Optical cell control system

Photocell Control System

The present invention relates to a control system of a photovoltaic cell (also known as a light valve).

The photovoltaic cell can be formed by clamping a layer of sensing material between two rigid parallel plates, usually a transparent sheet material, and each plate has a conductive surface layer facing the sensing material. Examples of the constituent components of the sensing material include suspended particles, liquid crystals, and electrochromic materials.

By applying or not applying a voltage across the opposing plate, the constituent components can be switched between the light penetration state and the light absorption, scattering or reflection state.

Photocells, including photocells with the control system of this case, can be used in mirrors or glass windows of vehicles and buildings to provide changes in light transmission. For example, it can be used as a glass window whose opacity and transparency can be adjusted to restrict the transmission of sunlight or to conceal the interior of a room or vehicle to ensure its internal privacy. It can also be applied to vehicle sun visors, roof sun windows or aircraft portholes.

The control system of the present invention is particularly suitable for photocells used in rearview mirrors of motor vehicles, and the control system of the present invention will be fully explained with reference to this application.

It is known to use photovoltaic cells for rear-view mirrors, such as the French patent specification FR2366958 (Brisard Gerard), to provide a rear-view element with reflectivity that changes as a function of the brilliance. Traditional vehicle rearview mirrors with anti-flash features, usually called prismatic mirrors, contain a "day" position and a "night" position. Vehicle driving can manually change the mirror position between day and night . In the daytime position, the rearview mirror needs to have a higher light reflectivity, usually greater than 50%. At night, the reflectivity is limited to 12% or less, usually about 4%, so that the driver can avoid dazzling, such as the dazzling caused by the headlights of a trailing vehicle.

The photocell provides a rear view mirror that can be automatically adjusted according to the received light conditions. It switches from the daytime position to the nighttime position, and vice versa. Its reflectivity changes within the aforementioned limits, thus providing convenience and safety benefits. . The photocell is located adjacent to and parallel to the reflective surface of the mirror, and is located in the line of sight between the reflective surface and the driving room of the vehicle. The photocell thus provides a variable degree of light reflectivity from the driver to the mirror. In a preferred structure, the reflective surface is provided by one of the conductive layers, which is also a reflective material.

The degree of light transmission or the reflectivity of the photocell is controlled by a control system triggered by external conditions. The control system is preferably located at the junction with the photovoltaic cell, so as to form a combined unit with the photovoltaic cell. However, the size of the conventional control system will encounter difficulties when miniaturizing any control system that includes the control system.

The main purpose of the present invention is to provide a photovoltaic cell control system that can be conveniently stored near the battery.

The present invention provides a photovoltaic cell control system. The system includes a first circuit and a second circuit. The first circuit is powered by a low-voltage power supply and includes an oscillator and a main winding of an induction coil. The second circuit includes The photovoltaic cell and the secondary winding of the aforementioned induction coil are characterized in that the second circuit is a resonance circuit including the inductance of the secondary winding and the photovoltaic cell, and the induction coil provides a weak coupling between the primary winding and the secondary winding.

Therefore, the control system of the present invention uses the inductance of the secondary winding of the coil as the inductance of a resonance (oscillation) circuit. The structure of the invention can effectively reduce the size of the control system.

The special advantage of the present invention is that the high voltage is limited to the second circuit, so the system can reduce the number of components withstanding high voltage. Since high voltage will cause safety issues and electromagnetic interference, limiting the high voltage to the second circuit is beneficial to reduce the space occupied by the high voltage component and reduce the amount of safety packaging required to surround the high voltage.

Many different types of photovoltaic cells are known. These photovoltaic cells include electrochromic (electrochromic) photovoltaic cells or liquid crystal photovoltaic cells or electrodeposition (electrodeposition) photovoltaic cells. In an electrodeposited photovoltaic cell, the current passing through a transparent liquid promotes the migration of metal ions to the glass surface and promotes the formation of a light-absorbing metal surface layer. The electrode in this example is SnO₂Plating. Liquid crystal photocells, electrodeposition photocells, and electrochromium photocells are usually transparent at rest, but under certain circumstances, such as the presence of overvoltage or prolonged excitation state, it may take some time, even several hours, from the self-excited state to return to the transparent state. Therefore, the switching rate of the photovoltaic cell is relatively reduced.

Preferably, the photovoltaic cell used in the control system of the present case includes dispersed particulate liquid suspension, which can change the orientation in response to an electric field to change the light transmission through the suspension. According to this, as described in the US Pat. Frontiers). These photovoltaic cells quickly switch from a clear state to a dark state. It also provides a wide range of luminosity. The fine particle liquid suspension is best placed in a suitable liquid such as iodine and herapathite fluid suspension, such as isoamyl acetate, although other types of particles, such as graphite, mica, and garnet can also be used. Periodides of alkaloid sulphate salts of aluminum and alkaloids.

The transparent material plates forming the photovoltaic cell are substantially separated by a certain distance, about 50 microns, across the entire opposed area therebetween. If the distance is not maintained within an error, for example, about 5 to 10 microns, the transparency of the battery will be uneven, and an electric field short circuit between two adjacent points on the opposite surface may occur. The requirements for the fixed distance required to form a flat plate impose restrictions on the material. Therefore, although plastic materials such as polyethylene terephthalate can be considered, it may be difficult to maintain a fixed distance between the plates of the photovoltaic cell if the entire surface of the plates is coated with plastic material. Therefore, in general, it is best to use glass sheets.

The opposite surfaces of the plates in the photovoltaic cell are coated with conductive materials. The preferred coating material is conductive and transparent indium tin oxide (ITO). The mirror surface of the rearview mirror can be a surface of the photocell plate opposite to the conductive coating layer, and the photocell can form a part of the rearview mirror. The reflective coating material on this kind of plate is usually silver, chromium or aluminum.

When the photovoltaic cell becomes a part of the rearview mirror of the vehicle, the reflector surface and the battery are located in a housing attached to the vehicle, such as the windshield or door of the vehicle. The circuit for controlling the adjustability of the photovoltaic cell is located inside or on the surface of the casing. There are also electronic connectors inside or on the surface of the housing to connect the photovoltaic cell to the electrical system of the vehicle.

In the control system of the present invention, the photovoltaic cell is preferably directly connected to the secondary coil, and the induction coil provides substantially all the inductance of the second (resonant) circuit. The parallel resonance circuit provides a larger overvoltage coefficient and is more stable than the series circuit. In fact, the induction coil provides all the inductance of the resonance circuit to ensure that the control system has a smaller size.

In this case, we used the term "weak coupling", which refers to the electromagnetic coupling between the main winding and the auxiliary winding, which is similar to the coupling of a transformer, but the difference is that the leakage inductance is arbitrarily increased. The coupling coefficient K can be calculated by the following formula:<maths><img file="TW299533B_D0001.tif" /></maths>

Among them, L_PIs the inductance of the main winding, L_SIt is the inductance of the secondary winding, and M is the mutual inductance between the two. To achieve the purpose of the present invention, the inductance of the coil is preferably less than 0.7, and more preferably less than 0.5.

When the energy must be transferred to the energy required to trigger and maintain the resonance of the second circuit, the inductance must be weak to reduce the impact of the first circuit on the impedance of the second circuit. Therefore, the energy is introduced by the bias voltage of the coil to avoid disturbing the characteristics of the second circuit.

Therefore, the coil of the present invention will not be made into a real transformer. The real transformer usually needs strong coupling as much as possible, and the coil in this case only has the function of a secondary transformer. The "weakly coupled" coil in this case does not have the purpose of transforming energy with the lowest possible loss in a real transformer.

The magnetic core of the induction coil is designed to provide the magnetic resistance required for magnetic flux transmission in the magnetic circuit formed by it. Magnetic resistance can be easily achieved by the air gap in the path of the magnetic field lines. The air gap is made of non-magnetic material, such as air, or usually resin or plastic material. The air gap size in the magnet core is preferably at least 0.1 mm, and most preferably at least 0.2 mm.

The second circuit provides reaction energy for driving the photovoltaic cell. The operating frequency of the system can be given by the second circuit itself. In this case, the pulses in the system are continuous and can be automatically adjusted to the resonant frequency of the second circuit. This situation is best achieved by the following electronic circuit. The second (resonant) circuit directly affects the components of the oscillator circuit, so it can provide the operating frequency itself.

In the example of a battery with particles suspended in the direction of electrical movement, the typical frequency level is 8 to 25 kHz, usually in the range of 16 to 25 kHz. The use of this alternating current avoids the movement of suspended particles across the narrow distance between adjacent plates, which movement will have an adverse effect on the opacity or transparency of the battery. The aforementioned frequencies can be used to avoid audio.

In an oscillator with a frequency of the first circuit, but not an automatic oscillation circuit, the frequency must be adjusted to the resonance frequency at the beginning, and the resonance frequency is determined by the battery circuit established by each battery.

The control system in this case provides the advantage that only a small amount of energy can maintain the required resonance. The special purpose of the system in this case is that if the battery breaks, the current will be retained in the circuit at a very low voltage.

The coil includes a conventional iron core, which is generally soft iron. The size of the iron core is preferably compatible with the housing of the rear view mirror including the photocell, and the iron core is located behind the mirror surface relative to the driver of the vehicle.

It is best not to overlap the main winding and the auxiliary winding of the coil. Therefore, the secondary winding preferably surrounds one part of the core, and the secondary winding preferably surrounds another part of the core. This non-overlapping structure can ensure weak coupling between the windings, and also helps to make the system small enough to fit in the mirror housing.

The number of turns of the main winding around the core is preferably less than 100 turns, especially 10 to 80 turns, and 40 to 80 turns are the best. The secondary winding generally includes 140 to 300 turns. Therefore, the winding (transformer) ratio is approximately 3 to 4:1. The main reason for achieving the required voltage across the battery is not the winding ratio, but the overvoltage of the second circuit. The overvoltage is a function of the capacitance, inductance and resistance of the components that make up the second circuit. The special advantage of the present invention is to use the overvoltage in the second circuit to achieve the voltage required by the battery.

Even if the pulse generated by the oscillator is not a sine wave, the signal waveform in the second circuit is a sine wave. The non-sine wave generated by the oscillator is easily converted into a sine wave in the second circuit by the weak coupling in the induction coil. During the adjustment of the pulse size, the voltage applied across the photovoltaic cell can be controlled by adjusting the energy value emitted by the oscillator, such as changing the period of the oscillator or adjusting the voltage peak value in the first circuit.

The system preferably includes one or more feedback lines from the first circuit to the second circuit. The feedback line can adjust the electronic parameters corresponding to the oscillator in the photovoltaic cell.

Therefore, a feedback line can be used to adjust the voltage in the second circuit, thus always ensuring the voltage across the photovoltaic cell required for the dark state of the photovoltaic cell. The aforementioned feedback line or another type of feedback line can also adjust the frequency that affects the oscillator frequency of the first circuit, so that the operating frequency of the second circuit can always be guaranteed to be the resonant frequency of the second circuit.

The control system also provides a response loop that can detect whether the operating frequency of the second circuit is indeed the resonant frequency of the second circuit, and can output any necessary correction signals to the oscillator of the first circuit to adjust the frequency of the first circuit , To get the resonance of the second circuit.

If the operating frequency is different from the resonance frequency in the second circuit, the overvoltage will be lower and the excitation energy consumption will increase. For good operation, it is beneficial to ensure that the operating frequency is the same as the resonant frequency, although to some extent, the voltage applied to the photovoltaic cell can be controlled by controlling the difference between the operating frequency and the resonant frequency by controlling the overvoltage factor.

In an embodiment of the present invention, the second circuit includes at least one capacitor device connected in parallel with the photovoltaic cell. It is usually better to connect two or more capacitors in series with each other. The use of capacitors in series has the advantage of reducing the voltage applied to each single capacitor.

The control system of the present invention is applicable to many different types of photovoltaic cells. The control system adjusts an AC power source to supply power to the photovoltaic cell. A photovoltaic cell with variable-direction suspended particles may require a voltage of at least 125 volts, which is applied between the conductive surfaces of the cell to generate an electric field to change the direction of the particles to allow light to pass through. In order to change the light reflectivity or transmission rate of the photovoltaic cell, the voltage applied to the photovoltaic cell must be changed. The frequency can also be changed to change its reflectivity or transmission rate, but it is less efficient. The change in luminosity is mainly proportional to the applied voltage, reaching a saturation limit. In the absence of an electric field, the particles perform Brownian motion, thus blocking light from passing through the battery. In the case of a weak electric field, the particles tend to align with the electric field, but continue to oscillate at their average position, thus causing some light absorption phenomenon. In order for the electric field to reach a certain critical value, for example, a voltage of about 100 volts, so that the particles are completely aligned with the electric field, and therefore the minimum light absorption rate can be produced.

The control system is preferably adjusted by at least one photosensitive optical element that can detect incident light falling on the photocell. Preferably, at least two of this type of light detection element should be used. The first light detection element is located to monitor the light from the vehicle The rear may cause dazzling light, and the second is where the ambient light level can be monitored, such as the light passing through the windshield, the light reflected by the top of the vehicle, or the light scattered by the transparent roof of the vehicle.

The control system follows the following rules: The signal detected by the photosensitive optical element is proportional to the light level, or the difference in light level detected by two such elements is used to stimulate the oscillator in the first circuit for adjustment The voltage applied to the terminal of the photovoltaic cell and the opacity of the photovoltaic cell.

Among them, in addition to an internal rearview mirror, there can also be one or more external rearview mirrors. The transmission and/or reflection characteristics of the external rearview mirror combination can be controlled by the same electronic circuit that controls the internal rearview mirror group. Provide synchronous adjustment of transmission and/or reflection characteristics. However, due to the low power consumption and small scale of the control system of the present invention, a separate control system can be included in each mirror. With this separation system, each mirror surface can therefore be adjusted according to the special light conditions falling on it.

The present invention will be further described below, by means of non-limiting embodiments and with reference to the accompanying drawings, in which: Fig. 1 is a circuit diagram of the control system of the present invention applied to a motor vehicle.

Figure 2 is a cross-sectional view of the induction coil of the present invention.

Figure 3 is a view different from the cross section of the second figure. The cross section of this figure is taken from the line AA' of Figure 2.

The exemplified control system includes a first circuit 1, the first circuit 1 includes a 12 volt DC battery 3, an oscillator 4, and a main winding 11 of an induction coil with a magnetic core 10. The system further includes a second circuit 2, which includes the secondary winding 12 of the induction coil, a photovoltaic cell 14, and a capacitor device 16 connected in parallel with the photovoltaic cell 14. Figure 1 shows the general outline of the induction coil, while Figures 2 and 3 show more details of the induction coil.

The battery 3 that supplies low-voltage power to the oscillator 4 is the power source of the electronic circuit. In addition to the battery 3, there are also components that can apply positive and negative reference voltages to specific parts of the circuit. The first of these components is a DC-DC converter 3'on the lines from battery 3 to oscillator 4.

The oscillator 4 has a combined trigger device 5. In this example, it is simply counted as a voltage with an adjustable oscillator 4 and frequency. In another example, a frequency feedback device 5'(shown by the dotted line in FIG. 1) is used to replace the trigger device 5. The frequency feedback device 5'can detect the frequency of the second circuit and adjust the oscillator 4 To that frequency. The advantage provided by this other exemplary embodiment is that the oscillator frequency can be continuously adjusted to the frequency of the second circuit.

The photovoltaic cell 14 is a type of combined liquid suspension of small solid particles that can show directions in response to an electric field. The capacitor device 16 is preferably formed by connecting 4 capacitors in series.

The system further includes a control circuit, denoted by the number 30, which includes photoelectric detectors 32 and 33 connected to a detection control unit 34. The cell 34 is applied with a reference voltage. A detector signal line 35 is connected from the unit 34 to a signal comparison unit 40. The circuit 30 further includes an operational amplifier 36 with a feedback circuit 39. A battery operation detection line 37 is connected from the second circuit 2 to the comparison unit 40, and from the comparison circuit 40 there is a signal line 38 leading to the operational amplifier 36.

In the illustrated system, the comparison unit 40 also has a driving device 41 (in this example, a voltmeter) to set a threshold voltage. The device 41 is not an essential part. It is used to limit the voltage to the level necessary for the main function of the mirror without causing the battery to reach an unnecessary high voltage.

The schematic details of the induction coil of the embodiment of this case are shown in the cross-sectional views of FIGS. 2 and 3. The magnetic core 10 is composed of two opposite E-type ferrites with a plastic spacer 13 in between. The spacer 13 provides the magnetic resistance required for magnetic flux transmission in the magnetic circuit of the iron core 10. The secondary winding 12 surrounds a central arm composed of two E-type ferrite opposite central rods, and the main winding 11 surrounds the opposite end of the ferrite rod.

All the control systems are arranged in a housing (not shown in the figure), and can be connected to the 12-volt battery 3 via the vehicle wiring device.

When in use, the photodetector 32 is placed where it can detect ambient light, for example, to capture the light in front of the vehicle and/or the light reflected by the roof, and the photodetector 33 is placed where it can detect the light behind the vehicle Place. The detection control unit 34 includes a difference detector that compares the signals from the light detectors 32 and 33, and gives the detector signal line 35 a signal whose intensity corresponds to the light received by the rear part (33 ) Is proportional to the amount of ambient light (32). Any flash shining on the light detector 33 can send a corresponding signal to the difference detector. The battery operation detection line 37 carries a signal proportional to the voltage of the second circuit. The signal sent by the control unit 34 via the detector signal line 35 is compared in the comparison unit 40 with the signal from the battery operation detection line 34. The battery operation detection line 37 indicates the secondary voltage, and the comparison unit 40 uses the signal The line 38 then sends a control signal to the operational amplifier 36. This control signal can take into account the degree of flash and the actual voltage across the photovoltaic cell. Similarly, the system may include another feedback device to provide a second control loop to feedback the established photovoltaic cell frequency to the oscillator 4 (as shown by the dotted line next to the feedback device 5').

The signal from the signal line 38 is amplified by the amplifier 36 to excite the oscillator 4 of the first circuit 1 to generate a low-voltage AC pulse wave (although a sine wave or a square wave is also a possible change). This wave then passes through the coil in the second circuit 2 and induces a high voltage that can be applied to both ends of the battery 14. The voltage at the two ends of the battery 14 is increased due to resonance in the second circuit, and is usually increased to about 120 volts alternating current. This allows the voltage applied to the battery 14 to partially or completely align the suspended particles. Full alignment can provide the maximum light transmission rate through the battery 14 and the maximum reflectivity of the mirror with the photocell 14 as a part.

If the ambient light detector 32 detects good daylight or high-intensity artificial light, and the rear light detector 33 detects the same situation, the difference between the individual photoelectric signals is small, and the unit 34 is sent by lines 35, 38 A signal, and the amplifier 36 triggers the oscillator 4 and generates a battery trigger voltage in the second circuit. The comparison unit 40 knows through the line 37 that the voltage is indeed present in the second circuit, that is, adjusts the command signal sent by the line 38 to obtain the maximum voltage across the battery 14.

The oscillator 4 converts the 12 volt voltage into an AC voltage, and obtains a 120 volt AC voltage in the second circuit 2. The frequency of the AC voltage of the oscillator 4 is adjusted to the resonance frequency of the second circuit 2 by the external action from the device 5, which is usually 20 kHz. This change can be easily achieved by measuring the dynamic current in the second circuit. When the frequency changes, the curve follows a curve that crosses the minimum. When the current is at a minimum, the resonance frequency is reached. The 120 volt voltage in the second circuit makes the suspended particles in the battery 14 completely aligned.

In another way, the frequency feedback device 5'provides the frequency control required by the oscillator 4.

If the ambient light detector 32 detects blur or night conditions, and the opposite detector 33 at the rear also detects the same situation, the difference between the individual photoelectric signals becomes smaller again. The unit 34 sends out a signal through the lines 35 and 38 again, and as described above, once again achieves the highest battery clarity and specular reflectance.

If the ambient light detector 32 detects blur or night conditions, and the rear-facing detector observes the entire beam of dazzling car front light, the difference between the individual photoelectric signals is large, and the unit 34 sends out a corresponding signal Pre-amp 36. Under this condition, no voltage is generated in the induction coil 11/12, and the battery 14 is also without voltage. When the circuit 2 lacks voltage, the battery particles are randomly distributed, making the battery opaque and minimizing the degree of specular reflection.

If the difference between the signal emitted by the ambient light detector 32 and the signal emitted by the rear-facing detector 33 falls between the above extreme conditions, such as a rather blurry situation and a mid-light beam after passing through the window, the unit 34 The amplifier 36 sends a signal to the oscillator 4, and the signal 4 gives the oscillator 4 some excitation, but the pulse width generated by the circuit 1 is very narrow, so the voltage in the second circuit 2 is relatively reduced. In this case, the second circuit voltage aligns the suspended particles in the battery 14 to produce an opaque shape in the battery, and overall, the mirror surface has a moderate reflectivity.

If necessary, the ambient light detector 32 can be equipped with a time delay element (not shown in the figure), so that when the light around the light detector 32 is temporarily increased by the light of passing vehicles, the photocell 14 will not be too early Transition to clarification status.

In the typical embodiment of the control system in this case, the battery 14 has a capacitance value of 11 microFaradays and a capacitor device 16 formed by connecting four 22 microFaraday capacitors in series, and therefore has a total capacitance value of 5.5 microFaradays. The size of each E-type ferrite is 25 mm (height) x 13 mm (width) x 8 mm (depth) and is made of 3C8 material. The first part of the inductance coil in the first circuit 1 has 66 turns, the other part of the coil in the second circuit 2 has 240 turns, and the magnetic circuit has an air gap of 2.5 mm. The main winding 11 has an inductance L of 0.318 millihenries_P, The secondary winding 12 has an inductance L of 6.31 millihenries_S, And the mutual inductance M is 0.6 millihenries inductance coil coupling coefficient K, which can be calculated by the foregoing formula to be 0.423.

Varying the above arrangement, the second circuit may be an automatic oscillation circuit. Another second (resonant) circuit provides the operating frequency of the oscillator.