An Adaptive DC Voltage Control Method and Device with Variable Integration Coefficient

Abstract

The present invention discloses an adaptive DC voltage control method and device with variable integral coefficients. The method includes: (1) collecting the DC bus voltage of the DC power transmission system in real time; (2) calculating the voltage difference between the DC bus voltage at the current moment and the given voltage value; (3) generating a voltage control signal based on the voltage difference by using an adaptive variable integral PI controller; (4) generating a PWM control wave according to the voltage control signal and sending it to the inverter of the DC power transmission system, and realizing the control of the DC voltage of the DC power transmission system through the inverter. The present invention improves the voltage dynamic response ability in the normal operation mode of the DC power transmission system and the practicality of the inverter technology.

Description

Technical Field

[0001] The present invention relates to voltage control technology, and in particular, to an adaptive DC voltage control method and device with variable integral coefficients. Background Art

[0002] Grid faults are usually unpredictable and uncontrollable. To meet the low-voltage ride-through test requirements of wind turbines and photovoltaic power stations, specific equipment is needed to simulate different grid faults. The voltage sag generator (VSG) based on power electronic conversion has received extensive attention due to its flexible form, strong controllability, and powerful functions. The circuit topology of the VSG usually consists of a three-phase voltage-source pulse width modulation (PWM) rectifier and a three-phase PWM inverter, and it should have good steady-state and transient characteristics when simulating various grid fault types. When the inverter side simulates a grid voltage sag fault, the input and output power of the VSG system will change greatly instantaneously, and the front-stage PWM rectifier will be severely tested. Therefore, the quality of the control strategy of the PWM rectifier will directly affect the performance of the entire VSG control system. When designing the traditional PWM rectifier control system, a cascaded double-closed-loop control system structure with a voltage outer loop and a current inner loop is usually adopted, and classical PI control is usually used. However, since the PI regulator is difficult to meet the requirements of high precision and fast response, and the size of the integral coefficient is directly related to the recovery ability of the rectifier side of the VSG system during "given voltage sag", integral saturation is extremely likely to occur during the transient process, thus affecting the performance of the control system. Summary of the Invention

[0003] Object of the Invention: Aiming at the problems existing in the prior art, the present invention provides an adaptive DC voltage control method and device with variable integral coefficients and better performance.

[0004] Technical Solution: The adaptive DC voltage control method with variable integral coefficients of the present invention includes:

[0005] (1) Real-time collect the DC bus voltage of the DC transmission system;

[0006] (2) Calculate the voltage difference between the DC bus voltage at the current moment and the given voltage value;

[0007] (3) Use an adaptive variable integral PI controller to generate a voltage control signal based on the voltage difference according to the following formula:

[0008]

[0009] In the formula, u(k) represents the voltage control signal at the kth moment, k p 、k iare the proportional and integral parameters of the variable integral PI controller; e(k) is the voltage difference; λ is the adaptive variable integral coefficient calculated based on e(k); T is the integral time constant;

[0010] (4) Generate a PWM control wave according to the voltage control signal and send it to the inverter of the DC transmission system to control the DC voltage of the DC transmission system through the inverter.

[0011] Further, step (2) specifically includes:

[0012] (2-1) Perform dq transformation on the DC bus voltage to obtain the DC voltage d-axis and q-axis components U d (k), U q (k);

[0013] (2-2) Calculate the differences e1(k) and e2(k) between U d (k), U q (k) and the given voltage value respectively;

[0014] (2-3) Take the sum of the differences e1(k) and e2(k) as the voltage difference e(k).

[0015] Further, the calculation method of the adaptive variable integral coefficient in step (3) is:

[0016]

[0017] In the formula, M and N are the integration intervals.

[0018] Further, step (4) specifically includes:

[0019] (4-1) Extract the phase signal of the voltage control signal;

[0020] (4-2) Transform the phase signal of the voltage control signal into radian information;

[0021] (4-3) Generate a PWM control wave based on the radian information using a pulse generator;

[0022] (4-4) Send the PWM control wave to the inverter of the DC transmission system to control the DC voltage of the DC transmission system through the inverter.

[0023] The adaptive DC voltage control device with variable integral coefficient according to the present invention includes:

[0024] A voltage acquisition module for real-time acquisition of the DC bus voltage of the DC transmission system;

[0025] A difference calculation module for calculating the voltage difference between the DC bus voltage at the current moment and the given voltage value;

[0026] An adaptive variable integral PI controller is used to generate a voltage control signal based on the voltage difference according to the following formula:

[0027]

[0028] In the formula, u(k) represents the voltage control signal at time k, and k p and k i are the proportional and integral parameters of the variable integral PI controller; e(k) is the voltage difference; λ is the adaptive variable integral coefficient calculated based on e(k); T is the integral time constant;

[0029] A PWM control wave generation module is used to generate a PWM control wave according to the voltage control signal and send it to the inverter of the HVDC system, so as to control the DC voltage of the HVDC system through the inverter.

[0030] Furthermore, the difference calculation module specifically includes:

[0031] A transformation unit is used to perform dq transformation on the DC bus voltage to obtain the d-axis and q-axis components Ud d (k), Uq q (k);

[0032] A difference calculation unit is used to calculate the differences e1(k) and e2(k) between Ud d (k) and Uq q (k) and the given voltage value respectively, and take the sum of the differences e1(k) and e2(k) as the voltage difference e(k).

[0033] Furthermore, the calculation method of the adaptive variable integral coefficient of the adaptive variable integral PI controller is:

[0034]

[0035] In the formula, M and N are the integral intervals.

[0036] Furthermore, the PWM control wave generation module specifically includes:

[0037] A phase extraction unit is used to extract the phase signal of the voltage control signal;

[0038] A radian transformation unit is used to transform the phase signal of the voltage control signal into radian information;

[0039] A pulse generator is used to generate a PWM control wave based on the radian information and send it to the inverter of the HVDC system, so as to control the DC voltage of the HVDC system through the inverter.

[0040] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are as follows: The present invention improves the control method for the DC bus voltage response speed of a DC power transmission system, enhancing the steady-state and dynamic performance of the system. Description of the Drawings

[0041] Figure 1 It is a schematic diagram of the steps of the adaptive DC voltage control method with variable integral coefficients provided by the present invention;

[0042] Figure 2 It is a structural diagram of the DC power transmission system applicable to the present invention;

[0043] Figure 3 is Figure 2 The flow control diagram of the adaptive DC voltage control in

[0044] Figure 4 It is a curve graph of the system frequency change when the active power increases under the comparison between the control method of the present invention and the fixed integral coefficient control method. Detailed Embodiments

[0045] The following will describe in detail the specific embodiments of the present invention in conjunction with the drawings.

[0046] Embodiment 1

[0047] Figure 1 As shown, it is the adaptive DC voltage control method with variable integral coefficients provided by this embodiment. The structure of the DC power transmission system applicable to the method of this embodiment is as Figure 2 shown, mainly composed of the sending-end power grid G1, the receiving-end power grid G2, the three-winding transformer T1, T2, the rectifier rectifier, and the inverter inverter. DC is direct current, and AC is alternating current. The sending-end power grid is used to generate a constant active power, and the receiving-end power grid can be connected or disconnected at different times. The voltage and current control of the rectifier and inverter branches adopts double-loop control technology. The adaptive DC voltage control adaptively changes the integral regulation coefficient through the feedback of the voltage deviation amount, thereby adjusting the DC voltage reference value of the inverter and optimizing the DC voltage response of the system.

[0048] The method of this embodiment specifically includes the following steps:

[0049] S1. Real-time collect the DC bus voltage of the DC power transmission system.

[0050] S2. Calculate the voltage difference between the DC bus voltage at the current moment and the given voltage value.

[0051] The specific calculation steps are as follows: Perform dq transformation on the DC bus voltage to obtain the DC voltage d-axis and q-axis components U d (k), U q (k); Calculate Ud (k), U q (k) are respectively the differences e1(k), e2(k) from the given voltage value u0; the sum of the differences e1(k), e2(k) is taken as the voltage difference e(k).

[0052] S3. An adaptive variable integral PI controller is used to generate a voltage control signal based on the voltage difference.

[0053] In specific implementation, as Figure 3 shown, the formula for generating the voltage control signal is:[[]]END]]

[0054]

[0055] In the formula, u(k) represents the voltage control signal at time k, k p , k i are the proportional and integral parameters of the variable integral PI controller; e(k) is the voltage difference; λ is the adaptive variable integral coefficient calculated based on e(k); T is the integral time constant.

[0056] The calculation method of the adaptive variable integral coefficient is:[[]]END]]

[0057]

[0058] In the formula, M, N are the integral intervals, and specifically can take values 1, 1.5. When |e(k)| ≤ N - M, the system deviation is too small, and the adaptive variable integral coefficient is 1. When N - M < |e(k)| ≤ M, the system deviation is between N - M and M, and the adaptive variable integral coefficient is a function of |e(k)|. When M < |e(k)| ≤ N, the system deviation is between N - M and M, and the adaptive variable integral coefficient is a function of |e(k)|. When N < |e(k)|, since the integral effect should be weakened or even disappear when the system deviation is large, the adaptive variable integral coefficient is 0.

[0059] S4. A PWM control wave is generated according to the voltage control signal and sent to the inverter of the DC power transmission system, and the DC voltage of the DC power transmission system is controlled through the inverter.

[0060] In specific implementation, first extract the phase signal θ ref of the voltage control signal; then transform the phase signal θ ref of the voltage control signal into radian information; a PWM control wave is generated based on the radian information using a pulse generator; finally, the PWM control wave is sent to the inverter of the DC power transmission system, and the DC voltage of the DC power transmission system is controlled through the inverter.

[0061] An experiment was conducted on the present invention. Under the normal operation mode, the given value of the rectifier-side current in the initial operation state was 1000 A, and the given value of the inverter-side DC voltage was 220 kV. The voltage was stable at 220 kV during normal operation. At 10 s, the given value of the rectifier-side current was increased to 1500 A, and the changes in the DC voltage of the microgrid system were observed and compared under adaptive control and fixed integral coefficient control. The operation results are as Figure 4 shown. When using the fixed integral coefficient control, if the value of k i is too small, it will cause the system voltage offset value to be too large and the frequency recovery time to be too long; when the value of k i increases, the system voltage recovery time will be shortened, but the maximum system voltage offset value is still relatively high. However, the adaptive fixed DC voltage control method of the present invention can effectively reduce the maximum voltage offset value when the DC voltage of the system fluctuates, and the recovery process is relatively gentle. From Figure 4 the operation results shown, it can be seen that the adaptive fixed DC voltage control with variable integral coefficient proposed by the present invention can flexibly adjust the integral coefficient, thereby effectively improving the voltage characteristics of the system, reducing the maximum system voltage offset value when the active power changes, and making the voltage recovery process more gentle. Generally speaking, Figure 4 the operation results shown prove the effectiveness of the variable integral coefficient adaptive fixed DC voltage control method described in the present invention, which has better frequency dynamic response under the normal operation mode and improves the practicability of the double closed-loop fixed DC voltage technology.

[0062] Embodiment 2

[0063] This embodiment provides an adaptive DC voltage control device with variable integral coefficient, including:

[0064] A voltage acquisition module for real-time acquisition of the DC bus voltage of the DC power transmission system;

[0065] A difference calculation module for calculating the voltage difference between the DC bus voltage at the current moment and the given voltage value;

[0066] An adaptive variable integral PI controller for generating a voltage control signal based on the voltage difference according to the following formula:

[0067]

[0068] where u(k) represents the voltage control signal at the kth moment, k p and k i are the proportional and integral parameters of the variable integral PI controller; e(k) is the voltage difference; λ is the adaptive variable integral coefficient calculated based on e(k); T is the integral time constant;

[0069] The PWM control wave generation module is used to generate a PWM control wave according to a voltage control signal and send it to the inverter of the HVDC system, so as to control the DC voltage of the HVDC system through the inverter.

[0070] Among them, the difference calculation module specifically includes:

[0071] A transformation unit for performing dq transformation on the DC bus voltage to obtain the DC voltage d-axis and q-axis components U d (k), U q (k);

[0072] A difference calculation unit for respectively calculating the differences e1(k) and e2(k) between U d (k), U q (k) and the given voltage value, and taking the sum of the differences e1(k) and e2(k) as the voltage difference e(k).

[0073] Among them, the calculation method of the adaptive variable integral coefficient of the adaptive variable integral PI controller is:

[0074]

[0075] In the formula, M and N are integration intervals.

[0076] Among them, the PWM control wave generation module specifically includes:

[0077] A phase extraction unit for extracting the phase signal of the voltage control signal;

[0078] A radian transformation unit for transforming the phase signal of the voltage control signal into radian information;

[0079] A pulse generator for generating a PWM control wave based on the radian information and sending it to the inverter of the HVDC system, so as to control the DC voltage of the HVDC system through the inverter.

[0080] The above-disclosed is only a preferred embodiment of the present invention, and it cannot be used to limit the scope of the rights of the present invention. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope covered by the present invention.

Claims

1. An adaptive DC voltage control method with variable integral coefficient, characterized in that Including: (1) Real-time collect the DC bus voltage of the HVDC transmission system; (2) Calculate the voltage difference between the DC bus voltage at the current moment and the given voltage value; (3) Use an adaptive variable integral PI controller to generate a voltage control signal based on the voltage difference according to the following formula: where u(k) represents the voltage control signal at time k, and k p , k i are the proportional and integral parameters of the variable integral PI controller; e(k) is the voltage difference; T is the integral time constant; λ is the adaptive variable integral coefficient calculated based on e(k), and the calculation method is as follows: In the formula, M and N are integral intervals; (4) Generate a PWM control wave according to the voltage control signal, send it to the inverter of the HVDC transmission system, and realize the control of the DC voltage of the HVDC transmission system through the inverter.

2. The adaptive DC voltage control method with variable integral coefficient according to claim 1, characterized in that: (2) specifically includes: (2-1) Perform dq transformation on the DC bus voltage to obtain the d-axis and q-axis components Ud(k) and Uq(k) of the DC voltage; d (k), U q (k); (2-2) Calculate U d (k), U q (k) and the differences e1(k), e2(k) from the given voltage values respectively; (2-3) Take the sum of the differences e1(k) and e2(k) as the voltage difference e(k).

3. The adaptive DC voltage control method with variable integral coefficient according to claim 1, characterized in that: (4) specifically includes: (4-1) Extract the phase signal of the voltage control signal; (4-2) Transform the phase signal of the voltage control signal into radian information; (4-3) Use a pulse generator to generate a PWM control wave based on the radian information; (4-4) Send the PWM control wave to the inverter of the HVDC transmission system, and realize the control of the DC voltage of the HVDC transmission system through the inverter.

4. An adaptive DC voltage control device with variable integral coefficient, characterized in that (1) Including: A voltage acquisition module for real-time collecting the DC bus voltage of the HVDC transmission system; A difference calculation module for calculating the voltage difference between the DC bus voltage at the current moment and the given voltage value; An adaptive variable integral PI controller for generating a voltage control signal based on the voltage difference according to the following formula: where u(k) represents the voltage control signal at time k, and k p , k i are the proportional and integral parameters of the variable integral PI controller; e(k) is the voltage difference; T is the integral time constant; λ is the adaptive variable integral coefficient calculated based on e(k), and the calculation method is as follows: In the formula, M and N are integral intervals; A PWM control wave generation module for generating a PWM control wave according to the voltage control signal, sending it to the inverter of the HVDC transmission system, and thus realizing the control of the DC voltage of the HVDC transmission system through the inverter.

5. The adaptive DC voltage control device with variable integral coefficient according to claim 4, characterized in that: The difference calculation module specifically includes: A transformation unit for performing dq transformation on the DC bus voltage to obtain the d-axis and q-axis components Ud(k) and Uq(k) of the DC voltage. d (k), U q (k); The difference calculation unit is used to calculate the differences e1(k) and e2(k) between U d (k) and U q (k) and the given voltage value respectively, and use the sum of the differences e1(k) and e2(k) as the voltage difference e(k).

6. The adaptive DC voltage control device with variable integral coefficient according to claim 4, characterized in that: The PWM control wave generation module specifically includes: A phase extraction unit for extracting the phase signal of the voltage control signal; A radian transformation unit for transforming the phase signal of the voltage control signal into radian information; A pulse generator for generating a PWM control wave based on the radian information and sending it to the inverter of the HVDC transmission system, and thus realizing the control of the DC voltage of the HVDC transmission system through the inverter.

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