Power Electronics

Power Semiconductor Devices

• Silicon Atom Structure:
  • Layer 1: 2 electrons
  • Layer 2: 8 electrons
  • Layer 3: 4 electrons

Operating Principles of Power Semiconductor Devices

• Diodes:

  • Forward Biased:
  • The external voltage attracts electrons to enter the junction, overcoming the electric field (E).
  • Reverse Biased:
  • Both E and reverse voltage (Ve) act to prevent electrons from entering the junction.

• BJT (Bipolar Junction Transistor):

  1. Apply forward bias to the base-emitter (BE) junction.
  2. Electrons enter the base, which is thin and lightly doped, allowing them to pass to the collector.
  3. If $V_{CE} = 0$, electrons accumulate at the collector.
  4. If $V_{CE} > 0$, electrons flow out of the collector.

• JFET (Junction Field Effect Transistor):

  1. Electrons flow from source to drain, passing through depletion layers.
  2. If $V<em>{GS} = 0$, $I</em>{D} = I<em>{P</em>{max}}$ (Normally ON).
  3. When $V_{GS} < 0$, the depletion layer expands and narrows the conducting channel.

• MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor):

  • Depletion Mode: Negative $V_{GS}$ pushes away electrons and attracts holes.
  • Enhanced Mode: Positive $V_{GS}$ pushes away holes, attracting electrons and forming an n-type inversion layer.

• IGBT (Insulated Gate Bipolar Transistor):

  1. When $U<em>{GE} = 0$, $i</em>{c} = 0$.
  2. When $V<em>{GE} o V</em>{GECO}$, electrons diffuse from heavily doped to lightly doped regions.
  3. If $V<em>{i} o 0$, $i</em>{c} = B<em>i^s$, $i</em>e - i<em>e = (B + 1)i</em>n$.

• Thyristors:

  1. As $i<em>s$ increases, $i</em>n$ also increases ($i<em>c = B</em>i b z$).
  2. If $i<em>s$ increases, $i</em>b i = (2)$.
  3. Current $i<em>c$ increases ($i</em>c = B_i b$).

Classification of Power Semiconductor Devices by Controllability

• Uncontrollable: Diode
• Semicontrollable: Thyristor
• Fully Controllable: BJT, MOSFET, IGBT

DC-DC Converters

• Types: Buck, Boost, Buck-Boost
• Output Voltage Relationships:
  • Buck: $V<em>o = V</em>i D$
  • Boost: $V<em>o = \frac{V</em>i}{1 - D}$
  • Buck-Boost: $V<em>o = \frac{V</em>i D}{1 - D}$

Current Waveforms

• Current waveforms for inductor, switch, and diode:
  • Buck: Simplified current relationships and switching behaviors.
  • Boost: Similar but consider current dynamics during charging and discharging of inductor.
  • Buck-Boost: Composite behavior corresponding to switching actions.

AC-DC Converters

• Types: Half-Wave, Full-Wave, Full-Bridge Rectifiers.
• Half-Wave: Current flows during positive cycle.
• Full-Wave: Both halves of the AC signal are used, yielding higher output.
• Full-Bridge: Achieves more efficient rectification by utilizing all four switching elements.
• Output Voltage Calculations:
  • Half-Wave: $V{o{avg}} = rac{V_{m}}{
    ho ext{ for the given cycle}}$
  • Full-Wave: $V<em>{o</em>{avg}} = 0.9 V_{rms}$ for perfect conditions.

Inverters

• Half-Bridge, Push-Pull, Full-Bridge Inverter Circuits:
  • Conduction Modes:
  • 180° conduction (Half-Bridge)
  • 120° conduction modes (Full-Bridge)
• SPWM (Sinusoidal Pulse Width Modulation):
  • Types: Unipolar/Bipolar, Double Frequency SPWM.
  • Advantages: Low THD (Total Harmonic Distortion), reduced switching loss.
  • Disadvantages: Complexity in implementation, requires multiple comparators.

Advanced Modulation Techniques

• Bipolar SPWM:
  • Advantages: Simple implementation, fundamental frequency strong.
  • Disadvantages: High harmonic distortion, difficult EMI management.

AC-AC Converters

• Phase Angle Control: Amplitude modulation through adjusting phase angle.
• Adjustment Outcomes:
  • Adjustments typically reduce total harmonic distortion and improve waveform quality but may increase switching losses.

Control Techniques

1. ON-OFF Control:
   • Low harmonic distortion but slow response times.
   • Ratio determining power delivered influenced by ON/OFF cycles.
2. Zero Voltage PWM Control:
   • Uses high-frequency switching for modulation, reducing harmonic issues.
3. Resonant Converters:
   • Advantages: Smaller sizes of components, better waveform quality.
   • Disadvantages: Increased switching losses and thermal stress.

Resonant Circuits

• Describe relationships and dynamics across various configurations:
  • Series and Parallel behaviors: Current and voltage profiles exhibit sine and cosine relationships across elements.