KR101870749B1 - Control apparatus for grid connected type single stage forward-flyback inverter - Google Patents

Abstract

The present invention relates to a technology capable of adjusting output power by simultaneously applying a current discontinuous mode and a current continuous mode to a grid-connected single stage flyback inverter and reducing a superharmonic distortion rate. A control device of the present invention comprises a control unit for tracking a grid voltage sensed from a system power source of a single stage flyback inverter unit to synchronize a current of a flyback converter unit and a voltage of the grid power source to have the same phase, and calculating a duty ratio of a pulse width modulation signal for switching switching elements of a single stage flyback converter unit on the basis of the summing result of a feedback current proportional to an error current which is a difference value between a synchronized output current and a reference output current and a running current updated while performing down-sampling and up-sampling on one cycle of error values.

Description

[0001] CONTROL APPARATUS FOR GRID CONNECTED TYPE SINGLE STAGE FORWARD-FLYBACK INVERTER [0002]

The present invention relates to a technique for controlling the driving of a grid-connected single-stage flyback inverter, and more particularly, to a grid-connected single-stage flyback inverter in which a current discontinuity mode and a current continuous mode are simultaneously applied to control output power, Stage fly-fly inverter that can attenuate the load of the single-stage fly-back inverter.

The grid-connected single-stage flyback inverter is a type of inverter that converts DC voltage generated from a renewable energy source such as a photovoltaic module that generates power using solar light into AC voltage and supplies it to the power grid. .

FIG. 1 is a circuit diagram of a single-stage flyback inverter unit included in a grid-connected single-stage flyback inverter according to the related art. As shown in FIG. 1, the grid- Unfolding bridge circuitry 120, an output filter 130, and a grid power supply 140. [

The flyback converter unit 110 converts the input DC power (V _DC ) into a voltage in the form of full wave rectification of a sinusoidal wave and outputs the converted voltage. To this end, the flyback converter unit 110 includes a primary side circuit unit and a secondary side circuit unit.

The primary side circuit unit includes an input capacitor C _in connected between both input terminals of the input DC power supply V _DC , a switch S 1 for switching the input power supplied through the input capacitor C _in , And a primary coil N _p of the transformer T switched by the switch S1. The switch S1 performs a switching operation by a control unit (not shown in the drawing) to transmit the input DC power supply V _DC to the secondary side of the transformer T. [

A secondary side circuit is provided with a secondary coil (N _s) and the diode (D) of the transformer (T), the switch (S1) when one off-state AC voltage is supplied through the secondary coil (N _s) (for example, : Sine wave) into a full-wave rectified voltage.

The unfolding bridge circuit unit 120 converts the voltage of the sine wave supplied from the flyback converter unit 110 into a full-wave rectified voltage to an AC voltage and links it to the system power supply 140. To this end, the unfolding bridge circuit unit 120 includes switches S2, S3, S4 and S5 connected in series between the output terminals of the flyback converter unit 110, respectively.

The switch S2 and the switch S5 are turned on and the switch S3 and the switch S4 are turned off when a positive sinusoidal wave is applied to the system power supply 140 in the unfolding bridge circuit unit 120, The half-period voltage is output as it is. However, when a negative sinusoidal wave is applied to the system power supply 140, the switches S3 and S4 are turned on and the switches S2 and S5 are turned off so that the remaining half of the full- Converted to a negative voltage and output.

The output filter 130 serves to attenuate the ripple of the voltage and current output from the unfolding bridge circuit unit 120. The output filter 130 includes a capacitor C _f connected between the output terminals of the unfolding bridge circuit unit 120 and one terminal of the capacitor C _f and one terminal of the system power supply 140. comprising an inductor (L _f), and connected to, the other terminal of said capacitor (C _f) is connected to the other terminal of the power grid 140. the

The grid-connected single-stage flyback inverter should be equipped with means for regulating the output power to supply the electric energy of the DC power source generated from the renewable energy source to the power grid in its entirety. In addition, the grid-connected single-stage flyback inverter must have a full harmonic distortion rate below a certain level to avoid harming the quality of the power grid. In order to control the output power and to reduce the distortion rate, the grid-connected single-stage flyback inverter is provided with a control device, and a feedback control method and a feedforward control method are mainly applied to the control device.

There are current continuous mode and current discontinuous mode in the operation mode of the grid-connected single-stage flyback inverter. Inevitably, when the output power is increased by the same circuit, the operation mode is changed from the current discontinuous mode to the current continuous mode.

2 is a graph showing an output current when a proportional-integral controller using a reference duty and an error current is applied to a grid-connected single-stage flyback inverter according to the related art.

However, the conventional single stage flyback inverter is designed to operate only in the current discontinuous mode due to difficulty in adjusting the output power or attenuating the distortion rate in the current continuous mode. As a result, the conventional single stage flyback inverter has a problem that the range of the output power that can be handled is limited.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a grid-type single-stage flyback inverter that uses a reference duty voltage in an electric current discontinuity mode and a current continuous mode, The duty ratio of the switching control signal for controlling the switching operation of the switching element of the single-stage flyback converter unit can be determined.

According to another aspect of the present invention, there is provided a control apparatus for a grid-connected single-stage flyback inverter, including a flyback converter unit for converting an input DC power source into a full-wave rectified voltage, Stage flywheel inverter unit having an unfolding bridge circuit unit for converting the full-wave rectified voltage into an alternating-current voltage and connecting it to the system power supply; A system voltage sensing unit for monitoring a system voltage sensed from the system power supply so as to synchronize the current of the flyback converter unit with the voltage of the system power supply so as to have the same phase, A control unit for calculating a duty ratio based on the sum of the updated running currents while performing downsampling and upsampling on feedback currents and error values of one cycle; A switch gate driver for controlling a switching operation of a first switch provided in the flyback converter unit using a pulse width modulation signal in which the duty ratio is reflected; And an unfolding gate driver for controlling switching operations of the second to fifth switches provided in the unfolding bridge circuit unit according to the pulse width modulation signal generated using the reference duty synchronized by the controller. do.

Stage flyback converter using the error current corresponding to the difference between the reference duty current and the reference current in the current discontinuous mode and the current continuous mode of the grid-connected single-stage flyback inverter, The duty ratio of the switching control signal for controlling the switching operation of the switching element of the sub-unit is determined, so that the output power can be appropriately adjusted and the ultrahigh harmonic distortion ratio can be reduced.

1 is a circuit diagram of a conventional single stage flyback inverter unit.
2 is a graph showing output currents of a conventional single-stage flyback inverter of a grid-connected type.
3 is a block diagram of a control apparatus for a grid-connected single-stage flyback inverter according to an embodiment of the present invention.
FIG. 4 is a detailed block diagram of the non-repetitive control unit and the repetitive learning control unit in FIG.
FIG. 5 is a graph showing output currents of a grid-connected single-stage flyback inverter to which the downsampled iterative learning control method according to the present invention is applied.

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

FIG. 3 is a block diagram of a control apparatus for a grid-connected single stage flyback inverter according to an embodiment of the present invention. As shown in FIG. 3, the grid-connected single stage flyback inverter 100 includes a single stage flyback inverter unit 100A And a control unit 100B.

The single stage flyback inverter unit 100A includes a flyback converter unit 110, an unfolding bridge circuit unit 120, an output filter 130, and a system power supply 140, and operates in the same manner as in FIG.

That is, the flyback converter unit 110 converts the input DC power (V _DC ) into a voltage in the form of full wave rectification of the sinusoidal wave and outputs it. To this end, the flyback converter unit 110 includes a primary side circuit unit and a secondary side circuit unit.

The primary side circuit unit includes an input capacitor C _in connected between both input terminals of the input DC power supply V _DC , a switch S 1 for switching the input power supplied through the input capacitor C _in , And a primary coil N _p of the transformer T switched by the switch S1. The switch S1 is switched by the control unit 220 to transmit the input DC power V _DC to the secondary side of the transformer T. [

A secondary side circuit is provided with a secondary coil (N _s) and the diode (D) of the transformer (T), the switch (S1) when one off-state AC voltage is supplied through the secondary coil (N _s) (for example, : Sinusoidal voltage) into a full-wave rectified voltage.

Unfolding bridge circuit 120 serves to change the voltage of the sine wave supplied from the flyback converter 110, to form the full-wave rectification AC voltage associated with the power system (v _g). To this end, the unfolding bridge circuit unit 120 includes switches S2, S3, S4 and S5 connected in series between the output terminals of the flyback converter unit 110, respectively.

The switch S2 and the switch S5 are turned on and the switch S3 and the switch S4 are turned off when a positive sinusoidal wave is applied to the system power supply 140 in the unfolding bridge circuit unit 120, The half-period voltage is output as it is. However, when a negative sinusoidal wave is applied to the system power supply 140, the switches S3 and S4 are turned on and the switches S2 and S5 are turned off so that the remaining half of the full- Converted to a negative voltage and output.

The output filter 130 serves to attenuate the ripple of the voltage and current output from the unfolding bridge circuit unit 120.

The control unit 100B includes a first low pass filter 210A and a second low pass filter 210B, a control unit 220, a switch gate driver 230 and an unfolding gate driver 240.

The first low pass filter 210A low-pass filters the system voltage v _g sensed from the system power supply 140.

The second low-pass filter 210B low-pass filters the output current i _Lf sensed from the system power supply 140.

The control unit 220 receives the low-pass filtered system voltage and the output current, calculates an error current corresponding to the difference between the output current and the reference current, and controls the switching operation of the flyback converter unit 110 Thereby determining the duty ratio of the switching control signal.

The control unit 220 includes a first analogue digital converter 221A and a second analogue digital converter 221B, a phase locked loop (PLL) 222, a line frequency switching unit 223, an output current calculator 224 A non-iterative control unit 226, a memory unit 227, an iterative learning controller 228, and a first adder 225A, a second adder 225B, a second adder 225B, a non-iterative control unit 226, And a modulation generator (PWM generator) 229.

A first analog-to-digital converter (221A) to convert a first low-pass filter (210A) low grid voltage (v _g) of the filtered analog by a digital signal.

The second analog-to-digital converter 221B converts the analog output current (i _Lf ) low-pass filtered by the second low-pass filter 210B into a digital signal.

The phase locked loop 222 tracks when the system voltage converted into the digital signal supplied through the first analog-to-digital converter 221A becomes 0 V and outputs the current of the flyback converter unit 110 to the system power supply 140. [ So that they can be synchronized with each other. For example, the phase locked loop 222 may perform a synchronization function by extracting a 60 Hz signal using a notch filter, and then continuously fixing the phase value using an error value.

The line frequency switching unit 223 compares the reference duty voltage supplied from the phase locked loop 222 with a first triangular waveform of a predetermined frequency (e.g., 50 KHz) and outputs pulse width modulated signals having a duty ratio corresponding thereto .

The output current calculation section 224 calculates an output current y (k) from the current supplied from the phase locked loop 222. [

delete

The first summer 225A calculates and outputs an error current e (k) which is a difference between the output current y (k) supplied from the output current calculator 224 and the reference output current y_d (k).

The non-repetitive control unit 226 outputs the fixed current u _ff (k) and the feedback current u _fb (k) on the basis of the output signal of the first summer 225A. To this end, the non-repetitive control section 226 includes a nominal duty voltage output section 226A and a proportional controller 226B.

As shown in FIG. 4, the nominal duty voltage output section 226A outputs the nominal duty voltage output 226A, which is a fixed constant current for each cycle according to the input / output voltage of the grid-connected single-stage flyback inverter 100 and the parameters of the grid- u _ff (k).

The proportional controller 226B outputs the feedback current u _fb (k) proportional to the error current e (k) output from the first summer 225A as shown in FIG. 4, thereby reducing the current error.

The memory unit 227 stores error values of one period using the error current e (k) output from the first summer 225A. The iterative learning control unit 228 down-samples and up-samples the error values of one cycle stored in the memory unit 227 and updates the learning values according to the update result. u _i (k). The nominal duty voltage output unit 226A does not operate smoothly in the continuous operation mode of the single stage flyback inverter unit 100A. The iterative learning control unit 228 plays a role of generating a desired output current through an iterative learning process do.

4, the repetition learning control unit 228 includes a downsampling unit 228A for downsampling the error values of the one cycle, a pair of error correction units 228A and 228B for storing error values downsampled by the downsampling unit 228A, A learning control arithmetic operation unit 228D for generating a desired output current by performing iterative learning on error values stored in the memory 228B, 228C, and the pair of memories 228B, 228C, And an up-sampling unit 228E for up-sampling the output current outputted from the calculating unit 228D and outputting the running current u _i (k).

There is a problem that the error grows instantaneously in the course of learning in the case of using the normal iterative learning controller. This causes a power semiconductor device having a high limit voltage value to be used, and the drain-source resistance value of the power semiconductor device is naturally increased, which lowers the power conversion efficiency of the circuit. Therefore, it is very important to satisfy the monotone reduction characteristic of errors when using the iterative learning controller.

However, in the single stage flyback inverter section 100A operating in the continuous conduction mode, the dynamics of the system can be reduced, There is a limit in that the gain of the proportional controller can not be increased in the single stage flyback inverter. In order to overcome this limitation, the iterative learning control unit 228 performs the downsampled iterative learning control as described above so that the monotone reduction property of the error is satisfied.

In addition, since the downsampled iterative learning controller can be implemented using a smaller capacity memory than a normal iterative learning controller, it has an advantage that the cost of the circuit configuration can be reduced.

The second summing unit 225B receives the fixed current u _ff (k) supplied from the nominal duty voltage output unit 226A, the feedback current u _fb (k) supplied from the proportional controller 226B and the repetitive learning control unit 228, And outputs a sum current u _c (k) corresponding to the sum of the running currents u _i (k). Here, the fixed current u _ff (k) is a current related to a nominal duty. By generating the fixed current u _ff (k), the feedback current u _fb (k), and the running current u _i (k) supplied to the second summer 225B through the above-described process, 100B can be simultaneously applied to the current discontinuous mode and the current continuous mode of the single stage flyback inverter unit 100A to adjust the output power and attenuate the ultrahigh harmonic distortion rate.

The pulse width modulation signal generator 229 outputs a pulse width modulation signal having a pulse width corresponding to the sum current u _c (k) supplied from the second summer 225B.

The switch gate driver 230 appropriately processes the pulse width modulated signal output from the pulse width modulated signal generator 229 and outputs the pulse width modulated signal PWM1 having a predetermined frequency to the flyback converter unit 110 And outputs it to the gate of the switch S1. As a result, the switch S1 is switched by the pulse width modulation signal PWM1.

The unfolding gate driver 240 appropriately processes the pulse width modulation signals supplied from the line frequency switching unit 223 and outputs a pulse width modulation signal PWM2-PWM5 having a predetermined frequency (e.g., 50 KHz) To the gates of the switches S2-S5 of the folding bridge circuit unit 120. [ Thus, the switches S2 to S5 are switched by the pulse width modulation signals PWM2 to PWM5.

Meanwhile, FIG. 5 is a graph showing output currents of a grid-connected single-stage flyback inverter to which the downsampled iterative learning control method according to the present invention is applied.

Although the preferred embodiments of the present invention have been described in detail above, it should be understood that the scope of the present invention is not limited thereto. These embodiments are also within the scope of the present invention.

100: Grid-connected single stage flyback inverter
100A: Single stage flyback inverter unit
100B: control unit 110: flyback converter unit
120: unfolding bridge circuit part 130: output filter
140: system power supply 210A, 210B: low-pass filter
221A, 221B: analog-to-digital converter 222: phase locked loop
223: Line frequency switching unit 224: Output current calculation unit
225A: first adder 225B: second adder
226: non-repetitive control section 226A: nominal duty voltage output section
226B: Proportional controller 227:
228: Repetition learning control section 229: Pulse width modulation signal generator
230: Switch gate driver 240: Unfolding gate driver

Claims (6)

Stage flyer having a flyback converter unit for converting an input DC power supply into a full-wave rectified voltage, and an unfolding bridge circuit unit for converting the full-wave rectified voltage supplied from the flyback converter unit to an AC voltage to be connected to a system power supply. Back inverter;
A system voltage sensing unit for monitoring a system voltage sensed from the system power supply so as to synchronize the current of the flyback converter unit with the voltage of the system power supply so as to have the same phase, A control unit for calculating a duty ratio based on the sum of the updated running currents while performing downsampling and upsampling on feedback currents and error values of one cycle;
A switch gate driver for controlling a switching operation of a first switch provided in the flyback converter unit using a pulse width modulation signal in which the duty ratio is reflected; And
And an unfolding gate driver for controlling switching operations of the second to fifth switches provided in the unfolding bridge circuit unit according to the pulse width modulation signal generated using the reference duty synchronized by the controller,
The control unit
A phase locked loop for tracking when the system voltage becomes 0V and synchronizing the current of the flyback converter unit and the voltage of the system power supply to have the same phase;
An output current calculation unit for calculating an output current from a current supplied from the phase locked loop;
A first summing unit for obtaining the error current which is a difference between the output current and the reference output current;
A non-repetitive control unit for outputting a fixed current and a feedback current based on an output signal of the first summer;
An iterative learning control unit for downsampling and upsampling the error values of one cycle for updating and outputting a running current according to the update result;
A second summing unit for summing the fixed current, the feedback current, and the running current to output a sum current corresponding thereto; And
And a pulse width modulation signal generator for generating a pulse width modulation signal reflecting the duty ratio based on the sum current.
delete The method of claim 1, wherein the phase locked loop
And a notch filter is provided for extracting a signal of a desired frequency.
The apparatus of claim 1, wherein the non-repetitive control unit
A nominal duty voltage output unit for outputting the fixed current; And
And a proportional controller for outputting the feedback current. 2. The control apparatus for a single-stage fly-by-wire inverter according to claim 1,
2. The apparatus of claim 1, wherein the iterative learning control unit
A downsampling unit for downsampling the error values of the period;
A pair of memories for storing downsampled error values by the downsampling unit;
A learning control operation unit for generating a desired output current by performing iterative learning on error values stored in the pair of memories; And
And an up-sampling unit for up-sampling an output current outputted from the learning control operation unit and outputting the running current.
The apparatus of claim 1, wherein the control unit
Generating a pulse width modulated signal having a duty ratio by comparing the reference duty voltage supplied from the phase locked loop with a triangular waveform having a predetermined frequency and outputting the pulse width modulated signals to the unfolding gate driver; Stage flywheel type inverter. 2. The system according to claim 1, further comprising:

Images