Power conversion device, lifting device, and power conversion method

Abstract

The power conversion device (3) includes: a power conversion circuit (30) that converts primary-side power into secondary-side power by switching on / off of a plurality of switching elements (35) in accordance with a carrier frequency; a heat evaluation unit (115) that evaluates a heat level of the plurality of switching elements (35) based on a secondary-side current value and the carrier frequency after the secondary-side current value of the power conversion circuit (30) exceeds a prescribed current threshold value; a frequency change unit (116) that decreases the carrier frequency over time after an evaluation result of the heat level exceeds a prescribed level; an inhibition evaluation unit (117) that evaluates a heat inhibition effect achieved by the decrease in the carrier frequency based on the evaluation result of the heat level; and a decrease stop unit (118) that stops the decrease in the carrier frequency by the frequency change unit (116) based on the evaluation result of the heat inhibition effect before the evaluation result of the heat level falls to the prescribed level.

Description

Technical Field

[0001] This disclosure relates to a power conversion device, a lifting device, and a power conversion method. Background Technology

[0002] Patent document 1 discloses an overload protection device for an inverter, which is configured to: calculate the integral value of the overcurrent based on the output current of the inverter and the derating amount based on the carrier frequency, and generate an overload fault output when the integral value of the overcurrent exceeds the trip reference value.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2007-215250 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] This disclosure provides a power conversion device that effectively combines heat suppression and noise suppression.

[0008] Technical solution

[0009] One aspect of the power conversion apparatus disclosed herein includes: a power conversion circuit that switches multiple switching elements on / off according to a carrier frequency to convert primary-side power into secondary-side power; a heat evaluation unit that evaluates the heat level of the multiple switching elements based on the secondary-side current value and the carrier frequency after the secondary-side current value of the power conversion circuit exceeds a predetermined current threshold; a frequency changing unit that decreases the carrier frequency over time after the heat level evaluation result exceeds a predetermined level; a suppression evaluation unit that evaluates the heat suppression effect achieved by decreasing the carrier frequency based on the heat level evaluation result; and a reduction stopping unit that stops the carrier frequency reduction performed by the frequency changing unit based on the heat suppression effect evaluation result before the heat level evaluation result drops to a predetermined level.

[0010] Another aspect of the lifting device disclosed herein includes: the aforementioned power conversion device; and an electric motor, which raises and lowers the object being lifted by being supplied with secondary power.

[0011] Another aspect of the power conversion method disclosed herein includes: controlling a power conversion circuit to switch multiple switching elements on / off according to a carrier frequency to convert primary-side power to secondary-side power; evaluating the heating level of the multiple switching elements based on the secondary-side current value and the carrier frequency after the secondary-side current value of the power conversion circuit exceeds a predetermined current threshold; decreasing the carrier frequency according to the elapsed time after the evaluation result of the heating level exceeds a predetermined level; evaluating the heating suppression effect achieved by decreasing the carrier frequency based on the evaluation result of the heating level; and stopping the decrease of the carrier frequency based on the evaluation result of the heating suppression effect before the evaluation result of the heating level drops to the predetermined level.

[0012] Invention Effects

[0013] According to this disclosure, a power conversion device that effectively combines heat suppression and noise suppression can be provided. Attached Figure Description

[0014] Figure 1 This is a schematic diagram illustrating the structure of a lifting system.

[0015] Figure 2 This is a block diagram illustrating the hardware configuration of a control circuit.

[0016] Figure 3 This is a flowchart illustrating the lifting control process.

[0017] Figure 4 This is a flowchart illustrating the process of adjusting the carrier frequency.

[0018] Figure 5 This is a flowchart illustrating the process of adjusting the carrier frequency.

[0019] Figure 6 The charts illustrate the changes in derating current values, changes in the evaluation results of heating levels, and changes in carrier frequency. Detailed Implementation

[0020] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. In the description, the same reference numerals are used to refer to the same elements or elements having the same function, and repeated descriptions are omitted.

[0021] [Apparatus]

[0022] The lifting system 1 of this embodiment is a system that uses electricity to raise and lower an object. Specific examples of the lifting system 1 include elevators and cranes. Figure 1 As shown, the lifting system 1 includes a lifting device 2 and a power conversion device 3.

[0023] The lifting device 2 is powered by electricity to move objects up and down. For example, the lifting device 2 is an elevator, having a passenger car 21, a counterweight 22, and a winch 23. The winch 23 has a motor 24 (electric motor). The motor 24 generates driving force by being powered by electricity (secondary-side electricity described later). The winch 23 winds up a rope by the driving force generated by the motor 24, thereby lowering the counterweight 22 while raising the passenger car 21, or raising the counterweight 22 while lowering the passenger car 21.

[0024] Motor 24 can be a synchronous motor or an induction motor. Specific examples of synchronous motors include permanent magnet synchronous motors or synchronous reluctance motors. Specific examples of permanent magnet synchronous motors include SPM (Surface Permanent Magnet) motors and IPM (Interior Permanent Magnet) motors.

[0025] The power conversion device 3 converts the power supplied from the power source 90 (primary power) into drive power (secondary power) and supplies it to the motor 24. The primary power can be alternating current (AC) or direct current (DC). The secondary power is alternating current (AC). As an example, both the primary and secondary power are three-phase AC. For example, the power conversion device 3 has a power conversion circuit 30 and a control circuit 100.

[0026] The power conversion circuit 30 switches multiple switching elements on / off according to a carrier frequency to convert primary-side power into secondary-side power, and supplies the secondary-side power to the motor 24. The power conversion circuit 30 is, for example, a voltage-source inverter, which applies a secondary-side voltage corresponding to a voltage command to the motor 24.

[0027] For example, the power conversion circuit 30 includes a conversion circuit 31, a smoothing capacitor 32, an inverter circuit 33, and a current sensor 34. The conversion circuit 31, for example, is a diode bridge circuit or a PWM (Pulse Width Modulation) conversion circuit, which converts the power supply into direct current. The smoothing capacitor 32 smooths the direct current.

[0028] The inverter circuit 33 performs the power conversion between the aforementioned DC power and the aforementioned drive power. For example, the inverter circuit 33 has multiple switching elements 35, and the power conversion is performed by switching the multiple switching elements 35 on / off. The switching elements 35 are, for example, power MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) or IGBTs (Insulated Gate Bipolar Transistors), which are switched on / off according to the gate drive signal.

[0029] Current sensor 34 detects the current flowing between inverter circuit 33 and motor 24. Hereinafter, the current flowing between inverter circuit 33 and motor 24 will be referred to as "secondary current". For example, current sensor 34 can be configured to detect the current of all three phases (U phase, V phase, and W phase) of a three-phase AC circuit, or it can be configured to detect the current of any two phases of the three-phase AC circuit. As long as zero-phase current is not generated, the total current of U phase, V phase, and W phase is 0, therefore, information about the current of all phases can be obtained even when detecting the current of two phases.

[0030] The configuration of the power conversion circuit 30 shown above is merely an example; it can be modified arbitrarily as long as it can supply drive power to the motor 24. For example, the power conversion circuit 30 can also be a current-source inverter. A current-source inverter outputs drive current to the motor 24 according to the current command. When the power supply is DC, the power conversion circuit 30 may not have a conversion circuit 31. The power conversion circuit 30 can also be a matrix conversion circuit that performs bidirectional power conversion between power supply and drive power without undergoing DC conversion.

[0031] Control circuit 100 controls power conversion circuit 30 to supply drive power to motor 24. For example, if power conversion circuit 30 is a voltage-source inverter, control circuit 100 controls power conversion circuit 30 to apply a drive voltage corresponding to the voltage command to motor 24. If power conversion circuit 30 is a current-source inverter, control circuit 100 controls power conversion circuit 30 to supply drive current corresponding to the current command to motor 24.

[0032] In devices that operate using secondary-side power generated by switching multiple switching elements on / off according to a carrier frequency, a higher carrier frequency reduces noise generation. However, a higher carrier frequency also leads to greater heat generation from the multiple switching elements due to switching losses. Therefore, when the load on the device increases and the secondary-side current increases, the total heat generation, including the heat generated by the steady-state current (hereinafter referred to as "steady-state heat") and the heat generated by the switching losses (hereinafter referred to as "switching heat"), can easily become excessive.

[0033] To address this, the control circuit 100 is configured to perform the following process: The control power conversion circuit 30 switches multiple switching elements 35 on / off according to a carrier frequency to convert primary-side power to secondary-side power; after the secondary-side current value of the power conversion circuit 30 exceeds a predetermined current threshold, the heating level of the multiple switching elements 35 is evaluated based on the secondary-side current value and the carrier frequency; after the heating level evaluation result exceeds a predetermined level, the carrier frequency is decreased according to the passage of time; the heating suppression effect achieved by decreasing the carrier frequency is evaluated based on the heating level evaluation result; and the carrier frequency decrease is stopped based on the heating suppression effect evaluation result before the heating level evaluation result drops to the aforementioned predetermined level. Thus, the carrier frequency can be adjusted to a value suitable for balancing noise suppression and heating suppression according to each load size.

[0034] The following provides a more specific example of the configuration of the control circuit 100. For instance... Figure 1 As shown, the control circuit 100 has a PWM control unit 111, a drive control unit 112, a base block unit 113, a derating unit 114, a heat evaluation unit 115, a frequency change unit 116, a suppression evaluation unit 117, a decrement stop unit 118, and an overload protection unit 119 as its functional configuration (hereinafter referred to as "functional blocks").

[0035] The PWM control unit 111 controls the power conversion circuit 30 to apply a secondary-side voltage corresponding to the voltage command to the motor 24. For example, the PWM control unit 111 switches the on / off states of multiple switching elements 35 within a control cycle of the carrier frequency, and outputs the secondary-side voltage corresponding to the voltage command based on the ratio of the on / off period of each switching element 35 in one cycle. There are no particular restrictions on the calculation method for the on / off period of each switching element 35; it can be a known triangular wave comparison method or a space vector modulation method. For example, the PWM control unit 111 switches the on / off states of each switching element 35 by outputting the aforementioned gate drive signal.

[0036] The carrier frequency can be changed according to user settings. Alternatively, the carrier frequency can also be changed by the frequency changing unit 116, described later. When the carrier frequency changes, the PWM control unit 111 switches the multiple switching elements 35 on / off according to the changed carrier frequency.

[0037] The drive control unit 112 calculates a voltage command and outputs it to the PWM control unit 111 in a manner that causes the lifting device 2 to operate according to instructions from the host controller 200. Specific examples of the host controller 200 include programmable logic controllers (PLCs). Specific examples of instructions from the host controller 200 include lifting start instructions and lifting stop instructions.

[0038] Upon receiving a lifting start command from the host controller 200, the drive control unit 112 repeatedly performs the following process within a predetermined control cycle: generating a voltage command and outputting it to the PWM control unit 111 in a manner that causes the rotational speed of the motor 24 to follow a predetermined speed pattern. Upon receiving a lifting stop command from the host controller 200, the drive control unit 112 repeatedly performs the following process within the aforementioned control cycle: generating a voltage command and outputting it to the PWM control unit 111 in a manner that causes the rotational speed of the motor 24 to follow a predetermined deceleration / stop pattern. After the drive control unit 112 stops the motor 24, the host controller 200 activates the brake of the winch 23 and outputs a basic stop command.

[0039] The basic blocking unit 113 stops the output of secondary power from the power conversion circuit 30 according to the basic blocking command from the upper controller 200. For example, the basic blocking unit 113 stops the output of secondary power by blocking the output of the gate drive signal from the PWM control unit 111 to each switching element 35.

[0040] The derating unit 114 acquires the secondary current value detected by the current sensor 34 and drates the secondary current value according to an adjustment rate that increases with the carrier frequency. Hereinafter, the drated secondary current value will be referred to as the "drated current value".

[0041] For example, the derating unit 114 derives an adjustment ratio corresponding to the carrier frequency based on a pre-generated rate profile that expresses the relationship between carrier frequency and ratio, and the current carrier frequency. It then multiplies the derived adjustment ratio by the secondary current value to calculate the drated current value. The derating unit 114 repeatedly performs derating within the aforementioned control loop.

[0042] The proportion in the proportional curve can also be determined as an approximation of the ratio of the total heat generation to the steady-state heat generation (the value obtained by dividing the total heat generation by the steady-state heat generation). Hereinafter, this proportional curve will be referred to as the "first proportional curve".

[0043] As described above, as the carrier frequency increases, the switch generates more heat, therefore the ratio in the first proportional curve increases with the carrier frequency. The derating unit 114 derives the ratio in the first proportional curve corresponding to the current carrier frequency as an adjustment ratio.

[0044] The proportion in the proportional curve can also be determined as an approximation of the ratio of the steady-state heat generation to the total heat generation (the value obtained by dividing the steady-state heat generation by the total heat generation). Hereinafter, this proportional curve will be referred to as the "second proportional curve".

[0045] As described above, as the carrier frequency increases, the switching heat increases, therefore the ratio in the second proportional curve decreases as the carrier frequency increases. The derating unit 114 derives the reciprocal of the ratio in the second proportional curve corresponding to the current carrier frequency as the adjustment ratio.

[0046] After the secondary current value of the power conversion circuit 30 exceeds a predetermined current threshold (hereinafter referred to as the "evaluation start threshold"), the heat evaluation unit 115 evaluates the heat level of the multiple switching elements 35 based on the secondary current value and the carrier frequency. The heat level refers, for example, to the magnitude of the total heat generated.

[0047] For example, after the derating current value (an example of the secondary current value) exceeds the evaluation start threshold, the heat evaluation unit 115 evaluates the heat level based on the cumulative value of the difference between the derating current value and the evaluation start threshold. For example, the heat evaluation unit 115 calculates the time integral value of the difference between the derating current value and the evaluation start threshold as the evaluation result of the heat level. Within the above control cycle, the heat evaluation unit 115 evaluates the heat level whenever derating is performed by the derating unit 114.

[0048] As described above, the dated current value is derived based on the secondary-side current value detected by current sensor 34 and the current carrier frequency. Therefore, evaluating the heating level based on the dated current value using the method described above is equivalent to evaluating the heating level based on the secondary-side current value and the evaluation start threshold. It should be noted that the method for evaluating the heating level is not limited to the method based on the dated current value.

[0049] Alternatively, the heat evaluation unit 115 may derive the total heat corresponding to the current secondary current value and the current carrier frequency based on a pre-generated heat curve that expresses the relationship between the secondary current value, the carrier frequency, and the total heat generation, and use this as the evaluation result of the heat generation level. In this case, the secondary current value can be either the secondary current value before derating or the drated current value.

[0050] Alternatively, the derating unit 114 may drate the evaluation start threshold based on a threshold adjustment ratio that decreases as the carrier frequency increases, instead of derating the secondary current value. Hereinafter, the drated evaluation start threshold will be referred to as the "drated threshold". For example, the derating unit 114 may derive a threshold adjustment ratio corresponding to the carrier frequency based on a pre-generated ratio curve expressing the relationship between carrier frequency and ratio, and the current carrier frequency, and then multiply the derived threshold adjustment ratio by the evaluation start threshold to calculate the drated threshold.

[0051] Alternatively, the derating unit 114 may derive the threshold adjustment ratio from the reciprocal of the ratio corresponding to the current carrier frequency in the first proportional curve. Alternatively, the derating unit 114 may derive the threshold adjustment ratio from the ratio corresponding to the current carrier frequency in the second proportional curve. In this case, the heat evaluation unit 115 may evaluate the heat level based on the cumulative value of the difference between the secondary current value and the derating threshold obtained by the derating unit 114. For example, after the secondary current value exceeds the derating threshold (an example of an evaluation start threshold), the heat evaluation unit 115 may evaluate the heat level based on the cumulative value of the difference between the secondary current value and the derating threshold. For example, the heat evaluation unit 115 may calculate the time integral value of the difference between the secondary current value and the derating threshold as the evaluation result of the heat level.

[0052] After the evaluation result of the heat level obtained by the heat evaluation unit 115 exceeds a predetermined level (hereinafter referred to as the "decline start level"), the frequency change unit 116 decreases the carrier frequency according to the elapsed time. For example, the frequency change unit 116 repeatedly performs the following process within the above-mentioned control loop: decreasing the carrier frequency by a predetermined decrease step size. During the decrease of the carrier frequency, the frequency change unit 116 may also change the decrease step size. For example, the frequency change unit 116 may decrease the decrease step size in response to a decrease in the rate of increase of the heat level.

[0053] Alternatively, the frequency changing unit 116 may respond to the basic blocking unit 113 by stopping the output of secondary power from the power conversion circuit 30, thereby restoring the carrier frequency to the frequency before the decrease began. Here, "responding to stopping" does not necessarily refer only to timing execution immediately before or after the timing of the stopping of secondary power output, but also includes execution between the stopping and the start of the next operation.

[0054] The suppression evaluation unit 117 evaluates the heat suppression effect achieved by the carrier frequency reduction performed by the frequency change unit 116 based on the heat level evaluation result obtained by the heat evaluation unit 115. For example, the suppression evaluation unit 117 calculates the rate of increase of the heat level evaluation result as the evaluation result of the suppression effect. As an example, the suppression evaluation unit 117 calculates the above-mentioned rate of increase based on the heat level evaluation result and the previous heat level evaluation result. The previous heat level evaluation result is the heat level evaluation result in the previous control cycle of the current control cycle. More specifically, the suppression evaluation unit 117 calculates the rate of increase as the value obtained by dividing the difference between the heat level evaluation result and the previous heat level evaluation result by the time of one control cycle.

[0055] Before the evaluation result of the heat level obtained by the heat evaluation unit 115 drops to the reduction start level, the reduction stop unit 118 stops the carrier frequency reduction performed by the frequency change unit based on the evaluation result of the heat suppression effect obtained by the suppression evaluation unit 117. For example, the reduction stop unit 118 stops the carrier frequency reduction performed by the frequency change unit 116 in response to the rise rate being less than a predetermined threshold (hereinafter referred to as the "reduction stop threshold"). The reduction stop threshold can also be 0 or a negative value. In this case, the carrier frequency reduction will continue until the rise rate becomes less than 0, thus improving the reliability of heat suppression. The reduction stop threshold can also be a positive value. In this case, the carrier frequency reduction will stop earlier, thus improving the reliability of noise suppression.

[0056] It should be noted that the evaluation result of the heat suppression effect is not necessarily limited to the rate of increase. As long as the heat suppression effect can be expressed, the suppression evaluation unit 117 can also derive any value. For example, the suppression evaluation unit 117 can calculate the rate of decrease after the heat level reaches its peak as the evaluation result of the heat suppression effect. In this case, the decrease stop unit 118 can stop the carrier frequency decrease performed by the frequency change unit 116 in response to the decrease rate exceeding a predetermined threshold.

[0057] The overload protection unit 119 trips the power conversion circuit 30 after the evaluation result of the heat level reaches an upper limit level higher than the starting level of the decrease. For example, the overload protection unit 119 requests the upper controller 200 to output a lifting stop command. Correspondingly, the upper controller 200 outputs a lifting stop command, and the drive control unit 112 stops the motor 24 accordingly. After the drive control unit 112 stops the motor 24, the upper controller 200 activates the brake of the winch 23 and outputs a basic stop command. The basic stop unit 113 stops the output of secondary power from the power conversion circuit 30 according to the basic stop command from the upper controller 200.

[0058] Figure 2 This is a block diagram illustrating the hardware configuration of the control circuit 100. For example... Figure 2 As shown, the control circuit 100 includes one or more processors 191, memory 192, storage 193, input / output ports 194, and switch control circuitry 195. The storage 193 may be a computer-readable storage medium, such as non-volatile semiconductor memory. The storage 193 stores a program for causing the control circuit 100 to perform the following steps: controlling the power conversion circuit 30 to switch multiple switching elements 35 on / off according to a carrier frequency to convert primary-side power to secondary-side power; evaluating the heating level of the multiple switching elements 35 based on the secondary-side current value and the carrier frequency after the secondary-side current value of the power conversion circuit 30 exceeds a predetermined current threshold; decreasing the carrier frequency according to the elapsed time after the evaluation result of the heating level exceeds a predetermined level; evaluating the heating suppression effect achieved by decreasing the carrier frequency based on the evaluation result of the heating level; and stopping the decrease of the carrier frequency based on the evaluation result of the heating suppression effect before the evaluation result of the heating level drops to a predetermined level. For example, the storage 193 stores a program for causing the control circuit 100 to constitute the above-described functional blocks.

[0059] Memory 192 temporarily stores the program loaded from the storage medium of memory 193 and the calculation results obtained by processor 191. Processor 191 and memory 192 cooperate to execute the program, thereby forming the functional blocks of control circuit 100. Input / output port 194 performs input and output of information with current sensor 34 based on instructions from processor 191. Switch control circuit 195 switches the multiple switching elements 35 in inverter circuit 33 on and off according to instructions from processor 191, thereby outputting the drive power to motor 24.

[0060] It should be noted that the control circuit 100 is not necessarily limited to having its functions configured by a program. For example, the control circuit 100 may also have at least a portion of its functions configured by a dedicated logic circuit or an ASIC (Application Specific Integrated Circuit) that integrates the dedicated logic circuit.

[0061] [Control Process]

[0062] Next, as an example of a power conversion method, a control process executed by the control circuit 100 is illustrated. This control process includes: controlling the power conversion circuit 30 to switch multiple switching elements 35 on / off according to a carrier frequency to convert primary-side power to secondary-side power; evaluating the heating level of the multiple switching elements 35 based on the secondary-side current value and the carrier frequency after the secondary-side current value of the power conversion circuit 30 exceeds a predetermined current threshold; decreasing the carrier frequency based on the time elapsed after the evaluation result of the heating level exceeds a predetermined level; evaluating the heating suppression effect achieved by decreasing the carrier frequency based on the evaluation result of the heating level; and stopping the decrease of the carrier frequency based on the evaluation result of the heating suppression effect before the evaluation result of the heating level drops to a predetermined level. The control process will be illustrated in detail below by dividing it into a rise / fall control process and a carrier frequency adjustment process within the rise / fall control.

[0063] (Lifting and lowering control process)

[0064] like Figure 3 As shown, the control circuit 100 sequentially executes steps S01, S02, S03, S04, S05, S06, S07, and S08. In step S01, the drive control unit 112 waits for a lifting start command from the upper controller 200. In step S02, the drive control unit 112 releases the basic stop performed by the basic stop unit 113. In step S03, the drive control unit 112 waits for the upper controller 200 to release the brake of the winch 23.

[0065] In step S04, the drive control unit 112 begins to control the rotational speed of the motor 24 to follow a predetermined speed pattern. Then, the drive control unit 112 repeatedly performs the following process within a predetermined control cycle: generating a voltage command and outputting it to the PWM control unit 111 in a manner that causes the rotational speed of the motor 24 to follow the predetermined speed pattern.

[0066] In step S05, the drive control unit 112 waits for a lifting / stop command from the upper controller 200. In step S06, the drive control unit 112 stops the motor 24 according to a predetermined deceleration / stop mode. For example, the drive control unit 112 repeatedly performs the following process within the above control cycle to stop the motor 24: generating a voltage command and outputting it to the PWM control unit 111 in a manner that makes the rotational speed of the motor 24 follow the predetermined deceleration / stop mode. In step S07, the basic blocking unit 113 waits for a basic blocking command from the upper controller 200. In step S08, the basic blocking unit 113 stops the output of secondary power from the power conversion circuit 30. The lifting / stopping control process is now complete.

[0067] (Carrier frequency adjustment process)

[0068] like Figure 4 As shown, the control circuit 100 first executes steps S11, S12, and S13. In step S11, the derating unit 114 acquires the secondary-side current value detected by the current sensor 34. In step S12, the derating unit 114 drates the secondary-side current value according to an adjustment ratio that increases with the carrier frequency. In step S13, the heat evaluation unit 115 confirms whether the drated current value exceeds the evaluation start threshold.

[0069] If, in step S13, it is determined that the derated current value has not exceeded the evaluation start threshold, the control circuit 100 returns the process to step S11. Thereafter, the control circuit 100 repeatedly acquires and derates the secondary current value within the aforementioned control loop until the derated current value exceeds the evaluation start threshold.

[0070] If, in step S13, it is determined that the derating current value exceeds the evaluation start threshold, the control circuit 100 begins evaluating the heating level based on the cumulative value of the difference between the derating current value and the evaluation start threshold. For example, the control circuit 100 first executes steps S14, S15, and S16. In step S14, the heating evaluation unit 115 sets an initial value for the heating level evaluation result. The initial value is, for example, 0.

[0071] In step S15, the heat evaluation unit 115 multiplies one cycle of the control cycle by the difference between the derating current value and the evaluation start threshold, and adds the multiplication result to the heat level evaluation result. Hereinafter, the multiplication result to be added will be referred to as the "evaluation result of one cycle quantity". In step S16, the frequency change unit 116 confirms whether the heat level evaluation result exceeds the aforementioned derating start threshold.

[0072] If, in step S16, the evaluation result of the heating level is determined not to exceed the decrement start level, the control circuit 100 executes steps S17 and S18. In step S17, the derating unit 114 acquires the secondary current value detected by the current sensor 34. In step S18, the derating unit 114 derates the secondary current value in the same manner as in step S12. Then, the control circuit 100 returns the processing to step S15. Afterward, the following process is repeated within the control loop until the evaluation result of the heating level exceeds the decrement start level: an evaluation result of a loop quantity is calculated and added to the evaluation result of the heating level.

[0073] If, in step S16, the evaluation result of the fever level is determined to exceed the decreasing start level, then... Figure 5As shown, the control circuit 100 executes steps S21, S22, S23, S24, and S25. In step S21, the frequency changing unit 116 subtracts the aforementioned decreasing step size from the carrier frequency and outputs the subtraction result as the new carrier frequency to the PWM control unit 111. In step S22, the derating unit 114 acquires the secondary current value detected by the current sensor 34.

[0074] In step S23, the derating unit 114 drates the secondary current value in the same manner as in step S12. In step S24, the heat evaluation unit 115 calculates an evaluation result of a cycle quantity in the same manner as in step S15, and adds it to the evaluation result of the heat level. In step S25, the overload protection unit 119 confirms whether the evaluation result of the heat level is below the aforementioned upper limit level.

[0075] If, in step S25, the evaluation result of the heat level is determined to be below the upper limit, the control circuit 100 executes steps S26 and S27. In step S26, the suppression evaluation unit 117 evaluates the heat suppression effect achieved by the carrier frequency reduction performed by the frequency change unit 116 based on the heat level evaluation result obtained by the heat evaluation unit 115. For example, the suppression evaluation unit 117 calculates the rate of increase of the heat level evaluation result as the evaluation result of the suppression effect. In step S27, the reduction stop unit 118 confirms whether the rate of increase is less than the reduction stop threshold.

[0076] If, in step S27, the rise rate is determined to be not less than the decrease stop threshold, the control circuit 100 returns the processing to step S21. Thereafter, the control circuit 100 repeatedly performs carrier frequency decrease, heat generation level evaluation, and heat generation suppression effect evaluation within the control loop until the heat generation level exceeds the upper limit or the rise rate is less than the decrease stop threshold.

[0077] If, in step S27, the rise rate is determined to be less than the decrease stop threshold, the control circuit 100 executes steps S28 and S29. In step S28, the decrease stop unit 118 stops the decrease of the carrier frequency performed by the frequency changing unit 116. In step S29, the frequency changing unit 116 waits for the basic blocking unit 113 to stop the output of secondary power by the power conversion circuit 30.

[0078] If, in step S25, the evaluation result of the heating level is determined to exceed the upper limit, the control circuit 100 executes steps S31, S32, and S33. In step S31, the overload protection unit 119 requests the upper controller 200 to output a lifting stop command. In step S32, the basic blocking unit 113 waits for a basic blocking command from the upper controller 200. In step S33, the basic blocking unit 113 stops the output of secondary power from the power conversion circuit 30.

[0079] After steps S28 and S33, the control circuit 100 executes step S34. In step S34, the frequency changing unit 116 restores the carrier frequency to the frequency before the decrease started and outputs it as the new carrier frequency to the PWM control unit 111. The carrier frequency adjustment process is thus completed.

[0080] [Example of waveform]

[0081] Reference Figure 6 Examples are given of the changes in current value after derating, changes in heat level evaluation results, and changes in carrier frequency during the above-mentioned carrier frequency adjustment process. Figure 6 (a) shows the change in current value after derating. Figure 6 In (a), the horizontal axis represents the elapsed time, and the vertical axis represents the magnitude of the secondary current value. Figure 6 (b) shows the changes in the evaluation results of the fever level. Figure 6 In (b), the horizontal axis represents the elapsed time, and the vertical axis represents the magnitude of the evaluation result of the heating level. Figure 6 (c) shows the change in carrier frequency. Figure 6 The horizontal axis of (c) represents the elapsed time, and the vertical axis represents the carrier frequency.

[0082] exist Figure 6 In the example, the derating current value rises to a level determined by the acceleration rate as the rise / fall begins. At time T1, the derating current value exceeds the evaluation start threshold A1. Simultaneously, the evaluation result of the heat level begins to rise. At time T2, the evaluation result of the heat level exceeds the decrement start level B1. Simultaneously, the carrier frequency decrement begins. As the carrier frequency decrement begins, the derating current value gradually decreases and falls below the evaluation start threshold A1. Therefore, at time T3, the rate of increase of the heat level evaluation result turns negative (begins to decrease), and the carrier frequency decrement stops.

[0083] At time T4, in response to the change from acceleration control of motor 24 to constant speed control of motor 24, the derating current value is further reduced. At time T5, when the secondary-side power output by the power conversion circuit 30 is completed, the carrier frequency returns to the value before the derating began.

[0084] Thus, during the aforementioned carrier frequency adjustment process, the heat generation level is suppressed by the decrease in carrier frequency, but the decrease in carrier frequency stops at a predetermined time when the increase in heat generation level is suppressed to the desired level. Therefore, it is possible to minimize the reduction in carrier frequency within a range that allows the increase in heat generation level to be suppressed to the desired level.

[0085] [Effects of this implementation method]

[0086] As described above, the power conversion device 3 includes: a power conversion circuit 30 that switches multiple switching elements 35 on / off according to a carrier frequency to convert primary power into secondary power; a heat evaluation unit 115 that evaluates the heat level of the multiple switching elements 35 based on the secondary current value and the carrier frequency after the secondary current value of the power conversion circuit 30 exceeds a predetermined current threshold; a frequency changing unit 116 that decreases the carrier frequency over time after the heat level evaluation result exceeds a predetermined level; a suppression evaluation unit 117 that evaluates the heat suppression effect achieved by decreasing the carrier frequency based on the heat level evaluation result; and a reduction stop unit 118 that stops the carrier frequency reduction performed by the frequency changing unit 116 based on the heat suppression effect evaluation result before the heat level evaluation result drops to a predetermined level.

[0087] In devices that operate using secondary-side power generated by switching multiple switching elements on / off according to a carrier frequency, a higher carrier frequency reduces noise generation. However, a higher carrier frequency also leads to greater heat generation from the multiple switching elements due to so-called switching losses. Therefore, when the load on the device increases, resulting in a larger secondary-side current, the total heat generation, including the heat generated by the secondary-side current and the heat generated by switching losses, can easily become excessive.

[0088] In response, this power conversion device 3 reduces the carrier frequency after the heat generation level exceeds a specified level, and stops reducing the carrier frequency based on the evaluation results of the heat generation suppression effect. Therefore, the carrier frequency can be adjusted to a value suitable for balancing noise suppression and heat generation suppression according to each load size. Thus, it is effective in balancing noise suppression and heat generation suppression.

[0089] Alternatively, the suppression evaluation unit 117 can calculate the rate of increase of the evaluation result of the heat generation level as the evaluation result of the heat generation suppression effect, and the reduction stop unit 118 can stop the carrier frequency reduction performed by the frequency change unit 116 in response to the rate of increase being less than a predetermined stop threshold. In this case, by using the rate of increase of the evaluation result of the heat generation level, the heat generation suppression effect can be evaluated more appropriately, and the carrier frequency reduction can be stopped at a more appropriate timing. Therefore, it is more effective in balancing heat generation suppression and noise suppression.

[0090] Alternatively, the stop threshold can be 0 or a negative value. In this case, heat generation can be suppressed more reliably.

[0091] Alternatively, the suppression evaluation unit 117 can calculate the rate of decrease in the heat generation level after it reaches its peak and use this as the evaluation result for the heat generation suppression effect. The reduction stop unit 118 then stops the carrier frequency reduction performed by the frequency change unit 116 in response to the rate of decrease exceeding a predetermined stop threshold. In this case, heat generation can be suppressed more reliably.

[0092] Alternatively, the power conversion device 3 may also include: a basic blocking unit 113 that stops the output of secondary power from the power conversion circuit 30, and a frequency changing unit 116 that, in response to the basic blocking unit 113 stopping the output of secondary power from the power conversion circuit 30, restores the carrier frequency to the frequency before the decrease began. In this case, heat suppression and noise suppression can be achieved more reliably.

[0093] Alternatively, the power conversion device 3 may also include an overload protection unit 119 that trips the power conversion circuit 30 after the evaluation result of the heat level reaches an upper limit higher than the specified level. In this case, by sharing the evaluation result of the heat level with the heat suppression achieved by the decrease of the carrier frequency and the overload protection achieved by the tripping of the power conversion circuit 30, the operational load within the power conversion device 3 can be reduced.

[0094] Alternatively, the power conversion device 3 may also include a derating unit 114 that drates the secondary current value according to a ratio that increases with the carrier frequency, and a heat evaluation unit 115 that evaluates the heat level based on the cumulative difference between the drated secondary current value and a current threshold value. In this case, the heat level can be easily evaluated based on the drated secondary current value.

[0095] Alternatively, the power conversion device 3 may also include a derating unit 114 that drates the current threshold according to a ratio that decreases as the carrier frequency increases, and a heat evaluation unit 115 that evaluates the heat level based on the cumulative value of the difference between the secondary current value and the current threshold value after derating by the derating unit 114. In this case, the reliability of the heat level evaluation based on the drated secondary current value can be improved.

[0096] The implementation methods have been described above, but this disclosure is not necessarily limited to the above implementation methods, and various changes can be made without departing from its spirit.

[0097] Explanation of reference numerals in the attached figures

[0098] 2: Lifting device;

[0099] 3: Power conversion device;

[0100] 24: Motor (electric motor);

[0101] 30: Power conversion circuit;

[0102] 35: Switching elements;

[0103] 113: Basic blocking section;

[0104] 114: Lowering the quota;

[0105] 115: Fever Assessment Department;

[0106] 116: Frequency Change Section;

[0107] 117: Inhibition Evaluation Department;

[0108] 118: Decreasing stop section;

[0109] 119: Overload Protection Department.

Claims

1. A power conversion device, comprising: A power conversion circuit converts primary-side power into secondary-side power by switching multiple switching elements on / off according to a carrier frequency. The heat evaluation unit evaluates the heat level of the plurality of switching elements based on the secondary current value and the carrier frequency after the secondary current value of the power conversion circuit exceeds a predetermined current threshold. The frequency changing unit decreases the carrier frequency based on the passage of time after the evaluation result of the heat level exceeds a predetermined level. The suppression evaluation unit evaluates the heat suppression effect achieved by decreasing the carrier frequency based on the evaluation result of the heat level; and The frequency reduction stop unit stops the reduction of the carrier frequency performed by the frequency change unit based on the evaluation result of the heat suppression effect before the evaluation result of the heat level drops to the predetermined level.

2. The power conversion device according to claim 1, wherein, The suppression evaluation unit calculates the rate of increase of the fever level as the evaluation result of the fever suppression effect. The decrease stop unit stops the decrease of the carrier frequency performed by the frequency change unit in response to the rise rate being less than a predetermined stop threshold.

3. The power conversion device according to claim 2, wherein, The stopping threshold is 0 or a negative value.

4. The power conversion device according to claim 1, wherein, The suppression evaluation unit calculates the reduction in the fever level after it reaches its peak as the evaluation result of the fever suppression effect. The decrease stop unit stops the carrier frequency decrease performed by the frequency change unit in response to the decrease magnitude exceeding a predetermined stop threshold.

5. The power conversion device according to any one of claims 1 to 4, wherein, It also has: The basic blocking unit stops the output of the secondary-side power by the power conversion circuit. The frequency changing unit responds to the basic blocking unit by stopping the output of the secondary power by the power conversion circuit to restore the carrier frequency to the frequency before the decrease began.

6. The power conversion device according to any one of claims 1 to 4, wherein, It also has: The overload protection unit trips the power conversion circuit after the evaluation result of the heat level reaches an upper limit level higher than the specified level.

7. The power conversion device according to any one of claims 1 to 4, wherein, It also has: The derating section reduces the secondary current value according to the proportion that increases with the carrier frequency. The heat evaluation unit evaluates the heat level based on the cumulative difference between the secondary current value after being reduced by the derating unit and the current threshold.

8. The power conversion device according to any one of claims 1 to 4, wherein, It also has: The derating section derating the current threshold according to a ratio that decreases as the carrier frequency increases. The heat evaluation unit evaluates the heat level based on the cumulative difference between the secondary current value and the current threshold value after being reduced by the derating unit.

9. A lifting device, comprising: The power conversion device according to any one of claims 1 to 8; and An electric motor, supplied with power to the secondary side, causes the object to be lifted to move up and down.

10. A power conversion method, comprising: The control power conversion circuit switches multiple switching elements on / off according to the carrier frequency to convert primary power into secondary power; After the secondary current value of the power conversion circuit exceeds a predetermined current threshold, the heating level of the plurality of switching elements is evaluated based on the secondary current value and the carrier frequency. After the evaluation result of the heat level exceeds the specified level, the carrier frequency is reduced according to the passage of time; The effect of suppressing heat generation by decreasing the carrier frequency is evaluated based on the evaluation results of the heat generation level. as well as Before the evaluation result of the heat generation level drops to the specified level, the reduction of the carrier frequency is stopped based on the evaluation result of the heat generation suppression effect.

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