AC pre-charging relay control method of photovoltaic energy storage inverter

Abstract

The invention discloses an AC pre-charging relay control method for a photovoltaic energy storage inverter, and the method comprises the steps: carrying out the switching-on and switching-off triggering of a relay, setting a threshold Uth1 and a voltage fluctuation threshold phi, and switching on an AC pre-charging relay when the periodically sampled battery voltage is greater than Uth1 and the periodically sampled battery voltage fluctuation is smaller than the voltage fluctuation threshold phi; a voltage difference U is set, and the voltage reduction state of the current battery is judged according to periodic sampling of the battery voltage; and when the difference value of any two of the periodic sampling voltages is greater than U and the sampling current of the battery is 0, the alternating-current pre-charging relay is switched off. The alternating-current relay replaces a direct-current relay to meet the design requirements of miniaturization and compactness, so that the size is reduced, the layout is flexible, and the cost is reduced. The circuit breaker protection device can realize circuit breaker protection of zero-current monitoring, avoids the generation of electric arcs, guarantees the use safety, meets the requirement for stable control of the on-off circuit of the relay, and avoids the occurrence of an abnormal circuit after the battery fault is recovered.

Description

Technical Field

[0001] The invention relates to an AC pre-charging relay control method for a photovoltaic energy storage inverter, and belongs to the technical field of battery circuit breaker protection for energy storage systems. Background Art

[0002] DC relays are often used in the battery pre-charging circuit of photovoltaic energy storage inverters. DC relays are equipped with arc extinguishing devices. When a circuit fails, if an arc is generated, it can be extinguished by the arc extinguishing cavity in the relay.

[0003] With the miniaturization, integration, and cost control requirements of photovoltaic energy storage inverters in recent years, the use of smaller and lower-cost AC relays has become a better choice.

[0004] AC current has its own zero-crossing point, and the arc will naturally extinguish at the zero-crossing point after it is generated. When using AC relays in DC circuits, since the current does not have a zero-crossing point, the arc cannot be extinguished naturally once it is generated. Therefore, it is difficult to implement the AC relay replacement solution.

[0005] In addition, during the use of the photovoltaic energy storage inverter, the battery of the energy storage inverter may have the main relay of the battery system tripping or the pre-charging circuit parallel relay tripping, that is, there is a slow decrease or rapid decrease in battery voltage. Generally, the pre-charging relay can only respond to a rapid decrease, but cannot detect a slow decrease. Therefore, after the battery fault is eliminated, if the pre-charging relay is still in a closed state, it will produce an abnormal path and cause damage to the inverter circuit. Summary of the invention

[0006] The purpose of the present invention is to solve the deficiencies of the above-mentioned prior art. Aiming at the problems that the AC pre-charging relay in the traditional photovoltaic energy storage inverter replaces the DC pre-charging relay, which is easy to generate arc and difficult to achieve voltage slow drop detection and closure, a control method for the AC pre-charging relay of the photovoltaic energy storage inverter is proposed.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is: A method for controlling an AC pre-charging relay of a photovoltaic energy storage inverter, wherein the photovoltaic energy storage inverter comprises a converter circuit, a battery, and a pre-charging parallel circuit located between the converter circuit and the battery, wherein the pre-charging parallel circuit comprises a relay branch and a pre-charging branch connected in parallel, wherein an AC relay is provided on the relay branch, and wherein the method for controlling the AC pre-charging relay comprises the following steps: S1 relay closes and triggers, setting the battery voltage threshold U th1 And the voltage fluctuation threshold Φ, the switching frequency fs of the photovoltaic energy storage inverter is used as the sampling frequency of the battery voltage, when the battery voltage is periodically sampled to be greater than Uth1 When the periodically sampled battery voltage fluctuation is less than the voltage fluctuation threshold Φ, the AC pre-charging relay is closed; The S2 relay is triggered by circuit breaking, and the voltage difference △U is set. The current battery voltage reduction state is determined based on the periodic sampling of the battery voltage; When the difference between any two voltages in the periodic sampling voltages is greater than △U and the battery sampling current is 0, the AC pre-charging relay is disconnected.

[0008] Preferably, in step S1, the switching frequency fs is set to 20kHz, and the 20ms average value U of the battery voltage is calculated based on the periodic sampling of the battery voltage. 1_20ms , 10-point sampling sliding average U 1_ma , 1s average value U 1_1s ; When U 1_20ms >U th1 , and U 1_ma and U 1_1s When the absolute value of the difference is less than Φ, the AC pre-charging relay is closed.

[0009] Preferably, the step S2 includes a rapid pressure reduction triggering step S21 and a slow pressure reduction triggering step S22; In step S21, U is calculated 1_1s and U 1_20ms If △U1>△U and the battery sampling current is 0, the AC pre-charge relay is disconnected; In step S22, the slow voltage drop difference △U' and the continuous cycle threshold number S are set to calculate U 1_1s and U 1_ma The difference between the current U 1_1s Update to record value U 1_1s ´, judge and update once every 20ms period. When △U2 is detected to be greater than △U´ for S consecutive periods, calculate the current U 1_1s ´ and U 1_20ms When △U3>△U and the battery sampling current is 0, the AC pre-charging relay is disconnected.

[0010] Preferably, step S3 is included, when △U1>△U appears, a rapid voltage reduction anomaly is triggered; when △U2 is detected to be greater than △U´ for S consecutive cycles, a slow voltage reduction anomaly is triggered; when △U3>△U appears, a slow circuit breaking anomaly is triggered.

[0011] The beneficial effects of the present invention are mainly reflected in: 1. Replacing DC relays with AC relays can meet the needs of miniaturization and compact design, making the size smaller, the layout more flexible, and the cost lowered.

[0012] 2. It can realize circuit-breaking protection with zero current monitoring, prevent the occurrence of arc, ensure the safety of use, and meet the demand for stable control of relay on and off circuits, and prevent abnormal circuits after battery failure recovery.

[0013] 3. Meet the needs of abnormal detection and feedback, and facilitate maintenance and troubleshooting. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Other features, objects and advantages of the present application will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings: Figure 1 The present invention is a flowchart of an AC pre-charging relay control method for a photovoltaic energy storage inverter.

[0015] Figure 2 It is a schematic diagram of the pre-charging circuit of the photovoltaic energy storage inverter in the present invention. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] The present application will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant inventions, rather than to limit the inventions. It should also be noted that, for ease of description, only the parts related to the relevant inventions are shown in the accompanying drawings. It should be noted that, in the absence of conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0018] The present invention provides an AC pre-charging relay control method for a photovoltaic energy storage inverter, such as Figure 2 As shown, the photovoltaic energy storage inverter includes a converter circuit, a battery, and a pre-charge parallel circuit located between the converter circuit and the battery. The pre-charge parallel circuit includes a relay branch and a pre-charge branch connected in parallel. The above circuit belongs to the prior art. Figure 2 In order to simplify the circuit structure, the difference is that in the prior art, the relay on the relay branch is a DC relay, while in this case, an AC relay is set on the relay branch.

[0019] Compared with DC relays, AC relays have the characteristic of occupying less space. The difference is that when using AC relays in DC circuits, arc extinguishing and other solutions need to be designed and constructed, while also meeting the circuit breaker protection requirements in the event of a battery failure.

[0020] In view of this situation, this case proposes an AC pre-charge relay control method, such as Figure 1 As shown, the specific steps include: Relay closure triggers, setting the battery voltage threshold U th1 And the voltage fluctuation threshold Φ, the switching frequency fs of the photovoltaic energy storage inverter is used as the sampling frequency of the battery voltage, when the battery voltage is periodically sampled to be greater than U th1 When the periodically sampled battery voltage fluctuation is less than the voltage fluctuation threshold Φ, the AC pre-charging relay is closed.

[0021] The relay is triggered to open the circuit, and the voltage difference △U is set. The current voltage reduction state of the battery is judged based on the periodic sampling of the battery voltage.

[0022] When the difference between any two voltages in the periodic sampling voltages is greater than △U and the battery sampling current is 0, the AC pre-charging relay is disconnected.

[0023] Specifically, AC current has its own zero-crossing point, and the arc will naturally extinguish at the zero-crossing point after it is generated. When using AC relays in DC circuits, the current does not have a zero-crossing point, so once the arc is generated, there is no way to extinguish it naturally. By reasonably controlling the on-off time of the AC relay and the switch of the inverter, zero current and zero voltage difference on-off can be achieved under any working conditions, thereby avoiding the generation of arcs. At the same time, it prevents the abnormal on-off of the relay in the battery from causing damage to the inverter circuit.

[0024] The energy storage inverter samples the battery input voltage U1. When the inverter is not working, the battery does not discharge. After U1 remains stable for a time greater than △U, the relay is closed.

[0025] After the relay is closed, if the battery fails, two situations may occur: First, the main relay in the battery trips, and the inverter detects that the voltage of U1 drops rapidly. Second, the parallel relay of the pre-charge circuit in the battery trips, and the inverter detects that the voltage U1 drops slowly. At this time, the inverter needs to quickly determine these two situations and stop output. In order to prevent the relay from disconnecting and generating an arc, the inverter disconnects the relay Re1 after detecting that the battery current is 0. This prevents the relay in the battery from closing after the internal fault of the battery is restored, and the large current generated will damage the related components in the inverter.

[0026] In a specific embodiment, the switching frequency fs is 20kHz, and the 20ms average value U of the battery voltage is calculated based on the periodic sampling of the battery voltage.1_20ms , 10-point sampling sliding average U 1_ma , 1s average value U 1_1s ; When U 1_20ms >U th1 , and U 1_ma and U 1_1s When the absolute value of the difference is less than Φ, the AC pre-charge relay is closed. Generally, the Φ setting value is 1V. Of course, according to the characteristics of each inverter, a suitable fluctuation range can be selected. At this time, it indicates that the battery voltage has not fluctuated, the pre-charge process is completed, and the relay is closed.

[0027] In a specific embodiment, referring to Figure 2 As shown, step S2 includes a rapid pressure reduction triggering step S21 and a slow pressure reduction triggering step S22; In step S21, calculate U 1_1s and U 1_20ms If △U1>△U and the battery sampling current is 0, the AC pre-charge relay is disconnected; In step S22, the slow voltage drop difference △U' and the continuous cycle threshold number S are set to calculate U 1_1s and U 1_ma The difference between the current U 1_1s Update to record value U 1_1s ´, judge and update once every 20ms period. When △U2 is detected to be greater than △U´ for S consecutive periods, calculate the current U 1_1s ´ and U 1_20ms When △U3>△U and the battery sampling current is 0, the AC pre-charging relay is disconnected.

[0028] Specifically, △U is generally set to 100V. Of course, it can be flexibly set according to the working and storage status of the battery, etc. to ensure that the inverter's full electrical parameter requirements are met.

[0029] When △U1>△U, it means that the battery voltage is decreasing rapidly, and the protection is shut down at this time.

[0030] If △U2<△U´, then the current U 1_1s Update to record value U 1_1s ', at this time it is judged to be slowly decreasing, which should be the normal fluctuation of battery voltage charging and discharging. When △U2 is detected to be greater than △U´ for S consecutive cycles, it means that the battery voltage is not caused by charging and discharging fluctuations, but by the disconnection of the relay in the battery. At this time, the protection is turned off.

[0031] In addition, during normal operation of the inverter, if the battery BMS information is received that the battery is faulty, the inverter turns off the switch tube and disconnects the inverter relay when the battery current is detected to be 0.

[0032] In a specific embodiment, when △U1>△U appears, a rapid voltage reduction anomaly is triggered; when △U2 is detected to be greater than △U´ for S consecutive cycles, a slow voltage reduction anomaly is triggered; when △U3>△U appears, a slow circuit breaking anomaly is triggered.

[0033] That is, there is an abnormal trigger of rapid drop, an abnormal trigger of voltage drop exceeding slow monitoring, and a circuit breaker trigger exceeding the cumulative drop.

[0034] At this time, the back-end monitoring can make corresponding fault alarms or command executions according to the abnormality. For example, when a rapid drop occurs, the fault information is fed back that the main relay is tripped. When the voltage drop triggers an abnormality, the feedback is that there is abnormal leakage, etc. When the voltage drop exceeds a certain drop, the battery pre-charge circuit parallel relay is fed back to trip, and the tripping situation is fed back at this time. In this way, the monitoring end can respond quickly and conduct relevant fault troubleshooting.

[0035] From the above description, it can be found that replacing DC relays with AC relays meets the requirements of miniaturization and compact design, making the size smaller, the layout more flexible, and the cost lowered. It can achieve zero-current monitoring circuit breaker protection, prevent arcing, and ensure safety. At the same time, it meets the requirements for stable control of relay on and off circuits, and prevents abnormal paths after battery failure recovery. It meets the requirements of abnormal detection and feedback, and facilitates maintenance and troubleshooting.

[0036] The term "comprise" or any other similar term is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus / device that includes a list of elements includes not only those elements but also other elements not expressly listed, or also includes elements inherent to such process, method, article, or apparatus / device.

[0037] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A method for controlling an AC pre-charge relay of a photovoltaic energy storage inverter, wherein the photovoltaic energy storage inverter comprises a converter circuit, a battery, and a pre-charge parallel circuit located between the converter circuit and the battery, wherein the pre-charge parallel circuit comprises a relay branch and a pre-charge branch connected in parallel, and an AC relay is provided on the relay branch, characterized in that The AC pre-charging relay control method comprises the following steps: S1 relay closes and triggers, setting the battery voltage threshold U th1 And the voltage fluctuation threshold Φ, the switching frequency fs of the photovoltaic energy storage inverter is used as the sampling frequency of the battery voltage, when the battery voltage is periodically sampled to be greater than U th1 When the periodically sampled battery voltage fluctuation is less than the voltage fluctuation threshold Φ, the AC pre-charging relay is closed; The S2 relay is triggered by circuit breaking, and the voltage difference △U is set. The current voltage reduction state of the battery is judged based on the periodic sampling of the battery voltage; When the difference between any two voltages in the periodic sampling voltages is greater than △U and the battery sampling current is 0, the AC pre-charging relay is disconnected.

2. According to claim 1, an AC pre-charging relay control method for a photovoltaic energy storage inverter is characterized in that: In step S1, the switching frequency fs is set to 20kHz, and the 20ms average value U of the battery voltage is calculated based on the periodic sampling of the battery voltage. 1_20ms , 10-point sampling sliding average U 1_ma , 1s average value U 1_1s ; When U 1_20ms >U th1 , and U 1_ma and U 1_1s When the absolute value of the difference is less than Φ, the AC pre-charging relay is closed.

3. According to claim 2, a method for controlling an AC pre-charging relay of a photovoltaic energy storage inverter is characterized in that: The step S2 includes a rapid pressure reduction triggering step S21 and a slow pressure reduction triggering step S22; In step S21, U is calculated 1_1s and U 1_20ms If △U1>△U and the battery sampling current is 0, the AC pre-charge relay is disconnected; In step S22, the slow voltage drop difference △U' and the continuous cycle threshold number S are set to calculate U 1_1s and U 1_ma The difference between the current U 1_1s Update to record value U 1_1s ´, judge and update once every 20ms period. When △U2 is detected to be greater than △U´ for S consecutive periods, calculate the current U 1_1s ´ and U 1_20ms When △U3>△U and the battery sampling current is 0, the AC pre-charging relay is disconnected.

4. According to claim 3, the AC pre-charging relay control method of the photovoltaic energy storage inverter is characterized in that: The method comprises step S3, wherein when △U1>△U appears, a rapid voltage reduction anomaly is triggered; when △U2 is detected to be greater than △U´ for S consecutive cycles, a slow voltage reduction anomaly is triggered; and when △U3>△U appears, a slow circuit breaking anomaly is triggered.

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