JP3524718B2 - Converter control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a control device for a converter for converting an alternating current supplied to an alternating current power supply into a direct current. The prediction device. 2. Description of the Related Art FIG. 3 is a diagram showing a converter circuit configuration for explaining a conventional principle of predicting an AC amount. In FIG. 3, reference numeral 11 denotes an AC power supply, 12 denotes an AC reactor, and 13 denotes a converter. It is a block showing the converter and DC circuit which comprise. L indicates the inductance value of the AC reactor. Vs is a power supply voltage, is is an alternating current,
Vc represents a control voltage generated by converter control. Focusing on the AC circuit, the circuit equation is expressed by equation (1). [0003] When the controller is implemented by a digital method, it is common to detect an AC amount at every fixed control period T and obtain a switching pattern based on the detected AC value. In principle, the switching pattern must start to be output at the same time as the AC amount detection time, but it becomes impossible to implement because of the computation time required by the CPU. To solve this problem, the AC amount is detected at the start point of the current control cycle [k], the AC value at the start point of the next control cycle [k + 1] is predicted by some method, and based on the predicted AC value, In general, a switching method of a next control cycle [k + 1] is obtained, and when the next control cycle is started, a control method of outputting the obtained switching pattern is generally adopted. In this case, it is clear that the accuracy of the predicted value of the AC amount largely depends on the performance of the entire system.
In the following description, the addition of [k] and [k + 1] to the symbols indicates the current control cycle or the next control cycle. Hereinafter, the basic principle of AC prediction will be described with reference to equation (1). The current control cycle is the k-th cycle, the detected values of the power supply voltage and the power supply current at the start point of the control cycle are Vs [k] and is [k], and the equivalent value of the control voltage output in the current control cycle is Vc. Assuming that [k], the current value at the start point of the next control cycle [k + 1] can be basically predicted as in equation (2) based on equation (1). [0006] Conventionally, equation (2) is applied as it is, and the current value is [k + 1] in the next control cycle is often predicted. However, as can be seen from the equation (2), an accurate value of the inductance L of the AC reactor is required. In practice, it is difficult to know the value of L accurately due to the presence of unknown factors such as system leakage inductance in the power supply. If the estimation is performed using the estimated value, the AC predicted value may have an offset error from the true value. Therefore, it is difficult to obtain an accurate predicted value by this method, and if it is used for control, it is impossible to configure a highly accurate control system, and in some cases, the system may be unstable. SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to estimate the prediction error offset caused by an unknown element in the system by the observer theory. It is another object of the present invention to provide an AC amount predicting apparatus capable of obtaining a highly accurate AC predicted value by correcting a predicted value of an AC amount with an estimated offset value. In order to achieve the above object, there is provided a method for predicting AC in an AC controller of a converter for converting AC to DC, wherein the AC amount Vs, is And a second means for detecting the change amount β [k + 1] of the AC amount is due to the switching pattern output in the current control cycle [k].
Means, the predicted value is1 [k] of the AC amount in the current control cycle obtained in the immediately preceding control cycle [k + 1], and the AC detected value is
AC prediction correction value v1 based on the prediction deviation from [k]
A third means for obtaining [k], a change β in the AC detection value is [k] obtained by the first means and the AC amount obtained by the second means,
From [k] and the AC prediction correction value v1 [k] obtained by the third means, the predicted value is1 of the AC amount in the next control cycle [k + 1]
A fourth means for obtaining [k + 1] is provided, and the AC amount predicted value is1 [k + 1] obtained by the fourth means is used as the control amount of the AC controller. Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS For the sake of simplicity, an embodiment of the present invention will be described below mainly for controlling an AC active current and a reactive current of a three-phase voltage source converter. The present invention can be applied not only to voltage type and current type converters.
Further, the power supply is not limited to three phases. further,
The present invention can be applied not only to active / inactive current control but also to polyphase current, power, and voltage control. FIG. 2 shows a main circuit configuration of the three-phase voltage source converter for ease of explanation. In the figure, 6 is a three-phase voltage source converter bridge, 7 is a three-phase AC power supply, 8
Denotes an AC reactor, 9 denotes a DC capacitor, 10 denotes a load, L denotes an inductance value of the AC reactor, and C denotes a capacitance value of the capacitor. FIG. 1 is a diagram showing a configuration of an AC amount predicting apparatus according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a first means for detecting the three-phase AC current and the DC voltage value shown in FIG. 2 for each control cycle. Reference numeral 2 denotes a second means, which is a switching pattern of the current control cycle of the output of the AC controller 5 and a three-phase AC current is detected by the first means.
[K], the detected values of the power supply voltage Vs [k] and the DC voltage VD [k] are input, and the variation β [k] of the alternating current due to the switching pattern is calculated. 3 is a third means,
The AC current value is [k] detected by the first means is compared with the predicted AC current value is1 [k] at the start point of the current control cycle [k] obtained by the fourth means in the immediately preceding control cycle. ,
Based on the estimated deviation value, the AC prediction correction value v1 [k +
1] is updated. 4 is a fourth means, and the first means 1
The AC current detection value is [k] obtained in step (2), the AC current variation β [k] obtained in the second means 2, and the AC prediction correction value v1 [k] obtained in the third means 3 are added. , The next control cycle [k +
1], the predicted value is1 [k + 1] of the AC current is obtained. 5
Is an AC controller, which uses a predicted AC current value is1 [k + 1] output from the fourth means 4 as a control amount and outputs a switching pattern of a semiconductor switch element constituting a converter based on some control method. Hereinafter, the operating principle of the AC current predicting apparatus shown in FIG. 1 will be described in detail. In FIG. 2, the three-phase power supply voltage is vs = [Vs1, Vs2, Vs3], and the power supply current is is =
[Is1, is2, is3], and assuming that the DC voltage is VD, the AC circuit equation is given by equation (3). [Equation 3] Here, u = [u1, u2, u3] is called a switching function or a switching vector.
It is defined as: uk = 1: upper arm on and lower arm off in FIG. 2 0: upper arm off and lower arm on k = 1 in FIG.
2, 3 In this embodiment, in order to make the control amount an active current id and a reactive current iq, each of the three-phase amounts is subjected to dq conversion. It looks like an expression. [Equation 4] Here, Vs = [Vd, Vq] represents valid and invalid components of the power supply voltage, and u = [ud, uq] represents valid and invalid components of the switching function. If the circuit equation of equation (4) is discretized so as to be easily controlled by digital control, it can be expressed as equation (5). [Equation 5] Here, [k] is the current control cycle, and [k +
1] means the next control cycle. Here, the second term on the right side of Expression (5) is described as β [k]. That is, The calculation formula of the formula (6) is the second formula of the present invention.
In the means, β [k] becomes the amount of change in the output current in the second means. Using the symbol of the vector β [k], the model of Expression (5) can be simply expressed as in Expression (7). [Equation 7] Where is [k] = [id [k], iq
[K]] represents a current vector. The current is [k + 1] in the next control cycle can be predicted from the equation (7),
As described above, factors unknown to the system may cause a prediction error for the offset v [k]. In consideration of the offset, the system can be formulated as shown in equation (8). (Equation 8) Equation (8) shows the current detection value i of the current control cycle.
s [k], the current variation β [k] due to the output switching pattern in the current control cycle can be detected and calculated. However, since the offset v [k] is unknown, is [k + 1] is predicted as it is. Can not. Therefore, the present invention applies the observer theory and calculates the offset v
While estimating [k], the AC current is in the next control cycle is
[K + 1] is predicted. Hereinafter, the current predicted value is represented by is1 [k
+1]. According to observer theory,
The general formula of the observer configuration for the model of formula (8) is as shown in formula (9). [Equation 9] That is, a value obtained by multiplying the current prediction error in the immediately preceding control cycle by the gain (K1, K2) into the model of the equation (8) is corrected so that the prediction error value converges to zero. . How to determine gains K1 and K2 is (9)
It is sufficient that the absolute value of the pole of the observer in the equation is 1 or less, but in the present invention, K1 = 1 and K2 = 1/4 are determined. In this case, the pole is halved and it is clear that it is stable. Observer (9) is finally expressed as (1
0), which is easy to calculate. [Equation 10] The calculation formula (11) is an embodiment of the third means of the present invention. That is, the detected value is [k] of the AC current in the current control cycle [k] and the immediately preceding control cycle [k +
1] The predicted value i of the AC current in the current control cycle obtained in 1)
s1 [k], and the prediction error value (is [k] −
is1 [k]) is multiplied by ４ and added to the current AC prediction correction value (offset) to update the AC prediction correction value. The equation (10) is an embodiment of the fourth means of the present invention. That is, the AC current detection value is [k] obtained by the first means, the AC current change amount β [k] obtained by the second means, and the AC current prediction correction value v1 obtained by the third means
[K] is added to obtain a predicted AC current value is1 [k + 1] for the next control cycle [k + 1]. As described above, according to the present invention, the first means detects the AC current value is [k], the power supply voltage value Vs [k] and the DC voltage value VD [k], and the second means detects the current value. Based on the switching pattern u [k] of the output in the control cycle and each detection value obtained by the first means, the change amount β [k] of the AC current is obtained as shown in the following equation (6). As shown in equation 11), the detected value of the AC current is [k] of the current control cycle and the predicted AC current of the current control cycle is1 obtained in the immediately preceding control cycle.
The prediction deviation value (is [k] -is1 [k]) from [k] is made 1/4 times and added to the current AC prediction correction value v1 [k] to obtain a new AC prediction correction value v1 [k + 1]. To update
The fourth means obtains the AC current detection value is [k] obtained by the first means as represented by the equation (10), the AC current variation β [k] obtained by the second means, and the third means. AC current prediction correction value v1
[K] is added and the predicted AC current value is1 in the next control cycle.
[K + 1] is obtained. The present invention achieves the object of predicting the alternating current value in the next control cycle by repeatedly operating the above-described means at regular intervals. Since the offset prediction error caused by an element unknown to the system is estimated and the current prediction value is corrected, a highly accurate current prediction value can be obtained. As described above, according to the present invention, a prediction error of an offset due to an element unknown to the system is estimated and an AC prediction value is corrected as a prediction correction amount. And a high AC predicted value can be obtained. Further, since the optimum gain is selected for the design of the prediction observer, the stability is ensured, the calculation is easy, and the utility is extremely high in practical use.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a configuration of an AC prediction device of the present invention. FIG. 2 is a diagram showing a main circuit configuration of a three-phase voltage source converter. FIG. 3 is a converter AC circuit diagram shown for explanation of the prior art. [Description of Signs] 1 First means (AC and DC amount detecting means) 2 Second means (AC change amount calculating means) 3 Third means (AC predicted correction amount detecting means) 4 Fourth means (AC Prediction value calculating means) 5 AC controller 6 Three-phase voltage source converter bridge 7 Three-phase AC power supply 8 AC reactor 9 DC capacitor 10 Load 11 AC power supply 12 AC reactor 13 Block L representing converter and DC circuit L Inductance value C of AC reactor Capacitance value T of DC capacitor Control period t Time variable Vs AC power supply voltage is AC current VD DC output voltage u Switching function ω Power supply angular frequency id AC active current iq AC reactive current ud Effective component iq of dq conversion value of switching function Invalid component Vd of dq conversion value of switching function Effective component Vq of power supply voltage Invalid component of power supply voltage β Change amount of AC change βd Effective component of change amount of AC βq Invalid component of change amount of AC Vc Control voltage generated by converter k kth control cycle v Prediction error offset v1 Estimated value of prediction error offset or AC prediction correction Value K1 Predicted observer gain K2 Predicted observer gain is1 AC current predicted value

Claims (1)

(1) A converter for converting AC supplied from an AC power supply into DC, a DC controller for obtaining an AC command value from a DC output of the converter and a DC output command value, and an AC converter. The AC controller operates at a constant control cycle, predicts an AC amount in the next control cycle, and converts the AC amount predicted value as a control amount to match the AC command value. A converter for outputting a switching pattern to a semiconductor switch element constituting a switch, wherein a first means for detecting an AC amount Vs, is and a DC amount VD for each control cycle ; The detected AC amount Vs,
The change amount β of the AC amount is due to the switching pattern output in the current control cycle [k] using is and the DC amount VD.
a second means for obtaining [k] and a predicted deviation between the predicted value is1 [k] of the AC amount and the detected value is [k] in the current control cycle obtained in the immediately preceding control cycle [k-1]. , AC prediction correction value v
A third means for obtaining 1 [k]; a change β [k] in the AC detection value is [k] obtained by the first means and the AC amount obtained by the second means.
And a fourth means for obtaining a predicted value is1 [k + 1] of the AC amount in the next control cycle [k + 1] from the AC predicted correction value v1 [k] obtained by the third means and the fourth means. AC predicted value is1 [k +
A control device for a converter, characterized in that an AC amount prediction value is calculated and controlled sequentially and continuously so that [1] is a control amount of the AC controller.