High-efficiency and low-consumption underwater sonar transmitter with improved triple-pulse HP-PWM signal model based on class D amplifier
© Li et al. 2016
Received: 29 March 2016
Accepted: 23 May 2016
Published: 7 July 2016
An improved triple-pulse high-power pulse-width modulation (HP-PWM) signal model is proposed to enhance the performance of current underwater sonar transmitter. The presented model is based on reducing the third and fifth harmonic energy of the HP-PWM signal. The achievement of low-power consumption has been implemented using class D amplifier and high-quality factor (High-Q) underwater acoustic transducer (UAT). High efficiency is demonstrated by simulations (reducing 41 % of the third and fifth harmonic energy). Feasibility of the presented model under different conditions has been proved by experiments.
Forward-looking sonar system is a common underwater communication technology of wireless sensor network [1–3]. Reducing power consumption in audio frequency power amplifiers (AFPAs)  of forward-looking sonar system  remains a great challenge. Some solutions are proposed to solve this problem, such as GaN-based gate driver circuit and power conditioning circuit . These solutions need extra hardware design based on pulse-width modulation (PWM)  to improve the efficiency of AFPA. Therefore, the design of the PWM signal model appears to be another important branch of many investigations .
For forward-looking sonar system, underwater sonar transmitter is an acoustic beam generator, and its performance directly determines the detection range and measuring accuracy of sonar equipment. The transmitter includes signal generator, power amplifier circuit, and acoustic transducer. Among them, the power amplifier circuit needs the maximum power consumption. However, recent system cannot achieve both high performance and low power consumption at the same time. Thus, the combination of PWM signal and underwater sonar transmitter remains to be an investigation to solve this above problem.
One key process encountered in the design of the PWM signal model concerns the selection of pulse driving form. In general, there are two forms for PWM signal: one is continuous wave (CW) pulse signal with fixed frequency and amplitude and the other is a linear frequency modulation (LFM) pulse signal whose frequency is time varying. In comparison of the above two forms, the CW pulse signal is more practical than LFM. Besides, due to the fast response and high efficiency of class D amplifier [9–14], CW pulse signal can be driven with high precision in power amplifier system. Consequently, the PWM signal model remains to be designed for low power consumption and high efficiency.
In this paper, an improved triple-pulse HP-PWM signal model based on class D amplifier is presented for AFPA of underwater sonar transmitter. This letter highlights our recent work on this topic and focuses on the enhancement of power consumption efficiency.
2 Background of class D amplifier used in underwater sonar transmitter
The second part is a switch amplifier, which is a large current switch controlled by PWM signal. It transforms the PWM signal into HP-PWM signal.
The last part is to recover the sound signal from the HP-PWM signal. A low-pass or band-pass filter is applied to achieve this function. The cut-off frequency is set near frequency of amplified audio signal. Then, the higher harmonics are eliminated and fundamental frequency of audio signal is reserved.
3 Single-pulse model of HP-PWM signal
where θ is the half pulse width and n is the odd harmonic order.
when the half width of the pulse is lower than 0.4 rad, the fundamental harmonic energy is less than 50 % of the total energy.
4 Improved triple-pulse model of HP-PWM signal
The purpose of simulations is to verify the feasibility of the proposed model. Firstly, for the single-pulse model of the HP-PWM signal, ratios of fundamental wave to total energy and the sum of the third and fifth harmonics to the total energy are compared to illustrate the infeasibility of this model.
Amplitudes of receiving signal under different conditions
Broad half-pulse width/rad
Amplitude of the receiving signal (α = 0.75)/mv
Amplitude of the receiving signal (α = 0.77)/mv
Amplitude of the receiving signal (α = 0.79)/mv
Amplitude of the receiving signal (α = 0.81)/mv
Amplitude of the receiving signal (α = 0.83)/mv
Through the results of Table 1, it is obvious that the proposed triple-pulse model of HP-PWM signal can basically achieve the performance of theoretical analysis. When α is 0.79 rad, the amplitudes of the receiving signal can reach the maximum value. Then, the output power can be easily controlled by adjusting Δ 1. It indicates that the proposed model can improve the efficiency and performance of underwater sonar transmitter under the condition of low power consumption.
This paper has proposed an improved triple-pulse model of HP-PWM signal to enhance the efficiency of power amplifier circuit in sonar transmitter system under the condition of low power consumption, which reduces 41 % of the third and fifth harmonic energy. The strategies are based on improving the driving model of power amplifier circuit and combining the features of underwater acoustic transducer to achieve a sonar transmitter system with high efficiency and low power consumption. Confirmatory simulations and experimental results are provided to highlight the feasibility of proposed model.
This work was supported by the Marine Economic Innovation and Development Project of China under Grant No.CXSF2014-2, the National Natural Science Foundation of China under Grant No.51275349, the China New Century Excellent Talents under Grant NECT, the China Tianjin Science and Technology to support key projects under Grant No.11ZCKFGX03600, and the China Tianjin Science and Technology Sea Project under Grant No.KX2010-0006. The authors declare that they have no competing interests.
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