Application-oriented research in Power Electronics by get11021


									Application-oriented research in Power

                                 Dr. Wajiha Shireen
           Department of Engineering Technology, College of Technology
    Department of Electrical & Computer Engineering, Cullen College of Engineering
                                University of Houston
• Power Electronics Systems
• Applications
• Research projects in the area:
     • A DSP Based SVPWM Control For Utility
       Interactive Inverters Used In Alternate Energy
     • Active filtering of input ripple current to obtain
       efficient and reliable power from fuel cell sources.
             Power Electronics
• Power Electronics deals with the application of solid state
  electronics for the control, conditioning, and conversion of
  electric power.
• Raw Power (120 V, 60 Hz AC) supplied by the utility in
  many cases need to be conditioned, controlled or converted
  for the following reasons:
   Ø to achieve energy efficiency
   Ø to improve reliability
   Ø to match different load requirements (eg. DC, high frequency AC,
    variable voltage variable frequency AC)
• Renewable energy sources like solar and wind power
  systems are power electronics intensive.
• It is estimated that 60% of electric power generated in the
  U.S flows through some power electronics system.
       Power conversion circuit
• The function of a power conversion circuit is to
  control the energy flow between a given electrical
  source and a given load.
• A power converter must manipulate energy flow
  but should not consume energy.
• A power converter connected between the source
  and load also affects system reliability. Hence the
  converter must be reliable to avoid degrading a
 Primary design objectives in Power
• Efficiency Target→100%
• Reliability Target →No failures over
  application lifetime.
    The Efficiency Objective—The
• Ideally when a switch is ON, it provides vswitch=0,
  and will carry any current imposed on it.
• When a switch is OFF, it blocks the flow of
  current (iswitch=0), regardless of the voltage across
  it. The device power, vswitch.iswitch, is zero at all
• A circuit built from ideal switches will be lossless.
  Other lossless elements such as capacitors,
  inductors and conventional transformers might
  also be used for the conversion.
The Reliability Objective-Simplicity
          and Integration
• Power Electronics circuits tend to have few parts
  specially in the main energy flow paths. Often this
  means complicated control strategies applied to
  seemingly simple conversion circuits.
• Manufacturers seek ways to package several
  switching devices, their interconnections, and
  protection components together as a unit.
  Power Electronics.vs.Linear Electronics
• The main differences are : power handling capability
  and efficiency requirements.
• A small power loss and hence high energy efficiency
  is important in power electronics systems because of
  two reasons: the cost of wasted energy and the
  difficulty in removing the heat generated due to the
  dissipated energy.
• High efficiency and high power cannot be achieved
  by simply scaling up low power circuits but a
  different approach to power conversion/control needs
  to be adopted – power electronics.
             Power converters
• It is a basic module of power electronic systems.
• It utilizes power semiconductor devices controlled by
  signal electronics along with energy storage elements.
• Power semiconductor switching devices like BJTs,
  MOSFETS, SCRs etc. are operated as a switch
  (cutoff region or saturation region) unlike in linear
  electronics where they are operated as variable
  resistors (active region).
• Broad categories of power converters:
  ac to dc
  dc to ac
  dc to dc
  ac to ac
• The controls take information from the source, load, and designer, then
  determine how the switches operate to achieve the desired conversion.
• Power Electronics is an interdisciplinary field including power systems,
  solid state electronics, machines, analog/digital control, signal processing
• Power semiconductor devices can be regarded as the muscle and
  microelectronics as the brain of the system.
Interdisciplinary Nature of Power Electronics
• UPS systems provide protection against
  power outage as well as voltage regualtion.
  They also suppress transients and harmonic
     Application in Adjustable Speed Drives

•   Conventional drive wastes energy across the throttling
    valve to adjust flow rate
•   Using power electronics, motor-pump speed is adjusted
    efficiently to deliver the required flow rate
  Variable speed operation of electric
• The capability of varying the speed of an electric motor to
  match the load required by their end-use system, optimizes
  its performance and minimizes energy use.
• Tests with pump, fan and compressor applications indicated
  typical energy savings of 20-50% using motors with
  variable speed drives.
• Switching power converters offer an easy way to regulate
  both the frequency and magnitude of the voltage applied to
  a motor for speed control.
Variable speed motor drives in a wide
       range of end equipment
            u Major Appliance and HVAC
              Motor Controls—Washers,
              Blowers, Compressors

            u Factory Automation Systems—
              Power Inverters, Industrial Drives

            u Automotive Systems—Electronic
              Power Steering, Anti-Lock Brakes,
              Suspension Control

            u Office Products—Tape Drives and
              Magnetic Optical Drives,
              Copiers, Printers
A DSP Based SVPWM Control For Utility
     Interactive Inverters Used In
      Alternate Energy Systems

                     - Dr. Wajiha Shireen
                     - Srinivas Vanapalli
                     - Hrishikesh Nene
ØAlternate energy systems have increasingly become popular
over the last few decades due to their inherent advantages over
conventional energy sources.

ØIn order to make a noteworthy impact, these systems must
be utility interactive.

ØA typical system consists of a DC-DC converter followed by
a DC-AC converter.
     A Typical Alternate Energy
                        DC Bus
                                            Load /
Alternate    DC-DC               DC-AC      Electric
 Energy     Converter            Inverter   Utility
       DC Bus which is not DC!
• Above system assumes a constant ripple free DC bus.
• Alternate energy sources themselves do not always
  produce voltages that are constant.
• In any practical converter, it is difficult to realize a
  constant ripple free DC bus.
• This ripple on the DC bus causes lower order
  harmonics to appear at the output of the inverter,
  deteriorating the output voltage quality.

• The magnitude of the fundamental component of the
  inverter output may not remain constant.
          Conventional Solution
Normally large DC Capacitors are employed to get a stiff
DC bus. However,
• They are bulky and occupy too much space.
• Contribute to slow response and increased cost.

So is there a way to get a quality output
    without those bulky capacitors?
Block diagram of the DSP-
     based interface.
                        PWM     Inverter

 DC voltage from                           Utility AC
 alternate energy                           System

                        MOSFET drivers
                         & isolation


 Voltage sensing &           DSP
 conditioning circuit      Controller
Pulse Width Modulation (PWM)
• The switching power converter (inverter) consists
  of power semiconductor switching devices.
• The ON and OFF periods of the switching devices
  are controlled by pulse width modulated (PWM)
  control signals.
• Space Vector Pulse Width Modulation (SVPWM)
  is a special switching sequence used in AC
  Induction motor and PM motor drives.
     Advantages of DSP control over
           analog techniques
• Precision with stability
• More reliable
• High Speeds
• Implementation of complicated Mathematics.
• Smaller Size
• Low cost
• Ability to make changes in software instead of re-
  designing equivalent analog circuitry
    Laboratory set-up of Inverter and DSP
• A single phase variable ac source (Variac).

• A three phase inverter Board (Spectrum Digital DMC 1500
  drive platform)

• A DSP Controller EVM Board (TMS320F240 EVM platform)

• A Personal computer with the DSP software (an IBM
  compatible PC with Code Composer Studio installed).
Hardware setup for a DSP controlled three phase
          AC Induction motor drive


  AC Motor

                        Inverter    DSP EVM

                                    30 % Ripple introduced                                               Manual variation of the
                                     using 47 uF capacitor                                               DC bus voltage over a
                                                                                                             wider range

                                           Without using the

                                                                              Output Voltage mag. in V
                                     14                                                                       Without using the
                                               Algorithm                                                 36
Output tVoltage m a g . in V V

                                    13.5                                                                          Algorithm
 O u t p u V o lt a g e mag. in .

                                    12.5                                                                 31

                                    11.5                                                                 26
                                                          Using the
                                     11                   Algorithm                                                          Using the
                                    10.5                                                                 21
                                     9.5                                                                 16




                                           25   27   29   31   32   35   34





                                               DC Bus Voltage in V.
                                            DC Bus Voltage in V                                               DC Bus Voltage in V
Active Filtering of Input Ripple Current
to Obtain Efficient and Reliable Power
        from Fuel Cell Sources

           Dr. Wajiha Shireen
            Hrishikesh Nene
          Block Diagram of a Typical
               Fuel Cell System

Inverter stage è Introduces a 2nd harmonic (120 Hz) current               h2
ripple into the system.                                                        h3

This low order current ripple, has been found to be detrimental to
the performance, efficiency and life of the fuel cell.
Slide 37

h1         Explain - DC-DC boost need and inverter need.
           hrnene, 7/16/2006

h2         It can reduce the fuel cell available output power by as much as 6 %, causing internal losses and increasing distortion of its
           terminal voltage
           hrnene, 7/16/2006

h3         Current ripple is boosted from inverter to the fuel cell.
           hrnene, 7/16/2006
              Proposed System
The goal of this research is to prevent this 120 Hz ripple current
from circulating through the fuel cell source so as to obtain a more
reliable and efficient system.

To achieve this, an active filter is connected across the DC-DC

The active filter provides an alternate path for the 2nd harmonic
current and saves the fuel cell.

No external energy storing device is required.
Proposed System Block Diagram
      Fuel    DC-DC                  DC-AC
      Cell   Converter               Inverter       LOAD

             Active                EzDSP F2808
             Filter                DSP Controller
                DSP Controller
• It provides switching signals for the boost, the inverter and the
  active filter switches.

• It senses the 120 Hz current ripple generated by the inverter.

• It calculates the amplitude and phase of the cancellation
  current and adjusts the PWM pulse widths and phase for the
  active filter switches accordingly.

• It can also modify inverter switching signals and/or boost
  switching signals to compensate for any variations on the DC
Side - by – Side Comparison
               Time Domain                        Time Domain


     120 Hz 240 Hz
                                                240 Hz
                                       120 Hz

            Frequency Domain                    Frequency Domain

  Fuel Cell Current for             Fuel Cell Current for
 a Conventional System              the Proposed System
    Conventional System Vs Proposed system
            (Experimental Results)
         Quantity                   Conventional   Proposed
                                      System        System
         Vdc (Bus Vltg)                 25 V         25 V

         Ifuel-cell@ 0 Hz                2A          1.9 A h4
       (DC current drawn)

        Ifuel-cell @ 120 Hz             1.2 A        0.6 A
(120 Hz ripple current imposed on
               the fuel cell)

      Ripple factor due to              50 %         29.5 %
        120 Hz current

       Total Ripple factor             >55.7 %       < 36 %
Slide 42

h4         Reduction in the DC current drawn
           hrnene, 7/16/2006
• Total elimination of the ripple should be possible by fine
  tuning the phase and amplitude of the active filter generated

• The proposed system, after its performance optimization, can
  contribute significantly in increasing the life, efficiency and
  reliability of fuel cell systems.

• Such a system can be targeted at low to medium power
  residential applications.

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