Implementation of a firmware for electrical energy management logics and verification in Labview simulation environment

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Implementation of a firmware for electrical energy management logics and verification in Labview simulation environment


application/pdf Implementation of a firmware for electrical energy management logics and verification in Labview simulation environment Beniamino Guida, Fabrizio Cuomo
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Implementation of a firmware for electrical energy management logics and verification in Labview simulation environment


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Implementation of a firmware for electrical energy management logics and verification in Labview simulation environment Beniamino Guida (1), Fabrizio Cuomo (2) 1 : Aeromechs srl - via Parente, 10 - Aversa – Italy - 2 : Alenia Aermacchi- viale dell’Aeronautica, snc - Pomigliano d’Arco – Italy – Abstract An approach for verification of a firmware devoted to electrical energy management application of aeronautical networks is proposed in this paper. Firstly, the energy management logics are discussed, as an innovative control strategy for reducing size and weight of electrical generators in aeronautics. Then, the firmware implemented for the control of an equipment able to perform the energy management is presented, focusing on the Petri Net approach adopted for its formalization. Finally, the framework adopted for firmware verification and validation is discussed, focusing on the interface between Labview and the C language function implementing the firmware itself. Results are discussed and further extensions of the work are presented, in order to extend the proposed approach for different applications. Introduction Currently any abnormal electrical condition (e.g., generator fault) on an aeronautical electrical network, that results into an extra demand of electrical power, is addressed to the overload capacity of generators. Besides, shouldn’t this features be enough to manage the peak power request, several loads may be totally shed as they are not flight or safelanding essential. This policy is the so called ”load management” [1]. The MEA trend will make generator rated sizes higher and higher. This implies that no overload capacity can be taken into account in the design. Moreover, most essential loads can’t be easily shed. The way proposed to face this key steps towards a new concept of electrical network is an Intelligent Load Power Management (I-LPM) [2]. By definition, I-LPM is an advanced smart control of aircraft electrical loads optimizing weight, volume and consumption, being able to ”smooth” extra power demands due to power transients and/or to electrical failures (normally addressed to the generator overload capacity) by compensating them with a proper reduction of the power demand from those loads which are ”non critical” for that specific flight phase or operating condition. The I-LPM operations are devoted to react to an electrical network overload condition by decreasing power on a subset of power loads, in order to smooth the extra power demand. As usual for engineering processes, an intensive simulation phase is required before proceeding with the realization of the physical equipment. Hence, also for I-LPM, the simulation phase must be appropriately carried out, trying to anticipate the real testing phase. In this paper, an approach for testing of the I-LPM logic, easily extendable to other supervisory control algorithm, is discussed. The main idea is to model the entire aeronautical electrical network at the “architectural” level, hence focusing just on the power absorption of the system, and integrate the firmware code of the real equipment in such schematic. The reference simulation environment is Labview, a tool that is largely used in industrial application where a simulation phase is required. Intelligent Load Power Management The selected power consumers for application of I- LPM are the Electrical Environmental Control System (E-ECS), constituting the main slow-dynamics power sink from which the necessary power to support some more critical overload is taken, and a number of resistive loads equipped with high-frequency switching contactors representative of the Non Critical Loads (NCL), constituting the fast-dynamics power sinks used to cope with temporary overloads. The intelligent power allocation is effectively obtained using a voltage chopping technique for the resistive loads equipped with SSPCs (Solid State Power Controllers) switching contactors, and through a devoted communication protocol for the E-ECS [3]. Referring to the aeronautical electrical network, the objective of the I-LPM logic is to demonstrate the feasibility of removing the overload capacity of the generator, used to provide 150% of nominal power for 5 minutes. Fig. 1: I-LPM aim As a matter of fact, the generator 5-minute overload capability is demonstrated to be the one which mostly affects the oversizing of the machine. By deleting the above capability, an estimated saving for the machine overall weight up to 10% can be gained. Some details have to be provided about the local control actions to be performed in order to require a variation of the electrical power absorbed by the I- LPM supervised loads, i.e. the SSPCs and the E- ECS. About the SSPCs, the power increase or decrease is directly linked to the duty cycle commanded by the I- LPM to the specific resistive load. Therefore, when a power decrease/increase is required, it is sufficient to issue a decreasing/increasing duty cycle to the local PWM generator of the SSPC. The decrease/increase step is a design parameter of the I-LPM, and can be specified as desired, with respect to performances. Instead, as already pointed out, the voltage chopping action used for NCL is replaced with a communication protocol for E-ECS power variation requests. Different signals have to be considered, specifically the absorbed power increase/decrease commands, and some additional signal in order to specify the power target consumption and the minimum machine flow. I-PRIMES project The I-LPM logic has been implemented in the context of I-PRIMES project, a Clean Sky initiative funded in the frame of FP7. About the I-PRIMES project, secondary power distribution cells (complementary to a primary EPC) have to be designed and realized, where a modular approach is considered for the overall equipment implementation. Each cell is composed by a programmable device, an interfacing stage and by an innovative power device switching component. Moreover, a “master” module is able to implement the I-LPM concept and communicate with “slave” modules for correct energy management strategy implementation. Different types of “slave” modules are considered, taking into account the necessity of I-LPM strategy implementation for both “fixed power” and “variable power” (e.g. pure resistive) loads. The I-PRIMES system has been inserted into a complex network denoted as “CopperBird”. A logical scheme is reported in following Fig. 2, referring to the Copper Bird structure, that is the Safran LPS bench offering a highly-versatile and representative test means where the complete electrical system of an aeronautical network is addressed, from electrical power generation to the loads. The equipment called “V-SLAVE” include an SSPC, specifically an high- frequency switch able to perform the voltage chopping action. Each V-SLAVE is connected to a resistive load bench, with different powers, used to represent the power absorption of typical aeronautical electrical loads, i.e. WIPS, galleys and other purely resistive loads. The Master module, on the upper left corner, includes the I-LPM logic as a devoted firmware. This module is responsible for controlling the power absorption of the different loads reported in the same Fig. 5, including also the E-ECS (i.e. the Electrical Environmental Control System) and the SPLS (i.e. a set of programmable loads). More specifically, a protocol (here not discussed) is implemented for power increase/decrease requests to the E-ECS, while a new power set-point is communicated, when required, to the SPLS load. All these communications are based on a CAN protocol, implemented thanks to the Local Control Cabinet (LCC) equipment, that are responsible for guaranteeing the communications between the different systems. Fig. 2: CopperBird structure In this paper, the focus is on the Master module, and specifically on the firmware developed for this equipment and its testing before integration of the I- PRIMES in the CopperBird Firmware for I-LPM The firmware for I-PRIMES can be split in four main functional modules, referring to different : 1) “Master” cell: composed by a computational device, where the supervisory control software is implemented. Specifically, the selected core is an ARM 9 Cortex microprocessor. In order to obtain more flexibility and maintainability, a real time operating system has been chosen for the master. In particular, FreeRTOS has been selected since it offers a light kernel and several libraries for the interface with a wide class of microcontrollers. 2) “Slave” cell for variable power loads (V-SLAVE): composed by a controller and an SSPC, devoted to power regulation through a high frequency switching on the load. Specifically, the selected core is a DSPIC33 microprocessor without operating system. 3) “Slave” cell for fixed power loads (F-SLAVE): virtual cell, the control is performed by directly communicating with the E-ECS. 4) “Slave” cell for SPLS (S-SLAVE): virtual cell, devoted to implement the communication protocol between MASTER and programmable loads for energy management purposes The I-LPM logic running on the Master module is implemented through the following tasks: • Measure task: It is in charge of gathering measurements from the loads. The measured data are included into messages transmitted by using the CAN protocol. The structure of the CAN messages is reported in the attached document. • Fault task: It implements fault detection and fault recovery logic. • Control Logic task: This task implements the I-LPM logic on the base of the Petri Nets. • User Panel task: It contains a user interface to debug and visualize the software state. • LED task: Used only for a rough check of the device states. The task simply turns ON and OFF LEDs associated to the devices. The execution of the tasks is handled through the semaphores. In particular, the Measurement Task is the first task being executed; afterwards, the Control Logic and Fault tasks are launched. The user panel task and LED task are always active but they have a lower priority and, then, are interrupted by all the other tasks. A schedule of all the tasks with their priority and execution order is shown in Figure 3. Fig. 3: Master firmware main tasks The data exchange among the different tasks is based on a logic memory mapped address: each value of the variables of interest, for example currents and voltage, is stored in a global variable shared by all the tasks. The semaphores allow correct read and write operations on the shared data. The firmware developed to implement the I-LPM logic is based on the Petri Net approach [4]. Note that, by using this approach, the core of the firmware can be implemented considering several instances of the switch-case instruction, where at each state corresponds one of the places of the I-LPM Petri Net, as reported in Figure 4. Fig. 4: I-LPM Petri Net After the implementation phase, it is necessary to perform the verification of the firmware, potentially already before the test phase involving the real hardware. In this view, the Labview software offers an interesting functionality named “Call Library Function”. The LabVIEW Call Library Functions are block diagram objects that link source code written in a conventional programming language to LabVIEW. They appear on the block diagram as icons with input and output terminals. Linking external code to LabVIEW includes the following steps: 1. Compile the source code and link it to form executable code. If already have a compiled DLL, this step is not necessary. 2. LabVIEW calls the executable code when the node executes. 3. LabVIEW passes input data from the block diagram to the executable code. 4. LabVIEW returns data from the executable code to the block diagram. Figure 5 shows the Call Library Function dialog box. Here it is possible to fill the different fields and automatically generate a C function prototype. This code shall be then populated with the I-LPM logic (or any other required code) and a .dll is required to be generated. Once the .dll is complete, the Labview schematic can interact with the C code, that will be the same adopted for the final firmware. Fig. 5: Call Library Function dialog box Moreover, it is necessary to let the C code included in the Labview model to interact with a schematic representative of the electrical power absorption on the electrical network, in order to react to the different stimuli coming from the equipment. In Labview, this is done by using the Multisim Design VI, a virtual instrument dedicated for electrical networks creation. The virtual model of the section of the CopperBird involved in I-LPM logic is represented in Fig. 6. Fig. 6: CopperBird Multisim design Note that the input and output of the schematic are represented with devoted connectors (e.g. “Duty_WIPS” and “WIPS_volt”), while the model of the SSPCs is simplified as a switch with a PWM control. Simulation results The Labview model interacting with the firmware code, included as a .dll, and the Multisim schematic as per Fig. 6, is depicted in Fig. 7. Fig. 7: DC bus regulated voltage and reference The Multisim design is highlighted in red, while the Call Function Library model in blue. Moreover, the model is linked to a visualization panel, as any schematic implemented in Labview, used to monitor the variables evolution in real time. This panel is reported in Fig. 8, where it is possible also to appreciate the possibility of changing some of the parameters (e.g. the DC bus voltage) by acting on a slider, as well as to insert/deinsert loads (e.g. the EMA) simply by clicking on some specific button. Fig. 8: LABVIEW panel Simulation results will be discussed in the final paper. Conclusions In this paper, an approach for implementing and testing a firmware for specific energy management applications has been presented, in the frame of an European project related to the MEA concept. After an introduction about I-LPM logic, the I-PRIMES project has been presented, focusing on the necessity to appropriately implement the Master firmware and simulate its behavior before the hardware testing phase. For this purpose, a specific Petri Net approach has been selected, and a Labview based testing procedure has been chosen, due to the possibility of introducing external C code and create in Multisim an electrical network for power balances. References 1 D. Schlabe, J. Lienig, “Energy Management of Aircraft Electrical Systems - State of the Art and Further Directions”, in Proc. Electrical Systems for Aircraft, Railways and Ship Propulsions, 2012. 2 B. Guida, A. Cavallo, “Average models for aeronautical electrical networks: an application for intelligent load power management”, in Proc. SAE Power System Conference, 2012. 3 B. Guida, A. Cavallo, “A Petri net application for energy management in aeronautical networks”, 18th Conference on IEEE Emerging Technologies & Factory Automation (ETFA), 2013. 4 B. Guida, F. Cuomo, A. Cavallo, “Intelligent Load Power Management Applied to Secondary Distributed Electrical Power Modules”, Greener Aviation Conference, 2014.