PCS and Inverter Systems

PCS for Power Conversion System

  • PCS encompasses the inverter and its associated skid.
  • Example given of a GE LV5 inverter, slightly larger than the 1 MW model.
    • Estimated at 4 MW output.
    • Similar setup with four doors, the far right dedicated to cooling.

Inverter Components and Functionality

  • DC input on one side, AC output via bus duct to an external medium voltage transformer.
  • Accessories located on the right-hand side:
    • Auxiliary transformer.
    • Disconnect.
    • Breaker box.
    • Communications and fiber optic for remote monitoring via SCADA.

Warning Labels

  • Warning labels are frequently replaced due to sun fading.
  • Teams are dedicated to applying stickers daily.
  • UV protective paint is suggested as a solution.

Switchgear

  • Medium voltage transformer with an oil switch.
  • Gas-insulated switchgear allows AC disconnect manipulation.
  • Switchgear switches on the high side of the transformer (higher voltage, lower current).
    • Allows manipulation without requiring a 40 cal suit.
  • Switchgear can be more complex but serves the same purpose as PE versions.

Switchgear Functionality

  • Controls upstream and downstream components.
  • Isolates inverters in a string.
  • SMA inverters typically involve manipulating the cabinet on the far right side.
  • Switching on the other side requires explicit instruction due to safety concerns.

Safety Concerns with Switchgear

  • Devices are not 100% mechanically interlocked.
  • Incorrect switching can lead to closing to ground at 34,500 volts.
  • Example of technicians causing a feeder breaker to open due to incorrect switching.
  • The switchgear's circuit protection snuffed out the arc all the way back to the substation.
  • The system is inherently safe to be around, but mistakes can still occur.

Inverter Layout

  • Three main parts:
    • DC input.
    • Power electronics.
    • AC output to medium voltage.
  • Additional components:
    • Controls.
    • Contactors.
    • Relays.
    • Circuit protection.
  • Function: Invert DC to AC to support IGBTs operation.

IGBTs (Insulated Gate Bipolar Transistors)

  • Typically in a plastic package with a metal heat sink.
  • Heat sink dissipates heat, preventing explosions.

Schematics and FRUs

  • IGBT assemblies (FRUs) are crucial for schematics.
  • Example: Six FRUs per version two PE.
    • 36 photovoltaic inputs with recombiner disconnects.
    • Positive and negative connections to six modules.
    • Three phases out (AC).
    • DC in, DC out.

Auxiliary Transformer and Filtering

  • Auxiliary transformer energizes control devices.
  • Inductors and capacitors with contactors form a filtering circuit.
  • Double hash marks on lines indicate two conductors.

Self-Sustaining System

  • Modules feed AC to the auxiliary transformer for self-sustainment.

Examples of IGBT Assemblies

  • Various manufacturers and models (GE, ABB, SMA, Solar Delta, PVP).
  • The "business end" of the inverter performing the actual inversion.
  • Some use the same package and are somewhat interchangeable with different drivers.

Scale and Perspective

  • Large PE container (30-40,000 lbs) primarily supports 54 small IGBT packages.
  • The container's size is to support the work of the IGBTs.

Advanced IGBT Configurations

  • GE two eight uses more IGBTs than needed, wired for redundancy and thermal management.
  • Firing cycles with rest periods for individual IGBTs.
  • Dynamic braking IGBTs used to slow the generator by creating a load.

Dynamic Braking

  • Reverses the action of the motor to act as a load.
  • In wind applications, it slows the generator down by taking the DC link down.
  • Creates a load on the generator to dissipate extra energy.

IGBT Functionality

  • Power inverters convert DC to AC.
  • Voltage as pressure pushing electrons.
  • Magnetic fields induce electron flow.
  • Sine wave generation through magnet rotation.
  • Frequency (e.g., 60 Hz in North America) is the number of sine wave repeats per second.
  • IGBTs act as fast-opening and closing switches to control electricity flow.

Pulse Width Modulation (PWM)

  • Controls the opening and closing of switches to create AC from DC.
  • Varying switch timing adjusts voltage and frequency.
  • Transformer steps up low voltage to required levels (e.g., 120V or 230V).

Three-Phase Electricity

  • Three phases are generated by coils 120 degrees apart.
  • Phases have different sine waves slightly out of sync.
  • Current flows between phases, with any excess going to neutral.
  • Three-phase delivers more power by filling gaps between peaks.
  • Used in larger applications (e.g., compressors in cooling systems).

Three-Phase Inverter Operation

  • Switches are opened and closed in pairs to direct current flow.
  • Simulates three phases to drive motors with alternating current.

Safety and Arc Flash

  • Arc flash hazards are significant, with energies above 40 cal/cm².
  • NextEra prioritizes de-energizing equipment over live work.

MET Stations

  • Mounted with pyranometers for radiant sensors with domes and sensors inside.
  • Mini solar panels charge batteries to output data to SCADA systems.

Reference Panels

  • Strategically placed to measure site output.
  • Clean and dirty panels are compared to assess performance.
  • Used to calculate potential output under perfect conditions.

Subcurve

  • Relates to wind energy capture.
  • It describes how much of the available wind energy is actually captured and converted into electricity.

Irradiance Meters

  • Track solar irradiance.
  • Stationary and moving meters provide reference data.