EVSE Reverse Power Flow Control During HEMS Communication Loss
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Solution Overview
Problem
The existing power system control methods for electric vehicles (EVs) used as distributed energy resources (DERs) face instability in communication between the EV supply equipment (EVSE) and the home energy management system (HEMS) controller, leading to potential over-discharge states when demand response information cannot be accurately relayed, causing continuous discharging without stop commands.
Innovation Solution
A power system with a control device that includes communication interruption detection and processing units to stop discharging and reverse power flow when unstable communication is detected, and also includes a communication abnormality detection unit to prevent overcharging by stopping power transmission and reception when communication abnormalities occur.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the HEMS controller and EVSE are connected via LAN for communication, then the system can function with a single controller, but the communication may become unstable and the HEMS controller may temporarily fail to operate normally
Solution Approach 1:
The patent introduces a gateway device as an intermediary between the server and EVSE. The gateway device acquires DR information from the server and communicates it to the EVSE, replacing the direct HEMS controller-EVSE communication path. This mediator approach isolates the EVSE from HEMS controller failures and LAN communication instability, allowing the EVSE to receive commands independently of the HEMS controller's operational status.
2Productivity
If the EVSE continuously discharges the power storage device based on DR information, then the reverse power flow can be maintained, but the power storage device may enter an over-discharge state when communication becomes unstable
Solution Approach 1:
The patent implements a feedback mechanism where the EVSE monitors communication status with the gateway device. When communication is stable, the EVSE receives and executes DR commands for discharging. When communication instability is detected (no command received within expected time), the EVSE automatically stops discharging to prevent over-discharge. This feedback loop allows the system to dynamically adjust operation based on communication conditions.
Solution Approach 2:
The EVSE is designed with preliminary protective action built-in: before over-discharge can occur, the system monitors for communication interruptions and preemptively stops discharging when instability is detected. This preliminary stop prevents the harmful over-discharge state from developing, rather than reacting after damage occurs.
3Device complexity
If the EVSE relies on the HEMS controller for charging commands, then the system structure remains simple, but the EVSE cannot be controlled when the HEMS controller fails or communication is unstable
Solution Approach 1:
The gateway device serves as an intermediary that delivers DR information directly to the EVSE, bypassing the HEMS controller for the critical charging/discharging commands. This allows the EVSE to operate independently based on server-generated DR information, gaining control independence while maintaining relatively simple system structure through the use of an existing gateway infrastructure.
Data Source
AI summary
When EVSE is unable to acquire DR command based on DR transmitted from the servers from HEMS, for example, when communication between HEMS and EVSE is interrupted, and when the battery of the vehicle is discharging (in reverse power flow), the discharge of the battery is stopped and the battery is charged.