JPH09312930A - Detection of defect in power system and protection of the system from the defect - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize stress applied to a device when an accident occurs and prevent a bad influence on a system and a load by judging a system defect using an arithmetic value for conducting a control in a power converter and immediately protecting the device from the defect. SOLUTION: A power converter 10 is constituted of an inverter section 11, a high harmonic wave suppressing and controlling block 12, a negative-phase-sequence component compensating and controlling block 13, a supply voltage constant controlling block 14, and a common operating section 15. A defect operating section 20 receives the results of operations from the higher harmonic wave suppressing and controlling block 12 and the negative-phase-sequence component compensating and controlling block 13 and then computates a defect and displays it and then outputs a gate control command signal Gbs to a PWM controlling section 11a to block a gate of the inverter section 11 and stop the operation of the inverter section 11. By collecting information about a defect using a control operation result and blocking the inverter section immediately after an accident appears in the system, stress applied to a device can be minimized when the accident occurs and a bad influence on the system and a connected load can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power system in which a semiconductor power converter is connected to a power system and the semiconductor power converter is provided with functions such as constant voltage control, active filter, unbalance voltage suppression, and flicker compensation. The present invention relates to a failure detection and protection system for a system side accident.

[0002]

2. Description of the Related Art In a power system (hereinafter abbreviated as a system), an increase or fluctuation of reactive power taken by a load has various adverse effects on the system or a load connected to the system. The effects of this reactive power include steady and transient voltage fluctuations in the power system, flicker, voltage imbalance, and harmonic interference.

In order to eliminate these adverse effects, a power converter using a semiconductor element is connected to the system to compensate the reactive power and the harmonic current to stabilize the system.

FIG. 3 is a basic configuration diagram of an active filter for compensating a harmonic current by using a power converter, and FIG. 3 shows an example in which a voltage type inverter is used.

In FIG. 3, reference numeral 1 denotes a power converter, which is composed of a main circuit section 2 centering on an inverter section IV and a control circuit section 3 for controlling the operation as an active filter. The inverter IV is composed of a semiconductor element such as a thyristor, a transistor, or an IGBT, and the control circuit unit 3 includes a current command unit calculation circuit 3a for calculating a current waveform to be output from the active filter.
The output current of the inverter unit is composed of the current control circuit 3b that controls the gate signal so that the output current follows the command value.

The current command calculation circuit 3a calculates a current waveform to be compensated for by the active filter and selects a function, and the current control circuit 3b performs an equivalent variable current source operation.

This power conversion device 1 is connected in parallel to a system 5 via a power receiving circuit breaker 4.

FIG. 3 shows the case where the power converter 1 is made to function as an active filter, but not limited to harmonic suppression, power factor improvement by continuous reactive power compensation, voltage fluctuation compensation, unbalanced load, etc. It is well known that a function of compensating the negative-phase power associated with can be added.

[0009] When a system accident occurs in the system to which the power conversion device 1 is connected, the protection is detected by various detectors provided in the system or the power conversion device and the abnormality is detected. This is done by tripping the vessel 4. For example, in the case of a three-wire ground fault accident, it is detected by the ground fault overvoltage relay, and in the case of a one-wire short circuit, it is detected by the overcurrent relay,
The operation of these relays trips the power receiving circuit breaker 4, disconnects (disconnects) the power converter 1 from the grid 5, and protects the grid, the power converter, and the load.

In FIG. 3, HCT is an optical current transformer,
ACL is an AC reactor, F is a ripple removal filter, T
_γ indicates a transformer.

[0011]

As described above, when an accident occurs in the grid, the detector detects it and trips the power receiving circuit breaker, and the power converter is disconnected from the grid, the power converter is disconnected. There is currently no special protection for the side. Then, it takes several hundred ms until the breaker trips after the relay operates, during which the power conversion device is left in a faulty state. Unlike devices such as transformers, discs, capacitors, and reactors, power converters use semiconductors for advanced control, and the delay of several hundred ms is too long in terms of both hardware and software. As a result, an uncontrollable state may occur by the time the shutoff ends, and the device may be destroyed. Further, a fault current is supplied to the system from the device side during that time.

In order to prevent these, it is necessary to perform protection by high-speed system fault detection, however, at present, there is no high-speed system fault detection protection relay.

In view of these points, the present invention utilizes the control calculation result to extract accident information, stop the operation of the power conversion device at high speed, and minimize the stress on the device during an accident. It is an object of the present invention to provide a protection system of this kind that instantaneously stops the outflow of fault current to the system and prevents the system and load from being adversely affected.

[0014]

SUMMARY OF THE INVENTION The present invention focuses on the fact that there is a correlation between the calculation result for the control performed inside the power converter and this calculation result and the system fault, and the calculated value is used. The system failure is discriminated (detected) and the protection operation is instantaneously performed. This allows fault detection to be performed within the calculation cycle (within several tens to several hundreds of μs),
This is a significant speedup compared to the past.

The power converter has various functions for stabilizing the system such as constant voltage control, reactive power compensation, anti-phase component compensation, and harmonic compensation, and these functions are selected to be selected functions. Controlling the gate of the inverter unit by calculating the matched control signal is the same as in the prior art.

The purpose of this invention is to determine the fault of the system by using the result of this calculation. That is, system failures are roughly classified into blackouts, short circuits, and ground faults. It is revealed that there is a correlation between the type of these failures and the calculation result, and the type of the failure is determined using the calculated value.

The failure determination is performed as follows.

(1) At the time of a power failure, since the power supply is lost, the input signals of all currents change to 0. Therefore, when the input signal is 0, it is determined that there is a power failure.

(2) At the time of three-phase short circuit, most of the three-phase short circuit current is the fundamental wave reactive current, and there is almost no fundamental wave active component current at the time of short circuit. Increase) and sudden change in the active current of the fundamental wave (decrease)
Determine the three-phase short circuit from.

When a two-wire short circuit occurs, the two-wire short circuit current is
The increase tendency of the reactive current of the fundamental wave and the decreasing tendency of the active current of the fundamental wave are the same, but a sudden change (increase) of the reactive current of the opposite phase is a characteristic phenomenon. Therefore, this determines a two-wire short circuit.

(3) The characteristic of the ground fault accident is that the same phenomenon as the three-phase short circuit in the case of three-wire ground fault and the two-wire short circuit in the case of two-wire ground fault, but the value of the ground fault resistance This increases the ratio of the fundamental wave effective component. In general, there are almost no complete ground faults, and most ground faults occur at high resistance. At this time, there is power consumption at the grounding resistance, so there is a sudden change in the ratio of the fundamental reactive power to the fundamental active power. Small compared to short circuit. Therefore, when this ratio is within a predetermined threshold value, it is determined to be a ground fault.

When these accidents are judged, the gate of the inverter section constituting the power converter is immediately blocked to prevent the abnormal operation of the power converter, and at the same time, the outflow of the fault current from the power converter to the system side. To prevent.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a control block diagram of the hardware section of the present invention, and FIG. 2 shows a failure determination processing flow of the software section.

The same or corresponding portions as in FIG.
The same reference numerals are given and the detailed description is omitted.

In FIG. 1, reference numeral 10 is a semiconductor power converter (hereinafter referred to as a power converter), and the example in the figure has three functions of harmonic suppression (compensation), negative phase compensation, and constant power supply voltage. It shows the case.

The power converter 10 includes an inverter section 11
A harmonic suppression control block 12, an anti-phase component compensation control block 13, a constant power supply voltage control block 14 and a common calculation unit 15.

The inverter section 11 is composed of a semiconductor element such as a thyristor, a transistor, or an IGBT, a capacitor C as a DC voltage source is connected to the DC side, and an AC side is connected to the grid 5 via a transformer T _γ. To work as.

The harmonic suppression control block 12 basically subtracts the active component of the fundamental wave from the load current to calculate the reactive component of the load current plus the harmonic component, and cancels it by the PWM inverter. It generates a compensation current and injects this compensation current into the system. As a configuration, an αβ that inputs the three-phase current of the system 5 detected by the current transformer CT and performs a three-phase / two-phase conversion on the orthogonal α-β coordinates
The conversion unit 12-1, the converted currents iα, iβ and the angular frequency of the power supply from the phase synchronization circuit PLL are input to perform rotational coordinate conversion to obtain two-phase currents I _d , I _q on the dq axes.
2 and a filter circuit 12-3 having a low-pass filter or a high-pass filter.

The dq axis two-phase currents I _d and I _q obtained by the dq converter 12-2 are composed of a direct current component and an alternating current component. The direct current component of the current I _d is the fundamental wave reactive current and the alternating current component is the harmonic reactive component. It is well known that the direct current component of the current I _q corresponds to the fundamental current effective component and the alternating current component corresponds to the harmonic effective component of the current I _q .

The output of the filter circuit 12-3 is the addition circuit 1
5-1 through the dq inverse transformation unit 15- of the common calculation unit 15
2. Two-phase / three-phase conversion is performed by the αβ inverse conversion unit 15-3, which is input to the PWM control unit 11a as a compensation current command signal.

Further, from the filter circuit 12-3, the harmonic operation effective component signal I _q ′, the harmonic ineffective component signal I _d ′, the fundamental effective component signal I _q ″, and the fundamental ineffective component signal I are sent to the failure calculation unit 20. Output _d ″.

The anti-phase component compensation control block 13 decomposes the load current into a positive-phase quadrature component and an anti-phase quadrature component from the instantaneous values of the load current and the system voltage, and compensates the positive-phase reactive component and the anti-phase component. It aims at reactive component compensation and three-phase balancing.

The anti-phase component compensation control block 13 is constructed such that the inverse rotation coordinate αβ conversion unit 13-1 for inputting the three-phase current detected by the current transformer CT is connected to this output, and is connected to the output of the phase synchronization circuit PLL. Reverse rotation coordinate dq converter 1 for inputting output
3-2, a filter circuit 13-3, an inverse rotation coordinate dq inverse conversion unit 13-4, which is connected to the output side of the filter circuit and inputs the output of the phase locked loop PLL, an inverse rotation coordinate αβ inverse conversion unit 13-5. The output of the reverse rotation coordinate αβ converter 13-5 is differentially input to the input side of the harmonic suppression control block 12. Further, the PWM control command signals I _U ′, I _V ′ and I _W ′ are added to the output side of the αβ inverse conversion unit 15-3 of the common calculation unit 15.

Further, the anti-phase effective component signal I _q and the anti-phase invalid component signal I _d are output from the filter circuit 13-3 to the failure calculating section 20.

The power source voltage constant control block 14 is for controlling the power source voltage to a set voltage at a constant level. The configuration is connected to the system 5, and a filter 14-1 for extracting a fundamental wave component and an output of the filter 14-1 are provided. An effective value conversion unit 14-2 for converting into an effective value, a comparison unit 14-3 for comparing the converted effective value with a set voltage, and a proportional-plus-integral calculation unit 14-4 for performing proportional-integral calculation of the output of the comparison unit 14-3. And the output thereof is input to the addition unit 15-1 of the common calculation unit 15.

Reference numeral 15-4 is for constant control of the voltage of the DC capacitor C of the inverter section, and compares the capacitor voltage -V _dc with the capacitor voltage set value V _sc ,
The difference voltage is smoothed and input to the addition unit 15-1.

The failure calculator 20 receives the output of the calculation results from the harmonic suppression control block 12 and the anti-phase component compensation control block 13, calculates and displays the failure, and
The gate control command signal G _bs is output, and the PWM control unit 11a
Signal to block the gate of the inverter unit 11 and stop the function of the inverter.

Next, a signal at the time of a failure input from the harmonic suppression control block 12 and the anti-phase component compensation control block 13 at the time of a system failure will be described.

The system failures are roughly classified into power failure, short circuit, and ground fault as described above. In case of power failure due to this failure,
Since the power supply is lost, all the signals input from the control blocks 12 and 13 to the failure calculation unit 20 are 0.
Changes to Therefore, a power failure accident can be determined from these signals.

In the case of a three-phase short-circuit accident, most of the three-phase short-circuit currents are fundamental wave reactive currents, and there is almost no fundamental wave active current during a short circuit. Therefore, the fundamental reactive component current signal I _d ″ suddenly changes (increases), and at the same time, the fundamental effective component current signal I _q ″ suddenly changes (decreases). Therefore, when this phenomenon occurs, it can be determined that a three-phase short circuit has occurred.

In the case of a two-wire short-circuit accident, the two-wire short-circuit current is
The fundamental wave reactive current increases and the fundamental active current decreases in the same tendency, but the reverse-phase reactive current suddenly changes and its signal I
_d suddenly changes (increases). Therefore, when this phenomenon occurs, it can be determined that a two-wire short circuit has occurred.

Next, in the case of a ground fault accident, there are a three-wire ground fault and a two-wire ground fault, but a three-wire ground fault is the same phenomenon as a three-wire short circuit, and a two-wire ground fault is the same phenomenon as a two-wire short circuit. However, in the case of a ground fault, the ratio of the fundamental wave effective component increases with the value of the ground fault point resistance. Generally, there is almost no complete ground fault, and most of them are high resistance ground faults. At this time, since there is power consumption by the ground resistance, the fundamental reactive component signal I _d ″ and the fundamental effective component signal are I _q ″
The amount of sudden change in the ratio to is smaller than that at the time of short circuit. Therefore, when this ratio is within a predetermined (set) threshold value, it can be determined as a ground fault.

The determination of these faults is performed by the fault calculator 20.

FIG. 2 shows the flow of this failure judgment processing.

In step S1, the fundamental wave reactive current signal I _d ″ is constantly monitored and compared with an accident determination parameter (hereinafter abbreviated as a set value) ε1.
2 to S4, the fundamental wave effective component signal I _q ″, the harmonic ineffective component signal I _d ′, and the harmonic effective component signal I _q ′ are set to respective set values ε.
2, .epsilon.3, .epsilon.4, and when all are less than or equal to the set values, it is determined in step S5 that there is a power failure, and a signal is sent to the protection sequence (S6). In step S7, if these currents are equal to or more than the set values, it is determined that there is no accident, the process returns to step S1, and the monitoring is repeated.

If the sudden change of the fundamental wave invalid signal I _d ″ is larger than the set value ε1 in step S1, the set value ε5 for determining the short circuit of the fundamental wave invalid signal I _d ″ is determined in step S8. compared to, when you are increasing, the fundamental wave active component signal I _q "is compared with a set value ε6 in step S9, when is decreasing than the set value, then reverse-phase reactive component signal I _d ，
The negative-phase effective component signal I _q is sequentially compared with the set values ε7 and ε8,
If both are larger than the set values, it is determined that there is a two-phase short circuit (S1
0, S11, S12) and sends a two-phase short circuit signal to the protection sequence.

When the anti-phase invalid component and the anti-phase effective component signals I _d and I _q are both smaller than the set values ε7 and ε8 in steps 10 and 11, it is determined in step S13 that a three-phase short circuit has occurred.

If the fundamental invalid signal I _d ″ has decreased from the set value ε5 in step S8, or if the fundamental effective signal I _q ″ has increased from the set value ε6, step S8.
At 14, the ratio of the fundamental wave effective component to the fundamental wave effective component signal I _d ″ /
I _q ″ is calculated, and the sudden variation is larger than the set value ε 9 and is ε.
If it is within the range smaller than 10, it is determined to be a ground fault in step S15, and if it is not determined, it is determined to be no accident in step S16.

In this way, the system fault can be determined by the signal of the calculation result.

As a control at the time of an accident, the failure calculation section 20 outputs a gate block signal G _bs to the PWM control section 11a of the inverter section 11 to block the gate of the inverter section.

[0052]

As described above, according to the present invention, since the accident information is extracted by using the control calculation result and the gate of the inverter section constituting the power conversion device is instantaneously blocked when a system accident occurs, Produce the effect of.

(1) Compared with the conventional protective relay, it is possible to detect accidents at an ultra-high speed.

(2) Since the accident information is extracted using the control calculation result, the addition of software can be reduced.

(3) Since the power conversion device can be stopped at an extremely high speed by high-speed detection, stress on the device at the time of an accident can be minimized.

(4) With respect to the system, it is possible to instantaneously stop the outflow of the fault current from the power converter side in the event of an accident, and prevent the system and the connected load from being adversely affected.

[Brief description of drawings]

FIG. 1 is a control block diagram for explaining the present invention.

FIG. 2 is a flow chart of a failure determination process of the present invention.

FIG. 3 is a basic configuration diagram of a power conversion device having a system stabilizing function.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electric power converter 2 ... Main circuit part 3 ... Control circuit part 4 ... Power receiving circuit breaker 5 ... Electric power system 10 ... Power converter device 11 ... Inverter part 12 ... Harmonic suppression control block 13 ... Reverse phase compensation control block 14 ... Power supply voltage constant control block 15 ... Common operation unit 20 ... Failure operation unit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication H02M 7/48 9181-5H H02M 7/48 R

Claims (2)

[Claims] 1. A power conversion device having a plurality of functions for compensating for stabilization of the power system is connected to the power system, these compensation functions are selected, and a control signal suitable for the selection function is calculated. In a fault detection and protection method for a power system that controls the power conversion device by a control signal of a calculation result to realize a selection function, the type of fault is determined from the calculation result, and the power consumption is determined based on the result of the fault determination. A fault detection and protection system for a power system, characterized in that a gate of an inverter unit that constitutes a converter is blocked to stop the operation of the inverter unit. 2. The determination of the failure type is performed by extracting at least a fundamental wave effective component signal, a fundamental wave ineffective component signal, and a negative phase ineffective component signal out of the control signals of the calculation result, and all of these signals are set. If it is less than the value, it is judged as a power failure accident,
Three-phase short circuit when there is a sudden change (increase) in the fundamental wave reactive component signal and a sudden change (decrease) in the fundamental wave effective component signal, an increase in the fundamental wave reactive component signal, and a decreasing trend and reverse phase in the fundamental effective component signal A two-phase short circuit was determined when the reactive component signal suddenly changed (increased), and a ground fault accident was determined when the ratio of the fundamental reactive component signal and the fundamental effective component signal was within the set range. Claim 1 characterized by the above-mentioned.
Fault detection and protection method for the power system described.