Electrical Energy Storage System Study Notes

Chapter 1: Introduction

  • Introduction of the course and instructors:
    • Flora Martin: Teacher member of the electrical engineering group for the course.
    • Jarno Kukkola: Fellow instructor.
    • Professor Marco Incan: Fellow instructor.
  • Overview of key concepts in electricity and electrical engineering to facilitate communication among students.
  • Introduction to electrical networks:
    • Questions raised: What happens when you want to charge your phone?
    • Definition: Electrical networks exist at various scales, including regional (e.g., Helsinki), national (e.g., Scandinavian countries), and international levels (e.g., EU).
    • Components of electrical distribution:
    • Generation of energy
    • Distribution of energy
    • Consumption of energy (e.g., charging a phone).

Electrical Energy Generation

  • 96% of electrical energy produced by electrical generators, often associated with turbines or windmills.
  • Classical representation of an electrical motor.

Electrical Energy Distribution

  • Components involved in electrical distribution:
    • Transformers: Visualized as Lego blocks; their purpose is voltage manipulation.
    • Function of transformers: Transform from medium voltage (production) to high voltage (distribution).
    • Long-distance electricity transmission is more efficient at high voltage.
    • Voltage details in the EU:
    • Common voltage values: 220 volts at 50 hertz (European standard); can vary up to 400 kilovolts.
    • Safety concerning high voltage.

Electricity Consumption

  • Charging a phone:
    • Phone batteries operate on direct current (DC); chargers utilize alternating current (AC).
    • Function of a rectifier: Converts AC to DC for battery charging.
  • Distribution process:
    • Involves electrical generator, transformer (for voltage increase), and rectifier (for voltage decrease and conversion to DC).

Key Electrical Quantities

  • Two primary electrical quantities discussed:
    • Voltage (potential difference) is depicted using battery electrodes (positive and negative).
    • Coating conventions: Positive electrode often in red, negative in black.
    • Voltage represented by an arrow; vectorial sum in a circuit loop is zero.
    • Current: Represents the flow of electrons, expressed in amperes.
    • Conservation of current in closed loops (e.g., no current drawn in an open loop).

Chapter 2: Average Electric Power

  • Overview of representations of electrical energy storage systems.
  • Closing the circuit:
    • Connecting a battery to a load (e.g., a resistor simulating a DC load).
    • DC quantities remain constant over time; time units can be adjusted (e.g., hours, days, years).
  • Introduction to AC quantities for motors and generators:
    • AC voltage source depicted using a sinusoidal waveform; direct connection to a resistor/EDR load observes sinusoidal voltage and current patterns.
    • Difference in frequency:
    • Charging a battery involves 220 volts at 50 hertz in Europe; some regions may have 60 hertz.

Electric Power and Energy

  • Definition: Instantaneous electric power is the product of voltage and current.
  • Variability in power representation:
    • DC power remains constant; AC produces a sinusoidal power profile with double the frequency of voltage and current.
    • Average power to be integrated over one period.
  • Mean electric power:
    • For DC systems, it remains constant.
    • For AC systems, there are RMS values for voltage and current giving the average power equivalent to the instantaneous DC power.

Chapter 3: The AC Power

  • Energy defined as the cumulative sum of instantaneous power over time.
  • Formula for energy:
    • Energy expressed in watt-seconds or watt-hours (divide watt-seconds by 3,600 for watt-hours).
  • RMS quantities allow measurement without extensive integration.
  • Calculation of energy consumption based on varying power levels throughout the day illustrated with a sequence of electrical activity.
  • Reference to a realistic load:
    • Example of a washing machine as a realistic load exhibits phase shifts in AC current and voltage.

Chapter 4: Energy and Power Balance

  • Efficiency defined as the ratio of output power to input power, often expressed in percentage.
  • Acknowledgment that input power is the sum of output power and losses.
  • Discussion of various efficiencies in electrical components:
    • Electrical generators: Efficiency range of 90-97%.
    • Transformers: High efficiency close to 95%.
    • Rectifiers: Discussed efficiency at about 90-95%.
  • Notion of power loss in long transmitting networks like Finland to Estonia or Sweden; optimizing efficiency through voltage adjustments.

Chapter 5: Passive Power Converter

  • Description of power converter and design considerations for a washing machine:
    • Introduction of an AC voltage source and the AC electrical motor configuration in the washing machine.
    • Use of frequency converters to modify electrical characteristics for better control of motor functions.
    • Role of transformers for galvanic isolation to protect machinery from power surges.
  • Diode bridge employed as a passive power converter:
    • Characteristics: High efficiency (>90%), cost-efficient, and simple operational principles.

Chapter 6: Conclusion

  • Role of inverters as active power converters:
    • Functionality: Reversible control between AC and DC.
  • Distinction made between different types of converters:
    • Buck converter (lowers voltage) and boost converter (raises voltage), both featuring controlled active elements like IGBTs and inductors.
  • Encouragement to use high-efficiency components when designing energy storage systems for optimal performance and reliability.