Reactors For Power Electronics

Overview

Meher Mangoldt also offers high performance reactors for motor drives and frequency converter applications. The Renewable Energy industry presents interesting challenges for reactor manufacturers. The electrical energy generated by wind turbines or PV panels is fed into the grid through special converters using either a series reactor or reactors combined with capacitors to form an input harmonic filter. The main issue for such reactors is the fundamental current load combined with a considerable amount of superimposed harmonics and ripple currents. In particular, these ripple currents can reach significant amplitudes and frequencies can be in the region of 3kHz to 28kHz.

These demanding characteristics create the need for precise design of the Iron-Core structure to achieve the desired electrical performance and to avoid excessive heat and noise. Our Reactors have proven to maintain their inductive properties and reliability in both rigorous and diverse applications throughout their lifespan. Mangoldt’s PolyGap™ technology achieves high linearity and stable inductance within the specified frequency spectrum while minimizing the intensity of stray magnetic fields.

PWM Load Reactors

Also called dv/dt reactors, these reactors are used in series between the AC inverter output terminals and the motor. Since the inverter voltage is comprised of impulses at high switching frequency, the insulation of the motor can become stressed. This situation is further exacerbated by motor cable length, due to a phenomenon referred to as voltage reflection which occurs in long cable lengths when the load impedance is higher than the line impedance. Voltage stress in the cable and motor windings is caused by the rapid rise of the voltage impulses as well as the repetitive nature of these impulses. Additionally, the ultimate peak voltage level appearing at the motor terminals increases by the magnitude of the reflected voltage pulses. The fast dv/dt pulses, in combination with the length of the cables, generate electrostatic currents which can destroy the motor winding insulation.

Meher-Mangoldt PWM Load Reactors reduce the dv/dt rate of voltage pulses, increase line impedance and restrict the development of electrostatic stress.

Smoothing Reactors

The scope of our capabilities includes smoothing reactors and DC reactors (chokes) for connection in the intermediate circuit (DC Bus) of power converters. This type of reactor is required to smooth and stabilize the DC current. It can prevent undesirable sharp rise and decrease of DC bus current as well as prevent interrupted flow of DC current by smoothing and maintaining continuous flow of lower ripple DC current. The natural electromagnetic property of these reactors enables them to restrict rapid changes in current and thus stabilizes the current through the DC circuit.

Line Reactors

DC adjustable speed motor drives
We typically use current source power converters and have a series connected DC reactor in the intermediate circuit between the rectifier and the inverter. The phase commutation of the SCR rectifiers in the input of the drive generates network harmonic distortion, the intensity of which is a function of the impedance of the upstream network. Line reactors add their impedance to the impedance of the electrical system which results in lower electrical system harmonic distortion.

In the case of AC (variable frequency) motor drives
a capacitor is connected (in parallel with the DC bus) in the intermediate circuit between the rectifiers and the inverter. The presence of this DC bus capacitor causes intermittent current flow form the power source to the rectifiers. The addition of a series connected line reactor reduces the discontinuity of the input current flow in the upstream network and results in less generation of harmonic distortion. Furthermore, the line reactor provides and additional benefit to the drive system through a considerable reduction of the inrush current in the intermediate DC bus capacitor due to the reactor’s impedance.