Energy storage dc side harmonics

What is a DC side harmonic?

A DC-side harmonic is an alternating component that is superimposed on a constant DC voltage or current and has periodicity. Corresponding to the fundamental frequency of the AC supply, this component is divided into 1st, 2nd, , kth order harmonics according to its frequency and multiple. This definition was proposed in IEEE Std 1124 for LCC-HVDC.

Why do battery energy storage systems have a harmonic problem?

In grid-connected mode, current-controlled battery energy storage systems (BESS) face the issues of harmonic caused by nonlinear loads and interactive instability under weak grids. Firstly, the mechanisms of mid-frequency oscillations (MFO) and mid-frequency harmonics (MFH) are revealed by the impedance network theory and the circuit principle.

What is the content of DC-side harmonic current in LCC-HVDC?

With references to LCC-HVDC, the content of DC-side harmonic current is described by equivalent interference current. This current is usually used to evaluate the influence of DC-side harmonic on the electromagnetic compatibility, communication systems, and transmission power losses.

Are low-order harmonic components affecting energy storage cells?

However, from the perspective of batteries, low-order harmonic components exist in each leg/arm/SM during the MMC normal operation, leading to high power ripple and jeopardizing the energy storage cells .

How do harmonics change in VSC?

VSC is rich in different harmonic components, including modulation harmonics and its sideband harmonics. These harmonics change with the variation in modulation method, modulation ratio, and switching frequency , . The content of even-order harmonics at the DC side increases significantly under unbalanced AC supply voltage .

Why does a 3 N order harmonic flow into a DC side?

The zero sequence component in common mode components, namely, the 3 n order harmonic, will flow into the DC side because the frequency and phase angle of 3 n order harmonics in three-phase bridge arms are equal.