Power conversion device

Abstract

To set a surge voltage within a rated range of a switching element in a power conversion device, reduce a switching loss, and optimize efficiency of the power conversion device.SOLUTION: A power conversion device includes a DC voltage unit and a switching element. A control circuit outputs an on / off command signal of the switching element. A gate drive circuit has a function of varying a gate resistance value, and outputs a gate signal of the switching element based on the on / off command signal. The control circuit determines the gate resistance value of the gate drive circuit based on a temperature of the switching element, a DC voltage of the DC voltage unit, a detected current of the power conversion device, and a command current of the power conversion device.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a technique for improving the efficiency of a power conversion device. [Background technology]

[0002] An inverter is a power conversion device that converts DC voltage into AC voltage by turning on and off switching elements (such as IGBTs) and supplies power to loads such as motors. Figure 1 shows a typical configuration.

[0003] When controlling the inverter current (current flowing through the load) to a desired value, a control circuit (such as a microcomputer) within the inverter device outputs an on / off command signal based on the inverter command current, and controls each switching element to operate on and off appropriately, thereby controlling the inverter detection current to be approximately equal to the inverter command current.

[0004] The control circuit outputs an on / off command signal to a gate drive circuit, which outputs a gate signal to the gate terminal of the switching element based on the on / off command signal.

[0005] The switching speed (turn-on time, turn-off time) of the switching element changes depending on the gate resistance value in the gate drive circuit. A fast switching speed reduces switching losses (i.e., increases inverter efficiency), but increases the surge voltage applied to the switching element when it is turned off, making the switching element more susceptible to overvoltage breakdown. A slow switching speed increases switching losses (i.e., decreases inverter efficiency), but reduces surge voltage, making the switching element less susceptible to overvoltage breakdown.

[0006] Furthermore, the switching loss and surge voltage change depending on the voltage applied to the switching element (which depends on the DC voltage of the inverter), the current flowing through the switching element (which depends on the current of the inverter), and the temperature of the switching element. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-142155 Summary of the Invention [Problem to be solved by the invention]

[0008] The switching speed of a typical inverter is arbitrarily designed on the hardware, taking into consideration the trade-off between surge voltage and efficiency within the ratings (usable voltage, current, temperature, etc.) of the switching elements.

[0009] If the gate resistance is fixed, the switching speed will be a constant characteristic value (hereinafter defined as slow) regardless of the operating environment conditions (voltage, current, temperature). As a result, switching loss will improve or worsen depending on the operating environment conditions, and inverter efficiency cannot be optimized.

[0010] On the other hand, Patent Document 1 discloses a prior art technique in which the switching speed is changed by making the gate resistance value variable.

[0011] As described above, the challenge in a power conversion device is to keep the surge voltage within the rated range of the switching element, reduce switching loss, and optimize the inverter efficiency of the power conversion device. [Means for solving the problem]

[0012] The present invention has been devised in view of the above-mentioned problems in the related art, and one aspect thereof is a power conversion device including a DC voltage unit and a switching element, the device comprising: a control circuit that outputs an on / off command signal for the switching element; and a gate drive circuit that has a function of varying a gate resistance value and outputs a gate signal for the switching element based on the on / off command signal, wherein the control circuit determines the gate resistance value of the gate drive circuit based on the temperature of the switching element, the DC voltage of the DC voltage unit, a detected current of the power conversion device, and a command current of the power conversion device.

[0013] In one aspect, the control circuit is characterized in that it sets the control circuit to high-speed A mode if the temperatures of all the switching elements are equal to or higher than a first temperature threshold, the DC voltage is equal to or lower than a first voltage threshold, the detected current is equal to or lower than a first detected current threshold, and the command current is equal to or lower than a first command current threshold, and sets the control circuit to high-speed B mode if, instead of the high-speed A mode, the state in which the temperatures of all the switching elements are equal to or higher than a second temperature threshold continues for a predetermined time or longer and the DC voltage is equal to or lower than the first voltage threshold, and sets the control circuit to low-speed mode in all other cases, and in the high-speed A mode and the high-speed B mode, it sets the gate resistance value lower than in the low-speed mode.

[0014] In one aspect, the control circuit determines whether the mode one sampling ago was the low-speed mode, the high-speed A mode, or the high-speed B mode. If the mode one sampling ago was the low-speed mode, and if the temperatures of all the switching elements are equal to or higher than a first temperature threshold, and the DC voltage is equal to or lower than a first voltage threshold, and the detected current is equal to or lower than a first detected current threshold, and the command current is equal to or lower than a first command current threshold, the control circuit transitions to the high-speed A mode. If the mode is not the high-speed A mode, and a state in which the temperatures of all the switching elements are equal to or higher than a second temperature threshold continues for a predetermined time or longer, and the DC voltage is equal to or lower than the first voltage threshold, the control circuit transitions to the high-speed B mode. Otherwise, the control circuit continues to be in the low-speed mode. In the fast A mode, if the temperature of at least one of the switching elements is equal to or lower than a third temperature threshold, or the DC voltage is equal to or higher than a second voltage threshold, or the detected current is equal to or higher than a second detected current threshold, or the command current is equal to or higher than a second command current threshold, a transition to the slow mode is made; otherwise, the fast A mode is continued; and if the mode one sampling before is the fast B mode, a transition to the slow mode is made if the temperature of at least one of the switching elements is equal to or lower than a fourth temperature threshold, or the DC voltage is equal to or higher than the second voltage threshold; otherwise, the fast B mode is continued; and the gate resistance value is set lower in the fast A mode and the fast B mode than in the slow mode. [Effects of the Invention]

[0015] According to the present invention, in a power conversion device, it is possible to keep surge voltage within the rated range of a switching element, reduce switching loss, and optimize inverter efficiency of the power conversion device. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a circuit diagram showing an example of a general power conversion device. [Figure 2] 5 is a time chart showing a switching operation of a gate resistance value in the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention sets an appropriate switching speed according to the operating environment conditions (voltage, detected current, command current, temperature). When driving a power conversion device using a gate drive circuit equipped with a main circuit switching speed variable function, the switching speed is controlled within the rated range based on the monitored DC voltage of the power conversion device, the detected current of the power conversion device, the command current, and the temperature conditions of the switching elements, optimizing the efficiency of the power conversion device.

[0018] Hereinafter, an embodiment of a power conversion device according to the present invention will be described in detail with reference to FIGS.

[0019] [Embodiment 1] First, a typical power conversion device (for example, an inverter, hereinafter referred to as an inverter) will be described based on the electrical circuit diagram in Fig. 1. As shown in Fig. 1, switching elements Su and Sx, switching elements Sv and Sy, and switching elements Sw and Sz are connected in series between the positive and negative poles of a direct current voltage section DC. The switching elements Su to Sz are, for example, IGBTs. A motor M is connected to the connection point of the switching elements Su and Sx, the connection point of the switching elements Sv and Sy, and the connection point of the switching elements Sw and Sz.

[0020] Furthermore, a control circuit (not shown) in the inverter device outputs an on / off command signal to a gate drive circuit (not shown). The gate drive circuit outputs gate signals to the gate terminals of the switching elements Su to Sz based on the on / off command signal. The gate drive circuit also has a function of varying the gate resistance value.

[0021] The inverter's control circuit software determines whether it is in low-speed mode or high-speed mode and sends a low-speed / high-speed switching signal to the gate drive circuit. The gate drive circuit used has the function of switching between two gate resistance values. The gate drive circuit switches the gate resistance value based on the low-speed / high-speed switching signal, switching the switching speed between low and high speed.

[0022] In this embodiment, the high-speed mode is divided into high-speed A mode and high-speed B mode. If the control circuit determines that the mode is high-speed A mode or high-speed B mode, it outputs a high signal to the gate drive circuit as a low-speed / high-speed switching signal, and if the mode is low-speed, it outputs a low signal to the gate drive circuit as a low-speed / high-speed switching signal. The control circuit is provided with a memory area for recording whether the determined mode is low-speed mode, high-speed A mode, or high-speed B mode.

[0023] Next, the determination of the high-speed A mode, high-speed B mode, and low-speed mode in the control circuit will be described.

[0024] If the temperatures of the switching elements Su to Sz of all phases are equal to or higher than the first temperature threshold, the DC voltage of the DC voltage unit DC is equal to or lower than the first voltage threshold, the detected current of the inverter is equal to or lower than the first detected current threshold, and the command current of the inverter is equal to or lower than the first command current threshold, the high-speed A mode is selected.

[0025] If the temperature of the switching elements Su to Sz of all phases remains at or above the second temperature threshold for a predetermined period of time or more and the DC voltage of the DC voltage unit DC is at or below the first voltage threshold, the mode is changed to high-speed B mode instead of high-speed A mode.

[0026] Otherwise, the slow mode is used. The gate resistance value is determined based on the selected mode. Here, the fast A mode takes priority over the fast B mode.

[0027] In order to prevent frequent transitions between the high-speed A mode or high-speed B mode and the low-speed mode, hysteresis may be set for the first temperature threshold, second temperature threshold, first voltage threshold, first detected current threshold, and first command current threshold. In this case, the following occurs.

[0028] If the previous sampling was in the low-speed mode, the mode will transition to the high-speed A mode if the temperatures of the switching elements Su to Sz of all phases are equal to or higher than the first temperature threshold, the DC voltage of the DC voltage unit DC is equal to or lower than the first voltage threshold, the detected current is equal to or lower than the first detected current threshold, and the command current is equal to or lower than the first command current threshold.

[0029] Furthermore, if the previous sampling was in the low-speed mode, the conditions for the high-speed A mode are not met, and the temperatures of the switching elements Su to Sz of all phases remain at or above the second temperature threshold for a predetermined time or more, and the DC voltage of the DC voltage unit DC is at or below the first voltage threshold, the mode transitions to the high-speed B mode. Otherwise, the mode continues to be in the low-speed mode.

[0030] If the previous sampling was in high-speed A mode, the mode transitions to low-speed mode if the temperature of at least one of the switching elements Su to Sz is equal to or lower than the third temperature threshold, or the DC voltage of the DC voltage unit DC is equal to or higher than the second voltage threshold, or the detected current is equal to or higher than the second detected current threshold, or the command current is equal to or higher than the second command current threshold. Otherwise, the high-speed A mode continues.

[0031] If the previous sampling was in high-speed B mode, the mode transitions to low-speed B mode if the temperature of at least one of the switching elements Su to Sz is equal to or lower than the fourth temperature threshold or the DC voltage of the DC voltage unit DC is equal to or higher than the second voltage threshold. Otherwise, the mode continues to be high-speed B mode.

[0032] Determine the gate resistor value based on the selected mode. For Fast A or Fast B modes, use a lower gate resistor value in the gate drive circuit than for slow mode.

[0033] Each transition threshold is designed in advance according to the specifications required for the inverter. An example of each transition threshold will be described below.

[0034] The first temperature threshold, which is the transition threshold from low speed mode to high speed A mode, is 30°C, the first voltage threshold is 335V, the first detected current threshold is 160Arms, and the first command current threshold is 160Arms.

[0035] The second temperature threshold, which is the transition threshold from low speed mode to high speed B mode, is 85°C, the predetermined time is 500 ms, and the first voltage threshold is 335 V, the same as when switching from low speed mode to high speed A mode.

[0036] The third temperature threshold, which is the transition threshold from high-speed A mode to low-speed mode, is 25°C, the second voltage threshold is 340V, the second detection current threshold is 170Arms, and the second command current threshold is 170Arms.

[0037] The fourth temperature threshold, which is the transition threshold from high-speed B mode to low-speed mode, is 80°C, and the second voltage threshold is 340V, the same as when switching from high-speed A mode to low-speed mode.

[0038] The DC voltage is, for example, a detected value from a sensor, and the detected current and command current are, for example, effective values ​​of dq-axis currents for control.

[0039] The temperatures of the switching elements Su to Sz may be calculated using the temperature detection sensor value provided in the module (e.g., IGBT module) that houses the switching elements, or may be estimated using the temperature detection value of the heat sink for cooling the switching elements, calculation of the loss of the switching elements, and the thermal resistance value of the switching elements.

[0040] An example of the switching operation flow will be described with reference to FIG.

[0041] In S1, it is determined whether the gate signal is in the ON state. If the gate signal is in the ON state, the process moves to S2, and if the gate signal is in the OFF state, the process moves to S10.

[0042] In S2, the mode determination process starts by reading the memory area for mode determination to determine whether the determination mode set in S5, S8, or S10 one sampling before is "low speed mode," "high speed A mode," or "high speed B mode."

[0043] In S3, it is determined whether the mode of the previous sampling was the low-speed mode. If it was the low-speed mode, the process proceeds to S4, and if it was not the low-speed mode, the process proceeds to S12.

[0044] In S4, it is determined whether the DC voltage is equal to or lower than a first voltage threshold (e.g., 335 V), the detected current is equal to or lower than a first detected current threshold (e.g., 160 Arms), the command current is equal to or lower than a first command current threshold (e.g., 160 Arms), and the temperatures of the switching elements Su to Sz of all phases are equal to or higher than a first temperature threshold (e.g., 30°C). If all of these conditions are met, the process proceeds to S5, and if at least one of the conditions is not met, the process proceeds to S7.

[0045] In S5, the high-speed A mode is set, and the fact that it is the high-speed A mode is recorded in the memory area for mode determination, and the process proceeds to S6.

[0046] In S6, the gate resistance value of the gate drive circuit is set to High (the gate resistance value is lower than that in the low-speed mode) based on the high-speed A mode determined by the control circuit, and the processing for this control cycle ends.

[0047] In S7, it is determined whether the temperatures of the switching elements Su to Sz of all phases remain above the second temperature threshold (85°C) for a predetermined time (500 ms) and whether the DC voltage is below the first voltage threshold (335V). If all conditions are met, the process proceeds to S8, and if at least one of the conditions is not met, the process proceeds to S10.

[0048] In S8, the high-speed B mode is set, and the fact that it is the high-speed B mode is recorded in the memory area for mode determination, and the process proceeds to S9.

[0049] In S9, the gate resistance value of the gate drive circuit is set to High (the gate resistance value is lower than that in the low-speed mode) based on the high-speed B mode determined by the control circuit, and the processing for this control cycle ends.

[0050] In S10, the low speed mode is set, and the fact that it is the low speed mode is recorded in the memory area for mode determination, and the process proceeds to S11.

[0051] In S11, the gate resistance value of the gate drive circuit is set to Low (the gate resistance value is higher than the values ​​in the high-speed A mode and the high-speed B mode) based on the low-speed mode determined by the control circuit.

[0052] In S12, it is determined whether the mode one sampling before was high-speed A mode. If it was high-speed A mode, the process proceeds to S13, and if it was not high-speed A mode (i.e., high-speed B mode), the process proceeds to S14.

[0053] In S13, it is determined whether the DC voltage is equal to or greater than the second voltage threshold (340 V), or the detected current is equal to or greater than the second detected current threshold (170 Arms), or the command current is equal to or greater than the second command current threshold (170 Arms), or the temperature of any of the switching elements Su to Sz is equal to or less than the third temperature threshold (25° C.). If at least one of the conditions is met, the process proceeds to S10, and if all of the conditions are not met, the process proceeds to S5.

[0054] In step S14, it is determined whether the temperature of any of the switching elements Su to Sz is equal to or lower than the fourth temperature threshold (80° C.) or whether the DC voltage is equal to or higher than the second voltage threshold (340 V). If at least one of the conditions is met, the process proceeds to step S10, and if all the conditions are not met, the process proceeds to step S8.

[0055] The switching speed in low-speed mode is designed so that the surge voltage of switching elements Su to Sz is 90% of the rating of the switching elements (maximum operating voltage (420V) / maximum current (600Arms)). This design condition guarantees the maximum rating of the inverter's instantaneous operation, and there is a deviation from the drive voltage / current in actual use.

[0056] As a continuous operating point taking into consideration actual use, the high-speed A mode is set when the DC voltage is 335V or less, the detection current effective value is 160Arms or less, the command current effective value is 160Arms or less, and the temperature of the switching elements Su to Sz is 30°C or more in all phases.

[0057] Compared to low-speed mode, the voltage / current is reduced, and the surge voltage of the switching elements Su to Sz has a larger design margin (allowance) relative to the rated voltage. Therefore, the gate resistance value is lowered to accommodate the design margin, increasing the switching speed and improving switching loss, thereby optimizing inverter efficiency.

[0058] Next, taking into consideration the tendency for switching to slow down when the peripheral circuits, including the switching elements Su to Sz, are at high temperatures, the high-speed B mode is set when the DC voltage is 335V or less and the temperature of all the switching elements Su to Sz of all phases is 80°C or higher for a predetermined period of time.

[0059] Only when the temperatures of all switching elements Su to Sz of all phases remain above the second temperature threshold (80°C) for a specified period of time will the switching speed be set to high-speed B mode, even if the detected current and command current are above the first detected current threshold and first command current threshold (160 Arms). This improves switching loss and optimizes inverter efficiency. When both conditions are met, high-speed A mode is prioritized.

[0060] In this embodiment, the switching speed (gate resistance value) is set based on both the detected current and the command current because, if a sudden load change occurs, the detected current may temporarily not be controlled according to the command current but may take on a transient oscillating waveform, making it impossible to select an appropriate switching speed and potentially damaging the switching element.

[0061] Therefore, by setting the switching speed (gate resistance value) based on both the detected current and the command current, damage to the switching element is prevented, the effect of detected current oscillation is reduced, and the accuracy of efficiency improvement is improved.

[0062] As described above, according to this embodiment, the efficiency of the power conversion device can be optimized by determining the gate resistance value based on the voltage, detected current, command current, and temperature so that the surge voltage is within the rated range of the switching element and switching loss is low. That is, when the surge voltage has a margin relative to the rated voltage depending on the voltage, detected current, command current, and temperature conditions, switching loss can be reduced by lowering the gate resistance value in high-speed A mode and high-speed B mode. This makes it possible to optimize the efficiency of the inverter. Furthermore, in actual operation, high-speed A mode and high-speed B mode are frequently used, which significantly improves the efficiency of the inverter.

[0063] Although the present invention has been described in detail above only with respect to the specific examples, it will be apparent to those skilled in the art that various modifications and variations are possible within the scope of the technical concept of the present invention, and it is natural that such modifications and variations fall within the scope of the claims.

[0064] The present invention is not limited to inverters, but can be applied to power conversion devices in general that have switching elements and DC voltage units (such as converters (AC / DC converters) and choppers (DC / DC converters)). For example, when applied to a converter, the inverter detection current and inverter command current used to determine each mode are replaced with the converter detection current and converter command current.

[0065] In addition, in the embodiment, the high-speed A mode and the high-speed B mode have the same gate resistance value (switching speed), but the high-speed A mode and the high-speed B mode may have different gate resistance values ​​(switching speeds). In this case, the gate resistance value of the high-speed A mode < the gate resistance value of the high-speed B mode < the gate resistance value of the low-speed mode are set. [Explanation of symbols]

[0066] DC: Direct current voltage section Su~Sz...Switching elements M...Motor

Claims

1. A power conversion device including a DC voltage unit and a switching element, a control circuit that outputs an on / off command signal for the switching element; a gate drive circuit that has a function of varying a gate resistance value and outputs a gate signal for the switching element based on the on / off command signal; Equipped with the control circuit determines the gate resistance value of the gate drive circuit based on a temperature of the switching element, a DC voltage of the DC voltage section, a detected current of the power conversion device, and a command current of the power conversion device.

2. The control circuit if the temperatures of all the switching elements are equal to or higher than a first temperature threshold, the DC voltage is equal to or lower than a first voltage threshold, the detected current is equal to or lower than a first detected current threshold, and the command current is equal to or lower than a first command current threshold, the high-speed A mode is selected; If the high-speed A mode is not selected and the state in which the temperatures of all the switching elements are equal to or higher than the second temperature threshold continues for a predetermined time or more and the DC voltage is equal to or lower than the first voltage threshold, the high-speed B mode is selected; Otherwise, it is in slow mode.

2. The power conversion device according to claim 1, wherein the gate resistance value is set lower in the high-speed A mode and the high-speed B mode than in the low-speed mode.

3. The control circuit Determine whether the mode one sampling before is the low speed mode, the high speed A mode, or the high speed B mode; If the mode one sampling before is the low-speed mode, transitioning to the high-speed A mode when the temperatures of all the switching elements are equal to or higher than a first temperature threshold, the DC voltage is equal to or lower than a first voltage threshold, the detected current is equal to or lower than a first detected current threshold, and the command current is equal to or lower than a first command current threshold; If the state where the temperatures of all the switching elements are equal to or higher than the second temperature threshold continues for a predetermined time or more and the DC voltage is equal to or lower than the first voltage threshold, instead of the high-speed A mode, the mode transitions to the high-speed B mode; otherwise, continue in the low speed mode; If the mode one sampling before is the high-speed A mode, transitioning to the low speed mode when the temperature of at least one of the switching elements is equal to or lower than a third temperature threshold, or the DC voltage is equal to or higher than a second voltage threshold, or the detected current is equal to or higher than a second detected current threshold, or the command current is equal to or higher than a second command current threshold; Otherwise, the high-speed A mode is continued. If the mode one sampling before is the high-speed B mode, transitioning to the low speed mode when the temperature of at least one of the switching elements is equal to or lower than a fourth temperature threshold or the DC voltage is equal to or higher than the second voltage threshold; Otherwise, continue with the fast B mode.

2. The power conversion device according to claim 1, wherein the gate resistance value is set lower in the high-speed A mode and the high-speed B mode than in the low-speed mode.

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