Abstract: An example system includes an inverter and at least one combiner box. The combiner box includes a plurality of direct current-direct current (DC-DC) circuits and one controller. The controller is configured to: when an output voltage of the combiner box is greater than or equal to a first preset voltage and less than or equal to a second preset voltage, control the combiner box to output a maximum power. When the output voltage of the combiner box is greater than the second preset voltage, the controller controls an output power of the combiner box to decrease as the output voltage increases. The second preset voltage is greater than the first preset voltage, and the maximum power is a sum of maximum powers of all photovoltaic strings connected to the combiner box.

Abstract: A photovoltaic system includes a controller and two groups of inverters. The two groups of inverters include a positive inverter group and a negative inverter group. The positive inverter group includes at least two inverters: a first inverter and a third inverter. The negative inverter group includes at least two inverters: a second inverter and a fourth inverter. Alternating current output ends of the first inverter and the third inverter are connected in parallel. Direct current input ends of the first inverter and the second inverter are connected in series. Alternating current output ends of the second inverter and the fourth inverter are connected in parallel. Direct current input ends of the third inverter and the fourth inverter are connected in series.

Abstract: A conversion circuit, a conversion circuit precharge control method, and a photovoltaic system avoid additional costs and avoid impact on a switch caused by a current generated in a circuit at a moment when an RSCC enters an operating state, thereby ensuring operating performance of the RSCC. The conversion circuit includes a first power supply, a resonant switched capacitor converter (RSCC), and a control circuit. The RSCC includes a switch unit, an output filter unit, a first input end, a second input end, and an output end. The first power supply is configured to supply an input voltage to the RSCC. The control circuit is configured to: before controlling the RSCC to operate, control the switch unit in the RSCC to transmit, to the output filter unit, electric energy supplied by the first power supply.

Abstract: A method and apparatus for suppressing cross current including: obtaining a common-mode current and a common-mode injection voltage of each inverter in an inverter parallel system; determining a virtual damping voltage of each inverter based on the common-mode current of each inverter and a preset common-mode damping factor, where if a direction in which a current flows out of the inverter is a positive direction, the preset common-mode damping factor is a negative value, or if a direction in which a current flows into the inverter is a positive direction, the preset common-mode damping factor is a positive value; superimposing the virtual damping voltage on the common-mode injection voltage of each inverter, to obtain a target common-mode voltage of each inverter; and controlling operation of each inverter based on the target common-mode voltage of each inverter and a differential mode voltage of each inverter.

Abstract: A direct current converter includes a three-level power switching circuit, a resonant circuit, and a controller. An output voltage at an output end of the three-level power switching circuit is used to charge the resonant circuit. The controller is configured to control power switching components in the three-level power switching circuit, so that when the resonant circuit performs charging or discharging at one half of a direct current voltage, one of the power switching components is connected to a current loop of the resonant circuit, and when the resonant circuit performs charging or discharging at the direct current voltage, two of the power switching components are connected to the current loop of the resonant circuit. By using the direct current converter, a voltage borne by the power switching component in the direct current converter during current conversion can be reduced, thereby improving reliability of the direct current converter.

Abstract: A photovoltaic system and a circulating current suppression method. The system includes a controller and at least two inverters. A direct current input terminal of each inverter is connected to a corresponding photovoltaic array. Alternating current output terminals of the at least two inverters are connected in parallel. The controller is configured to: obtain a direct current component of a common-mode output current of at least one of the at least two inverters and adjust a direct current bus voltage of the corresponding inverter based on a magnitude of the direct current component of the common-mode output current, to suppress a circulating current between the at least two inverters. A circulating current between a plurality of inverters connected in parallel can be suppressed, thereby reducing loss caused by a circulating current, and improving power supply efficiency.

Abstract: The photovoltaic power generation system includes a controller and M groups of DC-DC circuits. Each group of DC-DC circuits include N DC-DC circuits, where M is a positive integer, and N is an integer greater than 1. An input end of each DC-DC circuit is connected to at least one photovoltaic unit, and each photovoltaic unit includes at least one photovoltaic module. The controller controls the N DC-DC circuits in each group of DC-DC circuits to sequentially start online IV curve scanning and controls a time interval at which two adjacent DC-DC circuits start online IV curve scanning to be less than duration of online IV curve scanning performed by one DC-DC circuit. The photovoltaic power generation system can reduce a fluctuation of a power output during online IV curve scanning, reduce duration of online IV curve scanning performed by the photovoltaic power generation system.

Abstract: Example three-level inverters, control methods, and systems are provided. One example three-level inverter includes a first bus capacitor, a second bus capacitor, a power conversion circuit, and a controller. The first bus capacitor is connected in the middle of the current bus and the power conversion circuit. The power conversion circuit is configured to convert a direct current into a three-phase alternating current for output. The controller is configured to determine a balance reference by using a difference between absolute values of voltages of the positive and negative direct current buses and an even harmonic current in a grid-connected current, where the balance reference is used to enable the three-level inverter to generate a current signal for balancing the voltages of the positive and negative direct current buses.

Abstract: A string inverter control method includes: in a process of performing IV curve scanning on one or more first direct current/direct current step-up circuits, controlling a change of an output voltage of one or more second direct current/direct current step-up circuits on which the IV curve scanning does not need to be performed, where a change trend of the output voltage and a change trend of an input voltage of the one or more first direct current/direct current step-up circuits on which the IV curve scanning is performed present a non-strictly monotonically increasing relationship. Therefore, for the direct current/direct current step-up circuit on which the IV curve scanning is performed, a voltage difference between two ends of the direct current/direct current step-up circuit is not always in a relatively high state, so that a ripple current on an input inductor in the direct current/direct current step-up circuit can be reduced.

Abstract: A three-level inverter includes controllable switch components T1 to T6. Each of the controllable switch components includes a parallel connected junction capacitor and an anti-parallel connected diode. A first terminal of T1 is connected to a positive direct current bus, a second terminal of T4 is connected to a negative direct current bus, a second terminal of T1 is connected to first terminals of T2 and T5. A controller is configured to: in a positive half cycle, control T3 to be conducted after T1 is conducted, and control T3 to be disconnected before T1 is conducted next time; and in a negative half cycle, control T2 to be conducted after T4 is conducted, and control T2 to be disconnected before T4 is conducted next time. The three-level inverter can balance voltages of the controllable switch components.

Abstract: A common-mode voltage injection control method and apparatus for an inverter. For the method and apparatus, a common-mode voltage for a DPWM mode is calculated based on three-phase port voltages and an output power command; a common-mode voltage for an MPC modulation mode is calculated based on the direct current bus voltage, the three-phase port voltages, and the output power command; a modulation proportion is determined based on a maximum phase voltage peak value of the three-phase port voltages, the direct current bus voltage, and a power factor of the output power command; and a common-mode injection voltage is generated based on the common-mode voltage for the DPWM mode, the modulation proportion, and the common-mode voltage for the MPC modulation mode.

Abstract: A power supply system, a converter, and a circulating current suppression method of the converter. The power supply system includes at least two converters that are coupled between a direct current power supply and an alternating current grid. Each converter obtains target output reactive power when an output current of the converter starts to increase from an initial current, obtains a reactive power compensation parameter based on the three-phase output voltages. Further, each converter obtains compensated output reactive power of the converter based on the reactive power compensation parameter and adjusts actual output reactive power of the converter based on the target output reactive power and the compensated output reactive power, so that an absolute value of a difference between common-mode output voltages of any two of the at least two adjusted converters is less than a difference threshold.

Abstract: A converter and a power backfeed control method applied to a photovoltaic power generation system are provided. The power backfeed control method includes: controlling, according to a backfeed instruction, the converter to enter a backfeed mode, where in the backfeed mode, the converter can transmit energy of the power grid to a selected photovoltaic string with a corresponding number; determining a backfeed control voltage according to the backfeed instruction, and determining a voltage limit in a process of determining the backfeed control voltage; determining an actual backfeed voltage based on the backfeed control voltage and the voltage limit, where the actual backfeed voltage is a smaller one of the backfeed control voltage and the voltage limit; and controlling the converter to output the actual backfeed voltage to the selected photovoltaic string, to enable the selected photovoltaic string to generate an electroluminescent effect.

Abstract: One example method includes obtaining output powers at initial scanning points of photovoltaic strings in a first group and a second group. The output powers at the initial scan points of the photovoltaic strings in the first group can then be controlled to sequentially decrease, and the output powers at the initial scan points of the photovoltaic strings in the second group can then be controlled to sequentially increase. Scanning can then be performed in the initial scanning direction starting from output voltages corresponding to the output powers at the initial scan points of the first group. Scanning can then be performed in the initial scanning direction starting from output voltages corresponding to the output powers at the initial scan points of the second group, where output powers of the first group and the second group are kept to compensate each other during IV curve scanning.

Abstract: A power supply system and a method for controlling the power supply system includes a direct current voltage conversion apparatus, an inverter, and a diode. The direct current voltage conversion apparatus includes a controller and a direct current voltage conversion circuit. The controller is configured to: control the output voltage of the direct current voltage conversion circuit, so that the diode is in a conducted state; detect a voltage on the direct current bus; and determine, based on the voltage on the direct current bus, whether high voltage ride-through occurs in the power supply system. According to the power supply system and the method for controlling the power supply system provided in this application, high voltage ride-through can be quickly detected while fault isolation is implemented, thereby improving efficiency of detecting high voltage ride-through.

Abstract: An islanding detection method and apparatus, and a computer-readable storage medium. The detection method includes: determining a harmonic amplitude growth rate and a frequency growth rate of alternating current electricity output by an alternating current port of a grid-tied inverter; determining an islanding disturbance coefficient corresponding to the harmonic amplitude growth rate, where the harmonic amplitude growth rate and the islanding disturbance coefficient are in a monotonically increasing relationship; determining an islanding injection amount based on the frequency growth rate and the islanding disturbance coefficient corresponding to the harmonic amplitude growth rate; controlling, based on the islanding injection amount, the grid-tied inverter to output a reactive power or a reactive current over the alternating current port; and performing islanding detection based on a frequency of the alternating current electricity output by the alternating current port.

Abstract: Embodiments of this application disclose a heat dissipating element control method, including: obtaining a status parameter set and a detected temperature of a first device, where the status parameter set is associated with a running temperature of the first device; determining values of a first temperature parameter and a second temperature parameter in a target adjustment function based on the status parameter set; and determining the heat dissipating efficiency of the heat dissipating element based on the values of the first temperature parameter and the second temperature parameter and the detected temperature, and controlling running of the heat dissipating element. This resolves a problem that the heat dissipating efficiency is not adjusted in time because the detected temperature is unable to reflect an actual temperature in real time.

Abstract: A string inverter control method includes: in a process of performing IV curve scanning on one or more first direct current/direct current step-up circuits, controlling a change of an output voltage of one or more second direct current/direct current step-up circuits on which the IV curve scanning does not need to be performed, where a change trend of the output voltage and a change trend of an input voltage of the one or more first direct current/direct current step-up circuits on which the IV curve scanning is performed present a non-strictly monotonically increasing relationship. Therefore, for the direct current/direct current step-up circuit on which the IV curve scanning is performed, a voltage difference between two ends of the direct current/direct current step-up circuit is not always in a relatively high state, so that a ripple current on an input inductor in the direct current/direct current step-up circuit can be reduced.

Abstract: This application provides a converter and a power backfeed control method that are applied to a photovoltaic power generation system. One end of the converter is connected to at least one photovoltaic string, and another end of the converter is connected to a power grid. Each photovoltaic string corresponds to one string number.

Abstract: A photovoltaic inverter is provided, including an inverter circuit, a data sampling module, and a control module. The inverter circuit includes a switch component and an alternating current output terminal. The data sampling module is configured to collect, from the alternating current output terminal, an instantaneous current value at each sampling point moment in target sampling duration and an instantaneous value of each-phase current at a target moment. The control module is configured to: determine a valid current value of the target sampling duration based on the instantaneous current value at each sampling point moment, determine an upper switching frequency limit and a lower switching frequency limit of an Nth switching period based on the valid current value, and determine a target instantaneous current value IN based on the instantaneous value of each-phase current at the target moment.