Power Factor Corrector with Bridgeless Flyback Converter for DC

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Nov 9, 2018 - converters: DC/DC converter with battery source and power factor corrector ... Keywords: bridgeless flyback converter; PFC; active clamp circuit; ...
energies Article

Power Factor Corrector with Bridgeless Flyback Converter for DC Loads Applications Sheng-Yu Tseng * , Po-Jui Huang and Dong-Heng Wu Department of Electircal Engineering, Chang Gung University, Tao-Yuan 33302, Taiwan; [email protected] (P.-J.H.); [email protected] (D.-H.W.) * Correspondence: [email protected]; Tel.: +886-3-2118800 (ext. 5706) Received: 30 August 2018; Accepted: 5 November 2018; Published: 9 November 2018

 

Abstract: Since power systems with a DC distribution method has many advantages, such as conversion efficiency increase of about 5–10%, cost reducing by about 15–20% and so on, the AC distribution power system will be replaced by a DC distribution one. This paper presents a DC load power system for a DC distribution application. The proposed power system includes two converters: DC/DC converter with battery source and power factor corrector (PFC) with a line source to increase the reliability of the power system when renewable energy or energy storage equipment are adopted. The proposed PFC adopts a bridgeless flyback converter to achieve power factor correction for supplying power to DC loads. When the bridgeless flyback converter is used to achieve PFC, it needs two transformers to process positive and negative half periods, respectively. In order to increase conversion efficiency, the flyback one can add two sets of the active clamp circuit to recover energies stored in leakage inductances of transformers in the converter. Therefore, the proposed bridgeless flyback converter can not only integrate two transformers into a single transformer, but also share a clamp capacitor to achieve energy recovery of leakage inductances and to operate switches with zero-voltage switching (ZVS) at the turn-on transition. With this approach, the proposed converter can increase conversion efficiency and decrease component counts, where it results in a higher conversion efficiency, lower cost, easier design and so on. Finally, a prototype with a universal input voltage source (AC 90–265 V) under output voltage of 48 V and maximum output power of 300 W has been implemented to verify the feasibility of the proposed bridgeless flyback converter. Furthermore, the proposed power system can be operated at different cases among load power PL , output power PDC1 of DC/DC converter and output power PDC2 of the proposed PFC for supplying power to DC loads. Keywords: bridgeless flyback converter; PFC; active clamp circuit; ZVS; DC distribution

1. Introduction Since power systems with a DC distribution method has many advantages, such as conversion efficiency increase of about 5–10%, cost reducing by about 15–20% and so on, the AC distribution power system will be replaced by a DC distribution one [1]. Figure 1 shows a block diagram of a power system for DC load applications. The power sources of the power system can adopt utility line, solar arrays, battery or wind turbine, etc. The power system using a power processor is widely applied to the general electrical or electronic equipment. In order to obtain a lighter weight and a smaller volume, a switching-mode converter is regarded as the power processor of the power system. When a power factor corrector (PFC) is used for the AC/DC power system [2–12] to protect the line source from harmonic current pollution, it has to meet the recommended limits of harmonics in supply current by various international power quality standards, such as the International Electrotechnical Commission (IEC) 61000-3-2 [2]. Therefore, the AC/DC converter adopts PFC techniques to increase Energies 2018, 11, 3096; doi:10.3390/en11113096

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converter. Therefore, the topology of two stages is used to achieve a lower output voltage, resulting in a higher cost and a lower conversion efficiency. Single stage topology with buck-boost converter has been an alternative solution in various power conversions. In order to further increase the stepdown ratio, a bridgeless flyback converter is regarded as the power processor because of its topological advantages, such as simple circuit structure, low cost, and galvanic isolation, as depicted Appl. Sci.2018, 2017,11, 7, 3096 x FOR PEER REVIEW Energies 2 of 20 in Figure 4. It is adopted in not only low power isolated single-stage single-phase AC/DC converters which is regarded as the front end of the switching-mode power supply, but also uninterrupted techniques to increase power factor (PF), in which input voltage waveform can be made to be power supplies (UPS), induction heating, waveform electronic ballast, telecom power supplies, light emitting power factorin(PF), in with which can beapproximately made to be completely in phase completely phase theinput inputvoltage current one, implying unity power factor.with the diode [13–15], etc. approximately unity power factor. inputIndrivers current one, implying general, a boost converter, as shown in Figure 2, or buck-boost converter is adopted in the PFC system. In order to reduce the conduction losses of diodes, a bridgeless boost converter is DC in bus adopted to achieve a higher power factor, as shown Figure 3. Due to the universal input voltage source (AC 90–265 V), its output voltage is regulated at approximately 400 V. For a power system under a lower level output voltage condition, it needs an extra DC/DC converter as a step-down Power Factor Loadresulting converter. Therefore, the topology of two stages is used to achieve a lower output voltage, Corrector DC/DC Converter V in #1converter in a higher cost and a lower conversion efficiency. Single stage topology with buck-boost (PFC) has been anutility alternative solution in various power conversions. In order to further increase the stepline down ratio, a bridgeless flyback converter is regarded as the power processor because of its topological advantages, such as simple circuit structure, low cost, and galvanic isolation, as depicted in Figure 4. It is adopted in not only low power isolated single-stage single-phase AC/DC converters which is regarded as the front end of the switching-mode power supply, but also uninterrupted Loademitting DC/DC Converter power supplies (UPS), induction heating, electronic ballast, telecom power supplies, light DC/AC Inverter Vpv VB #1 (MPPT) diode drivers [13–15], etc. Battery

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In general, a boost converter, as shown in Figure 2, or buck-boost converter is adopted in the PFC Load DC/DC Converter D1 L1 DC/AC Inverter system. V InB order to reduce the conduction losses of diodes, a bridgeless boost converter is Vpv #1 adopted (MPPT) to achieve a higher power factor, as D1shown D3 in Figure 3. Due to the universal input voltage source Battery Solar Arrays M1 (AC 90–265 V), its output voltage is regulated For a power system under a CO 400RLV. V C1at approximately Vin O lower level output voltage condition, it needs an extra DC/DC converter as a step-down converter. D2 D 4 Therefore, the topology of two stages is used to achieve a lower output voltage, resulting in a higher cost and a lower conversion efficiency. Single stage topology with buck-boost converter has been an alternative solution in various power conversions. In order further increase step-down Figure 2. Schematic diagram ofConverter a boost converter for power to factor corrector (PFC)the applications. Load ratio, AC/DC Vw a bridgeless flyback converter is (MPPT) regarded as the power processor Electronic because ofBallast its topological advantages, #1 such as simple circuit structure, low cost, and galvanic isolation, as depicted in Figure 4. It is adopted wind turbine in not only low power isolated single-stage single-phase AC/DC converters which is regarded as the front end of the switching-mode power supply, but also uninterrupted power supplies (UPS), Figure 1. Block diagram of apower power system forlight DC load applications. induction heating, electronic ballast, telecom supplies, emitting diode drivers [13–15], etc.

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flybackconverter converter adopts transformer toregarded be regarded regarded as aa stored stored inductor and an an Since aaaflyback adopts a transformer to beto as a stored inductor and an isolated Since flyback converter adopts aa transformer be as inductor and Since a flyback converter adopts a transformer to be regarded as a stored inductor and an isolated transformer, transformer, leakage inductance exists in the the primary primary side, resulting resulting in aa higher higher voltage transformer, a leakage inductance exists inexists the primary side, resulting in a higher voltage stress isolated aa leakage inductance in side, in voltage isolated transformer, a leakage inductance exists in the primary side, resulting inalimit ahigh higher voltage stress across switches of the converter when switches are turned off. In order to a high voltage across switches of the converter when switches are turned off. In order to limit voltage stress stress across switches of the converter when switches are turned off. In order to limit a high voltage stress across switches of the converter when (RCD) switches are clamp turned off. Inisorder to limit a high voltage stress across switches, a resistor-capacitor-diode (RCD) circuit used to reduce switch voltage across switches, a resistor-capacitor-diode clamp circuit is used to reduce switch voltage spike. stress across switches, a resistor-capacitor-diode (RCD) clamp circuit is used to reduce switch voltage stress across switches, a resistor-capacitor-diode (RCD) clamp circuit is used to reduce switch voltage spike. Although Although the RCDcan circuit can out smooth out the thespike, voltage spike, the energy stored inductance in leakage leakage Although the RCD circuit smooth the voltage the spike, energythe stored in leakage spike. the RCD circuit can smooth out voltage energy stored in spike. Although theclamp RCDto circuit can smooth out the voltagethe spike, theofenergy storedconverter inthe leakage inductance is released the clamp resistor. As a result, conversion efficiency of flyback is released to the resistor. As a result, the conversion efficiency the flyback does inductance is released to the clamp resistor. As a result, the conversion efficiency of the flyback inductance is released to the clamp resistor. As a result, the conversion efficiency of the flyback converter does not increase. For improving conversion efficiency of the one with the RCD clamp not increase. For improving efficiency of theefficiency one with the RCD clamp an clamp active converter does not increase. conversion For improving conversion of the one with circuit, the RCD converter does not increase. For is improving conversion efficiency of the one with the RCD clamp circuit, an active clamp circuit used to replace the RCD clamp circuit, as shown in Figure 5. With clamp circuit is used to replace the RCD clamp circuit, as shown in Figure 5. With this approach, the circuit, an active clamp circuit is used to replace the RCD clamp circuit, as shown in Figure 5. With circuit, an stored active in clamp circuit is used tocan replace the RCD clamp circuit, as shown in Figure 5. With this approach, the energy stored in leakage inductance can be recycled and switches in the converter energy leakage inductance be recycled and switches in the converter can be operated this approach, the energy stored in leakage inductance can be recycled and switches in the converter this approach, the energy stored in leakage inductance recycled and switches in the converter can be operated with zero-voltage switching (ZVS) atcan thebe turn-on transition [16,17]. with zero-voltage switching (ZVS) at the turn-on transition [16,17]. can be operated with zero-voltage switching (ZVS) at the turn-on transition [16,17]. can be operated with zero-voltage switching (ZVS) at the turn-on transition [16,17]. D1 Vin

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Figure 5. Schematicdiagram diagram a bridgeless flyback converter an active clamp circuit for 5. Schematic Schematic diagram ofof bridgeless flyback converter withwith an active active clamp circuit for PFC PFC Figure of aa bridgeless flyback converter with an clamp circuit for Figure 5. Schematic diagram of a bridgeless flyback converter with an active clamp circuit for PFC PFC applications. applications. applications. applications.

When the PFC adopts adopts a bridgeless bridgeless flyback flyback converter, converter, it needs to process power in positive and and When the the PFC PFC it needs needs to to process process power power in in aaa positive positive When adopts aa bridgeless flyback converter, it and When the PFC adopts a bridgeless flyback converter, it needs to process power in a positive and negative half periods of the line source, resulting in that its component counts almost need twofold negative half half periods periods of of the the line line source, source, resulting resulting in in that that its its component component counts counts almost almost need need twofold twofold negative negative half periodscircuit of the[18,19]. line source, resulting in that its than component counts device almostin need twofold of its counterpart circuit Particularly, using more one magnetic the bridgeless of its counterpart [18,19]. Particularly, using more than one magnetic device in the bridgeless of its counterpart circuit [18,19]. Particularly, using more than one magnetic device in the bridgeless of flyback its counterpart circuit [18,19]. Particularly, using more thansimplicity. one magnetic in bridgeless converter impacts the isis the circuit In order to further simplify the flyback converter impacts theadvantage, advantage,which which the circuit simplicity. Indevice order to the further simplify flyback converter impacts the advantage, which is the circuit simplicity. In order to further simplify flyback converter impacts the advantage, which is the circuit simplicity. In order to further simplify circuit structure, two transformers in the bridgeless flyback converter is replaced with a three-winding the circuit circuit structure, structure, two two transformers transformers in in the the bridgeless bridgeless flyback flyback converter converter is is replaced replaced with with aa threethreethe thetransformer, circuit structure, two as transformers the bridgeless converter is replaced with a threeas illustrated in Figure 6.in Furthermore, twoflyback active clamp circuits share a capacitor. It will winding transformer, illustrated in Figure 6. Furthermore, two active clamp circuits share winding transformer, as illustrated in Figure 6. Furthermore, two active clamp circuits share aa winding transformer, as and illustrated in Figure 6. significantly. Furthermore, two active clamp circuits share a reduce weight, volume component counts, capacitor. It will reduce weight, volume and component counts, significantly. capacitor. It will reduce weight, volume and component counts, significantly. capacitor. It will reduce weight, volume and component counts, significantly.

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I Iinin V Vinin

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This paper paper proposes proposes aaa bridgeless bridgeless flyback flyback converter, converter,illustrating illustratingthat that the the proposed proposed one one is is without without This paper proposes bridgeless flyback converter, proposed is without This illustrating that the one bridge diodes diodesto toremove removethe thediode diodeconduction conduction loss and increase conversion efficiency. In addition, addition, bridge loss and increase conversion efficiency. In addition, the bridge diodes to remove the diode conduction loss and increase conversion efficiency. In the proposed one adopts a three-winding transformer to substitute for two transformers. When the proposed one adopts a three-winding transformer to substitute for two transformers. When the output the proposed one adopts a three-winding transformer to substitute for two transformers. When the output maximum maximum power of the the proposed proposed bridgeless flyback is the thethat same as that that of the the conventional conventional maximum power of the proposed bridgeless flyback isflyback the same as of the conventional bridgeless output power of bridgeless is same as of bridgeless flyback converter, as shown in Figure 5, its maximum input current I i is also the same as flyback converter, as shown in Figure 5, its maximum input current I is also the same as each other, i current Ii is also the same bridgeless flyback converter, as shown in Figure 5, its maximum input as each other, and maximum working flux B pk of the transformer in the proposed converter is also the and maximum working flux B of the transformer in the proposed converter is also the same as that pk each other, and maximum working flux Bpk of the transformer in the proposed converter is also the same as that in the conventional bridgeless flyback converter. shows B-H curve curve of ofTrthe the in the conventional bridgeless flyback converter. Figure 7 shows Figure aFigure B-H curve of the transformer in same as that in the conventional bridgeless flyback converter. 77 shows aa B-H transformer T r in theSince flyback converter. Since the conventional flyback converter uses a bridge the flyback converter. the conventional flyback converter uses a bridge rectifier to rectify input transformer Tr in the flyback converter. Since the conventional flyback converter uses a bridge rectifierIito to rectify input current the rectified inputby current can be obtained obtained by aa positive positive value current , the rectified input current Ii can be obtained a positive value during a by complete switching rectifier rectify input current IIi,i, the rectified input current IIii can be value duringItsaaB-H complete switching cycle. Its B-H B-HAs curve is illustrated illustrated in Figure Figure 7a. converter As aa result, result, the cycle. curve isswitching illustratedcycle. in Figure 7a. a result, the conventional flyback can use during complete Its curve is in 7a. As the conventional flyback converter can use a set of transformers to implement PFC function. While, the a set of transformers to implement PFC function. While, the bridgeless flyback converter, as shown conventional flyback converter can use a set of transformers to implement PFC function. While, the bridgeless flyback converter, as shown in in Figure Figure 5, needs needs twounder sets of ofthe transformers to process processand energy in Figure 5,flyback needs two sets ofas transformers to process energy positive half period the bridgeless converter, shown 5, two sets transformers to energy under the positive half period and the negative half period. Its B-H curve is illustrated in Figure 7b. negative half period. Its B-H curve is illustrated in Figure 7b. Due to the proposed bridgeless flyback under the positive half period and the negative half period. Its B-H curve is illustrated in Figure 7b. Due to the proposed bridgeless flyback converter with a three-winding transformer, its B-H curve is converter with a three-winding transformer, its B-H curve is the same as the conventional flyback one, Due to the proposed bridgeless flyback converter with a three-winding transformer, its B-H curve is theshown same as as the conventional flyback one, as shown shown in Figure Figure 7a. Therefore, Therefore, theaproposed proposed bridgeless as inthe Figure 7a. Therefore, theone, proposed bridgeless converter can save set of transformers. the same conventional flyback as in 7a. the bridgeless converter can save a set of transformers. It can simplify the circuit structure, significantly. Therefore, It can simplify the circuit structure, significantly. Therefore, the proposed bridgeless flyback converter converter can save a set of transformers. It can simplify the circuit structure, significantly. Therefore, the proposed bridgeless flyback converter for the PFC power system can achieve a higher power for the PFC power systemflyback can achieve a higher power to avoid line sourceafrom harmonic the proposed bridgeless converter for the PFCfactor power systemthe can achieve higher power factor to to avoid avoid the line line source from from harmonic pollution, possesses soft-switching featurestransition in which which pollution, possesses soft-switching features in which switches are operated in ZVS at features turn-on factor the source harmonic pollution, possesses soft-switching in switches are operated in ZVS at turn-on transition to increase conversion efficiency. It is suitable for to increase conversion efficiency. It is suitable for a low power level application. This paper focuses switches are operated in ZVS at turn-on transition to increase conversion efficiency. It is suitable for a low low power level application. This paper paper focuses on on design design and analysis analysis of the the management proposed bridgeless bridgeless design andlevel analysis of the proposed bridgeless flyback converter and power for DC aon power application. This focuses and of proposed flyback converter and power management for DC loads of power system. loads of power system. flyback converter and power management for DC loads of power system. B B

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t

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B

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a positive half period. When the proposed one is operated in the A and C areas, inductor current ILK is in the DCM state due to a lower voltage level of input voltage VC1. If input voltage VC1 is during the B area interval, the proposed converter is operated (b)in CCM. According to the operational method of the proposed one as mentioned above, input voltage Vin and current Ii are in phase. Therefore, the Figure 7. Plot of the B-H curve of transformer Tr (a) in the conventional flyback converter, and (b) in proposed converter can increase PF andTrreduce total harmonicflyback distortion (THD). Figureflyback 7. Plot of the B-H curve of transformer (a) in the conventional converter, and (b) in the conventional bridgeless flyback converter for PFC applications. In 8, when output current IDC2 of thefor proposed PFC is less than or is equal to the maximum theFigure conventional bridgeless flyback converter PFC applications. output current IDC2(max), the output feedback voltage VF is equal VDC2 (diode DP1 is forward biased). The ControlAlgorithm Algorithmofofthe theProposed ProposedSystem Systemfor forDC DCLoad LoadApplications Applications 2.2.Control proposed PFC is operated as the voltage regulator. If IDC2 is greater than IDC2(max), the output current proposed isisapplied DC power system. In order to implement a DCa IDC2 isThe regulated at Ibridgeless DC2(max) . ThatPFC is, the proposed isload operated as the current The voltage The proposed bridgeless PFC appliedtotoaone a DC load power system. Inregulator. order to implement load power system, the proposed one and a DC/DC converter with a battery source connected V F is equal to I DC2(max) and the diode D P2 is in the forwardly bias state. In addition, when the proposed DC load power system, the proposed one and a DC/DC converter with a battery source connected in in parallel to for Its diagram is in The power haspower an abnormal operational condition, shutdown signal8. SD2 isalgorithm changed parallelsystem to supply supply power for DC DC loads. loads. Its block block diagramthe is shown shown in Figure Figure 8.voltage The control control algorithm of system for DC load applications applications is described described in the the following following sections. from low level power to a high level.for The proposed PFC is shut down to protect the proposed one. of the theaproposed proposed power system DC load is in sections. positive negative half half period period

1.

Circuit Topology of the Proposed Power System I DC1

DB

DC/DC Converter

The proposed DC loadV power system consists of a DC/DC converter with a battery source and a V PWM control circuit bridgeless PFC and single-chip control circuit. The output voltage VDC2 of the bridgeless PFC is close to and is greater than the output voltage VDC1S of the DC/DC converter.C Therefore, the diode DB is used Single chip control circuit to block the voltage difference between voltages I D V D DC2 and VIDC1. The DC load RL is supplied power Battery R I V output the load power PL is less than or equal to protection unit V V When from the proposed PFC and the DC/DC converter. protection V V PDC2(max) which is the maximum output power PFC, the proposed PFC supplies power line source of VtheV proposed unit V I protection unit D D to load. If PL is greater than PDC2(max), the proposed PFC and the DC/DC converter supply power to D V load for achieving a DC load power system. B

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The DC/DC converter adopts a boost converter with a single-capacitor snubber [20]. It can transfer power from the battery load. Since outputpower voltage VDC1applications. is less than the voltage VDC2, a Figure 8. Block Blockto diagram of the theits proposed power system Figure 8. diagram of proposed system diode DB is used to protect the DC/DC converter. Therefore, the protection diode with the output 1. Circuit Topology Power System VC1 of the diode of boost converter is Proposed replaced by the extra diode DB. If the operational state is in the 0 < PL ≤ PDC2(max) state, the battery with the DC/DC converter be operated in the charging mode. It needs The proposed DC load power system consists ofcan a DC/DC converter with a battery source and a an extra charger to charge the battery. When the proposed power system is operated in an abnormal bridgeless PFC and single-chip control circuit. The output voltage VDC2 of the bridgeless PFC is close state, circuitvoltage sends aVshutdown signal SD1 under a high level t to the pulse width 0control to andthe is single-chip greater than the output DC1 of the DC/DC converter. Therefore, the diode DB is modulation (PWM) controldifference circuit of between the DC/DC converter. DC/DC can be in used to block the voltage voltages VDC2The and VDC1 . converter The DC load RL operated is supplied ID1 DCM CCM DCM the shutdown state to protect the DC/DC one. (A area) (B area) (C area) power from the proposed PFC and the DC/DC converter. When the load power PL is less than or equal which is the maximum output power of the proposed PFC, the proposed PFC supplies to PDC2(max) The Proposed PFC … ……… power to load. If PL is greater than PDC2(max)… , the proposed PFC and the DC/DC converter supply 0 The proposed PFC uses a bridgeless flyback converter Twhich is regardedt as a power factor T power to load for achieving a DC load power system. 2 2 Tl corrector for increasing power factor between input voltage and input current of a line source. Its 2. Control Algorithm of Each control circuit adopts a PWM ICUnit for PFC control. Figure 9 illustrates conceptual waveforms of voltage (a) VC1 and current ID1. Variation of current ID1 follows the sine waveform of input voltage VC1. Figure 9a DC/DC converter shows concept waveforms under a complete line period, while Figure 9b depicts those waveforms VC1 under a positive half period. From Figure 9b, it can be seen that the proposed flyback converter can be operated in discontinuous conduction mode (DCM) or continuous conduction mode (CCM) under l

l

0 ID1

t (A area) DCM

(B area)

(C area)

CCM

DCM

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a positive half period. When the proposed one is operated in the A and C areas, inductor current ILK is in the DCM state due to a lower voltage level of input voltage VC1. If input voltage VC1 is during the The interval, DC/DC converter adopts a boostisconverter with a single-capacitor snubber [20]. Itmethod can transfer B area the proposed converter operated in CCM. According to the operational of the proposed as mentioned above, voltage Vin V and current I i are in phase. Therefore, the power from theone battery to load. Since itsinput output voltage is less than the voltage V , a diode DC1 DC2 can increase PF Therefore, and reducethe total harmonicdiode distortion DBproposed is used toflyback protectconverter the DC/DC converter. protection with(THD). the output diode of In Figure 8, output current IDC2 of theDproposed PFC is less than orisisin equal boost converter is when replaced by the extra diode state the to 0 PDC2(max) + PB(max) When PL > PDC2(max) + PB(max) , the proposed power system is operated in the over-load state. Therefore, the DC/DC converter and the proposed PFC are in the shutdown state. There are three protection units in the proposed power system: Battery protection, line source protection and output protection units. In order to increase protections of the proposed power system, hardware and software methods are adopted to protect the proposed one. Due to the same protection functions between hardware and software methods, the operation of hardware protection circuit is introduced in this paper. Figure 10 shows a block diagram of the single chip control circuit for the hardware protection circuit. In the battery protection unit, when IB > IB(max) , the discharging current IB is in the over-current state. Voltage VB1 is changed from a low level to a high level. Voltage SD1 is equal to VS1 (=VB1 ). The DC/DC converter is shut down to protect the battery. If VB < VB(min) , the battery is in the under-voltage state. Voltage single VB2 is changed from a low level to a high level, and signal SD1 is the same as VS1 (=VB2 ). Therefore, the DC/DC converter is also shut down. In the line source protection unit, when Vi < Vi(min) (=AC 90 V), the proposed PFC is shut down by SD2 . In this case, the line source is in the under-voltage state, and voltage signal Vi1 varies from a low level to a high level. Since Vi1 = VS3 = SD2 , the proposed PFC is shut down by signal SD2 , which is in a high level state. If Ii > Ii(max) , the signal Vi2 is equal to VS3 (=SD2 ), and Vi2 is in a high level state. The proposed PFC is operated in the over-current state and it is shut down by SD2 . In the output protection unit, there are two cases to protect the proposed power system. One is that output voltage is in the under-voltage state. The other one is that output current is in the over-current state. When two protection cases occur, the proposed power system is shut down. In the under voltage state, VDC < VDC(min) , voltage VD1 = VS2 = SD1 = VS4 = SD2 is changed from a low level to a high level to shut down the proposed one. When IDC > IDC(set) , voltage VD2 = VS2 = SD1 = VS4 = SD2 is varied from a low level to a high level. The proposed one is shut down. Therefore, the proposed power system

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Table 1. Operational conditions of the proposed power system for DC load applications. Energies 2018, 11, 3096

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Power Distribution

Operational Conditions The The Cases DC/DC Converter DC/DC Converter Proposed unit and output protection unitProposed can use the battery protection unit, line source protection to avoid the with Battery Source with Battery Source PFC system. PFC abnormal operational condition in the proposed power PL = 0 W PB = 0 W PDC2 = 0 W shutdown shutdown 1. Operational of the proposed system forwork DC load applications.work 0 < PL ≤ PTable DC2(max) PB conditions =0W PDC2 = Ppower L PDC2(max) < PL ≤ Distribution PDC2 = Operational Conditions PB = PL − Power PDC2(max) work work PDC2(max) + PB(max) P DC2(max) Cases DC/DC Converter DC/DC Converter with The Proposed PFC The Proposed PFC with Battery Source Battery Source PL > PDC2(max) + PB = 0 W PDC2 = 0 W shutdown shutdown PPLB(max) =0W PB = 0 W PDC2 = 0 W shutdown shutdown 0 < PL ≤ PDC2(max) PB = 0 W PDC2 = PL work work PDC2(max) < PL ≤ PB = PLdefinition − PDC2(max) PDC2 = Ppower work 2. Symbol of the proposed load applications. work DC2(max)system for DC PDC2(max) + PTable B(max) PL > PDC2(max) + PB = 0 W PDC2 = 0 W shutdown shutdown Symbol Definition Expression PB(max)

PB PL IDC2

Output power of the DC/DC converter with battery source PB = VBIB Load power P L = VDCIDC Table 2. Symbol definition of the proposed power system for DC load applications. Output current of the proposed PFC IDC2 ≤ IDC2(max) Symbol Definition Expression IDC2(max) Output maximum current of the proposed PFC Output power ofVoltage the DC/DC converter with battery source PBV=B V VB PB of battery ≥BVIBB(min) P Load power PL = VDC IDC VB(min) I L The minimum work voltage of battery IDC2 ≤ IDC2(max) Output current of the proposed PFC DC2 IB IDC2(max) Discharge current of battery I B ≤ I Output maximum current of the proposed PFC - B(max) VB ≥ VB(min) Voltage of battery IB(max) VB The maximum discharge current of battery V The minimum work voltage of battery B(min) PB(max) The maximum output power of battery PB(max) = VBIB(max) IB ≤ IB(max) I Discharge current of battery Vi I B Input voltage of the line source The maximum discharge current of battery - B(max) Vi(min)PB(max) The minimum input voltage of theofline source Vi(min) < BAC 90 V PB(max) =V IB(max) The maximum output power battery voltage of the linesource source I i Vi InputInput current of the line Ii- ≤ Ii(max) Vi(min) < AC 90 V The minimum input voltage of the line source Ii(max)Vi(min) The maximum work current of the line source Ii ≤ Ii(max) Ii Input current of the line source VDC I Output voltage of the proposed The maximum work current ofpower the line system source - i(max) IDC VDC Output current of the proposed IDC- ≤ IDC(max) Output voltage of the proposedpower power system system IDC ≤ IDC(max) Output current of of thethe proposed power systemsystem IDC(max) IDC Output maximum current proposed power IDC(max) Output maximum current of the proposed power system PDC2(max) The maximum output power of the proposed PFC PDC2(max) = VDC2IDC2(max) PDC2(max) PDC2(max) = VDC2 IDC2(max) The maximum output power of the proposed PFC PDC2 PDC2 Output power of the proposed PFC PDC2 VDC2 IDC2 Output power of the proposed PFC PDC2 = V=DC2 IDC2 Battery protection unit IB

VB

IB> IB(max)

VB1

VB> VB(min)

VB2

DB1 V

S1

SD1 DS1

DS1 V S2

DB2

Ii

Vi> Vi(min) Ii> Ii(max)

VDC < VDC(min)

VDC

DO2

D D Vi1 i1 VS3 S3

Vi2

VD1

DO1

Line source protection unit Vi

output protection unit

DS4 V S4

VD2

IDC> IDC(set)

IDC

Di2 SD2

Figure 10. 10. Block Block diagram diagram of of the the single single chip chip control control circuit Figure circuit for for DC DC Load Load circuit. circuit.

3. Operational Principle of the Proposed PFC 3. Operational Principle of the Proposed PFC The proposed bridgeless flyback converter uses a three-winding transformer to achieve operations proposed bridgeless a three-winding achieve of theThe positive and negative halfflyback periodsconverter of the lineuses source, as depicted in transformer Figure 6. Its to equivalent operations of the positive and negative half periods of the line source, as depicted in Figure 6. Its circuit is illustrated in Figure 11a,b, respectively. When the line source enters the positive half period, switches M1 and M2 are operated in complementary. During this time interval, switches M3 and M4 are always turned off, as shown in Figure 11a. The input energy supplied by the line source is

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equivalent circuit is illustrated in Figure 11a,b, respectively. When the line source enters the positive Energies 2018, 11, 3096 9 of 20 half period, switches M1 and M2 are operated in complementary. During this time interval, switches M3 and M4 are always turned off, as shown in Figure 11a. The input energy supplied by the line source is transferred to loadwindings through windings 1 and 3 of the transformer. Furthermore, the transferred to load through N1 and N3Nof the N transformer. Furthermore, when the when proposed proposed in the negative period, M1 turned and M2off areand turned off and converter converter is operatedisinoperated the negative half period,half switches M1switches and M2 are switches M3 switches M 3 and M 4 , in turn, are operated in complementary, as depicted in Figure 11b. and M4 , in turn, are operated in complementary, as depicted in Figure 11b. D1

D3 LK T r

M3

Vin C2

M4 CC

Lm2 N2

N3

D2 CO

M1

Vin

RL VO

C1

M2 CC

Lm1 N 1

D2 N3

CO

RL VO

1:N

1:N

(a)

LK T r

(b)

Figure 11. Schematic Schematic diagram diagramof of the the proposed proposed bridgeless bridgelessflyback flyback operated operated in in (a) (a) positive, positive, and and (b) (b) Figure negative half half periods. negative

The operational operational principle principle of of the the proposed proposed flyback flyback converter converter is is divided divided into into two two different different half half The periods: Positive Positive and and negative negative half half periods. periods. According According to to operational operational principle principle of of equivalent equivalent circuit circuit periods: shown in Figure 11a,b, operational modes of the proposed one operated in the positive period are shown in Figure 11a,b, operational modes of the proposed one operated in the positive period are similar to to those those modes modes in in the the negative negative period, period, except and M M22 are arechanged changed to to switches switches similar except that that switches switches M M11 and M and M . Furthermore, since the period T of the line source is much greater than T of switching s 3 4 l M3 and M4. Furthermore, since the period Tl of the line source is much greater than Ts of switching converter, the is regarded as a constant value during switching period Ts .period Therefore, converter, theinput inputvoltage voltage is regarded as a constant value each during each switching Ts. the operational principle of principle the proposed bridgeless flyback converter can adopt, thatcan input voltage is Therefore, the operational of the proposed bridgeless flyback converter adopt, that a constant DC voltage and the proposed one is operated in the positive half period of the line source, input voltage is a constant DC voltage and the proposed one is operated in the positive half period to the explain operational principle. According to the operational of the proposed converter, of line its source, to explain its operational principle. Accordingprinciple to the operational principle of the operational modes of the proposed one are divided into seven modes. Each operational mode is shown proposed converter, operational modes of the proposed one are divided into seven modes. Each in Figure 12 over one and12 its over key waveforms are illustrated in Figure Its operational operational mode is switching shown incycle, Figure one switching cycle, and its key13.waveforms are principle isindescribed inIts theoperational following. principle is described in the following. illustrated Figure 13.

•

•

•

•

 •

Mode t1]:t1Before t0, tswitch M1M is1kept in the turn-on state, while M2 is Mode 11 [Figure [Figure 12a; 12a; tt00≤≤t