Power supply circuit and photovoltaic power generation system with this power supply circuit

Abstract

Power supply circuit used in a photovoltaic power generation system, comprising a switch K1, a current limiting device, a capacitor C1, a switch K2, and a CCFL converter circuit, wherein one end of switch K1 is a positive input of the power supply circuit, and another end of switch K1 is connected to one end of the current limiting device, and another end of the current limiting device is connected to both one end of capacitor C1 and one end of switch K2, and another end of capacitor C1 is a negative input of the power supply circuit, and a positive input of the CCFL converter circuit is connected to another end of switch K2, and a negative input of the CCFL converter circuit is connected to the negative input of the power supply circuit.and a first output of the CCFL converter circuit is a first output of the power supply circuit, and a second output of the CCFL converter circuit is a second output of the power supply circuit; wherein switch K1 is switched off upstream of switch K2 when a photovoltaic string is activated, and the CCFL converter circuit is supplied with an operating voltage by means of capacitor C1; and wherein the CCFL converter circuit comprises at least a start-up circuit, an inductor L2, a capacitor C3, a triode TR1, a triode TR2, a transformer B, primary windings NP1 and NP2, feedback windings NB1 and NB2, and a secondary winding NB1, wherein the start-up circuit has at least two terminals,comprising a start-up input and a start-up output; wherein the start-up input is connected to the other end of switch K2 and the start-up output is connected to a center tap of the feedback windings NB1 and NB2; wherein the emitters of triodes TR1 and TR2 are connected to the other end of capacitor C1, and collectors are connected to terminals of the primary winding NP1 and NP2 respectively, and the collectors are also connected to both terminals of capacitor C3, and ground electrodes are connected to terminals of the feedback winding NB1 and NB2 respectively; wherein a center tap of the primary windings NP1 and NP2 is connected via inductor L2 to the other end of switch K2; wherein one end of the secondary winding NB1 is the first output of the CCFL converter circuit and another end of the secondary winding NB1 is the second output of the CCFL converter circuit.

Description

Technical area

[0001] The present invention relates to a power supply circuit for a photovoltaic power generation system, in particular to a power supply circuit for activating aged photovoltaic strings. Background technology

[0002] Given the anticipated depletion of fossil fuels and the associated environmental pollution, research and application of renewable and clean energy sources are highly valued by countries worldwide. Technologies for generating electricity from wind power and photovoltaics are becoming key research priorities, with solar power being referred to as photovoltaic power generation. The development and research of photovoltaic power generation in China began in the 1970s, progressed steadily throughout the 1990s, and the focus in the 21st century shifted to solar photovoltaic power generation. From 2000 onwards, photovoltaic technology entered the stage of large-scale, grid-connected power generation.

[0003] In the field of photovoltaic power generation, the US company SunPower first discovered and proposed the PID effect in 2005. The full English name is Potential Induced Degradation. SunPower discovered and proposed that series-connected PV modules can generate higher system voltages (typically 600 V for the USA and typically 1,000 V for Europe). If the modules operate at high voltages for extended periods, leakage currents occur between the cover glass, the encapsulation material, and the frame. This leads to a significant accumulation of charge on the cell plate surface, which degrades the passivation effect on the cell plate surface. As a result, the fill factor (FF), short-circuit current (Isc), and open-circuit voltage (Voc) decrease, causing the module's performance to fall below its design standard.SunPower calls this phenomenon the surface polarization effect, but this degradation is reversible. Since then, engineers and technicians in the PV sector have been researching and discussing PID.

[0004] From 2012 onwards, PID-induced module quality problems began to occur in large numbers in PV power plants, bringing the PID phenomenon into the public eye. In December of that year, PV Evolution Labs (PVEL), an independent PV module testing laboratory in the United States, conducted the first PID test on five international Tier 1 module manufacturers, including Yingli Solar, JA Solar, Trina Solar in China, Kyocera in Japan, and Solarworld in Germany.

[0005] Since then, more and more PV module manufacturers have focused on PID. In the second quarter of 2015, major domestic and international PV manufacturers such as Panasonic, Canadian, Jinneng, ReneSola, Hanwha, and ET Solar successively announced that their modules had passed third-party PID testing.

[0006] According to the third testing agency, PID refers to the fact that when a high negative voltage is formed between the solar modules and the ground, the resulting potential difference will not only cause damage to the solar cells or modules, but also lead to the problem of deteriorating the efficiency of power generation.

[0007] PID can affect the power generation capacity and the overall output of the entire system; in severe cases, it directly reduces the return on investment of PV power plants. In recent years, it has become one of the main topics of complaints from international buyers regarding the quality of Chinese modules.

[0008] The most important methods for mitigating or avoiding PID effects in the prior art are as follows: 1. Module Grounding: When a negative bias is applied to a module (the cell plate voltage is negative relative to the frame), the accumulated negative charge can be discharged to ground, restoring battery power. This is the polarization effect that restores battery power. Based on the above analysis, to avoid polarization effects when using modules in series, SunPower suggested using positive grounding for n-type front-facing solar cells and negative grounding for p-type front-facing cells. 2. Improvement of the insulation and water resistance of modules as well as reduction of leakage current. For example, encapsulation materials with better stability are used, no metal frame is used, the body resistance of the cell is increased, the thickness and properties of the passivation layer are improved, a barrier layer is added in the device, etc. 3. Elimination of the source of ion generation. Quartz glass, low-sodium glass, etc. are used. 4. String Voltage Reduction For smaller projects, the use of micro-inverters to reduce string voltage can be considered. This is why Tesla proposed microgrid photovoltaic systems for residential use.

[0009] Furthermore, Chinese patent application CN107086601A discloses a photovoltaic power generation system and a voltage compensation method. In the invention, the voltage of the photovoltaic string is compensated by the pulse voltage output of the voltage compensation device, thus counteracting the undesirable effects generated by the PID effect. However, no specific implementation method for the voltage compensation device is specified; only its function as an output of a pulse voltage is proposed. The pulse voltage specified in the specific embodiment has three forms: square waves, triangular waves, and trapezoidal waves. Fig. 5Ain CN107086601A is essentially the same as in Fig. 5C, which is due to the fact that in Fig. 5A t1 and t2 are the rising edge and falling edge respectively, which is an unattainable ideal state, and since the rise and fall take a short time, it is precisely the small waveform that is in Fig. Figure 5C illustrates this. The ΔU / Δt variations of all three pulse voltages are very large, which causes the photovoltaic string to break and shortens its lifespan; and this pulse voltage acts directly on the photovoltaic string, and due to the difficult electromagnetic shielding of the photovoltaic string, the electromagnetic radiation to the environment is very high. It is known that the harmonics, as in Fig. 5A is extremely high, and although PV systems are mostly installed in deserted and inhospitable locations, the electromagnetic radiation is very high, and reflection by the ionosphere in the atmosphere still causes significant electromagnetic pollution. Furthermore, the costs of producing these three waveforms are not insignificant. Contents of the invention

[0010] In view of this, the technical problem to be solved by the present invention is to provide a power supply circuit and a photovoltaic power generation system with this power supply circuit, and the ΔU / Δt variation of the output voltage of the power supply circuit is small, thereby making the photovoltaic power generation system in which the power supply circuit is applied less harmful to the environment.

[0011] To solve the above technical problem, the present invention provides a technical solution as follows: A power supply circuit used in a photovoltaic power generation system, which have a switch K1 , a current limiting device, a capacitor C1 , a switch K2 and includes a CCFL converter circuit; one end of the switch K1 is a positive input of the power supply circuit, and the other end of the switch K1 is connected to one end of the current limiting device, and another end of the current limiting device is connected to both ends of the capacitor. C1 as well as with one end of the switch K2 connected, and another end of the capacitor C1 is a negative input of the power supply circuit, and a positive input of the CCFL converter circuit is connected to the other end of the switch.K2 connected, and a negative input of the CCFL converter circuit is connected to the negative input of the power supply circuit, and a first output of the CCFL converter circuit is a first output of the power supply circuit, and a second output of the CCFL converter circuit is a second output of the power supply circuit; When a photovoltaic string is activated, the switch K1 in front of the switch K2 switched off and the CCFL converter circuit is powered by the capacitor C1 an operating voltage is provided. In a specific embodiment of the current limiting device, it is characterized in that the current limiting device is an inductor or a resistor.

[0012] The capacitor is preferred C1 a supercapacitor or an electrolytic capacitor.

[0013] Preferably, the CCFL converter circuit is operated by the external drive.

[0014] In a specific embodiment of the CCFL converter circuit, the CCFL converter circuit comprises at least a start-up circuit, an inductor L2 , a capacitor C3 , a triode TR1, a triode TR2, a transformer B, primary windings N P1 and N P2 , feedback windings N B1 and N B2 and a secondary winding Nsi, and the starting circuit comprises at least two connections, i.e., a starting input and a starting output; the starting input is connected to the other end of the switch K2 connected, and the start-up output is connected to a middle tap of the feedback windings N B1 and N B2 connected; the emitters of triodes TR1 and TR2 are connected to the other end of the capacitor. C1 connected, and the collectors thereof are connected to terminals of the primary winding N P1or N P2 connected, and the collectors of these are also connected to both terminals of the capacitor. C3 connected, and the base electrodes thereof are connected to terminals of the feedback winding N B1 or N B2 connected; a central tap of the primary windings N P1 and N P2 is via the inductance L2 with the other end of the switch K2 connected; one end of the secondary winding N S1 is the first output of the CCFL converter circuit, and another end of the secondary winding Nsi is the second output of the CCFL converter circuit.

[0015] Preferably, the starting circuit includes a power supply device, and the power supply device is a resistor or a device with a constant current source.

[0016] Furthermore, the starting circuit includes a capacitor. C2 , and the capacitor C2is connected in parallel to the power supply device, or the capacitor C2 is connected to the start-up output and the other end of the capacitor C1 tied together.

[0017] Accordingly, the present invention further provides a photovoltaic power generation system with the following technical solution: A photovoltaic power generation system comprising a photovoltaic string and also a power supply circuit according to any one of claims 1 to 7, and a hot end of the photovoltaic string is electrically coupled to a first output of the power supply circuit and an earth terminal of the photovoltaic string is electrically coupled to a second output of the power supply circuit.

[0018] Furthermore, the above photovoltaic power generation system also includes a DC power supply, and the DC power supply and the outputs of the power supply circuit are connected in series, and the series connection is made by one of the following two methods: (1) a negative electrode of the DC power supply is electrically coupled to the second output of the power supply circuit, and the first output of the power supply circuit is electrically coupled to a positive electrode of the photovoltaic string, and a negative electrode of the photovoltaic string is electrically coupled to a positive electrode of the DC power supply; (2) a negative electrode of the DC power supply is electrically coupled to a positive electrode of the photovoltaic string, and a negative electrode of the photovoltaic string is electrically coupled to the second output of the power supply circuit, and the first output of the power supply circuit is electrically coupled to a positive electrode of the DC power supply.

[0019] Preferably, the peak of a high-frequency alternating current output by the CCFL converter circuit is not greater than the open-circuit voltage of the photovoltaic string to be activated.

[0020] With regard to the technical terms used in the present invention, the present invention and the prior art may include different nomenclatures, and the technical terms in the following articles denote the same meanings, and the lists in each article do not include all content: (1) Solar modules, where in many literature several individual solar modules connected in parallel and in series are also referred to as solar modules, or as photovoltaic strings or even as photovoltaic panel sets; (2) Hot end of the photovoltaic string, where, due to the preferences of different manufacturers, some manufacturers ground the positive electrode of the photovoltaic string and some manufacturers ground the negative electrode of the photovoltaic string, and the hot end refers to the end that is not grounded, and because there is no grounding, it is prone to generating an electric shock to the human body, it is called the hot end, normally it is also the end of the solar module that needs to be activated, it can be the positive or negative electrode of the photovoltaic string; (3) Grounding terminal of the photovoltaic string, grounded metal frame of the photovoltaic string; as described above, it can be the negative electrode of the photovoltaic string or it can be the positive electrode; (4) The Royer circuit of the collector resonance type, or referred to as a "cold cathode fluorescent lamp (CCFL) inverter," has also recently been called a CCFL inverter, CCFL converter, or CCFL converter circuit. CCFL is the abbreviation for "cold cathode fluorescent lamps" and originally referred to cold cathode fluorescent lamps. Before the advent of white LEDs, these were mostly used for LCD backlighting. Because the earlier LCD monitors were mostly used in notebooks, the backlight power supply was direct current (DC). At that time, a variant of the Royer circuit was introduced that converted the DC into pure alternating current to power the cold cathode fluorescent lamps. The classic Royer circuit uses the core saturation properties for oscillation, and the output is a square wave. See Chinese patent application number 201110436259.7.The CCFL converter circuit is characterized by the fact that in the Royer circuit, an inductor is connected in series between the center tap of the primary windings of the push-pull transformer and the power supply side, which is generally referred to in the industry as a damping inductor L. LC (corresponds to the inductance) L2 in Fig. 1 of this application) is known and whose inductance is generally more than ten times the inductance of the primary winding, while a capacitor CL (corresponds to the capacitor C3 in Fig. 1 of this application) is connected in parallel between the two collectors of the push-pull triodes, and this capacitor forms with the

[0021] The push-pull transformer is a known LC resonant circuit, and the capacitor is CL, where L is the total inductance of the primary windings of the push-pull transformer. The total inductance of the push-pull transformer is four times the inductance of the primary winding. 1 or 2 The output is a sine wave or an approximate sine wave. If the output is a square wave, it causes electromagnetic pollution due to the large number of harmonics. The CCFL converter circuit is described in more detail in Chinese patent application number 201110242377.4, which is also referenced in Fig. 3 and are described in detail using appropriate background technology.

[0022] For the following technical terms, this application specifies the following meanings: (1) Push-pull triodes: two triodes that realize self-excited oscillation and stable operation of the Royer circuit and the CCFL converter circuit; usually two triodes are provided and they are also known as tube pairs, also as push-pull triodes; usually they are bipolar semiconductors and can of course also be unipolar field-effect tubes; (2) Starting circuit: a circuit for providing a starting current or starting voltage for the push-pull triodes or field-effect tube in the CCFL converter circuit in order to achieve a fast start or a soft start of the CCFL converter circuit.

[0023] The working principle of the present invention is analyzed in the specific embodiments and is not described here.

[0024] The advantageous effects of the power supply circuit of the present invention are that: (1) the waveform ΔU / Δt of the voltage output by the power supply circuit is small, thereby enabling an extended lifetime of the photovoltaic string in the photovoltaic power generation system to which the power supply circuit is applied and little radiation to the environment. (2) the circuit is easy to implement, cost-effective and has high reliability and low energy consumption. List of characters Fig. Figure 1 is a schematic diagram of the power supply circuit in the exemplary embodiment. 1 of the present invention; Fig. Figure 2 is a waveform diagram of the voltage output by the standalone CCFL converter circuit in the power supply circuit in the exemplary embodiment. 1 of the present invention; Fig. Figure 3 is a waveform diagram of the voltage at both ends of the capacitor. C1and the voltage output by the CCFL converter circuit in the exemplary embodiment 1 of the present invention; Fig. Figure 4 is a schematic diagram of the power supply circuit after the improvement in the exemplary embodiment. 2 the present invention, which is applied in the photovoltaic power generation system; Fig. Figure 5 is a schematic diagram of the power supply circuit in the exemplary embodiment. 3 of the present invention. Specific embodiments

[0025] The photovoltaic power generation system operates primarily during the day under good solar irradiance, at the time when the local solar altitude reaches its maximum, recorded as 12 noon local time. The system can effectively generate power between 10 am and 2 pm local time, and the power generation output decreases before 10 am or after 2 pm local time and is practically ineffective. The output characteristic of the photovoltaic string is not that of a constant voltage source, but rather a constant current source. To obtain a higher output power, the principle of maximum power output is generally exploited as much as possible, ensuring the highest possible terminal voltage while maintaining system efficiency.The output voltage curve at both ends of the photovoltaic string behaves as follows: the output voltage rises faster in the morning because the load is almost empty, and with grid-connected power generation, the output voltage initially drops due to the load, and at midday, when the light is strongest, the output voltage reaches a maximum, and then slowly drops, and until the grid disconnection around 2 p.m. local time, the voltage rises again to the open-circuit voltage under the corresponding illuminance due to the load reduction, and then it drops over time to near zero at night, and if it is a rainy day, the voltage of the photovoltaic string remains at a low voltage near zero all day.

[0026] The invention provides a power supply circuit that outputs a voltage by discharging a capacitor. This voltage is a time-decreasing DC voltage. A CCFL converter circuit is connected downstream of the capacitor. The CCFL converter circuit converts the time-decreasing input DC voltage into a sinusoidal AC output. Since the CCFL converter circuit operates in an open loop, the peak-to-peak value of the sinusoidal AC output is proportional to the operating voltage of the CCFL converter circuit. This voltage decreases over time; that is, the peak-to-peak value of the sinusoidal AC output also decreases over time. Consequently, the RMS value of the sinusoidal AC also decreases over time, resulting in a decaying sinusoidal AC voltage.It acts on both ends of a photovoltaic string to be activated, so that the waveform ΔU / Δt of the voltage output by the power supply circuit is small, and since the sine wave has a single frequency, there are few harmonics and little radiation in the air, making it environmentally friendly, thus enabling a longer lifetime of the photovoltaic string in the photovoltaic power generation system to which the power supply circuit is applied, and little radiation to the environment, making the power supply circuit in the present invention simple and cost-effective to implement.

[0027] To facilitate the understanding of the present invention by technical personnel, the present invention is described below in conjunction with specific embodiments. Example 1

[0028] Regarding this embodiment, it should be noted that Fig. 1 referred, and Fig. Figure 1 is a schematic diagram of the power supply circuit in the exemplary embodiment. 1 of the present invention. The power supply circuit consists of the following components and is connected as follows: The in Fig. The power supply circuit shown includes a switch. K1 , an inductance L1 , a capacitor C1 , a switch K2 and a CCFL converter circuit;

[0029] One end of the switch K1 is a positive input of the power supply circuit, and the other end of the switch K1 is with one end of the inductance L1 connected, and another end of the inductance L1 is connected to both ends of the capacitor C1 as well as with one end of the switch K2 connected, and another end of the capacitor C1is a negative input of the power supply circuit, and a positive input of the CCFL converter circuit is connected to the other end of the switch. K2 connected, and a negative input of the CCFL converter circuit is connected to the negative input of the power supply circuit, and a first output of the CCFL converter circuit is a first output of the power supply circuit, and a second output of the CCFL converter circuit is a second output of the power supply circuit.

[0030] The CCFL converter circuit in this embodiment includes a start-up circuit consisting of a resistor R1 and a capacitor C2 consists of a capacitor C3 , an inductance L2 , a triode TR1, a triode TR2, a transformer B, primary windings N P1 and N P2 , feedback windings N B1 and N B2as well as a secondary winding Nsi, and the starting circuit includes at least two terminals, and one end of the resistor. R1 is a starting input, and a connection point between the other end of a resistor. R2 and one end of the capacitor C2 is the start-up output, and a device that provides the start-up current for the two push-pull triodes TR1 and TR2 in this embodiment is the resistor. R1 ;

[0031] The CCFL converter circuit is wired as follows: the start-up input is connected to the other end of the switch. K2 connected, and the start-up output is connected to a middle tap of the feedback windings N B1 and N B2 connected, and another end of the capacitor C2 is connected to the other end of the capacitor C1 connected; the emitters of triodes TR1 and TR2 are connected to the other end of the capacitor. C1connected, and the collectors of triodes TR1 and TR2 are connected to terminals of the primary windings N P1 or N P2 connected, and the collectors of triodes TR1 and TR2 are also connected to the capacitor terminals. C3 connected, and the base electrodes of the triodes TR1 and TR2 are connected to the terminals of the feedback windings N B1 or N B2 connected, and a central tap of the primary windings N P1 and N P2 is via the inductance L2 with the other end of the switch K2 connected; one end of the secondary winding Nsi is the first output of the CCFL converter circuit, and another end of the secondary winding Nsi is the second output of the CCFL converter circuit.

[0032] The capacitor C1 The present invention preferably uses a supercapacitor or a large electrolytic capacitor with low leakage current, connected in series or in parallel.

[0033] Since the CCFL converter circuit outputs alternating current, the first output and the second output of the power supply circuit in the present invention can be interchanged.

[0034] To overcome the shortcomings of the prior art pulse voltage, the voltage applied in the present application for activating the photovoltaic string is a sinusoidal alternating current, which is very difficult to obtain. If a switched-mode power supply is used to generate it directly, the waveform edge of the output voltage is very steep, as in the case of a self-excited push-pull converter, where the output voltage waveform is a square wave with a ΔU / Δt of nearly infinity, and thus suffers from the same shortcomings described in the background technology. If a digital audio power amplifier is used, the switched-mode power supply in conjunction with the output filter is expensive in terms of both cost and control circuitry.

[0035] The circuit for generating sinusoidal alternating current in this embodiment uses a CCFL converter circuit, and since the wavelength of a 1 MHz high-frequency alternating current is 30 m and its corresponding half-wave oscillator antenna length 1 / 4 Since its wavelength is 7.5 m, the high-frequency alternating current output by the power supply circuit in the present invention is below 1 MHz, then its radiation is easier to control, e.g., if the output frequency of the high-frequency alternating current is 100 kHz, the 1 / 4 wavelength is 75 meters, for antenna lengths far below 75 meters its radiation efficiency is very low, and therefore the embodiment requires the CCFL converter circuit to operate at a relatively “low frequency” below 1 MHz, however, the term “high-frequency alternating current” or “sinusoidal alternating current” is still used in the text.

[0036] The CCFL converter circuit is a type of self-excited push-pull converter, and its operating principle for achieving a sinusoidal output voltage waveform is explained as follows: The circuit to the right of the capacitor C1 in the Fig. 1 is the CCFL converter circuit, and the difference between the CCFL converter circuit and the self-excited push-pull converter is the addition of the capacitor. C3 and the inductance L2 The oscillation principle of the circuit is similar to that of the self-excited push-pull converter, but instead of using the core saturation characteristic for the push-pull oscillation, the CCFL converter circuit uses the capacitor C3 and the total inductance of the winding N P1 and N P2of the coupling transformer B for the oscillation of the LC circuit, and the output waveform of the circuit is a sine wave, no longer a square wave, where the inductance L2 This is achieved by: 1) providing a larger AC input impedance for the transformer and 2) ensuring a perfect sine wave output, and the waveform of the voltage output by the standalone CCFL converter circuit is in Fig. 2 shown, and Fig. L2 is not perfect and is only used here as an example; if L2 is amplified further, the waveform distortion THD will increase. Fig. 2. Less than 10%, which is practical at this point. This type of vibration requires a very strict selection of the devices. The smaller the waveform distortion (THD) in Fig. The higher the value of 2, the lower the energy consumption of the power supply circuit in the present invention.

[0037] The CCFL converter circuit is characterized by the fact that, through the use of the oscillation of the series-connected LC circuit, the frequency is relatively stable and the output is a sine wave or almost a sine wave, but due to the low efficiency, it is also necessary to use an inductor. L2 to connect in series with the supply circuit to increase efficiency.

[0038] This invention requires that the inductive strength of the inductance L2 more than 10 times the induction strength of winding N P1 or N P2 If the inductance is greater than the inductance, then a more perfect sine wave will be produced. L2 and the capacitor C3 achieved.

[0039] Since the operating voltage of the CCFL converter circuit is the terminal voltage of the capacitor C1The shape of the envelope formed by the peak value of the positive half-period of the high-frequency alternating current output by the CCFL converter circuit is similar to the terminal voltage variation of C1, and similarly, the shape of the envelope formed by the peak value of the negative half-period of the high-frequency alternating current output by the CCFL converter circuit, after reflection of the X-axis in common coordinates, is similar to the terminal voltage variation of C1.

[0040] When activation of the photovoltaic string is required in the present invention, the switch is activated by means of an external power supply of the power supply circuit in the present invention, which can be a battery, a direct current after rectification of the mains voltage. K1 initially closed to protect the capacitor C1 to recharge, then the switch will K1 opened and the switch K2closed to close the capacitor C1 to gradually discharge, thereby providing an activation voltage to the photovoltaic string.

[0041] To improve the efficiency of a PV power plant, the best activation scheme is to use the photovoltaic string itself as an external power source. When grid-connected power generation loses its significance around 2 PM, the switch is flipped. K1 closed to close the capacitor C1 to charge, and when the sun sets, the switch will turn off. K1 opened and the switch K2 closed to close the capacitor C1The capacitor gradually discharges, causing the terminal voltage to gradually decrease. This characteristic provides a gradually decaying operating voltage for the CCFL converter circuit, and the output of the CCFL converter circuit receives a decaying sinusoidal AC voltage that acts on both ends of the photovoltaic string to be activated. If activation is insufficient, it is enough to increase the capacitance of the capacitor. C1 to increase and vice versa.

[0042] Fig. Figure 3 shows the waveform of the voltage at both ends of the capacitor. C1 and the voltage output by the CCFL converter circuit in the exemplary embodiment 1 of the present invention, and the waveform of the voltage at both ends of the capacitor C1 will be like a straight line S1 in Fig. 3, decreased in a similar exponential manner, while the waveform of the voltage output by the CCFL converter circuit at that time, see curve S2 , a gradually decaying high-frequency alternating current, and the straight line S3 is the envelope of the curve S2 on the positive half-circumference, and the straight line S4 is the envelope of the curve S2 in the negative half-circle of the envelope, and the straight line S3 and the straight S4 are mirror-symmetrical along the X-axis.

[0043] The power supply circuit in this embodiment is used in a photovoltaic power generation system according to the following scheme: A hot end of the photovoltaic string to be activated is electrically coupled to the first output of the power supply circuit, and a grounding terminal of the photovoltaic string to be activated is electrically coupled to the second output of the power supply circuit.

[0044] If the photovoltaic string itself is used in the present invention to provide an operating voltage for the power supply circuit, the photovoltaic string providing the operating voltage and the photovoltaic string to be activated can be the same or different.

[0045] It should be noted that if a positive electrode of the photovoltaic string is grounded, its negative electrode is the hot end; if a negative electrode of the photovoltaic string is grounded, its positive electrode is the hot end, and the activation of the photovoltaic string can be achieved by both connection methods.

[0046] The meaning of the term "electrical coupling" includes not only direct coupling but also indirect connection (i.e., other components can be connected between the two electrically coupled objects) and also connection by inductive coupling, etc.

[0047] The second embodiment in the present application is an indirect connection, and the following description also refers to an indirect connection: If an electrolytic capacitor bank with a stable output voltage is connected in parallel to both ends of the photovoltaic string to be activated, in order to prevent the electrolytic capacitor bank from exceeding the voltage supplied by the Since the high-frequency alternating current output by the power supply circuit of the present invention is absorbed and therefore no activation of the photovoltaic string occurs, it is necessary to connect an inductor in series between the hot end of the photovoltaic string and a connection point connected to the electrolytic capacitor bank. This allows the high-frequency alternating current supplied to the two ends of the electrolytic capacitor bank to be supplied to the two ends of the photovoltaic string due to the insulation provided by the inductor, thus activating the photovoltaic string in this case. The hot end of the photovoltaic string is not directly connected to the first output of the power supply circuit, but nevertheless falls within the scope of protection of the present invention.

[0048] It is recommended to activate the photovoltaic string in this application at night, at intervals of a few days. The time required for activation depends on the aging of the photovoltaic string; the higher the aging, the longer the time required. To achieve a better activation effect, the slower the drop in voltage output by the BUCK circuit in the power supply circuit, the better, and the cumulative drop time should be greater than or equal to 20 minutes.

[0049] To test the effect of the activation circuit, we purchased a photovoltaic power generation system from Taobao with a nominal output power of only 2 kW. This system had been in use for six years and was originally intended for underdeveloped rural areas in the west. Measured under sunny weather in Guangzhou, its actual output power was only 690 W and its open-circuit voltage was 377 V. We used a power supply circuit according to the present invention in this system, which had the following parameters: the operating voltage corresponded to the aforementioned open-circuit voltage of 377 V, which was directly output by the photovoltaic string in the photovoltaic power generation system at 3 PM, and the capacitor C1 It was 2200 uF / 450 V and two capacitors were connected in parallel, and the switch K1 It opened at 5 pm and the counter K2It closed at 8 PM, and the operating frequency of the CCFL converter circuit was 3.4 kHz, and it only operated for 1 minute and 43 seconds, which already caused the voltage of the capacitor to drop. C1 The voltage had dropped to about 60 V, and measured the next day, the power output had risen to 757 W. That night, it operated again for 1 minute and 43 seconds, and on the third day, the power output had risen to 823 W. After 21 activations, the power output had risen to 1986 W, which was close to the rated output. Better results were achieved.

[0050] Furthermore, since the photovoltaic string internally corresponds to a constant current source or a basic unit consisting essentially of a PN junction diode, the diode cannot conduct during normal activation of the photovoltaic string. Otherwise, the CCFL converter circuit would burn out due to a current short circuit, even if protected by a well-designed current-limiting circuit, resulting in wasted power. To ensure the safety of the photovoltaic string, the present invention requires that the peak value of the high-frequency alternating current output by the CCFL converter circuit not exceed the open-circuit voltage of the photovoltaic string being activated, thus effectively preventing conduction of the diode in the photovoltaic string.Furthermore, the higher the frequency, the better the activation effect. However, since the photovoltaic string is inherently capacitive and also consumes a significant amount of current, different frequencies of high-frequency alternating current must be selected for different power outputs of the photovoltaic string. In general, the larger the area of ​​the photovoltaic string, the greater its output power. Conversely, the higher the junction capacitance of the PN junction, the lower the frequency, which can even reach 800 Hz. At this point, the power supply circuit in the present invention consumes less current for activation. If the frequency is further reduced, the required activation time becomes longer, which in turn increases power consumption.

[0051] For example, if the number of individual cells or base cells connected in series in a photovoltaic string is 24 (the minimum number of individual cells required for series connection of the photovoltaic string is 24, and the resulting open-circuit voltage is approximately 14.4 V to 16.8 V), and since the electrical characteristics of the photovoltaic string also follow the PN junction equation and the voltage drop across the diode is 0.7 V, then the maximum open-circuit voltage across both ends of the photovoltaic string is 0.7 V x 27 = 16.8 V, then the peak value of the high-frequency alternating current output by the CCFL converter circuit should be slightly lower than 16.8 V to ensure the safety of the photovoltaic string. For a US 600V photovoltaic string (with 1,008 basic units connected in series inside), the activation voltage requirement is, for example, just under 600 V.

[0052] Since the photovoltaic string is capacitive during activation, and this transition capacitance eventually leads to the parallel connection to the capacitor C3 This is equivalent, and since the CCFL converter operates in the resonant state of the sine wave and its LC circuit can absorb the energy of the photovoltaic string's transition capacitance, thereby achieving low-energy activation, especially when the CCFL converter abandons the self-excited push-pull oscillation mode and is driven by an external drive, triodes TR1 and TR2 only conduct when the sine wave is close to the peak value, resulting in a higher conversion efficiency. This is also why the CCFL converter capacitor in this invention uses the capacitor C1 A voltage is provided, thereby achieving the purpose of the invention.

[0053] The external drive is also called the external drive. It should be noted that if the CCFL converter uses the self-excited push-pull oscillation operating method, by adjusting the turns ratio of the feedback winding and primary winding, it is also possible to conduct triode TR1 or TR2 near its peak value during the sine wave, resulting in a very high conversion efficiency. Furthermore, to prevent the CCFL converter from oscillating at a low output voltage of the BUCK circuit, a resistor is used. R1 In the starting circuit, the constant current source is replaced, and as described above, when the operating voltage drops from 377 V to 60 V, the oscillation of the CCFL converter does not stop because the current supplied by the constant current source to the triode TR1 or TR2 at the base electrode is not reduced. This is shown in the third embodiment.

[0054] It should be noted that in the prior art, conventional color television receivers with glass picture tubes scanned by an electron gun use a decaying sinusoidal alternating current to demagnetize the picture tube. Its operating principle is simple: a PTC thermistor is connected in series with the demagnetizing coil. Over time, the resistance of the PTC thermistor increases from about 10 ohms to more than 220 kΩ, and the demagnetizing current also decreases from more than 10 A to less than 1 mA. However, this technique cannot be directly used to activate a photovoltaic string because the photovoltaic string is capacitive and cannot be connected in series with a PTC thermistor. Furthermore, the photovoltaic string requires a long activation time, and the type of PTC thermistor cannot be selected according to the specific requirements. Example 2

[0055] Fig. Figure 4 is a schematic diagram of the power supply circuit after the improvement in the exemplary embodiment. 2 of the present invention, which is applied in the photovoltaic power generation system, and since the photovoltaic string has an internal equivalent diode connected in series with it, a set of DC power supplies E is connected in series at the output of the power supply circuit to improve the activation effect, i.e., a set of DC power supplies E is connected in series with the photovoltaic string, and the series connection is carried out by one of the following two methods: (1) a negative electrode of the DC power supply is electrically coupled to the second output of the power supply circuit, and the first output of the power supply circuit is electrically coupled to a positive electrode of the photovoltaic string, and a negative electrode of the photovoltaic string is electrically coupled to a positive electrode of the DC power supply; (2) a negative electrode of the DC power supply is electrically coupled to a positive electrode of the photovoltaic string, and a negative electrode of the photovoltaic string is electrically coupled to the second output of the power supply circuit, and the first output of the power supply circuit is electrically coupled to a positive electrode of the DC power supply.

[0056] In this embodiment, too, the term "electrical coupling" is used to describe the circuit; thus, the meaning of the term "electrical coupling" includes not only direct coupling but also indirect connection (i.e., other components can be connected between the two electrically coupled objects) and also connection by inductive coupling, etc., which in the embodiment 1 is written.

[0057] The photovoltaic string PV1, which provides the operating voltage for the power supply circuit, and the photovoltaic string PV2 to be activated are in Fig. 4 are shown and can be the same photovoltaic string or different.

[0058] This allows the activation voltage obtained between the hot end and the ground terminal of the photovoltaic string to have an AC voltage waveform with a small positive half-period and a large negative half-period, and the small positive half-period ensures that the diodes within the photovoltaic string do not conduct during activation, and the large negative half-period voltage ensures a better activation effect. Example 3

[0059] Fig. Figure 5 is a schematic diagram of the power supply circuit in the exemplary embodiment. 3 of the present invention, and the third embodiment differs from the first embodiment in that the resistance R1The input voltage is replaced by a constant current source with the same current direction, enabling the CCFL converter circuit to supply a constant current to the ground electrodes of the two push-pull triodes TR1 and TR2. Due to the presence of the constant current source, when the input voltage drops, the input voltage of the power supply circuit can be wide. As described above, when the operating voltage drops from 377 V to 60 V, the oscillation of the CCFL converter does not stop because the current supplied by the constant current source to the ground electrode of triode TR1 or TR2 is not reduced. The operating voltage then corresponds to the terminal voltage of the photovoltaic string across its wide range. The operating principle in this embodiment and its applications in the photovoltaic power generation system are the same as in the first embodiment and are not described here.

[0060] The above descriptions are only preferred embodiments of the present invention, and it should be noted that the above preferred embodiments are not intended to be considered a limitation of the present invention. For general technical personnel in the field of technology, various improvements and modifications can be made without departing from the ideas and scope of the present invention, such as the inductance. L1 in Fig. 1 is replaced by a resistor and the other end of the capacitor C2 in Fig. 1 will be marked by an end to resistance R1 connects, or the self-propulsion in Fig.1 is replaced by the “external drive” under the condition that the CCFL circuit operates in the open loop, and it is also possible to sense the output voltage of the CCFL converter circuit to control the duty cycle of the BUCK circuit. These improvements and modifications are also to be considered within the scope of protection of the present invention and are not repeated here by way of example, and the scope of protection of the present invention is subject to the scope defined by the claims.Furthermore, all references to "electrical coupling" and "connection" in the patent do not only refer to the direct coupling of components, but also to the formation of an improved coupling structure by adding coupling means, depending on the specific embodiment. Where "electrical coupling" is explicitly used in the present invention, this serves only to emphasize this meaning, but does not preclude the same meaning from being associated with "connection." The various technical features of the invention can be combined without contradicting one another. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] CN 107086601 A

[0009] CN 201110436259

[0020] CN 201110242377

[0021]

Claims

[1] Power supply circuit used in the photovoltaic power generation system, characterized by, that comprising a switch K1, a current limiting device, a capacitor C1, a switch K2 and a CCFL converter circuit, wherein one end of switch K1 is a positive input of the power supply circuit, and another end of switch K1 is connected to one end of the current limiting device, and another end of the current limiting device is connected to both one end of capacitor C1 and one end of switch K2, and another end of capacitor C1 is a negative input of the power supply circuit, and a positive input of the CCFL converter circuit is connected to another end of switch K2, and a negative input of the CCFL converter circuit is connected to the negative input of the power supply circuit, and a first output of the CCFL converter circuit is a first output of the power supply circuit,and a second output of the CCFL converter circuit is a second output of the power supply circuit; wherein switch K1 is switched off before switch K2 when a photovoltaic string is activated, and the CCFL converter circuit is supplied with an operating voltage by means of capacitor C1. [2] Power supply circuit according to claim 1, characterized by that the current limiting device is an inductor or a resistor. [3] Power supply circuit according to claim 1, characterized by that capacitor C1 is a supercapacitor or an electrolytic capacitor. [4] Power supply circuit according to claim 1, characterized by that the CCFL converter circuit is powered by the external drive. [5] Power supply circuit according to claim 1, characterized bythat the CCFL converter circuit has at least a start-up circuit, an inductor L2, a capacitor C3, a triode TR1, a triode TR2, a transformer B, primary windings N P1 and N P2 , feedback windings N B1 and N B2 and includes a secondary winding Nsi, wherein the starting circuit includes at least two connections, i.e., a starting input and a starting output; wherein the starting input is connected to the other end of the switch K2 and the starting output is connected to a middle tap of the feedback windings N B1 and N B2 is connected; wherein the emitters of the triodes TR1 and TR2 are connected to the other end of the capacitor C1, and the collectors to terminals of the primary winding N P1 or N P2 are connected, and the collectors are also connected to both terminals of capacitor C3, and the ground electrodes to terminals of the feedback winding N B1 or NB2 are connected; wherein a central tap of the primary windings N P1 and N P2 are connected via the inductor L2 to the other end of the switch K2; wherein one end of the secondary winding Nsi is the first output of the CCFL converter circuit and another end of the secondary winding Nsi is the second output of the CCFL converter circuit. [6] Power supply circuit according to claim 5, characterized by that the starting circuit includes a power supply device and the power supply device is a resistor or a device with a constant current source. [7] Power supply circuit according to claim 6, characterized by that the start-up circuit includes a capacitor C2, wherein the capacitor C2 is connected in parallel to the power supply device or the capacitor C2 is connected to the start-up output and the other end of the capacitor C1. [8] Photovoltaic power generation system comprising a photovoltaic string, characterized by , that it further comprises a power supply circuit according to one of claims 1 to 7, wherein a hot end of the photovoltaic string is electrically coupled to the first output of the power supply circuit, and an earth terminal of the photovoltaic string is electrically coupled to the second output of the power supply circuit. [9] Photovoltaic power generation system according to claim 8, characterized by , furthermore, that it comprises a DC power supply, wherein the DC power supply and the outputs of the power supply circuit are connected in series and the series connection is made by one of the following two methods: (1) a negative electrode of the DC power supply is electrically coupled to the second output of the power supply circuit, and the first output of the power supply circuit is electrically coupled to a positive electrode of the photovoltaic string, and a negative electrode of the photovoltaic string is electrically coupled to a positive electrode of the DC power supply; (2) a negative electrode of the DC power supply is electrically coupled to a positive electrode of the photovoltaic string, and a negative electrode of the photovoltaic string is electrically coupled to the second output of the power supply circuit, and the first output of the power supply circuit is electrically coupled to a positive electrode of the DC power supply.

10. Photovoltaic power generation system according to claim 8 or 9, characterized bythat the high-frequency AC peak power of the CCFL converter circuit is not greater than the open-circuit voltage of the photovoltaic string to be activated.