JPH0628519B2 - Inverter control system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an inverter as a power supply for converting DC power into AC power and outputting the AC power, which is interconnected to a power supply system including other power supplies. The present invention relates to an inverter control method for controlling active power sent from a power supply system to a power supply system.

As such an inverter, there is an inverter (inverter for power generation) that converts battery power (DC power) obtained from a solar cell, a fuel cell, or the like into AC power, and such an inverter for power generation is connected to an existing power system, Detects the voltage and frequency (phase) in the system (for example, commercial power supply system) and outputs the inverter output voltage and frequency (phase) to the detected voltage and frequency
The active power (or reactive power) supplied from the inverter to the power supply system can be adjusted by controlling.

FIG. 3 is a conceptual diagram showing a power generation inverter, an existing power system, and interconnection connection. In the figure, 1 is a power generation inverter, 1A is a voltage source inverter, and 1B is a combined impedance that also serves as an AC filter (in this example, pure reactance L
2) is a commercial power supply system. Further, i is the output voltage vector of the voltage source inverter 1A, _L is the output current vector, ω is the angular frequency of the voltage source inverter 1A,
_s is the system voltage vector of the power system 2, and ω is the same system 2
Is the angular frequency of.

FIG. 4 is a vector diagram showing the vector relationship of the quantities shown in FIG.

From the figure, the inverter output voltage Vi, the system voltage Vs, the phase difference between the two, the active power P _G and the reactive power Q _G exchanged between the power generation inverter 1 and the commercial power system 2, It will be understood that the following equations hold.

P _G = (Vs · Vi · sin) / ωL …… (1) Q _G = (Vs ² −Vs · Vi · cos) / ωL …… (2) Also, under the condition of ≈0, P _G ∝ (3) Q _G ∝ (Vs-Vi) (4) That is, the active power P _G is changed by changing the output phase of the inverter 1A, and the reactive power Q is changed by changing the magnitude of the output voltage Vi. _The above is that _G changes respectively
It may be recognized from Eqs. (3) and (4).

On the other hand, the output voltage phase of the inverter 1A corresponds to the phase of the ignition pulse supplied to the switching element forming the inverter, so that the output voltage phase can be changed by changing this, and the output voltage amplitude can be the input DC voltage or the switching. It is well known that it is determined by the conduction time width of the element. That is, the ignition drive pulse of the switching element has a waveform as shown in FIG.
In accordance with this, the element is on / off controlled.

The angle display 360 ° shown in FIG. 5 is set so as to coincide with one cycle period of the power source system connected to each other.

Further, even when a current source inverter is used instead of the voltage source inverter 1A described above, by controlling the phase of the ignition pulse supplied to the switching element and the input side DC current,
It goes without saying that active power and reactive power sent to the power supply system can be controlled as in the above.

INDUSTRIAL APPLICABILITY As described above, the present invention interconnects an inverter as a power source with another power supply system and controls the output voltage and output phase of the inverter to control the power supplied from the inverter to the power supply system. The present invention relates to an inverter control method for controlling.

[Prior art and its problems]

Generally, a phase locked loop (PLL) circuit is used to synchronize the power generation inverter and another power supply system when they are connected to each other. Conventionally, such a PLL circuit is used. The inverter control as described above has been performed.

FIG. 6 is a block diagram showing a conventional inverter control system using a PLL circuit. In the figure, 11 is a phase difference detector (also includes a low-pass filter for further outputting the detected phase difference signal), 12 is an output power controller, 13 is an adder, and 14 is a voltage controlled oscillator. (VCO), 15 is a firing drive pulse generator, a is a power system voltage phase signal, b is an inverter output voltage fundamental wave phase signal, c is a phase difference detection signal, d is a leading phase command signal, and e is a frequency command signal. , F is a clock pulse, and g is a firing drive pulse signal of a switching element forming an inverter.

Although the signals b and g are shown as being output from the pulse generator 15, the signals b and g have a one-to-one correspondence with each other as described above.

Next, the circuit operation will be described. When the phase b of the fundamental wave of the inverter output voltage is ahead of the phase of the power system voltage phase signal a, the phase detector 11 outputs the phase difference detection signal c which is the degree of the advance. In response to the fluctuation of the phase difference detection signal c, the frequency command signal e changes to the voltage controlled oscillator (VC
O) 14 and the frequency of its output f goes up and down, the phase signals a and b have the same frequency, and the phases of both are in a constant relationship, so that a steady synchronization state is established.

Here, in order to control the phase difference between the power supply system voltage and the inverter output voltage and to control the output power from the inverter to the system, the phase relationship between the phase signals a and b must be changed, Therefore, the output (advancing phase command signal) d from the output power controller 12 is added to the output c of the phase difference detector 11 by the adder 13 and brought into the VCO 14. At this time, the clock signal f output from the VCO 14
A pulse train having the same cycle as the system voltage is read from the pulse generator 15 as a signal g and supplied as a firing drive signal to a switching element forming an inverter.

When it is desired to control the inverter output voltage and the reactive power supplied from the inverter to the power supply system, the pulse generator 15 is configured to generate a pulse train as shown in FIG. 5, for example. In accordance with the command of the inverter output voltage, a pulse train having different control angles α in FIG. 5 may be taken out and supplied to the switching element.

As described above, the conventional inverter control system has the following problems.

That is, for example, an ex-OR (exclusive OR) element is used as the phase difference detector 11 in FIG. 6, but in order to detect the phase difference between two signals,
Since at least a half cycle period of the signal is required, the low-pass filter added to this phase difference detector should have a longer time constant than the half cycle, and the output frequency of the VCO 14 during the half cycle. It is difficult to expect stable operation unless it is changed significantly.

In addition, the clock frequency from the VCO 14 is set to the pulse generator 1
Similarly, if the clock frequency is drastically changed in a half cycle time, it is unacceptable because it causes adverse effects such as an increase in harmonics of the inverter output.

In this way, when adjusting (increasing or decreasing) the power supplied from the inverter to the power supply system, resynchronization of the inverter output frequency with the system frequency at that time requires operation with a long time constant. Will be done. In other words, it takes a long time to adjust the power supplied from the inverter to the power supply system, and the voltage phase change at the interconnection connection point due to the load fluctuation connected to the power supply system, the change of the output command value to the inverter, etc. On the other hand, the conventional inverter control method has a problem in that the control system cannot be quickly adjusted to increase / decrease the supply power and lacks quick responsiveness.

[Object of the Invention]

The present invention has been made to solve the above-mentioned drawbacks of the prior art. Therefore, an object of the present invention is to connect an inverter as a power source to a power source system including another power source, It is an object of the present invention to provide an inverter control system that is capable of performing quick adjustment operation when adjusting the increase / decrease of the power supplied from the inverter to the power supply system and that is highly responsive as a control system.

[Main points of the invention]

The gist of the present invention is that the control system for synchronizing the inverter and the power supply system is composed of a PLL circuit, but the control system for adjusting the power supplied from the inverter to the power system is separate and separate. By configuring it, it is possible to realize an inverter control system that is highly responsive as a control system.

Example of Invention

 Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 11 is a phase difference detector (including a low pass filter), 12 is an output power controller, 14 is a voltage controlled oscillator (VCO), 16a, 16b and 16c are frequency dividers respectively, 17 is an edge trigger circuit, 18 Is an up-down counter, 19a and 19b are comparators, 20 is a ROM or level converter, and 21 is a firing drive pulse generator of a switching element which constitutes an inverter.

Further, a is a voltage phase signal of the power supply system, c is a phase difference detection signal, e is a frequency command signal, d (d ₁ , d ₂ ) is a lead phase signal, and f, h, and i are clock pulses with different frequencies, g Is a firing drive pulse signal of a switching element forming an inverter, j is a preset timing signal, and k is a preset timing signal.
Is the count output, l ₁ is the up-down reversal threshold, l ₂
Is the down-up inversion threshold, m is the up-down command,
n is an output voltage command, o is a switching phase command, p, q
Are switching phase display signals, respectively.

FIG. 1A is a time chart of signals of respective parts in FIG.

The circuit operation will be described with reference to FIGS. 1 and 1A. First, in FIG. 1, the loop circuit composed of the phase difference detector 11, the VCO 14, and the frequency dividers 16a and 16b is similar to the above-mentioned case.
Configure a PLL circuit.

However, here, the output of the PLL circuit is not related to the phase of the inverter output, and the angle unit corresponding to the system voltage cycle is provided as the clock signal f, and the timing signal for giving the lead / lag angle of the inverter output. The purpose is to give j.

In this embodiment, the output voltage command signal n of the inverter is changed to R
The OM 20 converts into a count set value for creating an ignition phase command for the switching element forming the inverter. The count set value (corresponding to α in FIG. 5) obtained by the above conversion and the up / down counter 18
The pulse pattern p obtained as a result of comparing the output k of the above with the comparator 19b and the basic pattern q of 180 ° conduction in the inverter are combined by the pulse generator 21 (in this case, the pulse generator 21 is an ex-OR element). The obtained pulse g corresponds to the pulse train shown in FIG.

That is, the width 2α between (90 ° -α) and (90 ° + α) shown in FIG. 5 is adjusted depending on the magnitude of the output voltage command signal n of the inverter to obtain the magnitude of the fundamental wave component of the inverter output voltage. The level of change (and by extension, the amount of reactive power exchanged between the inverter and the grid) is changed.
A description will be given again with reference to FIG.

In the steady state, the signal k from the counter 18 is a digitally represented triangular wave signal (a triangular wave signal represented by a count value). Also, the output voltage command signal n of the inverter
Has been converted by the ROM 20 into a set value represented by a count value for generating the pulse train p (display signal of the ignition phase).

Here, the ROM 20 corresponds to the maximum value of the output voltage command signal n from zero to the value l1 represented by the count number (l
It stores up to 1 + l2) / 2. The value l1 is (α
= 0 °), and the value (l1 + l2) / 2 is (α = 45
Corresponding to ()). That is, by giving the output voltage command signal n to the ROM 20 as an address, a value (l1 to (l1 + l2) / 2 represented by the corresponding count number is obtained.
Values within the range up to) are read from the ROM 20, and the values are also represented as n in FIG. 1A.

Next, the comparator 19b performs comparison to distinguish a section of k> n from a section of k <n to generate a pulse train p (display signal of firing phase), that is, k> n.
The pulse train p is formed by setting the high level in the section of (1) and the low level in the section of k <n.

Further, in the comparator 19a, when k ≧ l1,
The output m is inverted from high level to low level, and k ≦
When it becomes 12, the output m operates so as to invert from low level to high level.

A signal q is obtained by dividing the output signal m by 2 by the frequency divider 16c. The signal p and the signal q are introduced into the pulse generator 21, and e
A pulse train g can be obtained by operating the x-OR element.
Therefore, when the magnitude of the output voltage command signal n is reduced, a change occurs in which each pulse width 2α of the pulse train p is increased. The output pulse train g from the pulse generator 21 corresponds to the pulse train shown in FIG. 5, as described above.

The quantities d ₁ and d ₂ corresponding to the lead and lag angles of the pulse train g with respect to the phase a of the power supply system voltage are output power controller 12
This value is given to the up-down counter 18 periodically according to the preset timing j generated by the edge trigger circuit 17.

This up-down operation of the counter 18 is performed when the phase command d from the output power controller 12 is not changed.
Up-down and down-up thresholds l ₁ and l _{2 are} provided so that the cycle corresponds to 2 cycles of up-down.
The counter output k and the threshold values l ₁ and l ₂ are compared by the comparator 19 so that the up-down inversion occurs at these values.
It is carried out by using the output m as an up-down command.

One cycle of this up-down operation corresponds to a half cycle of the power supply system, and is the result adjusted by the phase command d. Therefore, the output m of the comparator 19a is doubled by the frequency divider 16c. By dividing the signal of
The basic pattern q of the 180 ° conduction of the inverter is obtained. When it is desired to control the magnitude of the inverter output voltage, the command signal n can be used to change the amount corresponding to the magnitude of α shown in FIG.

By operating the inverter with the circuit configuration as described above, the phase and amplitude of the output voltage of the inverter can be controlled, and active power and reactive power supplied from the inverter to the power supply system can be controlled.

The pattern of the ignition drive pulse signal g of the switching element may change depending on the order of the harmonics to be erased in the output of the inverter, and accordingly, the number of ROMs 20 and comparators 19b, the configuration of the pulse generator 21, The cycle of the updown in the counter 18 can be changed.

FIG. 2 is a block diagram showing an essential part of another embodiment of the present invention made from this point of view. That is, for the purpose of removing harmonics from the output of the inverter, an embodiment is shown in which the number of times of switching of the switching elements constituting the inverter is increased as compared with the case of the embodiment shown in FIG.

FIG. 2A is a time chart of signals of respective parts in FIG.

Please refer to FIG. 2 and FIG. 2A. For the same output voltage command n, different One was switching-phase command O _1, O ₂ and outputs the ROM 20a, 20b, 2 pieces of comparators 19b corresponding to them _1, 19b _2, also firing drive pulse generator 21 is shown Has been done.

The purpose of this embodiment will be easily understood by comparing and referring to the waveform of the switching element firing drive pulse signal g in FIG. 2A and the waveform of the signal g in FIG. 1A.

Since the circuit operation of this embodiment is essentially the same as the circuit operation described above with reference to FIGS. 1 and 1A,
I won't repeat it here.

When a current source inverter is used instead of the voltage source inverter, the conduction time zone differs depending on the number of output phases, and 180 degree conduction is not necessarily the basic pattern of pulses.
The method of forming the basic pattern q is different.

In the above description, the number of phases of the inverter is ignored. Therefore, it is assumed that the firing pulse pattern and the output voltage pattern supplied to the switching elements forming the inverter are the same, but the number of phases is ignored. Have to,
It goes without saying that different patterns with different phases are obtained accordingly.

〔The invention's effect〕

According to the present invention, when the inverter as the power source is connected to the power supply system for operation, the control system for system synchronization and the control system for supply power adjustment are separated, and the former PLL circuit is used. Since the phase adjustment of the inverter can be performed without changing the oscillation frequency of the VCO, the phase adjustment operation is not affected by the time constant of the filter in the phase difference detector of the PLL, and the supplied power is highly responsive. There is an advantage that the adjustment operation can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 1A is a time chart of signals of respective parts in FIG. 1, and FIG. 2 is a block diagram showing an essential part of another embodiment of the present invention, 2A. The figure shows the time chart of the signals in each part in Fig. 2, Fig. 3 is a conceptual diagram showing the interconnection connection between the power generation inverter and the existing power supply system, and Fig. 4 is the vector relation of the quantities shown in Fig. 3. FIG. 5 is a vector diagram showing a waveform diagram showing an example of an ignition drive pulse supplied to a switching element constituting an inverter, and FIG. 6 is a block diagram showing a conventional inverter control system using a PLL circuit. . Explanation of code 1 …… Inverter for power generation, 1A …… Voltage type inverter,
1B ... Coupling impedance, 2 ... Commercial power system, 1
1 ... Phase difference detector (including low-pass filter), 12
...... Output power regulator, 13 ...... Adder, 14 ...... Voltage controlled oscillator (VCO), 15, 21 ...... Ignition drive pulse generator, 16a, 16b, 16c ...... Divisor, 17 ・ ・ ・ Edge trigger Circuit, 18 ... Up-down counter, 19
a, 19b ... Comparator, 20a, 20b ... RO
M or level converter

Claims (1)

[Claims] 1. An inverter as a power source for converting DC power into AC power and outputting the AC power is interconnected to a power supply system including other power supplies, and active power supplied from the inverter to the power supply system is controlled. In the inverter control method, the voltage phase of the system is compared with the phase of a certain clock signal created from the oscillation output of the variable voltage oscillator to detect the phase difference, and the phase difference signal is sent to the variable voltage oscillator. A phase-locked loop circuit that is input so that the voltage phase and the phase of the clock signal match, and a triangular wave that is synchronized with the cycle of the system voltage is created by counting up and down when the clock signal is input. Output counter, an output voltage level setter, and a switching element that constitutes the inverter with the set level set by the setter. A conversion circuit for converting the count setting value for creating the ignition phase command for the child, and comparing the count setting value with the triangular wave to output a first pulse having a pulse width depending on the magnitude of the count setting value. A comparator, a circuit for generating a second pulse synchronized with the count-up and down cycles of the counter, and an ignition phase command signal for the inverter from the first pulse and the second pulse. An inverter comprising a circuit for outputting and a means for adjusting output power by vertically shifting the level of the triangular wave by a certain level at a specific timing synchronized with the cycle of the system voltage. control method.