技术领域technical field
本发明涉及隔离式电源变换器技术领域，特别涉及一种改善多模式数字原边反激变换器动态性能的控制系统。The invention relates to the technical field of isolated power converters, in particular to a control system for improving the dynamic performance of a multi-mode digital primary-side flyback converter.
背景技术Background technique
反激变换器的结构简单，成本低廉，所以常被用于消费电子产品等低功率电源方案中。随着对于消费电子产品安全性的重视，目前迫切要求使用的电源具有更好的电气隔离特性。传统方案中，通过在反激变换器中加入一个光耦器件来实现电气隔离，但是成本和体积无疑增加了。如图1，现在广泛采用的原边反激式电源则是在变压器中增加一个辅助绕组，通过采样辅助绕组上的电压来间接采样输出电压，从而改善了电源的电气隔离特性。The flyback converter has a simple structure and low cost, so it is often used in low-power power supply solutions such as consumer electronics products. With the emphasis on the safety of consumer electronic products, it is urgently required that the power supply used has better electrical isolation characteristics. In the traditional solution, electrical isolation is realized by adding an optocoupler device in the flyback converter, but the cost and volume undoubtedly increase. As shown in Figure 1, the primary-side flyback power supply that is widely used now adds an auxiliary winding to the transformer, and indirectly samples the output voltage by sampling the voltage on the auxiliary winding, thereby improving the electrical isolation characteristics of the power supply.
随着环保与节能的重要性的日益突出，开关电源的效率问题成为了人们关注的焦点。国际能源署(IEA)就在2000年提出了“1瓦计划”，即在10年将所有电器的待机能耗降低至1瓦以下；2013年发布的6级能效标准中要求5W的系统，最小平均效率大于73.6％，空载功耗小于0.1W。同时将平均功率定义为满载、75％负载、50％负载、25负载以及5％等5个负载点的功率平均值。为了提高数字原边反激变换器在上述负载点的效率，现在的反激变换器多采用多模式控制的方法，即根据负载情况的不同使用不同的模式控制。模拟技术应用在控制上较为复杂。由于数字控制可以调节参数以及更精确地控制模式状态，还能工作在多种模式下，所以在多模式控制的方法中选择采用数字控制技术相对于模拟技术有很大的优势。如图2，现在主流的反激变换器的工作过程中采用了5种不同的工作模式。与传统的模拟控制多模式方案相比，现有技术增加了3个工作模式，分别是深度脉宽调制(DPWM)、深度脉冲频率调制(DPFM)及极深度脉宽调制(DDPWM)。增加DPWM模式可以避免人耳音频噪声。当负载电流降低时，如果此时任由电源工作在PFM模式下，那么工作频率(Fsw)将相应的降低，当Fsw低到人耳音频范围内后，由于此时的负载电流相对来说还是很大，所以电流流过变压器时会产生人耳可以听到的噪声。显然这在消费电子产品中是不可以接受的现象。在控制模式中增加了DPWM模式，DPWM模式工作在20K Hz频率，当负载电流降到足够小之后再将模式切换到DPFM模式。这时虽然又进入了人耳音频范围，但由于此时负载电流比较小，流过变压器的电流也相应比较小，因此不会产生音频噪声。使用多模式控制的主要目的就是提高反激变换器在各个负载点下的效率以达到6级能效标准的要求。多模式控制中最主要的一点就是要提高轻载下的效率，尤其是25％负载点左右的效率。多模式控制的方法可以明显地提高轻载效率和避免人耳音频噪声，但是同时系统的动态响应能力也变弱了。可以从两个方面考虑多模式控制带来的影响。首先，系统由轻载向重载切换时，由于轻载时的电流相对很小，负载所处的状态能量很低，而重载所处的状态能量很高，这时负载突然的跳变会导致输出电压突然的下降然后再上升。如图3，仿真结果表明，当负载由轻载0.01A跳变到重载1A时，输出电压的下冲为2.51v，瞬态响应时间为8.0ms。在当今消费级电子系统方案中，这种长时间的欠压现象，会导致系统控制系统工作状态出现混乱。其次，系统由重载向轻载跳变的过程中，由于重载时的电流相对很大，负载所处的状态能量很高，而轻载所处的状态能量很低，这时系统负载突然的跳变，跳变后出现第一次过冲后还会出现第二个过冲，导致系统瞬态响应时间相应的增加。如图4，仿真结果可以看出，系统由1A重载切换到0.025A状态时，系统过冲虽然只有0.2v，但是系统的瞬态响应时间却达到了16ms。With the increasingly prominent importance of environmental protection and energy saving, the efficiency of switching power supplies has become the focus of attention. The International Energy Agency (IEA) put forward the "1 Watt Plan" in 2000, that is, to reduce the standby power consumption of all electrical appliances to less than 1 Watt in 10 years; the 6-level energy efficiency standard issued in 2013 requires a 5W system, the minimum The average efficiency is greater than 73.6%, and the no-load power consumption is less than 0.1W. At the same time, the average power is defined as the average power of 5 load points such as full load, 75% load, 50% load, 25% load and 5%. In order to improve the efficiency of the digital primary-side flyback converter at the above load point, the current flyback converter mostly adopts a multi-mode control method, that is, different mode control is used according to different load conditions. The application of simulation technology is more complicated in control. Since digital control can adjust parameters and control mode states more precisely, and can also work in multiple modes, digital control technology has great advantages over analog technology in multi-mode control methods. As shown in Fig. 2, five different working modes are adopted in the working process of the current mainstream flyback converter. Compared with the traditional analog control multi-mode scheme, the existing technology adds three working modes, namely deep pulse width modulation (DPWM), deep pulse frequency modulation (DPFM) and extremely deep pulse width modulation (DDPWM). Adding DPWM mode can avoid human ear audio noise. When the load current decreases, if the power supply is allowed to work in PFM mode at this time, the operating frequency (Fsw) will be reduced accordingly. It is very large, so when the current flows through the transformer, it will produce noise that can be heard by the human ear. Obviously this is not an acceptable phenomenon in consumer electronics. The DPWM mode is added in the control mode, the DPWM mode works at a frequency of 20K Hz, and the mode is switched to the DPFM mode when the load current drops to a small enough value. At this time, although it has entered the audio frequency range of the human ear, since the load current is relatively small at this time, the current flowing through the transformer is correspondingly relatively small, so no audio noise will be generated. The main purpose of using multi-mode control is to improve the efficiency of the flyback converter at each load point to meet the requirements of Level 6 energy efficiency standards. The most important point in multi-mode control is to improve the efficiency under light load, especially the efficiency around 25% load point. The method of multi-mode control can obviously improve light-load efficiency and avoid human ear audio noise, but at the same time, the dynamic response capability of the system is also weakened. The impact of multi-mode control can be considered from two aspects. First of all, when the system switches from light load to heavy load, because the current at light load is relatively small, the state energy of the load is very low, while the state energy of the heavy load is high, and the sudden jump of the load at this time will cause This causes the output voltage to drop suddenly and then rise again. As shown in Figure 3, the simulation results show that when the load jumps from light load 0.01A to heavy load 1A, the undershoot of the output voltage is 2.51v, and the transient response time is 8.0ms. In today's consumer electronics system solutions, this long-term undervoltage phenomenon will lead to confusion in the working state of the system control system. Secondly, when the system jumps from heavy load to light load, due to the relatively large current at heavy load, the state energy of the load is high, while the state energy of light load is very low. At this time, the system load suddenly After the jump, the second overshoot will appear after the first overshoot after the jump, resulting in a corresponding increase in the transient response time of the system. As shown in Figure 4, it can be seen from the simulation results that when the system is switched from 1A heavy load to 0.025A state, although the system overshoot is only 0.2v, the transient response time of the system has reached 16ms.
根据上述，多模式控制的数字原边反激变换器在由轻载向重载跳变和由重载向轻载跳变时均存在动态响应的问题。产生这种现象的主要原因是系统在采用多模式控制方法下不同的模式间存在能量差和模式切换。According to the above, the digital primary-side flyback converter with multi-mode control has the problem of dynamic response when jumping from light load to heavy load and from heavy load to light load. The main reason for this phenomenon is the energy difference and mode switching between different modes in the system under the multi-mode control method.
发明内容Contents of the invention
针对现有一些技术的缺陷，本发明提供了一种改善多模式数字原边反激变换器动态性能的控制系统。系统通过检测负载电压是否有大范围的变化以及输出电压的变化趋势，从而选择切换到合适的工作模式，这样可以极大的改善变换器的动态性能。Aiming at the defects of some existing technologies, the invention provides a control system for improving the dynamic performance of the multi-mode digital primary-side flyback converter. The system selects to switch to an appropriate working mode by detecting whether the load voltage has a wide range of changes and the change trend of the output voltage, which can greatly improve the dynamic performance of the converter.
为了实现上述发明目的，本发明采用的技术方案如下：一种改善多模式数字原边反激变换器动态性能的控制系统，交流电经过整流桥、共模电感、输入电容、RCD网络后输出给原边绕组，副边绕组通过输出电容和整流二极管后的输出电压经由辅助绕组通过分压电阻采样，作为输出电压反馈信号输出给含有波形分析模块、DAC模块、PI补偿模块、模式选择模块、参数设置模块以及驱动及RS触发器模块构成的多模式控制模块，多模式控制模块根据反馈信号选择合适的工作模式，经过驱动及RS触发器模块产生PWM波形，控制原边开关管的栅极，从而实现多模式数字控制；In order to achieve the above-mentioned invention, the technical scheme adopted by the present invention is as follows: a control system for improving the dynamic performance of a multi-mode digital primary-side flyback converter. The output voltage of the side winding and the secondary winding through the output capacitor and the rectifier diode is sampled through the auxiliary winding through the voltage dividing resistor, and output as the output voltage feedback signal to the waveform analysis module, DAC module, PI compensation module, mode selection module, parameter setting The multi-mode control module composed of the driver module and the driver and RS flip-flop module, the multi-mode control module selects the appropriate working mode according to the feedback signal, generates a PWM waveform through the driver and RS flip-flop module, and controls the gate of the primary switch tube, thereby realizing Multi-mode digital control;
其特征在于：在多模式控制模块中增设负载分析模块，用于检测负载电压是否有大范围的变化以及输出电压的变化趋势，从而选择切换到合适的工作模式，以改善变换器的动态性能；辅助绕组通过分压电阻采样的输出电压反馈信号通过四个比较器后输入到波形分析模块，波形分析模块得到数字参考电压Vref，并分别输入到负载分析模块和PI补偿模块，DAC模块将波形分析模块的输出转换为模拟值作为波形分析模块前的比较器的输入，PI补偿模块给出峰值电压补偿值Vpeak_pi并输入到模式选择模块和参数设置模块，模式选择模块与负载分析模块双向连接，模式选择模块输出当前工作模式work_mode给负载分析模块，然后负载分析模块通过对当前时刻的Vref(n)与上一时刻的Vref(n-1)的差值和当前工作模式的分析给出模式选择det_mode并输入到模式选择模块，模式选择模块根据模式选择det_mode和峰值电压补偿值Vpeak_pi给出当前合适的工作模式并输入到参数设置模块，由参数设置模块给出当前工作模式下所对应的控制参数峰值电流CS和周期Ts,然后经过驱动及RS触发器模块产生PWM波形，控制原边开关管的栅极，实现多模式动态数字控制；It is characterized in that: a load analysis module is added to the multi-mode control module to detect whether the load voltage has a large-scale change and the change trend of the output voltage, so as to select and switch to an appropriate working mode to improve the dynamic performance of the converter; The output voltage feedback signal sampled by the auxiliary winding through the voltage dividing resistor is input to the waveform analysis module after passing through four comparators. The output of the module is converted into an analog value as the input of the comparator in front of the waveform analysis module. The PI compensation module gives the peak voltage compensation value Vpeak_pi and inputs it to the mode selection module and the parameter setting module. The mode selection module and the load analysis module are bidirectionally connected. The selection module outputs the current working mode work_mode to the load analysis module, and then the load analysis module gives the mode selection det_mode by analyzing the difference between the Vref(n) at the current moment and the Vref(n-1) at the previous moment and the current working mode And input to the mode selection module, the mode selection module gives the current suitable working mode according to the mode selection det_mode and the peak voltage compensation value Vpeak_pi and inputs it to the parameter setting module, and the parameter setting module gives the corresponding control parameter peak value in the current working mode The current CS and period Ts, and then generate a PWM waveform through the drive and RS flip-flop module to control the gate of the primary switching tube to realize multi-mode dynamic digital control;
负载分析模块包括寄存器、减法器、比较器、数据选择器、模式赋值模块、模式变换检测模块和模式判断模块，D1和D2两个寄存器分别用来存储当前时刻的Vref(n)和上Vref(n-1)，Vref(n)和Vref(n-1)输入到减法器里得到两次采样的输出电压差值△Vref并通过比较器与阈值△Vref_th比较，数据选择器用来选择不同工作模式下的阈值△Vref_th，△Vref_th的确定方法为对应工作模式下保证输出电压不会出现大过冲时采样电压变化的最大值；为了提高动态性能，提前判断负载最合适的工作模式，当工作模式work_mode发生变化时，模式变换检测模块检测到工作模式的变化，并输出时钟信号给D3、D4和D5三个寄存器，通过D3、D4和D5三个寄存器存储最近三次模式发生变化时的Vref值，即Vref1、Vref2和Vref3，将它们输入到模式判断模块，通过模式判断模块内的比较器确定它们之间的大小关系，这些比较得到的数据可以用来判断当前负载工作下最合适的模式，并通过模式赋值模块给出对应的模式选择det_mode到多模式控制模块里的模式选择模块；The load analysis module includes a register, a subtractor, a comparator, a data selector, a mode assignment module, a mode conversion detection module and a mode judgment module. The two registers D1 and D2 are used to store the Vref(n) and the upper Vref(n) of the current moment respectively. n-1), Vref(n) and Vref(n-1) are input into the subtractor to obtain the output voltage difference △Vref of the two samples and compared with the threshold △Vref_th by the comparator, and the data selector is used to select different working modes The lower threshold value △Vref_th, the determination method of △Vref_th is the maximum value of the sampling voltage change when the output voltage is guaranteed not to have a large overshoot in the corresponding working mode; in order to improve the dynamic performance, judge the most suitable working mode of the load in advance, when the working mode When the work_mode changes, the mode change detection module detects the change of the working mode, and outputs the clock signal to the three registers D3, D4, and D5, and stores the Vref value when the mode changes the last three times through the three registers D3, D4, and D5. That is, Vref1, Vref2 and Vref3, input them to the mode judgment module, determine the size relationship between them through the comparator in the mode judgment module, the data obtained by these comparisons can be used to judge the most suitable mode under the current load, and Provide the corresponding mode selection det_mode to the mode selection module in the multi-mode control module through the mode assignment module;
负载分析模块包括以下执行过程：The load analysis module includes the following execution procedures:
(1)通过判断参考电压差△Vref的大小判断负载是否出现了大范围的负载跳变，这里定义△Vref为两次采样的输出电压差值，定义前一个开关周期采样的输出电压数字值为Vref(n-1)，当前开关周期采样的输出电压数字值为Vref(n)，则有(1) Determine whether the load has a large-scale load jump by judging the reference voltage difference △Vref. Here, △Vref is defined as the output voltage difference between two samples, and the output voltage digital value sampled in the previous switching cycle is defined as Vref(n-1), the output voltage digital value sampled in the current switching cycle is Vref(n), then there is
ΔVref＝Vref(n)-Vref(n-1)ΔVref=Vref(n)-Vref(n-1)
同时负载分析模块中定义了一个△Vref的阈值△Vref_th，其中阈值△Vref_th的大小由当前工作模式work_mode给出，经过比较器比较后，如果△Vref的值大于△Vref_th，则认为当前的负载发生了大范围的跳变，将恒压脉宽调制模式CV_PWM赋予模式选择det_mode，负载从当前工作模式直接跳变到PWM模式，以快速补偿能量，防止电压出现过大的下冲；At the same time, a threshold of △Vref, △Vref_th, is defined in the load analysis module, where the threshold △Vref_th is given by the current working mode work_mode. After comparison by the comparator, if the value of △Vref is greater than △Vref_th, it is considered that the current load occurs To achieve a wide range of jumps, the constant voltage pulse width modulation mode CV_PWM is assigned to the mode selection det_mode, and the load directly jumps from the current working mode to the PWM mode to quickly compensate energy and prevent excessive voltage undershoot;
(2)通过观察在负载切换的模式跳变过程中Vref的变化趋势，直接判定当前负载适合的模式，避免模式之间的来回切换；比如，当PWM模式切换到PFM模式时，采样这时候的输出电压值Vref1，当离开这个模式切换到DPWM模式时采样这时候的输出电压值Vref2，如果Vref2的值大于Vref1，说明当前模式对于负载来说能量偏高，不是适合的模式，则同样的方式采样到Vref3，如果Vref3小于Vref2，说明DPFM模式能量偏低，那么，DPWM模式就是合适的模式，当采样电压在DPFM模式中下降到等于程序设定参考值后，将模式选择det_mode的值设置为DPWM模式，这样系统能够工作在合适的模式而不会在两个模式之间来回的切换；(2) By observing the change trend of Vref during the mode jump process of load switching, directly determine the mode suitable for the current load, and avoid switching back and forth between modes; for example, when the PWM mode is switched to the PFM mode, sampling the current Output voltage value Vref1, when you leave this mode and switch to DPWM mode, sample the output voltage value Vref2 at this time, if the value of Vref2 is greater than Vref1, it means that the current mode has high energy for the load and is not a suitable mode, then the same way Sampling to Vref3, if Vref3 is less than Vref2, it means that the energy of DPFM mode is low, then, DPWM mode is a suitable mode, when the sampling voltage drops to equal to the reference value set by the program in DPFM mode, set the value of mode selection det_mode to DPWM mode, so that the system can work in the appropriate mode without switching back and forth between the two modes;
(3)负载分析模块程序优先判断是否出现轻载到重载的跳变，如果出现，将恒压脉宽调制模式CV_PWM模式赋予模式选择det_mode，否则将软启动模式SOFT_START赋予模式选择det_mode，然后程序判断是否出现重载向轻载跳变且振荡，如果出现则依照之前的原则将模式选择det_mode置于能量合适的模式。(3) The load analysis module program first judges whether there is a jump from light load to heavy load. If it occurs, assign the constant voltage pulse width modulation mode CV_PWM mode to the mode selection det_mode, otherwise assign the soft start mode SOFT_START to the mode selection det_mode, and then program Judging whether there is a jump from heavy load to light load and oscillation, if so, set the mode selection det_mode to a mode with appropriate energy according to the previous principle.
本发明的优点及显著效果：本发明在系统中添加了一个额外的load_analysis(负载分析)模块，负载分析模块的主要功能是通过检测负载电压是否有大范围的变化以及输出电压的变化趋势，从而选择切换到合适的工作模式，这样可以极大地改善变换器的动态性能。Advantages of the present invention and remarkable effects: the present invention has added an additional load_analysis (load analysis) module in the system, and the main function of load analysis module is whether there is the variation trend of large-scale change and output voltage by detecting load voltage, thereby Choose to switch to the appropriate working mode, which can greatly improve the dynamic performance of the converter.
本发明控制系统通过辅助绕组间接采样输出电压，采样电压经过模式转换后得到一个数字值Vref，通过对Vref当前时刻值Vref(n)和上一时刻值Vref(n-1)的差值△Vref的分析来避免电压出现过大的下冲，其次记录最近三次模式切换时的Vref值，即Vref1、Vref2和Vref3，通过对它们的比较可以判断出负载在各个模式下能量是过多、过小还是合适，从而提前选择负载合适的模式，避免模式之间来回切换引起的振荡。仿真结果表明经过优化之后系统轻载到重载直接跳变过冲下降945％，响应时间减少440％。系统重载到轻载跳变相应的过冲没有变化，但是瞬态响应时间减小了60％。可见本发明可以有效的提高数字多模式反激变换起器的动态响应性能，而且本发明并没有过多占用新的资源，它仍然是通过对采样电压值的分析来判断负载情况，并对不同工作模式设置来不同的参数，如阈值△Vref_th，可以进一步减小电压纹波、降低EMI和提高系统的效率。此外使用数字方法来实现逻辑关系和算法，节省了芯片面积，更利于集成。综上，本发明不仅拥有多模式控制效率尤其是轻载效率高的优点，同时极大的改善了系统的动态性能，提升了系统的稳定性，而且可实施性非常高，便于推广使用。The control system of the present invention indirectly samples the output voltage through the auxiliary winding, and the sampling voltage obtains a digital value Vref after mode conversion, and the difference △Vref between the current moment value Vref(n) and the previous moment value Vref(n-1) of Vref To avoid excessive undershoot of the voltage, and then record the Vref value of the last three mode switching, that is, Vref1, Vref2 and Vref3. By comparing them, it can be judged whether the energy of the load in each mode is too much or too small It is still appropriate to select the appropriate mode of the load in advance to avoid oscillation caused by switching back and forth between modes. The simulation results show that after the optimization, the overshoot of the direct transition from light load to heavy load of the system is reduced by 945%, and the response time is reduced by 440%. The overshoot corresponding to the system heavy load to light load transition has not changed, but the transient response time has been reduced by 60%. It can be seen that the present invention can effectively improve the dynamic response performance of the digital multi-mode flyback converter, and the present invention does not occupy too many new resources, it still judges the load situation by analyzing the sampled voltage value, and different Different parameters are set in the working mode, such as the threshold △Vref_th, which can further reduce the voltage ripple, reduce EMI and improve the efficiency of the system. In addition, digital methods are used to implement logical relations and algorithms, which saves chip area and is more conducive to integration. To sum up, the present invention not only has the advantages of multi-mode control efficiency, especially high light-load efficiency, but also greatly improves the dynamic performance of the system, improves the stability of the system, and has very high implementability, which is convenient for popularization and use.
附图说明Description of drawings
图1传统多模式控制数字原边反激变换器框图；Figure 1 Block diagram of traditional multi-mode control digital primary-side flyback converter;
图2现有技术采用的多种模式；Fig. 2 various modes adopted by the prior art;
图3传统多模式控制下0.01A切换到1A；Figure 3 Switching from 0.01A to 1A under traditional multi-mode control;
图4传统多模式控制下1A切换到0.01A；Figure 4 Switching from 1A to 0.01A under traditional multi-mode control;
图5本发明的负载分析模块框图；Fig. 5 load analysis module block diagram of the present invention;
图6负载分析模块中模块判断模式的模式切换示意图；Fig. 6 is a schematic diagram of the mode switching of the module judgment mode in the load analysis module;
图7本发明采用的改善动态性能的多模式控制数字原边反激变换器框图；Figure 7 is a block diagram of a multi-mode control digital primary side flyback converter for improving dynamic performance adopted by the present invention;
图8本发明多模式控制模块模式切换示意图；Fig. 8 is a schematic diagram of mode switching of the multi-mode control module of the present invention;
图9本发明负载分析模块控制流程图；Fig. 9 is a control flow chart of the load analysis module of the present invention;
图10本发明多模式控制下0.01A切换到1A；Fig. 10 Switching from 0.01A to 1A under the multi-mode control of the present invention;
图11本发明多模式控制下1A切换到0.025A。Fig. 11 Switching from 1A to 0.025A under the multi-mode control of the present invention.
具体实施方式detailed description
图1是传统多模式控制数字原边反激变换器的框图，它主要包括原边Np，副边Ns和辅助边Na。交流电从原边输入，原边主要包括整流桥，RCD网络，输入电容和开关管等；副边作为系统输出，包括输出电容和整流二极管；辅助边用于反馈信号，副边输出电压与辅助边电压成一次函数关系，副边电压经过分压网络R1和R2分压后作为反馈信号输入多模式控制模块。多模式控制模块中包括波形分析模块、PI补偿模块、模式选择模块和参数设置模块。波形分析模块主要用于分析辅助绕组通过分压电阻采样过来的输出电压反馈信号；PI补偿模块主要功能是判断当前输出是否达到预期值，如果没有达到预期值对当前输出进行补偿使输出达到预期值；模式选择模块主要根据PI模块输出的补偿值和当前的工作模式判断下一时刻最合适的工作模式；参数设置模块根据当前工作模式和PI模块的补偿值设置下一个时刻工作模式对应的参数。反馈电压经过比较器后输入波形分析模块，通过模数转换器得到反馈电压的数字参考电压(Vref),并输入到PI补偿模块，PI补偿模块给出峰值电压补偿值(Vpeak_pi)然后将其输入到模式选择模块和参数设置模块，模式选择模块根据当前工作模式和Vpeak_pi给出下一个时刻最合适的工作模式并输入到参数设置模块，由参数设置模块给出下一个时刻工作模式下所对应的控制参数峰值电流CS和周期Ts,然后经过RS触发器和驱动模块产生PWM波形，控制原边开关管的栅极，实现多模式动态数字控制。Figure 1 is a block diagram of a traditional multi-mode control digital primary side flyback converter, which mainly includes the primary side Np, the secondary side Ns and the auxiliary side Na. AC power is input from the primary side, the primary side mainly includes rectifier bridge, RCD network, input capacitor and switch tube, etc.; the secondary side is used as the system output, including output capacitor and rectifier diode; the auxiliary side is used for feedback signal, the output voltage of the secondary side and the auxiliary side The voltage is a linear function, and the secondary side voltage is divided by the voltage divider network R1 and R2 and then input to the multi-mode control module as a feedback signal. The multi-mode control module includes a waveform analysis module, a PI compensation module, a mode selection module and a parameter setting module. The waveform analysis module is mainly used to analyze the output voltage feedback signal sampled by the auxiliary winding through the voltage divider resistor; the main function of the PI compensation module is to judge whether the current output reaches the expected value, and if it does not reach the expected value, compensate the current output to make the output reach the expected value The mode selection module mainly judges the most suitable working mode at the next moment according to the compensation value output by the PI module and the current working mode; the parameter setting module sets the corresponding parameters of the working mode at the next moment according to the current working mode and the compensation value of the PI module. The feedback voltage is input to the waveform analysis module after passing through the comparator, and the digital reference voltage (Vref) of the feedback voltage is obtained through the analog-to-digital converter, and input to the PI compensation module. The PI compensation module gives the peak voltage compensation value (Vpeak_pi) and then inputs it To the mode selection module and the parameter setting module, the mode selection module gives the most suitable working mode at the next moment according to the current working mode and Vpeak_pi and inputs it to the parameter setting module, and the parameter setting module gives the corresponding Control the parameters peak current CS and period Ts, and then generate PWM waveform through RS flip-flop and drive module, control the gate of the primary side switch tube, and realize multi-mode dynamic digital control.
图2是现有技术采用的多种控制模式，相比传统的模拟控制多模式方案，我们多采用了三个模式，分别是DPWM、DPFM及DDPWM。增加DPWM模式的目的是为了避免音频噪声。当负载电流下降时，如果此时任然工作于PFM模式下，则工作频率Fsw将相应的降低，当降到音频范围内之后，由于此时的负载电流相对来说还是很大。电流流过变压器时会产生人儿可以听到的噪声。这在消费电子产品中显然是不可以接受的。因此在控制模式中增加了DPWM模式，该模式工作在20KHz频率上，当负载电流降到足够小之后再将模式切换到DPFM模式。此时再进入音频范围之后，由于负载电流比较小，流过变压器的电流也相应的比较的小，因此不会产生音频噪声。Figure 2 shows the multiple control modes used in the prior art. Compared with the traditional analog control multi-mode solution, we have adopted three more modes, namely DPWM, DPFM and DDPWM. The purpose of adding DPWM mode is to avoid audio noise. When the load current drops, if it is still working in PFM mode at this time, the working frequency Fsw will be reduced accordingly. After falling to the audio frequency range, the load current at this time is still relatively large. When current flows through the transformer, it produces noise that can be heard by humans. This is obviously not acceptable in consumer electronics. Therefore, the DPWM mode is added in the control mode, which works at a frequency of 20KHz, and the mode is switched to the DPFM mode when the load current drops sufficiently. At this time, after entering the audio frequency range, since the load current is relatively small, the current flowing through the transformer is correspondingly relatively small, so no audio noise will be generated.
图3为传统控制方法中负载由0.01A跳变到1A时的仿真图，可以看出输出电压向下的下冲为2.51v，而瞬态的响应时间则为8.0ms。由轻载向重载切换时，由于轻载时的电流很小，负载处于的能量状态很低，而重载的能量状态很高，此时负载突然的跳变，输出电压会突然的下降然后再上升。在消费电子系统方案中，如此长时间的欠压，会导致系统控制系统因为欠压而出现混乱。Figure 3 is the simulation diagram when the load jumps from 0.01A to 1A in the traditional control method. It can be seen that the downward undershoot of the output voltage is 2.51v, and the transient response time is 8.0ms. When switching from light load to heavy load, because the current at light load is very small, the energy state of the load is very low, while the energy state of heavy load is high. At this time, the load suddenly jumps, and the output voltage will suddenly drop and then rise again. In consumer electronics system solutions, such a long period of undervoltage will lead to confusion in the system control system due to undervoltage.
图4为传统控制方法中负载由1A切换到0.025A状态时的仿真图，系统过冲量只有0.2v，但是瞬态响应时间却达到了16ms。在重载向轻载跳变的过程中，由于重载时的电流很大，负载处于的能量状态很高，而轻载的能量状态很低，此时负载突然的跳变，跳变之后出现第一次过冲之后仍会出现第二个过冲，由此导致系统瞬态响应时间相应的增加。Fig. 4 is the simulation diagram when the load is switched from 1A to 0.025A in the traditional control method. The system overshoot is only 0.2v, but the transient response time reaches 16ms. In the process of jumping from heavy load to light load, due to the large current at heavy load, the energy state of the load is very high, while the energy state of light load is very low. At this time, the load suddenly jumps, and after the jump occurs A second overshoot still occurs after the first overshoot, resulting in a corresponding increase in the system's transient response time.
图5为本发明的负载分析模块的具体框图。负载分析模块包括寄存器、减法器、比较器、数据选择器、模式赋值模块、模式变换检测模块和模式判断模块，D1和D2两个寄存器分别用来存储当前时刻的Vref值，即Vref(n)和上一个时刻的Vref值，即Vref(n-1)，Vref(n)和Vref(n-1)输入到减法器里得到两次采样的输出电压差值△Vref并通过比较器与阈值△Vref_th比较，数据选择器用来选择不同工作模式下的阈值△Vref_th，△Vref_th的确定方法为对应工作模式下保证输出电压不会出现大过冲时采样电压变化的最大值；为了提高动态性能，提前判断负载最合适的工作模式，用D3，D4,和D5三个寄存器存储最近三次模式发生变化时的Vref值，即Vref1、Vref2和Vref3，将它们输入到模式判断模块，通过模式判断模块内的比较器确定它们之间的大小关系，这些比较得到的数据可以用来判断当前负载工作下最合适的模式，并通过模式赋值模块给出对应的模式选择det_mode到多模式控制模块里的模式选择模块。Fig. 5 is a specific block diagram of the load analysis module of the present invention. The load analysis module includes registers, subtractors, comparators, data selectors, mode assignment modules, mode conversion detection modules and mode judgment modules. The two registers D1 and D2 are used to store the Vref value at the current moment, namely Vref(n) And the Vref value at the previous moment, that is, Vref(n-1), Vref(n) and Vref(n-1) are input into the subtractor to obtain the output voltage difference △Vref of the two samples and pass the comparator and the threshold value △ Compared with Vref_th, the data selector is used to select the threshold △Vref_th in different working modes. The determination method of △Vref_th is the maximum value of the sampling voltage change when the output voltage is guaranteed not to have a large overshoot in the corresponding working mode; in order to improve the dynamic performance, advance To determine the most suitable working mode for the load, use the three registers D3, D4, and D5 to store the Vref values of the last three mode changes, that is, Vref1, Vref2 and Vref3, and input them to the mode judgment module. The comparator determines the size relationship between them, and the data obtained by these comparisons can be used to judge the most suitable mode under the current load work, and the corresponding mode selection det_mode is given to the mode selection module in the multi-mode control module through the mode assignment module .
图6为模式判断模块如何提前判断负载合适的模式并避免模式间来回切换的说明图。我们采取的方法是记录模式切换时的Vref值并进行比较来判断。当模式work_mode0切换到下一个模式work_mode1时记录下这时候的优化后多模式控制器框图输出电压值Vref1，当离开这个模式切换到work_mode2时记录下这时候的输出电压值Vref2.如果Vref2大于Vref1，则表示当前的模式对于负载能量偏高，不是适合的模式。同样的方式能够记录下Vref3.如果Vref3小于Vref2，则work_mode3的能量肯定是偏低的。那么，work_mode2就是合适的模式。当电压再work_mode3中下降到合适的值之后设置det_mode的值work_mode2，为让系统回到work_mode2。此时系统可以稳定的工作于work_mode2，而不会work_mode2和work_mode3之间来回的切换。FIG. 6 is an explanatory diagram of how the mode judging module judges the appropriate mode of the load in advance and avoids switching back and forth between the modes. The method we take is to record the Vref value when the mode is switched and compare it to judge. When the mode work_mode0 is switched to the next mode work_mode1, record the output voltage value Vref1 of the optimized multi-mode controller block diagram at this time. When leaving this mode and switching to work_mode2, record the output voltage value Vref2 at this time. If Vref2 is greater than Vref1, It means that the current mode is not suitable for the high load energy. In the same way, Vref3 can be recorded. If Vref3 is smaller than Vref2, the energy of work_mode3 must be low. Then, work_mode2 is the appropriate mode. When the voltage drops to an appropriate value in work_mode3, set the value of det_mode work_mode2 to let the system return to work_mode2. At this time, the system can work stably in work_mode2 without switching back and forth between work_mode2 and work_mode3.
图7为本发明采用的改善动态性能的多模式控制数字原边反激变换器框图。框图主要包括反馈信号采样模块、多模式控制模块和PWM波形产生模块；反馈信号采样模块的输入端连接辅助绕组分压网络的反馈输出，反馈信号采样模块连接多模式控制模块，多模式控制模块连接PWM波形产生模块。PWM波形产生模块的输出连接到变换器主开关管的栅极。通过这些模块实现了对系统开关的多模式动态数字控制。反馈信号采样模块包括辅助绕组Na，分压电阻网络R1和R2，变压器在副边绕组上Ns的电压与辅助绕组Na上的电压成匝比关系，辅助绕组上的电压经过分压电阻网络后与副边输出成一定的线性关系，所以可以作为反馈信号输入到多模式控制模块和负载分析模块，供多模式控制模块和负载分析模块分析。PWM波形产生模块内部包含一个RS触发器和一个驱动模块，PWM波形产生模块会据多模式控制模块和负载分析模块给出的控制信号，决定RS触发器何时输出“1”以及“0”，驱动模块的作用则是提供大电流以驱动外围MOS管。FIG. 7 is a block diagram of a multi-mode control digital primary-side flyback converter with improved dynamic performance adopted in the present invention. The block diagram mainly includes a feedback signal sampling module, a multi-mode control module and a PWM waveform generation module; the input terminal of the feedback signal sampling module is connected to the feedback output of the auxiliary winding sub-compression network, the feedback signal sampling module is connected to the multi-mode control module, and the multi-mode control module is connected to PWM waveform generation module. The output of the PWM waveform generation module is connected to the gate of the main switching tube of the converter. The multi-mode dynamic digital control of system switches is realized through these modules. The feedback signal sampling module includes the auxiliary winding Na, the voltage dividing resistor network R1 and R2, the voltage of the transformer on the secondary winding Ns and the voltage on the auxiliary winding Na have a turn ratio relationship, and the voltage on the auxiliary winding passes through the voltage dividing resistor network. The output of the secondary side has a certain linear relationship, so it can be used as a feedback signal input to the multi-mode control module and the load analysis module for analysis by the multi-mode control module and the load analysis module. The PWM waveform generation module contains an RS flip-flop and a drive module. The PWM waveform generation module will determine when the RS flip-flop outputs "1" and "0" according to the control signals given by the multi-mode control module and the load analysis module. The role of the driver module is to provide a large current to drive the peripheral MOS tube.
多模式控制模块包括波形分析模块、PI补偿模块、负载分析模块、模式选择模块和参数设置模块，其中波形分析模块、PI补偿模块、模式选择模块和参数设置模块是现有技术已有的，负载分析模块是本发明添加的。辅助绕组通过分压电阻采样的输出电压反馈信号通过四个比较器后输入到波形分析模块，波形分析模块通过模数转换器得到数字参考电压(Vref),并分别输入到负载分析模块和PI补偿模块，PI补偿模块给出峰值电压补偿值(Vpeak_pi)并输入到模式选择模块和参数设置模块，模式选择模块与负载分析模块双向连接，模式选择模块输出当前工作模式(work_mode)负载分析模块通过对当前时刻的Vref(n)与上一时刻的Vref(n-1)的差值和当前工作模式的分析给出模式选择(det_mode)并输入到模式选择模块，模式选择模块根据det_mode和Vpeak_pi给出当前合适的工作模式并输入到参数设置模块，由参数设置模块给出当前工作模式下所对应的控制参数峰值电流CS和周期Ts,然后经过RS触发器和驱动模块产生PWM波形，控制原边开关管的栅极，实现多模式动态数字控制。多模式控制模块的主要目的是提高各个负载点的效率，从而达到6级能效标准的要求。最主要的一点就是要提高轻载的效率，尤其是25％负载点左右的效率。整个工作过程中采用了5种工作模式。The multi-mode control module includes a waveform analysis module, a PI compensation module, a load analysis module, a mode selection module and a parameter setting module, wherein the waveform analysis module, the PI compensation module, the mode selection module and the parameter setting module are existing in the prior art, and the load The analysis module is added by the present invention. The output voltage feedback signal sampled by the auxiliary winding through the voltage dividing resistor is input to the waveform analysis module after passing through four comparators. module, the PI compensation module gives the peak voltage compensation value (Vpeak_pi) and inputs it to the mode selection module and the parameter setting module, the mode selection module is bidirectionally connected with the load analysis module, and the mode selection module outputs the current working mode (work_mode) through the load analysis module The difference between Vref(n) at the current moment and Vref(n-1) at the previous moment and the analysis of the current working mode give the mode selection (det_mode) and input it to the mode selection module, and the mode selection module gives according to det_mode and Vpeak_pi The current suitable working mode is input to the parameter setting module, and the parameter setting module gives the corresponding control parameters peak current CS and period Ts in the current working mode, and then generates PWM waveform through the RS trigger and the driving module to control the primary side switch The gate of the tube realizes multi-mode dynamic digital control. The main purpose of the multi-mode control module is to improve the efficiency of each load point, so as to meet the requirements of the energy efficiency standard of level 6. The most important point is to improve the efficiency of light load, especially the efficiency around 25% load point. 5 working modes are adopted in the whole working process.
本发明增加负载分析模块的主要目的是提高多模式数字反激变换器的动态性能，如图8，给出了负载分析模块的工作流程，通过检测负载电压是否有大的跳变及其变化趋势，避免了电压出现大的过冲并具有提前选择切换到合适的模式的功能，全面地提高了系统的动态响应性能。The main purpose of adding the load analysis module in the present invention is to improve the dynamic performance of the multi-mode digital flyback converter, as shown in Figure 8, the work flow of the load analysis module is given, by detecting whether the load voltage has a large jump and its change trend , to avoid a large overshoot of the voltage and has the function of selecting and switching to an appropriate mode in advance, which comprehensively improves the dynamic response performance of the system.
图8是多模式控制模块中的模式切换示意图。图中Vref表示的是辅助绕组上的波形经过采样模块得到的输出电压的数字值。当该值为396时对应输出电压为5V。Vpeak_pi则是PI补偿器的输出值，在同一个模式中，该值越大对应的每个开关周期由变压器提供给输出负载的能量越多。假定变换器工作于PWM模式且此时的Vpeak_pi为140、Vref>＝398，则表示此时PWM模式每个开关周期下所能够提供的最低能量仍然超过负载所能消耗的能量，导致此时的输出电压上升超过5V。因此需要切换到下一个能量更低的模式中去。同样假定变换器工作于PFM模式且此时的Vpeak_pi为150、Vref<＝394，则表示此时PFM模式每个开关周期下所能够提供的最高能量仍然不能满足负载所消耗的能量，导致此时的输出电压下降而低于5V。因此需要切换到下一个能量更高的模式中去。其他状态的切换原理和上述原理一致。Fig. 8 is a schematic diagram of mode switching in the multi-mode control module. Vref in the figure represents the digital value of the output voltage obtained by the waveform on the auxiliary winding through the sampling module. When the value is 396, the corresponding output voltage is 5V. Vpeak_pi is the output value of the PI compensator. In the same mode, the larger the value is, the more energy the transformer provides to the output load in each switching cycle. Assuming that the converter works in PWM mode and Vpeak_pi is 140 and Vref>=398 at this time, it means that the minimum energy that can be provided in each switching cycle of PWM mode still exceeds the energy that the load can consume, resulting in the current The output voltage rises above 5V. Therefore, it is necessary to switch to the next lower energy mode. Also assume that the converter works in PFM mode and Vpeak_pi is 150 and Vref<=394 at this time, it means that the highest energy that can be provided in each switching cycle of PFM mode still cannot meet the energy consumed by the load at this time, resulting in The output voltage drops below 5V. Therefore, it is necessary to switch to the next higher energy mode. The switching principles of other states are consistent with the above-mentioned principles.
图9是负载分析模块的流程图，该图示意了负载分析模块是如何工作的，采样到反馈信号后，程序首先判断的是否出现了轻载到重载的跳变。如果出现则程序的det_mode被赋予CV_PWM模式，否则被赋予SOFT_START模式。然后程序判断是否出现重载向轻载跳变且振荡，如果出现则将det_mode置于合适的模式。Figure 9 is a flow chart of the load analysis module, which illustrates how the load analysis module works. After sampling the feedback signal, the program first judges whether there is a transition from light load to heavy load. If present, the program's det_mode is assigned CV_PWM mode, otherwise it is assigned SOFT_START mode. Then the program judges whether there is a jump from heavy load to light load and oscillates, and if so, put det_mode in an appropriate mode.
图10是优化后系系统由0.01A的轻载直接跳变到1A重载时的动态响应，由图9可知，进过优化之后系统由0.01A的轻载直接跳变到1A重载时，系统的下冲由之前的2.51V降到了0.24V，相应的瞬态时间则有之前的8.1ms降低到了1.5ms，由轻载向重载跳变时系统的响应性能得到了大幅度的提升。Figure 10 is the dynamic response of the optimized system when the light load of 0.01A directly jumps to the heavy load of 1A. It can be seen from Figure 9 that after the optimization, the system directly jumps from the light load of 0.01A to the heavy load of 1A. The undershoot of the system has been reduced from the previous 2.51V to 0.24V, and the corresponding transient time has been reduced from the previous 8.1ms to 1.5ms, and the response performance of the system has been greatly improved when jumping from light load to heavy load.
图11是优化后系系统由1A的重载直接跳变到0.025A轻载时的动态响应，由图10可知，优化后系统由1A直接跳变到0.025A时，系统的上冲基本维持不变，但相应的瞬态响应时间则由之前的16ms降低到了10ms，由重载向轻载跳变的瞬态响应时间得到了减少。Figure 11 is the dynamic response of the optimized system when the heavy load of 1A directly jumps to the light load of 0.025A. It can be seen from Figure 10 that when the optimized system directly jumps from 1A to 0.025A, the overshoot of the system basically remains the same However, the corresponding transient response time has been reduced from 16ms to 10ms, and the transient response time from heavy load to light load has been reduced.
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