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Piezo Power Supply Module for Piezo Actuator Bench

Final Report Summary - PPSMPAB (Piezo Power Supply Module for Piezo Actuator Bench)

Executive Summary:
The development of the helicopters market is today limited because of their strong impact on environment: Their fuel consumption is high and produces a lot of emission; they generate a lot of noise both for the passengers (cabin noise) and for the people living close to the heliports (external noise). The main source of these inconvenient is due to the main rotor, especially its blades, which presently cannot dynamically adapt their aerodynamic profile to the desirable one. The consequence is a strong level of vibrations and noises from the rotor, such as Blade-vortex interaction (BVI) noise, also called “blade slap”. This is especially in the cases of fast forward and descent flights. Other impacts of the inability of rotor blades to adapt their aerodynamic profiles to flight conditions are limited performance regarding flight envelope, speed and range.
However because of present material and technological limitations, an ideal real-time adaption of the blade shape is not possible and several different options have been considered, including:
- The rotation of the blade, performed by actuating the rotor blade root
- The all-movable blade tip, driven in rotational motion by an induced-strain rotary actuator placed inside the blade.
- The twist of the blade, performed by distributed actuators along the blade
- The morphing of the blade cross section, performed by local actuators at the blade extremity:
- Actuating by articulation trailing edge flaps, leading edge flaps or bumps, or seamlessly deforming a part of the structure cross section for such functions.

Another completely different approach relies on the use of synthetic jets located along the blade surface, blowing or sucking air flow to generate turbulences allowing the boundary layer to stick on the blade surface. These jets can be produced by micro or miniature actuators located in cavities inside the blade and pulsating air by small holes on the blade surface.
In this context, the piezo technology seemed to be a good candidate for actuators and the Green Rotorcraft research Consortium of Clean Sky (CS-GRC) requested the development of a Piezo Power Supply module (PPS) to drive these powerful actuators. CEDRAT-TECHNOLOGIES (coordinator, SME) and UJF-G2ELAB (partner, lab from Grenoble Joseph Fourier University) formed a Consortium using their shared experience on piezoelectric actuators and high efficiency high power supplies to meet the GRC request by the PPSMPAB project.
The PPSMPAB project aimed at developing a PPS offering the highest required power (9kVA) with a high efficiency, for driving piezo actuators, accounting for further helicopter applications.
The proposed development split the need in 2 main items:
 The preferred DC-DC converter providing the DC sources would be an isolated full bridge resonant converter, with adjustable bus DC voltage to be interfaced with a +270VDC aeronautic bus
 The DC-AC 2-channels switching amplifier will provide the 2x4.5kVA power with adjustable output voltage range in a [-200+1000]V range following a specific frequency spectrum.

The development of such solution has followed a feasibility study covered by some trades off and demonstrators of the power cores, a detailed design of the solution covering the electronic functions and the associated packaging in regards of the embedded application and the realisation of a prototype to answer to the initial demands.

Project Context and Objectives:
The development of the helicopters market is today limited because of their strong impact on environment: Their fuel consumption is high and produces a lot of emission; they generate a lot of noise both for the passengers (cabin noise) and for the people living close to the heliports (external noise). The main source of these inconvenient is due to the main rotor, especially its blades, which presently cannot dynamically adapt their aerodynamic profile to the desirable one. The consequence is a strong level of vibrations and noises from the rotor, such as Blade-vortex interaction (BVI) noise, also called “blade slap”. This is especially in the cases of fast forward and descent flights. Other impacts of the inability of rotor blades to adapt their aerodynamic profiles to flight conditions are limited performance regarding flight envelope, speed and range.
However because of present material and technological limitations, an ideal real-time adaption of the blade shape is not possible and several different options have been considered, including:
- The rotation of the blade, performed by actuating the rotor blade root
- The all-movable blade tip, driven in rotational motion by an induced-strain rotary actuator placed inside the blade.
- The twist of the blade, performed by distributed actuators along the blade
- The morphing of the blade cross section, performed by local actuators at the blade extremity:
- Actuating by articulation trailing edge flaps, leading edge flaps or bumps, or seamlessly deforming a part of the structure cross section for such functions.

Another completely different approach relies on the use of synthetic jets located along the blade surface, blowing or sucking air flow to generate turbulences allowing the boundary layer to stick on the blade surface. These jets can be produced by micro or miniature actuators located in cavities inside the blade and pulsating air by small holes on the blade surface.
In this context, the piezo technology seemed to be a good candidate for actuators and the Green Rotorcraft research Consortium of Clean Sky (CS-GRC) requested the development of a Piezo Power Supply module (PPS) to drive these powerfull actuators. CEDRAT-TECHNOLOGIES (coordinator, SME) and UJF-G2ELAB (partner, lab from Grenoble Joseph Fourier University) formed a Consortium using their shared experience on piezoelectric actuators and high efficiency high power supplies to meet the GRC request by the PPSMPAB project.

The PPSMPAB project aimed at developing a PPS offering the highest required power (9kVA) with a high efficiency, for driving piezo actuators, accounting for further helicopter applications.
The proposed development split the need in 2 main items:
 The preferred DC-DC converter providing the DC sources would be an isolated full bridge resonant converter, with adjustable bus DC voltage to be interfaced with a +270VDC aeronautic bus
 The DC-AC 2-channels switching amplifier will provide the 2x4.5kVA power with adjustable output voltage range in a [-200+1000]V range following a specific frequency spectrum.

New concepts based on new power components was analysed and several architectures were proposed/analysed in depth to compare their main characteristics in regards of the embedded aeronautic solution.
During the project and as baseline, two main voltage ranges were studied to drive low voltage or high voltage piezo ceramics. In the world two type of piezo ceramics exist with their proper properties. At the beginning of the project, an analysis was performed in regards of the issued specifications to select low or high topology. With the comments from the topics manager to orientate the project towards the high voltage, the partners orientated their choices to develop a high voltage Piezo Power Supply but keepting in mind the possibility to adapt the topologies with low voltage ceramics.
Successively, technical studies concerning the two main elements of the PPS were performed concerning the power components, the architectures and the control laws.
These studies were focused the performances, the efficiency and the high power/volume ratio with the selected high voltage range.

Several keys technologies were identified and University of Joseph Fourier and Cedrat Technologies worked together to develop demonstrators to validate their proposed solution:
- An isolated half bridge was selected as the best solution for the DCDC converter.
For each power element design, Calculations were developed for high voltage and tables resuming high voltage and low voltage design for each component were established.
For each power component, the best solution was analysed keeping in mind the reliability and the total weight of the solution. Even if better technologies arised on the market, due to the high demand in maintenance, standard solutions were proposed.
A demonstrator was performed to valid the main characteristics

- A three levels Neutral Point Clamped (NPC) inverter as been selected as the best topology in high voltage range for the ACDC inverter and lower stressed component and better THD was indentified as better because of multi-level structure. However, more switches were required which made this structure more complex. For each power element design, Calculations were developed for high voltage and tables resuming high voltage and low voltage design for each component were established.
For each power component, the best solution was analysed keeping in mind the reliability and the total weight of the solution. Even if better technologies raised on the market, due to the high demand in maintenance, standard solutions were proposed.
In parallel, the voltage output control law was investigated to feedback the PPS in regards of the order and to include current limitation. The proposed solution was simulated taken into account the output load.
A demonstrator was performed to valid the main characteristics

Built on these baselines, Cedrat technologies has proposed a full design of a prototype including the two DCDC converters and the two DCAC inverters. Some studies about the packaging impacts on the volume and the mass were performed to valid a stiffener in regards of the aeronautic application.
The prototype was designed using the initial power core developed by University of Joseph Fourier and manufactured in one sample. This unit included the best proposed solutions and was autonomous (directly plug on the +270VDC Bus)

The main concretes objectives were:
1- Definition of specifications and analysis in regards of the state of the arts and new technology.

2- The investigation in piezo drivers - low or large voltage in view of a possible future integration in helicopters. Currently, no solution is proposed on the market for such electrical components. These components are now recognized as a large force /volume ratio in the industries.

3- The development of a piezo driver with high bandwidth with large loads, Functionality with loads up to 1000µF, Large reactive output power up to 9kVA,weight and size reduction for embedded applications

4- An objective identified in the project is to reach a TRL4 at the end of the project, which corresponds to a validation of the technology in laboratory conditions.

5- Prototyping of the PPS to validate their main characteristics

As we will see in the next paragraph and in the main S/T results description the main achievements for each part have been reached excepted for the final test of the prototype but its main challenge in term of design and manufacturing was a significant step in going beyond the state of the art for aeronautics.
:
- DCDC converter:
- This study has highlighted the advantages of the half bridge topology and the choice of IGBT switch for this application. For the future, GaN transistor must be considered, but during the project there were no 600V component commercially available. It will permit to increase the switching frequency and certainly to reduce the total weight of the converter.
- Nano-crystalline toroïds and Metglas material for transformer and output filter have been used in order to reduce the weight compare to regular ferrite material.
- DCAC converter:
- This study has highlighted the advantages of using SiC MOSFET component with a 3 level NPC inverter.
- New drivers of MOSSIC were studied
- The specific output control laws were validated. The obtained performances in regards of the controllability of the PPS were better than expected during simulation steps.
- In general, this project gave mode information concerning the technical possibilities of such PPS for aeronautic embedded application. In particularity, Cedrat technologies focused that a low voltage solution could be a better solution in regards of the power/volume ratio and will proposed their solutions for such applications.
- From these results, Cedrat technologies defined specifications for new product in their catalogue for low voltage piezo ceramics and a new portfolio for high power piezo driver was developed and proposed to their customers.



Project Results:
In the PPSMPAB project, a Piezo Power Supply has been developed during the last two years. Even if theses functions are well known in the industries to drive magnetics motors for example, for PPSMPAB, the partners have to analyse in depth the topology to be compatible with large capacitance load.

In order to achieve the objectives stated for the project, work was subdivided into 3 workpackages
(WPs): WP1: Management; WP2: Design, concept and architecture; WP3: Detailed design and manufacturing. The main results obtained in each are summarised in the following sections.

WP2. Design, concept and architecture

The objective of this Work Package lead by UJF-G2ELAB was to analyse the detailed specification of the actuation system to elaborate a design concept and the architecture of the PPSM in association with several preliminary designs. The order of priority for the PPSM study was:
- Weight and volume reduction,
- Cost (manufacturing and maintenance),
- Efficiency.

This work package is split into 3 phases for each power function keeping in mind that the technical interfaces between the two main functions should be common.

Based on the state of the art issued from the past works and the background of UJF-G2ELAB and CEDRAT in the field of power electronic and piezoelectricity, the most promising technologies are investigated in the field of the power amplifier for piezoelectric actuators. These works will be composed of an analysis of the technical specifications to focus the work on the key points. From the works on the design concept, a preliminary performance evaluation of the PPSM will be performed. Basic prototypes were developed by G2ELAB to back up the results of the preliminary performance evaluation.

During the period, the results were:
1- To fix the initial specifications versus the possible piezo utilisation from EC,
2- To analyse these specifications and to comment them to provide a first trade off concerning the power core of the PPS module,
3- To prove the feasibility of the power cores by simulating and prototyping. Demonstrators of the power functions will be manufactured,
4- PDR review with Topic manager.

During the specification analysis, review of the system general specifications and generation of final specifications for the PPSM was elaborated: As the PPSM is a structure typically formed of power supply electronic functions, amplifier electronic functions and auxiliary electronic functions to support the two main power functions: monitoring, regulation of the PPSM output, the architecture was elaborated and each electrical bloc was analysed.

Because of technology of piezo-electric actuator (multilayer ceramic or bulk ceramic), only three voltage ranges are possible and available on the market:
• Low voltage ranges: [-30V;150V] and [-50V;200V]
• High voltage range: [-200V;1000V]

Specifications mentioned several capacitance ranges. With low voltage range and operating spectrum or worst case, maximum power was widely below 8kVA.
The consortium studied the requirements of project topic manager Eurocopter that were provided in their compliance matrix document.
A one day workshop was organized with EC, and many considerations for the PPS specification were clarified: This has shown a contradiction between operating spectrum, maximum power of DC/AC converter (8kVA) and possible maximum PAB capacitance (1000µF). The main impact was the design of a larger high power amplifier with higher volume / lower efficiency for an application which demanded lower power.

With high voltage range and operating spectrum or worst case (100% of the 10th harmonic – 70Hz), 8kVA of power was reached for 634µF (operating spectrum) and 74µF (worst case). However, feasibility of high capacitance and high voltage PAB was not sure and could not be validated by Eurocopter.

Finally, EC selected the high voltage range for the PAB and validated a maximum power of 4.5kVA per channel corresponding of a capacitive load close to 42µF. The number of channel was maintained to 2 and working in 180° phase delay (opposition). This last point helped the mass and volume characteristics because electrical transfer between loads and capacitive buffers was maximised.

The D2.1. deliverable summarised these exchanges and specification analyses.



Several technical meetings with UJF and CTEC were organised. For each parts, an analysis of key technologies to launch specific technology works was done and the work was broken in several phases for the different parts:
- Modelling of the interesting topologies
- Preliminary designs of the interesting topologies
- Basic breadboards of interesting solutions (non deliverables)
- Reporting on the tradeoffs between different solutions
- Synthesis of the simulation and preliminary design results
- Details on the solution chosen and expected performance from preliminary design

Several DC-DC and DC-AC topologies were investigated by analysing their intrinsic losses and their magnetic component volume to take into account the mass/volume exigencies.

Comparing to the first specifications, the versatility of the proposed architecture was preferred to cover at this stage of the development low voltage or high voltage range. This will impact the mass volume ratio because the solution is oversized to cover the two specific ranges.

Concerning the DC-AC converter, in low voltage range ([-30V;150V] and [-50V;200V]), the H-bridge topology was proven as the most adapted because of simplicity and reliability of this system. The results will be used by Cedrat Technologies to develop their own piezo driver.

In high voltage range ([-200V;1000V]), 5 levels NPC topology and 5 levels cascaded H-bridge topology was indentified as the most adapted. The 5 levels NPC topology needed a strategy to balance the neutral point which could be a serious problem. On the other hand, the 5 level cascaded H-bridge needed isolated DC source which coul be problematic in terms of size and weight. A priority was given to the 5 levels NPC topology and a hardware solution providing neutral point equilibrium will be done.

Concerning the DC-DC converter and with the versatility requirements at this stage of the development, the solution with isolation seemed to be the best way. Indeed, the transformer turn ratio was easily adaptable and thus output voltage level was easily mutable. A solution to reduce transformer size and weight was to work in symmetric condition (magnetic induction in transformer is alternative and centred into 0). Thus, the full bridge topology is the best solution. This topology could work in hard or soft switching mode. In low voltage range only one converter will be done to provide +250V. In high voltage range, as NPC topology was advised for DC/AC converter, two full bridges will be done to provide two times 600V. Each full bridge will be regulated to ensure neutral point equilibrium (600V).

Concerning the DCAC inverter, three transistors types were available: IGBT, Silicium carbide (SiC) MOSFET and Silicium carbide (SiC) JFET. These three components were studied in regards of their performances. However, JFET control is more problematic and can be a serious point in the project. SiC MOSFET is the best compromise between performance increase and simplicity. It will be also a good introduction of SiC transistors in aeronautics environment which seems to have good perspectives in the domain.

In parallel, the anti parallel diode was analysed to limit the losses.

Finally a first PDR was held (June 2012) at EC Marignane to present the initial performances and proposed architecture for the power cores. During the performed works, several trade off were proposed to EC:
- For the DCDC converter, Isolation of the DC-DC converter, Switching topology comparison, Mode of control, Technology for transformer, Technology for switch, Technology for output filter, Bus capacitor, Technology of capacitor,

- For the DCAC inverter, Switching topology comparison, Technology for switch and anti parallel diodes, Mode of control, Output filter: Value of inductance vs Output capacitance Technology for output filter.

These trade off were used to define the best solutions. To help the decisions, some mock-ups were designed and tested to establish the main characteristics.

The support of the meeting is the D2.2 written by UJF. The D2.2 deliverable was written including these remarks and will be used for the rest of the project.

A lot of effort between the partners was done to establish the best technical solution for the power core (DCDC converter and DCAC inverter) after the PDR and under remarks from EC. The PDR was closed out at the mid of June 2013 with a demonstrator tested at UJF level to validate the main characteristics of the PPS.
The demonstrators shown the possibilities of the PPS in regards of the compliance matrix validated at the beginning of the work package.

This demonstrator was split into the DCDC converter and DCAC inverter and tested on a electrical load simulating the piezo actuators with inputs from the topic manager.
It has validated successively for the DCDC converter:
- The waveform inside the power components (switching, magnetic elements, diode…)
- The capabilities of regulation,
- The power capabilities,
- The ripple inside the magnetic elements
- The losses and associated efficiency in each main element

In parallel, the DCAC inverter validated:
- The waveform inside the power components (switching, magnetic elements, diode…) during switching
- The optimisation of dead times of the NPC in regards of the THD
- The bandwidth in open loop
- The bandwidth in closed loop
- The associated THD

Several tests in closed loop were performed using the fist established laws from Cedrat technologies analyses. In the workpackage 3, an optimisation of these laws has been performed to increase the closed loop bandwidth.

It was clear that the demonstrator established by UJF was part of the WP3 because the WP2 was defined as a design concept phase concluded with a PDR.

On the next figure, the demonstrators of the DCDC converter and the DCAC inverter are proposed.

Figure 1 : Photo of the G2ELAB demonstrator at the PDR close out.



WP3. Detailed design and manufacturing

The main objectives during this work package lead by Cedrat Technologies was to design in detail the PPS starting from the detailed specification selected with the topic manager and with the works provided from the WP2. In this work package a first engineering iteration will be performed to validate the core functions and auxiliary functions. Breadboards of the core of the DC/DC converter and the core of the amplifier will be done by G2ELAB.

1- To absorb the work done by UJF on the power core and add the auxiliaries function in view of the final prototype.
2- To finalise the output voltage control loop with new simulations and tests on mock-up to validate its performance.
3- To fully design the auxiliaries electronic functions of the PPS module
4- To design the mechanical packaging of the PPS module in accordance with embedded aeronautics application to reduce volume and then weight.

5- To establish the associated electrical schematics and the associated routing
6- To manufacture the different electronics printed circuit boards
7- To valid the PPS module thought functional testing on electrical load.

Additional modelling tasks of the electronics were performed in this work package. Those models were used to simulate and verify the expected functionality of the main functions of the PPS module. Only the core functions were modelled and simulated, the rest of the functions were verified by design, but not modelled nor simulated. This means that there was no complete electronic model of the PPS module available.

As main result of these steps through the prototype, the obtained information on the possibility to integrate piezo drive in embedded aeronautics application including the possibilities to develop such high voltage piezo driver for high voltage piezo actuators will be validated.

Concerning the detailed design several works were performed:
- A new solution around hybrid controller was developed because the first trials were not very confidant. This controller was implemented in digital and analogue and included two loops and tested on mock-ups before the final implementation in the prototype

- To be compatible with the hybrid controller, 2 types of sensors should monitor the output- Current measurement & - Isolated voltage measurement. . A validation of their performances on mock-up and CTEC switching product was performed to verify delay and frequency response because their characteristics impacted directly the closed loops performances (stability)

- Low voltage functions supplied with VICOR bricks were designed and implemented. Additionally, EMI input filter supplied with off the shell SynQor products were added in interface with the +270VDC input. The proposed solution allows reducing electromagnetic interference on the power Bus.

- A specific IHM controlled with DSPIC to perform start up and protections was implemented.

- A specific works on 3D CAD overview was performed to couple the mechanical packaging and the pcbs. As the electrical architecture of the PPS module required 7 PCBs (including 2x DC-DC converters, 2x DC-AC amplifiers, 1x Supervisor and 1x input EMI filter+ low voltage power supplies), a specific work to define a stiffener compatible with the aeronautic standard was performed.

In parallel of the 3D mechanical design, specific works on the schematic and routing were performed. Cedrat Technologies subcontracted specific people for the manufacturing of the total assembly.

The main objectives for each part have been reached excepted for the final test of the prototype but its main challenge in term of design and manufacturing was a significant step in going beyond the state of the art for aeronautics.
Nevertheless, the different mock-ups and demonstrators separately demonstrated the main performances for this piezo power supply for aeronautic application.

As main results for the topic manager, the proposed work by the partner had shown the difficulties to implement a PPS in a helicopter. Initial performances issued by EC were challenging and required much works than initial planned DOW. Aeronautic application focused on weight and size and it means not compatible with the challenging requirements (versatility of the driver in regards of the piezo load). At the end of the project, this aspect is well identified for future developments

Cedrat technologies worked on solutions with low voltage piezo actuators. They clearly identified piezo driver for high voltage could not be significantly reduced and to improve the power/mass ratio, possible solution is to use low voltage piezo ceramics (identified as solution at the beginning of the projectCedrat technologies). Currently Cedrat Technologies is working with helicopter actor to develop such technology.

In the next figure, the prototype is proposed.



Figure 2 : Coupling between mechanical CAO and electrical CAO



Figure 3 : Photos of the PPS:
a- PCBs, b-Mechanical overall + electrical cards


To summarize, the main scientific and technological results are going to be reviewed analyzing one by one all these new functions/components

DCDC converter

In this way, the aim was to adapt the Helicopter bus to the piezo high voltages.

Generally, the system in helicopter are directly connected on +28V Bus. Due to the high power demand, the PPS should be connected on the +270V Bus. Alternatively, the converter should be isolated to limit propagation of damage on other systems. During the project


A new DCDC converter was designed using half bridge topology. High frequency was selected to reduce the magnetic elements. Due to large losses and small switching timing, works on the body diode and commutations were performed to reduce the switching losses.


The piezo load could be characterised by a large reactive power. In case of single channel and to limit the power consumption on the +270V bus, this necessitated large capacitive buffer which limited the volume and weight. In the PPSMPAB project, specific analyses were performed to validate a possible energy recovery between the two channels. The proposed regulated DCDC converter managed this specific point.


Magnetic elements were analysed to reduce their sizes. In standard DCDC converters, the magnetic elements fixed the volume and the weight of the functions. In parallel, they introduce large losses and to improve their characteristics, specific analyses were performed for the transformers and the output filter.


The switching elements in the DCDC converters were analysed to compare the MOSFET SIC, IGBT and FET GAN performances. GaN transistor must be considered, but during the project there were no 600V component commercially available. It will permit to increase the switching frequency and certainly to reduce the total weight of the converter.


The DCDC converters were tested to establish their performances in regards of the specifications. The functionalities were demonstrated and the performances were measured. The efficiency was two points lower as expected

TRL4 is reached by demonstrating the possibility to drive capacitive load with high voltage.


DCAC inverter

In this way, the aim was to amplify the order to be compatible with the large piezo voltages and large power and including current limitation.

For the DCAC inverter, a three levels Neutral Point Clamped (NPC) inverter using MOSSIC was developed. In standard piezo driver, full bridge inverter is commonly used. Due to their high losses, this solution could not be implemented in an embedded application and the proposed solution around a NPC topology was proposed.


A second aspect using piezo actuator is the reliability. The current and voltage ripples impat directly the life time of the ceramics and the DCAC inverter should present very low ripples to limit damage in the piezo electrodes. The proposed solution in the project framework limits this impact by increasing the number of level. The signal to noise ratio of such solution is better than standard high voltage piezo driver.


For piezo driver, the output voltage is generally controlled to limit the possible overshoot on the piezo ceramics impacting considerably their reliabilities. In a linear driver, this feedback is easily implemented. In a switching amplifier, due to the inductive filter coupled with the capacitive load, the feedback is instable if no precautions are taken. During the project, Cedrat Technologies developed a hybrid controller able to damp the electrical resonance of the output filter in view to be unconditionally stable.


In some standard product for piezo actuator and to limit the instability with the output filter, the designers don’t implement feedback or limit the feedback to the input of the output filter. In this case, the output voltage is not really controlled and the load could be powered with larger voltage than expected. The partners’s proposed solution implemented a fully output feedback control law to avoid some damage on the piezo due to large voltage.


In parallel, always in view of reducing the power consumption and to increase the power efficiency, energy recovery system built around MOSFET SIC power components was designed. This allowed to improve the power consumption and to take the benefits of the reactive load.


MOSFET SIC technology was applied on the aeronautic application for the first time and will be promising for the future in term of loss.

The functionalities were demonstrated and the performances were measured. The efficiency was two points lower as expected


TRL4 is reached by demonstrating the possibility to drive capacitive load with high voltage.


Overall piezo power supply

Even if the TRL4 is reached, as main results for the topic manager, the proposed work by the partner had shown the difficulties to implement a PPS in a helicopter. Initial performances issued by EC were challenging and required much works than initial planned DOW. Aeronautic application focused on weight and size and it means not compatible with the challenging requirements (versatility of the driver in regards of the piezo load). At the end of the project, this aspect is well identified for future developments


(*) Validated : Val, Partially Validated : PVal, Non validated : NVal, Modelisation : Mod
(**) Vehicle: G2ELAB power core, CTEC PPS or CTEC mock-up
Figure 4 : Validated functions during the project



Potential Impact:

4.2.4 Potential Impact

The overall objective of the PPSMPAB consortium was to develop a prototype in the field of Piezo power supply technologies for aeronautics application with the main aim of providing improved technologies for safety, reliability and reduced environment impact of air-engines. The technologies that the PPSMPAB project has worked on are power electronics including new components, new architectures to drive piezoelectric load.

Two main impacts are relevant: The helicopter market with this new technology and the electric/actuator demands.

From the first point, the development of the helicopters market is today limited because of their strong impact on environment: Their fuel consumption is high and produces a lot of emission; they generate a lot of noise both for the passengers (cabin noise) and for the people living close to the heliports (external noise). The main source of these inconvenient is due to the main rotor, especially its blades, which presently cannot dynamically adapt their aerodynamic profile to the desirable one. The consequence is a strong level of vibrations and noises from the rotor, such as Blade-vortex interaction (BVI) noise, also called “blade slap”. This is especially in the cases of fast forward and descent flights. Other impacts of the inability of rotor blades to adapt their aerodynamic profiles to flight conditions are limited performance regarding flight envelope, speed and range.

To reduce vibration, noise and power consumption, US scientists including V.Giurgiutu I.Choppra etc have suggested in the early 90’s, the concept of individual blade control (IBC) systems [1, 2, 3, 4]: Each blade would be individually controlled by actuation mechanisms based in general on active materials (often called smart material in the US). At each angular position of the blade along the rotation, the blade shape would be adapted (“morphing” concept) in real time.

However because of present material and technological limitations, an ideal real-time adaption of the blade shape is not possible and several different options have been considered, including:
- The rotation of the blade, [5] performed by actuating the rotor blade root
- The all-movable blade tip, driven in rotational motion by an induced-strain rotary actuator placed inside the blade [6].
- The twist of the blade [7, 8], performed by distributed actuators along the blade
- The morphing of the blade cross section, performed by local actuators at the blade extremity:
- Actuating by articulation trailing edge flaps [1,9], leading edge flaps [10] or bumps [11], or
- Seamlessly deforming a part of the structure cross section for such functions [12].
Another completely different approach relies on the use of synthetic jets located along the blade surface, blowing or sucking air flow to generate turbulences allowing the boundary layer to stick on the blade surface [13, 14]. These jets can be produced by micro or miniature actuators located in cavities inside the blade and pulsating air by small holes on the blade surface.

A recent list of all projects aiming helicopter active rotor blades established by EADS (Table 1), shows the trailing edge flaps is probably the most popular morphing concept.

Active Twist Trailing Edge Flap Further concepts
Model Scale DLR / ONERA:
1:2.5 scale rotor blade
Boeing / MIT:
1/6th scaled CH-47 Rotor and
AMR Rotor

NASA/Army/MIT:
Active Twist Rotor ATR

U.S. Army Vehicle Technology Directorate:
Advanced Active Twist Rotor
AATR ONERA / DLR / Eurocopter:
RPA (Développement Technique Probatoire Rotor à Pale Active) &
ABC (Active Blade Concept)
Boeing / MIT:
1/6th scaled CH-47 Rotor
McDonnell Douglas:
Active Flap Model Rotor
JAXA, Mitsubishi Heavy Industries:
Model rotor
University of Maryland, Alfred
Gessow Rotorcraft Center:
Mach-scaled rotor with trailing edge flaps Auburn University:
Solid State Adaptive Rotor
Full Scale


Boeing:
Active Low Vibration Rotor CH-47 Boeing:
SMART Active Control Flap
Eurocopter/EADS IW:
ADASYS
Diversified Technologies:
Heliflap
JAXA:
Full Scale On-board Active Flap System
Kawasaki Heavy Industries:
Full Scale Rotor System including active flap system and HHC actuators
Diversified Technologies:
LEEMA (Leading Edge Electro
Magnetic Airfoil)
PenState University:
Gurney Flap
DLR/EADS IW:
Leading Edge Flap
Boeing:
SMART Trim Tab
Alfred Gessow Rotorcraft Center:
SMA actuated trimtab
Eurocopter / EADS IW:
Active Trailing Edge
Table 1: Some examples of Active Rotor Blade Projects in the recent years [ ]

In Europe, first works on Innovative Rotor Blades have been undertaken from 1997 to 2005 in the framework of the RPA / ABC projects. The RPA project, standing for Rotor à Pales Actives, meaning Active blades rotor, was a French-German project involving DLR, EUROCOPTER and ONERA. ABC is the acronym for "Active Blade Concept" and represents a 38% Mach scaled model rotor of the Advanced Technology Rotor (ATR) of Eurocopter Germany (ECD) [16, 17].


Figure 5: Helicopter Active blade segment (38% Mach scaled model) including active flap based on an APA500L from CEDRAT, Bravos test rig used for the centrifugal test; Mach1 wind tunnel test of the segment; High Power Linear Amplifier LA75C delivered to ONERA & DLR and used to supply the actuators during wind tunnel tests.


Figure 6: Helicopter Scale-1 blade with active flap including including APA1000XL from CEDRAT


Figure 7: EUROCOPTER first flight of a BK117 helicopter with piezo actuated trailing edge flaps from EADS.

The results obtained by ONERA and DLR from 2000 to 2005 [20] have been quite satisfactory even if some improvements still have to be done. Functional performance of the flap mechanism included a 10° tilt motion with a bandwidth of more than 200Hz. The flap mechanisms were separately tested under centrifugal and aerodynamic loads. A good behaviour under centrifugal loads was noticed from tests on Bravo Test Rig. Although the actuators were standard one, they survive the 2000g acceleration. Performance under aerodynamic loads was fully satisfactory at low Mach numbers. At higher speeds (mach 1), a small reduction of the 10° flap tilting stroke was recorded and later on attributed to the lack of stiffness of the gear mechanism transferring the linear motion from the APA to the tilt motion of the flap. The main limitation of this piezo actuated trailing edge flaps was the added mass from the standard actuators. Therefore it was concluded by the RPA ABC project team that customized actuators with mass optimization would be beneficial. So a R&D work of ONERA with CEDRAT on customized light-weight APAs has started in end 2009.

From these investigations, it is clear that the piezo technology is a promising candidate and the previous state of art solutions demand in any case large power in regards of the large piezoelectric actuators. Their requested electric power may reach order of magnitude.

From the second point, the 2013 global market for piezoelectric operated actuators and motors was estimated to be $11.1 billion, and is estimated to reach $16 billion by 2018, showing a growing of 7.7 percent per year [21].

During the PPSMPAB project, power drivers were orientated towards the high voltages and the topic manager has evaluated the weigh/volume of such solutions. PPSMPAB was an exploration ways for EC to acquire several data in view of potential future developments

CTEC and UJF clearly identified piezo driver for high voltage could not be significantly reduced and to improve the power/mass ratio, possible solution is to use low voltage piezo ceramics (identified as solution at the beginning of the project).
In this way, Cedrat Technologies has developed a new portfolio of switching amplifier for piezoactuators following the results from PPSMPAB in low voltage range.


Figure 8: Switching amplifier developed by Cedrat Technologies

The market for such high power driver is considered as a growth market because the number of applications is increasing year after year. As the piezo actuator is recognise as a very fast actuator and this demands large current, the associated large power amplifier should be proposed to the market.
Such amplifiers don’t exist on the market and Cedrat technologies with its SA75D provides the most powerful piezo amplifier on the market.
In parallel, this new power solution should open market of large industries as machining because piezo actuators are used as active vibration control and request fast actuation (ie large power)

References:
[1] Giurgiutiu, V.; Chaudhry, Z.; Rogers, C.A. "Engineering Feasibility of Induced-Strain Actuators for Rotor Blade Active Vibration Control", Smart Structures and Materials ' 94, Orlando, Florida, 13-18 February 1994 Paper # 2190-11, SPIE Volume 2190, pp. 107-122.
[2] Giurgiutiu, V.; Chaudhry, Z.; Rogers, C.A."Effective Use of Induced Strain Actuators in Aeroelastic Vibration Control", Proceedings of the 36th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference and Adaptive Structures Forum, New Orleans, LA, April 13-14, 1995, Paper # AIAA-95-1095.
[3] Chopra, I., Status of Application of Smart Structures Technology to Rotorcraft Systems, Innovation in Rotorcraft Technology, Royal Aeronautical Society, London, UK, June 1997.
[4] Barrett, R.; Frye, P.; Schliesman, M., “Design, Construction, and Characterization of a Flightworthy Piezoelectric Solid State Adaptive Rotor”, Smart Materials and Structures, Vol. 7, pp.422-431 1998.
[5] Teves, D., Niesl, D., Blaas, A., and Jacklin, S., “The Role of Active Control in Future Rotorcraft,” 21st European Rotorcraft Forum, Saint Petersburg, Russia, 30 August - 1 September 1995.
[6] Bernhard, A. P. F. and Chopra, I. (1998) “Hover Testing of Active Blade-Tips Using a Piezo-Induced Bending-Torsion Coupled Beam”, Journal of Intelligent Material Systems and Structures, Vol. 9, No. 12, pp. 963--974, December 1998
[7] Chen, P. C. and Chopra, I. “Wind Tunnel Test of a Smart Rotor Model with Individual Blade Twist Control”, SPIE Vol. 3041, pp. 217-229.
[8] Wilbur, Mathew L.; Wilkie, W. Keats; Yeager, Jr., William T.; Lake, Renee C.; Langston, W; Cesnik, Carlos E. S.; Shin, Sang Joon “Hover Testing of a NASA/ARL/MIT Active Twist Rotor”, 8th ARO Workshop on Aeroelasticity of Rotorcraft Systems, Penn State University, October 18-20, 1999.
[9] Millott, T.A.; and Friedmann, P.P. "Vibration Reduction in Hingeless Rotors in Forward Flight Using an Actively Controlled Trailing Edge Flap: Implementation and Time Domain Simulation”, ", Proceedings of the AA/ASME/ASCE/AHS/ASC 35th Structures, Structural Dynamics, and Materials Conference, Hilton Head, SC, April 18-20, 1994, paper AIAA-94-1306-CP, pp. 8-22.
[10] W.Geissler M.Trenker H.Sobieczky , Active Dynamic Flow Control Studies on Rotor Blades, RTO AVT Symposium on “Active Control Technology for Enhanced Performance Operational Capabilities of Military Aircraft, Land Vehicles and Sea Vehicles”,Braunschweig, Germany, 8-11 May 2000, and published in RTO MP-051.
[11] L. F. Campanile, V. Carli, D. Sachau, Adaptive Wing Model for Wind Channel Tests, RTO A VT Symposium on "Active Control Technology for Enhanced Performance Operational Capabilities of Military Aircraft, Land Vehicles and Sea Vehicles, held in Braunschweig, Germany, 8-11 May 2000, and published in RTO MP-051
[12] Hall, S. R. and Prechtl, E. F, Development of a Piezoelectric Servoflap for Helicopter Rotor Control, Journal of SmartMaterials and Structures, Vol. 5, pp. 26-34, February 1996.
[13] AA Hassan, RD JanakiRam, MDC Fellow, Effects of Zero-Mass “Synthetic” Jets on the Aerodynamics of the NACA-0012 Airfoil, J. Am. Helicopter Society 43, pp 303-312
[14] Allrefai,M., Acharya,M. ,”Controlled Leading Edge Suction for the Management of Unsteady Separation over Pitching Airfoils”, AIAA Paper 95-2188, June 1995.
[14] C. K. Maucher, B. A. Grohmann, P. Janker, A. Altmikus, H. Baier, Actuator design for the active trailing edge of a helicopter rotor blade, E.R.F 33, Sept.2007.
[15] Mainz, Henning, van der Wall, Berend G., Leconte, Philippe, Ternoy, Frederic, des Rochettes, Hugues M., ABC Rotor Blades: Design, Manufacturing and Testing. In: 31st European Rotorcraft Forum, 2005-09-13 - 2005-09-15, Florence (Italy). http://elib.dlr.de/21466/
[16] http://www.onera.fr/actualites/2006-011.php
[17] Giurgiutiu, V.; Chaudhry, Z.; Rogers, C.A." Design of Displacement Amplified Induced Strain Actuators for Maximum Energy Output", ASME Journal of Mechanical Design, Vol. 119, No. 4, December 1997, pp. 421-524.
[18] Leletty, R.; Claeyssen, F.; Lhermet, N.; Bouchilloux, P. New amplified piezoelectric actuator for precision positioning and active damping, Proc. SPIE Vol. 3041, p. 496-504, Smart Structures and Materials 1997: Smart Structures and Integrated Systems; June 1997
[19] H. M.ercier Des Rochettes, P. Leconte, Experimental assessment of an active flap device, AHS International, 58th Annual Forum Proceedings - Volume I, Montreal, Canada; UNITED STATES; 11-13 June 2002. pp. 1285-1296. 2002
[20] O. Dieterich, B.Enenkl D.Roth Trailing Edge Flaps for Active Rotor Control Aeroelastic Characteristics of the ADASYS Rotor System, AHS 62, May, 2006
[21] http://www.ciol.com/ciol/news/199113/global-market-piezoelectric-operated-actuators-motors-reach-usd16-billion-2018


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