A DC voltage control method for a grid-connected frequency converter

Abstract

The present application provides a DC voltage control method for a grid-connected inverter, which belongs to the technical field of power electronic equipment and specifically includes the following steps: modeling a DC voltage loop control object from a power perspective. During the DC voltage loop control object modeling process, the three-phase power grid is equivalent to an AC motor with an angular frequency of ω = 50*2πrad / s, and the equivalent torque T is obtained. e , equivalent flux vector ψ and equivalent pole pair number n p Based on the active power, the electrical relationship between the active current output by the current loop and the DC voltage loop based on the virtual motor is obtained; the DC voltage loop controller is designed based on the internal model principle. Through the processing solution of this application, the control performance of the DC bus voltage is improved.

Description

Technical Field

[0001] The present application relates to the field of power electronic equipment, and in particular to a method for controlling a DC voltage of a grid-connected frequency converter. Background Art

[0002] One of the control objectives of the grid-connected inverter is to balance the active power of the inverter input and output. The control method for active power balance is the stability of the DC bus voltage. Therefore, the control performance of the DC bus voltage is crucial to the grid-connected inverter.

[0003] Traditional grid-connected inverter DC bus voltage control is based on current and assumes a constant DC bus voltage during design. However, in reality, DC voltage inevitably fluctuates, which leads to a decrease in control performance. Summary of the Invention

[0004] In view of this, the present application provides a DC voltage control method for a grid-connected inverter, which solves the problems in the prior art and improves the control performance of the DC bus voltage.

[0005] The present application provides a method for controlling the DC voltage of a grid-connected inverter using the following technical solutions:

[0006] A DC voltage control method for a grid-connected frequency converter comprises the following steps:

[0007] The DC voltage loop control object is modeled from the power perspective. During the DC voltage loop control object modeling process, the three-phase power grid is equivalent to an AC motor with an angular frequency of ω = 50*2πrad / s, and the equivalent torque T e , equivalent magnetic flux rotation vector ψ and equivalent pole pair number n p ,According to the active power, the electrical relationship between the active current output by the current loop and the DC voltage loop based on the virtual motor is obtained;

[0008] The DC voltage loop controller is designed based on the internal model principle.

[0009] Optional modeling of the DC voltage loop control object from a power perspective includes:

[0010] T e *ω=P g ;

[0011] P g -P loss -P o =P cap ;

[0012] Get the square value of the actual DC bus voltage transient value;

[0013] Among them, T e is the grid-side equivalent torque, P g is the grid-side active power, P loss is the active power loss, P o is the load active power, P cap is the active power consumed by the capacitor, s is the frequency domain complex operator, C dc is the DC bus capacitance, v dc is the instantaneous value of the DC bus voltage.

[0014] Optionally, the DC voltage loop controller is designed based on the internal model principle, including:

[0015] The DC bus voltage theoretical value V dc * And square it to get V dc 2* ;

[0016] According to V dc 2* and V dc 2 The deviation control quantity after the difference indirectly represents the theoretical value of the DC bus voltage V dc * and the DC bus voltage transient value v dc Deviation between

[0017] The deviation control quantity is fed forward by the proportional integral controller and the load active power and loss active power and divided by the virtual motor angular frequency to obtain the grid-side equivalent torque theoretical value T e * ;

[0018] According to the theoretical value of the grid-side equivalent torque T e * The relationship between torque and active current and the current inner loop adjustment are used to obtain the actual value of the grid-side equivalent torque T e , actual value of grid-side equivalent torque T e As the input of the DC voltage loop control object, the DC bus voltage transient value v is output by the DC voltage loop control object. dc The square value of

[0019] Real-time comparison of DC bus voltage theoretical value V dc * and the DC bus voltage transient value v dc , and adjust the DC bus voltage value in real time in closed loop.

[0020] Optionally, the V dc 2* and V dc 2 Compare the DC bus voltage theoretical value V dc* and the DC bus voltage transient value v dc Specifically including: dc 2* and V dc 2 Take the difference and use the proportional integral controller to get the theoretical value of the DC capacitor equivalent torque T cap * .

[0021] Optionally, a proportional-integral controller is selected to achieve zero static error for DC flow.

[0022] Optionally, the grid-side equivalent torque theoretical value T is obtained based on the comparison result. e * include:

[0023] T cap * *ω=P cap * ;

[0024] P cap * +P loss * +P o * =P g * ;

[0025]

[0026] Among them, P cap * is the theoretical value of DC capacitor active power, P loss * is the active power loss feedforward value, P o * is the load power feedforward value, P g * is the theoretical value of grid-side active power, T e * is the theoretical value of the grid-side equivalent torque.

[0027] Optionally, the grid-side equivalent torque theoretical value T e * Get the grid side equivalent torque T e include:

[0028]

[0029] i q *3n p ψ=T e ;

[0030] Among them, np is the equivalent pole pair number of the power grid, ψ is the equivalent magnetic flux rotation vector, τ i is the simplified equivalent time constant of the current inner loop, s is the frequency domain complex operator, i q is the actual value of active current, i q * is the theoretical value of active current.

[0031] Optionally, the proportional coefficient and integral coefficient are selected based on the internal model principle and the voltage loop bandwidth:

[0032]

[0033] Among them, G c (s) is the proportional-integral controller transfer function, k p is the proportionality coefficient, k i is the integral coefficient, ω B is the voltage loop bandwidth (rad / s), k ωb is the coefficient representing the corner frequency of the proportional-integral controller.

[0034] To sum up, the present application includes the following beneficial technical effects: The DC voltage loop design method of the grid-connected inverter based on the virtual motor designed in the present application starts from the essential control target of the DC bus voltage loop, that is, the input and output active power balance perspective, and analyzes the intrinsic relationship between active power and DC bus voltage in detail, and provides a simplified controller parameter design method based on the internal model principle, and the physical interpretation of the control parameters is clear. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0036] Figure 1 This is a schematic diagram of the active power flow of a three-phase two-level grid-connected inverter;

[0037] Figure 2 It is the DC bus voltage control object model based on current angle analysis;

[0038] Figure 3 This is the DC bus voltage control object model based on power analysis in this application;

[0039] Figure 4 This is the control structure diagram of the grid-connected inverter based on the virtual motor in this application;

[0040] Figure 5 This application is filed by Vdc * Get T e * Flowchart of the method;

[0041] Figure 6 This application is submitted by T e * To the final output V dc Flowchart of the process. DETAILED DESCRIPTION

[0042] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0043] The following describes the embodiments of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the features in the following embodiments and embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of this application.

[0044] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on this application, it should be understood by those skilled in the art that an aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects described herein can be used to implement an apparatus and / or practice a method. In addition, other structures and / or functionalities other than one or more of the aspects described herein can be used to implement this apparatus and / or practice this method.

[0045] It should also be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present application. The illustrations only show components related to the present application and are not drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component can be changed at will, and the component layout type may also be more complicated.

[0046] Additionally, in the following description, specific details are provided to provide a thorough understanding of the examples. However, one skilled in the art will appreciate that the aspects described can be practiced without these specific details.

[0047] like Figure 1 As shown, this application takes the three-phase two-level grid-connected inverter topology as the object for modeling analysis, where e a,b,c is the grid phase voltage, Z ea,b,c is the equivalent impedance of the grid-connected line, L a,b,c is the AC side filter inductor, S1~6 are power switch tubes, V dc is the DC bus voltage constant, C dc is the DC bus capacitance, P g is the grid side active power, T e is the grid-side equivalent torque, P loss is the active power loss, P inv is the converter output active power, T inv is the converter output equivalent torque, P o is the load active power, T o is the load equivalent torque, P cap is the active power consumed by the capacitor, T cap is the equivalent torque consumed by the capacitor, i dc is the converter output current, i o is the load, i cap is the capacitor current.

[0048] Figure 1 In the equation, the relationship between DC side power and DC bus voltage is:

[0049]

[0050] Among them, v dc -DC bus voltage transient value, C dc -DC bus capacitor, P g -Grid-side active power, T e -Grid-side equivalent torque, P loss - Active power loss, P o -Load active power, P cap -Capacitor consumes active power, ω-grid vector (equivalent magnetic flux) rotation angular frequency.

[0051] like Figure 2 As shown in the figure, the DC voltage loop of the traditional grid-connected inverter is usually modeled from the current perspective, where V dc is the DC bus voltage constant, v dc is the transient value of DC bus voltage, i d is the d-axis component of the grid-side current after park transformation, e d is the d-axis component of the grid-side voltage after park transformation, and s is the frequency domain complex operator. It can be seen that in the model, when representing active power, there is v dc (Transient value) is constant value Vdc (Constant) Premise assumption.

[0052] An embodiment of the present application provides a method for controlling the DC voltage of a grid-connected inverter.

[0053] A DC voltage control method for a grid-connected frequency converter comprises the following steps:

[0054] The DC voltage loop control object is modeled from the power perspective. During the DC voltage loop control object modeling process, the three-phase power grid is equivalent to an AC motor with an angular frequency of ω = 50*2πrad / s, and the equivalent torque T e , equivalent magnetic flux rotation vector ψ and equivalent pole pair number n p According to the active power, the electrical relationship between the active current output by the current loop and the DC voltage loop based on the virtual motor is obtained; the DC voltage loop controller is designed based on the internal model principle.

[0055] This application starts from the essential control goal of the DC bus voltage loop, that is, the input and output active power balance perspective, and analyzes in detail the intrinsic relationship between active power and DC bus voltage, and provides a simplified controller parameter design method based on the internal model principle, with a clear physical interpretation of the control parameters.

[0056] This application models the DC voltage loop control object from a power perspective, including:

[0057] T e *ω=P g ;

[0058] P g -P loss -P o =P cap ;

[0059] Get the square value of the actual DC bus voltage transient value;

[0060] Among them, T e is the grid-side equivalent torque, P g is the grid-side active power, P loss is the active power loss, P o is the load active power, P cap is the active power consumed by the capacitor, s is the frequency domain complex operator, C dc is the DC bus capacitance, v dc is the instantaneous value of the DC bus voltage.

[0061] From the perspective of power, this application equates the three-phase power grid to an AC motor with an angular frequency of ω = 50*2πrad / s. The voltage balance equation of the three-phase power grid is added together to obtain the voltage space vector equation:

[0062]

[0063] Where, e is the grid voltage space vector, and Ψ is the flux rotation vector.

[0064] When the three-phase grid voltage is balanced, the equivalent flux amplitude is constant, and its space vector rotates at a constant speed. The running trajectory of the top of the flux vector is circular. The flux rotation vector is:

[0065] Ψ=ψe jωt

[0066] Where ψ is the equivalent magnetic flux rotation vector and ω is the equivalent magnetic flux rotation angular frequency.

[0067] From the voltage space vector equation and the flux rotation vector equation, we can get

[0068]

[0069] It can be seen that the phase angle of the phase-locked loop output based on the grid voltage vector orientation in the conventional synchronous rotating coordinate system needs to be subtracted by π / 2 in the loop control described in this application to be converted into the flux linkage orientation.

[0070] The relationship between DC side power and DC bus voltage is converted into the following: Figure 3 Frequency domain model of the voltage loop control object modeled from a power perspective.

[0071] Relationship between grid-side current and grid equivalent torque

[0072] T g =3n p ψi q

[0073] Relationship between grid-side active power and grid-side equivalent torque

[0074] P g =T g ω

[0075] The DC bus voltage differential term (dynamic voltage) in the relationship between DC side power and DC bus voltage can be obtained through a proportional-integral controller. Since the current loop bandwidth and the voltage loop bandwidth are not of the same order of magnitude, the current loop closed-loop model can be equivalent to a first-order inertia link.

[0076]

[0077] Among them, G i (s) is the current closed-loop transfer function, i q (s) Actual value of active current, i q * (s) is the theoretical value of active current, τ iis the simplified equivalent constant of the current loop.

[0078] like Figure 4-Figure 6 As shown in Figure 1, the design of the DC voltage loop controller based on the internal model principle includes:

[0079] The DC bus voltage theoretical value V dc * And square it to get V dc 2* .

[0080] According to V dc 2* and V dc 2 The deviation control quantity after the difference indirectly represents the theoretical value of the DC bus voltage V dc * and the DC bus voltage transient value v dc The deviation between.

[0081] The deviation control quantity is fed through the proportional integral controller and the load active power and loss active power are added to the feedforward and divided by the virtual motor angular frequency to obtain the theoretical value of the grid-side equivalent torque T. e * .

[0082] According to the theoretical value of the grid-side equivalent torque T e * The relationship between torque and active current and the current inner loop adjustment are used to obtain the actual value of the grid-side equivalent torque T e , actual value of grid-side equivalent torque T e As the input of the DC voltage loop control object, the DC bus voltage transient value v is output by the DC voltage loop control object. dc The square value of .

[0083] Real-time comparison of DC bus voltage theoretical value V dc * and the DC bus voltage transient value v dc , and adjust the DC bus voltage value in real time in closed loop, and adjust the V dc 2 Square root output V dc .

[0084] According to V dc 2* and V dc 2 Compare the DC bus voltage theoretical value V dc * and the DC bus voltage transient value v dc Specifically including: dc 2* and V dc 2Take the difference and use the proportional integral controller to get the theoretical value of the DC capacitor equivalent torque T cap * . Select a proportional-integral controller that achieves zero static error for DC flow.

[0085] The grid-side equivalent torque theoretical value T is obtained based on the comparison results. e * include:

[0086] T cap * *ω=P cap * ;

[0087] P cap * +P loss * +P o * =P g * ;

[0088]

[0089] Among them, P cap * is the theoretical value of DC capacitor active power, P loss * is the active power loss feedforward value, P o * is the load power feedforward value, P g * is the theoretical value of grid-side active power, T e * is the theoretical value of the grid-side equivalent torque.

[0090] According to the theoretical value of the grid-side equivalent torque T e * Get the grid side equivalent torque T e include:

[0091]

[0092] i q *3n p ψ=T e ;

[0093] Among them, n p is the equivalent pole pair number of the power grid, ψ is the equivalent magnetic flux rotation vector, τ i is the simplified equivalent time constant of the current inner loop, s is the frequency domain complex operator, i q is the actual value of active current, i q * is the theoretical value of active current.

[0094] The proportional coefficient and integral coefficient are selected based on the internal model principle and the set voltage loop bandwidth:

[0095]

[0096] Among them, G c (s) is the proportional-integral controller transfer function, k p is the proportionality coefficient, k i is the integral coefficient, ω B is the voltage loop bandwidth (rad / s), k ωb is the coefficient representing the corner frequency of the proportional-integral controller.

[0097] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A DC voltage control method for a grid-connected frequency converter, characterized in that: The steps include: The DC voltage loop control object is modeled from the power perspective. During the DC voltage loop control object modeling process, the three-phase power grid is equivalent to an AC motor with an angular frequency of ω = 50*2πrad / s, and the equivalent torque T e , equivalent magnetic flux rotation vector ψ and equivalent pole pair number n p ,According to the active power, the electrical relationship between the active current output by the current loop and the DC voltage loop based on the virtual motor is obtained; Design of DC voltage loop controller based on internal model principle, including: The DC bus voltage theoretical value V dc * Squaring this gives V dc 2* ; According to V dc 2* and V dc 2 The deviation control quantity after the difference indirectly represents the theoretical value of the DC bus voltage V dc * and the DC bus voltage transient value v dc Deviation between The deviation control quantity is fed forward by the proportional integral controller and the load active power and loss active power and divided by the virtual motor angular frequency to obtain the grid-side equivalent torque theoretical value T e * ; According to the theoretical value of the grid-side equivalent torque T e * The relationship between torque and active current and the current inner loop adjustment are used to obtain the actual value of the grid-side equivalent torque T e , actual value of grid-side equivalent torque T e As the input of the DC voltage loop control object, the output of the DC voltage loop control object is the DC bus voltage transient value v dc The square value of Real-time comparison of DC bus voltage theoretical value V dc * and the DC bus voltage transient value v dc , and adjust the DC bus voltage value in real time in closed loop.

2. The DC voltage control method of the grid-connected inverter according to claim 1, characterized in that: Modeling of the DC voltage loop control object from a power perspective includes: T e *ω=P g ; P g -P loss -P o =P cap ; Get the square value of the actual DC bus voltage transient value; Among them, T e is the grid-side equivalent torque, P g is the grid-side active power, P loss is the active power loss, P o is the load active power, P cap is the active power consumed by the capacitor, s is the frequency domain complex operator, C dc is the DC bus capacitance, v dc is the instantaneous value of the DC bus voltage.

3. The DC voltage control method of the grid-connected inverter according to claim 1, characterized in that: According to V dc 2* and V dc 2 Compare the theoretical value of DC bus voltage V dc * and the DC bus voltage transient value v dc Specifically including: dc 2* and V dc 2 Take the difference and use the proportional integral controller to get the theoretical value of the DC capacitor equivalent torque T cap * .

4. The DC voltage control method of the grid-connected inverter according to claim 3, characterized in that: Select a proportional-integral controller that can achieve zero static error for DC flow.

5. The DC voltage control method of the grid-connected inverter according to claim 3, characterized in that: According to the comparison results, the theoretical value of the grid-side equivalent torque T is obtained. e * include: T cap * *ω=P cap * ; P cap * +P loss * +P o * =P g * ; Among them, P cap * is the theoretical value of DC capacitor active power, P loss * is the active power loss feedforward value, P o * is the load power feedforward value, P g * is the theoretical value of grid-side active power, T e * is the theoretical value of the grid-side equivalent torque.

6. The DC voltage control method of the grid-connected inverter according to claim 5, characterized in that: According to the theoretical value of the grid-side equivalent torque T e * Get the grid side equivalent torque T e include: i q *3n p ψ=T e ; Among them, n p is the equivalent pole pair number of the power grid, ψ is the equivalent magnetic flux rotation vector, τ i is the simplified equivalent time constant of the current inner loop, s is the frequency domain complex operator, i q is the actual value of active current, i q * is the theoretical value of active current.

7. The DC voltage control method of the grid-connected inverter according to claim 5, characterized in that: The proportional coefficient and integral coefficient are selected based on the internal model principle and the set voltage loop bandwidth: Among them, G c (s) is the proportional-integral controller transfer function, k p is the proportionality coefficient, k i is the integral coefficient, ω B is the voltage loop bandwidth (rad / s), k ωb is the coefficient representing the corner frequency of the proportional-integral controller.

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