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A Compact BiDirectional PowerConversion System Scheme with Extended SoftSwitching Range

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A Compact Bi-Directional Power-Conversion System Scheme with Extended Soft-Switching Range ... A 1 kVA RHFL-converter is designed to validate the proposed soft ... – PowerPoint PPT presentation

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Title: A Compact BiDirectional PowerConversion System Scheme with Extended SoftSwitching Range


1
A Compact Bi-Directional Power-Conversion System
Scheme with Extended Soft-Switching Range
IEEE Electric Ship Technologies Symposium
(ESTS09) Baltimore, Maryland April, 2009
Funding Agencies National Science Foundation
(NSF)
2
Overview of the Presentation
  • Introduction and Background
  • Principles of the Proposed ZCS Scheme
  • Operation modes of the ZCS scheme
  • Unique features of the proposed ZCS scheme
  • General Methodology and Optimization Method for
    the Proposed ZCS Scheme
  • General requirements for the ZCS scheme with
    nonzero pulsating Dc output and the optimal ZCS
    range
  • Particular examples for ZCS control condition
  • Implementation of the proposed ZCS scheme
  • Simulated and Experimental Validations for the
    Proposed ZCS Scheme
  • Key Conclusions

3
Introduction and Background
  • The need for realizing power-dense
    power-conversion modules that support
    bi-directional power flow is an important factor
    for Navy and Defense from the standpoints of
    reduced-footprint-space, weight, labor cost, and
    mobility.
  • The existing megawatt class converters usually
    operate at low switching frequency limited to
    about 1.2 kHz due to the limited turn on/off
    performances of the high-voltage power devices,
    resulting in high efficiency but, also yield
    bulky and costly magnetic materials and filters.
  • New problems related to the high-frequency
    conversion schemes occur, such as, low
    efficiency, high stress and high EMI, because of
    the high frequency hard switching. One proper
    solution for these problems is the soft switching
    technique.

4
Topology Overview for High-frequency-link
Converter
  • Bridge I Three single-phase full-bridge dc-ac
    converter
  • Bridge II Three-phase active rectifier
  • Output voltage of the rectifier can be expressed
    as
  • Bridge III Pulsating Dc/three phase Ac converter

5
Principles of the Proposed ZCS Scheme
  • Implement the pulse-width and pulse-placement
    modulation (PWM PPM) scheme to make the
    switching control more flexible
  • Take advantage of the features of three-phase
    rectifier to create the zero current condition
    for Bridge I and zero voltage condition for the
    Bridge II
  • Generate the voltage overlaps between lead and
    lag phases (considering the leakage inductance of
    the HFL transformers)
  • Regulate the average value of the rectifier
    output voltage equal to the six-pulsed modulated
    reference defined as (u(t), v(t) and w(t) are
    the three-phase sinusoidal reference signals, M
    represents the modulation index)

6
Modes of Operation of the Proposed ZCS Scheme I
  • Mode 1
  • the top switches U2T and W1T turn on
  • Vu provides -Vdc and Vw provides Vdc to the
    secondary side
  • the bottom switches V1B and V2B are on, so Vv is
    equal to zero
  • Mode 2
  • VV supplies negative voltage to the secondary
    side rectifier, and VU is also negative
  • the negative current from the load side flows
    through the diode DUB
  • the top switch V2T is ZCS turn on.

7
Modes of Operation of the Proposed ZCS Scheme II
  • Mode 3
  • U2T turns off and the voltage VU equals zero
  • the diode DVB will handle the negative current
  • U2T suffers a hard switching off
  • Vv is negative since last mode, so DVB endures
    zero voltage, which creates a ZVS condition for
    DVB on
  • Mode 4
  • V1T turns on
  • phase W supplies positive voltage and the rest
    provide zero voltage to the secondary side
  • V1T goes on flowing the negative current, so the
    switch V1T achieves ZVZCS turn on.

8
Modes of Operation of the Proposed ZCS Scheme III
  • Mode 5
  • U1T switches on, therefore, the VU will be Vdc.
  • DWT occupies the positive current and DVB the
    negative one.
  • based on the same principle as Mode 2, U1T is
    ZCS turn on
  • Mode 6
  • W2T turns on.
  • U1T starts taking off the positive current and
    V2T still handles the negative portion of the
    current
  • W2T is a ZVZCS turn on.
  • DUT has a ZVS on

9
Modes of Operation of the Proposed ZCS Scheme IV
  • Mode 7
  • W1T turns off, and W2T begins to handle negative
    current
  • anti-parallel diode of W1T may take off the
    negative current
  • W1T is made a ZCS turn off
  • this mode is similar to Mode 1 and DWB obtains a
    ZVS on
  • Mode 8
  • V2T is off, and DUT (positive) and DWB (negative)
    take the current on the secondary side
  • the current flows through V1T is zero, which
    corresponds to a ZCS turn off for V2T.
  • this mode is similar to Mode 2.

10
Unique features of the proposed ZCS scheme
  • The voltage Vrec on the secondary side has only
    two voltage levels 2NVdc and NVdc but no zero
    level
  • Advantage
  • Less requirement for the clamp circuit owing to
    the reduced parasitic device body capacitance on
    the secondary side under the nonzero voltage.
  • Using linear programming to implement the
    optimal solution for the soft switching range

Switching waveforms of the proposed ZCS scheme
11
General Requirements for the ZCS Scheme with
Nonzero Pulsating Dc Output and the Optimal ZCS
Range I

The figure above is shown to denote the
definitions for phase voltage PWM widths (ai),
phase shift between phase voltages (ßi) and the
width of gap (?) for NVdc. So the conditions and
constraints can be listed as follows
12
General Requirements for the ZCS Scheme with
Nonzero Pulsating Dc Output and the Optimal ZCS
Range II

It can be expressed in the linear programming
format
where,
For the optimal ZCS range, we can define our
desired objective function as
13
Implementation of the Proposed ZCS Scheme
Solve the linear programming problem and get the
control coefficients for the ZCS scheme (Plotted
and rated at FPGA clock signal frequency )
Optimal value
DSP looks up data for optimization from an inside
embedded table, then packs, compacts and
transmits it to the FPGA with 2 WORDS. To balance
the power for each phase, we can rotate the order
of the gate signals every 1/6 line period
Phase (deg)
14
Particular Examples for ZCS Control Condition I
Case 1 Various-width-constant-phase-shift The
constraints for this case are
And we can also fix and the simulation
waveforms will be shown later. In this particular
case, the modulation index M should be
.
15
Particular Examples for ZCS Control Condition II
Case 2 Various-phase-shift-constant-width The
constraint for this case is
Also we can also set to facilitate the
implementation on the hardware platform.
In this particular situation, the modulation
index M should be
16
1 kVA RHFL Converter Prototype
Main Components Used in the Prototype
  • A 1 kVA RHFL-converter is designed to validate
    the proposed soft-switching scheme.
  • The designed input voltage is 36 V dc and rated
    output voltage is 208 V ac (line to line).
  • Switching frequency at Bridge I is 21.6 kHz and
    at the Bridge III is 43.2 kHz.
  • Transformer turns ratio is around 1 8.4.

Figure of the 1 kVA RHFL converter prototype
17
Simulated and Experimental Validations of the
Proposed ZCS Scheme I
Switching sequences
Diode current and voltage in Bridge II
Simulation result for Various-width-constant-phase
-shift case
18
Simulated and Experimental Validations of the
Proposed ZCS Scheme II
Experimental result for Various-width-constant-pha
se-shift case
19
Simulated and Experimental Validations of the
Proposed ZCS Scheme III
Experimental results for the optimal soft
switching range
20
Measured Efficiency Comparison Result
21
Key Conclusions
  • The proposed ZCS scheme achieves 75 ZCS for
    all the switching actions on the Bridge I as well
    as ZVS on for the secondary-side three-phase
    rectifier.
  • With a special objective function, a practical
    optimum solution is given and two practical
    modulation conditions are also presented.
  • Through the simulations and hardware experiments,
    all the proposed ZCS situations are validated.
  • The overall efficiency of the prototype is
    measured to be promoted compared with
    hard-switched Bridge I and II.

22
Thank You!
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