study and simulation of airborne transmitters power … · 2016. 4. 11. · study and simulation of...

Proceedings of 08th IRF International Conference, 05th July-2014, Bengaluru, India, ISBN: 978-93-84209-33-9

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STUDY AND SIMULATION OF AIRBORNE TRANSMITTERS POWER SUPPLY

1SWAPNA C M, 2MADHU S, 3K V S C SASTRY

1,2,3BNM Institute of Technology, Bangalore

Abstract- Electric Power generated on the aircraft is the prime power for all electromechanical instruments, systems and subsystems used for aircraft control, navigation etc. The dominant method of generating and distributing electric power on aircraft has been 400 Hz three-phase 115 V AC. This type of power is suitable for transmission throughout the aircraft without excessive penalties for feeder weight. All the avionic subsystems draw power from the aircraft at these voltages and convert them to various voltages specific to their application. On most aircraft, electric power is also available as 28 V DC achieved through transformer rectifier units. This type of power is compatible with batteries and can be easily paralleled for emergency loads. In this work, power supply for a miniature MPM (Micro Power Module) based high power transmitter is suggested and the design is simulated. The transmitter’s power demand is 800 W and operates at an input voltage of 270 V DC according to MIL 741 C standards. Two solutions namely AC – DC conversion (115 V AC to 270 V DC) and DC – DC conversion (28 V DC to 270 V DC) are suggested to meet 270 V DC. Simulations of both the schemes are carried out using MATLAB software. A prototype model has been built for the DC – DC converter (28 V DC to 200 V DC) in the laboratory and the results are presented. The hardware design has been simulated in Matlab and simulation results have been presented Index Terms- Airborne Transmitter power supply, Power converters, MIL Standards and Specifications. I. INTRODUCTION Electric Power generated on the aircraft is the prime power for all electromechanical instruments, systems and subsystems used for aircraft control, navigation etc. The advent of electronics and their proliferation in aircraft systems gave birth to avionics (aviation - electronics). A brief chronology of military avionics development illustrates the advances that have been made from the first airborne radio experiments in 1910 and the first autopilot experiments a few years later. Since late 1940s, the dominant method of generating and distributing electric power on aircraft has been, and is in the process of being, 400 Hz three-phase 115 V AC. This type of power is suitable for transmission throughout the aircraft without excessive penalties for feeder weight. On most aircraft, electric power is also available as 28 V DC. This type of power is compatible with batteries and can be easily paralleled. It is therefore used for critical loads. II. TYPE OF CONVERTERS Power conversion has a critical role to play in the operation of avionic subsystems. Each subsystem uses different voltage levels at board level and catering to these requirements is essentially done by power converter units. There are three types of power converters used on aircraft.

AC to DC converter DC to AC converter DC to DC converter

A. AC TO DC CONVERTERS Three phase converters are extensively used in industrial applications up to 120 KW levels, where a two quadrant operation is required.

Fig.1: Three phase full wave thyristor controlled converters

B. DC TO AC CONVERTERS

A power inverter is an electronic device that changes DC to AC. Inverters are designed to operate in the most stringent environments. A battery is the most common source of DC power. Most of aircraft generate AC power at variable frequency and is converted to DC using TRUs.

Fig .2: Basic Inverter

Study And Simulation of Airborne Transmitters Power Supply


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C. DC to DC Converters In many aircraft loads, it is required to convert a fixed voltage dc source to a variable voltage dc source. A dc-dc converter converts directly from dc to dc and is known as dc converters. DC converters are widely used in traction motor control in electric automobiles, trolley cars, mine haulers etc.

Fig 3: Boost chopper

III. OPERATING ENVIRONMENT Aircraft power systems present a unique set of power quality problems in an environment that demands the highest level of reliability of the equipment being powered. Due to the ever increasing amount of microprocessor-based flight systems, navigation and communications equipment being incorporated into today’s aircraft, power quality is of the utmost importance. Equipment designed for use in aircraft is typically very robust, being designed in accordance with FAA and military standards, and are tolerant of most power quality anomalies. A typical aircraft power system is a multiple generator based system consisting of a ground based generator, an auxiliary power unit (APU) generator, the main engine generator, the main power bus. IV. FACTORS AFFECTING AIRCRAFT BEHAVIOR

Altitude Temperature Rain, Humidity, Moisture Fungus Salt Fog/Salt Mist Acceleration Vibration Acoustic Noise Shock Icing/Freezing Rain RF Radiation Lightning

V. TRANSMITTER Vacuum tubes were once the active devices of choice in high frequency systems. With increasing use of

solid state devices, however vacuum electron devices (VEDs) play less dominant roles in microwave and millimeter wave systems, although they still offer the most power per device for most applications. Among the types of vacuum tubes, the travelling wave tubes (TWT s), continue to retain their solid position in defense applications and even in some commercial and industrial applications. The TWT is arguably the most widely used VED for microwave defence, instrumentation and satellite communication applications. It provides the extremely high output power density required by these applications at microwave frequencies with time-tested reliability. A TWT is an inherently high-gain, low-noise amplifier with wider bandwidth. A good example of a TWT amplifier (TWTA) application is radar transmitter as shown in fig.4.

Fig.4: Block diagram of a transmitter

A pulsed signal from the radar waveform generator is applied to an amplifier that employs RF power transistors to provide an output that drives TWT. This signal is sent to input of the TWT where isolators are used to ensure proper input matching and inter-stage isolation, and a PIN-diode switch is present to shut of the driver’s output to protect the TWT from overload. In addition to the TWT, the RF output section includes a dual-directional coupler to determine the RF output level as well as the reflected power level to protect the TWT from damage in high VSWR conditions. Other components include an isolator and often a harmonic suppression filter and a waveguide switch that can divert the TWT output to a dummy load testing. An arc detector is generally included in very high power transmitters, which senses breakdown in the waveguide and turns off the RF drive power to the TWT at high speed to prevent damage to its output port window. Other protective mechanisms cover excessive current in the high-voltage power supply, modulator and TWT, which are carefully designed to prevent false alarms while providing high levels of safety. TWTs, from various manufacturers vary considerably in many respects. The ample reason for this caution is, as the core element of the transmitter, which is TWT, affects nearly every aspect of performance. The key TWT considerations include power supply requirements, operating voltage levels and power consumptions, thermal design, size and



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weight, temperature, altitude and vibration performance and demonstrated record of reliability. A. PRIME ELECTRIC POWER

REQUIREMENTS The PCU (Power Converter Unit) shall be designed to convert 115V AC/400Hz/ 3 phase input, compliant with MIL-STD-704C, to 270V DC nominal output and three auxiliary outputs,

Table 1: Electric Power Requirements

Vout[V] Min Load[A]

Max Load[A]

Output Ripple[V]

[ptp]

243-300 V

Nominal 270 DC

0.15 (50 W)

2.8 (680 W)

12V

243-300 V

Nominal 270 DC

0.15 (50 W)

2.8 (680 W)

12V

28V (+/-10%) 0 1[A] 1.5V

+5V (+/-5%) 0 1[A] 100mV

-5V (+/-5%) 0 1[A] 100mV

+12V (+/-5%) 0 0.5[A] 100mV

-12V (+/-5%) 0 0.5[A] 100mV

VI. PROPOSED SCHEMES The figure 3.2 shows the block diagram of the design, the input voltage is 28 V DC/115 V AC 400 Hz, taken as the power supply in the aircraft and is given to the converter block, it converters the input 28 V DC/ 115 V AC voltage from one level to required 270V DC. This is accomplished with high frequency. The converter is designed in two schemes either by converting AC to DC voltage or DC to DC voltage. Other than the nominal output auxiliary outputs are also obtained, they are 28 V DC, 12 V DC and 5 V DC. In the first scheme, a controlled full wave rectifier is used and in the second scheme, a boost chopper is used. The output 270 V DC is generated for the purpose of functioning of the transmitter.

A. SCHEME I- AC TO DC CONVERTER (FULL WAVE CONTROLLED RECTIFIER)

Fig.5: Power converter module (AC to DC converter)

B. SCHEME II- DC TO DC CONVERTER

Fig.6: Power converter module (DC to DC converter)

C. CONNECTOR DETAILS

1. The input voltage is 115 V AC/400 Hz, 3 phase or 28 V Dc.

2. At the turn on command (J4-1), the 28 V DC aircraft activates a 3-phase relay connecting the 115 V AC/400Hz input and 28 V switched output.

3. The power supply shall provide two separated nominal 270 V DC output voltages. The two output voltages shall be independent in such a way, that failure in any output shall affect only the respective output voltage.

4. The enabling and disabling time of 270 V DC output voltages by HBPA1_ON (J4-7) & HBPA2_ON (J4-8) commands shall be 50msec.

5. The 115 V AC input at connector J1 shall be the source of the +/-12 V output and +/-5 V output at connector J4.

6. +/-12 V output and +/-5 V output at connector J4 shall be floating with respect to the PCU chassis.

VII. SIMULATION STUDIES

A. Schematic diagram of three phase full wave controlled rectifier

Fig.7: Three phase full wave thyristor converters



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The simulated circuit of three phase full wave controlled rectifier is as shown in fig.8.

Fig.8: Matlab simulation of three phase full wave controlled

rectifier The three phase supply voltage, output voltage and output current waveforms of three phase full wave controlled rectifier are as shown in fig.9.

Fig.9: Output waveforms of three phase full wave controlled

rectifier

B. BLOCK DIAGRAM OF BOOST CONVERTER

Fig.10: Boost converter

The simulation of both open loop and closed loop boost converter are done and the closed loop boost converter using PI controller is shown in fig.11. Design parameters

Input voltage, Vin=28 V Output voltage, VO=270 V Inductor, L=50m H Capacitor, C=12µ F Resistor, R=180 Ohm Switching Frequency, FS=10K Hz

Fig.11: Closed loop boost converter using PI controller

The DC supply voltage, output voltage and Gain voltage waveforms of closed loop boost converter are as shown in Fig.12.

Fig.12: Output waveforms of closed loop boost converter using

PI controller For the protection of aircraft transmitter a relay is necessary. Therefore the relay is inserted with the boost converter as shown in the Fig.13.

Fig.13: Relay operation of closed loop boost converter



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The reference input, relay input and relay output waveforms of closed loop boost converter with relay operation for both current controlled and voltage controlled method are as shown in Fig.14 and Fig.15.

Fig.14: Output waveforms of boost converter- current

controlled

Fig.15: Output waveforms of boost converter- voltage controlled

The converter circuit to obtain auxiliary outputs [5V, 12V] using Boost and Buck converter

Fig.16: Converter circuit to obtain auxiliary outputs

The output voltage and output current of Boost and Buck converters are as shown in Fig.17, Fig.18 and Fig.19.

Fig.17: Output waveforms of boost converter- 270V, 1.5A

Fig.18: Auxiliary output waveforms of 12V, 0.5A using buck

converter

Fig.19: Auxiliary output waveforms of 5V, 1A using buck

converter

VIII. HARDWARE DESIGN OF CONVERTER

A. SCHEMATIC DIAGRAM OF BOOST CONVERTER

The selection of operating frequency, design of PWM circuit, design of inductor and selection of switches for the boost converter are designed.



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Fig.20: Schematic diagram of Boost converter

B. DESIGN OF PWM CIRCUIT

Astable multivibrator TS= 1.1*R*C F=1/TS Considering,

Switching frequency, F=10 KHz C=0.1 µF-constant

R=TS / (1.1*C) R=0.1m / (1.1*0.1µ) R=909.09Ω

C. DESIGN OF BOOST CONVERTER

The design considerations are, Vs=28 V (Aircraft supply), load= 270 V DC, switching frequency Fs= 10K Hz as shown in the fig 5.1. And the other components as R (load) = 200Ω and VOUT = 200 V. So the output current IOUT is given by, IOUT (max) = VOUT/R =200/200=1 A. Ripple voltage, ∆VC=10 V (5% of the output voltage). Ripple current, ∆IL=0.05 A (5% of the load current).

D. CALCULATION OF INDUCTANCE AND

CAPACITANCE: L=Vs*D / (ΔIL*Fs)= 48 mH C=Vo*D / (R*ΔVo*Fs)= 8.6 F Where ΔVo= Ripple voltage, Fs= Switching frequency R= Load resistance, D= duty cycle, F=frequency Design of Inductor Step 1: determine L The inductor value for this converter is given by eq. L=Vs*D / (ΔIL*Fs) =48.16 mH Step 2: Area product The energy and area product calculations are as follows Im=Io+ ΔIL/2

Im=1+0.05/2=1.025 EL=(1/2)*L*Im2 =25.215 m

Ap=Aw*Ac=2*EL/(Kw*Kc*J*Bm) Where Kw, Kc, J and BM are design parameters that have to be chosen by the designer for the particular application. The starting values or default values for these parameters are also, Kw=0.6 for single winding inductor and 0.3 to 0.4 for multiple-winding inductors like the flyback transformer, Kc=(Im / Irms)=1.025. Also J=3*106 A/m2, Bm=0.25 T for ferrites, 1 T for cold rolled non-grain oriented (CRNGO) cores, 1.2 T for cold rolled grain oriented (CRGO) cores, 1.5 T for amorphous cores. Ap=2*25.215 m/(0.6*1.025*3e6*0.25) Ap==10.93 mm4 The core is selected according to the standards, which has an Ap higher than the value calculated above. Let T45 be selected (Ac=93 mm2, Aw=615.7 mm2, Ap=575.6 mm4, Im=114.5 mm). Step3: Number of turns The number of turns can be calculated as, N=L*lm / (Ac*Bm)= 286.25~ 286 turns Where, lm= mean magnetic length, from the data sheet we can select its value, Step4: Wire Gauge selection The gauge of the wire now estimated as follows: In step (3) the value of current density J used is J=3*106 A/m2. The cross-section area of the wire is calculated as

a=Irms/J=1/3*106=0.33 mm2 The SWG21 is selected according to the standard. Step 5: Available Window area check The inequality AwKw> aN has to be checked AwKw=615.7*10-6*0.6=369.4mm2

aN=0.33*10-6*286=94.38 mm2 The inequality is satisfied, which means that the windings will fit in to the available window area. IX. EXPERIMENTAL RESULTS

Fig.21: Boost converter Hardware



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Fig.22: hardware model output for 10V Input

Fig.22: Hardware model output for 20V Input

Fig.23: The cross sectional view of the PCU used in the Aircraft

CONCLUSION In this work, power supply for a miniature MPM (Micro Power Module) based high power transmitter is suggested and the design is simulated. The transmitter’s power demand is 800 W and operates at an input voltage of 270 V DC according to MIL 741 C standards. The Boost chopper and the three phase full wave controlled rectifier is been simulated using Matlab software according to the requirements of the aircraft applications. A prototype design of the Boost chopper produces an output voltage of 200 V. The input voltage fed to the Boost chopper is 28 V DC bus available in aircraft. The simulated results are in good agreement with the practical results obtained. REFERENCES:

[1] Mitulkumar R. Dave1, K.C.Dave2 ”Analysis of Boost Converter Using PI Control Algorithms”.

[2] G. A. Karvelis , S. N. Manias, G. Kostakis. “A DC-DC Boost Converter With Short Circuit Protection”

[3] Kaz Furmanczyk ” Demonstration of very high power airborne AC to DC converters”.

[4] John Brewer, Jr. and Kamaljit Bagha “High Voltage Switched-Mode Power Supply for Three-Phase AC Aircraft Systems ”.

[5] M. Hartmann, J. Miniböck, J. W. Kolar “A Three-Phase Delta Switch Rectifier for Use in Modern Aircraft”

[6] Meppalli Shandas ” TWTs still drive high-power systems”

[7] R.P.G Collinson “Introduction to Avionics systems”

[8] Ian Moir and Allan Seabridge “Aircraft systems”

[9] Ian Moir and Allan Seabridge “Military Avionics system”

[10] Young- Ju Park “development of airborne high density high voltage power supply for travelling wave tube”, Journal of power electronics, vol-5, No.4, Oct 2005, pp. 257-263.

study and simulation of airborne transmitters power … · 2016. 4. 11. · study and simulation of...

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