A novel pwm high voltage conversion ratio bi directional three-phase dcdc converter with y-δ connected transformer

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A Novel PWM High Voltage Conversion
Ratio Bi-Directional Three-Phase DC/DC
Converter with Y-Δ Connected Transformer
Abstract
Bi-directional DC-DC converter (BDC) is usually applied
between DC bus and energy storage unit in DC micro-grid. The
DC bus voltage level is about 360-400V, while the voltage of
battery cell is as low as 12V or 48V. Thus there is a big disparity
between the two power sources in which the BDC needs high
voltage conversion ratio (HVCR). A high voltage level can be
acquired with batteries in series; however, extra charging and
discharging balance circuits are needed in order to avoid the
problems of overcharge and over discharge which will influence
the lifespan of batteries. In high power conditions, the voltage of
battery cell is 12V or 48V that the power semiconductors and
magnetic components face severe current stress. Paralleling of
power switches becomes popular solution to increase the current
rating; however, it may incur several problems, such as current
sharing and complicated control strategy. Therefore, it’s
necessary and meaningful to research BDC with HVCR in high
power ratings application.

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Call: 0413-4205444, +91 9566355386, 99625 88976.
Existing system:
The TPDAB is composed of three interleaving single-phase
dual active bridge current source bidirectional DC/DC
converters (DAB), and each phase output is 120 degree apart
from each other. In this mode, the input current rating is
increased by interleaving three phases, not by paralleling
components, and the ripple frequency will be increased to three
times the switching frequency and current ripple will be greatly
reduced due to cancelling effects between each phase. The
power flow of the TPDAB is controlled by the shifting phase
between active bridges at low voltage side (LVS) and high
voltage side (HVS). When energy flows from the 12V net side
to the high voltage DC (HVDC) netside, the TPDAB works in
boost mode, in which the driving pulses at LVS are ahead of that
at HVS. The leakage inductances La~Lc of the high frequency
transformer are acting as intermediate elements to store and
transfer the power. The 12V net, the coupling three-phase input
inductors L1~L3, and the switches S2, S4, S6 compose boost
circuits. The duty cycles of the switches S1, S3, S5 are set at D,
so the voltage V1 of capacitor C1 is boosted to 1/D times of Vin.
The capacitors C1, C2 are used to handle high switching current
ripple and maintain a nearly constant dc bus voltage. The stress
of each switch of TPDAB converter is about one third of the
single-phase topology, although the total stress is about the same
for both converters since the number of switches is increased

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Call: 0413-4205444, +91 9566355386, 99625 88976.
three times in TPDAB converter. The current stress of capacitors
C1 and C2 of three-phase topology is much lower than that of
the single-phase circuit therefore smaller capacitor could be used
for three-phase topology and power density will be improved.
Proposed system:
The topology of proposed three-phase BDC with Y-Δ
connected transformer. The high voltage side (HVS) connected
to DC bus is three-phase full-bridge chopper unit composed of
power MOSFETs QH1-QH6 paralleled with body diodes DH1
DH6. The low voltage side (LVS) is a current-tripler unit
composed of power MOSFETs QL1-QL3 paralleled with body
diodes DL1-DL3, filter inductors Lf1-Lf3 and filter capacitor
CfL. If the energy transfers from HVS to LVS, the converter
works in Buck mode, otherwise in Boost mode.

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Call: 0413-4205444, +91 9566355386, 99625 88976.
Advantages:
 The current stress of power switches decreases, and the
converter is preferred in high power applications.
 The voltage conversion ratio is doubled, thus the turn ratio
of transformer is halved in high voltage conversion ratio
conditions.
 The primary voltage of transformer is 2/3Vin, therefore
the insulation requirement of transformer reduces.
 The ripple frequency of input and output current is three
times of switching frequency, so the input and output filter
capacitors can be smaller to improve dynamic
performance of the converter.
 Compared with traditional asymmetrical PWM control,
the equivalent voltage ratio is doubled, thus the rms
current of primary switches and transformers decreases.
Applications:
 High step-up or high step-down application.

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Call: 0413-4205444, +91 9566355386, 99625 88976.
Block diagram:
BUFFER
circuit
5VDC
PIC controller
circuit
Gate driver circuit
12 V DC
Load
INPUT
DC supply
Filter
3 phase
converter 1
3 phase
converter 2
3 phase
high
frequency
transformer

Page number 6
LeMeniz Infotech
Call: 0413-4205444, +91 9566355386, 99625 88976.
Tools and software used:
 MPLAB – microcontroller programming.
 ORCAD – circuit layout.
 MATLAB/Simulink – Simulation.

A novel pwm high voltage conversion ratio bi directional three-phase dcdc converter with y-δ connected transformer

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A novel pwm high voltage conversion ratio bi directional three-phase dcdc converter with y-δ connected transformer