KR20170137272A - Current Control Methods for Single-Phase Voltage Source Inverters - Google Patents

Abstract

The present invention provides a current control method using a single-phase voltage source inverter, to reduce errors in the normal state current in comparison with an existing model prediction current control (MPCC) method. According to the present invention, the method comprises the following steps: (A) dividing a sampling cycle in two during a k^th sampling period; (B) multiplying an output current, and each output voltage of pre-voltage and post-voltage applying t = kT_s and t = kT_s +T_F^k by an inclination of an output current in a (k + 1)^th step, respectively; (C) calculating a second step future output current in a moment of (k + 2)^th sampling acquired by pre and post output voltage applied during T_F^k and T_L^k; (D) replacing an actual current in a moment of (k + 2)^th sampling with a reference current value; (E) determining whether or not T_F^(k + 1) is greater than zero and is smaller than a sampling period; (F) minimizing a current error to two moments from one sampling period when a determination result is correct; and (G) calculating the reference current value based on an application time of the pre-output voltage.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current control method using a single-

The present invention relates to a current control method using a single-phase voltage source inverter to control a single-phase output current using two output voltages.

For decades, good output waveform quality feedback based current control has been regarded as the most important research area for both single-phase and three-phase voltage source inverters (VSIS). In particular, separate pulse width modulation (PWM) blocks and traditional proportional-integral (PI) control methods with non-linear hysteresis currents have been widely used for single-phase and three-phase voltage source inverters (VSIS).

In addition to these traditional current control schemes, simple and effective current control techniques for three-phase voltage source inverters have been developed due to simplicity with control flexibility as well as non-independent PWM blocks in model predictive current control (MPCC).

In particular, the MPCC method determines all predicted current values of the predefined cost function to predict the current future behavior based on the system model and to select the optimal output voltage to be applied to the next step. The MPCC method has been used to control the load current of various power converters such as a multi-inverter polyphase inverter, an active power filter, a matrix converter as well as a three-phase voltage source inverter due to the simplicity without requiring the control flexibility as well as the respective PWM block.

In addition to the various three-phase converters operated by the MPCC method, it is easy to derive the MPCC method for the single-phase voltage source inverter based on the same approach used for the three-phase voltage source inverter.

However, the main limitation of single-phase voltage-source inverters is that they can generate new, different output voltages compared to only seven voltage vectors.

The reduced number of output voltages can be generated by a single-phase voltage source inverter that requires an increased sampling frequency to achieve an output current having a higher waveform quality and smaller current error than a three-phase voltage source inverter.

However, it is clear that increasing the sampling frequency of the controller results in increased computational burden and consequently increased system cost.

Japanese Patent Application Laid-Open No. 10-2013-0031379 (published on March 31, 2013) Published Patent Publication No. 10-2010-0017597 (Published Date: Feb. 16, 2010)

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide an MPCC method using two output voltages having a variable application period in one sampling period. ? The purpose of the method is to provide.

Other objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned can be clearly understood by those skilled in the art from the following description.

번째 단계에서 출력 전류를

및

이 적용되는 전자 전압 및 후자 전압의 각 출력 전압에 출력 전류의 기울기를 각각 곱하여 산출하는 단계와, (C)

및

동안 인가되는 전자와 후자의 출력 전압에 의해 얻어지는 (k+2) 번째 샘플링 순간에 2 단계 미래 출력 전류를 산출하는 단계와, (D) 상기 (k + 2)번째 샘플링 순간에서의 실제 전류 값을 기준 전류 값으로 대체하는 단계와, (E) 상기

가 제로(zero)보다 크고, 샘플링 기간

보다 작은지 판단하는 단계와, (F) 상기 판단 결과 맞으면, 전류 오류가 하나의 샘플 주기에서 다음 수식

를 이용하여 두 순간으로 최소화시키는 단계와, (G) 상기 전자 출력 전압

의 인가 시간을 기반으로 기준 전류 값

을 산출하는 단계를 포함하여 이루어지며, 이때, 상기

및

는 각각 k 번째 샘플링 기간 동안 사용되는 전자 전압

및 후자 전압

에 적용되는 적용 기간을 나타내는 것을 특징으로 한다.According to an aspect of the present invention, there is provided a current control method using a single-phase voltage source inverter, comprising: (A) dividing a sampling period into two during a k-th sampling period;

In the second stage,

And

(C) multiplying each of the output voltages of the electron voltage and the latter voltage to which the slope of the output current is applied,

And

(K + 2) < th > sampling instant obtained by the former and the latter output voltage during the (k + Replacing the reference current value with the reference current value, (E)

Is greater than zero, and the sampling period

(F) judging whether the current error is smaller than the current error,

(G) minimizing the electronic output voltage < RTI ID = 0.0 >

The reference current value

, Wherein the step of calculating

And

Lt; RTI ID = 0.0 > k < / RTI >

And the latter voltage

And the application period to which the application is applied.

로 분할되며, 이때, 상기

는 샘플링 기간인 것을 나타내는 것을 특징으로 한다.Preferably, the step (A)

, And at this time,

Is a sampling period.

및

)는 Preferably, the slope of the two output currents in the step (B)

And

)

및

로 산출되며, 이때, 상기

는 기준 전류값이고, 상기

는 전자 전압을, 상기

는 후자 전압을 나타내는 것을 특징으로 한다.Equation

And

Is calculated,

Is the reference current value,

The electron voltage,

Is the second voltage.

를 이용하여 2 단계 미래 출력 전류(

)를 산출하는 것을 특징으로 한다.Preferably, the step (C)

The second stage future output current (

). ≪ / RTI >

및 후자의 출력 전압

로 표현되며, 다음 수식

및

로 산출되는 것을 특징으로 한다.Preferably, the current instant in the (k + 1) th stage is the output voltage of the electrons used in the (k + 1)

And the latter output voltage

And the following equation

And

.

The current control method using the single-phase voltage source inverter according to the present invention as described above has the following effects.

First, using the two voltages with variable duration, the proposed MPCC method reduces the error of the steady-state current compared to the conventional MPCC method despite only three characteristic output voltages allowed in the single-phase voltage source inverter, The output voltage ripple can be reduced without increasing the frequency.

Second, in the proposed method, the duration of the two selected voltages in addition to the selection of the two output voltages used in the future sampling period minimizes the current error within the future sampling period, eliminates the current error at the end of the future sampling period To be included in the optimization process.

Third, one proposed method, referred to as the generic 2V-MPCC method, considers all possible future combinations that can be produced by the two voltages of a single-phase voltage source inverter.

1 is a block diagram showing the overall configuration of a general 2V-MPCC method according to the present invention.
Figure 2 is a flow chart for determining the optimum output voltage and optimal duration in a typical 2V-MPPC method according to the present invention.
3 is a diagram showing a concept of a current control method using a single-phase voltage source inverter according to the present invention.
Figures 4 (a), (b) and (c) show nine possible current trajectories obtained by nine voltage sets
5 is a graph showing a slope of a reference current change during one sampling period

Other objects, features and advantages of the present invention will become apparent from the detailed description of the embodiments with reference to the accompanying drawings.

A preferred embodiment of a current control method using a single-phase voltage source inverter according to the present invention will now be described with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. It is provided to let you know. Therefore, the embodiments described in the present specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and are not intended to represent all of the technical ideas of the present invention. Therefore, various equivalents It should be understood that water and variations may be present.

For reference, the proposed method refers to the general 2V-MPCC method. In addition, the sampling period is divided into two periods in a changing period which is changed in accordance with each sampling period in order to eliminate current errors of the actual and reference currents at the sampling instant every sampling period.

1 is a block diagram showing the overall configuration of a general 2V-MPCC method according to the present invention.

1, the overall configuration includes a one-step lagrange extrapolation unit 10, a two-stage raglane estimation unit 20, a predictive future reference unit 20, current predictor 30, a predictive one-step future current 40, a calculator 50, a minimum cost function 60, a two-stage current prediction And a predict tow-step future current 70. [

And FIG. 2 is a flowchart for determining an optimum output voltage and an optimal duration in a conventional 2V-MPPC method according to the present invention, considering an unavoidable delay through a delay compensation technique. As such, by applying the delay compensation technique, almost one sampling period can be allocated for calculation and prediction necessary to determine the two optimal output voltages and their respective optimal durations.

1 and 2, the following will be described in detail.

FIG. 3 is a diagram illustrating a concept of a current control method using a single-phase voltage source inverter according to the present invention. First, during a k-th sampling period, a sampling period is divided into two as shown in Equation (1) .

및

는 각각 k 번째 샘플링 기간 동안 사용되는 전자 전압

및 후자 전압

에 적용되는 적용 기간이다. 이때, 두 지속 시간은 제로(zero)보다 크고 샘플링 기간

보다 작아야 한다. 출력 전압은 단상 전압원 인버터에서 전자 전압 및 후자 전압을 사용할 수 있기 때문에, 2개의 출력 전압이 이루어진 9개의 가능한 세트가 단상 전압원 인버터에 존재한다.At this time,

And

Lt; RTI ID = 0.0 > k < / RTI >

And the latter voltage

. At this time, the two durations are greater than zero,

. Since the output voltage can use the electron voltage and the latter voltage in a single-phase voltage source inverter, there are nine possible sets of two output voltages in a single-phase voltage source inverter.

번째 단계에서 출력 전류는 각각

및

이 적용되는 전자 전압 및 후자 전압의 출력 전압을 가지며, 수학식 2와 같이 나타낼 수 있다(S20).

In the second stage, the output current is

And

And the output voltage of the latter voltage can be expressed as Equation (2) (S20).

와

는 각각 k 번째 샘플링 기간 동안 전자와 후자의 출력 전압에 의해 생성된 출력 전류의 기울기이고, 상기

는 기준 전류값이다. 도 4에서 표현되는

및

동안 출력 전류의 기울기는 다음 수학식 3과 같이 나타낼 수 있다.here,

Wow

Is the slope of the output current generated by the former and the latter output voltage during the kth sampling period,

Is the reference current value. 4

And

The slope of the output current can be expressed by the following equation (3).

와

동안 인가되는 전자와 후자의 출력 전압에 의해 얻어지는 (k+2) 번째 샘플링 순간에 2 단계 미래 출력 전류는 다음 수학식 4와 같이 나타낼 수 있다(S40). In the proposed method, two-stage prediction of the output current is used to compensate for the unavoidable control delay. Therefore, as shown in FIG. 4,

Wow

(K + 2) th sampling instant obtained by the former and the latter output voltage can be expressed by the following Equation 4 (S40).

및 후자의 출력 전압

로 표현되며, 다음 수학식 5와 같이 나타낼 수 있다.Also, the current instant in the (k + 1) th stage is the output voltage of the electrons used in the (k + 1)

And the latter output voltage

And can be expressed by the following equation (5).

According to the proposed general 2V-MPCC method, the actual output current of Equation (4) becomes equal to the reference current at the end of the (K + 1) th sampling period. As a result, the actual current value at the (k + 2) th sampling instant in Equation (4) is replaced by the reference value as shown in Equation (6).

을 계산하기 위해 수학식 4에서 실제 출력 전류는 상기 기준 전류와 동일하게 된다. 또한,

에서의 전류값에 의해 지정 될 수 있으며, 이는 수학식 7과 같이 나타낼 수 있다.All time

The actual output current in Equation (4) becomes equal to the reference current. Also,

Which can be expressed by Equation (7). &Quot; (7) "

에 대한 이차 형태를 갖는 상기 수학식 5 ~ 수학식 7에 기초하여 얻어진다. 따라서 전 시간

는 다음 수학식 8에 의해 계산된다.The following equation (8)

(5) to (7) having a quadratic form with respect to the above equation (5). Therefore,

Is calculated by the following equation (8).

및

로 설정된 소정의 샘플링 주기의 끝에서 제로 전류 오류가 발생하는 (k + 1) 번째 샘플링 주기 동안 전 출력 전압

을 적용하는 인가 기간

이 될 수 있다. 그리고 전자 전압

의 인가 기간이 결정되면, 후자 전압

의 나머지 시간은 자동으로 수학식 1로부터 결정될 수 있다.Therefore, by calculating using Equations 1, 2, 5, and 6,

And

(K + 1) < th > sampling period at which a zero current error occurs at the end of a predetermined sampling period set at

Application period to apply

. Then,

Is determined, the latter voltage

Can be determined automatically from Equation (1).

및

는 상기 선택된 전자 및 후자의 출력 전압에 따라 결정될 수 있다. 그리고 시간 간격

에 대한 두 값은 전자 및 후자 전압으로 선택된 두 전압의 상태로 상기 수학식 8에 의해 얻어진다. 적절한 동작을 위해, 간격

은 제로(zero)보다 크고, 샘플링 기간

보다 작아야 한다(S50).Therefore, the application time of the two future voltages used in the (k + 1)

And

May be determined according to the selected output voltage of the former and the latter output voltage. And time interval

Are obtained by the above equation (8) in the states of the two voltages selected by the former and latter voltages. For proper operation,

Is greater than zero, and the sampling period < RTI ID = 0.0 >

(S50).

는 수학식 8에서 계산된 두 값 사이에 선택된다. 이때, 두 전압 상태가 하나의 샘플링 기간에 사용되는 것으로 결정되면, 수학식 8에서 계산된 하나의 값은 마이너스 또는 결정되는 샘플링 기간

보다 클 수 있다.Therefore, the zero and the sampling period

Is selected between the two values calculated in Equation (8). At this time, if it is determined that two voltage states are used in one sampling period, one value calculated in Equation (8) is negative or determined in a sampling period

.

It should be noted that, as shown in Fig. 4, which of the nine possible voltage sets at the (k + 2) th sampling instant uses the actual output current to obtain a more appropriate program time.

Figures 4 (a), (b) and (c) illustrate nine possible current trajectories obtained by nine voltage sets.

및

으로 (k + 1) 번째 순간에 기준에 도달할 수 없다.As shown in Fig. 4 (a), the output currents generated by the voltage sets (-Vdc, -Vdc) and (-Vdc, 0)

And

, The reference can not be reached at the (k + 1) th instant.

Also, as shown in FIG. 4, the current error does not occur in the instantaneous (k + 2) th sampling result in different output current operations within the future (k + 1) Set some possible voltages.

As a result, the proposed invention not only generates a small future output current trajectory within the sampling period, but also selects the best future voltage set to eliminate the current error at the end of the sampling period.

For the purpose of selecting the optimal set in terms of current error, the cost function in the proposed method is defined by the following equation (9) in such a manner that the current error is minimized from one sample period to two instants (S60).

는 전자 및 후자 출력 전압에 따라 변화하기 때문에, 미래의 출력 전류는 두 전압의 전환점인 하나의 변하는 순간 및 다음 샘플링 순간인 하나의 고정된 순간에 상기 수학식 9에서 비용 함수가 평가된다.Sampling moment

The cost function is evaluated in Equation (9) above at one fixed instant at which the future output current is a turning point of the two voltages and at the next instant of sampling.

동안 전류의 오류에 의해 구성된 영역에 비례한다. 이 비용 함수의 정당화는 두 전압의 전환점은 물론 다음 샘플링 순간에 정의된다(S70).Assuming that the reference current can be regarded as the same during a sufficiently small sampling period, the cost function value obtained by Equation (9)

Is proportional to the area configured by the current error. The justification of this cost function is defined at the next sampling instant as well as at the turning point of the two voltages (S70).

에서의 기준 전류를 비교하기 위해, 순간 t에서의 기준 전류도 필요하다. 따라서 가변 순간

에서의 기준 전류값은 다음 수학식 10과 같이 계산된다.Actual output current and variable instantaneous

In order to compare the reference current at t, the reference current at instant t is also needed. Therefore,

The reference current value is calculated by the following equation (10).

이다.At this time,

to be.

은 전자 출력 전압

의 인가 시간이 산출되면 얻을 수 있다(S80).Accordingly, the reference current value

The electronic output voltage

(S80). ≪ / RTI >

The optimal future set of two output voltages and optimal duration producing a small current error between the two sampling instants on the basis of the cost function of equation (7) can be selected from among several candidates to generate a zero current error in the next sampling have.

As a result, the proposed 2V-MPCC method can predict the optimal output voltage and optimal application interval in the next step to minimize the current error between sampling instants.

The method of the present invention may generally correspond to the actual current for the reference current at the instant of sampling, but the current error during the sampling period can not be zero in a transient state such as a large step change to the reference current.

5 is a graph showing the slope of the reference current change during one sampling period, wherein the slope is larger than the maximum slope of the actual current generated by the output voltage applied during the entire sampling period.

As shown in Fig. 5, the output voltage applied during the sampling period can not completely invalidate the current error in the (k + 2) th instant.

In the case of a transient state such as a non-zero current error at the next sampling instant, a single voltage based conventional MPCC method using only one output voltage during the sampling period based on the cost function of the proposed general 2V-MPCC method same.

The proposed method operates in the same manner as the single voltage based MPCC method in the instantaneous state, so that the proposed method does not cause any damage to the instantaneous response of the single voltage based MPCC method.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It will be apparent to those skilled in the art that various modifications may be made without departing from the scope of the present invention. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

Claims (5)

(A) dividing the sampling period into two during the k-th sampling period,
(B)

In the second stage,

And

Calculating a slope of the output current by multiplying each of the output voltages of the electron voltage and the latter voltage to be applied,
(C)

And

Stage future output current at a (k + 2) th sampling instant obtained by the former and the latter output voltage;
(D) replacing the actual current value at the (k + 2) th sampling instant with the reference current value,
(E)

Is greater than zero, and the sampling period

Determining whether the difference is smaller than a predetermined value,
(F) If the result of the determination is correct,

To minimize to two moments,
(G) The electronic output voltage

The reference current value

And a step of calculating,
At this time,

And

Lt; RTI ID = 0.0 > k < / RTI >

And the latter voltage

And the application time period is applied to the current control method using the single-phase voltage source inverter. The method of claim 1, wherein the step (A)
Equation

Lt; / RTI >
At this time,

Is a sampling period. ≪ RTI ID = 0.0 > A < / RTI > The method according to claim 1,
The slope of the two output currents in the step (B)

And

)
Equation

And

Lt; / RTI >
At this time,

Is the reference current value,

The electron voltage,

And the second voltage is the second voltage. 2. The method of claim 1, wherein step (C)
Equation

The second stage future output current (

) Is calculated by multiplying the current value by the current value. 5. The method of claim 4,
The current instant in the (k + 1) th stage is the output voltage of the electrons used in the (k + 1)

And the latter output voltage

Lt; / RTI >
The following formula

And

And a current control method using a single-phase voltage source inverter.

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