The development of modern electronic industry has promoted the development of power supply industry. Any electronic equipment cannot do without power supply of various precisions. Power converter can convert various voltages into voltages required by users. For example, power transformer can convert the transmitted kilovolt high voltage AC power into normal mains power; various chargers, as well as industrial and communication power supply modules, can convert AC or DC voltage into DC or AC voltage required by users. Such equipment are power converters that provide power conversion. Compared with signal-level converters, power converters have much greater power, ranging from a few watts to tens of kilowatts, and their work is accompanied by huge energy conversion. In the production process of power supply equipment, routine testing and aging of power supply equipment is a necessary part of equipment inspection, which can improve the reliability of power supply equipment and reduce the rework and warranty costs of the factory. However, due to equipment aging, the power consumption cost of production is also increased. Usually, routine aging of equipment is to connect the equipment to simulated load for simulated work. Of course, energy is consumed on the simulated load, and this consumption is usually not optimally utilized. Based on the characteristics of power converters that convert electrical energy into different levels of electrical energy, this paper proposes to realize the recycling of most energy through energy feedback, thereby achieving the purpose of energy saving. How to save energy and reduce energy consumption is the goal that people have always pursued. In today's construction of a conservation-oriented society, the significance of energy saving and consumption reduction is even more important.
2 Working Principle
The power converter can process electrical energy into the required electrical energy. Its routine aging use only requires connecting a suitable resistive load or an electrical device with equivalent impedance to the output end of the power converter to ensure a certain load operation. As shown in Figure 1: The input voltage Vin is converted to Vout by the power converter and added to the resistive load. During routine operation, the power consumed by the power converter (excluding the loss in the conversion process) is Po="Vout2" /R1.
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Figure 1 Converter operation diagram |
In this case, the electric energy consumption is not utilized at all, but directly converted into heat energy and dissipated from the resistive load, which is a serious waste of electric energy.
To achieve energy conservation and recycling, the main consideration is to make more reasonable use of the energy consumed on the resistive load. If the output voltage Vout can be restored to the input voltage Vin, the output electric energy is converted into the input electric energy, and the recycling of electric energy can be achieved, as shown in Figure 2: the resistive load R1 of the original converter is replaced by a converter 2 with an equivalent input impedance, and the output of converter 2 is connected to the input of converter 1. Then the energy consumed by converter 2 with an equivalent input impedance to R1 from the output end of converter 1 is converted to the input end of converter 1, and then to the input end of converter 2 through converter 1, realizing the recycling of energy. If in an ideal situation, there is no conversion loss, the system can work in a self-circulating manner. Of course, this is impossible to achieve, so when analyzing energy, the consumption of the conversion process should be introduced.
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Figure 2 Schematic diagram of converter energy cycle |
The energy consumption in the above two working modes is analyzed as follows:
The first working mode is when there is no energy circulation, Pi is the input energy of the converter, Pw is the energy consumed in the conversion process of the power converter, and Po is the output energy consumed by the converter on the resistive load. Assuming that the conversion efficiency of the converter is 80%, the energy consumed by the converter in the conversion process can be set as Pw=25% Po, then the overall total energy consumption is the input energy of the converter Pi=Po+Pw=1.25Po.
Pwf
The second working mode is when energy feedback is introduced, and the energy conversion is shown in Figure 3: Converter 1 is a power converter that needs to be used routinely, and converter 2 is a converter for energy feedback. Pi is the input energy given to converter 1 by the system, Pw is the energy consumed in the conversion process of converter 1, and Po is the energy that the power converter 1 should normally output for routine use, and it is also the input energy of converter 2; Pwf is the energy consumed in the conversion process of converter 2 for energy feedback, and Pf is the energy fed back to the power converter 1 by converter 2.
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Figure 3 Energy conversion diagram with feedback mode |
Assuming that the conversion efficiency of power converter 1 and converter 2 is 80%, the energy consumed in the conversion process of converter 1 is the same as mode 1: Pw=25%Po. The energy consumed in the conversion process of converter 2 is obtained from the conversion efficiency of the converter: Pwf=20%Po. According to the law of energy conservation, the overall total energy consumption is: Pi=Pw+Pwf=25%Po+20%Po=45%Po.
From the above two modes, the energy consumption analysis can conclude that when the working mode with energy feedback is used for routine aging, the energy consumed is only 0.45 of the working energy. Compared with the routine aging without energy feedback, the total energy consumption is 1.25 times the working energy. Therefore, the routine aging mode with energy feedback saves energy.
3 System Implementation
From the analysis of the above two working modes, energy feedback can be used to form an energy circulation system to reduce energy consumption. The system operation can be illustrated by Figure 4, which includes three parts:
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Figure 4 Schematic diagram of energy feedback system implementation |
a) The power supply part provides an external excitation source for the system;
b) The converter part is a power supply device that needs routine aging, which converts the input power supply voltage into the required output voltage;
c) The energy feedback part can convert the output voltage of the converter into the input voltage of the converter.
The energy feedback part and the converter that needs routine trial form an energy circulation system. Under the excitation of the external power supply, the system maintains the rated power operation. According to the power formula P=U*I, U is stable by the power converter that needs routine aging. To ensure the rated power, it is necessary to ensure the output current I, that is, the energy feedback part is designed as a constant current circuit. Therefore, the equivalent control quantity that ensures the stable operation of the energy cycle under the rated power is the output current of the power converter that needs routine use.
In the energy feedback part, the above requirements must be achieved to ensure the stable output current of the power converter. The current sensor is used to detect the output current of the power converter. At the same time, the feedback part adopts the inverse proportional coefficient relationship between the feedback voltage and the output control current, that is, Uf∝K/Io. For the convenience of analysis, the power supply voltage Ui is set as a stable value. When the output current is small, by adjusting the feedback voltage to make it larger, the voltage difference △U=Uf-Ui between the feedback voltage and the input becomes larger, and the corresponding current flowing from the feedback voltage to the input voltage increases, resulting in an increase in the corresponding feedback power; when the output current is large, by adjusting the feedback voltage to make Uf smaller, the voltage difference △U between the feedback voltage and the input becomes smaller, and the corresponding current flowing from the feedback voltage to the input voltage decreases, resulting in a decrease in the power of the cycle; the whole process maintains negative feedback control, and finally reaches a dynamic balance to maintain the set rated power.
4 Feedback Design
From the above analysis of the energy feedback system, it can be seen that the energy feedback part provides the necessary guarantee for the stable operation of the system. The composition of the energy feedback part can be shown in Figure 5, which mainly includes seven components: input part, power conversion part, output part, sampling, reference, comparator and controller.
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Figure 5 Energy feedback composition block diagram |
a) The input part is to filter the input electric energy and provide auxiliary working power for the controller circuit;
b) The power conversion part is mainly to convert the input electric energy into the required electric energy under the control of the controller;
c) The output filter part is mainly to filter the output electric energy of the power conversion part;
d) The sampling part is mainly to provide a sampling signal with a linear relationship with the output for the output electric energy sampling;
e) The reference part provides a stable reference value for comparison;
f) The comparator compares the sampling signal with the reference signal to generate an error signal between the two;
g) The controller part is to give a control signal to the power conversion part according to the error signal provided by the comparator.
For the circuit topology of the power conversion part, buck type or boost type and various circuit forms derived from it can be selected according to the power size and conversion voltage. The controller can choose a special control chip or a general processing chip to achieve the control required above.
5 Test process and results
According to the design requirements of the feedback part mentioned above, a DC converter with a conversion voltage of 48V to 200V and a power of 180W is used as the converter 1 that needs routine aging. The converter 2 circuit for energy feedback mainly includes two main parts: power conversion part and controller part. The push-pull conversion circuit and full-bridge rectifier circuit are used in the power conversion part. The controller uses the fixed frequency, current mode PWM control chip 3846 of UNITRODE, and its internal circuit diagram consists of an oscillator, an error amplifier, a reference source, a latch, a totem output, etc. Its main features are: cycle-by-cycle current limitation, support for slow start, differential current detection amplification, an operating frequency of up to 500, a peak totem output of 500, and undervoltage lockout, which is relatively convenient for peripheral function setting. According to the above system design, according to routine aging.
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Figure 6 Comparison of test results |
The output power of converter 1, the corresponding power consumption of the test system, and the power consumption in the mode without power feedback are compared. The comparison results are shown in Figure 6. It can be seen from the figure that in the normal working mode, the power consumption is greater than the output power, and it rises rapidly with the increase of output power; for the mode with energy feedback, the system power consumption is less than the working cycle power. Before the output power is 100W, the growth rate of the curve is large. After the output power is greater than 100W, the growth rate of the curve is small and has a certain convergence trend.
Result analysis: In the normal working mode, the fluctuation of the curve is caused by the conversion efficiency of the power converter. From the previous principle analysis, it can be seen that the power consumption is Pi=Po+Pw. If the conversion efficiency is, then Pi=Po/η. The conversion efficiency η usually fluctuates with the change of output power, so the fluctuation of the curve is consistent with the theoretical analysis; in the working mode with feedback, the power consumption of the system is Pi=Pw+Pwf according to the previous principle analysis. Let the conversion efficiency of converter 1 be η1 and the conversion efficiency of the feedback part be η2, then the power consumption of the system is:
6 Conclusion
The aging energy saving implementation method based on energy cycle has obvious energy-saving effect, can greatly reduce the power consumption of the power aging process, and essentially solve the problem of high energy consumption of power aging equipment. It is conducive to reducing the production cost of production enterprises, improving the level of enterprise production modernization, and contributing to national energy conservation and consumption reduction.
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