WO2016068381A1

WO2016068381A1 - Current control method of wind power generator

Info

Publication number: WO2016068381A1
Application number: PCT/KR2014/011328
Authority: WO
Inventors: 이성룡; 고성훈; 김차현; 이종희; 서범근
Original assignee: (주) 세스
Priority date: 2014-10-30
Filing date: 2014-11-24
Publication date: 2016-05-06
Also published as: KR101690222B1; KR20160050688A

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 of wind power generator

The present invention relates to a current control method of a wind turbine, and more particularly, by using a maximum power point trace (MPPT) tracking method using a slope of power vs. voltage, while rapidly following the maximum output of a wind turbine due to environmental changes. The present invention relates to a current control method of a wind power generator that minimizes a drop in tracking speed.

Energy sources based on coal or petroleum inevitably lead to environmental pollution as well as resource depletion. As an alternative to resource depletion and environmental pollution, environmentally friendly power generation methods such as wind power generation, solar power generation and tidal power generation are emerging. These environmental power generation methods are used in the surrounding environment such as wind strength, solar irradiation time and tidal wave. There is a variation in the power production according to the change of, and the maximum value of power, which is the product of the output voltage and the current, does not always coincide with the maximum voltage, so it is necessary to deliver power to the system through current control.

Accordingly, control methods for directing the generator to the maximum power point (maximum output point of electric power) have been proposed in an environmentally friendly power generation method. Representatively, the IncCond control method and the P & O control method have been proposed as one of the Maximum Power Point Trace (MPPT) control methods. The IncCond control method refers to the output conductance of the generator and the incremental conductance according to the environmental change. As a method of controlling power point tracking, it has a fast response to environmental changes, but it takes a lot of time to calculate conductance and incremental conductance, requiring a high performance processor and a system including the same, which leads to a cost increase. There is difficulty in dissemination. In addition, the IncCond control method follows the maximum power point by using the amount of change in conductance, and thus is easy to apply to the solar power generation method, but is not suitable for the wind power generation method.

P & O control method to ensure that the generator is to follow the maximum power point, measure the output power and the output voltage to be output from the generator and, corresponding to the output power and the output voltage control method for feeding back the control signal to advance reaches the set reference value, do. The P & O control method is simple to control and easy to disseminate. However, since the P & O control method is based on the fluctuating output power and output voltage, the P & O control method tends to use an average value for the output power and the output voltage. The response speed is not fast.

In this regard, Korean Patent Laid-Open Publication No. 10-2013-0079846 has proposed a maximum power tracking device that follows the maximum power point through MPPT control. MPPT control increases or decreases the output power to follow the maximum output point at which the maximum voltage and maximum power match. However, in Patent Publication No. 10-2013-0079846, the output power and output voltage depend on the information corresponding to the maximum output, and determining the maximum output point is the main point, which is calculated according to the position of the sun or the irradiation amount of sunlight. The maximum power point is inquired or recalculated so that the output of the generator follows the maximum power point. This method of obtaining and using the maximum output point is difficult to apply to the wind power generator as the wind direction and the amount of wind changes from time to time.

An object of the present invention is to control the current of each phase so that the current of each phase generated in the wind generator corresponds to the maximum power, the current control method of the wind power generator so that the power generated in the wind generator can quickly and accurately follow the maximum power point In providing.

The above object is, according to the present invention, a wind power generator for generating a three-phase alternating current, a converter for converting the three-phase alternating current to a direct current and an inverter for converting the direct current of the converter into grid alternating current current control method In the present invention, the reference current for each phase corresponding to the converter output power is determined based on the converter output power output from the converter, and the output current of the converter is used by using the command current in the form of PWM pulse to follow the instruction current for each phase. Switching control, the command current is generated by each phase of the three-phase alternating current, it is achieved by the current control method of the wind turbine generator for receiving feedback correction of the output current for each phase output from the inverter.

According to the present invention, by using the voltage and current of the output power output from the wind power generator to determine the command current and the command current for each phase (three phase), and the deviation between the output current controlled by the command current and the command current This allows for fast and accurate tracking of the wind turbine's maximum power point.

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

Figure 2 shows an example of the output characteristics graph for each wind speed of the wind power generator.

3 is a conceptual diagram illustrating a method of generating a command current using the command current according to the embodiment.

4 is a conceptual diagram for a method of generating a command current for each phase.

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

6 is a conceptual diagram illustrating a process of generating a command current of a PWM pulse type for each of the three phase currents in the current control device according to the embodiment.

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

FIG. 8 shows an operational waveform diagram for the current control device of FIG. 7 determining switching pattern of the next period with switching information of the previous period.

9 shows a waveform diagram of a voltage error signal according to each period.

Referring to FIG. 1, the wind power generator according to the present invention includes a power generation unit 20 for generating three-phase AC power by rotation of a blade 10 rotating in accordance with wind power, and a converter for converting three-phase AC power to DC. 30, and an inverter 40 for converting the direct current converted by the converter 30 into alternating current of the system required by the system. The wind power generator transfers power to the system through a process of converting a three-phase alternating current-direct current-alternating current system, and the converter 30 and the inverter 40 generate voltage and current for three phases. As shown in FIG. 2, when the output power increases in proportion to the wind speed, and the wind speed exceeds a predetermined speed (eg, 12 m / s), the wind power generator is saturated without increasing the output power. In addition, since the voltage and the current of the output power do not form the same phase, when the maximum of the three-phase current (ia, ib, ic) output from the power generation unit 20 and the maximum output occurs does not coincide. Therefore, in order for the output power to become the maximum power, a voltage value and a current value having a maximum multiplication value of the voltage and current are required, and the current value at this time is referred to as "instruction 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, and ic may be determined in advance in the design stage or the trial run stage.

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 is provided to the inverter 40 by performing PLL control to control the output current. The output current of each phase is increased and decreased, and thus the output power of the inverter 40 follows the maximum power point. In this case, the instruction current may be increased or decreased according to the voltage of the output power output from the power generation unit 20.

In order to apply this current control method to the converter 30, the current control apparatus according to the embodiment detects the output power generated by the power generation unit 20, and after detecting the output voltage of the output power, the instruction according to the output voltage Determine the current.

Subsequently, after detecting the output current provided from the inverter 40 to the converter 30, a PLL (Phase Locked Loop) control is performed such that the detected output current follows the indicated current, according to the output voltage of the power generation unit 20. It is characterized by the maximum output power of the converter 30. This will be described with reference to FIGS. 3 and 4 together.

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

First, FIG. 3 illustrates an example of calculating and applying the result of comparing the output power P_real and the instruction power P_ref for tracking the maximum power to the PI controller 52.

The comparator 51 calculates a difference between the output power P_real of the power generation unit 20 and the instruction power P_ref for the output power P_real to follow the maximum power, and converts the calculated difference power into the PI controller 52. To provide.

At this time, the comparator 51 sets the maximum power determined according to the wind speed for rotating the blade 10 to the indication power (P-ref), and the actual output output from the power generation unit 20 as the output power (P_real). The difference can be calculated.

In this embodiment, the maximum power is determined according to the amount of air to rotate the blade 10, not to mean the maximum value that the power generation unit 20 itself can be output, it is determined that it is determined by the wind speed. For example, when the wind speed is 10 m / s, the maximum output that can be expected from the power generation unit 20 is around 350 kW, and the instruction power P_ref applied to the comparator 51 also corresponds to 350 kW.

In addition, the indicated current corresponds to the current value for each phase at 350 kW. That is, the command power and the command current are determined by the wind speed, and are not determined by the model of the power generation unit 20 or the blade 10. It is noted that such matters apply equally throughout this specification.

The output power P_real applied to the comparator 51 corresponds to the actual output power output from the power generation unit 20, and the indication power P_ref corresponds to the maximum power output from the power generation unit 20 according to the wind speed. . The PI controller 52 may generate a command current with reference to the difference between the output power P_real and the instruction power P_ref, and the voltage of the output power P_real, where the command current is the output power P_real. It is a control signal for increasing to a maximum value and may have a form of a pulse width modulation (PWM) pulse. When the converter 30 converts three-phase alternating current into direct current, switching control using an electronic switching element is required, and the command current may be implemented in the form of a control pulse for on-off control of the switching element.

Three command currents may be generated according to three-phase currents 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 has the form of a PWM pulse, and the current output value is switched on and off using a PWM pulse. To increase or decrease the current output value.

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 reduce the current output value. At this time, the current control device according to the embodiment is a method of directly increasing or decreasing the output current of the converter 30 in accordance with the deviation of | maximum power-indicating power | It is distinguished from the conventional PLL control method in that it is used. In consideration of the deviation of | maximum power-directed power | and output voltage, the current increment is converted into a switching signal of the converter 30, and the converter 30 supplies the difference of | maximum power-directed power | to "0". By generating a PWM pulse to converge to the output current of the converter 30 can be increased or decreased.

When the conventional PI controller is applied to the converter 30, for the frequency stability of the switching frequency in the converter 30, there is a tendency to lower the proportional gain (Proportional gain), in this case, there is a disadvantage that the response speed is lowered. However, the current control device according to the embodiment generates a PWM pulse corresponding to the control amount when the control amount for the current increase and decrease in the PI controller 52, by performing 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, and when formed separately from the converter 30, an individual device that exchanges signals with the converter 30. It may be implemented as. However, to help understand 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.

Referring to FIG. 5, the wind power generator according to the embodiment may include a converter 30, an inverter 40, and a current control device 100. The converter 30 may rectify the three-phase alternating current output from the power generation unit 20 to generate a direct current, and may include a switching device in which the output current is increased or decreased by PWM control of the current control device 100. At this time, the converter 30 rectifies the three-phase alternating current output from the power generation unit 20 to generate a direct current to the inverter 40, the inverter 40 may again generate three-phase alternating current. The converter 30 may increase or decrease the current to the DC by switching the output current in response to the PWM pulse provided from the current control device 100. At this time, the output current for each of the three-phase current is on-off according to the PWM pulse provided from the current control device 100 to the converter 30, the average value of the on-off controlled current is the duty ratio of the PWM pulse (Duty Ratio) The higher), the larger, and the lower the duty ratio, the smaller.

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 provided to the command value calculating unit 100b, and the command value calculating unit 100b uses the reference current for the maximum current point and the reference power according to the wind speed to calculate the command current for the maximum output. Can be calculated. The calculated command current is provided to the feedback control unit 100c, and the feedback control unit 100c generates a PWM pulse according to the command current and provides it to the switching control unit 32, and the return current value IF output from the inverter 40 (IF). ) And the indicated current to determine an error, and PLL control may be performed based on the determined error. As described above, the command current represents a current value at the maximum power, and the data for the command current and the maximum power at the command current may be provided and used in the command value calculator 100b.

6 is a conceptual diagram illustrating a process of generating a command current of a PWM pulse type for each of the three phase currents in the current control device 100 according to the embodiment.

Referring to FIG. 6, the current control device 100 according to the embodiment generates command currents c-ia, c-ib, and c-ic for each phase in the

PI controllers

52, 53, and 54 for each phase. The generated command current is compared with the return current value IF of the inverter 40 by each phase in the

comparators

61, 62, and 63 corresponding to each phase, and calculates a current difference. Generates a PWM signal to increase or decrease the output current by the current error.

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

Since the three-phase currents (ia, ib, ic) for each phase are generated sequentially without generating waveforms at the same time, the phase and voltage of each phase are similar, but the waveforms of three-phase currents (ia, ib, ic) It should be formed with time difference. However, since the current value for each phase may have a mutual deviation, in order to maintain the maximum power according to the wind speed, the output current output for each phase should be set to follow the maximum power. The

controllers

61, 62, and 63 individually control the currents ia, ib, and ic for each phase. Thus, as shown in Figure 6, the current control device according to the embodiment generates the A-phase PWM signal, the B-phase PWM signal and the C-phase PWM signal separately.

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

First, the current error signal (es) mentioned in the embodiment corresponds to "1" if it is a positive direction value and "0" if it is a negative direction value, and the command current and the inverter 40 The error between the actual current of the output power output, which corresponds to a digital signal consisting of 1 and 0. That is, if the current error signal es is "1", the current error has a positive value, and if the current error signal es is "0", the current error is negative. The output signal "S" of the comparator 122 is a switching signal and may be output in the form of a PWM pulse.

The current error signal es described with reference to FIG. 6 is applied to each of the

integrators

104, 108, 113, and 118, and at this time, the non-inverted current error signal es is applied to the

integrators

104, 108, The current error signal / es inverted by the inverter 111 is applied to the

integrators

113 and 118. Accordingly, the comparator 116,

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

2) The ramp waveform TB-Ramp obtained through the integrator 112 and the ramp generator 115 may be received and compared. As shown in the ramp waveform shown in FIG. 8, when the current error signal es has a positive value, the waveform of the ramp waveform ramps monotonically and vice versa. Can be. Meanwhile, the integrator 104 and the integrator 118 count the time by integrating the non-inverted current error signal es and the inverted current error signal / es, respectively, and the counted times are compared in the comparator 121. To obtain the waveform Ex.

Comparator 122 receives the output waveform (Ramp) of the comparator 116 to the inverting terminal, and compares the time coefficient value of the comparator 121 to the non-inverting terminal to compare the form of "0" or "1" Generates a pulse, and the generated pulse controls the current switching of the converter 20 as a PWM pulse.

In FIG. 8, the waveform G1 corresponds to a waveform which measures an output voltage (ripple voltage flowing through an inductor) of the inverter 40 and compares it with a reference current signal. Ta and Tb represent the time when es is 1 and when 0, and the ramp waveform is generated as an integral in analog circuit and as a counter in digital circuit. Tar represents the time until the 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.

Equation 1

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

In addition, the voltage error signal es is a digital signal composed of 1s and 0s as error information between the command voltage and the actual voltage, and S is a switching signal. here,

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

Reference numeral 115: Integrator for generating a ramp waveform having a slope proportional to Tb,

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

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

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

The current control method of the wind turbine generator according to the present invention activates manufacturers, developers and distributors of the wind turbine generator as well as grid operators and energy distributors associated with the grid network using the power generated by the wind turbine. Can contribute to

Claims

In the current control method of the wind power generator comprising a wind generator for generating three-phase alternating current, a converter for converting the three-phase alternating current to direct current, and an inverter for converting the direct current of the converter into grid alternating current,
Determining the instruction current for each phase corresponding to the converter output power, based on the converter output power output from the converter,
Switching control of the output current of the converter using a command pulse in the form of a PWM pulse so as to follow the instruction current for each phase,
The command current is generated for each phase of the three-phase alternating current, the current control method of the wind turbine generator, characterized in that for correcting by receiving the feedback output current for each phase output from the inverter.
The method of claim 1,
The instruction current is,
It is provided for each converter output power,
The current control method of the wind power generator, characterized in that provided for each phase with respect to the converter output power.
The method of claim 1,
The command current is
And controlling the amount of current output from the converter to follow the maximum power point of the converter.
The method of claim 1,
The command current is
The current control method of the wind turbine, characterized in that it is generated separately according to each phase.
The method of claim 1,
The command current is
Acquiring an output current for each of the inverter through the inverter output power and the converter output power,
And calculating a deviation between the obtained output current and the following value of the command current for each phase to control a PLL (Phase Locked Loop).