(Full length version of article published in the Feb 2021 issue of Power Design “Selecting DC Link Capacitors for Inverters”)
This paper offers main considerations and a per unit methodology used in the selection of inverter DC Link capacitors.
This paper addresses application of protected AC output filter capacitors for UPS systems.
Learn how to select output filter capacitors for inverter applications.
Modeling of Transient Electrical, Thermal and Lifetime Behavior of Aluminum Electrolytic Capacitors, Focusing on Large (>0.1 Liter) DC Link Capacitors.
Types MC & MCH Chips and Clad SMT Types Min & MCM
ESR vs. Frequency, RMS Current vs. Frequency, Q vs. Frequency, Impedance vs. Frequency
All design engineers who consider using aluminum electrolytic capacitors want to know how long they will last and how many they can expect to fail. Many engineers do not realize that these are actually two different but related questions. In this paper we define life and reliability in a manner that will hopefully make the distinction clear.
Aluminum electrolytic capacitors are routinelyused as input bus capacitors in the power supplysections of electronic equipment such as motordrives, UPS systems, and welders. Most of thesecapacitors fail eventually from wearout. This article offers a brief explanation of how capacitor manufacturers quantify the effects of applied voltage, ripple current, frequency, ambient temperature, and airflow on capacitor life.
Impedance modeling of aluminum electrolytic capacitors presents a challenge to design engineers due to the complex nature of the capacitor construction. Unlike an electrostatic capacitor, an electrolytic capacitor behaves like a lossy coaxial distributed RC circuit element whose series and distributed resistances are strong functions of temperature and frequency. Existing public domain Spice models do not accurately account for this behavior. In this paper, a physics based approach is used to develop an improved impedance model that is interpreted both in pure Spice circuit models and in math functions.
Aluminum electrolytic capacitors are widely used in all types of inverter power systems, from variable-speed drives to welders to UPS units. This paper discusses the considerations involved in selecting the right type of aluminum electrolytic bus capacitors for such power systems.
The 125°C, solid polymer aluminum (SPA) capacitors have performance advantages over other types of low ESR capacitors when used as output filters in DC-DC modules. The principal advantage of an SPA capacitor is that its ultra low ESR permits filtering in a DC-DC converter with fewer capacitors. This reduces the cost and size of the converter. This paper shows the performance advantages of the new Type ESRH, 125°C, SPA capacitor in DC-DC modules.
Snubbers are suppression circuits which are placed across IGBTs and switching transistors in power conversion circuits to suppress voltage transients and protect semiconductor devices from overvoltage. This paper shows how to design resistor-capacitor (RC) damping snubbers and the resistor-capacitor-diode (RCD) turn-off snubbers.
With so many types of capacitors available, circuit designers are faced with the challenge of selecting a capacitor that will be suitable for a specific snubber application. It is essential that the designer know the approximate conditions to which the capacitors will be exposed. The most important being peak voltage, temperature, dV/dt, and frequency. The designer may also be faced with constraints such as size, maximum allowable inductance, and cost. Once these conditions and constraints are identified the designer can begin the selection process.
Capacitor heating occurs in all aluminum electrolytic capacitor applications where a current is present, since the electrolytic capacitor is a nonideal capacitor which has resistive and other losses. Generally this heating is undesirable and is often a limit to the life of the capacitor. This paper explains the heating mechanisms so that life and reliability can be predicted.
Large-can aluminum electrolytic capacitors are widely used as bus capacitors in variable-speed drives, UPS systems and inverter power systems. Accurate thermal modeling of the capacitor's internal temperature is needed to predict life, and this is a challenge because of the anisotropic nature of the capacitor winding and the complexity of the thermal coupling between the winding and the capacitor case. This paper translates analytical models for heat flow in bus capacitors into an equivalent three-loop, seven-resistor, lumped-parameter thermal circuit model.
A comprehensive thermal model for screw-terminal aluminum electrolytic capacitors is developed in this paper. The test methodology and data upon which the model is based are discussed. Exact one-dimensional solutions, multi-dimensional heat equations, and finite-element analysis (FEA) model simulation results are presented. The effects of conduction, heat sinking, natural (free) convection, forced convection, and radiation are quantified and compared. Complex issues, such as anisotropism and multi-phase heat transfer, are discussed. A comparison of model results to test data is presented. Varying capacitor construction techniques are evaluated.
Economic evolution dictates that companies which offer the best, highest-valued products to its customers will thrive. For capacitor manufacturers, this translates into helping their customers build products with the best performance per unit price. Whether this means helping a customer reduce component count, lower impedance per board space, implement a custom capacitor for heat sink mounting, or select the lowest cost capacitor per ripple ampere, capacitor manufacturers are rising to the challenge of providing ever-increasing value.