Photovoltaic power system and control method thereof
A photovoltaic power system includes a DC/AC inverter circuit, N DC/DC converter circuits that are located at a previous stage of the DC/AC inverter circuit and that are respectively connected to photovoltaic strings, and a controller connected to the DC/AC inverter circuit and the N DC/DC converter circuits. The controller is configured to: perform MPPT control on n DC/DC converter circuits, and perform CPG control on (N−n) DC/DC converter circuits. In the two control manners, a fast and accurate power reserve or limit of a photovoltaic string inverter with any illumination intensity and ambient temperature can be implemented, and fluctuation of a DC bus voltage and AC output power of the photovoltaic string inverter can be eliminated. Control on a virtual synchronous generator of the photovoltaic string inverter is implemented, and a lifespan of the photovoltaic string inverter is prolonged, without a need to add an energy storage element.
1. A photovoltaic power system, comprising:
a plurality of photovoltaic strings;
a direct current-to-alternating current (DC/AC) inverter circuit;
N DC/DC converter circuits located at a previous stage of the DC/AC inverter circuit, wherein each DC/DC converter circuit is connected to at least one of the photovoltaic strings, and a value of N is a positive integer greater than or equal to 2; and
a controller connected to each of the DC/AC inverter circuit and the N DC/DC converter circuits, and is configured to:
perform maximum power point tracking (MPPT) control on n DC/DC converter circuits,
determine a first control parameter that enables the n DC/DC converter circuits to be in a maximum power point operating state, and
control, based on the first control parameter and an active-power reserve parameter, N−n DC/DC converter circuits to operate in a constant power generation (CPG) mode, wherein a value of n is a positive integer greater than or equal to 1 and less than or equal to N−1; and
wherein the photovoltaic power system is connected to a power grid through an output end of the DC/AC inverter circuit.
2. The photovoltaic power system according to claim 1 , wherein the controller comprises:
an MPPT controller configured to:
perform the MPPT control on the n DC/DC converter circuits,
determine the first control parameter that enables the n DC/DC converter circuits to be in the maximum power point operating state, and
obtain a second control parameter based on the first control parameter and the active-power reserve parameter; and
a CPG controller configured to perform CPG control on the N−n DC/DC converter circuits based on the second control parameter, so that the N−n DC/DC converter circuits operate in the CPG mode.
3. The photovoltaic power system according to claim 1 , wherein the controller comprises:
a virtual synchronous generator (VSG) controller configured to calculate a VSG power parameter based on a grid connection parameter for the power grid and a VSG control algorithm;
an MPPT controller, configured to:
perform the MPPT control on the n DC/DC converter circuits,
determine the first control parameter that enables the n DC/DC converter circuits to be in a maximum power point operating state, and
obtain a second control parameter based on the first control parameter, the VSG power parameter, and the active-power reserve parameter; and
a CPG controller configured to perform CPG control on the N−n DC/DC converter circuits based on the second control parameter, so that the N−n DC/DC converter circuits operate in the CPG mode.
4. The photovoltaic power system according to claim 3 , wherein the VSG controller is configured to calculate the VSG power parameter based on an actually detected current power grid frequency, a rated power grid frequency, and any virtual inertia of a constant virtual inertia, an adaptive zero virtual inertia, and an adaptive negative virtual inertia by using the VSG control algorithm, wherein
the constant virtual inertia is a constant virtual inertia time constant in the VSG control algorithm, the adaptive zero virtual inertia is an adaptive zero virtual inertia time constant in the VSG control algorithm, and the adaptive negative virtual inertia is an adaptive negative virtual inertia time constant in the VSG control algorithm.
5. The photovoltaic power system according to claim 2 , wherein the MPPT controller comprises n control circuits, a first arithmetic unit, and a second arithmetic unit;
each control circuit comprises an MPPT processing unit and a multiplier;
the MPPT processing unit is configured to:
detect a first input voltage and a first input current of a corresponding DC/DC converter circuit,
determine current input power of the corresponding DC/DC converter circuit based on the first input voltage and the first input current, and
obtain a second input current at a maximum power point of the DC/DC converter circuit using an MPPT control algorithm;
the multiplier is connected to the MPPT processing unit, and is configured to calculate a product of the first input voltage and the second input current to obtain a maximum output active-power parameter;
the first arithmetic unit connected to the n control circuits is configured to:
determine a maximum output active-power parameter output by each control circuit,
perform summation and averaging operations on n maximum output active-power parameters, and
use an obtained maximum output active-power average value as the first control parameter; and
the second arithmetic unit is configured to:
determine a power parameter based on the active-power reserve parameter and the first control parameter, and
use the power parameter as the second control parameter.
6. The photovoltaic power system according to claim 2 , wherein the MPPT controller comprises n control circuits, a first arithmetic unit, and a third arithmetic unit;
each control circuit comprises an MPPT processing unit and a multiplier;
the MPPT processing unit is configured to:
detect a first input voltage and a first input current of a corresponding DC/DC converter circuit,
determine current input power of the corresponding DC/DC converter circuit based on the first input voltage and the first input current, and
obtain a second input current at a maximum power point of the DC/DC converter circuit using an MPPT control algorithm;
the multiplier is connected to the MPPT processing unit, and is configured to calculate a product of the first input voltage and the second input current to obtain a maximum output active-power parameter;
the first arithmetic unit connected to the n control circuits is configured to:
determine a maximum output active-power parameter output by each control circuit,
perform summation and averaging operations on n maximum output active-power parameters, and
use an obtained maximum output active-power average value as the first control parameter; and
the third arithmetic unit is configured to:
determine a current parameter based on the active-power reserve parameter and the first control parameter, and
use the current parameter as the second control parameter.
7. The photovoltaic power system according to claim 2 , wherein the MPPT controller comprises n MPPT processing units, a first arithmetic unit, and a fourth arithmetic unit;
each MPPT processing unit is configured to:
detect a first input voltage and a first input current of a corresponding DC/DC converter circuit,
determine current input power of the corresponding DC/DC converter circuit based on the first input voltage and the first input current, and
obtain a second input voltage at a maximum power point of the DC/DC converter circuit by using an MPPT control algorithm;
the first arithmetic unit connected to the n MPPT processing units is configured to
determine a second input voltage output by each MPPT processing unit,
perform summation and averaging operations on n second input voltages, and
use an obtained second input voltage average value as the first control parameter; and
the fourth arithmetic unit is configured to:
perform calculation based on the active-power reserve parameter and the first control parameter, and
use an obtained voltage parameter as the second control parameter.
8. The photovoltaic power system according to claim 3 , wherein the MPPT controller comprises n control circuits, a first arithmetic unit, and a second arithmetic unit;
each control circuit comprises an MPPT processing unit and a multiplier;
the MPPT processing unit is configured to:
detect a first input voltage and a first input current of a corresponding DC/DC converter circuit,
determine current input power of the corresponding DC/DC converter circuit based on the first input voltage and the first input current, and
obtain a second input current at a maximum power point of the DC/DC converter circuit by using a maximum power point tracking MPPT control algorithm; and
the multiplier is connected to the MPPT processing unit, and is configured to calculate a product of the first input voltage and the second input current to obtain a maximum output active-power parameter;
the first arithmetic unit connected to the n control circuits is configured to:
determine a maximum output active-power parameter output by each control circuit,
perform summation and averaging operations on n maximum output active-power parameters, and
use an obtained maximum output active-power average value as the first control parameter; and
the second arithmetic unit is configured to:
determine a power parameter based on the active-power reserve parameter, the first control parameter, and the VSG power parameter, and
use the power parameter as the second control parameter.
9. The photovoltaic power system according to claim 3 , wherein the MPPT controller comprises n control circuits, a first arithmetic unit, and a third arithmetic unit;
each control circuit comprises an MPPT processing unit and a multiplier;
the MPPT processing unit is configured to:
detect a first input voltage and a first input current of a corresponding DC/DC converter circuit,
determine current input power of the corresponding DC/DC converter circuit based on the first input voltage and the first input current, and
obtain a second input current at a maximum power point of the DC/DC converter circuit by using a maximum power point tracking MPPT control algorithm;
the multiplier is connected to the MPPT processing unit, and is configured to calculate a product of the first input voltage and the second input current to obtain a maximum output active-power parameter;
the first arithmetic unit connected to the n control circuits is configured to:
determine a maximum output active-power parameter output by each control circuit,
perform summation and averaging operations on n maximum output active-power parameters, and
use an obtained maximum output active-power average value as the first control parameter; and
the third arithmetic unit is configured to:
determine a current parameter based on the active-power reserve parameter, the first control parameter, and the virtual synchronous generator VSG power parameter, and
use the current parameter as the second control parameter.
10. The photovoltaic power system according to claim 3 , wherein the MPPT controller comprises n MPPT processing units, a first arithmetic unit, and a fourth arithmetic unit;
each MPPT processing unit is configured to:
detect a first input voltage and a first input current of a corresponding DC/DC converter circuit,
determine current input power of the corresponding DC/DC converter circuit based on the first input voltage and the first input current, and
obtain a second input voltage at a maximum power point of the DC/DC converter circuit by using an MPPT control algorithm;
the first arithmetic unit connected to the n MPPT processing units is configured to
determine a second input voltage output by each MPPT processing unit,
perform summation and averaging operations on n second input voltages, and
use an obtained second input voltage average value as the first control parameter;
the fourth arithmetic unit is configured to:
determine a voltage reference value based on the active-power reserve parameter, the first control parameter, and the VSG power parameter,
determine a voltage parameter based on the voltage reference value and the first control parameter, and
use the voltage parameter as the second control parameter; and
the CPG controller is configured to control, based on the second control parameter, N−n DC/DC converter circuits to operate in a voltage adjustment-based CPG mode.
11. The photovoltaic power system according to claim 1 , wherein the DC/AC inverter circuit comprises a string three-phase inverter or a string single-phase inverter.
12. A method for controlling a photovoltaic power system, wherein the photovoltaic power system comprises a plurality of photovoltaic strings, a controller, a direct current-to-alternating current (DC/AC) inverter circuit, and N DC/DC converter circuits located at a previous stage of the DC/AC inverter circuit, wherein each DC/DC converter circuit is connected to at least one of the photovoltaic strings, a value of N is a positive integer greater than or equal to 2, the DC/AC inverter circuit is connected to the N DC/DC converter circuits and the controller, and the photovoltaic power system is connected to a power grid through an output end of the DC/AC inverter circuit, the method comprising:
performing maximum power point tracking (MPPT) control on n DC/DC converter circuits, and determining a first control parameter that enables the n DC/DC converter circuits to be in a maximum power point operating state, wherein a value of n is a positive integer greater than or equal to 1 and less than or equal to N−1; and
controlling, based on the first control parameter and an active-power reserve parameter, N−n DC/DC converter circuits to operate in a constant power generation (CPG) mode.
13. The method according to claim 12 , wherein the controlling, of the N−n DC/DC converter circuits to operate in the CPG mode comprises:
obtaining a second control parameter based on the first control parameter and the active-power reserve parameter; and
controlling, based on the second control parameter, the N−n DC/DC converter circuits to operate in the CPG mode.
14. The method according to claim 12 , wherein the controlling, of the N−n DC/DC converter circuits to operate in the CPG mode comprises:
obtaining a virtual synchronous generator (VSG) power parameter based on a grid connection parameter for the power grid and a VSG control algorithm;
obtaining a second control parameter based on the first control parameter, the VSG power parameter, and the active-power reserve parameter; and
controlling, based on the second control parameter, the N−n DC/DC converter circuits to operate in the CPG mode.
15. The method according to claim 14 , wherein the obtaining of the VSG power parameter based on the grid connection parameter for the power grid and the VSG control algorithm comprises:
calculating the VSG power parameter based on an actually detected current power grid frequency, a rated power grid frequency, and any one of a constant virtual inertia, an adaptive zero virtual inertia, and an adaptive negative virtual inertia using the VSG control algorithm, wherein
the constant virtual inertia is a constant virtual inertia time constant in the VSG control algorithm, the adaptive zero virtual inertia is an adaptive zero virtual inertia time constant in the VSG control algorithm, and the adaptive negative virtual inertia is an adaptive negative virtual inertia time constant in the VSG control algorithm.
16. A controller, comprising:
a processor; and
a memory coupled to the processor to store instructions, which when executed by the processor, cause the processor to perform operations of controlling a photovoltaic power system, wherein the photovoltaic power system comprises a plurality of photovoltaic strings, a controller, a direct current-to-alternating current (DC/AC) inverter circuit, and N DC/DC converter circuits located at a previous stage of the DC/AC inverter circuit, wherein each DC/DC converter circuit is connected to at least one of the photovoltaic strings, a value of N is a positive integer greater than or equal to 2, the DC/AC inverter circuit is connected to the N DC/DC converter circuits and the controller, and the photovoltaic power system is connected to a power grid through an output end of the DC/AC inverter circuit, the operations comprising:
performing maximum power point tracking (MPPT) control on n DC/DC converter circuits, and determining a first control parameter that enables the n DC/DC converter circuits to be in a maximum power point operating state, wherein a value of n is a positive integer greater than or equal to 1 and less than or equal to N−1; and
controlling, based on the first control parameter and an active-power reserve parameter, N−n DC/DC converter circuits to operate in a constant power generation (CPG) mode.
17. The controller according to claim 16 , wherein the controlling of the N−n DC/DC converter circuits to operate in the CPG mode comprises:
obtaining a second control parameter based on the first control parameter and the active-power reserve parameter; and
controlling, based on the second control parameter, the N−n DC/DC converter circuits to operate in the CPG mode.
18. The controller according to claim 16 , wherein the controlling of the N−n DC/DC converter circuits to operate in the CPG mode comprises:
obtaining a virtual synchronous generator (VSG) power parameter based on a grid connection parameter for a power grid and a VSG control algorithm;
obtaining a second control parameter based on the first control parameter, the VSG power parameter, and the active-power reserve parameter; and
controlling, based on the second control parameter, the N−n DC/DC converter circuits to operate in the CPG mode.
19. The controller according to claim 18 , wherein the obtaining of the VSG power parameter based on the grid connection parameter for the power grid and the VSG control algorithm comprises:
calculating the VSG power parameter based on an actually detected current power grid frequency, a rated power grid frequency, and any one of a constant virtual inertia, an adaptive zero virtual inertia, and an adaptive negative virtual inertia using the VSG control algorithm, wherein
the constant virtual inertia is a constant virtual inertia time constant in the VSG control algorithm, the adaptive zero virtual inertia is an adaptive zero virtual inertia time constant in the VSG control algorithm, and the adaptive negative virtual inertia is an adaptive negative virtual inertia time constant in the VSG control algorithm.