JP3333415B2 - Power outage detection method in grid-connected inverter system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a power failure in an inverter system for converting electric power generated by photovoltaic power generation or the like into AC power of a commercial frequency and performing an interconnection operation with a commercial power supply.

[0002]

2. Description of the Related Art The power generated by photovoltaic power generation is DC, and the power generation possible time and the generated power are extremely unstable power determined by the amount of sunlight irradiation during daytime. It is desirable that the inverter be converted to AC power by an inverter and further operated in connection with a commercial power supply.

FIG. 3 shows a conventional system interconnection inverter.
It is a block diagram showing an example of a system. In FIG. 3, a DC power supply 104 by photovoltaic power generation or the like is connected to an inverter 1.
At 01, the power is converted to AC power, and the power is supplied to a load 112 together with a commercial AC power supply 113 via an AC filter including a reactor 106 and a capacitor 107 and a circuit breaker 109 provided at a system interconnection point.

[0004] A detection signal from a current detector 108 provided in an output circuit of the inverter 101 and a signal processing circuit 111 are inputted to a signal processing circuit 111 via a voltage detector 110 provided on the system side of the circuit breaker 109 to be processed. The detected signal is input to the current control circuit 103 and calculated, and the PWM control circuit 10
2 to generate a PWM signal for controlling the inverter 101. The disturbance signal from the disturbance signal source 105 is input to the inverter 101 via the PWM control circuit 102, and the fundamental wave output signal and the disturbance signal are transmitted from the inverter 101 in a superimposed manner.

[0005]

When the commercial AC power supply 113 suddenly loses power, the inverter system alone supplies power to the load. However, the power generated by photovoltaic power generation or the like depends on the load capacity and load fluctuation. It is difficult to perform control in a corresponding manner, and if the circuit breaker 109 is left closed, the output voltage of the inverter 101 is applied to the system side, and there is a risk of occurrence of an electric shock accident or the like. Therefore, when the commercial AC power supply 113 fails, a disturbance is detected via the voltage detector 110 and the signal processing circuit 111, and the signal processing circuit 111
The circuit breaker 109 is turned off based on the detection signal from the inverter 101, the inverter 101 is disconnected from the system, and the inverter 1 is connected via the current control circuit 103 and the PWM control circuit 102.
01 had been stopped.

Although the above-described signal processing circuit 111 is constituted by an analog band-pass filter, it is difficult to constitute an ideal filter due to large variations in filter constants, it is difficult to adjust, and noise is reduced. It was weak and a false difference occurred.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks of the prior art, and is directed to a fundamental wave output voltage signal Vcos .theta. Output from an inverter and an inverter through a PWM control circuit. a disturbance signal V _c cos n.theta inputting detected in a signal processing circuit provided in the system side, the two sets of the calculated value of the signal V _d cos n.theta were respectively multiplied by the detection signal by one cycle integration, resulting obtains the DC component πV _c V _d in the calculation values may be stored in the memory as a reference value the DC component at the time of normal operation, larger than the reference value level, and, on condition that the predetermined time or longer, mains failure Is detected.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration of an inverter system that performs an interconnection operation with a commercial AC power supply 13. Power generated from solar power generation or the like is supplied to the inverter 1 as a DC power supply 4. The DC power input to the inverter 1 is converted into AC power, and the reactor 6 and the capacitor 7
The AC power supply is connected to a commercial AC power supply 13 via a circuit breaker 9 provided at an interconnection point of the AC filter and a system interconnection point, and supplies AC power to a load 12.

[0009] disturbance signal V _c cos n.theta output from the disturbance signal generating source 5, since the input to the inverter 1 through the PWM control circuit 2, the fundamental wave output voltage of the inverter from the inverter 1 signal Vcosθ and the disturbance signal V _c cos nθ is superimposed and output. The signal detected by the voltage detector 10 provided on the system side of the circuit breaker 9 is transmitted to a signal processing circuit 11.
And the signal is processed.

Next, a signal processing method in the signal processing circuit 11 will be described. Output voltage V ₀ from inverter 1 is represented by equation (1). _{V 0 = Vcosθ + V c cos} nθ ··· (1) (1) formula V _d cos a calculation value obtained by multiplying the n.theta V _a
When _{V a = VV d cosθ · cos} nθ + V c V d cos 2 nθ = VV d cosθ · cos nθ + 1/2 · V c V d (1 + cos2nθ) = VV d cosθ · cos nθ + 1/2 · V c V d cos2nθ +1 _{/ 2 · V c V d ···} (2) (2) When V _ai calculated value obtained by one cycle integrates the V _a in formula, the DC component shown in the third term in (2) of the right side You only need to calculate

[0011]

(Equation 1)

That is, by processing the signal input to the signal processing circuit 11 as described above, it is possible to detect the presence or absence of a disturbance.

The DC component shown in equation (3) during normal operation is stored in a memory as a reference value, and a power failure of the system power supply is monitored based on the reference value. As shown in FIG. 2, the inverter 1 is connected to a commercial power supply 13 via an AC filter.
If the inverter power supply voltage is V ₁ , the commercial power supply voltage is V ₂ , the impedance of the inverter including the AC filter is Z ₁ , and the impedance of the commercial power supply is Z ₂ , The voltage at the interconnection point can be expressed by equation (4). V = (Z ₂ V ₁ + Z ₁ V ₂ ) / (Z ₁ + Z ₂ ) (4) Generally, | Z ₁ | ≫ | Z ₂ | In this case, V ≒ V ₂ .
Further, when the commercial power supply is interrupted, it is assumed that V ₂ = 0 and Z ₂ = ∞, so that V ≒ V ₁ . As described above, when the inverter 1 is connected to the commercial power supply 13 from the relationship between the impedance on the commercial power supply side and the impedance on the inverter side, the disturbance component superimposed on the output voltage of the inverter 1 is connected. Although the signal is hardly detected at this point, when the inverter 1 is operated independently, the DC component of the disturbance signal sent from the inverter side is detected in the signal processing circuit 11.

In the above description, the disturbance signal is V _c cos
Although nθ is used, n may be any positive integer, and a plurality of disturbance signals may be added. Since the signal processing in this case can be similarly described, the description thereof is omitted.

[0015]

As described above, in the method for detecting a power failure in the system operation inverter system according to the present invention, the disturbance signal input to the inverter via the PWM control circuit is provided on the system side of the system interconnection point. detecting the signal processing circuit, V _d cos this signal processing circuit inverter output voltage signal inputted to Vcosθ disturbance signal V _c cos n.theta
After multiplying nθ, the signal is processed and its DC component πV _c
Find Vd. Since the DC component during normal operation is stored in the memory as a reference value, and the system operation state can be monitored based on the reference value, the power failure detection sensitivity is increased, and no malfunction error occurs. In addition, by storing the detected amount of disturbance during normal operation in the memory, it is possible to eliminate the need for adjustment.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration of a system interconnection inverter system according to the present invention.

FIG. 2 is an impedance map of a commercial power supply and an inverter-side power supply.

FIG. 3 is a block diagram of a conventional grid-connected inverter system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inverter 2 PWM control circuit 3 Current control circuit 4 DC power supply 5 Disturbance signal generation source 6 Reactor 7 Capacitor 8 Current detector 9 Circuit breaker 10 Voltage detector 11 Signal processing circuit 12 Load 13 Commercial power supply

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H02J 3/00-5/00 H02H 3/24 H02M 7/48

Claims (1)

(57) [Claims] 1. An inverter for converting input DC power into AC, and a grid-connected inverter that is connected to a commercial power supply via an AC filter provided at an output terminal of the inverter and a circuit breaker provided at a grid connection point. In the system, a disturbance signal source that supplies a disturbance signal to the inverter via a PWM control circuit, and an inverter output voltage signal and a disturbance signal superimposed on the inverter output voltage signal via a voltage detector provided on the system side of the system interconnection point Is provided, and a fundamental wave output voltage signal Vcosθ output from the inverter is provided.
And a disturbance signal V _c cos nθ superimposed on the inverter output voltage signal via the PWM control circuit in the signal processing circuit, and two sets of detection signals are converted into a signal V _d cos nθ.
Respectively multiplying by one cycle integral calculation value was obtains the DC component πV _c V _d in the obtained calculated value may be stored in the memory as a reference value the DC component in the normal operation, the signal processing circuit The system detects a power failure on condition that the DC component detected by the DC component is larger than the reference value level and continues for a predetermined time or more, and disconnects the inverter system from the system by a circuit breaker provided at a system interconnection point. A method of detecting a power failure in a system interconnection inverter system, wherein the control method of the inverter is changed or the inverter is stopped.