JP4172633B2 - AC load power system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention converts an AC power of a DC power source such as a fuel cell, a secondary battery (storage battery), a solar cell, or a wind power generator into an AC power by an inverter, and supplies the AC power to a power load such as an electric motor. The present invention relates to a load power system.
[0002]
[Prior art]
In the power supply system, if a ground fault occurs on the DC power supply side, power loss may occur. As a result, the DC power supply may be damaged, and it is necessary to detect the ground fault and stop the DC power supply. Also, if a ground fault occurs on the AC load side due to a person touching the load, the person may be electrocuted and dangerous, and there is a need to protect the circuit. Need to be stopped. It is also necessary to inform the manager that there is a ground fault and repair it quickly.
[0003]
Here, the DC ground fault means that a ground fault current flows between the DC power source and the ground due to a trouble of the DC power source. The causes include, for example, insulation deterioration of the DC power supply and insulation failure of the DC power cable.
The AC ground fault means that a ground fault current flows between the load and the ground due to a power load trouble. The causes include, for example, contact with a living body, insulation deterioration of a load, and insulation failure of a cable that supplies AC power to the load.
[0004]
FIG. 5 shows a schematic block diagram of a conventional AC load power supply system having a ground fault detection function. This AC load power supply system includes a DC power supply E, an orthogonal transformation device 11, a power load 12, a circuit breaker 15, a zero-phase current transformer 20, a DC ground fault relay 13, and an AC ground fault relay 14.
The output of the DC power source E is supplied to the orthogonal transformation device 11 through the input terminals P and N. In the orthogonal transform device 11, the output of the DC power source E is boosted to a necessary voltage by the booster circuit 16 and supplied to the inverter circuit 17, where three-phase PWM control is performed to convert it to an output AC voltage. The output AC voltage is output from the orthogonal transformation device 11 through the output terminals U, V, and R. This output AC voltage is supplied to the power load 12 via the circuit breaker 15.
[0005]
In the AC load power supply system, the voltage, ground voltage, and ground current of the DC power supply E supplied through the input terminals P and N are monitored by the ground fault detector 19. When a ground fault is detected by the ground fault detector 19, a ground fault current signal is input to the DC ground fault relay 13.
On the other hand, the zero-phase current component of the three-phase output AC voltage supplied to the power load 12 is detected by the zero-phase current transformer 20 and input to the AC ground fault relay 14.
[0006]
When a ground fault occurs on the power supply side, a DC ground fault current signal is input from the ground fault detection unit 19 to the DC current detection circuit 13 a of the DC ground fault relay 13. The comparison circuit 13c of the DC ground fault relay 13 compares the magnitude of the ground fault current with the DC reference current set by the DC reference current setting circuit 13b in the DC ground fault relay 13 to determine the ground fault current. If it is larger, a ground fault generation signal indicating that a DC ground fault has occurred is output to the control circuit 18. Based on this ground fault generation signal, the control circuit 18 opens the circuit breaker 15 or controls the inverter circuit 17 to stop the power supply to the power load 12.
[0007]
When a ground fault occurs on the load side, an AC ground fault current signal is input to the AC ground fault relay 14 from the zero-phase current transformer 20. The magnitude of the ground fault current is compared with the AC reference current set by the AC reference current setting circuit 14b. If the ground fault current is larger, it indicates that the control circuit 18 has an AC ground fault. Outputs a ground fault signal. Based on this ground fault generation signal, the control circuit 18 opens the circuit breaker 15 or controls the inverter circuit 17 to stop the power supply to the power load 12.
[0008]
[Patent Document 1]
JP-A-6-117678 [Patent Document 2]
Japanese Patent Laid-Open No. 2002-233045 [0009]
[Problems to be solved by the invention]
However, in the AC load power supply system of FIG. 5, it is necessary to install a circuit for detecting a ground fault at two places on the power supply side and the load side. In particular, the zero-phase current transformer 20 that detects a ground fault on the load side is large and heavy, which is an obstacle to downsizing the entire system. In addition, the zero-phase current transformer is disadvantageous from the viewpoint of workability because it takes time to assemble and install.
[0010]
Accordingly, an object of the present invention is to provide an AC load power supply system that can simplify a circuit for detecting a ground fault as much as possible, and is light and compact as a whole.
[0011]
[Means for Solving the Problems]
An AC load power supply system according to the present invention includes a DC power supply, and an AC load power supply system including an orthogonal transform device that converts direct current to AC and supplies the same to the load side. A ground fault detection impedance element is connected to the DC power supply side, and the DC fault of the ground fault current flowing from the ground fault point on the DC power supply side to the ground through the DC power supply and impedance element is detected. A detection unit, a load-side ground fault detection unit that detects an AC component of a ground fault current flowing from the load-side ground fault point to the ground through an orthogonal transformation device and an impedance element, and a power-side ground fault detection unit or a load-side ground. And a control circuit that stops the function of supplying power to the AC load when a ground fault is detected by the fault detection unit (claim 1).
[0012]
According to the above configuration, when a ground fault occurs on the load side, the ground fault current is detected for a ground fault that is connected to the DC power source side through the orthogonal transformation device in which the input and output are not insulated. Flows through the impedance element. By detecting this ground fault current with the load side ground fault detector, it is possible to detect a ground fault on the DC power source side without installing a large-scale electric facility such as a zero-phase current transformer on the load side. In addition, when a ground fault occurs on the DC power source side, the ground fault current flowing through the impedance element can be detected by the power source side ground fault detection unit.
[0013]
The impedance element may be a coil or the like, but simply a resistor may be used (Claim 2).
The load-side ground fault detection unit stores a reference current value, compares the reference current value with a ground fault current, and detects a ground fault on the load side when the ground fault current exceeds the reference current value. (Claim 3).
The load-side ground fault detection unit stores the value of the reference resistance value R0, measures the DC power supply voltage V, and compares the load-side zero-phase voltage V0 corresponding to the DC power supply voltage V with the reference resistance value R0. V0 / R0 may be compared with a ground fault current, and when the ground fault current exceeds the ratio V0 / R0, an AC ground fault on the load side may be detected (claim 4). Since the DC power supply voltage V of the DC power supply is unstable and may fluctuate with time, if the reference current is set in the load side ground fault detector, the ground fault will occur on the load side when the DC power supply voltage V is low. Even if this occurs, the ground fault current may be small and cannot be detected. Therefore, assuming that the ground fault resistance to be detected is R0, when a ground fault occurs in the ground fault resistance R0, a ground fault current having a value obtained by dividing the load side ground fault voltage V0 by the ground fault resistance R0 flows. When this value V0 / R0 is calculated by the load-side ground fault detection unit, and a signal informing the AC ground fault is output when the actual ground fault current exceeds this value V0 / R0, the fluctuation of the DC power supply voltage V is output. Regardless of this, it is possible to reliably detect a ground fault of the ground fault resistance R0 or less.
[0014]
The power supply side ground fault detector stores a reference current value, compares the reference current value with a ground fault current, and detects a DC ground fault when the ground fault current exceeds the reference current value. (Claim 5). However, if the DC reference resistance R is set in order to cope with the time fluctuation of the DC power supply voltage V, a ground fault generated by a ground fault resistance below the DC reference resistance R regardless of the fluctuation of the power supply voltage V. A fault can be detected. That is, the power-supply-side ground fault detection unit stores the value of the reference resistance value R, measures the DC power supply voltage V, and determines the ratio V / R between the DC power supply voltage V and the reference resistance value R as the ground fault current. When the ground fault current exceeds the ratio V / R, a DC ground fault may be detected (Claim 6).
[0015]
If a ground fault is detected, a means for distinguishing and displaying whether the ground fault is on the DC power supply side or the load side is provided (Claim 7).
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic block diagram of an AC load power supply system according to an embodiment of the present invention. This system includes a DC power source E, an orthogonal transformation device 2, and an electric motor 3 as a power load. The orthogonal transformation device 2 includes a power supply side ground fault detection unit 4, a load side ground fault detection unit 5, and a control circuit 6.
[0017]
As the DC power source E, a solar cell, a fuel cell, a secondary battery (storage battery), a wind power generator, or the like can be used. In particular, when a solar cell is used, the solar cell is configured by connecting a plurality of solar cell strings formed by connecting a plurality of solar cell modules in series. For the photoelectric conversion part of the solar cell module, an element such as crystalline silicon or amorphous silicon is appropriately employed depending on the application and installation location.
The output of the DC power supply E is supplied to the orthogonal transformation device 2 through the input terminals P and N. The supplied voltage is boosted by the booster circuit 7 to a voltage that allows for the peak value of the three-phase output AC voltage. The booster circuit 7 is constituted by, for example, a booster chopper circuit, but a high-frequency transformer is not interposed between the input and output of the booster circuit 7. In the case of a system that does not require voltage regulation of the input voltage, the booster circuit 7 is not necessary.
[0018]
The boosted voltage is supplied to the inverter circuit 8, where it is converted into, for example, a three-phase three-wire AC voltage having a waveform that keeps the voltage / current operating point of the motor 3 at the maximum power, and is output from the orthogonal transformation device 2. It is output through terminals U, V, and R. The inverter circuit 8 uses an IGBT (Insulated Gate Bipolar Transistor) as a switching element and has an operating frequency higher than an audible frequency. The inverter circuit 8 is composed of six IGBTs, and performs sinusoidal modulation PWM control by repeatedly turning on and off the IGBTs. In addition to the IGBT, an FET (Field Effect Transistor), an IPM (Intelligent Power Module), or the like may be used.
[0019]
The output AC voltage of the inverter circuit 8 is supplied to the electric motor 3 that is a power load.
In this AC load power supply system, the orthogonal transformation device 2 does not have an insulation transformer or the like for insulating between the input and output including the booster circuit 7, and the input terminals P and N and the output terminals U, V, and R Are directly connected.
In the present invention, a ground fault detection circuit 9 is provided between the input terminals P and N of the orthogonal transformation device 2 and the booster circuit 7. In the ground fault detection circuit 9, four series resistors R 1, R 2, R 3, and R 4 that divide the DC voltage V between the input terminals P and N are connected in parallel to the input terminals P and N. For example, when the value of the DC voltage V is 300 V, the series resistances R1 = 60 kΩ, R2 = 300Ω, R3 = 300Ω, and R4 = 60 kΩ.
[0020]
The role of these series resistors R1, R2, R3, and R4 is to detect the ground fault state of the present AC load power supply system by detecting the current flowing between any connection point of the resistors and the ground. . The ground fault state is detected by the power supply side ground fault detection unit 4 and the load side ground fault detection unit 5.
The power-supply side ground fault detection unit 4 detects a DC current flowing between the connection point b of the resistors R2 and R3 of the ground fault detection circuit 9 and the ground, and compares it with the DC reference current value to determine the DC reference current value. When it exceeds, it is a circuit that outputs a signal for notifying the occurrence of a power supply side ground fault.
[0021]
As shown in FIG. 1, the power supply side ground fault detection unit 4 includes a DC current detection circuit 41, a DC reference current setting circuit 42, and a comparison circuit 43. The DC current detection circuit 41 is a circuit that detects and amplifies the current flowing between the connection point b of the resistors R2 and R3 and the ground through a low-pass filter that removes AC components other than DC components. This low-pass filter needs to have a characteristic of removing main AC components other than the DC component, which are included in the frequency spectrum of the output AC voltage signal of the inverter circuit 8. For example, it can be realized by a resistor or a smoothing circuit of a coil and a capacitor.
[0022]
The DC reference current setting circuit 42 is a circuit that stores a preset DC reference current value. The comparison circuit 43 is a circuit that compares the output value of the DC current detection circuit 41 with the DC reference current value. When (output value of the DC current detection circuit 41)> (DC reference current value), the power source side The signal which alert | reports generation | occurrence | production of the ground fault in is output.
The load-side ground fault detection unit 5 detects, for example, an effective value of the alternating current flowing between the connection point b of the resistors R2 and R3 and the ground, and when the value exceeds the set value, It is a circuit that outputs a signal notifying the occurrence of an AC ground fault.
[0023]
The load-side ground fault detection unit 5 includes an AC current detection circuit 51, an AC reference resistance setting circuit 52, and a comparison circuit 53. The AC current detection circuit 51 is a circuit that detects an AC component of the current flowing between the connection point b of the resistors R2 and R3 and the ground through a high-pass filter, a band-pass filter, and the like, and outputs an effective value of the detected AC signal. is there. The high-pass filter or the band-pass filter needs to have a characteristic that allows main AC components other than the DC component to pass through in the frequency spectrum of the output AC voltage signal of the inverter circuit 8.
[0024]
The AC reference resistance setting circuit 52 is a circuit for creating a set value. The reference resistance value R0 is stored in a nonvolatile memory, and the connection point a between the resistors R1 and R2 and the connection point between the resistors R3 and R4. The DC component of the voltage difference from c is input. A DC power supply voltage V is obtained based on the difference voltage, a ground fault voltage V0 is estimated based on the DC power supply voltage V, and a ratio V0 / R0 between V0 and the reference resistance value R0 is calculated and output. . The direct-current power supply voltage V is expressed by the equation V = Vdiff (R1 + R2 + R3 + R4) / (R2 + R3)
Is required.
[0025]
The relationship between the DC power supply voltage V and the ground fault voltage V0 will be described later.
The comparison circuit 53 compares the output value of the AC current detection circuit 51 with the ratio V0 / R0 output from the AC reference resistance setting circuit 52, and the output value of the AC current detection circuit 51 determines the ratio V0 / R0. When it exceeds, the signal which alert | reports generation | occurrence | production of the ground fault on the load side is output.
Here, the meaning of the reference resistance value R0 will be described. If the AC load power supply system is turned off every time a fine ground fault without electric shock damage is detected, the system operation efficiency will decrease, so there is a demand to detect only ground faults that are potentially harmful. . On the other hand, in the case of a DC power supply, the DC power supply voltage V is unstable and may fluctuate with time. Therefore, when the reference current is set, a ground fault occurs on the load side when the DC power supply voltage V is low. However, there are cases where the ground fault current is small and cannot be detected.
[0026]
Therefore, the ground fault resistance to be detected is R0. This indicates that only a ground fault of the ground fault resistance R0 or less is detected, and a ground fault exceeding the ground fault resistance R0, for example, a light ground fault due to a ground capacitance or the like is not detected. When a ground fault occurs at the ground fault resistance R0, a ground fault current corresponding to a value V0 / R0 obtained by dividing the voltage V0 at the ground fault by the ground fault resistance R0 flows. Therefore, when the DC power supply voltage V is a predetermined value, for example, a ground fault is actually generated on the load side by the resistor R0, and the voltage V0 at the ground fault point at that time is measured and stored. If the voltage V is changed and the voltage V0 is measured and stored in the same manner, the relationship between the DC power supply voltage V and the ground fault voltage V0 can be known. The AC reference resistance setting circuit 52 generates and outputs this value V0 / R0 according to the DC power supply voltage V at that time. The ground fault resistance value R0 to be detected is a value selected from 500Ω to 2 kΩ, for example.
[0027]
The comparison circuit 53 outputs a signal for informing a ground fault on the load side when the AC current value actually output from the AC current detection circuit 51 exceeds this value V0 / R0. Thereby, regardless of the fluctuation of the DC power supply voltage V, it is possible to reliably detect the ground fault below the ground fault resistance R0.
When the ground fault occurrence notification signal is output from the comparison circuit 43 or the comparison circuit 53 and the control circuit 6 detects that a ground fault has occurred on the power supply side or the load side, the control circuit 6 uses a gate block signal to prevent electric shock and protect the electric circuit. And the inverter circuit 8 is stopped. Further, an alarm sound is output from the speaker 61 or a ground fault occurrence display is performed on the display device 62 to notify the administrator of the occurrence of the ground fault. In this case, in order to distinguish and transmit the ground fault on the power source side or the ground fault on the load side, it is preferable to change the alarm sound or put ground fault location information in the ground fault occurrence display.
[0028]
In the above AC load power supply system, the current flow when a ground fault occurs and the operation of each part will be described together.
FIG. 2 is a diagram illustrating a route of a ground fault current that flows during a ground fault on the power supply side. It is assumed that a ground fault has occurred on the negative (N) side of the DC power supply E. Let the ground fault resistance be Rf.
The ground fault current If flows through the DC power source E, the resistors R1 and R2, the DC current detection circuit 41 to the ground terminal FG, and forms a loop that returns to the original state through the ground fault resistor Rf.
[0029]
The power-supply side ground fault detection unit 4 detects this ground fault current If and compares it with the set current value stored in the DC reference current setting circuit 42. Transmit to the control circuit 6. The control circuit 6 puts a gate block on the inverter circuit 8 to stop the PWM control. At the same time, the display device 62 displays a warning notifying that a ground fault has occurred on the power supply side, or reproduces an alarm sound with the speaker 61.
[0030]
In FIG. 2, it is assumed that a ground fault occurs on the negative (N) side of the DC power supply E. However, when a ground fault occurs on the positive (P) side of the DC power supply E, a ground fault current is similarly generated. Can be detected, so the ground fault can be detected. In this case, unlike in FIG. 2, the ground fault current flows through a loop from the DC power source E through the resistors R3 and R4.
FIG. 3 is a diagram illustrating a route of a ground fault current that flows during a ground fault on the load side. It is assumed that a ground fault has occurred in one of the cables supplied to the electric motor 3. Let the ground fault resistance be Rf.
[0031]
The ground fault current If flows through the inverter circuit 8, the booster circuit 7, the resistors R1 and R2 or the resistors R4 and R3, the alternating current detection circuit 51 to the ground terminal FG, and returns to the original state through the ground fault resistor Rf. Form.
The load-side ground fault detection unit 5 detects the current flowing through this loop, and exceeds the value V0 / R0 calculated based on the reference resistance R0 stored in the AC reference resistance setting circuit 52. In this case, a signal notifying the ground fault is sent to the control circuit 6. The control circuit 6 puts a gate block on the inverter circuit 8 to stop the electric motor 3. At the same time, a warning notifying that a ground fault has occurred on the load side is displayed on the display device 62, or an alarm sound is reproduced by the speaker 61.
[0032]
FIG. 4 is a schematic block diagram of an AC load power supply system according to another embodiment of the present invention. The difference from the system of FIG. 1 is that the DC reference current setting circuit 42 of the power supply side ground fault detection unit 4 is replaced with a DC reference resistance setting circuit 42a. The DC reference resistance setting circuit 42a stores the value of the reference resistance value R in a nonvolatile memory and inputs a voltage difference between a connection point a between the resistors R1 and R2 and a connection point c between the resistors R3 and R4. . A DC power supply voltage V is estimated based on the difference voltage, a ratio V / R between the DC power supply voltage V and the reference resistance value R is calculated and output as a reference current.
[0033]
Therefore, the comparison circuit 43 of the power supply side ground fault detection unit 4 does not compare the detected ground fault current with the set DC reference current, but stores the DC power supply voltage V in the DC reference resistance setting circuit 42a. Compared with the value V / R divided by the reference resistance R, if this value is exceeded, a signal indicating a ground fault is output.
Thus, the reference current is not set in the case of a DC power supply, the DC power supply voltage V may fluctuate depending on the time. When the reference current is set, the power supply side This is because even if a ground fault occurs, the ground fault current is small and cannot be detected. If the DC reference resistance R is set, the ground fault generated by the ground fault resistance below the DC reference resistance R can be detected regardless of the fluctuation of the power supply voltage V. The DC reference resistance R is 1 kΩ, for example, when the input voltage is 300V.
[0034]
In FIG. 4, if the wiring is rewired as an AC reference current setting circuit instead of the AC reference resistance setting circuit 52, the ground fault current on the load side can be accurately detected at the set current value when the DC power supply side has a stable voltage. It can be detected.
Although the embodiments of the present invention have been described above, the embodiments of the present invention are not limited to the above-described embodiments. For example, it is possible to adopt a configuration in which a circuit breaker is inserted into the power cable of the electric motor 3 and a trip signal is output from the control circuit 6 to the circuit breaker in the event of a ground fault. Further, it is preferable to add a function of stopping or disconnecting the DC power supply in the case of a DC power supply side ground fault, and it is preferable to add a function of stopping the orthogonal transformation device in the case of a load side ground fault. Moreover, it is preferable to provide a return function after removing the cause of the ground fault. Further, it is preferable that various set values such as the reference current described in this embodiment are stored in a nonvolatile memory so that the values can be variably set easily. In addition, various modifications can be made within the scope of the present invention.
[0035]
【The invention's effect】
As described above, according to the present invention, it is possible to detect a ground fault on the power supply side and the load side with a detection unit having a simple configuration installed on the power supply side, and as a whole is inexpensive, lightweight and compact AC load power supply. A system can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic block diagram of an AC load power supply system according to an embodiment of the present invention.
FIG. 2 is a diagram showing a route of a ground fault current that flows during a ground fault on the power supply side;
FIG. 3 is a diagram showing a route of a ground fault current that flows during a ground fault on the load side;
FIG. 4 is a schematic block diagram of an AC load power supply system according to another embodiment of the present invention.
FIG. 5 is a schematic block diagram of a conventional AC load power supply system having a ground fault detection function.
[Explanation of symbols]
2 orthogonal transformation device 3 electric motor 4 power supply side ground fault detection unit 5 load side ground fault detection unit 6 control circuit 7 boost circuit 8 inverter circuit 9 ground fault detection circuit 41 DC current detection circuit 42 DC reference current setting circuit 43 comparison circuit 51 AC Current detection circuit 52 AC reference resistance setting circuit 53 Comparison circuit 61 Speaker 62 Display device E DC power supply P, N Input terminals U, V, W Output terminals

Claims (7)

In an AC load power supply system including a DC power supply and an orthogonal conversion device that converts DC to AC and supplies the load to the load side,
Between the input and output of the orthogonal transformation device is in a non-insulated state,
An impedance element for ground fault detection is connected to the DC power supply side,
A power-supply-side ground fault detection unit that detects a DC component of a ground-fault current that flows from the ground fault point on the DC power source side to the ground through the DC power source and impedance element;
A load-side ground fault detection unit that detects an alternating current component of a ground fault current flowing from the ground fault point on the load side to the ground through the orthogonal transformation device and the impedance element;
An AC load power supply system comprising: a control circuit that stops a power supply function to an AC load when a ground fault is detected by a power supply side ground fault detection unit or a load side ground fault detection unit. The AC load power supply system according to claim 1, wherein the impedance element is a resistor. The load-side ground fault detection unit stores a reference current value, compares the reference current value with a ground fault current, and detects a ground fault on the load side when the ground fault current exceeds the reference current value. The AC load power supply system according to claim 1, wherein the AC load power supply system is one. The load-side ground fault detection unit stores the value of the reference resistance value R0, measures the DC power supply voltage V, and compares the load-side zero-phase voltage V0 corresponding to the DC power supply voltage V with the reference resistance value R0. 3. The AC load according to claim 1 or 2, wherein V0 / R0 is compared with a ground fault current, and a ground fault is detected when the ground fault current exceeds a ratio V0 / R0. Power system. The power supply side ground fault detection unit stores a reference current value, compares the reference current value with a ground fault current, and detects a ground fault on the DC power source side when the ground fault current exceeds the reference current value. The AC load power supply system according to any one of claims 1 to 4, wherein: The power supply side ground fault detection unit memorizes the value of the reference resistance value R, measures the DC power supply voltage V, and compares the ratio V / R of the DC power supply voltage V and the reference resistance value R with the ground fault current. 5. The AC load power supply according to claim 1, wherein when the ground fault current exceeds the ratio V / R, a ground fault on the DC power source side is detected. system. The AC load according to any one of claims 1 to 6, further comprising means for distinguishing between a ground fault on the DC power source side and a ground fault on the load side when a ground fault is detected. Power system.

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