Incremental PID lead compensation excitation control method and system

Abstract

The invention relates to an incremental PID lead compensation excitation control method and system, and the method comprises the steps: calculating a voltage effective value uk outputted by a generator at a kth sampling point, reading a voltage preset value rk, and reading a voltage effective value ukx of a sampling point before a preset time period from the kth sampling point; calculating a compensation voltage deviation Ekx = ukx-uk; the basic output increment unit of the PID controller is M0; at the (k + 1) th sampling point, the actual output increment unit M of the PID controller is equal to M0 + N; the compensation voltage deviation Ekx is compared with a preset value rk of the generator end voltage at the kth sampling point, and when Ekx is larger than or equal to rk * t, the compensation unit N is a non-zero value; when Ekxlt; when rk * t, the compensation unit N is equal to 0; the embodiment of the invention improves the response speed of the system, and ensures that the voltage change amplitude is far smaller than that in the prior art when the load is suddenly increased and suddenly discharged.

Description

Technical Field

[0001] The present invention relates to the field of generators, and particularly to an incremental PID lead compensation excitation control method and system. Background Art

[0002] In a synchronous generator excitation system, the excitation control principle is to achieve the voltage regulation and stabilization functions by controlling the magnitude of the excitation current of the excitation winding. Generally speaking, the larger the excitation current, the greater the power that the generator can output. Therefore, when the load changes, in order to maintain the voltage stability of the generator, the excitation current also needs to be adjusted accordingly.

[0003] In an industrial automatic control system, incremental PID is a commonly used control method. This algorithm has a small computational load and high stability. In a generator excitation system, the output voltage of the generator is used as the feedback and set value, and the magnitude of the voltage input to the generator excitation winding is controlled by means of DC chopping, thus realizing the automatic control of the generator voltage. In this system, when using DC chopping to control the output voltage, the duty cycle of the chopping is adjusted using incremental PID. Specifically in terms of the hardware circuit and software control, the magnitude of the duty cycle is actually the magnitude of the output unit value output from the digital processing chip to the switching tube.

[0004] However, due to the inherent hysteresis of the hardware, and incremental PID only relates to the most recent three sampling errors, this results in the disadvantage that the algorithm has untimely regulation when the load changes greatly. Excessive voltage mutations may affect the normal operation of the system, and in severe cases, it may damage the electrical equipment. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention discloses an incremental PID lead compensation excitation control method and system.

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

[0007] An incremental PID lead compensation excitation control method includes the following steps:

[0008] Calculate the effective value u of the voltage output by the generator at the k-th sampling point k And read the voltage preset value r k , and read the effective value u of the voltage at the sampling point before a predetermined time from the k-th sampling point kx ; k is a natural number; the predetermined time is 1 / 4T to 1 / 2T, and T is a generator output voltage period;

[0009] Calculate the compensation voltage deviation E kx =u kx -u k ;

[0010] The basic output increment unit of the PID controller is M0; at the (k + 1)-th sampling point, the actual output increment unit M of the PID controller is M = M0 + N; compare the compensation voltage deviation E kx and the preset value r of the generator terminal voltage at the k-th sampling point k , when |E kx | ≥ r k *t, the compensation unit N is a non-zero value; when |E kx | < r k *t, the compensation unit N = 0; t is the percentage of the maximum voltage change value to the target value of the generator output voltage;

[0011] Let k = k + 1, and return to the initial step.

[0012] A further technical solution thereof is: before calculating the compensation voltage deviation E kx at the k-th sampling point, the effective voltage values of the sampling points within a predetermined time period closest to the k-th sampling point are continuously recorded at least.

[0013] A further technical solution thereof is: before the compensation voltage deviation E kx is not calculated, the compensation unit N is always 0.

[0014] A further technical solution thereof is: the maximum voltage change value is 5 - 15V.

[0015] A further technical solution thereof is: when |E kx | ≥ r k *t, let D x ≤ N < 1.5*D x , the sign of N is the same as that of E kx ; D x is the PID output unit representing the actual duty cycle when the generator is fully loaded.

[0016] A further technical solution thereof is: the output signal of the PID controller controls the magnitude of the excitation current by controlling the duty cycle of the switching tube in the excitation circuit; the switching tube controls the conduction and cut-off of the excitation current in the excitation circuit.

[0017] A further technical solution thereof is: use the current voltage deviation E k as the feedback value of the PID controller at the k-th sampling point; the current voltage deviation E k = r k - u k .

[0018] A further technical solution thereof is: the basic output increment unit M0 is:

[0019] M0 = Kp*(E k - E k-1 ) + Ki*Ek +Kd*(E k -2E k-1 +E k-2 )

[0020] Among them, Kp is the proportional gain coefficient of the PID controller; Ki is the integral coefficient of the PID controller; Kd is the differential coefficient in the PID controller; E k =r k -u k ,E k is the current voltage deviation at the kth sampling point, E k-1 is the current voltage deviation at the (k - 1)th sampling point, E k-2 is the current voltage deviation at the (k - 2)th sampling point.

[0021] An incremental PID lead compensation excitation control system for operating the incremental PID lead compensation excitation control algorithm as described in any one of the above, includes:

[0022] A voltage sampling module for collecting the voltage signal output by the generator;

[0023] A PID control module that receives the output signal of the voltage sampling module as a feedback signal and calculates and outputs a control signal through the control algorithm;

[0024] A power module including a switching tube; the power module receives the control signal, changes the duty cycle of the switching tube, and controls the magnitude of the excitation current;

[0025] An exciter that adjusts the output voltage of the synchronous generator according to the excitation current.

[0026] The beneficial effects of the embodiments of the present invention are as follows:

[0027] Based on the incremental PID algorithm, the embodiments of the present invention introduce an output incremental unit compensation amount, which introduces the influence of system hysteresis into the algorithm, greatly improving the response speed of the system. Especially when the load changes greatly, this compensation amount ensures that the voltage change amplitude is much smaller than the effect that can be achieved by separate PID regulation. It solves the problem that general incremental PID controllers are not timely in regulation and the voltage change amplitude is too large when the load suddenly increases or decreases. Description of the Drawings

[0028] Figure 1 is the flowchart of the incremental PID lead compensation excitation control method of the embodiments of the present invention.

[0029] Figure 2 is the control block diagram of the incremental PID lead compensation excitation control method of the embodiments of the present invention.

[0030] Figure 3Schematic diagram of the transfer function of the basic PID model.

[0031] Figure 4 Schematic diagram of the incremental PID lead compensation excitation control system according to an embodiment of the present invention.

[0032] Figure 5 Another schematic diagram of the incremental PID lead compensation excitation control system according to an embodiment of the present invention. Detailed implementation manners

[0033] The following will describe the detailed implementation manners of the present invention with reference to the accompanying drawings.

[0034] Embodiment 1

[0035] This embodiment discloses an incremental PID lead compensation excitation control method. Figure 1 As shown in the flowchart of the incremental PID lead compensation excitation control method according to an embodiment of the present invention, Figure 1 it includes the following steps:

[0036] Taking the k-th sampling point as the basic sampling point, calculating the effective value u of the voltage output by the generator at the k-th sampling point k , reading the preset value r of the terminal voltage of the generator at the k-th sampling point k , and reading the effective value u of the voltage output by the generator at the sampling point a predetermined time before the k-th sampling point kx . k is a natural number. The predetermined time is 1 / 4T to 1 / 2T, and T is a cycle of the generator output voltage.

[0037] Calculating the compensation voltage deviation E kx , E kx = u kx - u k .

[0038] At the (k + 1)-th sampling point, the actual output increment unit M of the PID controller is M0 + N, where M0 is the basic output increment unit of the PID controller. Comparing the compensation voltage deviation E kx and the voltage preset value r k , when |E kx | ≥ r k * t, the compensation unit N is a non-zero value; when |E kx | < r k * t, the compensation unit N = 0. t is the percentage of the maximum voltage change value to the target value of the generator output voltage.

[0039] In this embodiment, the target value of the generator output voltage is 400V, the sampling frequency is 20K, and the alternating current frequency is 50HZ. Then, the number of voltage sampling points within one period is 400 points. When the load suddenly increases and decreases at a 0.4 power factor and 60% rated current load according to the national standard requirements, the preferred predetermined time is 1 / 4T. At this time, within 1 / 4T, there are 100 corresponding sampling points, and the effective voltage u k is compared with the effective voltage u kx 100 sampling points before to calculate and compensate for the voltage deviation E kx .

[0040] In this embodiment, the maximum voltage change value is preferably 5 - 15V. Then, when the target value of the generator output voltage is 400V, 0.0125 ≤ t ≤ 0.0375. Further, in this embodiment, the maximum voltage change value is preferably 8V, and at this time, t = 0.02. The maximum voltage change value is the condition for triggering compensation.

[0041] When the maximum voltage change value increases or the predetermined time increases, it means that compensation is triggered when the voltage changes more. When the voltage change value is too large, the system may respond slowly, and when the voltage change value is too small, it may be mis-triggered. During actual experiments, when the predetermined time is 1 / 4T - 1 / 2T and the maximum voltage change value is 5 - 15V, a better compensation effect can be achieved. It is also necessary to select a better value according to the specific experimental environment.

[0042] Further, when |E kx | ≥ r k *t, let the compensation unit D x ≤ N < 1.5*D x , the sign of N is the same as that of E kx , and D x is determined by the output unit when the generator is fully loaded, and the output unit representing the actual duty cycle at full load is taken. If D x is too large, it means that the situation of sudden increase and decrease of a larger load (such as 100% rated power load) can also be satisfied. At this time, when a smaller load change also triggers this compensation, it may cause a certain amount of over-compensation. In this embodiment, the preferred compensation unit N = D x .

[0043] Make k = k + 1, return to the initial step, and perform sampling and calculation for the next sampling point.

[0044] Further, at the kth sampling point, calculate the current voltage deviation E k , E k = r k - u k , and use the current voltage deviation E k as the feedback value of the PID controller. That is, the effective voltage u sampled and calculated at the Kth sampling pointk , on the one hand, it is used to calculate the basic output increment unit M0, and on the other hand, it is compared with the effective voltage value u before a predetermined time period with a length of 1 / 4T to 1 / 2T kx to obtain the voltage change before and after the sampling point in the predetermined time period, that is, the compensation voltage deviation E kx .

[0045] In this embodiment, the compensation voltage deviation E kx is compared with the voltage preset value r k . When the compensation voltage deviation E kx is greater than or equal to the voltage preset value r k *t, the basic output increment unit M0 output by the PID controller is added with the compensation unit N. At this time, the compensation unit N is a non-zero value. When the compensation voltage deviation E kx is less than the voltage preset value r k *t, the compensation unit n is set to 0. Then the actual output increment unit M at the next sampling moment after adding the compensation unit N is equal to the sum of the basic output increment unit M0 and the compensation unit N, and the actual output increment unit M is output to the excitation system to make the current voltage effective value u of the generator output voltage k tend to the voltage preset value r k .

[0046] The incremental PID lead compensation excitation control method in this embodiment is an improvement and optimization of the incremental PID controller. It combines the characteristics of high stability and small calculation amount of the incremental PID, and introduces the change rate of the feedback quantity within a period of time as the control quantity, solving the problem that the general incremental PID controller fails to adjust in time and the voltage change amplitude is too large when the load suddenly increases or decreases.

[0047] Further, before calculating the compensation voltage deviation E at the kth sampling point kx , at least the effective voltage values of the sampling points in the predetermined time period closest to the kth sampling point are continuously recorded. Before the compensation voltage deviation E kx is not calculated, the compensation unit N is always 0.

[0048] Further, the control signal of the PID controller controls the magnitude of the excitation current by controlling the duty cycle of the switching tube. The switching tube controls the conduction and cut-off of the excitation current in the excitation circuit. Figure 2 is the control block diagram of the incremental PID lead compensation excitation control method of the embodiment of the present invention. As Figure 2As shown, the switching tube plays a role in controlling the on / off of the current in the excitation circuit. When the switching tube is turned on, a path is formed between the power supply and the excitation winding, allowing current to pass through the excitation winding. When the switching tube is turned off, the path is disconnected and current cannot pass through. By controlling the duty cycle of the switching tube, the magnitude of the excitation current in the excitation winding can be controlled, thereby controlling the output voltage of the generator.

[0049] Furthermore, the relationship between the basic output increment unit M0 and the current voltage deviation E k is as follows:

[0050] M0 = Kp * (E k - E k-1 ) + Ki * E k + Kd * (E k - 2E k-1 + E k-2 )

[0051] where Kp is the proportional gain coefficient of the PID controller, Ki is the integral coefficient of the PID controller, Kd is the differential coefficient in the PID controller, E k-1 is the voltage deviation at the (k - 1)th sampling point, and E k-2 is the voltage deviation at the (k - 2)th sampling point. Figure 3 is a schematic diagram of the transfer function of the basic PID model. Combining Figure 3 can help understand the above relationship.

[0052] Based on the traditional incremental PID controller, this embodiment introduces the voltage change amount of the generator before and after a predetermined time of 1 / 4T to 1 / 2T as the trigger condition for incremental unit compensation, and determines the PID compensation incremental unit in combination with the laws of the excitation system, forming an improved incremental PID algorithm for the generator excitation system.

[0053] Embodiment 2

[0054] This embodiment discloses an incremental PID lead compensation excitation control system for implementing the incremental PID lead compensation excitation control algorithm in Embodiment 1. Figure 4 This is a schematic diagram of the incremental PID lead compensation excitation control system according to an embodiment of the present invention. As Figure 4 shown, the system includes a voltage sampling module, a PID control module, a power module, and an exciter.

[0055] The voltage sampling module is used to collect the voltage signal output by the synchronous generator and, after calculation and processing, serve as the feedback signal for the PID control module. The PID control module receives the output signal of the voltage sampling module as the feedback signal and outputs a control signal. The power module receives the control signal of the PID control module and outputs an adjustable voltage to control the excitation current. The exciter adjusts the output voltage of the synchronous generator according to the excitation current.

[0056] Embodiment 3

[0057] Figure 5 This is another schematic diagram of the incremental PID lead compensation excitation control system according to the embodiment of the present invention. Figure 5 A more detailed implementation is shown. As Figure 5 shown, the system further includes a current sampling circuit. The voltage sampling circuit can sample the voltage from the machine terminal or the network terminal. The parameters and operating status in the central processor DSP can be set through the host computer and other interaction modules. The central processor DSP conducts interactions through the communication module. The central processor DSP also includes an ADC module, which converts the sampled analog signal into a digital signal for processing, and outputs a control signal through the control signal output module to control the duty cycle of the switching tube, and finally controls the voltage of the synchronous generator by controlling the Tongzhou rotating exciter. Combining Figures 1 to 5 , and based on Embodiment 1 and Embodiment 2, Embodiment 3 will use a more specific usage scenario to illustrate the incremental PID lead compensation excitation control system and the control method.

[0058] In Figure 5 , the voltage sampling circuit samples the output voltage of the synchronous generator to the central processor DSP. The central processor is the DSP, which is used to implement the function of processing the voltage analog signal into a digital signal, the function of implementing incremental PID control, and the function of compensating unit determination and calculation.

[0059] In this embodiment, the sampling frequency of the central processor DSP is 20K, then the number of sampling points per cycle when sampling the standard power frequency voltage is 400. The predetermined time is 1 / 4T. At this time, there are 100 sampling points corresponding to the 1 / 4T time, and the maximum voltage change value is preferably 8V. At this time, t = 0.02. When the compensation unit N is a non-zero value, N = D x . The central processor DSP uses a 32-bit timer to implement PWM (pulse width modulation) output. The timer clock is 240M, and the set switching frequency is 300HZ. Then the total output unit D is:

[0060]

[0061] The system hardware circuit is set to be high-level effective, that is, the larger the output unit, the larger the duty cycle, the larger the excitation current, and the larger the output power of the generator. For example, when the duty cycle of the timer output is 25% waveform, the actual output unit is 800000 * 25% = 200000 units.

[0062] Specifically in this embodiment, without introducing the incremental unit compensation algorithm, after reasonably adjusting the parameters of Kp, Ki, and Kd, the steady-state fluctuation of the generator is about 0.1%. When switching from full load to no load instantaneously, the voltage overshoot is more than 30%, and when switching from no load to full load instantaneously, the voltage drop is more than 30%. In both cases, it takes about 2 s to adjust and recover to the preset voltage. By adjusting the parameters of Kp, Ki, and Kd, the performance of the generator during sudden load increase and sudden load removal cannot be further improved. At this time, the Kp, Ki, and Kd set in the incremental PID algorithm are already in the optimal state.

[0063] In such a case, the incremental PID lead compensation excitation control method of this embodiment is introduced. For the convenience of explanation, the special processing description of shielding the incremental compensation algorithm during the start-up of the synchronous generator is omitted, and the processing descriptions such as output unit limiting in the algorithm are omitted.

[0064] Write the voltage preset value r to the central processor DSP through the communication terminal k It is 400 V. At this time, a certain sampling point k under the no-load steady-state condition is taken as the reference sampling point. The actual output unit under the current no-load condition is 8000. The central processor DSP has recorded the effective values of the nearest 100 sampling points and has recorded the output unit D x = 30000.

[0065] At the reference sampling point k, the effective voltage value u after sampling and processing calculation k is 399.8 V. The effective voltage value u of the sampling point 1 / 4T before the reference sampling point kx is 400.5 V. At this moment, the compensation voltage deviation E kx is:

[0066] |E kx | = 400.5 - 399.8 = 0.7 V < r k *0.02 = 8 V

[0067] Then the compensation unit N is 0 at this time.

[0068] When 20% of the full power of the generator is put into the load, the voltage drop before and after 1 / 4T still does not exceed 8 V, so the non-zero condition of the compensation unit N will not be triggered either.

[0069] When the load is connected to the generator at full power, starting from the moment the load is connected until after the 1 / 4T sampling point, under the action of the incremental PID, the basic output increment unit M0 rapidly increases from 0 in the steady state to more than 10,000, and the output unit also rapidly rises from 8,000 under the original no-load condition to 20,000, and this value is expected to continue to rise. However, due to the existence of various objective factors causing control lag mentioned above, there is still a large voltage drop and drop rate in the output voltage of the generator. Since the central processing unit DSP detects that the voltage change has exceeded 8V at this moment, it immediately makes N = D x = 30,000 units, then the actual output increment unit at the current sampling point is:

[0070] M0 + N = 20,000 + 30,000 = 50,000

[0071] In fact, this output unit has far exceeded the output unit at full-load steady state. That is, starting from the current moment, the control system begins to perform lead compensation, which greatly curbs the voltage drop rate. After compensating 12 more sampling points, the voltage begins to change from decreasing to increasing. At this time, the central processing unit DSP detects that compared with the effective voltage value recorded before the current 1 / 4T sampling point, the voltage change is less than 8V. So it makes the compensation unit N be 0, that is, starting from the current sampling point, the output unit no longer performs compensation. At this time, the output unit is the basic output increment unit M0 = 40,000 calculated by the incremental PID. The subsequent voltage adjustment is taken over by the incremental PID algorithm. After about 200 more sampling points, the effective value of the generator output voltage stabilizes at 400V. At this time, the system returns to the stable state, the output increment unit fluctuates around 0, and the output unit also fluctuates around 30,000.

[0072] When the load is disconnected from the generator at full power, it is basically the same as the previous process. First, the incremental PID intervenes in the processing. After 1 / 4T sampling points, the increment unit changes from 0 to -10,000, and the output unit rapidly drops from 30,000 at the steady state moment to 20,000. However, there is still a large overvoltage situation in the voltage. At this time, the central processing unit DSP detects that the compensation voltage deviation |E kx | has been greater than 8V. Therefore, starting from this moment, the compensation unit N = -20,000 is added. In fact, starting from this moment, under the intervention of the lead compensation algorithm, the actual output unit has become 0, that is, the switching tubes of the power module will be in a fully off state in the next few cycles, which achieves the maximum voltage callback speed. After compensating about 10 sampling points, the voltage has begun to drop. At this time, the compensation unit makes N be 0, and the incremental PID takes over the next control until the steady state is restored.

[0073] Compared with the simple incremental PID algorithm, after adding the compensation algorithm, the above two examples of sudden increase and sudden unloading under full load can reduce the voltage transient change rate by more than 50% through testing, that is, the voltage drop and voltage overshoot amplitude can be reduced by more than half, and the recovery time can be shortened from the original 2s to within 1s.

[0074] In the above examples, only the situation of sudden increase and sudden unloading under full load is described. In fact, when the load change exceeds 80% of the total power of the generator, the incremental compensation will be triggered. This situation does not require additional adjustment and can be directly applied to the judgment and assignment principle of the incremental compensation value N during sudden increase and sudden unloading under full load.

[0075] The above description is an explanation of the present invention, not a limitation of the invention. The scope defined by the present invention can be seen in the claims. Without violating the basic structure of the present invention, the present invention can be modified in any form.

Claims

1. An incremental PID lead compensation excitation control method, characterized in that, It includes the following steps: Calculate the effective value u of the voltage output by the generator at the k-th sampling point k And read the preset voltage value r k , read the effective value u of the voltage at the sampling point a predetermined time before the k-th sampling point kx ; k is a natural number; the predetermined time is 1 / 4T to 1 / 2T, where T is a cycle of the voltage output by the generator; Calculate the compensation voltage deviation E kx = u kx - u k ; The basic output increment unit of the PID controller is M0; at the (k + 1)-th sampling point, the actual output increment unit M of the PID controller is M = M0 + N; Compare the compensation voltage deviation E kx with the preset value r of the generator terminal voltage at the k-th sampling point k , when |E kx | ≥ r k *t, the compensation unit N is a non-zero value; when |E kx | < r k *t, the compensation unit N = 0; t is the percentage of the maximum voltage change value to the target value of the generator output voltage; Let k = k + 1, and return to the initial step.

2. The incremental PID lead compensation excitation control method according to claim 1, wherein Before calculating the compensation voltage deviation E at the k-th sampling point kx it is necessary to record at least continuously the effective voltage values of the sampling points within a predetermined time period closest to the k-th sampling point.

3. The incremental PID lead compensation excitation control method according to claim 1, characterized in that Before calculating the compensation voltage deviation E kx the compensation unit N is constantly 0.

4. The incremental PID lead compensation excitation control method according to claim 1, characterized in that The maximum voltage change value is 5 - 15V.

5. The incremental PID lead compensation excitation control method according to claim 1, characterized in that When |E kx | ≥ r k *t, let D x ≤ N < 1.5 * D x , the sign of N is the same as that of E kx ; D x is the PID output unit representing the actual duty cycle when the generator is fully loaded.

6. The incremental PID lead compensation excitation control method according to claim 1, characterized in that The output signal of the PID controller controls the magnitude of the excitation current by controlling the duty cycle of the switching tube in the excitation circuit; the switching tube controls the conduction and cutoff of the excitation current in the excitation circuit.

7. The incremental PID lead compensation excitation control method according to claim 1, wherein Using the current voltage deviation E k as the feedback value of the PID controller at the k-th sampling point; the current voltage deviation E k = r k - u k .

8. The incremental PID lead compensation excitation control method according to claim 1, characterized in that The basic output increment unit M0 is: M0 = Kp * (E k - E k-1 ) + Ki * E k + Kd * (E k - 2E k-1 + E k-2 ) Among them, Kp is the proportional gain coefficient of the PID controller; Ki is the integral coefficient of the PID controller; Kd is the differential coefficient in the PID controller; E k = r k - u k , E k is the current voltage deviation at the k-th sampling point, E k-1 is the current voltage deviation at the (k - 1)-th sampling point, E k-2 is the current voltage deviation at the (k - 2)-th sampling point.

9. An incremental PID lead compensation excitation control system, characterized in that, For running the incremental PID lead compensation excitation control algorithm according to any one of claims 1 - 8, it includes: A voltage sampling module for collecting the voltage signal output by the generator; A PID control module that receives the output signal of the voltage sampling module as a feedback signal and calculates and outputs a control signal through the control algorithm; A power module including a switching tube; the power module receives the control signal, changes the duty cycle of the switching tube, and controls the magnitude of the excitation current; An exciter that adjusts the output voltage of the synchronous generator according to the excitation current.

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