A two-stage power load limiting control method for photovoltaic inverter

Abstract

The present invention discloses a two-stage power load limiting control method for a photovoltaic inverter. The method uses inner-loop current control to obtain a target output power according to a real-time active power control instruction Power Set ref. Based on the target output power, the PV input power and PV input current of each solar controller are reasonably distributed to achieve a basic match between input power and output function without overmatching. Through outer-loop voltage control, the current DC bus voltage value Vbus is collected in real time and compared with the DC bus voltage threshold Vbus_ref. When the DC bus voltage value Vbus>Vbus_ref, the voltage error after PI adjustment is applied to the Boost current loop or the Boost voltage loop to achieve the target voltage value of the DC bus, and quickly pull the bus voltage back to a reasonable voltage, so as to solve the DC bus voltage overshoot problem in both steady-state and transient power conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic inverter power load limiting, and in particular to a two-stage power load limiting control method for a photovoltaic inverter. Background Art

[0002] In recent years, the development and utilization of renewable energy sources, represented by photovoltaics and wind power, have received increasing attention worldwide. Photovoltaic power generation, constrained by solar energy resources, is characterized by randomness, intermittency, cyclicality, and volatility. Solar photovoltaic power generation requires the use of photovoltaic inverters, which boost and invert the DC power generated by photovoltaic panels before connecting it to the grid. These inverters are one of the most critical components in the photovoltaic power generation process. With the rapid growth of installed capacity of photovoltaic power plants, their impact on the power system is also increasing. To minimize the impact of large-scale photovoltaic grid connection on the grid, large and medium-sized photovoltaic power plants should be equipped with active power control systems with active power regulation capabilities to limit the output power of photovoltaic inverters. These systems should also be able to accept and automatically execute active power change control commands sent by the dispatching department, ensuring that active power and active power changes comply with the requirements of the power dispatching department.

[0003] Traditional load limiting methods often limit the output AC current. When the input PV power is overmatched, the excess current will accumulate on the bus due to the output power limitation, causing the bus capacitance to rise rapidly, resulting in overvoltage and reduced system stability. Summary of the Invention

[0004] To address the above technical deficiencies, the present invention adopts a technical solution that provides a two-stage power load limiting control method for a photovoltaic inverter, comprising the following steps:

[0005] According to the real-time active power control instruction Power Set ref, the target output power is obtained;

[0006] According to the target output power, the PV input power and PV input current of each solar controller are reasonably allocated;

[0007] Collect the current DC bus voltage value Vbus in real time and compare it with the DC bus voltage threshold Vbus_ref;

[0008] When the voltage value of the DC bus Vbus>Vbus_ref, the voltage error after PI adjustment is applied to the Boost current loop or the Boost voltage loop to achieve the target voltage value of the DC bus.

[0009] Furthermore, the PV input power and PV input current of each solar controller are reasonably distributed, including the following steps:

[0010] The solar controller receives the input current Ipv and input voltage Vpv output by each PV unit, and outputs the Boost reference voltage value Vpv_ref;

[0011] The power controller receives the active power control command Power Set ref and the Boost reference voltage value Vpv_ref output by the solar controller, and calculates the current reference maximum value I of the Boost current loop based on the target output power and the Boost reference voltage value;

[0012] Obtain the error voltage value between the Boost reference voltage value Vpv_ref of the Boost voltage loop of each PV unit and the input voltage Vpv, obtain the error voltage output value after PI adjustment and limit it;

[0013] According to the error voltage output value after PI adjustment, the current reference value Ipv_ref of the Boost current loop is obtained;

[0014] Limit the maximum current reference I and the current reference value Ipv_ref of each PV unit.

[0015] Furthermore, the voltage error after PI adjustment acts on the Boost current loop, including the following steps:

[0016] The limited current reference maximum value I and current reference value Ipv_ref are regulated by PI and act on the power conversion circuit in the DC / DC unit;

[0017] The error voltage value between the real-time collected DC bus voltage value Vbus and the DC bus voltage threshold Vbus_ref is obtained. After the error voltage value is adjusted by PI, the bus controller acts on the Boost current loop to output a square wave to the power conversion circuit in the DC / DC unit.

[0018] Furthermore, the voltage error after PI adjustment is applied to the Boost current loop, which includes the following steps:

[0019] The limited current reference maximum value I and current reference value Ipv_ref are regulated by PI and act on the power conversion circuit in the DC / DC unit;

[0020] The error voltage value between the real-time collected DC bus voltage value Vbus and the DC bus voltage threshold Vbus_ref is obtained. After the error voltage value is PI-regulated, the bus controller acts on the current reference value Ipv_ref of the Boost current loop.

[0021] Furthermore, the voltage error after PI adjustment acts on the Boost voltage loop, including the following steps:

[0022] Before obtaining the error voltage value between the Boost reference voltage value Vpv_ref of each PV unit Boost voltage loop and the input voltage Vpv, the Boost reference voltage value Vpv_ref is first limited. Then, the obtained maximum current reference value I and the current reference value Ipv_ref are successively limited and PI-regulated and then act on the power conversion circuit in the DC / DC unit.

[0023] Obtain the error voltage value between the voltage value Vbus of the DC bus collected in real time and the voltage threshold value Vbus_ref of the DC bus. After this error voltage value is PI-regulated, the bus controller acts on the Boost reference voltage value Vpv_ref of the Boost voltage loop.

[0024] Further, when Vpv < Vpv_ref, the error voltage output value after PI regulation between the Boost reference voltage value Vpv_ref and the input voltage Vpv is not limited.

[0025] The beneficial effects of the technical solution of the present invention compared with the prior art are as follows:

[0026] A two-stage power limiting control method for a photovoltaic inverter provided by the present invention. First, through inner-loop current control, the PV input power and PV input current of each MPPT are respectively limited according to the active power control instruction, so as to achieve the purpose of basically matching and not over-matching the input power and output function. Second, through outer-loop voltage control, it is detected in real time whether the bus voltage is in an abnormal state. If it is detected that the bus voltage is greater than the voltage threshold value of the DC bus, the voltage error after PI regulation is applied to the Boost current loop or the Boost voltage loop to quickly pull the bus voltage back to a reasonable voltage, realizing that the problem of overshoot of the DC bus voltage can be solved both in the power steady state and the transient state. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0028] Figure 1 is a flowchart of Embodiment 1 of a two-stage power limiting control method for a photovoltaic inverter provided by an embodiment of the present invention;

[0029] Figure 2 is a flowchart of Embodiment 2 of a two-stage power limiting control method for a photovoltaic inverter provided by an embodiment of the present invention;

[0030] Figure 3 This is a flowchart of Example 3 of a two-stage power load limiting control method for a photovoltaic inverter provided by an embodiment of the present invention.

[0031] The reference numerals are as follows:

[0032] 1. Solar controller, 2. Power controller, 3. Bus controller. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0034] Example 1

[0035] See also Figure 1 As shown, the present invention provides a two-stage power load limiting control method for a photovoltaic inverter, comprising the following steps:

[0036] According to the real-time active power control instruction Power Set ref, the target output power is obtained;

[0037] According to the target output power, the PV input power and PV input current of each solar controller 1 are reasonably distributed;

[0038] The current DC bus voltage value Vbus is collected in real time and compared with the DC bus voltage threshold Vbus_ref;

[0039] When the voltage value of the DC bus Vbus>Vbus_ref, the voltage error after PI adjustment is applied to the Boost current loop or the Boost voltage loop to achieve the target voltage value of the DC bus.

[0040] First, through inner-loop current control, the PV input power and PV input current of each MPPT are limited according to the active power control command, achieving a basic match between input power and output power, with no over-matching. Second, through outer-loop voltage control, the bus voltage is detected in real time to determine if it is in an abnormal state. If the bus voltage is greater than the DC bus voltage threshold, the voltage error, after PI adjustment, is applied to the Boost current loop or Boost voltage loop to quickly return the bus voltage to a reasonable level. Through two-stage load limiting control, bus stability is achieved, resolving DC bus voltage overshoot issues during both steady-state and transient power conditions. This system is applicable to, but not limited to, single-phase and three-phase inverter circuits in photovoltaic grid-connected inverters and energy storage inverters.

[0041] Preferably, the PV input power and PV input current of each solar controller 1 are reasonably distributed, including the following steps:

[0042] The solar controller 1 (i.e., MPPT) receives the input current Ipv and input voltage Vpv output by each PV unit, and outputs the Boost reference voltage value Vpv_ref;

[0043] The power controller 2 receives the active power control instruction Power Set ref and the Boost reference voltage value Vpv_ref output by the solar controller 1, and calculates the maximum current reference value I of the Boost current loop according to the target output power and the Boost reference voltage value;

[0044] Obtain the error voltage value between the Boost reference voltage value Vpv_ref of the Boost voltage loop of each PV unit and the input voltage Vpv, and after PI regulation, obtain the error voltage output value and perform limitation;

[0045] According to the error voltage output value after PI regulation, obtain the current reference value Ipv_ref of the Boost current loop;

[0046] Limit the maximum current reference value I and the current reference value Ipv_ref of each PV unit.

[0047] Specifically, divide the target output power by the Boost reference voltage value Vpv_ref to obtain the maximum current reference value I of the Boost current loop.

[0048] Limit the integration of the PI link of the Boost voltage loop of each PV unit to prevent the integration of the PI link of the Boost voltage loop from being overly saturated, and limit the maximum current I of the current reference of the Boost current loop of each PV unit to prevent the PV input power and PV input current from being too large, and at the same time achieve the purpose of reasonably distributing the current and power on each PV unit.

[0049] When Vpv < Vpv_ref, do not limit the error voltage output value obtained after PI regulation between the Boost reference voltage value Vpv_ref and the input voltage Vpv.

[0050] Preferably, the voltage error after PI regulation acts on the Boost current loop, including the following steps:

[0051] The limited maximum current reference value I and the current reference value Ipv_ref are regulated by PI and then act on the power conversion circuit in the DC / DC unit;

[0052] Obtain the error voltage value between the voltage value Vbus of the DC bus collected in real time and the voltage threshold Vbus_ref of the DC bus. After the error voltage value is regulated by PI, the bus controller 3 acts on the current reference value Ipv_ref of the Boost current loop.

[0053] Example 2

[0054] The difference from Example 1 is that the voltage error after PI adjustment acts on different objects, such as Figure 2 As shown, preferably, the voltage error after PI adjustment acts on the Boost voltage loop, including the following steps:

[0055] Before obtaining the error voltage between the Boost reference voltage Vpv_ref of the Boost voltage loop of each PV unit and the input voltage Vpv, the Boost reference voltage Vpv_ref is first limited. The obtained current reference maximum value I and current reference value Ipv_ref are then applied to the power conversion circuit in the DC / DC unit after being limited and PI-adjusted.

[0056] The error voltage value between the DC bus voltage value Vbus acquired in real time and the DC bus voltage threshold Vbus_ref is obtained. After the error voltage value is PI-regulated, the bus controller 3 acts on the Boost reference voltage value Vpv_ref of the Boost voltage loop.

[0057] Example 3

[0058] The difference from Example 1 is that the voltage error after PI regulation acts on different objects. Since the bus controller 3 acts on the Boost reference voltage value Vpv_ref of the Boost voltage loop or the current reference value Ipv_ref of the Boost current loop, it needs to be regulated by PI integral before it can act on the DC / DC duty. It takes a long time for the bus to react. By acting directly on the DC / DC duty, the bus can be stabilized more quickly. Therefore, Figure 3 As shown, preferably, the voltage error after PI adjustment acts on the Boost current loop, including the following steps:

[0059] The limited current reference maximum value I and current reference value Ipv_ref are regulated by PI and act on the power conversion circuit in the DC / DC unit;

[0060] The error voltage value between the real-time collected DC bus voltage value Vbus and the DC bus voltage threshold Vbus_ref is obtained. After the error voltage value is PI-regulated, the bus controller 3 acts on the Boost current loop to output a square wave to the power conversion circuit in the DC / DC unit.

[0061] Through the combined effect of two-stage power load limit control, the inner current loop rationally distributes PV input power and PV input current according to the output power command, ensuring normal bus voltage tracking and no overshoot during system steady state. The outer voltage loop plays an outstanding role during transient conditions such as sudden power changes in the system, and can quickly act on the input Boost current loop duty to quickly stabilize the bus.

[0062] The specific steps are as follows:

[0063] The solar controller receives the input voltage Vpv and input current Ipv of the PV unit and outputs the Boost reference voltage value Vpv_ref;

[0064] The power controller receives the active power control command Power Set ref and the Boost reference voltage value Vpv_ref output by the solar controller, and calculates the current reference maximum value I of the Boost current loop based on the target output power and the Boost reference voltage value;

[0065] Obtain the error voltage value between the Boost reference voltage value Vpv_ref of the Boost voltage loop of each PV unit and the input voltage Vpv, obtain the error voltage output value after PI adjustment and limit it;

[0066] According to the error voltage output value after PI adjustment, the current reference value Ipv_ref of the Boost current loop is obtained;

[0067] Limit the maximum current reference I and current reference value Ipv_ref of each PV unit;

[0068] The limited current reference maximum value I and current reference value Ipv_ref are regulated by PI and act on the power conversion circuit in the DC / DC unit;

[0069] The error voltage value between the real-time collected DC bus voltage value Vbus and the DC bus voltage threshold Vbus_ref is obtained. When the DC bus voltage value Vbus>Vbus_ref, the error voltage value is adjusted by PI and acts on the Boost current loop through the bus controller to output a square wave to the power conversion circuit in the DC / DC unit.

[0070] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiment. All technical solutions based on the concept of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A two-stage power load limiting control method for a photovoltaic inverter, characterized in that: The steps include: According to the real-time active power control instruction Power Set ref, the target output power is obtained; According to the target output power, the PV input power and PV input current of each solar controller are reasonably allocated; The current DC bus voltage value Vbus is collected in real time and compared with the DC bus voltage threshold Vbus_ref; When the voltage value of the DC bus Vbus>Vbus_ref, the voltage error after PI adjustment is applied to the Boost current loop or Boost voltage loop to achieve the target voltage value of the DC bus; The reasonable distribution of the PV input power and PV input current of each solar controller includes the following steps: The solar controller receives the input current Ipv and input voltage Vpv output by each PV unit, and outputs the Boost reference voltage value Vpv_ref; The power controller receives the active power control command Power Set ref and the Boost reference voltage value Vpv_ref output by the solar controller, and calculates the current reference maximum value I of the Boost current loop based on the target output power and the Boost reference voltage value; Obtain the error voltage value between the Boost reference voltage value Vpv_ref of the Boost voltage loop of each PV unit and the input voltage Vpv, obtain the error voltage output value after PI adjustment and limit it; According to the error voltage output value after PI adjustment, the current reference value Ipv_ref of the Boost current loop is obtained; Limit the maximum current reference I and the current reference value Ipv_ref of each PV unit.

2. The two-stage power load limiting control method for a photovoltaic inverter according to claim 1, wherein: The voltage error after PI regulation acts on the Boost current loop, including the following steps: The limited current reference maximum value I and current reference value Ipv_ref are regulated by PI and act on the power conversion circuit in the DC / DC unit; The error voltage value between the real-time collected DC bus voltage value Vbus and the DC bus voltage threshold Vbus_ref is obtained. After the error voltage value is adjusted by PI, the bus controller acts on the Boost current loop to output a square wave to the power conversion circuit in the DC / DC unit.

3. The two-stage power load limiting control method for a photovoltaic inverter according to claim 1, wherein: The voltage error after PI regulation acts on the Boost current loop, including the following steps: The limited current reference maximum value I and current reference value Ipv_ref are regulated by PI and act on the power conversion circuit in the DC / DC unit; The error voltage value between the real-time collected DC bus voltage value Vbus and the DC bus voltage threshold Vbus_ref is obtained. After the error voltage value is PI-regulated, the bus controller acts on the current reference value Ipv_ref of the Boost current loop.

4. The two-stage power load limiting control method for a photovoltaic inverter according to claim 1, wherein: The voltage error after PI regulation acts on the Boost voltage loop, including the following steps: Before obtaining the error voltage value between the Boost reference voltage value Vpv_ref of each PV unit Boost voltage loop and the input voltage Vpv, the Boost reference voltage value Vpv_ref is first limited. Then, the maximum current reference value I and the current reference value Ipv_ref obtained are successively limited and PI-regulated and then act on the power conversion circuit in the DC / DC unit; Obtain the error voltage value between the voltage value Vbus of the DC bus collected in real time and the voltage threshold value Vbus_ref of the DC bus. After this error voltage value is PI-regulated, the bus controller acts on the Boost reference voltage value Vpv_ref of the Boost voltage loop.

5. The two-stage power load limiting control method for a photovoltaic inverter according to any one of claims 1 to 4, characterized in that: When Vpv < Vpv_ref, the output value of the error voltage after PI regulation between the Boost reference voltage value Vpv_ref and the input voltage Vpv is not limited.

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