Electric power conversion device

Abstract

A DC / DC converter unit (10) comprises: a first arm that includes a first switching element (Q1) and a second switching element (Q2) connected in series, and is connected in parallel to a DC electric power supply (SB1) and a first smoothing capacitor (C1); a second arm that includes a third switching element (Q3) and a fourth switching element (Q4) connected in series, and is connected in parallel to a DC bus (Bdc) and a second smoothing capacitor (C2); and an inductor (L1) connected to a midpoint of the first arm and a midpoint of the second arm. A control unit (11) estimates a temperature change of the inductor (L1) on the basis of an electric current detected by an inductor electric current detection unit (A3), and corrects the duty ratios of the first switching element (Q1) to the fourth switching element (Q4) on the basis of the estimated temperature change.

Description

Power Conversion Device

[0001] The present disclosure relates to a power conversion device capable of stepping up and down a DC voltage.

[0002] One type of DC / DC converter is an H-bridge buck-boost DC / DC converter capable of both boost and buck operations (see, for example, Patent Document 1). H-bridge buck-boost DC / DC converters are often used with DC power sources whose voltage fluctuates, such as storage batteries and solar cells. H-bridge buck-boost DC / DC converters use inductors. The inductance of an inductor is temperature-dependent, and with a typical inductor, the inductance increases as the temperature rises. The increase in inductance due to temperature rise may cause unstable control of the H-bridge buck-boost DC / DC converter.

[0003] Prior Art Document 2 discloses a control method in which the temperature of a reactor used in a DC / DC converter is estimated based on detected values ​​of the reactor's voltage and current, and if the estimated temperature is greater than a threshold value, the output of the DC / DC converter is limited or stopped. However, with this control, situations can arise in which the DC / DC converter is unable to fully utilize its capabilities.

[0004] JP 2023-7755 A JP 2014-175656 A

[0005] The present disclosure has been made in consideration of these circumstances, and its purpose is to provide a power conversion device that has stable and sufficient output characteristics even when the temperature of the inductor changes, without complicating the circuit configuration.

[0006] In order to solve the above problem, a power conversion device according to an aspect of the present disclosure includes: a first arm including a first switching element and a second switching element connected in series and connected in parallel to a DC power supply and a first smoothing capacitor; a second arm including a third switching element and a fourth switching element connected in series and connected in parallel to a DC bus and a second smoothing capacitor; an inductor connected to a midpoint of the first arm and a midpoint of the second arm; a control unit that controls the first switching element and the fourth switching element; and an inductor current detection unit that detects a current flowing through the inductor. The control unit estimates a temperature change of the inductor based on the current detected by the inductor current detection unit, and corrects a duty ratio of the first switching element and the fourth switching element based on the estimated temperature change.

[0007] According to the present disclosure, it is possible to realize a power conversion device that has stable and sufficient output characteristics even when the temperature of the inductor changes, without complicating the circuit configuration.

[0008] It is a diagram showing a configuration example of a power conversion device according to an embodiment. It is a diagram showing a control model when the power conversion device according to embodiment 1 is operated in a peak current mode. It is a flowchart showing a flow of temperature compensation control in the power conversion device according to an embodiment.

[0009] FIG. 1 is a diagram illustrating an example of the configuration of a power conversion device 1 according to an embodiment. The power conversion device 1 is an H-bridge type step-up / step-down DC / DC converter and includes a DC / DC converter unit 10 and a control unit 11. A DC power supply SB1 is connected to the input side of the power conversion device 1, and a DC bus Bdc is connected to the output side. A load (not shown) and a charger (not shown) are connected to the DC bus Bdc. For example, the load may be a server or storage device in a data center. The charger includes an inverter that converts AC power supplied from a commercial power system into DC power. The DC power supply SB1 may be a storage battery. In this case, the storage battery functions as a backup power source for the server or storage device.

[0010] The DC / DC converter unit 10 includes a first smoothing capacitor C1, an inductor L1, a first switching element Q1 to a fourth switching element Q4, a second smoothing capacitor C20, a first current sensor A1 to a fourth current sensor A4, and a first voltage sensor V1 to a second voltage sensor V2. For example, electrolytic capacitors may be used for the first smoothing capacitor C1 and the second smoothing capacitor C2. For the first switching element Q1 to the fourth switching element Q4, MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) or IGBTs (Insulated Gate Bipolar Transistors) may be used.

[0011] A first smoothing capacitor C1 is connected between the positive and negative wiring of the DC power supply SB1. A first arm including a first switching element Q1 and a second switching element Q2 connected in series is connected in parallel to the DC power supply SB1 and the first smoothing capacitor C1. A second smoothing capacitor C2 is connected between the positive and negative wiring of the DC bus Bdc. A second arm including a third switching element Q3 and a fourth switching element Q4 connected in series is connected in parallel to the DC bus Bdc and the second smoothing capacitor C2.

[0012] The first switching element Q1 functions as a high-side switching element for stepping down, the second switching element Q2 functions as a low-side switching element for stepping down, the third switching element Q3 functions as a high-side switching element for stepping up, and the fourth switching element Q4 functions as a low-side switching element for stepping up.

[0013] An inductor L1 is connected between the midpoint of the first arm (the connection point between the first switching element Q1 and the second switching element Q2) and the midpoint of the second arm (the connection point between the third switching element Q3 and the fourth switching element Q4).

[0014] A first diode D1 to a fourth diode D4 are formed or connected in anti-parallel to the first switching element Q1 to the fourth switching element Q4, respectively, as body diodes. When N-channel MOSFETs are used for the first switching element Q1 to the fourth switching element Q4, parasitic diodes formed in the source-drain direction can be used as the first diode D1 to the fourth diode D4. When IGBTs are used for the first switching element Q1 to the fourth switching element Q4, external diodes are connected as the first diode D1 to the fourth diode D4.

[0015] The first voltage sensor V1 detects the input voltage Vin of the power conversion device 1 and outputs it to the control unit 11. The second voltage sensor V2 detects the output voltage Vout of the power conversion device 2 and outputs it to the control unit 11. The first voltage sensor V1 and the second voltage sensor V2 are each formed of, for example, a resistive voltage divider circuit.

[0016] The first current sensor A1 detects the input current Iin of the power conversion device 1 and outputs it to the control unit 11. The second current sensor A2 detects the output current Iout of the power conversion device 1 and outputs it to the control unit 11. The third current sensor A3 detects the current IL flowing through the inductor L1 and outputs it to the control unit 11. The third current sensor A3 is connected between the midpoint of the first arm and the inductor L1. The fourth current sensor A4 detects the current Ic flowing through the second smoothing capacitor C2 and outputs it to the control unit 11. The fourth current sensor A4 is connected in series with the second smoothing capacitor C2 between the positive wiring and the negative wiring of the DC bus Bdc.

[0017] Each of the first current sensor A1 to the fourth current sensor A4 may be configured with a shunt resistor and an amplifier that amplifies and outputs the voltage across the shunt resistor, or may be configured with a Hall element and an amplifier that converts the magnetic field generated in the Hall element into a voltage. Although not shown in Fig. 1, a fifth current sensor that detects the current flowing through the first smoothing capacitor C1 may be connected in series with the first smoothing capacitor C1 between the positive wiring and the negative wiring of the DC power supply SB1.

[0018] The control unit 11 is composed of a plurality of analog elements and a microcontroller, and can control the first switching element Q1 to the fourth switching element Q4 to cause the DC / DC converter unit 10 to perform a step-up operation or a step-down operation in both directions.

[0019] In the step-down mode, the control unit 11 fixes the third switching element Q3 to the ON state, fixes the fourth switching element Q4 to the OFF state, and controls the ON / OFF of the first switching element Q1 and the second switching element Q2. The control unit 11 causes the first switching element Q1 and the second switching element Q2 to operate in a complementary manner. When the first switching element Q1 is in the ON state and the second switching element Q2 is in the OFF state, power is transmitted from the DC power supply SB1 to the output side while charging the inductor L1. When the first switching element Q1 is in the OFF state and the second switching element Q2 is in the ON state, the DC power supply SB1 and inductor L1 are disconnected, and only the power stored in inductor L1 is transmitted to the output side.

[0020] The output voltage Vout in the step-down mode is expressed by the following equation (1). The duty ratio D is the ratio of the on-period (the period during which the first switching element Q1 is on and the second switching element Q2 is off) in a unit cycle. Vout=D / Vin (Equation 1)

[0021] The control unit 11 can increase the output voltage Vout by increasing the duty ratio D, and can decrease the output voltage Vout by decreasing the duty ratio D.

[0022] In the boost mode, the control unit 11 fixes the first switching element Q1 to the ON state, fixes the second switching element Q2 to the OFF state, and controls the ON / OFF of the third switching element Q3 and the fourth switching element Q4. The control unit 11 causes the third switching element Q3 and the fourth switching element Q4 to operate in a complementary manner. When the fourth switching element Q4 is in the ON state and the third switching element Q3 is in the OFF state, power transmission from the input side to the output side is stopped, and the inductor L1 is charged from the DC power supply SB1. When the fourth switching element Q4 is in the OFF state and the third switching element Q3 is in the ON state, power is transmitted to the output side from both the DC power supply SB1 and the inductor L1.

[0023] The output voltage Vout in the boost mode is expressed by the following equation (2). The duty ratio D is the ratio of the ON period (the period during which the fourth switching element Q4 is ON and the third switching element Q3 is OFF) in a unit cycle. Vout=1 / (1-D)·Vin (Equation 2)

[0024] The control unit 11 can increase the output voltage Vout by increasing the duty ratio D, and can decrease the output voltage Vout by decreasing the duty ratio D.

[0025] 2 is a diagram showing a control model when the power conversion device 1 according to the first embodiment is operated in peak current mode. The peak current mode is a method of feeding back the output voltage Vout and the current IL flowing through the inductor L1. The control unit 11 includes a subtractor 111, a compensator 112, a limiter 113, a digital-to-analog converter 114, a comparator 115, a PWM (Pulse Width Modulation) generator 116, an observer 117, and a look-up table 118. In this embodiment, the subtractor 111, the compensator 112, the limiter 113, and the observer 117 are realized by digital signal processing using a microcontroller.

[0026] The subtractor 111 outputs to the compensator 112 the error err between the output voltage out detected by the second voltage sensor V2 and the reference voltage Vref.

[0027] The compensator 112 generates a control voltage Vc by multiplying the error err input from the subtractor 111 by the gain G set in the observer 117, and performs phase compensation on the generated control voltage Vc. As phase compensation, the compensator 112 shapes the frequency response to control the safety and responsiveness of the closed-loop control. Since the transfer function of the plant in peak current mode control can be regarded as a first-order system, it can be realized using a type-2 compensator G(s) expressed by the following (Equation 3). The type-2 compensator adds one pole and one zero to the integrator that ensures DC gain, and achieves a phase boost of up to 90 degrees. G(s) = -G ０ ・(1+ω ｚ / s) / (1+s / ω ｐ ) ... (Formula 3)

[0028] The limiter 113 limits the upper or lower limit of the control voltage Vc that has been phase compensated by the compensator 112. The digital-to-analog converter 114 converts the digital value of the control voltage Vc into an analog voltage.

[0029] The comparator 115 compares the control voltage Vc with the current IL flowing through the inductor L1, which is detected by the third current sensor A3. The control voltage Vc increases as the load increases and decreases as the load decreases. The comparator 115 outputs a significant signal when the current IL flowing through the inductor L1 increases to the control voltage Vc. The comparator 115 may be configured, for example, as a comparator. In the example shown in FIG. 2 , the control voltage Vc is input to the inverting input terminal of the comparator, and the current IL flowing through the inductor L1 is input to the non-inverting input terminal. The comparator outputs a high level when the current IL flowing through the inductor L1 increases to the control voltage Vc.

[0030] The PWM generator 116 generates a PWM signal for driving the first switching element Q1 to the fourth switching element Q4 based on the reference clock and the output signal of the comparator 115. The PWM generator 116 transitions the PWM signal to OFF at the timing when a significant signal is input from the comparator 115 in each period of the reference clock.

[0031] In the step-down mode, a driver (not shown) for the first switching element Q1 generates a drive signal for the first switching element Q1 based on the PWM signal generated by the PWM generator 116, thereby driving the first switching element Q1. A driver (not shown) for the second switching element Q2 generates a drive signal for the second switching element Q2 based on a PWM signal that is in opposite phase to the PWM signal generated by the PWM generator 116, thereby driving the second switching element Q2. When the switching element is a MOSFET, the driver generates a gate-source voltage and applies it between the gate and source of the MOSFET.

[0032] In the step-up mode, a driver (not shown) of the fourth switching element Q4 generates a drive signal for the fourth switching element Q4 based on the PWM signal generated by the PWM generator 116, thereby driving the fourth switching element Q4. A driver (not shown) of the third switching element Q3 generates a drive signal for the third switching element Q3 based on a PWM signal that is in the opposite phase to the PWM signal generated by the PWM generator 116, thereby driving the third switching element Q3.

[0033] The electromotive force of the inductor L1 depends on the rate of change of the current flowing through the inductor L1 (ΔI / Δt) and the inductance [H]. The inductance of the inductor L1 is temperature dependent, and with a typical inductor L1, the inductance increases as the temperature rises.

[0034] The observer 117 estimates the temperature change of the inductor L1 based on the current IL flowing through the inductor L1 detected by the third current sensor A3.

[0035] For example, from the formula for heat capacity, the temperature change characteristics of inductor L1 can be described by the following (Equation 4): T(t) - T(0) = (Rth x P(t)) x (exp(-t / (Rth x Cth))) (Equation 4) T(t): Temperature of inductor L1 after a predetermined time [°C] T(0): Initial temperature [°C] Rth: Thermal resistance [°C / W] P: Power loss [W] t: Elapsed time [sec] Cth: Heat capacity [W sec / °C]

[0036] The power loss P when the inductor L1 is energized can be expressed by the following equation (5): P=Rb×IL ２ ... (Equation 5) Rb: Electrical resistance component [Ω]

[0037] The thermal resistance Rth of the inductor L1 depends on the heat transfer coefficient and the surface area. The heat capacity Cth depends on the mass and the specific heat. The thermal resistance Rth, heat capacity Cth, and electrical resistance Rb of the inductor L1 may be values ​​listed in the catalog or may be derived through experiments or simulations.

[0038] The initial temperature T(0) is the temperature at the start of operation of the power conversion device 1 and may be regarded as a room temperature, or the value detected by the temperature sensor may be used if a temperature sensor is installed in the power conversion device 1. Note that a moving average value may be used for the current IL.

[0039] The method of estimating the temperature of inductor L1 from the current IL flowing through inductor L1 using the above (Equation 4) and (Equation 5) is just one example, and the temperature of inductor L1 may also be estimated from the current IL flowing through inductor L1 using a simpler model.

[0040] The lookup table 118 is a table that describes the relationship between the temperature of the inductor L1 and the gain G of the compensator 112. The designer derives in advance the gain G of the compensator 112 for each temperature of the inductor L1 based on the temperature characteristics of the inductance of the inductor L1 so that the inductance of the inductor L1 remains constant regardless of the temperature. That is, the designer generates the lookup table 118 for reducing the gain G of the compensator 112 in response to an increase in the temperature of the inductor L1 so that an increase in the inductance due to an increase in the temperature of the inductor L1 is compensated for. Note that instead of the lookup table 118, a function that approximates the relationship between the temperature of the inductor L1 and the gain G of the compensator 112 may be used.

[0041] The observer 117 refers to the lookup table 118 to identify the gain G corresponding to the estimated temperature of the inductor L1, and sets it as the gain G of the compensator 112. As a result, the gain G of the compensator 112 is adaptively controlled in accordance with the temperature of the inductor L1, and the duty ratio of the first switching element Q1-fourth switching element Q4 is adaptively corrected in accordance with the change in temperature of the inductor L1.

[0042] When determining the gain G of the compensator 112, the temperature of the second smoothing capacitor C2 may be taken into consideration in addition to the temperature of the inductor L1. The current Ic flowing through the second smoothing capacitor C2 depends on the rate of change (ΔV / Δt) of the voltage across the second smoothing capacitor C2 and its capacitance [F]. The capacitance of the second smoothing capacitor C2 is temperature dependent; for example, in the case of an electrolytic capacitor, the capacitance increases as the temperature rises.

[0043] The observer 117 estimates a temperature change of the second smoothing capacitor C2 based on the current Ic flowing through the second smoothing capacitor C2 detected by the fourth current sensor A4. For example, the temperature of the second smoothing capacitor C2 may be estimated from the current Ic flowing through the second smoothing capacitor C2 using the heat capacity formulas shown in (Equation 4) and (Equation 5) above, or the temperature of the second smoothing capacitor C2 may be estimated from the current Ic flowing through the second smoothing capacitor C2 using a simpler model.

[0044] When the temperature of the second smoothing capacitor C2 is also taken into consideration, the lookup table 118 is a table that describes the relationship between the combination of the temperature of the inductor L1 and the temperature of the second smoothing capacitor C2 and the gain G of the compensator 112. The designer derives in advance the gain G of the compensator 112 for each combination of the temperature of the inductor L1 and the temperature of the second smoothing capacitor C2 based on the temperature characteristics of the inductor L1 and the temperature characteristics of the capacitance of the second smoothing capacitor C2 so that the inductance of the inductor L1 is constant regardless of the temperature of the inductor L1 and the capacitance of the second smoothing capacitor C2 is constant regardless of the temperature of the second smoothing capacitor C2. Note that instead of the lookup table 118, a function that approximates the relationship between the combination of the temperature of the inductor L1 and the temperature of the second smoothing capacitor C2 and the gain G of the compensator 112 may be used.

[0045] The observer 117 refers to the lookup table 118 to identify a gain G corresponding to a combination of the estimated temperature of the inductor L1 and the estimated temperature of the second smoothing capacitor C2, and sets the identified gain G as the gain G of the compensator 112. As a result, the gain G of the compensator 112 is adaptively controlled in accordance with the temperatures of the inductor L1 and the second smoothing capacitor C2, and the duty ratio of the first switching element Q1-fourth switching element Q4 is adaptively corrected in accordance with the temperature change of the inductor L1 and the temperature change of the second smoothing capacitor C2.

[0046] 3 is a flowchart showing the flow of temperature compensation control in the power conversion device 1 according to the embodiment. During operation of the power conversion device 1 (Y in S10), the observer 117 acquires the current I L flowing through the inductor L1 from the third current sensor A3 and the current I c flowing through the second smoothing capacitor C2 from the fourth current sensor A4 (S11). The observer 117 estimates the temperature of the inductor L1 from the current I L flowing through the inductor L1 and estimates the temperature of the second smoothing capacitor C2 from the current I c flowing through the second smoothing capacitor C2 (S12).

[0047] The observer 117 refers to the lookup table 118 and determines the gain G of the compensator 112 from the combination of the temperature of the inductor L1 and the temperature of the second smoothing capacitor C2 (S13). If the currently determined gain G is different from the previously determined gain G (Y in S14), the observer 117 changes the gain G of the compensator 112 to the currently determined gain G (S15). If the currently determined gain G is the same as the previously determined gain G (N in S14), the process of step S15 is skipped. The process proceeds to step S10. The processes of steps S10 to S15 described above are continuously executed until the operation of the power conversion device 1 is completed (N in S10).

[0048] As described above, according to this embodiment, the relationship between the heat generation amount of inductor L1, the heat generation amount of second smoothing capacitor C2, and the gain G of compensator 112 is created in lookup table 118 based on the heat generation amount predicted from the current flowing through inductor L1 and the heat generation amount predicted from the current flowing through second smoothing capacitor C2, and dynamic gain adjustment of compensator 112 is performed using a gain schedule. This makes it possible to eliminate the effects of fluctuations in the inductance eigenvalue associated with temperature rises in inductor L1 and fluctuations in the capacitance eigenvalue associated with temperature rises in second smoothing capacitor C2 simply by adjusting the gain of compensator 112. Therefore, it is possible to realize a power conversion device 1 that has stable and sufficient output characteristics even when the temperatures of inductor L1 and second smoothing capacitor C2 change, without complicating the circuit configuration.

[0049] The present disclosure has been described above based on the embodiments. The embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in the combination of the respective components and processing steps, and that such modifications are also within the scope of the present disclosure.

[0050] In the above-described embodiment, an example has been described in which power is transmitted from the DC power supply SB1 to the DC bus Bdc, but it is also possible to transmit power from the DC bus Bdc to the DC power supply SB1 to charge the DC power supply SB1. In this case, it is sufficient to interchange the PWM signals for driving the first switching element Q1 and the second switching element Q2 with the PWM signals for driving the third switching element Q3 and the fourth switching element Q4.

[0051] The control unit 11 estimates the temperature change of the inductor IL based on the current IL detected by the third current sensor A3, estimates the temperature change of the first smoothing capacitor C1 based on the current detected by the fifth current sensor (not shown), and corrects the duty ratio of the first switching element Q1-fourth switching element Q4 based on the temperature change of the inductor L1 and the temperature change of the first smoothing capacitor C1.

[0052] In the above-described embodiment, an example has been described in which the power conversion device 1 is operated in peak current mode. In this regard, the temperature compensation control according to this embodiment can also be applied when the power conversion device 1 is operated in voltage mode. The voltage mode is a method in which only the output voltage Vout is fed back. In the voltage mode, the comparator 115 outputs the result of comparison between the control voltage Vc and a predetermined sawtooth wave. Note that in the voltage mode, it is also possible to omit the PWM generator 116 and directly output the comparison result of the comparator 115 to the driver as a PWM signal.

[0053] Since the plant transfer function in voltage mode control can be considered a second-order system, it can be realized using the type 3 compensator G(s) expressed in the following (Equation 6). The type 3 compensator adds two poles and two zeros to the integrator that ensures DC gain, achieving a phase boost of up to 180 degrees. G(s) = -G ０ ・((1+ω ｚ１ / s)·(1+s / ω ｚ２)) / ((1+s / ω ｐ１ ) · (1 + s / ω ｐ２ ))...(Formula 6)

[0054] The embodiment may be specified by the following items.

[0055] [Item 1] A power conversion device (1) comprising: a first arm including a first switching element (Q1) and a second switching element (Q2) connected in series and connected in parallel to a DC power supply (SB1) and a first smoothing capacitor (C1); a second arm including a third switching element (Q3) and a fourth switching element (Q4) connected in series and connected in parallel to a DC bus (Bdc) and a second smoothing capacitor (C2); an inductor (L1) connected to a midpoint of the first arm and a midpoint of the second arm; a control unit (11) that controls the first switching element (Q1) and the fourth switching element (Q4); and an inductor current detection unit (A3) that detects a current flowing through the inductor (L1), wherein the control unit (11) estimates a temperature change of the inductor (L1) based on the current detected by the inductor current detection unit (A3), and corrects a duty ratio of the first switching element (Q1) and the fourth switching element (Q4) based on the estimated temperature change. This makes it possible to obtain stable and sufficient output characteristics even when the temperature of the inductor (L1) changes, without complicating the circuit configuration. [Item 2] The control unit (11) includes: a compensator (112) that generates a control voltage based on the error between the output voltage of the power conversion device (1) and a reference voltage; and an observer (117) that identifies a gain corresponding to the estimated temperature of the inductor (L1) by referring to a table (118) or a function that describes the relationship between the temperature and gain of the inductor (L1), and sets the identified gain as the gain of the compensator (112). This makes it possible to achieve control that takes into account the influence of temperature changes of the inductor (L1) simply by adding control that dynamically adjusts the gain of the compensator (112).[Item 3] The power conversion device (1) according to Item 1 further includes a capacitor current detection unit (A4) that detects a current flowing through the second smoothing capacitor (C2), wherein the control unit (11) estimates a temperature change of the inductor (L1) based on the current detected by the inductor current detection unit (A3), estimates a temperature change of the second smoothing capacitor (C2) based on the current detected by the capacitor current detection unit (A4), and corrects a duty ratio of the first switching element (Q1) to the fourth switching element (Q4) based on the temperature change of the inductor (L1) and the temperature change of the second smoothing capacitor (C2). This makes it possible to obtain stable and sufficient output characteristics even when the temperatures of the inductor (L1) and the second smoothing capacitor (C2) change, without complicating the circuit configuration. [Item 4] The control unit (11) includes: a compensator (112) that generates a control voltage based on an error between the output voltage of the power conversion device (1) and a reference voltage; and an observer (117) that identifies a gain corresponding to a combination of the estimated temperature of the inductor (L1) and the estimated temperature of the second smoothing capacitor (C2) by referring to a table (118) or a function that describes a relationship between a combination of the temperature of the inductor (L1) and the temperature of the second smoothing capacitor (C2) and a gain of the compensator (112), and sets the identified gain as the gain of the compensator (112). According to this, control that takes into account the influence of temperature changes of the inductor (L1) and the second smoothing capacitor (C2) can be realized simply by adding control that dynamically adjusts the gain of the compensator (112).

[0056] The present disclosure can be used in an H-bridge type step-up / step-down DC / DC converter.

[0057] SB1 DC power supply, Bdc DC bus, 1 Power conversion device, 10 DC / DC converter unit, 11 Control unit, 111 Subtractor, 112 Compensator, 113 Limiter, 114 Digital / Analog converter, 115 Comparator, 116 PWM generator, 117 Observer, 118 Lookup table, L1 Inductor, Q1-Q4 Switching elements, D1-D4 Diodes, C1-C2 Smoothing capacitors, A1-A4 Current sensors, V1-V2 Voltage sensors.

Claims

1. A power conversion device comprising: a first arm including a first switching element and a second switching element connected in series, and connected in parallel to a DC power supply and a first smoothing capacitor; a second arm including a third switching element and a fourth switching element connected in series, and connected in parallel to a DC bus and a second smoothing capacitor; an inductor connected to a midpoint of the first arm and a midpoint of the second arm; a control unit that controls the first switching element and the fourth switching element; and an inductor current detection unit that detects a current flowing through the inductor, wherein the control unit estimates a temperature change of the inductor based on the current detected by the inductor current detection unit, and corrects a duty ratio of the first switching element and the fourth switching element based on the estimated temperature change.

2. The power conversion device according to claim 1, wherein the control unit includes: a compensator that generates a control voltage based on the error between the output voltage of the power conversion device and a reference voltage; and an observer that identifies a gain corresponding to the estimated temperature of the inductor by referring to a table or function that describes the relationship between the temperature and gain of the inductor, and sets the identified gain as the gain of the compensator.

3. The power conversion device according to claim 1, further comprising a capacitor current detection unit that detects the current flowing through the second smoothing capacitor, wherein the control unit estimates a temperature change of the inductor based on the current detected by the inductor current detection unit, estimates a temperature change of the second smoothing capacitor based on the current detected by the capacitor current detection unit, and corrects the duty ratio of the first switching element - the fourth switching element based on the temperature change of the inductor and the temperature change of the second smoothing capacitor.

4. The power conversion device according to claim 3, wherein the control unit includes: a compensator that generates a control voltage based on the error between the output voltage of the power conversion device and a reference voltage; and an observer that identifies a gain corresponding to a combination of the estimated temperature of the inductor and the estimated temperature of the second smoothing capacitor by referring to a table or function that describes the relationship between the combination of the temperature of the inductor and the temperature of the second smoothing capacitor and the gain of the compensator, and sets the gain as the gain of the compensator.

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