| With the rapid development of modern wireless communication systems,non-constant-envelope modulation formats have be widely used to accelerate the data transmitting rate.Thus,the envelope of the radio frequency signals is no longer constant,and it features with random amplitude.When delivering the radio frequency signals with non-constant amplitude,the power amplifiers in base stations will suffer from very low efficiency when they are powered by constant voltage.If the supplied voltage tracks the envelope of radio frequency signal,the efficiency of the power amplifiers will be greatly improved.Such power supply is called envelope tracking(ET)power supply,and it is the key equipment of ET system for improving the system efficiency and linearity.ET power supply can be implemented with various structures,and among which,the switch-linear hybrid(SLH)ET power supply integrates the advantages of high efficiency of switched-mode converter and high tracking bandwidth of linear amplifier.This dissertation is dedicated to the configurations and control schemes for the SLH ET power supply to achieve high efficiency and high tracking bandwidth.The SLH ET power supply has two basic configurations,namely,series-form and parallel-form.For parallel-form SLH ET power supply,a multilevel converter with step-wave approach(shorted as step-wave converter)is proposed in this dissertation to increase the equivalent switching frequency,thus,achieving a higher tracking bandwidth.The choice of the number of the voltage levels and the values of the voltage levels are discussed in terms of the voltage synthesis accuracy and voltage total harmonics distortion.The output current of the switched-mode converter can be directly controlled or indirectly controlled by controlling the output current of the linear amplifier.The control models of the two current control methods are established and discussed,and it shows that controlling the output current of the linear amplifier is preferred,as the requirement of the control bandwidth is lower.Besides,the full feed-forward of load voltage scheme is adopted to eliminate the effect of the load voltage on the output current of the switched-mode converter,therefore,the output current of the switched-mode converter can track the load current well.As a consequence,the linear amplifier only provides the switching current ripple,leading to an improved overall efficiency.A prototype is built aiming for 300 kHz sine-wave tracking,with 50 W peak output power.The experimental results show that the proposed configuration can obtain a higher overall efficiency.Series-form SLH ET power supply consists of a step-wave converter and a linear amplifier,which are connected in series.The step-wave is usually constituted by a level provider and a level selector.To simplify the step-wave converter,a switched-capacitor converter based level provider is proposed.It has simple structure and can achieve a high efficiency.Besides,the values of two levels can be optimized by regulating the duty cycle,which is beneficial to reducing the loss of the linear amplifier,and thus a higher overall efficiency can be achieved.A precise power loss model is established,and the related parameters are optimized.Finally,a prototype is fabricated,aiming for 5 MHz tracking bandwidth with maximum output power of 40 W.The experimental results verify the effectiveness of the proposed level provider.Moreover,for low power series-form ET power supply,a single-stage step-wave switched-capacitor converter is proposed,which integrates the level provider and the level selector.Thus,the structure of ET power supply is greatly simplified and a relatively high efficiency can be achieved.In both series-and parallel-form SLH ET power supplies,the power loss of the linear amplifier is still high.Thus,a series-parallel-form is proposed for the SLH ET power supply,which adopts two switched-mode converters and a linear amplifier.One switched-mode converter is used to reduce the output voltage swing of the linear amplifier,and the other one is used to reduce the output current of the linear amplifier.Thus,the loss of the linear amplifier is significantly reduced,leading to an increased overall efficiency of the ET power supply.The operating principle and parameters design are analyzed in detail for the proposed series-parallel-form SLH ET power supply.Besides,to perform high-frequency current control,a current prediction control scheme and a delay compensation method are proposed for the switched-mode converter,which avoids the use of the current sensor and compensates the delay introduced by analog devices.Finally,a prototype is built for 10 MHz tracking bandwidth and 40 W peak output power.The experimental results show that the proposed series-parallel-form can achieve a higher efficiency and higher tracking bandwidth than both seriesand parallel-form SLH ET power supplies. |
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