Power Supply Design Of Solid State Amplifier Based On Active Clamp Forward Circuit

One of the most representative products of microwave active technology is the solid-state power amplifier,which has the functions of amplifying the power of microwave signal,controlling its gain and phase,and is one of the key equipment of digital transmission communication and radar system.The output power of the solid-state amplifier,the efficiency mainly depends on the power synthesis amplifier.With the development of the 3rd generation wide band gap semiconductor materials,the new generation of gallium nitride microwave power field effect transistors are often used as core microwave power amplifiers.Gallium nitride power devices have the advantages of high output power,high operating frequency and high power additional efficiency.The efficiency of solid-state power amplifier is the ratio of the difference between microwave output and input power to single-machine dissipative power.As a solid-state power amplifier loaded on space,the matching power supply has high reliability,which means that the power supply is required to work stably under the conditions of high temperature 70 ?,low temperature-35 ?,acceleration 12 g and so on.At present,there are mainly Interpoint,VPT,IR,GAIA,24,43 and 771 power supply modules that meet the requirements of high reliability and space environment at home and abroad.The high reliability power supply module of each manufacturer mainly adopts flyback or forward converter.The circuit of flyback and forward converter is simple and reliable,the use of components is less,but the utilization rate of transformer is not high,duty cycle is not high,the switch is in a hard switching state,so the power efficiency is not very high.The power supply module power of each manufacturer ranges from 5W to120 W,and the efficiency is about 80%.For example,the maximum efficiency of interpoint smflhp 100 W series module is 86%.Selecting such a power module as the power supply of the solid-state power amplifier can not meet the requirements of the high-efficiency solid-state power amplifier.The efficiency of the high-efficiency solid-state power amplifier designed in this thesis is not less than 90%.Therefore,the first problem to be solved in the power supply of high efficiency solid-state power amplifier is that the selection of appropriate power supply topology can not only achieve high reliability but also meet the requirements of high efficiency.In recent years,the development of the soft switching technology can effectively reduce the switching loss of the switching tube and improve the power supply efficiency.The power supply topology commonly used with soft switching conditions has a phase-shifted full-bridge,and the LLC resonance and the active noise level are positive.The first two full-bridge circuits are more efficient than the latter,but in terms of reliability,the first two full-bridge circuits are complex and the components are many,and in the space environment,the switching tube may be subjected to a direct-through phenomenon of interference,resulting in an input short-circuit.And the active noise level is only two components which are connected in parallel to the two ends of the primary or the switching tube of the transformer,and the circuit is simple and reliable,the components are easy to control,and the high-reliability is more easily achieved.The flyback and forward-excitation converter adopted by the high-reliability power supply module of the manufacturer has the following advantages that:(1)the reset of a transformer is realized by using an active noise level technology,the leakage inductance peak voltage is reduced;(2)the switching tube is switched to a certain voltage value,the voltage stress of the switching tube is reduced;(3)the duty ratio can be more than 50 percent,and the duty ratio of the flyback and forward converter is within 50 percent;(4)the energy of the exciting and the leakage inductance is repeatedly used for realizing zero-voltage conduction of the switching tube.These advantages make the active parity bit more dominant in terms of efficiency,and without the disclosure of confidentiality and technical data,there is no available information developed in this respect.In view of this,this thesis has independently developed a switching power supply based on active-bit forward topology.The maximum efficiency of the solid-state power amplifier designed in this thesis is91.5%,which is effectively improved compared with about 80% of the module power supply.The active clamping forward can reset the transformer through clamping tube and clamp capacitance,which makes the transformer work in one or three quadrants,improves the utilization ratio of magnetic core,and makes the transformer not saturate.compared with the traditional forward circuit,in order to prevent the transformer from saturation,the duty cycle can be increased to 50% ?70%.At the same time,the reverse voltage of the transformer can be clamped to prevent the switch tube from being broken down.The active clamping forward excitation can reuse the energy of excitation inductance and leakage inductance,make it resonate with the parasitic capacitance of the switch tube,realize the zero voltage conduction of the main switch tube,and realize the soft switch.These characteristics of active clamp forward are helpful to improve the power supply efficiency,in which the zero voltage conduction of the main switch plays a major role in improving the efficiency.However,the zero voltage conduction of the main switch in the active clamp forward is conditional,that is,in the dead zone before the clamp tube is turned off and the main switch is turned on,the parasitic capacitance of the two tubes resonates with the excitation inductor.When the leakage source voltage of the supervisor drops to the input voltage,the magnetic core of the transformer completes the magnetic reset.In the next time,if the excitation current is large enough to not only provide the load current,but also help to charge and discharge the parasitic capacitance of the clamp tube and the parasitic capacitance of the main switch,the leakage source voltage of the supervisor can resonate to zero,so that the zero voltage conduction of the main switch can be realized.On the contrary,if the excitation current is not large enough,zero voltage conduction can not be realized.In this thesis,according to the theoretical calculation of the parameters after selection,the simulation is carried out by using saber software,and each parameter is optimized according to the simulation situation,and the soft switch can be realized.However,due to the influence of error,parasitic inductance and capacitance in the manufacturing process of transformer,the experimental results show that the main switch does not fully realize zero voltage conduction.Although the main switch is not turned on at zero voltage,the switching loss of the main switch has been effectively reduced compared with the hard switch,which is very helpful to the improvement of efficiency.In this thesis,the following two aspects are optimized in the design process:(1)The stability of the power loop is improved.In this thesis,a current-type control mode is used to collect the current waveform of the output inductor and form an internal current feedback loop.The outside is a voltage loop that controls the output of the duty cycle after comparing with the inductor current.The current control mode is used for hiding the inductance in the inner ring,converting the two poles of the output filter into a single lower frequency main pole,a pole close to or exceeding the higher frequency of the system bandwidth,making the design of the compensation network easy,and being beneficial to the stability design of the loop.According to the calculated parameters of the loop design,a loop port diagram of the power supply is obtained by using the mathcad software.According to the port diagram,the phase margin of the system at the open-loop cut-off frequency is 67 °,the requirement of the far-over-stability criterion is 45 °,and the power supply can be used for a long time and the power supply can work stably.(2)The one-5V power supply of the solid-state power amplifier is provided,and the power of the solid-state power amplifier is small and is generated by adopting a flyback circuit.The negative pressure is the gate voltage of the microwave power amplifying tube,which controls the conduction and the cut-off of the amplifying tube,and the upper electric time is before the leakage source voltage of the amplifying tube,that is,the positive pressure.This is determined by the characteristics of the Nitrided microwave power amplifier tube,and if the negative pressure is not in accordance with the above-mentioned negative pressure and the positive pressure,the amplification tube will be damaged.Therefore,this thesis uses the negative pressure to control the power of the positive pressure control chip to reach the time,that is,the negative pressure control chip can work normally and the positive pressure can be output normally.Finally,the power supply is modeled and simulated by Saber software,and the simulation waveform is analyzed to verify the correctness of the theoretical design.After the completion of the prototype,the power supply is tested and experimented synthetically.The main performance indexes such as power supply power(200W),voltage accuracy(better than 1%)and efficiency(rated working time > 90%)meet the requirements of high efficiency solid state power amplifier.