JPH0479216B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a power supply device using a solar cell, a fuel cell, or the like for supplying power to a load in conjunction with an electric power system.

Conventional configurations and their problems When a power supply device using fuel cells or solar cells is linked to the power grid, even if the power grid side is stopped (opened), the power supply device is established and power is supplied from the power supply device to the load. Therefore, there is a problem in terms of safety for workers during load maintenance and inspection.

In order to solve the above problems, conventional power supplies (single-phase or three-phase) are connected to the power grid 1 and feed power to the load 2 in conjunction with the power grid 1, as shown in Figure 8. Specifically, for example, a self-excited inverter 4 is driven by the solar cell 3 so that the inverter 4 generates an AC output at the same frequency as the power grid 1, and the inverter 4 The output end is connected to the power system 1 via an interconnection transformer 5. Then, the control circuit 6
The outflow current I〓s to the power system 1 is detected through the current transformer 7, and the system voltage _V〓S is detected through the transformer 8.
is detected, and the active power Ps is determined by the control circuit 6 based on equation (1) from both of them, or a current I〓 _S ′ is created by shifting the outflow current I〓 _S by 90 degrees based on the fundamental wave. Determine the reactive power Q _S based on equation (2),
Active power P _S or reactive power Qs when power system 1 side is stopped by turning off switch 9
detects the amount of change or rate of change in the level, and when these levels exceed a predetermined value, it is assumed that the power system 1 has stopped, and a stop signal is given to the inverter 4, stopping the power supply from the inverter 4 to the load 2, and ensuring safety. It is becoming more and more secure.

P _S = 1/T∫ ^T _O V _S I _S dt ……(1) Q _S = 1/T∫ ^T _O V _S I _S ′dt ……(2) However, in such a conventional power supply device, , when the load 2 and the output of the inverter 4 are almost perfectly balanced, P _S ≒ Q _S ≒ 0 ...(3), and even if the power system 1 is opened, the active power P _S and the reactive power Q _S does not change, and it is not possible to detect that the power system 1 has been opened. On the other hand, when load 2 changes (starting or stopping a cooler, etc.), active power P _S and reactive power Q _S also change,
Inverter 4 is disconnected even though power grid 1 is not open.
There was a risk that the system would be stopped.

In this way, with the conventional system, an open circuit in the power system 1 may or may not be detected depending on the state of the load 2, etc., or the inverter 4 may be stopped by mistake even though the power system 1 is not open. There was a problem that the system was damaged, and it lacked reliability.

Purpose of the Invention The present invention is capable of reliably detecting the stoppage (opening) of the power system and stopping the operation of the inverter.
Moreover, it is an object of the present invention to provide a power supply device that can prevent erroneous operations.

Composition of the Invention A power supply device of a first invention includes an inverter using a battery as a power source, and a grid interconnection transformer that connects the inverter to a power system that supplies power to a load and interconnects the inverter and the power system. , an inverter control section that controls the inverter so that the output voltage of the inverter periodically fluctuates minutely; a reactive power detection section that detects reactive power on the power system side of the interconnection transformer; A reactive power fluctuation extraction section extracts a variation having the same period as the periodic minute fluctuation of the output voltage of the inverter from among the reactive power detected by the detection section; The power supply device of the second invention is characterized in that it is configured to include a level discriminator that provides an inverter stop signal to the inverter control unit when the amount of variation in power variation is less than a predetermined value. an inverter that connects the inverter to a power system that supplies power to a load to interconnect the inverter and the power system; an inverter control unit that controls an inverter; a voltage detection unit that detects a grid-side voltage of the interconnection transformer; a grid-side voltage fluctuation extractor that extracts a fluctuation having the same period as the fluctuation; and a grid-side voltage fluctuation extractor that extracts a fluctuation in the grid-side voltage fluctuation extractor, and when the amount of fluctuation in the grid-side voltage fluctuation extracted by the grid-side voltage fluctuation extractor is equal to or greater than a predetermined value, the inverter controller and a level discriminator that provides an inverter stop signal to the inverter.

Here, the principle of detecting the stoppage (opening) of the power system in this invention will be explained.

FIG. 7A shows a simplified circuit diagram when the inverter 10 is interconnected with the power system 11 to supply power to the load 12. (It is assumed that the power system 11 is sufficiently larger than the capacity of the inverter 10). In the same figure, V _I
is the inverter output voltage (pu value), V _S is the grid voltage (pu value), and X _T is the leakage reactance (pu value) of the interconnection transformer, which is 0.1 based on the self-capacity of inverter 10.
It is about ~0.3pu. θ _I is the inverter output voltage phase, and θ _S is the system voltage phase. P is active power, Q
is the reactive power.

Now, assuming θ _I = θ _S , P = 0 Q = V _I (V _I − V _S )/X _T ...(4), and when X _T = 0.1 pu, V _I = Vs = 1 pu, , if the inverter output voltage V _I slightly changes to V _I +ΔV _I , the change ΔQ in reactive power Q is ΔQ=2V _I −Vs/X _T ΔV _I =1/X _T ΔV _I =
10・ΔV _I ...(5) When ΔV _I =0.01pu (1%), ΔQ=
This results in a reactive power fluctuation of 10% of the self-capacity.

On the other hand, FIG. 7B shows a circuit diagram when the power system 11 is opened. In the figure, Z _L is the load impedance (=R _L +jX _L ).

Now, if R _L <<X _L and θ _I =θ _S , then P=0...(6) Q=V _L /X _T +X _L ...(7). Minute fluctuation of inverter output voltage V _I ΔV _I
The change ΔQ in the ineffective electrode Q due to is ΔQ=2V _I ΔV _I /X _T +X _L (8). Generally, from the relationship between the inverter capacity and the load 12, it is considered that X _L = 5 to 10X _T (pu), so
For example, if X _L = 9X _T , then ΔQ = 2ΔV _I ...(9). Therefore, when ΔV _I =0.01pu (1%), ΔQ=0.02pu, and a reactive power fluctuation of only 2% of the self-capacity occurs.

As described above, the reactive power fluctuation with respect to the inverter output voltage fluctuation becomes smaller when the power system 11 side is opened. Therefore, if the inverter output voltage V _I is always slightly fluctuated at a certain period and the inverter's reactive power fluctuation is monitored, the stoppage (opening) of the power system 11 can be reliably and promptly detected based on the level. Inverter 10 can now be stopped. Therefore, the load 12
The influence of the state etc. on detection can be made very small.

In addition, when the grid-side voltage Vs' of the interconnection transformer is interconnected with the power grid 11, the capacity of the power grid 11 is much larger than the capacity of the inverter 10, so the output voltage _V Even if the value fluctuates, it remains a constant value without being affected by it at all. On the other hand, when the power system 11 is opened, the system side voltage V _S ' will fluctuate according to the voltage fluctuation of the inverter 10. Therefore, the grid side voltage
By monitoring the fluctuations in V _S ', it is possible to detect the disconnection of the power system 11 and promptly stop the inverter 10 in the same way as described above.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. 1 to 6. This power supply (single phase or
As shown in FIG. 1, the inverter output voltage outputted from the inverter 22 is
V〓 _I is interconnected with a power system 24 (voltage V〓s) via a interconnection transformer 23 to supply power to a load 25 . The ignition control circuit 26 controls the ignition of the inverter 22 based on the comparison result of the carrier wave V _CAR and the reference wave _VSIG by the comparison circuit 27 .

The carrier wave V _CAR is the DC output voltage of the solar cell 21
It is created by multiplying E _DC by a triangular wave with a peak value of 1.0 in a multiplier 28.

Further, the reference wave V _SIG is created as follows. That is, the voltage detection circuit 29 composed of a rectifier etc. detects the effective value V _S ' of the grid side voltage V _S ' of the interconnection transformer 23 via the transformer 30, and the output of this voltage detection circuit 29 is A low pass filter (120
31 (remove ripples higher than Hz) to obtain a voltage Vα corresponding to the effective value V _S ′, and to periodically slightly fluctuate this DC voltage Vα and the effective value V _I of the inverter output voltage V〓 _I. (a rectangular wave with duty 1/2, amplitude α, and period Tα) is added by an adder 32, and the output of this adder 32 and the frequency are
It is created by multiplying it by a sine wave with a peak value of √2 at 60Hz or 50Hz using a multiplier 33.

Here, the operation around the inverter 22 will be explained. However, for the sake of simplicity, a case will be described in which no additional signal is added and the effective value V _I of the output voltage V 〓 _I is constant. That is, when the carrier wave V _CAR and the reference ratio V _SIG as shown in FIG. 3A are applied to the comparison circuit 27, the comparison circuit 27 compares them and calculates the third
A pulse width modulated wave as shown in FIG.

The voltage detection circuit 29 and the low-pass filter 31 detect the effective value V _S ′ of the grid side voltage V〓 _S ′ as a DC component, but the reference wave V _SIG is the effective value V _S of the above grid side voltage V〓 _S ′. ′ and a sine wave with a peak value of √2.
The carrier wave V _CAR is the triangular wave DC output voltage E _DC with a peak value of 1.
Therefore, the effective value V _I of the output voltage V〓 _I of the inverter 22 is proportional to √2V _S /E _DC .

√2V _I = (√2V _S ′/E _DC )×E _DC =√
2V _S ′=√2V _S , and it can be instantaneously operated with V _I =V _S ′.

Note that FIG. 4A shows the output voltage of the voltage detection circuit 29, and FIG. 4B shows the low-pass filter 31 and the output voltage.

Then, when an unadded signal is added, the inverter 22
The effective value V _I of the output voltage V 〓 _I will fluctuate with the fluctuation period of the additional signal.

The reactive power detection circuit 34 detects the grid side voltage V〓 _S ' of the grid interconnection transformer 23 via the transformer 30, and detects the grid side current I of the grid interconnection transformer 23 via the current transformer 35. 〓 Detects _S , performs arithmetic processing, and generates voltage Qα according to reactive power through low-pass filter 36
is sent to the reverse pressure determination circuit 37. This reverse judgment circuit 37
A voltage Vα is also applied to .

Next, the back pressure determination circuit 37 will be explained in detail with reference to FIG. This reverse pressure determination circuit 37 applies the voltages Qα and Vα to the signal detection filters 38 and 39 of the center frequency fα (=1/Tα), respectively, thereby detecting the component of the frequency fα in the voltages Qα and Vα, that is, the additional signal. Components that fluctuate at the same period are extracted and converted to DC by passing through square circuits 40, 41 and ripple removal filters 42, 43, respectively, and are further added to level discriminators 44, 45. The output of the AND gate 46 and the OR gate 47 is applied to the AND gate 46 and the OR gate 47, and the output of the AND gate 46 or the OR gate 47 is applied to the ignition control circuit 26 as an inverter stop signal.

The operation will be explained in detail below based on FIGS. 5 and 6. Now, assume that the additional signal amplitude α is 0.01 pu and the period Tα is 4/60 seconds. In addition, the leakage reactance X _T of the interconnection transformer 23 is
Assume that the self-capacitance is 0.1pu, and the effective value V _S of the system voltage V〓s is 1.0pu. For further simplicity, it is assumed that the fundamental wave of the inverter output voltage V〓 _I and the system voltage S〓s are in phase.

(a) When connected to the power grid: Reference wave V _SIG
fluctuates as shown in Figure 5A, and this reference wave
Depending on the fluctuation of V _SIG , the inverter output voltage V〓 _I is also 5
It fluctuates as shown in Figure B. Due to this inverter output voltage V _I , a system side current S s as shown in FIG. 5C flows to the system side of the interconnection transformer 23. The amplitude of this system side current I〓 _S is √2α/X _T =(√2×0.01)/0.1=√2×0.1pu.

When such a grid-side current I〓 _S flows, a rectangular waveform voltage Qα with a period Tα as shown in FIG. 5D is obtained by the reactive power detection circuit 34 and the low-pass filter 36. On the other hand, a constant potential voltage Vα as shown in FIG. 5E is obtained from the voltage detection circuit 29 and the low-pass filter 31.

The voltages Qα and Vα are both applied to the reverse pressure determination circuit 37. Signal detection filter 38
passes only the frequency fα component of the voltage Qα,
When the output of this signal detection filter 38 is applied to a squaring circuit 40, a voltage Qβ shown in FIG. . In addition, the signal detection filter 39 has a voltage Vα
When only the component of frequency fα is passed and the output of this signal detection filter 39 is added to the square circuit 41, the square circuit 41 generates the voltage Vβ shown in FIG. 5G.
is obtained. In this case, since the voltage Vα is constant, the voltage Vβ and the average voltage V^β are zero.

Then, the average voltage Q^β is input to the level discriminator 44, but in this case, since the average voltage Q^β is above a certain level, the output Qγ of the level discriminator 44 is as shown in FIG. 5H. This is the "0" level. In addition, the average voltage V^β is determined by the level discriminator 45
However, in this case, since the average V^α is below a certain level, the output of the level discriminator 45 is
Vγ is at the "0" level as shown in FIG. 5I.

Therefore, the outputs of the AND gate 46 and the OR gate 47 are both at the "0" level as shown in FIG. 5J, and the inverter 22 is not stopped.

(b) When the power system 24 is cut off by the switch 48: Reference wave V _SIG and inverter output voltage
As shown in Figure 6A and B, the level of V^ _I changes periodically as in the case of interconnection.
Then, the grid-side current I〓s fluctuates in accordance with the fluctuation of the inverter output voltage V^ _I , but the amount of fluctuation decreases greatly as shown in Figure 6C, and therefore the voltages Qα and Qβ also change as shown in Figure 6C. This results in a decrease as shown in Figures D and F. On the other hand, for voltage Vα, E
As shown in FIG. 6, the fluctuation of the inverter output voltage I– _I appears almost unchanged, so the voltage Vβ increases as shown in FIG. 6G. Therefore, the average voltage
Qβ will decrease and the average voltage V^β will increase.

The average voltage Q^β is input to the level discriminator 44, but since the average voltage Q^β is below a certain level, the output Qγ of the level discriminator 44 becomes "1" as shown in FIG. 6H. level. Further, the average voltage Q〓β is input to the level discriminator 45, but since the average voltage Q〓 is above a certain level, the output Vγ of the level discriminator 45 is at the "1" level as shown in FIG. 6I. becomes.

Therefore, the outputs of the AND gate 46 and the OR gate 47 are both at the "1" level as shown in FIG. 6J, and an inverter stop signal is given to the ignition control circuit 26 to stop the inverter 22.

Note that the threshold levels of the level discriminators 44 and 45 can be set to optimal values if the impedance of the power system 24, the load 25, and the reactance of the interconnection transformer 23 are known.

In this way, this embodiment periodically fluctuates the inverter output voltage V〓 _I , monitors the reactive power fluctuations and grid-side voltage fluctuations based on this fluctuation, and controls the power system 24 to be interrupted or disconnected depending on the magnitude of the fluctuation. is detected, and the operation of the inverter 22 is controlled based on this, so regardless of the state of the load 25, interruptions in the power system 24 are detected reliably and without false detection, and the inverter 2
2 operation control can be performed, and reliability can be improved.

In addition, in the above embodiment, the inverter output voltage
Although the level of the reference wave V _SIG is periodically varied in order to periodically vary the effective value V _I of V〓 _I , the level of the carrier wave V _CAR may also be varied periodically. In addition, in the example, the solar cell 21
Although the present invention is shown using a fuel cell, the present invention can be similarly applied to a case where a fuel cell is used.

Effects of the Invention According to the power supply device of the present invention, it is possible to reliably detect the stoppage (opening) of the power system, stop the operation of the inverter, and prevent malfunctions.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a detailed block diagram of its main parts, Figs. 3 and 4 are waveform diagrams for explaining the operation, and Figs. 5 and 6 are Similarly, FIG. 7 is a waveform diagram for explaining the operation, FIG. 7 is a circuit diagram for explaining the principle, and FIG. 8 is a circuit diagram of a conventional example. 21...Solar cell, 22...Inverter, 23
...Grid connection transformer, 24...Power system, 25...
Load, 26...Ignition control circuit (inverter control section), 27...Comparison circuit (inverter control section), 2
9... Voltage detection circuit (voltage detection section), 34... Reactive power detection circuit (reactive power detection section), 38... Signal detection filter (reactive power fluctuation extraction section), 3
9...Signal detection filter (grid side voltage fluctuation extractor), 44, 45...Level discriminator.

Claims (1)

[Scope of Claims] 1. An inverter using a battery as a power source, an interconnection transformer that connects the inverter to a power system that supplies power to a load and interconnects the inverter and the power system, and an output of the inverter. an inverter control section that controls the inverter so that the voltage periodically fluctuates slightly; a reactive power detection section that detects reactive power on the power system side of the interconnection transformer; a reactive power fluctuation extraction unit that extracts a fluctuation in the same period as the periodic minute fluctuation of the output voltage of the inverter from among the reactive power generated by the inverter; a level discriminator that provides an inverter stop signal to the inverter control unit when the amount is less than a predetermined value. 2. An inverter that uses a battery as a power source, an interconnection transformer that connects the inverter to an electric power system that supplies power to a load and interconnects the inverter and the electric power system, and an interconnection transformer that connects the inverter to the electric power system, and the output voltage of the inverter periodically becomes small. an inverter control unit that controls the inverter to vary; a voltage detection unit that detects the grid-side voltage of the interconnection transformer; and an output voltage of the inverter among the grid-side voltages detected by the power detection unit. A grid-side voltage fluctuation extractor that extracts a fluctuation with the same period as the periodic minute fluctuation of the grid-side voltage fluctuation extractor, and when the amount of fluctuation in the grid-side voltage fluctuation extracted by the grid-side voltage fluctuation extractor is greater than a predetermined value. and a level discriminator that provides an inverter stop signal to the inverter control section.