Components of Frequency Converters: Exploring Internal Structure

Frequency converters, also known as power converters or frequency changers, are electronic devices used to convert electrical power from one frequency to another. The composition of a frequency converter can vary depending on its specific application and power rating. However, here are the common components found in frequency converters:

  1. Rectifier: The rectifier is responsible for converting the incoming alternating current (AC) power into direct current (DC) power. It typically consists of diodes arranged in a bridge configuration to rectify the AC waveform.
    • Diodes: Rectifiers use semiconductor diodes, typically in a bridge configuration, to convert AC power to DC power. Diodes are made up of semiconductor materials, such as silicon or germanium, with a p-n junction that allows current flow in one direction while blocking it in the reverse direction.
    • Heat sinks: Since rectifiers can generate heat during operation, heat sinks are often attached to diodes to dissipate heat and prevent damage to the components. Heat sinks are made of thermally conductive materials, such as aluminum or copper, with fins to increase the surface area for efficient heat dissipation.
    • How are the Diodes, Heat sinks inside the Rectifier of Frequency Converters made?
  2. DC Link: The DC link is a capacitor bank or an energy storage device that smoothens the rectified DC voltage and provides a stable DC voltage source to the inverter.
    • Capacitors: The DC link uses capacitors to store electrical energy and provide a stable DC voltage source to the inverter. Electrolytic capacitors, with high capacitance values, are commonly used in DC link applications. They are made of two conductive plates separated by an insulating material (dielectric) and are typically enclosed in a cylindrical or rectangular case.
    • How are the Capacitors inside the DC Link of Frequency Converters made?
  3. Inverter: The inverter is a key component that converts the DC power from the rectifier into the desired AC frequency and voltage. It uses semiconductor switches (typically insulated gate bipolar transistors or IGBTs) to generate a high-frequency AC waveform. The inverter’s output voltage and frequency can be controlled to match the requirements of the target application.
    • nsulated Gate Bipolar Transistors (IGBTs): IGBTs are the main switching devices used in the inverter. They are three-terminal devices that combine the advantages of both bipolar junction transistors (BJTs) and metal-oxide-semiconductor field-effect transistors (MOSFETs). IGBTs consist of multiple layers of semiconductors and are controlled by a gate signal to switch on and off, allowing the conversion of DC power to AC power.
    • Gate Driver Circuitry: The gate driver circuitry provides the necessary voltage and current signals to control the switching of IGBTs. It ensures precise timing and synchronization of the switching process to achieve the desired output voltage and frequency.
    • How are the Insulated Gate Bipolar Transistors (IGBTs), Gate Driver Circuitry inside the Inverter of Frequency Converters made?
  4. Filters: Filters are used to reduce harmonic distortion in the output waveform of the inverter. Harmonics are unwanted frequency components that can cause interference or damage to other equipment in the electrical system. Filters can be designed to mitigate these harmonics and provide a cleaner output waveform.
    • Inductors: Filters include inductors to reduce harmonic distortion by filtering out unwanted high-frequency components from the output waveform. Inductors are made of coils of wire wound around a core, which can be air, iron, or ferrite. They store energy in a magnetic field and impede the flow of high-frequency currents.
    • Capacitors: Capacitors are also used in filters to further suppress harmonics and smooth the output waveform. These capacitors are typically connected in parallel with the load or in series with the inductors to form LC (inductor-capacitor) filter circuits.
    • How are the Inductors, Capacitors inside the Filters of Frequency Converters made?
  5. Control System: The control system consists of a microprocessor or a digital signal processor (DSP) that monitors and controls the operation of the frequency converter. It regulates the output voltage and frequency, ensures protection against faults, and provides various control modes and functions.
    • Microprocessor/Digital Signal Processor (DSP): The control system incorporates a microprocessor or DSP that receives feedback signals, executes control algorithms, and generates control signals for regulating the output voltage and frequency. These components consist of integrated circuits (ICs) with complex electronic circuits and computational capabilities.
    • Feedback Sensors: Feedback sensors, such as voltage sensors, current sensors, and temperature sensors, are used to measure various parameters in the system and provide feedback to the control system for closed-loop control.
    • Control Algorithms: Control algorithms are software programs that run on the microprocessor or DSP. These algorithms implement control strategies, such as pulse width modulation (PWM) techniques, to adjust the output voltage and frequency according to the desired specifications.
    • How are the Microprocessor/Digital Signal Processor (DSP), Feedback Sensors, Control Algorithms inside the Control System of Frequency Converters made?
  6. Cooling System: Frequency converters generate heat during operation, and a cooling system is necessary to maintain optimal temperature and prevent component damage. The cooling system may include fans, heat sinks, or liquid cooling methods, depending on the power rating and design of the converter.
    • Fans: Fans are commonly used in frequency converters to provide forced air cooling. They consist of an electric motor and blades that circulate air over heat sinks or other components to dissipate heat.
    • Heat Sinks: Heat sinks are made of thermally conductive materials and are often attached to power electronic components, such as diodes, IGBTs, or other heat-generating elements, to absorb and dissipate heat efficiently.
    • How are the Fans, Heat Sinks inside the Cooling System of Frequency Converters made?
  7. Protection and Safety Devices: Frequency converters incorporate various protection and safety features to ensure reliable operation and protect against faults. These may include overcurrent protection, overvoltage protection, short-circuit protection, thermal protection, and various interlocks.
    • Circuit Breakers: Circuit breakers are electromechanical devices that automatically interrupt the current flow in the event of an overload or short circuit. They consist of a bimetallic strip or an electronic trip unit that responds to excessive current and opens the circuit.
    • Overvoltage Protection Devices: These devices, such as metal oxide varistors (MOVs) or transient voltage suppressors (TVS), protect against voltage spikes or surges that could damage the converter or connected equipment.
    • Temperature Sensors: Temperature sensors are used to monitor the temperature of critical components and trigger protective actions, such as reducing the output power or shutting down the system, in case of excessive heat.
    • How are the Circuit Breakers, Overvoltage Protection Devices, Temperature Sensors inside the Protection and Safety Devices of Frequency Converters made?
  8. Control and Monitoring Interfaces: Frequency converters often have control and monitoring interfaces to enable communication with external systems or user interfaces. These interfaces can include digital communication ports, analog input/output signals, and human-machine interfaces (HMI) such as touchscreens or keypad displays.
    • Digital Communication Ports: Frequency converters may include serial communication ports (such as RS-485, Ethernet, or CAN) to facilitate communication with external systems, such as programmable logic controllers (PLCs) or supervisory control and data acquisition (SCADA) systems.
    • Analog Input/Output Signals: Analog signals, such as voltage or current signals, can be used for control and monitoring purposes. These signals may be used to set the desired output voltage or frequency or to provide feedback on the system’s status.
    • Human-Machine Interfaces (HMI): HMIs provide a user interface for operators to interact with the frequency converter. They can include touchscreens, keypads, displays, and indicators to show system parameters, alarms, and allow configuration adjustments.
    • How are the Digital Communication Ports, Analog Input/Output Signals, Human-Machine Interfaces (HMI) inside the Control and Monitoring Interfaces of Frequency Converters made?