The company is already thinking of how to make use of EV batteries at its campuses

Mitsubishi Electric has developed an advanced energy management system for big facilities, which could lower electricity costs through optimizing on-site generation (like photovoltaic) and charging/discharging electric vehicles.

The system regularly monitors the status of EVs (checking how many is connected at the moment) and tries to minimize energy usage at peak demand from the grid. One of the ways is to stop charging some EVs or even put electricity back from batteries.

"By optimizing the schedules for not only charging EVs but also discharging their power back into the company, as well as optimizing the operation of PV and other power-generation systems according to the fluctuating unit price of electricity sold on the grid, Mitsubishi Electric's new system enables companies to reduce their electric-power costs."

This month Mitsubishi Electric and its affiliate Mitsubishi Electric (China) Co., Ltd. will conduct joint-demonstration tests at its own factory - Mitsubishi Electric Automotive (China) Co., Ltd. in Changshu in China. According to the Japanese company, the right system could bring 5% of savings on electricity costs (in 1,000-employee factory with 10 connected EVs).

Mitsubishi Electric: Energy-management system for power generation and power storage
Mitsubishi Electric: Energy-management system for power generation and power storage

Press release:

1) Reduces users' electric power costs by 5% by optimizing EV charging/discharging schedules

Mitsubishi Electric's new solution uses a multi-directional power conditioning system (PCS) to reduce or shift the use of grid power during peak hours by calculating minimized power costs, coordinating the charging/discharging of EVs parked at the user's company with the use of PV and other power-generation systems, and forecasting power demand and PV power generation. A mathematical programming embedding a proprietary model is used to calculate an optimized plan for on-site power generation and EV charging/discharging based on inputs such as contracted power from the grid, electricity unit prices, power demand and expected use of EVs in the fleet under the constraints of the received-power capacity, supply-demand balance, and the maximum and minimum charge/discharge levels of EVs and on-site storage batteries.

Conventional energy-management systems set a threshold to prevent the user's power demand from exceeding its contracted power from the grid. EVs are charged in advance, allowing them to be discharged if power demand exceeds the threshold. However, if a number of EVs must be used off-site unexpectedly, this can result in the need to charge EVs when the electricity unit price is still relatively high.

In simulations using a scaled-down 1:10 model of a 1,000-employee factory, typical power demand, and EV usage, power costs in the case of using 10 EVs were found to be 5 percent less than in the case of using no energy-management system.

2) Uses multi-step control to minimize electric power cost increases in case of unexpected EV usage

The EV operation plan and charge/discharge schedule are regularly optimized through the use of a "one-day plan" that is calculated several times each day to establish the charge/discharge schedule for the next 24 hours, a "correction plan" calculated every several minutes to refine plans for the next several hours, and a "control command" calculated every several seconds. Concurrently, the system continuously monitors the amount of electricity purchased from the grid and the state of charge of EVs parked on the company's campus.

Conventional energy-management systems correct plans when PV power generation or power demand deviate significantly from the projected one-day plan. However, since these systems do not make allowances for factors such as delays in EVs arriving at the company or undercharged EVs, purchasing power during peak hours sometimes becomes unavoidable, resulting in higher costs to the company.

Mitsubishi Electric's system regularly monitors the status of EVs connected to or disconnected from the PCS, minimizes power costs by using connected EVs as storage batteries, and refines the charge/discharge schedule every few minutes, thereby minimizing power-cost increases due to any unexpected use of EVs.