WO2010011118A1

WO2010011118A1 - Self-oscillating boost converter for solar applications

Info

Publication number: WO2010011118A1
Application number: PCT/MX2008/000094
Authority: WO
Inventors: Sergio GARCÍA DE ALBA GARCIN
Original assignee: Garcia De Alba Garcin Sergio
Priority date: 2008-07-21
Filing date: 2008-07-21
Publication date: 2010-01-28

Abstract

The invention relates to a self-oscillating circuit for transferring power to an electric charge storage means in a circuit, which can store large quantities of power, whereby the storage capacity thereof can be increased gradually. The self-oscillating circuit is particularly suitable for portable applications using photocells and having relatively low power consumption requirements, e.g. TV remote controls, car keys, LED lamps, electronic paper (portable OLED type displays), wireless sensors and other portable applications for which batteries are not to be used.

Description

A SELF-OSCILLATING BOOST CONVERTER FOR SOLAR APPLICATIONS

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to systems for energy storage and more specifically with a system for transferring energy to a storage medium, which can store significant amounts of energy very efficiently, and its storage capacity can be increased so that It makes it possible to ignore the use of rechargeable batteries.

The scope of the new invention is wide, but it is particularly useful for portable applications with relatively low power consumption, in which it is desired to operate without batteries, and using photocells, for example, TV remote controls, car keys, LED flashlights, electronic paper (portable OLED displays), wireless sensors, etc.

Previous Art

The circuit that is technically more similar to innovation is a "boost" DC-DC converter. However, there are clear differences between the two since the boost converter usually requires an oscillator, while the new proposal uses feedback to generate the oscillation, instead of using an external oscillator, and the voltage gain does not It is a fixed relationship, but it increases as necessary to store more energy, taking advantage of the fact that in a capacitor the stored energy is ¹ A CV. Other devices that can be considered similar are the so-called "solar engines", but these do not have the ability to increase the voltage in the capacitor to store more and more energy. Rather, such devices are characterized in that they charge a capacitor at a fixed voltage, to subsequently discharge it, and repeat the operation, or else store the energy in rechargeable type batteries.

Solar-powered products currently store energy in rechargeable batteries or store small amounts of energy in capacitors and then release it in bursts as in the case of Miller's solar device. However, in the latter case, the amount of energy stored in the capacitor is so small that it does not guarantee sufficient charging autonomy to result in prolonged use of the solar device so it necessarily uses rechargeable batteries. There are other similar devices of good efficiency that help make applications based on solar energy more practical, however, they have the disadvantage that the voltage gain is fixed. For example, Texas Instruments Incorporated has introduced the industry's lowest input voltage DC / DC boost converter in the market, which will allow electronic portable equipment to extract energy from new energy sources, such as solar cells and microcell cells. fuel. The tiny power circuit can operate with input voltages lower than 0.3 volts with high efficiency allowing designers to solve the barrier of low voltage designs by incorporating these alternative energy sources into applications such as mobile phones, portable medical devices and players media. However, the drawback of this device is that it handles a fixed voltage gain ratio which does not appropriate for storing significant amounts of energy in a capacitor.

In US Patent No. 6,597,155 to Huang, a DC-DC auto-oscillation converter circuit is described which includes a first transistor electrically connected with a positive input terminal, a second transistor electrically connected with the first transistor and operable to pass a part of a base current of the first transistor, and a circuit to stabilize the output voltage, electrically connected between the second transistor and a positive output terminal. The negative output terminal is directly connected to the negative input terminal. The DC-DC auto-oscillation converter circuit does not use an auxiliary turn, thus allowing the use of NPN transistors. The positive regeneration is obtained by a change of the Y _cel voltage of the first transistor from a saturation state to a non-saturation state. In the non-saturation state, the second transistor is turned on, the first transistor is turned off and auto-oscillation is reached. With this structure, the DC-DC auto-oscillation converter works normally when the input voltage is lower than 5V ¿ _C.

For its part, Nerone US Patent No. 6,525,488 proposes a self-oscillating boost converter that includes a resistor starter network configured to initiate a converter load. A resonant regeneration circuit is designed to generate an oscillating signal immediately after the circuit starts through the resistor start-up network. A complementary switching network has a pair of complementary switches connected to a common source configured to receive the oscillation signal generated by the resonant regeneration circuit. The oscillation signal determines a switching index, or a service cycle of the pair of complementary switches. A boost inductor is in operational connection with the torque of complementary switches. The switching speed of the complementary switching network acts to determine the boost voltage supplied to a load. Among the differences that exist with the new converter are that the components to generate the self-oscillation are analog and not digital, this converter does not include a memory element and is not designed to gradually store energy at increasing voltages.

Renyolds U.S. Patent No. 6,657,419 refers to a micro-solar isolation circuit that has a boost regulator or DC-DC converter used to transfer available energy from a solar cell source, at a value close to optimal, at a load. The micro-solar isolation circuit comprises a comparator to generate an error signal based on a reference voltage of the solar cell where a modulator controller receives the error signal and changes its duty cycle based on the error signal. The modulator controller controls a high-speed switch in association with a synchronous rectifier to limit the current without causing loss. The circuit of this patent seeks to transfer the energy of solar cells to a load in the most efficient way in real time, however, it is not designed to store said energy.

SUMMARY OF THE INVENTION

The main object of the present invention is to propose a novel system for transferring energy or load to a medium (Je storage of charge in a circuit, by taking advantage of the internal resistance of certain energy sources, for example photocells, so that together with certain logic is achieved a self-oscillation that allows the structure type converter "boost" to charge the capacitor at increasing voltages as necessary. This is achieved by the way the work cycle is self-adjusting.

Another object of the invention is to propose a converter that, unlike those currently used, does not require an oscillator, since it uses feedback to generate the self-oscillation. This has the advantage of reducing the cost of the device.

In a preferred embodiment, the invention consists of a self-oscillating boost converter for solar applications of the type that can be used to operate low energy consumption devices, and which makes it possible to dispense with the use of rechargeable batteries, said converter is characterized by a circuit that makes use of feedback to generate the oscillation, instead of using an external oscillator, in addition said circuit is characterized in that it handles a non-fixed voltage ratio, which varies in increment so that it can gradually increase its storage capacity. The new self-oscillating converter comprises: a) an autonomous or self-contained energy source; b) a boost type voltage converter that is powered by the power source to increase the voltage of said power source; c) an energy storage device that can store energy at different voltages that is connected to the output of the converter; and d) a logic feedback circuit that is connected to the input node of the boost converter and its switching element, which serves to generate the necessary oscillation for said converter; further said logic circuit allows a dynamic relationship in the voltage gain produced by the boost converter; said logic circuit includes a memory element to allow operation with hysteresis. In an alternate embodiment, the converter may also include a restorative circuit that goes into operation to restore or restart the operation of the converter when a fault occurs, caused for example by noise or electromagnetic interference.

In another aspect of the invention, a method for transferring energy to an energy storage medium in a self-oscillating circuit is also described, which can gradually increase its energy storage capacity.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a diagram of a conventional boost converter, in which we can see that the oscillation is usually generated by an oscillator or an external logic medium, for example a microcontroller, and the ratio of the output voltage to the input voltage is set. for the work cycle of the swing.

Figure 2 corresponds to a typical circuit commonly used in devices supplied with solar energy.

Figures 3 and 4 are circuit diagrams of a low-energy boost converter of the prior art, wherein the circuit of Figure 3 corresponds to the external connection of the integrated circuit and Figure 4 to its internal structure. Figure 5 is an exemplary schematic representation of a structured auto-oscillatory boost converter according to the new invention.

Figure 6 is a diagram of a test of the new concept developed under ideal conditions. Figure 7 is an enlarged view of a part of the diagram of the previous figure.

Figure 8 is a schematic diagram of the new converter with the difference that in this mode a restorative circuit is included to reset said converter if a fault occurs.

Figure 9 is representative of a diagram of a simulation of the circuit of Figure 8, under non-ideal conditions.

Figure 10 is an enlargement of the diagram of the previous figure.

Figure 11 is a flow chart describing the charging procedure of the energy storage element of the new converter.

Figure 12 is a flow chart describing the operation of the restorative circuit.

Figure 13 is a diagram of a simulation of the operation of the converter restorative circuit.

DETAILED DESCRIPTION OF THE PREFERRED MODE

OF THE INVENTION

The invention consists of a self-oscillating boost converter that is suitable for application where the energy source has an internal resistance / impedance, similar to photocells and in which the energy is stored in capacitors or other suitable energy storage medium. . The new converter is characterized in that it uses the internal resistance of the power source, together with the inductor and the logic components, to create the oscillation necessary to increase the input voltage and in which the frequency and duty cycle are self adjust to increase the voltage on the capacitor of storage and, consequently, the amount of energy that is stored in it. In this way, the internal resistance / impedance of the energy source is used to materialize the converter of the present invention. The reason why the present innovation allows to store significant amounts of energy (eg solar energy) in a capacitor, is because it causes the voltage in the capacitor to increase as necessary, and the energy stored in a capacitor is given by the formula: E ^ and ₂ C v ² where:

C is the capacitance; Y

V is the voltage on the capacitor.

With reference to Figure 5, the system is characterized by the following basic elements: photocells (F) with the negative terminal connected to ground and the positive terminal connected to the identified node Vx, an inductor (Ll) with a terminal connected to the node Vx and the other connected to the collector of a NPN (M3) Mosfet transistor. Said transistor (M3) has its emitter connected to ground, and its base to the identified node Vsw. There is also a diode (Dl) with its positive terminal connected to the inductor terminal (Ll) that is connected to the transistor collector (M3), and with its negative terminal connected to the storage capacitor (C), which has its Another grounded terminal. A second diode (D2) has its positive terminal connected to the Vx node, and its negative terminal to a capacitor terminal (C2) and pins 0 (CLRBAR) and 3 (PREBAR) of the memory element (Ul), said node is identified as Vref. The second capacitor terminal (C2) is grounded.

The circuit also includes a PNP (Ml) Mosfet transistor with its base connected to the node Vx ₅ thereof connected to the node Vret emitter and its collector connected to a terminal of the impedance (Zl) and to one input of the gate (XNOR) and said node is identified as Va. The other impedance terminal (Zl) is grounded. For its part, the Mosfet NPN type transistor (M2) has its base connected to node Vx ₅ its emitter connected to ground, and its collector connected to an impedance terminal (Z2) as well as to a gate input (XNOR) and said node is identified as Vb. The other impedance terminal (Z2) is connected to the Vref node. The output of the XNOR, identified as Logical, is connected to pin 2 (CLK) of the memory element (Ul). The rest of the pins of the memory element (Ul) are connected as follows: pin 5 (QBAR) connected to pin 1 (D) and node Vsw, and pin 4 (Q) is left offline.

In accordance with the preferred embodiment of the invention, shown in Figure 5, the voltage Vx ₅ at the node between the photocells (F) and the inductor Ll decreases when the transistor M3 is closed (Vsw high). Eventually, this causes Va and Vb to have a logical voltage of 1, and a pulse is generated at the output of the XNOR gate (Vlogic), changing the output state of the memory element (Ul), which in turn it opens the transistor M3, and causes Vx to start increasing. Eventually, both Va and Vb have a logical O voltage, which changes the state of the memory element (Ul) again, and the entire process described above is repeated.

The repetition of the previous process generates a gradual increase in the load stored in the capacitor, which can be used to supply a device without the need for traditional batteries.

The diode Dl is arranged to prevent the storage capacitor C from discharging. The way the voltage in the capacitor goes increasing is the same as in a conventional "boost" converter, that when the transistor (M3) is opened, the energy that was stored in the inductor causes the voltage in it to increase and the polarity that it had when the transistor is reversed It was closed, so that they end up adding the source and inductor voltage, thus charging the capacitor to a higher voltage.

The relationship between the input voltage (Vdc) and the voltage at which the capacitor is charged (Vo) is given by the formula:

V ₀ _ 1 Vi 1 - D where:

D is the duty cycle, that is, the relationship between the time that transistor M3 is on of the total cycle time.

The longer the transistor M3 is closed, the more energy is stored in the inductor Ll, and when there is less time (transistor M3 open) to discharge (charging the capacitor) the inductor voltage is forced to increase (to respect the energy conservation).

Unlike a traditional "boost" type circuit, in which the Vo / Vi ratio is fixed (or semi-fixed, since the oscillator signal would have to be generated and modified artificially), with the present invention it is sought that said relationship It increases as it becomes necessary, in a more dynamic, economical and simple way. This is achieved by being an auto-oscillatory circuit, so that the work cycle is self-adjusting to generate the voltage necessary to charge the storage capacitor.

CONVERTER OPERATION MODE: Based on the flowchart of Figure 11, the operation of this converter is described below: State 1:

When starting the converter, the voltage Vx tends to decrease at a certain speed, mainly due to the values of the inductor Ll and the resistance / internal impedance of the solar cells. At this time, the voltage Vsw is at its high value and the transistor M3 is closed. State 2:

Vx continues to decrease, now at a certain distance from the reference voltage Vref, while the voltage Va changes to logical 1. State 3:

As Vx approaches OV, the voltage Vb changes from logic 0 to logic 1, then the logic voltage produces a pulse and the memory element (Ul) switches state so that, at this time, the state is reversed of the voltage Vsw, going from high Vsw to low Vsw, and the transistor (M3) changes to open state. State 4:

The voltage Vx is increased at a rate influenced by the internal resistance of the solar cells, the value of the inductor Ll and the size of the capacitor C. At this moment, the voltage Vsw is low and the transistor M3 is open. State 5:

The voltage Vx continues to increase, now at a distance from the OVs, while the voltage Vb changes to logical 0. State 6:

Bl voltage Vx approaches the reference voltage Vref, changing the voltage Va from logic 1 to logic 0, the logic voltage generates a pulse and the memory element (Ul) switches status. At this time, it invert the voltage state Vsw, going from low Vsw to high Vsw, and the transistor (M3) changes to closed state.

The repetition of the previous cycle causes the amount of energy accumulated in the storage medium C provided in the circuit to be gradually increased for that purpose.

Figure 7 shows a partial representation of a simulation test of the operation of the circuit illustrated in Figure 5, which shows how the voltage increases in the storage capacitor (Vo) and the oscillation is also appreciated in the voltage Vx which is related to the charge and discharge of the inductor (Ll). Furthermore, in said diagram Vsw represents the voltage at the output of the memory element (Ul), which controls the switching of transistor M3.

With reference to figure 8, this corresponds to the circuit of an alternative system to that of figure 5, which is characterized in that a circuit (M4, Z3, C3, XOR) has been incorporated to restore or put the converter back into operation. in the event of a failure, for example, by noise or electromagnetic interference. For that purpose, the restorative circuit includes an analog counter (Z3, C3), which is being periodically reset by the transistor (M4) which in turn is activated by the oscillation of the memory element (Ul) when the device is working correctly; when a fault occurs, this counter exceeds a certain threshold and produces an inversion in the output of the XOR gate which in turn reverses the state of the switching element (M3), reactivating the system and allowing the converter to function normally again. The impedance Z3 is the medium that controls the charging speed of the capacitor C3.

In this alternate implementation, represented by way of example in Figure 8, the restorative circuit comprises the capacitor (C3) that during the normal operation of the system is cyclically charged and unloaded from partially so that when the size is presented left αe be downloading to said capacitor, so the voltage on it exceeds a threshold which in turn inverts the output of the XOR ₃ gate which reactivates the system and makes continue functioning as described here in advance.

As seen in the exemplification shown in Figure 8, the collector of transistor M4, which in the illustrated case consists of a Mosfet transistor type PNP ₅ is grounded and its emitter is connected to a reference voltage through the impedance Z3, as well as to a C3 capacitor terminal and an XOR gate input. The second terminal of capacitor C3 is grounded and the base of transistor M4 is connected to the non-denied output of the memory element (Ul).

With reference to the diagram of Figure 10, which corresponds to the simulation of the operation of the converter under non-ideal conditions, specifically, a circuit fault is simulated within a pre-selected time range and it is observed that the restorative circuit makes a first attempt to reinitialize the operation of the converter without achieving it, since the fault / interference was still present, and on a second occasion said circuit manages to successfully restore the operation of the circuit. It can also be seen in this diagram that during the fault period the capacitor load is interrupted, which can be observed in the Vo voltage that stops increasing. Similarly, it can be seen that during the fault period the oscillation of Vx and Vsw is interrupted. Another aspect of the present invention is to propose a method for transferring energy to an electric charge storage medium in a self-oscillating circuit, which can gradually increase its energy storage capacity. The method comprises the steps of: a) supply energy from a self-contained autonomous source at an auto-oscillatory circuit input; b) during a first interval, store energy in an inductor and monitor the loading progress of said inductor and, when a predetermined level of the inductor charging process is reached, generate a signal that changes the state of a memory element and cause the inductor to stop charging; c) during a second interval, the inductor transfers the energy to a variable voltage storage device, and the progress of energy transfer from the inductor to the storage device is monitored, and when a predetermined advance in the transfer process is achieved of energy, changes the state of said memory element and returns to the first interval. The diagram in Figure 12 refers to the operation of the restorative circuit in which, from the initialization of the system, a variable or counter (analog or digital) will be increasing and periodically this variable will be reset whenever the circuit It is working properly. So when a fault occurs this will cause the value of the variable to exceed a certain threshold which will invert the voltage Vsw, as described above, so that the operation of the system will be reactivated.

The converter reset circuit operates as follows: a) during a first interval, the counter value '(M4, Z3, C3) is increased; b) during a second interval, it is verified if the value of said counter has exceeded a predetermined value, where: bl) if this has been exceeded, the state of a switching element is reversed whereby the operation of the auto-oscillating circuit is restored and the counter is reset; and b2) if said value has not exceeded the predetermined value, it is verified if the memory element is oscillating: i) if the memory element is oscillating, the counter is reset and returns to the first interval, ii) if the memory element it is not oscillating, it returns to the first interval where the counter is increased.

For its part, in Figure 13, which corresponds to the simulation of the operation of the converter under non-ideal conditions; specifically, a fault in the circuit is simulated within a preselected time range, and the voltage that is used as the analog counter of the restorative circuit (Vreinicio) is shown, when the fault occurs it is seen as said voltage begins to increase notably. When said voltage exceeds a predetermined value or threshold, the restorative circuit reverses the voltage Vsw which in turn reverses the switching element (M3) to try to reset the circuit, which is successfully achieved until the second attempt (since during the first attempt the induced fault was still present) as described in the previous paragraph. Also, the value of the analog counter (Vreinicio) is reset when it exceeds said threshold.

For the present invention, a high performance, low power consumption type D flip flop has been proposed as a memory element. However, for a person skilled in the art it will be understood that said element can be replaced by someone else who performs the same function. It is also planned that some other components such as analog filters and shielding elements can be added to the circuit or decoupling, to mitigate the effects of electrical noise or electromagnetic interference.

Although this invention has been described in the context of the preferred embodiment or embodiment, it will be apparent to those skilled in the art that the scope of the exemplified concept extends beyond the design specifically described and illustrated to other possible alternative modalities of materialization of the invention that are feasible or viable. In addition, although the invention has been described in detail, any expert in the field to which the invention belongs may deduce that some of the constituent elements of the converter may be substituted or other different elements incorporated in the light of the foregoing description without modifying it in essence the result for which it has been conceived.

In view of the foregoing, it will be understood that several elements of the device may be combined with others or replaced by others to form alternate embodiments that lead to the same result. Accordingly, it is intended that the scope of the present invention not be construed as limited by the particularly described embodiment, but rather be determined by a reasonable interpretation of the content of the following claims.

Claims

1. IJn auto-oscillatory boost converter of the type that can be used to operate devices with low energy consumption, and that allows to dispense with the use of rechargeable batteries, said converter is characterized by a circuit that makes use of feedback to generate the oscillation, in addition said circuit is characterized in that it handles a non-fixed voltage ratio, which varies in increment so that it can gradually increase its storage capacity; The circuit comprises: a) an autonomous or self-contained energy source; b) a boost type voltage converter that is powered by the power source to increase the voltage of said power source; c) an energy storage device that can store energy at different voltages and that is connected to the output of the converter; and d) a logic feedback circuit that is connected to the input node of the boost converter and the switching element of said converter, which serves to generate the necessary oscillation for said converter; further said logic circuit allows a dynamic relation Qn the voltage gain produced by the boost converter; said logic circuit includes a memory element to allow operation with hysteresis.

2. The converter of claim 1, characterized in that it further includes a restoration circuit for resetting or restoring said converter when a fault occurs; said restorative circuit consists of a counter that is being reset periodically when the device is working correctly; when a fault occurs, this counter exceeds a certain threshold and produces an inversion in the state of the element of switching, reactivating the system and allowing the converter to function normally again.

3. The converter of claim 2, wherein the counter is analog or digital.

4. The converter of claim 1, which further includes other components such as analog filters and shielding or decoupling elements, to mitigate the effects of electrical noise or electromagnetic interference.

5. A self-oscillating boost converter of the type that can be used to operate devices with low energy consumption, and that allows to dispense with the use of rechargeable batteries, said converter is characterized by a circuit that makes use of feedback to generate the oscillation; furthermore said circuit is characterized in that it handles a non-fixed voltage ratio, which varies in increment so that it can gradually increase its storage capacity; The circuit comprises: a) an autonomous or self-contained energy source; b) a boost type voltage converter that is powered by the power source to increase the voltage of said power source; c) an energy storage device that can store energy at different voltages that is connected to the output of the converter; d) a logic feedback circuit that is connected to the input node of the boost converter and its switching element, which serves to generate the necessary oscillation for said converter; in addition said logic circuit allows a dynamic relationship in the voltage gain produced by the boost converter; said logic circuit includes a memory element to allow operation with hysteresis; Y e) a restoration circuit to restore or reset said converter when a fault occurs; said restorative circuit consists of a counter that is being reset periodically when the device is working correctly; when a fault occurs, this counter exceeds a certain threshold and produces an inversion in the state of the switching element, reactivating the system and allowing the converter to function normally again.

6. The converter of claim 5, wherein the counter is analog or digital.

7. The converter of claim 5, further including other components such as analog filters and shielding or decoupling elements, to mitigate the effects of electrical noise or electromagnetic interference.

8. A method for transferring energy to an electric charge storage medium in a self-oscillating circuit, which can gradually increase its energy storage capacity, said method consists of the steps of: a) feeding energy from an autonomous source self contained in an auto-oscillatory circuit input; b) during a first interval, store energy in an inductor and monitor the loading progress of said inductor and, when a predetermined level of the inductor charging process is reached, generate a signal that changes the state of a memory element and cause the inductor to stop charging; c) during a second interval, the inductor transfers the energy to a variable voltage storage device, and the progress of energy transfer from the inductor to the storage device is monitored, and when a predetermined advance is achieved in the process of transferring energy, change the state of said memory element and the first interval is returned.

9. The method of claim 8, wherein the voltage in the storage device is increased in order to store a greater amount of energy in said device.

10. The method of claim 8, which includes verifying the proper functioning of the auto-oscillatory circuit and in the event of a failure, restore or reset it.

11. The method of claim 8, wherein the restorative circuit operates in the following manner: a) during a first interval, the value of a counter is increased; b) during a second interval, it is verified if the value of said counter has exceeded a predetermined value, where: bl) if this counter has been exceeded, the state of a switching element is reversed whereby the operation of the circuit is restored auto-oscillating and the counter is reset; and b2) if said value has not exceeded the predetermined value, it is verified if the memory element is oscillating: i) if the memory element is oscillating, the counter is reset and returns to the first interval, ii) if the memory element it is not oscillating, it returns to the first interval where the counter is increased.

12. The method of claim 8, wherein the duty cycle is self-adjusting to generate the voltage necessary to store increasing amounts of energy in the storage medium.