JP2013021868A - Control device for switching circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the loss of a switching circuit while preventing an increase in cost required for the configuration.SOLUTION: A PWM operation unit 25 capable of independently setting each on-duty of a high-side switching element and a low-side switching element determines whether a forward current does not flow through any of the high-side switching element and the low-side switching element on the basis of a load current flowing through a motor detected by a phase-current detection unit 32. A reverse-direction duty determination unit 25a determines that the on-duty of the switching element, which is determined that the forward current does not flow therethrough, is set to be zero when an absolution value of the load current or conduction loss of the forward current is more than or equal to a predetermined value. The PWM operation unit 25 sets the on-duty of the switching element, which is determined that the forward current does not flow therethrough, to be zero on the basis of the determination result of the reverse-direction duty determination unit 25a.

Description

  The present invention relates to a control device for a switching circuit.

2. Description of the Related Art Conventionally, there is known a voltage converter that is mounted on, for example, an electric vehicle and drives a load such as a motor by controlling ON / OFF of a switching element of a switching circuit using electric power supplied from a DC power source (for example, , See Patent Document 1).
A switching circuit included in the voltage converter includes a high-side switching element that is connected to a high-potential side terminal to configure a high-side arm, and a low-side switching element that is connected to a low-potential-side terminal to configure a low-side arm. Each of the switching elements includes a free-wheeling diode connected in parallel in the reverse conduction direction, and an inductive load such as a motor is connected to a connection point between the high-side arm and the low-side arm.

Japanese Patent No. 4306236

  By the way, in the switching circuit provided in the voltage converter according to the above-described prior art, a bidirectional semiconductor element capable of reverse conduction such as a MOSFET (Metal Oxide Semi-conductor Field Effect Transistor) is employed as a switching element, for example. For example, when the switching elements of the high side arm and the low side arm are alternately turned ON / OFF by complementary PWM (pulse width modulation), the commutation current that flows in the switching circuit when each switching element is switched from ON to OFF. (Reverse current) flows through the switching element and the free wheel diode connected in parallel.

In this case, for example, the commutation current (reverse current) flows only in the freewheeling diode, and as a result, the combined resistance of the switching element connected in parallel and the freewheeling diode is reduced. Loss can be reduced.
In addition, since the conduction loss and heat generation of the freewheeling diode are reduced, the heat resistance performance of the freewheeling diode can be reduced by reducing the size of the freewheeling diode, for example, and the cost required for the freewheeling diode can be reduced. .

However, in the switching element, conduction loss occurs in both the case where the forward current flows and the case where the commutation current (reverse current) flows. For example, compared to the case where only the forward current flows, heat generation in the switching element There is a possibility that the heat resistance performance needs to be increased with the increase.
In order to increase the heat resistance performance of the switching element, for example, there are known methods such as increasing the size of the switching element or configuring the switching element by a plurality of elements arranged in parallel. Compared to having a complicated structure, the cost required to increase the heat resistance performance of the switching element may exceed the cost reduced by reducing the heat resistance performance of the reflux diode, and the cost required for the configuration will increase. Problems arise.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a switching circuit control device capable of preventing thermal damage to the switching circuit while preventing an increase in cost required for the configuration. .

  In order to solve the above problems and achieve the object, a switching circuit control device according to claim 1 of the present invention includes a high-side switching element (for example, each transistor UH, VH, WH in the embodiment) and A high-side arm formed by connecting free-wheeling diodes (for example, the free-wheeling diodes DUH, DVH, and DWH in the embodiment) in antiparallel, and a low-side switching element (for example, each of the transistors UL, VL, WL) and a freewheeling diode (for example, each freewheeling diode DUL, DVL, DWL in the embodiment) connected in series to a low-side arm, and a switching circuit control device configured in series In the predetermined switching cycle, the on-duty of the high-side switching element and the on-state of the low-side switching element Duty setting means (for example, PWM calculation unit 25 in the embodiment) capable of independently setting the duty and a load (for example, in the embodiment) connected to a connection point of the high side arm and the low side arm Load current detection means (for example, each phase current detection unit 32 in the embodiment) for detecting the load current flowing in the motor 12) and the high side based on the load current detected by the load current detection means First determination means (for example, also serving as the PWM calculation unit 25 in the embodiment) for determining which of the switching element and the low-side switching element a forward current does not flow through; The duty setting means is configured to detect the on-duty of the switching element that is determined by the first determination means that the forward current is not flowing. Setting the I to zero.

  Furthermore, the switching circuit control apparatus according to claim 2 of the present invention sets whether or not the on-duty of the switching element, which is determined by the first determination means that the forward current is not flowing, is set to zero. In the case where it is determined that the on-duty is set to zero by the second determination means. The on-duty of the switching element determined by the first determination means that the forward current is not flowing is set to zero.

  Further, in the switching circuit control device according to claim 3 of the present invention, the second determination means may perform the first determination when the absolute value of the load current or the conduction loss of the forward current is equal to or greater than a predetermined value. It is determined that the on-duty of the switching element determined by the means that the forward current is not flowing is set to zero.

According to the switching circuit control device of the first aspect of the present invention, a bidirectional switching element capable of reverse conduction as compared with the case where the high-side switching element and the low-side switching element are turned on / off in a complementary operation. The conduction loss can be reduced.
As a result, for example, it is possible to prevent the necessity of increasing the heat resistance performance of the switching element by increasing the size of the switching element or configuring the switching element by a plurality of elements arranged in parallel. It is possible to prevent the switching element and the reflux diode from being thermally damaged while preventing the bulking.
Moreover, since the detection result of the load current detection means for detecting the load current used for load control is used, which of the high-side switching element and the low-side switching element does not have a forward current flowing therethrough Therefore, it is possible to prevent an increase in the cost required for the apparatus configuration without requiring a special detection device for determining the above.

Furthermore, according to the switching circuit control apparatus of the second aspect of the present invention, the on-duty of the switching element determined by the second determination means that the forward current is not flowing by the first determination means is set to zero. Whether or not to do so can be determined.
Therefore, according to the operation state of the switching circuit, the on-duty of the switching element determined that the forward current is not flowing by the first determination unit is set to zero, and the loss generated in the switching element due to the reverse current is reduced. In this case, the reverse current flows through both the switching element and the free wheeling diode without setting the on-duty of the switching element determined that the forward current is not flowing by the first determination means to zero. Thus, the switching operation can be switched between the case of reducing the loss of the switching circuit.

Furthermore, according to the switching circuit control apparatus of the third aspect of the present invention, when the load current is small and the heating of the switching element is small, the commutation current (reverse current) is generated between the switching element and the free wheel diode. It can be made to flow in both.
When the commutation current (reverse current) flows through both the switching element and the return diode, compared to when the commutation current flows only through the return diode or when the reverse current flows only through the switching element, The conduction resistance can be reduced, the conduction loss caused by the reverse current flowing can be reduced, and the loss of the switching circuit can be reduced.

It is a block diagram of the control apparatus of the switching circuit which concerns on embodiment of this invention. It is a block diagram of the control apparatus of the switching circuit which concerns on embodiment of this invention. It is a figure which shows an example of the correspondence of the target torque of a motor, the rotation speed, and a forward current in the control apparatus of the switching circuit which concerns on embodiment of this invention. It is a figure which shows an example of the electric current which flows into the high side switching element, the low side switching element, and freewheeling diode in the control apparatus of the switching circuit which concerns on embodiment of this invention. It is a figure which shows an example of the ON / OFF state of the high side switching element and the low side switching element in the control apparatus of the switching circuit which concerns on embodiment of this invention. In the control device for a switching circuit according to the embodiment of the present invention, a case where a current flows only to the switching element (MOSFET), a case where a current flows only to the freewheeling diode, a switching element (MOSFET) connected in antiparallel, and It is a figure which shows the example of the current-voltage characteristic with respect to the case where an electric current flows into both the free-wheeling diodes. It is a figure which shows the example of the ON / OFF state of the high side switching element and the low side switching element in the control apparatus of the switching circuit which concerns on embodiment of this invention. It is a flowchart which shows operation | movement of the control apparatus of the switching circuit which concerns on embodiment of this invention. It is a flowchart which shows operation | movement of the control apparatus of the switching circuit which concerns on embodiment of this invention. It is a flowchart which shows operation | movement of the control apparatus of the switching circuit which concerns on the 1st modification of embodiment of this invention. It is a figure which shows the example of the energization ratio of the commutation current (reverse direction current) of the switching element of the control apparatus of the switching circuit which concerns on the 1st modification of embodiment of this invention, and a return diode. It is a flowchart which shows operation | movement of the control apparatus of the switching circuit which concerns on the 1st modification of embodiment of this invention. It is a flowchart which shows operation | movement of the control apparatus of the switching circuit which concerns on the 2nd modification of embodiment of this invention. It is a flowchart which shows operation | movement of the control apparatus of the switching circuit which concerns on the 3rd modification of embodiment of this invention. It is a flowchart which shows operation | movement of the control apparatus of the switching circuit which concerns on the 4th modification of embodiment of this invention.

Hereinafter, a control device for a switching circuit according to an embodiment of the present invention will be described with reference to the accompanying drawings.
The switching circuit control device 10 according to the present embodiment is mounted on a vehicle, for example, and has three phases (for example, three phases of U phase, V phase, and W phase) using a battery 11 as a DC power source as shown in FIGS. Phase) An inverter 13 that controls an AC brushless DC motor 12 (hereinafter simply referred to as a motor 12) and a processing device 14 are provided.

  The inverter 13 includes a bridge circuit (switching circuit) 13a formed by bridge connection using a plurality of switching elements (for example, bidirectional MOSFET: Metal Oxide Semiconductor Field Effect Transistor) and a smoothing capacitor C. The bridge circuit 13a is driven by a pulse width modulated (PWM) signal.

In this bridge circuit 13a, for example, a high-side and low-side U-phase transistor UH, UL paired for each phase, a high-side and low-side V-phase transistor VH, VL, a high-side and low-side W-phase transistor WH, WL is bridge-connected.
Each of the transistors UH, VH, and WH has a drain connected to the positive terminal of the battery 11 to form a high-side arm, and each of the transistors UL, VL, and WL has a source connected to the negative terminal of the battery 11 that is grounded. And constitutes the low-side arm.
For each phase, the sources of the high-side arm transistors UH, VH, WH are connected to the drains of the low-side arm transistors UL, VL, WL, and the transistors UH, UL, VH, VL, WH, The free-wheeling diodes DUH, DUL, DVH, DVL, DWH, and DWL are connected between the drain and source of WL so as to be in the forward direction from the source to the drain.

That is, the bridge circuit 13a connects the high-side switching elements (transistors UH, VH, WH) and the free wheel diodes (return diodes DUH, DVH, DWH) in anti-parallel for each phase (that is, bidirectional conduction type). A high-side arm formed by connecting in parallel a high-side switching element and a free-wheeling diode reversely conducting with respect to the forward conduction of the high-side switching element, and a low-side switching element (each transistor UL, VL, WL) and free-wheeling diodes (respective free-wheeling diodes DUL, DVL, DWL) are connected in antiparallel (that is, bidirectional conduction type low-side switching element and reverse conduction with respect to forward conduction of the low-side switching element) A low-side arm that is connected in parallel with a free-wheeling diode that is connected in series for each phase. That.
And the stator winding 12a of the motor 12 is connected to the connection point of the high side arm and the low side arm for each phase.

  For example, when the motor 12 is driven, the inverter 13 is a gate signal (that is, a PWM signal) that is a switching command output from the processing device 14 and input to the gates of the transistors UH, VH, WH, UL, VL, and WL. Based on the above, the on (conducting) / off (shut off) state of each transistor paired for each phase is switched. As a result, the DC power supplied from the battery 11 is converted into three-phase AC power, and energization to the three-phase stator winding 12a is sequentially commutated, so that the AC U-phase is supplied to the stator winding 12a of each phase. Current Iu, V-phase current Iv and W-phase current Iw are energized.

  On the other hand, at the time of regeneration of the motor 12, for example, the inverter 13 is synchronized for each phase based on the gate signal (that is, PWM signal) output from the processing device 14 in synchronization with the rotation angle of the motor 12. By switching the on / off (cutoff) state of each of the transistors, the three-phase AC power output from the motor 12 can be converted into DC power and the battery 11 can be charged.

  The processing device 14 performs, for example, feedback control (vector control) of current on the dq coordinates forming the rotation orthogonal coordinates, and calculates the target d-axis current Idc and the target q-axis current Iqc. Then, each phase voltage command Vu, Vv, Vw is calculated based on the target d-axis current Idc and the target q-axis current Iqc, and a PWM signal that is a gate signal for the inverter 13 according to each phase voltage command Vu, Vv, Vw. Is output. Then, the d-axis current Id and q-axis current Iq obtained by converting the phase currents Iu, Iv, and Iw actually supplied from the inverter 13 to the motor 12 on the dq coordinate, the target d-axis current Idc, and the target q Control is performed so that each deviation from the shaft current Iqc becomes zero.

  The processing device 14 includes, for example, a current command calculation unit 21, a difference calculation unit 22, a current feedback calculation unit 23, a dq-3 phase conversion unit 24, a PWM calculation unit 25, and a three phase-dq conversion unit 26. It is configured with.

  The current command calculation unit 21 calculates a current command for designating each phase current Iu, Iv, Iw supplied from the inverter 13 to the motor 12 based on the target torque and the rotation speed of the motor 12. The current command is output to the difference calculation unit 22 as the target d-axis current Idc and the target q-axis current Iqc on the rotating orthogonal coordinates.

  The rotation speed of the motor 12 is detected from a rotation angle sensor 31 that detects a rotation angle of a rotor (not shown) (for example, a rotation angle of a rotor magnetic pole from a predetermined reference rotation position), for example. It may be calculated based on the value, or may be detected by a rotational speed sensor (not shown) that detects the rotational speed of the rotor (not shown).

For example, as shown in FIG. 3, the current command calculation unit 21 stores data such as a map indicating a predetermined correspondence relationship between the target torque of the motor 12, the rotation speed, and the forward current of the switching element in advance with a plurality of different power supply voltages ( That is, it is stored in association with each output voltage of the battery 11.
Then, the current command calculation unit 21 acquires the forward current of the switching element according to the target torque, the rotation speed, and the power supply voltage of the motor 12 by a map search or the like for a map stored in advance, and this forward current The target d-axis current Idc and the target q-axis current Iqc corresponding to the above are calculated.

  Note that, for example, in a predetermined map for an appropriate power supply voltage A shown in FIG. 3, the forward current is set to increase as the target torque increases, the rotation speed increases, or the power supply voltage decreases. However, the present invention is not limited to this, and for example, it may be set to show an appropriate tendency according to the characteristics of the motor 12 and the inverter 13 or the element characteristic data.

Further, the dq coordinate forming the rotation orthogonal coordinate is, for example, a direction perpendicular to the d axis, where the magnetic flux direction of the field pole by the permanent magnet provided in the rotor (not shown) of the motor 12 is the d axis (field axis). Is the q-axis (torque axis) and rotates in synchronization with the rotational phase of the rotor.
As a result, the target d-axis current Idc and the target q-axis current Iqc, which are DC signals, are given as current commands for the AC signal supplied from the inverter 13 to each phase of the motor 12.

The difference calculation unit 22 includes each of the target d-axis current Idc and target q-axis current Iqc output from the current command calculation unit 21 and the d-axis current Id and q-axis current Iq output from the three-phase-dq conversion unit 26. Deviations ΔId and ΔIq are calculated.
The current feedback calculation unit 23 controls and amplifies the deviations ΔId and ΔIq by, for example, a PID (proportional integral differentiation) operation to calculate the d-axis voltage command value Vd and the q-axis voltage command value Vq.

  The dq-3 phase conversion unit 24 uses the rotation angle detection value output from the rotation angle sensor 31 that detects the rotation angle of the rotor (not shown) of the motor 12 to detect the d-axis voltage command value Vd on the dq coordinate. The q-axis voltage command value Vq is converted into a U-phase output voltage Vu, a V-phase output voltage Vv, and a W-phase output voltage Vw, which are voltage command values on a three-phase AC coordinate that is a stationary coordinate.

  For example, when the motor 12 is driven, the PWM calculation unit 25 outputs each phase output voltage in order to pass the AC sine-wave U-phase current Iu, V-phase current Iv, and W-phase current Iw to the stator windings 12a of each phase. Vu, Vv, Vw and a carrier signal such as a triangular wave are compared to generate a gate signal (that is, a PWM signal) for driving each transistor UH, VH, WH, UL, VL, WL of the inverter 13 on / off. .

The PWM calculation unit 25 can independently set the on-duty of each switching element of the high side arm and the low side arm.
For example, as shown in FIGS. 4 (A), 4 (B) and FIGS. 5 (A), (B), the PWM calculation unit 25 performs high-side arm and low-side of the bridge circuit 13a by so-called complementary PWM (pulse width modulation). This is an on-duty of an operation in which each switching element of the arm is alternately turned ON / OFF and a switching element in which a forward current does not flow (that is, a switching element connected in parallel to a free-wheeling diode in which a commutation current flows). The operation of setting the reverse duty to zero is switched and executed.
The ON ratio of the high-side switching element and the low-side switching element for each phase is as follows: high-side and low-side on-duty DutyU (H, L), DutyV (H, L), DutyW (H, for each phase) L).

  Based on the detected values of the phase currents Iu, Iv, and Iw detected by the phase current detectors 32, the PWM calculator 25 applies a forward current to any of the high-side switching elements and the low-side switching elements. Further, it is determined whether or not the on-duty (that is, the reverse duty) of the switching element determined that the forward current is not flowing in the determination result is set to zero. A reverse duty determination unit 25a is provided.

  For example, the PWM calculation unit 25 performs an operation by complementary PWM (pulse width modulation) as a normal control operation. In this case, the high-side switching element (SW1) of the high-side arm is turned on and the low-side arm is turned on. The low-side switching element (SW2) is switched off and the high-side switching element (SW1) of the high-side arm is off and the low-side switching element (SW2) of the low-side arm is alternately switched on. .

Accordingly, for example, as shown in FIGS. 4A and 5A, when a forward current flows through the high-side switching element (SW1) when the high-side switching element (SW1) of the high-side arm is turned on. When the low-side switching element (SW2) of the low-side arm is turned on, a reverse current flows through the low-side switching element (SW2), and the free-wheeling diode (2) connected in reverse parallel to the low-side switching element (SW2) ) Commutation current.
In this case, for example, the on-duty (SW2_Ton) of the switching element in which the forward current does not flow is a value (= 100% −) corresponding to the on-duty (SW1_Ton) and the dead time (Tdead) of the switching element in which the forward current flows. SW1_Ton% -Tdead%).

  On the other hand, when a forward current flows through the low-side switching element (SW2) when the low-side switching element (SW2) of the low-side arm is on, high-side switching is performed when the high-side switching element (SW1) of the high-side arm is on. A reverse current flows through the element (SW1), and a commutation current flows through the freewheeling diode (1) connected in antiparallel to the high-side switching element (SW1).

  Note that, in a state where the switching element in which the forward current does not flow (that is, the switching element connected in parallel to the freewheeling diode in which the commutation current flows) is on, both the switching element and the freewheeling diode connected in parallel When the commutation current (reverse current) flows, for example, as shown in FIG. 6, compared to the case where the commutation current (reverse current) flows only to the switching element or only to the freewheeling diode, As the combined resistance of the switching element and the freewheeling diode decreases, the loss of the entire switching circuit can be reduced.

Further, the PWM calculation unit 25 determines the on-duty (that is, the reverse duty) of the switching element that is determined that the forward current is not flowing (that is, the switching element that is connected in parallel to the free-wheeling diode where the commutation current is flowing). If the reverse duty is determined by the reverse duty determination unit 25a when set to zero, the reverse duty is set to zero.
In this case, the ON state of the switching element in which the forward current flows and the OFF state of the switching element connected in parallel to the free wheel diode in which the commutation current flows, and the OFF state and the commutation current of the switching element in which the forward current flows are The switching element connected in parallel to the flowing free-wheeling diode is alternately switched off.

As a result, for example, as shown in FIGS. 4B, 5B and 7A, 7B, the high side switching element (SW1) of the high side arm is turned on as shown in FIG. When a forward current flows through the high-side switching element (SW1), the low-side switching element (SW2) of the low-side arm is not turned on regardless of whether the high-side switching element (SW1) is turned on or off. Sometimes a commutation current flows only through the freewheeling diode (2) connected in antiparallel to the low-side switching element (SW2).
In this case, the on-duty (SW2_Ton) of the switching element in which the forward current does not flow is zero.

  On the other hand, when a forward current flows through the low-side switching element (SW2) when the low-side switching element (SW2) of the low-side arm is turned on, the high-side regardless of whether the low-side switching element (SW2) is on or off. The high-side switching element (SW1) of the arm is not turned on, and a commutation current flows through the free-wheeling diode (1) connected in antiparallel to the high-side switching element (SW1).

  The reverse duty determination unit 25a is, for example, when the absolute value of each phase current Iu, Iv, Iw detected by each phase current detection unit 32 or the absolute value of the forward current is a predetermined value or more, or the forward current When the conduction loss is equal to or greater than a predetermined value, it is determined that the on-duty (that is, the reverse duty) of the switching element that is determined to have no forward current flowing is set to zero.

  The three-phase-dq converter 26 uses the detected value of each phase current Iu, Iv, Iw detected by each phase current detector 32 and the detected value of the rotation angle output from the rotation angle sensor 31 to The d-axis current Id and the q-axis current Iq on the rotation coordinate, that is, the dq coordinate, are calculated.

  The switching circuit control device 10 according to the present embodiment has the above-described configuration. Next, an operation example of the switching circuit control device 10 will be described.

First, for example, in step S01 shown in FIG. 8, the target torque, rotation angle and phase current of the motor 12 and the power supply voltage (that is, the output voltage of the battery 11) are acquired.
Next, in step S02, the forward current of the switching element according to the target torque, rotation speed, and power supply voltage of the motor 12 is calculated by a map search or the like for a map stored in advance.

Next, in step S03, it is determined whether or not the load current (for example, the phase current of the motor 12) is greater than zero (that is, the sign is positive).
If this determination is “NO”, the flow proceeds to step S 10 described later.
On the other hand, if this determination is “YES”, the flow proceeds to step S 04.

In step S04, the high-side on-duty DutyH of the high-side switching element is calculated based on the forward-direction current as the forward-direction duty that is the on-duty of the switching element through which the forward-direction current flows.
Next, in step S05, it is determined whether or not the absolute value of the forward current is less than a predetermined value Xa.
If this determination is “NO”, the flow proceeds to step S 06, and in this step S 06, the low-side on-duty DutyL of the low-side switching element is set to zero, and the flow proceeds to step S 09 described later.
On the other hand, if this determination is “YES”, the flow proceeds to step S07.

In step S07, a dead time Tdead (for example, a predetermined minimum dead time) for a switching element in which a forward current does not flow is acquired based on, for example, data stored in advance.
Next, in step S08, the low-side switching element is turned on as the on-duty of the switching element in which no forward current flows according to the forward duty (that is, the high-side on-duty DutyH) and the dead time Tdead. Duty DutyL (= 100% −DutyH% −Tdead%) is calculated.
In step S09, high-side and low-side on-duty duty U (H, L), Duty V (H, L), and Duty W (H, L) for each phase are output, and the process proceeds to the end.

In step S10, the low-side on-duty DutyL of the low-side switching element is calculated based on the forward-direction current as the forward-direction duty that is the on-duty of the switching element through which the forward-direction current flows.
Next, in step S11, it is determined whether or not the absolute value of the forward current is less than a predetermined value Xa.
If this determination is “NO”, the flow proceeds to step S 12, and in this step S 12, the high-side on-duty DutyH of the high-side switching element is set to zero, and the flow proceeds to step S 09 described above.
On the other hand, if the determination is “YES”, the flow proceeds to step S13.

In step S13, for example, based on data stored in advance, a dead time Tdead (for example, a predetermined minimum dead time) for a switching element in which no forward current flows is acquired.
Next, in step S14, the high-side switching element is turned on as the on-duty of the switching element in which no forward current flows according to the forward duty (that is, the low-side on-duty DutyL) and the dead time Tdead. The duty DutyH (= 100% −DutyL% −Tdead%) is calculated, and the process proceeds to step S09 described above.

  In step S05 and step S11 described above, instead of determining whether or not the absolute value of the forward current is less than the predetermined value Xa, for example, as in step S05a and step S11a shown in FIG. It may be determined whether or not the absolute value of the current conduction loss (forward loss) is less than a predetermined value Ploss.

As described above, according to the switching circuit control device 10 according to the present embodiment, the high-side switching element and the low-side switching element are set by setting the on-duty of the switching element in which the forward current does not flow to zero. The conduction loss of the bidirectional switching element capable of reverse conduction can be reduced as compared with the case where the on / off driving is performed by the complementary operation.
As a result, for example, it is possible to prevent the necessity of increasing the heat resistance performance of the switching element by increasing the size of the switching element or configuring the switching element by a plurality of elements arranged in parallel. It is possible to prevent the switching element and the reflux diode from being thermally damaged while preventing the bulking.

  Moreover, the detection result of each phase current detection unit 32 that detects the load current (that is, each phase current Iu, Iv, Iw) used for controlling the motor 12 is used to select a high-side switching element or a low-side switching element. Since it is determined to which switching element no forward current flows, it is possible to prevent an increase in the cost required for the apparatus configuration without requiring a special detection device.

  Furthermore, according to the operating state of the switching circuit, when the on-duty of the switching element determined that the forward current is not flowing is set to zero, the loss generated in the switching element due to the reverse current is reduced, Loss of switching circuit by setting reverse current (commutation current) through both switching element and freewheeling diode without setting on-duty of switching element determined that forward current is not flowing to zero It is possible to operate flexibly by switching between the cases of reducing the power consumption.

Furthermore, when the load current is small and the heat generation of the switching element is small, the commutation current (reverse direction current) can flow through both the switching element and the free wheeling diode.
When the commutation current (reverse current) flows through both the switching element and the return diode, compared to when the commutation current flows only through the return diode or when the reverse current flows only through the switching element, The conduction resistance can be reduced, the conduction loss caused by the reverse current flowing can be reduced, and the loss of the switching circuit can be reduced.

  In the above-described embodiment, when the absolute value of the forward current is less than the predetermined value Xa or the absolute value of the forward loss is less than the predetermined value Ploss, the on-duty of the switching element in which no forward current flows. Is a predetermined value (= 100% −forward duty% −Tdead%) corresponding to the on-duty (forward duty) and dead time (Tdead) of the switching element through which the forward current flows. However, the present invention is not limited to this. For example, it is good also as a value according to the energization ratio of the commutation current (reverse direction current) of a switching element and a return diode.

In the first modification, first, for example, in step S21 shown in FIG. 10, the target torque, rotation angle, phase current, and power supply voltage (that is, the output voltage of the battery 11) of the motor 12 are acquired.
Next, in step S22, the forward current of the switching element corresponding to the target torque, the rotation speed, and the power supply voltage of the motor 12 is calculated by a map search for a map stored in advance.

Next, in step S23, it is determined whether or not the load current (for example, the phase current of the motor 12) is greater than zero (that is, the sign is positive).
If this determination is “NO”, the flow proceeds to step S 32 described later.
On the other hand, if this determination is “YES”, the flow proceeds to step S24.

In step S24, the high-side on-duty DutyH of the high-side switching element is calculated based on the forward-direction current as the forward-direction duty that is the on-duty of the switching element through which the forward-direction current flows.
Next, in step S25, it is determined whether or not the absolute value of the forward current is less than a predetermined value Xa.
If this determination is “NO”, the flow proceeds to step S 26, and in this step S 26, the low-side on-duty DutyL of the low-side switching element is set to zero, and the flow proceeds to step S 31 described later.
On the other hand, if this determination is “YES”, the flow proceeds to step S27.

In step S27, the energization ratio of the commutation current (reverse current) between the switching element and the return diode is acquired with reference to, for example, a predetermined map or mathematical formula stored in advance.
For example, in the predetermined map shown in FIG. 11, the energization ratio (on-duty) of the freewheeling diode tends to increase from zero to a predetermined value larger than 50% as the commutation current (reverse current) increases. However, the present invention is not limited to this. For example, the motor 12, the inverter 13, and the like are set to change in a decreasing trend from a predetermined value larger than 50% toward zero. It may be set so as to show an appropriate tendency according to the characteristic or element characteristic data.
In step S28, the reverse current is calculated according to the energization ratio of the commutation current (reverse current) between the switching element and the return diode.
Note that the greater the forward current, the greater the commutation current (reverse current).

In step S29, for example, based on data stored in advance, a dead time Tdead (for example, a predetermined minimum dead time) for a switching element in which a forward current does not flow is acquired.
Next, in step S30, the low-side on-duty DutyL of the low-side switching element is calculated as the on-duty of the switching element in which no forward current flows, according to the reverse current and the dead time Tdead. Then, a limit process is performed on the calculation result with a predetermined upper limit value (= 100% −DutyH% −Tdead%) corresponding to the forward duty (that is, the high-side on-duty DutyH) and the dead time Tdead.

In this limit processing, if the calculation result is equal to or less than a predetermined upper limit value for the low-side on-duty DutyL, the calculation result is output as the low-side on-duty DutyL.
On the other hand, when the calculation result is larger than a predetermined upper limit value for the low-side on-duty duty L, the predetermined upper limit value is output as the low-side on-duty duty L.
In step S31, high-side and low-side on-duty duty U (H, L), Duty V (H, L), and Duty W (H, L) for each phase are output, and the process proceeds to the end.

In step S32, the low-side on-duty DutyL of the low-side switching element is calculated based on the forward-direction current as the forward-direction duty that is the on-duty of the switching element through which the forward-direction current flows.
Next, in step S33, it is determined whether or not the absolute value of the forward current is less than a predetermined value Xa.
If this determination is “NO”, the flow proceeds to step S 34, and in this step S 34, the high-side on-duty DutyH of the high-side switching element is set to zero, and the flow proceeds to step S 31 described above.
On the other hand, if the determination is “YES”, the flow proceeds to step S35.

In step S35, for example, the energization ratio of the commutation current (reverse current) between the switching element and the return diode is acquired with reference to a predetermined map or mathematical formula stored in advance.
In step S36, the reverse current is calculated according to the energization ratio of the commutation current (reverse current) between the switching element and the return diode.

In step S37, for example, based on data stored in advance, a dead time Tdead (for example, a predetermined minimum dead time) for a switching element in which no forward current flows is acquired.
Next, in step S38, the high-side on-duty DutyH of the high-side switching element is calculated as the on-duty of the switching element in which no forward current flows, according to the reverse current and the dead time Tdead. Then, a limit process is performed on the calculation result with a predetermined upper limit value (= 100% −DutyL% −Tdead%) according to the forward duty (that is, the low-side on-duty DutyL) and the dead time Tdead, It progresses to step S31 mentioned above.

In this limit processing, if the calculation result is equal to or less than a predetermined upper limit value for the high-side on-duty DutyH, the calculation result is output as the high-side on-duty DutyH.
On the other hand, when this calculation result is larger than a predetermined upper limit value for the high-side on-duty duty H, the predetermined upper limit value is output as the high-side on-duty duty H.
In step S09, high-side and low-side on-duty duty U (H, L), Duty V (H, L), and Duty W (H, L) for each phase are output, and the process proceeds to the end.

  In the first modified example, in step S25 and step S33 described above, whether or not the absolute value of the forward current is less than the predetermined value Xa, for example, as in step S25a and step S33a shown in FIG. Instead of determining, it may be determined whether or not the absolute value of forward current conduction loss (forward loss) is less than a predetermined value Ploss.

  According to this first modification, the reverse duty is set by setting the on-duty of the switching element in which the forward current does not flow according to the energization ratio of the commutation current (reverse current) between the switching element and the return diode. The operation of reducing the loss generated in the switching element due to the directional current and the operation of reducing the loss of the switching circuit can be controlled more flexibly.

  In the above-described embodiment, the PWM calculation unit 25 performs a switching operation by complementary PWM (pulse width modulation) as a normal control operation. However, the present invention is not limited to this, and a forward current simply flows. The on-duty (that is, the reverse duty) of the switching element determined not to be set may be set to zero.

In the second modification, first, for example, in step S41 shown in FIG. 13, the rotation angle and phase current of the motor 12 and the power supply voltage (that is, the output voltage of the battery 11) are acquired.
Next, in step S42, the forward current of the switching element corresponding to the target torque, the rotation speed, and the power supply voltage of the motor 12 is calculated by searching a map stored in advance.

Next, in step S43, the forward duty is calculated based on the forward current.
Next, in step S44, based on, for example, data stored in advance, a dead time Tdead (for example, a predetermined minimum dead time) for a switching element in which a reverse current flows is acquired.
Next, in step S45, a reverse duty (= 100% -forward duty% -Tdead%) is calculated according to the forward duty and dead time Tdead.

Next, in step S46, it is determined whether or not the load current (that is, the phase current of the motor 12) is greater than zero (that is, the sign is positive).
If this determination is “YES”, the flow proceeds to step S 47, in which the high-side on-duty DutyH of the high-side switching element is set as the forward duty, and the low-side on-duty DutyL of the low-side switching element is set to Zero.
On the other hand, if this determination is “NO”, the flow proceeds to step S 48, in which the low-side on-duty DutyL of the low-side switching element is the forward duty, and the high-side on-duty of the high-side switching element is Set DutyH to zero.
In step S49, the high-side and low-side on-duty duty U (H, L), Duty V (H, L), and Duty W (H, L) for each phase are output, and the process proceeds to the end.

  In the second modification of the above-described embodiment, instead of the processes of steps S41 to S49, the processes of steps S51 to S60 such as the third modification shown in FIG. 14 may be executed. Good.

In the third modification, first, for example, in step S51 shown in FIG. 14, the rotation angle and phase current of the motor 12 and the power supply voltage (that is, the output voltage of the battery 11) are acquired.
Next, in step S52, the forward current of the switching element according to the target torque, the rotation speed, and the power supply voltage of the motor 12 is calculated by searching a map stored in advance.

Next, in step S53, it is determined whether or not the load current (that is, the phase current of the motor 12) is greater than zero (that is, the sign is positive).
If this determination is “NO”, the flow proceeds to step S 57 described later.
On the other hand, if this determination is “YES”, the flow proceeds to step S54.
Next, in step S54, based on, for example, data stored in advance, a dead time Tdead (for example, a predetermined minimum dead time) for a switching element through which a forward current flows is acquired.

Next, in step S55, based on the forward current and the dead time Tdead, the forward duty is calculated as the high-side on-duty DutyH of the high-side switching element.
Next, in step S56, the low-side on-duty duty L of the low-side switching element is set to zero.
In step S57, the high-side and low-side on-duty duty U (H, L), Duty V (H, L), and Duty W (H, L) for each phase are output, and the process proceeds to the end.

In step S58, a dead time Tdead (for example, a predetermined minimum dead time) for a switching element through which a forward current flows is acquired based on, for example, data stored in advance.
Next, in step S59, the forward duty is calculated as the low-side on-duty DutyL of the low-side switching element based on the forward current and the dead time Tdead.
Next, in step S60, the high-side on-duty duty H of the high-side switching element is set to zero, and the process proceeds to step S57 described above.

  Further, in the third modified example of the above-described embodiment, instead of the process of step S51 to step S60, the process of step S61 to step S60 as in the fourth modified example shown in FIG. Good.

In the fourth modification, first, for example, in step S61 shown in FIG. 15, the rotation angle and phase current of the motor 12 and the power supply voltage (that is, the output voltage of the battery 11) are acquired.
Next, in step S62, the forward current of the switching element according to the target torque, the rotation speed, and the power supply voltage of the motor 12 is calculated by searching a map stored in advance.

Next, in step S63, it is determined whether or not the load current (that is, the phase current of the motor 12) is greater than zero (that is, the sign is positive).
If this determination is “NO”, the flow proceeds to step S 68 described later.
On the other hand, if this determination is “YES”, the flow proceeds to step S64.
Next, in step S64, based on, for example, data stored in advance, a dead time Tdead (for example, a predetermined minimum dead time) for a switching element through which a forward current flows is acquired.

Next, in step S65, based on the forward current and the dead time Tdead, the forward duty is calculated as the high-side on-duty DutyH of the high-side switching element.
Next, in step S66, the low-side on-duty duty L of the low-side switching element is set to zero.
In step S67, the high-side and low-side on-duty duty U (H, L), Duty V (H, L), and Duty W (H, L) for each phase are output, and the process proceeds to the end.

In step S68, a dead time Tdead (for example, a predetermined minimum dead time) for a switching element through which a forward current flows is acquired based on, for example, data stored in advance.
Next, in step S69, the reverse duty is calculated as the high-side on-duty DutyH of the high-side switching element with reference to, for example, a map or formula stored in advance based on the forward current.
Next, in step S70, the low-side on-duty duty L (= 100% −DutyH% −Tdead%) of the low-side switching element is calculated based on the high-side on-duty DutyH (that is, reverse duty) and the dead time Tdead. .
Next, in step S71, the high-side on-duty duty H of the high-side switching element is set to zero, and the process proceeds to step S67 described above.

  According to these first to fourth modifications, the conduction loss of the bidirectional switching element capable of reverse conduction can be reduced as compared with the case where the high-side switching element and the low-side switching element are driven on / off in a complementary operation. Can be reduced.

10 Switching circuit controller 12 Motor (load)
13 Inverter 13a Bridge circuit (switching circuit)
14 processor 25 PWM calculation part (duty setting means, first determination means)
25a Reverse duty determination unit (second determination means)
32 phase current detector (load current detection means)

Claims (3)

Switching configured by connecting in series a high-side arm formed by connecting a high-side switching element and a freewheeling diode in antiparallel and a low-side arm formed by connecting a low-side switching element and a freewheeling diode in antiparallel. A control device for a circuit,
Duty setting means capable of independently setting an on-duty of the high-side switching element and an on-duty of the low-side switching element in a predetermined switching cycle;
Load current detecting means for detecting a load current flowing in a load connected to a connection point of the high side arm and the low side arm;
Based on the load current detected by the load current detection means, a first determination means for determining which of the high-side switching element and the low-side switching element a forward current is not flowing; With
The control apparatus for a switching circuit, wherein the duty setting means sets the on-duty of the switching element that is determined by the first determination means that the forward current is not flowing to zero. Second determining means for determining whether or not to set the on-duty of the switching element determined by the first determining means that the forward current is not flowing to zero;
The duty setting means includes
When the on-duty is determined to be set to zero by the second determining means, the on-duty of the switching element that is determined by the first determining means that the forward current is not flowing is set to zero. The control apparatus for a switching circuit according to claim 1. The second determination means includes
When the absolute value of the load current or the conduction loss of the forward current is greater than or equal to a predetermined value, the on-duty of the switching element determined by the first determination means that the forward current is not flowing is set to zero. 3. The switching circuit control device according to claim 2, wherein it is determined to be set.

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