Improved direct current bus voltage sliding mode control method

Abstract

The invention provides an improved direct-current bus voltage sliding-mode control method, and the direct-current bus voltage sliding-mode control method is designed by analyzing and modeling a direct-current bus voltage control system of a permanent magnet synchronous generator, so that rapid dynamic response can be realized. The disturbance power observer based on the recursive least square method is adopted, the disturbance power can be observed in real time, the disturbance power serves as the feed-forward quantity, and therefore the steady-state control performance of the direct-current bus voltage can be remarkably improved. According to the method, the sliding mode controller and the disturbance observer are organically combined, faster dynamic performance is achieved, large switching gain is avoided, and the steady-state performance of sliding mode control is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of direct current bus voltage control of permanent magnet synchronous generators, and in particular relates to an improved direct current bus voltage sliding mode control method. Background Art

[0002] At present, the DC bus voltage control of the permanent magnet synchronous generator (PMSG) system mostly adopts a cascaded dual-loop structure. When working, the voltage outer loop generates the command current of the current inner loop according to the voltage tracking error, and the current inner loop is responsible for ensuring that the actual current can quickly and accurately follow the command current. Therefore, in order to achieve fast and stable DC bus voltage control, both the voltage outer loop and the current inner loop must have excellent steady-state performance and dynamic response. In the prior art, the most commonly used means is to perform proportional integral (PI) control on the voltage outer loop, but since this method only uses the feedback information of the DC bus voltage and does not make full use of the model information of the system, it is difficult to achieve excellent dynamic performance and anti-interference performance. In order to take into account the steady-state performance and dynamic performance of the DC bus voltage control, some prior arts adopt nonlinear control methods such as two-degree-of-freedom control (TDOF) and sliding mode control (SMC). However, although TDOF control shows better dynamic performance and anti-interference ability than traditional PI control, its design process is too complicated and difficult to promote and apply. SMC is well-known for its fast dynamic response, simple structure, robustness to system parameter changes and anti-interference ability. It is more suitable for the voltage outer loop of PMSG system. However, since the load power of most PMSG DC bus voltage control systems is time-varying, the switching gain needs to be increased to achieve strong robustness, which will lead to serious jitter problems and is not conducive to the steady-state control performance of the DC bus voltage. Therefore, there is an urgent need in the art for a DC bus voltage control method that can effectively eliminate the jitter problem while ensuring the dynamic performance of SMC. Summary of the invention

[0003] In view of this, in order to solve the technical problems existing in the art, the present invention provides an improved DC bus voltage sliding mode control method, which specifically includes the following steps:

[0004] Step 1: Real-time acquisition of bus voltage, motor speed, and motor current data during the operation of the permanent magnet synchronous generator system;

[0005] Step 2: Considering the power and loss of the permanent magnet synchronous generator, a mathematical model of the DC bus voltage control system of the permanent magnet synchronous generator is established; based on the established mathematical model, a DC bus voltage sliding mode controller is designed, including designing a corresponding sliding mode surface and sliding mode approach rate;

[0006] Step 3: The DC bus voltage control system of the permanent magnet synchronous generator is regarded as a system whose state variables cannot be directly measured, and a disturbance power observer based on recursive least squares (RLS) is established for it; based on the disturbance power observer and using the data collected in step 1, the disturbance power of the system is estimated in real time;

[0007] Step 4: Feed forward the obtained disturbance power to the DC bus voltage sliding mode controller to obtain the output of the voltage outer loop, that is, the q-axis reference current value; the current inner loop performs PI control, and obtains the dq-axis reference voltage vector according to the difference between the command current and the actual current, and controls the switching time of the PWM rectifier through space vector pulse width modulation (SVPWM).

[0008] Furthermore, the mathematical model of the DC bus voltage control system of the permanent magnet synchronous generator established in step 2 specifically includes:

[0009] P m =P cooper_loss +P iron_loss +P converter_loss +P C +P L

[0010] P m =-ω m T e

[0011]

[0012] Where P m is the output power of the prime mover; P copper_loss and P iron_loss Respectively represent the copper loss and iron loss of the permanent magnet synchronous generator; P converter_loss Represents the power loss of the PWM rectifier; P C Represents the power absorbed by the DC bus capacitor; P L Represents load power; i d 、i q are dq axis current respectively; R s is the stator resistance; ω m is the mechanical angular velocity of the rotor; T e Represents the electromagnetic torque of the permanent magnet synchronous generator, and its expression is:

[0013] T e =1.5pψ f i q

[0014] In the formula, Ψ f is the permanent magnet flux of the motor rotor; p is the number of motor pole pairs;

[0015] The following power equation can be obtained from the above mathematical model:

[0016]

[0017] In the sliding mode controller, the following sliding mode surface is designed to make the DC bus voltage follow the corresponding voltage command value:

[0018]

[0019] The sliding mode approach rate is designed as:

[0020]

[0021] In the formula, ε and k are the approach rate coefficients, respectively, and the superscript · represents the first-order derivative of the corresponding parameter.

[0022] Furthermore, in step three, the permanent magnet synchronous generator DC bus voltage control system is specifically expressed as the following equation form:

[0023] y k =H k x k +v k

[0024] According to the principle of optimal recursive least squares method, the following optimal estimation equation is derived:

[0025]

[0026] In the formula, are the optimal estimates corresponding to adjacent moments; the subscript k represents the kth observation period; y k is an observable variable; H k is the observation matrix; K k is a weighted matrix, and its specific form is as follows:

[0027]

[0028] Where λ is the forgetting factor; P k-1 is the covariance matrix, and its update equation is expressed as:

[0029]

[0030] According to the power equation of the DC bus voltage of the permanent magnet synchronous generator, the following state equation of the disturbance power observer is obtained:

[0031]

[0032] Then the state variable x k , observable variable y k and the observation matrix Hk Can be expressed as:

[0033] x k =f V

[0034]

[0035] H k =1

[0036] Furthermore, in step 4, the disturbance power is fed forward to the DC bus voltage sliding mode controller to obtain the q-axis current reference value in the following form:

[0037]

[0038] The current inner loop obtains the dq axis reference voltage vector u by executing PI control d 、u q , and finally get the switching time of the PWM rectifier.

[0039] The improved DC bus voltage sliding mode control method provided by the present invention can achieve at least the following beneficial effects compared with the prior art:

[0040] 1. This method designs a DC bus voltage sliding mode control method by analyzing and modeling the DC bus voltage control system of the permanent magnet synchronous generator, which can achieve fast dynamic response.

[0041] 2. By adopting a disturbance power observer based on the recursive least squares method, the disturbance power can be observed in real time and used as a feedforward quantity, thereby significantly improving the steady-state control performance of the DC bus voltage.

[0042] 3. The organic combination of sliding mode controller and disturbance observer not only achieves faster dynamic performance, but also avoids the use of large switching gain, thereby improving the steady-state performance of sliding mode control. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A flowchart of the method provided by the present invention;

[0044] Figure 2 The figure is a diagram showing the effect of controlling the DC bus voltage in an example of the present invention. DETAILED DESCRIPTION

[0045] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] The improved DC bus voltage sliding mode control method provided by the present invention is as follows: Figure 1 As shown, the specific steps include:

[0047] Step 1: Real-time acquisition of bus voltage, motor speed, and motor current data during the operation of the permanent magnet synchronous generator system;

[0048] Step 2: Considering the power and loss of the permanent magnet synchronous generator, a mathematical model of the DC bus voltage control system of the permanent magnet synchronous generator is established; based on the established mathematical model, a DC bus voltage sliding mode controller is designed, including designing a corresponding sliding mode surface and sliding mode approach rate;

[0049] Step 3: The DC bus voltage control system of the permanent magnet synchronous generator is regarded as a system whose state variables cannot be directly measured, and a disturbance power observer based on recursive least squares (RLS) is established for it; based on the disturbance power observer and using the data collected in step 1, the disturbance power of the system is estimated in real time;

[0050] Step 4: Feed forward the obtained disturbance power to the DC bus voltage sliding mode controller to obtain the output of the voltage outer loop, that is, the q-axis reference current value; the current inner loop performs PI control, and obtains the dq-axis reference voltage vector according to the difference between the command current and the actual current, and controls the switching time of the PWM rectifier through space vector pulse width modulation (SVPWM).

[0051] In a preferred embodiment of the present invention, the mathematical model of the DC bus voltage control system of the permanent magnet synchronous generator established in step 2 specifically includes:

[0052] P m =P cooper_loss +P iron_loss +P converter_loss +P C +P L

[0053] P m =-ω m T e

[0054]

[0055] Where P m is the output power of the prime mover; P copper_loss and P iron_loss Respectively represent the copper loss and iron loss of the permanent magnet synchronous generator; P converter_loss Represents the power loss of the PWM rectifier; P C Represents the power absorbed by the DC bus capacitor; P L Represents the load power; id 、i q are dq axis current respectively; R s is the stator resistance; ω m is the mechanical angular velocity of the rotor; T e Represents the electromagnetic torque of the permanent magnet synchronous generator, and its expression is:

[0056] T e =1.5pψ f i q

[0057] In the formula, Ψ f is the permanent magnet flux of the motor rotor; p is the number of motor pole pairs;

[0058] The following power equation can be obtained from the above mathematical model:

[0059]

[0060] In the sliding mode controller, the following sliding mode surface is designed to make the DC bus voltage follow the corresponding voltage command value:

[0061]

[0062] The sliding mode approach rate is designed as:

[0063]

[0064] In the formula, ε and k are the approach rate coefficients, respectively, and the superscript · represents the first-order derivative of the corresponding parameter.

[0065] In a preferred embodiment of the present invention, in step 3, the DC bus voltage control system of the permanent magnet synchronous generator is specifically expressed as the following equation:

[0066] y k =H k x k +v k

[0067] According to the principle of optimal recursive least squares method, the following optimal estimation equation is derived:

[0068]

[0069] In the formula, are the optimal estimates corresponding to adjacent moments; the subscript k represents the kth observation period; y k is an observable variable; H k is the observation matrix; K k is a weighted matrix, and its specific form is as follows:

[0070]

[0071] Where λ is the forgetting factor, whose value is between 0.9 and 1. The larger λ is, the greater the impact of historical data on the observation results. k-1 is the covariance matrix, and its update equation is expressed as:

[0072]

[0073] According to the power equation of the DC bus voltage of the permanent magnet synchronous generator, the following state equation of the disturbance power observer is obtained:

[0074]

[0075] Then the state variable x k , observable variable y k and the observation matrix H k Can be expressed as:

[0076] x k =f V

[0077]

[0078] H k =1

[0079] In a preferred embodiment of the present invention, in step 4, the disturbance power is fed forward to the DC bus voltage sliding mode controller to obtain a q-axis current reference value in the following form:

[0080]

[0081] The current inner loop obtains the dq axis reference voltage vector u by executing PI control d 、u q , and finally get the switching time of the PWM rectifier.

[0082] The method provided by the present invention can achieve fast dynamic response of DC bus voltage while avoiding the jitter problem caused by the SMC method. In a preferred embodiment based on the present invention, a waveform diagram is given when the generator operates at a rated speed of 1000r / min, the DC bus voltage reference value is 160V, and the disturbance power steps from 500W to 1000W. Figure 2 As shown. It can be seen that in steady state, the actual voltage perfectly follows the reference voltage without obvious jittering; in the case of a disturbing power step, the DC bus voltage drops by 3.75%, which is much less than the national standard of 10%, and it recovers stability within 3.2ms. This proves that the method of the present invention can effectively achieve excellent steady-state performance and dynamic performance.

[0083] It should be understood that the size of the serial numbers of the steps in the embodiment of the present invention does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0084] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An improved DC bus voltage sliding mode control method, characterized in that: The specific steps include: Step 1: Real-time acquisition of bus voltage, motor speed, and motor current data during the operation of the permanent magnet synchronous generator system; Step 2: Considering the power and loss of the permanent magnet synchronous generator, a mathematical model of the DC bus voltage control system of the permanent magnet synchronous generator is established; based on the established mathematical model, a DC bus voltage sliding mode controller is designed, including designing a corresponding sliding mode surface and sliding mode approach rate; Step 3: The DC bus voltage control system of the permanent magnet synchronous generator is regarded as a system whose state variables cannot be directly measured, and a disturbance power observer based on the recursive least squares method is established for it; based on the disturbance power observer and using the data collected in step 1, the disturbance power of the system is estimated in real time; Step 4: Feed forward the obtained disturbance power to the DC bus voltage sliding mode controller to obtain the output of the voltage outer loop, that is, the q-axis reference current value; the current inner loop performs PI control, and obtains the dq-axis reference voltage vector according to the difference between the command current and the actual current, and controls the switching time of the PWM rectifier through space vector pulse width modulation.

2. The method according to claim 1, characterized in that: The mathematical model of the DC bus voltage control system of the permanent magnet synchronous generator established in step 2 specifically includes: P m =P cooper_loss +P iron_loss +P converter_loss +P C +P L P m =-ω m T e Where P m is the output power of the prime mover; P copper_loss and P iron_loss Respectively represent the copper loss and iron loss of the permanent magnet synchronous generator; P converter_loss Represents the power loss of the PWM rectifier; P C Represents the power absorbed by the DC bus capacitor; P L Represents load power; i d 、i q are dq axis current respectively; R s is the stator resistance; ω m is the mechanical angular velocity of the rotor; T e Represents the electromagnetic torque of the permanent magnet synchronous generator, and its expression is: T e =1.5pψ f i q In the formula, Ψ f is the permanent magnet flux of the motor rotor; p is the number of motor pole pairs; The following power equation can be obtained from the above mathematical model: In the sliding mode controller, the following sliding mode surface is designed to make the DC bus voltage follow the corresponding voltage command value: The sliding mode approach rate is designed as: In the formula, ε and k are the approach rate coefficients, respectively, and the superscript · represents the first-order derivative of the corresponding parameter.

3. The method according to claim 2, characterized in that: In step 3, the DC bus voltage control system of the permanent magnet synchronous generator is specifically expressed as the following equation: y k =H k x k +v k According to the principle of optimal recursive least squares method, the following optimal estimation equation is derived: In the formula, are the optimal estimates corresponding to adjacent moments; the subscript k represents the kth observation period; y k is an observable variable; H k is the observation matrix; K k is a weighted matrix, and its specific form is as follows: Where λ is the forgetting factor; P k-1 is the covariance matrix, and its update equation is expressed as: According to the power equation of the DC bus voltage of the permanent magnet synchronous generator, the following state equation of the disturbance power observer is obtained: Then the state variable x k , observable variable y k and the observation matrix H k Can be expressed as:

4. The method according to claim 3, characterized in that: In step 4, the disturbance power is fed forward to the DC bus voltage sliding mode controller to obtain the q-axis current reference value in the following form: The current inner loop obtains the dq axis reference voltage vector u by executing PI control d 、u q , and finally get the switching time of the PWM rectifier.

Images