⚡ electrical engineering

Reproducible Coordinated P--Q Dispatch Optimization of a Smart-Inverter BESS for PV--EV Distribution Networks

This study demonstrates that a coordinated active- and reactive-power dispatch strategy for a smart-inverter battery energy storage system significantly outperforms active-power-only control in reducing daily feeder energy losses and voltage deviations within a PV-EV integrated distribution network, while maintaining robustness under deterministic load perturbations.

Original authors: Thananan Chooseang, Siriwat Ninlawat, Prakasit Prabpal, Somchat Sonasang, Niwat Angkawisittpan, Praphat Phuangchuen, Thunyaput Kittiphotiklang

Published 2026-10-30

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Thananan Chooseang, Siriwat Ninlawat, Prakasit Prabpal, Somchat Sonasang, Niwat Angkawisittpan, Praphat Phuangchuen, Thunyaput Kittiphotiklang

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The electric grid that powers our homes and businesses is a delicate balance of supply and demand, a system that has traditionally relied on steady, predictable flows of energy from large power plants. Today, however, this landscape is shifting rapidly. Rooftop solar panels and electric vehicle chargers are being added to local neighborhoods, introducing a new kind of variability. Solar power fluctuates with the clouds, and electric vehicles draw massive amounts of power when plugged in, often at the same time in the evening. This creates a challenge for the local wires that distribute electricity: too much power can cause voltage to spike, while too little can cause it to sag, potentially damaging equipment or causing lights to dim. To keep the lights on and the grid stable, engineers are turning to battery energy storage systems. These batteries can store excess energy and release it when needed, acting as a buffer. But modern batteries are connected to the grid through sophisticated devices called smart inverters. These inverters do more than just move energy back and forth; they can also adjust the "pressure" of the electricity, a property known as reactive power, which helps maintain the correct voltage levels without necessarily using up the battery's stored energy.

A team of researchers set out to understand exactly how much extra value comes from using this second capability. They asked a specific question: if a battery system is already installed with a fixed size and a fixed location, does it help the grid more if it only manages the flow of energy, or if it also manages the voltage pressure at the same time? To find the answer, they built a detailed computer simulation of a standard electrical network, similar to what might be found in a suburban area. They programmed this virtual grid to experience a full day of real-world conditions, including the rise and fall of solar power generation and a heavy surge of electric vehicle charging in the late afternoon and evening. They then ran three different scenarios. In the first, the battery did nothing. In the second, the battery was optimized to only charge and discharge energy to smooth out the load. In the third, the battery was optimized to do both: charge and discharge energy while simultaneously adjusting the voltage pressure using its smart inverter.

The results showed that the battery's ability to manage voltage pressure provided a significant, measurable benefit beyond simply moving energy around. When the battery only managed energy flow, it reduced the total energy lost as heat in the wires by about 2.6 percent over the course of a day. However, when the battery was allowed to coordinate its energy flow with its voltage control, the reduction in energy loss jumped to nearly 10 percent. This improvement was not just about saving a little bit of power; it was about how the electricity moved through the network. By injecting the right amount of voltage support locally, the battery reduced the strain on the long wires connecting the neighborhood to the main substation, allowing electricity to flow more efficiently. The researchers also looked at the stability of the voltage itself. In the worst-case scenario, when demand was highest, the voltage in the network dropped to a low level that was still safe but far from ideal. The energy-only strategy helped raise this low point slightly, but the coordinated strategy raised it even higher, bringing the grid closer to a stable, healthy state.

Crucially, the researchers were careful to ensure that this improvement came from the smart control strategy and not from simply having a bigger battery or a more powerful device. They kept the battery size, the inverter capacity, and the location exactly the same across all tests. They also ensured that the battery started and ended the day with the same amount of charge, so the benefits could not be blamed on the battery simply running out of energy. The study demonstrated that the smart inverter's ability to provide reactive power is a powerful tool that works alongside energy storage. However, the researchers also found a clear limit to what a single device could do. Even with the best possible coordination, the voltage in the most stressed parts of the network did not reach the perfect target level. This indicates that while smart control strategies can significantly improve performance and reduce waste, they cannot fully replace the need for adequate equipment size and proper placement. The study concludes that for existing battery systems, enabling this dual control mode is a highly effective way to get more value out of the hardware, reducing energy waste and stabilizing the grid, but it is not a magic solution that fixes every problem without additional infrastructure.

Technical Summary: Reproducible Coordinated P–Q Dispatch Optimization of a Smart-Inverter BESS for PV–EV Distribution Networks

Problem Statement
Distribution networks face increasing stress from the combined variability of photovoltaic (PV) generation, electric vehicle (EV) charging, and converter-interfaced distributed energy resources. Uncoordinated EV charging exacerbates feeder loading, active-power losses, and voltage deviations, while high PV penetration introduces complex voltage-regulation requirements. While Battery Energy Storage Systems (BESS) offer active-power shifting capabilities, their integration through four-quadrant smart inverters also enables reactive-power exchange. The specific research gap addressed is the lack of controlled comparisons that isolate the incremental network benefit of reactive-power capability. Existing studies often vary storage sizing, converter ratings, or placement, making it difficult to distinguish the value of coordinated active-reactive power dispatch from improvements derived simply from larger hardware or different operating scenarios.

Methodology
The study develops a reproducible 24-hour optimization framework for a radial distribution network (IEEE 33-bus system) containing a fixed BESS installation at Bus 18. The system includes a 200-kW peak PV source and a 400-kW EV charging hub (hours 16–19). The BESS consists of an 800-kWh battery with a ±200-kW active-power limit, interfaced via a 250-kVA four-quadrant smart inverter.

The core methodology integrates a backward/forward-sweep (BFS) power-flow solver with a Sequential Least-Squares Programming (SLSQP) optimizer. The framework evaluates three distinct operating cases under identical external profiles and fixed hardware:

Base Case: PV and EV loads present without BESS support.
Optimized P-Only: BESS active power ( $P$ ) is optimized while reactive power ( $Q$ ) is fixed at zero.
Coordinated P–Q: Both $P$ and $Q$ are optimized simultaneously.

The optimization minimizes a normalized objective function combining daily feeder active-energy loss and the system-wide voltage-deviation index (VDI). Constraints include BESS power limits, inverter apparent-power capability ( $P^2 + Q^2 \leq S_{inv}^2$ ), charge/discharge efficiencies (95%), State-of-Charge (SOC) bounds (5–95%), and a terminal SOC equality constraint ( $SOC_{24} = SOC_0 = 50\%$ ) to ensure daily energy neutrality.

To assess robustness, the nominal coordinated P–Q schedule is applied to perturbed scenarios (±10% load, ±20% PV, ±20% EV) without re-optimization, distinguishing the persistence of mitigation benefits from guaranteed voltage compliance.

Key Results
Under the specified severe loading and EV-charging conditions, the coordinated P–Q dispatch strategy demonstrated significant improvements over both the base case and the P-only optimized case:

Feeder Loss Reduction: The coordinated strategy reduced daily feeder active-energy loss from 4267.86 kWh (Base) to 3842.57 kWh, a 9.97% reduction. In contrast, P-only dispatch achieved only a 2.65% reduction. The coordinated approach provided an additional 7.52% reduction relative to the P-only case.
Voltage Performance: The daily voltage-deviation index (VDI) decreased by 17.77% with coordinated dispatch, compared to a 3.09% reduction with P-only dispatch. The worst-case minimum bus voltage improved from 0.83871 p.u. (Base) to 0.86695 p.u. (Coordinated), whereas P-only improved it only to 0.85732 p.u.
Operational Dynamics: The coordinated strategy effectively utilized the inverter's reactive-power headroom to reduce reactive current flow in upstream branches, complementing the active-power reduction. The SOC trajectory remained within 19.41–95.00% and returned to 50% at the end of the horizon, confirming that benefits were not achieved through net battery depletion.
Robustness: Under deterministic perturbations without re-optimization, the fixed P–Q schedule maintained feeder-loss reductions of 9.42–10.61% and VDI reductions of 16.48–19.37%, indicating the persistence of mitigation benefits despite profile mismatches.

Significance and Claims
The paper claims that its primary contribution is a controlled, reproducible comparison that isolates the incremental network value of smart-inverter reactive-power capability. By holding all hardware parameters (BESS capacity, inverter rating, location) and external profiles constant, the study demonstrates that coordinated P–Q dispatch extracts substantially more network value than active-power scheduling alone, particularly regarding system-wide voltage deviation and resistive losses.

The authors modestly clarify that the results represent a "locally optimized feasible solution" rather than a certified global optimum, given the nonconvex nature of the embedded power-flow calculations. Furthermore, the study explicitly states that while coordinated dispatch improves the voltage profile, a single 250-kVA inverter at Bus 18 is insufficient to restore all buses to the 0.95 p.u. reference under the tested severe conditions. Therefore, the work highlights the practical limitations of fixed inverter capacity and emphasizes that dispatch optimization cannot substitute for adequate converter rating, appropriate placement, or network reinforcement. The study concludes that the remaining undervoltage represents a practical boundary, suggesting that future work should focus on coordinated BESS placement, sizing, and stochastic scheduling.

Technical Summary: Reproducible Coordinated P–Q Dispatch Optimization of a Smart-Inverter BESS for PV–EV Distribution Networks

More like this