Memory-Based Set Point Modulation for Improved Transient Response of Distributed Energy Resources

TL;DR

The paper tackles the limited transient performance of distributed energy resources (DERs) in low-inertia grids by enhancing the SPAACE set-point modulation approach with a memory term. SPAACE-M augments the linear predictor with a memory component, using the average of past errors $e_{past}(t_k)$ in the update $x'_{ref}(t_k)=x_{ref}(t_k)+m_{1}\,e_{pred}(t_k)+m_{2}\,e_{past}(t_k)$, enabling effective control at lower sampling rates. Through PSCAD/EMTDC simulations on a modified CIGRE 14-bus system and a single-bus system across varying sampling rates, fault scenarios, and grid strengths (SCR), SPAACE-M consistently reduces overshoot, undershoot, and settling time compared with SPAACE and the base PI controller, albeit with some rise-time increase. These results demonstrate a practical, model-free means to improve DER transient response without modifying internal controllers, supporting robust performance in both strong and weak grids and under fault conditions.

Abstract

As the composition of the power grid evolves to integrate more renewable generation, its reliance on distributed energy resources (DER) is increasing. Existing DERs are often controlled with proportional integral (PI) controllers that, if not properly tuned or if system parameters change, exhibit sluggish performance or large overshoot. The use of set point automatic adjustment with correction-enabled (SPAACE) with a linear predictor improves the transient response of these DERs without the need to access the PI controller parameters. The limitation of the existing SPAACE method is the high sampling rate needed for improved performance, which is not always practical. This paper proposes the addition of a memory term to the SPAACE with a linear predictor. This memory term is the integral of the errors of previous samples, which adds another layer to the prediction to improve the response at lower sampling rates and further reduces the overshoot and settling time compared to the existing SPAACE method. Time-domain simulation studies are performed in PSCAD/EMTDC to show the effectiveness of the proposed controller.

Figures (11)

• Figure 1: High-level schematic of SPAACE.
• Figure 2: SPAACE pseudocode.
• Figure 3: Set point modulation with SPAACE for a step change in $i_d$ from 0.1 pu to 0.3 pu at $t=1~\rm{ms}$.
• Figure 4: SPAACE-M pseudocode.
• Figure 5: Modified CIGRE 14-bus north American benchmark test system.