A Compact Bi-Directional Power- Conversion System Scheme with Extended Soft-Switching Range IEEE Electric Ship Technologies Symposium (ESTS’09) Baltimore,

A Compact Bi-Directional Power-A Compact Bi-Directional Power-Conversion System Scheme with Conversion System Scheme with Extended Soft-Switching RangeExtended Soft-Switching Range

IEEE Electric Ship Technologies Symposium (ESTS’09)Baltimore, Maryland

April, 2009

Sudip. K. Mazumder, Liang JiaSudip. K. Mazumder, Liang JiaLaboratory of Energy and Switching-Electronics System

Department of Electrical and Computer EngineeringUniversity of Illinois, Chicago

Funding Agencies: National Science Foundation (NSF)

1

Overview of the Presentation

Introduction and Background Principles of the Proposed ZCS Scheme

Operation modes of the ZCS schemeOperation modes of the ZCS scheme Unique features of the proposed ZCS schemeUnique features of the proposed ZCS scheme

General Methodology and Optimization Method for the Proposed ZCS Scheme General requirements for the ZCS scheme with nonzero General requirements for the ZCS scheme with nonzero

pulsating Dc output and the optimal ZCS rangepulsating Dc output and the optimal ZCS range Particular examples for ZCS control conditionParticular examples for ZCS control condition Implementation of the proposed ZCS schemeImplementation of the proposed ZCS scheme

Simulated and Experimental Validations for the Proposed ZCS Scheme

Key Conclusions2

Introduction and Background

The need for realizing power-dense power-conversion modules that support bi-directional power flowbi-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 costlybulky and costly magnetic materials and filters.

New problems related to the high-frequency conversionhigh-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 techniquesoft switching technique.

Topology Overview for High-frequency-link Converter

Bridge IBridge I: Three single-phase full-bridge dc-ac converter

Bridge IIBridge II: Three-phase active rectifier

Output voltage of the rectifier can be expressed as:

Bridge IIIBridge III: Pulsating Dc/three phase Ac converter

MAX , , MIN , ,rec U V W U V WV V V V V V V

4

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)

P1: / 6 / 6

P2: / 6 / 2

P3: / 2 5 / 6

P4: 5 / 6 7 / 6

P5: 7 / 6 3 / 2

P6: 3 / 2 11 / 6

w t v t t

u t v t t

u t w t tref t

v t w t t

v t u t t

w t u t t

5

sin

sin 2 / 3

sin 2 / 3

u t t

v t t

w t t

6ref t M ref t

6

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.

Modes of Operation of the Proposed ZCS Scheme I

Modes of Operation of the Proposed ZCS Scheme II

7

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

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

Modes of Operation of the Proposed ZCS Scheme III

9

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.

Modes of Operation of the Proposed ZCS Scheme IV

10

Unique features of the proposed ZCS scheme

The voltage Vrec on the secondary side has only two voltage levels: 2∙N∙Vdc and N∙Vdc but no zero level

Advantage:Advantage:Less requirement for the clamp circuit Less requirement for the clamp circuit owing to the reduced parasitic device owing to the reduced parasitic device body capacitance on the secondary side body capacitance on the secondary side under the nonzero voltageunder the nonzero voltage..

Using linear programming to implement the optimal solution for the soft switching range

Switching waveforms of the proposed ZCS scheme

VV

UV

WV

2U T

1U T

2V T

1V T

2W T

1W T

recV

refW

refV

refU

0t 1t 2t 3t 4t 6t 7t5t 8t 9t 10t 11t 12t

t

t

t

t

t

t

t

t

t

t

t

ZCS edge

11

The figure above is shown to denote the definitions for phase voltage PWM widths (αi),

phase shift between phase voltages (βi) and the

width of gap (γ) for N∙Vdc. So the conditions and

constraints can be listed as follows:

1 1

2 2

3 1 2

1 1 2

2 3 2

1 2

3 1 2

0

0

2

0

0

1

0 1 1, 2,3

0 1 1, 2,3

2 6

i

i

i

i

ref

General Requirements for the ZCS Scheme with Nonzero Pulsating Dc Output and the Optimal ZCS Range I

WV UV VV

2

231

1

12

It can be expressed in the linear programming format:

min Txx

Ax b

lb x ub

Aeq x beq

f

1 1

2 2

3 1 2

1 1 2

2 3 2

1 2

3 1 2

0

0

2

0

0

1

0 1 1, 2,3

0 1 1, 2,3

2 6

i

i

i

i

ref

1 2 1 2min min( )Txx

f

1 0 0 1 0

0 1 0 0 1

0 0 1 1 1

1 0 0 1 1

0 1 1 0 1

0 0 0 1 1

A

0 0 2 0 0 1T

b

where,

For the optimal ZCS range, we can define our desired objective function as

General Requirements for the ZCS Scheme with Nonzero Pulsating Dc Output and the Optimal ZCS Range II

Implementation of the Proposed ZCS Scheme

60 70 80 90 100 110 120500

600

700

800

900

1000

1100

12312

60 70 80 90 100 110 1201650

1700

1750

1800

1850

1900

1950

2000

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

13

Solve the linear programming problem and get the control coefficients for the ZCS scheme (Plotted and rated at FPGA clock signal frequency )

Optim

al value

Phase (deg)

14

Case 1: Various-width-constant-phase-shiftCase 1: Various-width-constant-phase-shiftThe constraints for this case are:

1 2 3

2

3

3

42 6

3ref

And we can also fix

and the simulation waveforms will be shown later. In this particular case, the modulation index M should be

.

1 2 5 / 6

21

3M

1 1

2 2

3 1 2

1 1 2

2 3 2

1 2

3 1 2

0

0

2

0

0

1

0 1 1, 2,3

0 1 1, 2,3

2 6

i

i

i

i

ref

Particular Examples for ZCS Control Condition I

WV UV VV

2

231

1

Particular Examples for ZCS Control Condition II

15

Case 2: Various-phase-shift-constant-widthCase 2: Various-phase-shift-constant-width The constraint for this case is:

1 2 3

2

3

Also we can also set

to facilitate the implementation on the hardware platform.

1 2 6 1, 2, 32

iref i

In this particular situation, the modulation index M should be

11

3M

1 1

2 2

3 1 2

1 1 2

2 3 2

1 2

3 1 2

0

0

2

0

0

1

0 1 1, 2,3

0 1 1, 2,3

2 6

i

i

i

i

ref

WV UV VV

2

231

1

1 kVA RHFL Converter Prototype

16Figure of the 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.

Simulated and Experimental Validations of the Proposed ZCS Scheme I

17

Simulation result for Various-width-constant-phase-shift case

Switching sequences

Diode current and voltage in

Bridge II

18

Experimental result for Various-width-constant-phase-shift case

Simulated and Experimental Validations of the Proposed ZCS Scheme II

19

Experimental results for the optimal soft switching range

Simulated and Experimental Validations of the Proposed ZCS Scheme III

Measured Efficiency Comparison Result

20

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.

Key Conclusions

21

Thank You!

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