Microprocessor system for controlling the operation of renewable energy resources Miroslaw Wlas *, Wojciech Kolbusz **, Marek Gackowski *** * Gdansk University of Technology, Gdansk, Poland, e-mail:
[email protected] ** Energy Management Systems, Gdansk, Poland, e-mail:
[email protected] *** Energy Management Systems, Gdansk, Poland, e-mail:
[email protected]
Abstract- This paper describes the management system to control, monitor and supervisory of renewable energy resources, energy storages and loads. System can also be implemented as management controller for local grid, which may cooperates with distribution networks. The system uses real-time Ethernet technology, which combined with a fast signal processor allows to perform a complex analysis of the network and to control local loads and distributed energy resources. Extensive communication protocols and low cycle time provide technical mean to control whole microgrid, Virtual Power Plant and communicate with distribution network operators. Keywords — Distributed Energy Resources, microgrid, openPOWERLINK, Energy Management System, Virtual Power Plant
I.
INTRODUCTION
There are more and more Distributed Energy Resourced (DER) which work without collaboration of the distribution network, thus DER can be source of disturbance to the grid. Increase the number of DER cause that they become active players on an open electricity market. Hence, the major objective of grid operators is to minimize the impact smallscale generations and integrated them together in order to offer new services to the grid. Therefore, it is necessary to exchange information between renewable energy sources, loads and network in order to enable cooperation them. Consequently local loads and generation could take part in management of the network and in improving the quality of energy. Aggregation of small generations, storage devices and controllable loads may give such benefits as active power reserves for frequency control, reactive power reserves for local voltage control, stability and safety of the power grid, reduction transmission losses, reduction CO2 emission, etc. Some of loads are constant, but some could be controllable, that could switched on at night when electricity is cheaper, or held at zero during times of system stress. Addition, the microgrid may utilizes waste heat from cogeneration system (uCHP) to improve overall efficiency. Therefore, it is need to use Energy Managemet System in order to making decisions, based upon the power grid state, the heat requirements of the local consumers, the price of the electric power and cost of fuel, weather, etc. It would enable management of microgrid and allow to function well together renewable energy sources, controllable loads and storage devices to provide a high quality source of power, simultaneously reducing costs.
Most DER connection philosophy is based on a “fit and forget” approach, so the DER isn’t manageable by the Distribution System Operators (DSO) [10]. The DER penetration rate is increasing significantly, therefore integration them with distribution network and other DER is very important. Connecting some local DER together, may form Virtual Power Plant (VPP) which enables them to be fully integrated into distribution power systems and makes possible operation them to electricity market. So, EMS functionality is not just the management and control of local grid, but also collaborate with the DSO. This article presents the ECV-10 EMS controller (Fig. 1.) and research lab, that will be contain storage devices, some renewable energy sources such as wind turbine (WD), photovoltaic cell (PV), combined heat and power gas turbine (uCHP) and some constant and controllable loads (small office building, production hall, boilers). That equipment will form microgrid, which will by management and control by ECV-10. The ECV-10 EMS is a superior unit, that can manage generation and transmission of energy from renewable resources such as wind turbines, photovoltaic panels, cogeneration systems, etc. Besides the typical function such monitoring, reporting, supervisory and control, it can perform power quality analysis according to EN 50160 [1]. The ECV10 supports IEC-61850, so it can communicate with transformer stations, cooperate with devices from other manufactures and enables visibility and controllability of microgrid equipments for DSO. Mainboard L138C3, which is the heart of ECV-10, consists of two integrated circuits: OMAP-L138 [2] and field programmable gate array CYCLONE III [3]. Management of electricity transmission in distributed systems requires a short cycle time. As a result in ECV-10 openPOWERLINK [5] protocol was developed, which is a free version of Ethernet POWERLINK real-time, industrial Ethernet protocol. One can find numerous publications highlighting the positive features of this protocol [6], [7]. Ethernet POWERLINK supports fast communication with cycle time down to 200 µs [4]. For a long distances, that often occur in DER, fiber-optic cable might be used. II.
OTHERT SOLUTION
On the market there are several commercial solutions to power and energy measurement, management of local loads,
(Sescom SES Control, Schneider PowerLogic) nad control of uCHP (InteliSys-NT). But these are often no fully developed systems, with modular casings consisting of multiple elements, which increase their complexity, reliability and cost. These systems do not allow to communicate with converters, solar inverters and implement algorithms to control them. They have a limited parameters to configure, thus these systems can’t control and inflict active and reactive power and can’t management whole microgrid and cooperate with network. The ECV-10 is a stand-alone control system with multiprotocol integration, energy and power meter and analyzer, smartgrid management unit, embedded data base and www server that allows remote monitoring. Thank for these, ECV10 may be implemented as a uCHP controller, management system of energy, heat and cooling in small factories, college campus, office, farms, agritourism or to control DER, microgrid and VPP. III.
ENERGY QUALITY ANALISYS
ECV-10 enables measurement of eight currents and six voltages, which combined with powerful DSP processor OMAP-L138 allows making advanced analysis of energy quality in the network, in accordance with the requirements set out in regulations and standards. The measurements can be carried out both on the side of energy plant, as well as on the side of renewable energy resources. The system shall appoint key values describing the network: • Power: apparent, active, passive • Energy: active, passive, • Power factor, • Current and voltage THD (up to 40th harm.), • Current and voltage harmonic (up to 50).
In view of the combined algorithms it is possible to detect abnormal situation in power system, such as: • network frequency changes, • voltage collapse, • voltage oscillation, • short and long interruption of power supply, • overvoltage. The system also makes it possible recording waveforms of the above events. IV.
EXTENSIVE COMMUNICATION PROTOCOLS
Taking into account prevailing on the market trends, ECV-10 is fully equipped with numerous communication interfaces. It has three ports that can operate both in mode RS-232 as well as RS-485. Each device has also been equipped with two real-time Ethernet ports using Ethernet POWERLINK standard. Thanks to that it is possible to send large quantities of information on significant distance. Very short communication cycle, ensure the rapid response to changes occurring in the control system. The system can also be extended with optional cards. They provide communication using technologies such as GPRS, EDGE, WIFI, M-BUS or ZigBee. In view of the embedded web server it is possible to subject the operation of the appliance from any place. After passing through an appropriate authentication procedure it is also possible to take control over managed system. ECV-10 has also numerous input and output, both analogue and digital, so that it is possible to control other technological equipment such as inverters, uCHPs, soft starters, or valves. V.
EMS MAINBOARD L138C3 V.1.0
The main logical unit of the ECV-10 is multiprocessor EMS Mainboard L138C3 controller, which is equipped with fast floating point DSP and programmable logic device (FPGA). The major elements of the L138C3 (Fig. 2.) are two integrated circuits: OMAP-L138 and the Cyclone III EP3C40. The OMAP-L138 contains in its structure: C674x DSP unit and the general purpose ARM926EJ microprocessor. Cyclone III provides support for peripheral devices and increases computing and communications capabilities through the implemented softcore NIOS II processor. The L138C3 mainboard provides operate simultaneously up to three independent systems: Linux, the real-time DSP/BIOS system and the NIOS II. Thanks to this combination, the board is a versatile tool which can be used to handle many devices that communicate through interfaces such as USB, RS-232, RS-485, Ethernet LAN, Ethernet POWERLINK, SATA. Additionally, it can also perform complex floating-point calculations, store information in an extensive database and support easy user interface using a graphical touch screen or Web page. With built-in Linux drivers, system can be connected to the data storage devices such as hard drives, USB flash drives or micro SD card. Fig. 1. Visualization of the front panel of ECV-10
VI.
Fig. 2. Block diagram of Mainboard L138C3 v.1.0
Depending on customer’s needs board can be expanded with additional: wire and wireless connectivity, analog-digital and digital-analog converters, character displays and much more.
ENERGY MANAGEMENT SYSTEM OF RENEWABLE ENERGY RESOURCES
Advanced analytical capacity and numerous communication protocols make that the ECV-10 is ideal system for the efficient energy management. In fig. 3 is presented the use of the ECV-10 for controlling loads and processing and management energy generated from renewable and combined energy resources. That research microgrid, will consist of super cap (42F), storage battery (65Ah 168V), wind turbine (12kW), photovoltaic cell (2kW), cogeneration system (15kW of power and 39kW of heat), small office building, production hall and controllable loads such as boiler of domestic hot water DHW (4.5kW) and boiler of central heating CH (9kW). Object of that project will be research and testing operating of microgrid and cooperation renewable energy sources and loads with the power network. Produced energy will be used to power loads, while its surplus will be discharged and sold to the network. Generated heat will be
Fig. 3. An example of applying ECV-10 system to manage the installation of renewable energy resources
used for office and production hall. The office building and production hall are constant loads. They will be disabled only during islanding operating, when both the power generated by renewable sources will be not enough to meet loads and battery will be discharged. Boilers will be controllable loads and will operate depending of time of day, cost of energy and gas, sunlight and speed wind. Storage battery will be charged during surplus of energy generated by renewable sources or when the energy will be cheaper. Then its energy will be used to power loads during peak-hour, when the energy is more expensive, or during grid fault. If ECV-10 cooperated with network operator, it would disable boilers during system stress in order to maintain grid. Additional, at this moment, it would supply grid from the super capacitor and battery Two energy analyzers will be located both on the network and renewable sources. Thanks for that, will be possible power quality measurement from network, power quality measurement from renewable sources, islanding detecting and re-connection after return main power grid. General purpose I/O of ECV-10 can be used for direct control the operating panels, signalers, end switches, relays, etc. In fig. 3 some binary I/O are used for controlling relays and others work as a counter input for energy meter equipped with pulse output. Implemented Ethernet POWERLINK Protocol provides complete control over the system, providing reaction in time less than 1 ms. Support for this protocol enable ECV-10 to cooperate with devices from different manufactures. For example communication with scattered I/O stations X20 produced by B&R allows direct impact on the system (e.g. switching off burden, heat exchanger control). In fig. 3 water temperature in the tanks is measured remotely via POWERLINK, allowing to control of domestic hot water (DHW) and central heating (CH) on the production hall. ECV-10 has two analog input that can be use for various purpose such as outside temperature measurement, which in conjunction with remote measurement of water temperature in the tanks and the possibility of controlling uCHP allows for optimal management of the heat. Depending on the needs, the ECV-10 controller can communicate via RS-232 or RS-485. It has three serial communications ports. The first can operate as a RS-232 or RS-485, the second as a RS-232 and third as a RS-485 halfor full-duplex. Mode of RS-485 port is determined by switches mounted on a board L138C3 v1.0. All three ports can work simultaneously. In fig. 3 ECV-10 communicates with energy storage charger and photovoltaic panels inverters via RS-485. With built-in AC/DC converters controller can performs direct measurements of voltages and currents. Currents can be measured by the LEMs, the Rogowski coils or by the current transformers. Each inputs for current sensors can be set to work in mode 4-20mA, 0-10V or to work with a current transformer with 1A rated secondary current.
ECV-10 was designed in such a way that it is possible to install additional expansion modules. It can be quickly designed and manufactured PCB-adapter, that allows connecting modules with different types of terminals from different manufactures. In this way ECV-10 can be easily adapted to the customer’s needs and installations demands. For example one may used Digi ZigBee XBee module, MultiTech Systems SocketModem GPRS or SocketWireless Wi-Fi module. The results of network analysis and parameters describing current state of work, can be presented in a simple manner on the web page. Implemented database engine, collects the measurement data in accordance with the required period of time resulting from the averaging imposed by the relevant standards. The database can be stored on hard disk drive, USB flash drive or micro SD card and allows to generate wider reports according to the user requirements. ECV-10 can supervise the work of renewable energy resources working on isolated system (island system) or connected to the grid. VII.
ISLAND OPERATING
When the some distributed generations (DG) are separated from the grid, due to failure of the utility power grid or maintenance work, DGs change their operating from gridconnected operation to the island operation. Islanding has some drawbacks, such as: instantaneous reclosing can damage generators or prime movers, islanding system may be inadequately grounded by the DG interconnection, voltage and frequency may not be maintained within a permissible level [9]. Due to these reason it is very important to quick detected islanding and disconnected it from the power system and disconnected local loads from DG. By means of monitoring the quality of the connected grid and checking the voltage, frequency and impedance it is possible to fast islanding detecting. Adoption one of the proposed methods in [9] and use of efficient C674x DSP core allows to detect the islanding quickly and accurately. The disconnection takes place by means of automatic grid disconnection, described in DIN VDE 0126 standard. During islanding, research microgrid operation will be maintained by uCHP. On the basis of speed wind, sunlight and power demand by loads, ECV-10 will control and balance energy between renewable sources, storage devices and loads in order to maintain continuous work of office and production hall. Because WD and PV working depend on weather, only uCHP is reliable source of energy. In the case when WD and PV generate to low energy and occurs overload of uCHP, ECV-10 will disconnect appropriate load, depending on their priorities. Such solution provides constant work of load, which have the highest priority (for example office or hall).
with the power network without causing adverse effects. It may reduced the burden and improve the efficiency of the whole system. Through the use of energy storage IPS can perform arbitrage on power prices by buying energy at off-peak times and sell back at peak demand times [8]. The DER can contain various power generation technologies such as PV, uCHP, WD or fuel cells. Some of that can cause energy and voltage fluctuation, because they depend on solar or wind energy. Then, voltage fluctuation can cause interference of devices, voltage rising contributes to more Fig. 4. The idea of LoCal grid with the device ECV-10 operating as IPS energy consumption by loads (Fig. 5a). For this purpose it can be adopted Intelligent VIII. CONTROL NODE ECV-GEPL Transformer Station (Fig 5b) proposed by Dr. Tevfik Sezi The ECV-GEPL device is a hub of Ethernet (Principal Key Expert for Smart Grids at Siemens in POWERLINK interface, equipped with two RJ45 connectors. Nuremberg). It is possible to reduce voltage fluctuation It can work as a gateway between Ethernet POWERLINK and both RS-232 or RS-485 interfaces. Figure 3 presents distributed power management system in which there are five power inverters. Each of them communicate via serial RS485 interface. Due to implemented RS-485 ports in ECVGEPL gateway, it is possible to make fast communication between scattered energy resources and energy controller ECV-10. IX.
EXAMPLE APPLICATION
In [8] was proposed an innovative electric power architecture, in which the authors singled out the network elements, named “Local” grid. In each Local grid there is an intelligent power switch (IPS) present, which is responsible for control loads, energy sources, and energy storage. Local grid may work independent or together with the other. Presented in this article ECV-10 may act as an IPS (Fig. 4). Real-time Ethernet and other types of fieldbus allows to control devices included in the Local grid, while the standard Ethernet port enables communication between different subnets. Implementation of the proposed approach brings several advantages. It allows to integrate renewable energy resources
Fig. 5. The idea of Intelligent Transfomer Station proposed by Dr. Tevfik Sezi
thanks to communicating Intelligent Transformer Station, controlled by the EMS, with DER and loads. Using smart meters and voltage level monitoring, EMS could control transformer on-load tap-changing gaer. In this way it allows stabilizing the voltage level and reduction of power consumption. X.
CONCLUSIONS
Due to the large scattering and complexity of control system, there is a need for very rapid and time determined communication. Reliability and high speed of data transfer, allows to transfer large amounts of data and fast response of system in dynamic states. Also, high speed has an impact on operating of distributed energy source. It improves power quality and increases safety of the system. High-performance DSP allows network management, perform advanced network analysis and simultaneous survey of power quality from renewable energy resources and from power system. With built-in database ECV-10 can generate alarms and emergency reports such as overcompensation, power outage, etc. Using visualization on the web page provides remote monitoring and control of the grid. It also allows to set tariffs and optimize energy bills. Multiple communication ports and possible connection of an additional expansion to the ECV-10 allows to adapt it to operate in different systems. Thus it can act as an executive, communication gateway, sensor, meter or the main controller and management unit cooperated with distribution network operators. REFERENCES [1]
EN 50160:2007. Voltage characteristics of electricity supplied by public distribution networks. [2] OMAP-L138 Low-Power Applications Processor. SPRS586B–JUNE 2009–REVISED AUGUST 2010 [3] Cyclone III Device Handbook, Volume 1. January 2010 Altera Corporation [4] Ethernet Powerlink communication profile specification version EPSG_DS_301_V-1-1-0_01 www.ethernet-powerlink.org Ethernet Powerlink Standardisation Group, 2008. [5] openPOWERLINK: Ethernet POWERLINK Protocol Stack Software Manual Edition August 2010 [6] J. A. Maestro, P. Reviriego: Energy Efficiency in Industrial Ethernet: The Case of Powerlink IEEE Transactions On Industrial Electronics, Vol. 57, No. 8, August 2010 [7] Josef Baumgartner, S. Schoenegger "POWERLINK and Real-Time Linux: A Perfect Match for Highest Performance in Real Applications Realtime" Linux Workshop, Nairobi, Kenya October 2010 [8] Mike M. He, Evan M. Reutzel, Xiaofan Jiang, Randy H. Katz, Seth R. Sanders, David E. Culler, Ken Lutz: An Architecture for Local Energy Generation, Distribution, and Sharing. IEEE Energy2030 Atlanta, Georgia, USA 17-18 November 2008 [9] Mahat P., Chen Z., Bak-Jensen B.: Review of Islanding Detection Methods for Distributed Generation. DRPT2008 6-9 April 2008 Nanjinga China. [10] Bel I., Valenti A., Maire J, Corera J. M., Lang P., Innovative Operation With Aggregated Distributed Generation. 19th International Conference on Electricity Distribution, 21-24 May 2007, Vienna.
