Control method for power converter and power converter

Abstract

To provide a control method of a power conversion device which can reduce discomfort of a crew member due to switching noise while suppressing heat generation of a transistor.SOLUTION: There is provided a control method of a power conversion device 100 comprising: a plurality of switching elements for controlling operation of a power generator 3 to be driven by a drive motor 2 and an engine; a first drive circuit 10 which actuates the plurality of switching elements; a flyback transistor 41 which controls power to be supplied to the first drive circuit 10 with switching operation; and a second drive circuit 42 which actuates the flyback transistor 41. The control method determines a drive state of the drive motor 2 and an operation state of the engine, and switches switching speed of the flyback transistor 41 with the second drive circuit 42 on the basis of the drive state of the drive motor 2 and the operation state of the engine.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a control method for a power conversion device and a power conversion device.

Background Art

[0002] In a vehicle equipped with a wireless receiver such as a radio, there is a problem that noise (switching noise) associated with the switching operation of an inverter (power conversion device) is superimposed on the wireless receiver, causing discomfort to the passengers.

[0003] Patent Document 1 discloses a power conversion device disposed near a wireless receiver. In this power conversion device, when the wireless receiver is operating, the gate resistance of a transistor (switching element) in the power conversion device is increased to reduce the switching speed, thereby suppressing the generation of surge voltage and reducing the switching noise superimposed on the wireless receiver.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the power conversion device described in Patent Document 1, when the wireless receiver is operating, the gate resistance is constantly increased to cause power loss. Therefore, there is a risk of damage to the switching element due to heat generation.

[0006] In view of the above problems, an object of the present invention is to provide a control method for a power conversion device and a power conversion device capable of reducing the discomfort of passengers caused by switching noise while suppressing heat generation of a transistor.

Means for Solving the Problems

[0007] According to one aspect of the present invention, a control method for a power converter is provided, comprising: a plurality of switching elements for controlling the operation of a drive motor and a generator driven by an engine; a first drive circuit for operating the plurality of switching elements; a flyback transistor for controlling the power supplied to the first drive circuit by switching operation; and a second drive circuit for operating the flyback transistor. In this control method, the drive state of the drive motor and the operating state of the engine are determined, and based on the drive state of the drive motor and the operating state of the engine, the switching speed of the flyback transistor is switched by the second drive circuit. [Effects of the Invention]

[0008] According to the present invention, the switching speed of the flyback transistor is switched based on the driving state of the drive motor and the operating state of the engine. This makes it possible to reduce the switching speed of the flyback transistor when the driving force of the drive motor and the generator driven by the engine is small, that is, when the noise sensitivity is high and the power supplied to the first drive circuit that operates the switching element is small. Therefore, it is possible to reduce the discomfort to the occupants caused by switching noise while suppressing power loss due to switching speed. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic diagram of a vehicle equipped with a power conversion device according to the first embodiment of the present invention. [Figure 2] Figure 2 shows an example of a second drive circuit. [Figure 3] Figure 3 shows the operating waveform of a flyback transistor. [Figure 4] Figure 4 is a timing chart illustrating the control performed by the drive state determination means. [Figure 5] Figure 5 is a timing chart illustrating the control performed by the engine operating state determination means. [Figure 6]Figure 6 is a timing chart illustrating the control of the drive state determination means in a power conversion device according to a first modification of the first embodiment. [Figure 7] Figure 7 is a timing chart illustrating the control of the engine operating state determination means in a power converter according to a second modification of the first embodiment. [Figure 8] Figure 8 shows an example of a second drive circuit in a power converter according to the second embodiment. [Figure 9] Figure 9 illustrates the switching speed in the power converter according to the second embodiment. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described below with reference to the drawings and other figures.

[0011] (First Embodiment) Figure 1 is a schematic diagram of a vehicle 1 equipped with a power converter 100 controlled by a power converter control method according to the first embodiment of the present invention. The vehicle 1 is a so-called series hybrid vehicle that uses the engine for power generation.

[0012] The power converter 100 includes a switching circuit 10, a first drive circuit 20, a control circuit 30, and a power supply circuit 40. The power converter 100's input side is connected to a control power supply (not shown), and its output side is connected to a generator 3 driven by the vehicle's drive motor 2 and engine (not shown). While the vehicle 1 is running, the drive motor 2 is supplied with power from the generator 3 and a battery (not shown). During regeneration, power is supplied from the drive motor 2 to the battery via the power converter 100.

[0013] The switching circuit 10 is composed of multiple switching elements (semiconductor elements, IGBTs), and these multiple switching elements are connected to the drive motor 2 and the generator 3. The operation of the power supplied to the drive motor 2 and the generator 3 is controlled by the switching operation of these multiple switching elements. The switching circuit 10 includes a motor-side switching circuit 11 connected to the drive motor 2 and controlling the operation of the drive motor 2, and a generator-side switching circuit 12 connected to the generator 3 and controlling the operation of the generator 3. A current sensor (not shown) is provided between the drive motor 2 and the switching circuit 10 to detect the current value between the drive motor 2 and the power converter 100, and the detected current value is transmitted to the drive state determination means 43, which will be described later.

[0014] The first drive circuit 20 is a circuit that operates multiple switching elements of the switching circuit 10 based on control signals from the control circuit 30, which will be described later. The first drive circuit 20 includes, for example, multiple gate drive circuits and outputs gate signals to the switching elements of the switching circuit 10. The switching elements of the switching circuit 10 are turned on and off based on the input gate signals. The first drive circuit 20 includes a motor-side circuit 21 that operates the switching elements of the motor-side switching circuit 11 and a generator-side circuit 22 that operates the switching elements of the generator-side switching circuit 12.

[0015] The control circuit 30 is a circuit that controls the first drive circuit 20. The control circuit 30 generates, for example, a control signal for motor drive and outputs the control signal to the first drive circuit 20. Based on the control signal from the control circuit 30, the first drive circuit 20 turns each switching element of the switching circuit 10 on and off at predetermined timings. The control circuit 30 includes a motor-side control circuit 31 that controls the motor-side circuit 21 and a generator-side control circuit 32 that controls the generator-side circuit 22.

[0016] The power supply circuit 40 is a flyback converter whose input side is connected to the control power supply, boosts or buck-boosts the power supply voltage while being insulated from the control power supply, and outputs power to the first drive circuit 20. The power supply circuit 40 includes a smoothing capacitor C1, a transformer L, a primary-side diode D1 of the transformer L, secondary-side diodes D2 to D5, a primary-side smoothing capacitor C2 and a resistor R of the transformer L, secondary-side smoothing capacitors C3 to C6, and a flyback transistor 41. Further, the power supply circuit 40 further includes a second drive circuit 42 that operates the flyback transistor 41, a drive state determination means 43 that determines the drive state of the drive motor 2, and an engine operation state determination means 44 that determines the operation state of the engine.

[0017] The flyback transistor (MOS transistor) 41 is a switching element that turns on and off the energization to the primary-side winding of the transformer L. When the primary-side winding of the transformer L is energized, power is stored in the transformer L, and when the power is cut off, the stored power is released from the secondary-side winding. The released power is rectified by the diodes D2 to D5 and smoothed by the smoothing capacitors C3 to C6, and then supplied to the first drive circuit 20. That is, the power supplied to the first drive circuit 20 is controlled by the switching operation of the flyback transistor 41. Note that the flyback transistor 41 includes a motor-side flyback transistor 411 that controls the power supplied to the motor-side circuit 21 and a generator-side flyback transistor 412 that controls the power supplied to the generator-side circuit 22.

[0018] The second drive circuit 42 is a circuit that operates the flyback transistor 41, and includes a motor-side second circuit 421 that operates the motor-side flyback transistor 411 and a generator-side second circuit 422 that operates the generator-side flyback transistor 412. The second drive circuit 42 outputs a gate signal to the flyback transistor 41, and the flyback transistor 41 is turned on and off based on the gate signal. When the flyback transistor 41 is in the on state, power is accumulated in the primary winding of the transformer L, and when it is in the off state, the power stored in the primary winding is released from the secondary winding. Also, output signals from the drive state determination means 43 and the engine operating state determination means 44, which will be described later, are input to the second drive circuit 42. The second drive circuit 42 switches the switching speed of the flyback transistor 41 based on the input signals from the drive state determination means 43 and the engine operating state determination means 44. The details of the switching speed switching by the second drive circuit 42 will be described later.

[0019] The drive state determination means 43 determines the drive state of the drive motor 2. Information on the vehicle speed, the accelerator pedal operation amount, and the current value between the drive motor 2 and the power conversion device 100 is input to the drive state determination means 43, and the drive state determination means 43 determines whether the drive motor 2 is in operation, that is, whether the vehicle 1 is running, based on the vehicle speed, the accelerator pedal operation amount, and the current value between the drive motor 2 and the power conversion device 100. Here, the operation during regeneration also includes the state in which the drive motor 2 is operating. The signal of the determination result by the drive state determination means 43 is output to the second drive circuit 42.

[0020] The engine operating state determination means 44 determines the operating state of the engine, that is, the driving state of the generator 3. The engine operating state determination means 44 receives voltage information of a battery (not shown) as input, and based on the battery voltage Vdc, the engine operating state determination means 44 determines whether the engine is running or not, that is, whether the generator 3 is driving or not. The signal of the determination result by the engine operating state determination means 44 is output to the second drive circuit 42. The second drive circuit 42 switches the switching speed of the flyback transistor 41 based on the determination result (input signal) of the aforementioned drive state determination means 43 and the determination result (input signal) of the engine operating state determination means 44.

[0021] As described above, in the power converter 100, power from the control power supply is boosted or stepped down in the power supply circuit (flyback converter) 40 and supplied to the first drive circuit 20 which operates the switching elements of the switching circuit 10. The power supplied to the first drive circuit 20 is controlled by the switching operation of the flyback transistor 41.

[0022] Incidentally, in vehicles equipped with radios or other wireless receivers, there is a problem in that noise (switching noise) associated with the switching operation of the power converter (inverter) is superimposed on the wireless receiver, causing discomfort to the occupants.

[0023] In response to this, one possible approach is to reduce switching noise by increasing the gate resistance of the transistor (switching element) in the power converter during the operation of the wireless receiver, thereby decreasing the switching speed. However, if the gate resistance is constantly increased during the operation of the wireless receiver, generating power loss, there is a risk that the transistor may be damaged due to overheating.

[0024] Therefore, in this embodiment, the switching speed of the flyback transistor 41 is switched based on the driving state of the drive motor 2 and the generator 3. That is, in this embodiment, as will be explained below, when the drive motor 2 and the generator 3 are stopped, the switching speed of the flyback transistor 41 is slowed down compared to when the drive motor 2 or the generator 3 is operating. When the drive motor 2 and the generator 3 are stopped, the power supply to the first drive circuit 20 that operates the switching element is small or nonexistent, so the power loss when the switching speed is slowed down is small, and the heat generation of the flyback transistor 41 is suppressed. In addition, wireless receivers such as radios have high noise sensitivity when the drive motor 2 or the generator 3 are stopped, such as when the vehicle 1 is stopped, and low noise sensitivity when the drive motor 2 or the generator 3 is operating because the sound of the vehicle 1 running and the engine operating sound can be heard. Therefore, by slowing down the switching speed when the drive motor 2 or the generator 3 is stopped, when noise sensitivity is high, the discomfort of occupants due to switching noise can be reduced more effectively. In this way, when the noise sensitivity is high and the power supplied to the first drive circuit 20 is low (or nonexistent), the switching speed of the flyback transistor 41 is slowed down, thereby reducing discomfort to the occupants due to switching noise and suppressing power loss due to switching speed changes.

[0025] Furthermore, when the drive motor 2 and generator 3 are stopped, the switching elements (IGBTs) of the switching circuit 10 also stop operating, so no switching noise is generated in the switching circuit 10.

[0026] The following details the switching speed of the flyback transistor 41.

[0027] Figure 2 shows the second drive circuit 42.

[0028] As shown in Figure 2, the second drive circuit 42 includes a second control circuit 423, a first switching element S1, a second switching element S2, a third switching element S3, a first resistor R1, a second resistor R2, and the like.

[0029] The second control circuit 423 is a circuit that controls the on / off state of the first switching element S1 and the second switching element S2. The first switching element S1 is connected to a voltage source, and the second switching element S2 is connected to ground. The first switching element S1 and the second switching element S2 are connected in series with respect to the voltage source. By controlling the first switching element S1 to be on and the second switching element S2 to be off, the second control circuit 423 outputs a high-level gate signal to the flyback transistor 41, thereby turning the flyback transistor 41 on. On the other hand, by controlling the first switching element S1 to be off and the second switching element S2 to be on, the second control circuit 423 outputs a low-level gate signal to the flyback transistor 41, thereby turning the flyback transistor 41 off.

[0030] The output terminals of the first switching element S1 and the second switching element S2 are connected in parallel to a line connected to the first resistor R1 and a line connected in series to the third switching element S3 and the second resistor R2. The gate of the third switching element S3 receives signals of the determination result from the drive state determination means 43 and the engine operation state determination means 44. Specifically, if it is determined that the drive motor 2 is in operation, a low-level signal is input from the drive state determination means 43, and if it is determined that the engine is running, a low-level signal is input from the engine operation state determination means 44. When a low-level signal is input from the drive state determination means 43 or the engine operation state determination means 44, the third switching element S3 turns ON and conducts. On the other hand, if it is determined that the drive motor 2 is stopped, a high-level signal is input from the drive state determination means 43, and if it is determined that the engine is stopped, a high-level signal is input from the engine operation state determination means 44. When a high-level signal is input from the drive state determination means 43 and the engine operation state determination means 44, the third switching element S3 is turned off and shut off.

[0031] The first resistor R1 is connected to the outputs of the first switching element S1 and the second switching element S2, and the second resistor R2 is connected to the output of the third switching element S3. The first resistor R1 and the second resistor R2 are connected in parallel. When the drive motor 2 or engine (i.e., generator 3) is running, the third switching element S3 is in the ON state. At this time, because the first resistor R1 and the second resistor R2 are connected in parallel, the combined resistance of the first resistor R1 and the second resistor R2, which is the total resistance (gate resistance) of the second drive circuit 42, is smaller than the first resistor R1. On the other hand, when the drive motor 2 and the engine are stopped and the third switching element S3 is in the OFF state, the resistance of the second drive circuit 42 becomes the first resistor R1, and the total resistance (gate resistance) of the second drive circuit 42 is larger than when the third switching element S3 is ON.

[0032] Here, the larger the resistance (gate resistance) of the second drive circuit 42, the slower the switching speed of the flyback transistor 41, which is a switching element controlled by the gate signal output from the second drive circuit 42. Therefore, when the drive motor 2 and engine are stopped, the switching speed of the flyback transistor 41 is slower than when the drive motor 2 or engine is running, as the gate resistance is higher. In other words, when the drive motor 2 and engine are stopped, the second drive circuit 4 switches the switching speed of the flyback transistor 41 to a slower speed (first switching speed) than when the drive motor 2 is operating.

[0033] In this way, the second drive circuit 42 switches the resistance based on the drive state of the drive motor 2 and the operating state of the engine, thereby switching the switching speed of the flyback transistor 41.

[0034] Figure 2 shows an example of the second drive circuit 42, and the second drive circuit 42 is not limited to the circuit shown in Figure 2. In other words, the second drive circuit 42 can be any configuration as long as it switches the switching speed of the flyback transistor 41 based on the driving state of the drive motor 2 and the operating state of the engine. For example, the second drive circuit 42 can be configured to switch the switching speed of the flyback transistor 41 by adjusting the amount of current rather than the resistance value.

[0035] Figure 3 shows the operating waveform of the flyback transistor 41. In Figure 3, Vgs is the gate voltage of the flyback transistor 41, Vds is the drain-source voltage, and Id is the drain current. As described above, the flyback transistor 41 is turned on or off based on the gate signal from the second drive circuit 42.

[0036] The period between t10 and t20 in Figure 3 shows the state in which the drive motor 2 or engine (generator 3) is running. Between t10 and t20, when a high-level gate signal is input from the second drive circuit 42, the gate voltage Vgs of the flyback transistor 41 instantly becomes high, and the flyback transistor 41 is turned on. When the flyback transistor 41 is turned on, the drain current Id flowing through the flyback transistor 41 gradually increases. Also, when a low-level gate signal is input from the second drive circuit 42, the gate voltage Vgs of the flyback transistor 41 instantly becomes low, and the flyback transistor 41 is turned off. When the flyback transistor 41 is turned off, the drain current Id flowing through the flyback transistor 41 is interrupted and instantly decreases to zero.

[0037] On the other hand, Figure 3 from t20 onwards shows the state in which the drive motor 2 and engine (generator 3) are stopped. Even after t20, when a high-level gate signal is input from the second drive circuit 42, the gate voltage Vgs of the flyback transistor 41 becomes high, the flyback transistor 41 is turned on, and the drain current Id gradually increases. Also, when a low-level gate signal is input from the second drive circuit 42, the gate voltage Vgs of the flyback transistor 41 becomes low, the flyback transistor 41 is turned off, and the drain current Id decreases to zero. However, from t20 to t30, since the drive motor 2 and engine are stopped, as mentioned above, the resistance value (gate resistance) of the second drive circuit 42 is greater than the resistance value (gate resistance) at t10 to t20. Therefore, the rate at which the gate voltage Vgs rises and falls is slower than at t10 to t20. In other words, from t20 onward, when the drive motor 2 and the engine are stopped, the switching speed of the flyback transistor 41 is slower than from t10 to t20, when the drive motor 2 is running. As a result, the rate at which the drain current Id decreases with turn-off of the flyback transistor 41 is also slower.

[0038] Here, if the current flowing through the flyback transistor 41 (drain current Id) changes rapidly, a large amount of switching noise is generated. Specifically, a large amount of noise is generated at t11 ​​and t12 when the flyback transistor 41 is turned off and the drain current Id drops sharply. However, at t11 ​​and t12, the drive motor 2 or engine (generator 3) is running, so the noise sensitivity due to switching noise is low, and the discomfort caused by the switching noise to the occupants is not high.

[0039] On the other hand, at t21 and t22, when the drive motor 2 and engine are stopped, the drain current Id decreases as the flyback transistor 41 turns off. However, at t21 and t22, the second drive circuit 42 slows down the switching speed of the flyback transistor 41, so the rate of decrease in the drain current Id is gradual. Therefore, the switching noise from the flyback transistor 41 is reduced, and the discomfort of the occupants is reduced. Also, at t21 and t22, since the drive motor 2 and engine are stopped, the power supply to the first drive circuit 20 is small (or nonexistent). Therefore, the power loss when the switching speed is slowed is small, and the heat generated by the flyback transistor 41 due to the reduced switching speed is suppressed.

[0040] Figure 4 is a timing chart illustrating the control by the drive state determination means 43. Note that, at least from t2 onwards in Figure 4, it is assumed that the engine is stopped.

[0041] As described above, the drive state determination means 43 determines whether the drive motor 2 is running or not based on the vehicle speed of the vehicle 1, the amount of accelerator pedal operation, and the current value between the drive motor 2 and the power converter 100. For example, the drive state determination means 43 determines that the drive motor 2 is running if at least one of the vehicle speed, the amount of accelerator pedal operation, or the current value between the drive motor 2 and the power converter 100 exceeds a predetermined value set for each. These predetermined values ​​can be, for example, the vehicle speed during coasting, the amount of accelerator pedal operation that indicates the driver has pressed the accelerator pedal, or the minimum value of the current value between the drive motor 2 and the power converter 100 during vehicle driving, including regenerative braking. However, the method for determining whether the drive motor 2 is running or not is not limited to this. For example, the drive state of the drive motor 2 may be detected by a sensor or the like.

[0042] Between t1 and t2 in Figure 4, at least one of the following is a state in which the vehicle speed, the accelerator pedal operation amount, or the current value between the drive motor 2 and the power converter 100 exceeds a predetermined value set for each. Therefore, the drive state determination means 43 determines that the drive motor 2 is in operation and outputs a low-level signal to the second drive circuit 42. Consequently, between t1 and t2, the third switching element S3 of the second drive circuit 42 is in the ON state (Figure 2), and the gate resistance is small. For this reason, the gate voltage Vgs when the flyback transistor 41 is switched on and off rises and falls instantaneously. That is, between t1 and t2, the switching speed of the flyback transistor 41 is steep.

[0043] Here, at t2, when the vehicle speed, accelerator pedal operation amount, and the current value between the drive motor 2 and the power converter 100 all fall below predetermined values, the drive state determination means 43 determines that the drive motor 2 is stopped and switches the output signal to high level (High). Consequently, a high-level signal is input to the second drive circuit 42, and the third switching element S3 of the second drive circuit 42 is turned off (Figure 2). As a result, the gate resistance increases. Therefore, from t2 onward, the rate at which the gate voltage Vgs rises and falls when the flyback transistor 41 is switched on and off becomes slower compared to the case at t1 to t2. That is, when the drive state determination means 43 determines that the drive motor 2 is stopped, it outputs a high-level signal, and the switching speed of the flyback transistor 41 becomes slower than when the drive motor 2 is running.

[0044] Furthermore, if, after t2, the vehicle speed, the accelerator pedal operation amount, or the current value between the drive motor 2 and the power converter 100 again exceeds a predetermined value, the drive state determination means 43 determines that the drive motor 2 is in operation and switches the output signal to a low level (Low). This reduces the gate resistance and increases the switching speed.

[0045] In this manner, the drive state determination means 43 determines the drive state of the drive motor 2, and based on the drive state of the drive motor 2, the second drive circuit 42 switches the switching speed of the flyback transistor 41.

[0046] Figure 5 is a timing chart illustrating the control performed by the engine operating state determination means 44. Note that, at least from time t4 onwards in Figure 5, it is assumed that the drive motor 2 is stopped.

[0047] As described above, the engine operating state determination means 44 determines whether the engine is running, that is, whether the generator 3 is being driven, based on the battery voltage Vdc. For example, the engine operating state determination means 44 determines that the engine is running when the battery voltage Vdc is less than or equal to a predetermined threshold Vth1. Here, the predetermined threshold Vth1 can be set to a specified value at which power generation by the generator 3 begins. However, the method for determining whether the engine is running is not limited to this. For example, the operating state of the engine may be directly detected by a sensor or the like.

[0048] Between t3 and t4 in Figure 5, the battery voltage Vdc exceeds a predetermined threshold Vth1. Therefore, the engine operation state determination means 44 determines that the engine is stopped and outputs a high-level signal to the second drive circuit 42. Consequently, between t3 and t4, the third switching element S3 of the second drive circuit 42 is in the off state (Figure 2), and its gate resistance is high. For this reason, the rate at which the gate voltage Vgs rises and falls when the flyback transistor 41 is switched on and off is gradual. That is, between t3 and t4, the switching speed of the flyback transistor 41 is slower than when the engine is running, as described later.

[0049] Here, at t4, when the battery voltage Vdc falls below a predetermined threshold Vth1, the engine operating state determination means 44 determines that the engine is running and switches the output signal to low level. Consequently, a low level signal is input to the second drive circuit 42, and the third switching element S3 of the second drive circuit 42 is turned on (Figure 2). This reduces the gate resistance. Therefore, from t4 onward, the gate voltage Vgs rises and falls instantaneously when the flyback transistor 41 is switched on and off. That is, when it is determined that the engine is running, the engine operating state determination means 44 outputs a low level signal, and the switching speed of the flyback transistor 41 is steep and faster than when the engine is stopped.

[0050] Furthermore, if the battery voltage Vdc exceeds a predetermined threshold Vth1 again after t4, the engine operating state determination means 44 determines that the engine is stopped and switches the output signal to high level (High). This increases the gate resistance and slows down the switching speed.

[0051] In this way, the engine operating state determination means 44 determines the engine's operating state, and based on the engine's operating state, the second drive circuit 42 switches the switching speed of the flyback transistor 41.

[0052] According to the control method for the power converter 100 of the first embodiment described above, the following effects can be obtained.

[0053] According to the control method of the power converter 100, the switching speed of the flyback transistor 41 is switched based on the driving state of the drive motor 2 and the operating state of the engine. This allows the switching speed of the flyback transistor 41 to be reduced when the driving force of the generator 3 driven by the drive motor 2 and the engine is small, that is, when the noise sensitivity is high and the power supplied to the first drive circuit 20 that operates the switching element is small. Therefore, it is possible to reduce the discomfort to the occupants caused by switching noise while suppressing power loss due to switching the switching speed.

[0054] Furthermore, switching noise can be suppressed by switching the switching speed of the flyback transistor 41, thus suppressing noise without adding any additional components. Consequently, the power converter 100 can be made lower cost and smaller.

[0055] According to the control method of the power converter 100, when the drive motor 2 and engine are stopped, the switching speed of the flyback transistor 41 is switched to a slower speed (first switching speed) than when the drive motor 2 or engine is operating. By slowing the switching speed when the drive motor 2 and engine are stopped, power loss due to the slowing of the switching speed can be suppressed, and heat generation of the flyback transistor 41 can be suppressed. Furthermore, by slowing the switching speed when the drive motor 2 and engine, which have high noise sensitivity for wireless receivers such as radios, are stopped, discomfort to occupants due to switching noise can be more effectively reduced. Therefore, it is possible to reduce discomfort to occupants due to switching noise while suppressing power loss due to switching of the switching speed.

[0056] Furthermore, since the switching speed is slowed down (dulled) only when the drive motor 2 and engine are stopped, heat generation of the flyback transistor 41 can be suppressed, and switching noise can be suppressed without adding a separate cooling mechanism. Therefore, the power converter 100 can be made lower cost and smaller.

[0057] In this embodiment, the switching speed of the flyback transistor 41 is set to a slower speed than when the drive motor 2 or engine is operating when the drive motor 2 and engine are stopped, but this is not necessarily the only option. For example, the switching speed of the flyback transistor 41 may be set to a slower speed than when the drive motor 2 and engine are operating when at least one of the drive motor 2 or engine is stopped. Also, for example, even if the drive motor 2 and engine are not completely stopped, the switching speed of the flyback transistor 41 may be set to a slower speed than when the drive motor 2 and engine (generator 3) have a large driving force when the driving force of the drive motor 2 and engine (generator 3) is small.

[0058] (First Modification Example of the First Embodiment) Referring to FIG. 6, a control method of the power conversion device 100 according to the first modification example of the first embodiment will be described. In this modification example, the method for determining the driving state of the drive motor 2 is different from that of the first embodiment. Note that the same reference numerals are assigned to elements similar to those in the first embodiment, and the description thereof will be omitted.

[0059] In this modification example, when the current (drain current) Id flowing through the flyback transistor 41 exceeds a predetermined threshold value Ipth, the drive state determination means 43 determines that the drive motor 2 is driving.

[0060] Here, when the drive motor 2 is driving, since the switching element (IGBT) of the switching circuit 10 is operating, a larger power is supplied to the first drive circuit 20 for operating the switching element than when the drive motor 2 is stopped. Therefore, the peak current Ip1 of the drain current Id when the drive motor 2 is driving is larger than the peak current Ip2 of the drain current Id in the state where the drive motor 2 is stopped. Thus, in this modification example, the threshold value Ipth of the drain current Id for determining whether the drive motor 2 is driving is set to a value between the peak current Ip1 when the drive motor 2 is driving and the peak current Ip2 when the drive motor 2 is stopped. That is, in this modification example, the threshold value Ipth of the drain current Id is determined such that Ip2 < Ipth < Ip1.

[0061] FIG. 6 is a timing chart for explaining the control of the drive state determination means 43 in the power conversion device 100 according to this modification example. In FIG. 6, it is assumed that the engine is in a stopped state.

[0062] As shown in FIG. 6, the threshold value Ipth of the drain current Id for determining whether the drive motor 2 is driving is set between the peak current Ip1 when the drive motor 2 is driving and the peak current Ip2 when the drive motor 2 is stopped.

[0063] In Figure 6, at t21-t22, the peak current Ip of the drain current Id exceeds the threshold Iph. Therefore, the drive state determination means 43 determines that the drive motor 2 is in a driving state and outputs a low-level signal to the second drive circuit 42. Consequently, the gate resistance is small, and the switching speed of the flyback transistor 41 is steep.

[0064] On the other hand, at t22, when the drain current Id (and its peak current Ip) falls below the threshold Ipth, the drive state determination means 43 determines that the drive motor 2 is in a stopped state and outputs a high-level signal to the second drive circuit 42. Consequently, the gate resistance becomes higher than when the drive motor 2 is running, and the switching speed of the flyback transistor 41 slows down.

[0065] Thus, even if the driving state of the drive motor 2 is determined by whether or not the peak current Ip of the drain current Id exceeds the threshold Ipth, the switching speed of the flyback transistor 41 can be slowed down only when the drive motor 2 is stopped. In other words, the same effect as in the first embodiment can be obtained with this modified example as well.

[0066] (Second modified example of the first embodiment) Referring to Figure 7, a power converter 100 according to a second modification of the first embodiment will be described. In this modification, the method for determining the engine's operating state differs from that of the first embodiment. Elements similar to those in the first embodiment are denoted by the same reference numerals, and their descriptions are omitted.

[0067] In this modified example, the engine operating state determination means 44 determines that the engine is running when the battery voltage Vdc is decreasing and the battery voltage Vdc falls below a predetermined first threshold Vth1. Furthermore, when the battery voltage Vdc is increasing, the engine is determined to be stopped after a predetermined time Δt has elapsed when the battery voltage Vdc exceeds a second threshold Vth greater than the first threshold Vth1. The predetermined first threshold Vth1 here can be set to a specified value, similar to the first embodiment, at which power generation by the generator 3 begins. The predetermined second threshold Vth2 can be set to, for example, a specified value at which power generation by the generator 3 stops.

[0068] Figure 7 is a timing chart illustrating the control of the engine operating state determination means 44 in the power conversion device 100 according to this modified example. In Figure 7, it is assumed that the drive motor 2 is in a stopped state.

[0069] As shown in Figure 7, in the period t31 to t33 when the battery voltage Vdc is decreasing, if the battery voltage Vdc exceeds a predetermined first threshold Vth1, the engine operating state determination means 44 determines that the engine is stopped and outputs a high-level signal to the second drive circuit 42. Therefore, the gate resistance is greater than when the engine is running, and the switching speed of the flyback transistor 41 is slower.

[0070] At time t32, when the battery voltage Vdc falls below a predetermined first threshold Vth1, the engine operating state determination means 44 determines that the engine is running and switches the output signal to a low level (Low). This increases the gate resistance and makes the switching speed of the flyback transistor 41 steeper. Note that starting the engine requires a rise time (time lag), so the engine actually starts running after a predetermined time has elapsed from time t32 when the battery voltage Vdc falls below the predetermined first threshold Vth1.

[0071] On the other hand, as shown in Figure 7, when the battery voltage Vdc is rising at t33 to t35, if the battery voltage Vdc is below a predetermined second threshold Vth2, the engine operation status determination means 44 determines that the engine is running and outputs a low-level signal to the second drive circuit 42. Here, at t34, the battery voltage Vdc exceeds the predetermined second threshold Vth2, but stopping the engine requires a stopping time (time lag), so the engine is stopped after a certain period of time has elapsed from t34. That is, at t34, when the battery voltage Vdc exceeds the predetermined second threshold Vth2, the engine (generator 3) is still running. Therefore, if the switching speed of the flyback transistor 41 is slowed down at t34, when the battery voltage Vdc exceeds the predetermined second threshold Vth2, the heat generated due to power loss will increase. Therefore, in this modified example, even if the battery voltage Vdc exceeds a predetermined second threshold Vth while the battery voltage Vdc is rising, the system determines that the engine is operating until a predetermined time Δt has elapsed. That is, at t34, even after the battery voltage Vdc exceeds the predetermined second threshold Vth2, the engine operating state determination means 44 determines that the engine is operating until t36, when a predetermined time Δt has elapsed, and outputs a low-level signal to the second drive circuit 42. Consequently, the switching speed of the flyback transistor 41 is steep from t32, when the battery voltage Vdc falls below a predetermined first threshold Vth1, until t36, when the battery voltage Vdc rises above the predetermined second threshold Vth2 and a predetermined time Δt has elapsed. On the other hand, at t36, after a predetermined time Δt has elapsed since t34 when the battery voltage Vdc exceeds a predetermined second threshold Vth2, the engine operating state determination means 44 determines that the engine is stopped and outputs a high-level signal to the second drive circuit 42. This slows down the switching speed of the flyback transistor 41.

[0072] Thus, in this modified example, while the battery voltage Vdc is rising, the engine is determined to be stopped after a predetermined time Δt has elapsed since the battery voltage Vdc exceeded a predetermined second threshold Vth. This prevents the switching speed of the flyback transistor 41 from slowing down while the engine is running. In other words, heat generation due to power loss can be further suppressed.

[0073] (Second Embodiment) The power converter 100 of the second embodiment will be described with reference to Figures 8 and 9. In this embodiment, the switching speed of the flyback transistor 41 is switched from the switching speed in the normal state when the drive motor 2 and engine are operating to three different speeds. Elements that are the same as in the other embodiments are denoted by the same reference numerals and their descriptions are omitted.

[0074] Figure 8 shows the second drive circuit 42 in the power converter 100 according to the second embodiment.

[0075] As shown in Figure 8, the second drive circuit 42 in this embodiment includes a second control circuit 423, first to third switching elements S1 to S3, first to second resistors R1 to R2, as well as a fourth switching element S4 and a third resistor R3.

[0076] Similar to the first embodiment, the second control circuit 423 controls the first switching element S1 to turn on and the second switching element S2 to turn off, thereby outputting a high-level gate signal to the flyback transistor 41 and turning the flyback transistor 41 into an ON state. Conversely, by controlling the first switching element S1 to turn off and the second switching element S2 to turn on, it outputs a low-level gate signal to the flyback transistor 41 and turns the flyback transistor 41 into an OFF state.

[0077] The first switching element S1 and the second switching element S2 are connected in series with respect to the voltage source. The output terminals of the first switching element S1 and the second switching element S2 are connected in parallel to a line to which the first resistor R1 is connected, a line to which the third switching element S3 and the second resistor R2 are connected in series, and a line to which the fourth switching element S4 and the third resistor R3 are connected in series. The gates of the third switching element S3 and the fourth switching element S4 receive signals of the determination result from the drive state determination means 43 and the engine operation state determination means 44.

[0078] Thus, the first resistor R1, the second resistor R2, and the third resistor R3 are connected in parallel. In this embodiment, the second resistor R2 has a lower resistance than the third resistor R3.

[0079] In this embodiment, as will be explained below, the signals input from the drive state determination means 43 and the engine operation state determination means 44 are different for the second drive circuit 42 (motor-side second circuit 421) that operates the motor-side flyback transistor 411 and the second drive circuit 42 (generator-side second circuit 422) that operates the generator-side flyback transistor 412.

[0080] First, let's explain the signal input to the motor-side second circuit 421.

[0081] When it is determined that the drive motor 2 is operating, the drive state determination means 43 and the engine operation state determination means 44 input low-level signals to the gates of the third and fourth switching elements S3 and S4 of the motor-side second circuit 421, respectively. As a result, the third and fourth switching elements S3 and S4 turn on and conduct. At this time, since the first resistor R1, the second resistor R2, and the third resistor R3 are connected in parallel, the combined resistance of the first to third resistors R1 to R3, which is the total resistance (gate resistance) of the motor-side second circuit 421, is smaller than the first resistor R1 and the combined resistance of the first resistor R1 and the second resistor R2 or the third resistor R3. In other words, in this case, the gate resistance is at its lowest, and the switching speed of the motor-side flyback transistor 411 becomes the fastest switching speed (the switching speed under normal conditions).

[0082] On the other hand, if it is determined that both the drive motor 2 and the engine are stopped, the drive state determination means 43 and the engine operation state determination means 44 input high-level signals to the gates of the third and fourth switching elements S3 and S4 of the motor-side second circuit 421, respectively. As a result, the third and fourth switching elements S3 and S4 are turned off and disconnected. At this time, the total resistance (gate resistance) of the motor-side second circuit 421 becomes the first resistance R1, which is greater than the combined resistance of the first to third resistances R1 to R3. Therefore, in this case, the switching speed of the motor-side flyback transistor 411 becomes a slower switching speed (first switching speed) than the switching speed in the normal state when the drive motor 2 and the engine are operating.

[0083] In contrast, if the drive motor 2 is stopped and the engine is determined to be running, the drive state determination means 43 and the engine operation state determination means 44 input a high-level signal to the gate of the third switching element S3 of the motor-side second circuit 421, and a low-level signal to the gate of the fourth switching element S4. As a result, the third switching element S3 of the motor-side second circuit 421 is turned off and disconnected, and the fourth switching element S4 is turned on and conducts. Therefore, the total resistance (gate resistance) of the motor-side second circuit 421 is the combined resistance of the first resistor R1 and the third resistor R3, which is greater than the combined resistance of the first to third resistors R1 to R3, and less than the first resistor R1. Therefore, in this case, the switching speed of the motor-side flyback transistor 411 is slower than the switching speed in the normal state when the drive motor 2 and engine are running, but faster than the first switching speed (second switching speed).

[0084] Next, we will explain the signal input to the generator-side second circuit 422.

[0085] If the engine is determined to be running, the drive state determination means 43 and the engine operation state determination means 44 input low-level signals to the gates of the third and fourth switching elements S3 and S4 of the generator-side second circuit 422, respectively. As a result, the third and fourth switching elements S3 and S4 turn on and conduct. Therefore, the total resistance (gate resistance) of the generator-side second circuit 422 becomes the combined resistance of the first to third resistors R1 to R3, which is smaller than the first resistor R1, and the combined resistance of the first resistor R1 and the second resistor R2 or the third resistor R3. In other words, in this case, the gate resistance is at its lowest, and the switching speed of the generator-side flyback transistor 412 becomes the fastest switching speed (the switching speed under normal conditions).

[0086] On the other hand, if it is determined that both the drive motor 2 and the engine are stopped, the drive state determination means 43 and the engine operation state determination means 44 input high-level signals to the gates of the third and fourth switching elements S3 and S4 of the generator-side second circuit 422, respectively. As a result, the third and fourth switching elements S3 and S4 are turned off and disconnected. At this time, the total resistance (gate resistance) of the generator-side second circuit 422 becomes the first resistance R1, which is greater than the combined resistance of the first to third resistances R1 to R3. Therefore, in this case, the switching speed of the generator-side flyback transistor 412 becomes a slower switching speed (first switching speed) than the switching speed in the normal state when the drive motor 2 and the engine are operating.

[0087] In contrast, if it is determined that the drive motor 2 is running and the engine is stopped, the drive state determination means 43 and the engine operation state determination means 44 input a low-level signal to the gate of the third switching element S3 of the generator-side second circuit 422, and a high-level signal to the gate of the fourth switching element S4. As a result, the third switching element S3 of the motor-side second circuit 421 turns on and conducts, and the fourth switching element S4 turns off and disconnects. Therefore, the total resistance (gate resistance) of the generator-side second circuit 422 is the combined resistance of the first resistor R1 and the second resistor R2, which is greater than the combined resistance of the first to third resistors R1 to R3, and less than the first resistor R1 and the combined resistance of the first resistor R1 and the third resistor R3. Therefore, in this case, the switching speed of the generator-side flyback transistor 412 is slower than the switching speed in the normal state when the drive motor 2 and engine are operating, and faster than the first switching speed and the second switching speed (the third switching speed).

[0088] Thus, the second drive circuit 42 of this embodiment switches the switching speed of the flyback transistor 41 from the switching speed in the normal state when the drive motor 2 and engine are operating to one of three different speeds, based on the driving state of the drive motor 2 and the operating state of the engine.

[0089] Figure 9 illustrates the switching speed in the power converter 100 according to the second embodiment.

[0090] As shown in Figure 9, when the drive motor 2 is stopped and the engine is running, the switching speed of the motor-side flyback transistor 411 is controlled to a second switching speed that is slower than the switching speed in the normal state when both the drive motor 2 and the engine are running. That is, even when the engine is running, if the drive motor 2 is stopped, the noise sensitivity of wireless receivers such as radios is somewhat high, so the switching speed of the motor-side flyback transistor 411 is slowed down to some extent to reduce switching noise. On the other hand, if the switching speed of the generator-side flyback transistor 412 is slowed down while the engine is running, power loss will increase and the heat generated by the generator-side flyback transistor 412 will increase. Therefore, even when the drive motor 2 is stopped, if the engine is running, the switching speed of the generator-side flyback transistor 412 is controlled to the fastest speed (the same speed as the switching speed in the normal state).

[0091] When both the drive motor 2 and the engine are stopped, the noise sensitivity of radios and other devices is highest. Therefore, the switching speed of both the motor-side flyback transistor 411 and the generator-side flyback transistor 412 is controlled to a first switching speed that is slower than the normal switching speed and slower than the second switching speed. Also, since both the drive motor 2 and the engine are stopped, even if the switching speed is slowed, power loss is small and the heat generation of the flyback transistor 41 is suppressed.

[0092] When both the drive motor 2 and the engine are operating, the noises from the vehicle 1 during operation and the engine operating noise are easily audible, resulting in low noise sensitivity for radios and other devices. Therefore, the switching speed of both the motor-side flyback transistor 411 and the generator-side flyback transistor 412 is controlled to the fastest normal switching speed.

[0093] When the drive motor 2 is operating and the engine is stopped, the noises from the vehicle 1 in motion are easily audible, so the noise sensitivity of radios and other devices is somewhat low. Therefore, the switching speed of the motor-side flyback transistor 411 is controlled to the fastest speed (similar to the switching speed in the normal state). This suppresses heat generation due to power loss in the motor-side flyback transistor 411. On the other hand, since the engine (generator 3) is stopped, even if the switching speed of the generator-side flyback transistor 412 is slowed down to some extent, power loss is small, and heat generation in the generator-side flyback transistor 412 is suppressed. Therefore, the switching speed of the generator-side flyback transistor 412 is controlled to a third switching speed, which is slower than the switching speed in the normal state when the drive motor 2 and engine are operating, but faster than the second switching speed.

[0094] As described above, in this embodiment, the driving state of the drive motor 2 and the operating state of the engine are divided into four different scenes, and for each scene, it is determined whether or not to slow down the switching speed, and if so, to what extent. Therefore, it is possible to suppress slowing down the switching speed of the flyback transistor 41 more than necessary, and to suppress the power loss of the flyback transistor 41.

[0095] In this embodiment, the switching speed of the flyback transistor 41 is switched to three different speeds, but this is not necessarily the only option. For example, the switching speed of the flyback transistor 41 may be switched to two different speeds. In this case, for example, when the drive motor 2 is running and the engine is stopped, the switching speed of the generator-side flyback transistor 412 is switched to the second switching speed. Alternatively, the switching speed of the flyback transistor 41 may be switched to four or more different speeds. In other words, as long as the switching speed of the flyback transistor 41 is switched to two or more different speeds, substantially the same effects as in the second embodiment can be obtained.

[0096] Furthermore, the second drive circuit 42 shown in Figure 8 is merely an example of the second drive circuit 42 in the second embodiment, and the second drive circuit 42 in this embodiment is not limited to the circuit in Figure 8. That is, the second drive circuit 42 can be any configuration as long as it switches the switching speed of the flyback transistor 41 to two or more different speeds based on the driving state of the drive motor 2 and the operating state of the engine.

[0097] According to the control method for the power converter 100 of the second embodiment described above, the following effects can be obtained.

[0098] According to the control method of the power converter 100, the second drive circuit 42 switches the switching speed of the flyback transistor 41 to at least two different speeds (first switching speed, second switching speed) based on the driving state of the drive motor 2 and the operating state of the engine. Therefore, it is possible to suppress the unnecessarily slowing down of the switching speed of the flyback transistor 41 and to suppress the power loss of the flyback transistor 41.

[0099] According to the control method of the power converter 100, when the drive motor 2 is stopped and the engine is running, the motor-side second circuit 421 switches the switching speed of the motor-side flyback transistor 411 to a second switching speed that is slower than the normal state when the drive motor 2 and engine are running, but faster than the first switching speed when the drive motor 2 and engine are stopped. In this way, even when the drive motor 2 is stopped, if the engine is running, the engine operating sound can be heard, so the switching speed of the motor-side flyback transistor 411 is slowed down to a certain extent. This reduces discomfort for the occupants and prevents the switching speed of the flyback transistor 41 from being slowed down more than necessary, thereby preventing increased power loss.

[0100] According to the control method of the power converter 100, when the drive motor 2 is operating and the engine is stopped, the generator-side second circuit 422 switches the switching speed of the generator-side flyback transistor 412 to a third switching speed that is slower than the normal state but faster than the second switching speed, or to the second switching speed. In this way, even when the engine is stopped, if the drive motor 2 is operating, the various noises during vehicle 1 operation are easily heard, and the noise sensitivity of radios, etc., is somewhat low, so only the switching speed of the generator-side flyback transistor 412 is slightly slowed down. This reduces discomfort for the occupants and prevents increasing power loss by slowing down the switching speed of the flyback transistor 412 more than necessary.

[0101] Although embodiments of the present invention have been described above, these embodiments only represent a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments.

[0102] Although each of the embodiments described above has been explained as a standalone embodiment, they may be combined as appropriate. [Explanation of symbols]

[0103] 1. Vehicle, 2. Drive motor, 3. Generator, 10. Switching circuit, 20. First drive circuit, 30. Control circuit, 40. Power supply circuit, 41. Flyback transistor, 42. Second drive circuit, 100. Power converter

Claims

1. Multiple switching elements for controlling the operation of a drive motor and a generator driven by an engine, A first drive circuit for operating the plurality of switching elements, A flyback transistor that controls the power supplied to the first drive circuit by switching operation, A control method for a power converter comprising a second drive circuit for operating the flyback transistor, The drive state of the drive motor and the operating state of the engine are determined, Based on the drive state of the drive motor and the operating state of the engine, the second drive circuit switches the switching speed of the flyback transistor. When the drive motor and the engine are stopped, the second drive circuit switches the switching speed of the flyback transistor to a first switching speed that is slower than when the drive motor or the engine is operating. A method for controlling a power converter.

2. A control method for a power converter according to claim 1, Based on the driving state of the drive motor and the operating state of the engine, the second drive circuit switches the switching speed of the flyback transistor to at least two different speeds. A method for controlling a power converter.

3. A control method for a power converter according to claim 1 or 2, The first drive circuit includes a motor-side circuit that operates a plurality of switching elements for controlling the operation of the drive motor, and a generator-side circuit that operates a plurality of switching elements for controlling the operation of the generator. The flyback transistor includes a motor-side flyback transistor that controls the power supplied to the motor-side circuit and a generator-side flyback transistor that controls the power supplied to the generator-side circuit. The second drive circuit includes a motor-side second circuit for operating the motor-side flyback transistor and a generator-side second circuit for operating the generator-side flyback transistor. When the drive motor is stopped and the engine is running, the motor-side second circuit switches the switching speed of the motor-side flyback transistor to a second switching speed that is slower than the normal state when the drive motor and engine are running, but faster than the first switching speed. A method for controlling a power converter.

4. A control method for a power converter according to claim 3, When the drive motor is operating and the engine is stopped, the generator-side second circuit switches the switching speed of the generator-side flyback transistor to a third switching speed that is slower than the normal state and faster than the second switching speed, or to the second switching speed. A method for controlling a power converter.

5. Multiple switching elements for controlling the operation of a drive motor and a generator driven by an engine, A first drive circuit for operating the plurality of switching elements, A flyback transistor that controls the power supplied to the first drive circuit by switching operation, A second drive circuit for operating the aforementioned flyback transistor, A drive state determination means for determining the drive state of the drive motor, The system includes an engine operating state determination means for determining the operating state of the engine, The second drive circuit switches the switching speed of the flyback transistor based on the drive state of the drive motor and the operating state of the engine, and when the drive motor and the engine are stopped, it switches the switching speed of the flyback transistor to a first switching speed that is slower than when the drive motor or the engine is operating. Power converter.

Images