Power electronics
Power electronics is a branch of electrical engineering that deals with the conversion and control of electrical energy. Electrical circuits and components are used to efficiently transfer energy between different voltage, current or frequency levels. Power electronics are used in a wide range of applications, from industrial machines to electric vehicles and renewable energies.
Tasks of power electronics
Rectifier: Converts alternating current (AC) into direct current (DC).
Inverters: Convert direct current into alternating current.
DC-DC converters: Adapt the DC voltage to different voltage levels.
AC-AC converters: Change the frequency or amplitude of alternating current signals.
Targeted control of the current and voltage ratios means that the power can be optimally adapted to consumers.
This control is often carried out via electronic switches such as transistors, thyristors or MOSFETs.
The aim of power electronics is to minimize energy losses during conversion and control in order to maximize the efficiency of systems.
This plays a particularly important role in mobility (electric cars) and renewable energy (e.g. solar systems, wind turbines).
Power electronic systems can precisely regulate the voltage and current flow in a system and thus help to protect consumers and optimize grid stability.
In electric motors, such as those used in industry or in electric vehicles, the power electronics control the speed, torque and energy consumption.
Typical applications of power electronics:
Photovoltaic systems: Conversion of direct current from solar cells into grid-compatible alternating current.
Wind turbines: Control and conversion of electrical energy from generators.
Electric vehicles: motor control, battery management and charging infrastructure.
Energy supply grids: Conversion and distribution of electrical energy to ensure grid stability.
Industrial automation: Control of machines and processes using controlled electric drives.
Power electronics components and circuits
In power electronics, special circuits and components are used to efficiently convert, control and regulate electrical energy. The choice of circuits and components depends on the specific application, e.g. whether it is a matter of converting direct current (DC) into alternating current (AC) or adjusting the voltage. Some of the typical power electronics circuits and components are explained below:
Typical power electronics circuits
Function: Converts alternating current (AC) into direct current (DC).
Types:
- Half-wave rectifier: Uses only one half-wave of the alternating current.
- Bridge rectifier: Uses both half-waves and therefore provides better rectification.
Application: In power supply units and for energy conversion in solar systems.
Task: Converts direct current into alternating current.
Types:
- Full bridge inverter: Switches the current through a bridge circuit to generate alternating voltage.
- PWM inverter (pulse width modulation): Generates alternating current with variable frequency and amplitude through rapid switching operations.
Anwendung: In Photovoltaikanlagen, Elektrofahrzeugen und Motorsteuerungen.
Function: Converts a DC voltage into another DC voltage (up or down).Task: Converts a Function: Converts a DC voltage into another DC voltage (up or down).DC voltage into another DC voltage (up or down).
Types:
- Buck converter: Reduces the voltage.
- Boost converter: Increases the voltage.
- Buck-boost converter: Can both increase and decrease the voltage.
Application: Battery management systems, power supply units and electronic devices.
Function: Converts alternating current with a certain frequency into alternating current with a different frequency.
Types:
- Direct AC-AC converter: Does not use an intermediate stage with direct current.
- Indirect AC-AC converter: First converts AC to DC and then back to AC at a different frequency.
Application: In motor controls, frequency converters and for voltage regulation in electrical networks.
Typical power electronics components
Function: Conducts current in one direction only, often used for rectification.
Power semiconductor diodes: Used in high-power applications such as rectifiers.
Fast diodes: For applications where fast switching is required, such as in high-frequency circuits.
Function: Semiconductor switches that are made conductive by a control pulse and remain conductive until the current through them is zero.
Application: In high-power applications such as phase angle control, rectifiers and in high-voltage direct current (HVDC) transmissions.
MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor): Fast switch with low switching losses, particularly suitable for low-voltage and high-frequency applications.
IGBT (Insulated Gate Bipolar Transistor): Combines the advantages of MOSFETs (easy control) and bipolar transistors (high voltage and current carrying capacity). Frequently used in inverters and motor drives.
Bipolar transistors (BJT): Are used less frequently in power electronics because they switch more slowly than MOSFETs and IGBTs.
Function: Bidirectional switch that can control alternating current.
Application: In dimmable light switches and leading edge phase control systems.
Function: Storage of electrical energy and smoothing of voltages.
Application: In rectifiers for smoothing direct current and in circuits for filtering and energy storage.
Function: Storage of energy in the form of magnetic fields and filtering of interference signals.
Application: In DC-DC converters and for interference suppression in circuits.
Function: Convert voltages in AC systems by electromagnetic induction.
Application: In inverters, power supplies and grid substations.
Switching strategies
Pulse width modulation (PWM): A commonly used technique in which the on and off time of a transistor is varied to control the average output voltage.
Phase angle control: Uses thyristors or triacs to control the power by delaying the ignition timing in the AC cycle.
Cooling the power electronics
The cooling of power electronics plays a crucial role because power electronics components such as transistors, diodes and thyristors operate at high currents and voltages and generate considerable amounts of heat in the process. This heat must be dissipated effectively to protect the components from overheating and to ensure the performance and reliability of the entire system. Here are the main reasons why cooling is of central importance in power electronics:
1. avoidance of thermal damage
Overheating protection: Electronic components have specific temperature limits. If these are exceeded, this can lead to permanent damage to the semiconductor materials and malfunctions. In extreme cases, a thermal runaway can occur, in which the component is completely destroyed.
Reduction in service life: Semiconductor components are sensitive to high temperatures. Even if no immediate damage occurs, the permanent exposure to increased temperatures can significantly shorten the service life of the components. A long service life is particularly important in industrial applications.
2. maintaining efficiency
Performance losses due to heat: The electrical properties of semiconductors change with temperature. Overheating often leads to increased losses through switching and on-state resistances, which reduces the efficiency of the circuit. In power electronics systems designed for high efficiency, it is important to keep temperatures low in order to minimize power loss.
Power loss in the form of heat: Each switching operation in transistors or diodes generates a small amount of energy loss that must be dissipated in the form of heat. Particularly in systems that constantly process high power, this heat loss can add up and cause considerable temperatures.
3. increase in reliability
Temperature-dependent component parameters: The electrical parameters of power semiconductors, such as on-resistance or switching times, are highly dependent on temperature. Insufficient cooling can lead to unstable operating points that impair the controllability and controllability of the system.
Temperature stress: Constant temperature cycles, i.e. the heating and cooling of components, can lead to mechanical stresses in the materials and solder joints. In the long term, these stresses lead to microcracks or other mechanical defects, causing the electronics to fail.
4. miniaturization and high power density
Compact design: Modern power electronic systems are often very compact and have a high power density. This means that a lot of power is processed in a small space, which leads to increased heat density. Without efficient cooling, the heat generated in such compact systems could quickly lead to overheating.
Thermal management requirements: As power density increases in modern devices such as electric vehicles, solar inverters or industrial drives, advanced cooling solutions are needed to safely and reliably manage the high energy density.
5. prevention of thermal runaway
Thermal runaway: This is a dangerous phenomenon where an increase in temperature leads to a further increase in current, which in turn further increases the temperature. This cycle can lead to failure of the component. Efficient cooling prevents such situations from developing.
Cooling methods in power electronics
There are various methods that are used for cooling in power electronics:
Passive cooling: Uses heat sinks that dissipate heat to the ambient air by convection. This method is used in many systems because it is simple and low-maintenance.
Active cooling: Involves the use of fans or liquid cooling systems to dissipate heat more efficiently. Active cooling is often used in high-performance systems where passive cooling is not sufficient.
Liquid cooling: For particularly powerful applications, liquid cooling can be used, in which a cooling liquid is pumped through the system to dissipate the heat.
Thermal interface materials (TIMs): These materials help to transfer heat from the components to the heat sinks by reducing thermal resistance.
Intelligent cooling solutions for power electronics
An intelligent cooling solution for power electronics that relies exclusively on the use of fans can be achieved by integrating modern control and monitoring technologies as well as an optimized arrangement of components. Here are some aspects that such a solution could take into account:
1. temperature monitoring and control
Sensor-based temperature detection: To enable precise control of the fans, temperature sensors are placed at critical points in the power electronics, such as on the semiconductors (MOSFETs, IGBTs) or on the heat sinks. These sensors monitor the temperature in real time and provide continuous feedback to a central control system.
Dynamic fan control: Instead of running the fans continuously at a fixed speed, the fan speed can be dynamically adjusted to the current temperature of the components. This saves energy and reduces the noise level, as the fans only operate at full power when required. PWM-controlled fan regulation (pulse width modulation) could ensure that the fan speed is adapted precisely to the cooling requirements.
2. optimized airflow routing
Geometric optimization of the fan arrangement: Well-planned airflow routing is crucial for cooling efficiency. The airflow should be directed specifically over the components that generate the most heat. For this purpose, the housing geometry can be designed in such a way that air flows are directed specifically to the components and hot air is effectively dissipated.
Channel structure for airflow: Channels or baffles can be integrated within the housing to direct the airflow. These prevent the air from accumulating in blind spots and ensure that all critical components are cooled evenly.
Push-pull fan configuration: In this configuration, fans are located at both the inlet and outlet of the enclosure. The front fan pulls cool air into the enclosure, while the rear fan blows the heated air out. This method increases the air flow and ensures more effective cooling.
3. fan optimization and selection
Highly efficient fans: The use of energy-efficient, low-noise fans with optimized fan blades can maximize cooling with minimal energy consumption and noise. Modern fans are designed to provide higher airflow at lower speeds.
Variable geometry fans: Some modern fans have adaptable blade geometries that can adjust the airflow to move more or less air depending on requirements. This could further increase efficiency by automatically optimizing the airflow as required.
4. combination with heat conducting components
Thermal interface materials (TIMs): To maximize fan efficiency, highly conductive thermal materials (such as thermal pastes or pads) can be used between the heat-generating components and the heat sinks. These materials ensure that the heat is effectively transferred to the heat sinks so that the fans can work efficiently.
High-performance heat sinks: The fans work most efficiently in combination with well-designed heat sinks that have large surfaces for heat dissipation. Finned heat sinks or heat sinks with finned structures can be used to increase surface area and maximize airflow.
5 Intelligent control and communication
Microcontroller-based fan control: A microcontroller or integrated control system can automatically regulate the fans. This system would access the data from the temperature sensors and adjust the fan speed and airflow to ensure optimal cooling. When temperatures rise, the microcontroller would increase the speed, and when temperatures fall, it could reduce the fan speed or even switch off the fans to save energy.
Networked fan control: In large systems with several fans, a networked fan control system could be used in which the fans communicate with each other to coordinate the air flow. This ensures that no fans operate unnecessarily or that no superfluous flow barriers are created.
Warning systems and protection mechanisms: If a fan fails or overheats, alarm systems could be activated to shut down the system or switch on replacement fans. This protects the power electronics from damage.
6. dust and dirt management
Dust filters: To ensure the long-term efficiency of the fans, dust filters can be used to prevent dust particles from blocking the airways and impairing cooling performance. These filters should be easily accessible to enable regular maintenance.
Automatic cleaning mechanisms: Some advanced fan solutions offer automatic cleaning technologies where fans run backwards at regular intervals to blow away accumulated dust and dirt.
7. software-supported optimization
Cooling optimization software: Thermal management software can be used to simulate and analyse the temperature distribution in the power electronics. This software helps to identify critical points and optimize the cooling system so that the fans work as efficiently as possible.
Machine learning: Future systems could be based on artificial intelligence (AI) or machine learning algorithms that learn from past operating data in order to optimize cooling behaviour. The fans could be controlled so intelligently that they react proactively to possible heat developments and adjust the cooling capacity accordingly.