Literature review on energy management system and charging strategy of battery in DC Nano grid

This literature review is for the ongoing research on DC Nano grid which is a possible approach towards achieving electrification to certain areas where grid connectivity is still unavailable.

Literature review: Energy management system and charging strategy of battery in DC Nano grid

1. Control and Operation of a DC Micro grid with Variable Generation and Energy Storage^[1]

Summary:

Lie Xu and Dong Chen discussed about the control and operation of DC Microgrid. They proposed a coordinated strategy of battery system, wind and load management system.

• Under different mode of operation, they classified battery system simply as a standby system or charge/ discharge mode based on the order given by the system or battery management system.

They have considered three modes of operation for secure and reliable power supply

• Mode 1: In this mode of operation the power deficit is adjusted by the supply from AC grid. The wind turbine operates at maximum power, no load shedding required and battery can be charged or discharged accordingly.
• Mode 2: This mode considered the temporary situation when the total power required from grid exceeds its limit or in case of any fault. In this mode the battery switches its role from standby mode to voltage regulation to provide necessary power balancing.
• Mode 3: This mode is considered as islanding mode and AC grid supply is completely unavailable. The DC voltage in now regulated by battery and required power by energy source. But the load shedding may be required in this mode to maintain the grid operation.

2. Control of Bidirectional DC/DC Converters in Reconfigurable, Modular Battery Systems^[2]

Summary:

M. Muneeb Ur Rehman, and Fan Zhang et. al. proposed a control approach to connect converter modules which are reconfigurable and serve as an interface between battery and DC bus.

• The control approach achieves bus voltage regulation and voltage sharing among converters under bidirectional power flow.
• It can interconnect N number converters (modules) in either series or parallel configuration.
• The control strategy balance energy flow by distributing power differentially among converters according to the relative state-of-charge and capacities of the battery.
• The controller estimate and monitor battery SOC and control the sub-module converters.
• The proposed control strategy is verified in hardware experiments using a module composed of two 480 W, 27-37 V series or parallel output dual-active bridge converters, and twelve 25 Ah Li-ion NMC battery cells.

3. A Distributed Control Strategy Based on DC Bus Signaling for Modular Photovoltaic Generation Systems with Battery Energy Storage^[3]

Summary:

Kai Sun, and Li Zhang et. al. proposed a distributed control strategy for a modular photovoltaic (PV) generation system with battery energy storage elements.

• The modular system is composed of three dc/dc converters for PV arrays, two grid-connected dc/ac converters, and one dc/dc converter for battery and local loads.
• The operation is categorized into four modes: islanding with battery discharging, grid-connected rectification, grid-connected inversion, and islanding with constant voltage (CV) generation.
• The dc bus voltage is used as an information carrier and four operation modes are identified by different dc bus voltage levels.

4. Control and Optimization of Residential Photovoltaic Power Generation System with High Efficiency Isolated Bidirectional DC–DC Converter^[4]

Summary:

Rui Li and Fangyuan Shi proposed an energy management system to bring stability of the system as well as to increase financial benefits.

• A three-level boost converter extracts maximum power from the PV module.
• A two-stage isolated bidirectional DC-DC converter is used to control the voltage and current of the battery. It also increases DC gain and efficiency. The converter consists of two configuration of isolated bidirectional DC-DC converter in the proposed system. The module is a two-stage isolated bidirectional DC-DC converter, in which a bidirectional LLC or CLLC can be employed in providing electrical isolation. To achieve higher efficiency, the isolated bidirectional DC-DC converter works as a DCX and a buck/boost is added to improve the DC gain.
• The highest efficiency of the isolated bidirectional DC-DC converter achieved was 97.50% under charging mode and 96.03% under discharging mode.
• A three-phase five-level inverter is used which operates in islanding mode or grid connection mode.

5. Bidirectional DC-DC Converter Topologies and Control Strategies for Interfacing Energy Storage Systems in Micro grids: An Overview^[5]

Summary:

Nisha Kondrath over-viewed three control strategies of bidirectional converters used for microgrid energy storage applications.  

• A bidirectional converter is used to maintain constant DC bus voltage and to regulate charge/discharge of the battery.
• The first control strategy is Current-mode control with two feedback loops, an inner current loop and an outer voltage loop, is a popular control method.
• In power control strategy during the grid-connected mode, battery is controlled based on SOC (State of  Charge). But during the islanded mode, fuzzy control or advanced droop control is used based on the voltage variation.
• And the third strategy to stabilize the dc bus voltage is sliding mode control. This method is robust against system variations as well as input and load variations.

6. Control Strategy for Power Flow Management in a PV System Supplying DC Loads^[6]

Balasubramanian Indu Rani, and Ganesan Saravana Ilango et.al. developed a power flow management system where operating mode of the bidirectional converter is selected by sensing the battery voltage.

• A dual H-bridge bidirectional converter is used to charge and discharge the battery which is capable of operating in both buck and boost modes. It is used to regulate the dc link voltage also.
• The power management system senses the battery voltage and selects the mode of operation for the bidirectional converter. It also provides the reference current for the hysteresis current controller.
• A hysteresis current controller is used for the current control of an inverter. The reference signal for the hysteresis current controller is generated as a function of the phase of the grid voltage using Phase Locked Loop (PLL).

7. Power Control of DC Micro Grid Using DC Bus Signaling^[7]

Li Zhang, Tianjin Wu, and Yan Xing et. al. proposed power management scheme for DC micro grid which consists of four operation modes.

• The DC bus voltage is used as an information carrier for mode selection. Operation mode provides the control signal for the PV converters, battery converter and grid-connected converter.
• The switching between different modes and the corresponding changes in control methods for converters is achieved through DC bus voltage without additional communication links.
• The Power management scheme maintains the power balance and stability of DC microgrid under variation of power generation or load.
• Battery DC/DC converter is employed as the grid forming unit and to regulate the DC bus voltage by battery discharging.

8. Power Balance Modes and Dynamic Grid Power Flow in Solar PV and Battery Storage Experimental DC-Link Micro grid^[8]

Rupak Kanti Dhar, and Adel Merabet et. al. proposed an energy management system for a DC-link micro grid  based on different power balance modes and dynamic grid power flow.

• The control system includes the local control units for the PV system, the battery storage system, and the voltage source inverter,
• In Battery Storage System a buck-boost converter is operated for the purpose of controlling the battery current to track a reference. Its local control includes a current controller based on a proportional-integral (PI) controller. The energy management system provides the reference current for the battery in order to charge-discharge the battery to meet the demand.
• The inverter control unit regulates the DC link voltage to maintain it constant also controls the inverter AC current.
• Based on the available power from the PV source, the battery SOC, and the grid power, the microgrid is operated under a power balance mode to meet the demand while optimizing the use of the battery storage.

9. A Unified Control and Power Management Scheme for PV-Battery-Based Hybrid Micro grids for Both Grid-Connected and Islanded Modes^[9]

Zhehan Yi, and Wanxin Dong et. al. proposes a comprehensive control and power management system (CAPMS) for PV-battery-based hybrid micro grids with both ac and dc buses, for both grid-connected and islanded modes.

• CAPMS is a centralized power management system consisting of a monitoring modules that senses the real-time parameters from PV system, battery system and all the power converters.
• After sensing the parameters, CAPMS selects specific control method to be applied to the converters to provide reliable power.
• Depending on the PV output power, SoC and power limit of the battery, DC and AC loads, and the grid demand, CAPMS decides the operation modes of the PV array and the battery  and provides proper reference values to the controllers.
• As the DC bus voltage is controlled, DC loads of certain voltage level can be connected to the DC bus without additional converters.

10. Energy Management Strategy of Islanded Micro grid Based on Power Flow Control^[10]

Ye Zhang and Hong Jie Jia et. al. proposes a new energy management strategy of islanded microgrid based on power flow control.

• Battery storage system keeps the DC bus voltage constant, PV array as a current source is connected to the DC bus and a main DC/AC inverter in VF mode is used to provide the voltage and frequency references for the AC bus.
• Dual-loop control is applied in the DC/DC converter connected with the battery. The outer voltage loop keeps the DC bus voltage constant and the inner loop improves the dynamic behavior.

11. A Management of power flow for DC Micro grid with Solar and Wind Energy Sources^[11]

Gowtham.K,and Hariprasath.P et..al. presented a control strategy for Management of power flow in DC micro grid with solar and wind energy sources.

• DC link voltage is regulated by the battery circuit while maximum power is extracted from Solar and Wind to feed the loads connected at the DC bus
• A ceaseless power is provided in the DC side with the help of Management of power flow algorithm.

12. Low Voltage Direct Current(LVDC) Nano grid for Home Application^[12]

Sigi C Joseph, and Dr. Ashok S et. al. Investigated power and control architectures for the purpose of implementing Low Voltage Direct Current (LVDC) Nanogrids for residential applications.

• A Nano grid controller (NSC) is used which is apparently the central controller for the system. It controls and manages all the modules within the LVDC.
• LVDC Nano grid has intelligent power switch and outlet which has the ability to measure and control electrical devices connected in this system.
• The NSC communicates with the other nodes in LVDC network, remotely controls and monitors nodes such as solar PV controller, battery charge controller and LVDC power socket.
• The NSC make decisions such as selection mode of operation, management of power socket and switch and controlling the battery.
• The LVDC Nano grid allow plug and play operation of the system where the new systems can be added or removed from the nanogrids network seamlessly.

13. Power Management Strategy Based on Virtual Inertia for DC Micro grids^[13]

Pedro José dos Santos Neto and João Pedro Carvalho Silveira et. al. proposed a power management system where virtual inertia concept is applied with a state of charge to regulate the charging and discharging process of battery.

• The microgrid becomes vulnerable due to low inertia during the transients.
• In this virtual inertia technique, the ESS transient response is controlled by increasing the inertia of the DC grid system. Thus, high-rate peaks of power are avoided, which improves the ESS life cycle.
• A SOC-based function, ψ(soc), is applied to manage the ESS charge and discharge process.
• The proposed power management technique is a centralized control.
• Also the proposed strategy simplifies the communication link between the grid inverter and the ESS (Since VSC power is the only information exchanged).