AN3971
Application note
STEVAL-ISV005V2: solar battery charger for lead acid batteries
based on the SPV1020 and SEA05
By Giuseppe Rotondo
Introduction
For photovoltaic standalone installations, both battery charging management and an
efficient solar energy harvesting system are required.
The lead acid battery charging control (which is a key feature, in terms of costs, in off-grid
PV installations) must optimize both the charging time and the lifetime of the battery.
To optimize the energy extraction, the solar energy harvesting system needs a power
conversion unit which performs an MPPT (max. power point tracking) algorithm.
The STEVAL-ISV005V2 is a demonstration board for users designing an MPPT-based lead
acid battery charger using the SPV1020, which is a high efficiency, monolithic, step-up
converter, with interleaved topology (IL4) and implementing MPPT.
In addition to the SPV1020, and to prevent battery overvoltage and overcurrent, the
STEVAL-ISV005V2 system architecture proposes a solution with the SEA05 (CC-CV:
constant current-constant voltage) IC.
Figure 1.
May 2012
STEVAL-ISV005V2 demonstration board
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www.st.com
Contents
AN3971
Contents
1
Application overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2
Optimizing the energy from the panel . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1
3
4
Regulations, protection, and features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Charging a lead acid battery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1
Constant current – constant voltage control . . . . . . . . . . . . . . . . . . . . . . . 11
3.2
SEA05 features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.3
Interaction between the SPV1020 and SEA05 . . . . . . . . . . . . . . . . . . . . . 12
External component selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.1
Output current regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2
Battery voltage control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5
STEVAL-ISV005V2 schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6
Bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7
Layout guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
8
Application connection example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
9
Experimental results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
10
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
11
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
12
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
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AN3971
List of figures
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Figure 19.
Figure 20.
Figure 21.
Figure 22.
STEVAL-ISV005V2 demonstration board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Typical stand-alone PV systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
SPV1020 equivalent circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
I/V panel electrical curve. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
MPPT perturb & observe tracking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Input voltage partitioning sample circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
System architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Architecture with DC-DC buck converter (for 12 V batteries) . . . . . . . . . . . . . . . . . . . . . . . . 9
Typical SLA battery charging curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
SEA05 internal architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Internal duty cycle reference. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
System architecture SPV1020 + SEA05. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
SEA05 schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
STEVAL-ISV005V2 schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
STEVAL-ISV005V2 (top view) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
STEVAL-ISV005V2 (bottom view) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
STEVAL-ISV005V2 board connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
SLA battery (12 V, 4 Ah) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Solar array simulator (SAS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
SLA battery charging profile (24 V, 4 Ah) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
SLA battery charging profile (12 V, 12 Ah) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
SLA battery charging profile (24 V, 24 Ah) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
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Application overview
1
AN3971
Application overview
The standalone photovoltaic (PV) system is a solution normally used in remote or isolated
locations where the electric supply from the power-grid is unavailable or not available at a
reasonable cost, such as mountain retreats or remote cabins, isolated irrigation pumps,
emergency telephones, isolated navigational buoys, traffic signs, boats, camper vans, etc.
They are most suitable for users with a limited power need.
It is estimated that about 60% of all PV modules are used in these standalone applications,
where the rechargeable batteries are normally used to store the energy surplus and supply
the load in case of low renewable energy production.
Figure 2.
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Typical stand-alone PV systems
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AN3971
Application overview
The primary function of a charge controller in a standalone PV system is to maintain the
battery at the highest possible state of charge, and to protect it from overcharge by the array
and from over-discharge by the loads.
Although some PV systems can be effectively designed without the use of charge control,
any system that has unpredictable loads, user intervention, optimized or undersized battery
storage (to minimize initial cost), typically requires a battery charge controller.
The algorithm or control strategy of a battery charge controller determines the effectiveness
of battery charging and PV array utilization, and ultimately the ability of the system to meet
the load demands.
Important functions of battery charge controllers and system controls are:
●
To prevent battery overcharge: to limit the energy supplied to the battery by the PV
array when the battery becomes fully charged
●
To prevent battery over-discharge: to disconnect the battery from electrical loads when
the battery reaches a low state of charge
●
To provide load control functions: to automatically connect and disconnect an electrical
load at a specified time, for example, operating a lighting load from sunset to sunrise.
The most common battery type used is the valve regulated lead acid (VRLA) battery,
because of its low cost, maintenance-free operation and high efficiency characteristics.
Although the battery installation cost is relatively low compared to that of PV systems, the
lifetime cost of the battery is greatly increased because of the limited service time.
The lifetime parameter is reduced if there is low PV energy availability for prolonged periods
or improper charging control, both resulting in low battery state of charge (SOC) levels for
long time periods.
An increase in the lifetime of the battery results in improved reliability of the system and a
significant reduction in operating costs. The life of a lead acid battery can be extended by
avoiding critical operating conditions such as overvoltage and overcurrent during the
charge.
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Optimizing the energy from the panel
2
AN3971
Optimizing the energy from the panel
To guarantee the maximum power extraction from a photovoltaic panel, a real-time
execution of a MPPT algorithm is needed. In the SPV1020 implementation the algorithm
allows the changing of the DC-DC converter duty cycle according to the panel irradiation. In
other words, the power conversion system based on the SPV1020 matches the impedance
of the load to the dynamic output impedance of the panel.
Figure 3.
SPV1020 equivalent circuit
306
) IN
) OUT
6 OUT
#IN
#OUT
6 IN
06
: $#
2 OUT
0ANEL
Each Z affects power transfer between the input source and output load and for each Z an
input voltage (Vin) and current (Iin) can be measured. The purpose of the MPPT algorithm is
to guarantee Z = ZM, where Zm is the impedance of the source and Z is the impedance of
the load which must match Zm to guarantee maximum power is extracted from the source.
(Pin = Vin * Iin) is maximum (Pmpp = Vmpp* Impp).
In order to understand the tracking efficiency, it is best to graph the voltage-current curve,
which shows all the available working points of the PV panel at a given solar irradiation. The
voltage-power curve is derived from the voltage-current curve, plotting the product V*I for
each voltage applied. Figure 4 shows both the typical curves voltage-power and voltagecurrent of a photovoltaic panel.
Figure 4.
6/28
I/V panel electrical curve
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Optimizing the energy from the panel
This algorithm approach is defined as perturb & observe because the system is excited
(perturbed) with a certain DC, then power is monitored (observed) and then perturbed with
a new duty cycle depending on the monitoring result.
The SPV1020 IC executes the MPPT algorithm with a fixed period (equal to 256 times the
switching period), required for the application to stabilize its behavior (voltages and currents)
with the new duty cycle.
The duty cycle increase or decrease depends on the update done in the previous step and
by the direction of the input power.
The MPPT algorithm compares the current input power (Ptn) with the input power computed
in the previous step (Ptn-1).
If power is increasing then the update is done in the same direction as in the previous step.
Otherwise the update is swapped in the opposite direction (from increasing to decreasing or
vice-versa).
Figure 5 shows the sampling/working points (red circles) set by the SPV1020 and how they
change (red arrows) during normal operating mode.
Figure 5.
MPPT perturb & observe tracking
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The input voltage is sampled by an external resistive partitioning, while the input current is
sampled internally in order to reduce the external component. Here follows a simple
schematic of the input voltage sensing circuitry (see the SPV1020 datasheet).
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Optimizing the energy from the panel
Figure 6.
AN3971
Input voltage partitioning sample circuit
06
4O)NDUCTORS
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6IN
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6IN?SNS 06
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6 IN
2
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06 Input voltage partitioning is important in order to adapt the correct panel to insert in the
standalone PV system, also according to the battery current capability and the charging
time necessary to reach the total battery SOC.
2.1
Regulations, protection, and features
The STEVAL-ISV005V2 implements the application settings to use the protection provided
by the SPV1020 IC, which can be summarized as follows:
●
Overtemperature protection
●
Output overvoltage regulation
●
Output overvoltage protection: input overcurrent protection
●
Current balance
●
Input MPPT settings.
For details regarding the above list of protection and functionalities, please refer to the
SPV1020 datasheet and its basic application STEVAL-ISV009V1.
In addition to the above list, the STEVAL-ISV005V2 also implements an output overcurrent
protection through the SEA05 IC (details in Section 3.2 of this document).
Figure 7 offers a brief description of the architecture implemented.
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Optimizing the energy from the panel
Figure 7.
System architecture
PV +
Vbatt +
R17
Vout_sns
SPV1020
R1
Vin_sns
R2
PZ_Out
R18
Vctrl
SEA05
R19
R9
PV -
Vbatt -
IOUT control
AM10277V1
The SPV1020 only implements an interleaved 4-boost converter, causing a voltage increase
from input to output, so in order to charge a lead acid battery, it is mandatory to use a panel
with Voc <= V_batt_min, just to keep a step-up voltage configuration.
If a 12 V battery charging is needed, it is necessary to add an additional buck stage to the
system, in order to decrease the output voltage from STEVAL-ISV005V2 higher than
Vbatt_min. A generic schematic may be that in the image below:
Figure 8.
Architecture with DC-DC buck converter (for 12 V batteries)
Ipv
Energy Flow
Vbatt
Ibatt
VOUT
VCTRL
SEA05
GND
Feedback Pin
DC/DC
Buck
converter
VOUTsns
L1
L2
L3
L4
SPV1020
VINsns
PZOUT
OUT
IOUT control
AM10278V1
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Charging a lead acid battery
3
AN3971
Charging a lead acid battery
A proper charging profile is important to guarantee a long battery lifetime.
The following figure shows the correct voltage/current charging profile (for a single cell only):
Figure 9.
Typical SLA battery charging curve
Some of the charging constraints are given below and must be applied to all types of lead
acid batteries.
1.
2.
3.
10/28
Starting from a battery discharge, the maximum current must be lower than a value of
C/4 (where C is the maximum battery capacity in Ampere hour [Ah]) →I_batt_max =
0.25 * C
In any charging step, the voltage applied must not be greater than the gassing voltage
→V_batt_max = 2.4 V per cell
During the recharge and up to 100% of the previous discharge capacity, the current
should be controlled to maintain a voltage lower than the gassing voltage →to reduce
charge time, this voltage can be just below the gassing voltage.
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AN3971
Charging a lead acid battery
So, to respect all the constraints mentioned above, the charging strategy used is a multivoltage battery charging profile with:
3.1
●
Constant current to perform a bulk charge, when the battery is charged using a current
regulation to I_batt_max, up to 70% SOC, in about 4 hours, and the battery voltage
slowly increases up to the nominal value (equal to 2 V per cell)
●
Constant voltage to perform a floating charge, when the battery is charged using a
voltage regulation to V_batt_max, up to the remaining 30% SOC, with a slow current
decrease down to C/10 or C/100 values. This stage lasts 6 hours and is essential for
the battery lifetime
●
Constant current to perform a trickle charge, which compensates the self-discharge of
the battery, even after it has been fully charged. Normally the charging current is less
than C/100, and even if the battery is not completely saturated, the SLA can eventually
lose its ability to accept a full charge and its performance is reduced.
Constant current – constant voltage control
In order to properly control the lead acid charging profile in terms of max. current during the
bulk charge, and the max. voltage during the floating charge, the SEA05 IC has been used.
The lead acid battery chemistry and physics behavior affect the charging strategy itself.
This occurs particularly during the last two steps of the lead acid charging profile:
3.2
●
During the floating charge, the sink current decreases slowly because of the battery
features keeping a constant voltage charge at the maximum value
●
During the trickle charge (which is normally necessary just after the natural battery
discharging), in order to keep the battery at a maximum SOC. In this case, no control
acts, just to allow the energy flow directly from the panel towards the battery, without
any constraints or voltage/current limitation.
SEA05 features
The SEA05 is a highly integrated solution for SMPS applications requiring a dual control
loop to perform CV (constant voltage) and CC (constant current) regulation, implemented by
two operational amplifiers, and a low-side current sensing circuit.
Figure 10. SEA05 internal architecture
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Charging a lead acid battery
AN3971
The voltage reference, along with one op amp, is the core of the voltage control loop; the
current sensing circuit and the other op amp make up the current control loop.
The external components needed to complete the two control loops are:
●
A resistor divider that senses the output of the power supply and fixes the voltage
regulation set-point at the specified value
●
A sense resistor that feeds the current sensing circuit with a voltage proportional to the
DC output current, setting the current regulation set-point (it must be adequately rated
in terms of power dissipation)
●
The frequency compensation components (R-C networks) for both loops.
Please refer to the SEA05 datasheet for further details.
3.3
Interaction between the SPV1020 and SEA05
The SPV1020 usually sets the duty cycle according to the MPPT algorithm except when
even one of the protection or regulation thresholds is triggered.
Regarding overvoltage regulation, if the voltage on the Vout_sns pin triggers 1 V, the output
voltage feedback loop enters regulation, implying an upper limit to the duty cycle computed
by the MPPT. The higher the voltage on the Vout_sns pin, the lower the upper limit on the
duty cycle. The output voltage regulation acts in the range 1 V = Vout_sns
< 1.04 V. If the 1.04 V threshold is triggered then the overvoltage protection forces the burst
mode.
The stability of the regulation loop can be externally regulated by connecting a resistor and a
capacitor (pole-zero compensation) between the PZ_OUT pin and SGND pin.
The PZ_OUT pin may have two different roles:
●
To perform compensation loop to control the Vout_sns behavior
●
To force an imposed duty cycle proportional to its voltage on the pin.
Figure 11. Internal duty cycle reference
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The final duty cycle results from the minimum value between the one due to MPPT
algorithm, and the second one imposed by the PZ_OUT external voltage.
The SEA05 provides two independent internal thresholds designed to separately control
battery voltage and current control.
If one of the two thresholds is triggered, the common output is proportionally forced low, and
the internal duty cycle imposed is proportional too.
Therefore, the output behavior of the SEA05 is perfectly compatible with the PZ_OUT pin of
the SPV1020.
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4
External component selection
External component selection
The STEVAL-ISV005V2 is based on two ST key devices: the SPV1020 and SEA05.
In order to perform properly, both the SPV1020 and SEA05 require different application
components whose selection depends on the electrical characteristics of the PV panel and
of the battery.
The electrical characteristics of the PV panel limit the selection of the application
components of the SPV1020. Please refer to the SPV1020 datasheet.
In order to properly define the application components for the SEA05, the user should
simply define the following parameters:
●
Output resistor partitioning (R7/R8) according to the SEA05 internal voltage control
threshold, to control the maximum overvoltage battery protection
●
Sensing resistor (Rsns: R9 and/or R10) in the PV-loop, to control the maximum
overcurrent battery protection, according to the internal current threshold
●
The PV panel must be selected in order to guarantee the SPV1020 functionality; and
so, in order to respect the SPV1020 step-up conditions, the Voc of the PV panel must
be lower than Vbat_min (voltage when the battery is deeply discharged).
The STEVAL-ISV005V2 application example has been developed for the following features:
SLA battery: Vbatt_nom = 24 V & C = 4 Ah
PV panel: Vmp = 18 V & Voc = 20 V, Imp = 1.6 A & Isc = 2 A
So the SEA05 IC must limit at the following voltage and current:
Vbatt_max = (24 * 1.2) V = 28.8 V
Ibatt_max = (4/4) A = 1 A
Figure 12. System architecture SPV1020 + SEA05
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External component selection
4.1
AN3971
Output current regulation
Output current regulation is implemented by the SEA05 current control loop.
The voltage threshold related to the current control is equal to 50 mV.
So to perform a current regulation, Rsense must be selected by the following equation:
R sense ⋅ Iomax = V csth
For example, with Iomax = 1 A, Vcsth = 50 mV, then Rsense = 50 mΩ.
V csth
R sense = ------------I omax
Note that the Rsense resistor should be chosen taking into account the maximum power
dissipation (Plim) through it during full load operation.
P lim = V csth ⋅ I omax
4.2
Battery voltage control
The voltage loop is controlled via a voltage divider R7, R8 directly inserted on the SPV1020
output voltage.
It is possible to choose their values using the following equations:
( R1 + R2 )
VO = V csth ⋅ ------------------------R2
and
( VO + V ctrl )
R 1 = R 2 ⋅ -----------------------------V ctrl
where VO is the desired output voltage = V_batt_max.
In the case of V_batt_max = 28.8 V, with Vctrl internally fixed by the SEA05 to 2.5 V, the
values must be:
R7 = 2.7 MΩ ; R8 = 255 kΩ.
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AN3971
External component selection
Here follows a schematic regarding SEA05 connections for the application example:
Figure 13. SEA05 schematic
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STEVAL-ISV005V2 schematic
AN3971
STEVAL-ISV005V2 schematic
Figure 14. STEVAL-ISV005V2 schematic
!-V
Bill of materials
Table 1.
Bill of materials
Item Quantity Reference
Part
/value
Voltage
current
Watt
(mW)
Tecnology
information
Bill of materials
17/28
6
Package
Manufacturer
Manufacturer code
More Info
PSS036
ST
SPV1020
STM SUPPLY
Murata
GRM188R71C104KA01D
TDK
C1608X7R1H104K X7R
Bootstrap
capacitors
Murata
GRM188R71E474KA12D
EPCOS
C1608X7R1C474K
Murata
GRM188R71C223KA01
EPCOS
C1608X7R1H223K
Murata
GRM188R71E221KA01
EPCOS
C1608C0G1H221J
Murata
GRM31MR71H105KA88
EPCOS
C3216X7R1H105K
Murata
GRM32ER71H475KA88L
EPCOS
C3225X7R1H475K
SPV1020 section
Doc ID 022119 Rev 2
1
1
J35
2
4
C1, C2,
C3,C4
100nF
C7
470nF
6
7
8
10
11
1
1
2
1
7
C8
C9, C10
C11
22nF
220pF
1µF
C5, C6,
C12, C13,
C14, C15,
C16
4.7µF
16V
50V
X7R
25V
X7R
25V
50V
50V
50V
X7R
X7R
X7R
X7R
0603
0603
0603
0603
1206
Internal reference
voltage capacitor
Compensation
capacitor
Voltage sensing
capacitor
Input capacitor
1210
Output capacitor
2
D1, D2
Diode
15A, 60V
MLPD5x6
STM
SPV1001N40
Bypass diodes
20
1
D3
Diode
1A, 60V
SMB
STM
STPS160U
Noise filter on
supply pin
21
2
D4, D5
Transil
™
40V
SMB
STM
SMBJ36CA-TR
600W, 40V
unidirectional
protection Transil™
AN3971
18
Bill of materials (continued)
Item Quantity Reference
Part
/value
Voltage
current
1.8V, 2mA
Watt
(mW)
Tecnology
information
Package
Manufacturer
Manufacturer code
More Info
TH
AVAGO TECH.
HLMP-1700
Output limitation led
control
MULTICOMP
MCHP03W8F2204T5E
Input voltage
pertitioning resistor
VISHAY DALE
CRCW0603110KFKEA
MULTICOMP
MC0603SAF1103T5E
23
1
D9(1)
TH
RED
LED
24
1
R1
2.2MΩ
125
0603
25
1
R2
110kΩ
125
0603
Input voltage
pertitioning resistor
Doc ID 022119 Rev 2
26
1
R5
1kΩ
100
0603
YAGEO
RC0603FR-101KL
Compensation
resistor
27
1
R13(1)
1.5kΩ
100
0603
YAGEO
RC0603FR-071K5L
LED polarization
resistor
28
1
R6
0Ω
100
0603
YAGEO
RC0603FR-070RL
Pull up resistor(2)
0
R7
(optional)
Depend
ing on
desired
Fsw
29
29
4
L1, L2, L3,
L4
DNM
Oscllator resistor (1)
0603
EPCOS(3)
B82477G4473M
Coilcraft
MSS1278T-473ML
CYNTEC
PIMB136T-470MS-11
Murata
49470SC
Phoenix
Contact
1723672
TH
Phoenix
Contact
1714955
SOT23-6L
STM
SEA05TR
47µH
1
J36
4pin
conn.
34
2
J47, J48
Faston
conn.
36
1
J40
2pin
conn.
J37
SEA05
Pitch2.54mm
TRH
Phase x (x=1..4)
inductors
TH
Pitch6.35mm
SEA05 section
37
1
CV-CC controller
AN3971
33
Bill of materials
18/28
Table 1.
Bill of materials (continued)
Item Quantity Reference
Watt
Part
/value
Voltage
current
(mW)
Tecnology
information
Package
Manufacturer
Manufacturer code
50ppm/°C
2010
Welwyn
ULR1SR005FT2
Farnell:
1469782
Current sensing resistor
More Info
Doc ID 022119 Rev 2
38
1
R9
5mΩ (4)
39
1
R10
220kΩ
100
0603
YAGEO
(PHYCOMP)
RC0603FR-07220KL
Voltage comp. loop
resistor
40
1
R11
22kΩ
100
0603
YAGEO
(PHYCOMP)
RC0603FR-0722KL
Current comp. loop
resistor
41
1
R17
3MΩ
100
0603
VISHAY
DRALORIC
CRCW06033M00FKEA
42
1
R18
187kΩ
100
0603
VISHAY
DRALORIC
CRCW0603187KFKEA
43
1
R19
100kΩ
100
0603
VISHAY
DRALORIC
CRCW0603100KFKEA
Murata
GRM188R71C472KA01B
44
1
C14
4.7nF
MULTICOMP
MCCA001139
Murata
GRM188R71C223KA01
MULTICOMP
MCCA001143
Murata
GRM188R71C104KA01D
TDK
C1608X7R1H104K X7R
45
46
1
1
C15
C17
22nF
100nF
16V
16V
16V
50V
X7R
X7R
X7R
0603
0603
0603
AN3971
Table 1.
output voltage part.
resistor(5)
Current comp. loop
capacitor
Voltage comp. loop
capacitor
Output filter
1. Do not mounted (DNM).
2. R6 must be removed if R7 is soldered.
3. Better performances can be obtained using part number B82477G4473M003 (DCR = 52mΩ)
4. Default value to sense 50 mV @10 A max.
19/28
Bill of materials
5. Two threshold is suited: # 2.5 V for SEA05: R17=3MΩ, R18+R19=287kΩ => Vmax=28.8 V # 1V for SPV1020: R17+R18=3.187 , R19=100kΩ => Vmax= 35 V.
Layout guidelines
7
AN3971
Layout guidelines
PCB layout is very important, especially for the SPV1020, in order to minimize noise, high
frequency resonance problems, and electromagnetic interference.
Paths between each inductor and the relative pin must be designed with the same
resistance. Different resistance between the four branches can be the root cause of
unbalanced currents flowing between the four branches. Unbalanced currents can imply
damage and a bad tracking of the MPPT.
It is essential to keep the paths as small as possible where the high switching current
circulates, to reduce peak voltages, radiation and resonance problems.
Large traces for high current paths and an extended ground plane under the metal slug of
the package help reduce noise and heat dissipation, and furthermore, increase the
efficiency. Depending on the maximum power of the application, two or more ground plane
layers may be required, and in this case thermal vias must connect the ground plane layers.
The number of layers, their thickness and number of thermal vias, affect the thermal
resistance (Rth) of the SPV1020: for a proper design according to the power of the specific
application it is suggested to refer to the TN0054 technical note.
The boost capacitors, output and input capacitors, must be placed as close as possible to
the pins of the IC. Output capacitance must be shared in at least four capacitors, each one
connected to the four Vout pins of the SPV1020 IC.
The external resistor dividers, if used, should be as close as possible to the Vin_sns and
Vout_sns pins of the device, and as far as possible from the high current circulating paths, to
avoid pick-up noise.
Figure 15. STEVAL-ISV005V2 (top view)
AM10267V1
20/28
Doc ID 022119 Rev 2
AN3971
Layout guidelines
Figure 16. STEVAL-ISV005V2 (bottom view)
AM10268V1
Doc ID 022119 Rev 2
21/28
Application connection example
8
AN3971
Application connection example
Figure 17. STEVAL-ISV005V2 board connection
PV panel
PV-
PV+
STEVAL-ISV005V2
SPV1020
SEA05
Current Sense
Voltage Sense
Vbat -
Vbat +
AM10266V1
22/28
Doc ID 022119 Rev 2
AN3971
9
Experimental results
Experimental results
In order to test all the functionalities regarding the MPP tracking, and battery charging
capability, the following parts are used:
●
Two SLA batteries (12 V, 4 Ah), connected in series
Figure 18. SLA battery (12 V, 4 Ah)
●
A solar array simulator (SAS), that allows total emulation of a PV panel electrical
behavior
Figure 19. Solar array simulator (SAS)
●
Four multimeters, to check the voltage and current values in the input and the output of
the STEVAL-ISV005V2, to evaluate the MPP tracking efficiency, such as the power
efficiency, and obviously to trace the battery charging curve.
Doc ID 022119 Rev 2
23/28
Experimental results
AN3971
Figure 20. SLA battery charging profile (24 V, 4 Ah)
4RICKLE
#HARGE
)?BATT
!
"ULK#HARGE
&LOATING#HARGE
6?BATT
6
6?BATT?-AXX6?"ATT?.OM
)?BATT?MAX#
3/#
-AINTENANCE
)?"ATT
6?"ATT
3/#
3/#
4IMEH
Figure 21. SLA battery charging profile (12 V, 12 Ah)
)?BATT
!
4RI CKLE
"ULK#HARGE
&LOATING#HARGE #HARGE
)?BATT?MAX#
6?BATT
6
6?BATT?-AXX6BATT?NOM
3/#
-AINTENANCE
)?"ATT
6?"ATT
3/#
3/#
4IMEH
24/28
Doc ID 022119 Rev 2
AN3971
Experimental results
Figure 22. SLA battery charging profile (24 V, 24 Ah)
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Doc ID 022119 Rev 2
25/28
Conclusion
10
AN3971
Conclusion
In a standalone PV system, an SPV1020 with MPPT and step-up IL4 embedded
architecture, used in an application field together with the constant voltage - constant
current SEA05, allows the proper charging of an SLA battery, without any damage or lifetime
reduction.
The architecture, compared with a similar one implemented with a microcontroller, external
discrete components and IL4 step-up, performs better in terms of power and MPPT
efficiency.
Furthermore, the distributed approach, directly applied on the panel, allows the
management of any power reduction due to shadow, clouds, etc.; all features which are
unsuitable to centralized architecture.
The proposed solution is cost effective when compared with other systems, because of its
MPPT algorithm, and IL4 architecture, which are fully integrated inside the SPV1020.
26/28
Doc ID 022119 Rev 2
AN3971
11
12
References
References
●
SPV1020 datasheet
●
SEA05 datasheet
●
TN0054 technical note
●
E. Koutroulis, K. Kalaitzakis, “A Novel Battery Charging Regulation System for
Photovoltaic Applications” IEEE Proc.-Electr. Power Appl., 2004, vol. 151 n.2,.
Revision history
Table 2.
Document revision history
Date
Revision
Changes
15-Feb-2012
1
Initial release.
11-May-2012
2
Minor text changes in Section 2: Optimizing the energy from the
panel.
Updated BOM list Table 2 item 29.
Doc ID 022119 Rev 2
27/28
AN3971
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Doc ID 022119 Rev 2