
In figure-5&6 trace-1 shows combined primary
current with drives of corresponding switches of
PSPWM inverter. Switches can be seen turning ON
with negative current conforming ZVS operation.
Fig 6: Primary current: Blue with corresponding
Switch drives for higher duty.
With a double two-switchpower bridge duty factor
can be extended to higher side to make use of full
time. Figure-6 shows operation at higher duty factor.
CONCLUSION
A double two-switchpower bridgehas enhanced
reliability. PSPWM has reduced switching losses.
The control scheme has simplified average current
control. The scheme is a good choice for capacitor
charging with constant average current.
ACKNOWLEDGEMENT
The authors thank Shri P. Renukanath& his team for
his active support for designing and providing
transformers and shri Yogesh Raikwar & Shri Yunus
Khan for technical assistance during assembly and
testing.
REFERENCES
1: Yashpal Singh et. al. “Development of Indus-2
Kicker Power Supplies” InPAC-2003”
2: U.S.Karandikar et. al. “Current Control Mode Flyback as CCPS” InPAC-2006.
3: Min Chen, et. al.“Transformer Secondary Leakage
Inductance Based ZVS Dual Bridge DC/DC
Converter” 0-7803-7768-0/03/$17.00© 2003 IEEE
4: Nasser H. Kutkutet. al. “A dual bridge high current
DC to DC converter with soft switching capability”
IEEE Industry Applications Society Annual Meeting
New Orleans, Louisiana, October-5-9,1997.
5: Texas Instruments ‘SLUS157N − DECEMBER
1999 − REVISED MAY 2009.