JP3199339B2 - Control device for grid-connected inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an inverter which converts a DC voltage into an AC voltage by an inverter and supplies the AC voltage to a load, and operates in connection with an AC power system.

[0002]

2. Description of the Related Art One example of a conventional control device for a grid-connected solar inverter will be described with reference to FIG. The DC power supply 1 is converted from DC to AC by the inverter bridge 2, and a high frequency component with PWM is removed by the filter action of the reactor 3 and the capacitor 4, and power with a good waveform ratio is injected into the system. The current detector 5 is for detecting inverter current.
An inductance 6 (of a transmission line) exists between the system power supply 8 and the inverter, and is connected via the circuit breaker 7.

A load 9 is connected to a distribution line and its voltage is detected by a voltage detector 10. The control circuit of the inverter compares the DC voltage reference V ^* with the DC power supply voltage V, amplifies it with the amplifier 11, inputs Vc to the current reference circuit 12, and generates a sine wave generation circuit.
An AC current reference I ^* is made from the product of the sine wave signal of a constant amplitude outputted from 16 and Vc, compared with the output of the current detector 5, amplified by the amplifier 12, and made into a PWM signal by the PWM circuit 14 to form a driving circuit section. 15 controls the power of the inverter bridge 2 by PWM. With this control loop, a current is output from the inverter to the system so that the DC power supply voltage V that changes according to the load current becomes constant. Thus, when the DC power supply is a solar cell, almost the maximum power can be obtained by selecting the DC voltage.

Since the grid-connected inverter always operates at a power factor of 1 by passing a current in phase with the AC voltage, a signal synchronized with the voltage of the AC system is taken out of the output of the voltage detector 10 by the PLL circuit 18 to obtain a phase detection circuit. At 19, a phase signal is used as a phase reference of the phase shift circuit 17.

[0005] The low voltage interconnection requirement guideline was enacted in March 1993, and the following protection functions were required for inverters to be interconnected. That is, in order to prevent the isolated operation, the abnormality detecting circuit 24 is operated by the output of the voltage relay 22 and the frequency relay 23 to drive the drive unit.
Lock 15 and stop the inverter. In addition, anomaly detection protection by a passive method (for example, harmonic detection or phase jump detection) and an independent method must be more reliably protected by an active method (for example, frequency bias or power fluctuation). Active method is frequency bias method and PL
A bias is applied to the oscillator of the L circuit so that the frequency shifts in the direction of decreasing the frequency during the single operation.

When the AC voltage exceeds a certain value, the inverter in the system interconnection detects this by a voltage difference detection circuit 20 and inputs it to a phase shift circuit 17 via an amplifier 21 to advance the current phase. As a result, a delay current increases from the system power supply 8, and a voltage control function of reducing the voltage at the load end due to the inductance 6 is also required for an inverter having a certain capacity or more.

[0007]

However, the above-mentioned voltage control function is closely related to the protection against islanding operation, and the voltage control function often acts in a direction that hinders the shift of the frequency or phase particularly during the islanding operation. Was nearly impossible to satisfy.

[0008] In particular, the conventional protection time for islanding prevention is that the power of the inverter and the load are balanced for both the effective and reactive powers, and when an induction motor is present in the load, it takes 10 seconds to 1 minute to protect the load. If the voltage control function is operated during this time, protection may not be possible in the worst case.

[0009] Recently, constant power loads have been increasing in household loads. For example, many of them have a constant voltage power supply circuit, such as an inverter air conditioner, an inverter fluorescent lamp, an IH electric gama, a TV, and an OA device.

When a load close to the power generation capacity of the system is applied in summer or the like, the voltage is reduced, the current is increased (because of a constant power load), the voltage is reduced, and the current is increased.
For this reason, recently, a method has been adopted in which an SVC (static var compensatin) system is installed and a current is advanced from the system at the time of voltage drop to flow a current to increase the voltage and stabilize the system.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has been made in consideration of the above-described problems. Accordingly, a distributed inverter device capable of stabilizing a system and suppressing harmonics without impairing an islanding prevention function is provided. The aim is to obtain a control device.

[0012]

In order to achieve the above object, the present invention provides an inverter which converts a DC voltage into an AC voltage and operates in connection with an AC system, and wherein the frequency of the AC voltage is close to a rated frequency. In a device provided with phase adjusting means for changing the current phase of the inverter in the leading direction in accordance with the change in the frequency when the frequency changes, the phase adjusting means is controlled by a voltage variation of the AC voltage. Voltage compensating means for controlling the current phase of the inverter in a direction to suppress the voltage fluctuation is provided.

Further, the voltage compensating means is provided with a dead zone so as to perform an operation for suppressing the voltage fluctuation when the AC voltage fluctuates beyond a predetermined range of the set voltage.
Further, an inverter that converts a DC voltage to an AC voltage and operates in connection with an AC system, and when the frequency of the AC voltage changes in the direction of increasing near a rated frequency, the inverter according to the change in the frequency. A phase adjusting means for changing a current phase of the AC power in a leading direction, and an abnormality detecting means for detecting a state of the inverter when the inverter is disconnected from the AC system and stopping the operation of the inverter, wherein the AC voltage Voltage compensating means for controlling the phase adjusting means in accordance with the voltage fluctuation amount to control the current phase of the inverter in a direction for suppressing the voltage fluctuation amount, and providing a control response time for suppressing the voltage fluctuation of the voltage compensating means. Set it later than the detection response time of the abnormality detection means.

An inverter that converts a DC voltage to an AC voltage and operates in connection with an AC system, and an inverter that operates in accordance with a change in the frequency when the frequency of the AC voltage changes in the direction of increasing near a rated frequency. A phase adjusting means for changing a phase of a current reference of the inverter in a leading direction, wherein the phase adjusting means is controlled by a voltage variation of the AC voltage to suppress the phase of the current reference to the voltage variation. Voltage compensating means for controlling the current reference in a direction in which the AC voltage is applied, and harmonic compensating means for compensating the current reference so that the harmonic component of the current flowing to the load to which the AC voltage is applied is supplied from the inverter side. Is made faster than the control response for suppressing the voltage fluctuation.

[0015]

In the above configuration, the inverter usually has a power factor of 1
Is operated so as to supply the electric current to the AC system. When the inverter is disconnected from the AC system and enters an isolated operation state, the frequency of the AC voltage changes, and the frequency changes rapidly due to the operation of the phase adjusting means, and the isolated operation state is detected. On the other hand, when the inverter is operated in connection with the AC system, when the AC voltage fluctuates, the reactive current flowing in the AC system changes due to the change in the current phase of the inverter by the voltage compensating means, and the reactance on the AC system side changes. The fluctuation of the AC voltage is suppressed by the action of the voltage. Further, normal operation is stably performed by not responding to the voltage fluctuation in the dead zone.

Further, when the inverter is disconnected from the AC system, the independent operation state of the inverter is detected by the abnormality detecting means, and the operation of the inverter is stopped. in this case,
By setting the control response of the voltage compensating means later than the detection response of the abnormality detecting means, the isolated operation state of the inverter is reliably detected. In addition, since the harmonic component of the current flowing to the load is supplied from the inverter side by the operation of the harmonic compensation means, the harmonic component of the current flowing to the AC system is suppressed.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention is shown in FIG. The same parts as those in FIG. 5 are denoted by the same reference numerals and will not be described. The AC power supply is detected by the voltage detection circuit 10 and input to the phase detector 18 via the filter 27 having a phase characteristic as shown in FIG.

On the other hand, when the output of the voltage detection circuit 10 is detected by the voltage difference detector 20 and exceeds a set value, the phase of the phase shift circuit 17 is shifted in the advance or delay direction via the amplifier 21 and the delay circuit 28. I do.

The operation of the case where the output of the delay circuit 28 is zero will be briefly described. (For details, refer to Japanese Patent Application No. Hei 5-96199. Method for protecting system interconnection of inverter and its device) When the current phase characteristic of the inverter is the characteristic of inverter (1) in FIG. L,
In the case of C and R loads), when the frequency increases, the load becomes an advanced load, so that the upper right characteristic load is shown.

In this state, when the circuit breaker 7 shown in FIG. 1 is opened to operate independently, the frequency becomes f ₀ + Δf ₁ or f ₀ −Δf ₁
Shifts to either of them and becomes stable. That is, when the frequency slightly rises from f ₀ , the inverter supplies more advanced reactive power than the reactive power required by the load to increase the frequency.
If it is slightly lower than f _{0, the} operation is performed to lower the frequency, and the f ₀ point is an unstable point.

As described above, by suppressing the current phase or the reactive power of the inverter, the frequency in the isolated operation can be rapidly shifted to detect an abnormality by a frequency relay, phase jump detection or the like, and stop the inverter. FIG. 3 shows the measurement results. The load is LCR load and LC
In the state where the active power is balanced (approximately ΔP = 0) with respect to the R + IM (induction motor) load, the frequency abnormality detection time during the independent operation was measured for the unbalance (ΔQ) of the reactive power.

In each case, detection was possible within 0.3 seconds.
Therefore, even if the characteristic of the inverter is shifted in the characteristic direction of the inverter (2) or the inverter (3) in FIG. It is clear that.

For this reason, when the load voltage becomes higher than the set value, this is detected by the voltage difference detector 20 and amplified by the amplifier 21.
When the phase shift circuit 17 shifts the inverter phase characteristic of FIG. 2 in the direction from the inverter (1) to the inverter (2) (in the direction in which the current advances) in a response (or sampling) slower than 0.3 seconds by the delay circuit 28. A function of increasing the delay current from the system and reducing the voltage by the action of the inductance 6 can be provided.

When the voltage falls below the set value, the phase shift circuit causes the inverter current phase to be sent from the inverter (1) to the inverter (3), so that the current flows from the system and the voltage rises, thereby stabilizing the system. The probability of occurrence of a major power outage can be reduced by providing the function of making a power failure.

As described above, according to the present embodiment, the voltage stabilization control is performed in a loop that is slower than the frequency shift operation speed at the time of the isolated operation, so that the protection that satisfies the low-voltage interconnection technical requirement guideline and the function that prevents the voltage rise can be achieved. At the same time,
Furthermore, it is possible to prevent the positive feedback effect of the voltage drop when the power consumption increases, thereby reducing the probability of a power failure.

FIG. 4 shows another embodiment of the present invention. Load current is detected by current transformer 30 and its harmonic component is detected by harmonic detection circuit.
An adder 33 adds an active filter function to the sine wave (fundamental wave) in the direction of detecting the harmonic component and canceling the harmonic component, thereby canceling the harmonic component.

When there is also a purpose of controlling the power factor of the fundamental wave, it is detected by the invalid component detection circuit 32, and the phase shift circuit 17 changes the fundamental wave current phase via the amplifier 21 and the delay circuit 28 to improve the power factor. Operate in the following direction.

Also in this case, the delay circuit 28 is effectively operated so as not to interfere with the islanding detection function as described with reference to FIG. In FIG. 1, the inverter is described as a current control type. However, when a voltage control type inverter is connected to a system, P (active power) is generally controlled and Q (reactive power) is controlled to zero, so that Q It can be seen that the same operation is obtained by controlling about Isin θ = Iθ as shown in FIG.

It is needless to say that the seed pattern of the characteristics of the synthesis filter 27 shown in FIG. 1 can be changed by a microcomputer or the like. In FIG. 1, the frequency change rate (df / dt)
A circuit is provided, and if there is a frequency change, the possibility of islanding is high. Therefore, the present invention can be modified and implemented by holding the control of the reactive power or the voltage control circuit.

[0030]

As described above, according to the present invention, the inverter has the characteristic that the current phase advances when the frequency rises near the rated frequency and the reactive power increases, and the voltage stability control and the reactive power control are performed. By performing the control gently and performing the harmonic component control at a high speed, it is possible to provide a control device for an interconnected inverter having an improved voltage stability and an active filter function without impairing the islanding detection function.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a characteristic diagram for explaining the operation of the present invention.

FIG. 3 is a detection characteristic diagram of abnormality detection used in the present invention.

FIG. 4 is a configuration diagram of another embodiment of the present invention.

FIG. 5 is a configuration diagram of a conventional device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... DC power supply, 2 ... Inverter bridge, 3 ... Reactor, 4 ... Capacitor, 5 ... Current detector, 6 ... Inductance, 7 ... Circuit breaker, 8 ... AC system, 9 ... Load, 10 ... Voltage detector, 11 , 13 ... amplifier, 14 ... PWM circuit, 15 ... drive circuit, 16 ... sine wave circuit, 17 ... phase shift circuit, 18 ... PL
L circuit, 19: phase detection circuit, 20: voltage difference detection circuit, 21 ...
Amplifier, 22… Voltage relay, 23… Frequency relay, 24… Abnormality detection circuit, 25… Passive method, 26… Active method, 27… Synthesis filter, 28… Delay circuit, 30… Current transformer, 31… Harmonic Detection, 32: Invalid part detection circuit, 33: Adder

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-311653 (JP, A) JP-A-7-7857 (JP, A) JP-A-3-256534 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H02M 7/48 H02J 3/12 H02J 3/38

Claims (4)

(57) [Claims] 1. An inverter that converts a DC voltage into an AC voltage and operates in connection with an AC system, and an inverter that operates in accordance with a change in the frequency when the frequency of the AC voltage changes in the direction of increasing near a rated frequency. A device having phase adjusting means for changing the current phase of the inverter in the leading direction,
A control device for a grid-connected inverter, comprising: voltage compensating means for controlling the phase adjusting means based on a voltage variation of the AC voltage to control a current phase of the inverter in a direction for suppressing the voltage variation. . 2. The control device for a grid-connected inverter according to claim 1, wherein the voltage compensating means suppresses the voltage fluctuation when the AC voltage fluctuates beyond a predetermined range of a set voltage. A control device for a grid-connected inverter having a dead zone so as to perform an operation. 3. An inverter which converts a DC voltage into an AC voltage and operates in connection with an AC system, and an inverter which operates in response to a change in the frequency of the AC voltage when the frequency changes in the direction of increasing near a rated frequency. A phase adjusting means for changing the current phase of the inverter in the leading direction, and an abnormality detecting means for detecting the state of the inverter and stopping the operation of the inverter when the inverter is disconnected from the AC system, Voltage compensating means for controlling the phase adjusting means in accordance with the voltage fluctuation of the AC voltage to control the current phase of the inverter in a direction for suppressing the voltage fluctuation; and a control response for suppressing the voltage fluctuation of the voltage compensating means. A system interconnection inverter control device, wherein a time is set later than a detection response time of the abnormality detection means. 4. An inverter which converts a DC voltage into an AC voltage and operates in connection with an AC system, and an inverter which operates in accordance with a change in the frequency when the frequency of the AC voltage changes in the direction of increasing near a rated frequency. A phase adjusting means for changing a phase of a current reference of the inverter in a leading direction, wherein the phase adjusting means is controlled by a voltage variation of the AC voltage to suppress the phase of the current reference to the voltage variation. Voltage compensating means for controlling the current reference in a direction in which the AC voltage is applied, and harmonic compensating means for compensating the current reference so that the harmonic component of the current flowing to the load to which the AC voltage is applied is supplied from the inverter side. A control device for a grid-connected inverter, wherein the control response of the system interconnection is made faster than the control response of suppressing the voltage fluctuation.