A method for decoupling control of a DPP structured photovoltaic system power converter

Abstract

The application discloses a power converter control decoupling method of a differential power processing (DPP) structure photovoltaic system, and belongs to the technical field of solar photovoltaic power generation. The application introduces a double closed-loop control structure to simplify the coupling of the DPP structure photovoltaic system. Based on the control structure, the complex coupling between DPP converter controls can be decomposed into two parts with smaller coupling effect and simpler coupling form. According to the coupling strength and decoupling difficulty of the control objects obtained by the decomposition, a V specification decoupling mode is used to completely decouple the outer loop control object playing a leading role in the system coupling. According to the characteristics of the double closed-loop control structure, an easily implemented partial decoupling scheme is designed. The method is suitable for the decoupling between DPP converter controls of any scale DPP structure photovoltaic system. The method enables the synchronous maximum power point (MPPT) control of the DPP structure photovoltaic system, greatly improves the MPPT efficiency of the DPP structure photovoltaic system, and has simple algorithm implementation, remarkable decoupling effect and strong scalability.

Description

TECHNICAL FIELD

[0001] The application discloses a DPP structure photovoltaic system power converter control decoupling method and belongs to the technical field of solar photovoltaic power generation. BACKGROUND

[0002] As a renewable clean energy with great development and application prospect, solar energy has been widely used in many fields. However, the harsh working conditions make the photovoltaic power generation system need to apply the maximum power point tracking (MPPT) technology to realize the maximization of solar energy utilization. In the current popular distributed maximum power point tracking technology, the differential power processing (DPP) structure is considered to be a high-potential high-granularity MPPT topology structure due to the advantages of effectively weakening mismatch, processing less power and high energy efficiency. However, as a typical multi-input multi-output (MIMO) system, there is a serious coupling problem in the power converter control of the DPP structure photovoltaic system, and the complex coupling between the DPP converter controls brings challenges to the MPPT control of the whole system. Meanwhile, with the continuous expansion of the system scale, the coupling form becomes more complex, so that the popularization and application of the DPP structure photovoltaic system are limited, therefore, the decoupling of the coupling between the power converter controls in the DPP structure photovoltaic system helps to get rid of this predicament.

[0003] In recent years, scholars at home and abroad have made a lot of researches on the decoupling problem of the power converter control of the MIMO system, in which, the accurate system model is a prerequisite for realizing the decoupling of the power converter control, and many decoupling technologies of the MIMO system have been proposed in the academic circle, but most of the research methods only analyze the systems with few coupling channels and simple coupling forms in detail, and few studies are made on the systems with many coupling channels and complex coupling forms, mainly including feedforward decoupling method, feedback decoupling method, compensator decoupling method, multi-stage time-sharing decoupling method and other decoupling methods.

[0004] The above-mentioned decoupling methods have their own applicability and limitations, and each method has its own advantages and disadvantages. The feedforward decoupling method is to add a feedforward link in the control loop to offset the coupling elements in the coupling channel without affecting the main control channel. This method requires an accurate system model and is complex to design. The feedback decoupling method is to weaken the coupling effect by redesigning the feedback loop. This method also requires an accurate system model and is suitable for systems with a small number of coupling channels. The compensator decoupling method is to design a compensator with decoupling function according to the coupling form of the system control object. This method is only suitable for systems with simple coupling form. The multi-stage time-sharing decoupling method is to realize decoupling by step-by-step control of the DPP converter in the photovoltaic system, that is, MPPT control of the next photovoltaic component is only performed after the previous photovoltaic component realizes MPPT. Obviously, this method requires a long MPPT process and is not suitable for large-scale photovoltaic systems. SUMMARY

[0005] The present application aims to solve the technical problems of the prior art, and provides a DPP structure photovoltaic system power converter control decoupling method which is simple to implement, has good universality and strong portability. The method can realize decoupling between power converter controls in a DPP structure photovoltaic system without relying on characteristic parameters and accurate mathematical models of the photovoltaic system, and solves the technical problems of traditional decoupling methods such as feedforward decoupling, negative feedback decoupling, compensator decoupling, and multi-stage time-sharing decoupling, which rely on control object parameters, are complex to design, and are not suitable for large-scale systems.

[0006] To achieve the above technical purposes, the technical solutions adopted by the present application are as follows:

[0007] A DPP structure photovoltaic system power converter control decoupling method is provided, which is suitable for any scale of DPP structure photovoltaic system. A double-loop control structure is adopted. A control unit runs a synchronous MPPT control algorithm according to the collected output voltage and current of each photovoltaic component, outputs MPPT voltage reference signals of all components, and performs operations on all MPPT voltage reference signals and measured voltages of the corresponding components. After processing by an outer loop compensator of the corresponding converter, inductance current reference signals are obtained, which are the same as the number of converters. The inductance current reference signals are processed by a decoupling device to obtain new inductance current reference signals. The new inductance current reference signals are operated with the measured inductance current of the corresponding converter, and after processing by an inner loop compensator of the corresponding converter, duty cycle signals are obtained, which are the same as the number of converters. Finally, decoupling control of the power converter of the DPP structure photovoltaic system is realized.

[0008] The DPP structure photovoltaic system power converter control decoupling method does not rely on the characteristic parameters of the DPP structure photovoltaic system and is not limited by the scale of the system.

[0009] MPPT control of all components in the photovoltaic system is performed simultaneously.

[0010] The power converter control object of the DPP structure photovoltaic system is decomposed into two parts: an outer loop control object and an inner loop control object through a dual closed-loop control structure.

[0011] The evaluation index of system coupling level is represented by the relative gain array number (RGA-number).

[0012] The output variable of the outer loop control object is a voltage vector composed of the MPPT reference voltages of each photovoltaic module, while the output variable of the inner loop control object is a current vector composed of the inductor currents of each DPP converter and the centralized converter.

[0013] The V-specification decoupling structure is applied to completely decouple the outer-loop control object.

[0014] A partial decoupling scheme is adopted, in which the outer loop control object is completely decoupled, while the inner loop control object is partially decoupled by suppressing coupling through a closed-loop circuit.

[0015] The decoupling device is placed after the outer loop compensator and before the inner loop.

[0016] Beneficial effects:

[0017] The present invention adopts the above technical solution and has the following technical effects: The present invention does not require an accurate system model for the decoupling of the power converter control of the DPP structure photovoltaic system. It simplifies the coupling form in the DPP structure photovoltaic system through a dual closed-loop control structure and completely decouples the dominant part of the system coupling relationship through the V-specification decoupling form. The method is simple to implement and is not affected by the photovoltaic system parameters. It has good decoupling performance and strong versatility. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a dual closed-loop control structure;

[0019] Figure 2 It is a waveform diagram showing the coupling between the outer loop and the inner loop controlled objects of the system.

[0020] Figure 3 This is a schematic diagram of the V-specification decoupling structure.

[0021] Figure 4 This is a schematic diagram of the physical implementation scheme for decoupling;

[0022] Figure 5 This is the coupling horizontal waveform diagram of the decoupled system;

[0023] Figure 6This is a waveform diagram of the power converter control before and after system decoupling. Detailed Implementation

[0024] An embodiment of the present invention will be further described below with reference to the accompanying drawings:

[0025] This invention decomposes the coupling between power converters in a DPP structure photovoltaic system into two parts through a dual closed-loop control structure, and selectively decouples the coupling objects that play a dominant role in the system coupling. This partial decoupling method takes into account both decoupling performance and the difficulty of decoupling implementation, and has strong versatility and portability.

[0026] Figure 1 This is a schematic diagram of a dual-loop control structure. Using a dual-loop control structure, the control object of the power converter in a DPP photovoltaic system can be decomposed into an inner-loop control object and an outer-loop control object. Here, V*(s) represents the MPPT voltage vector composed of the voltage reference signals of each component obtained by the control unit after MPPT calculation, and V(s) represents the voltage vector composed of the actual measured voltage signals of each component. The difference between the reference voltage vector and the measured voltage vector is compensated by the outer-loop compensator G. c1 (s) After processing, the current vector I is obtained, which is composed of the reference signals of the inductor currents of each power converter. L *(s), reference current vector and measured inductor current vector I L The difference between (s) and the inner loop compensator G c2 After processing, the control signal vector D(s) and G are obtained, which are composed of the duty cycles of each power converter. id (s) and G vi (s) represent the intrinsic models of the inner and outer loop control objects in the power converter control of a DPP structure photovoltaic system, respectively.

[0027] Figure 2 This is a waveform diagram showing the coupling level between the inner and outer loop controlled objects of the system. The coupling level is represented by the RGA number, and its expression is:

[0028]

[0029] In the formula: Λ represents the relative gain matrix, G(s) represents the transfer function matrix of the controlled object, I represents the identity matrix of the same order as Λ, and λ ij This represents the element at the corresponding position in Λ. The decomposition of the inner-loop control object and the outer-loop control object simplifies the coupling form of the system. Compared with the complex and slightly ineffective coupling of the inner-loop control object, the coupling effect of the outer-loop control object is obvious and its form is simpler.

[0030] For power converter control in a DPP (Dynamic Power Adapter) photovoltaic system, both the inner and outer loop control objects clearly conform to the definition of a P-specification control object (where each output variable of the control object is affected by all input variables). Complete decoupling of the P-specification control object can be easily achieved using a V-specification decoupling structure. The transfer function form of V-specification decoupling is...

[0031]

[0032] The schematic diagram of the proposed V-canonical decoupling structure is as follows: Figure 3 As shown.

[0033] Considering the difficulty of complete decoupling and the changes in system coupling form under a dual-loop control structure, a partial decoupling scheme is proposed, using a V-canonical decoupling structure to completely decouple the outer-loop control object that plays a dominant role in system coupling. Combining this with the small-signal model of the DPP structure photovoltaic system, the V-canonical decoupling matrix for complete decoupling of the outer-loop control object can be obtained as follows:

[0034]

[0035] In the formula: D is the duty cycle of the power converter. Since the voltages of different photovoltaic modules under MPPT states are very close, D can usually be considered to be 0.5. Obviously, the obtained V-gauge decoupling matrix is ​​consistent with the characteristic parameters of the photovoltaic system.

[0036] Due to limitations in the placement of the decoupling device in the physical implementation, and considering the characteristics of the dual-loop control structure and the practical need for the decoupling method to be easily integrated into the control loop, a compromise implementation scheme is proposed, placing it after the voltage outer loop compensator and before the current inner loop closed-loop circuit. The physical implementation scheme is as follows: Figure 4 As shown.

[0037] Figure 5 The figure shows the coupling level waveform of the system after decoupling. It is clear that the RGA number of the entire system is very small in the entire frequency domain, which means that the above decoupling scheme can effectively suppress the coupling of the system.

[0038] Figure 6 The diagram shows the power converter control waveforms before and after system decoupling. When no decoupling method is applied to the DPP structure photovoltaic system, there is relatively complex coupling between its power converter controls. When a partial decoupling method is applied to the DPP structure photovoltaic system, the coupling between the system's power converter controls under different conditions can be effectively suppressed. This makes the control of the power converters in the DPP structure photovoltaic system independent of each other, enabling simultaneous operation of all component MPPT control.

Claims

1. A method for decoupling the control of a DPP structured photovoltaic system power converter, the method comprising: The application is suitable for DPP structure photovoltaic system of any scale, adopts double closed loop control structure, and the control unit runs synchronous MPPT control algorithm according to the collected output voltage and current of each photovoltaic component, outputs MPPT voltage reference signal of all components, and the difference value operation is carried out between all MPPT voltage reference signals and the measured voltage of corresponding components, the inductance current reference signal same as the number of converters is obtained through the outer loop compensator of corresponding converter, the new inductance current reference signal is obtained through the decoupling algorithm based on V specification decoupling structure, the difference value operation is carried out between the new inductance current reference signal and the measured inductance current of corresponding converter, the duty cycle signal same as the number of converters is obtained through the inner loop compensator of corresponding converter, and finally the decoupling control of the power converter of DPP structure photovoltaic system is realized. ​ 2. The method of claim 1, wherein the DPP structured photovoltaic system power converter control decoupling method is characterized by, The decoupling method is not dependent on the characteristic parameters of DPP structure photovoltaic system and is not limited by the system scale.

3. The method of claim 1, wherein the DPP structured photovoltaic system power converter control decoupling method is characterized by, The MPPT control of all components in the photovoltaic system is carried out at the same time.

4. The method of claim 1, wherein the DPP structured photovoltaic system power converter control decoupling method is characterized by, The power converter control object of DPP structure photovoltaic system is divided into two parts of outer loop control object and inner loop control object through the double closed loop control structure.

5. The method of claim 1, wherein the DPP structured photovoltaic system power converter control decoupling method is characterized by, The evaluation index of system coupling level is expressed by the number of relative gain matrix.

6. The method of claim 1, wherein the DPP structured photovoltaic system power converter control decoupling method is characterized by, The output variable of the outer loop control object is the voltage vector composed of the MPPT reference voltage of each photovoltaic component, and the output variable of the inner loop control object is the current vector composed of the inductance current of each DPP converter and centralized converter.

7. The method of claim 1, wherein the DPP structured photovoltaic system power converter control decoupling method is characterized by, The V specification decoupling structure is applied to completely decouple the outer loop control object.

8. The DPP structure photovoltaic system power converter control decoupling method according to claim 1 adopts the outer loop control object completely decoupling, and the inner loop control object is partially decoupled by the closed loop circuit to inhibit coupling.

9. The DPP structure photovoltaic system power converter control decoupling method according to claim 1, and the decoupling device is placed after the outer loop compensator and before the inner loop closed loop circuit.

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