PV-ESS DC Bus Disconnection for Fault Current and MPPT Conflicts
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Solution Overview
Problem
Existing DC-coupling systems face issues such as reduced power efficiency, increased system risk due to fault current inflow, and conflicts between MPPT control and ESS voltage control, particularly during photovoltaic power supply at night.
Innovation Solution
A PV recombining apparatus that includes a disconnector to connect and disconnect the photovoltaic system from a DC bus based on external conditions, using a current monitoring device and ground fault detector, and a power management control device to optimize operation modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a DC-coupling system connects PV system and ESS directly to a DC bus, then installation costs are reduced and power generation efficiency is maximized, but system risk increases due to fault current inflow and control conflicts
Solution Approach 1:
The system is segmented into distinct functional modules: PV system, ESS, inverter, and power management control device, each connected to the DC bus through dedicated connection terminals. This modular segmentation allows independent control and isolation of fault currents while maintaining the DC-coupling configuration, thus reducing installation costs without compromising system reliability.
Solution Approach 2:
The power management control device acts as an intermediary between the PV system, ESS, and inverter. It receives information from current monitoring devices and ground fault detectors, processes this data, and issues control commands to disconnectors to prevent fault current inflow and resolve control conflicts, thereby maintaining system reliability in the DC-coupling configuration.
2Device complexity
If PV system is directly connected to DC bus in DC-coupling system, then number of inverters is minimized, but control conflicts arise between MPPT control and ESS voltage control
Solution Approach 1:
The power management control device performs multiple functions: it monitors current from the PV system, detects ground faults, manages ESS voltage control, and coordinates MPPT operation. This multi-functional controller eliminates the need for separate control devices for each function, simplifying the overall system while resolving control conflicts through centralized intelligence.
Solution Approach 2:
The system implements feedback control through current monitoring devices that continuously measure PV system output and ground fault detectors that monitor system integrity. This feedback information is sent to the power management control device, which adjusts control commands in real-time to resolve conflicts between MPPT and ESS voltage control, ensuring stable operation with minimal inverter infrastructure.
3Device complexity
If PV system remains connected to DC bus during nighttime, then system configuration is simplified, but power efficiency is reduced due to partial discharge
Solution Approach 1:
The connection between the PV system and DC bus is made dynamic through controllable disconnectors that can change their state based on operational conditions. During nighttime when PV generation is unavailable, the disconnector opens to prevent partial discharge and energy loss. During daytime, it closes to enable power generation. This dynamic configuration maintains simplicity while optimizing power efficiency.
Solution Approach 2:
The system changes its operational parameters based on time of day and generation conditions. The power management control device receives external condition inputs and adjusts the connection state parameter of the PV system to the DC bus accordingly. This parameter change enables the system to maintain simple configuration during operation while preventing energy loss during non-generation periods.
4Reliability
If disconnector separates PV system from DC bus based on external conditions, then fault current inflow is prevented, but device complexity increases
Solution Approach 1:
The disconnector function is extracted as a separate, dedicated component that can be independently controlled by the power management control device. This extraction allows the fault prevention function to be implemented without complicating the main PV system or ESS architecture. The disconnector is a simple switching device that executes control commands to isolate the PV system from the DC bus when faults are detected, maintaining reliability while adding minimal complexity.
Data Source
AI summary
Discussed is a photovoltaic (PV) recombining apparatus configured to connect a photovoltaic (PV) system with a Direct Current (DC) bus connected to Direct Current (DC) power lines of an energy storage system (ESS) and an inverter (PCS). The PV recombination apparatus can include an inverter connection terminal connecting the photovoltaic system and the inverter, an ESS connection terminal connecting the photovoltaic system and the energy storage system, and a disconnector configured to disconnect the photovoltaic system and the DC bus according to a control command which is based on external conditions.