TWI381263B - Maximum power tracking device - Google Patents

Description

Maximum power tracking device

The present invention relates to a tracking device, and more particularly to a maximum power tracking device for finding the maximum output power of an energy generating device.

Since the output power of solar power generation is affected by external environmental factors such as temperature and illuminance changes, a method for finding the maximum value of the output power for solar power generation is proposed. As shown in Fig. 1, the disturbance observation method is currently the largest. A method of power tracking, which is based on the characteristic curve between the output power and the voltage of solar power generation, and the operation area is divided into two types, which are the positive slope region RP and the negative slope region, centering on the maximum output power point. RN, when the power output of the solar panel operates at a positive slope, its output voltage can be increased to bring the operating point closer to the maximum power point P _max , and when the power output of the solar panel operates at a negative slope, the output voltage can be lowered to enable The operating point approaches the maximum power point _Pmax .

As shown in FIG. 2, in order to implement the above-mentioned maximum power tracking method in hardware, the concept is that at two different time points, the maximum power tracking device 2 estimates the power according to the measured output voltage and output current of the solar panel. Before and after the power is compared, the energy output from the solar panel to the battery via the power converter 1 is dynamically adjusted according to the power change to optimize the conversion of the energy.

A maximum power tracking device is disclosed in the prior art US Pat. No. 7,053,506 B2, which has the disadvantage that it is disabled during power tracking when the illuminance is changed, and the pulse width modulation (PWM) signal cannot be output, as shown in FIG. During the period from t1 to t2, the equivalent input resistance of the power converter is approximately infinite, causing the solar panel to fail to output current, resulting in waste of energy. The parameters I _MAX and I _OMB are the outputs of the solar panel under two different stable illuminations. Current.

Accordingly, it is an object of the present invention to provide a maximum power tracking device that avoids the aforementioned deficiencies and increases efficiency.

The maximum power tracking device is adapted to be coupled to an energy generating device and a power converter having a switch, and includes: a voltage detector, a current detector, an offset correction unit, and a pulse Wave modulation unit.

The voltage detector is configured to detect an output voltage of the energy generating device outputted to the power converter to provide a detected voltage value, and a current detector for detecting the output of the energy generating device to the power converter An output current to provide a detected current value.

The offset correction unit includes: a power comparison module, and a voltage level generator.

The power comparison module estimates a current power and a previous power according to the detected voltage value, the detected current value, and the previously received detected voltage value and the detected current value respectively. And comparing the current power with the magnitude of the previous power to output a control signal that varies between high and low potentials.

The voltage level generator receives the control signal and increases or decreases an analog offset voltage to be output according to the change of the control signal.

The pulse wave modulation unit includes a first difference value operator, a second difference value operator, and a pulse wave signal generation module.

The first difference operator receives the detected voltage value and the offset voltage value respectively, performs subtraction, and then multiplies a gain value to output a first difference.

The second difference operator receives the detected current value and the first difference value respectively, and performs subtraction to output a second difference value.

The pulse wave signal generating module receives the second difference value and outputs a pulse width modulation driving voltage whose duty cycle ratio changes according to the second difference value, and controls the power conversion by using the pulse width modulation driving voltage Switching of the switch of the device.

The above and other technical contents, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments.

Introduction to design theory:

If the input resistance Rin of the power converter is regarded as a variable resistor, and the parallel output resistance Rs inside the solar panel is ignored, only the internal series output resistance Ro is considered, and the equivalent circuit is as shown in FIG. The output voltage _{Vpv_sen} and an output current _{Ipv_sen are} varied to adjust the duty cycle ratio of the PWM signal to adjust the input resistance Rin of the power converter to match the series output resistance Ro to maximize the output power of the solar panel.

As shown in FIG. 5, the broken line 33 is a maximum power load line designed according to the input resistance Rin of the power converter under a plurality of illumination conditions, and the design formula is to measure the maximum power of the solar panel according to different illumination conditions. Point to get a lot of data, and then adjust the majority of the data to a straight line by one approximation method to introduce its maximum power load line formula as

V _{pv_sen} -V _step -kI _{pv_sen} =0

Wherein, the parameter V _{pv_sen} is the solar panel output voltage, V _step is the predetermined offset voltage amount, I _{pv_sen} is the solar panel output current, and k is a load slope, which determines different load slopes according to different solar panels.

Circuit design:

As shown in FIG. 6, a preferred embodiment of the maximum power tracking device of the present invention is suitable for detecting an energy generating device under different illumination and temperature conditions (in the embodiment, a solar panel is taken as an example, but not In this case, an output voltage V _{pv_se} n and an output current I _{pv_sen} of the power converter 34 having the switches S1 and S2 may be supplied to the wind power generator or other device to generate a pulse-wave modulation (PWM) drive. The voltage changes the duty cycle ratio of the switches S1 and S2 of the power converter 34 such that the input resistance Rin of the power converter 34 conforms to the maximum power load line formula, and includes: a voltage detector 31 and a current detector 32. An offset correction unit 40 and a pulse wave adjustment unit 6.

The voltage detector 31 and the current detector 32 respectively detect the output voltage V _{pv_sen} and the output current I _{pv_sen} provided by the solar panel to the power converter 34 to respectively provide a detection voltage value and a detection current value.

The offset correction unit 40 outputs an offset voltage V _step according to the change of the detected voltage value and the detected current value, and includes a power comparison module 4 and a voltage level generator 5.

The power comparison module 4 estimates a current power P(t) and a previous power according to the currently detected detection voltage value, the detected current value, the previously received detection voltage value, and the detected current value. P(t-1), comparing the current power P(t) with the magnitude of the previous power P(t-1) to output a control signal that varies between high and low potentials, and having a multiplier 41, A sample holder 42, and a power comparator 43.

The multiplier 41 multiplies the current and previous detected voltage values and the detected voltage values to obtain the current power P(t) and the previous power P(t-1), respectively.

The sample holder 42 samples the current power P(t) and temporarily stores it, and outputs the previous power P(t-1) temporarily stored.

The power comparator 43 has a first end (ie, a non-inverting input (+)) that receives the current power signal P(t), and a second end that receives the previous power signal P(t-1). (ie: the inverting input (-)), and an output, and comparing and outputting a control signal from the output.

The voltage level generator 5 receives the control signal and increases or decreases an analogy of the offset voltage _Vstep to be output according to the change of the control signal. In the embodiment, the voltage level generator 5 includes: A counter 51 and a digital to analog converter 52, but are not limited thereto, may be implemented in other circuit architectures.

The counter 51 receives the control signal to output a digital code having a multi-bit and digital representation of the value, and is at a high or low level to increase or decrease its value depending on the control signal.

The digit to analog converter 52 receives the digit code and converts it to the offset voltage _Vstep based on its value.

As an example, as shown in FIG. 7, the operation timing chart of the sample holder 42 is a sampling mode during time t0~t1, and is a hold mode during t1~t2, assuming the previous one of the clock period signal CK. The positive edge time point t0 samples the previous power signal P(t-1), and during the period t1~t2, the previous power signal P(t-1) is maintained, and the current positive time point t2 of the clock period signal CK is The current power P(t) is sampled while the previous power signal P(t-1) is simultaneously output to the power comparator, and the current power signal P(t) is compared with the previous power signal P(t-1).

And if the current power signal P(t) is greater than the previous power signal P(t-1), outputting a high potential signal causes the counter 51 to increase the current digit code by one unit, and vice versa by one unit. The shift voltage V _step also increases or decreases.

Referring back to FIG. 6, the pulse wave adjusting unit 6 outputs a PWM driving voltage according to the change of the offset voltage _Vstep , and includes a first and second difference computing units 61, 62, and a pulse signal generating module 7 .

The first difference computing unit 61 receives the detected voltage value and the offset voltage V _{step respectively} , performs subtraction, multiplies the gain by a gain, and outputs a first difference value. In this embodiment, the first difference operation is performed. The device 61 is an operational amplifier OP having a gain equal to the reciprocal (1/k) of the load slope shown in equation (1) and having a first end receiving the detected voltage value (ie, a non-inverting input terminal ( +)), receiving a second end of the offset voltage _Vstep (i.e., an inverting input (-)), and an output providing the first difference value.

The second difference operator 62 receives the detected current value and the first difference value, and performs subtraction to output a second difference value. In this embodiment, the second difference operator 62 is an operational amplifier OP. And having a first end receiving the detected current value (ie, a non-inverting input terminal (+)), a second end receiving the first difference value (ie, an inverting input terminal (-)), and An output that provides the second difference value.

The pulse wave signal generating module 7 receives the second difference value and outputs a pulse width modulation driving voltage whose duty cycle ratio changes according to the second difference value, and controls the power conversion by using the pulse width modulation driving voltage The switches S1, S2 of the switch 34 are switched, and include a compensator 72, a triangular wave generator 71, a comparator 73, and a buffer 74.

The triangular wave generator 71 outputs a sawtooth wave signal that changes periodically.

The compensator 72 receives the second difference value and provides a zero point to offset the high frequency pole of the second difference value to output a low frequency comparison signal. In the embodiment, the low frequency comparison signal is relative to the sawtooth wave signal. It can be considered DC and the compensator 72 can be considered a low pass filter.

The comparator 73 includes a first end receiving the low frequency comparison signal (ie, a non-inverting input terminal (+)), a second end receiving the sawtooth wave signal (ie, an inverting input terminal (-)), and An output terminal, according to whether the low frequency comparison signal is higher than the sawtooth wave signal to provide a PWM driving voltage, and the PWM driving voltage is at a high potential when the low frequency comparison signal is higher than the sawtooth wave signal, and vice versa. .

The buffer 74 receives the PWM drive voltage and enhances its drive capability for supply to the power converter 34, thereby adjusting the duty cycle ratio of the switches S1, S2 of the power converter 34.

The following is a discussion of the transient tracking of the actual simulation of illumination fixation and illumination change in the present invention:

First, the transient tracking under fixed illumination:

As shown in FIG. 8, when the illuminance is constant, and the current power P(t) calculated according to the measured output voltage _{Vpv_sen} and the output current _{Ipv_sen} is greater than the previous estimated previous power P ( When t-1), it means that the tracking point is located to the left of the maximum power line, so the offset correction unit 40 will gradually increase the offset voltage _Vstep to cause the pulse wave adjusting unit 6 to increase the duty cycle ratio of the PWM driving voltage to reduce The input resistance Rin of the power converter 34 is gradually matched to the output impedance Ro of the solar panel to obtain the maximum power, thus causing the tracking point A of FIG. 8 to approach the right direction of the arrow 1 toward the maximum on the first illuminance curve 81. Power point B, and when the maximum power point B is reached, since the first difference between the current power P(t) and the previous power P(t-1) will vary between positive and negative, the tracking point will be at the maximum power point B. Oscillating left and right.

If the current power P(t) is less than the previous power P(t-1), it means that the tracking point is located to the right of the maximum power point, so the offset voltage _Vstep will gradually decrease to reduce the duty cycle ratio of the PWM driving voltage. The input resistance Rin of the power converter 34 is increased and causes the tracking point to approach the maximum power point to the left.

Second, the transient tracking when the illuminance changes:

Since the point position on the maximum power load line approximates the position of each actual maximum power point of different illumination conditions, if the illuminance gradually decreases from large to large, the output current I _{pv_sen of the} solar panel also becomes smaller, so that the tracking point will follow each The maximum power point of one illuminance oscillates left and right and moves down until the illuminance is fixed, causing the tracking point B of FIG. 8 to move downward in the direction indicated by the arrow 2 until the illuminance is stable and falls on the tracking point C on the second illuminance curve, Because the smaller the illuminance, the smoothing range at the approximate maximum power on the illuminance curve is larger, that is, the slope of the power increase near the smoothing range is approximately 0, so the offset correction unit 40 will adjust between the smoothing ranges. The voltage V _{step is} offset and reaches the maximum power point D on the second illuminance curve in the direction indicated by the arrow 3, and oscillates left and right.

In summary, the preferred embodiment of the present invention has the advantage of continuously tracking the output power of the energy generating device with the maximum estimated power load line under different environmental conditions, which can not only be quickly found. The maximum power tracking point, and can avoid wasting energy during the tracking process, and according to the maximum power load line to realize the circuit, the required number of circuit components can be reduced relative to the prior art to reduce the manufacturing cost, and the number of components can be reduced. The bulk circuit is integrated into the power converter to reduce the size.

The above is only the preferred embodiment of the present invention, and the scope of the invention is not limited thereto, that is, the simple equivalent changes and modifications made by the scope of the invention and the description of the invention are All remain within the scope of the invention patent.

31. . . Voltage detector

32. . . Current detector

34. . . Power converter

S1, S2. . . switch

40. . . Offset correction unit

4. . . Power comparison module

41. . . Multiplier

42. . . Sample holder

43. . . Power comparator

5. . . Voltage level generator

51. . . counter

52. . . Digital to analog converter

6. . . Pulse wave adjustment unit

61. . . First difference operator

62. . . Second difference operator

7. . . Pulse signal generation module

71. . . Triangle wave generator

72. . . Compensator

73. . . Comparators

74. . . buffer

Rin. . . Input resistance

Ro. . . Output resistance

1 is a schematic diagram showing the relationship between output power and output voltage of a conventional maximum power tracking method;

Figure 2 is a block diagram illustrating a conventional maximum power tracking system;

Figure 3 is a schematic diagram showing the output current when conventionally performing power tracking;

4 is a circuit diagram illustrating an equivalent circuit for power tracking using the present invention;

Figure 5 is a schematic view showing the relationship between the output voltage of the solar panel and the output current;

Figure 6 is a circuit diagram illustrating a circuit of a preferred embodiment of the present invention;

Figure 7 is a timing diagram illustrating the timing of the sample holder of the preferred embodiment;

Figure 8 is a simulation of the preferred embodiment illustrating power tracking under illumination changes.

31. . . Voltage detector

32. . . Current detector

34. . . Power converter

S1, S2. . . switch

40. . . Offset correction unit

4. . . Power comparison module

41. . . Multiplier

42. . . Sample holder

43. . . Power comparator

5. . . Voltage level generator

51. . . counter

52. . . Digital to analog converter

6. . . Pulse wave adjustment unit

61. . . First difference operator

62. . . Second difference operator

7. . . Pulse signal generation module

71. . . Triangle wave generator

72. . . Compensator

73. . . Comparators

74. . . buffer

Claims (8)

A maximum power tracking device is coupled to an energy generating device and a power converter having a switch, and includes: a voltage detector for detecting an output of the energy generating device to the power converter Outputting a voltage to provide a detected voltage value; a current detector for detecting an output current output from the energy generating device to the power converter to provide a detected current value; an offset correcting unit The method includes: a power comparison module, respectively estimating a current power according to the detected voltage value, the detected current value, and the previously received detection voltage value and the detected current value respectively received Comparing the current power with the previous power to output a control signal that varies between high and low potentials; and a voltage level generator that receives the control signal and changes according to the control signal Increasing or decreasing an offset voltage to be output; and a pulse modulation unit, comprising: a first difference operator, respectively receiving the detected voltage value and the offset voltage value, and performing Subtracting and multiplying a gain value to output a first difference; a second difference computing unit respectively receiving the detected current value and the first difference value, and performing subtraction to output a second difference value; And a pulse wave signal generating module, receiving the second difference value and outputting a pulse width modulation driving voltage according to the second difference value, and controlling the driving voltage by using the pulse width modulation driving voltage Switching of the switch of the power converter. According to the maximum power tracking device of claim 1, wherein the power comparison module comprises a multiplier, a sample holder, and a power comparator, the multiplier is respectively based on the current and previous detections. And multiplying the voltage value and the detected voltage value to obtain the current power and the previous power, the sample holder samples the current power and temporarily stores the previous power stored previously, and the power comparator has a receiving The first end of the current power, the second end receiving the previous power, and an output end, and comparing the current power and the magnitude of the previous power, the control signal is output by the output end. The maximum power tracking device according to claim 1, wherein the first difference computing unit is an operational amplifier, and has a first end receiving the detected voltage value and receiving the offset voltage. a second end, and an output providing the first difference value. According to the maximum power tracking device of claim 1, wherein the second difference computing unit is an operational amplifier, and has a first end receiving the detected current value and receiving the first difference value. a second end, and an output providing the second difference value. The maximum power tracking device according to claim 1, wherein the pulse signal generating module has a compensator, a triangular wave generator, and a comparator, and the triangular wave generator outputs a periodically varying sawtooth. a wave signal, the compensator receives the second difference value, and provides a zero point to offset the high frequency pole of the second difference value to output a low frequency comparison signal, the comparator having a first receiving the low frequency comparison signal a second end and an output end receiving the sawtooth signal, and the output terminal provides the pulse width modulation driving voltage according to whether the low frequency comparison signal is higher than the sawtooth wave signal, and the pulse width modulation The driving voltage is at a high potential when the low frequency comparison signal is higher than the sawtooth signal, and vice versa. The maximum power tracking device according to claim 5, wherein the compensator is a low pass filter. The maximum power tracking device according to claim 1, wherein the pulse wave signal generating module further has a buffer, the buffer receiving the pulse width modulation driving voltage and enhancing the driving capability thereof to provide The power converter. The maximum power tracking device according to claim 1, wherein the voltage level generator has: a counter that receives the control signal to output a digital code having a multi-bit and digital representation value, and The control signal is at a high or low potential to increase or decrease its value; and a digit to analog converter that receives the digital code and converts to the offset voltage based on its value.