Control method for avoiding motor overvoltage, and control device and inverter using same

Abstract

The present invention relates to a control method for avoiding motor overvoltage, and a control device and an inverter using same. The method according to one embodiment of the present invention is a control method performed by a control device of an inverter before a line-to-line voltage for a three-phase voltage to be output from the inverter to a motor is switched from the current state to the next state, and comprises the steps of: identifying a period (T) for oscillation of a voltage reflection wave for the current state; identifying an application time for the current state; and using the identified period (T) and the identified application time so as to control that the line-to-line voltage of the next state is applied in a safe region of oscillation of the voltage reflection wave, thereby preventing a double pulsing effect caused by the voltage reflection wave and the line-to-line voltage of the next state.

Description

Control method for avoiding motor overvoltage, and control device and inverter using the same

[0001] The present invention relates to a control technique for avoiding overvoltage from being applied to a motor driven by an inverter, and more specifically, to a technique for avoiding overvoltage from being applied to the input of a motor due to a double pulsing effect at the output of an inverter.

[0002] An inverter, as a motor drive system, delivers power to the motor for driving. At this time, the inverter is a power conversion device that converts input AC power into AC power with a certain frequency and supplies it to the motor. Specifically, the inverter converts input three-phase AC power into direct current (DC), and then converts the converted DC into three-phase alternating current (AC) to supply it to the motor.

[0003] Meanwhile, when the output voltage of the inverter is driven and transmitted to the motor through the line, a voltage reflection wave is generated due to the impedance mismatch between the inverter's output line and the motor. At this time, if the next voltage pulse of the inverter is applied in the rising (or falling) time domain of the oscillation of the voltage reflection wave, if the oscillation of the next voltage pulse overlaps in the same direction, a double pulsing effect may occur in which the voltage instantaneously increases by nearly twice. Due to this double pulsing effect, an overvoltage of a momentary voltage (dv / dt) or voltage spike higher than a general single pulse is applied to the motor input, which may cause damage to the motor.

[0004] To address these issues, conventional technology utilizes a filter placed between the inverter output and the motor input. This filter increases the rise time of the line voltage at the motor input, thereby suppressing voltage oscillation. This suppresses the double pulsing effect, which occurs when oscillations overlap with short voltage pulses.

[0005] However, conventional techniques, which rely on hardware-based filters, not only increase the inverter's volume, weight, and cost, but also incur power losses due to filter operation. Furthermore, conventional techniques require optimal filter design for each system environment, limiting their implementation in diverse environments. In other words, a filter optimally designed for one system environment may not function optimally in another, requiring a new, optimal design.

[0006] However, the above-described content merely provides background information on the present invention and does not correspond to previously disclosed technology.

[0007] In order to solve the problems of the prior art as described above, the purpose of the present invention is to provide a technology for avoiding overvoltage caused by the occurrence of a double pulsing effect at the output of an inverter from being applied to the input of a motor.

[0008] In particular, another purpose of the present invention is to provide a technology that can avoid the occurrence of a double pulsing effect without adding separate hardware such as a filter, through a control method that adjusts the application time of the output voltage of an inverter according to the oscillation period of a voltage reflection wave.

[0009] However, the problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0010] A method according to one embodiment of the present invention for solving the above-described problem is a control method performed in a control device of an inverter before a line voltage for a three-phase voltage output from an inverter to a motor is switched from a first state to a second state, the method including: a step of determining a period (T) for an oscillation of a voltage reflection wave for the first state; a step of determining an application time for the first state; and a step of controlling the line voltage of the second state to be applied within a safe region of the oscillation of the voltage reflection wave based on the period (T) and the application time.

[0011] In one embodiment of the present invention, the first state may be a time period in which the line voltage is high, the second state may be a time period in which the line voltage is low, and the safe region may be a time period in which the voltage of the voltage reflection wave rises.

[0012] In one embodiment of the present invention, the first state may be a state in which the line voltage is low, the second state may be a state in which the line voltage is high, and the safe region may be a time region in which the voltage of the voltage reflection wave decreases.

[0013] In one embodiment of the present invention, the safety region may be a region included in 3 / 4T to 5 / 4T of the oscillation period of the voltage reflection wave.

[0014] In one embodiment of the present invention, the period (T) is the propagation time (t) of the line through which the three-phase voltage is transmitted. p ) can be four times that of the original.

[0015] In one embodiment of the present invention, the step of determining the application time may be performed in a region including each maximum point or each minimum point in a triangle wave for comparing the command voltages for the three phases.

[0016] In one embodiment of the present invention, the controlling step can control the line voltage of the next state to be applied in a safe region by adjusting the application time to increase or decrease.

[0017] In one embodiment of the present invention, the controlling step can control the application time by controlling the magnitude of the command voltage related to the line voltage.

[0018] In one embodiment of the present invention, the controlling step may include: determining whether the application time is a multiple of the period (T), and if it is a multiple of the period (T), adjusting the application time to be reduced by T / 4; and if it is not a multiple of the period (T), increasing the application time so that the application time becomes a multiple of the period (T), and then adjusting the application time to be reduced by T / 4.

[0019] According to one embodiment of the present invention for solving the above-described problem, a device is a control device of an inverter, comprising: a memory; and a processor for performing control to prevent overvoltage before the line voltage for three-phase voltage output from the inverter to the motor switches from a first state to a second state using information stored in the memory; wherein the processor controls to determine a period (T) for oscillation of a voltage reflection wave for the current state, controls to determine an application time for the first state, and controls to apply the line voltage of the second state within a safe range of oscillation of the voltage reflection wave based on the period (T) and the application time.

[0020] In one embodiment of the present invention, the first state is a high state of line voltage, the second state is a low state of line voltage, and the processor can control the line voltage of the next state to be applied in the safe region corresponding to a time region in which the voltage of the voltage reflection wave rises.

[0021] In one embodiment of the present invention, the first state is a state in which the line voltage is low, the second state is a state in which the line voltage is high, and the processor can control the line voltage of the next state to be applied in the safe region corresponding to a time region in which the voltage of the voltage reflection wave decreases.

[0022] In one embodiment of the present invention, the processor can control the line voltage of the next state to be applied in the safe region included in 3 / 4T to 5 / 4T of the oscillation period of the voltage reflection wave.

[0023] In one embodiment of the present invention, the processor determines that the period (T) is the propagation time (t) of the line through which the three-phase voltage is transmitted. p ) can be determined to be four times that of the original.

[0024] In one embodiment of the present invention, the processor can be controlled to determine the application time in a region including each maximum point or each minimum point in a triangle wave for comparing the command voltage for the three phases.

[0025] In one embodiment of the present invention, the processor can control the line voltage of the next state to be applied in a safe region by adjusting the application time to increase or decrease.

[0026] In one embodiment of the present invention, the processor can control the application time by controlling the magnitude of the command voltage related to the line voltage.

[0027] In one embodiment of the present invention, the processor determines whether the authorization time is a multiple of the period (T), and if it is a multiple of the period (T), adjusts the authorization time to be reduced by T / 4, and if it is not a multiple of the period (T), adjusts the authorization time to be increased so that the authorization time becomes a multiple of the period (T) and then to be reduced by T / 4.

[0028] According to an embodiment of the present invention for solving the above-described problem, an inverter includes a converter unit that rectifies AC power and converts it into DC; a DC link capacitor that smoothes the DC voltage rectified by the converter unit and charges the DC voltage; an inverter unit that converts the DC voltage charged in the capacitor into a three-phase AC voltage for providing the DC voltage to a motor using a plurality of switching elements; and a control unit that controls the plurality of switching elements and performs control to prevent overvoltage before the line voltage for the three-phase AC voltage switches from a first state to a second state, wherein the control unit determines a period (T) for oscillation of a voltage reflection wave for the first state, controls to determine an application time for the first state, and controls to apply the line voltage of the second state within a safe range of oscillation of the voltage reflection wave using the determined period (T) and the determined application time.

[0029] The present invention, configured as described above, has the advantage of being able to avoid the occurrence of a double pulsing effect in the output of an inverter, thereby protecting a motor from damage caused by overvoltage due to the double pulsing effect.

[0030] In addition, the present invention has an advantage in that it can avoid the occurrence of the double pulsing effect without the addition of separate hardware such as a filter, through a control method that adjusts the application time of the output voltage of the inverter according to the oscillation period of the voltage reflection wave. Accordingly, the present invention can implement a double pulsing effect avoidance technology that can be applied to various system environments without increasing the volume, weight, and cost of the inverter, and as a result, can solve the problems of the prior art.

[0031] The effects that can be obtained from the present invention are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by a person having ordinary skill in the art to which the present invention belongs from the description below.

[0032] Figure 1 shows a schematic block diagram of an inverter system (10) according to one embodiment of the present invention.

[0033] Figure 2 shows examples of safe and dangerous areas for oscillation of voltage reflection waves.

[0034] Figure 3 shows a separate display of the safety zone in the oscillation of the voltage reflection wave according to Figure 2.

[0035] Figure 4 shows a flowchart of a control method according to one embodiment of the present invention.

[0036] Fig. 5 shows an example of the waveforms of the switching signals (U, V), the command voltage of each phase (U, V, W), the triangle wave, and the UV line voltage of the inverter (200) operating according to the PWM method.

[0037] The above-described objects, means, and resulting effects of the present invention will become more apparent through the following detailed description, taken in conjunction with the accompanying drawings. Accordingly, those skilled in the art will be able to readily implement the technical concepts of the present invention. Furthermore, in describing the present invention, if a detailed description of known technology related to the present invention is deemed to unnecessarily obscure the gist of the invention, such detailed description will be omitted.

[0038] The terminology used herein is for the purpose of describing embodiments and is not intended to limit the present invention. In this specification, singular forms also include plural forms, unless specifically stated otherwise. In this specification, terms such as "include," "provide," "provide," or "have" do not exclude the presence or addition of one or more other components other than the mentioned components.

[0039] In this specification, terms such as "or", "at least one", etc. may refer to one of the words listed together, or to a combination of two or more. For example, "A or B", "at least one of A and B" may include only one of A or B, or may include both A and B.

[0040] In this specification, descriptions using the phrase "for example" or the like should not be construed as limiting the embodiments of the invention in terms of the effects of variations such as tolerances, measurement errors, limitations of measurement accuracy, and other commonly known factors, including the information presented, such as cited characteristics, variables, or values, may not be exact matches.

[0041] In this specification, when a component is described as being "connected" or "connected" to another component, it should be understood that it may be directly connected or connected to that other component, but that there may be other components in between. Conversely, when a component is described as being "directly connected" or "directly connected" to another component, it should be understood that there are no other components in between.

[0042] In this specification, when a component is described as being "on" or "in contact with" another component, it should be understood that it may be directly on or connected to the other component, but there may be another component in between. Conversely, when a component is described as being "directly on" or "in direct contact with" another component, it should be understood that there is no other component in between. Other expressions that describe the relationship between components, such as "between" and "directly between", can be interpreted similarly.

[0043] In this specification, terms such as "first" and "second" may be used to describe various components, but the components should not be limited by these terms. Furthermore, these terms should not be construed to limit the order of each component, but rather may be used to distinguish one component from another. For example, a "first component" may be referred to as a "second component," and similarly, a "second component" may also be referred to as a "first component."

[0044] Unless otherwise defined, all terms used herein may be used in their common sense by those of ordinary skill in the art to which the present invention pertains. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise.

[0045] Hereinafter, a preferred embodiment according to the present invention will be described in detail with reference to the attached drawings.

[0046] Figure 1 shows a schematic block diagram of an inverter system (10) according to one embodiment of the present invention.

[0047] An inverter system (10) according to one embodiment of the present invention (hereinafter referred to as “the system”) includes an AC power supply unit (100) that supplies three-phase (R, S, T) AC power, an inverter (200) that sequentially converts the supplied three-phase (R, S, T) AC power into direct current (DC) and three-phase (U, V, W) alternating current (AC), and a motor (300) that operates according to the three-phase (U, V, W) alternating current supplied from the inverter (200).

[0048] At this time, the inverter (200) is a power conversion device that converts the AC power input from the AC power source (100) into AC power having a certain frequency and provides it to the motor (300). That is, the inverter (200) can convert the input three-phase (R, S, T) AC power into direct current, and then change the converted direct current into three-phase (U, V, W) AC power having a set voltage and frequency and provide it to the motor (300). For example, the inverter (200) can control the magnitude and frequency of the three-phase (U, V, W) AC power supplied to the motor (300), and can be applied to a system requiring variable speed operation.

[0049] Referring to FIG. 1, the inverter (200) may include an input switching unit (210), a converter unit (220), a DC link capacitor (230), an inverter unit (240), a measurement unit (250), and a control unit (260).

[0050] The input switching unit (210) performs a switching operation to turn on / off the connection with the AC power supply unit (100). Accordingly, the input switching unit (210) may include switching elements connected to each phase to turn on / off the connection between the input terminals of the three phases (R, S, T) and the converter unit (220). Control of the on / off of the input switching unit (210) may be performed according to a control signal of the control unit (260).

[0051] The converter unit (220) is configured to rectify and convert the input three-phase (R, S, T) AC power into DC when the input switching unit (210) is turned on. For example, the converter unit (220) may be configured to include a diode, and may be configured in the form of an SCR-diode connected to a silicon controlled rectifier (SCR) of an initial charge switch (not shown).

[0052] The DC link capacitor (230) (hereinafter referred to as “capacitor”) is configured to charge the DC voltage rectified by the converter unit (220) to smooth the DC voltage, and the inverter unit (240) is configured to convert the DC voltage (Vdc) charged in the capacitor (230) into a three-phase (U, V, W) AC voltage to be provided to the motor (300). At this time, the inverter unit (240) may include a plurality of switching elements, and the on / off of each switching element may be controlled by the control unit (260).

[0053] For example, the switching element may include, but is not limited to, a transistor, a metal-oxide-semiconductor field-effect-transistor (MOSFET), an insulated gate bipolar transistor (IGBT), or a gate turn-off thyristor (GTO). In addition, each switching element of the inverter unit (240) may output an AC voltage of a magnitude and frequency modulated by pulse width modulation (PWM) of a variable frequency in three phases (U, V, W) according to a control signal of the control unit (260).

[0054] The measuring unit (250) is configured to measure the power factor applied to each line (i.e., cable) of the three phases (U, V, W) output from the inverter unit (240), i.e., input to the motor (300). That is, the measuring unit (250) can measure the amount of current flowing in each line of the three phases (U, V, W), and can measure the amount of voltage applied to each line of the three phases (U, V, W) (i.e., the voltage size of each line based on GND). To this end, the measuring unit (250) may include a current detector and a voltage detector for each of the three phases (U, V, W). In this way, the power factor values ​​for the three phases (U, V, W) measured by the measuring unit (250) are transmitted to the control unit (260).

[0055] Meanwhile, the inverter (200) may further include a pre-charge resistor (not shown), a pre-charge switch (not shown), and a regenerative braking unit (not shown). At this time, the pre-charge resistor and the pre-charge switch are configured to prevent inrush current from being applied to the DC link capacitor (230) when power is applied. That is, when power is applied, the pre-charge switch is turned off, so that the inrush current is suppressed by the pre-charge resistor, and after the inrush current is suppressed, the pre-charge switch is turned on, so that the pre-charge resistor can be separated from the circuit. For example, the pre-charge switch may be configured as a magnetic contactor (MC), and may also be configured as a silicon controlled rectifier (SCR) connected to a diode of an upper leg of the converter unit. In addition, the regenerative braking unit can consume regenerative energy through a resistor (not shown) when the DC voltage that has increased due to regenerative driving or other reasons is greater than the set voltage.

[0056] The control unit (260) is a component that controls the operation of the inverter (200), and may be referred to differently as a "control device." For example, the control unit (260) determines various information, such as the power elements applied to each line of the three phases (U, V, W) of the inverter (200), through the measurement unit (250), and generates a PWM control signal for controlling each switching element of the inverter unit (240) based on the determined information, thereby controlling various operations of the inverter (200) by adjusting the magnitude and frequency of the three phases (U, V, W) AC voltage output from the inverter unit (240) and applied to the motor (300) through each line.

[0057] In particular, the control unit (260) obtains information on the line voltages (i.e., UV voltage, VW voltage, and WU voltage) of the three-phase (U, V, W) lines of the inverter (200) through the measurement unit (250), and controls the application time of the output voltage of the inverter unit (240) according to the oscillation frequency of the voltage reflection wave based on the obtained information so that the double pulsing effect does not occur at any line voltage. However, this will be described in more detail through the control method described later.

[0058] Of course, the control unit (260) can control the on / off of the input switching unit (210).

[0059] This control unit (260) may include a processor and memory. In this case, the memory may store a program for the operation of the processor and various data measured by the measurement unit (250). In particular, the memory may store a program related to a control method described below.

[0060] For example, the memory may include, but is not limited to, volatile memory such as DRAM or SRAM, non-volatile memory such as PRAM, MRAM, ReRAM, Read Only Memory (ROM), Erasable Programmable Read Only Memory (EPROM), or flash memory, or a hard disk drive (HDD) or a solid state drive (SSD).

[0061] The processor performs various processing or control using information stored in memory. That is, the processor is responsible for various processing or control performed in the control unit (200) and can control the execution of the control method described below.

[0062] Hereinafter, a control method according to one embodiment of the present invention will be described.

[0063] When the inverter (200) is driven, the output voltage of the inverter (200) (i.e., the output voltage of the inverter unit (240)) is transmitted to the motor (300) through each of the three-phase (U, V, W) lines. In this process, if the impedance between the three-phase (U, V, W) lines and the motor (300) is mismatched, a voltage reflection wave is generated. This voltage reflection wave is reflected in the form of an oscillation (i.e., a pulse shape). At this time, a double pulsing effect, in which the voltage instantaneously increases by nearly two times, may or may not occur depending on in which time domain of the oscillation of the voltage reflection wave the voltage of the next state is output from the inverter unit (240) of the inverter (200).

[0064] That is, when the oscillation of the voltage reflection wave corresponds to the danger zone, and the oscillation (oscillation) form (i.e., pulse form) according to the next voltage occurs in the inverter unit (240) of the inverter (200), a double pulsing effect may occur. That is, when the oscillation (oscillation) of the pulse according to the voltage reflection wave is not finished and the oscillation (oscillation) of the pulse according to the next voltage overlaps in the same direction as the oscillation (oscillation) of the pulse according to the voltage reflection wave at the rising or falling point corresponding to the danger zone of the pulse, a double pulsing effect occurs. When a double pulsing effect occurs like this, an overvoltage of instantaneous voltage (dv / dt) or voltage spike higher than a normal single pulse is applied to the input of the motor (300), which may cause damage to the motor (300).

[0065] Specifically, when the first vibration (or first pulse) of the voltage reflection wave according to the output voltage of the current state of the inverter unit (240) of the inverter (200) and the second vibration (or second pulse) according to the voltage of the output of the next state proceed in the same direction and overlap, a voltage of a third vibration (or third pulse) having an amplitude larger than each amplitude of the first and second vibrations is generated, and this effect is referred to as a double pulsing effect. Accordingly, the overvoltage due to the double pulsing effect is the voltage of the third vibration, which corresponds to a voltage having an amplitude larger than that of the first and second vibrations. This double pulsing effect is the same as the principle in which two waves overlap and constructive interference occurs from a wave perspective. Accordingly, the double pulsing effect may also be referred to as the "constructive interference effect", which is an unintended effect in the inverter system design.

[0066] On the other hand, when the oscillation of the voltage reflection wave corresponds to the safe zone and a pulse according to the next voltage is output from the inverter section (240) of the inverter (200), the double pulsing effect does not occur. That is, when the oscillation of the pulse according to the next voltage does not overlap in the same direction as the oscillation of the pulse according to the voltage reflection wave, the double pulsing effect does not occur.

[0067] Fig. 2 shows an example of safe and dangerous areas for oscillation of voltage reflection waves, and Fig. 3 shows that the safe areas for oscillation of voltage reflection waves are separately indicated according to Fig. 2.

[0068] For example, referring to FIG. 2A, when the output voltage of the current state of the inverter unit (240) of the inverter (200) is high and the output of the next state changes to a low voltage state (hereinafter referred to as the “first switching case”), the time region in which the oscillation of the voltage reflection wave according to the output voltage of the current state falls is a dangerous region. In this dangerous region, when the voltage according to the low state, which is the next state, is applied from the inverter unit (240) of the inverter (200), the oscillation of the voltage reflection wave according to the output voltage of the current state and the oscillation of the pulse according to the voltage of the low state, which is the next state, overlap in the same direction, resulting in a double pulsing effect.

[0069] On the other hand, with respect to Fig. 2a, in the first switching case, the time region in which the oscillation of the voltage reflection wave according to the output voltage of the current state rises is the safe region. In this safe region, when the voltage according to the next low state is applied from the inverter unit (240) of the inverter (200), the oscillation of the voltage reflection wave according to the output voltage of the current state and the oscillation of the pulse according to the voltage of the next low state do not overlap in the same direction, so that the double pulsing effect does not occur.

[0070] In addition, referring to FIG. 2b, in a case where the output voltage of the current state of the inverter unit (240) of the inverter (200) is in a low state and the output of the next state changes to a high voltage state (hereinafter referred to as the “second switching case”), the time region in which the oscillation of the voltage reflection wave according to the output voltage of the current state rises is a dangerous region. In this dangerous region, when the voltage according to the next high state is applied from the inverter unit (240) of the inverter (200), the oscillation of the voltage reflection wave according to the output voltage of the current state and the oscillation of the pulse according to the voltage of the next high state overlap in the same direction, which may cause a double pulsing effect.

[0071] On the other hand, with respect to Fig. 2b, in the second switching case, the time region in which the oscillation of the voltage reflection wave according to the output voltage of the current state falls is the safe region. In this safe region, when the voltage according to the next high state is applied from the inverter unit (240) of the inverter (200), the oscillation of the voltage reflection wave according to the output voltage of the current state and the oscillation of the pulse according to the voltage of the next high state do not overlap in the same direction, so that the double pulsing effect does not occur.

[0072] That is, the area where the first rising or falling curve after switching can be subject to constructive interference during the entire switching period can be defined as a risk area, and the area where destructive interference can be defined as a safe area.

[0073] In particular, shielding is implemented between each line in the three-phase (U, V, W) input of the motor (300). That is, shielding is implemented between UV, VW, and WU in the motor input. However, if a double pulsing effect occurs in any one of the UV line voltage, VW line voltage, and WU line voltage, the shielding provided between the corresponding lines may be destroyed, resulting in damage to the motor.

[0074] For example, when a double pulsing effect occurs in the UV line voltage, the motor (300) may be damaged when the first shield provided between the UV and the input of the motor (300) is destroyed by the overvoltage caused by the double pulsing effect. In addition, when a double pulsing effect occurs in the VW line voltage, the motor (300) may be damaged when the second shield provided between the VW and the input of the motor (300) is destroyed by the overvoltage caused by the double pulsing effect. In addition, when a double pulsing effect occurs in the WU line voltage, the third shield provided between the input of the motor (300) and the WU may be destroyed by the overvoltage resulting from the double pulsing effect, thereby damaging the motor (300).

[0075] Accordingly, it may be preferable that the voltage in the high or low state according to FIG. 2 be the line voltage for the three phases (U, W, V) rather than the three phase (U, W, V) voltage. Information on each of these line voltages can be acquired by the control unit (260) through the measurement unit (250).

[0076] FIG. 4 shows a flowchart of a control method according to one embodiment of the present invention, and FIG. 5 shows an example of a switching signal (U, V) of an inverter (200) operating according to a PWM method, a command voltage of each phase (U, V, W), a triangle wave, and a waveform of a UV line voltage.

[0077] A control method according to one embodiment of the present invention (hereinafter referred to as “the control method”) performs control reflecting the above-described contents. That is, the control method is a method of controlling so that the next voltage is not output in a dangerous area but in a safe area by adjusting the application time of the output voltage of the inverter unit (240) in consideration of the propagation time (tp) of the current (voltage) transmitted in each line according to the impedance of each line of the three phases (U, V, W) and the oscillation period of the line-to-line voltage on the input side of the motor (300). Through this, the control method can avoid the occurrence of a double pulsing effect.

[0078] Referring to FIGS. 4 and 5, the present control method may include S310 to S330. Of course, S310 to S330 may be performed by the control unit (260). That is, information related to S310 to S330 is stored in the memory of the control unit (260), and the processor of the control unit (260) may perform S310 to S330 using the information stored in the memory.

[0079] First, in S310, the control unit (260) determines the period (T) of the oscillation of the voltage reflection wave for the line voltage transmitted through each line of the three-phase (U, V, W) output of the inverter (200).

[0080] At this time, the corresponding period (T) can be determined by the propagation time (tp) of each line of the three phases (U, V, W). Of course, the propagation time (tp) corresponds to the time for the three phase (U, V, W) voltage or each line voltage to be transmitted from the starting point to the ending point through each line, and can be obtained according to the following [Mathematical Formula 1].

[0081] [Mathematical Formula 1]

[0082]

[0083] Here, l c represents the length of the line, L represents the inductance of the line, and C represents the capacitance of the line. Of course, this propagation time (t p ) corresponds to a fixed value and can thus be stored in memory.

[0084] These propagation times (t p ), the period (T) of oscillation of line voltage for three phases (U, V, W) is as follows [Mathematical Formula 2].

[0085] [Equation 2]

[0086] T = 4t p

[0087] That is, since the waveform reflected from the motor (300) and transmitted through the three-phase (U, V, W) line is repeatedly transmitted back and forth, the propagation time (t) is p ) is considered, and accordingly the period (T) is the propagation time (t p ) is a value that is four times that of the voltage reflection wave. That is, one cycle of the oscillation of the voltage reflection wave is equal to the propagation time of the line (t p ) is four times that of the period (T). Of course, this period (T) corresponds to a fixed value and can thus be stored in memory.

[0088] That is, in S310, if a value according to [Mathematical Formula 1] is already stored in the memory, the control unit (260) uses each value stored in the memory and [Mathematical Formula 1] to calculate the propagation time (tp ) and then the propagation time (t) is calculated. p ) can be obtained by multiplying the value of the period (T) by 4 times the value of the propagation time (t) in the memory. Or, p ) is stored, the control unit (160) stores the corresponding propagation time (t) stored in the memory. p ) can be obtained as a value of the period (T) that is 4 times the value of the period (T). Alternatively, if the period (T) is already stored in the memory, the control unit (160) can read the value of the corresponding period (T) from the memory.

[0089] Next, in S320, the control unit (260) determines the application time for the current state before the line voltage is switched.

[0090] At this time, switching means that the line voltage changes from a high state to a low state, or from a low state to a high state. In particular, the line voltage according to the PWM method can be derived by using a triangle wave for comparing the command voltage of each phase (U, V, W) with each command voltage. At this time, the application time for the current state before the switching of the line voltage is checked. Accordingly, the application time means the time for which the current state before the switching of the line voltage continues.

[0091] Of course, it is necessary to monitor (i.e., determine the application time) in a short region that affects the oscillation of the pulse according to the voltage of the next state after switching from the current state. Accordingly, it may be desirable to monitor in a short region that includes each maximum point or each minimum point of the triangle wave. This is because the switching of the line voltage occurs near the region that includes each maximum point or each minimum point. That is, near the region that includes each maximum point or each minimum point, the line voltage of the current state switches to the line voltage of the next state. For example, near the region that includes each maximum point or each minimum point, the line voltage switches from the current high state to the next low state, or from the current low state to the next high state.

[0092] Accordingly, when the current state's acceptance time is determined in a short region including each maximum point or each minimum point of the triangle wave, the acceptance time for the current state is determined only in a short region before the switching occurs, thereby preventing waste of resources due to unnecessary continuous performance of the acceptance time determination. That is, when the current state's acceptance time is determined in a region other than a short region including each maximum point or each minimum point of the triangle wave, the monitoring time for acceptance time determination is unnecessarily increased, resulting in waste of processing resources of the control unit (260).

[0093] Next, in S330, the control unit (260) controls the line voltage of the next state to be applied in a safe area by using the period (T) of the oscillation of the voltage reflection wave identified in S310 and the application time for the current state identified in S320.

[0094] At this time, the next state means a state in which the line voltage switches from the current high state to the low state, or from the current low state to the high state. However, since the safe area or the dangerous area has already been described above according to Fig. 2, the description thereof will be omitted.

[0095] For example, in the first switching case, the safe area according to Fig. 2a is an area corresponding to 3 / 4T to 5 / 4T in the oscillation of the voltage reflection wave, as illustrated in Fig. 3a (the illustrated area may correspond to the entire switching cycle). Similarly, in the second switching case, the safe area according to Fig. 2b is an area corresponding to 3 / 4T to 5 / 4T in the oscillation of the voltage reflection wave, as illustrated in Fig. 3b.

[0096] However, referring to Fig. 3a, among the safe areas of 3 / 4T to 5 / 4T in the first switching case, the area of ​​3 / 4T to T is an area that includes a portion from where the oscillation of the voltage reflection wave begins to rise to the middle of the rise. In this 3 / 4T to T, it is a very safe area in which the occurrence of the double pulsing effect can be completely avoided even if an error occurs in the application of the line voltage in the next state. On the other hand, among the safe areas of 3 / 4T to 5 / 4T in the first switching case, the area of ​​T to 5 / 4T is an area that includes a portion from the middle of the rise of the oscillation of the voltage reflection wave to the peak of the rise. In this T to 5 / 4T, it is a relatively less safe area in which the double pulsing effect can easily occur if an error occurs in the application of the line voltage in the next state.

[0097] However, referring to FIG. 3b, among the safe areas of 3 / 4T to 5 / 4T in the second switching case, the area of ​​3 / 4T to T is an area including a portion where the oscillation of the voltage reflection wave begins to fall to the middle portion of the fall. In this 3 / 4T to T, even if an error occurs in the application of the line voltage in the next state, it corresponds to a very safe area where the occurrence of the double pulsing effect can be completely avoided. On the other hand, among the safe areas of 3 / 4T to 5 / 4T in the second switching case, the area of ​​T to 5 / 4T is an area including a portion where the middle portion of the fall of the oscillation of the voltage reflection wave to the peak portion of the fall. In these T to 5 / 4T ranges, a double pulsing effect may occur in case of an error in the application of line voltage in the following state, which is a relatively less safe area.

[0098] Accordingly, the control unit (260) controls the oscillation of the voltage reflection wave of the previous state from 3 / 4T to 5 / 4T (e.g., 3t). p 5 tons p ) so that the line voltage is applied in the safety zone corresponding to , more preferably 3 / 4T to T (e.g. 3t p 4 tons p ) can be controlled so that the line voltage of the following state is applied to a very safe area corresponding to:

[0099] To this end, the control unit (260) controls to increase or decrease the application time for the current state, thereby controlling the pulse of the line voltage of the next state to be applied within the safe area. At this time, since the application time for the current state is determined by comparing the command voltage related to the line voltage with a triangle wave, the control unit (260) can control the application time by adjusting the size of the command voltage.

[0100] For example, the control unit (260) has an authorization time of 4t, which is a period (T). p A multiple of (i.e. T is 4mt) p It can be determined whether it corresponds to , but m is a natural number greater than or equal to 1. If 4t p If it is a multiple of , a very safe area is 3 / 4T to T (e.g. 3t p 4 tons p ), the control unit (260) sets the corresponding authorization time to T / 4 (e.g., 1t). p ) can be controlled so that the line voltage of the next state is applied within the safe area. On the other hand, 4t p If it is not a multiple of , the control unit (260) increases the authorization time so that the authorization time is 4t. p Then, make it a multiple of 4t p By reducing the applied time, which is a multiple of T / 4 (e.g., 1tp), the line voltage of the next state can be controlled to be applied in a very safe area.

[0101] Of course, the control unit (260) can determine whether the line voltage of the next state is applied to a safe area or a dangerous area by comparing the period (T) of the oscillation of the voltage reflection wave with the application time for the current state.

[0102] At this time, when the line voltage of the next state is applied to the danger zone, the control unit (260) controls to increase or decrease the application time for the current state so that the pulse of the line voltage of the next state can be applied in the safe zone.

[0103] Of course, in S330, if it is determined that the line voltage of the next state is applied in the safe area, the control unit (260) can control the line voltage of the next state to be applied after maintaining the original application time without adjusting the application time.

[0104] In this way, by controlling the application time, etc., when the next state line voltage is applied in the safe area, the oscillation of the voltage reflection wave according to the current state line voltage and the oscillation of the pulse according to the next state line voltage do not overlap in the same direction, so that the double pulsing effect does not occur.

[0105] Of course, it is desirable that the control according to the above-described S310 to S330 be performed for each line voltage according to the three phases (U, W, V).

[0106] The present invention, configured as described above, has the advantage of being able to avoid the occurrence of the double pulsing effect in the output of the inverter (200), thereby protecting the motor from damage caused by overvoltage due to the double pulsing effect. In addition, the present invention has the advantage of being able to avoid the occurrence of the double pulsing effect without adding separate hardware such as a filter, through a control method of adjusting the application time of the output voltage of the inverter (200) according to the oscillation period of the voltage reflection wave. Accordingly, the present invention can implement a double pulsing effect avoidance technology that can be applied to various system environments without increasing the volume, weight, and cost of the inverter (200), and as a result, can solve the problems of the prior art.

[0107] While the detailed description of the present invention has described specific embodiments, it should be understood that various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention is not limited to the described embodiments, but should be determined by the claims and their equivalents.

Claims

A control method performed in a control device of an inverter before the line voltage for the three-phase voltage output from the inverter to the motor is switched from the first state to the second state, A step of determining the period (T) of oscillation of the voltage reflection wave for the first state; A step of determining the authorization time for the first state; and A control method comprising: a step of controlling the line voltage of the second state to be applied within a safe range of oscillation of the voltage reflection wave based on the above period (T) and the above application time. In the first paragraph, The above first state is when the line voltage is high, The second state above is when the line voltage is low, and A control method in which the above safety zone is a time zone in which the voltage of the voltage reflection wave rises. In the first paragraph, The above first state is when the line voltage is low, The second state is when the line voltage is high, and A control method in which the above safety zone is a time zone in which the voltage of the voltage reflection wave decreases. In the first paragraph, A control method in which the above-mentioned safe zone is a zone included in the oscillation cycle of the voltage reflection wave, from 3 / 4T to 5 / 4T. In the first paragraph, The above period (T) is the propagation time (t) of the line through which the three-phase voltage is transmitted. p ) Control method equivalent to 4 times that of the previous method. In the first paragraph, A control method in which the step of determining the above-mentioned application time is performed in an area including each maximum point or each minimum point in a triangle wave for comparing the command voltage for the three phases. In the first paragraph, The above controlling step is a control method for controlling the line voltage of the next state to be applied within a safe area by adjusting the application time to increase or decrease. In paragraph 7, The above controlling step is a control method for controlling the application time by controlling the magnitude of the command voltage related to the line voltage. In the first paragraph, The above controlling step is, A step of determining whether the above-mentioned authorization time is a multiple of the above-mentioned period (T), and then adjusting the above-mentioned authorization time to be reduced by T / 4 if it is a multiple of the above-mentioned period (T); and A control method including a step of increasing the authorization time so that the authorization time becomes a multiple of the period (T) when it is not a multiple of the period (T), and then reducing it by T / 4. As a control device for the inverter, memory; and A processor that performs control to prevent overvoltage before the line voltage of the three-phase voltage output from the inverter to the motor switches from the first state to the second state using information stored in the memory; The above processor, A control device that controls to determine the period (T) of the oscillation of the voltage reflection wave for the current state, controls to determine the application time for the first state, and controls to apply the line voltage of the second state within the safe range of the oscillation of the voltage reflection wave based on the period (T) and the application time. In Article 10, The above first state is when the line voltage is high, The above second state is when the line voltage is low, The above processor is a control device that controls the line voltage of the next state to be applied in the safe region corresponding to the time region in which the voltage of the voltage reflection wave rises. In Article 10, The above first state is when the line voltage is low, The above second state is when the line voltage is high, The above processor is a control device that controls the line voltage of the next state to be applied in the safe region corresponding to the time region in which the voltage of the voltage reflection wave decreases. In Article 10, The above processor is a control device that controls the line voltage of the next state to be applied in the safe area included in 3 / 4T to 5 / 4T of the oscillation cycle of the voltage reflection wave. In Article 10, The above processor is configured such that the period (T) is the propagation time (t) of the line through which the three-phase voltage is transmitted. p ) is determined to be four times that of the control device. In Article 10, The above processor is a control device that controls to determine the application time in an area including each maximum point or each minimum point in a triangle wave for comparing the command voltage for the three phases. In Article 10, The above processor is a control device that controls the line voltage of the next state to be applied within a safe area by controlling the application time to increase or decrease. In Article 16, The above processor is a control device that controls the application time by controlling the magnitude of the command voltage related to the line voltage. In Article 10, The above processor is a control device that determines whether the authorization time is a multiple of the period (T), and if it is a multiple of the period (T), adjusts the authorization time to be reduced by T / 4, and if it is not a multiple of the period (T), increases the authorization time so that the authorization time becomes a multiple of the period (T), and then adjusts the authorization time to be reduced by T / 4. A converter section that rectifies AC power and converts it into DC; A DC link capacitor that charges a DC voltage by smoothing the DC voltage rectified by the above converter unit; An inverter unit that converts the DC voltage charged in the capacitor into a three-phase AC voltage for providing the motor using a plurality of switching elements; and A control unit that controls the above-mentioned plurality of switching elements and performs control to prevent overvoltage before the line voltage for the three-phase AC voltage switches from the first state to the second state; The above control unit, An inverter that prevents overvoltage by determining a period (T) for oscillation of a voltage reflection wave for the first state, controlling the application time for the first state, and controlling the line voltage of the second state to be applied within a safe range of oscillation of the voltage reflection wave using the determined period (T) and the determined application time.

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