JP2013021869A - Control device for switching circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the loss of a switching circuit.SOLUTION: A control device for a switching circuit includes a PWM operation unit 25 capable of independently setting each on-duty of a high-side switching element and a low-side switching element in a predetermined switching period. The PWM operation unit 25 includes an energization-ratio operation unit 25a for calculating the integrated value of the on-duty in a plurality of previous switching periods. The PWM operation unit 25 sets the on-duty of the switching element through which a forward current does not flow on the basis of the integrated value of the on-duty calculated by the energization-ratio operation 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 connected to a high-potential side terminal to constitute a high-side arm, and a low-side switching element connected to a low-potential side terminal to constitute a low-side arm. And a free-wheeling diode connected in parallel to each switching element 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, when each switching element switches from ON to OFF, for example, by adopting an IGBT (Insulated Gate Bipolar Transistor) as the switching element, the switching circuit If the commutation current (reverse current) flowing in the circuit is configured to flow only to the freewheeling diode without flowing to the switching element, the conduction loss in the freewheeling diode increases and the loss of the entire switching circuit increases. There is a risk of it.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a control device for a switching circuit capable of reducing the loss of the switching circuit.

  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 A duty setting means (for example, the PWM calculation unit 25 in the embodiment) that can set the duty independently, and the duty setting means has a forward current out of the high-side switching element and the low-side switching element. The on-duty of the non-flowing switching element is set based on the on-duty in the switching cycle until the previous time of the switching element.

  Further, the switching circuit control device according to claim 2 of the present invention is an integrated value calculating means for calculating an integrated value of the on-duty in the plurality of switching cycles up to the previous time (for example, an energization ratio calculation in the embodiment). 25a), and the duty setting means sets the on-duty of the switching element in which the forward current does not flow, based on the integrated value of the on-duty calculated by the integrated value calculating means.

  Furthermore, the switching circuit control device according to claim 3 of the present invention provides a load current flowing through a load (for example, the motor 12 in the embodiment) connected to a connection point of the high side arm and the low side arm. Load current detection means for detecting (for example, each phase current detection unit 32 in the embodiment), the duty setting means based on the load current detected by the load current detection means, the forward current The on-duty of the switching element where no current flows is set.

  Furthermore, in the switching circuit control device according to claim 4 of the present invention, the duty setting means stores a map or a mathematical expression related to the on-duty of the switching element in which the forward current does not flow, and the map Alternatively, the on-duty of the switching element in which the forward current does not flow is set based on a mathematical formula.

According to the switching circuit control device of the first aspect of the present invention, the switching element in which the forward current does not flow in the previous switching cycle (that is, the switching element connected in parallel to the free-wheeling diode in which the commutation current flows) ), The on-duty of the switching element can be set according to the time during which the commutation current (reverse current) flows, that is, the degree of heat generation of the switching element in which no forward current flows. And the occurrence of thermal damage can be prevented.
In addition, the temperature of the switching element can be controlled without requiring a special detection device for detecting the temperature of the switching element, and it is possible to prevent the cost required for the device configuration from increasing.

  Furthermore, according to the switching circuit control apparatus of the second aspect of the present invention, it is possible to improve the estimation accuracy of the degree of heat generation of the switching element in which no forward current flows, and more accurately generate heat of the switching element. And the occurrence of thermal damage can be prevented.

Furthermore, according to the switching circuit control device of the third aspect of the present invention, the switching element in which the forward current flows among the high-side switching element and the low-side switching element is periodically switched. The on-duty of a switching element that does not flow can be set in consideration of the degree of heat generation when a forward current flows through the switching element.
For example, as the forward current increases, the degree of heat generation of the switching element increases, so that the estimation accuracy of the degree of heat generation of the switching element can be improved, and the heat generation of the switching element is more accurately suppressed, The occurrence of thermal damage can be prevented.

  Furthermore, according to the control device for a switching circuit according to claim 4 of the present invention, it is possible to quickly estimate the degree of heat generation of the switching element in which the forward current does not flow, based on a map or formula stored in advance. Thus, while reducing the load of the control process, the heat generation of the switching element can be suppressed accurately and the occurrence of thermal damage can be prevented.

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 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 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. 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 past on-duty log | history of a high side switching element and a low side switching element in the control apparatus of the switching circuit which concerns on embodiment of this invention. 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 figure which shows the example of the energization state of the electric current in the Example and comparative example of the control apparatus of the switching circuit which concern on embodiment of this invention. Correspondence between integrated value of on-duty, forward current, and reverse current of switching element in which forward current does not flow in a plurality of switching periods until the previous time of switching circuit control device according to an embodiment of the present invention It is a figure which shows an example of a relationship. 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 the calculation process of the forward duty shown in FIG. It is a flowchart which shows the calculation process of the reverse direction duty shown in FIG. It is a figure which shows the example of the electric current waveform in the Example of the control apparatus of the switching circuit which concerns on embodiment of this invention, and a 1st comparative example and a 2nd comparative example. It is a figure which shows the example of the current waveform in the Example of the control apparatus of the switching circuit which concerns on embodiment of this invention, and a 1st comparative example. It is a flowchart which shows the operation | movement of the control apparatus of the switching circuit which concerns on the modification of embodiment of this invention, especially the calculation process of a reverse direction duty.

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 FIG. 4, the PWM calculation unit 25 alternately turns on / off the switching elements of the high-side arm and the low-side arm of the bridge circuit 13 a by so-called complementary PWM (pulse width modulation). 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).

  Accordingly, the high-side switching element (SW1) of the high-side arm is turned on and the low-side switching element (SW2) of the low-side arm is turned off, and the high-side switching element (SW1) of the high-side arm is turned off and low. The low-side switching element (SW2) of the arm is alternately switched on.

  For example, as shown in FIG. 5, 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, the low-side switching element ( When SW2) is turned on, a reverse current flows through the low-side switching element (SW2), and a commutation current flows through the freewheeling diode (2) connected in reverse parallel to the low-side switching element (SW2).

  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).

  For example, as shown in FIG. 5, the switching elements that are not forward-flowing current (that is, the switching elements that are connected in parallel to the free-wheeling diode where the commutation current is flowing) are connected in parallel. When commutation current (reverse current) flows through both the switching element and the return diode, for example, as shown in FIG. 6, the commutation current (reverse current) flows through only the switching element or only the return diode. As compared with the above, as the combined resistance of the switching element and the freewheeling diode connected in parallel is reduced, the loss of the entire switching circuit can be reduced.

  Then, the PWM calculation unit 25 determines the on-duty (ON ratio) of the high-side switching element in a predetermined switching period based on the detected values of the phase currents Iu, Iv, Iw detected by the phase current detection unit 32. An energization ratio calculation unit 25a that can independently set the on-duty (on ratio) of the low-side switching element is provided.

  The energization ratio calculation unit 25a is a switching element (that is, commutation) in which no forward current flows among the high-side switching elements (transistors UH, VH, WH) and the low-side switching elements (transistors UL, VL, WL). The on-duty (reverse duty) of the switching element connected in parallel with the free-wheeling diode through which the current flows is set to the on-duty in the switching cycle up to the previous time of the switching element (for example, the reverse in a plurality of switching cycles up to the previous time Set based on direction duty integrated value).

  That is, the on-duty of the switching element through which the forward current flows among the high-side switching elements (each transistor UH, VH, WH) and the low-side switching elements (each transistor UL, VL, WL) is On the other hand, the on-duty of the switching element in which the forward current does not flow is switched between the switching element and the free wheel diode by the energization ratio calculator 25a. It is set according to the energization ratio of the current (reverse direction current).

  For example, in the plurality of switching cycles shown in FIG. 7, the on-duty of the switching element in which the forward current does not flow among the high-side switching element and the low-side switching element is the predetermined number of times (for example, five times) in the past. It is set based on the integrated value of the on-duty (reverse direction duty) of the switching element in which the forward current does not flow in the switching cycle.

Note that a predetermined upper limit value is set for the on-duty (SW2_Ton) of the switching element in which the forward current does not flow set by the energization ratio calculation unit 25a, and this upper limit value is a switching element in which the forward current flows. Is a value (= 100% −SW1_Ton% −Tdead%) corresponding to the on-duty (SW1_Ton) and dead time (Tdead).
Accordingly, the on-duty (SW2_Ton) of the switching element in which the forward current set by the energization ratio calculation unit 25a does not flow is an appropriate value between zero and a predetermined upper limit value, for example, as shown in FIG. (For example, a%, b%, c%, etc.).

  Thus, for example, in a comparative example employing an IGBT as a switching element as shown in FIG. 9A, a reverse current does not flow through the switching element even when the switching element is on, and a commutation current is present only in the return diode. For example, in the embodiment in which a MOSFET is used as the switching element as shown in FIGS. 9B and 9C, both the switching element and the free wheel diode are set at the energization ratio set by the energization ratio calculation unit 25a. A commutation current (reverse direction current) flows in the.

  The energization ratio calculation unit 25a stores, for example, a map or a mathematical formula related to the on-duty (reverse direction duty) of a switching element in which a forward current does not flow among the high-side switching element and the low-side switching element. Alternatively, the energization ratio of the commutation current (reverse current) between the switching element and the return diode is adjusted by setting the on-duty (reverse duty) of the switching element in which no forward current flows based on the mathematical formula. .

  For example, in the predetermined map for the appropriate power supply voltage A shown in FIG. 10, the reverse of the integrated value of the on-duty (reverse duty) of the switching element in which the forward current does not flow or the forward current increases. The direction current (reverse duty) is set to decrease (that is, the energization ratio of the commutation current to the switching element changes to decrease with respect to the energization ratio of the return diode) It is not limited to this, For example, you may set so that the suitable tendency according to the characteristics or element characteristic data, such as the motor 12 and the inverter 13, may be shown.

  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. 11, 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 S02, the forward duty (for example, the on-duty of a switching element (a high-side switching element or a low-side switching element, for example, a high-side switching element) through which a forward current flows is set (for example, High-side duty (DutyH) is calculated.

Next, in step S03, the reverse duty (ON duty of the switching element in which the forward current does not flow (either the high-side switching element or the low-side switching element, for example, the low-side switching element) ( For example, the low-side duty (DutyL) is calculated.
Next, in step S04, the high-side and low-side on-duty duty U (H, L), Duty V (H, L), Duty W (H, H) for each phase according to the calculation results of the forward duty and the reverse duty. L) and go to the end.

The forward duty calculation process in step S02 described above will be described below.
First, for example, in step S11 shown in FIG. 12, 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 a map search or the like for a map stored in advance.
Next, in step S12, based on, for example, data stored in advance, a dead time (for example, a predetermined minimum dead time) for a switching element through which a forward current flows is acquired.
Next, in step S13, the forward duty is calculated based on the forward current and the dead time, and the process proceeds to return.

Below, the process of the reverse duty calculation in step S03 mentioned above is demonstrated.
First, for example, in step S21 shown in FIG. 13, a history of the on-duty (reverse duty) of the switching element in which no forward current flows in the previous switching cycle is acquired.
Next, in step S22, the integrated value of the reverse duty in the past predetermined number of times (for example, five times) until the previous time is calculated.

  Next, in step S23, based on the integrated value of the reverse duty in the switching period of the past predetermined number of times (for example, 5 times) up to the previous time and the magnitude of the forward current in the current switching period, for example, FIG. The reverse current (or reverse duty corresponding to the magnitude of the reverse current) in the current switching cycle is calculated with reference to a map or formula stored in advance as shown in FIG.

Next, in step S24, a reverse duty (for example, low-side duty DutyL) is calculated based on the reverse current.
Next, in step S25, based on, for example, data stored in advance, a dead time (for example, a predetermined minimum dead time) for the switching element through which the reverse current flows is acquired.

Next, in step S26, reverse duty limit processing is performed.
In this process, first, a predetermined upper limit value (= 100) for the reverse duty based on the forward duty (for example, the high-side duty DutyH) in the current switching cycle and the dead time for the switching element through which the reverse current flows. %-Forward duty%-dead time%).
If the calculation result of the reverse duty is equal to or less than a predetermined upper limit value with respect to the reverse duty, the calculation result is output as the reverse duty and the process proceeds to return.
On the other hand, if the calculation result of the reverse duty is larger than the predetermined upper limit value for the reverse duty, the predetermined upper limit value is output as the reverse duty and the process proceeds to return.

For example, as shown in FIGS. 14A to 14D, when each phase current Iu, Iv, Iw is positive in a state where the motor 12 is supplied with the three-phase alternating currents Iu, Iv, Iw. The forward current flows through the high-side switching element, and when the phase currents Iu, Iv, and Iw are negative, the forward current flows through the low-side switching element.
For example, as shown in FIG. 14C, in the first comparative example in which a bidirectional complementary MOSFET is employed as a switching element and normal complementary PWM control is executed, the target torque, the rotational speed, and the power source of the motor 12 The high-side switching element and the low-side switching element are alternately turned ON / OFF according to a predetermined forward duty and reverse duty set by the voltage.
That is, there is a relationship of reverse duty% = 100% −forward duty% −dead time% between the forward duty of the switching element of one arm and the reverse duty of the switching element of the other arm. Is true.

  On the other hand, for example, as shown in FIG. 14B, a bidirectional MOSFET is adopted as the switching element, and the reverse duty in the switching cycle of the past predetermined number of times (for example, five times) up to the previous time is adopted. In the embodiment in which the reverse duty in the current switching cycle is set based on the integrated value, the dead time at the time of commutation is changed according to the reverse duty.

  For example, as shown in FIG. 14D, in the second comparative example in which the normal complementary PWM control is performed by adopting the IGBT as the switching element, reverse conduction at the time of commutation does not occur in the switching element.

  For example, as shown in FIGS. 15A and 15B, when the phase current of the motor 12 is negative and the forward current flows to the low-side switching element, the first comparative example has a dead time during commutation. In contrast to the constant reverse current flowing through the high-side switching element, the dead time during commutation is variable in the embodiment, and the reverse current flowing through the high-side switching element is It changes according to the integrated value of the reverse duty in a predetermined number of times (for example, 5 times) switching period.

As described above, according to the control device 10 of the switching circuit according to the present embodiment, the time during which the commutation current (reverse current) flows in the switching element in which the forward current does not flow in the previous switching cycle, That is, the on-duty of the switching element can be set according to the degree of heat generation of the switching element in which no forward current flows, and the heat generation of the switching element can be suppressed and the occurrence of thermal damage can be prevented.
In addition, the temperature of the switching element can be controlled without requiring a special detection device for detecting the temperature of the switching element, and it is possible to prevent the cost required for the device configuration from increasing.

  Furthermore, the on-duty (that is, reverse duty) of the switching element in which the forward current does not flow is set based on the integrated value of the on-duty of the switching element in which the forward current does not flow in the plurality of switching cycles up to the previous time. Therefore, it is possible to improve the estimation accuracy of the degree of heat generation of the switching element in which the forward current does not flow, and more accurately suppress the heat generation of the switching element and prevent the occurrence of thermal damage.

  Furthermore, the degree of heat generation of the switching element in which no forward current flows can be quickly estimated based on a map or mathematical formula stored in advance, and the heat generation of the switching element can be accurately performed while reducing the control processing load. And the occurrence of thermal damage can be prevented.

  In the above-described embodiment, the energization ratio calculation unit 25a sets the reverse duty in the current switching cycle based on the integrated value of the reverse duty in the plurality of switching cycles until the previous time. This is not limited and is based on other values related to the reverse duty in a plurality of switching cycles up to the previous time, such as an average value, and an appropriate value related to the degree of heat generation of the switching element in which no forward current flows. You may set the reverse direction duty in the switching period.

In the above-described embodiment, the energization ratio calculation unit 25a sets the reverse duty based on the past on-duty history of the switching element in which the forward current does not flow. However, the present invention is not limited to this. Since the switching element in which the forward current flows among the switching elements on the low side and the switching element on the low side is periodically switched, the reverse duty in the current switching cycle is determined by the forward current flowing in this switching element. It may be set in consideration of the on-duty, that is, the degree of heat generation when a forward current flows.
In this case, for example, as the forward current increases, the degree of heat generation of the switching element increases, so that the estimation accuracy of the degree of heat generation of the switching element can be improved, and the switching element can be more accurately detected. Heat generation can be suppressed and occurrence of thermal damage can be prevented.

  In the above-described embodiment, the energization ratio calculation unit 25a determines the current switching cycle based on a map or a mathematical expression indicating a predetermined correspondence relationship between the integrated value of the reverse duty and the forward current and the reverse current. However, the present invention is not limited to this. For example, the chip temperature of the switching element of the inverter 13 is estimated, and the reverse current or the reverse duty is calculated based on the estimation result. May be.

Hereinafter, in this modification, the reverse duty calculation process in step S03 of the above-described embodiment will be described.
First, for example, in step S31 shown in FIG. 16, a history of reverse duty in the previous switching cycle is acquired.
Next, in step S32, the integrated value of the reverse duty in the past predetermined number of times (for example, five times) until the previous time is calculated.

Next, in step S33, the chip temperature of the switching element of the inverter 13 is estimated based on the integrated value of the reverse duty in the past predetermined number of times (for example, five times) until the previous time.
In this estimation process, for example, a predetermined map or mathematical expression showing the correspondence between the integrated value of the reverse duty and the estimated value of the chip temperature, or the integrated value of the reverse duty and the estimated value of the forward current and the chip temperature, for example, The estimated value of the chip temperature is calculated with reference to a predetermined map or mathematical expression showing the correspondence relationship between the two.

Next, in step S34, for example, the backward current is calculated with reference to a predetermined map or a mathematical formula showing the correspondence between the estimated value of the chip temperature and the forward current and the backward current.
Next, in step S35, a reverse duty (for example, low-side duty DutyL) is calculated based on the reverse current.
Next, in step S36, based on, for example, data stored in advance, a dead time (for example, a predetermined minimum dead time) for the switching element through which the reverse current flows is acquired.

Next, in step S37, reverse duty limit processing is performed.
In this process, first, a predetermined upper limit value (= 100) for the reverse duty based on the forward duty (for example, the high-side duty DutyH) in the current switching cycle and the dead time for the switching element through which the reverse current flows. %-Forward duty%-dead time%).
If the calculation result of the reverse duty is equal to or less than a predetermined upper limit value with respect to the reverse duty, the calculation result is output as the reverse duty and the process proceeds to return.
On the other hand, if the calculation result of the reverse duty is larger than the predetermined upper limit value for the reverse duty, the predetermined upper limit value is output as the reverse duty and the process proceeds to return.

  According to this modification, the on-duty of the switching element can be set more appropriately based on the estimated value of the chip temperature related to the degree of heat generation of the switching element in which no forward current flows.

10 Switching circuit controller 12 Motor (load)
13 Inverter 13a Bridge circuit (switching circuit)
14 processor 25 PWM calculation part (duty setting means)
25a Energization ratio calculation unit (integrated value calculation means)
32 phase current detector (load current detection means)

Claims (4)

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,
A duty setting means capable of independently setting the on-duty of the high-side switching element and the on-duty of the low-side switching element in a predetermined switching cycle;
The duty setting means includes
The on-duty of a switching element in which a forward current does not flow among the high-side switching element and the low-side switching element is set based on the on-duty in the switching period until the previous time of the switching element. A switching circuit control device. An integrated value calculating means for calculating an integrated value of the on-duty in a plurality of the switching cycles up to the previous time;
The duty setting means sets the on-duty of a switching element in which the forward current does not flow based on the integrated value of the on-duty calculated by the integrated value calculating means. 2. A control device for a switching circuit according to 1. Load current detection 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;
The duty setting unit sets the on-duty of the switching element in which the forward current does not flow, based on the load current detected by the load current detection unit. 3. The switching circuit control device according to 2. The duty setting means stores a map or a mathematical expression related to the on-duty of the switching element in which the forward current does not flow, and based on the map or mathematical expression, the duty setting means of the switching element in which the forward current does not flow The switching circuit control device according to any one of claims 1 to 3, wherein the on-duty is set.

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