KR20200142329A - Control system and control method for rectifying - Google Patents

Abstract

The rectifier control system according to an embodiment includes: a power supply unit generating three-phase input power; a diode rectifier receiving the input of the three-phase input power and converting it into a direct current voltage; a load terminal supplied with the direct current voltage after the conversion at the diode rectifier; and a control unit detecting the input voltage and current input to the diode rectifier and controlling an output waveform output to the load terminal. The control unit includes: a first integrator integrating k^th input voltage; a future prediction voltage measuring unit measuring the future prediction voltage of the input voltage integrated from the first integrator; a future reference voltage measuring unit measuring a future reference voltage from the voltage of the load terminal; a cost function application unit measuring the absolute value of the difference between the future reference voltage and the future prediction voltage; and a switching control unit controlling the diode rectifier using a switching state where the absolute value of the difference between the future reference voltage and the future prediction voltage is minimum. According to the embodiment, there is an effect of preventing performance from being degraded due to distortion in output by distorted input voltage by integrating the distorted input voltage and removing distorted components included in the input voltage.

Description

Rectifier control system and control method {CONTROL SYSTEM AND CONTROL METHOD FOR RECTIFYING}

The embodiment relates to a rectifier control system for improving power efficiency.

With the recent increase in power consumption, the importance of continuous energy saving activities and product energy efficiency rethinking has emerged. Energy saving is also important, but it is very important to use the power supplied from the power plant without wasting it.

Industrial electrical products include power conversion devices for stabilizing commercial power, and power conversion devices include automatic voltage regulators (AVR), uninterruptible systems (UPS), rectifiers, and the like.

Among them, the three-phase rectifier includes an input unit generating a three-phase voltage, a diode rectifier receiving the three-phase AC voltage and converting it into a DC voltage, a capacitor for charging the DC voltage converted by the diode rectifier, and the capacitor. It consists of a load terminal that operates by receiving a charged voltage.

However, in the three-phase rectifier, a current distortion problem occurs in each phase, and the current distortion problem is caused by a harmonic component included in the input current. When harmonics are generated in the input current, the output value is also distorted, which degrades the performance of the rectifier.

In order to solve this problem, conventionally, model predictive control (MPC) and MPDPC that directly control input current, and model predictive direct power control (MPCC) control techniques that directly control input power have been proposed.

This control technique lowers Total Harmonic Distortion (THD) and output voltage, but has limitations in lowering Total Harmonic Distortion (THD) and output voltage with distorted input voltage.

The embodiment relates to a rectifier control system and a control method for preventing output performance from being degraded by a distorted input voltage.

The rectifier control system according to the embodiment includes a power supply for generating three-phase input power, a diode rectifier receiving the three-phase input power and converting it into a DC voltage, a load terminal to which the DC voltage converted by the diode rectifier is supplied, and And a control unit configured to detect the input voltage and current input to the diode rectifier and control an output waveform output to the load terminal, wherein the control unit includes a first integrator for integrating a k-th input voltage, and from the first integrator. An absolute difference between the future reference voltage and the future reference voltage, a future reference voltage measurement unit that measures a future prediction voltage of the integrated input voltage, a future reference voltage measurement unit that measures a future reference voltage from the voltage of the load terminal A cost function application unit measuring a value, and a switching control unit controlling the diode rectifier using a switching state in which an absolute value of a difference between the future reference voltage and the future predicted voltage is minimum.

The control unit may further include a first input voltage delay unit that delays the k-th input voltage to generate a k+1-th input voltage. The future prediction voltage measuring unit may receive a k+1 th input voltage and predict a k+2 th input voltage. The cost function application unit may use a k+2 th virtual future voltage and a k+2 th future voltage. The future reference voltage measurement unit may measure the future reference voltage by using the output value obtained by PI-controlling the voltage of the load terminal and the k+2 input power obtained by delaying the k-th input voltage twice.

The control unit includes a second input voltage delay unit that delays the k+1th input voltage output from the first input voltage delay unit to generate a k+2th input voltage, and k output from the second input voltage delay unit. A second integrator for integrating the +2th input voltage may be included.

The future prediction voltage measurement unit may be determined by the following equation.

<Equation>

는 k+2번째 미래 전압이고,

는 k+1번째 미래 전압, L은 선로 인덕턴스 이고, R은 선로 저항이고, icon은 정류기의 전류이고, vcon은 정류기의 전압이고, Ts는 샘플링 시간(sampling period)이다.)(here,

Is k+2th future voltage,

Is the k+1th future voltage, L is the line inductance, R is the line resistance, icon is the current of the rectifier, vcon is the voltage of the rectifier, and Ts is the sampling period.)

The embodiment is a method of controlling a three-phase rectifier having a three-phase input terminal, a diode rectifier, and a load terminal, the step of removing a harmonic component by integrating the k-th input voltage of the three-phase input terminal, and removing the harmonic component. Measuring a future predicted voltage of the input voltage, measuring a future reference voltage from a voltage of a load terminal of the three-phase rectifier, measuring an absolute value of a difference between the future reference voltage and the future predicted voltage, and And controlling the diode rectifier using a switching state in which an absolute value of a difference between the future reference voltage and the future prediction voltage is minimum.

By delaying the k-th input voltage, a k+1-th input voltage may be generated. In the measuring of the predicted future voltage, the k+2 th input voltage may be predicted by receiving the k+1 th input voltage. In the measuring of the absolute value of the difference between the future reference voltage and the future prediction voltage, a k+2 th virtual future voltage and a k+2 th future voltage may be used.

The future reference voltage may be measured by using the output value obtained by PI-controlling the voltage of the load terminal and the k+2 input power obtained by delaying the k-th input voltage twice.

In the embodiment, by integrating the distorted input voltage, there is an effect of removing a harmonic component included in the input voltage.

In addition, according to the embodiment, by removing a distorted component included in the input voltage, it is possible to prevent the performance from deteriorating due to distortion in the output due to the distorted input voltage.

1 is a circuit diagram showing a three-phase rectifier according to an embodiment.
2 is a block diagram showing a control structure of a three-phase rectifier according to an embodiment.
3 is a simplified circuit diagram for one phase of FIG. 1 of a three-phase rectifier according to an embodiment.
4 is a block diagram showing the structure of a control unit of a three-phase rectifier according to an embodiment.
5 is a graph showing the magnitude and phase difference between the input voltage and the integrated input voltage.
6 to 8 are graphs comparing output values according to the control method of the conventional three-phase rectifier and the control method of the three-phase rectifier according to the embodiment.

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

1 is a circuit diagram showing a three-phase rectifier according to an embodiment, FIG. 2 is a block diagram showing a control structure of a three-phase rectifier according to the embodiment, and FIG. 3 is a one-phase diagram of a three-phase rectifier according to the embodiment. Is a simplified circuit diagram, FIG. 4 is a block diagram showing the structure of a control unit of a three-phase rectifier according to an embodiment, and FIG. 5 is a graph showing the magnitude and phase difference between the input voltage and the integrated input voltage, and FIGS. 8 is a graph comparing output values according to the control method of the conventional three-phase rectifier and the control method of the three-phase rectifier according to the embodiment.

1 to 3, the three-phase rectifier according to the embodiment is supplied with a power supply unit 100, a diode rectifier 200 that receives input power and converts it into a DC voltage, and the DC voltage converted by the diode rectifier. The load terminal 300 may include a controller configured to detect an input voltage and an input power input to the diode rectifier 200 and control an output waveform output to the load terminal 300.

The power supply unit 100 may include three input power sources. Three input power supplies can generate alternating current. The three input power sources may include a phase input power, b phase input power, and c phase input power. Phase a, phase b, and phase c may be different from each other. Transmission lines may be respectively connected between the three input power sources and the diode rectifier 200. Each transmission line may include a line inductance (L) and a line resistance (R).

The diode rectifier 200 may convert a three-phase AC voltage into a DC voltage. The diode rectifier 200 may include 6 diodes. The output current output through the six diodes flows with one of the upper diodes and one of the lower diodes turned on in the circuit diagram. That is, in the upper part, the diode of the phase having the largest voltage in the positive direction among the values of each of the three-phase power sources passing through the resonance circuit at a certain time is turned on, and the remaining two diodes are reverse biased to maintain the OFF state. In the lower part, the diode of the phase having the largest voltage in the negative direction among values passed through the resonance circuit of each of the three-phase power supplies is turned on.

A capacitor C may be disposed at the load end 300. The capacitor C is charged by distributing the DC voltage output from the diode rectifier 200 to the first capacitor C1 and the second capacitor C2, and the charged power is finally supplied to the load terminal 300.

The controller 300 detects voltage and current input to the diode rectifier 200 and determines an optimal switching state to determine an output waveform. Unlike the prior art, the controller 300 removes the harmonic component of the input voltage and controls the output using the input voltage from which the harmonic is removed, so that the performance of the rectifier can be prevented from deteriorating.

More specifically, the controller 300 may measure a virtual future predicted voltage and a virtual future reference voltage and compare them to determine an optimal switching state.

Hereinafter, the configuration of the control unit according to the embodiment will be described in more detail.

Referring to FIG. 4, the controller 400 may include a future predicted voltage measurement unit 430, a future reference voltage measurement unit 450, and a cost function application unit 460.

The future prediction voltage measurement unit 430 serves to measure a virtual future prediction voltage from the input voltage. The predicted future voltage can be obtained by integrating the kth input voltage. In addition, the future prediction voltage measurement unit 430 may measure a k+1 th input current value input to the diode rectifier 200. The k+1 th input current value may be measured from the future current measuring unit 440.

Hereinafter, a process of calculating the predicted future voltage will be described in detail.

Referring to FIG. 3, the dynamic equation in the continuous time domain can be represented by Equation 1 below. Here, x includes any one of a, b, and c, L is the line inductance, R is the line resistance, Vconx is the voltage applied to the diode rectifier, and Icon is the current applied to the diode rectifier.

[Equation 1]

The dynamic equation obtained from FIG. 3 can be expressed as a dynamic equation in a discrete time domain as shown in Equation 2 through Euler approximation. Here, Ts represents a sampling period.

[Equation 2]

The predicted current of the k+1 th diode rectifier on the αβ axis is obtained through Equation 2 as shown in Equation 3. The abc to αβ transformation for deriving Equation 3 may be expressed by the following matrix.

[Equation 3]

In the same manner as in Equation 3, the predicted voltage Vcon of the k+1 th diode rectifier on the αβ axis can be obtained.

Integrating both sides of the dynamic equation of FIG. 3 can be expressed by Equation 4 below. Here, Ψsx(t) refers to a virtual input voltage.

[Equation 4]

As described above, when the input voltage is integrated, the magnitude becomes 1/w and the phase is changed by -90 degrees, as shown in FIG. 5. Since integrating the voltage is the same as passing the voltage through a low-frequency filter, if the integrated voltage is used, harmonics included in the input voltage can be effectively removed.

When the virtual input voltage calculated by Equation 4 is changed to the αβ axis equation, it can be expressed as Equation 5 below.

[Equation 5]

When the k+1th virtual future prediction voltage is calculated using Equation 5, it may be expressed as Equation 6 below.

[Equation 6]

Here, since the three-phase voltage is a sinusoidal voltage, when the k-th input voltage is delayed by the sample period Ts, the k+1-th input voltage can be obtained by Equation 7.

[Equation 7]

By Equation 6, Ψcon(k+1) can be expressed as Equation 8.

[Equation 8]

Equation 8 can be expressed as Equation 9 when summarized through a series of processes based on Equation 5.

[Equation 9]

In addition, in actual control, since the k+2th input voltage is used for delay compensation, Equation 10 can be obtained as follows.

[Equation 10]

Meanwhile, the future reference voltage measurement unit 450 may measure a future reference voltage by using the voltage of the load terminal 300. The future reference voltage measurement unit 450 may measure the k+2th integrated input current and the voltage of the load terminal using a PI-controlled output value. The k+2th integrated input current may be obtained through the first input voltage delay unit 411, the second input voltage delay unit 412, and the second integrator 422. The voltage of the load terminal 300 may be PI controlled from the PI controller 470 connected to the load terminal 300.

Equation 11 can be obtained as follows using Equation 5 for the future reference voltage. Here, Ψ*con(k+1) represents the virtual future reference voltage of k+1 on the αβ axis, Ψs(k+1) is the k+1th virtual future predicted voltage value, and i*con(k +1) represents the k+1th future reference current value of the αβ axis.

[Equation 11]

In actual control, since the k+2 th input voltage is used for delay compensation, Equation 12 can be obtained based on Equation 11 as follows.

[Equation 12]

Meanwhile, the cost function application unit 460 may obtain an output value using a future reference voltage and a future prediction voltage. The cost function application unit 460 may obtain an absolute value of a difference between the k+2 th future reference voltage and the k+2 th future prediction voltage. The cost function application unit 460 may be represented by Equation 13 below.

[Equation 13]

The switching control unit 480 may control the diode rectifier 200 using a switching state in which the output value measured by the cost function application unit 460 is minimum.

6A and 6B show simulation results of an MPCC control method in a steady state and an MPVFC control method according to an embodiment.

It can be seen that the output value Vdc in the normal state well follows the reference voltage of 260V for both the conventional MPCC control method and the MPVFC control method according to the embodiment. In addition, it can be seen that the current waveforms of the diode rectifier are all balanced.

However, looking at THD (Total Harmonic Distortion) in the conventional MPCC control method, phase a, phase b, and phase c show 4.03%, 4.83%, and 4.94%, respectively, and THD in the MPVFC control method according to the embodiment is Phase a, phase b, and phase c showed 4.16%, 4.74%, and 4.68%, respectively.

In the normal state, it can be seen that the THD value of the MPVFC control method according to the embodiment is low. Here, THD may be measured by Equation 14 below.

[Equation 14]

7A and 7B show simulation results of the MPCC control method and the MPVFC control method according to the embodiment when 20% of the fifth harmonic component is present in the input voltage of the phase a in a steady state.

It can be seen that both the MPCC control method and the MPVFC control method are severely distorted in phase a.

Looking at the THD value, the MPCC control method shows 14.13%, 8.15%, and 8.38% in phase a, phase b, and phase c, respectively. On the other hand, the MPVFC control method shows 5.28%, 4.85% and 6.41% in phase a, phase b, and phase c, respectively.

That is, in the MPVFC control method according to the embodiment, although the phase a is severely distorted, it can be seen that the current distortion is alleviated compared to the prior art. In addition, even looking at the output value, it can be seen that the MPVFC control method according to the embodiment has a considerably low value.

It can be seen that the MPVFC control method according to the embodiment has a low THD value and a low output value when distortion occurs in the input voltage, thereby preventing the performance of the rectifier from deteriorating.

8 shows simulation results of the MPCC control method and the MPVFC control method according to the embodiment when a harmonic component is present in the input voltages a, b and c in a steady state.

As in FIG. 7, it can be seen that the current value of the conventional MPCC control method is severely distorted compared to the MPVFC control method according to the embodiment, and the THD and output values are significantly larger than the MPVFC control method according to the embodiment. Able to know.

As described above, the control system of the three-phase rectifier according to the embodiment controls the switching state by comparing the predicted future voltage and the future reference voltage while removing the distortion of the input voltage, thereby preventing distorted output from being generated. There is an effect that can effectively prevent performance degradation.

Features, structures, effects, and the like described in the embodiments above are included in at least one embodiment of the present invention, and are not necessarily limited to only one embodiment. Further, the features, structures, effects, etc. illustrated in each embodiment may be implemented by combining or modifying other embodiments by a person having ordinary knowledge in the field to which the embodiments belong. Accordingly, contents related to such combinations and modifications should be interpreted as being included in the scope of the present invention.

100: power supply
200: diode rectifier
300: load end
400: control unit

Claims (12)

A power supply for generating three-phase input power;
A diode rectifier receiving the three-phase input power and converting it into a DC voltage;
A load terminal to which the DC voltage converted by the diode rectifier is supplied; And
And a controller configured to detect the input voltage and current input to the diode rectifier and control an output waveform output to the load terminal,
The control unit includes a first integrator for integrating the k-th input voltage, a future prediction voltage measurement unit for measuring a future prediction voltage of the input voltage integrated from the first integrator, and a future reference voltage from the voltage at the load terminal. A future reference voltage measurement unit, a cost function application unit that measures an absolute value of a difference between the future reference voltage and the future prediction voltage, and a switching state in which the absolute value of the difference between the future reference voltage and the future prediction voltage becomes minimum Rectifier control system comprising a switching control unit for controlling the diode rectifier by using. The method of claim 1,
The control unit further comprises a first input voltage delay unit for generating a k + 1 th input voltage by delaying the k th input voltage. The method of claim 2,
The future prediction voltage measuring unit receives a k+1 th input voltage and predicts a k+2 th input voltage. The method of claim 3,
The cost function application unit is a rectifier control system using a k+2th virtual future voltage and a k+2th future voltage. The method of claim 4,
The future reference voltage measurement unit measures the future reference voltage using a k+2 input power obtained by delaying the output value obtained by PI control of the voltage of the load terminal and the k-th input voltage twice. The method of claim 5,
The control unit includes a second input voltage delay unit configured to delay the k+1th input voltage output from the first input voltage delay unit to generate a k+2th input voltage,
A rectifier control system including a second integrator for integrating the k+2th input voltage output from the second input voltage delay unit. The method according to any one of claims 1 to 6,
The rectifier control system including the future prediction voltage measurement unit determined by the following equation.
<Equation>

(here,

Is k+2th future voltage,

Is the k+1th future voltage, L is the line inductance, R is the line resistance, icon is the current of the rectifier, vcon is the voltage of the rectifier, and Ts is the sampling period.) In the method of controlling a three-phase rectifier having a three-phase input stage, a diode rectifier, and a load stage,
Removing a harmonic component by integrating the k-th input voltage of the three-phase input terminal;
Measuring a predicted future voltage of the input voltage from which the harmonic component has been removed;
Measuring a future reference voltage from the voltage of the load terminal of the three-phase rectifier;
Measuring an absolute value of a difference between the future reference voltage and the future prediction voltage; And
And controlling the diode rectifier using a switching state in which an absolute value of a difference between the future reference voltage and the future prediction voltage becomes minimum. The method of claim 8,
A rectifier control method for generating a k+1 th input voltage by delaying the k th input voltage. The method of claim 9,
The measuring of the future predicted voltage includes receiving a k+1 th input voltage and predicting a k+2 th input voltage. The method of claim 10,
The step of measuring the absolute value of the difference between the future reference voltage and the future prediction voltage may include a rectifier control method using a k+2th virtual future voltage and a k+2th future voltage. The method of claim 11,
A rectifier control method for measuring the future reference voltage by using an output value obtained by PI control of the voltage of the load terminal and a k+2 input power obtained by delaying the k-th input voltage twice.

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