Control system and method for medium-voltage photovoltaic distribution system

A control system for a medium-voltage photovoltaic distribution system, the medium-voltage photovoltaic distribution system comprising:

• N photovoltaic modules, N DC-DC converters connected to the N photovoltaic modules respectively, a DC-AC converter and a line-frequency transformer connected to the DC-AC converter, wherein outputs of the N DC-DC converters are connected in parallel to a DC bus, the DC bus is connected to the DC-AC converter, the line-frequency transformer is configured to connect to a medium-voltage AC grid, and N is a natural number larger than or equal to 1, wherein
• the control system comprises a DC-AC converter control circuit corresponding to the DC-AC converter, wherein
• the DC-AC converter control circuit comprises a bus voltage sampling circuit, an AC grid sampling and calculating circuit, an active power loop regulator, an amplitude limiting unit, a bus voltage loop regulator, an active current loop regulator, a reactive current loop regulator and a sine pulse width modulation wave generating circuit, wherein
• the bus voltage sampling circuit is configured to sample a bus voltage signal Udc of the DC bus;
• the AC grid sampling and calculating circuit is configured to sample an AC voltage signal and an AC current signal output by the DC-AC converter, and calculate an active current signal id, a reactive current signal iq and an active power signal P based on the AC voltage signal and the AC current signal;
• the active power loop regulator is connected to the AC grid sampling and calculating circuit, and is configured to receive a power difference signal obtained by subtracting the active power signal P from a predetermined active power reference signal Pref and output a voltage-regulating signal;
• the amplitude limiting unit is connected to the active power loop regulator, and is configured to receive the voltage-regulating signal from the active power loop regulator and output a DC bus voltage reference signal Udcref;
• the bus voltage loop regulator is connected to the amplitude limiting unit and a bus voltage sampling circuit, and is configured to receive a voltage difference signal obtained by subtracting the bus voltage signal Udc from the DC bus voltage reference signal Udcref and output an active current reference signal idref;
• the active current loop regulator is connected to the bus voltage loop regulator and the AC grid sampling and calculating circuit, and is configured to receive a first current difference signal obtained by subtracting the active current signal id from the active current reference signal idref and output a first modulation signal ur1;
• the reactive current loop regulator is connected to the AC grid sampling and calculating circuit, and is configured to receive a second current difference signal obtained by subtracting the reactive current signal iq from a predetermined reactive current reference signal iqref and output a second modulation signal ur2;
• and
• the sine pulse width modulation wave generating circuit is connected to the active current loop regulator and the reactive current loop regulator, and is configured to receive the first modulation signal ur1 from the active current loop regulator and the second modulation signal ur2 from the reactive current loop regulator, generate a drive signal corresponding to the first modulation signal and the second modulation signal, and output the drive signal to the DC-AC converter.

A control method for a medium-voltage photovoltaic distribution system, the medium-voltage photovoltaic distribution system comprising:

• N photovoltaic modules, N DC-DC converters connected to the N photovoltaic modules respectively, a DC-AC converter and a line-frequency transformer connected to the DC-AC converter, wherein outputs of the N DC-DC converters are connected in parallel to a DC bus, the DC bus is connected to the DC-AC converter, the line-frequency transformer is configured to connect to a medium-voltage AC grid, and N is a natural number larger than or equal to 1, wherein the control method comprises:
• performing the following operations for any of the N DC-DC converters:
• step S510:
• sampling a photovoltaic voltage signal UPV and a photovoltaic current signal IPV output by a photovoltaic module corresponding to the DC-DC converter, and sampling a bus voltage signal Udc of the DC bus;
• step S520:
• receiving the bus voltage signal Udc and outputting a power weight coefficient KMPPT by a droop controller in a DC-DC converter control circuit corresponding to the DC-DC converter;
• step S530:
• receiving the photovoltaic voltage signal UPV, the photovoltaic current signal IPV and the power weight coefficient KMPPT and tracking a power point based on the photovoltaic voltage signal UPV, the photovoltaic current signal IPV and the power weight coefficient KMPPT by a maximum power point tracking controller in the DC-DC converter control circuit, to obtain a photovoltaic input voltage reference signal UPVref;
• step S540:
• receiving a voltage difference signal obtained by subtracting the photovoltaic voltage signal UPV from the photovoltaic input voltage reference signal UPVref, and outputting a modulation signal for the DC-DC converter by an input voltage loop regulator in the DC-DC converter control circuit;
• and
• step S550:
• receiving the modulation signal, generating a drive signal corresponding to the modulation signal, and outputting the drive signal to the DC-DC converter by a pulse width modulation wave generating circuit in the DC-DC converter control circuit.

A control method for a medium-voltage photovoltaic distribution system, the medium-voltage photovoltaic distribution system comprising:

• N photovoltaic modules, N DC-DC converters connected to the N photovoltaic modules respectively, a DC-AC converter and a line-frequency transformer connected to the DC-AC converter, wherein outputs of the N DC-DC converters are connected in parallel to a DC bus, the DC bus is connected to the DC-AC converter, the line-frequency transformer is configured to connect to a medium-voltage AC grid, and N is a natural number larger than or equal to 1, wherein the control method comprises:
• step S610:
• sampling a bus voltage signal Udc of the DC bus;
• step S620:
• sampling an AC voltage signal and an AC current signal output by the DC-AC converter, and calculating an active current signal id, a reactive current signal iq and an active power signal P based on the AC voltage signal and the AC current signal;
• step S630:
• receiving a power difference signal obtained by subtracting the active power signal P from a predetermined active power reference signal Pref, and outputting a voltage-regulating signal by an active power loop regulator in a DC-AC converter control circuit corresponding to the DC-AC converter;
• step S640:
• receiving the voltage-regulating signal and outputting a DC bus voltage reference signal Udcref by an amplitude limiting unit in the DC-AC converter control circuit;
• step S650:
• receiving a voltage difference signal obtained by subtracting the bus voltage signal Udc from the DC bus voltage reference signal Udcref, and outputting an active current reference signal idref by a bus voltage loop regulator in the DC-AC converter control circuit;
• step S660:
• receiving a first current difference signal obtained by subtracting the active current signal id from the active current reference signal idref, and outputting a first modulation signal ur1 by an active current loop regulator in the DC-AC converter control circuit;
• step S670:
• receiving a second current difference signal obtained by subtracting the reactive current signal iq from a predetermined reactive current reference signal iqref, and outputting a second modulation signal ur2 by a reactive current loop regulator in the DC-AC converter control circuit;
• step S680:
• receiving the first modulation signal ur1 and the second modulation signal ur2, generating a drive signal corresponding to the first modulation signal ur1 and the second modulation signal ur2, and outputting the drive signal to the DC-AC converter by a sine pulse width modulation wave generating circuit in the DC-AC converter control circuit.