Speed ​​stability analysis method for low-carrier-ratio current source motor drive system

Abstract

The present invention discloses a method for analyzing the speed stability of a low-carrier-ratio current source motor drive system. The method first constructs a discrete-time small-signal model comprising a current source converter, a motor controlled object, and a stator current controller. Based on the discrete-time small-signal model, the eigenvalue trajectory of the speed loop open-loop transfer function is obtained. The stability range of the speed controller parameters is then analyzed based on the eigenvalue trajectory. This technical solution can reflect the multi-input, multi-output, and discrete characteristics of a low-carrier-ratio pulse-width modulation current source converter motor drive system based on a digital controller, providing a theoretical basis for analyzing the stability of the speed controller of the low-carrier-ratio current source converter motor drive system. Furthermore, the method improves the system's dynamic response performance based on control requirements, making the current source converter motor drive system suitable for high-performance applications.

Description

Technical Field

[0001] The present invention belongs to the field of power electronics and electric transmission, and in particular relates to a speed stability analysis method and system for a low-carrier-ratio current source converter motor drive system based on a discrete small signal model. Background Art

[0002] Pulse-width modulation current source converters have been widely used in medium-voltage, high-power, adjustable-speed power transmission systems. They have advantages such as simple topology, inherent DC short-circuit protection, sinusoidal output current and voltage waveforms, and load-friendly operation. Therefore, they are also suitable for industrial applications such as wind power generation and high-voltage DC transmission.

[0003] In medium-voltage, high-power, adjustable-speed electric drive systems, the carrier ratio (the ratio of the switching frequency to the fundamental frequency) is typically low due to limitations on the switching frequency of power devices. Under these conditions, current-source converter motor drive systems suffer from significant digital control delays caused by the low sampling frequency of the digital controller and the low switching frequency of the pulse-width modulation converter. Furthermore, severe cross-coupling between the d-axis and q-axis variables in a synchronously rotating coordinate system can reduce system stability.

[0004] However, existing research on the stability of pulse-width modulated current source converter motor drive systems primarily focuses on the inner current loop. Analysis of this loop often assumes decoupling from the outer speed loop, assuming speed stability without considering the speed loop's impact on system stability. Furthermore, existing research often derives analytical models in the continuous-time domain, disregarding the discrete characteristics of digital controllers and pulse-width modulated converters. Furthermore, to simplify analysis, coupling between synchronously rotating coordinate axes is often neglected. The resulting single-input, single-output system models are inaccurate and fail to capture the multi-input, multi-output characteristics of current source converter motor drive systems, nor the impact of coupling between state variables. Summary of the Invention

[0005] The purpose of the present invention is to provide a speed stability analysis method for a low-carrier ratio current source type motor drive system, which can reflect the multi-input and multi-output characteristics and discrete characteristics of a low-carrier ratio pulse width modulation current source type converter motor drive system based on a digital controller, provide a theoretical basis for the stability analysis of the speed controller of the low-carrier ratio current source type converter motor drive system, and improve the dynamic response performance of the system according to the control requirements, so that the current source type converter motor drive system is suitable for high-performance applications.

[0006] In order to achieve the above object, the solution of the present invention is:

[0007] A method for analyzing the speed stability of a low-carrier-ratio current source motor drive system comprises the following steps:

[0008] Step 1: construct a discrete-time small-signal model including a current source converter, a motor controlled object, and a stator current controller;

[0009] Step 2: obtaining an eigenvalue trajectory of a speed loop open-loop transfer function based on the discrete-time small-signal model including the current source converter, the motor controlled object, and the stator current controller;

[0010] Step three: analyzing the stability range of the speed controller parameters based on the eigenvalue trajectory.

[0011] The specific content of the above step one is:

[0012] Step A, constructing a continuous-time state-space model reflecting the relationship between state variables and input variables of a current source converter permanent magnet synchronous motor drive system;

[0013] Step B: linearizing the continuous-time state-space model of step A to obtain a continuous-time small-signal model of the current source converter permanent magnet synchronous motor drive system at the operating point;

[0014] Step C, discretizing the continuous-time small signal model of step B to obtain a discrete-time small signal model of the current source converter permanent magnet synchronous motor drive system at the operating point, wherein the discrete-time small signal model includes the motor controlled object;

[0015] Step D, based on the discrete-time small-signal model of step C, adding the converter current as a state variable to obtain a discrete-time small-signal extended model including a current source converter and a motor controlled object;

[0016] Step E, based on the discrete-time small-signal expansion model including the current source converter and the motor controlled object in step D, and according to the relationship between the various state variables in the stator current controller, obtains a discrete-time small-signal expansion model including the current source converter, the motor controlled object, and the stator current controller.

[0017] The specific content of the above step 2 is:

[0018] Step a, based on the discrete-time small signal model including the current source converter, the motor controlled object, and the stator current controller, obtaining a speed loop control block diagram of the current source converter permanent magnet synchronous motor drive system including the speed controller at the operating point;

[0019] Step b, obtaining a small signal open-loop transfer function of the speed loop according to the speed loop control block diagram;

[0020] Step c: obtaining the characteristic value trajectory of the speed loop according to the small signal open-loop transfer function of the speed loop.

[0021] The specific content of the above step three is:

[0022] Step i, drawing a corresponding eigenvalue trajectory block diagram according to the eigenvalue trajectory of the speed loop open-loop transfer function;

[0023] Step ii, analyze when the time constant reaches a certain value τ w0 When at least one characteristic root has a tendency to move outside the unit circle, the corresponding proportional gain is k wp0 , then it is considered that when the time constant τ w0 When the proportional gain range that makes the system stable is less than k wp0 .

[0024] A low-carrier-ratio current source type motor drive system speed stability analysis system, comprising:

[0025] A discrete-time small-signal model building module is configured to build a discrete-time small-signal model including a current source converter, a motor controlled object, and a stator current controller;

[0026] an eigenvalue trajectory acquisition module configured to obtain an eigenvalue trajectory of a speed loop open-loop transfer function based on the discrete-time small signal model; and

[0027] The stability analysis module is configured to analyze the stability range of the speed controller parameters according to the characteristic value trajectory.

[0028] The above discrete time small signal model building module includes,

[0029] a continuous-time state-space model building module configured to build a continuous-time state-space model reflecting the relationship between state variables and input variables of a current source converter permanent magnet synchronous motor drive system;

[0030] a continuous-time small-signal model acquisition module configured to linearize the continuous-time state-space model to obtain a continuous-time small-signal model of the current source converter permanent magnet synchronous motor drive system at an operating point;

[0031] a discrete-time small-signal model acquisition module configured to discretize the continuous-time small-signal model to obtain a discrete-time small-signal model of the current source converter permanent magnet synchronous motor drive system at an operating point, wherein the discrete-time small-signal model includes a motor controlled object;

[0032] A first discrete-time small-signal extended model acquisition module is configured to add the converter current as a state variable based on the discrete-time small-signal model to obtain a discrete-time small-signal extended model including a current source converter and a motor controlled object; and

[0033] The second discrete-time small signal extension model acquisition module is configured to obtain a discrete-time small signal extension model including a current source converter, a motor controlled object, and a stator current controller based on the discrete-time small signal extension model including the current source converter and the motor controlled object and according to the relationship between the various state variables in the stator current controller.

[0034] The above-mentioned eigenvalue trajectory acquisition module includes:

[0035] a speed loop control block diagram acquisition module configured to obtain a speed loop control block diagram of the current source converter permanent magnet synchronous motor drive system including the speed controller at an operating point based on the discrete time small signal model including the current source converter, the motor controlled object, and the stator current controller;

[0036] an open-loop transfer function acquisition module configured to obtain a small-signal open-loop transfer function of the speed loop according to the speed loop control block diagram; and

[0037] The characteristic value trajectory acquisition module is configured to obtain the characteristic value trajectory of the speed loop according to the small signal open-loop transfer function of the speed loop.

[0038] The above stability analysis module includes,

[0039] an eigenvalue trajectory block diagram drawing module, configured to draw a corresponding eigenvalue trajectory block diagram according to the eigenvalue trajectory of the speed loop open-loop transfer function; and

[0040] The proportional gain range analysis module is configured to analyze the proportional gain when the time constant reaches a certain value τ w0 When at least one characteristic root has a tendency to move outside the unit circle, the corresponding proportional gain is k wp0 , then it is considered that when the time constant τ w0 When the proportional gain range that makes the system stable is less than k wp0 .

[0041] After adopting the above scheme, compared with the existing technology, the present invention derives and establishes a discrete-time small-signal model that takes into account speed variables, which can reflect the multi-input and multi-output characteristics and discrete characteristics of the low-carrier-ratio pulse-width modulation current source converter motor drive system based on a digital controller. Based on the discrete-time small-signal model, the characteristic value trajectory of the system speed loop open-loop transfer function is obtained, which can provide a theoretical basis for the stability analysis of the speed controller of the low-carrier-ratio current source converter motor drive system. In addition, the discrete-time state-space equation model established by the technical solution of the present invention can provide a theoretical analysis model for the subsequent optimization design of the speed controller parameters, and can improve the dynamic response performance of the system according to the control requirements, making the current source converter motor drive system suitable for high-performance applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is the overall circuit and control diagram of the current source converter motor drive system;

[0043] Figure 2 It is a block diagram of the discrete time model of the extended controlled object including the converter current;

[0044] Figure 3 is the block diagram of the discrete-time model including the current controller;

[0045] Figure 4 This is a block diagram of the speed loop control including the speed controller;

[0046] Figure 5 This is the block diagram of the trajectory of the eigenvalue of the small signal open-loop transfer function of the speed loop;

[0047] Figure 6 This is the simulation result diagram of the stable operation of the current source converter motor drive system;

[0048] Figure 7 This is the simulation result diagram of unstable operation of current source converter motor drive system. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0050] In view of the fact that the analytical models established in existing research are not accurate enough and cannot reflect the multi-input and multi-output characteristics and system discrete characteristics of the low-carrier-ratio pulse-width modulation current source converter motor drive system based on a digital controller, and the deficiency that the speed stability is not taken into account in the existing stability analysis, the present invention aims to provide a discrete-time small-signal model that takes into account the speed variable, which can reflect the multi-input and multi-output characteristics and discrete characteristics of the current source converter motor drive system. The characteristic value trajectory of the speed loop open-loop transfer function is obtained based on the system discrete-time small-signal model, which can provide a theoretical basis for the stability analysis of the speed controller of the low-carrier-ratio current source converter motor drive system. The established discrete-time state-space equation model can provide a theoretical analysis model for the subsequent optimized speed controller parameter design, improve the dynamic response performance of the system according to the control requirements on the basis of ensuring the stability of the system, and make the current source converter motor drive system suitable for high-performance applications.

[0051] The present invention provides a method for analyzing the speed stability of a low-carrier-to-current-source motor drive system, comprising the following steps:

[0052] Step 1: construct a discrete-time small-signal model including a current source converter, a motor controlled object, and a stator current controller;

[0053] The specific content of step one is:

[0054] Step A, constructing a continuous-time state-space model reflecting the relationship between state variables and input variables of a current source converter permanent magnet synchronous motor drive system;

[0055] Step B: linearizing the continuous-time state-space model of step A to obtain a continuous-time small-signal model of the current source converter permanent magnet synchronous motor drive system at the operating point;

[0056] Step C, discretizing the continuous-time small signal model of step B to obtain a discrete-time small signal model of the current source converter permanent magnet synchronous motor drive system at the operating point, wherein the discrete-time small signal model includes the motor controlled object;

[0057] Step D, based on the discrete-time small-signal model of step C, adding the converter current as a state variable to obtain a discrete-time small-signal extended model including a current source converter and a motor controlled object;

[0058] Step E, based on the discrete-time small-signal expansion model including the current source converter and the motor controlled object in step D, and according to the relationship between the various state variables in the stator current controller, obtains a discrete-time small-signal expansion model including the current source converter, the motor controlled object, and the stator current controller.

[0059] Step 2: obtaining an eigenvalue trajectory of a speed loop open-loop transfer function based on the discrete-time small-signal model including the current source converter, the motor controlled object, and the stator current controller;

[0060] The specific content of the step 2 is:

[0061] Step a, based on the discrete-time small signal model including the current source converter, the motor controlled object, and the stator current controller, obtaining a speed loop control block diagram of the current source converter permanent magnet synchronous motor drive system including the speed controller at the operating point;

[0062] Step b, obtaining a small signal open-loop transfer function of the speed loop according to the speed loop control block diagram;

[0063] Step c: obtaining the characteristic value trajectory of the speed loop according to the small signal open-loop transfer function of the speed loop.

[0064] Step 3: analyzing the stability range of the speed controller parameters according to the characteristic value trajectory;

[0065] The specific content of step three is:

[0066] Step i, drawing a corresponding eigenvalue trajectory block diagram according to the eigenvalue trajectory of the speed loop open-loop transfer function;

[0067] Step ii, analyze when the time constant reaches a certain value τ w0 When at least one characteristic root has a tendency to move outside the unit circle, the corresponding proportional gain is k wp0 , then it is considered that when the time constant τ w0 When the proportional gain range that makes the system stable is less than k wp0 .

[0068] The present invention also provides a low-carrier ratio current source type motor drive system speed stability analysis system, comprising:

[0069] A discrete-time small-signal model building module is configured to build a discrete-time small-signal model including a current source converter, a motor controlled object, and a stator current controller;

[0070] an eigenvalue trajectory acquisition module configured to obtain an eigenvalue trajectory of a speed loop open-loop transfer function based on the discrete-time small signal model; and

[0071] The stability analysis module is configured to analyze the stability range of the speed controller parameters according to the characteristic value trajectory.

[0072] Wherein, the discrete time small signal model building module includes:

[0073] a continuous-time state-space model building module configured to build a continuous-time state-space model reflecting the relationship between state variables and input variables of a current source converter permanent magnet synchronous motor drive system;

[0074] a continuous-time small-signal model acquisition module configured to linearize the continuous-time state-space model to obtain a continuous-time small-signal model of the current source converter permanent magnet synchronous motor drive system at an operating point;

[0075] a discrete-time small-signal model acquisition module configured to discretize the continuous-time small-signal model to obtain a discrete-time small-signal model of the current source converter permanent magnet synchronous motor drive system at an operating point, wherein the discrete-time small-signal model includes a motor controlled object;

[0076] A first discrete-time small-signal extended model acquisition module is configured to add the converter current as a state variable based on the discrete-time small-signal model to obtain a discrete-time small-signal extended model including a current source converter and a motor controlled object; and

[0077] The second discrete-time small signal extension model acquisition module is configured to obtain a discrete-time small signal extension model including a current source converter, a motor controlled object, and a stator current controller based on the discrete-time small signal extension model including the current source converter and the motor controlled object and according to the relationship between the various state variables in the stator current controller.

[0078] Wherein, the eigenvalue trajectory acquisition module includes:

[0079] a speed loop control block diagram acquisition module configured to obtain a speed loop control block diagram of the current source converter permanent magnet synchronous motor drive system including the speed controller at an operating point based on the discrete time small signal model including the current source converter, the motor controlled object, and the stator current controller;

[0080] an open-loop transfer function acquisition module configured to obtain a small-signal open-loop transfer function of the speed loop according to the speed loop control block diagram; and

[0081] The characteristic value trajectory acquisition module is configured to obtain the characteristic value trajectory of the speed loop according to the small signal open-loop transfer function of the speed loop.

[0082] Wherein, the stability analysis module includes:

[0083] an eigenvalue trajectory block diagram drawing module, configured to draw a corresponding eigenvalue trajectory block diagram according to the eigenvalue trajectory of the speed loop open-loop transfer function; and

[0084] The proportional gain range analysis module is configured to analyze the proportional gain when the time constant reaches a certain value τ w0 When at least one characteristic root has a tendency to move outside the unit circle, the corresponding proportional gain is k wp0 , then it is considered that when the time constant τ w0 When the proportional gain range that makes the system stable is less than k wp0 .

[0085] The technical solution of the present invention will be described in detail below through a specific embodiment. Figure 1 For the current source converter permanent magnet synchronous motor drive system shown in the figure, a low carrier ratio system speed stability analysis method based on a discrete small signal model is proposed, which includes the following two parts:

[0086] (S1) A discrete-time small-signal model including a current source converter, a motor controlled object, and a stator current controller is derived and established;

[0087] (S2) The characteristic value trajectory of the speed loop open-loop transfer function is obtained according to the discrete-time small signal model of the system, and the stability range of the speed controller parameters can be analyzed and determined.

[0088] The detailed instructions are as follows:

[0089] The derivation and establishment of the discrete time small signal model of the current source converter, the motor controlled object, and the stator current controller in (S1) specifically includes the following steps:

[0090] (S1.1) The continuous-time nonlinear state-space equation model of the system is obtained. The specific implementation process is as follows:

[0091] according to Figure 1 The relationship between the electrical variables in the current source converter permanent magnet synchronous motor drive system shown in FIG, the continuous time state space model of the current source converter motor drive system is obtained as follows:

[0092] px=Ax+Bu (1)

[0093] In formula (1), p is a differential operator, x=[i sd ,i sq ,u sd ,u sq ,ω r ] T is the system state variable vector, u=[i wid ,i wiq ,T L ] T is the system input variable vector, where i sd and i sqis the dq axis stator current of the permanent magnet synchronous motor, u sd and u sq is the dq axis stator voltage of the permanent magnet synchronous motor, ω r is the motor electrical angular velocity (unit: rad / s), i wid and i wiq They represent the dq axis converter current of the current source inverter, T L is the motor load torque. A is the system matrix, B is the input matrix, and their respective expressions are shown in Equation (2) and Equation (3).

[0094]

[0095]

[0096] In formula (2) and formula (3), C s is the filter capacitor of the current source inverter, R s is the stator resistance of the motor, L sd and L sq They are the dq axis stator inductance of the motor (L in the surface mounted permanent magnet synchronous motor sd =L sq =L s ), ψ f is the amplitude of the permanent magnet flux of the motor rotor, J is the motor moment of inertia (unit: kg·m2), N p is the number of motor pole pairs.

[0097] (S1.2) The continuous-time small-signal linear model of the system at the operating point is obtained. The specific implementation process is as follows:

[0098] The nonlinear state space equation shown in equation (1) is linearized using the first-order Taylor expansion method, and the continuous-time small signal model expression of the system at the operating point is obtained as follows:

[0099] pΔx=A o Δx+B o Δu (4)

[0100] In formula (4), Δx and Δu are small signal disturbances at the operating point. Δx=[Δi sd ,Δi sq ,Δu sd ,Δu sq ,Δω r ] T is the small signal state variable vector of the system, Δu=[Δi wid ,Δi wiq ,ΔT L ] T is the small signal input variable vector of the system. The system matrix A of the small signal modelo and the input matrix B o The expressions of are shown in equations (5) and (6) respectively. System matrix A o The elements in with the subscript “o” indicate that this variable is the steady-state value at the operating point.

[0101]

[0102]

[0103] (S1.3) The discrete-time small-signal linear model of the system at the operating point is obtained. The specific implementation process is as follows:

[0104] The discrete method based on zero-order hold discretization is used to accurately discretize the continuous-time small signal model (4). The expression of the small signal discrete-time state space model obtained is as follows:

[0105] Δx(k+1)=ΦΔx(k)+ΓΔu(k) (7)

[0106] In formula (7), is the transfer matrix, is the input matrix.

[0107] (S1.4) Adding the converter current as a state variable in Equation (7) yields the expanded discrete-time small-signal model. The specific implementation process is as follows:

[0108] Since the controller's converter current reference and The actual value of the converter current i of the controlled object wid and i wiq There is a delay between the two, so we need to consider the actual value i wid and i wiq As a state variable, the reference value and As a new input variable, the state space model is expanded. Considering the one-shot delay of the digital controller, the complex vector mathematical model in the synchronous rotating coordinate system is: The expanded state space model diagram of the controlled object is as follows: Figure 2 shown.

[0109] from Figure 2 It can be seen that a one-shot delay in the synchronously rotating coordinate system will cause a delay phase angle of -T s ω e In order to eliminate the coupling component of one-beat delay, the converter current reference value can be and The phase angle is advanced compensation (the advanced phase angle is T s ωe ), thereby eliminating the related coupling of the delayed phase angle. At this time, the relationship between the actual value and the reference value of the converter current is as follows:

[0110]

[0111] Perform first-order Taylor expansion on the actual value and reference value of the converter current after phase compensation, and convert the small signal disturbance Δi of the actual value of the converter current into wid and Δi wiq As the expanded state variable, the expanded small signal state space equation can be obtained as follows:

[0112]

[0113] In formula (9), the expanded state variable is Δx b =[Δx,Δi wid ,Δi wiq ] T , the new input variable is The expanded state transfer matrix is ​​Φ b , the expanded input matrix is ​​Γ b The zero matrix subscripts in the state transfer matrix and the input matrix represent the rows and columns of the matrix, such as "0 1×2 ” represents a zero matrix with 1 row and 2 columns.

[0114] (S1.5) Based on equation (9), the discrete-time small-signal extended model of the system including the stator current controller is obtained. The specific implementation process is as follows:

[0115] The stator current controller is further included into the state space equations. Figure 3 The figure shows the control block diagram of the stator current closed loop control using a cascade controller with a stator current outer loop and a capacitor voltage inner loop. ic (z) and G uc (z) are stator current and capacitor voltage controllers respectively, and their expressions are as follows: Figure 3 As shown in ic (z) is a discrete proportional-integral controller, and G uc (z) is set as a proportional controller.

[0116] Considering the current controller G ic (z) contains an integral part, which is in the form of k i T s / (z-1), so the integral state variable of the stator current needs to be included in the state variable. Since the integral controller is a linear controller, the integral state variable of the dq axis small signal stator current can be made Δi sid and Δi siq, the small signal stator current reference value is and The modeling is as follows:

[0117]

[0118] Δi sid and Δi siq As an additional state variable added to Δx b The state space equation for the second expansion is as follows:

[0119]

[0120] In formula (11), Δx c =[Δx b ,Δi sid ,Δi sid ] T is the expanded small signal state variable, is the new small signal input variable. The expanded state transfer matrix is ​​Φ c , and the expanded input matrix is ​​Γ c and Γ rc , and their expressions are shown in formula (11). c Contains the matrix C b1 =[1,0,0,0,0,0] and C b2 =[0,1,0,0,0,0].

[0121] according to Figure 3 The control loop shown derives the converter current reference value and The relationship between the other state variables is as follows:

[0122]

[0123] It can be seen that the expression of the control loop also contains the product between the state variables, indicating that this cascade controller is a nonlinear controller and needs to be linearized before being cascaded with the small signal model of the controlled object. Performing a first-order Taylor expansion on Equation (12) yields the linearized small signal converter current reference value: and The relationship between it and other small signal state variables is as follows:

[0124]

[0125] In formula (13), the matrix F c The expression is as follows:

[0126]

[0127] From this, the state space equation including the stator current control loop can be obtained as follows:

[0128]

[0129] Equation (15) is the discrete-time small-signal model derived from (S1), where the small-signal state variable Δx d =Δx c , small signal input variable Δu d =Δu rc The state transfer matrix of the discrete time state space equation after including the stator current control loop is Φ d , the input matrix is ​​Γ d .

[0130] Considering the output equation shown in equation (16), according to the output matrix C d The transfer function G(z) between different input variables and output variables can be obtained as shown in formula (17):

[0131] y(k)=C d x d (k) (16)

[0132] G(z)=C d (zI-Φ d ) -1 Γ d (17)

[0133] Furthermore, the analysis and determination of the stability range of the speed controller parameters in (S2) specifically includes the following steps:

[0134] (S2.1) According to the discrete time small signal expansion model of the system, the speed loop control block diagram of the system including the speed controller at the operating point is obtained, as shown in Figure 4 As shown. Figure 4 In, G sc (z) is the speed controller, and its expression is the discrete time proportional integral controller, k wp is the proportional gain of the speed controller, τ w is the time constant of the speed controller. The transfer function of the current inner loop is G ma (z) can be obtained from the above formula (17) as the angular velocity △w r and q-axis current reference value Functions between .

[0135] (S2.2) According to the speed loop control block diagram, the small signal open-loop transfer function G of the speed loop is obtained. w_op (z) as follows:

[0136]

[0137] (S2.3) Based on the eigenvalue trajectory range of the small-signal open-loop transfer function of the speed loop, analyze the speed controller parameter stability of the drive system. The specific implementation process is as follows:

[0138] According to formula (18), we can get Figure 5 As shown in the figure, when the time constant τ w The open-loop transmission function G of the speed loop under 50ms w_op The characteristic root locus of (z), where the proportional gain k of the speed controller is wp The range is from 0 to infinity. Figure 5 It can be seen that the system has a total of 10 poles P1 to P10, of which 9 poles come from the discrete time state space equation and 1 pole comes from the speed controller. Figure 5 The right side of the figure is an enlarged view of the poles and zeros in the left pole and zero diagram close to the unit circle on the right. Figure 5 It can be obtained that there are two characteristic roots P1 and P2 in the proportional gain k of the speed control loop wp When the value is smaller, there is wp The system will become unstable if τ increases and moves outside the unit circle. w =50ms, k that makes the system stable wp The range is less than 0.32.

[0139] In order to verify the speed stability results of theoretical analysis, Figure 6 Shown is the time constant τ of the speed controller w Take 50ms, proportional gain k wp When the value is 0.2, the simulation result of the stable operation of the current source converter motor drive system is shown in the figure. Figure 7 Shown is the time constant τ of the speed controller w Take 50ms, proportional gain k wp The simulation results of the unstable operation of the current source converter motor drive system when the value is 0.4. In the simulation, the parameters of the current source converter motor drive system are shown in Table 1.

[0140] Table 1 Theoretical analysis and simulation parameters

[0141]

[0142] from Figure 6 It can be seen that when the time constant τ of the speed controller w Take 50ms, proportional gain k wpWhen the value is 0.2, the current source converter motor drive system can operate stably. At this time, the actual speed value is basically stable around the speed reference value of 1500rpm (fundamental frequency 100Hz, carrier ratio 10), and the motor phase current is also a sine waveform. Figure 7 It can be seen that when the time constant τ of the speed controller w Take 50ms, proportional gain k wp When the value is 0.4, the current source converter motor drive system becomes unstable. At this time, the actual speed value fluctuates periodically around the speed reference value of 1500rpm (fundamental frequency 100Hz, carrier ratio 10), and the motor phase current also has non-characteristic subharmonics. Figure 6 and Figure 7 The stability simulation results and Figure 5 The system stability analyzed in the theory is consistent, that is, under a certain speed controller time constant, when the proportional gain takes a small value (less than 0.32), the system root locus is located within the unit circle, and the system is stable; when the proportional gain takes a large value (greater than 0.32), the system root locus moves out of the unit circle, and the system becomes unstable.

[0143] While the present invention has been disclosed above with reference to preferred embodiments, this is not intended to limit the present invention. Persons skilled in the art will readily appreciate that various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

[0144] It will be understood by those skilled in the art that the embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention may be implemented in various computer languages, for example, the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0145] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0146] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0147] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 The steps for the function specified in one or more boxes.

[0148] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0149] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for analyzing the speed stability of a low-carrier-to-current-source motor drive system, characterized in that The steps include: Step 1: construct a discrete-time small-signal model including a current source converter, a motor controlled object, and a stator current controller; Step 2: obtaining an eigenvalue trajectory of a speed loop open-loop transfer function based on the discrete-time small-signal model including the current source converter, the motor controlled object, and the stator current controller; Step 3: analyzing the stability range of the speed controller parameters according to the characteristic value trajectory; The specific content of step one is: Step A, constructing a continuous-time state-space model reflecting the relationship between state variables and input variables of a current source converter permanent magnet synchronous motor drive system; Step B: linearizing the continuous-time state-space model of step A to obtain a continuous-time small-signal model of the current source converter permanent magnet synchronous motor drive system at the operating point; Step C, discretizing the continuous-time small signal model of step B to obtain a discrete-time small signal model of the current source converter permanent magnet synchronous motor drive system at the operating point, wherein the discrete-time small signal model includes the motor controlled object; Step D, based on the discrete-time small-signal model of step C, adding the converter current as a state variable to obtain a discrete-time small-signal extended model including a current source converter and a motor controlled object; Step E, based on the discrete-time small-signal expansion model including the current source converter and the motor controlled object in step D, and according to the relationship between the various state variables in the stator current controller, obtains a discrete-time small-signal expansion model including the current source converter, the motor controlled object, and the stator current controller.

2. The method according to claim 1, wherein: The specific content of step 2 is: Step a, based on the discrete-time small signal model including the current source converter, the motor controlled object, and the stator current controller, obtaining a speed loop control block diagram of the current source converter permanent magnet synchronous motor drive system including the speed controller at the operating point; Step b, obtaining a small signal open-loop transfer function of the speed loop according to the speed loop control block diagram; Step c: obtaining the characteristic value trajectory of the speed loop according to the small signal open-loop transfer function of the speed loop.

3. The method according to claim 1, wherein: The specific content of step three is: Step i, drawing a corresponding eigenvalue trajectory block diagram according to the eigenvalue trajectory of the speed loop open-loop transfer function; Step ii, analyze when the time constant reaches a certain value τ w0 When at least one characteristic root has a tendency to move outside the unit circle, the corresponding proportional gain is k wp0 , then it is considered that when the time constant τ w0 When the proportional gain range that makes the system stable is less than k wp0 .

4. A low-carrier-ratio current source motor drive system speed stability analysis system, characterized by: include, A discrete-time small-signal model building module is configured to build a discrete-time small-signal model including a current source converter, a motor controlled object, and a stator current controller; an eigenvalue trajectory acquisition module, configured to obtain an eigenvalue trajectory of a speed loop open-loop transfer function based on the discrete-time small signal model; as well as, a stability analysis module configured to analyze the stability range of the speed controller parameters according to the eigenvalue trajectory; The discrete time small signal model building module includes: a continuous-time state-space model building module configured to build a continuous-time state-space model reflecting the relationship between state variables and input variables of a current source converter permanent magnet synchronous motor drive system; a continuous-time small-signal model acquisition module configured to linearize the continuous-time state-space model to obtain a continuous-time small-signal model of the current source converter permanent magnet synchronous motor drive system at an operating point; a discrete-time small-signal model acquisition module configured to discretize the continuous-time small-signal model to obtain a discrete-time small-signal model of the current source converter permanent magnet synchronous motor drive system at an operating point, wherein the discrete-time small-signal model includes a motor controlled object; A first discrete-time small-signal extended model acquisition module is configured to add the converter current as a state variable based on the discrete-time small-signal model to obtain a discrete-time small-signal extended model including a current source converter and a motor controlled object; and The second discrete-time small signal extension model acquisition module is configured to obtain a discrete-time small signal extension model including a current source converter, a motor controlled object, and a stator current controller based on the discrete-time small signal extension model including the current source converter and the motor controlled object and according to the relationship between the various state variables in the stator current controller.

5. The system according to claim 4, wherein: The characteristic value trajectory acquisition module includes: a speed loop control block diagram acquisition module configured to obtain a speed loop control block diagram of the current source converter permanent magnet synchronous motor drive system including the speed controller at an operating point based on the discrete time small signal model including the current source converter, the motor controlled object, and the stator current controller; an open-loop transfer function acquisition module, configured to obtain a small-signal open-loop transfer function of a speed loop according to the speed loop control block diagram; as well as, The characteristic value trajectory acquisition module is configured to obtain the characteristic value trajectory of the speed loop according to the small signal open-loop transfer function of the speed loop.

6. The system according to claim 4, wherein: The stability analysis module includes: The eigenvalue trajectory block diagram drawing module is configured to draw a corresponding eigenvalue trajectory block diagram according to the eigenvalue trajectory of the speed loop open-loop transfer function; as well as, The proportional gain range analysis module is configured to analyze the proportional gain when the time constant reaches a certain value τ w0 When at least one characteristic root has a tendency to move outside the unit circle, the corresponding proportional gain is k wp0 , then it is considered that when the time constant τ w0 When the proportional gain range that makes the system stable is less than k wp0 .

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