JPH0728538A - System interconnection type inverter controller - Google Patents

Abstract

PURPOSE:To always take out a maximum power from a DC power source by satisfactorily performing the maximum power point tracking control regardless of the variance in voltage-current characteristic of the DC power source like a solar battery. CONSTITUTION:A CPU 48 outputs the waveform pattern read out from a ROM 49 to a D/A converter 51 to obtain a reference sine wave signal S11 and switches an FET bridge 36 through a PWM modulation circuit 43 and a gate drive circuit 42 to convert the DC power from a solar battery 32 to an AC power. A detected inverter output current IOUT is converted to a digital value by an A/D converter 47 and stored in a RAM 50. The CPU 48 compares the preceding output current value and the present, output current value with each other to discriminate whether the output current IOUT is increased or not. The amplitude changing direction of the reference sine wave signal S11 is kept if it is increased, but this direction is inverted if it is reduced, and the amplitude of the reference sine wave signal S11 is changed in the determined direction by one stage to perform the maximum power point tracking control of the solar battery 32.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention converts DC power output from a DC power source such as a solar cell into AC power in order to connect it to a commercial power source, so that the output power from the DC power source is always in the maximum state. The present invention relates to a grid-connected inverter control device that supplies a general load.

[0002]

2. Description of the Related Art FIG. 2 shows an example of a grid-connected photovoltaic power generation system to which a conventional grid-connected inverter control device is applied. In the case of this conventional example, a constant input voltage control method is adopted as the control method. In this system, the DC power of the solar cell 2 is converted into AC power by a system interconnection inverter 1 that is PWM (pulse width modulation) controlled, and is connected to a commercial system power source 3 to supply power to a load 4. is there.

The grid-connected inverter 1 has the functions of an input capacitor 5, an FET bridge 6, and an output filter P
It is composed of an output choke coil 7 for changing a WM-modulated rectangular wave into a sine wave, a smoothing capacitor 8 and a control section 9. The control unit 9 includes an input voltage detection circuit 10, a bandpass filter (BPF) 11, an output current detector 12,
DC voltage constant control circuit 13, DC voltage reference voltage source 14,
Multiplier 15, error amplifier 16 for controlling output current, PWM
It is composed of a modulation circuit 17 and a gate drive circuit 18 for driving the FET bridge 6.

The control method will be described below.

The inverter input voltage V _DC is detected by the input voltage detection circuit 10, and the DC voltage constant control circuit 13 outputs the inverter input voltage V _DC and the DC voltage reference voltage source 14.
Error signal S1 with respect to the reference voltage V _REF is generated, and this error signal S1 is used as one input of the multiplier 15. Further, the commercial system voltage V _CS is detected, only the fundamental wave component is extracted by the bandpass filter 11, and the reference sine wave signal S2 is used as the other input of the multiplier 15. The multiplier 15 multiplies the input error signal S1 and the reference sine wave signal S2 to generate an inverter output current reference signal S3.

The error amplifier 16 receives the inverter output current reference signal S3 from the multiplier 15 and the inverter output current I _OUT detected by the output current detector 12, and a modulation reference error signal S4 obtained by amplifying the difference between the two. PWM modulation circuit 1
Output to 7. PWM modulation circuit 17 performs PWM control based on the modulation reference error signal S4 inputted by driving the FET bridge 6 via the gate drive circuit 18, the reference voltage V _{RE F} to the matched inverter input voltage V _DC is Control to obtain. That is, the solar cell 2
The input characteristic of the grid interconnection inverter 1 is controlled by the operating voltage of.

In the FET bridge 6, when the transistors Q1 and Q2 are simultaneously turned on, the transistors Q3 and Q4 are simultaneously turned off, and conversely, the transistor Q1 is turned off.
Transistors Q1 and Q2 when 3 and Q4 are turned on simultaneously
Are controlled so that they are simultaneously turned off.

Due to the characteristics of the solar cell 2, the operating voltage at which the maximum power can be taken out changes every moment depending on weather conditions such as the amount of solar radiation and the element temperature. By the way, the characteristic of the above-mentioned conventional method is that it is operated at a maximum output point of the solar cell 2 on the assumption that the operating voltage can be approximated by a constant voltage regardless of the amount of solar radiation and the element temperature.

However, it is naturally expected that the preset constant voltage value does not match the voltage value at which the maximum power can be taken out. In this case, the operation is performed at a point deviating from the maximum output point, and maximum power cannot be output. Especially, when the amount of solar radiation is large, a large amount of power is wasted. Further, since the maximum output point voltage greatly changes depending on the element temperature, it is necessary to change a preset constant voltage value depending on the season, which is complicated.

[0010]

A major feature of a solar cell is that its output characteristics are greatly affected by weather conditions, and even if the weather conditions are the same, its output varies depending on the operating point. Can be mentioned.

Therefore, in order to effectively use the generated power of the solar cell, it is conceivable that maximum power point tracking control should be performed. There is a fundamental problem that it is impossible to positively control the output power by changing the operating point on the characteristic curve.

As is well known, the output characteristic of the solar cell is as shown in FIG. 3, and if the weather conditions are constant, the output characteristic of the solar cell is changed according to the impedance of the load. The values of the output voltage and output current of the solar cell change on the output characteristic curve, and the output power value of the solar cell also changes accordingly.

Here, when the impedance of the load provided at the output end of the solar cell is R as shown in the figure, the output voltage and output current of the solar cell at this time are the values at point p on the characteristic curve. By changing the load impedance R, the operating point p of the solar cell moves on the characteristic curve,
The output voltage, output current, and output power of the solar cell change. In order to extract the maximum electric power of the solar cell, it is sufficient to control so that the impedance R of the load viewed from the solar cell side is optimum even when the weather conditions change.

By the way, when the solar cell maximum power point tracking control is performed by the output current control type inverter, the amplitude of the output current reference signal is manipulated and the error signal between the output current reference signal and the detected output current signal is calculated. PWM-modulates and drives the inverter. As a result of the operation, it is determined whether the input power has increased or decreased, and the amplitude of the next output current reference signal is changed.

When starting from the open circuit voltage side of the solar cell and gradually increasing the amplitude of the output current reference signal, the error signal with the detected output current signal becomes large, and the switching duty ratio becomes large in PWM modulation. Become. Then, the input impedance of the inverter, that is, the impedance viewed from the solar cell is reduced, and the output power is increased according to the solar cell output characteristic curve. Since the inverter output voltage is considered to be almost constant at the voltage of the commercial system power supply 3, the inverter output current also increases as the output power increases.

However, the amplitude of the output current reference signal is gradually increased, and the output power continues to increase accordingly,
It is assumed that the maximum power point has been reached. Then, when the amplitude of the output current reference signal is further increased to exceed the maximum power point, the inverter input power is reduced this time, and the inverter output current is also reduced.

At this time, the output current signal to be fed back becomes small and the error signal with respect to the output current reference signal becomes large, so that the switching duty ratio becomes large in PWM modulation and the input impedance becomes small. Above, the operating point tries to move to the short circuit side. Then, since the output power is reduced, the output current is further reduced, and the error signal from the output current reference signal is further increased. As a result, if the maximum power point is exceeded, the operating point will move to the short-circuit side. Then, the maximum power point tracking control cannot be performed as it is.

For this reason, when the maximum power point is exceeded, it is necessary to reduce the output current reference signal in accordance with the decrease in the output current signal. However, the characteristics of the solar cell depend on the amount of solar radiation or the element temperature at that time. In addition, in the control, the amplitude of the next output current reference signal is changed in a feed-forward manner by changing the input power as a result of the operation of the amplitude of the output current reference signal. The battery operating point cannot be predicted.

That is, with the control as described above, an increase / decrease in the input power is detected, the amplitude of the output current reference signal is changed,
It is extremely difficult to perform maximum power point tracking control.

The present invention was devised in view of such circumstances, and even if the voltage-current characteristics of a DC power source such as a solar cell fluctuates, the maximum power point tracking control is performed well, The purpose is to always be able to extract the maximum power from the DC power supply.

[0021]

DISCLOSURE OF THE INVENTION A system interconnection type inverter control device according to the present invention is a DC power input from a DC power source such as a solar cell by ON / OFF controlling a bridge of a switching element based on a switching pattern signal. To AC power and supply the load to the commercial system power supply by linking it, a means for generating the switching pattern signal by pulse width modulation based on a reference sine wave signal, and a voltage of the commercial system power supply. A means for detecting and generating the reference sine wave signal in the same phase as the commercial system voltage; and a means for changing the amplitude of the reference sine wave signal in a direction to increase or decrease by one step periodically. Means for storing the inverter output current value and means for determining the direction of change in the output current value by comparing the previous output current value and the current output current value , When the changing direction of the output current value increases, the changing direction of the amplitude of the reference sine wave signal is maintained as it is, and when the changing direction of the output current value decreases, the changing direction of the amplitude of the reference sine wave signal is inverted. It is characterized in that it is provided with a means for making it.

[0022]

[Operation] Based on the detection of the commercial system voltage, a reference sine wave signal is generated in the same phase as that, a pulse width modulation is performed based on this reference sine wave signal to generate a switching pattern signal, and the switching pattern signal is generated based on the switching pattern signal. ON / OFF control of the bridge of the switching element is performed to convert DC power from a DC power supply such as a solar cell into AC power, which is connected to a commercial power supply and supplied to a load. By periodically changing the amplitude of the reference sine wave signal, the inverter output current value is detected and stored, and by comparing it with the previous output current value, it is judged whether the output current value is increasing or decreasing, and it is increased. Maintain the amplitude change direction of the reference sine wave signal (increase in increasing direction, decrease in decreasing direction),
When decreasing, the amplitude change direction of the reference sine wave signal is reversed (decreasing in the increasing direction and increasing in the decreasing direction), and the amplitude of the reference sine wave signal is set to 1 in the determined direction.
Change in steps. By repeating the above, the maximum power point tracking control in which the output power of the DC power source is always the maximum power point can be performed.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a grid interconnection type inverter control device according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a configuration diagram of a grid interconnection type photovoltaic power generation system to which a control device according to an embodiment of the present invention is applied.
In this system, the solar cell 32 is connected to the grid interconnection inverter 31, and the grid interconnection inverter 31 converts the DC power output by the solar cell 32 into AC power having the same phase as the commercial grid power supply 33 by PWM control, and System power supply 3
The electric power is supplied to the load 34 such as a general household electric appliance by connecting the electric power to the load 3 with the electric power source 3.

The system interconnection inverter 31 is a voltage type current control type inverter, and includes an input capacitor 35 for suppressing fluctuations in input power from the solar cell 32, a FET bridge 36 as a switching element for DC-AC conversion, and an output filter. Functioning as an output choke coil 37 and a smoothing capacitor 38 for converting a PWM-modulated rectangular wave into a sine wave, an interconnection relay 39 for disconnecting the grid interconnection inverter 31 from the commercial grid power supply 33 and the load 34 when an abnormality occurs, and It is composed of a control unit 40.

A flywheel diode is connected in reverse polarity to each of the four transistors Q1 to Q4 in the FET bridge 36. FET bridge 36
Is controlled by the gate drive circuit 42 described later.
When the transistors Q1 and Q2 are simultaneously turned on, the transistors Q3 and Q4 are simultaneously turned off. Conversely, when the transistors Q3 and Q4 are simultaneously turned on, the transistor Q1,
Q2 is configured to be turned off at the same time.

The control section 40 is composed of the following elements. That is, a control circuit 41 that performs maximum power point tracking control of the grid interconnection inverter 31, output current control, and system protection, a gate drive circuit 42 that drives and controls the FET bridge 36, and a reference sine wave output from the control circuit 41. The PWM modulation circuit 43 that PWM-modulates the signal S11 to generate the switching pattern signal S12 and outputs it to the gate drive circuit 42, and the synchronization signal detector 44 that makes the output of the inverter 31 the same phase as the commercial system power supply 33. And the positive / negative direction detector 45 and the output current detector 4
6 and 6.

The control circuit 41 is a digital circuit,
An A / D converter 47 that converts the signal detected by the output current detector 46 into a digital signal, a CPU 48 that performs various calculations necessary for control, and a reference sine wave that is the basis of each pulse width for PWM control. A ROM 49 that stores waveform pattern data for producing the signal S11, a RAM 50 that is a memory for temporary storage, and digital waveform pattern data is converted into an analog reference sine wave signal S11 by D / A conversion. The D / A converter 51 outputs the reference sine wave signal S11 to the PWM modulation circuit 43.

The operation of the system configured as above will be described below.

The system interconnection inverter 31 is subjected to PWM control by the PWM modulation circuit 43 and based on the gate pulse signal S13 output from the gate drive circuit 42, the pair of switching transistors Q1 and Q2 in the FET bridge 36 and the pair of switching transistors Q1 and Q2. By alternately turning ON / OFF the switching transistors Q3 and Q4 for switching, the output current of the grid interconnection inverter 31 is controlled, and the output of the solar cell 32 is supplied to the load 34.

In this case, the PWM modulation circuit 43 is
PWM is performed by comparing the reference sine wave signal S11 from the converter 51 and the triangular wave serving as the switching carrier wave.
The switching pattern signal S12 as a waveform is generated and output to the gate drive circuit 42. Gate drive circuit 42 to which switching pattern signal S12 is input
Outputs the gate pulse signal S13 to the FET bridge 36, and the transistors Q1 and Q2 and the transistor Q
A rectangular wave is generated by turning ON / OFF Q3 and Q4. The rectangular wave has an output choke coil 37 and a smoothing capacitor 38.
Is converted into a sine wave current by the output filter and is supplied to the load 34 via the interconnection relay 39. The reference sine wave signal S11 is controlled to have the same phase as the voltage waveform of the commercial system power supply 33, and the duty ratio of the PWM pattern is determined by the magnitude of its amplitude.

Next, the reference sine wave signal S11 will be described. As described above, the reference sine wave signal S11 causes the PW
The duty ratio of the M pattern is determined, the operating point of the solar cell 32 is determined, and the grid interconnection inverter 31 according to the operating point is determined.
Output current is obtained. By the way, in order to perform the solar cell maximum power point tracking control, the amplitude of the reference sine wave signal S11 must be variable. Below is the reference sine wave signal S
11 shows a method of varying the amplitude of 11.

When the maximum reference sine wave signal pattern when the duty ratio of the grid interconnection inverter 31 is maximum is set to the maximum, the data of one cycle of the maximum reference sine wave signal is decomposed at certain time intervals. The amplitude value is represented as a digital value. In the case of this embodiment, the frequency is 60 Hz and 1
The cycle is 1/60 seconds, which is divided into 256 equal to about 65.1μ.
Let sec be the unit cycle. In this case, one cycle of the reference sine wave signal is composed of 256 digital values in the time axis direction. Consider this set of digital values for one cycle as a group. Next, with respect to each of a large number of reference sine wave patterns obtained by dividing the amplitude of the maximum reference sine wave signal at equal intervals (200 equally divided in this embodiment), one cycle of each of them is the same as above. Consider as a set of 256 digital values. That is, the reference sine wave signal is a waveform pattern formed of a set of 256 digital values, and there are a total of 200 types of such waveform patterns having different amplitudes.

Data of such 200 kinds of reference sine wave patterns are stored in the ROM 49 of the control circuit 41 in advance. Number 1 for each reference sine wave pattern
When the reference sine wave pattern is designated to the ROM 49 by numbers, the CPU 48 sequentially reads out 256 digital values from the ROM 49 for the reference sine wave pattern of the designated number, and the D / A converter 51 Send to. The D / A converter 51 is a CP
An analog reference sine wave signal S11 having a reference sine wave pattern corresponding to the number designated by U48 is generated, and PW is generated.
Output to the M modulation circuit 43.

The timing at which the CPU 48 reads the digital value of the reference sine wave pattern is as follows. At the same time that the synchronization signal detector 44 reads the zero cross point of the commercial system voltage V _{CS from} the commercial system power supply 33 as a synchronization signal, the CPU 48 starts a built-in timer to read the first data and read 1 cycle of 1/60 seconds to 256, etc. The second data is read after waiting 65.1 μsec. That is, the digital values for the reference sine wave pattern of the designated number are sequentially read out every 65.1 μsec, and the digital values are D / A converted by the D / A converter 51 to generate the reference sine wave signal S11.
Is generated and output to the PWM modulation circuit 43. At this time, the synchronization signal detector 44 detects the zero cross point of the commercial system voltage V _CS , and the positive / negative direction detector 45 detects the positive / negative direction of the waveform of the commercial system voltage V _CS , and C
The PU 48 outputs the data in the positive and negative directions to output the reference sine wave signal S11 to the commercial system voltage V.
It can be output in the same phase as _CS .

Further, the control circuit 41 simultaneously executes the following controls. The CPU 48 uses the A / D converter 47 to output the output current I _OUT of the inverter 31 detected by the output current detector 46 to the A / D in a relatively long fixed cycle.
It is converted and temporarily stored in the RAM 50. Then, the previously stored inverter output current value and the inverter input current value input this time are compared to determine whether the inverter output current value has increased or decreased. Depending on the result of the determination, it is determined whether to increase or decrease the number of the next reference sine wave pattern. Specifically, it is as follows.

At the first time, "0" is set as the previous inverter output current value, the minimum value "1" is designated as the reference sine wave pattern number, and the reference sine wave pattern number changing direction increases. Set in the direction of. To determine the changing direction of the increase or decrease of the reference sine wave pattern number after the second time, compare the previous inverter output current value with the current inverter output current value, and if the inverter output current value increases, The changing direction of the number is maintained as it is, and when the output current value of the inverter decreases, the changing direction of the number is reversed. In other words, when the inverter output current value increases, if the number changing direction at that time is in the increasing direction, it is continuously maintained in the increasing direction, and if the number changing direction is in the decreasing direction, it is continuously maintained in the decreasing direction. . On the contrary, when the inverter output current value decreases, if the number changing direction is in the increasing direction at that time, it is inverted and becomes the decreasing direction, and if the number changing direction is the decreasing direction, it is inverted and becomes the increasing direction. That is.

Setting the changing direction of the reference sine wave pattern number to the increasing direction means outputting the reference sine wave signal S11 having a sine wave pattern having a larger amplitude, and conversely, the reference sine wave pattern. Setting the direction in which the number is changed to the decreasing direction means that the reference sine wave signal S11 having a sine wave pattern having a smaller amplitude is output. In this embodiment, there are 200 reference sinusoidal pattern numbers, but when the number is increased or decreased, the number is increased or decreased by one.

In this embodiment, the above control is performed by the control circuit 4
It is realized by software control using a microcomputer including the CPU 48, the ROM 49, and the RAM 50 in the first embodiment.

By performing the control as described above, under constant weather conditions, the solar cell operating point is moved from the open voltage side toward the maximum power point each time the amplitude of the reference sine wave signal S11 is increased. When the inverter output current value decreases beyond the maximum power point, the direction of change of the amplitude of the reference sine wave signal S11 is inverted to decrease the amplitude, thereby bringing the solar cell operating point closer to the maximum power point again. be able to.

Therefore, after that, the solar cell 32 can always be operated in the vicinity of the maximum power point by the same control of the amplitude changing direction, and the operating point moves to the short circuit side as in the conventional example. Does not occur. It is not necessary to reduce the output current reference signal in accordance with the decrease in the output current signal, and the input power increases or decreases as a result of the amplitude operation of the output current reference signal. This is because it is not necessary to change the amplitude.

Further, no matter how the characteristics of the solar cell change due to changes in weather conditions, the amplitude of the reference sine wave signal S11 can be adjusted by performing the above-described control according to the increase / decrease of the inverter output current value. By controlling, the solar cell operating point can be quickly moved to the maximum power point. That is, regardless of weather conditions and load fluctuations,
The maximum power point tracking control can always be performed well.

[0043]

As described above, according to the present invention, the maximum power point tracking control can be easily performed even if the output characteristics of the DC power source such as a solar cell fluctuates, and the maximum power is always supplied from the DC power source. Can be taken out.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a grid-connected photovoltaic power generation system to which a grid-connected inverter control device according to an embodiment of the present invention is applied.

FIG. 2 is a configuration diagram of a system interconnection solar power generation system to which a system interconnection inverter control device according to a conventional example is applied.

FIG. 3 is a voltage-current characteristic diagram of a solar cell.

[Explanation of symbols]

31 ... Grid interconnection inverter 32 ... Solar cell 33 ... Commercial grid power supply 34 ... Load 35 ... Input capacitor 36 ... FET bridge 37 ... Output choke coil (filter) 38 ... Smoothing capacitor (filter) 39 ...... Interconnection relay 40 ...... Control unit 41 ...... Control circuit 42 ...... Gate drive circuit 43 ...... PWM modulation circuit 44 ...... Sync signal detector 45 ...... Positive and negative direction detector 46 ...... Output current detector 47 ... ... A / D converter 48 ... CPU 49 ... ROM 50 ... RAM 51 ... D / A converter S11 ... reference sine wave signal S12 ... switching pattern signal S13 ... gate pulse signal _VCS ... commercial system voltage I _OUT ...... Inverter output current

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number in the agency FI Technical indication location H02M 7/77 9181-5H (72) Inventor Hiroshi Nakata 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation

Claims (1)

[Claims] 1. A bridge of a switching element is ON / OFF controlled based on a switching pattern signal to convert DC power input from a DC power source such as a solar cell into AC power, which is connected to a commercial power source to form a load. A means for supplying, a means for generating the switching pattern signal by pulse width modulation based on a reference sine wave signal, a voltage for the commercial system power supply, and the reference sine wave signal in the same phase as the commercial system voltage. Means, a means for periodically changing the amplitude of the reference sine wave signal in a direction of increasing or decreasing by one step, a means for storing the detected inverter output current value, and a previous output current value. Means for determining the direction of change in the output current value by comparison with the current output current value, and the reference sine wave when the direction of change in the output current value increases A system interconnection type inverter control, characterized in that the system is provided with means for maintaining the changing direction of the signal amplitude as it is and inverting the changing direction of the amplitude of the reference sine wave signal when the changing direction of the output current value decreases. apparatus.