1. Introduction
Currently, advances in switching power supply technology have created high energy density with lower volume, size and cost. It is widely applied to power systems to generate electric power to load, such as ac/dc converter, dc/dc converter, uninterrupted power supply (UPS), induction heating, electronic ballast, telecom power supplies, light emitting diode drivers and battery charger and dischargers [
1,
2,
3,
4,
5]. In particular, battery power is rapidly replacing fossil fuel as an energy storage system in a variety of power system application, such as energy storage cabinet system, UPS, electric vehicle, small bikes, garden tools, vacuum cleaners and 3C products [
6,
7,
8,
9,
10].
In general, battery power is combined with renewable energy sources to generate electric power to load due to zero pollution. In particular, when solar power is regarded as an input power source of power processor, different types of power sources should be merged to transfer less fluctuated and more reliable energy to load due to its intermittent feature. In order to supply power to the battery, a utility line source is selected to help solar power to sustain continuous energy to battery when solar power is functioning with less intense solar radiation. Therefore, solar power sources and utility line sources are simultaneously selected in the proposed power system to increase power reliability for battery charging applications.
When charger is widely used in power systems, various battery types are chosen to achieve storage energy. Since lithium battery possesses high energy density, small size and low self-discharge [
11,
12,
13], it is extensively adopted in portable products. However, the lifetime of lithium battery is easily affected by the charging method. In order to increase life time of lithium battery, many battery charging methods have been proposed [
14,
15,
16]. They include constant trickle current (CTC), constant current (CC) and constant current/constant voltage (CC-CV) charging methods. In these methods, since CTC charging method requires a longer charging time, its applications are limited. Since the CC-CV charging method can reduce charging time, it is suitable for the utility line source system. In addition, battery charger adopts solar power as it input source. To implement maximum power point tracking (MPPT) of solar power, the CC charging method can be used to extract its maximum power. Therefore, CC-CV and CC charging methods are, respectively, adopted in the proposed power system operated in the utility line and solar power source conditions.
In general, a battery cell is connected in series or parallel to form a battery pack for power system applications. Since a battery pack uses a lot of battery cells connected in series, it will result in voltage difference between each battery cell. Therefore, the lifetime and maximum storage capacity of battery pack can be reduced. In order to obtain better lifetime and maximum storage capacity of the battery, a battery pack with two or three battery cells connected in series is usually adopted without a battery equalizer. Its output voltage is less than 13 V. When a battery charger uses the utility line source as its input source, it needs a high step-down converter. Due to the low-level power application of the proposed charger, a flyback or forward converter can be selected as the charging converter. Moreover, a flyback converter has a better circuit and costs less. It is regarded as the charger when the proposed power system is operated in the utility line source condition, as shown in
Figure 1. If the proposed one adopts solar power as its input source, a buck converter can be chosen as the charger because of low voltage differences between the output voltage of solar power and the battery, as shown in
Figure 2. Therefore, the proposed power system operated in the utility line source condition adopts a flyback converter as its charger, while the proposed one operated in the solar power source condition uses a buck converter as its charger.
The proposed power system can select flyback and buck converters to achieve multiple sources for lithium battery charger applications, as shown in
Figure 3. Since transformer
Tr in flyback converter exists with leakage inductance
LK, it will induce a spike voltage across switch
M1 when switch
M1 is switched off. In order to recover the energy trapped in leakage inductance
LK, an active clamp circuit is introduced into the flyback converter to increase conversion efficiency [
17,
18,
19,
20]. Moreover, a buck converter can adopt a bidirectional circuit to implement the battery charger. For further simplifying circuit topology of the proposed power system, switches of active clamp flyback and bidirectional buck converters can be merged to form a hybrid converter, as shown in
Figure 4. In
Figure 4, since the utility line source and solar power source conditions are separately operated and their exchange time is very long, switch
S1 with a low speed and low cost is adopted to control operational conditions. In addition, the proposed hybrid converter can use less components and is of lighter volume, smaller size, lower cost and higher conversion efficiency. It is suitable for battery charger systems with multiple sources, such as Ni-Cd, Ni-MH, lead-acid, lithium batteries, etc.
The multiport converter has been widely applied to generate electric power [
21,
22,
23,
24,
25,
26]. In [
21], a multi-port converter was used in smart grid for the integration of storage and distributed generator. The authors of [
22] proposed a multi-input dc-dc converter to transfer power from different power sources to the load. In order to implement input source of converter with multiple power sources, their component counts were added, and their driving circuits are complex. In [
23,
24,
25,
26], they are adopted in PV and battery system for supplying power to load. They possess dual input and single output ports. The proposed hybrid converter is shown in
Figure 4. It is similar to three-port converter: dual inputs and single output. Comparison of component counts with the proposed hybrid converter and its counterparts is illustrated in
Table 1. From
Table 1, it can be observed that the proposed one can implement dual inputs and single output. It only uses one transformer, three switches, one capacitor and one extra switch. Compared with its counterparts, the proposed hybrid converter can reduce component counts to achieve approximately functions.
2. Derivation of the Proposed Hybrid Converter
Since the proposed hybrid converter includes an active clamp flyback and buck converter for battery charging applications, illustrated in
Figure 3, it will become a complex circuit structure. In
Figure 3, the active clamp flyback and buck converters are operated at different times, and the operational time of each converter is very long. Therefore, two sets of converters can be integrated as a hybrid converter. In the following, a circuit structure derivation is briefly described.
In order to simplify circuit structure of the proposed hybrid converter, diodes
D5 and
D6 shown in
Figure 3 are, respectively, changed by switches
MD5 and
MD6 illustrated in
Figure 5a. In
Figure 5a, when switch
MD5 is moved from the upper regions to the lower loop, which consists of switch
MD5, voltage
VB and inductor
LS, the operation of the proposed power system is not affected, as shown in
Figure 5b. If switches
MD5 and
MD6 are operated synchronously, two switches can be merged by switch
MD56. Moreover, inductors
L1 and
LS can be integrated to form inductors
L1S, as shown in
Figure 5c.
In order to further simplify the proposed power system, nodes A and A’ are regarded as the same node AA’. Its circuit structure is illustrated in
Figure 5d. When the operational condition of the proposed one is operated in the flyback converter condition, switches
M2 and
MD56 are switched on or switched off at the same time. Therefore, the S terminal of switch
M2 connected in node AA’ can be moved to node B. The operation of the proposed one is not affected, as shown in
Figure 5e. Since flyback and buck converters are operated at different times and their exchange time is very long, switch
S1 with low speed and low cost can be used to control the operational condition of the proposed power system. Therefore, switches
M2 and
M3 are integrated to form switch
M23, as shown in
Figure 5f. To simplify component symbol, the component devices of the proposed hybrid converter are renamed, as shown in
Figure 4. From
Figure 4, it can be observed that proposed hybrid converter can use less component counts to implement battery charger under utility line and solar power sources.
3. Operational Principle of the Proposed Hybrid Converter
The proposed hybrid converter can be operated in the utility line source and solar power source conditions for lithium battery charging applications. When the proposed one is operated in the solar power source condition, its equivalent circuit is illustrated in
Figure 6a by the blue line.
Figure 6b shows equivalent circuit of the proposed one operated in the utility line source condition by the blue line. In order to explain the operational principle of the proposed one, each converter is briefly described in the following.
- A.
The solar power source condition: buck converter
When the proposed hybrid converter is operated in the solar power source condition, its equivalent circuit is shown in
Figure 6a. Its equivalent circuit is a buck converter. Since the operational state of the proposed converter is always in continuous conduction mode (CCM) from light load to heavy load, its operational principle with CCM is briefly described. According to the operational principle of the proposed converter operated in the solar power source condition, its operational principle can be divided into five modes.
Figure 7 illustrates an equivalent circuit of each operational mode by the blue line. While
Figure 8 shows conceptual waveforms of each operational mode over a complete switching cycle. In the following, each operational mode is briefly explained.
Mode 1 (
Figure 7a:
t0 ≤
t <
t1): Before
t0, switches
M2 and
M3 are in the off state. Diode
DM3 is in the forward bias state. When
t =
t0, switch
M2 is switched on. Since switch current
IDS3 is equal to (–
IB), switch current
IDS2 abruptly increases from 0 A to
IB. Therefore, diode is
DM3 reversely biased. During this time interval, current
IB linearly increases and inductor
Ls is in the storage energy state.
Mode 2 (
Figure 7b:
t1 ≤
t <
t2): At
t1, switch
M2 is switched off and switch
M3 is kept in the off state. Within this time interval, since inductor current
IB has to be sustained at continuous state, capacitor
CM2 is operated in the charging state, while
CM3 is sustained in the discharging state. Therefore, voltage
VDS2 varies from 0 V to
VPV and voltage
VDS3 changes from
VPV to 0 V.
Mode 3 (
Figure 7c:
t2 ≤
t <
t3): When
t =
t2, switches
M2 and
M3 are kept in the off state. At the moment, voltage
VDS3 is equal to 0 V. Diode
DM3 is forwardly biased. During this time period, inductor
Ls is in the released energy state. Its current,
IB, linearly decreases.
Mode 4 (
Figure 7d:
t3 ≤
t <
t4): At
t =
t3, switch
M2 is in the off state and
M3 is switched on. Since diode
DM3 is forwardly biased before
t =
t3, switch
M2 is operated with zero-voltage switching (ZVS) at the turn-on transition. During this time interval, inductor
LS releases energy to the battery. Its current,
IB, linearly decreases.
Mode 5 (
Figure 7e:
t4 ≤
t <
t5): When
t =
t4, switch
M2 is in the off state and
M3 is switched off. Within this mode, switch current
IDS3 is a negative value. Diode
DM3 is forwardly biased to release energy stored in inductor
Ls to the battery. Inductor current
IB linearly decreases. When the operational mode is at the end of mode 5, one new switching cycle will start.
- B.
The utility line source condition: active clamp flyback converter
When the proposed hybrid converter is operated in the utility line source condition, an active clamp flyback converter is used to charge battery. Since the operational state of active clamp flyback converter is always kept in CCM from light load to heavy load, the operational principle of the one is briefly described for CCM operation. According to the operational principle of active clamp flyback converter, its operational mode can be divided into 10 modes. The equivalent circuit of each operational mode is shown in
Figure 9 by the blue line, while the conceptual waveforms of each operational mode is illustrated in
Figure 10. In the following, each operational mode is briefly explained.
Mode 1 (
Figure 9a:
t0 ≤
t <
t1): Before
t0, switches
M1~M3 are in the off state, and diodes
DM1 and
DM1 are in the forwardly bias state. When
t =
t0, switch
M1 is switched on, and switches
M2 and
M3 are kept in the off state. At the moment, since diode
DM1 is forwardly biased before
t0, switch
M1 is operated with ZVS at turn-on transition. During this time interval, current
ILK varies from a negative value to 0 A. Since current
IDS3 is a negative value, diode
DM3 is in the forwardly bias state. Current
IB linearly decreases and inductor
Lm releases energy through transformer
Tr and diode
DM3 to the battery.
Mode 2 (
Figure 9b:
t1 ≤
t <
t2): At
t1, switch
M1 is kept in the on state, and switches
M2 and
M3 are sustained in the off state. Within this mode, inductor current
ILK varies from 0 A to the initial value, which is the maximum inductor current of inductor
Lm operated in CCM. Moreover, since current
IDS3 is kept at the negative value, diode
DM3 is sustained in the forwardly bias state. The magnetizing inductor
Lm releases energy to battery.
Mode 3 (
Figure 9c:
t2 ≤
t <
t3): When
t =
t2, switch
M1 is sustained in the on state, and switches
M2 and
M3 are in the off state. At the moment, inductor current
ILK is equal to current
ILm. Diode
DM3 is reversely biased. During this time interval, inductor
Lm is in the storage energy state. Inductor current
ILm linearly increases.
Mode 4 (
Figure 9d:
t3 ≤
t <
t4): When
t =
t3, switch
M1 is switched off, and switches
M2 and
M3 are kept in the off state. During this time interval, since inductor current
ILK has to be kept in the continuous state, capacitor
CM1 is charged, and capacitors
CM2 and
CM3 are simultaneously discharged. Therefore, voltage
VDS1 varies from 0 V to [
VDC +
NVB]. Voltage
VDS3 changes from [(
VDC/N) +
VB] to 0 V, while voltage
VDS2 varies from [(
N-1)
VB +(
N-1)
VDC/N] to 0 V.
Mode 5 (
Figure 9e:
t4 ≤
t <
t5): At
t4, switch
M1~M3 are kept in the off state. In this moment, voltages
VDS2 and
VDS3 are equal to 0 V. Diode
DM2 and
DM3 are forwardly biased, simultaneously. During this time interval, inductor
LK and capacitor
CC form a resonant network, and they start to generate resonance. Inductor current
ILm releases energy through transformer
Tr and diode
DM3 to battery.
ILm linearly increases.
Mode 6 (
Figure 9f:
t5 ≤
t <
t6): When
t =
t5, switch
M1 is sustained in the off state, while switches
M2 and
M3 are simultaneously switched on. At the moment, switches
M2 and
M3 are simultaneously operated with ZVS at the turn-on transition. Within this mode, inductor
LK and capacitor
CC are sustained in the resonant state. Current
ILK with the resonant manner varies from a maximum negative value to 0 A. Inductor
Lm is kept in the released energy state. Therefore, inductor current
ILm linearly increases.
Mode 7 (
Figure 9g:
t6 ≤
t <
t7): When
t =
t6, switch
M1 is in the off state and switches
M2 and
M3 are kept in the on state. In this moment, current
ILK is equal to 0 A. During this time interval, inductor
LK and capacitor
CC are sustained in the resonant state. Inductor
Lm releases energy through transformer
Tr and switch
M3 to the battery. Therefore, inductor current
ILm linearly increases. Since switch current
IDS3 is equal to (
IB–
IDS2), it varies from a negative value to 0 A.
Mode 8 (
Figure 9h:
t7 ≤
t <
t8): At
t7, switch
M1 is kept in the off state, while switches
M2 and
M3 are simultaneously sustained in the on state. Within this mode, Inductor
LK and capacitor
CC are kept in the resonant state. Inductor current
ILK with the resonant manner varies from 0 A to the maximum value. Inductor
Lm is in the released energy state. Its value linearly increases.
Mode 9 (
Figure 9i:
t8 ≤
t <
t9): When
t =
t8, switch
M1 is in the off state, while switches
M2 and
M3 are simultaneously switched on. In this mode, current
IDS3 is equal to (−
IB). Diode
DM3 is forwardly biased. Since inductor current
ILK must be kept in the continuous state, capacitor
CM1 is discharged, and capacitor
CM2 is charged. Voltage
VDS1 varies from [
VDC +
NVB] to 0 V, while voltage
VDS2 changes from 0 V to [(
N − 1)
VB +(
N − 1)
VDC/N]. Inductor
Lm is kept in the released energy state.
Mode 10 (
Figure 9j:
t9 ≤
t <
t10): At
t =
t9, switch
M1 ~ M3 are in the off state. At the moment, voltage
VDS1 is equal to 0 V. Thus, diode
DM1 is forwardly biased. During this time interval, inductor current
ILK varies from the maximum negative value to 0 A. Inductor current
Lm is still in the released energy state. When operational mode is at the end of mode 10, one new switching cycle will start.
5. Control Circuit of the Proposed Hybrid Converter
The proposed hybrid converter adopts the utility line and solar power as its input source, respectively. In order to achieve a power supply system with multiple sources, the proposed one needs a controller to implement battery charging control and MPPT functions.
Figure 13 illustrates the block diagram of the controller for the proposed hybrid converter. In
Figure 13, the proposed one is divided into two parts: power circuit and controller. The controller is used to control power circuit for supplying power to battery. Therefore, the controller includes MPPT, power source selection, CC command selection, CC/CV command, PWM generator and battery protection units.
Table 2 lists definitions of key parameters in
Figure 13, while
Table 3 illustrates the operational condition of the proposed hybrid converter. In the following, each control unit is briefly described.
5.1. MPPT Unit
The proposed hybrid converter possesses two operational conditions: the utility line source and solar power source conditions. When the proposed one uses solar power as its input source, it regulates charging current
IB with the CC method to charge the battery and implement MPPT. For implementing MPPT of solar power, the perturb and observe algorithm (P&O) was used for tracking the maximum power point (MPP) of solar power [
27]. Since its algorithm is described in [
27], it will not be described in this paper. As mentioned above, the MPPT unit in the controller adopts voltage
VPV and current
IPV to obtain the maximum power
PPV (max) of solar power.
5.2. CC Command Selection Unit
When the proposed hybrid converter is operated for a battery charger, charging current IB uses the CC-CV method to supply power to the battery. In order to implement the battery charging function with the CC method, the controller must generate CC command value IBCOM to regulate charging current IB. The CC command selection unit is used to generate CC command value IBCOM. When the maximum power PPV(max) of solar power is obtained, the solar power command can produce a command value IBCOM1, which can be expressed by (PPV(max)/VB). Since the charging current IB is limited within IB(max), charging the current selector can generate control signal SCC, which is obtained by the relationship between IBCOM1 and IB(max). When IBCOM1 ≥ IB(max), signal SCC varies from low levels to high levels. It is used to control the CC command selector, and signal IBCOM is equal to IB(max). If IBCOM1 < IB(max), signal SCC is kept at low levels. It can control CC command selector to obtain IBCOM = IBCOM1.
Since the battery charging method adopts the CC–CV hybrid method to obtain better charging efficiency, the CC/CV command unit can produce a selecting signal SCm to control the battery charger operated in the CC charging mode or the CV charging mode. When voltage VB is equal to or greater than voltage VB(max), signal SCm varies from low levels to high levels. The proposed battery charger is operated in the CV charging mode. The command value Vref is equal to VB(max). Moreover, the feedback selector can induce feedback signal Vf, which is equal to VB. The error value can be obtained by difference between the command value Vref and feedback value Vf when signals Vref and Vf are sent to PWM generator for generating error value. The error value compared with a triangle wave in the PWM generator can produce signal SPWM to drive switches in the proposed hybrid converter for battery charging. In addition, when VB < VB(max), the proposed one is operated in the CC charging mode. Signal Vref = IBCOM and Vf = IB. PWM generator can receive signals Vref and Vf to generate SPWM for battery charging.
5.3. PWM Generator Unit
The PWM generator unit includes a feedback selector, PWM generator, gate driver under utility line source, gate driver under solar power source and PWM signal selector. The feedback selector and PWM generator receives command value Vref and feedback value Vf to generate PWM signal SPWM for implementing CC or CV charge. The PWM signal SPWM can be sent to gate driver under utility line source and gate driver under solar power source for generating different PWM signals under different power source to implement battery charger.
In the gate driver under utility line source, the PWM signal SPWM is sent to this control circuit to generate three PWM signals. The PWM signal M11 is used to drive switch M1, which is regarded as the main switch. PWM signals M11 and M12 are operated in complementary, while PWM signals M12 and M13 are operated synchronously. Switches M2 and M3 are regarded as auxiliary switches and are driven by PWM signals M12 and M13, respectively. In addition, the gate driver under the solar power source can produce three PWM signals, M21, M22 and M23, by PWM signal SPWM. PWM signal M22 is the main PWM signal for driving switch M2. The PWM signals M22 and M23 are operated complementarily. Therefore, PWM signal M23 is used to drive auxiliary switch M3. In this operational condition, signal M21 is switched off. Two pairs of PWM signals (M11, M12, M13) and (M21, M22, M23) are sent to a PWM signal selector to produce PWM signals selector to produce PWM signals M1, M2 and M3. When operational signal PSP is in the high level, PWM signals, M1 = M11, M2 = M12, M3 = M13, are adopted to drive switches M1, M2 and M3, respectively. During this operational condition, the proposed hybrid converter is operated in the solar power source condition. Switch S1 is switched off. If operational signal PUL is in the high level, PWM signals M1 = M21, M2 = M22 and M3 = M23 are used to drive switches M1, M2 and M3 separately. Within this operational condition, utility line source is regarded as the input source of the proposed hybrid converter. Switch S1 is switched on. Moreover, signal SD is the shutdown signal of the proposed hybrid converter. When signal SD is in the high level, the proposed one enters the shutdown condition. During this time interval, battery operational condition is under IB ≥ IBP or VB ≥ VBP.
5.4. Power Source Selection Unit
A power source selection unit is used to select power source as input source of the proposed hybrid converter. When solar power can supply enough power to battery, the proposed one can use solar power to supply power for the battery. During this operational condition, the solar power detector is in the
VPV ≥
VPV(min) condition. Signal
SPV is in the high level. Therefore, signal
PSP is under the high level, and signal
PUL is in the low level. If
VPV ≥
VPV(min) and
VDC ≥
VDC (min), signals
SPV and
SDC are simultaneously in the high level. When
VPV ≥
VPV(min) and
VDC ≥
VDC (min), signals
SPV and
SDC are simultaneously in the high level. Within this operational condition, the powers of solar power and utility line are large enough to supply power to battery. Since the power source in the proposed hybrid converter is a priority selection to solar power, the proposed one is operated in the solar power condition. Signal
PSP is in the high level state. In addition, when
VPV <
VPV(min) and
VDC ≥
VDC (min), solar power is not enough to supply power to the battery, and the utility line is large enough to supply power to battery. Therefore, a utility line can supply power to the battery. Signal
PUL is in the high level state. When
VPV <
VPV(min) and
VDC <
VDC (min), solar power and utility lines are not enough to supply power to battery, simultaneously. Signals
PSP and
PUL are under the low level state. The proposed hybrid converter is operated in the shutdown condition. The operational condition of the proposed one is listed in
Table 3.
5.5. Battery Protection Unit
The battery does not operate in overcurrent and overvoltage conditions. When IB ≥ IBP, the charging current IB is greater than the maximum charging current IB(max). Signal SDI is in the high level state, and the proposed hybrid converter must be shut down. If VB ≥ VBP, battery voltage VB is greater than maximum charging voltage VB(max). Signal SDV is in the high level state, and the proposed one can be shut down. Therefore, shutdown signal SD is equal to SDI + SDV. When signal SD is in the high level state, the proposed hybrid converter is operated in the shutdown condition.
6. Experimental Results
The proposed hybrid converter can be operated in the utility line source and solar power source conditions. In order to verify battery charging features, a prototype was implemented with the following specifications:
A. The utility line source condition: active clamp flyback converter
Input voltage VDC: DC127~183 V (AC90 V~130 V);
Switching frequency fs1: 50 kHz;
Output voltage VB: DC5 V~8.4 V (battery pack: 2 series*8 parallel);
Maximum charging current IB(max): 12 A.
B. The solar power source condition: buck converter
Input voltage VPV: DC30~45 V (solar panel: PPV(max) = 100 W);
Switching frequency fs2: 50 kHz;
Output voltage VB: DC5 V~8.4 V (battery pack: 2 series*8 parallel);
Maximum charging current IB(max): 12 A.
According to the previous specifications of the proposed hybrid converter operated in different power source conditions, the specifications of solar power is illustrated in
Table 4, from which it can be observed that maximum output power
PPV(max) = 100 W, maximum power voltage
VPV = 36 V and maximum power current
IPV = 2.78 A. In addition, the battery pack includes 16 sets of battery cells. Specifications of each battery cell are illustrated in
Table 5. Two battery cells connected in series are regarded as a string. Eight sets of strings compose battery pack. In
Table 5, the voltage of the battery pack varies from 5 V to 8.4 V, and the maximum charging current
IB(max) is equal to 12 A. Therefore, the battery pack is expressed by two series*8 parallel.
According to the design of the proposed hybrid converter, the key components are listed in
Table 6. In order to verify the performances of the proposed hybrid converter, the experimental results are separately measured under solar power and utility line conditions. When solar voltage
PPV = 36 V, the measured switch voltage
VDS and current
IDS waveforms of switches
M2 and
M3 are shown in
Figure 14 and
Figure 15.
Figure 14 shows those waveforms under 25% of the full-load condition, while
Figure 15 depicts those waveforms under 100% of the full-load condition. From
Figure 14 and
Figure 15, it can be observed that the proposed hybrid converter can adopt solar power to charge battery from light load to heavy load.
Figure 16 illustrates measured battery voltage
VB and current
IB waveforms under different charging currents. When charging current
IB = 3 A, those waveforms are shown in
Figure 16a. In addition, when
IB = 6 A, those waveforms are expressed in
Figure 16b. From measured voltage
VB and current
IB waveforms, the proposed hybrid converter operated in the solar power condition can achieve different charging currents under a constant value.
When the proposed hybrid converter uses solar power as its input source, it has to possess a good dynamic response. In order to verify the dynamic response of the proposed hybrid converter,
Figure 17 illustrates measured battery voltage
VB and current
IB waveforms under step-load changes between
IB = 0 A and
IB(max) = 12 A. In
Figure 17, battery voltage
VB varies within ±1%, from which it can be observed that the proposed hybrid converter operated in the solar power condition has a good dynamic response.
Figure 18 shows measured solar power voltage
VPV, current
IPV and power
PPV waveforms under the maximum solar power
PPV(max) = 50 W. In
Figure 18, when solar power
PPV varies from 0 W to 50 W, the MPPT time interval is about 330 ms. That is, the proposed hybrid converter can achieve MPPT features.
Figure 19 expresses the conversion efficiency curve of the proposed hybrid converter operated in the solar power condition from light load to heavy load. In
Figure 19, the maximum conversion efficiency is 95% under 80% of the full-load condition. When the proposed hybrid converter is operated under 100% of full-load condition, its conversion efficiency is about 91%. According to power loss analysis, driving circuit and stray losses are about 21.7% of total power loss. Losses of switches are approximated to 42.7%, while losses of transformer
Tr are approximately 35.6%. As mentioned above, the proposed hybrid converter can be operated in the solar power condition to achieve battery charging.
When the proposed hybrid converter adopts the utility line as its input source, some experimental results are measured to verify its feasibility.
Figure 20 and
Figure 21 illustrate measured switch voltage
VDS and current
IDS of the proposed hybrid converter operated in the utility line condition.
Figure 20 shows those waveforms under 45% of the full-load condition, while
Figure 21 expresses those waveforms under 100% of the full-load condition. From
Figure 20 and
Figure 21, it can be observed that switches
M1 and
M2 are operated with ZVS at the turn-on transition.
Figure 22 depicts measured battery voltage
VB and current
IB waveforms of the proposed one operated in the utility line condition under different charging currents.
Figure 22a shows those waveforms under
IB = 3 A, while
Figure 22b illustrates those waveforms under
IB = 6 A. In
Figure 22, the charging current
IB can be successfully changed. Measured battery voltage
VB and current
IB waveforms of the proposed one operated in the utility line condition under step-load changes from
IB = 2.4 A to
IB(max) = 12 A are illustrated in
Figure 23. Its battery voltage,
VB, can be kept within ±1% to verify a good dynamic response.
Figure 24 draws the conversion efficiency curve of the proposed one operated in the utility line condition from light loads to heavy loads. The maximum conversion efficiency is about 93% under 70% of the full-load condition. When the proposed hybrid converter is operated under 100% of the full-load condition, its conversion efficiency is about 89%. According to power loss analysis, driving circuit and stray losses is about 4.3% of total power loss. Losses of switches are approximated to 88.1%, while losses of transformer
Tr are approximately 7.6%. As previously experiment results, the proposed hybrid converter can be operated in the utility line condition to achieve battery charging.