WO2010032954A2

WO2010032954A2 - Generator control system using peak voltage

Info

Publication number: WO2010032954A2
Application number: PCT/KR2009/005262
Authority: WO
Inventors: 안진우; 이동희; 김태형; 김태옥
Original assignee: 경성대학교 산학협력단
Priority date: 2008-09-19
Filing date: 2009-09-16
Publication date: 2010-03-25
Also published as: WO2010032954A9; WO2010032954A3; KR100993109B1; KR20100032976A

Abstract

The generator control system using the peak voltage of the generator of the present invention comprises: a peak voltage detection unit for detecting the peak value of a generator voltage; a comparator for comparing the peak voltage with a preset value; and a control unit for adjusting the control gain when the detected peak voltage is smaller than a lower threshold value, and for maintaining the voltage of the generator in its current state when the detected peak voltage is above an upper threshold value. The present invention can provide a fast voltage response to sudden load changes.

Description

Generator control system using peak voltage

The present invention relates to a generator control system using a peak voltage and a method thereof, and more particularly, to improve the responsiveness of the generator voltage control according to the delay detection of the rms voltage of the generator, PID controller and peak voltage detector And it relates to a generator control system and method using a peak voltage having a fast voltage response according to a sudden load change by applying a control gain converter.

Engine generators are widely used for marine power generation and emergency generators. In recent years, a self-powered generation system using engine generators has been applied in remote islands where infinite bus connections are difficult to connect, and in the case of foreign countries, the application of engine generator operation systems is largely applied in mountainous areas where power is not supplied to large land plant power generation facilities. It is increasing.

Diesel-engine generators are widely used as power supplies in areas where electricity is difficult to supply from onshore power generation and distribution systems. In the case of ships, in particular, the supply of power is entirely supplied from the engine generator. In this case, high quality power is required for power supply of various control equipment, communication equipment, and navigation equipment.

The control characteristics of the engine generator operating system are determined by the Governor for controlling the engine and the AVR controlling the generator voltage. Therefore, the engine generator operating system, unlike the infinite bus system, the output voltage is severely variable according to the load, there is a problem that the frequency fluctuation occurs. This instability of power can cause malfunction of the electrical device. In particular, in the case of a single operation system that can not be connected to the infinite bus, such as in the case of ships, the engine generator must supply the full power of the system in a stable manner and must have a stable response characteristics against sudden changes in load.

Recently, AVR for voltage control of a generator is applying a PWM control structure using a microprocessor in an analog control method using an SCR. This is because the digital controller is easy to apply to various generators and is suitable for complex system control such as droop control and parallel control. The digital AVR controller is generally applied to a PID controller that is well known in the industry. This is because it can be applied to various generators according to the control gain setting, and it is a method that is widely used by users. However, the conventional PID generation control system has the following problems.

In the conventional generator voltage control system, the generator output voltage inputs an effective voltage (r.m.s. voltage). The detection signal has a time delay with respect to the actual generator instantaneous voltage output. Due to such a time delay problem, it is difficult to largely set the control gain of the AVR controller. If the control gain is set large, the response can be improved, but it may be a problem in stability. In particular, when control is difficult due to time delay, such as the generator control system of the present invention, if the control gain is set large, the error may increase, rather it is difficult to set large. On the contrary, if the control gain is set small, the response is poor. In addition, the response characteristics of the actual generator has a problem that has a low response to the sudden change of the load.

This is due to the instantaneous r.m.s. The detection is easy, but in the engine-generator system, the frequency of the generator varies structurally depending on the load, and it is difficult to attach a separate device for instantaneous frequency detection. Therefore, the voltage control responsiveness of the engine-generator control system is highly dependent on the selection of the control gain of the AVR and the time constant of the generator.

The present invention is to provide a generator control system using a peak voltage that can improve the problem of the response characteristics caused by the generator effective voltage (r.m.s. voltage) detection delay.

In addition, the present invention is to provide a generator control system using a peak voltage having a stable and fast response to rapid load changes.

The generator control system using the peak voltage of the generator according to the present invention includes a peak voltage detector for detecting a peak value of the generator voltage, a comparator for comparing the peak voltage with a set value, and when the detected peak voltage is smaller than a predetermined lower limit value. And a control unit for adjusting the control gain and maintaining the voltage of the generator in a current state when the detected peak voltage is greater than a preset upper limit value.

The peak voltage detection unit preferably detects the peak value of the generated voltage according to the frequency of the generator.

Preferably, the peak voltage detector is operated by noise and a fixed resistor (R) and capacitor (C).

The comparator preferably includes a first comparator comparing the peak voltage and the lower limit and a second comparator comparing the peak voltage and the upper limit.

When the undershoot occurs because the peak voltage is lower than the lower limit, the control gain conversion unit increases the control gain, and when the undershoot occurs, the control current command of the exciter by the increased control gain is selected. It is preferable to include a switch part which selects the control current command of a predetermined exciter when the overshoot generate | occur | produces higher than a value.

It further comprises a PID control unit for performing PID control by the effective voltage (r.m.s. voltage) of the generator, the control gain is preferably adjusted Kp, Ki, Kd PID control unit.

When an overshoot occurs, it is preferable that the control current command of the predetermined exciter is zero so as to keep the voltage of the generator in the current state.

It is preferable that the lower limit is 95% of the control command () of the exciter and the upper limit is 105% of the control command () of the exciter.

The generator control method using the peak voltage according to the present invention detects the peak value of the generator voltage, comparing the peak voltage with the lower limit value and the upper limit value, and if the detected peak voltage is less than the lower limit value, the control gain is adjusted. If the detected peak voltage is greater than the upper limit, it is preferable to include maintaining the voltage of the generator in a current state.

If undershoot occurs because the peak voltage is lower than the lower limit, select the control current command of the exciter by increased control gain.If the overshoot occurs because the peak voltage is higher than the upper limit, control the predetermined exciter. It is preferable to select the current command.

When an overshoot occurs, it is preferable to select a control current command of a predetermined exciter as zero (0) so as to maintain the voltage of the generator in the current state.

According to the present invention, by applying the peak voltage detector and the control gain converter, it is possible to improve the responsiveness of the generator voltage control according to the r.m.s. voltage detection delay and to provide a fast response characteristic against a sudden load change.

In addition, the present invention applies a switch control method for detecting a peak voltage for a sudden change in the load, varying the control gain of the controller according to the detected signal, and to prevent overshoot. Therefore, the present invention can provide a stable and fast response characteristics compared to the conventional PID control method. This is because the peak voltage detection unit detects the signal instantaneously and controls the voltage using the stable r.m.s. voltage detection unit signal.

The effect of the method according to the present invention was verified through a real load test on the actual 200kW diesel engine generator for ships.

1 is a view showing a voltage control structure of a diesel-engine generator,

2 is a block diagram of a control system of the diesel engine generator of FIG. 1;

3 is a block diagram of a generator control system to which a PID controller is applied;

4 is a diagram showing characteristics of proportional control;

5 is a diagram showing characteristics of the PI control;

6 is a diagram showing characteristics of PID control;

7 is a diagram illustrating a difference in characteristics by PID parameters;

8 is a block diagram of a generator control system using a peak voltage according to the present invention;

9 illustrates an example of an operation according to the present invention;

10 is a block diagram of a marine generator system to which the present invention is applied;

11 is a view showing an example of a control system circuit according to the present invention;

12 is a view showing an experimental environment of a control system according to the present invention, FIGS. 13 and 14 are diagrams respectively showing response characteristics of a general PID controller and a control system according to the present invention;

15 and 16 are diagrams each showing an example of a response characteristic to an inductance load; and

17 is a flowchart of a control method according to the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a diagram illustrating a voltage control structure of a diesel engine generator.

In the case of a general engine-generator, a brushless generator having an exciter is widely used due to performance and reliability problems. Referring to FIG. 1, the brushless generator uses a method of supplying the generator voltage of the exciter by the field current of the exciter to the field of the main generator again through the semiconductor rectifying diode inside the generator. Therefore, the brushless generator is more reliable and easier to maintain than the method of directly supplying the field through the brush.

Referring to the voltage control structure of the diesel engine generator of Figure 1, both the exciter and the main generator is mounted inside the generator. The diesel engine generator controls the field current of the exciter by detecting the voltage and current of the generator from a PT (Current Transformer) and a CT (Current Transducer) connected to a three-phase output line outside the generator.

The power management system (PMS) controls the power of the generator control system. These PMSs typically supply the power of an automatic voltage regulator (AVR) to a transformer or external power source connected to the generator's output.

FIG. 2 is a block diagram of a control system of the diesel engine generator of FIG. 1.

Referring to FIG. 2, the AVR is modeled as a primary delay element having control gain and time delay. In addition, the exciter and generator can also be simplified by a delay factor due to the electric time constant.

In Figure 2 the output voltage of the generator can be expressed as follows.

Recently, AVR for voltage control of a generator is applying a PWM control structure using a microprocessor in an analog control method using an SCR. This is because the digital controller is easy to apply to various generators and is suitable for complex system control such as droop control and parallel control.

3 is a block diagram of a generator control system employing a PID controller.

Referring to FIG. 3, a PID controller is applied to a control of an AVR for controlling a generator. This is because it can be applied to various generators according to the control gain setting, and it is a method that is widely used by users.

PID control method is the most commonly used control method among control methods. In this case, PID is P: Proportinal, I: Integral, D: Differential, and it is possible to control flexibly with three combinations.

4 is a diagram illustrating the characteristics of proportional control.

Proportional control is a control method that gradually adjusts the manipulated value to a magnitude proportional to the difference between the command value (target value) and the current output value. In such proportional control, a subtle control can be applied when the command value is approached, so that the target value can be finely approached.

5 is a diagram showing characteristics of the PI control.

If only the proportional control is used, when the control amount approaches the target value, the manipulation amount becomes too small, and a state in which fine control cannot be further performed may occur. It remains stable in the state of the control amount very close to the target value and approaches the target value, but no matter how much time passes, the state does not completely match the control amount (residual deviation). Integral control is used to eliminate this residual deviation. Integral control is a method of accumulating a small residual deviation in time, and operating in such a way as to increase the manipulated value at a certain size to eliminate the deviation. Control in which the integral action is added to the proportional action may be referred to as "PI control (proportional-integral control)".

6 is a diagram showing the characteristics of PID control.

When using PI control, the control close to the actual target value can be perfected, but there is a problem that the response speed is slow. In PI control, it can be controlled to the target value, but a certain time (time constant) is required, and a large integer deteriorates the response performance in case of disturbance. There is a problem that can not react quickly to the disturbance, and immediately return to the original target value. It is equivalent to "differentiation" to look at the deviation for the sudden disturbance, and to see the difference in the deviation from the previous time by causing a large amount of manipulation to react quickly if the difference with the previous deviation is large. As shown in Fig. 6, the PID control is controlled as if to overshoot at first, and is actively controlled to quickly reach the target value.

7 is a diagram illustrating differences in characteristics caused by PID parameters.

In the PID control, overshoot is very noticeable when the parameter is large, so the derivative and integration effects are effective quickly. On the other hand, when the parameter is small, there is almost no overshoot.

Since the responsiveness of the PID controller is variable according to the control gain, an appropriate gain is calculated through tuning the control gain before the generator is shipped. The detection of generator output voltage in power generation control system is r.m.s. Enter the voltage, r.m.s. The detection signal has a time delay with respect to the actual generator instantaneous voltage output. Due to this problem of time delay, it is difficult to largely set the control gain of the AVR controller. In addition, the response characteristics of the actual generator has a low response to the sudden change of the load. In onshore power generation systems, instantaneous r.m.s. Although easy to detect, in an engine-generator system, the frequency of the generator varies structurally depending on the load, and it is difficult to attach a separate device for instantaneous frequency detection. The voltage control responsiveness of the engine-generator control system is thus very dependent on the choice of control gain of the AVR and the time constant of the generator.

8 is a block diagram of a generator control system using a peak voltage according to the present invention.

In the generator control system using the peak voltage according to the present invention, the peak voltage detection unit 420 for detecting the peak voltage of the generator, the peak voltage lower limit value and Comparator 500 to compare with the upper limit value, the control gain is adjusted if the detected peak voltage is less than the lower limit value, and the control unit for maintaining the voltage of the generator in the current state if the detected peak voltage is greater than the upper limit value ( 600).

The peak voltage detector 420 detects a peak value of the AC power generation voltage according to the frequency of the generator. The peak voltage detector 420 may detect the maximum magnitude of the generator voltage without delay with respect to the response of the generator. Since the peak voltage detector 420 operates by noise and fixed R and C, continuous control is possible, and a value smaller than the peak value is detected in the discharge portion. According to the present invention, it is possible to detect the voltage variation in each period by a method of continuously detecting the voltage of the peak voltage detector by using an AD converter and finding the maximum value among them by generator frequency detection.

The comparator 500 preferably compares the voltage detected by the peak voltage detector with a set value using two comparators. The first comparator 510 compares the detected peak voltage with a predetermined lower limit value VL_SET and outputs a / UVINT signal. The second comparator 520 compares the detected peak voltage with a preset upper limit value VH_SET and outputs a / OVINT signal. At this time, the lower limit value VL_SET and the upper limit value VH_SET are preferably set to 95% and 105% of the control command, respectively. Typical generator response should be less than 15% undershoot and 20% overshoot for 80% load. Therefore, it is desirable to determine the set value in consideration of noise and detection error of the peak voltage detector.

When the voltage detected by the peak voltage detector 420 is smaller than VL_SET or larger than VH_SET, it may be determined that a sudden load on the generator is changed.

If no overshoot or undershoot occurs, it is desirable to maintain the previous stabilized control gain (i.e., control gain when no overshoot or undershoot has occurred).

What is to be controlled in the system according to the invention is the output stage voltage of the generator. That is, the output terminal voltage of the generator is to be constantly output to the voltage desired by the user. Therefore, from the control point of view, the output voltage of the generator becomes the output to be controlled, and the output voltage desired by the user is input. In other words, an input is a command. Since the command is given in the form of a value, it is also called an input value command value. In the system according to the present invention, it is expressed as Vref because it is a command for the output voltage. In the case of a generator, it is difficult to handle this value because the output voltage is alternating instantaneously. Therefore, the concept of root mean square (RMS) is used, and Vrms is the output terminal effective voltage of the generator.

It is the purpose of control in the system according to the invention that the value of this Vrms is equal to Vref, and the method used for this is PID. The current error should be checked by comparing the output voltage value Vref desired by the user with the output value Vrms of the actual generator. Control the amount of errors that occur so that Vref and Vrms are equal. Using the error value, the current command value Ifd * is generated as much as it needs to be controlled through the PID controller, and switching is performed to satisfy this value.

9 is a diagram illustrating an example of an operation according to the present invention.

In case of controlling only the detected r.m.s. voltage, there is a problem that a time delay occurs when a load variation occurs. When the voltage decreases due to a sudden load on the generator, the RMS detector gradually changes due to the detection delay.

However, according to the present invention, the peak voltage detection section quickly detects the application of the load. The control gain converter 610 greatly increases the control gain by the detected / UVINT signal. It is desirable for the control gain to greatly increase the control gain of the AVR controller in the digital signal processing apparatus (DSP). At this time, it is preferable that the control gain is converted so as to operate robustly even for a small error. The conversion of the control gain is to adjust the Kp, Ki, Kd, the adjusted value is input to the PID control unit 620 that performs PID control to the effective voltage (r.m.s. voltage) of the generator.

On the contrary, when the load is abruptly removed and the voltage of the generator rises, the control current command of the exciter is drastically reduced by the / OVINT signal. The switch unit 630 preferably selects the control current command of the exciter as zero. In other words, if it is determined that the overshoot, it is processed as a value of 0 without using Ifd * (generator field current command value) generated by the PID controller 620. In this case, since the setpoint is 0, the operation of outputting the voltage of the generator afterwards is maintained. If the command is 0, there is no need to increase or decrease the output since the generator output = target value.

Particularly, the strong operation for overshoot is set because the characteristic of the exciter causes the voltage of the generator to rise due to the removal of the load while the excitation current is reduced to zero, and the overshoot can exceed 20%. Because there is.

10 is a block diagram of a marine generator system to which the present invention is applied.

Referring to Figure 10, the generator is driven by a diesel engine, the field of the generator is operated by the generation of the exciter. The AVR is operated by PWM control by IGBT driving to control the field current of the exciter. CCS is a current control system to control the field current of the exciter.

The voltage and current of the generator are detected by a PT (Potential Transformer) and a Current Transducer (CT) installed at the generator output. The voltage is detected by the U-W phase and the current detects the current in the V phase.

Droop controller is a controller to determine the characteristics of parallel operation according to the load phase.

Since the digital AVR must be started by a feedback loop by the generator's residual voltage, the self-starter circuit determines the generator's operation while establishing the control power of the AVR.

11 is a view showing an example of a control system circuit according to the present invention.

In order to verify the validity of the control system according to the present invention, an experiment was performed on a three-phase 380V, 200kW diesel generator. The generator according to the present invention is designed as an emergency generator for small and medium-sized ships, the excitation field resistance of the generator is 16.5 [Ω], and the maximum output voltage is set to 45 [V].

12 is a diagram illustrating an experimental environment of a control system according to the present invention.

The experiment of the generator according to the invention was carried out on the rated resistance load and the inductance load. The main controller of the digital AVR is Texas Instruments' TMS320F2811-100, and the generator and bus voltage and current are designed to detect using Analog Device's AD637 and a second-order Sallen Key filter. The peak voltage detector is instantaneously detected using a precision rectifier circuit and a high-speed AD converter built into the DSP. The peak voltage detector is programmed to find the maximum of the AD-converted values in synchronization with the voltage-frequency detector connected to the DSP's CAP. The maximum current of the excitation field is designed to be 15A and consisted of IXYS's FID60-060D (600V, 65A).

The self-driving circuit of the AVR controller is composed of an initial starting current control method using a transistor, and is configured in parallel circuit so as to operate stably against the quiescent starting and the full voltage starting in parallel operation. The communication between controller and monitoring device uses CAN and RS-232. The voltage detection was possible to detect 110/220/380 / 450V without changing the hardware through the analog switch. The CBS (Current Boosting System) is composed of an SCR module and a voltage controller.

13 and 14 illustrate response characteristics of a general PID controller and a control system according to the present invention, respectively.

13 and 14 show the response characteristics of the PID controller and the control structure according to the present invention, respectively, in the state of 100% load application and load removal. Also the field current of the exciter, r.m.s. The waveforms of the detected voltage, generator output terminal voltage and load current are shown.

As shown in FIG. 13, it can be seen that in the general PID controller, undershoot and overshoot vary more than 90% and 110% of the set voltage indicated by dotted lines in the state of applying and removing the load. In particular, overshoot is increasing by about 24%.

As shown in Fig. 14, undershoot and overshoot are greatly reduced in the control system according to the present invention. In addition, it can be seen that the control structure according to the present invention has a faster response than the PID controller with respect to the change in the control gain. In the control structure according to the present invention, it can be seen that undershoot is within 11% and overshoot is within 12%.

15 and 16 are diagrams each showing an example of a response characteristic to an inductance load.

Referring to FIG. 15, it can be seen that the control system according to the present invention also exhibits stable voltage control characteristics for the application and removal of the inductance load. In addition, referring to FIG. 16, it can be seen that the voltage of the generator for the Droop 10% setting is also stably controlled according to the magnitude and power factor of the load current.

17 is a flowchart of a control method according to the present invention.

The peak voltage detector detects a peak value of the generator voltage (S1100).

The comparator compares the peak voltage with a lower limit and an upper limit (S1200).

If the detected peak voltage is smaller than the lower limit value, the control gain is adjusted (S1300 and S1350). When undershoot occurs because the peak voltage is smaller than the lower limit, the switch section selects the control current command of the exciter by the increased control gain.

If the detected peak voltage is higher than the upper limit value, the generator voltage is kept at the present state (S1400 and S1450). If the peak voltage is higher than the upper limit value and an overshoot occurs, the switch unit resets the control current command of the exciter to zero. Select with.

In the control method according to the present invention, a sudden change in load is detected by a designed peak voltage detector, a control gain of the controller is changed according to the detected signal, and a switch control method is applied to prevent overshoot. The digital AVR controller according to the present invention showed improved response characteristics compared to the PID control method of the same controller in a real load test of a 200kW generator for ships. In addition, the initial magnetic dynamic and full load fluctuations, droop characteristic test, and V / Hz characteristic test showed stable response characteristics.

Claims

A peak voltage detector detecting a peak value of the generator voltage;

A comparator for comparing the peak voltage with a set value; And

A control unit for adjusting the control gain when the detected peak voltage is smaller than a predetermined lower limit value, and maintaining the voltage of the generator in a current state when the detected peak voltage is larger than a predetermined upper limit value. Generator control system using peak voltage.
The method of claim 1,

The peak voltage detector

Generator control system using peak voltage to detect peak value of power generation voltage according to generator frequency.
The method of claim 1,

The peak voltage detection unit using a peak voltage operated by noise and a fixed resistor (R) and a capacitor (C).
The method of claim 1,

The comparator

A first comparator for comparing the peak voltage with the lower limit value; And

And a second comparator for comparing the peak voltage with the upper limit value.
The method of claim 1,

The control unit

A control gain converter for increasing control gain if the peak voltage is less than the lower limit and an undershoot occurs; And

When the undershoot occurs, the control current command of the exciter by the increased control gain is selected. When the overshoot occurs because the peak voltage is higher than the upper limit, the control current command of the predetermined exciter is selected. Generator control system using the peak voltage of the generator comprising a switch unit.
The method of claim 1,

And a PID controller for performing PID control with an effective voltage (r.m.s. voltage) of the generator.

The control gain generator control system using the peak voltage of the generator for adjusting the Kp, Ki, Kd PID control unit.
The method of claim 1,

The generator control system using the peak voltage of the generator of which the control current command of the predetermined exciter is zero (0) to maintain the voltage of the generator in the current state when the overshoot occurs.
The method of claim 5,

The lower limit is the control command of the exciter (
95% of), the upper limit value is the control command (
Generator control system using peak voltage of generator which is 105% of
Detecting a peak value of the generator voltage;

Comparing the peak voltage with a lower limit and an upper limit; And

If the detected peak voltage is less than the lower limit value, the control gain is adjusted, and if the detected peak voltage is greater than the upper limit value, maintaining the voltage of the generator in the current state; a generator using the peak voltage Control method.
The method of claim 9,

When the undershoot occurs because the peak voltage is smaller than the lower limit value, the control current command of the exciter is selected by the increased control gain. When the overshoot occurs because the peak voltage is higher than the upper limit value, the predetermined current is selected. Generator control method using peak voltage to select control current command of exciter.
The method of claim 10,

And a peak voltage for selecting a control current command of the predetermined exciter to zero to maintain the voltage of the generator in a current state when the overshoot occurs.