A study on improvement Efficiency of Shared Reactor by Polyphase Switching Method

Transcription

1 Volume 118 No , ISSN: (printed version); ISSN: (on-line version) url: ijpam.eu A study on improvement Efficiency of Shared Reactor by Polyphase Switching Method Lim Sang-Kil* 1,Park Seong-Mi 2,Jung-Hwan Lee 3, Park Sung-Jun 4, 1,3,4 Chonnam National University,77, Buk-gu, Gwangju,61186, Korea 2 Korea Lift College, 120,Unjeong-ro,geochangeup, Gyeongnam, , Korea sklim@epskorea.kr 1,seongmi@klc.ac.kr 2 sjpark1@jnu.ac.kr 3, Corresponding author* Phone: February 4, 2018 Abstract Background/Objectives: In the modern society, the power generation capacity is gradually increasing due to the trend of increasing the capacity of power generation facilities. Because of this increase in DC-type power generation capacity, research on large-capacity DC / DC power converters is urgently needed. Methods/Statistical analysis: Recently researches on various energy sources including renewable energy sources are being actively carried out. Such energy sources have been developed in a way that the number of energy sources that are developed in the form of direct current from AC increase. A new type of polyphase switching DC / DC converter topology with reactor sharing is verified through simulation and experiment

2 Findings:Inductors, switches, and diodes are connected in parallel for high capacity. However, the output capacitor is actively studied for a common multiphase DC / DC power converter. These multiphase DC / DC power converters share the output capacitor, so the ripple of the output voltage can be reduced, but ripple reduction of the inductor is difficult. Therefore, this paper proposes a new concept DC / DC power converter that can share inductor and output capacitor by using polyphase switch. Improvements/Applications:The proposed DC / DC power converter has the structure to increase the active switching frequency of the output capacitor as well as increase the active switching frequency of the output capacitor, so that the inductor current ripple can be reduced and the capacity of the inverter can be reduced. Key Words:Polyphase switch, DC/DC Converter, switching frequency, battery, reactor sharing 1 Introduction Demand for large capacity DC / DC power converters is rapidly increasing at the present time as the use of various energy sources, including renewable energy sources and the transmission of power such as DC transmission and distribution, are increasing. In order to increase the capacity of the power converter, it is necessary to increase the capacity of the switch device. In general, as the switch capacitance increases, the switching frequency limit of the switch decreases, resulting in a relatively large inductor value. In order to solve the problem of the switching frequency of the high capacity DC / DC power converter, the switch and the diode are connected in parallel, but the output capacitor is actively studied for the common multiphase DC / DC power converter 1. Multiphase DC / DC power converters have the advantage of reducing output voltage ripple because they share an output capacitor, but complex driving methods such as a parallel operation algorithm for sharing the same load caused by parallel operation are required 2. In particular, in the case of a bidirectional polyphase DC / DC power converter, there is a problem that a circulating current problem may occur when the load sharing algorithm is applied incorrectly. In addition,

3 multiphase DC / DC power converters share the output capacitor, but the inductor is used independently, so it is known that inductor ripple reduction and hysteresis loss reduction are difficult to expect 3. In this paper, we propose a new concept DC / DC power converter and a switching algorithm for power converter that can share inductor and output capacitor and increase equivalent switching frequency of inductor and output capacitor because polyphase switch is used. In order to verify the feasibility of the proposed method, we applied it to the bi - directional charger for ESS of 50k [VA] class micro-grid and verified its superiority. 2 Power converter configuration for increasing active switching frequency and switching algorithm 2.1 Interleaved DC / DC Power Converter In Figure 1, it shows the interleaved DC / DC power converter configuration diagram. Figure (a) shows the uni-directional interleaved power converter and Figure (b) shows the bidirectional interleaved power converter. Fig.1. interleaved DC/DC power converter (a) uni-directional interleaved DC/DC converter(b) bi-directional interleaved DC/DC converter As shown in Figure 1 (a), which is a conventional 2-phase stepup DC / DC power converter, switches, diodes and inductors are connected independently to each power converter, but the input, output terminals, and output capacitors are commonly used. The multi-phase step-up DC / DC power converter can be defined as a

4 parallel control of a single step-up DC / DC power converter, and the input / output characteristics according to the time ratio are the same as those of a single step-up DC / DC power converter. As a way to maximize the parallel operation effect, the input voltage is boosted by controlling the interleaved method to increase the active switching frequency on the input / output side45. Multiphase boost DC / DC power converters can reduce the current rating and current stress of the device by connecting the input currents in parallel and transferring power5-7. Also, since the input currents are superimposed on the input current of each single step-up DC / DC power converter, the input current ripple can be reduced and the resulting output voltage ripple can be reduced. The same magnitudes of Input current ripple like a single-phase step-up DC / DC power converters can be obtained even if the inductor size is reduced by half. Especially at a specific application rate, ripple size smaller than the output voltage and current ripple size of a singlephase step-up DC / DC power converter can be obtained8-10. In Figure 1 (b), it shows the configuration of a bidirectional interleaved DC / DC power converter. In Figure 1 (b), it shows a case where the diode is replaced with a switching element in order to feed power in both directions in Figure 1 (a). The differences in this method are as follows. Unidirectional interleaved DC / DC power converters are designed to transfer power in one direction only by diodes. The role of the diodes is to take charge of both power transfer and reverse power blacking, but bi-directional interleaved DC / DC power converters, in order to improve the quick response in the direction of sending and receiving, the upper switch and the lower switch are switched by the interlock function, which requires a dead time between the switches. Unidirectional interleaved DC / DC power converters should be interpreted as a continuous or discontinuous mode of inductor current, but bi-directional interleaved DC / DC power converters switch the top and bottom switches by interlock function so that only the characteristics of unidirectional interleaved power converter s continuous current mode are present. Unidirectional interleaved DC / DC power converters do not generate circulating currents by diodes, but bi-directional interleaved DC / DC power converters can generate circulating currents. Based on the above, the interleaved DC / DC power converter has the advantage of reducing the output voltage and current ripple due to

5 the sharing of input and output capacitors. However, it has various disadvantages of the complexity such as parallel operation and load sharing algorithm, and the hysteresis loss problem due to the current ripple reduction limit. 2.2 Switch interleaved DC/DC converter In Figure 2, it shows the proposed switch interleaved DC / DC power converter structure to overcome the disadvantages of interleaved DC / DC power converters. As shown in the figure, the proposed switched interleaved DC / DC power converter architecture takes the form of a switching element in parallel with a bidirectional half-bridge DC / DC power converter. In a bidirectional half-bridge DC / DC power converter with switching elements connected in parallel, the parallel switches connected to the upper and lower arms simultaneously turn on and off. However, the switch interleaved DC / DC power converter proposed in this paper, only one switch is turned on and off each time. That is, in the parallel-type bidirectional half-bridge DC / DC power converter of the switching device, the switch is configured in parallel to increase the rated current, but the proposed switch interleaved DC / DC power converter has the switches arranged in parallel to increase the active switching frequency. In addition, the proposed topology is characterized in that it can operate as a switching device parallel-type bidirectional half-bridge DC / DC power converter according to the need of increasing the switch capacity

6 Fig. 2. Switch interleaved DC/DC power converter Fig. 3. Two-Switch interleaved DC/DC power converter In Figure 3, it shows a switched interleaved DC / DC power converter using two parallel switches. In the switch interleaved DC / DC power converter of Figure 3, when the upper switch is on, the arm voltage (Varm) becomes the output voltage (Vout), and when the switch below is turned on, the arm voltage becomes zero. In each arm voltage domain time, the two switches are turned on for half of the time, and each turn-on time is 180 out-of-phase, taking twice the active switching frequency. In order to prevent an arm short circuit, when the upper arm group and the lower arm group have to be interlocked with each other, there is a restriction condition that only one switch should be turned on in each

7 group. Under the above constraint, the equivalent circuit of the fourswitchmodesare shown in Fig 4. Fig. 4. Two-Switch interleaved DC/DC power converter Figure 4 (a) shows the area where the arm voltage appears as zero voltage by SW1 switch on. Figure 4 (b) shows the area where the arm voltage appears as the output voltage by SW4 switch-on. Figure 4 (c) shows the area where the arm voltage appears as zero voltage due to SW2 switch on. Figure 4 (d) shows the area where the arm voltage appears as the output voltage due to SW3 switchon. In Figure 4, each switch switches once, but the arm voltage cycle appears twice. Therefore, the arm voltage is twice as high as the switching frequency. 2.3 Proposed Switching Algorithm Figure 5 shows the analysis of the 2-switch interleaved switching pattern based on the mode equivalent circuit of Fig

8 Fig. 5. Two-switch interleaved switching pattern As shown in Fig. 5, when the input / output voltage ratio to be controlled is determined, the controller generates the PWM signal corresponding to the duty ratio. One pair of switches is responsible for one cycle of the first PWM signal (Te), and next pair of switches is responsible for next cycle of the next PWM signal. Thus, the two PWM periods become one cycle (Tt) in the switch position. That is, the upper arm switch and the lower arm switch pair take charge as a reference based on the half period (Td) of the whole cycle Tt of the switch element

9 Fig. 6. Two-switch interleaved switching generation techniques Figure 6 shows the waveform for generating the actual signal at the specified rate as shown in Fig 5. The PWM waveform is generated by a counter and a comparator, and is generated by using the PWM function of the DSP in this paper. There are two compare registers in the DSP. One counter stores the counter value corresponding to the duty ratio time (Td), and the other compare register stores the counter value corresponding to half of the switching period (Te). Then, when the Action is defined as shown in the figure, it occurs as SW1, SW2, SW3, and SW4 as shown in Fig 6. 3 Simulation and Experimental Results 3.1 Simulation results In order to verify the feasibility of the proposed switch interleaved scheme compared with the conventional scheme, a simulation circuit diagram using Psim is shown in Fig 7. The simulation results show that the switch interleaved method under the same switching frequency as the conventional method can reduce the inductor current ripple by half while maintaining the same average current

10 as the conventional method. Therefore, the proposed method can reduce the inductor value by half compared with the conventional method. Fig. 7. Simulation circuit diagram Fig. 8. Simulation results 3.2 Experimental Results Figure 9 shows the system configuration for micro-grid. The system consists of a switch interleaved converter, a generator charging converter, a solar converter, and a three-phase inverter

11 Fig [kVA] Micro-gird system Figure 10 plots the proposed converter gate signal. As can be seen in Fig. 10 (a), it can be observed that the gate signals are sequentially generated in good order. SW1 and SW4, and SW2 and SW3 in the gate signals use PWMA and PWMB to set their own dead time in the DSP, but SW1 and SW3, and SW2 and SW4 can not set their own dead time so that the function is realized by programming. In this paper, the PWM counter comparison value is implemented as shown in Fig. 6, and it can be seen that the PWM counter comparison value satisfies 4u [sec] as shown in Fig. 10 (b). Fig. 10. Switch interleaved gate signal Figure 11 shows the waveforms of the gate waveform, inductor current, and arm voltage for analyzing the characteristics of the

12 proposed converter characteristics. Figure 11 (a) is a waveform for verifying that the applied frequency of the inductor is twice the switching frequency. As can be seen in the figure, it can be witnessed that the twice frequency of the switching frequency appears at the arm voltage, and as a result, the frequency applied to the inductor is twice as high as the switching frequency. Figure 11 (b) and (c) are waveforms showing the start and stop characteristics of the converter. As shown in the figure, a smooth current is generated when starting and stopping. Fig. 11.The characteristics of proposed converter Figure 12 shows the bidirectional characteristics of the converter and waveforms to compare the current ripple with the conventional converter. This waveform is a case where the power generated from PV is supplied while supplying power to the 3-phase inverter using the converter proposed in the battery. From this waveform, DC Link voltage, which is the output of the converter, the DC current supplied to the inverter, the current of the converter, and the current of the PV converter are presented. As shown in the figure, during the process of transferring power from the battery side to the load side, when the power is supplied by the operation of the PV converter, the battery converter changes the direction of the current and switches its mode of charging the power. Figure 12 (b) enlarges the waveform of the rectangular box section in the normal state in Figure 12 (a). It is confirmed that the current ripple of the proposed switch interleaved battery charger converter can be the half of the current ripple of the conventional converter

13 Fig. 12.Proposed converters linkage characteristics 4 Conclusion In the modern society, the demand for large capacity DC / DC power converters is rapidly increasing due to the use of various DC power sources such as solar power and the increase of power transmission methods such as DC transmission and distribution. For high capacity DC / DC power converter configuration, it is implemented by power converter parallel drive. Particularly, in order to emphasize the advantages of parallel driving, researches on interleaved multiphase DC / DC power converters are actively conducted. Since the multiphase DC / DC power converters share the input / output capacitors, the ripple of the input / output voltage can be reduced. However, since each converter uses independent inductors, it is difficult to reduce the inductor current ripple. Therefore, in this paper, we proposed a DC / DC power converter topology applying a novel polyphase switch concept that can share inductors and input / output capacitors. As a result of the study on the proposed topology, the following results were obtained. - Unlike the parallel driving method, the proposed method requires only one inductor with the switch elements sharing the inductor. - In the proposed method driven by the polyphase switching method, the active switching frequency applied to the inductor is multiplied by the switching frequency of each switch and the number of parallel switches, thereby reducing the inductor ripple

14 - It is advantageous to increase the switch capacity when the operation mode is changed by driving the parallel switch in the gate signal of the proposed polyphase switch method. - In the case of a bidirectional DC / DC power converter, the conventional parallel driving method has a disadvantage in that a circulating current may be generated, but the proposed multiphase switching method has an advantage of not generating a circulating current. From the above results, the proposed multiphase switching scheme increases the active switching frequency in the configuration of large capacity DC / DC power converter, and greatly reduces the inductor and input / output smoothing capacitor capacity so that it is expected that the power converter will be applied actively in industry because it is excellent in economical aspect and size. Acknowledgment Research and Development for Regional Industry - This research was financially supported by the Ministry of Trade, Industryand Energy(MOTIE) and Korea Institute for Advancement oftechnology(kiat) through the Research and Development for RegionalIndustry References [1] Bor-Ren Lin, Chung-Wei Chu, DC/DC converter with parallel input and parallel output with shared power switches and rectifier diodes, IET Power Electronics, Vol. 8, No. 5, pp , April [2] Le An, Dylan Dah-Chuan Lu, Analysis of DC Bus Capacitor Current Ripple Reduction in Basic DC/DC Cascaded Two-Stage Power Converters, IEEE Transaction on Industrial Electronics, Vol. 63, Issue. 12, pp , [3] Katsuyoshi Takeo, Yukihiro Ota, Shigenori Suziki, Fumihito Toyota, Multi-Layer Power Inductor and DC/DC Converter, Power Electronics Systems and Applications, ICPESA 06. 2nd International Conference on, pp ,

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