Finally, the stability analysis in terms of normal operation is carried out in case studies and power source exchange strategies in different situations are summarized. The generating capacity of the conventional aircraft is relatively small, so some equipments have to be driven by hydraulic or pneumatic systems. The existence of hydraulic and pneumatic systems need many valves and control devices, which make the aircraft burdensome and unreliable.
Equipments that used to be driven by hydraulic or pneumatic systems such as environmental controls and wing anti-ice are partly supplied by electric system now [ 1 ]. Reducing hydraulic and pneumatic systems can simplify the design and maintenance of the aircraft, decrease the operational cost and improve the fuel efficiency.
However, the increasing use of power electronics and electric-driven devices make the EPS of MEA much more complicated and thus impose a big challenge for its modeling and simulation, especially the difficulty in improving the simulation speed in case of large-scale model based on detailed components [ 2 ]. These 2 generators work in parallel power supply way to improve the reliability of EPS. This structure observably improves the generating capacity and makes the VFSG more reliable than the conventional generator, but also lead to a failure in parallel power supply between these VFSGs.
But recently, a large number of research on aircraft EPS modeling are focused on conventional aircrafts, and only a few researchers devoted to the research on MEA. But they still focused on either component-wise level, such as Transformer Rectifier Unit TRU [ 3 ], generators and various kinds of power conversion devices [ 4 ], or system-wise level of small-scale.
For example, Griffo et al. The model only simulated a single-generator one-line system that consisted of a synchronous generator and an pulse rectifier. The key components including generators, rectifiers, loads, breakers, control devices, cables and other supplementary elements are modeled from the system's point of view and the switching strategies of power sources in different situations are discussed.
B is the most typical MEA model at present.
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This paper illustrates the overall EPS structure according to its functional principles as shown in Fig. As shown in Fig. Among all power source systems having been designed so far, VSVF is the most efficient one because of its simplified structure of the generator and reduced procedure of the energy conversion. This large generating capacity makes the EPS extremely reliable. A test showed that B could fly on one engine for 5. To improve the generating capacity and power-to-weight ratio, VFSG has abolished the CSD and greatly reduced the weight of the generator.
VFSG is a 3-level brushless generator whose structure is shown in Fig. Through the voltage measurement and voltage regulator, the output voltage can be directly controlled by adjusting the exciting current. In a normal flight, all the BTBs are off and the system operates in a 4-line isolated configuration. The practical structure of BPCU is very complex and it contains many integrated cells and control devices.
It is very difficult to simulate the structure of BPCU integrally and it is also not necessary. An inter-phase reactor L is added to connect two rectifiers in parallel. When the output voltages of the two converters are equal, the inter-phase reactor is transparent. However, when the output voltages of the converters are not equal, the winding of the inter-phase reactor presents sufficient inductance to support the voltage imbalance [ 10 ]. Due to the existing of power converters, the system contains a lot of harmonics.
Filters on the AC side are needed to meet the standards of harmonic contents. The models are usually as simple as a single-generator system and their structure won't change with different working situations of the aircraft. In our study, the complete structure of the most complex MEA B is modeled; and the EPS structure will be changed with different switching strategies of the power sources as requested by the flight. The modeling focuses on the components' functionality instead of on their detailed structures.
The performance of the output voltage is stable and suitable for the B EPS. The voltage regulator model is shown in Fig. U ref is the reference voltage, usually V. So they can be modeled in the same way as shown in Fig. Buses are connected together through BTBs. In the event that one generator should fail it is automatically isolated from its respective bus and all associated loads are taken over by the operative generator.
A controlled three-phase breaker can achieve this function. When one of the left generators turn off, the control signal status becomes TRUE and breaker will switch on to transfer the power source.
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To avoid the error operations, a time delay block was added in this model. The breaker won't close unless the control signal keeps TRUE for at least 0. These breakers can share this BTB model because they function in the same way. A given disable signal can cut off the generator from the EPS to imitate the generator fault in a simple way.
When three or more generators turn off, the ASG starts up and some power-off devices must be transferred to the backup power sources. The logic elements were used to implement the switching function. The purpose of this module is to create the power switch strategy under different generator fault conditions, by building a logical relations between the generators working states i. This is just one simple example of the power switch strategy to realize the power sources change function of BPCU.
Other BTBs work at the same way. By judging the different signal status of GCBs, BPCU can manipulate the control signals of all BTBs through the power switch strategy to switch the power sources under different fault conditions. By changing the working state of the generators, BPCU can imitate the other different generator-fault situations. Because of using the basic logic elements in the Simulink platform, this BPCU model has a quick response ability. Where, V l is the input line voltage and. V d is the desired DC voltage. R ef is the equivalent resistance on DC side.
There are many kinds of loads in the MEA power system but in this study, different types of loads are not considered. Assume that the power-factor of AC loads is constantly 0. MEA employs the three-phase four-wire system, neutral line on the airframe. The MEA lines are relatively short so we can ignore the capacitive in the PI-type equivalent model and directly represented as an equivalent impedance, using the experimental measured parameters.
Other supplementary elements like bus bars and measurements can be simply modeled by the built-in blocks of Simulink. Finally, combined all the key component models referring to Fig. Though the scale of this comprehensive model is very large, it does not need too much computing time using the original Simulink models. This section will assess the performance of the comprehensive model for simulation study under two different conditions: the normal operation and the fault cases.
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The parameters for this study are list in Table 1 [ 11 ]. The loads of the MEA do not remain a constant value because the system have to change the power of different devices to adapt to the environment changes in flight. So the load disturbance of the MEA EPS in flight is a good method to verify the stability of this comprehensive model. At the beginning, only half of loads are working. In this case, all the BTBs are off and the system operates in a 4-line isolated configuration. Each single line is independent so we choose one of them to observe the simulation performance.
That shows a very well regulation performance of this generator mode.
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The current of VAC Bus has an obvious rise and fall following the increase and derating of loads. In this section, a series of fault cases will be assumed to observe the response of BPCU and the performance of some important buses. Run the simulation model and get the state of associated BTBs shown in Fig. The voltage and current performance in Figs. As Fig. The voltage and current in Figs. Compared with the conventional aircraft, MEA is lighter, easier to maintain and more efficient due to its hydraulic and pneumatic systems partially replaced by electric system.
Having large generating capacity and advanced solid-state power distribution system, the EPS of MEA is reliable but complex. By means of functional modeling approach, a comprehensive Simulink model has been built to study the performance of the EPS in case of both normal conditions and different faults.
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Besides, the logic procedures representing the control strategies for switching power in case of different faults were implemented. The case study demonstrated that the system can be effectively recovered from different generator faults. All simulations were carried out within acceptable times. Paperback Fri frakt!
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