CN112242712B - Power control method for two-stage photovoltaic inverter system - Google Patents
Power control method for two-stage photovoltaic inverter system Download PDFInfo
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Abstract
A power control method for a two-stage photovoltaic inverter system, comprising: the method comprises the steps of firstly, acquiring actual output voltage of a booster circuit of a front-stage DC/DC circuit in a two-stage photovoltaic inverter system; determining a first upper limit value of the PV current according to the actual output voltage and the preset direct-current bus limiting voltage; thirdly, determining a PV current effective upper limit value of the front-stage DC/DC circuit according to the PV current first upper limit value and a preset PV current second upper limit value; and step four, determining the PV current effective instruction value of the front-stage DC/DC circuit according to the actual input voltage and the preset reference input voltage of the booster circuit based on the PV current effective upper limit value. The method does not need the cooperative control of a front-stage controller and a rear-stage controller, can realize that a front-stage multipath DC/DC circuit can respond to the power requirement of a rear-stage DC/AC in real time, and avoids the adverse effects of generating capacity loss, even circuit damage and the like caused by the inconsistency of front-stage and rear-stage power adjustment.
Description
Technical Field
The invention relates to the technical field of photovoltaic power generation, in particular to a power control method for a two-stage photovoltaic inverter system and a control method for the two-stage photovoltaic inverter system.
Background
At present, the mainstream photovoltaic power generation inversion system comprises a centralized type, a distributed type and a series type.
As shown in fig. 1, the centralized inverter has a large single-machine power (500kW, 1MW and more), a small number of MPPT lines (one or two MPPTs), can directly adopt a single-stage structure of DC/AC, and is suitable for a large-scale ground power station in a plain.
As shown in fig. 2, the distributed power generation system is composed of a preceding-stage intelligent MPPT controller and a subsequent-stage high-power inverter, which replace a traditional combiner box in a centralized system, has the characteristics of preceding-stage multi-path MPPT optimization and subsequent-stage centralized inversion internet access, and is suitable for power stations with hills, mountains, parks, fishing light complementation and the like.
As shown in fig. 3, the group-string power generation system is similar to the distributed type and also has multi-path MPPT optimization, but the front-stage DC/DC optimization circuit and the rear-stage inverter circuit are all integrated in one inverter cabinet, the single-machine power is small, generally 30-80kW, and the alternating current output is merged into the power grid.
Disclosure of Invention
In order to solve the above problem, the present invention provides a power control method for a two-stage photovoltaic inverter system, the method including:
the method comprises the steps of firstly, acquiring actual output voltage of a booster circuit of a front-stage DC/DC circuit in a two-stage photovoltaic inverter system;
determining a first upper limit value of the PV current according to the actual output voltage and a preset direct current bus limiting voltage;
thirdly, determining the PV current effective upper limit value of the front-stage DC/DC circuit according to the PV current first upper limit value and a preset PV current second upper limit value;
and fourthly, determining a PV current effective instruction value of the front-stage DC/DC circuit according to the actual input voltage and a preset reference input voltage of the booster circuit based on the PV current effective upper limit value.
According to an embodiment of the present invention, in the third step, the first upper limit value of the PV current and the second upper limit value of the PV current are compared, and the smaller value is selected as the effective upper limit value of the PV current.
According to one embodiment of the present invention, in the second step,
calculating a deviation voltage of the actual output voltage and the preset direct current bus limiting voltage, wherein if the actual output voltage is less than the preset direct current bus limiting voltage, the deviation voltage is zero, and if the actual output voltage is greater than or equal to the preset direct current bus limiting voltage, the deviation voltage is a difference value of the preset direct current bus limiting voltage and the actual output voltage;
and generating the PV current first upper limit value according to the deviation voltage.
According to an embodiment of the present invention, in the second step, a first PI regulator and a first preset limiter are used to generate the first upper limit value of the PV current according to the offset voltage, wherein a maximum limiting current of the first preset limiter is a maximum allowable current of the pre-stage DC/DC circuit.
According to one embodiment of the present invention, in the fourth step,
calculating a difference value between the preset reference input voltage and the actual input voltage of the booster circuit;
and generating the PV current effective instruction value according to the difference value and the PV current effective upper limit value by using a second PI regulator and a second amplitude limiter.
The invention also provides a power control method for the two-stage photovoltaic inverter system, which comprises the following steps:
the method comprises the following steps of firstly, acquiring actual output voltage of a front-stage DC/DC circuit in a two-stage photovoltaic inverter system;
determining an adjustment coefficient according to the actual output voltage and the power limiting voltage of the preceding-stage DC/DC circuit;
thirdly, determining a PV current effective upper limit value of the preceding-stage DC/DC circuit according to the maximum allowable current and the minimum allowable current of the preceding-stage DC/DC circuit based on the adjusting coefficient;
when the actual output voltage is smaller than or equal to the power-limited initial voltage of the preceding DC/DC circuit, the adjusting coefficient can enable the PV current effective upper limit value to be kept at the maximum allowable current of the preceding DC/DC circuit.
According to an embodiment of the present invention, in the step two, the adjustment coefficient is determined according to the following expression:
k＝V dc -V dc_bgn +|V dc -V dc_bgn |
wherein k represents an adjustment coefficient, V dc Representing the actual output voltage, V dc_bgn Representing a power limited initial voltage.
In the third step, according to an embodiment of the present invention, the PV current effective upper limit value is determined according to the following expression:
wherein, I PV_lmt Represents the effective upper limit value of PV current, I PV_up And I PV_lo Respectively representing the maximum and minimum allowable currents of the DC/DC circuit, k representing the adjustment coefficient, V dc_bgn And V dc_end Respectively representing a power limit initial voltage and a power limit end voltage.
According to an embodiment of the present invention, in the third step, the PV current effective upper limit value is further limited by a minimum allowable current of the pre-stage DC/DC circuit, so as to ensure that the PV current effective upper limit value is greater than or equal to the minimum allowable current of the pre-stage DC/DC circuit.
The invention also provides a control method for the two-stage photovoltaic inverter system, which adopts the method as described in any one of the above methods to determine the PV current effective upper limit value of the front-stage DC/DC circuit in the two-stage photovoltaic inverter system.
According to the power control method for the two-stage photovoltaic inverter system, the output voltage ring is introduced into a traditional double-ring control structure, when the output voltage is higher than the voltage limit value of the direct current bus, the output voltage value is converted into the control quantity related to the instruction value in the current ring through the PI regulator, namely, the output voltage negative feedback is introduced into the double-ring control structure, the output voltage is stabilized at the voltage limit value of the direct current bus, and the situation that the output voltage continuously rises and damages the circuit is avoided.
Compared with the prior art, the method does not need the cooperative control of front and rear two-stage controllers, can realize that the front-stage multi-path DC/DC circuit can respond to the power requirement of the rear-stage DC/AC in real time, and avoids the adverse effects of power generation loss, circuit damage and the like caused by the inconsistency of front and rear two-stage power adjustment.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required in the description of the embodiments or the prior art:
fig. 1 is a schematic configuration diagram of a conventional centralized power generation system;
FIG. 2 is a schematic diagram of a conventional distributed power generation system;
FIG. 3 is a schematic diagram of a prior art string-type power generation system;
FIG. 4 is a schematic diagram of a control unit of a conventional BOOST BOOST circuit;
FIG. 5 is a schematic diagram of a control unit of a conventional post-stage DC/AC inverter circuit;
fig. 6 is a schematic flow chart of an implementation of a power control method for a two-stage photovoltaic inverter system according to an embodiment of the invention;
FIG. 7 is a logic diagram of an implementation of the method of FIG. 6 according to one embodiment of the invention;
fig. 8 is a schematic implementation flow diagram of a power control method for a two-stage photovoltaic inverter system according to an embodiment of the invention.
Detailed Description
The following detailed description will be given with reference to the accompanying drawings and examples to explain how to apply the technical means to solve the technical problems and to achieve the technical effects. It should be noted that, as long as there is no conflict, the embodiments and the features of the embodiments of the present invention may be combined with each other, and the technical solutions formed are within the scope of the present invention.
In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details or with other methods described herein.
Additionally, the steps illustrated in the flow charts of the figures may be performed in a computer system such as a set of computer-executable instructions and, although a logical order is illustrated in the flow charts, in some cases, the steps illustrated or described may be performed in an order different than here.
The centralized type inverter belongs to a single-stage inverter system, only has one DC/AC stage, and the centralized type inverter and the group string type inverter belong to a double-stage inverter system, and have two stages of DC/DC + DC/AC. The two-stage inversion system is provided with a direct current bus, the front stage DC/DC and the rear stage DC/AC are controlled by different controllers, the front stage MPPT and boosting are performed, and the rear stage stabilizes the voltage of the direct current bus and inverts the direct current bus.
When the output power of the front stage DC/DC is less than or equal to the output power of the rear stage DC/AC, the direct current bus voltage is controlled by the rear stage DC/AC and is kept constant. When the inverter is subjected to power scheduling, the output power of the front-stage DC/DC is always larger than that of the rear-stage DC/AC, so that redundant energy is stored in a direct-current bus capacitor, and the bus voltage is increased. If the bus voltage is not controlled, the power electronic devices at the front and rear stages can be directly damaged, and even fire can be caused in serious cases.
Therefore, in a two-stage system, a front-stage controller and a rear-stage controller are required to perform coordinated control so as to ensure that the output power of the front stage cannot exceed the output power of the rear stage. The current common solution is to communicate with the back-stage controller in real time by the front-stage controller.
When a power dispatching instruction of the photovoltaic power station is issued to the inverter circuit controller, the inverter circuit controller calculates the power value of each preceding stage circuit according to the number of the preceding stage DC/DC circuits accessed at the time and the access condition of the battery pack, and distributes the power value to the controller of each preceding stage DC/DC circuit through communication.
In the string inverter, the controllers of the front-stage DC/DC and the rear-stage DC/AC are on the same PCB, and the reliability and the real-time performance of communication can be ensured. However, there is a certain reaction time (including communication interval and response time, time for controller control and DC/DC circuit response control, etc.) between the power distribution and power response of the preceding stage DC/DC, and when the reaction time is longer, the DC bus voltage may exceed the standard.
For a distributed system, the intelligent MPPT controllers are distributed below the photovoltaic modules and are not together with the inverters, and the direct current output of each intelligent MPPT controller is connected to the direct current input end of each inverter through a wire cable. At the moment, the inverter and each intelligent MPPT combiner box are communicated through a long communication line, so that the communication reliability and the real-time performance of the inverter are weak, bus voltage is easily overhigh to cause the shutdown of front-stage and rear-stage protection when the power of the inverter is scheduled, or a front-stage intelligent MPPT controller enters an intermittent working state to cause large system power generation loss.
Some power stations directly carry out power scheduling on each intelligent MPPT controller and the inverter at the same time, and since the photovoltaic power stations basically adopt MODBUS communication protocols to carry out point-to-point communication, the time for each intelligent MPPT controller and the time for each inverter to receive scheduling instructions are inconsistent, so that the voltage of the direct current bus is increased.
The invention provides a control method for a two-stage photovoltaic inverter system, aiming at the problem that a front-stage DC/DC circuit cannot respond to the power requirement of a rear-stage DC/DC circuit in real time in the prior art.
Through analysis, the preceding-stage DC/DC circuit in the existing two-stage photovoltaic inverter system is usually composed of a BOOST circuit, and is used for realizing MPPT optimization of the photovoltaic string and boosting the output voltage of the photovoltaic string to the DC bus voltage.
As shown in fig. 4, the control unit of the BOOST circuit includes a PV voltage outer loop and a PV current inner loop. Command value V of PV voltage outer loop ref The instruction value I of the inner ring of the PV current is given by the MPPT calculation unit ref Then this is given by the PV voltage error after the PI regulator. To prevent the output current command value I of the PI regulator ref Beyond the practical allowable range, the command value therefore needs to be limited by a limiter before entering the PV current inner loop.
As shown in fig. 5, the control unit of the post-stage DC/AC inverter circuit in the two-stage photovoltaic inverter system includes a DC bus voltage outer loop and an AC current inner loop. When the output power of the front-stage DC/DC circuit is not greater than the power requirement of the rear-stage DC/AC inverter circuit, the direct-current voltage outer ring can stabilize the direct-current bus voltage at a command value. When the output power of the front-stage DC/DC circuit is greater than the power requirement of the rear-stage DC/AC inversion, the current instruction value output by the PI regulator of the direct-current voltage outer ring reaches the maximum amplitude value, so that the direct-current voltage outer ring fails, and the direct-current bus voltage cannot be stabilized.
Based on the implementation principle of the control system of the two-stage photovoltaic inverter system, the control method for the two-stage photovoltaic inverter system introduces the direct-current bus voltage into each DC/DC control system, converts the change of the direct-current bus voltage into a part of the current instruction value limit value of the figure 4, and then adjusts the output power of the DC/DC circuit in real time according to the direct-current bus voltage value, so that the direct-current bus voltage can be prevented from being out of control, and the power requirement of the front-stage DC/DC real-time response rear-stage DC/AC is met.
The control method for the two-stage photovoltaic inverter system comprises a power control method for determining a PV current effective instruction value of a front-stage DC/DC circuit. Fig. 6 shows a schematic flow chart of implementation of the power control method in the present embodiment, and fig. 7 shows a schematic logic diagram of implementation of the power control method. In order to more clearly illustrate the implementation principle, implementation process and advantages of the power control method, the power control method is further described below with reference to fig. 6 and 7.
As shown in fig. 6 and 7, the power control method for a two-stage photovoltaic inverter system provided in this embodiment preferably first obtains the actual output voltage V of the front-stage DC/DC circuit in the two-stage photovoltaic inverter system in step S601 dc . Subsequently, the method proceeds to step S602 to obtain the actual output voltage V according to the actual output voltage V obtained in step S601 dc And presetting the limit voltage of the direct current bus
Determining a first upper limit value I of the PV current PV_lmt1 。
In this embodiment, the preset dc bus limit voltage
Preferably at the bus voltage command value
Then the preset voltage threshold (for example, 20V) is increased. Of course, in various embodiments of the present invention, the predetermined dc bus limit voltage is set as described above
The specific value can be configured into different reasonable values according to actual needs, and the invention does not limit the voltage of the preset direct current bus
The specific value of (b) is particularly limited.
Specifically, in the present embodiment, the method preferably calculates the actual output voltage V first in step S602 dc And the preset DC bus limit voltage
The offset voltage of (2). WhereinIf the actual output voltage V is dc Less than the preset DC bus limit voltage
The deviation voltage err generated by the method is zero; whereas if the voltage V is actually output dc Greater than or equal to the preset direct current bus limiting voltage
The deviation voltage err generated by the method is the preset direct current bus limiting voltage
And the actual output voltage V dc The difference of (c).
Namely, there are:
after obtaining the offset voltage err, the method may generate the first upper limit PV current according to the offset voltage err.
Specifically, as shown in fig. 7, in the present embodiment, the method preferably uses a first PI regulator and a first preset limiter to generate a first upper limit value I of the PV current according to the deviation voltage err PV_lmt1 . Wherein, the maximum amplitude limiting current of the first preset amplitude limiter is the maximum allowable current I of the front-stage DC/DC circuit PV_up The minimum limiting current is the minimum allowable current I of the preceding DC/DC circuit PV_lo . Using a first preset limiter to carry out a first upper limit value I on the generated PV current PV_lmt1 The method can effectively avoid the first upper limit value I of the PV current PV_lmt1 Larger than the maximum allowable current I of the preceding DC/DC circuit PV_up And less than the minimum allowable current I PV_lo 。
As shown in FIG. 6, in the present embodiment, the first upper limit value I of the PV current is obtained PV_lmt1 Then, the method preferably proceeds to step S603 according to the first upper limit value I of the PV current PV_lmt1 And a predetermined second upper limit value I of the PV current PV_lmt2 To determine the PV current effective upper limit value I of the preceding DC/DC circuit PV_lmt . Wherein the PV current second upper limit value I PV_lmt2 Preferably, it can be used for generating the reference current I in the prior art like in FIG. 4 ref The upper limit of PV current used.
In the embodiment, the method generates the PV current effective upper limit value I of the front-stage DC/DC circuit PV_lmt Then, it is preferable to set the first upper limit value I for the PV current in step S603 PV_lmt1 And a second upper limit value I of the PV current PV_lmt2 Comparing, and selecting the PV current with smaller value as the effective upper limit value I of the PV current of the preceding-stage DC/DC circuit PV_lmt 。
As shown in FIG. 6, in the present embodiment, the effective upper limit value I of the PV current of the front-stage DC/DC circuit is obtained PV_lmt Then, the method may also base the PV current effective upper limit value I in step S604 PV_lmt According to the actual input voltage V of the booster circuit of the preceding DC/DC circuit PV And a preset reference output voltage
Determining PV current valid command value of preceding stage DC/DC circuit
Specifically, as shown in fig. 7, in the present embodiment, the PV current valid command value is generated
The method preferably first calculates a predetermined reference input voltage of a boost circuit of the preceding stage DC/DC circuit
And the actual input voltage V of the booster circuit PV Then a second PI regulator and a second limiter are used, based on the difference and the PV current effective upper limit value I PV_lmt Generating PV Current valid Command values
The upper limit PV current limit of the second limiter is then also limited by the effective upper limit PV current I PV_lmt Instead of that. Since the specific principle and implementation manner of the process may adopt the prior art as shown in fig. 4, the present invention will not be described in detail in this section.
As can be seen from the above description, the power control method for the two-stage photovoltaic inverter system provided by the invention introduces the output voltage loop into the conventional double-loop control structure, and when the output voltage is higher than the dc bus voltage limit value, the output voltage value is converted into the control quantity related to the command value in the current loop through the PI regulator, that is, the output voltage negative feedback is introduced into the double-loop control structure to stabilize the output voltage at the dc bus voltage limit value, so as to prevent the output voltage from continuously rising and damaging the circuit.
Compared with the prior art, the method does not need the cooperative control of front and rear two-stage controllers, and can effectively realize that the front-stage multipath DC/DC circuit responds to the power requirement of the rear-stage DC/AC in real time, thereby avoiding the adverse effects of generating capacity loss, circuit damage and the like caused by the inconsistency of the front and rear two-stage power adjustment.
The invention also provides a power control method for the two-stage photovoltaic inverter system, which is realized by adopting another mode to determine the effective upper limit value of the PV current of the preceding-stage DC/DC circuit in the method. Fig. 8 outputs a schematic flow chart of the implementation of the method in this embodiment.
As shown in fig. 8, in this embodiment, the method preferably first obtains the actual output voltage V of the previous stage DC/DC circuit in the two-stage photovoltaic inverter system in step S801 dc Then, the method proceeds to step S802 to output the voltage V according to the actual output voltage V dc And the power limiting voltage of the preceding stage DC/DC circuit to determine the adjustment coefficient.
In this embodiment, the power-limiting voltage of the preceding-stage DC/DC circuit preferably includes a power-limiting initial voltage V of the DC/DC circuit dc_bgn And power limit end voltage V dc_end . Wherein, the power limit end voltage V dc_end The value of (A) cannot endanger the working safety of the whole circuit, and a certain margin needs to be reserved.
Specifically, in the present embodiment, the method may preferably determine the above-mentioned adjustment coefficient according to the following expression:
k＝V dc -V dc_bgn +|V dc -V dc_bgn | (2)
wherein k represents an adjustment coefficient, V dc Representing the actual output voltage, V, of the preceding DC/DC circuit dc_bgn Representing a work limited initial voltage.
Based on the expression (2), it can be seen that the actual output voltage V of the current stage DC/DC circuit dc Less than or equal to the power-limited initial voltage V dc_bgn Then, the value of the adjustment coefficient k is zero; while the actual output voltage V of the current stage DC/DC circuit dc Greater than the power-limited initial voltage V dc_bgn The value of the adjustment coefficient k will be positive.
As shown in fig. 8, after obtaining the adjustment coefficient k, the method preferably proceeds to step S803 according to the maximum allowable current I of the previous stage DC/DC circuit based on the adjustment coefficient k PV_up And minimum allowable current I PV_lo To determine the PV current effective upper limit value of the front-stage DC/DC circuit.
Specifically, in the present embodiment, the method may preferably determine the PV current effective upper limit value of the front-stage DC/DC circuit according to the following expression:
wherein, I PV_lmt Represents the effective upper limit value of PV current, I PV_up And I PV_lo Respectively representing the maximum allowable current and the minimum allowable current of the DC/DC circuit, k representing the adjustment coefficient, V dc_bgn And V dc_end Respectively representing a power limit initial voltage and a power limit end voltage.
According to the expression (3), when the value of the adjustment coefficient k is zero, the PV current effective upper limit value I PV_lmt Will equal the maximum allowable current I of the DC/DC circuit PV_up (ii) a When the value of the adjustment coefficient k is gradually increased from zero, the effective upper limit value I of the PV current PV_lmt Maximum allowable current I to be supplied by DC/DC circuit PV_up And gradually decreases.
That is, the actual output voltage V of the current stage DC/DC circuit dc Less than or equal to the power-limited initial voltage V dc_bgn When the adjustment coefficient k is zero, the effective upper limit value I of the PV current is PV_lmt Will equal the maximum allowable current of the DC/DC circuit without affecting the original DC/DC control structure shown in fig. 4; while the actual output voltage V of the DC/DC circuit of the current stage dc Greater than the power-limited initial voltage V dc_bgn When the adjustment coefficient k takes the positive value, the effective upper limit value I of the PV current is obtained PV_lmt Will be less than the maximum allowable current I of the DC/DC circuit PV_up And as the value of the adjustment coefficient k gradually increases, the effective upper limit value I of the PV current PV_lmt Will gradually decrease, which will also have an effect on the upper limit of the limiter in the prior DC/DC control structure shown in fig. 4.
In the present embodiment, the PV current effective upper limit value I is obtained PV_lmt The method then preferably also makes use of the minimum allowable current I of the preceding DC/DC circuit PV_lo For the above PV current effective upper limit value I PV_lmt Limiting to ensure the above PV current effective upper limit value I PV_lmt Greater than or equal to the minimum allowable current I of the preceding DC/DC circuit PV_lo 。
Namely, there are:
of course, in other embodiments of the present invention, the method may also use other reasonable ways to generate the above-mentioned PV current effective upper limit value I according to actual needs PV_lmt 。
It can be seen from the above description that the power control method for the two-stage photovoltaic inverter system provided by the present invention introduces the output voltage loop into the conventional DC/DC dual-loop control structure, and when the output voltage of the previous-stage DC/DC circuit is higher than the DC bus limit voltage or the power-limited initial voltage, the current limit value in the conventional DC/DC dual-loop control structure is replaced, that is, the output voltage negative feedback is introduced into the dual-loop control structure, so that the output voltage is stabilized at the DC bus voltage limit value, and the continuous rise of the output voltage is avoided, and the circuit is prevented from being damaged.
Compared with the prior art, the method does not need the cooperative control of front and rear two-stage controllers, can realize that the front-stage multi-path DC/DC circuit can respond to the power requirement of the rear-stage DC/AC in real time, and avoids the adverse effects of power generation loss, circuit damage and the like caused by the inconsistency of front and rear two-stage power adjustment.
It is to be understood that the disclosed embodiments of the invention are not limited to the particular structures or process steps disclosed herein, but extend to equivalents thereof as would be understood by those skilled in the relevant art. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.
Reference in the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrase "one embodiment" or "an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment.
While the above examples are illustrative of the principles of the present invention in one or more applications, it will be apparent to those of ordinary skill in the art that various changes in form, usage and details of implementation can be made without departing from the principles and concepts of the invention. Accordingly, the invention is defined by the appended claims.
Claims (8)
1. A power control method for a two-stage photovoltaic inverter system, the method comprising:
the method comprises the steps of firstly, acquiring actual output voltage of a front-stage DC/DC circuit in a two-stage photovoltaic inverter system;
determining an adjustment coefficient according to the actual output voltage and the power-limited initial voltage of the preceding-stage DC/DC circuit;
thirdly, determining a PV current effective upper limit value of the preceding-stage DC/DC circuit according to the maximum allowable current and the minimum allowable current of the preceding-stage DC/DC circuit based on the adjusting coefficient;
when the actual output voltage is less than or equal to the power-limited initial voltage of the preceding DC/DC circuit, the adjusting coefficient can enable the PV current effective upper limit value to be kept at the maximum allowable current of the preceding DC/DC circuit;
determining a PV current effective upper limit value of a preceding stage DC/DC circuit according to the following expression:
wherein, I PV_lmt Represents the effective upper limit value of PV current, I PV_up And I PV_lo Respectively representing the maximum allowable current and the minimum allowable current of the DC/DC circuit, k representing the adjustment coefficient, V dc_bgn And V dc_end Respectively representing a power limit initial voltage and a power limit end voltage.
2. The method according to claim 1, wherein in the step two, the adjustment coefficient is determined according to the following expression:
k＝V dc -V dc_bgn +|V dc -V dc_bgn |
wherein k represents an adjustment coefficient, V dc Representing the actual output voltage, V dc_bgn Representing a power limited initial voltage.
3. The method according to any one of claims 1-2, wherein in the third step, the PV current effective upper limit value is further limited by a minimum allowable current of the pre-stage DC/DC circuit to ensure that the PV current effective upper limit value is greater than or equal to the minimum allowable current of the pre-stage DC/DC circuit.
4. A power control method for a two-stage photovoltaic inverter system, the method comprising:
the method comprises the steps of firstly, acquiring actual output voltage of a booster circuit of a front-stage DC/DC circuit in a two-stage photovoltaic inverter system;
determining a first upper limit value of the PV current according to the actual output voltage and a preset direct current bus limiting voltage;
thirdly, determining the PV current effective upper limit value of the front-stage DC/DC circuit according to the PV current first upper limit value and a preset PV current second upper limit value;
determining a PV current effective instruction value of the front-stage DC/DC circuit according to the actual input voltage of the booster circuit and the preset reference input voltage of the booster circuit based on the PV current effective upper limit value;
in the second step, the first step is carried out,
calculating a deviation voltage of the actual output voltage and the preset direct current bus limiting voltage, wherein if the actual output voltage is less than the preset direct current bus limiting voltage, the deviation voltage is zero, and if the actual output voltage is greater than or equal to the preset direct current bus limiting voltage, the deviation voltage is a difference value of the preset direct current bus limiting voltage and the actual output voltage;
and generating the PV current first upper limit value according to the deviation voltage.
5. The method according to claim 4, wherein in step three, the first upper limit value of the PV current and the second upper limit value of the PV current are compared, and the lower value is selected as the effective upper limit value of the PV current.
6. The method as claimed in claim 4, wherein in the second step, the first upper limit value of the PV current is generated according to the offset voltage by using a first PI regulator and a first preset limiter, wherein the maximum limiting current of the first preset limiter is the maximum allowable current of the pre-stage DC/DC circuit.
7. The method according to any one of claims 4 to 6, wherein in the fourth step, a difference between the preset reference input voltage and an actual input voltage of the boost circuit is calculated;
and generating the PV current effective instruction value according to the difference value and the PV current effective upper limit value by using a second PI regulator and a second amplitude limiter.
8. A control method for a two-stage photovoltaic inverter system, characterized in that the control method adopts the method as claimed in any one of claims 1 to 7 for power control.
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