JP2007143229A - Inverter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce power loss of an inverter having a bidirectional switching element. <P>SOLUTION: A dead time management section 105 performs adaptive control of the length of dead time when a pair of semiconductor switching elements are tuned off simultaneously for every phase based on the direction of currents I<SB>U</SB>, I<SB>V</SB>and I<SB>W</SB>and neutral voltages V<SB>MU</SB>, V<SB>MV</SB>and V<SB>MW</SB>. When current I<SB>U</SB>of U phase is supplied from a semiconductor switching element SWUH to a load 10, gate voltage is operated at first through a gate driver 106 such that the element SWUH is turned off and the neutral voltage V<SB>MU</SB>is measured at the same time. If the neutral voltage V<SB>MU</SB>starts to drop even during the period of dead time, it can be considered that change to off state of the element SWUH has completed, and the gate voltage is operated such that a switching element SWUL on the low potential side is turned on at that moment. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to an inverter configuration, and more particularly to a means for reducing power loss.
The present invention is very useful for reducing power loss in an inverter and miniaturizing the configuration of the main circuit of the inverter.

  For example, in a bidirectional switching element formed of a unipolar semiconductor or the like, a current can flow in both positive and negative directions in the on state. In such a semiconductor switching element, there is no constant relatively large on voltage as in the case of a junction type element, and the voltage drop during conduction (on voltage) is a relatively small on resistance and current. Determined by product.

On the other hand, even in the case of flywheel diodes even if the elements are made of the same semiconductor material, these are generally Schottky junction type, PN junction type, or PIN junction type diodes, and therefore flow through them. The relationship between current and on-voltage is approximately exponential. This exponential characteristic can be generally regarded as having a constant on voltage regardless of the magnitude of the current as a first order approximation.
On the other hand, in the case of the bidirectional semiconductor switching element as described above, since the element is basically of a resistance modulation type, the switching element has a constant value as in the above junction type element. Therefore, the on-voltage drop (on voltage) is determined by the product of the on-resistance and the current, as described above.

For this reason, a flywheel having a high regenerative current by increasing the proportion of current flowing from the load toward the DC power source (hereinafter referred to as “regenerative current”) to the bidirectional switching element. The power loss can be greatly reduced as compared to the case where only the diode flows.
As described above, an inverter composed of bidirectional switching elements has a feature that power loss due to regenerative current is basically small.
Transistor technology, March 2004 issue

  However, during the dead time period provided to prevent the occurrence of the shoot-through current due to the power supply short-circuit state, the switching elements on both the high potential side and the low potential side are simultaneously in the off state. The regenerative current cannot be shunted to the switching element side. That is, during the dead time period, the regenerative current flows exclusively through the flywheel diode having a high on voltage, and at this time, the problem of on loss due to the regenerative current also appears.

In addition, when the above regenerative current is applied to the flywheel diode, the reverse current (that is, the known reverse current) is applied for a short time after the voltage applied to the flywheel diode is reversed from the forward direction to the reverse direction. Direction recovery current) flows. Since the reverse recovery current flowing through the flywheel diode temporarily induces a power supply short-circuit state through the other semiconductor switching element in the pair, this causes a large switching loss.
At this time, the reverse recovery current increases as the regenerative current flowing through the flywheel diode increases. Therefore, even if the dead time is short, if the regenerative current flowing through the flywheel diode is large, the reverse recovery current also increases accordingly, which leads to an increase in power loss that cannot be ignored.

  Recently, high-temperature operability for inverters has been strongly demanded. For example, when a semiconductor switching element using a GaN crystal or a diode using a GaN crystal is used for the main circuit of the inverter, An era in which an inverter that can operate in a high-temperature environment that greatly exceeds the current temperature of about 120 ° C. can be assumed. However, according to such a high-temperature-oriented circuit configuration, the on-voltage of the flywheel diode becomes significantly higher than the conventional circuit configuration in which a junction diode made of, for example, Si is used for the flywheel diode. . For this reason, the above-mentioned on-loss problem associated with regenerative current may develop into a more serious problem in the future.

The present invention has been made to solve the above-described problems, and an object thereof is to further reduce power loss in an inverter having a bidirectional semiconductor switching element.
Another object of the present invention is to reduce the size and cost of the inverter.

In order to solve the above problems, the following means are effective.
That is, the first means of the present invention has a bidirectional semiconductor switching element capable of flowing a current bidirectionally in a controlled current path to be controlled for opening and closing, and the controlled current path In the inverter provided with a pair of semiconductor switching elements connected in series for each phase, a flywheel diode connected in parallel to each semiconductor switching element, and the pair of semiconductor switching elements A midpoint voltage measuring means for measuring the voltage at the connection point for each phase, a current detecting means for detecting the current direction of each phase, and a dead time when both the pair of semiconductor switching elements are simultaneously turned off. A dead time management means for adaptively controlling the length for each phase based on the direction of the current and the voltage described above is provided. The amount of displacement in which the increase or decrease in the voltage from when the OFF command signal for switching one pair of the semiconductor switching elements from the ON state to the OFF state is output exceeds a predetermined threshold (> 0). At the time shown, it is to output an ON command signal for switching the pair of other semiconductor switching elements from the OFF state to the ON state.

However, any number of the above phases may be provided. The present invention can be applied to a single-phase or multi-phase inverter having any number of phases. Further, the current detection means may be any means that can detect the direction of the current of each phase, and does not necessarily need to be a means for accurately obtaining the current value.
Further, the DC voltage of the DC power source to be used may be arbitrary. For example, an inverter with a relatively high power supply voltage of about several hundred volts or more is used according to the present invention by using a semiconductor switching element having a high breakdown voltage and a low on-resistance constructed using a wide band gap semiconductor such as GaN. It is also possible to produce

Also, the second means of the present invention is the dead time management means of the first means, when the displacement amount reaches a value not less than 10% and not more than 20% of the DC power supply voltage used. A first voltage increase / decrease determination means for determining that the above-described ON command signal should be output is provided.
However, this threshold value can be optimized according to the characteristics of the semiconductor switching element to be used, the characteristics of the load, the power supply voltage, the number of phases of the inverter, or the like.

According to a third means of the present invention, in the dead time management means of the first or second means, the voltage drop amount (> 0) when the semiconductor switching element is conductive and the on-voltage of the flywheel diode It is to provide a second voltage increase / decrease determining means for determining that the ON command signal should be output when the displacement amount reaches the average value.
However, the above average value does not necessarily have to be obtained accurately, and may include an error of about ± 30% with respect to the true value. This threshold value can be optimized according to the characteristics of the semiconductor switching element to be used, the characteristics of the load, the power supply voltage, the number of phases of the inverter, or the like.

According to a fourth means of the present invention, in the dead time management means of any one of the first to third means, a period measuring means for defining an upper limit value of the dead time length is provided. It is.
Such period measuring means can be configured using, for example, a computer timer or a computer dynamic step counter.
By the above means of the present invention, the above-mentioned problem can be effectively or rationally solved.

The effects obtained by the above-described means of the present invention are as follows.
That is, according to the first means of the present invention, based on the adaptive control of the above dead time management means, even within the dead time period, in the conventional configuration, the regenerative regenerative power flowed exclusively through the flywheel diode. At least a part of the current can be passed through the semiconductor switching element. In the best case, all of the regenerative current can be passed through the semiconductor switching element even within the dead time period.

  In these cases, instead of reducing the amount of regenerative current flowing through the flywheel diode, the reduced regenerative current flows through the semiconductor switching element, increasing the on-loss due to the regenerative current of the semiconductor switching element. However, the increase in the on loss generated in the semiconductor switching element is significantly smaller than the reduction in the on loss generated in the flywheel diode. As a result, the loss in the inverter can be greatly reduced. In addition, by setting an appropriate dead time, it is possible to effectively prevent the occurrence of a shoot-through current due to a power supply short-circuit state at the same time.

Further, according to the first means of the present invention, the regenerative current flowing through the flywheel diode is greatly reduced, so that the reverse recovery current that flows when the applied voltage to the flywheel diode is reversed from the forward direction to the reverse direction. Can also be greatly suppressed. For this reason, according to the 1st means of this invention, the switching loss resulting from the reverse direction recovery current which flows through a flywheel diode can also be reduced reliably.
In addition, according to the first means of the present invention, the flywheel diode itself can be reduced in size by greatly reducing the current flowing through the flywheel diode, thereby promoting the downsizing and cost reduction of the device. Can do.

  In addition, if the above-mentioned dead time is managed more strictly, it is possible to eliminate the current flowing through the flywheel diode or to omit the flywheel diode itself. However, according to the above configuration, since each flywheel diode is provided for each semiconductor switching element, such strict management is not necessarily required. For this reason, according to the above configuration, compared to the case where the flywheel diode itself is omitted, the inverter operating environment conditions are expanded, or the inverter design related to the voltage threshold value used for the determination of the dead time length, etc. Can be further facilitated.

When managing the dead time, when the OFF state of both the pair of semiconductor switching elements is just realized, an ON command signal is sent to the semiconductor switching element that has been in the OFF state so far. However, according to the second or third means of the present invention, each of the corresponding threshold values is optimized so that the ON command signal is output at such a desirable timing. Can be set.
Therefore, according to the second or third means of the present invention, it is possible to optimally and surely realize an inverter with less power loss and higher efficiency than conventional. Further, by optimizing the above threshold value, the burden on the semiconductor switching element can be reduced.

  Further, according to the fourth means of the present invention, it is possible to reliably complete the dead time even when there is a measurement error or erroneous detection due to noise or the like.

Hereinafter, the present invention will be described based on specific examples.
However, the embodiments of the present invention are not limited to the following examples.

FIG. 1 shows a circuit diagram of the inverter 100 according to the first embodiment, and FIG. 2 shows a control block diagram of the inverter 100. The six semiconductor switching elements SWUH, SWVH, SWWH, SWUL, SWVL, SWWL constituting the main circuit 101 of the inverter 100 are all GaN-HEMT (High Electron Mobility Transistor), that is, a GaN-based high electron mobility transistor type. A pair of semiconductor switching elements each having a controlled current path connected in series for each phase (U phase, V phase, W phase) of the three-phase motor 10. It is equipped with. In addition, flywheel diodes DUH, DVH, DWH, DUL, DVL, DWL are connected in parallel to the semiconductor switching elements SWUH, SWVH, SWWH, SWUL, SWVL, SWWL, respectively.
The connection point of each pair of semiconductor switching elements in each phase is hereinafter referred to as a midpoint, and the voltage at each midpoint of each phase (U phase, V phase, W phase) is hereinafter referred to as a midpoint voltage. _They are called V _MU , midpoint voltage V _MV , and midpoint voltage V _MW . The output of the inverter 100, that is, the currents I _U , I _V , and I _W of each phase flowing through the three-phase motor 10 can be controlled by manipulating the timing for switching the level of the midpoint voltage.

  A low-pass filter may be provided between the inverter 100 and the load (three-phase motor 10). Here, the frequency of the rectangular wave in the chopper control of the PWM circuit of the inverter 100 is assumed to be about several kHz to several tens of kHz, and the frequency of the alternating current to be supplied to the load is assumed to be about 10 to 240 Hz. is doing.

Each phase midpoint voltage measurement unit 102 measures the above midpoint voltages V _MU , V _MV , and V _MW as needed. Each phase current measurement unit 103 measures currents I _U , I _V , and I _W of each phase as needed. Each phase midpoint voltage high / low command signal generation unit 104 is constituted by a PWM circuit, and outputs the above midpoint voltage command value for each phase. Hereinafter, this command value is referred to as a high / low command signal S.

The dead time management unit 105 corresponds to the dead time management means according to claim 1 of the present invention. The dead time management unit 105 determines the length of the dead time during which both the pair of semiconductor switching elements are simultaneously turned off for each phase. The adaptive control is performed based on the directions of the currents I _U , I _V and I _W and the midpoint voltages V _MU , V _MV and V _MW . This part may be constituted by hardware (electric circuit) or software that operates on a computer.
Further, the gate driver 106 controls each gate of each of the semiconductor switching elements to be in an ON state or an OFF state in accordance with a command (predetermined command signal) issued by the dead time management unit 105.

  Hereinafter, the logic of the gate control of the semiconductor switching element performed in order to flow as much of the regenerative current as possible within the dead time period to the semiconductor switching element side in the inverter in the inverter 100 will be described with reference to FIG. This gate control is divided into four cases (cases 1 to 4 in Table 1) according to the operation direction of each midpoint voltage given by the above-described high and low command signal S and the direction of the load current of each phase (positive and negative). Each can be executed separately.

In Table 1, the current in the direction from the inverter 100 toward the load (three-phase motor 10) is a positive current. Since the following description regarding the logic of gate control is common to each phase, the following description will be made assuming that the first phase in FIG. 3 is the U phase.

(Case 1)
Midpoint voltage operation direction: High ⇒ Low
Load current: positive The operation (gate control) in this case is an operation to switch the semiconductor switching element SWUH on the high potential side to the ON state so that the semiconductor switching element SWUL on the low potential side is turned on. .

Here, first, the gate voltage is operated via the gate driver 106 (: high potential SW off operation a1) so that the high potential side semiconductor switching element SWUH is turned off, and at the same time, the midpoint voltage _VMU is Measure (: midpoint voltage drop determination b1). If reduction of the so-called midpoint even within the dead time period the voltage V _MU starts, since the change of the semiconductor switching devices SWUH the OFF state of the high potential side it can be regarded as complete, at which time The gate voltage is manipulated through the gate driver 106 so that the low potential side semiconductor switching element SWUL is turned on (low potential side SW on operation e1).

At this time, it is appropriate to set the drop of the midpoint voltage _VMU to about 10 to 20% of the power supply voltage. By doing this, it is possible to reduce the time width during which both the high potential side and low potential side semiconductor switching elements (SWUH, SWUL) are turned off simultaneously, and the low potential side semiconductor switching element SWUL is conductive. In this case, the load current I _U is supplied to the load (three-phase motor 10) through the low potential side semiconductor switching element SWUL.

  And by this processing system, generation | occurrence | production of the on loss by the on voltage of a flywheel diode can be suppressed, preventing generation | occurrence | production of the shoot through current resulting from a power supply short circuit state. In addition, since the regenerative current passing through the flywheel diode is greatly reduced, the reverse recovery current that flows when the applied voltage of the diode is reversed from the forward direction to the reverse direction is greatly reduced. The occurrence of the state is prevented, and the switching loss corresponding to that is suppressed.

  Note that dead time period measurements c1, c2, c3, and c4 in FIG. 3 constitute the period measurement means of the present invention, and even when there is a measurement error or erroneous detection due to noise or the like, this period measurement is performed. The dead time can be surely completed by the action. OR determinations d1, d2, d3, and d4 in FIG. 3 are timing determinations from either the midpoint voltage determination processing (b1, b2, b3, b4) or the dead time period measurement (c1, c2, c3, c4). It consists of logical operation processing or logical sum circuit that adopts the result. However, when one is adopted, the other is ignored until the next start of the program or does not operate until the next start of the program.

(Case 2)
Midpoint voltage operation direction: High ⇒ Low
Load current: negative The operation (gate control) in this case is also an operation for switching the semiconductor switching element SWUH on the high potential side to the ON state so that the semiconductor switching element SWUL on the low potential side is turned on. .

Here, first semiconductor switching devices SWUH high potential side operates the gate voltage so that the OFF state (: high potential side SW off operation a2), to measure the midpoint voltage V _MU simultaneously (: midpoint voltage rise Decision b2). In this case, since the load current is negative, a regenerative current flows through the semiconductor switching element SWUH on the high potential side. Since the semiconductor switching devices SWUH the high potential side from the state regenerative manner was flowing in the OFF state, which is the midpoint voltage V _MU from the time it is in the OFF state starts to rise. Therefore, it can be regarded as the change to the OFF state of the high potential side of the semiconductor switching devices SWUH is completed if elevated even midpoint voltage V _MU be within the period of the so-called dead time Hajimare. When the rise is detected, the gate voltage is manipulated so that the low-potential side semiconductor switching element SWUL is turned on (low-potential side SW-on operation e2).

As a guideline the rise of the middle point voltage V _MU at this time the voltage drop during conduction of the semiconductor switching devices SWUH (> 0) and appropriate to set the average value of about between on voltage of the flywheel diode DUH It is. By doing so, the semiconductor switching element SWUL on the low potential side can be conducted in a short time after the semiconductor switching element SWUH on the high potential side is turned off. As a result, a regenerative current (negative load) Current) can continue to flow smoothly through the semiconductor switching element SWUL on the low potential side.

  And by this processing system, generation | occurrence | production of the on loss by the on voltage of a flywheel diode can be suppressed, preventing generation | occurrence | production of the shoot through current resulting from a power supply short circuit state. In addition, since the regenerative current passing through the flywheel diode is greatly reduced, the reverse recovery current that flows when the applied voltage of the diode is reversed from the forward direction to the reverse direction is also greatly reduced. The occurrence of the state is prevented, and the switching loss corresponding to that is suppressed.

(Case 3)
Midpoint voltage operation direction: Low ⇒ High
Load current: positive In this case, the operation (gate control) is an operation for switching the semiconductor switching element SWUL on the low potential side to the ON state so that the semiconductor switching element SWUH on the high potential side is turned on. .

Here, first low-potential-side semiconductor switching element SWUL operates the gate voltage so that the OFF state (: low potential side SW off operation a3), to measure the midpoint voltage V _MU simultaneously (: midpoint voltage falling Determination b3). In this case, since the load current I _U is positive, a regenerative current (I _U ) flows through the semiconductor switching element SWUL on the low potential side. Since the state where the regenerative manner was flowing in the semiconductor switching element SWUL OFF state of the low potential side, the midpoint voltage V _MU is lowered. Therefore, can be regarded as the change to the OFF state of the low potential side of the semiconductor switching element SWUL is completed if a so-called dead time of the midpoint voltage V _MU even within a period of lowered Hajimare. Therefore, when the falling began the midpoint voltage V _MU, as semiconductor switching devices SWUH the high potential side is turned ON to operate the gate voltage via a gate driver 106 (: high potential side SW ON Operation e3).

As a guideline for the range of decrease of the midpoint voltage V _MU, it is appropriate to set the average value of about between on voltage of the semiconductor switching element voltage drop during conduction of SWUL (> 0) and the flywheel diode DUL. Thereby, the low-potential side semiconductor switching element SWUL conducts the high potential side of the semiconductor switching devices SWUH within a short time from when the OFF state, the load current I _U, through the semiconductor switching devices SWUH the high potential side Smoothly supplied to the load.

  And by this processing system, generation | occurrence | production of the on loss by the on voltage of a flywheel diode can be suppressed, preventing generation | occurrence | production of the shoot through current resulting from a power supply short circuit state. In addition, since the regenerative current passing through the flywheel diode is greatly reduced, the reverse recovery current that flows when the applied voltage of the diode is reversed from the forward direction to the reverse direction is also greatly reduced. The occurrence of the state is prevented, and the switching loss corresponding to that is suppressed.

(Case 4)
Midpoint voltage operation direction: Low ⇒ High
Load current: negative The operation (gate control) in this case is also an operation for switching the semiconductor switching element SWUL on the low potential side so that the semiconductor switching element SWUH on the high potential side is turned on. .

Here, first low-potential-side semiconductor switching element SWUL operates the gate voltage so that the OFF state (: low potential side SW off operation a4), to measure a midpoint voltage V _MU simultaneously (: midpoint voltage rise Determination b4). Since it can be regarded as a change to the low potential side of the semiconductor switching element SWUL OFF state is completed if rises the midpoint voltage V _MU be within the period of the so-called dead time starts, at that time, a high potential The gate voltage is manipulated via the gate driver 106 so that the semiconductor switching element SWUH on the side is turned on (high potential side SW on operation e4).

As a guideline for the rise of the midpoint voltage _VMU , it is appropriate to set it to about 10 to 20% of the power supply voltage. Thereby, the low-potential side semiconductor switching element SWUL is rendered conductive semiconductor switching device SWUH of the high-potential-side in a short time from when the OFF state, the regenerative amperometric I _U semiconductor switching element having a high potential side SWUH It can continue to flow smoothly through.

  And by this processing system, generation | occurrence | production of the on loss by the on voltage of a flywheel diode can be suppressed, preventing generation | occurrence | production of the shoot through current resulting from a power supply short circuit state. In addition, since the regenerative current passing through the flywheel diode is greatly reduced, the reverse recovery current that flows when the applied voltage of the diode is reversed from the forward direction to the reverse direction is also greatly reduced. The occurrence of the state is prevented, and the switching loss corresponding to that is suppressed.

FIG. 4 illustrates a control procedure for concretely executing the above gate control logic (gate operation). Since the above description regarding the logic of gate control is common to each phase, the following description will be made assuming that the first phase in FIG. 3 is the U phase.
The program 200 in FIG. 4 is for executing processing for the first phase of the dead time management unit 105 in FIG. Here, the above-described high / low command signal S is defined by the following 2-bit signal.
(High / Low command signal S)
S = 00: High ⇒ Low (The SWUH is in the ON state.
Operation command to switch SWUL to ON state)
S = 10: Low ⇒ High (If SWUL was in the ON state,
Operation command to switch SWUH to ON state)

The program 200 is activated from the above-described midpoint voltage high / low command signal generation unit 104 at the time when these switching operations become necessary. At that time, first, in the first step 210, the current current I _U in the U phase is input from each phase current measuring unit 103. Next, in step 220, the direction of the current I _U is determined. If I _U <0, the process proceeds to step 225, and if not, the process proceeds to step 230.

In step 225, a logical sum of a 2-bit mask pattern mp for logical sum operation defined as follows and the above high / low command signal S is calculated corresponding to each bit, and the result is stored in a variable K. To do. This variable K is a 2-bit variable used as one of the work areas of the program 200.
(Mask pattern)
mp: 01
As a result, as shown in Table 1, the variable K stores the following contents for each of the cases 1 to 4 described above. And the case division part 1050 of FIG. 3 is realizable by the above process (steps 210-225).
(1) Case 1: K = 0
(2) Case 2: K = 1
(3) Case 3: K = 2
(4) Case 4: K = 3

In step 230, enter the midpoint voltage V _MU each phase midpoint voltage measuring unit 102, the next step 235, saves the value to the variable V _0. In step 240, it reads the current time t from the timer saves that value in a variable T _0. These saving processes (steps 230 to 240) are for storing the initial state at the start of the dead time period. By these saving processes, “initial state saving” i1, i2 in FIG. , I3, i4 can be realized simultaneously.

Next, in step 245, command AU (K) is executed in accordance with the contents shown in Table 2 below. This command AU (K) (0 ≦ K ≦ 3) is stored in the form of an array in a predetermined storage area, and each of the commands AU (K) (0 ≦ K ≦ 3) indicating each predetermined process corresponding to the variable K described above. Each command code (stored code) is held. Thereby, for example, when K = 0, the command code AU (0) is selected, and the operation of turning off the semiconductor switching element SWUH is executed via the gate driver 106.
This process corresponds to each control process of “OFF operation” a1, a2, a3, a4 in FIG.

Next, in step 250, the midpoint voltage V _MU is input from each phase midpoint voltage measurement unit 102. In step 255, determination process 1 shown in the following equation (1) is performed. If this relationship is established, the process proceeds to step 265, and if not, the process proceeds to step 260.
(Judgment process 1)
| V _MU −V ₀ |> D (K) (1)
Here, the threshold value D (K) is defined as follows in the form of an array in a predetermined storage area.
(Definition of array D (K))
D (0) = α (α is a value of 15% of the power supply voltage)
D (1) = β (β is a voltage drop amount (> 0) when SWUH is conducted)
(Average value with DUH on voltage)
D (2) = β
D (3) = α
This process (steps 250 to 255) corresponds to determination processes b1, b2, b3, and b4 related to the midpoint voltage in FIG. In other words, the first voltage increase / decrease determination unit and the second voltage increase / decrease determination unit of the present invention are simultaneously realized by step 255 according to such an array definition.

Next, in step 260, the determination process 2 shown in the following equation (2) is performed. If this relationship is established, the process proceeds to step 265, and if not, the process proceeds to step 250.
(Judgment process 2)
t−T ₀ > ΔT (2)
Here, ΔT is a threshold value that defines an upper limit value of the length of the dead time, and may be about 3 μm to 5 μsec, for example. Further, for example, each case may be individually defined in the same manner as the threshold value D (K) described above.
The dead time period measurement c1, c2, c3, c4 in FIG. 3 corresponding to the period measurement means of the present invention is composed of the above-mentioned steps 240 and 260, and defines the upper limit value of the dead time length. The OR determinations d1, d2, d3, d4 in FIG. 3 are realized by a combination of step 255 and step 260.

Finally, in step 265, command BU (K) is executed according to the contents shown in Table 2 above. This command BU (K) (0 ≦ K ≦ 3) is stored in the form of an array in a predetermined storage area, and each of the commands BU (K) (0 ≦ K ≦ 3) indicating each predetermined process corresponding to the variable K described above. Each command code (stored code) is held. Thereby, for example, when K = 0, the command code BU (0) is selected, and the operation of turning on the semiconductor switching element SWUL is executed via the gate driver 106.
This process corresponds to the off operations e1, e2, e3, and e4 in FIG.

  According to the above control procedure, the above-described logic (gate operation) of gate control can be specifically executed. Further, since the above control procedure is common to each phase, the other phases can be controlled in the same manner as the first phase (U phase). And by these controls, generation | occurrence | production of on loss by the on voltage of a flywheel diode can be suppressed, preventing generation | occurrence | production of the shoot through current resulting from a power supply short circuit state. In addition, since the regenerative current passing through the flywheel diode is greatly reduced, the reverse recovery current that flows when the applied voltage of the diode is reversed from the forward direction to the reverse direction is also greatly reduced. The occurrence of the state is prevented, and the switching loss corresponding to that is suppressed.

  Moreover, if a semiconductor switching element having a high breakdown voltage and a low on-resistance composed of a wide band gap semiconductor is used as a bidirectional semiconductor switching element which is a main component of the inverter, a relatively high power supply voltage of about several hundred volts or more. The inverter can be realized with low loss. Further, the number of output phases can be arbitrarily increased or decreased according to the configuration of the main circuit 101. Further, as mentioned above, these control processes may of course be realized by hardware.

[Other variations]
The embodiment of the present invention is not limited to the above-described embodiment, and other modifications as exemplified below may be made. Even with such modifications and applications, the effects of the present invention can be obtained based on the functions of the present invention.
(Modification 1)
For example, in the first embodiment, each semiconductor switching element used in the main circuit has no parasitic diode, but the semiconductor switching element used has substantially the same function as an intentionally provided normal flywheel diode. Floating diodes that perform the following may be parasitic.

FIG. 5 shows a circuit diagram of the inverter 200 of the first modification. The inverter 200 is a two-phase AC output inverter configured in the same manner as in the first embodiment. However, the semiconductor switching element SWDH originally has a parasitic diode DDH that is unintentionally parasitic. is doing. As a result, this floating diode DDH exhibits substantially the same operation as the flywheel diode DUH in the inverter 100 of the first embodiment. The other floating diodes DDL, DQH, DQL have the same effect.
For example, even in an inverter using such a semiconductor switching element, it is possible to obtain substantially the same operation and effect as in the first embodiment based on the present invention.

  In the inverter of the present invention, a bidirectional semiconductor switching element is used for the main circuit, but the loss reduction technique of the present invention is an effective technique regardless of the level of the power supply voltage. That is, the present invention should not be limited to an inverter having a relatively low power supply voltage of about several tens of volts, and the present invention can be applied to a relatively high power supply of about several hundred volts or more from such a low power supply voltage inverter. It is also suitable for reducing the loss of voltage inverters.

Circuit diagram of the inverter 100 according to the first embodiment. Control block diagram of inverter 100 of Embodiment 1 Control block diagram of dead time management unit 105 Flowchart illustrating the control procedure of dead time management unit 105 Circuit diagram of inverter 200 of modification 1

Explanation of symbols

DESCRIPTION OF SYMBOLS 100: Inverter 101: Main circuit 102: Each phase midpoint voltage measurement part 103: Each phase current measurement part 104: Each phase midpoint voltage high / low command signal generation part 105: Dead time management part 106: Gate driver

Claims (4)

A pair of semiconductors having a bidirectional semiconductor switching element capable of flowing a current bidirectionally in an ON state in a controlled current path to be controlled for opening and closing, wherein the controlled current paths are connected in series In an inverter provided with a switching element for each phase,
Flywheel diodes connected in parallel to each of the semiconductor switching elements;
A midpoint voltage measuring means for measuring a voltage at a connection point of the pair of semiconductor switching elements for each phase;
Current detection means for detecting the current direction of each phase;
Dead time management means for adaptively controlling, based on the direction of the current and the voltage, for each phase, the length of the dead time in which both of the pair of semiconductor switching elements are simultaneously turned off,
The dead time management means includes
The increase or decrease in the voltage from the time when the OFF command signal for switching the pair of one of the semiconductor switching elements from the ON state to the OFF state is output indicates a displacement amount exceeding a predetermined threshold (> 0). An inverter that outputs an ON command signal for switching the pair of other semiconductor switching elements from an OFF state to an ON state. The dead time management means includes
1st voltage raising / lowering determination means which determines that the said ON command signal should be output when the said displacement amount reaches the value of 10 to 20% of the direct-current power supply voltage to be used, It is characterized by the above-mentioned. The inverter according to claim 1. The dead time management means includes
A second voltage increase / decrease that determines that the ON command signal should be output when the amount of displacement reaches an average value of the amount of voltage drop when the semiconductor switching element is conductive and the on-voltage of the flywheel diode. The inverter according to claim 1, further comprising a determination unit. The dead time management means includes
The inverter according to any one of claims 1 to 3, further comprising period measuring means for defining an upper limit value of the length of the dead time.

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