KR100707081B1 - Apparatus and method for controlling instantaneous current - Google Patents

Abstract

The present invention compensates the phase delay of the coupling reactor and the control stress of the PI controller by using the vector relationship between the output voltage of the inverter and the output voltage supplied to the grid in controlling the inverter of the solar power generation system.

According to the present invention, a current vector controller is provided, and the current vector controller calculates and calculates a phase angle to be corrected by the phase angle delay in the coupling reactor and the control delay phase angle generated by digitally controlling the inverter. The phase angle is corrected by generating a current phase correction value and a voltage phase correction value according to the phase angle. Therefore, the phase angle of the voltage and current supplied to the grid by the solar power system is matched, so that no reactive power is generated and the stress of the PI (Proportional Integral) controller is alleviated.

Inverter, instantaneous current, reactor, photovoltaic, PI controller, phase delay, compensation

Description

Instantaneous current control device and method {Apparatus and method for controlling instantaneous current}

1 is a circuit diagram showing the configuration of a typical grid-tied photovoltaic power generation system.

2 is a circuit diagram showing a configuration of a conventional instantaneous current control device.

3 is a diagram illustrating a phase relationship between an output voltage of the inverter of FIG. 1 and a power supply voltage supplied to a grid.

Figure 4 is a circuit diagram showing the configuration of the instantaneous current control device of the present invention.

5 is a signal flow diagram showing an instantaneous current control method of the present invention.

6A and 6B are waveform diagrams for explaining the phase relationship between voltage and current supplied to a system according to the prior art and the present invention;

* Explanation of symbols for main parts of drawings *

100: solar cell 120: inverter

130: coupling reactor 140: DC power capacitor

150: system 160: current sensor

170: PT (Potential Transformer) 400: current vector controller

410, 450: first and second multipliers 420: subtractor

430: PI (Proportional Integral) controller

440: adder 460: triangle wave generator

470: comparator P _LL : phase difference detection signal

I _REF : Reference Current I _ME : Current Detection Signal

I _ER : error current signal V _ME : voltage detection signal

The present invention relates to an instantaneous current control device and method for controlling the switching operation of the inverter when the inverter converts the DC power charged in the battery into a single-phase AC power supply to the grid.

More specifically, in the solar power generation system, when the inverter converts the high current and low voltage DC power charged into the battery into a single phase AC power and supplies it to the system, the output voltage of the inverter and the output voltage supplied to the system The instantaneous current control device and method for compensating the phase delay of the coupling reactor generated when the instantaneous current is controlled and the control stress of the PI (Proportional Integral) controller using the vector relationship

In general, a photovoltaic power generation system generates DC power using a solar cell, and the generated DC power is usually charged in a battery or the like. And the high current and low voltage DC power charged in the battery is converted into a commercial AC power of 60 kW, which is easy to use using an inverter, an energy converter, and transferred to the system to supply the load.

In the photovoltaic power generation system, in order to maximize the conversion efficiency of converting the DC power charged in the battery into AC power and transferring it to the system, the efficiency of the inverter should be maximized.

In general, the grid-connected type applied to linear and nonlinear loads uses a control method for synchronizing the output voltage of the inverter with the voltage supplied to the grid when controlling the instantaneous current. In this case, a coupling reactor must be used between the inverter and the grid.

However, when the switching operation of the inverter is controlled by the instantaneous current, a phase delay occurs by the coupling reactor, and a voltage drop occurs in the coupling reactor.

1 is a circuit diagram showing the configuration of a typical grid-tied photovoltaic power generation system.

Here, reference numeral 100 denotes a solar cell. The solar cell 100 receives direct sunlight to generate direct current power. Reference numeral 110 denotes a DC power capacitor. The DC power capacitor 110 is configured of, for example, a battery to charge the DC power of the high current and the low voltage generated by the solar cell 100.

Reference numeral 120 is an inverter. The inverter 120 uses, for example, an Insulated Gate Bipolar Transistor (IGBT) as a switching element, and the switching element of the inverter 120 repeatedly turns on and off in response to a pulse width modulation (PWM) switching signal input. The DC power supplied from the DC power capacitor 110 is switched to generate PWM power.

Reference numeral 130 is a coupling reactor, and reference numeral 140 is a capacitor. The coupling reactor 130 and the capacitor 140 constitute a high frequency filter and convert the PWM power generated by the inverter 120 into AC power of a sine wave.

Reference numeral 150 is a strain. The system 150 serves to supply the AC power filtered through the high frequency filter composed of the coupling reactor 130 and the capacitor 140 to the load. Here, in the system linkage type, a plurality of systems 150 may be connected in parallel.

In the photovoltaic power generation system having such a configuration, the solar cell 100 receives solar light to generate DC power, and the generated DC power is charged in the DC power capacitor 110.

The high current and low voltage DC power charged in the DC power capacitor 110 is supplied to the inverter 120.

The inverter 120 is repeatedly switched on and off in accordance with the PWM switching signal input from the instantaneous current control device.

Then, the DC power supplied from the DC power capacitor 110 is switched according to the on and off of the switching element of the inverter 120 to generate PWM power.

The PWM power generated by the inverter 120 is transferred to the grid 150 by a predetermined level of current I _L through the coupling reactor 130 and the capacitor 140, thereby generating energy generated by photovoltaic power generation. It is delivered to system 150 by 120.

Here, the high frequency filter composed of the coupling reactor 130 and the capacitor 140 serves to filter the PWM power generated by the inverter 120 to transmit sinusoidal AC power to the system 150.

In such a photovoltaic power generation system, the inverter 120 is an energy converter that supplies AC power to the system 150 by switching high current and low voltage DC power charged in the DC power capacitor 110. Several types of inverters 120 are known, including several.

The grid type inverter used for general household uses instantaneous current control to control 60 VAC commercially.

In general, when supplying only the effective power having a power factor of 1 to the system 150, a coupling reactor 130 must be provided between the inverter 120 and the system 150. In order to supply only active power from the inverter 120 to the grid 150, the current flowing through the coupling reactor 130 is in phase with the voltage of the grid 150, and the magnitude thereof is equal to the amplitude of the voltage output from the inverter 120. You can adjust the phase appropriately.

As shown in FIG. 2, the output voltage V _I of the inverter 120 is out of phase with the voltage Vs of the system 150, and the amplitude 150 maintains a relationship of V _I = Vs / cos θ. The current I _L , in phase with, can be supplied.

However, in this case, in order to prevent a circulating current generated between the plurality of systems 150, a coupling reactor 130 of an appropriate value is required, and thus, a voltage drop (V _L ) that cannot be ignored in the coupling reactor 130. ) Occurs.

The voltage drop in the coupling reactor 130 increases the reactive power that the inverter 120 should supply to the coupling reactor 130 so that the capacity of the combined apparent power KVA of the inverter 120 increases. do.

And if the relationship for supplying only the active power to the system 150 is not correctly established, if the previous relationship for the flow is not correctly established, the current of the reactive power component also flows to the system 150.

Therefore, the conventional instantaneous current control device detects the output current supplied to the system 150 by using a current sensor 160 such as a current transformer to prevent the current of reactive power component flows to the system 150, PT ( Potential Transformer (170) is used to detect the output voltage supplied to the system (150).

The output current detected by the current sensor 160 is classified into an active power component and a reactive power component, and the output voltage and frequency of the inverter 120 are finely adjusted using the output current.

This conventional instantaneous current control device will be described with reference to FIG. 3.

3 is a circuit diagram showing the configuration of a conventional instantaneous current control device. Here, the symbol P _LL is a phase angle detection signal. The phase angle detection signal P _LL is a signal that detects a phase angle synchronized with the voltage output to the system 150 and has a maximum value of sin θ of ± 1.

The phase angle detection signal P _LL is multiplied by a preset proportional constant K ₁ in the first multiplier 300 to generate a reference current I _REF for switching the switching element of the inverter 120. That is, I _REF = K ₁ sin θ is generated.

The generated reference current (I _REF) is a detected current (I _ME), i.e., the detected current (I _ME) having a predetermined magnitude and phase of the current sensor 160 is subtracted by the subtractor 310, the error current signal ( I _ER ) is calculated, and the calculated error current signal I _ER is PI controlled by the PI controller 320 to calculate a compensation voltage.

The compensation voltage calculated by the PI controller 320 is added to the detection voltage V _ME of the system 150 detected by the PT 170 in the adder 330. That is, the detection voltage V _ME having a predetermined magnitude and phase is added.

The output signal of the adder 330 is multiplied by a preset proportional constant K ₂ in the second multiplier 340 to generate a switching voltage for switching the inverter 120. The switching voltage is compared with the triangular wave generated by the triangular wave generator 350 in the comparator 360 to generate a PWM signal, and the generated PWM signal is output as a switching signal to switch the switching element of the inverter 120. .

As described above, the output voltage (V _I ) of the inverter 120 is in phase with the voltage (Vs) of the system 150, and the amplitude must maintain the relational expression of V _I = Vs / cos θ in phase with the system 150. Phosphorous current I _L can be supplied.

However, the relational expression as described above is an ideal case. In the case of controlling the inverter 120 substantially, in the digital control system, the measured value is necessarily calculated by a digital signal processor (DSP), which means that the switching period of the inverter 120 Therefore, the phase delay occurs according to the interrupt time generated when switching several inverters.

This phase delay is caused by a digital system rather than an analog system that is controlled in real time, and a time delay inevitably occurs as much as the computation time of the digital system. In addition, since there is a voltage drop component generated in the coupling reactor, a phase difference occurs when the instantaneous current is controlled.

Therefore, in the case where the PI controller 320 follows the current reference value, the portion that the PI controller 320 is responsible for becomes substantially large.

In addition, since the instantaneous current is an alternating current, current reference values are alternately instantaneously, which increases the control stress of the instantaneous current controller.

In general, in the case of a current controller or a voltage controller of a three-phase inverter system, the PI controller does not control alternating alternating currents, but controls the direct current so that the PI controller has less control stress.

However, in the case of single-phase AC inverter system, the control of alternating current generally increases the stress of the PI controller. Actually, the P (Proportional) gain in the PI controller is mostly responsible, and the value of I (Integral) gain is the value of P gain. It is significantly smaller than that.

Since the power supply voltage is not a perfect AC value in most cases, when the power supply voltage is distorted, the part that the P controller must take charge of in the rapidly changing part becomes large and the control is not performed smoothly.

The object of the present invention is to use the phase delay of the coupling reactor generated when controlling the instantaneous current and the control stress of the PI (Proportional Integral) controller by using the vector relationship between the output voltage of the inverter and the output voltage supplied to the grid. The present invention provides a supplementary instantaneous current control device and method.

According to the instantaneous current control apparatus and method of the present invention having this purpose, there is provided a current vector controller for compensating the delayed phase angle. The current vector controller calculates a phase angle at which a voltage is delayed in a coupling reactor provided between the inverter and the grid, and calculates the delay phase angle and the control delay phase angle generated by controlling the inverter and the phase of the voltage supplied to the grid. Calculate the phase angle to be corrected for each detected signal. And multiplying the calculated phase angle by a current magnitude value and a voltage magnitude value to generate a current phase correction value and a voltage phase correction value, and generate a PWM switching signal according to the generated current phase correction value and the voltage phase correction value. To control the switching operation of the inverter.

Therefore, the instantaneous current control device of the present invention, the inverter for converting DC power into PWM power; A coupling reactor and a capacitor for filtering and outputting the output power of the inverter; A current vector controller which calculates a current phase correction value and a voltage phase correction value from the phase angle detection signal, the current detection signal, and the voltage detection signal of the voltage output to the system; A first multiplier generating a reference current signal by multiplying the phase angle detection signal by a predetermined proportional constant; A subtractor for calculating an error current signal by subtracting a current phase correction value generated by the current vector controller from a reference current signal generated by a first multiplier; A PI (Proportional Integral) controller for generating a compensation voltage by PI controlling the error current signal calculated by the subtractor; An adder for adding a voltage phase correction value generated by the current vector controller to a compensation voltage calculated by the PI controller; A second multiplier generating a switching voltage by multiplying an output signal of the adder by a preset proportional constant; And a comparator for generating a PWM switching signal by comparing a level of the switching voltage generated by the second multiplier with a triangle wave of a predetermined frequency and outputting the PWM switching signal to the inverter.

In addition, the instantaneous current control device of the present invention includes a solar cell for converting sunlight into direct current power; And a DC power capacitor which charges the DC power converted by the solar cell and supplies the DC power to the inverter, and detects a current supplied to the system and outputs a current detection signal to the current vector controller. And a PT (Potential Transformer) for detecting a voltage supplied to the system and outputting a voltage detection signal to the current vector controller.

And instantaneous current control method of the present invention, the step of calculating the phase angle at which the voltage is delayed in the coupling reactor provided between the inverter and the grid; Calculating a phase angle to be corrected using the calculated delay phase angle; Generating a current phase correction value and a voltage phase correction value at the calculated phase angles to be corrected; And generating a PWM switching signal according to the current phase correction value and the voltage phase correction value to control the switching operation of the inverter.

Calculating the delay phase angle; Calculating a voltage across the coupling reactor by a preset equation; And calculating a delay phase angle of the coupling reactor by a preset equation.

Calculating the phase angle to be corrected; And a phase angle of the coupling reactor, a control delay phase angle generated by digitally controlling the inverter, and a phase angle of a voltage supplied to the system.

Generating the current phase correction value and the voltage phase correction value; Generating a current phase correction value by multiplying the magnitude value of the current supplied to the system by the value of the phase angle to be corrected; And generating a voltage phase correction value by multiplying the magnitude value of the voltage supplied to the system by the value of the phase angle to be corrected.

4 is a circuit diagram showing the configuration of the instantaneous current control device of the present invention. Here, the symbol P _LL is a phase angle detection signal. The phase angle detection signal P _LL is a signal that detects a phase angle synchronized with the voltage output to the system 150 and has a maximum magnitude of sin θ of ± 1.

Symbol I _ME is a current detection signal. The current detection signal I _ME is a signal that detects the magnitude and phase angle of the current supplied to the system using the current detection sensor 160 such as a current transformer.

The symbol V _ME is a voltage detection signal. The voltage detection signal V _ME is a signal that detects the magnitude and phase angle of the voltage supplied to the system using a PT (Potential Transformer) 170.

Reference numeral 400 is a current vector controller. The current vector controller 400 uses a phase angle detection signal P _LL , a current detection signal I _ME , and a voltage detection signal V _ME to determine a current phase correction value having a current and phase angle of a predetermined magnitude. I _COM ) and a voltage phase correction value V _COM having a voltage and phase angle of a predetermined magnitude are calculated.

Reference numeral 410 is a first multiplier. The first multiplier 410 multiplies the phase angle detection signal P _{LL by} a predetermined proportional constant K ₁ to generate a reference current signal I _REF having a predetermined magnitude and phase.

Reference numeral 420 is a subtractor. The subtractor 420 subtracts the current phase correction value I _COM generated by the current vector controller 400 from the reference current signal I _REF generated by the first multiplier 410, thereby generating an error current signal I. _ER ).

Reference numeral 430 is a PI controller. The PI controller 430 PI-controls the error current signal I _ER calculated by the subtractor 420 to generate a compensation voltage.

Reference numeral 440 is an adder. The adder 440 adds the voltage phase correction value V _COM generated by the current vector controller 400 to the compensation voltage calculated by the PI controller 430.

Reference numeral 450 is a second multiplier. The second multiplier 450 multiplies the output signal of the adder 440 by a preset proportional constant K ₂ to generate a switching voltage.

Reference numeral 460 denotes a triangular wave generator. The triangular wave generator 460 generates a triangular wave of a predetermined frequency.

Reference numeral 470 is a comparator. The comparator 470 generates a PWM switching signal by comparing the switching voltage generated by the second multiplier 450 with the level of the triangular wave generated by the triangular wave generator 460.

The instantaneous current control device of the present invention configured as described above includes a phase angle detection signal P _LL for detecting a phase angle of a voltage supplied to a system according to the operation of an inverter, and a current detection for detecting a supply current of a system by a current detection sensor. A signal I _ME and a voltage detection signal V _{ME at which} PT detects a supply voltage of a system are input to the current vector controller 400.

As illustrated in FIG. 5, the current vector controller 400 multiplies the magnitude value I _I of the current in the current detection signal I _ME by ωL to form the coupling reactor 130. The voltage VL at both ends is calculated (S500).

Where ω is 2πf, f is frequency, and L is the inductance of the coupling reactor 130.

When the voltage V _L at both ends of the coupling reactor 130 is calculated, the current vector controller 400 calculates a phase angle θ ₁ delayed by the coupling reactor 130 using Equation 2 below. Calculate (S502).

Here, V _S is a magnitude value of the voltage in the voltage detection signal V _ME .

When the phase angle θ ₁ delayed by the coupling reactor 130 is calculated, the phase of the control delay phase generated as the instantaneous current control device controls the switching of the inverter 120 as shown in Equation 3 is determined. The total delayed phase angle θ ₂ is calculated by adding to the angle θ ₁ (S504).

When the total delayed phase angle θ ₂ is calculated as described above, the phase angle θ to be corrected is calculated by adding the phase angle θ ₂ to the phase angle of the phase angle detection signal P _LL as shown in Equation 4. (S506).

And a current phase correction value I _COM having a magnitude value of the current detection signal I _ME and the phase angle θ to be corrected, a magnitude value of the voltage detection signal V _ME , and a phase angle to be corrected. A voltage phase correction value V _COM having a θ is calculated (S508), and the calculated current phase correction value I _COM and the voltage phase correction value V _COM are output to generate a switching signal.

As shown in FIG. 4, the switching signal is generated by the first multiplier 410 multiplying the phase angle detection signal P _LL by a preset proportional constant K ₁ to the reference current I _REF . The subtractor 420 subtracts the current phase correction value I _COM to calculate the error current signal I _ER .

The error current signal I _ER is PI controlled by the PI controller 430 to calculate a compensation voltage, and the calculated compensation voltage is added by the adder 440 to the voltage phase correction value V _COM . In the multiplier 450, a preset proportional constant K ₂ is multiplied to generate a switching voltage for switching the inverter 120.

The switching voltage is compared with the triangular wave generated by the triangular wave generator 460 in the comparator 470 to generate a PWM signal, and the generated PWM signal is output as a switching signal to switch the switching element of the inverter 120. .

The present invention substantially compensates the delay compensation of the phase angle to be handled by the PI controller 430 so that the current vector controller 400 is ahead of the phase of the actual voltage.

Therefore, the compensation of the phase delay is improved as well as the power factor.

FIG. 6A is a graph illustrating a phase of voltage and current output to the system 150 when the switching of the inverter 120 is controlled by the conventional instantaneous current controller shown in FIG. 2, and FIG. 6B is a graph of FIG. 4. 5 is a graph showing the phase of the voltage and current output to the system 150 when controlling the switching of the inverter 120 according to the instantaneous current control apparatus and method of FIG. 5.

As shown in FIG. 6A, when the switching of the inverter 120 is controlled by the conventional instantaneous current controller, the phases of the voltage and the current output to the system 150 do not match, and are invalid as the phase does not match. It can be seen that the power is generated and the efficiency is low, and the glitch is generated in the part where the voltage is distorted.

However, when controlling the switching of the inverter 120 with the instantaneous current control device of the present invention, as shown in FIG. 6B, the phases of the voltage and the current output to the system 150 coincide.

Therefore, almost no reactive power was generated. In addition, even when the power output to the system 150 is distorted, since the stress of the PI controller 430 is reduced, it could be confirmed that distortion of the current does not occur.

On the other hand, while the present invention has been shown and described with respect to specific preferred embodiments, various modifications and changes of the present invention without departing from the spirit or field of the invention provided by the claims below It can be easily understood by those skilled in the art.

As described in detail above, the present invention calculates the current phase correction value and the voltage phase correction value with the phase angle detection signal, the current detection signal, and the voltage detection signal of the voltage output from the current vector controller to the system, and calculates the current phase correction. Compensate for the phase delay according to the value and the voltage phase correction value.

Therefore, the phase of voltage and current supplied to the system is matched to improve the power factor, to reduce the stress of the PI controller, and to improve the overall performance and efficiency of the photovoltaic system.

Claims (7)

An inverter for converting DC power into PWM power; A coupling reactor and a capacitor for filtering and outputting the output power of the inverter; A current vector controller which calculates a current phase correction value and a voltage phase correction value from the phase angle detection signal, the current detection signal, and the voltage detection signal of the voltage output to the system; A first multiplier generating a reference current signal by multiplying the phase angle detection signal by a predetermined proportional constant; A subtractor for calculating an error current signal by subtracting a current phase correction value generated by the current vector controller from a reference current signal generated by a first multiplier; A PI (Proportional Integral) controller for generating a compensation voltage by PI controlling the error current signal calculated by the subtractor; An adder for adding a voltage phase correction value generated by the current vector controller to a compensation voltage calculated by the PI controller; A second multiplier generating a switching voltage by multiplying an output signal of the adder by a preset proportional constant; And And a comparator for comparing the level of the switching voltage generated by the second multiplier with a triangle wave of a predetermined frequency to generate a PWM switching signal and outputting the PWM switching signal to the inverter. The method of claim 1, A solar cell converting sunlight into direct current power; And Instantaneous current control device characterized in that it further comprises a DC power capacitor to charge the DC power converted by the solar cell and to supply to the inverter. The method of claim 1, A current sensor detecting a current supplied to the system and outputting a current detection signal to the current vector controller; And And a PT (Potential Transformer) for detecting a voltage supplied to the system and outputting a voltage detection signal to the current vector controller. Calculating a phase angle at which a voltage is delayed in a coupling reactor provided between the inverter and the grid; Calculating a phase angle to be corrected using the calculated delay phase angle; Generating a current phase correction value and a voltage phase correction value at the calculated phase angles to be corrected; And And generating a PWM switching signal according to the current phase correction value and the voltage phase correction value to control a switching operation of the inverter. 5. The method of claim 4, wherein calculating the delay phase angle; Calculating a voltage across the coupling reactor by Equation 1; And The instantaneous current control method comprising the step of calculating the delay phase angle of the coupling reactor by the equation (2). Equation 1

Where V _L is the voltage across the coupling reactor, ω is 2πf, f is the frequency, and L is the inductance of the coupling reactor. Equation 2

Here, θ ₁ is the delay phase angle of the coupling reactor, and V _S is the magnitude value of the voltage supplied to the system. 5. The method of claim 4, wherein calculating the phase angle to be corrected comprises: And calculating a phase angle of the coupling reactor, a control delay phase angle generated by digitally controlling the inverter, and a phase angle of a voltage supplied to the system. 5. The method of claim 4, wherein generating the current phase correction value and the voltage phase correction value; Generating a current phase correction value by multiplying the magnitude value of the current supplied to the system by the value of the phase angle to be corrected; And And multiplying the magnitude value of the voltage supplied to the system by the value of the phase angle to be corrected to generate a voltage phase correction value.

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