Measurement and Analysis of Weather Phenomena with K-Band Rain Radar

Jun-Hyeong Park Dept. of Electrical Engineering

KAIST DaeJeon, Republic of Korea

bdsfh0820@kaist.ac.kr

Ki-Bok Kong Development team Kukdong Telecom

Nonsan, Republic of Korea Kbkong@kdtinc.co.kr

Seong-Ook Park Dept. of Electrical Engineering

KAIST DaeJeon, Republic of Korea

soparky@kaist.ac.kr

Abstract—To overcome blind spots of an ordinary weather radar which scans horizontally at a high altitude, a weather radar which operates vertically, so called an atmospheric profiler, is needed. In this paper, a K-band radar for observing rainfall vertically is introduced, and measurement results of rainfall are shown and discussed. For better performance of the atmospheric profiler, the radar which has high resolution even with low transmitted power is designed. With this radar, a melting layer is detected and some results that show characteristics of the meting layer are measured well.

Keywords—K-band; FMCW; rain radar; low transmitted power; high resolution; rainfall; melting layer

I. INTRODUCTION A weather radar usually measures meteorological

conditions of over a wide area at a high altitude. Because it observes weather phenomena in the area, it is mainly used for weather forecasting. However, blind spots exist because an ordinary weather radar scans horizontally, which results in difficulties in obtaining information on rainfall at higher and lower altitudes than the specific altitude. Therefore, a weather radar that covers the blind spots is required.

A weather radar that scans vertically could solve the problem. This kind of weather radar, so called an atmospheric profiler, points towards the sky and observes meteorological conditions according to the height [1]. Also, because the atmospheric profiler usually operates continuously at a fixed position, it could catch the sudden change of weather in the specific area.

In this paper, K-band rain radar which has low transmitted power and high resolutions of the range and the velocity is introduced. The frequency modulated continuous wave (FMCW) technique is used to achieve high sensitivity and reduce the cost of the system. In addition, meteorological results are discussed. Reflectivity, a fall speed of raindrops and Doppler spectrum measured when it rained are described, and characteristics of the melting layer are analyzed as well.

II. DEVELOPMENT OF K-BAND RAIN RADAR SYSTEM

A. Antenna To suppress side-lobe levels and increase an antenna gain,

offset dual reflector antennas are used [2]. Also, separation

wall exists between the transmitter (Tx) and receiver (Rx) antennas to improve isolation between them. With these methods, leakage power between Tx and Rx could be reduced. Fig. 1 shows manufactured antennas and the separation wall.

B. Design of Tranceiver Fig. 2 shows a block diagram of the K-band rain radar.

Reference signals for all PLLs in the system and clock signals for every digital chip in baseband are generated by four frequency synthesizers. In the Tx baseband module, a field programmable gate array (FPGA) controls a direct digital synthesizer (DDS) to generate an FMCW signal which decreases with time (down-chirp) and has a center frequency of 670 MHz. The sweep bandwidth is 50 MHz which gives the high range resolution of 3 m. Considering the cost, 2.4 GHz signal used as a reference clock input of the DDS is split and used for a local oscillator (LO). the FMCW signal is transmitted toward raindrops with the power of only 100 mW. Beat frequency which has data of the range and the radial velocity of raindrops is carried by 60 MHz and applied to the input of the Rx baseband module. In the Rx baseband module, quadrature demodulation is performed by a digital down converter (DDC). Thus, detectable range can be doubled than usual. Two Dimensional-Fast Fourier Transform (2D-FFT) is performed by two FPGAs. Because the 2D FFT is performed with 1024 beat signals, the radar can have high resolution of the radial velocity. Finally, data of raindrops are transferred to a PC with local LAN via the an UDP protocol. TABLE I. shows main specification of the system.

Fig. 1. Manufactured antenna and separation wall.

2016 URSI Asia-Pacific Radio Science Conference August 21-25, 2016 / Seoul, Korea

1

Evaluation on Active Power of Common-mode Conducted Disturbance

Farhan Mahmood, Ken Okamoto, Yuichiro Okugawa, and Kazuhiro Takaya

NTT Network Technology Laboratories Musashino-shi, Japan

mahmood.farhan@lab.ntt.co.jp

Takaaki Ibuchi, and Tsuyoshi Funaki Osaka University Suita-shi, Japan

ibuchi@eei.eng.osaka-u.ac.jp

Abstract—Power conversion equipment is known to generate

common-mode conducted disturbance. The authors have studied about common-mode apparent power evaluation, which have magnitude and phase information of the disturbance, for clarifying the generating mechanism of the disturbance. This paper describes the importance of evaluation of active power, a part of apparent power of common-mode conducted disturbance, and the validation of the active power evaluation. Additionally, verification of the active power evaluation with using DC-DC converter as EUT has been considered. As a result, validation of evaluation result has been proved by comparing common-mode apparent power, calculated from active power and measured common-mode apparent power.

Keywords— Power conversion equipment; common-mode conducted disturbae; active power;

I. INTRODUCTION

Power conversion equipment, such as power conditioning systems (PCSs), is widely used for renewable energy, such as photovoltaic systems. Fast switching operation of power semiconductor devices in internal switching circuit, such as DC-DC converter and DC-AC inverter, also lead to generate conducted disturbance in broadband [1-4]. The International Electrotechnical Commission (IEC) regulates measurement method and limit level of common-mode conducted disturbance from these power conversion equipment. The authors have discussed on evaluating common-mode apparent power, which has both magnitude and phase information, for clarifying the generating mechanism of conducted disturbance.

This paper describes the evaluation method for common-mode power from power conversion equipment, with focusing on active power and reactive power.

II. ACTIVE, REACTIVE, AND APPARENT POWER

The apparent power S is a product of voltage and current without reference to phase angle. S is related to two type of power; active power P, and reactive power Q [5]. P is the actual amount of dissipated power, and Q is the power, which continuously bounce back and forth between source and load. As a point of view from disturbance generation, P could affect around as a conducted disturbance, though Q couldn’t. For this reason, P should be measured and evaluated for clarifying the generating disturbance.

S is related to P and Q as

= + …(1) The common-mode voltage in the phasor form V, and the

common-mode current in the phasor form I are related to P and Q as ∗ = + …(2) ∗ = − …(3) where V* and I* represent conjugation of V and I, respectively.

V, I and phase difference of V and I (θVI) are related to Vc, θV, Ic, and θI, as = …(4) = …(5) = − …(6) , where Vc, θV, Ic, and θI represent the magnitude of common-mode voltage, the phase of common-mode voltage, the magnitude of common-mode current, and the phase of common-mode current.

According to equation (2) - (6), P and Q are expressed by = +2 = …(7) = +2 = …(8)

From equation (7), P can be calculated by measured Vc, θV, Ic, and θI.

III. EVALUATION ON ACTIVE POWER MEASUREMENT

In this section, evaluation of the calculation result of active power by measured common-mode voltage and current with using equation (7) would be described.

A. Measurement system for evaluation Figure 1 shows the measurement system for Vc, θV, Ic, and

θI, which applies arbitrary waveform generator (33522A, Keysight Technologies) in place of power conversion equipment. A current probe (F-65A, FCC) is applied for measuring Ic, and θI, and Δ-type Line Impedance Stabilization Network (LISN) (KNW-403D2, Kyoritsu Corporation) are applied for measuring Vc, and θV. Both the current probe and the common-mode measurement port of the LISN are connected to Digital oscilloscope (RTO1004, R&S) by coaxial

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cable. The waveform generator provides continuous wave (CW) of 30 MHz with 2 V peak to peak toward both line A, which connects Ch1 of the generator to EUT port of the LISN, and line B, which connects Ch2 of the generator to EUT port of the LISN. CW has phase difference θVI by 30 degree intentionally, for evaluating its validity. AE ports of the LISN are terminated by 50 Ω resistors. Furthermore, effect of LISN and current probe to Vc, θV, Ic, and θI , are rejected by correction.

Fig. 1. Measurement system for active power

B. Evaluation result Figure 2 shows the frequency characteristics of calculated

S, P, and Q by measured Vc, θV, Ic, and θI, using equation (7). Measured apparent power S’, by using Spectrum Analyzer (E4402B, Keysight Technologies), is also shown in this figure. According to the figure, the validity of the calculation result of P and Q would be proved, because the calculated S have a good agreement with measured S’.

Fig. 2. Measuremnt and calculation result of common-mode power

IV. VERIFICATION WITH DC-DC CONVERTER

In this section, verification of the active power by measured common-mode voltage and current from DC-DC converter with using equation (7) would be described.

A. Measurement system Figure 3 shows the measurement system for Vc, θV, Ic, and

θI from DC-DC converter. Digital oscilloscope, V-type LISN (9117-5-PJ-50N, Solar Electronics), and current probe were applied. Furthermore, DC power supply (EC1000SA, NF

Corporation) are applied as AE, and CM/DM noise separator (CMDM8700, SCHWARZBECK) is applied between the measurement port of the LISN and the digital oscilloscope. Table 1 shows the parameters of the DC-DC converter, which boost the DC voltage from 100 V to 200 V.

Fig. 3. Measurement system for active power from DC-DC converter

TABLE I. CONFIGUTRATION PARAMETERS OF DC-DC CONVERTER

Component Parameter

MOSFET C2M0080120D, Cree

(Switching frequency 100 kHz) Diode C4D20120D, Cree

Inductor 530 μH (CCM operation) Load (Resistor) 94 Ω

Input voltage/current 100 V / 4.25 A Output voltage/current 200 V / 2.12 A

B. Measurement result Figures 4 and 5 show the frequency characteristics of

measured common-mode voltage Vc and common-mode current Ic, respectively. Because the switching frequency of the DC-DC converter are set as 100 kHz, disturbance voltage and current could be observed at harmonics of 100 kHz. In addition, Vc and Ic became 110 dBμV and 80 dBμA, the largest spectrum level at 9 MHz, respectively.

Figure 6 shows active power P of conducted disturbance from the DC-DC converter, calculated by Vc, θV, Ic, and θI with equation (7). At 9 MHz, the peak frequency of common-mode disturbance voltage and current, P of 2 mW peak to peak could be observed.

Fig. 4. Measurement result of common-mode voltage Vc

29.96 29.98 30 30.02 30.040

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Fig. 5. Measurement result of common-mode current IC

Fig. 6. Calcutation result of active power

V. CONCLUSION

This paper describes the evaluation method of active power of conducted disturbance from power conversion equipment, and its validity, for clarifying the generating mechanism. The active power could be calculated from measured magnitude and phase of common-mode voltage and current. In addition, verification of the active power evaluation with using DC-DC converter as EUT has been considered.

As a result, it is shown that the validity of the measurement system for the active power evaluation would be proved, because apparent power, calculated from the active power, have a good agreement with measured apparent power.

For future works, pre-measurement calibration process for the measurement system and disturbance modeling with using the active power is needed.

References [1] S. Ayswarya and P. Prabhu, “Leakage current suppression for

transformerless inverter for grid connected PV power systems,” in Proc. International Conference on Electronics, Communication and Computer Engineering (ICECCE) 2014, Nov. 2014.

[2] S. A. M. Verhoeven, “Impacts of PV penetration in distribution networks,” in Proc. IEA Task V Workshop, Jan. 2002.

[3] A. F. Povlsen, “Distributed power using PV: Challenges for the grid,” in Proc. Renewable ENERGY World, vol. 6, no. 2, pp. 62–73, Mar.–Apr. 2003.

[4] S. Chandhaket, Y. Konishi, K. Ogura, E. Hiraki, and M. Nakaoka, “A sinusoidal pulse width modulated inverter using three-winding high-frequency flyback transformer for PV power conditioner,” in Proc. Power Electronics Specialist Conference, 2003.

[5] N. Balabanian, Electric Circuits, pp.384-pp.394, Mcgraw-Hill College, Jan. 1993

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