Power converter

Abstract

In a power conversion device equipped with multiple power conversion units, the switching timing of the switching elements is adjusted to reduce switching losses without adding a temperature sensor. [Solution] The power conversion device comprises a plurality of power conversion units connected in parallel via an inductance component. Each of the plurality of power conversion units includes a switching element. The power conversion device has a current identification unit and a timing adjustment unit. The current identification unit identifies the current of the inductance component and the current of at least one of the plurality of power conversion units. Based on the current value identified by the current identification unit, the timing adjustment unit adjusts the timing of the input of the turn-off signal to at least one of the plurality of switching elements so that the turn-off timings of the plurality of switching elements included in the plurality of power conversion units are synchronized.

Description

Technical Field

[0001] The present invention relates to a power conversion device.

Background Art

[0002] Power conversion devices are mounted in a wide variety of applications, such as industrial equipment and infrastructure equipment. In order to increase the power capacity, a power conversion device may be configured by connecting a large number of power conversion units including switching elements in parallel. On the other hand, improving the energy conversion efficiency of a power conversion device is important for addressing global warming. To improve the efficiency of such a power conversion device, it is effective to reduce the switching loss of the switching element. To reduce the switching loss of the switching element, it is necessary to adjust the switching timing of the switching element.

[0003] Patent Document 1 describes a "control device for controlling a plurality of switching elements connected in parallel". Patent Document 1 also describes that the "control device" includes "temperature acquisition means for acquiring the temperatures of the switching elements respectively, and change means for comparing the temperatures acquired by the temperature acquisition means and changing the opening / closing timing of the switching elements based on the comparison result".

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The control device described in Patent Document 1 changes the switching timing of multiple switching elements according to their temperatures. Therefore, this control device requires the addition of temperature sensors on the switching elements. Furthermore, depending on the shape of the switching elements, it may not be possible to provide temperature sensors on them. Thus, the problem is to enable adjustment of the switching timing of switching elements in a power conversion device equipped with multiple power conversion units including switching elements, so as to reduce switching losses, without adding temperature sensors. [Means for solving the problem]

[0006] According to one embodiment, the power conversion device comprises a plurality of power conversion units connected in parallel via an inductance component, each of the plurality of power conversion units includes a switching element, and the power conversion device includes a current identification unit that identifies the current of the inductance component and the current of at least one of the plurality of power conversion units, and a timing adjustment unit that adjusts the timing of inputting a turn-off signal to at least one of the plurality of switching elements so that the turn-off timings of the plurality of switching elements included in the plurality of power conversion units are synchronized, based on the current value identified by the current identification unit. [Effects of the Invention]

[0007] According to one embodiment, in a power conversion device equipped with multiple power conversion units including switching elements, the switching timing of the switching elements can be adjusted to reduce switching losses without adding a temperature sensor. [Brief explanation of the drawing]

[0008] [Figure 1] This is a circuit diagram of a power conversion device according to the first embodiment. [Figure 2] This figure shows an example of the hardware configuration of the control device according to the first embodiment. [Figure 3]This is a control block diagram of a power converter according to the first embodiment. [Figure 4] This figure shows an example of a switching waveform in a power conversion device according to the first embodiment. [Figure 5] This figure shows a modified example of the control block of the power converter according to the first embodiment. [Figure 6] This figure shows an example of the current dependence of the turn-off surge voltage and turn-off loss of a switching element according to the first embodiment. [Figure 7] This is a control block diagram of a power converter according to the second embodiment. [Figure 8] This figure shows an example of a switching waveform in a power converter according to the second embodiment. [Figure 9] This is a circuit diagram of a power converter according to the third embodiment. [Figure 10] This is a circuit diagram of a power conversion device according to the fourth embodiment. [Figure 11] This is a circuit diagram of a power converter according to the fifth embodiment. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below. In each embodiment, the same or corresponding components are denoted by the same reference numerals, and repeated descriptions will be omitted unless necessary.

[0010] (History of the inventor's research) The embodiments will be described below, but before that, the history of the inventors' research will be explained. To date, various studies have been conducted on power conversion devices that include multiple power conversion units connected in parallel via an inductance component. Here, a power conversion unit is, for example, a basic circuit that converts power using a combination of a switching element and a diode. There is variation in the characteristics of the switching elements included in each of the multiple power conversion units. For example, the gate threshold voltage at which a switching element turns on differs depending on the switching element. Furthermore, its characteristics also fluctuate with the temperature of the switching element.

[0011] Therefore, even if gate signals for turning on are simultaneously input to each switching element, one switching element will turn on first, followed by the other switching elements. The current flowing through the switching element that turns on first will be greater than the current flowing through the switching element that turns on later. Also, even if gate signals for turning off are simultaneously input to each switching element, one switching element may turn off first, followed by the other switching elements. Generally, a switching element with a large current flowing through it will turn off more slowly than a switching element with a small current flowing through it.

[0012] Thus, even when gate signals for turning on or off are simultaneously input to multiple switching elements, a timing difference will occur between the turn-on and turn-off states. In particular, the turn-off loss caused by timing differences between switching elements is very large. Therefore, it is extremely important to synchronize the turn-off timing of multiple switching elements. Furthermore, enabling the adjustment of the on / off timing of switching elements without adding temperature sensors to the switching elements is important from the standpoint of addressing the structural constraints of power conversion devices, reducing manufacturing costs, and saving space.

[0013] In addition, according to the study by the present inventors, it has been found that the total turn-on loss is reduced when the turn-on timing between switching elements is slightly shifted rather than being aligned. However, if only a specific switching element is turned on first, the current in that switching element alone increases and heat is generated. Since heat generation in the element damages the element, it is necessary to provide a radiator for the switching element. Therefore, when intentionally shifting the turn-on timing between switching elements, it is also important to sequentially change the switching element that is turned on first. For example, when there are two switching elements, it is important to alternately change the switching element that is turned on first.

[0014] Hereinafter, embodiments of the invention devised as a result of the intensive study by the present inventors will be described. The embodiments described hereinafter are those in which, in a power conversion device including a plurality of power conversion units connected in parallel via an inductance component, the turn-off timing of a plurality of switching elements can be aligned without adding a temperature sensor. Further, in the power conversion device, the turn-on timing of a plurality of switching elements can be intentionally shifted or made simultaneous. Furthermore, when shifting the turn-on timing of a plurality of switching elements, the power conversion device can sequentially change the switching element that becomes the on state first.

[0015] (First Embodiment) FIG. 1 is a circuit diagram of a power conversion device according to the first embodiment. The power conversion device 1000 shown in FIG. 1 is a boost chopper circuit that performs DC-DC power conversion. The power conversion device 1000 includes a DC power supply 1, a filter capacitor 6, a main reactor 3, switching elements Q1, Q2, diodes D1, D2, a main circuit parasitic inductance 5, a DC capacitor 2, and a load 7. Further, the power conversion device 1000 further includes a voltage sensor 9 and a control device 10.

[0016] The control device 10 is configured using, for example, a processor. The processor is, for example, a CPU (Central Processing Unit), MPU (Micro Processor Unit), etc. The control device 10 may also be an MCU (Micro Controller Unit), or a PROM (Programmable Read Only Memory), etc. In this embodiment, as an example, it is assumed that the control device 10 is a computer including a processor.

[0017] In the power conversion device 1000, the DC power supply 1 supplies power to the load 7, and the voltage applied to the load 7 becomes higher than the voltage of the DC power supply 1. Note that the DC power supply 1 may be a power supply obtained by smoothing the output of a single-phase AC power supply or a three-phase AC power supply.

[0018] The diode D1 and the switching element Q1 are connected in series to form one leg. Also, the diode D2 and the switching element Q2 are connected in series to form one leg. An auxiliary reactor 4 is connected between the diode D1 and the switching element Q1. Also, a main reactor 3 is connected between the DC power supply 1 and the auxiliary reactor 4. Here, a leg is a basic circuit for power conversion in a circuit such as a DC-DC conversion circuit (DC-DC converter) or an inverter circuit, and is generally composed of a switching element and its accessories. Note that a leg is an example of the "power conversion unit" in the present application. Therefore, the power conversion device 1000 has two power conversion units.

[0019] Here, the auxiliary reactor 4 is inserted between the main reactor 3 and the connection point of the diode D1 and the switching element Q1. However, the auxiliary reactor 4 may be inserted between the main reactor 3 and the connection point of the diode D2 and the switching element Q2. Also, the auxiliary reactor 4 may be inserted on both the switching element Q1 side and the switching element Q2 side.

[0020] The filter capacitor 6 is connected in parallel to the DC power supply 1 and has the function of inputting and outputting high-frequency current associated with the switching operation of the switching elements Q1 and Q2. Note that the filter capacitor 6 is not required to be installed in the power conversion device 1000.

[0021] There is a main circuit parasitic inductance 5 between each leg and the DC capacitor 2. The components of the main circuit parasitic inductance 5 exist, for example, at the lead terminals of switching elements Q1, Q2, diodes D1, D2, etc. Also, for example, the components of the main circuit parasitic inductance 5 exist as the equivalent series inductance of the DC capacitor 2. Furthermore, the components of the main circuit parasitic inductance 5 also exist in the wiring connecting components such as switching elements Q1, Q2, diodes D1, D2, and DC capacitor 2. Here, the main circuit parasitic inductance 5 is considered to be the sum of the inductance present at the lead terminals of diodes D1, D2, etc., the equivalent series inductance of the DC capacitor 2, and the inductance present in the wiring connecting the components.

[0022] The current flowing through the main circuit parasitic inductance 5 changes abruptly in conjunction with the switching operation of switching elements Q1 and Q2. As a result, an induced electromotive force is generated in the main circuit parasitic inductance 5. In particular, during the turn-off operation when switching elements Q1 and Q2 transition from the ON state to the OFF state, the induced electromotive force of the main circuit parasitic inductance 5 is applied to switching elements Q1 and Q2 as a surge voltage. If this surge voltage exceeds the withstand voltage of switching elements Q1 and Q2, switching elements Q1 and Q2 will fail. Therefore, the surge voltage generated during the turn-off operation of the switching elements must be kept below the withstand voltage of switching elements Q1 and Q2.

[0023] Switching elements Q1 and Q2 are semiconductor devices capable of switching between an on state and an off state. Switching elements Q1 and Q2 are composed of, for example, IGBTs (Insulated Gate Bipolar Transistors). Switching elements Q1 and Q2 are also composed of, for example, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). Alternatively, for example, switching elements Q1 and Q2 are composed of multiple semiconductor devices connected in series. As a specific example, switching elements Q1 and Q2 may be cascode-type semiconductor devices in which a normally-on JFET (Junction Field Effect Transistor) and a normally-off MOSFET are connected in series.

[0024] Diodes D1 and D2 are composed of, for example, PN diodes, FRDs (Fast Recovery Diodes), or SBDs (Schottky Barrier Diodes).

[0025] Here, as an example, we assume that switching elements Q1 and Q2 are both MOSFETs, and diodes D1 and D2 are both SBDs. Note that the switching elements Q1 and Q2 and diodes D1 and D2 constituting the two legs may be housed in the same package for each leg, and the two packages may be formed integrally. Using components configured in this way can improve the mounting density in the circuit. Furthermore, this allows for miniaturization of the power converter 1000.

[0026] The semiconductor material for the switching elements Q1 and Q2 and the diodes D1 and D2 is, for example, Si (silicon). This semiconductor material may also be SiC (silicon carbide) or GaN (gallium nitride), which have a wider bandgap than Si. By using these wide-bandgap semiconductors, it is possible to reduce power loss and operate at high temperatures compared to Si. Therefore, the power converter 1000 can be miniaturized.

[0027] The on / off states of the switching elements Q1 and Q2 are controlled via a gate drive circuit (not shown) based on gate signals output from the control device 10. The control device 10 detects the current of the main reactor 3 using a current sensor 8a, the current of the auxiliary reactor 4 using a current sensor 8b, and the voltage of the load 7 using a voltage sensor 9. The control device 10 controls the on / off state of the gate signals input to the switching elements Q1 and Q2 so that the detected voltage or current values ​​of each part become the set desired values.

[0028] When switching elements Q1 and Q2 are ON, energy is stored in the main reactor 3. When switching elements Q1 and Q2 are OFF, the energy stored in the main reactor 3 is supplied to the load 7 via diodes D1 and D2. This operation allows a voltage higher than that of the DC power supply 1 to be supplied to the load 7. The inductance value of the auxiliary reactor 4 can be smaller than that of the main reactor 3. By reducing the inductance value, the number of turns of the auxiliary reactor 4 can be reduced. This also allows for miniaturization of the power converter 1000.

[0029] Figure 2 shows an example of the hardware configuration of a control device according to the first embodiment. The control device 10 is a so-called computer. As shown in Figure 2, the control device 10 has a processor 101, memory 102, interface 103, storage 104, and communication bus 105. The processor 101, memory 102, interface 103, and storage 104 are connected to the communication bus 105. A predetermined program is stored in the memory 102 or storage 104. The processor 101 functions as various functional blocks by reading and executing this predetermined program. Various signal lines are connected to the interface 103, and various signals are transmitted and received through the interface 103.

[0030] Figure 3 is a control block diagram of the power converter according to the first embodiment. This control block diagram corresponds to the functional block diagram of the control device 10 shown in Figure 1. The control device 10 has, as functional blocks, a control unit 201, a reference PWM signal generation unit 202, a delayed PWM signal generation unit 203, a turn-on delay generation unit 204, a turn-off delay calculation unit 205, a storage unit 206, and a turn-off delay generation unit 207. The functions of each functional block will be described below.

[0031] The control unit 201 has the function of controlling each part so that the boost reactor current and the load voltage are, respectively, set to desired values. Here, the boost reactor current is the current value of the main reactor 3 detected by the current sensor 8a. The load voltage is the voltage value of the load 7 detected by the voltage sensor 9. As an example, the control unit 201 applies proportional or integral control to each part so that the error between the voltage command value and the current command value and the detected voltage and current values ​​is minimized. As another example, the control unit 201 calculates and outputs the duty cycle of the PWM signal so that the error between the voltage command value and the detected voltage and current values ​​is minimized.

[0032] The reference PWM signal generation unit 202 generates a reference PWM signal to be input to the switching elements Q1 and Q2 using the duty cycle output by the control unit 201. For example, the reference PWM signal is generated by comparing the duty cycle with carriers such as a triangular wave or a sawtooth wave.

[0033] The delayed PWM signal generation unit 203 generates a delayed PWM signal including a turn-on delay α and a turn-off delay β using the reference PWM signal generation unit 202, the turn-on delay generation unit 204, and the turn-off delay generation unit 207. The turn-on delay α is the delay between when one of the switching elements Q1 and Q2 turns on and when the other turns on. The turn-off delay β is the delay between when one of the switching elements Q1 and Q2 turns off and when the other turns off. The delayed PWM signal is output as the gate signal for the switching elements Q1 and Q2.

[0034] The turn-on delay generation unit 204 generates a turn-on delay α. In this embodiment, the turn-on delay α is set to a constant value. However, the turn-on delay α may be changed according to the power supplied to the load 7, the voltage of the DC power supply 1, etc.

[0035] For example, when the power supplied to load 7 is large, the current flowing through switching elements Q1 and Q2 also increases. As a result, both the turn-on loss and conduction loss of switching elements Q1 and Q2 increase. In this case, the turn-on loss can be reduced by increasing the turn-on delay α, but the conduction loss increases. When the on-voltage of switching elements Q1 and Q2 is low, that is, when switching elements Q1 and Q2 are elements with low conduction loss, and the power supplied to load 7 is large, it is possible to reduce the sum of switching loss and conduction loss by increasing the turn-on delay α.

[0036] Therefore, the turn-on delay generation unit 204 adjusts and generates the turn-on delay α to be longer when, for example, the on-voltage of the switching elements Q1 and Q2 is low and the power supplied to the load 7 is large.

[0037] In this way, by adjusting the length of the turn-on delay α, i.e., the delay amount, according to the power consumption of the load 7 and the voltage of the DC power supply 1, the losses related to switching in the switching elements Q1 and Q2 can be reduced. Furthermore, this allows for miniaturization of the power converter 1000.

[0038] The turn-off delay calculation unit 205 calculates the turn-off delay β using the current of the auxiliary reactor 4 detected by the current sensor 8b and the current of the main reactor 3 detected by the current sensor 8b. One example of the calculation method is to use a predetermined function with the voltage value of the DC power supply 1, the inductance value of the auxiliary reactor 4, and the turn-on delay α as parameters.

[0039] For example, the turn-off delay calculation unit 205 identifies a leg among several legs in which the current value identified as the flowing current is relatively higher than that of the other legs. Then, the turn-off delay calculation unit 205 determines the value of the turn-off delay β, i.e., the delay amount, so that the input timing of the turn-off signal to the switching element included in the identified leg is relatively earlier than that of the other legs. This makes it possible to synchronize the turn-off timing of multiple switching elements included in multiple legs.

[0040] In this embodiment, the control device 10 uses current sensors 8a and 8b to identify the current of the inductance component of the main reactor 3 and the current of at least one of the two legs. The control device 10 also identifies the current values ​​flowing through the two switching elements Q1 and Q2 based on the identified inductance component current and the current of at least one of the two legs. The turn-off delay calculation unit 205 identifies the leg with the relatively higher current value and determines the value of the turn-off delay β so as to relatively advance the input timing of the turn-off signal input to the switching elements included in the identified leg. This makes it possible to synchronize the turn-off timing of the two switching elements Q1 and Q2 included in the two legs.

[0041] The turn-off delay calculation unit 205 may also determine the value of the turn-off delay β1 for switching element Q1 and the value of the turn-off delay β2 for switching element Q2, and ultimately ensure that the turn-off timings of the two switching elements Q1 and Q2 are synchronized.

[0042] The memory unit 206 stores the value of the turn-off delay β calculated by the turn-off delay calculation unit 205. The timing at which the memory unit 206 stores the value can be any timing corresponding to the switching period of the switching elements Q1 and Q2, or signals from external devices (not shown), etc.

[0043] The turn-off delay generation unit 207 generates a turn-off delay β based on the value of the turn-off delay β stored in the memory unit 206.

[0044] The current sensors 8a and 8b, and the control device 10 are examples of the "current identification unit" in this application. The turn-on delay generation unit 204 is an example of the "timing adjustment unit" in this application. The turn-off delay calculation unit 205, the storage unit 206, and the turn-off delay generation unit 207 are examples of the "timing adjustment unit" in this application.

[0045] Figure 4 shows an example of a switching waveform in a power converter according to the first embodiment. The switching waveforms shown in Figure 4 represent the gate signals of switching elements Q1 and Q2, and the currents flowing through switching elements Q1 and Q2. Specifically, in Figure 4, the horizontal axis represents time, and the vertical axis represents the gate signal or current. The waveforms in Figure 4, from top to bottom, represent the gate signal of switching element Q1, the gate signal of switching element Q2, the current flowing through switching element Q1, and the current flowing through switching element Q2.

[0046] The current of switching element Q1 can be determined based on the current flowing through auxiliary reactor 4 and the gate signal of switching element Q1 in the ON state. The current of switching element Q2 can be determined based on the current difference between the current flowing through main reactor 3 and the current flowing through auxiliary reactor 4 and the gate signal of switching element Q2 in the ON state. Note that the currents of switching elements Q1 and Q2 may also be determined by estimation without using current sensors, gate signal measurement systems, etc.

[0047] Figure 5 shows a modified example of the control block of the power converter according to the first embodiment. In the modified control block shown in Figure 5, a voltage detection unit 208 and a current calculation unit 209 are newly added compared to the control block shown in Figure 3. For example, the power converter 1000 is provided with a voltage detection unit 208 that detects the voltage of the source inductance of the switching elements Q1 and Q2. The voltage detection unit 208 detects the voltage of the source inductance based on the output from, for example, a voltage sensor or voltage detection circuit provided on the switching elements Q1 and Q2. Then, for example, the current calculation unit 209 calculates the current of the switching elements Q1 and Q2 based on the detected voltage value of the source inductance.

[0048] In this way, the currents of switching elements Q1 and Q2 can be determined without using current sensors, gate signal measurement systems, etc. Furthermore, in this case, the number of current sensors in the power converter 1000 can be reduced. In addition, this allows the power converter 1000 to be made smaller.

[0049] Returning to Figure 4, let's explain the switching waveform. At time t1, a gate signal is input to switching element Q1, causing switching element Q1 to switch from the off state to the on state, and current flows through switching element Q1. At time t2, a gate signal is input to switching element Q2, causing switching element Q2 to switch from the off state to the on state, and current flows through switching element Q2. Between time t1 and time t2, switching element Q1 is in the on state and switching element Q2 is in the off state. Therefore, the potential on the side of auxiliary reactor 4 facing switching element Q1 becomes the ground potential, and the potential on the side of auxiliary reactor 4 facing switching element Q2 becomes the positive terminal potential of DC power supply 1.

[0050] As a result, current flows from switching element Q2 to switching element Q1 via auxiliary reactor 4. At this time, since switching element Q1 is already in the ON state, no turn-on loss occurs in switching element Q2 when it transitions from the OFF state to the ON state. On the other hand, the current in switching element Q2 decreases, so the current in switching element Q2 when it turns on at time t2 also decreases, thereby reducing the turn-on loss of switching element Q2.

[0051] In the next turn-on timing, switching element Q2 is turned on first, followed by switching element Q1. This reduces the turn-on loss of switching element Q1. In this way, by alternately delaying the turn-on timing of switching elements Q1 and Q2, the turn-on losses of switching elements Q1 and Q2 can be reduced (alternating adjustment mode). Furthermore, by reducing the turn-on loss, it is possible to simplify the cooling system and achieve miniaturization and increased efficiency of the power converter 1000.

[0052] Next, we focus on the turn-off operation in which switching elements Q1 and Q2 change from the ON state to the OFF state. It is desirable for the turn-off operations of switching elements Q1 and Q2 to occur simultaneously. For example, if switching element Q2 turns off first, switching element Q1 remains in the ON state, so the potential on the side of the auxiliary reactor 4 facing switching element Q1 becomes the ground potential, and the potential on the side facing switching element Q2 becomes the positive electrode potential of the DC power supply 1. As a result, current flows from switching element Q2 to switching element Q1 via the auxiliary reactor 4.

[0053] At this time, since the switching element Q1 is in the ON state, the current through the switching element Q1 increases. When the switching element Q1 turns off while this increased current is flowing, the induced electromotive force of the main circuit parasitic inductance 5 increases, causing the surge voltage at the time of the switching element Q1's turn-off to increase. If the surge voltage at the time of turn-off increases and exceeds the voltage rating of the switching element Q1, the switching element Q1 will fail. Furthermore, the increase in the surge voltage at the time of turn-off leads to an increase in turn-off losses, which can result in the need for a larger cooler for the power converter 1000 and a decrease in efficiency.

[0054] Therefore, it is desirable that the turn-off timing of switching elements Q1 and Q2 be simultaneous. For this reason, generally, at time t3, gate signals to turn off are input to switching elements Q1 and Q2 simultaneously. However, the characteristics of switching elements Q1 and Q2 are not identical and vary. For example, if there is variation in the gate threshold voltage, even if the gate signals to turn off are input at the same time at time t3, the switching element with the higher threshold voltage will start turning off first.

[0055] Specifically, if the threshold voltage of switching element Q2 is higher than the threshold voltage of switching element Q1, switching element Q2 will start turning off first, even if the turn-off gate signal is input simultaneously. As a result, as described above, current flows from switching element Q2 to switching element Q1 via the auxiliary reactor 4, and the current when switching element Q1 turns off at time t4 increases to I1. Furthermore, the threshold voltage also depends on the temperature of the switching element, and generally, the higher the temperature, the lower the threshold voltage. That is, if the temperature of switching element Q1 is higher than the temperature of switching element Q2, the threshold voltage of switching element Q2 will be higher than that of switching element Q1. In this case as well, the current when switching element Q1 turns off increases, similar to the above. Therefore, it is necessary to reduce the turn-off timing difference caused by variations in the characteristics of the switching elements, temperature differences, etc.

[0056] Variations in the characteristics of switching elements, or temperature differences, can cause timing differences not only in turn-off but also in turn-on. For example, suppose the threshold voltage of switching element Q2 is higher than the threshold voltage of switching element Q1. In this case, even if a turn-on delay α is provided in the gate signals for the turn-on of switching elements Q1 and Q2, the turn-on delay will be longer than α because the threshold voltage of switching element Q2 is higher.

[0057] Here, the steady-state current difference when switching elements Q1 and Q2 are in the ON state with a turn-on delay α can be calculated as (voltage of DC power supply 1) × (turn-on delay α) ÷ (inductance value of auxiliary reactor 4). For example, the measured value and the calculated value of the current difference between switching elements Q1 and Q2 at time ts, which is approximately midway between time t2 and time t3, are compared. This comparison allows for the detection of characteristic variations or temperature differences between switching elements Q1 and Q2.

[0058] For example, let's assume that the calculated current difference is 10A higher for switching element Q1, and the measured current difference is 15A higher for switching element Q1. In this case, because the measured current difference is large, it can be seen that the threshold voltage of switching element Q2 is higher than the threshold voltage of switching element Q1. In this way, by using the calculated and measured steady-state current differences when switching elements Q1 and Q2 are in the ON state, it is possible to detect the magnitude of the threshold voltages of switching elements Q1 and Q2.

[0059] Using these detection results, the turn-off timing of switching elements Q1 and Q2 can be adjusted. Specifically, since the threshold voltage of switching element Q2 is higher than that of switching element Q1, in order to synchronize the turn-off timing of switching elements Q1 and Q2, the turn-off timing of switching element Q1 should be advanced. That is, instead of inputting the turn-off gate signals simultaneously, the turn-off gate signal for switching element Q1 is input at time t5, and the turn-off gate signal for switching element Q2 is input at time t6. By adjusting the turn-off gate signals in this way, the turn-off timing of switching elements Q1 and Q2 can be made simultaneous. As a result, the turn-off current is reduced to I2, and an increase in turn-off surge voltage or turn-off loss can be prevented.

[0060] The turn-off delay β of switching elements Q1 and Q2 is calculated by the turn-off delay calculation unit 205 in Figure 3. The calculation result of the turn-off delay calculation unit 205 is reflected at the earliest at the timing of one switching cycle ahead. The calculation by the turn-off delay calculation unit 205 and the reflection of the calculation result can be at any timing, not one switching cycle ahead. In addition, the turn-off delay β calculated by the turn-off delay calculation unit 205 may be processed in multiple steps. For example, when applying a 100 ns turn-off delay, a 50 ns turn-off delay can be applied, then the current difference between switching elements Q1 and Q2 can be detected, the turn-off delay can be recalculated, and then another 50 ns turn-off delay can be applied as needed. In this case, subsequent turn-off delays may overwrite the previous turn-off delay.

[0061] Figure 6 shows an example of the current dependence of the turn-off surge voltage and turn-off loss of a switching element according to the first embodiment. In the graph shown in Figure 6, the horizontal axis represents the current at the time of turn-off of the switching element, and the vertical axis represents the turn-off surge voltage and turn-off loss. The turn-off surge voltage depends on the induced electromotive force of the main circuit parasitic inductance 5. The induced electromotive force is calculated as (inductance value of the main circuit parasitic inductance 5) × (rate of change of current of the switching element at the time of turn-off). In other words, the larger the current at the time of turn-off, the higher the rate of change of current of the switching element at the time of turn-off. Also, the higher the turn-off surge voltage, the greater the turn-off loss. Therefore, it is desirable for the current at the time of turn-off of the switching element to be low.

[0062] As shown in Figure 6, the current I2 during the turn-off of the switching element after applying the proposed technology is reduced compared to the current I1 during the turn-off of the switching element before applying the proposed technology. As a result, it is possible to reduce both the turn-off surge voltage and the turn-off loss by applying the proposed technology.

[0063] (Second Embodiment) Figure 7 is a control block diagram of the power converter according to the second embodiment. The differences between the control block of the power converter according to the second embodiment and the control block according to the first embodiment will be explained. The control block of the power converter according to the second embodiment is configured to have a simultaneous mode in addition to an alternating adjustment mode.

[0064] In other words, the turn-on delay generation unit 204 has an alternating adjustment mode as one of its adjustment modes, which alternately adjusts the turn-on timing of the two switching elements Q1 and Q2. The turn-on delay generation unit 204 also has a simultaneous mode as another adjustment mode, which simultaneously inputs a turn-on signal to each of the two switching elements Q1 and Q2. The simultaneous mode corresponds to the mode when the turn-on delay α is set to zero. The turn-on delay generation unit 204 is configured to allow the user to switch between the alternating adjustment mode and the simultaneous mode through a predetermined operation. Alternatively, the turn-on delay generation unit 204 is configured to allow the adjustment mode to be fixed in advance to either the alternating adjustment mode or the simultaneous mode.

[0065] Figure 8 shows an example of a switching waveform in a power converter according to the second embodiment. Here, it is assumed that the gate threshold voltage of switching element Q2 is higher than the gate threshold voltage of switching element Q1 due to variations in the characteristics of the switching elements and the effects of temperature differences. In simultaneous mode, at time t1, a signal to turn on switching elements Q1 and Q2 is input simultaneously. Here, since the threshold voltage of switching element Q2 is higher than the threshold voltage of switching element Q1, current starts to flow through switching element Q1 first, and then through switching element Q2. As a result, a current difference occurs between switching elements Q1 and Q2 at time ts. Specifically, the current of switching element Q1, which has a lower threshold voltage, is greater than the current of switching element Q2, which has a higher threshold voltage.

[0066] By comparing the currents of switching elements Q1 and Q2 in simultaneous mode in this way, it is possible to detect differences in characteristics and the relative magnitudes of threshold voltages due to temperature differences. The turn-off timing is adjusted using the currents of switching element Q1 and switching element Q2. The method for adjusting the turn-off timing is the same as in the first embodiment.

[0067] (Third embodiment) Figure 9 is a circuit diagram of the power converter according to the third embodiment. The power converter 1000 according to the first and second embodiments was a boost chopper circuit. The power converter 1001 according to the third embodiment is a buck chopper circuit. In a boost chopper circuit, the voltage across the load 7 becomes higher relative to the DC power supply 1, but in a buck chopper circuit, the voltage across the load 7 becomes lower relative to the DC power supply 1. Switching elements Q1 and Q2 are controlled to achieve this function.

[0068] In this type of step-down chopper, as in the first embodiment, it is desirable that switching elements Q1 and Q2 be turned off simultaneously. The means for simultaneous turn-off can be either the method of adjusting with a turn-on delay α as in the first embodiment, or the method of adjusting in a simultaneous mode with zero turn-on delay α as in the second embodiment. In this way, switching elements Q1 and Q2 can be turned off simultaneously even in the step-down chopper circuit. As a result, surge voltage and turn-off losses can be reduced. Furthermore, this makes it possible to miniaturize the power converter 1001.

[0069] (Fourth Embodiment) Figure 10 is a circuit diagram of the power converter according to the fourth embodiment. The power converters 1000 according to the first and second embodiments, and the power converter 1001 according to the third embodiment, were DC-DC power conversion circuits. The power converter 1002 according to the fourth embodiment is a DC-AC power conversion circuit. A DC-DC power conversion circuit outputs DC power to the load 7 in relation to the DC power source 1, while a DC-AC power conversion circuit has the function of outputting AC power to the load 7 in relation to the DC power source 1. Switching elements Q3 to Q6 are controlled to realize this function.

[0070] In this embodiment, as shown in Figure 10, the switching elements Q3 and Q4 and the diodes D3 and D4 constitute one leg, and the switching elements Q5 and Q6 and the diodes D5 and D6 constitute another leg. Furthermore, a DC capacitor 2a is connected in parallel to the series circuit of switching elements Q3 and Q4, and a DC capacitor 2b is connected in parallel to the series circuit of switching elements Q5 and Q6. In addition, instead of the auxiliary reactor 4, an auxiliary reactor 4a corresponding to the switching elements Q3 and Q4 and an auxiliary reactor 4b corresponding to the switching elements Q5 and Q6 are provided. Furthermore, a current sensor 8c for detecting the current flowing through the auxiliary reactor 4a and a current sensor 8d for detecting the current flowing through the main reactor 3a are provided.

[0071] In this configuration, it is desirable that the upper arms of each leg, i.e., switching elements Q3 and Q5, be turned off simultaneously. Similarly, it is desirable that the lower arms of each leg, i.e., switching elements Q4 and Q6, be turned off simultaneously. The means for simultaneously turning off the upper or lower arms may be either the method of adjustment with a turn-on delay α as in the first embodiment, or the method of adjustment in a simultaneous mode with a turn-on delay α set to zero as in the second embodiment.

[0072] In this way, in the DC-AC power conversion circuit, the upper arm of each leg can be turned off simultaneously, as can the lower arm of each leg. As a result, surge voltage and turn-off losses can be reduced. Furthermore, this allows for miniaturization of the power converter 1002.

[0073] As described above, according to the embodiment described, in a power conversion device equipped with multiple power conversion units, the switching timing of the switching elements can be adjusted to reduce switching losses without adding a temperature sensor.

[0074] (Fifth embodiment) Figure 11 is a circuit diagram of the power converter according to the fifth embodiment. The power converter according to the first to third embodiments described above has two power conversion units, each containing one switching element. The power converter 1003 according to the fourth embodiment is a boost chopper circuit and has three power conversion units, each containing one switching element.

[0075] Compared to the circuit of the first embodiment, the leg consisting of diode D7 and switching element Q7 is connected in parallel with the other two legs. Also, an auxiliary reactor 4c is provided between the main reactor 3 and the connection point between diode D7 and switching element Q7. Furthermore, a current sensor 8e is provided between the main reactor 3 and the auxiliary reactor 4c. The power converter 1003 uses the current sensor to determine the current value flowing through each switching element, and based on the determined current value, adjusts the length of the turn-off delay β for one or more switching elements so that the turn-off timing of each switching element is synchronized.

[0076] Alternatively, the power converter 1003 may simultaneously input a gate signal to each switching element to turn it on. Alternatively, the power converter 1003 may sequentially input gate signals with adjusted turn-on delays to each switching element. In other words, the power converter 1003 may have a mode that adjusts the timing of the input of the turn-on signal to each switching element so that each switching element included in the three power conversion units turns on first in rotation.

[0077] Thus, even when a power converter includes three or more power conversion units, the above method can reduce switching losses in the switching elements.

[0078] It goes without saying that the present invention is not limited to the embodiments described above, and can be modified in various ways without departing from its essence. [Explanation of symbols]

[0079] 1 DC power supply 2,2a,2b DC Capacitors 3,3a Main reactor 4,4a,4b,4c Auxiliary reactors 5. Parasitic Inductance of the Main Circuit 6 Filter Capacitors 7 Load 8a, 8b, 8c, 8d, 8e Current Sensor 9. Voltage Sensor 10 Control device Q1-Q7 Switching elements D1~D7 Diodes 101 Processors 102 memory 103 Interface 104 storage 105 Communications Bus 201 Control Unit 202 Reference PWM signal generation section 203 Delayed PWM signal generation unit 204 Turn-on delay generation unit 205 Turn-off delay calculation unit 206 Memory section 207 Turn-off delay generation unit 208 Voltage detection unit 209 Current Calculation Unit 1000~1003 Power converter

Claims

1. A power conversion device comprising a plurality of power conversion units connected in parallel via an inductance component, Each of the aforementioned power conversion units includes a switching element, The aforementioned power converter is A current identification unit that identifies the current of the inductance component and the current of at least one of the plurality of power conversion units, The system includes a timing adjustment unit that adjusts the timing of inputting a turn-off signal to at least one of the multiple switching elements so that the turn-off timings of the multiple switching elements included in the multiple power conversion units are synchronized, based on the current value identified by the current identification unit. Power converter.

2. In the power conversion device according to claim 1, The timing adjustment unit synchronizes the turn-off timings of the multiple switching elements by making the input timing of the turn-off signal to the switching element included in the power conversion unit whose current value, as determined by the current determination unit, is relatively higher than that of the other power conversion units, relatively earlier than that of the other power conversion units. Power converter.

3. In the power conversion device according to claim 1, The aforementioned plurality of power conversion units consist of two power conversion units, The timing adjustment unit has a mode for adjusting the input timing of the turn-on signal to each switching element so that the switching element in one of the two power conversion units and the switching element in the other of the two power conversion units turn on alternately first. Power converter.

4. In the power conversion device according to claim 1, The timing adjustment unit has a mode in which the input timing of the turn-on signal to the switching element included in each of the plurality of power conversion units is set to be simultaneous. Power converter.

5. In the power conversion device according to claim 1, The aforementioned plurality of power conversion units include three or more power conversion units, The timing adjustment unit has a mode for adjusting the input timing of the turn-on signal to each switching element so that each switching element included in the three or more power conversion units turns on first in rotation. Power converter.

6. In the power conversion device according to claim 1, Each of the aforementioned switching elements is composed of silicon or a semiconductor material with a wider bandgap than silicon. Power converter.

7. In the power conversion device according to claim 1, Each of the aforementioned switching elements is an IGBT, a MOSFET, or a series-connected set of semiconductor elements. Power converter.

8. In the power conversion device according to claim 1, Each of the aforementioned switching elements is either an IGBT or a MOSFET. The aforementioned power converter is A voltage detection unit for detecting the voltage of the source inductance of the plurality of switching elements, A current calculation unit that calculates the current of the plurality of switching elements by performing calculations based on the detected source inductance voltage value, and has Power converter.

9. In the power conversion device according to claim 1, Includes a boost chopper circuit, Power converter.

10. In the power conversion device according to claim 1, Including a step-down chopper circuit, Power converter.

11. In the power conversion device according to claim 1, Includes a DC-AC power conversion circuit, Power converter.

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