Power quality application examples

Solutions for reliable electricity supply

Reliable electricity supply sets high requirements to infeed, retrieval and consumption of electrical energy, which can be summarized under the term "power quality". Important applications are, for example, rule-compliant and evened supply from renewable energy sources locally generated electricity into the grid, the limitation of network distortion in energy retrieval and the protection of sensitive consumers against supply failures. SEMIKRON offers highly suitable power modules for each of these applications with which the existing demanding requirements can be met reliably and cost-effectively.

In order to reduce dimensions, weight and cost of line filters and transformers, and to minimise mains disturbance, it is necessary to achieve the highest possible switching frequencies. By using 3-level IGBT modules in NPC and TNPC topologies – which are produced by SEMIKRON for a wide range of outputs in the product groups SKiM, SEMITRANS, MiniSKiiP and SEMITOP – it is possible to achieve high pulse frequencies with comparatively low switching losses.

Block diagram of an active power filter

Active line filters (power quality management)

Operators of industrial facilities and rail networks, in particular, use active line filters with IGBT modules to meet the requirements of energy suppliers in terms of low mains feedback. The applications cover a wide range of outputs, from 1 kVA to several MW with parallel power converters. Active line filters are controlled power sources that can feed current into the network with any amplitude, frequency or phasing to compensate for harmonics and reactive power caused by the load. Their topology is that of an inverter with DC bus voltage which is connected to the network via a filter (see figure 2).

Constant comparison of the actual value of the current in the network against the target value determines the energy that must be fed from the DC link capacitors via the inverter into the network, separately for each phase. In order to achieve good control dynamics, the highest possible pulse frequencies must be used.

System size and discharge time of storage systems for electrical energy

Energy Storage

The application "Energy Storage" includes very diverse fields of application, e.g.:

  • Back-up of power failures to protect sensitive consumers with UPS systems (Uninterruptible Power Supplies)
  • Electric energy storage for short-term support of wind energy and PV solar systems during grid faults and compensate for short-term production deficits
  • Storing large amounts of energy for long term support in a limited supply network or to integrate producers into the grid with non-predictable, uneven power generation.

Depending on the storage volume and discharge time, today electric energy storage systems either store directly (e.g. battery storage or capacitor storage, superconducting magnetic storage) as mechanical energy (flywheel energy storage, pump storage, compressed air storage), or in the form of electrolytically produced hydrogen.

Most common today are battery storage systems with lead, NaS, Radox-Flow or Li-Ion batteries used in UPS.

3-level inverter topologies NPC and TNPC

UPS systems

Standard UPS systems for home and industrial use in the power range of about 1kW to 1MW have, among other functions, an IGBT inverter (usually three-phase) and DC/AC converter. Currently, many different topologies of inverters for UPS systems are on the market. Solutions with 3-level topologies are gaining in importance in order to achieve high efficiency, which is a major selling point for UPS systems. Due to the 3-stage switching levels of the output voltage, the 3-level topology also helps to reduce the amount of filtering due to low line harmonics.