A Compact BiDirectional PowerConversion System Scheme with Extended SoftSwitching Range - PowerPoint PPT Presentation

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.

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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
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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
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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
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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)
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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
.
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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
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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.

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Thank You!