JP2003061363A - Boot capacitor charging method and load driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To charge a boot capacitor properly in controlling an inverter. SOLUTION: A high-arm controlling circuit 33 controls a transistor 42, a high-arm-side switching element, provided in an inverter 4U. The controlling circuit 33 operates by a charging voltage supplied from the boot capacitor 32. The boot capacitor 32 is charged in a pre-charging period prior to an ordinary operation period for driving a load 6. In the pre-charging period, while the transistor 42 is left in an 'off' state, a transistor 41, a low-arm side switching element, is turned on and off repeatedly. This structure enables a controlling power circuit 30 to charge the boot capacitor 32 prior to the ordinary operation period without causing a heavy load to be put on the controlling power circuit 30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control technique for an inverter having a low arm side switching element and a high arm side switching element connected in series with each other. In particular, the present invention relates to a boot technique for charging a boot capacitor that supplies operating power to a circuit that controls the inverter.

[0002]

2. Description of the Related Art An inverter includes a low arm side switching element and a high arm side switching element connected in series with each other via an output line. Some techniques for controlling this inverter use a boot capacitor. In order to obtain a power source for a circuit that generates a high potential on the output line and controls the high-arm side switching element (hereinafter, referred to as a “high arm control circuit”), a boot capacitor whose one end is connected to the output line is charged. With this boot capacitor charged, the high arm control circuit operates normally. The boot capacitor is charged by using a DC power supply.

[0003]

Since a large current flows to charge the boot capacitor in the initial stage of controlling the inverter, the output voltage of the DC power supply may decrease. In that case, the charging of the boot capacitor is delayed, and the period during which the high-arm control circuit does not operate normally in the initial stage of controlling the inverter is prolonged. Due to this, the loss of the switching element on the low arm side increases, which may lead to destruction.

The present invention has been made in view of the above problems, and an object thereof is to provide a technique for appropriately charging a boot capacitor in controlling an inverter.

[0005]

[Means for Solving the Problems] Claim 1 of the present invention
Is the switching element (4
A boot capacitor (32) that supplies operating power to a high arm control circuit (33) that is connected in series to 1) and controls the operation of a high arm side switching element (42) provided in an inverter (4U). It is a method of charging the boot capacitor, which is charged in 30). In the inverter, in the pre-charge period before the normal operation period in which the low-arm side switching element and the high-arm side switching element perform normal switching, the high-arm side switching element is always turned off and the low-arm side switching element is turned on. The boot capacitor is charged by the power supply circuit via.

According to claim 2 of the present invention,
A method of charging a boot capacitor according to claim 1, wherein
During the precharge period, the low arm side switching element repeats on / off.

According to claim 3 of the present invention,
A method of charging a boot capacitor according to claim 2, wherein
The period during which the low arm side switching element is turned on is
It is at least the minimum detection time (T _wmin ) necessary to protect the inverter when the load (6) of the inverter is short-circuited.

According to claim 4 of the present invention,
The boot capacitor charging method according to any one of claims 2 and 3, wherein during a period in which the low-arm side switching element is turned on, the inductance (L) of the load (6) of the inverter and the It is less than the value obtained by dividing the line induced electromotive force (V2) of the load of the inverter by the product of the output allowable current value (I _L ) of the low arm side switching element.

According to claim 5 of the present invention,
The method of charging a boot capacitor according to any one of claims 2 to 4, wherein a boot resistor (3) is connected in series to the boot capacitor (32) with the power supply circuit.
6) is connected. Then, the product of the current value obtained by dividing the output voltage (V1) of the power supply circuit by the resistance value (R1) of the boot resistor, the resistance value of the boot resistor, and the capacitance value (C2) of the boot capacitor is used as the power source. A value obtained by dividing the maximum outputtable current (I1M) of the circuit (30) is obtained as an effective charging time constant (τ) of the boot capacitor during the charging period, and is set to the boot capacitor for the output voltage of the power supply circuit. A value (T) obtained by multiplying the effective charging time constant of the boot capacitor by the natural logarithm of the reciprocal of the value obtained by subtracting the ratio (Vbm / V1) of the minimum value (Vbm) of the voltage (Vb) to be charged from 1. ) Is adopted as the pre-charge period.

According to claim 6 of the present invention,
A method of charging a boot capacitor according to claim 5, wherein
A value obtained by dividing the output voltage (V1) of the power supply circuit by the resistance value (R1) of the boot resistor is larger than the maximum outputtable current (I1M) of the power supply circuit (30).

According to claim 7 of the present invention,
The boot capacitor charging method according to any one of claims 1 to 6, wherein the inverter corresponds to a plurality of phases and the low arm side switching element (4).
1) and a plurality of high-arm side switching elements (42) connected in series, and there are a plurality of boot capacitors (32) corresponding to the plurality of phases, and the pre-charge period corresponding to the plurality of boot capacitors. (TU, TV,
TW) is exclusive.

According to claim 8 of the present invention,
The boot capacitor charging method according to any one of claims 1 to 7, wherein the low-arm side switching element (41) and the high arm are provided between the pre-charge period and the normal operation period. A pause period is provided in which all of the side switching elements (42) are turned off.

According to claim 9 of the present invention,
An inverter (4U) including a low arm side switching element (41) and a high arm side switching element (42) connected in series to each other, to which a load (6) is connected;
An inverter control circuit (3U) having a high arm control circuit (33) for controlling the operation of the high arm side switching element and a boot capacitor (32) for supplying an operating power source of the high arm control circuit; and the boot capacitor (32). It is a load drive device including a power supply circuit (30) for charging. In the inverter, in the pre-charge period before the normal operation period in which the low-arm side switching element and the high-arm side switching element perform normal switching, the high-arm side switching element is always turned off and the low-arm side switching element is turned on. The boot capacitor is charged by the power supply circuit via.

According to a tenth aspect of the present invention, in the load drive device according to the ninth aspect, the low-arm side switching element repeats on / off during the pre-charging period.

According to an eleventh aspect of the present invention, in the load driving device according to the tenth aspect, the inverter is turned on when the load (6) is short-circuited while the low arm side switching element is on. It is longer than the minimum detection time (T _wmin ) necessary for protection.

According to a twelfth aspect of the present invention, there is provided the load driving device according to any one of the tenth and eleventh aspects, wherein the low-arm side switching element is turned on during the period. Inverter load (6)
Is less than the value obtained by dividing the line induced electromotive voltage (V2) of the load of the inverter by the product of the inductance (L) and the output allowable current value (I _L ) of the low-arm side switching element.

A thirteenth aspect of the present invention is the load driving apparatus according to any one of the tenth to twelfth aspects, wherein the boot capacitor (32) is connected to the power supply circuit. ) In series with a boot resistor (36)
Are connected. Then, the output voltage (V
1) divided by the resistance value (R1) of the boot resistor, the product of the current value of the boot resistor and the capacitance value (C2) of the boot resistor, the maximum outputtable current of the power supply circuit (30). A value obtained by dividing by (I1M) is an effective charging time constant (τ) of the boot capacitor during the charging period.
And the ratio of the minimum value (Vbm) of the voltage (Vb) to be charged in the boot capacitor to the output voltage of the power supply circuit (Vbm / V1) is subtracted from 1 to obtain the natural logarithm of the inverse of the boot value. A value (T) obtained by multiplying the effective charging time constant of the capacitor is adopted as the pre-charging period.

According to a fourteenth aspect of the present invention, in the load driving apparatus according to the thirteenth aspect, the output voltage (V1) of the power supply circuit is divided by the resistance value (R1) of the boot resistor. The value is larger than the maximum outputtable current (I1M) of the power supply circuit (30).

According to a fifteenth aspect of the present invention, there is provided the load driving device according to any one of the ninth to fourteenth aspects, in which the inverter corresponds to a plurality of phases. A plurality of low arm side switching elements (41) and a plurality of high arm side switching elements (42) are connected in series, and there are a plurality of boot capacitors (32) corresponding to the plurality of phases, which correspond to the plurality of boot capacitors. Pre-charge period (TU, TV, TW)
Is exclusive.

A sixteenth aspect of the present invention is the load driving apparatus according to any one of the ninth to fifteenth aspects, wherein the precharge period and the normal operation period are In between, the low arm side switching element (41) and the high arm side switching element (4
A rest period is provided in which both of 2) are turned off.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram illustrating the configuration of an apparatus for driving a load using inverter control. The present invention can be applied to the structure. Although the AC power supply 1 is shown as a single phase, it may be multi-phase. The diode bridge 2 full-wave rectifies the AC power supply 1 and outputs a DC voltage between its high potential end (denoted by “+” in the figure) and low potential end (denoted by “−” in the figure).

Intelligent power circuits 5U, 5V and 5W are connected in parallel between the high potential end and the low potential end of the diode bridge 2. Intelligent power circuits 5U, 5V, 5W are output lines 7U, 7 respectively.
V, 7 W, which are connected to a three-phase load 6. Of course, the number of intelligent power circuits can be appropriately increased or decreased according to the number of phases of the load 6. Here, the intelligent power circuits 5U, 5V, and 5W operate corresponding to the U phase, V phase, and W phase, respectively.

In FIG. 1, the intelligent power circuit 5U
However, the intelligent power circuits 5V and 5W have the same structure. Intelligent power circuit 5U, 5
V and 5W may be modularized as an intelligent power device, for example.

The intelligent power circuit 5U includes an inverter 4U and an inverter control circuit 3U for controlling the operation of the inverter 4U. The inverter 4U includes an insulated gate bipolar transistor (which is simply referred to as a "transistor" in the present invention) 41 which is a low arm side switching element, and an N which is a high arm side switching element.
A PN transistor 42 and freewheel diodes 43 and 44 are provided. The collector of the transistor 41 and the cathode of the freewheel diode 43 are the emitter of the transistor 41 and the freewheel diode 4
The anode of the transistor 3 is connected to the collector of the transistor 42 and the cathode of the freewheel diode 44, and the emitter of the transistor 42 is connected to the anode of the freewheel diode 44. The transistors 41 and 42 are connected in series with each other between the high potential end and the low potential end of the diode bridge 2 via the output line 7U. More specifically, the collector of the transistor 41 and the emitter of the transistor 42 are commonly connected to the output line 7U. In the transistors 41 and 42, current flows from the collector side to the emitter side.

The inverter control circuit 3U includes a control power supply circuit 30 and a smoothing capacitor 31 connected in parallel with the control power supply circuit 30.
Are supplied with a DC voltage V1 and a DC current I1. The control power supply circuit 30 has a high potential end (denoted by “+” in the figure) and a low potential end (denoted by “−” in the figure). Although illustration is omitted, the high-potential end and the low-potential end of the control power supply circuit 30 are also connected to the inverter control circuit provided corresponding to the inverter control circuit 3U in the intelligent power circuits 5V and 5W.

The inverter control circuit 3U comprises a high arm control circuit 33 and a boot capacitor 32 for supplying the operating power source for the high arm control circuit 33. The high arm control circuit 33 gives a control signal to the gate of the transistor 42. The low-arm control circuit 34 that gives a control signal to the gate of the transistor 41 is also included in the inverter control circuit 3U. However, the operating power source is omitted because it has little relation to the present invention.

The boot capacitor 32 has one end connected to the output line 7U, and the other end connected to the high potential end of the control power supply circuit 30 through the series connection of the boot resistor 36 and the diode 35. The anode and cathode of the diode 35 are connected to the high potential end side of the control power supply circuit 30 and the boot capacitor 32 side, respectively. Although the anode of the diode 35 is connected to the high potential terminal of the control power supply circuit 30 via the boot resistor 36 in FIG. 1, the order of the series connection of the boot resistor 36 and the diode 35 may be changed. good.

In such a configuration, the transistor 4
The emitter of 2 is connected to the output line 7U.
A diode bridge 2 is connected to U by a transistor 42.
Since the voltage at the high potential end of
As a control signal to be applied to the base of, the voltage higher than the voltage at the high potential end of the diode bridge 2 must be applied. Therefore, the output line 7U is connected to the high arm control circuit 33.
The boot capacitor 32 is charged by using the control power supply circuit 30 in order to supply a high potential with respect to the potential.

In order to prevent the DC voltage V1 output from the control power supply circuit 30 from being lowered when the boot capacitor 32 is charged, it is possible to increase the resistance value R1 of the boot resistor 36. However, in that case, the boot capacitor 32
The time constant for charging is increased, and it takes a long time to charge the boot capacitor 32 with a voltage required for normal operation. Further, when the capacitance value C1 of the smoothing capacitor 31 is increased, there is a problem that the fluctuation of the DC voltage V1 is increased and the size of the smoothing capacitor 31 is increased.

In the present invention, the transistors 41 and 42 in the inverter 4U perform switching for driving the load 6, for example, rotation thereof when the load is a motor (referred to as "normal switching" in the present invention). The pre-charge period is provided before the normal operation period to be performed. In the precharge period, the transistor 42 is always turned off, and the boot capacitor 32 is charged by the control power supply circuit 30 via the transistor 41.

The transistor 42 is the high arm control circuit 3
3 will remain off unless it works properly. on the other hand,
Since the emitter of the transistor 41 is connected to the low potential end of the diode bridge 2, it is not necessary to use a boot capacitor for operating the low arm control circuit 34. Therefore, during the precharge period, the switching of the transistor 41 can be controlled arbitrarily from the initial stage. That is, during the pre-charge period, the above-mentioned charge can be performed while the high arm control circuit 33 does not operate normally.

Since the boot capacitor is charged in the pre-charge period before the normal operation period, it is easy to operate the inverter control circuit 3U normally from the beginning of the normal operation period. Further, during the precharge period, the transistor 42 is always off, so that the boot capacitor 32 can be charged without the load 6 operating.

FIG. 2 is a graph illustrating switching of the transistors 41 and 42. In the precharge period,
The transistor 42 remains off, while the transistor 41 repeats on / off. A current is supplied from the control power supply circuit 30 to the boot capacitor 32 during the _ON period T _ON when the transistor 41 is turned on. Therefore, the boot capacitor 32 can be charged with the current flowing from the control power supply circuit 30 kept low, the control power supply circuit 30 is less likely to be burdened, and the transistor 41 is easily prevented from being destroyed. The point of reducing the load on the control power supply circuit 30 will be described later in detail.

In the normal operation period, normal switching for driving the load 6 is performed. Note that the illustrated pause period between the pre-charge period and the normal operation period may be omitted. However, when the transistor 41 is turned on at the end of the precharge period and the transistor 42 is turned on at the beginning of the normal operation period, a large current flows in the inverter 4U unless a margin is provided between the two periods. It may be destroyed. Therefore, it is desirable to provide a pause period in which both the transistors 41 and 42 are turned off.

In addition, in order to prevent a large current from flowing into the inverter 4U and destroying it, a technique of protecting the inverter 4U when the load 6 is short-circuited may be adopted.
In that case, it is desirable to make the _ON period T _ON longer than the minimum time T _wmin required to detect the short circuit of the load 6.
Even when the boot capacitor 32 is charged with the load 6 short-circuited, the inverter 4U can be protected.

Further, when the boot capacitor 32 is charged while the load 6 is being driven, the inverter 4U should be protected from the overcurrent which may be generated by the line induced electromotive voltage of the load 6. The line induced electromotive voltage is, for example, the output lines 7U and 7W.
Can occur during. When the transistor 41 of the inverter 4U is on, an overcurrent may occur in the transistor 41 via the freewheel diode corresponding to the freewheel diode 43 and provided in the intelligent power circuit 5W. Therefore, load 6
And the inductance L of the output allowable current value I _L of the transistor 41, by introducing a line-to-line induced electromotive voltage V2, it is desirable to satisfy the following equation.

[0037]

[Equation 1]

When the transistor 41 is turned on, the boot capacitor 32 and the boot resistor 36 are connected in series between the high potential end and the low potential end of the control power supply circuit 30. Therefore, the charging of the boot capacitor 32 requires the capacitance value C2 and
The time constant τ ′ is determined by the product R1 · C2 of the boot resistor 36 and the resistance value R1. If the discharge of the boot capacitor 32 when the transistor 41 is off during the precharge period output from the control power supply circuit 30 is ignored, the voltage Vb across the boot capacitor 32 is calculated by the following equation.

[0039]

[Equation 2]

However, T'is the cumulative time from the start of the pre-charging period of the _ON period T _ON , and e is the base of the natural logarithm.

By introducing the minimum value Vbm of the voltage to be charged in the boot capacitor 32, the integrated time T'is calculated by the following equation. However, ln (x) shows the natural logarithm of x.

[0042]

[Equation 3]

When charging the boot capacitor 32, the maximum value of the current that can flow in the boot capacitor 32 is V1 / R1.
Becomes On the other hand, the direct current I output from the control power supply circuit 30
There is a maximum value I1M that is the upper limit in the magnitude of 1. If the maximum value I1M is smaller than V1 / R1, it is necessary to determine the period during which the transistor 42 is turned off in the precharge period. In other words, it is necessary to determine the duty D of the _ON period T _ON of the transistor 42. Otherwise, a large current load is applied to the control power supply circuit 30, a sufficient current may not be obtained from the control power supply circuit 30 in the _ON period T _ON , or the output voltage V1 may decrease. The duty D is calculated by the following formula.

[0044]

[Equation 4]

Therefore, the length T of the precharge period is calculated by the following equation.

[0046]

[Equation 5]

Expressions (2) to (5) can also be expressed as the following expressions.

[0048]

[Equation 6]

That is, the product of the output voltage V1 of the control power supply circuit 30 divided by the resistance value R1 of the boot resistor 36, the resistance value R1 of the boot resistor and the capacitance value C2 of the boot capacitor 32, τ '. (V1 / R1 ) Is divided by the maximum outputtable current I1M of the control power supply circuit 30 to obtain an effective charging time constant τ. Voltage Vb to charge the boot capacitor 32
Of the minimum value Vbm of the control power supply circuit 30 to the output voltage V1 (Vbm / V1) is subtracted from 1 to obtain a value (1-V
bm / V1) is calculated. The reciprocal (1-Vbm / V1)
The length T of the pre-charging period is obtained by multiplying the natural logarithm of ^-1 by the effective charging time constant τ.

If the maximum value I1M of the DC current I1 output from the control power supply circuit 30 is larger than the value (V1 / R1), the control power supply circuit 30 will not be overloaded, and the DC voltage V1 will not drop. Possibility is low. Therefore, the boot capacitor 32 can be appropriately charged without applying the present invention.

For example, the DC voltage V1 output from the control power supply circuit 30 is 15 volts, and the maximum value I of the DC current I1 is I.
Suppose 1 M is 0.1 amps. The resistance value R1 of the boot resistor 36 is 15 ohms, the boot capacitor 3
Assuming that the capacitance value C2 of 2 is 10 microfarads, the duty D = 0.1 from the equation (4). Since the charging time constant τ ′ is 1.5 × 10 ⁻⁴ (second), the charging time constant τ
Is 1.5 milliseconds. When the boot capacitor 32 is charged to 14 volts, the length T of the pre-charging period becomes -ln (1-14 / 15) times the charging time constant τ 4.0.
It will be 6 milliseconds.

The above-described operation of the transistors 41 and 42 in the intelligent power circuit 5U can be adopted in other intelligent power circuits 5V and 5W. However, the boot capacitors 3 provided corresponding to different phases, that is, the intelligent power circuit 5U
2, and correspondingly, intelligent power circuit 5
For the boot capacitors provided at V and 5 W, it is desirable that the precharge period be exclusive.

As described above, the control power supply circuit 30 is connected not only to the intelligent power circuit 5U but also to the intelligent power circuits 5V and 5W. Then, since the charging current of the boot capacitor provided in these is supplied, the DC current I1 output by the control power supply circuit 30 is suppressed, and the decrease of the DC voltage V1 output is easily avoided.

FIG. 3 shows an intelligent power circuit 5U,
It is a graph which illustrates switching of a low arm side switching element and a high arm side switching element in 5V and 5W. The low arm side switching element and the high arm side switching element of the intelligent power circuit 5U correspond to the transistors 41 and 42, respectively.

Intelligent power circuit 5U, 5V,
By exclusively providing the pre-charge periods TU, TV, and TW for 5 W, the boot capacitors provided in each are charged before the normal operation period while avoiding a decrease in the DC voltage V1. Therefore, it is easy to operate the inverter control circuit 3U normally from the beginning of the normal operation period.

The pre-charge period TV, TW can be understood as a rest period for the intelligent power circuit 5U, and the pre-charge period TW is understood as a rest period for the intelligent power circuit 5V. You can also

[0057]

According to the method for charging the boot capacitor according to claim 1 and the device for driving the load according to claim 9 of the present invention, the boot capacitor is charged in the pre-charging period before the normal operation period. Therefore, it is easy to normally operate the inverter control circuit from the beginning of the normal operation period. Further, since the high-arm side switching element is always turned off during the precharge period, the boot capacitor can be charged without the load of the inverter operating.

According to the second aspect of the present invention, the boot capacitor charging method and the load driving apparatus according to the tenth aspect of the present invention charge the boot capacitor while suppressing the current flowing from the power circuit to a low level. The load is hard to apply and damage to the switching element on the low arm side is easy to prevent.

According to the third aspect of the present invention, the method of charging a boot capacitor and the eleventh aspect of the load driving apparatus according to the present invention, even when the boot capacitor is charged when the load of the inverter is short-circuited, Can be protected.

According to the fourth aspect of the present invention, the method of charging a boot capacitor and the load driving apparatus according to the twelfth aspect of the invention, when the load is restarted immediately after the drive is stopped, the inverter is driven from the regenerative current flowing from the load. Can be protected.

The method of charging the boot capacitor according to claims 5 and 6 of the present invention, claim 13 and claim 1
According to the drive device of the load applied to 4, the current flowing from the power supply circuit is suppressed to be low, and the boot capacitor is charged.
It is hard to overload the power circuit.

According to the boot capacitor charging method of the seventh aspect and the load driving device of the fifteenth aspect of the present invention, the output current from the power supply circuit is suppressed, and the decrease of the output voltage is easily avoided. .

According to the boot capacitor charging method of the eighth aspect and the load driving device of the sixteenth aspect of the present invention, at the boundary between the pre-charging period and the normal operation period, the low-arm side switching element and the high arm are provided. It prevents any of the side switching elements from turning on. This avoids the possibility that a large amount of current will flow through the inverter and destroy it.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration to which the present invention can be applied and which is used for operating a load under inverter control.

FIG. 2 is a graph showing charging of a boot capacitor according to an embodiment of the present invention.

FIG. 3 is a graph showing charging of a boot capacitor according to an embodiment of the present invention.

[Explanation of symbols]

3U inverter control circuit 4U inverter 6 load 30 Control power circuit 32 boot capacitor 33 High Arm Control Circuit 36 Boot resistor 41, 42 insulated gate transistor TU, TV, TW Pre-charging period

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masanobu Tomoe             2 of 1000 Otani, Okamoto-cho, Kusatsu-shi, Shiga             Daikin Air Conditioning Technology Laboratory Co., Ltd. F-term (reference) 5H007 AA06 CA01 CB05 DB03 DB09

Claims (16)

[Claims] 1. A low arm side switching element (41)
A power supply circuit (30) that includes a boot capacitor (32) that is connected in series to the high arm control circuit (33) that controls the operation of the high arm side switching element (42) provided in the inverter (4U). In the pre-charge period before the normal operation period in which the low arm side switching element and the high arm side switching element perform normal switching in the inverter, the high arm side switching element is always turned off. Then, the boot capacitor is charged by the power supply circuit via the low arm side switching element. 2. The method of charging a boot capacitor according to claim 1, wherein the low-arm side switching element is repeatedly turned on and off during the pre-charge period. 3. The low arm side switching element is turned on for a period _{equal to} or _longer than a minimum detection time (T _wmin ) necessary for protecting the inverter when the load (6) of the inverter is short-circuited. How to charge the boot capacitor. 4. The inverter is a product of an inductance (L) of a load (6) of the inverter and an allowable output current value (I _L ) of the low arm side switching element during a period in which the low arm side switching element is turned on. The boot capacitor charging method according to claim 2, wherein the boot capacitor is less than a value obtained by dividing the line induced electromotive voltage (V2) of the load. 5. A boot resistor (36) is connected in series to the boot capacitor (32) between the power circuit and the output voltage (V1) of the power circuit and a resistance value (R1) of the boot resistor. The value obtained by dividing the product of the current value divided by, the resistance value of the boot resistor, and the capacitance value (C2) of the boot capacitor by the maximum outputtable current (I1M) of the power supply circuit (30) is the charging period. And the ratio (Vbm / V1) of the minimum value (Vbm) of the voltage (Vb) to be charged to the boot capacitor with respect to the output voltage of the power supply circuit. A value (T) obtained by multiplying the natural logarithm of the reciprocal of the value subtracted from 1 by the effective charging time constant of the boot capacitor is adopted as the pre-charging period,
The charging method for a boot capacitor according to claim 2. 6. The value obtained by dividing the output voltage (V1) of the power supply circuit by the resistance value (R1) of the boot resistor is larger than the maximum outputtable current (I1M) of the power supply circuit (30). 5. The method for charging the boot capacitor described in 5. 7. The inverter comprises a plurality of series connections of the low arm side switching element (41) and the high arm side switching element (42) corresponding to a plurality of phases, and the boot corresponding to the plurality of phases. Capacitor (32)
7. The charging of the boot capacitor according to any one of claims 1 to 6, wherein there are a plurality of, and the pre-charge period (TU, TV, TW) corresponding to the plurality of boot capacitors is exclusive. Method. 8. The idle period in which both the low-arm side switching element (41) and the high-arm side switching element (42) are turned off is provided between the pre-charge period and the normal operation period. 1 to claim 7
The method for charging a boot capacitor according to any one of 1. 9. An inverter (4U) having a low arm side switching element (41) and a high arm side switching element (42) connected in series to each other, to which a load (6) is connected, and a high arm side switching element. An inverter control circuit (3U) having a high arm control circuit (33) for controlling the operation and a boot capacitor (32) for supplying the operating power of the high arm control circuit, and a power supply circuit (3 for charging the boot capacitor (32)
0), the high arm side switching element is always turned off in a precharge period before a normal operation period in which the low arm side switching element and the high arm side switching element perform normal switching in the inverter, A drive device for a load, wherein the boot capacitor is charged by the power supply circuit via a low-arm side switching element. 10. The load driving device according to claim 9, wherein the low-arm side switching element is repeatedly turned on and off during the pre-charge period. 11. A minimum detection time (T _wmin ) necessary for protecting the inverter when the load (6) is short-circuited during a period when the low-arm side switching element is turned on.
The load driving device according to claim 10, which is the above. 12. The inverter is a product of an inductance (L) of a load (6) of the inverter and an allowable output current value (I _L ) of the low arm side switching element during a period when the low arm side switching element is turned on. The drive device for a load according to any one of claims 10 and 11, which is less than a value obtained by dividing the line induced electromotive voltage (V2) of the load. 13. A boot resistor (36) is connected in series to the boot capacitor (32) between the power supply circuit and an output voltage (V1) of the power supply circuit and a resistance value (R1) of the boot resistor. The value obtained by dividing the product of the current value divided by, the resistance value of the boot resistor, and the capacitance value (C2) of the boot capacitor by the maximum outputtable current (I1M) of the power supply circuit (30) is the charging period. And the ratio (Vbm / V1) of the minimum value (Vbm) of the voltage (Vb) to be charged to the boot capacitor with respect to the output voltage of the power supply circuit. A value (T) obtained by multiplying the natural logarithm of the reciprocal of the value subtracted from 1 by the effective charging time constant of the boot capacitor is adopted as the pre-charging period,
The drive device for a load according to any one of claims 10 to 12. 14. A value obtained by dividing an output voltage (V1) of the power supply circuit by a resistance value (R1) of the boot resistor is larger than a maximum outputtable current (I1M) of the power supply circuit (30). 13. The load driving device according to item 13. 15. The inverter comprises a plurality of serial connections of the low arm side switching element (41) and the high arm side switching element (42) corresponding to a plurality of phases, and the boot corresponding to the plurality of phases. Capacitor (32)
15. The load driving device according to any one of claims 9 to 14, wherein there are a plurality of, and the pre-charge period (TU, TV, TW) corresponding to the plurality of boot capacitors is exclusive. . 16. The low-arm side switching element (41) between the pre-charge period and the normal operation period.
16. The load driving device according to claim 9, further comprising a rest period in which both the high-arm side switching element (42) is turned off.