Control method of inverter, and control device of inverter

Abstract

To provide a control method and a control device of an inverter which changes dead time according to a situation to reduce conduction loss of reflux current.SOLUTION: A control method of an inverter 12 includes: converting input DC power (Vdc) into AC power by PWM control by using switching elements UU to WL each comprising a body diode 23 which forms a channel for conducting a drain (D) and a source (S) by gate voltage VG to supply reflux current U-, L-, and having a reverse conducting property by the channel; and supplying AC power to a rotary electric machine 10. In this control method, the gate voltage VG is controlled so that the source (S) and the drain (D) are conducted by having dead time τ when the reflux current U-, L- flow to the body diode 23, and the dead time τ is changed according to switching frequencies of the switching elements UU to WL.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present invention relates to a method for controlling an inverter and a control device.

Background Art

[0002] Patent Document 1 discloses that when a voltage-driven semiconductor element is used in a power conversion device, in order to prevent a dead time shortage and a short circuit between positive and negative arms, and an overcurrent from flowing through the device, when the current flowing through the semiconductor element is equal to or greater than a predetermined value, the dead time is shortened, and when the current flowing through the semiconductor element is less than the predetermined value, the dead time is lengthened.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An inverter (power conversion device) is used to convert input DC power into AC power for supplying to a rotating electrical machine or the like. In an inverter, as switching elements, IGBTs (Insulated Gate Bipolar Transistors), MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), etc. are used.

[0005] The switching elements used in an inverter are formed in a vertical layer structure that allows current to flow in the front-back direction of the substrate in order to improve the power transmission efficiency. In particular, a MOSFET (Power MOSFET) used in an inverter inevitably includes a diode (so-called body diode) that allows a reflux current to flow when a reverse bias is applied between the source and drain due to this vertical layer structure.

[0006] A MOSFET has reverse conductivity through a channel. That is, a MOSFET can also conduct a reflux current through a channel formed between the source and the drain by controlling the gate voltage. And the conduction loss of the channel is smaller than that of the body diode. Therefore, in an inverter using a MOSFET as a switching element, it is desirable to reduce the conduction loss of the reflux current by forming a channel not only at the timing of flowing a forward current but also at the timing of flowing a reflux current.

[0007] However, in an inverter, a dead time is provided to prevent short circuits. And during the dead time, as described above, a channel cannot be formed to flow a reflux current, so a reflux current flows through the body diode. And the setting of the dead time is excessive in some situations and can be reduced. Therefore, it is required to appropriately change (adjust) the dead time according to the situation to further reduce the conduction loss of the reflux current.

[0008] An object of the present invention is to provide a control method and a control device for an inverter that can change the dead time according to the situation and reduce the conduction loss of the reflux current.

Means for Solving the Problems

[0009] One aspect of the present invention is a control method for an inverter that forms a channel for conducting between the source and the drain by a gate voltage, includes a body diode for flowing a reflux current, and uses a switching element having reverse conductivity through the channel, and converts the input DC power into AC power by PWM control and supplies the AC power to a rotating electrical machine. In this control method for the inverter, when a reflux current flows through the body diode, the gate voltage is controlled to make the source and the drain conduct with a dead time left, and the dead time is changed according to the switching frequency of the switching element.

Effects of the Invention

[0010] According to the present invention, it is possible to provide a control method and a control device for an inverter that change a dead time according to a situation and reduce conduction loss of a reflux current.

Brief Description of the Drawings

[0011]

Figure 1

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Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0013] [Embodiment] FIG. 1 is an explanatory diagram showing the configuration of the rotating electrical machine system 100. The rotating electrical machine system 100 is a system for controlling the rotating electrical machine 10, and includes a battery 11, an inverter 12, a gate driver 13, and a controller 14.

[0014] The rotating electrical machine 10 is a motor or a generator. The rotating electrical machine 10 is mounted on an electric vehicle such as an electric vehicle or a hybrid vehicle. In the present embodiment, the rotating electrical machine 10 is a three-phase AC synchronous motor and functions as a driving power source of the electric vehicle.

[0015] The battery 11 is a DC power source. In the present embodiment, the battery 11 is composed of a lithium-ion battery or the like and is rechargeable. The battery 11 supplies power for driving the rotating electrical machine 10 via the inverter 12.

[0016] In addition, the battery 11 may be connected to the inverter 12 via a booster circuit or the like (not shown). In this case, the battery 11 can change the DC power input to the inverter 12. In the present embodiment, the DC voltage V dc input from the battery 11 to the inverter 12 can be switched, for example, between 400 V and 800 V.

[0017] Note that, by continuously supplying power, the DC power (V dc ) supplied from the battery 11 to the inverter 12 may naturally decrease. Thereafter, if the battery 11 is charged, the DC power (V dc ) supplied from the battery 11 to the inverter 12 recovers. However, in the present embodiment, for simplicity, the battery 11 is assumed to be used within a range where the DC voltage V dc substantially hardly decreases due to its use.

[0018] The inverter 12 converts the DC power output from the battery 11 into AC power by PWM (Pulse Width Modulation) control and supplies it to the rotating electrical machine 10. The DC power input from the battery 11 is input to the inverter 12 via the smoothing capacitor 21.

[0019] The inverter 12 is composed of a plurality of switching elements. In this embodiment, since the rotating electrical machine 10 has windings of three phases of U, V, and W, the inverter 12 has legs for controlling the power supplied to each of these phases respectively.

[0020] The leg for controlling the U phase (hereinafter referred to as the U-phase leg) is composed of the switching element U that constitutes the upper arm U and the switching element U that constitutes the lower arm L and the winding (U) of the U phase is connected between them. The leg for controlling the V phase (V-phase leg) is composed of the switching element V that constitutes the upper arm U and the switching element VL that constitutes the lower arm, and the winding (V) of the V phase is connected between them. Similarly, the leg for controlling the W phase (W-phase leg) is composed of the switching element W that constitutes the upper arm U and W that constitutes the lower arm L and the winding (W) of the W phase is connected between them.

[0021] In this embodiment, the switching elements U U ~W L are constituted by, for example, so-called power MOSFETs.

[0022] Specifically, the switching elements U U ~W L form a channel for conducting between the source (S) and the drain (D) by applying a gate voltage V G to the gate (G), and control the conduction between the drain and the source (hereinafter referred to as between DS) by disappearing (narrowing) it. Hereinafter, in the switching elements U U ~W L , the part that controls the conduction of the channel between DS by the gate (G), the source (S), and the drain (D) is called the MOSFET 22. The state of forming a channel and making conduction between DS possible is the state of the switching elements U U ~W L(Or each MOSFET 22) is in the "ON" state. The state in which the channel is eliminated and the conduction between D and S is made non-conductive is the switching element U U ~W L (Or each MOSFET 22) is in the "OFF" state. Also, hereinafter, the switching element U U ~W L The switching of the on / off of (each MOSFET 22) is called switching, and the frequency thereof (for example, the number of on / off switches per unit time) is called the switching frequency.

[0023] The switching element U U ~W L includes a body diode 23 (freewheel diode) that allows current to flow between D and S without passing through the channel when a reverse bias is applied between D and S by a vertical layer structure that forms a gate (G), a drain (D), and a source (S). Hereinafter, the reverse current flowing through the body diode or the like when a reverse bias is applied between D and S is called the reflux current.

[0024] Furthermore, the switching element U U ~W L has reverse conductivity due to the channel. That is, when a reverse bias is applied between D and S, a channel is formed between D and S by the gate voltage V G , so that the switching element U U ~W L can substantially pass the reflux current through the channel. The conduction loss of the reflux current is smaller when passing through the channel than when passing through the body diode 23.

[0025] Note that the switching element U U ~W L is preferably configured by a wide-gap semiconductor using a compound such as SiC (silicon carbide) or GaN (gallium nitride). In this embodiment, the switching element U U ~W LIn particular, it is a MOSFET (SiC-MOSFET) formed using SiC, which has high breakdown voltage, low on-resistance (resistance value between S and D), and is suitable for high-speed switching. Also, in FIG. 1, only the switching element U that constitutes the upper arm of the U-phase leg U is marked with the symbols of gate (G), drain (D), source (S), MOSFET22, and body diode 23, but the other switching elements U L ~W L are configured similarly.

[0026] The gate driver 13 operates the inverter 12 by controlling the gate voltage V U ~W L of the gate (G) of the switching elements U G ~W U ~W L of the gate (G). The gate driver 13 adjusts (changes) the gate voltage V G of the gate (G) of the switching elements U U ~W L according to the PWM signal input from the controller 14. As a result, in the switching elements U

[0027] ~W L a channel between D and S is formed or disappears. The controller 14 generates a PWM signal that determines the on / off timing of the switching elements U dc ~W U ~W L based on the DC voltage V dc input by the battery 11 to the inverter 12, the current flowing through the rotating electrical machine 10 (hereinafter referred to as the rotating electrical machine current), etc. As a result, the controller 14 controls the operation of the inverter 12, and as a result, controls the operation of the rotating electrical machine 10. That is, the controller 14 is a control device for the inverter 12 and also a control device for the rotating electrical machine 10. The controller 14 is constituted by, for example, one or more computers.

[0028] In this embodiment, the DC voltage V dc is downstream of the smoothing capacitor 21 (the switching elements U U ~W LIt can be appropriately acquired by the voltage sensor 24 provided on the (side). Further, the rotating electrical machine current can be appropriately acquired by the current sensor 25 provided between the inverter 12 and the rotating electrical machine 10. Further, in the present embodiment, specifically, the rotating electrical machine current is the current flowing through each phase of the rotating electrical machine 10 (hereinafter, referred to as phase current I ph ). The phase current I ph is the current flowing through the U-phase winding (U) (U-phase current I U ), the current flowing through the V-phase winding (V) (V-phase current I V ), and the current flowing through the W-phase winding (W) (W-phase current I W ). The phase current I ph can be acquired for each phase respectively.

[0029] FIG. 2 is an explanatory diagram showing the configuration of the gate driver 13 and the controller 14. As shown in FIG. 2, the gate driver 13 includes a floating power supply 31 and a gate resistor R G .

[0030] The floating power supply 31 applies a voltage (gate voltage V G ) to the gate (G). The floating power supply 31 changes or adjusts the gate voltage V G according to the PWM signal.

[0031] The gate resistor R G is a resistor interposed between the floating power supply 31 and the gate (G). In the present embodiment, the gate resistor R G is constituted by a variable resistor having a variable resistance value. Therefore, the gate resistor R G can be changed stepwise or continuously. The specific value of the gate resistor R G is appropriately adjusted, for example, so as to reduce noise such as a surge superimposed on the current flowing through the channel (so-called drain current). The larger the gate resistor R G , the slower the switching of the MOSFET 22 becomes, and the smaller the gate resistor R G , the faster the switching of the MOSFET 22 becomes. In the present embodiment, for simplicity, the gate resistor R Gis selected from two values of a low value (R G1 ) and a high value (R G2 ). Further, hereinafter, the switching speed of the MOSFET 22 or the switching element U U ~W L is represented by the time required for the drain current to substantially reach the target value after starting the change of the gate voltage V G .

[0032] In addition, in FIG. 2, as the configuration of the gate driver 13, a constituent part for controlling the switching element U U constituting the upper arm of the U-phase leg is shown, but the configuration for controlling the switching element U L of the lower arm is the same as this. And the above configuration for controlling the switching elements U U , U L of the U-phase leg is paired, and the switching elements U U , U L are controlled so as not to turn on simultaneously and short-circuit. Further, the switching elements V U , V L of the V-phase leg and the switching elements W U , W L of the W-phase leg are also configured in the same manner as above. However, each of the U, V, and W phase legs is controlled independently of each other. For example, the switching elements U U , U L of the U-phase leg and the switching elements V U , V L of the V-phase leg are controlled independently. That is, the gate driver 13 can control (set or change) the switching timing and switching frequency for each of the plurality of phases of the rotating electrical machine 10.

[0033] The controller 14 includes a carrier control unit 32, a PWM generation unit 33, a dead time generation unit 34, a dead time control unit 35, and a gate resistance control unit 36.

[0034] The carrier control unit 32 includes a torque command value T * and the rotational speed ω m of the rotating electrical machine 10.Based on this, the carrier signal (fundamental wave) used for PWM control is selected or changed. Rotational speed ω m When it is relatively small, the carrier control unit 32 selects a carrier signal with a predetermined constant frequency, such as a triangular wave, regardless of the torque command value T * When the rotational speed ω m is relatively large, the carrier control unit 32 selects a carrier signal whose frequency increases in response to, for example, an increase in the rotational speed ω m and / or an increase in the torque command value T * . The timing at which the carrier control unit 32 switches the carrier signal is determined in advance by experiments, simulations, or the like. Also, the carrier control unit 32 inputs the frequency of the selected carrier signal (hereinafter referred to as the carrier frequency f c ) to the dead time control unit 35.

[0035] Note that the torque command value T * is a command value for the torque T that the rotating electrical machine 10 should output, and is determined by the controller 14 or other controllers, etc., based on, for example, the operation amount of the accelerator. In this embodiment, it is assumed that the torque command value T * is known.

[0036] Also, the rotational speed ω m is appropriately calculated by the controller 14 or other controllers, etc., based on, for example, the phase current I ph or the like. In this embodiment, it is assumed that the rotational speed ω m is known. Also, in this embodiment, the rotational speed ω m is the angular velocity (mechanical angular velocity or electrical angular velocity of the rotor). However, as a parameter representing the rotational speed of the rotating electrical machine 10, the rotational speed [rpm] can be used instead of the angular velocity [rad / s]. These can be mutually converted by calculation.

[0037] The PWM generation unit 33 uses the torque command value T *Based on the carrier signal selected by the carrier control unit 32, a basic PWM signal is generated. Ideally, according to this basic PWM signal, the switching elements U U ~W L of the inverter 12 are driven, so that an alternating current flows through the windings of each phase of the rotating electrical machine 10, and the rotating electrical machine 10 generates a torque T corresponding to the torque command value T * .

[0038] However, the basic PWM signal generated by the PWM generation unit 33 is a basic PWM signal that determines the ideal timing for switching the on / off of the switching elements U U ~W L . That is, the PWM signal generated by the PWM generation unit 33 does not include the dead time τ. The dead time τ is the time to surely turn off both of them once when switching the on / off of the switching elements (for example, U U and U L ) that constitute the upper arm and the lower arm in each phase leg. The dead time τ is provided to prevent the switching elements of the upper arm and the lower arm from being short-circuited by being turned on simultaneously.

[0039] Based on the dead time τ determined by the dead time control unit 35, the dead time generation unit 34 generates a final PWM signal (PWM) with the dead time τ provided. Specifically, in the basic PWM signal generated by the PWM generation unit 33, the dead time τ is inserted (set) at the place where the on / off of the switching elements of the upper arm and the lower arm (for example, U U , U L ) is switched. The final PWM signal (PWM) generated by the dead time generation unit 34 is input to the gate driver 13.

[0040] The dead time control unit 35 sets or changes the dead time τ. The dead time τ is the gate voltage V U for turning off one of the switching elements (for example, U G ) of the upper arm and the lower arm. After starting the input, the other switching element (for example, UL The gate voltage V to turn on G represents the blank period to be provided before starting the input of

[0041] The dead time control unit 35 sets or changes the dead time τ according to at least the switching frequency of the switching elements U U ~W L . The dead time control unit 35 performs the setting / change of the dead time τ corresponding to this switching frequency for each phase of the rotating electrical machine 10.

[0042] In the present embodiment, the dead time control unit 35 determines the switching frequency by comparing the carrier frequency f c of the PWM control with the frequency threshold f th . Then, when the carrier frequency f c is greater than the frequency threshold f th , the dead time control unit 35 shortens the dead time τ as compared with the case where the carrier frequency f c is less than or equal to the frequency threshold f th . That is, when the carrier frequency f c is large and the switching frequency is high, the dead time control unit 35 reduces the dead time τ. The frequency threshold f th is determined in advance by adaptation based on experiments or simulations considering conduction losses, heat generation amounts, etc. when the reflux current flows.

[0043] When the carrier frequency f c changes according to the rotational speed ω m of the rotating electrical machine 10, the dead time control unit 35 can also determine the switching frequency by comparing the rotational speed ω m with a rotational speed threshold ω th (not shown). At this time, when the rotational speed ω m is greater than the rotational speed threshold ω th , the dead time control unit 35 shortens the dead time τ as compared with the case where the rotational speed ω m is less than or equal to the rotational speed threshold ω th . That is, when the rotational speed ω mis large and the switching frequency is high, the dead time control unit 35 can reduce the dead time τ. Note that the rotational speed threshold ω th is determined in advance by adaptation based on experiments or simulations considering conduction losses, heat generation amounts, etc. when the reflux current flows.

[0044] The dead time control unit 35 determines whether the dead time τ can be changed (reduced) based on the switching speed of the switching elements U U ~W L (MOSFET 22). When it is possible to change the dead time τ, the dead time τ can be shortened compared to the case where the dead time τ cannot be changed. In particular, when reducing the dead time τ according to the switching frequency as described above, the dead time control unit 35 first determines whether the dead time τ of the PWM signal can be changed. When the dead time can be changed, it is desirable to change the dead time τ according to the switching frequency.

[0045] In this embodiment, the dead time control unit 35 determines whether the dead time τ can be changed by the gate resistance R G . Specifically, when the gate resistance R G is a low value (R G1 ) and the switching speed is fast, the dead time control unit 35 determines that the dead time τ can be reduced. In this case, the dead time control unit 35 can set the dead time τ to a value equal to or less than the dead time τ (hereinafter referred to as the first dead time τ 1 ) when the dead time τ cannot be reduced. On the other hand, when the gate resistance R G is a high value (R G2 ) and the switching speed is slow, the dead time control unit 35 determines that the dead time τ cannot be reduced and sets the dead time τ to the longest first dead time τ 1 .

[0046] The dead time control unit 35 compares the DC voltage V dc with the voltage threshold V th , and the DC voltage Vdc is less than the voltage threshold V th , the DC voltage V dc is less than the voltage threshold V th compared with the case where it is equal to or higher than the voltage threshold V, the dead time τ can be shortened. In particular, when changing the dead time τ according to the switching frequency as described above, the dead time control unit 35 further compares the DC voltage V dc with the voltage threshold V th , and when the DC voltage V dc is less than the voltage threshold V th , the DC voltage V dc is preferably shorter than the dead time τ compared with the case where it is equal to or higher than the voltage threshold V th . The voltage threshold V th is determined in advance by adaptation based on experiments or simulations considering conduction losses and heat generation amounts when the reflux current flows. The dead time control unit 35 sets / modifies the dead time τ according to the above DC voltage V dc for each phase of the rotating electrical machine 10.

[0047] The dead time control unit 35 compares the phase current I ph (rotating electrical machine current) with the current threshold I th , and when the phase current I ph is greater than the current threshold I th , the phase current I ph is preferably shorter than the dead time τ compared with the case where it is equal to or less than the current threshold I th . In particular, when changing the dead time τ according to the switching frequency as described above, the dead time control unit 35 further compares the phase current I ph with the current threshold I th , and when the phase current I ph is greater than the current threshold I th , the phase current I ph is preferably shorter than the dead time τ compared with the case where it is equal to or less than the current threshold I th . The current threshold I th is determined in advance by adaptation based on experiments or simulations considering conduction losses and heat generation amounts when the reflux current flows. The dead time control unit 35 sets / modifies the dead time τ according to the above phase current I phThe setting / change of the dead time τ according to the phase of the rotating electrical machine 10 is performed for each phase.

[0048] The gate resistance control unit 36 adjusts the gate resistance R, for example, to reduce noise such as surges superimposed on the drain current. G The gate resistance control unit 36 can determine the gate resistance R, for example, based on the carrier frequency f, c the phase current I, ph the DC voltage V, dc other parameters, or a combination thereof. In the present embodiment, the gate resistance control unit 36 switches the gate resistance R between a low value (R G ) and a high value (R dc ) based on the DC voltage V. G More specifically, when the DC voltage V G1 is, for example, 400 V, the gate resistance control unit 36 sets the gate resistance R G2 to the low value (R dc ). Also, when the DC voltage V G is, for example, 800 V, the gate resistance control unit 36 sets the gate resistance R G1 to the high value (R dc ). The gate resistance control unit 36 notifies the dead time control unit 35 of the value of the gate resistance R G . G2 G

[0049] FIG. 3 is an explanatory diagram showing the relationship between the control states of the switching elements U U to W L and the current flowing through the switching elements U U to W L . In FIG. 3, the control states when the phase current I ph flows from each phase leg to the winding of the rotating electrical machine 10 are shown. Hereinafter, the current flowing from each phase leg to the winding of the rotating electrical machine 10 is referred to as the positive-direction phase current I ph , and the current flowing from the winding of the rotating electrical machine 10 to each phase leg is referred to as the negative-direction phase current I ph . In the following, unless otherwise particularly necessary, each phase leg and the switching elements U U to WL does not distinguish.

[0050] Figure 3(A) shows a state in which the MOSFET 22 in the upper arm is turned on (ON) and the MOSFET 22 in the lower arm is turned off (OFF). In this case, the positive-phase current I ph is realized by the drain current U flowing in the forward direction through the channel formed in the MOSFET 22 in the upper arm. + is realized by.

[0051] Figure 3(B) shows a state in which the MOSFET 22 in the upper arm is turned off (OFF) and the MOSFET 22 in the lower arm is also turned off (OFF). In this case, the positive-phase current I ph is realized by the reflux current L flowing through the body diode 23 in the lower arm. - is realized by.

[0052] Figure 3(C) shows a state in which the MOSFET 22 in the lower arm is turned on (ON - ) in synchronization with the timing when the reflux current L sync flows through the lower arm as shown in Figure 3(B). As described above, since the MOSFET 22 has reverse conductivity due to the channel, when the MOSFET 22 in the lower arm is turned on (ON - ) at the timing when the reflux current L sync flows through the lower arm, the reflux current L - substantially conducts through the channel of the MOSFET 22. Therefore, the positive-phase current I ph is realized by the drain current flowing in the reverse direction through the MOSFET 22 in the lower arm (hereinafter, this drain current is also referred to as "reflux current L - "). And when comparing the channel of the MOSFET 22 and the body diode 23, the channel of the MOSFET 22 has a smaller conduction loss of the reflux current L - . Therefore, as described above, if synchronous rectification is performed to turn on (ON - ) the MOSFET 22 in accordance with the timing when the reflux current L sync flows, the conduction loss of the reflux current L - is reduced.

[0053] Figure 4 shows the switching element U U ~W L and the relationship between the control state of the switching element U U ~W L and the current flowing through it. In Figure 4, the control state when the negative-phase current I ph flows is shown.

[0054] Figure 4(A) shows the state where the upper-arm MOSFET 22 is turned off (OFF) and the lower-arm MOSFET 22 is turned on (ON). In this case, the negative-phase current I ph is realized by the drain current L + flowing in the forward direction through the channel formed in the lower-arm MOSFET 22.

[0055] Figure 4(B) shows the state where the upper-arm MOSFET 22 is turned off (OFF) and the lower-arm MOSFET 22 is also turned off (OFF). In this case, the negative-phase current I ph is realized by the reflux current U - flowing through the body diode 23 of the upper arm.

[0056] Figure 4(C) shows the state where the upper-arm MOSFET 22 is turned on (ON - ) in synchronization with the timing when the reflux current U sync flows through the upper arm as in Figure 4(B). In this case, the reflux current L - substantially conducts through the channel of the MOSFET 22. That is, the negative-phase current I ph is realized by the drain current flowing in the reverse direction through the upper-arm MOSFET 22 (hereinafter, this drain current is also referred to as "reflux current U - "). Thus, by performing synchronous rectification to turn on the MOSFET 22 (ON sync ) in accordance with the timing when the reflux current U- flows, the conduction loss of the reflux current U - is reduced.

[0057] Figure 5 shows the phase current I ph and the switching element U U ~W LIt is an explanatory diagram showing the control state. Fig. 5(A) shows the sinusoidal phase current I ph and another current that realizes this. In Fig. 5(A), for convenience, the reflux current U - ,L - The part realized by is shown by a broken line. Fig. 5(B) shows the on / off timing of the upper arm. Fig. 5(C) shows the on / off timing of the lower arm.

[0058] As shown in Fig. 5(A), the positive-phase current I ph is realized by alternately flowing the drain current U + of the upper arm and the reflux current L - of the lower arm. And, as shown in Fig. 5(B), the upper arm is controlled to turn on (ON) at the timing of flowing the drain current U + . On the other hand, if the lower arm is maintained in the off (OFF) state, the reflux current L - can flow through the body diode 23. However, in this embodiment, as shown in Fig. 5(C), even at the timing of flowing the reflux current L - , synchronous rectification is performed with the lower arm turned on (ON sync ).

[0059] At this time, a dead time τ is provided between the timing when the upper arm turns on (ON, ON sync ) and the timing when the lower arm turns on (ON sync ) so that the upper arm and the lower arm do not short-circuit simultaneously. That is, when the reflux current L - flows through the body diode 23 of the lower arm, the gate voltage V G of the lower arm is controlled so that the source (S) and drain (D) of the lower arm conduct with a dead time τ with respect to the timing when the upper arm turns on (ON).

[0060] The case of flowing the negative-phase current I ph is the same as above. That is, as shown in Fig. 5(A), the negative-phase current I ph is the reflux current U -and the drain current L of the lower arm + is realized by alternately flowing them. And, as shown in FIG. 5(C), the lower arm is controlled to turn on (ON) at the timing of flowing the drain current L + . On the other hand, if the upper arm is maintained in the off (OFF) state, the reflux current U - can flow through the body diode 23. However, in this embodiment, as shown in FIG. 5(B), even at the timing of flowing the reflux current U - , synchronous rectification is performed with the upper arm turned on (ON sync ).

[0061] At this time, a dead time τ is provided between the timing when the lower arm turns on (ON, ON sync ) and the timing when the upper arm turns on (ON sync ) so that the lower arm and the upper arm do not short-circuit simultaneously. That is, when the reflux current U - flows through the body diode 23 of the upper arm, the gate voltage V G of the upper arm is controlled so that the source (S) and drain (D) of the upper arm conduct with a dead time τ left with respect to the timing when the lower arm turns on (ON).

[0062] FIG. 6 is an explanatory diagram showing the fall time T U ~W L of the switching element U F , the rise time T R , and the dead time τ. In FIG. 6, as an example, the MOSFET 22 of the lower arm that was flowing the reflux current L - is turned off, and subsequently the MOSFET 22 of the upper arm is turned on to show a scene of flowing the drain current U + . The fall time T F of the MOSFET 22 is, for example, the time until the drain current (the reflux current that conducts the channel) decreases to about 10% or less and can be regarded as substantially reaching zero. The rise time T Ris the time until, for example, the drain current (the return current flowing through the channel) increases to about 90% or more of the target value and can be regarded as having substantially reached the target value.

[0063] As shown in FIG. 6, the dead time τ set by the dead time control unit 35 (hereinafter referred to as the set dead time τ set is the time from when the gate voltage V of the lower arm starts to be controlled so that the lower arm turns off until the gate voltage V of the upper arm starts to be controlled so that the upper arm turns on. On the other hand, the effective dead time τ (hereinafter referred to as the effective dead time τ G considering the fall time T and rise time T of the MOSFET 22 G is, for example, the time from when the return current L of the lower arm substantially becomes zero until the drain current U of the upper arm substantially reaches the target value. F and rise time T R is the time from when the return current L of the lower arm substantially becomes zero until the drain current U of the upper arm substantially reaches the target value. act is, for example, the time from when the return current L of the lower arm substantially becomes zero until the drain current U of the upper arm substantially reaches the target value. - is, for example, the time from when the return current L of the lower arm substantially becomes zero until the drain current U of the upper arm substantially reaches the target value. + is, for example, the time from when the return current L of the lower arm substantially becomes zero until the drain current U of the upper arm substantially reaches the target value.

[0064] Therefore, the set dead time τ set and the effective dead time τ act are represented by the relationship shown in the following formula (1). That is, the effective dead time τ act is obtained by subtracting the fall time T of the MOSFET 22 from the set dead time τ set and adding the rise time T of the MOSFET 22. For this reason, the dead time control unit 35 sets or changes the set dead time τ F so that the effective dead time τ R is equal to or greater than the dead time τ (hereinafter referred to as the lower limit dead time τ act ) that should be actually ensured as the minimum for safety and stable operation. The lower limit dead time τ LL is determined in advance by experiments or simulations. On the other hand, the fall time T of the MOSFET 22 F and rise time T R is considered. The lower limit dead time τ set is set or changed. The lower limit dead time τ LL is determined in advance by experiments or simulations. On the other hand, the fall time T of the MOSFET 22 F and rise time T Ris, as will be described later, the gate resistance R G and the current flowing through the MOSFET 22 (phase current I ph ). Here, for simplicity, in Equation (1), the delay time required for controlling the gate voltage V G is not considered. However, it is more preferable to consider the delay time required to increase the gate voltage V G and the delay time required to reduce the gate voltage V G .

[0065]

Number

[0066] Figure 7 is a graph schematically showing the relationship between the gate resistance R G and the turn-off time T U ~W L and the turn-on time T F of the switching element U R . As shown in Figure 7, the larger the gate resistance R G , the larger (longer) the turn-off time T F and the turn-on time T R of the MOSFET 22 become. That is, the larger the gate resistance R G , the slower the switching of the switching element U U ~W L . Therefore, based on the set dead time τ G when the gate resistance R G2 is a high value (R set ), the set dead time τ G when the gate resistance R G1 is a low value (R set ) has room for shortening by the amount by which the turn-off time T F and the turn-on time T R of the MOSFET 22 become shorter. In other words, when the switching speed of the switching element U U ~W L (MOSFET 22) is high and it switches quickly, the set dead time τ setcan be reduced. As shown in FIG. 7, normally, the fall time T F and the rise time T R of MOSFET 22 are different, and the fall time T F is larger than the rise time T R (T F >T R ).

[0067] FIG. 8 is a graph schematically showing the relationship between the phase current I ph and the fall time T U ~W L and the rise time T F of the switching element U R . As shown in FIG. 8, the fall time T F of MOSFET 22 decreases as the phase current I ph (the current flowing through the channel) increases. On the other hand, the rise time T R of MOSFET 22 does not change significantly even when the phase current I ph (the current flowing through the channel) increases. More practically, the rise time T R of MOSFET 22 increases as the phase current I ph (the current flowing through the channel) increases, but the increase amount is small compared to the decrease amount of the fall time T F .

[0068] FIG. 9 is a flowchart related to the setting and change of the dead time τ. As shown in FIG. 9, in step S10, the dead time control unit 35 determines whether there is room to reduce the dead time τ (set dead time τ set ) according to the switching speed of MOSFET 22. In this embodiment, the dead time control unit 35 discriminates the switching speed of MOSFET 22 based on the gate resistance R G .

[0069] That is, when the gate resistance R G is a high value (R G2When the switching of MOSFET 22 is slow, the dead time control unit 35 determines that there is no (little) room to reduce the dead time τ. In this case (S10: NO), the process proceeds to step S11, and the dead time control unit 35 sets the set dead time τ set to the longest first dead time τ 1 .

[0070] On the other hand, when the gate resistance R G is a low value (R G1 ) and the switching of MOSFET 22 is fast, the dead time control unit 35 determines that there is room to reduce the dead time τ. In this case (S10: YES), the process proceeds to step S12.

[0071] In step S12, the dead time control unit 35 determines the switching frequency of MOSFET 22. In the present embodiment, the dead time control unit 35 determines the switching frequency of MOSFET 22 by comparing the carrier frequency f c of the PWM control with the frequency threshold f th .

[0072] And when the carrier frequency f c is less than or equal to the frequency threshold f th , the dead time control unit 35 determines that the switching frequency of MOSFET 22 is low. In this case (S12: NO), the process proceeds to step S13, and the dead time control unit 35 sets or changes the set dead time τ set to a second dead time τ 1 that is less than or equal to the longest first dead time τ 2 .

[0073] On the other hand, when the carrier frequency f c is greater than the frequency threshold f th , the dead time control unit 35 determines that the switching frequency of MOSFET 22 is high. In this case (S12: YES), the process proceeds to step S14.

[0074] In step S14, the dead time control unit 35 compares the DC voltage V dc with the voltage threshold V th . When the DC voltage V dc is equal to or higher than the voltage threshold V th (step S14: NO), the process proceeds to step S15, and the dead time control unit 35 sets or changes the set dead time τ set to a third dead time τ 2 that is smaller than the second dead time τ 3 . On the other hand, when the DC voltage V dc is smaller than the voltage threshold V th (step S14: YES), the process proceeds to step S16.

[0075] In step S16, the dead time control unit 35 compares the phase current I ph with the current threshold I th . When the phase current I ph is equal to or lower than the current threshold I th (step S16: NO), the process proceeds to step S17, and the dead time control unit 35 sets or changes the set dead time τ set to a fourth dead time τ 3 that is smaller than the third dead time τ 4 . On the other hand, when the phase current I ph is larger than the current threshold I th (step S16: YES), the process proceeds to step S18, and the dead time control unit 35 sets or changes the set dead time τ set to a fifth dead time τ 4 that is smaller than the fourth dead time τ 5 .

[0076] As described above, the dead time control unit 35 appropriately reduces the dead time τ (set dead time τ set ) according to the switching frequency of the MOSFET 22 or the like. As a result, the conduction loss of the reflux current U - , L - is reduced.

[0077] Specifically, in the present embodiment, the reflux current U- ,L - Current flows through switching element U U ~W L Turn on (ON sync ), the return current U - ,L - This causes the body diode 23 to generate a reflux current U - ,L - The return current U - ,L - However, this does not apply to the dead time τ, and the return current U - ,L - Since the current flows through the body diode 23, the conduction loss is not reduced. Therefore, in this embodiment, as described above, the dead time τ (set dead time τ set ) itself, the reflux current U during the dead time τ - ,L - Therefore, in this embodiment, the inverter 12 can convert the DC power of the battery 11 into AC power more efficiently than in the past. Also, heat generation by the inverter 12 can be suppressed.

[0078] FIG. 10 shows the effective dead time τ act As shown in FIG. ph That is, switching element U U ~W L The larger the current flowing through the act This is mainly due to the phase current I ph The fall time T of the MOSFET 22 is F On the other hand, the set dead time τ set If becomes smaller, the effective dead time τ act Therefore, in the above embodiment, the set dead time τ set is the fifth dead time τ 5 and the phase current I ph is the current threshold Ith when it is equal to, the effective dead time τ act becomes the smallest.

[0079] Therefore, the dead time control unit 35 determines that the carrier frequency f of the PWM control c is greater than the frequency threshold f th , the DC voltage V dc is less than the voltage threshold V th , and the phase current I ph is the current threshold I th In the case of (the effective dead time τ act ), the set dead time τ (the set dead time τ LL ) is set so as to be equal to or greater than the lower limit dead time τ set which is the minimum guaranteed value. As a result, when reducing the dead time τ (the set dead time τ set ) according to the switching frequency of the MOSFET 22 or the like, even if the effective dead time τ ph changes due to the phase current I act , the lower limit dead time τ LL is ensured. For this reason, even if the dead time τ (the set dead time τ set ) is reduced, the inverter 12 can operate stably.

[0080] In FIG. 10, for convenience, the intervals between the adjacent first to fifth dead times τ 1 ~τ 5 are constant, but this is not the only case. All or part of the intervals between the adjacent first to fifth dead times τ 1 ~τ 5 may be different.

[0081] FIG. 11 is an explanatory diagram showing an example of a method for determining the set dead time τ set . To determine the set dead time τ set , first, a reference phase current I ph is selected with respect to the phase current I std . Then, the gate resistance R G is set to a high value (R G2 ), and the reference phase current I stdThe fall time T of the MOSFET 22 in F The reference fall time T Fstd and the reference phase current I std The rise time T of the MOSFET 22 in R The reference rise time T Rstd and are obtained by experiment or simulation. At this time, the reference phase current I std The dead time τ to be set in std The lower limit of the dead time τ LL , reference fall time TF std , and the reference rise time TR std Using this, it can be expressed by the following equation (2).

[0082]

number

[0083] And the gate resistor R G Effective dead time τ due to switching act The reduction in ΔT 1 , phase current I ph Effective dead time τ due to current value act The reduction in ΔT 2 Then, any set dead time τ set can be determined by the following equation (3):

[0084]

number

[0085] ΔT 1 As shown in the above equation (4), ΔT F1 and ΔT R1 It is expressed by the difference between ΔT F1 For example, the gate resistance R G is high (R G2 ) the reference phase current I std Fall time T F and the gate resistance R G is low (RG1 ) when the reference phase current I std The falling time T in F And the difference between them. Similarly, ΔT R1 Is, for example, the gate resistance R G Is a high value (R G2 ) when the reference phase current I std The rise time T in R And the gate resistance R G Is a low value (R G1 ) when the reference phase current I std The rise time T in R And the difference between them.

[0086] Also, ΔT 2 Is, as shown in the above formula (5), ΔT F2 And ΔT R2 Is represented by the difference between them. ΔT F2 Is, for example, the gate resistance R G Is a low value (R G1 ) when the reference phase current I std The falling time T in F And the gate resistance R G Is a low value (R G1 ) when the current threshold I th The falling time T in F And the difference between them. Similarly, ΔT R2 Is, for example, the gate resistance R G Is a low value (R G1 ) when the reference phase current I std The rise time T in R And the gate resistance R G Is a low value (R G1 ) when the current threshold I th The rise time T in R And the difference between them.

[0087] ΔT 1 Is the gate resistance R G Is switched to a low value (R G1 ) and is activated, and is zero when the gate resistance R G Is a high value (R G2 ). Also, ΔT 2 Is the phase current I phis equal to or greater than the current threshold I th and is activated, and the phase current I ph is equal to or greater than the current threshold I th is set to zero when it is smaller. In this embodiment, the dead time control unit 35 stores the set dead time τ set determined by experiments, simulations, etc. as described above in the form of a map, and determines the specific set dead time τ set by referring to the map.

[0088] Note that in the above embodiment, the dead time control unit 35 switches the dead time τ according to the gate resistance R G , the carrier frequency f c (or the rotational speed ω m ), the DC voltage V dc , and the phase current I ph , but is not limited thereto. The dead time control unit 35 can switch the dead time τ according to any one or more of the parameters of the gate resistance R G , the carrier frequency f c (or the rotational speed ω m ), the DC voltage V dc , and the phase current I ph . For example, the dead time control unit 35 can switch the dead time τ simply according to the carrier frequency f c (or the rotational speed ω m ). Also, for example, when the gate resistance R G is not variable, the switching of the dead time τ according to the gate resistance R G can be omitted.

[0089] As described above, the control method of the inverter according to the above embodiment forms a channel that conducts between the drain (D) and the source (S) by the gate voltage V G , includes the body diode 23 that allows the reflux current U - ,L - to flow, and uses the switching elements U U ~W L having reverse conductivity due to the channel, and by PWM control, the input DC power (Vdc ) is a control method of an inverter 12 that converts [it] into AC power and supplies the AC power to a rotating electrical machine 10. In this control method, when a reflux current U - ,L - flows, a dead time τ is provided, and the gate voltage V G is controlled so that conduction occurs between the source (S) and the drain (D), and the dead time τ is changed according to the switching frequency of the switching elements U U ~W L .

[0090] Thus, at the timing when the reflux current U - ,L - flows, the switching elements U U ~W L are turned on (ON sync ), and the reflux current U - ,L - is made to flow through the channel, thereby reducing the conduction loss of the reflux current U - ,L - . At this time, only during the dead time τ, the reflux current U - ,L - flows through the body diode 23. However, as described above, in the control of the inverter according to the above embodiment etc., by changing the dead time τ according to the switching frequency of the switching elements U U ~W L (MOSFET 22), the period during which the reflux current U - ,L - flows through the body diode 23 is reduced. As a result, the conduction loss of the reflux current U - ,L - is further reduced. Further, by reducing the conduction loss of the reflux current U-,L-, heat generation of the inverter 12 is suppressed. In particular, even when the rotating electrical machine 10 is driven at a high load such that it rotates at a high speed and has a high torque, heat generation of the inverter 12 is easily suppressed.

[0091] In the control method of the inverter according to the above embodiment etc., the carrier frequency f c of the PWM control is set to a frequency threshold f thThe switching frequency is determined by comparison. Then, the carrier frequency f c is greater than the frequency threshold f th , the dead time τ is shortened compared to the case where the carrier frequency f c is less than or equal to the frequency threshold f th .

[0092] When the carrier frequency f c is high, the switching frequency increases. As a result, the commutation current U - ,L - flows, and the switching elements U U ~W L are switched to on (ON sync ) more frequently. That is, the number of times the dead time τ is inserted increases. Therefore, as described above, by determining the switching frequency according to the carrier frequency f c of the PWM control and shortening the dead time τ when the carrier frequency f U ~W L (MOSFET22) is high and the switching frequency is high, particularly, the benefits of reducing the conduction loss of the commutation current U c and suppressing heat generation are easily obtained. - ,L -

[0093] In the control method of the inverter according to the above embodiment, etc., the switching frequency is determined by comparing the rotational speed ω m of the rotating electrical machine 10 with a predetermined rotational speed threshold ω th . Then, when the rotational speed ω m is greater than the rotational speed threshold ω th , the dead time τ is shortened compared to the case where the rotational speed ω m is less than or equal to the rotational speed threshold ω th .

[0094] When the rotational speed ω m of the rotating electrical machine 10 is high, the switching frequency increases. As a result, the commutation current U - ,L - flows, and the switching elements U​U ~W L is also turned on (ON sync ) more frequently. That is, the number of times the dead time τ is inserted increases. Therefore, as described above, the rotational speed ω of the rotating electrical machine 10 m determines the switching frequency of the switching element U U ~W L (MOSFET22), and when the rotational speed ω m is large and the switching frequency is high, reducing the dead time τ can particularly easily obtain the benefits of reducing the conduction loss of the reflux current U - ,L - and suppressing heat generation.

[0095] In the inverter control method according to the above embodiment, etc., based on the switching speed of the switching element U U ~W L , it is determined whether the dead time τ can be changed. And when the dead time τ can be changed, the dead time τ is changed according to the switching frequency.

[0096] The change of the dead time τ according to the switching frequency should be performed when there is room to reduce the dead time τ, and it is not desirable to force it until there is no room to reduce the dead time τ. Therefore, as described above, it is preferable to determine whether the change (reduction) of the dead time τ is possible, and to execute the change of the dead time τ according to the switching frequency only when the dead time τ is changed. Also, if the dead time τ is reduced after confirming that there is room to reduce the dead time τ, the inverter 12 can be operated safely and stably even if the dead time τ is reduced.

[0097] In the inverter control method according to the above embodiment, etc., the gate resistance R U ~W L of the switching element U G is variable, and when changing the switching speed by changing the gate resistance R G , when changing the switching speed by changing the gate resistance R GDetermine whether the dead time τ can be changed according to the value.

[0098] Thus, when the gate resistance R G is variable, it is preferable to determine whether the dead time τ can be changed according to the value of the gate resistance R G . The dead time τ is usually set according to the most severe conditions, that is, when the gate resistance R G is high and the switching of the MOSFET 22 is slow. Therefore, when the gate resistance R G is lowered, there is room to reduce the dead time τ. Therefore, as described above, the gate resistance R G is easy to use as a criterion for whether the dead time τ can be changed.

[0099] In the inverter control method according to the above embodiment, etc., when changing the dead time τ according to the switching frequency, further, compare the DC voltage V dc , which is the voltage of the DC power, with a predetermined voltage threshold V th . Then, when the DC voltage V dc is smaller than the voltage threshold V th , shorten the dead time τ compared with the case where the DC voltage V dc is equal to or higher than the voltage threshold V th .

[0100] The DC voltage V dc is a measure of the voltage applied between the DS of the switching elements U U ~W L (so-called V DS ). When the DC voltage V dc is low, the switching (especially turn-off) of the switching elements U U ~W L becomes faster. That is, the turn-off time T F of the MOSFET 22 becomes shorter. Therefore, as described above, when the DC voltage V dc is low, by shortening the dead time τ, in particular, the benefits of reducing the conduction loss of the reflux current U - , L - and suppressing heat generation can be easily obtained.

[0101] In the inverter control method according to the above-described embodiment, etc., when changing the dead time τ according to the switching frequency, further, the rotational electric machine current (I ph ) which is the current flowing through the rotational electric machine 10 is compared with a preset current threshold value I th . Then, when the rotational electric machine current (I ph ) is larger than the current threshold value I th , the dead time τ is made shorter as compared with the case where the rotational electric machine current (I ph ) is equal to or less than the current threshold value I th .

[0102] The rotational electric machine current (phase current I ph ) is a measure of the current flowing through the switching elements U U to W L . That is, when the rotational electric machine current (phase current I ph ) is large, the reflux current U U to L L flowing through the switching elements U - to W - also becomes large. Therefore, as described above, when the dead time τ is made shorter when the rotational electric machine current (phase current I ph ) is large, in particular, the benefits of reducing the conduction loss of the reflux current U - to L - and suppressing heat generation are easily obtained.

[0103] In the inverter control method according to the above-described embodiment, etc., for each of the plurality of phases of the rotational electric machine 10, the dead time τ is changed according to the switching frequency of the switching elements U U to W L .

[0104] Thus, by changing the dead time τ according to the switching frequency for each phase of the rotational electric machine 10, it is possible to set a dead time τ suitable for each phase without being affected by other phases. Therefore, it is easy to reduce the conduction loss of the reflux current U - to L - and suppress heat generation.

[0105] In the inverter control method according to the above-described embodiment, etc., the carrier frequency f of the PWM control c is greater than a predetermined frequency threshold f th , and the DC voltage V, which is the voltage of the DC power dc is less than a predetermined voltage threshold V th , and when the current flowing through the rotating electrical machine 10, i.e., the rotating electrical machine current (I ph ), is equal to a predetermined current threshold I th , the dead time τ is set so as to be equal to or greater than the minimum guaranteed value (τ LL ).

[0106] Thus, by setting the dead time τ, even when the dead time τ is changed according to the switching frequency, the lower limit dead time τ LL is ensured. Therefore, the inverter 12 can operate stably.

[0107] The inverter control device according to the above-described embodiment, etc., forms a channel that conducts between the drain (D) and the source (S) by the gate voltage V G , and includes a body diode 23 that allows the reflux current U - ,L - to flow through, and is a control device (controller 14) of the inverter 12 that converts the input DC power (V dc ) into AC power by PWM control using switching elements U U ~W L and supplies the AC power to the rotating electrical machine 10. In this control device, when the reflux current U - ,L - flows through the body diode 23, the gate voltage V G is controlled to leave a dead time τ and to conduct between the drain (D) and the source (S), and the dead time τ is changed according to the switching frequency of the switching elements U U ~W L .

[0108] Thus, when the reflux current U - ,L -At the timing when the current flows, the switching element U U ~W L is turned on (ON sync ), and the reflux current U - , L - is made to flow through the channel, so that the conduction loss of the reflux current U - , L - is reduced. At this time, only during the dead time τ, the reflux current U - , L - flows through the body diode 23. However, as described above, in the control of the inverter according to the above embodiment etc., by changing the dead time τ according to the switching frequency of the switching element U U ~W L (MOSFET22), the period during which the reflux current U - , L - flows through the body diode 23 is reduced. As a result, the conduction loss of the reflux current U - , L - is further reduced. Also, by reducing the conduction loss of the reflux current U-, L-, the heat generation of the inverter 12 is suppressed. In particular, when the rotating electrical machine 10 is driven at a high load such that it rotates at a high speed and has a high torque, the heat generation of the inverter 12 is easily suppressed.

[0109] As described above, the embodiments of the present invention have been described. However, the configurations described in the above embodiments and modification examples only show a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention.

Explanation of Reference Numerals

[0110] 10: Rotating electrical machine, 11: Battery, 12: Inverter, 13: Gate driver, 14: Controller, 21: Smoothing capacitor, 23: Body diode, 24: Voltage sensor, 25: Current sensor, 31: Floating power supply, 32: Carrier control unit, 33: PWM generation unit, 34: Dead time generation unit, 35: Dead time control unit, 36: Gate resistance control unit, 100: Rotating electrical machine system

Claims

1. A control method for an inverter that uses a switching element that forms a channel for conducting between a drain and a source by a gate voltage, includes a body diode through which a reflux current flows, and has reverse conductivity by the channel, and converts input DC power into AC power by PWM control and supplies the AC power to a rotating electrical machine, comprising: When the reflux current flows through the body diode, controlling the gate voltage so that the drain and the source are conductive with a dead time, and changing the dead time according to the switching frequency of the switching element. A control method for an inverter.

2. A control method for an inverter according to claim 1, comprising: determining the switching frequency by comparing a carrier frequency of the PWM control with a preset frequency threshold, when the carrier frequency is greater than the frequency threshold, shortening the dead time as compared with the case where the carrier frequency is less than or equal to the frequency threshold. A control method for an inverter.

3. A control method for an inverter according to claim 1, comprising: determining the switching frequency by comparing a rotational speed of the rotating electrical machine with a preset rotational speed threshold, when the rotational speed is greater than the rotational speed threshold, shortening the dead time as compared with the case where the rotational speed is less than or equal to the rotational speed threshold. A control method for an inverter.

4. A control method for an inverter according to claim 1, comprising: determining whether the dead time can be changed based on a switching speed of the switching element, when the dead time can be changed, changing the dead time according to the switching frequency. A control method for an inverter.

5. A control method for an inverter according to claim 4, comprising: when the gate resistance of the switching element is variable and the switching speed is changed by changing the gate resistance, determining whether the dead time can be changed according to the value of the gate resistance. A control method for an inverter.

6. A control method for an inverter according to claim 1, comprising: when changing the dead time according to the switching frequency, further comparing a DC voltage, which is a voltage of the DC power, with a preset voltage threshold. When the DC voltage is less than the voltage threshold, the dead time is shortened as compared with the case where the DC voltage is equal to or greater than the voltage threshold. Inverter control method.

7. The inverter control method according to claim 1, When changing the dead time according to the switching frequency, further compare the rotating electrical machine current, which is the current flowing through the rotating electrical machine, with a predetermined current threshold, When the rotating electrical machine current is greater than the current threshold, the dead time is shortened as compared with the case where the rotating electrical machine current is equal to or less than the current threshold. Inverter control method.

8. The inverter control method according to claim 1, For each of a plurality of phases of the rotating electrical machine, the dead time is changed according to the switching frequency of the switching element. Inverter control method.

9. The inverter control method according to claim 1, The dead time is set so that when the carrier frequency of the PWM control is greater than a predetermined frequency threshold, the DC voltage, which is the voltage of the DC power, is less than a predetermined voltage threshold, and the rotating electrical machine current, which is the current flowing through the rotating electrical machine, is equal to a predetermined current threshold, the dead time is equal to or greater than a minimum guaranteed value. Inverter control method.

10. An inverter control device that forms a channel that conducts between the drain and the source by a gate voltage, includes a body diode that conducts a reflux current, and uses a switching element having reverse conductivity by the channel to convert the input DC power into AC power by PWM control and supply the AC power to the rotating electrical machine 10, When the reflux current flows through the body diode, control the gate voltage so that the drain and the source are conductive with a dead time, and Change the dead time according to the switching frequency of the switching element. Inverter control device.

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