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

Abstract

The application discloses an AC pre-charging relay control method of a photovoltaic energy storage inverter, which comprises relay closing and triggering of circuit breaking, setting of a threshold value U th1 and a voltage fluctuation threshold value Φ, closing of an AC pre-charging relay when periodically sampled battery voltage is greater than U th1 and periodically sampled battery voltage fluctuation is less than the voltage fluctuation threshold value Φ, setting of a pressure difference △U, judgment of a current battery voltage reduction state according to periodic sampling of the battery voltage, and breaking of the AC pre-charging relay when any two voltage difference values in the periodically sampled voltage are greater than △U and battery sampling current is 0. The application replaces a DC relay with an AC relay to meet the design requirements of miniaturization and compactness, so that the volume is reduced, the layout is flexible, and the cost is reduced. The circuit breaking protection of zero current monitoring can be realized, the generation of electric arc is avoided, the safety in use is ensured, the stable control requirements of relay on-off circuit are met, and abnormal paths after battery fault recovery are avoided.

Description

TECHNICAL FIELD

[0001] The application relates to an alternating current pre-charging relay control method of a photovoltaic energy storage inverter, and belongs to the technical field of battery circuit breaker protection of an energy storage system. BACKGROUND

[0002] A direct current relay is often used in a battery pre-charging circuit of a photovoltaic energy storage inverter, and the direct current relay is provided with an arc extinguishing device, and when a circuit fault occurs, an electric arc can be extinguished by the arc extinguishing cavity in the relay.

[0003] In recent years, with the miniaturization, integration and cost control requirements of photovoltaic energy storage inverters, an alternating current relay with a smaller size and a lower cost becomes a better choice.

[0004] An alternating current naturally extinguishes an electric arc at a zero-crossing point. When an alternating current relay is used in a direct current circuit, the electric arc cannot be naturally extinguished because the current does not have a zero-crossing point. Therefore, it is difficult to realize the replacement scheme of the alternating current relay.

[0005] In addition, during the use of the photovoltaic energy storage inverter, the battery of the energy storage inverter may jump off the main relay of the battery system or jump off the pre-charging circuit parallel relay, that is, there are slow reduction and rapid reduction of the battery voltage. Generally, the pre-charging relay can only be turned off in the rapid reduction condition, and cannot be detected in the slow reduction condition. Therefore, when the pre-charging relay is still in the closed state after the battery fault is eliminated, an abnormal path is generated, causing damage to the inverter circuit. SUMMARY

[0006] The application aims to solve the problems of the prior art, that is, the alternating current pre-charging relay in the traditional photovoltaic energy storage inverter is prone to produce an electric arc and it is difficult to realize voltage slow reduction detection and closing, and proposes an alternating current pre-charging relay control method of a photovoltaic energy storage inverter.

[0007] In order to achieve the above-mentioned purpose, the technical scheme adopted by the application is as follows:

[0008] An alternating current pre-charging relay control method of a photovoltaic energy storage inverter, the photovoltaic energy storage inverter comprising a converter circuit, a battery, a pre-charging parallel circuit located between the converter circuit and the battery, the pre-charging parallel circuit comprising a relay branch and a pre-charging branch in parallel, and an alternating current relay being arranged on the relay branch, characterized in that the alternating current pre-charging relay control method comprises the following steps:

[0009] S1, the relay is closed and triggered, and a battery voltage threshold U is set th1and voltage fluctuation threshold Φ, taking the switching frequency fs of the photovoltaic energy storage inverter as the sampling frequency of the battery voltage, when periodically sampling the battery voltage greater than U th1 and the periodically sampled battery voltage fluctuation is less than voltage fluctuation threshold Φ, closing the AC pre-charging relay;

[0010] S2 relay open trigger, set pressure difference △U, according to the periodic sampling of the battery voltage to determine the current battery voltage state;

[0011] When any two voltage difference values greater than △U and the battery sampling current is 0, the AC pre-charging relay is opened.

[0012] Preferably, in step S1, the switching frequency fs is 20kHz, and the 20ms average value U 1_20ms , 10-point sampling sliding average value U 1_ma , 1s average value U 1_1s of the battery voltage is calculated according to the periodic sampling of the battery voltage.

[0013] When U 1_20ms > U th1 , and the absolute value of U 1_ma and U 1_1s difference is less than Φ, the AC pre-charging relay is closed.

[0014] Preferably, the step S2 includes a rapid voltage reduction trigger step S21 and a slow voltage reduction trigger step S22.

[0015] In step S21, the difference △U1 between U 1_1s and U 1_20ms is calculated, and if △U1>△U and the battery sampling current is 0, the AC pre-charging relay is opened.

[0016] In step S22, the slow voltage reduction difference value △U' and the continuous period threshold number S are set, the difference △U2 between U 1_1s and U 1_ma is calculated, and if △U2<△U', the current U 1_1s is updated to the record value U 1_1s ', which is judged and updated every 20ms period, and when S consecutive periods are detected △U2 greater than △U', the difference △U3 between the current U 1_1s ' and U 1_20ms is calculated, and if △U3>△U and the battery sampling current is 0, the AC pre-charging relay is opened.

[0017] Preferably, the step S3 is included, when △U1>△U occurs, triggering the rapid voltage drop abnormality; when S consecutive periods are detected that △U2 is greater than △U', triggering the slow voltage drop abnormality; when △U3>△U occurs, triggering the slow circuit breaking abnormality.

[0018] The beneficial effects of the present application mainly include:

[0019] 1. Replacing DC relays with AC relays to meet the design requirements of miniaturization and compactness, making the volume smaller and the layout more flexible, and reducing the cost.

[0020] 2. Zero-current monitoring circuit breaking protection can prevent the occurrence of electric arc, ensuring safety in use, and meeting the stable control requirements of relay on-off circuit, preventing abnormal on-off circuit after battery failure recovery.

[0021] 3. Meet the abnormal detection and feedback requirements, and facilitate troubleshooting. BRIEF DESCRIPTION OF DRAWINGS

[0022] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments, made with reference to the accompanying drawings:

[0023] Figure 1 is a flowchart of an AC pre-charging relay control method of a photovoltaic energy storage inverter of the present application.

[0024] Figure 2 is a pre-charging circuit schematic diagram of the photovoltaic energy storage inverter in the present application. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application will be described clearly and completely below with reference to the drawings of the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0026] The present application will be further described in detail below with reference to the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related application, and not to limit the application. In addition, it should be noted that, in order to facilitate description, only the parts related to the application are shown in the drawings. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0027] The present application provides an AC pre-charging relay control method of a photovoltaic energy storage inverter, as Figure 2As shown, the photovoltaic energy storage inverter includes a converter circuit, a battery, a pre-charge parallel circuit between the converter circuit and the battery, the pre-charge parallel circuit includes a relay branch and a pre-charge branch in parallel, the above circuit belongs to the prior art, Figure 2 To simplify the circuit structure, the difference is that in the prior art, the relay on the relay branch is a DC relay, and in the present case, an AC relay is arranged on the relay branch.

[0028] Compared with the DC relay, the AC relay has the characteristics of small occupied space, and the difference is that the AC relay is used in the DC circuit, which needs to be designed and constructed with arc extinguishing scheme, and at the same time, it needs to meet the circuit protection requirement under the condition of battery failure.

[0029] In view of this situation, the present application proposes an AC pre-charge relay control method, such as Figure 1 As shown, it specifically includes the following steps:

[0030] The relay is closed and triggered, and the battery voltage threshold U is set 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 periodically sampled battery voltage is greater than U th1 and the periodically sampled battery voltage fluctuation is less than the voltage fluctuation threshold Φ, the AC pre-charge relay is closed.

[0031] The relay is opened and triggered, and the pressure difference ΔU is set, and the current battery voltage is periodically sampled to determine the voltage drop state.

[0032] When any two voltage difference values in the periodically sampled voltage are greater than ΔU and the battery sampling current is 0, the AC pre-charge relay is opened.

[0033] Specifically, the AC current has a zero point, and the arc will naturally extinguish at the zero point. When the AC relay is used in the DC circuit, the current has no zero point, and the arc cannot be naturally extinguished once it is generated. By reasonably controlling the on-off time of the AC relay and the switching of the inverter, zero current and zero voltage difference under any working condition are achieved, so as to avoid the generation of arc. At the same time, prevent the abnormal on-off of the relay in the battery from causing damage to the inverter circuit.

[0034] The energy storage inverter samples the battery input voltage U1, when the inverter is not working, the battery is not discharged, U1 keeps stable for more than ΔU, and the relay is closed.

[0035] If a battery malfunctions after the relay closes, two scenarios can occur: First, the main relay inside the battery trips, and the inverter detects a rapid drop in voltage U1. Second, the parallel relay in the pre-charge circuit inside the battery trips, and the inverter detects a slow drop in voltage U1. The inverter needs to quickly determine these two scenarios and stop outputting. To prevent arcing caused by the relay disconnecting, the inverter disconnects relay Re1 after detecting zero battery current. This prevents the large current generated when the battery recovers from the internal fault from damaging related components within the inverter.

[0036] In one 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 moving average U 1_ma The average value U in 1 second 1_1s ;

[0037] 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, Φ is set at 1V. Of course, depending on the characteristics of each inverter, a suitable fluctuation range can be selected. At this point, it indicates that the battery voltage is not fluctuating, the pre-charge process is complete, and the relay is closed.

[0038] In one specific embodiment, refer to Figure 2 As shown, step S2 includes a rapid voltage reduction triggering step S21 and a slow voltage reduction triggering step S22;

[0039] In step S21, calculate U 1_1s and U 1_20ms If the difference ΔU1 > ΔU and the battery sampling current is 0, disconnect the AC precharge relay;

[0040] In step S22, the slow pressure drop differential value ΔU´ and the number of consecutive cycle thresholds S are set, and U is calculated. 1_1s and U 1_ma The difference △U2, if △U2<△U´, then the current U 1_1s Update to record value U 1_1s The algorithm checks and updates every 20ms. After detecting that ΔU2 is greater than ΔU' for S consecutive cycles, it calculates the current U. 1_1s ´ and U 1_20ms The difference ΔU3 is used to disconnect the AC precharge relay when ΔU3 > ΔU and the battery sampling current is 0.

[0041] Specifically, △U is generally set to 100V, and can be flexibly set according to the working and storage state of the battery, to ensure that the full charging parameter requirement of the inverter is met.

[0042] When △U1> △U, it indicates that the battery voltage is rapidly decreasing, and at this time, the shutdown protection is performed.

[0043] If △U2< △U´, the current U 1_1s is updated to the recorded value U 1_1s ´, at this time, it is determined that the battery voltage is slowly decreasing, which should be the normal fluctuation of the battery voltage during charging and discharging.

[0044] When △U2 is greater than △U´ for S consecutive periods, it indicates that the battery voltage is not caused by the fluctuation during charging and discharging, but by the disconnection of the battery relay, and at this time, the shutdown protection is performed.

[0045] In addition, during normal operation of the inverter, if the battery BMS information indicates that the battery fails, the inverter closes the switch tube, and when the battery current is 0, the inverter relay is disconnected.

[0046] In one embodiment, when △U1> △U, the rapid voltage decrease anomaly is triggered; when △U2 is greater than △U´ for S consecutive periods, the slow voltage decrease anomaly is triggered; and when △U3> △U, the slow circuit breaking anomaly is triggered.

[0047] That is, there are rapid decrease anomaly triggering, voltage decrease exceeding slow monitoring anomaly triggering, and circuit breaking triggering exceeding the accumulated decrease amplitude.

[0048] At this time, the back-end monitoring can perform corresponding fault alarm or instruction execution according to the anomaly, for example: when the rapid decrease occurs, the feedback fault information is that the main relay is tripped; when the voltage slow decrease triggers an anomaly, it is fed back that there is an abnormal leakage; and when the voltage slow decrease exceeds a certain decrease amplitude, the feedback is that the pre-charge circuit of the battery is parallelly connected to the relay, and at this time, the feedback is that the tripping condition. In this way, the monitoring end can quickly respond and perform related fault troubleshooting.

[0049] As can be seen from the above description, replacing the DC relay with the AC relay meets the design requirements of miniaturization and compactness, reduces the volume and layout flexibility, and reduces the cost. The zero-current monitoring circuit breaking protection can prevent the generation of electric arc, and the safety of use is guaranteed. At the same time, the stable control requirement of the relay on-off circuit is met, and the abnormal path after the battery fault recovery is avoided. The abnormal detection and feedback requirements are met, and the maintenance and fault troubleshooting are facilitated.

[0050] The term "comprising" or any other similar word is intended to encompass the inclusion of one or more steps, features, or elements but not to the exclusion of any other steps, features, or elements. The term "comprising" therefore indicates that the inclusion of one or more steps, features, or elements is not a requirement and that other steps, features, or elements can also be included.

[0051] So far, the technical solutions of the present application have been described in combination with the preferred embodiments shown in the drawings, but it is easy for those skilled in the art to understand that the protection scope of the present application is obviously not limited to these specific embodiments. Those skilled in the art can make equivalent changes or replacements to the related technical features without deviating from the principles of the present application, and the technical solutions after these changes or replacements will all fall within the protection scope of the present application.

Claims

1. A method for controlling an AC precharge relay in a photovoltaic energy storage inverter, the photovoltaic energy storage inverter comprising a converter circuit, a battery, and a precharge parallel circuit located between the converter circuit and the battery, the precharge parallel circuit comprising a relay branch and a precharge branch connected in parallel, wherein an AC relay is provided on the relay branch, characterized in that... The AC precharge relay control method includes the following steps: S1 relay closure triggers, setting battery voltage threshold U. th1 And the voltage fluctuation threshold Φ, using the switching frequency fs of the photovoltaic energy storage inverter as the sampling frequency for the battery voltage, when the battery voltage is periodically sampled to be greater than U th1 Furthermore, when the periodically sampled battery voltage fluctuation is less than the voltage fluctuation threshold Φ, the AC relay is closed; S2 relay circuit break trigger, set voltage difference ΔU, and determine the current battery voltage drop state based on periodic sampling of battery voltage; When the difference between any two voltages in the periodic sampling voltage is greater than ΔU and the battery sampling current is 0, disconnect the AC relay; 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 moving average U 1_ma The average value U in 1 second 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, close the AC relay; Step S2 includes a rapid voltage reduction triggering step S21 and a slow voltage reduction triggering step S22; In step S21, U is calculated. 1_1s and U 1_20ms If the difference ΔU1 > ΔU and the battery sampling current is 0, the AC relay is disconnected. In step S22, the slow pressure drop differential value ΔU´ and the number of consecutive cycle thresholds S are set, and U is calculated. 1_1s and U 1_ma The difference △U2, if △U2<△U´, then the current U 1_1s Update to record value U 1_1s The algorithm checks and updates every 20ms. After detecting that ΔU2 is greater than ΔU' for S consecutive cycles, it calculates the current U. 1_1s ´ and U 1_20ms The difference ΔU3 is used to disconnect the AC relay when ΔU3 > ΔU and the battery sampling current is 0.

2. The AC pre-charge relay control method for a photovoltaic energy storage inverter according to claim 1, characterized in that: Including step S3, when △U1 > △U, a rapid voltage drop anomaly is triggered; when △U2 is detected to be greater than △U´ for S consecutive cycles, a slow voltage drop anomaly is triggered; when △U3 > △U, a slow circuit breaker anomaly is triggered.

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