JP2003199357A - Power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a power converter which comprises semiconductor devices and supplies a power to a load such as an induction motor, etc., whose capacity need not be increased excessively, and whose economic performance is improved. <P>SOLUTION: This power converter has a voltage-limiting circuit 11, which limits the output voltage of an inverter 1 to be a prescribed level so as to have a current applied to a semiconductor device IGBT of the inverter 1 not to exceed the short-time overcurrent strength of the semiconductor device IGBT according to a signal which is outputted by a comparator (1) 10, when a current value detected by a load current detector 6 exceeds a first overcurrent set value IL1, set according to the short-time overcurrent strength of the semiconductor device IGBT, and a device cooling reinforcing apparatus control circuit 17, which reinforces the cooling conditions of the semiconductor device IGBT, according to a signal which is outputted by a comparator (2) 131, when the current value detected by the current detector 6 exceeds a second overcurrent set value IL2. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power conversion device which is composed of semiconductor elements and which converts power on the input side and supplies the power to the output side, and supplies the power to a load such as an induction motor through which a large current flows at startup. The present invention relates to a technology for realizing a device in a reasonable and economical manner.

[0002]

2. Description of the Related Art In buildings such as buildings and factories of a certain scale, it is obligatory to install an emergency load under the Fire Defense Law and Building Standards Law, and power is supplied to these emergency loads. As an emergency power source for doing so, conventionally, rotating equipment such as a diesel generator and static equipment combining a storage battery and an AC / DC converter are used. By the way, as the emergency load, there are sprinklers, smoke exhaust equipment, fire hydrant equipment, emergency lighting equipment and the like, and many of them are driven by an induction motor. When this induction motor starts by applying a voltage, the first very short time,
A so-called starting current of an induction motor, which will be described later, is superposed with a transient DC component due to voltage application, and an inrush current of, for example, about ten times the rated current flows. After that, in the process in which the induction motor starts from zero speed and reaches a steady speed, a starting current that gradually attenuates from several times the rated current flows.

When the power supply equipment is a rotary machine equipment, the rush current is very short, and thus it is not a problem in many cases, but in the case of static equipment, it is used especially for the AC / DC power converter. Due to the overload withstand characteristics of semiconductor elements, this inrush current cannot be ignored, and in consideration of this inrush current, a power converter with an excessive capacity of several times the rated capacity of the load may be required. There was a problem that it became disadvantageous. If the Y-Δ starter is inserted and the induction motor is started in two stages and the induction motor is started, the inrush current is suppressed to some extent, but the above problem is not solved.

In recent years, an electric power storage device including a secondary battery and an AC / DC power conversion device is installed in a building, factory or the like to store nighttime electric power and discharge the electric power at the peak of power in the daytime to perform load leveling. A power storage system for leveling is being put to practical use, and a system in which the power storage device is also used as an emergency power source has been proposed in order to increase the added value of the system. In these devices, static equipment that uses semiconductor elements such as IGBTs is indispensable because of the required power conversion control function, and at the same time, power supply to an emergency load, which is often an induction motor, is imposed, which results from the inrush current described above. The problem to do becomes serious.

The present invention has been made in order to solve the above problems, and it is an electric power converter which is composed of semiconductor elements and supplies electric power to a load such as an induction motor. It is an object of the present invention to obtain a power conversion device that does not need to be large and that has improved economy.

[0006]

A power conversion device according to the present invention controls a power converter which is composed of a semiconductor element and which converts power on an input side and supplies the power to an output side, and an output of the power converter. In a power conversion device including an output control unit, a current detection unit that detects the current on the output side, a first overcurrent set value in which the current detection value is set based on a short-time overcurrent withstanding capability of the semiconductor element. Voltage limit means for limiting the output voltage of the power converter to a predetermined level so that the current flowing through the semiconductor element does not exceed the short-time overcurrent withstanding value when the current detection value exceeds the first value.
The cooling strengthening means for strengthening the cooling condition of the semiconductor element when the second overcurrent set value set to a value lower than the overcurrent set value of is exceeded.

Further, in the power converter according to the present invention, when the lower limit voltage at which the load connected to the output side of the power converter is operable is set as the load lower limit voltage, the current detection value by the current detecting means is the first value. When the set value of overcurrent is exceeded, the voltage limiting means performs the voltage limiting operation with the load lower limit voltage value as the initial value of the output voltage command.

Also, in the power converter according to the present invention, when the current detection value by the current detecting means exceeds the second overcurrent set value and this state continues for a predetermined set time or longer, the output of the power converter is output. Is provided with an output stopping means for stopping.

Further, in the electric power converter according to the present invention, the electric power converter supplies electric power to a load including an induction motor, and the induction motor is started by applying a voltage from a stopped state. In this case, the starting current of the load calculated as the starting current of the induction motor, which does not include the transient DC component associated with voltage application, is calculated, and the first overcurrent set value is set in a range exceeding the calculated load starting current. Is to be set.

Further, the power converter according to the present invention obtains the load current calculated as the steady-state current value after the starting current flows through the current flowing through the induction motor, and the second current is calculated in the range exceeding the calculated load current. The overcurrent set value is set.

Further, the power converter according to the present invention sets the set time of the output stopping means in a range exceeding the starting current flowing period of the induction motor, and when the calculated load starting current flows within the set time. The cooling strengthening condition of the cooling strengthening means is set so that the semiconductor element does not exceed the allowable temperature limit.

Further, in the electric power converter according to the present invention, when the loads include a plurality of induction motors and the induction motors are sequentially started so that the starting current flow periods of the induction motors do not overlap, each of the induction motors is The first overcurrent setting value is set in a range exceeding the maximum value of the calculated load starting current obtained each time the induction motor is started.

Further, the cooling enhancement means of the power converter according to the present invention is adapted to continue the operation for a predetermined time even after the detected current value becomes equal to or lower than the second overcurrent set value.

The power converter according to the present invention is a power storage system for leveling loads by converting power between a DC power storage device and an AC power system, and when the AC power system fails. The present invention is applied to a power converter that converts DC power of the DC power storage device into AC power and supplies the AC power to an emergency load including an induction motor.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. FIG. 1 is a single-line connection diagram showing the overall configuration of a power storage system that also serves as an emergency power source. In the figure, 1 is an inverter as a power converter, which converts DC power of the secondary battery 2 into AC power in the daytime to supply power to a general load 31 such as an air conditioning load, a lighting load or a power load, Power is supplied to the power grid 30 that is interconnected. In addition, at night, the power system 30
The AC power from is converted into DC power to charge the secondary battery 2. Further, in the event of an emergency such as a fire, the VCB 32 is opened to disconnect the interconnection with the power system 30, and the direct current power of the secondary battery 2 is converted into alternating current power to use a large number of induction motors such as sprinklers and smoke exhaust fans. Emergency load 33
Supply power to.

Here, the inverter 1 has, for example, as shown in FIG. 2, a DC capacitor connected in parallel with the secondary battery 2 and an arm composed of an IGBT as a semiconductor element capable of high frequency switching operation. It is composed of an AC / DC converter formed by phase bridge connection and a control device for controlling the IGBT. The AC output side of the inverter 1 is connected to the power system 30 via a filter L3, a filter C4, and a step-up transformer that remove high-frequency components from the output of the inverter 1. Further, as the secondary battery 2, for example,
Lead acid batteries, redox flow batteries, NAS batteries, zinc bromine batteries, lithium ion batteries and the like are used.

FIG. 3 is a diagram showing the configuration of the power converter according to the first embodiment of the present invention, particularly in the case of functioning as an emergency power source. In the figure, 1 is the inverter described in FIG. 2 above, to which the secondary battery 2 is connected on the DC side,
The AC side is connected to the emergency load 33 via the filter L3 and the filter C4. Reference numeral 5 is a voltage detector for detecting the output voltage of the inverter 1, and 6 is a load current detector for detecting the output current of the inverter 1, that is, the current flowing into the emergency load 33. 8 is a voltage control circuit for inputting a deviation between the detection output of the voltage detector 5 and the output of the voltage reference generator 7 and outputting a voltage control signal. 10 is a load current detector 6
Of the load current detector 6 is compared with the first overcurrent setting value of the overcurrent setting device (1) 9 (the setting of this value will be described later). The voltage limiting circuit receives the output of the comparator (1) 10 and outputs a voltage limiting signal when the detected output exceeds the first overcurrent setting value. Details of the voltage limiting circuit 11 will be described with reference to FIG.

A comparator (2) 13 compares the detected output of the load current detector 6 with a second overcurrent setting value of the overcurrent setting device (2) 12 (the setting of this value will be described later). ), 14 receives the output of the comparator (2) 13 and starts counting when the detection output of the load current detector 6 exceeds the second overcurrent setting value, and a predetermined set time (for setting this value, A timer circuit that outputs a signal when the signal exceeds a value (described later), and 15 is an output stop signal circuit that receives a signal from the timer circuit 14 and outputs an output stop signal. Reference numeral 16 is a PWM generation circuit for inputting a voltage control signal from the voltage control circuit 8, a voltage limit signal from the voltage limit circuit 11 and an output stop signal from the output stop signal circuit 15 to generate an IGBT gate signal of the inverter 1. Is.

Reference numeral 17 indicates that the detection output of the load current detector 6 is the second
When the overcurrent set value of is exceeded, the element cooling enhancement device control circuit for controlling the operation of the element cooling enhancement device as the cooling enhancement means by receiving the output of the comparator (2) 13, and 18 is the element cooling enhancement device control circuit 17 Inverter 1 by control signal from
Element strengthening cooler that performs the operation of cooling strengthening of the IGBT of 1
Reference numeral 9 is an element cooler for cooling the IGBT of the inverter 1 during normal operation. The cooling strengthening means will be described in detail with reference to FIG.

Next, the operation will be described. As the power storage system, an operation of converting AC power from the power grid 30 into DC power by the inverter 1 to store the secondary battery 2, and converting DC power of the secondary battery 2 into AC power by the inverter 1. Then, the operation is performed by the so-called soft start in which the voltage is gradually increased or the phase synchronization is turned on. Therefore, in any case, a transiently large current does not flow, and its explanation is given. It is omitted, and here, the operation in the case where a voltage is applied to the emergency load 33 to supply electric power exclusively in the circuit of FIG. 3 will be described.

First, the IG is set against the overcurrent that flows when the emergency load 33 including many induction motors is turned on.
The operation of suppressing the current flowing in the IGBT by detecting the overcurrent and limiting the output voltage so that the current rating of the BT (semiconductor element) does not have to be set excessively high is shown in FIGS.
This will be described with reference to FIG. FIG. 4 shows a more detailed configuration by extracting the portion for suppressing the overcurrent from FIG. FIG. 6 shows output voltage and current waveforms in the conventional case (a) and the present invention case (b).

Here, the first overcurrent set value IL1 set by the overcurrent setter (1) 9 is set based on the short-time overcurrent withstand capability of the semiconductor element (IGBT) used. Specifically, when the current of this withstand amount flows in the semiconductor element, the current flowing to the output side of the inverter 1, in other words, the current detected by the load current detector 6 or the margin is set to a value slightly lower than that. Is set. This short time corresponds to a time period equal to or shorter than a half cycle of the AC commercial wave frequency.

Further, the first overcurrent set value IL1 needs to satisfy the following conditions. That is, as mentioned above,
When the induction motor is started by applying a voltage, a starting current larger than the steady current flows in the process of starting the induction motor from zero speed and accelerating to the steady speed. A transient DC component accompanying the voltage application is further superimposed on the current. When the transient current value in which the transient DC component is superimposed on the starting current is defined as the starting inrush current, when the first overcurrent setting value IL1 is set to suppress the overcurrent flowing through the semiconductor element, Suppressing only the transient DC component that depends on the voltage phase when the load is turned on in the inrush current does not hinder the starting of the induction motor.However, if this is suppressed, the starting torque of the motor Decreases in proportion to the square of the voltage (current). Therefore, in the case of a motor load that requires a large torque at the time of starting, the starting time is prolonged, or the worst starting is impossible. May not be obtained. Therefore, it is necessary to set the first overcurrent setting value IL1, which is the threshold value for current suppression, in a range exceeding (the maximum value of) the starting current of the induction motor that does not include the transient DC component. Although one motor (induction motor) load is shown as the emergency load 33 in FIG. 3, there are loads other than the induction motor in practice, and a plurality of motor loads may be sequentially input. , The load starting current is obtained by adding another load current to the starting current component of the starting target motor, and the first overcurrent set value I is obtained in a range exceeding the calculated load starting current.
Set L1.

By the way, the rated current of the inverter 1 is determined with consideration given to the current during the load leveling operation and the steady load current of the emergency load 33, and with an appropriate margin, as shown in FIG. In the example shown in, when the rated current of the inverter 1 is 100%, the first overcurrent setting value IL1 is 1
It is set to 50%.

In FIG. 6B, another load current of the emergency load 33 is flowing during the time period until the motor is started.
That is, in this time zone, in FIG. 4, the current | I | obtained by the current feedback signal from the load current detector 6 through the absolute value circuit 40 is smaller than the first overcurrent set value IL1. (1) 10 outputs “0”, and the PWM generation circuit 16 exclusively controls the voltage feedback value from the voltage detector 5 to match the voltage reference value of the voltage reference generator 7 from the voltage control circuit 8. Constant voltage control is performed based on the signal.

In FIG. 6, when the induction motor load in the emergency load 33 is switched in and the motor is started, a steep starting rush current flows, and its instantaneous value current | I | becomes the first overcurrent set value IL1. When it exceeds, in FIG. 4, the comparator (1)
The output of 10 rises to "1" (at time T in FIG. 6B).
1), the voltage control signal from the voltage control circuit 8 is the multiplier 41
After that, a signal multiplied by a constant magnification is further generated in the multiplier 42, and the PWM generation circuit 16 creates a gate signal using a signal obtained by subtracting the signal of the multiplier 42 from the signal of the voltage control circuit 8 as a command signal. That is, as shown in the voltage waveform of FIG. 6B, the output voltage is suppressed, and as a result, the inverter 1
Output current is controlled so as not to exceed the first overcurrent setting value IL1. Therefore, the IGBT, which is a semiconductor element,
Use within the short-term overcurrent withstand capability is compensated.

As the multiplication factor set by the multiplier 42, the value subtracted from the signal of the voltage control circuit 8, that is, the initial value of the output voltage command for the voltage limit control is the lower limit voltage at which the load can be operated. If it is set to the lower limit voltage value,
An extremely quick voltage suppression effect can be obtained within a range that does not hinder the operation of the load, and the element is reliably protected.

In the example of FIG. 4, the voltage command is directly reduced to suppress the output voltage, but when a minor loop for current control is provided in the control system of the inverter 1, the command value for current control is reduced. By doing so, the output voltage may be suppressed.

For comparison, FIG. 6A shows voltage / current at the time of starting the motor when the present invention is not applied.
Naturally, the starting inrush current exceeds 150% of the first overcurrent setting value IL1. In other words, if it is left as it is, it will be used beyond the short-time overcurrent withstand capability of the semiconductor element.
As a practical matter, the semiconductor element needs to have a higher current rating, and the inverter must be expensive.

Next, the cooling strengthening operation for suppressing the overheat temperature rise of the semiconductor element due to the supply of the starting current which cannot be suppressed in order to compensate the starting operation of the induction motor is shown in FIG.
This will be described with reference to FIG.

FIG. 5 shows a portion extracted from FIG. 3 for performing the cooling strengthening operation. Here, the overcurrent setting device (2)
The second overcurrent set value IL2 set at 12 is determined within a range in which the steady-state current value of the load, and thus the induction motor exceeds the current value after the starting current conduction period has passed. In other words, when the load current is less than or equal to the second overcurrent set value IL2, the cooling intensifying means to be described below does not operate, so that cooling is performed only by the operation of the element cooler 19 described in FIG. become. In the example of FIG. 6, 100% of the rated current of the inverter 1 is the second overcurrent setting value IL2. 6, when the induction motor in the emergency load 33 is switched in and the motor is started, a steep starting rush current flows and the voltage limiting operation described above with reference to FIG. 4 is started. At the same time, in FIG. Irms obtained by the current feedback signal from the load current detector 6 passing through the effective value circuit 43 exceeds the second overcurrent set value IL2, and the output of the comparator (2) 13 rises to "1" (see FIG. 6). (B)
At time T1), the element cooling enhancement device control circuit 17 outputs a control signal and the element enhancement cooling device 18 starts operating, so that the amount of air blown to the cooling fins of the IGBT elements of the inverter 1 increases rapidly. That is, the withstand capability of the device against overcurrent is enhanced.

The following method can be considered as a concrete measure of the element cooling strengthening means. That is, the amount of air blown to the element fins is increased by increasing the rotation speed of the blower that is normally used. In addition to a blower that is normally used, a dedicated blower is provided close to the element fins, and by driving this dedicated blower, the amount of blown air to the element fins is increased. In addition, various cylinders, such as a cylinder in which a refrigerant is compressed and stored, are jetted from the nozzle to rapidly cool the tank.

In FIG. 5, the effective value circuit 43 determines the effective value of the current feedback signal and compares it with the second overcurrent set value IL2. It is because it is a thermal thing of about several tens of seconds. Therefore, not only the effective value calculation but also the average value of absolute values may be calculated. Further, in the case of making a determination based on the instantaneous value of the current, for example, by providing a self-holding function of about one cycle of the commercial frequency,
Instability factors such as chattering accompanying the comparison operation can be avoided. However, it is needless to say that the specific value of the second overcurrent set value IL2 needs to be changed accordingly if the form of the current to be compared changes.

When the induction motor normally starts, the starting current gradually decreases, and the effective current value Irms becomes equal to or less than the second overcurrent set value IL2, the output of the comparator (2) 13 is inverted. However, in the example of FIG.
The output of the comparator (2) 13 is inverted to “0” at time T3, which is a predetermined output holding time TS ahead of time T2 when s ≦ IL2. That is, the operation for strengthening the element cooling is continued until time T3. This is because, as shown in FIG. 6B, the end of the starting current energization period may be delayed from the current determination time T2 depending on the setting of the second overcurrent setting value IL2. This is to secure a margin on the element temperature surface by continuing the cooling strengthening operation for a certain period of time. In the circuit of FIG. 5, this output holding time TS
Is set by the comparator (2) 13 itself,
The comparator (2) 13 may output by a comparison calculation only from the current value, and the element cooling enhancement device control circuit 17 in the subsequent stage may have this holding time setting function.

At the time, the output of the comparator (2) 13 is "1".
5, the timer circuit 14 starts counting in response to the output change of the comparator (2) 13 in FIG. The timer circuit 14 outputs a signal when the count value exceeds a set time in a range exceeding the starting current flowing period of the induction motor, and the output stop signal circuit 15 receives the signal and stops the output to the PWM generating circuit 16. A signal is sent and the inverter 1 stops its operation. The overcurrent determined by the comparator (2) 13 is not due to the normal starting current of the induction motor, and can continue for a long time.
In the case of a short circuit of a part of the load or an abnormal phenomenon, the protection of the element cannot be compensated by the cooling strengthening measures assumed in advance.
The inverter 1 is stopped. Therefore, the element-enhanced cooler 18 needs to have a cooling capacity such that the element does not exceed its allowable temperature limit even if the load starting current including the starting current flows for the time set by the timer circuit 14. .

Here, the first overcurrent setting value IL1
A specific example of the setting procedure will be described. As the most severe usage condition, it is assumed that after the 200 kVA emergency load is started, the maximum capacity 37 kW induction motor is finally started. The starting rush current that flows when this 37 kW induction motor is started using a Y-Δ starter corresponds to 320 kVA, which is about eight times the rated value in terms of capacity (the total of 200 kVA of the base is 520 kVA). On the other hand, the starting current corresponds to 120 kVA (320 kVA in total with the base), which is about three times the rated value in terms of capacity. Therefore, conventionally, when supplying electric power to such an emergency load, in the rotating machine equipment, about 350 k in consideration of the starting current among the above.
A capacity of about W is required. Further, in the case of static equipment using semiconductor elements, a capacity of about 550 kVA is required in consideration of the starting rush current described above. On the other hand, when the present invention is applied, the base 200 kVA
A power converter with a rated value of about 250 kVA, which takes into consideration the value obtained by adding the maximum capacity electric motor of 37 kW, is sufficient. That is, the short-term overload withstanding capability of the semiconductor element used, for example, the IGBT, is set to 150% of the rating (250 kVA), and the first
With the overcurrent setting value, the voltage limit control is performed so that the maximum current at startup does not exceed 375 kVA (= 250 × 1.5) in terms of capacity.
The cooling strengthening measure described later is executed so that the temperature rise of the GBT is, for example, about 90 ° C. or less. As a result, compared with the case of the conventional static equipment, the capacity of less than half is sufficient, and the apparatus can be made compact and the cost can be reduced.

As described above, in the power converter according to the first embodiment of the present invention, even if a semiconductor element having a lower current rating than that of the conventional one is used, the semiconductor element of the inverter is over-excited due to the starting rush current of the induction motor. Prevents breakdown due to current, and continuously supplies power to the motor and load that has already started without causing element breakdown due to heating due to overload operation while starting current is being supplied or inverter stoppage due to temperature abnormality. You can do it.

In the above description, the comparator (2) 13
It is determined that the load current has exceeded the second overcurrent set value IL2 by the above, and the element enhanced cooler 18 is activated by the output signal thereof, but power is supplied to the emergency load 33 shown in FIG. In this case, since the fire detector operates prior to that, the element reinforced cooler 18 may be activated using the output signal of this fire detector. On the control circuit,
The element reinforced cooler is started by the logical sum output of the output of the fire detector and the output of the comparator (2). In this case, since the cooling strengthening operation is started at an earlier point, a sufficient cooling effect is expected. Of course, the element-enhanced cooler is started even if the overcurrent does not occur, so that its operation frequency increases, but since the frequency of emergency operation itself is low, there is no problem in terms of life.

[0039]

As described above, the power converter according to the present invention controls the output of the power converter, which is composed of semiconductor elements and which converts the power on the input side and supplies it to the output side. In the power conversion device including the output control means, a current detecting means for detecting a current on the output side, and a first overcurrent setting in which the current detection value is set based on the short-time overcurrent withstanding capability of the semiconductor element. When the value exceeds the value, voltage limiting means for limiting the output voltage of the power converter to a predetermined level so that the current flowing through the semiconductor element does not exceed the short-time overcurrent withstanding value, and the current detection value is the first value.
The current rating of the semiconductor element is excessively increased because the cooling enhancement means for enhancing the cooling condition of the semiconductor element is provided when the second overcurrent setting value set to a value lower than the overcurrent setting value of is exceeded. It is possible to obtain a highly economical power conversion device that does not require and can carry over expected overcurrent without trouble.

Further, in the power converter according to the present invention, when the lower limit voltage at which the load connected to the output side of the power converter is operable is set as the load lower limit voltage, the current detection value by the current detecting means is the first value. When the overcurrent set value is exceeded, the voltage limiting means performs the voltage limiting operation using the load lower limit voltage value as the initial value of the output voltage command, so that a rapid voltage suppression characteristic can be obtained within the range that does not hinder the operation of the load. The semiconductor element is surely protected.

Further, in the power converter according to the present invention, when the current detection value by the current detection means exceeds the second overcurrent set value and this state continues for a predetermined set time, the output of the power converter is output. Since the output stopping means for stopping the device is provided, damage to the device can be prevented even when the overcurrent continues for a time longer than the expected time.

Further, in the electric power converter according to the present invention, the electric power converter supplies electric power to the load including the induction motor, and the induction motor is started by applying a voltage from the stopped state. In this case, the starting current of the load calculated as the starting current of the induction motor, which does not include the transient DC component associated with voltage application, is calculated, and the first overcurrent set value is set in a range exceeding the calculated load starting current. Is set, the semiconductor element can be used under the condition of the short-time overcurrent withstand capability or less without affecting the starting characteristic of the induction motor.

Further, the power converter according to the present invention obtains the load current calculated as the steady-state current value after the starting current flows through the current flowing through the induction motor, and within the range exceeding the calculated load current, the second current is calculated. Since the overcurrent set value is set, it is possible to avoid the adverse effect that the cooling intensifying means is continuously operated for a long time even when the load is in the steady state.

Further, in the power converter according to the present invention, when the set time of the output stopping means is set within a range exceeding the starting current flowing period of the induction motor and the calculated load starting current flows within the set time. Since the cooling strengthening condition of the cooling strengthening means is set so that the semiconductor element does not exceed the allowable temperature limit, the capacity of the cooling strengthening means can be set rationally.

Further, in the electric power converter according to the present invention, when the loads include a plurality of induction motors and the induction motors are sequentially started so that the starting current flow periods of the induction motors do not overlap, each of the induction motors is Since the first overcurrent set value is set within the range that exceeds the maximum value of the calculated load start current obtained each time the induction motor is started, the first overcurrent set value is lower than the value set according to the operating condition of the load. The value can be set, and the economic efficiency of the power conversion device increases.

Further, since the cooling intensifying means of the power converter according to the present invention is adapted to continue the operation for a predetermined time even after the detected current value becomes equal to or less than the second overcurrent set value, the expected excess Even if the duration of the current is longer than the overcurrent detection time, the temperature protection of the semiconductor element is surely performed.

The power converter according to the present invention is a power storage system for leveling the load by converting power between the DC power storage device and the AC power system, and when the AC power system fails. Since the present invention is applied to a power converter that converts the DC power of the DC power storage device to AC power and supplies it to an emergency load including an induction motor, it is highly economical and can perform power supply to the emergency load without any trouble. You can get the device.

[Brief description of drawings]

FIG. 1 is a single line connection diagram showing an overall configuration of a power storage system to which a power conversion device according to a first embodiment of the present invention is applied.

FIG. 2 is a circuit diagram showing a configuration centering on the inverter 1 of FIG.

FIG. 3 is a circuit diagram showing the configuration of the power conversion device shown in FIG. 1, particularly a portion functioning as an emergency power supply.

FIG. 4 is a circuit diagram showing a configuration centered on the voltage limiting circuit 11 of FIG.

5 is a circuit diagram showing a configuration centered on a device cooling enhancement device control circuit 17 of FIG.

FIG. 6 is a diagram showing waveforms of voltage and load current when the induction motor is started.

[Explanation of symbols]

1 inverter, 2 secondary battery, 5 voltage detector, 6
Load current detector, 8 voltage control circuit, 9 overcurrent setting device (1), 10 comparator (1), 11 voltage limiting circuit, 1
2 Overcurrent setting device (2), 13 Comparator (2), 14
Timer circuit, 15 output stop signal circuit, 16 PWM
Generation circuit, 17 element cooling enhancement device control circuit, 30 power system, 33 emergency load, IL1 first overcurrent set value, IL2 second overcurrent set value.

Continued front page    (72) Inventor Nobuyuki Tokuda             3-3-22 Nakanoshima, Kita-ku, Osaka City, Osaka Prefecture             Kansai Electric Power Co., Inc. (72) Inventor Taihei Kikuoka             3-3-22 Nakanoshima, Kita-ku, Osaka City, Osaka Prefecture             Kansai Electric Power Co., Inc. (72) Inventor Naoto Sumi             4-1-1 Hommachi, Chuo-ku, Osaka-shi, Osaka Prefecture             Takenaka Corporation Co., Ltd. (72) Inventor Kosuke Nishibata             4-1-1 Hommachi, Chuo-ku, Osaka-shi, Osaka Prefecture             Takenaka Corporation Co., Ltd. (72) Inventor Shuji Sakashita             2-11-1, Tagawa, Yodogawa-ku, Osaka-shi, Osaka             Daihen Co., Ltd. (72) Inventor Tetsuhiro Kawamoto             2-11-1, Tagawa, Yodogawa-ku, Osaka-shi, Osaka             Daihen Co., Ltd. F-term (reference) 5H007 AA17 BB00 BB06 CA01 CB02                       CB05 CC32 DA06 DB02 DC02                       DC05 EA13 FA03 FA13 FA16                       FA19                 5H530 AA05 BB40 CC27 CD32 DD03                       DD13                 5H740 AA03 BA11 BB09 BB10 BC01                       BC02 KK01 MM08 MM11 MM12

Claims (9)

[Claims] 1. A power converter comprising a semiconductor device, which includes a power converter that converts power on the input side and supplies the converted power to the output side, and an output control device that controls the output of the power converter. Current detecting means for detecting the current on the side of the semiconductor element, and the current flowing through the semiconductor element is short when the current detection value exceeds a first overcurrent setting value set based on the short-time overcurrent withstanding capability of the semiconductor element. Voltage limiting means for limiting the output voltage of the power converter to a predetermined level so as not to exceed the time overcurrent withstanding capacity, and a second current detection value set to a value lower than the first overcurrent setting value. A power converter comprising: a cooling strengthening means for strengthening a cooling condition of the semiconductor element when an overcurrent set value is exceeded. 2. When the load lower limit voltage is set to the operable lower limit voltage of the load connected to the output side of the power conversion device, when the current detection value by the current detection means exceeds the first overcurrent set value, The power conversion device according to claim 1, wherein the voltage limiting means performs a voltage limiting operation with the load lower limit voltage value as an initial value of the output voltage command. 3. An output stop means for stopping the output of the power converter when the current detection value by the current detection means exceeds the second overcurrent set value and this state continues for a predetermined set time or longer. The power conversion device according to claim 1 or 2, characterized in that. 4. When the power converter supplies electric power to a load including an induction motor, and the induction motor starts by applying a voltage from a stopped state, the starting current of the induction motor is changed. The starting current of the load, which is calculated only as the starting current that does not include the transient DC component due to the voltage application, is obtained, and the first overcurrent setting value is set in a range exceeding the calculated load starting current. The power conversion device according to any one of claims 1 to 3. 5. A load current calculated as a steady current value after the starting current flows through the current flowing through the induction motor, and a second overcurrent set value is set in a range exceeding the calculated load current. The power conversion device according to claim 4, wherein 6. The semiconductor device does not exceed an allowable temperature limit when the set time of the output stop means is set in a range exceeding the starting current flowing period of the induction motor and the calculated load starting current flows within the set time. 5. The cooling strengthening condition of the cooling strengthening means is set as described above.
Alternatively, the power conversion device according to 5. 7. When the load includes a plurality of induction motors, and when the induction motors are sequentially started so that the starting current flow periods of the induction motors do not overlap, the calculation obtained each time the induction motors are started. The power converter according to claim 4, wherein the first overcurrent set value is set in a range exceeding the maximum value of the load starting current. 8. The cooling strengthening means is configured to continue the operation for a predetermined time even after the detected current value becomes equal to or lower than the second overcurrent set value, according to any one of claims 1 to 7. The power converter described. 9. A power storage system for leveling a load by converting power between a DC power storage device and an AC power system, wherein the DC power of the DC power storage device is supplied when the AC power system fails. 9. The power conversion device according to claim 1, wherein the power conversion device is applied to a power conversion device that converts the AC power to supply an emergency load including an induction motor.