KR20160050688A - Current control method for wind power generator - Google Patents

Abstract

The present invention calculates control current per phase (3-phase) by using the voltage and current of output power outputted from a wind power generator, and reduces deviation between the calculated control current and a reference value to be thereby capable of following the maximum power point of a wind power generator rapidly and accurately. To this end, the present invention determines, on the basis of a converter output power outputted from a converter, an instruction current per each phase corresponding to the converter output power; and switching-controls the output current of the converter by using a command current in the form of a PWM pulse so as to follow the instruction current per phase, wherein the command current is generated per each phase of 3-phase alternating current and may be compensated for by receiving feedback of the output current per phase outputted from an inverter.

Description

Current control method for wind power generator.

[0001] The present invention relates to a current control method for a wind power generator, and more particularly to a power control method of a wind power generator, which uses a maximum power trace (MPPT) And to a current control method of a wind power generator that minimizes degradation of follow-up speed.

Energy sources based on coal or oil will inevitably lead to environmental pollution as well as resource depletion. As an alternative to resource depletion and environmental pollution, eco-friendly power generation methods such as wind power generation, solar power generation, and tidal power generation have emerged. These eco-friendly power generation methods are based on the surrounding environment such as wind intensity, And the maximum value of the power, which is the product of the output voltage and the current, does not coincide with the maximum voltage, it is necessary to transmit the power to the system through the current control.

Accordingly, in the eco-friendly power generation method, control methods have been proposed in which the generator is directed to the maximum power point (the maximum output point of the power). The IncCond control method and the P & O control method have been proposed as one of the MPPT (Maximum Power Point Trace) control methods. The IncCond control method refers to the output conductance of the generator and the increase conductance according to the environment change, A method for controlling a power point to follow, which requires a high-performance processor and a system including the same, which requires a large amount of time to calculate conductance and incremental conductance, while having quick response to environmental changes, There is a difficulty in spreading. IncCond control method is easy to apply to solar power generation method because it follows maximum power point by using variation of conductance, but it is not suitable for wind power generation system.

The P & O control method corresponds to a control method of measuring the output power and output voltage output from the generator and feeding back the control signal so that the output power and the output voltage reach a predetermined reference value in order to allow the generator to follow the maximum output point . The P & O control method tends to use the mean value of the output power and the output voltage because the control method is simple and easy to supply, but it is based on the fluctuating output power and the output voltage. According to this characteristic, There are some cases where the response speed is not fast.

Korean Patent Laid-Open No. 10-2013-0079846 has proposed a maximum power follower that follows a maximum power point through MPPT control. The MPPT control increases or decreases the output power so as to follow the maximum output point at which the maximum voltage and the maximum power match. However, in the patent document 10-2013-0079846, it is determined that the output power and the output voltage depend on the information corresponding to the maximum output, and it is determined that the maximum output point is the correct value, which is calculated according to the position of the sun or the dose of sunlight The maximum power point is inquired or re-calculated so that the output of the generator follows the maximum output point. Such a method of acquiring and using a maximum output point is difficult to apply to a wind power generation apparatus in which the wind direction and the wind amount are changed from time to time.

An object of the present invention is to provide a current control method of a wind power generator which controls a current for each phase so that a current for each phase generated by a wind turbine corresponds to a maximum power so that the power generated by the wind turbine follows a maximum power point accurately .

According to the present invention, there is provided a current control method of a wind power generator including a wind power generator for generating three-phase alternating current, a converter for converting the three-phase alternating current into direct current, and an inverter for converting a direct current of the converter into a system ac The output current of the converter is determined by using the command current of the PWM pulse type so that the command current for each phase corresponding to the converter output power is determined on the basis of the converter output power outputted from the converter, And the command current is generated for each phase of the three-phase alternating current, and is corrected by feedback of the phase-by-phase output current output from the inverter.

According to the present invention, the command current and the command current for each phase (three phases) are determined using the voltage and current of the output power from the wind power generator, and the deviation between the command current and the command current So that the maximum power point of the wind turbine can be followed quickly and accurately.

Fig. 1 shows a schematic diagram of a system of a wind power generator to which the present invention is applied.
Fig. 2 shows an example of a graph of the output characteristic of the wind turbine according to the wind speed.
FIG. 3 shows a conceptual diagram of a method of generating a command current using an instruction current according to an embodiment.
FIG. 4 shows a conceptual diagram of a method for generating a command current for each phase.
5 is a conceptual diagram of a current control device and a wind turbine generator including the same according to an embodiment of the present invention.
FIG. 6 shows a conceptual diagram of a process of generating a PWM pulse-shaped command current for each of the three-phase currents in the current control apparatus according to the embodiment.
FIG. 7 is a block diagram illustrating an example of a current control apparatus to which the current control method described with reference to FIGS. 1 to 6 is applied.
Fig. 8 shows an operation waveform diagram for the current control device of Fig. 7, which has the switching information of the previous period and determines the switching pattern of the next period.
9 shows waveform diagrams of voltage error signals according to each period.

Fig. 1 shows a schematic diagram of a system of a wind power generator to which the present invention is applied.

Referring to FIG. 1, a wind turbine generator according to the present invention includes a generator 20 for generating three-phase alternating current by rotation of a blade 10 rotating in accordance with wind power, a converter 20 for converting three- (30), and an inverter (40) for converting the direct current converted by the converter (30) into an alternating current of a system required in the system. The wind turbine generator transmits electric power to the system through a process of converting AC to AC of a three-phase AC-DC-system. Voltage and current for three phases are generated in the converter 30 and the inverter 40. As shown in FIG. 2, the output power of the wind power generator increases in proportion to the wind speed, but when the wind speed exceeds a predetermined speed (for example, 12 m / s), the output power does not increase and becomes saturated. In addition, since the voltage and current of the output power do not form the same phase, the maximum value of the three-phase currents (ia, ib, ic) output from the power generation unit 20 does not coincide with the point at which the maximum output occurs. Therefore, in order for the output power to be the maximum power, a voltage value and a current value at which the multiplication value of the voltage and the current are the maximum are required, and the current value at this time is referred to as "indicating current". Since the command current is determined according to the characteristics of the blade 10 and the power generation unit 20, the command current for ia, ib, ic can be determined in advance in the designing or trial operation.

The converter 30 controls the output current of the power generation unit 20 so that the output power of the power generation unit 20 follows the maximum power and performs PLL control to control the output current to be supplied to the inverter 40 Thereby increasing or decreasing the output current for each phase, thereby causing the output power of the inverter 40 to follow the maximum power point. At this time, the indicating current can be increased or decreased according to the voltage of the output power outputted from the power generation section 20. [

In order to apply the current control method to the converter 30, the current control device according to the embodiment detects the output power generated in the power generation section 20, detects the output voltage of the output power, Determine the current.

Thereafter, the inverter 40 detects an output current supplied to the converter 30, and performs PLL (Phase Locked Loop) control so that the detected output current follows the indicated current, The output power of the converter 30 is maximized. This will be described with reference to FIGS. 3 and 4. FIG.

Referring to FIG. 3, there is shown a conceptual diagram of a method of generating a command current using an instruction current according to an embodiment.

3 shows an example in which the PI controller 52 applies a result of comparing the output power P_real with the command power P_ref for maximum power follow-up.

The comparator 51 calculates the difference between the output power P_real of the power generation section 20 and the command power P_ref for the output power P_real to follow the maximum power and outputs the calculated difference power to the PI controller 52 ).

At this time, the comparator 51 sets the maximum power determined according to the wind speed for rotating the blade 10 to the indicating power P-ref, and outputs the actual output from the power generating section 20 as the output power P_real So that the difference power can be calculated.

In the present embodiment, it is found that the maximum power is determined according to the air volume for rotating the blade 10, not the maximum value that can be output by the power generator 20 itself, and is determined according to the wind speed. For example, when the wind speed is 10 m / s, the maximum power that can be expected from the power generator 20 is about 350 kW, and the command power P_ref applied to the comparator 51 also corresponds to 350 kW.

Further, the instruction current corresponds to the current value for each phase at 350 kW. That is, the indicated power and the indicated current are determined in accordance with the wind speed, and are not determined depending on the type of the power generation section 20 or the blade 10. It should be noted that these matters are equally applied throughout this specification.

The output power P_real applied to the comparator 51 corresponds to the actual output power output from the power generator 20 and the indicated power P_ref corresponds to the maximum power that can be output from the power generator 20 according to the wind speed . The PI controller 52 can generate the command current by referring to the difference power between the output power P_real and the command power P_ref and the voltage of the output power P_real where the command current is the output power P_real To a maximum value, and may have a form of a PWM (Pulse Width Modulation) pulse. When the converter 30 converts the three-phase alternating current into direct current, switching control using an electronic switching element is required, and the command current can be implemented in the form of a control pulse for on-off control of the switching element.

Three command currents can be generated in accordance with the three-phase current output from the power generation unit 20. [ As shown in FIG. 4, the command current is generated by c_ia, c_ib, and c_ic for each phase, and the output form is in the form of a PWM pulse, and the current output value is on- So that the current output value can be increased or decreased.

When the current output value of the converter 30 is small, the command current may generate a PWM pulse having a large duty ratio to increase the current output value, and in the opposite case, decrease the duty ratio to decrease the current output value. In this case, the current control apparatus according to the embodiment directly increases or decreases the output current of the converter 30 according to the deviation of the maximum power-pointed power | instead of increasing or decreasing the gain fed back according to the normal PLL control method And is different from the conventional PLL control method in that it is used. The difference between the maximum power-point power | and the output voltage is converted into a switching signal of the converter 30 and supplied to the converter 30, and the converter 30 sets the difference between the maximum power- So that the output current of the converter 30 can be increased or decreased.

When a conventional PI controller is applied to the converter 30, there is a tendency to lower the proportional gain for the frequency stability of the switching frequency in the converter 30. In this case, the response speed is lowered. However, when the control amount for current increase / decrease is calculated in the PI controller 52, the current control apparatus according to the embodiment generates the PWM pulse corresponding to the control amount and performs the switching control of the converter 30 with the generated PWM pulse , The response characteristic of the PI controller 52 can be improved.

The current control device according to the embodiment may be built in the converter 30 or may be formed separately from the converter 30. When the current control device is formed separately from the converter 30, . ≪ / RTI > However, in order to facilitate understanding of the embodiment, an example in which the current control device is formed separately from the converter 30 will be described with reference to FIG.

5 is a conceptual diagram of a current control device and a wind turbine generator including the same according to an embodiment of the present invention.

Referring to FIG. 5, the wind turbine generator according to the embodiment may include a converter 30, an inverter 40, and a current controller 100. The converter 30 may include a switching device that rectifies the three-phase alternating current output from the power generating unit 20 to generate a direct current and the output current is increased or decreased by the PWM control of the current control device 100. [ At this time, the converter 30 rectifies the three-phase alternating current output from the power generating section 20 to generate a direct current and provides the direct current to the inverter 40. The inverter 40 can generate three-phase alternating current again. The converter 30 can increase or decrease the current to the direct current by switching the output current in response to the PWM pulse provided by the current control device 100. [ At this time, the output current for each of the three-phase currents is turned on and off according to the PWM pulse provided from the current control device 100 to the converter 30, and the average value of the currents to be controlled on and off is the duty ratio ) Is higher, and the lower the duty ratio, the smaller it can be.

Preferably, the current control device 100 may include a control value obtaining unit 100a, a command value calculating unit 100b, and a feedback control unit 100c.

The control value obtaining unit 100a obtains information on the output power, the output voltage, the output current, and the wind speed for each of the three-phase currents Ia, Ib, and Ic as control values. The obtained control value is supplied to the command value calculation unit 100b, and the command value calculation unit 100b calculates the command current for the maximum output using the reference data for the indicated current and indicated power of the maximum power point according to the wind speed Can be calculated. The calculated command current is supplied to the feedback control section 100c and the feedback control section 100c generates PWM pulses in accordance with the command current and provides the generated PWM pulses to the switching control section 32. The feedback control section 100c calculates the feedback current value IF ) And the instruction current to determine an error, and perform PLL control based on the determined error. As described above, the command current represents the current value at the maximum power, and data on the maximum power at the command current and command current can be provided and used in the command value calculation section 100b.

FIG. 6 shows a conceptual diagram of a process of generating a PWM pulse-shaped command current for each of the three-phase currents in the current control device 100 according to the embodiment.

6, the current controller 100 generates the command currents c-ia, c-ib and c-ic for each phase by the PI controllers 52, 53 and 54 for each phase And the generated command current is compared with the forward current value IF of the inverter 40 at each phase in the comparators 61, 62 and 63 corresponding to the respective phases to calculate a current error, And generates a PWM signal for increasing or decreasing the output current by a predetermined current error.

For example, when three phase currents are A, B, and C phases, three command currents (A phase PWM signal, B phase PWM signal, C phase PWM signal) are calculated using one current error signal I * Can be generated.

Since the three-phase currents (ia, ib, ic) for each phase do not generate a waveform at the same time and are generated sequentially, the magnitudes of voltage and current for each phase are similar, Should be formed with a time lag. However, since the current values of the respective phases may have mutual deviations, in order to maintain the maximum power according to the wind speed, the output currents output for the respective phases must be set so as to follow the maximum power. For this purpose, The controllers 61, 62 and 63 individually control the currents ia, ib and ic for each phase. Therefore, as shown in Fig. 6, the current control device according to the embodiment separately generates the A-phase PWM signal, the B-phase PWM signal, and the C-phase PWM signal.

FIG. 7 is a block diagram illustrating an example of a current control apparatus to which the current control method described with reference to FIGS. 1 to 6 is applied. 7 will be described with reference to FIGS. 1 to 6. FIG.

First, the current error signal es referred to in the embodiment corresponds to " 1 "if the direction value is positive (+) and corresponds to" 0 & The error between the actual output current and the output current corresponds to a digital signal composed of 1 and 0. That is, when the current error signal es is "1", the current error has a positive value, and when the current error signal es is "0", the current error is a negative value. The output signal "S" of the comparator 122 can be output as a switching signal in the form of a PWM pulse.

The current error signal es described with reference to Figure 6 is applied to each of the integrators 104,108, 113 and 118 at which time a non-inverting current error signal es is applied to the integrator 104,108, The inverted current error signal / es is applied to the integrators 113 and 118 by the inverter 111. Accordingly, the comparator 116 compares

1) receives the ramp waveform (Ta-Ramp) obtained through the integrator 108 and the ramp generator 110,

2) the lamp waveform (TB-Ramp) obtained through the integrator 112 and the ramp generator 115 can be input and compared. 8, when the current error signal es has a positive value, the waveform of the ramp waveform Ramp monotonously increases, and when the current error signal es has a positive value, monotonously decreases in the opposite case, as shown in the Ramp waveform shown in Fig. . On the other hand, the integrator 104 and the integrator 118 integrate the non-inverted current error signal es and the inverted current error signal / es to count the time, and the counted times are compared in the comparator 121 To obtain the waveform (Ex).

The comparator 122 receives the output waveform Ramp of the comparator 116 as the inverting terminal and receives the time count value of the comparator 121 as the non-inverting terminal to compare the input signal with the non-inverting terminal to obtain the form of "0" And the generated pulses control the current switching of the converter 20 as PWM pulses.

8, the waveform G1 corresponds to a waveform for measuring the output voltage (ripple voltage flowing through the inductor) of the inverter 40 and comparing it with the reference current signal. Ta and Tb represent the time when es is 1 and 0, respectively, and integrate in analog circuits, and generate ramp waveforms as counters in digital circuits. Tar represents the time until switch s is turned off when es is 1, and Tar1 of the next period can be determined through the operation of Equation (1) below.

Here, * denotes a target value, # denotes a calculated value, and ^ denotes a measured value.

The voltage error signal (es) is a digital signal composed of 1 and 0 as error information between the command voltage and the actual voltage, and S is a switching signal. here,

110: an integrator for generating a ramp waveform having a slope proportional to Ta,

115: an integrator for generating a ramp waveform having a slope proportional to Tb,

105: an integrator (or counter) that makes time when es is 1 and s is 1, and

Reference numeral 120: corresponds to an integrator (or counter) that makes time when es is 0 and s is zero.

Tbf represents the time until switch s turns on when es is 0, which determines T # bf1 of the next cycle by the operation of Table 1 (b). Using the thus generated signal, the comparator 122 generates the output signal Ex, and determines the next period switching sequence through comparison of Ta1 and Tb1 in the next period.

10: blade 20:
30: converter 40: inverter
100: current control device

Claims (5)

1. A current control method for a wind power generator having a wind power generator for generating three-phase alternating current, a converter for converting the three-phase alternating current into a direct current, and an inverter for converting a direct current of the converter into a system ac,
Determining a direct current for each phase corresponding to the converter output power based on a converter output power output from the converter,
Controls the output current of the converter so as to follow the phase-by-phase command current by using a PWM pulse-type command current,
Wherein the command current is generated for each phase of the three-phase alternating current, and corrects the phase-by-phase output current output from the inverter by feedback. The method according to claim 1,
The indication current
Wherein the converter is provided for each of the converter output powers,
Wherein the converter is provided for each phase with respect to the converter output power. The method according to claim 1,
The command current
Wherein the controller controls the switching of the amount of current output from the converter so as to follow the maximum power point of the converter. The method according to claim 1,
The command current
Wherein the currents are individually generated according to the respective phases. The method according to claim 1,
The command current
Obtaining an output current for each of the inverter output power of the inverter and the converter output power,
And a PLL (Phase Locked Loop) control is performed by calculating a deviation between the obtained output current and the follow-up value of the command current for each phase.

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