Current loop design method of high-speed double three-phase generator grid-connected control system

Abstract

The invention discloses a current loop design method of a high-speed dual three-phase generator grid-connected control system, and relates to the technical field of converter vector control, and the method comprises the steps: designing an FC-DOF PI regulator; the FC-DOF PI regulator is a feedback compensation type two-degree-of-freedom proportional-integral regulator and is used for controlling a fundamental current loop in vector control of the six-phase converter on the generator side; the two degrees of freedom are a first control degree of freedom enabling the current tracking performance to be optimal and a second control degree of freedom enabling the disturbance suppression performance to be optimal; designing a complex vector PI regulator; the complex vector PI regulator is a complex vector decoupling-based proportional-integral regulator and is used for controlling a current loop in vector control of a three-phase converter at a power grid side; and the complex vector is a rotation vector synthesized by the synchronous rotation shaft system in a complex plane. According to the invention, the purposes of reducing system loss and improving control reliability can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of converter vector control, and in particular to a current loop design method for a high-speed dual three-phase generator grid-connected control system. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] High-speed dual three-phase generators meet the development needs of high-power and miniaturization of grid-connected power generation systems with their advantages of large single-unit capacity and wide speed regulation range. In the grid-connected control system of high-speed dual three-phase generators, the control performance of the current loop is extremely critical. The current loop is usually designed by the zero-pole cancellation method, that is, the regulator zero point and the generator pole are mutually reduced, and the regulator gain is the design bandwidth. Good control performance depends on accurate regulator parameters. Under medium and low speed conditions, the bandwidth is large enough relative to the operating frequency. Even if the parameters are inaccurate, the zero pole can be approximately reduced, which is easy to meet the control requirements.

[0004] Strong coupling is a significant problem under high-speed conditions. As the operating frequency increases, inaccurate regulator parameters lead to a greater proportion of current loop coupling. Since the pulse width modulation (PWM) frequency limits the bandwidth setting range, it causes current transient process oscillation and even overcurrent loss of control. Strong coupling undoubtedly increases system losses and reduces control reliability. Summary of the invention

[0005] The purpose of the present invention is to provide a current loop design method for a high-speed dual three-phase generator grid-connected control system in order to reduce system losses and improve control reliability in view of the strong coupling problem of the current loops on both sides of the generator and the power grid under high-speed conditions in the current high-speed dual three-phase generator grid-connected control system.

[0006] The technical solution of the present invention is as follows:

[0007] A current loop design method for a high-speed dual three-phase generator grid-connected control system, comprising:

[0008] Designing an FC 2-DOF PI regulator; the FC 2-DOF PI regulator is a feedback compensation type dual-degree-of-freedom proportional-integral regulator, used to control the fundamental current loop in the vector control of the six-phase converter on the generator side; the dual degrees of freedom are a first control degree of freedom for optimizing the current tracking performance and a second control degree of freedom for optimizing the disturbance suppression performance;

[0009] A complex vector PI regulator is designed; the complex vector PI regulator is a proportional-integral regulator based on complex vector decoupling, and is used to control the current loop in the vector control of the three-phase converter on the grid side; the complex vector is a rotating vector synthesized by a synchronous rotating shaft system in a complex plane.

[0010] Furthermore, the FC 2-DOF PI regulator comprises:

[0011] A proportional gain term and an integral gain term of the error value of the fundamental component of the stator current relative to its reference current; the proportional gain and the integral gain are both design parameters;

[0012] A feedback decoupling term, a proportional gain term formed by the product of the stator current fundamental component and the generator electrical angular velocity; the proportional gain is an estimated value of the generator's AC and DC axis inductance;

[0013] Feedback compensation term, a proportional gain term composed of the actual value of the fundamental component of the stator current; the proportional gain is the compensation resistance of the FC 2-DOF PI regulator to virtually increase the stator resistance; the compensation resistance is a design parameter, which virtually enlarges the stator resistance, shifts the system pole to the left to the equivalent pole, and improves the system stability; the design bandwidth of the equivalent pole is consistent with the regulator bandwidth.

[0014] Furthermore, reasonable design parameters are selected to convert the zero point of the FC 2-DOF PI regulator into a proportional gain term of the system equivalent pole, so as to achieve mutual reduction of the zero point and the pole; the proportional gain is the bandwidth of the FC 2-DOF PI regulator;

[0015] When the design parameter estimation is inaccurate, that is, the zero point of the FC 2-DOF PI regulator and the system equivalent pole cannot be accurately reduced, the FC 2-DOF PI regulator has a second control degree of freedom that optimizes the disturbance suppression performance and can suppress the coupled oscillation caused by inaccurate parameters.

[0016] Furthermore, the complex vector PI regulator comprises:

[0017] A proportional gain term and an integral gain term of the error value of the AC and DC axis components of the grid-connected current relative to its reference current; the proportional gain and the integral gain are both design parameters;

[0018] The complex vector decoupling term is an integral gain term composed of the product of the error value of the AC and DC axis components of the grid-connected current relative to its reference current and the electrical angular velocity of the grid; the integral gain is a design parameter; the complex vector decoupling term has an integral property, which can reduce its sensitivity to parameters, thereby weakening the coupling oscillation caused by inaccurate parameters.

[0019] Further, reasonable design parameters are selected to convert the complex zeros of the complex vector PI regulator into proportional gain terms of the complex poles on the grid side, so as to achieve mutual reduction of the complex zeros and the complex poles; the proportional gain is the bandwidth of the complex vector PI regulator;

[0020] When the design parameter estimation is inaccurate, that is, the complex zeros of the complex vector PI regulator and the complex poles on the grid side cannot be accurately reduced, the decoupling term of the complex vector PI regulator reduces its sensitivity to the design parameters, thereby weakening the coupled oscillation caused by inaccurate parameters.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] A current loop design method for a high-speed dual three-phase generator grid-connected control system comprises: designing an FC 2-DOF PI regulator; the FC 2-DOF PI regulator is a feedback compensation type dual-degree-of-freedom proportional-integral regulator, which is used to control the fundamental current loop in the vector control of a six-phase converter on the generator side; the dual degrees of freedom are a first control degree of freedom for optimizing current tracking performance and a second control degree of freedom for optimizing disturbance suppression performance; designing a complex vector PI regulator; the complex vector PI regulator is a proportional-integral regulator based on complex vector decoupling, which is used to control the current loop in the vector control of a three-phase converter on the grid side; the complex vector is a rotating vector synthesized by a synchronous rotating shaft system in a complex plane; the present invention effectively solves the strong coupling problem of the high-speed DTP-PMSG grid-connected control system, and has the advantages of reducing system loss and improving control reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a structural block diagram of the generator side vector control according to an embodiment of the present invention;

[0024] Figure 2 This is a block diagram of the fundamental current loop feedback decoupling control structure of the generator side according to an embodiment of the present invention;

[0025] Figure 3 This is a block diagram of the generator side fundamental current loop FC 2-DOF PI control structure according to an embodiment of the present invention;

[0026] Figure 4 This is a structural block diagram of the grid-side vector control according to an embodiment of the present invention;

[0027] Figure 5 This is a block diagram of a grid-side current loop vector model according to an embodiment of the present invention;

[0028] Figure 6 This is a block diagram of the grid-side dq-axis current loop vector PI control structure according to an embodiment of the present invention; DETAILED DESCRIPTION

[0029] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0030] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0031] Embodiment 1

[0032] A current loop design method for a high-speed dual three-phase generator grid-connected control system, comprising:

[0033] Designing an FC 2-DOF PI regulator; the FC 2-DOF PI regulator is a feedback compensation type dual-degree-of-freedom proportional-integral regulator, used to control the fundamental current loop in the vector control of the six-phase converter on the generator side; the dual degrees of freedom are a first control degree of freedom for optimizing the current tracking performance and a second control degree of freedom for optimizing the disturbance suppression performance;

[0034] A complex vector PI regulator is designed; the complex vector PI regulator is a proportional-integral regulator based on complex vector decoupling, and is used to control the current loop in the vector control of the three-phase converter on the grid side; the complex vector is a rotating vector synthesized by a synchronous rotating shaft system in a complex plane.

[0035] In this embodiment, specifically, the FC 2-DOF PI regulator includes:

[0036] A proportional gain term and an integral gain term of the error value of the fundamental component of the stator current relative to its reference current; the proportional gain and the integral gain are both design parameters;

[0037] A feedback decoupling term, a proportional gain term formed by the product of the stator current fundamental component and the generator electrical angular velocity; the proportional gain is an estimated value of the generator's AC and DC axis inductance;

[0038] Feedback compensation term, a proportional gain term composed of the actual value of the fundamental component of the stator current; the proportional gain is the compensation resistance of the FC 2-DOF PI regulator to virtually increase the stator resistance; the compensation resistance is a design parameter, which virtually enlarges the stator resistance, shifts the system pole to the left to the equivalent pole, and improves the system stability; the design bandwidth of the equivalent pole is consistent with the regulator bandwidth.

[0039] In this embodiment, specifically, reasonable design parameters are selected to make the zero point of the FC 2-DOF PI regulator become a proportional gain term of the system equivalent pole, so as to achieve mutual reduction of the zero point and the pole; the proportional gain is the bandwidth of the FC 2-DOF PI regulator;

[0040] When the design parameter estimation is inaccurate, that is, the zero point of the FC 2-DOF PI regulator and the system equivalent pole cannot be accurately reduced, the FC 2-DOF PI regulator has a second control degree of freedom that optimizes the disturbance suppression performance and can suppress the coupled oscillation caused by inaccurate parameters.

[0041] In this embodiment, specifically, the complex vector PI regulator includes:

[0042] A proportional gain term and an integral gain term of the error value of the AC and DC axis components of the grid-connected current relative to its reference current; the proportional gain and the integral gain are both design parameters;

[0043] The complex vector decoupling term is an integral gain term composed of the product of the error value of the AC and DC axis components of the grid-connected current relative to its reference current and the electrical angular velocity of the grid; the integral gain is a design parameter; the complex vector decoupling term has an integral property, which can reduce its sensitivity to parameters, thereby weakening the coupling oscillation caused by inaccurate parameters.

[0044] In this embodiment, specifically, reasonable design parameters are selected to convert the complex zeros of the complex vector PI regulator into proportional gain terms of the complex poles on the grid side, so as to achieve mutual reduction of the complex zeros and the complex poles; the proportional gain is the bandwidth of the complex vector PI regulator;

[0045] When the design parameter estimation is inaccurate, that is, the complex zeros of the complex vector PI regulator and the complex poles on the grid side cannot be accurately reduced, the decoupling term of the complex vector PI regulator reduces its sensitivity to the design parameters, thereby weakening the coupled oscillation caused by inaccurate parameters.

[0046] Embodiment 2

[0047] This embodiment uses a 30° Y-shifted dual three-phase permanent magnet synchronous generator (DTP-PMSG) as the control object and performs current loop design, specifically including:

[0048] Firstly, the mathematical model of the controlled object under the synchronous rotating shaft system is established to determine the vector control structure. Then, the stability and coupling of the current loop are analyzed, and the current loop control structure that meets the decoupling and stability requirements is constructed. Finally, the control parameters that conform to the theory are designed according to the zero-pole cancellation method.

[0049] The control object of the six-phase converter on the generator side is the DTP-PMSG with neutral point isolation. The mathematical model of the DTP-PMSG based on equal amplitude VSD transformation can be described as:

[0050]

[0051] In formula (1), u d 、u q 、u x 、u y and i d 、i q 、i x 、i y are the fundamental wave (dq subspace) and harmonic wave (xy subspace) components of the stator voltage and current respectively; L d , L q , L ls are the dq axis inductance and the self-leakage inductance of each phase winding respectively; R s is the stator resistance; ω e is the rotor electrical angular velocity; ψ f is the permanent magnet flux; n p is the number of rotor pole pairs; J is the rotor inertia; B is the damping coefficient; T m is the mechanical torque; T e is the electromagnetic torque;

[0052] See also Figure 1 The six-phase converter on the generator side adopts the vector control method based on the rotor magnetic field orientation. The outer loop is the speed control, and the inner loop contains four-dimensional current control. d 、i q and i x 、i y Independent closed-loop control is performed to form a fundamental current loop and a harmonic current loop. The speed regulator outputs a reference current The other three current reference values ​​are set to 0. The fundamental current loop contains a cross-coupling term -ω that increases with the increase of speed. e L q i q ,ω e L d i d and the back EMF term -ω e ψ f , decoupling control should be added to improve the transient performance of the current loop.

[0053] See also Figure 2 , the fundamental current loop adopts feedback decoupling control to eliminate cross coupling and ignores the influence of digital control delay, where: is the estimated value of dq axis inductance, is the estimated value of permanent magnet flux; K is the regulator parameter, and its subscript indicates the gain type of the corresponding coordinate axis. After adding feedback decoupling, the coupling term becomes and When the inductance and flux linkage are estimated correctly, regardless of ω e No matter how it changes, the coupling term is always zero, and the open-loop transfer function of the fundamental current loop can be simplified to:

[0054]

[0055] In formula (2), let Among them, ω b1 is the fundamental current loop bandwidth. When the resistance and inductance parameters are estimated accurately, The regulator zero point and the generator pole are mutually reduced, so that the current can be tracked without static error, and the current loop performance remains unchanged in any speed range. However, in practical applications, the generator parameters are difficult to estimate accurately, the coupling term cannot be completely eliminated, the coupling is serious under high-speed conditions, and the transient performance of the current loop is significantly reduced. Therefore, the dynamic stiffness of the current loop transient process must be further enhanced.

[0056] Traditional PI control uses current error as a single control dimension and pursues optimal current tracking performance, but its disturbance suppression performance is not optimal. Figure 3 , a current feedback with proportional gain is added to the output point of the regulator of the fundamental current loop, so that the regulator adds a new control dimension and forms an FC 2-DOF PI control structure. After adopting FC 2-DOFPI control, the equivalent mathematical model of the decoupled DTP-PMSG fundamental subspace can be described as:

[0057]

[0058] In formula (3), K rd , K rq For the compensation resistor.

[0059] From equation (3), we know that the FC 2-DOF PI control method essentially increases the stator resistance by K on the dq axis. rd and K rq (considered as "active resistance"), the system pole is shifted to the left, improving the system stability. This method adds a control dimension that optimizes the disturbance suppression performance and changes the design parameters. After adding the "active resistance", equation (2) becomes:

[0060]

[0061] Let the bandwidth of the system equivalent poles be consistent with the fundamental current loop bandwidth, and then solve the control parameters of the FC2-DOF PI regulator according to the zero-pole cancellation method, that is:

[0062]

[0063] In the synchronous rotating coordinate system, the grid-side mathematical model can be described as:

[0064]

[0065] In formula (6), is the dq-axis component of the grid-side voltage; is the dq axis component of the grid-connected current; e d 、e q is the dq axis component of the grid voltage; R g , L g is the line resistance on the grid side; is the electrical angular velocity of the grid; C is the DC side capacitance; U dc is the DC side voltage; S d , S q It is a switch quantity, which is 1 when it is on and 0 when it is off.

[0066] See also Figure 4 The three-phase converter on the grid side adopts a vector control method oriented by the grid voltage, that is, it satisfies e d =E,e q = 0, where E is the grid voltage vector amplitude. The outer loop is voltage control, and the inner loop is dq axis current control. The voltage regulator outputs the d axis reference current Q-axis reference current Given as 0. For a 50Hz power grid, adding feedback decoupling to the dq axis current loop is sufficient to obtain a better control effect. The current regulator model can be described as:

[0067]

[0068] When the regulator parameter K pg , K ig Or estimate the inductance When there is a deviation, the cross-coupling term still exists, which is affected by the change of generator speed, causing continuous oscillation of the grid-connected current. In order to weaken the influence of the coupling term, a complex vector PI regulator is designed to improve the transient performance of the current loop.

[0069] With the d-axis as the real part and the q-axis as the imaginary part, the dq coordinate system is placed in the complex plane, and the rotating complex vector is synthesized. The complex vectors of the voltage and current on the grid side are expressed as:

[0070]

[0071] In formula (8), j is an imaginary unit.

[0072] Combining equations (6) and (8), the grid-side complex vector model is obtained as follows:

[0073]

[0074] E d Ignored as an external disturbance, the transfer function model of equation (9) can be described as:

[0075]

[0076] The complex vector PI regulator model designed according to the complex zero-pole cancellation method is:

[0077]

[0078] In formula (11), ω b2 is the dq axis current loop bandwidth, are the estimated values ​​of line resistance and inductance on the grid side.

[0079] According to equations (10) and (11), the complex vector model block diagram of the current loop is drawn. Figure 5 When the control parameters are estimated accurately, the complex zeros of the regulator and the complex poles on the grid side completely cancel each other. Since the existence of the imaginary unit j is not conducive to the implementation of the algorithm, substituting equation (8) into equation (11), the scalar form of the complex vector PI regulator model is obtained as follows:

[0080]

[0081] According to equations (6) and (12), the complex vector PI control structure of the dq axis current loop is drawn. Figure 6 . Comparing equation (7) and equation (12), it can be seen that the difference between the feedback decoupling PI regulator and the complex vector PI regulator is that the form of the decoupling term is different. The former is the proportional gain of the current, and the latter is the integral gain of the current error. When the control parameter is inaccurate, the integral gain of the current error suppresses the rate of change of the decoupling term to a certain extent compared with the proportional gain of the current, thereby reducing the sensitivity of the controller to inaccurate parameters. Therefore, the complex vector PI regulator improves the transient performance of the current loop.

[0082] In this embodiment, a dual three-phase permanent magnet synchronous generator (DTP-PMSG) with a Y shift of 30° is used as a control object, and a back-to-back dual PWM converter is used to realize the "AC-DC-AC" power conversion between the generator side and the grid side; through vector space decoupling (VSD) transformation, the six-phase stator current of the generator side is mapped to the fundamental subspace and the harmonic subspace respectively, and a fundamental current loop and a harmonic current loop are respectively formed in the vector control of the six-phase converter. The fundamental current loop contains cross-coupling that increases with the increase of the speed. On the basis of feedback decoupling control, the fundamental current loop of the generator side adopts FC 2-DOF PI control to ensure the system stability when inaccurate regulator parameters cause its incomplete decoupling; through Clark transformation and Park transformation, the three-phase current of the grid side is transformed into a two-phase synchronous rotation (dq) coordinate system, and a dq axis current loop is formed in the vector control of the three-phase converter. In order to suppress the cross-coupling, the dq axis current loop of the grid side adopts complex vector PI control to reduce its sensitivity to the regulator parameters. This method effectively solves the strong coupling problem of the high-speed DTP-PMSG grid-connected control system and has the advantages of reducing system losses and improving control reliability.

[0083] The above-mentioned embodiments only express the specific implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the protection scope of the present application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the technical solution concept of the present application, and these all belong to the protection scope of the present application.

[0084] This background section is provided to generally present the context of the invention, and the work of the presently named inventors, the work to the extent described in this background section, and aspects of this section that did not constitute prior art at the time of application are neither explicitly nor implicitly admitted to be prior art to the present invention.

Claims

1. A design method for the current loop of a high-speed dual-three-phase generator grid-connected control system, characterized in that, it includes: Design an FC 2-DOF PI regulator; the FC 2-DOF PI regulator is a feedback compensation type two-degree-of-freedom proportional-integral regulator, which is used to control the fundamental current loop in the vector control of the six-phase converter on the generator side; the two degrees of freedom are the first control degree of freedom that optimizes the current tracking performance and the second control degree of freedom that optimizes the disturbance rejection performance; Design a complex vector PI regulator; the complex vector PI regulator is a proportional-integral regulator based on complex vector decoupling, which is used to control the current loop in the vector control of the three-phase converter on the grid side; the complex vector is the rotating vector synthesized in the complex plane of the synchronous rotating coordinate system.

2. The design method for the current loop of a high-speed dual-three-phase generator grid-connected control system according to claim 1, characterized in that, the FC 2-DOF PI regulator includes: The proportional gain term and integral gain term of the error value of the fundamental component of the stator current relative to its reference current; both the proportional gain and the integral gain are design parameters; A feedback decoupling term, a proportional gain term composed of the product of the fundamental component of the stator current and the electrical angular velocity of the generator; the proportional gain is an estimated value of the direct-axis and quadrature-axis inductances of the generator; A feedback compensation term, a proportional gain term composed of the actual value of the fundamental component of the stator current; the proportional gain is the compensation resistance that virtually increases the stator resistance by the FC 2-DOF PI regulator; the compensation resistance is a design parameter, which virtually enlarges the stator resistance, shifts the system poles to the equivalent poles, and improves the system stability.

3. The design method for the current loop of a high-speed dual-three-phase generator grid-connected control system according to claim 2, characterized in that, The designed bandwidth of the equivalent poles is consistent with the regulator bandwidth.

4. The design method for the current loop of a high-speed dual-three-phase generator grid-connected control system according to claim 2, characterized in that, Select reasonable design parameters to make the zero point of the FC 2-DOF PI regulator become the proportional gain term of the system equivalent poles, and realize the mutual cancellation of the zero point and the poles; The proportional gain is the bandwidth of the FC 2-DOF PI regulator.

5. The design method for the current loop of a high-speed dual-three-phase generator grid-connected control system according to claim 4, characterized in that, When the design parameters are estimated inaccurately, that is, when the zero point of the FC 2-DOF PI regulator and the system equivalent poles cannot be accurately cancelled, the FC 2-DOF PI regulator has the second control degree of freedom that optimizes the disturbance rejection performance and can suppress the coupled oscillation caused by inaccurate parameters.

6. The design method for the current loop of a high-speed dual-three-phase generator grid-connected control system according to claim 1, characterized in that, the complex vector PI regulator includes: The proportional gain term and integral gain term of the error value of the direct-axis and quadrature-axis components of the grid-connected current relative to their reference currents; both the proportional gain and the integral gain are design parameters; The complex vector decoupling term, an integral gain term formed by the product of the errors of the direct and quadrature axis components of the grid-connected current relative to their reference currents and the grid electrical angular velocity; the integral gain is a design parameter; the complex vector decoupling term has an integral property, which can reduce its sensitivity to parameters, thereby weakening the coupling oscillation caused by inaccurate parameters.

7. The current loop design method of a high-speed dual three-phase generator grid-connected control system according to claim 6, characterized in that a reasonable design parameter is selected to make the complex zero of the complex vector PI regulator become the proportional gain term of the grid-side complex pole, so as to realize the mutual reduction of the complex zero and the complex pole; the proportional gain is the bandwidth of the complex vector PI regulator.

8. The current loop design method of a high-speed dual three-phase generator grid-connected control system according to claim 6, characterized in that when the design parameter is estimated inaccurately, that is, the complex zero of the complex vector PI regulator and the grid-side complex pole cannot be accurately reduced, the decoupling term of the complex vector PI regulator reduces its sensitivity to the design parameter, thereby weakening the coupling oscillation caused by inaccurate parameters.

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