Smart Time-Division-Multiplexing Control Strategy for Voltage Multiplier Rectifier

Smart Time-Division-Multiplexing Control Strategy for Voltage Multiplier Rectifier Bin-Han Liu, Jen-Hao Teng, Yi-Cheng Lin Department of Electrical Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan Abstract- A novel 4-times voltage multiplier rectifier with smart Time-Division-Multiplexing (TDM) control strategy for high step-up converters is proposed in this paper. Based on the proposed TDM control strategy, two full-wave voltage doubler rectifiers can be combined to realize the proposed 4-times voltage multiplier rectifier. The novel 4-times voltage multiplier rectifier and TDM control strategy can reduce transformer turn ratio and transformer size for high step-up converters and also reduce voltage stress for the output capacitors and rectifier diodes. Simulations and experiments are conducted in this paper to validate the proposed 4-times voltage multiplier rectifier with smart TDM control strategy for high step-up converters. The results show that the proposed smart TDM control strategy has great potential to be used in high step-up converters. Keywords - Voltage Multiplier Rectifier, Time Division Multiplexing, Full-wave Voltage Doubler, Voltage Stress. I. INTRODUCTION conversion of renewable energy into electricity not only improves electricity generation but also reduces the world energy-related CO 2 emissions. Consequently, Renewable Energy Generation Systems (REGSs) have continued to build up its share of the global electricity market. Photovoltaic Generation (PVG) has enabled new projects and therefore brought PV much closer to full competitiveness with fossil fuel alternatives. The cumulative capacity of installed PVGs worldwide was around 184GW until the end of 2014. Furthermore, with the sharply reduced cost of PVGs, it is expected that at least a 4-5% increase in PVG market growth can be reached in the next few years [1-2]. Therefore, new power converters designed for the special output characteristics of PVGs cannot only increase the practicability of PVGs but also make the PV industry more competitive. This work was supported in part by National Science Council of Taiwan under Contract MOST 105-3113-E-214-002 One of the special output characteristic of PVGs is that the output voltage is usually lower than 48V. Meanwhile, 200/380V DC-bus voltages are necessary in a single-phase full-bridge inverter used in PVG to interconnect to the 110/220V AC grid. Particularly, 760V DC-bus voltage might be usually required in the half-bridge inverter, neutral point clamp inverter and so on. Although the PV panels are usually series connected to generate sufficient voltage to prevent high step-up voltage conversion, the independent converter applied to each PV panel can be used to maximize the output power during partial shading and to reduce the panel hot-spot risk [3-4]. For the independent converter applied to each PV panel, high step-up converter is essential. Generally, large voltage conversion ratio can be realized by using transformer. The conventionally employed voltage-fed and current-fed converters with higher transformer turn ratio are not the best candidates for the high step-up applications. Higher transformer turn ratio often results in larger transformer size, larger leakage inductance, more complicated transformer design and so on, which might also cause higher voltage stress on diodes and output capacitors and lower switching frequency. Therefore, the voltage doubler rectifiers such as half-wave and full-wave voltage doubler rectifiers are better choices for high step-up application because its output voltage is twice that of the transformer secondary winding. Accordingly, the transformer turn ratio can be halved [5-16]. This paper proposes a novel 4-times voltage multiplier rectifier for high step-up converters. The control strategy designed for the proposed 4-times voltage multiplier rectifier is based on Time-Division-Multiplexing (TDM) principle. The smart TDM control strategy is used to transfer energy to the output capacitors at different time intervals. With the smart TDM control strategy, two full-wave voltage doubler circuits can be combined to realize the proposed 4- times voltage multiplier rectifier. The novel 4-times voltage multiplier rectifier and TDM control strategy can reduce 978-1-5090-0806-3/16/$31.00 copyright 2016 IEEE ICIS 2016, June 26-29, 2016, Okayama, Japan

transformer turn ratio and transformer size for high step-up converters and also reduce voltage stress for the output capacitors and rectifier diodes. Diodes and capacitors with lower rated voltage can be adopted in the proposed rectifier and it usually means that better switching characteristics can be achieved. A full-bridge converter is adopted in the primary side of the proposed 4-times voltage multiplier rectifier to realize a full-bridge quadrupler converter. A proposed full-bridge quadrupler converter with specifications of input DC voltage of 48V, output DC voltage of 200V and rated power of 150W is designed and implemented in this paper. Simulations are conducted in this paper to validate the proposed 4-times voltage multiplier rectifier with smart TDM control strategy and to compare the voltage stress of each circuit component. Experiments are used to verify the performances of the proposed fullbridge quadrupler converter. Simulation and experimental results demonstrate that the proposed TDM control strategy has great potential to be used in high step-up converters of REGSs. [12-16]. For example, a Symmetrical Voltage Quadrupler Rectifier (SVQR) as shown in Fig. 3 derived from the halfwave voltage doubler was proposed in [12]. The output voltage of SVQR is four times of the conventional fullbridge voltage rectifier, which helps to reduce the turns of the secondary winding and decrease the parasitic parameters of the transformer. Fig. 1: Half-wave Voltage Doubler Rectifier II. BASIC CONCEPTS OF VOLTAGE MULTIPLIER RECTIFIERS Fig. 1 illustrates the circuit configurations of half-wave voltage doubler rectifier. Assuming the value of secondary winding voltage can be +V S, V S, and zero in one switching cycle. From Fig. 1(a), it can be observed that the energy in the negative half-cycle voltage of secondary-side transformer is transferred to the capacitor C m and then the voltage of C m reach V S. In the positive half-cycle voltage of secondary-side transformer as illustrated in Fig. 1(b), energy from the secondary-side transformer and capacitor C m are transferred to the output capacitor C O and then the voltage of C O reaches 2V S. Fig. 2 shows the circuit configuration of full-wave voltage doubler rectifier. Figs. 2(a) and 2(b) show that energy transferred to output capacitors C O2 and C O1 in the negative and positive half-cycle voltages of secondaryside transformer, respectively. The voltages of C O2 and C O1 both reach V S and then the output voltage is 2V S by superposition. Although, higher step-up voltage ratio can be realized by adopting voltage doubler rectifiers, the voltage stresses of the diodes in the rectifiers are equal to the output voltage and are still high. Therefore, some state-of-the-art voltage multiplier circuits, such as the M-type voltage multiplier, Dickson-type voltage multiplier and Cockcroft Walton voltage multiplier and so on, are proposed to reduce either the diode voltage stresses or the capacitor current stresses Fig. 2: Full-wave Voltage Doubler Rectifier Fig. 3: Symmetrical Voltage Quadrupler Rectifier III. PROPOSED VOLTAGE MULTIPLIER RECTIFIER A novel 4-times voltage multiplier rectifier derived from full-wave voltage doubler rectifier is proposed in this paper. Fig. 4 illustrates the basic concepts of proposed novel 4-times voltage multiplier rectifier. From Fig. 4, it can be observed that two full-wave voltage doubler rectifiers are combined to construct the basic circuit configuration. The smart TDM control strategy is designed to transfer and store energy to the rectifier diodes and output capacitors at different time intervals. Each voltage of output capacitor as shown in Fig. 4 can almost achieve equalizing voltage and then 4-times output voltage can be realized because of the superposition of the output capacitor voltages.

Fig. 5(a) and 5(b) shows the smart TDM driving signals and the circuit configuration of proposed voltage multiplier rectifier, respectively. Four switches (Q 5 Q 8 ) constructing the TDM control circuit are used to coordinate with the smart TDM control signals. Fig. 6 illustrate the operational process when switches Q 5 and Q 6 are in the ON state. From Fig. 6(a) and 6(b), it can be seen that energy are transferred to output capacitors C O1 and C O2 in the positive and negative half-cycle voltages of secondary-side transformer, respectively. The voltages of C O1 and C O2 can both reach V S. Similarly, the voltages of C O3 and C O4 also can both reach V S when switches Q 7 and Q 8 are in the ON state. Accordingly, each voltage of output capacitor can reach V S and 4-times voltage multiplier can then be realized because of the superposition of the output capacitor voltages. SIMetrix/SIMPLIS [17] is used to simulate the circuit as shown in Fig. 5 to demonstrate the validity of the proposed 4-times voltage multiplier rectifier and smart TDM control strategy and to compare the voltage stress of each circuit component. The voltage magnitude of V S is set 50V. Fig. 7 shows the simulation results for output capacitor voltages and output voltage. From Fig. 7 (a), it can be seen that each voltage of output capacitor can almost achieve equalizing voltage. Fig. 7(b) shows that 4-time voltage multiplier, i.e. 200V, can be obtained. Therefore, the validity of proposed 4-times voltage multiplier rectifier and smart TDM control strategy can be demonstrated. The output voltage of proposed rectifier is 2-times of the half-wave and full-wave voltage doubler rectifiers. Therefore, the turn ratio of transformer winding can be further reduced. Fig. 7: Smart TDM Driving signal and Circuit Configuration Fig. 4: Basic Concepts of Proposed Voltage Multiplier Rectifier Fig. 5: Smart TDM Driving Signals and Circuit Configuration Table I compares the performances of the proposed 4- times voltage multiplier rectifier with SVQR as proposed in [12]. From Table I, it can be observed that the proposed rectifier and SVQR have same performances on diode number, capacitor number, diode voltage stress and diode current stress. However, lower output capacitor voltage stress can be realized by the proposed rectifier. Diodes and capacitors with lower rated voltage usually means better switching characteristics and conversion efficiency. The disadvantage of the proposed rectifier is four additional switches (Q 5 Q 8 ) have to be used to construct the TDM control circuit. In order to reduce switching losses induced by the four additional switches (Q 5 Q 8 ), different TDM driving signals can be applied to the TDM control circuit. Fig. 6: Smart TDM Driving signal and Circuit Configuration For example, another smart TDM driving signals is shown in Fig. 8. From Fig. 8, it can be seen that the switching frequency for switches (Q 5 Q 8 ) in TDM control circuit can be decreased. If the voltage frequency in the secondary-side transformer is 50kHz, then the switching frequencies for switches (Q 5 Q 8 ) in Fig. 5(a) and Fig. 8 are 25kHz and 12.5kHz, respectively. Because of lower switching frequency, lower-cost switches can be utilized in

the TDM control circuit. The special characteristic of the proposed smart TDM control strategy is that a N-times voltage multiplier rectifier can be extended straightforwardly. Fig. 9 is the circuit configuration of the proposed N-times voltage multiplier rectifier. The TDM driving signals can be easily modified from Figs. 5(a) and Figs. 8 and are not shown here due to limited space. Consequently, the proposed rectifier and smart TDM control circuit can be extend to construct a N-times voltage multiplier rectifier without extra burden. TABLE I PERFORMANCE COMPARISONS OF PROPOSED RECTIFIER AND SVQR Multiplier Rectifier Proposed Rectifier SVQR[12] Diode Number 4 4 Capacitor Number 4 4 Diode Voltage Stress V out /2 V out /2 Diode Current Stress I out I out Output Capacitor Voltage Stress V out /4 V out /2 Potential for N-times Voltage Multiplier Yes No where V out and I out are output voltage and output current, respectively. As a simple example, a conventional full-bridge converter is adopted in the primary side of the proposed 4- times voltage multiplier rectifier to construct a full-bridge quadrupler converter. Fig. 10 illustrates the circuit configuration of the proposed full-bridge quadrupler converter. In Fig. 10, switches (Q 1 Q 4 ) are the main switches for the conventional full-bridge converter and switches (Q 5 Q 8 ) are used for TDM control circuit. Fig. 11 shows the theoretic key waveforms for the proposed fullbridge quadrupler converter. From Figs. 10 and 11, it can be easily observed that the output capacitor voltages can be expressed as n V = V = V = V = V D (1) 2 CO1 CO2 CO3 CO4 in n1 where V C Oi is the voltage of output capacitors C Oi ; V in is the input voltage; n 1 and n 2 are the transformer winding turns for primary side and secondary side, respectively; D is the duty cycle of the driving signals for the conventional full-bridge converter. The output voltage can be calculated by superposition and be written as: Fig. 8: Another Smart TDM Driving Signals V = V + V + V + V (2) Out CO1 CO2 CO3 CO4 where V Out is the output voltage. Therefore, the voltage gain of the proposed full-bridge quadrupler converter can be derived by V V Out in n2 D = 4 (3) n 1 The specifications of input DC voltage of 48V, output DC voltage of 200V, and rated power of 150W are designed and implemented in this paper. Table II lists the parameters of the proposed full-bridge quadrupler converter. Microchip dspic33fj16gs504 [18], is used to realize a fullydigitalized controller. Fig. 12 illustrates the driving signals for Q 1, Q 2, Q 5, and Q 7. From Fig. 12, the proposed smart TDM driving signals can be confirmed. Fig. 9: Proposed N-times Voltage Multiplier Rectifier IV. EXPERIMENTAL RESULTS AND DISCUSSIONS Fig. 13 shows the output capacitor voltages. It can be observed from Fig. 13, almost same voltage, i.e. 50V in this example, for each capacitor voltage can be achieved.

Therefore, 4-times voltage gain, that is output voltage 200V as shown in Fig. 14, can be attained by the proposed fullbridge quadrupler converter. (V GS1, V GS2, V GS5, V GS7 :20V/div; time:4 s/div) Fig. 12: Driving Signals for Q 1, Q 2, Q 5, and Q 7 Fig. 10: Proposed Full-bridge Quadrupler Converter (V Co1, V Co2, V Co3, V Co4 :20V/div; time:10 s/div) Fig. 13: Output Voltage of each Capacitor (V Out :100V/div, time:10 s/div) Fig. 14: Output Voltage V. CONCLUSIONS Fig. 11: Key Waveforms of Proposed Full-bridge Quadrupler Converter TABLE II PARAMETERS OF PROPOSED FULL-BRIDGE QUADRUPLER CONVERTER Input Voltage 48V Output Voltage 200V Rated Power 150W Switching Frequency of Full-Bridge Converter 50kHz Switching Frequency of TDM Control Circuit 25kHz Q 1 Q 2 Q 3 Q 4 IRFP4227PbF Q 5 Q 6 Q 7 Q 8 SPW35N60CFD D O1 D O2 D O3 D O4 DHG30I600HA C O1 C O2 C O3 C O4 330 F 4 Transformer Turn Ratio (n 2 /n 1 ) 1.7 A novel 4-times voltage multiplier rectifier with smart TDM control strategy for high step-up converters was proposed in this paper. Based on the proposed TDM control strategy, two full-wave voltage doubler circuits can be combined to realize the proposed 4-times voltage multiplier rectifier. The output voltage of proposed rectifier is 2-times of the half-wave and full-wave voltage doubler rectifiers. The extension of proposed TDM control strategy for N- times voltage multiplier rectifier was also introduced in this paper; therefore, the proposed smart TDM control strategy has great potential to be used in high step-up converters. Other issues such as integrating the proposed N-times voltage multiplier rectifier into phase-shifted full-bridge converter and dual boost converter to realize isolated and non-isolated high step-up converters will be discussed and implemented in the future.

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