Voltage control device and voltage control method

Abstract

To provide a voltage control device and a voltage control method with which it is possible to smooth the magnetic flux amount in the device when controlling the device using the magnetic flux generated by application of AC voltage.SOLUTION: Provided is a voltage control device 10 for controlling output voltages by turning the switching elements 22A-24C of an inverter 20 on and off by control pulses in a system 100. The voltage control device comprises: a modulation wave generation unit that generates a sine wave based on drive voltage and drive frequency as a modulation wave; a computation unit that calculates, following the formula (1), the moving average value of a voltage [v] outputted in each time width [δ] smaller than the time period of the modulation wave at a given discrete time [t], at a time [t-Nδ to t-δ] tracing back to before N (positive integer) steps from the discrete time [t]; and a control pulse generation unit that generates a control pulse in accordance with the result of comparison of the moving average value with the instantaneous value of the modulation wave at the discrete time [t].SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a voltage control device and a voltage control method. [Background technology]

[0002] Rotating electric machines, invented in the 19th century, are now essential engineering devices for human activity. For example, Japan's annual electricity consumption is approaching 1,000 billion kWh, with more than 55% of that consumed by various motors. Furthermore, to realize a low-carbon society in the future, it is expected that electrification of transportation equipment will progress, not only for trains but also for cars, buses, trucks, ships, and aircraft. This means that the role of rotating electric machines will become increasingly important. Therefore, even a 1% improvement in the efficiency of rotating electric machines would have a significant effect on power savings.

[0003] To achieve the above-mentioned power saving effect, a highly efficient drive control technology for rotating electrical machines is essential. In recent years, inverters that generate AC voltage from DC voltage using semiconductor switches have been widely used as a drive control technology for rotating electrical machines. Furthermore, the PWM (Pulse Width Modulation) method is used as a method for generating this voltage. For example, a method that generates AC voltage using a pulsed voltage waveform generated by triangular wave comparison (comparison of a triangular carrier wave and a sinusoidal modulation wave) is used to drive rotating electrical machines such as motors. Many techniques for adjusting the waveform of inverter output voltage have been developed. For example, a PWM-controlled voltage-type inverter that can reduce waveform distortion of the inverter output voltage has been developed, in which an electric motor is driven by a three-phase AC voltage output that is pulse-width modulated using an instantaneous space vector method rather than a triangular wave (see, for example, Patent Document 1 below). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-337000 Summary of the Invention [Problem to be solved by the invention]

[0005] On the other hand, PWM waveforms are a method for generating pseudo-sine voltage waveforms. However, the electrical-mechanical energy conversion in rotating electrical machines is performed by a temporally and spatially controlled "magnetic flux," while torque is generated by a current. Therefore, even if the voltage waveform forms an ideal sine curve, the time harmonics of the PWM voltage waveform actually affect the electrical-mechanical energy conversion and torque generation, resulting in reduced efficiency, high starting current, and torque pulsation in rotating electrical machines. For this reason, there is a need to develop new pulse generation methods, such as PWM voltage waveforms, that suppress starting current and torque pulsation compared to the commonly used triangular wave comparison PWM when controlling AC rotating electrical machines.

[0006] In order to solve the above-mentioned problems, the present invention aims to provide a voltage control device and a voltage control method that can smooth the amount of magnetic flux within a device when controlling the device using magnetic flux generated by the application of an AC voltage. [Means for solving the problem]

[0007] The inventors noticed that the operation of moving average of output voltage obtains a quantity proportional to the "magnetic flux" in an AC rotating electric machine, and discovered that the moving average of output voltage can be used to smooth out the oscillations of the magnetic flux amount in an AC rotating electric machine by averaging it, leading to the present invention.

[0008] The present invention provides a voltage control device that controls an output voltage by turning on and off a switching element using a control pulse, and includes: a modulated wave generation unit that generates a sine wave based on a drive voltage and a drive frequency as a modulated wave; a calculation unit that calculates, at an arbitrary discrete time [t], a moving average value of a voltage [v] output for each time width [δ] smaller than the time period of the modulated wave over a time [t-Nδ to t-δ] going back from the discrete time [t] to N (positive integer) steps ago, in accordance with the following formula (1); and a control pulse generation unit that generates the control pulse in accordance with a comparison result between the moving average value and the instantaneous value of the modulated wave at the discrete time [t].

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[0009] According to the voltage control device of the present invention, the moving average value of the voltage [v] output for each time interval [δ] is compared with the instantaneous value of the modulated wave, which is a sine wave, and the output voltage can be controlled by turning on and off the switching elements using control pulses based on the comparison result. In this way, by using the comparison result between the moving average value of the output voltage and the instantaneous value of the modulated wave, which is a sine wave, it is possible to average out the oscillations of the magnetic flux amount in the AC rotating electric machine and smooth the magnetic flux amount in the rotating electric machine.

[0010] One aspect of the present invention provides a voltage control device in which the control pulse generating unit generates a control pulse that outputs a voltage of 0 when the moving average value is positive and greater than the instantaneous value of the modulated wave, a positive pulse voltage [+V0] when the moving average value is positive and smaller than the instantaneous value of the modulated wave, a negative pulse voltage [-V0] when the moving average value is negative and greater than the instantaneous value of the modulated wave, or 0 when the moving average value is negative and smaller than the instantaneous value of the modulated wave.

[0011] According to this aspect, the control pulse generator can generate control pulses that generate 0, a positive pulse voltage [+V0], or a negative pulse voltage [-V0] based on the comparison result between the moving average value of the output voltage and the instantaneous value of the modulated wave. In this way, by generating control pulses based on the comparison between the moving average value and the instantaneous value, it is possible to control the on / off of the switching elements so as to output a voltage that can smooth the amount of magnetic flux in the rotating electric machine.

[0012] The present invention provides a voltage control method for controlling an output voltage by turning a switching element on and off with a control pulse, which generates a sine wave based on a drive voltage and a drive frequency as a modulating wave, calculates a moving average of a voltage [v] output at any discrete time [t] for each time width [δ] smaller than the time period of the modulating wave over a time [t-Nδ to t-δ] going back from the discrete time [t] to N (positive integer) steps ago according to the following formula (1), and generates the control pulse according to a comparison result between the moving average and the instantaneous value of the modulating wave at the discrete time [t].

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[0013] According to the voltage control method of the present invention, the moving average value of the voltage [v] output for each time interval [δ] is compared with the instantaneous value of the modulated wave, which is a sine wave, and the output voltage can be controlled by turning on and off the switching elements using control pulses based on the comparison result. In this way, by using the comparison result between the moving average value of the output voltage and the instantaneous value of the modulated wave, which is a sine wave, it is possible to average out the oscillations of the magnetic flux amount in the AC rotating electric machine and smooth the magnetic flux amount in the rotating electric machine.

[0014] One aspect of the present invention provides a voltage control method that generates a control pulse that outputs a voltage of 0 when the moving average value is positive and greater than the instantaneous value of the modulated wave, a positive pulse voltage [+V0] when the moving average value is positive and smaller than the instantaneous value of the modulated wave, a negative pulse voltage [-V0] when the moving average value is negative and greater than the instantaneous value of the modulated wave, or 0 when the moving average value is negative and smaller than the instantaneous value of the modulated wave.

[0015] According to this aspect, the control pulse generator can generate control pulses that generate 0, a positive pulse voltage [+V0], or a negative pulse voltage [-V0] based on the comparison result between the moving average value of the output voltage and the instantaneous value of the modulated wave. In this way, by generating control pulses based on the comparison between the moving average value and the instantaneous value, it is possible to control the on / off of the switching elements so as to output a voltage that can smooth the amount of magnetic flux in the rotating electric machine.

[0016] Another aspect of the present invention is to provide a rotating electric machine, a ship, an automobile, or an aircraft, which includes the voltage control device described above. According to this aspect, by using the voltage control device or voltage control method described above, it is possible to manufacture a rotating electric machine, a ship, an automobile, or an aircraft with excellent energy efficiency. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a voltage control device and a voltage control method that can smooth the amount of magnetic flux in a device when controlling the device using magnetic flux generated by application of an AC voltage. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram showing a line voltage waveform in a conventional PWM method. [Figure 2] FIG. 2 is a schematic diagram showing a line voltage waveform in the voltage control device of the present embodiment. [Figure 3] 1 is a diagram illustrating an example of an overall configuration including a voltage control device according to an embodiment of the present invention. [Figure 4] FIG. 3 is a schematic diagram for explaining a moving average value Av(t) in the present embodiment. [Figure 5] 3 is a flowchart showing the flow of a voltage control method according to the present embodiment. [Figure 6] FIG. 1 is a frequency spectrum analysis diagram of a line voltage waveform during driving using a conventional PWM method (pseudo-sine wave output method: carrier frequency 1 kHz). [Figure 7] FIG. 10 is a frequency spectrum analysis diagram of a line voltage waveform during driving in the moving average method according to the present embodiment. [Figure 8] 10 is a graph showing the simulation results of motor characteristics when driven using a conventional PWM method (pseudo sine wave output method: carrier 1 kHz). [Figure 9] 10 is a graph showing simulation results of motor characteristics during driving using the moving average method in this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] The voltage control device and voltage control method of this embodiment will be described below with reference to the appropriate drawings. However, the present invention is not limited to the following embodiment. Furthermore, in the following description, the same or corresponding components will be given the same reference numerals, and their description may be omitted. In this specification, unless otherwise specified, the AC voltage applied to the rotating electric machine is a polyphase AC voltage (for example, a three-phase AC voltage), and unless otherwise specified, the voltage applied to the rotating electric machine means a "line voltage."

[0020] The voltage control device and voltage control method of this embodiment (hereinafter, these may be collectively referred to as "the voltage control device, etc. of this embodiment") can be suitably used in devices that use magnetic flux generated by the application of AC voltage, such as rotating electrical machines that utilize magnetic flux generated by an applied voltage. The voltage control device, etc. of this embodiment can be applied to PWM inverters, etc. that control the on / off of switching elements using control pulses to control the output voltage. However, the control pulses formed by the voltage control device, etc. of this embodiment are not limited to PWM pulses.

[0021] The voltage control device etc. of this embodiment compares the moving average value of a predetermined voltage [v] with the instantaneous value of the modulated wave, which is a sine wave, every time interval [δ] (for example, δ = 0.1 msec for a drive frequency (50 Hz)) which is sufficiently smaller than the time period of the modulated wave, and controls the output voltage by turning on and off a switching element using a control pulse based on the comparison result. If we interpret the voltage control device etc. of this embodiment from a physical perspective, first, the operation of taking the moving average of the voltage [v] output every time interval [δ] is equivalent to obtaining a quantity proportional to the "magnetic flux" in a rotating electric machine such as a motor to which voltage is applied. The voltage control device etc. of this embodiment uses the moving average of the voltage to generate a pulse pattern, and hereinafter, the method of controlling the output voltage using the moving average of the voltage [v] may be referred to as the "moving average method."

[0022] More specifically, electrical-mechanical energy conversion in rotating electrical machines and the like is achieved not directly by controlling voltage but by controlling magnetic flux. In other words, voltage is necessary to realize magnetic flux within rotating electrical machines and the like, but voltage does not directly cause electrical-mechanical energy conversion in rotating electrical machines and the like. For this reason, in voltage control devices and the like used in rotating electrical machines and the like, it is more important to make the spatial distribution of magnetic flux a sine wave with few harmonic components than to make the voltage waveform a sine wave with few harmonic components.

[0023] For example, Figure 1 shows the line voltage waveform (carrier 1 kHz) obtained in the conventional PWM method from the simulation results when driven under the conditions described below. As shown in Figure 1, in the conventional PWM method, the duty ratio is adjusted to control the line voltage waveform so that it becomes a sine wave with few harmonic components. For this reason, in the conventional PWM method, voltage is output according to a sine wave waveform, and no voltage with reversed polarity is applied in any of areas A, B, and C, for example.

[0024] In contrast, FIG. 2 shows a line voltage waveform in the voltage control device, etc. of this embodiment, obtained from a simulation result when driven under the conditions described below. In the voltage control device, etc. of this embodiment, the output voltage is controlled by the moving average method, and as shown in FIG. 2, it cannot be said that the waveform of the line voltage is a sine wave with few harmonic components. For example, in FIG. 2, there are regions such as regions A', B', and C' where positive and negative voltages are mixed and do not conform to a sine wave. In this way, in the voltage control device, etc. of this embodiment, the output voltage is not a sine wave with few harmonic components, but the moving average method is used to make the spatial distribution of magnetic flux in the rotating electric machine, etc., a sine wave with few harmonic components.

[0025] Faraday's law supports the idea that the moving average method can convert the spatial distribution of magnetic flux in rotating electrical machines and other devices into a sine wave with few harmonic components. According to Faraday's law, the time derivative of magnetic flux linkage is voltage, and conversely, the time integral of voltage is the magnetic flux linkage. Therefore, by using the PWM pulse width to change the magnetic flux that gives the magnetic flux linkage, the magnetic flux can be changed into a pseudo-sine wave. For example, according to Faraday's law, the relationship between induced electromotive force (e) and magnetic flux linkage (Ψ) is expressed as in equation (A) below. In other words, by integrating the induced electromotive force (e), the magnetic flux linkage (Ψ) in a rotating electrical machine can be calculated as shown in equation (B) below.

[0026]

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[0027]

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[0028] On the other hand, the moving average value Av of the voltage [v] outputted for each time interval [δ], over the time going back N (positive integer) steps from the discrete time [t], i.e., [t-Nδ to t-δ], is obtained by integrating the voltage [v] for each time interval [δ] and dividing the obtained value by N, according to the above-mentioned formula (1). Therefore, the obtained moving average value Av corresponds to the value obtained by dividing the flux linkage (Ψ) obtained by the above-mentioned formula (B) by Nδ. In other words, the moving average value Av of the voltage obtained in the voltage control device etc. of this embodiment corresponds to the moving average value of the flux linkage (Ψ) generated by the induced electromotive force (e) in the rotating electric machine.

[0029] In this way, by using the moving average method to compare the moving average value of a predetermined voltage [v] with the instantaneous value of the modulated wave, which is a sine wave, and controlling the output voltage by turning on and off switching elements using control pulses based on the comparison result, the moving average of the output voltage can be adjusted, and as a result, the oscillations (fluctuations) of the magnetic flux amount in a rotating electric machine or the like can be smoothed by averaging, and the spatial distribution of the magnetic flux in the rotating electric machine or the like can be made into a sine wave with few harmonic components. In other words, the operation of taking the moving average of the voltage [v] output per time width [δ] in the voltage control device or the like of this embodiment corresponds to smoothing the oscillations of the magnetic flux amount by averaging.

[0030] As described above, the magnetic flux in a rotating electric machine or the like is responsible for the essence of electrical-mechanical energy conversion. Therefore, according to the voltage control device or the like of this embodiment, by making the spatial distribution of the magnetic flux in the rotating electric machine or the like a sine wave with few harmonic components, it is possible to suppress the primary current and torque pulsation, and furthermore, to suppress the starting current.

[0031] [Voltage control device] An example of a voltage control device according to this embodiment will be described below with reference to FIG. 3. FIG. 3 is a diagram showing an example of an overall configuration including a voltage control device according to this embodiment. In FIG. 3, a system 100 is an example in which the load is an AC motor, and is configured to include an inverter 20, a motor 30, and a direct current (DC) power supply 40. The inverter 20 is also equipped with a voltage control device 10.

[0032] The voltage control device 10 includes a modulated wave generating unit 12, a calculation unit 14, and a control pulse generating unit 16, and controls the on / off of the switching elements 22A to 22C and the switching elements 24A to 24C of the inverter 20 by the control pulses.

[0033] The modulated wave generating unit 12 generates a sine wave based on the drive voltage and drive frequency as a modulated wave. The modulated wave generating unit 12 may generate a modulated wave based on the drive voltage and drive frequency when driving the system 100, or may generate a modulated wave according to the drive voltage and drive frequency when outputting a control pulse.

[0034] The calculation unit 14 calculates the moving average value of the voltage [v] output at any discrete time [t] for each time width [δ] smaller than the time period of the modulated wave, over a time period [t-Nδ to t-δ] going back N (positive integer) steps from the discrete time [t], according to the following formula (1). Hereinafter, the moving average value of the voltage [v] at the discrete time [t] may be referred to as the "moving average value Av(t)".

[0035]

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[0036] The voltage control device 10 outputs a control pulse to the inverter 20, for example, every 0.1 msec. The arbitrary discrete time (t) is not particularly limited, but is preferably an integer multiple of the time width [δ], and corresponds to the time at which the control pulse is transmitted. The calculation unit 14 calculates a moving average value for each time width [δ] according to equation (1).

[0037] The control pulse generating unit 16 generates a control pulse in response to a comparison result between the moving average value calculated by the calculation unit and the instantaneous value of the modulated wave at discrete time [t]. The instantaneous value of the modulated wave at discrete time [t] is the voltage at discrete time [t] of the sine wave generated as a modulated wave by the modulated wave generating unit 12 (hereinafter, the instantaneous value of the modulated wave at discrete time [t] may be referred to as the "instantaneous value S(t)").

[0038] The control pulse generating unit 16 generates a control pulse that outputs "0" when the moving average value Av(t) is positive and greater than the instantaneous value S(t) of the modulated wave, a positive pulse voltage [+V0] when the moving average value Av(t) is positive and smaller than the instantaneous value S(t), a negative pulse voltage [-V0] when the moving average value Av(t) is negative and greater than the instantaneous value S(t), or 0 when the moving average value Av(t) is negative and smaller than the instantaneous value S(t), as shown in the table below. The positive pulse voltage [+V0] and the negative pulse voltage [-V0] are DC voltages determined by the inverter 20 and the DC power supply 40 and are used to drive the motor 30.

[0039] [Table 1]

[0040] The voltage control device 10 can be configured with a control circuit including a CPU (central processing unit) 17, an interface (I / F) 18, and a memory 19, and can be configured based on a circuit for a specific application, such as an ASIC (application-specific integrated circuit). Although not particularly limited, the CPU 17 functions as the modulated wave generator 12, the arithmetic unit 14, and the control pulse generator 16. The interface 18 outputs pulse signals for controlling the switching elements 22A-22C and 24A-24C of the inverter 20 in response to control signals transmitted from the CPU 17. The memory 19 includes a read-only memory (ROM) or random access memory (RAM) that serves as a main storage unit, and a volatile or nonvolatile memory that serves as an auxiliary storage unit. The memory 19 can store the modulated wave generated by the modulated wave generator 12, the voltages [v] output for each time interval [δ], and the like.

[0041] A method for calculating the moving average value of the voltage [v] output for each time interval [δ] in this embodiment will be described with reference to FIG. 4. FIG. 4 is a schematic diagram for explaining the moving average value Av(t) in this embodiment. As described above, the calculation unit 14 calculates the moving average value Av(t) at the current time (discrete time [t]) to transmit a control pulse. The moving average value Av(t) is obtained by integrating the voltage [v] output for each time interval [δ] over a period [t-Nδ to t-δ] going back a predetermined N steps from the discrete time [t] and dividing the result by N. As shown in FIG. 4, for example, if N=6, the voltage [v] from time interval δ1 to time interval δ6 is integrated. In FIG. 4, the voltage [v] is output six times within the N steps. Specifically, a positive voltage [+V0] is output four times in time intervals δ1, δ3, δ4, and δ6, and a negative voltage [-V0] is output once in time interval δ5. Furthermore, the output voltage becomes "0" during the time interval δ2 as shown in Figure 4. For example, if the time interval [δ] is 0.1 msec and |V0| is 300 V, the moving average value Av(t) is (300 × 4 - 300 × 1 + 0 × 1) / 6 = 150 (V).

[0042] Next, the control pulse generation unit 16 determines the instantaneous value S(t) of the modulated wave at discrete time [t] based on the sine wave generated as a modulated wave by the modulated wave generation unit 12, and compares it with the moving average value Av(t). As described above, if the moving average value Av(t) is 150 V (i.e., moving average value Av(t) > 0), for example, if the instantaneous value S(t) is greater than 150 V, the control pulse generation unit 16 sets the output voltage at discrete time [t] to "0." On the other hand, if the instantaneous value S(t) is less than 150 V, the control pulse generation unit 16 sets the output voltage at discrete time [t] to "+V0." Furthermore, if the moving average value Av(t) is smaller than 0 (e.g., −150 V), and if the instantaneous value S(t) is greater than −150 V, the control pulse generation unit 16 sets the output voltage at the discrete time [t] to “+V0.” If the instantaneous value S(t) is smaller than −150 V, the control pulse generation unit 16 sets the output voltage at the discrete time [t] to “0.” Note that, although not particularly limited, when the moving average value Av(t) = the instantaneous value S(t) or when the moving average value Av(t) = 0, the control pulse generation unit 16 can set the output voltage to “0” at the discrete time [t]. However, this embodiment is not limited to this example. For example, the output voltage may be controlled to +V0 or −V0 based on “0” and depending on the trend of the voltage waveform before time t (e.g., whether the voltage is rising or falling).

[0043] In the voltage control device of this embodiment, the time width [δ] can be set without any particular limitation as long as it is a time width sufficiently smaller than the time period of the modulated wave (for example, 20 msec when the drive frequency is 50 Hz), but from the viewpoint of sampling theorem, it can be set, for example, to 0.001 msec to 10 msec, and preferably 0.01 msec to 0.1 msec. Furthermore, from the viewpoint of smoothing, the number N (an integer) of N steps for determining the moving average value of the voltage [v] can be set, for example, to 100 to 10,000, and preferably 2 to 100.

[0044] Furthermore, the time (interval) at which the voltage control device 10 outputs control pulses to the inverter 20 is not particularly limited, but the shorter the time, the finer the waveform can be with fewer harmonic components, but the number of times the semiconductor switch is switched increases, which may result in greater switching loss. Considering this point of view, the time (interval) at which the voltage control device 10 outputs control pulses to the inverter 20 can be set to, for example, 0.001 msec to 10 msec, and preferably 0.01 msec to 0.1 msec.

[0045] In this embodiment, the time width [δ] is a constant value (time) throughout the processing, and the |V0| applied to the motor 30 is also a constant value. However, the present invention is not limited to this, and for example, the applied |V0| may be configured to vary based on the comparison result between the moving average value and the instantaneous value, or may be finely controlled taking the duty ratio into consideration.

[0046] The inverter 20 is a PWM-controlled inverter including switching elements. To drive the motor 30, which is an AC rotating electric machine, using a DC power supply 40 that supplies DC voltage, the inverter 20 converts DC power into a three-phase AC voltage with a variable voltage and frequency based on control pulses output by the voltage control device 10. The inverter 20 includes switching elements 22A-22C and switching elements 24A-24C, and the on / off of each switching element is controlled based on the control pulses output by the voltage control device 10. The inverter 20 is connected to the stator windings of the motor 30 so as to be able to apply a drive voltage to each winding. The inverter 20 applies the converted three-phase AC voltage to the stator of the motor 30 as the drive voltage. The switching elements 22A-22C and switching elements 24A-24C are not particularly limited, but may be, for example, an insulated gate bipolar transistor (IGBT), which is a type of power semiconductor. In this embodiment, each switching element is provided with a freewheel diode, which is designed to return the back electromotive force generated when the switching element is turned off to the DC power supply 40.

[0047] The motor 30 is a three-phase, four-pole AC motor, and the rotor rotates when a three-phase AC voltage is applied to the stator. The motor 30 is not particularly limited, but from the viewpoint of fully utilizing the effects of suppressing primary current and torque pulsation and suppressing starting current by the voltage control device and the like of this embodiment, a rotating machine that drives with high efficiency can be suitably used. Examples of such rotating machines include the superconducting rotating machine described in International Publication WO 2009 / 116219, which is capable of induced rotation and synchronous rotation, has good heat dissipation, and is easy to capture magnetic flux for synchronous rotation.

[0048] As described above, the voltage control device of this embodiment controls the output voltage by turning on and off switching elements using control pulses. It includes a modulation wave generator that generates a sine wave based on a drive voltage and a drive frequency as a modulation wave, a calculation unit that calculates, in accordance with Equation (1), a moving average of a voltage (v) output at a given discrete time (t) for a time interval (δ) smaller than the time period of the modulation wave over a period (t-Nδ to t-δ) going back N (positive integer) steps from the discrete time (t), and a control pulse generator that generates the control pulse based on a comparison between the moving average and the instantaneous value of the modulation wave at the discrete time (t). This allows the voltage control device of this embodiment to smooth the magnetic flux within the rotating electric machine. This allows the voltage control device of this embodiment to suppress primary current and torque pulsation and starting current of the rotating electric machine.

[0049] [Voltage control method] The following describes a voltage control method of this embodiment, which controls output voltage by turning on and off a switching element with a control pulse. The method generates a sine wave based on a drive voltage and a drive frequency as a modulating wave, calculates a moving average of a voltage (v) output at any discrete time (t) for a time interval (δ) smaller than the time period of the modulating wave over a period (t-Nδ to t-δ) going back N (a positive integer) steps from the discrete time (t) in accordance with Equation (1), and generates the control pulse in accordance with a comparison between the moving average and the instantaneous value of the modulating wave at the discrete time (t). Figure 5 is a flowchart showing the flow of the voltage control method of this embodiment.

[0050] First, in the system 100, a modulated wave is generated in the modulated wave generating unit 12 to generate a control pulse for controlling the switching elements of the inverter 20 at any discrete time [t]. The modulated wave generating unit 12 generates a sine wave based on the drive voltage and drive frequency and stores it in the memory 19 (step S1). In this embodiment, in step S1, an instantaneous value S(t) of the modulated wave at the discrete time [t] is determined and stored in the memory 19. Note that in the second and subsequent processing, it is not necessary to generate a new modulated wave in step S1, and the instantaneous value S(t) can be determined based on the sine wave (modulated wave) stored in the memory 19.

[0051] Next, in the system 100, the calculation unit 14 calculates the moving average value Av(t) of the voltage [v] output every time interval [δ] for the time [t-Nδ to t-δ] going back N (positive integer) steps from the discrete time [t] in accordance with the above-mentioned formula (1) (step S2). Next, in the system 100, the control pulse generation unit 16 compares the moving average value Av(t) with the instantaneous value S(t) of the modulated wave (step S3). The control pulse generation unit 16 first compares the magnitudes of the moving average value Av(t) and the instantaneous value S(t) (step S4), and if the moving average value Av(t) is greater than the instantaneous value S(t) (YES in step S4), the system proceeds to step S5.

[0052] In step S5, the control pulse generating unit 16 determines whether the moving average value Av(t) is greater than 0. If the moving average value Av(t) is less than 0 (No in step S5), the process proceeds to step S7, where a control pulse is generated to set the voltage to "-V0", and the voltage control device 10 outputs a control pulse signal to the inverter 20.

[0053] In step S5, if the moving average value Av(t) is greater than 0 (YES in step S5), the process proceeds to step S8, where a control pulse for setting the voltage to "0" is generated and the voltage control device 10 outputs a control pulse signal to the inverter 20.

[0054] On the other hand, in step S4, if the moving average value Av(t) is smaller than the instantaneous value S(t) (step S4: No), the process proceeds to step S6, where the control pulse generator 16 determines whether the moving average value Av(t) is greater than 0. In step S6, if the moving average value Av(t) is greater than 0 (step S5: Yes), the process proceeds to step S9, where a control pulse is generated to set the voltage to "+V0", and the voltage control device 10 outputs a control pulse signal to the inverter 20.

[0055] In step S6, if the moving average value Av(t) is smaller than 0 (No in step S6), the process proceeds to step S8, where a control pulse for setting the voltage to "0" is generated and the voltage control device 10 outputs a control pulse signal to the inverter 20.

[0056] When the control pulse signals from steps S7 to S9 are input to the inverter 20, the on / off of the switching elements is controlled in accordance with these signals, and a voltage corresponding to each PWM signal is applied to the motor 30, thereby completing the processing at any discrete time [t].

[0057] In this embodiment, the moving average value Av(t) and the instantaneous value S(t) of the modulated wave are compared in magnitude in step S4, and then it is determined in steps S5 and S6 whether the moving average value Av(t) is greater than 0. However, the present invention is not limited to this configuration. After determining whether the moving average value Av(t) is greater than 0, the moving average value Av(t) and the instantaneous value S(t) of the modulated wave are compared in magnitude, and a control pulse signal is generated based on the comparison result. Furthermore, in this embodiment, it is determined whether the moving average value Av(t) is greater than 0 and the instantaneous value S(t) of the modulated wave, and whether the moving average value Av(t) is greater than 0. However, the present invention is not limited to this configuration. For example, the moving average value Av(t) may be compared with a numerical value or numerical range other than 0, or the difference between the moving average value Av(t) and the instantaneous value S(t) of the modulated wave may be used as the comparison target.

[0058] [effect] According to the system 100 configured as described above, the amount of magnetic flux in an AC rotating electric machine can be smoothed when controlling the rotating electric machine. As a result, the voltage control device etc. of this embodiment can suppress the primary current and torque pulsation of the rotating electric machine etc., as well as the starting current.

[0059] Furthermore, the voltage control device 10 configured as described above can be applied to devices that use magnetic flux generated by the application of AC voltage, such as rotating electrical machines such as motors, high-frequency transformers, electrolytic elements such as MEMS, etc. Furthermore, the system 100 can be widely applied to applications where rotating machines are used, such as automobiles (compact cars, medium-sized cars, and large cars such as buses and trucks), railways, submarines, aircraft, ships, and liquid circulation transfer pumps, and can be applied, for example, to the superconducting motor system described in International Publication WO2009 / 116219.

[0060] The validity of the voltage control device and voltage control method according to the present disclosure is shown below with reference to the results of a drive simulation (MATLAB® / Simulink® by MathWorks) of a three-phase cage induction motor carried out under the following conditions. (conditions) Inverter: Uses an inverter equipped with IGBT / diodes Switching time: 0 (ideal) Motor: Three-phase squirrel-cage type Rated power: 2.238kW Rated voltage: 220V Rated frequency: 60Hz Number of poles: 4 Load torque: 7Nm Drive frequency: 50Hz Drive voltage: 200V (effective value) Output: 1.1kW Moving average denominator [N] (number of steps: N=12) Moving average interval (δ): 0.1 msec

[0061] First, as shown in FIGS. 1 and 2 above, when comparing the line voltage waveform when a three-phase squirrel-cage induction motor is driven by the general PWM modulation method obtained based on the above conditions with the line voltage waveform when a three-phase squirrel-cage induction motor is driven by the voltage control method using the moving average method of this embodiment, it is found that the PWM waveform obtained by the voltage control method using the moving average method of this embodiment in FIG. 2 is slightly more distorted than the PWM waveform obtained by the general PWM modulation method in FIG. 1.

[0062] Similarly, Figures 6 and 7 show a line-to-line waveform frequency spectrum analysis diagram when a three-phase squirrel-cage induction motor is driven by a conventional PWM method (quasi-sine wave output method: carrier frequency 1 kHz), and a line-to-line waveform frequency spectrum analysis diagram when a three-phase squirrel-cage induction motor is driven by the voltage control method using the moving average method of this embodiment. As can be seen from a comparison of Figures 8 and 9, when comparing the line-to-line voltage waveform when a three-phase squirrel-cage induction motor is driven by a general PWM modulation method with the line-to-line waveform frequency spectrum analysis diagram when a three-phase squirrel-cage induction motor is driven by the voltage control method using the moving average method of this embodiment, it is clear that the line-to-line waveform frequency spectrum analysis diagram using the general PWM modulation method in Figure 6 and the line-to-line waveform frequency spectrum when using the voltage control method using the moving average method of this embodiment in Figure 7 show completely different waveforms.

[0063] Next, based on the above-mentioned conditions, simulation results of the rotor speed (unit: Hz), stator current Is (unit: A), rotor current Ir (unit: A), and electromagnetic torque Te (unit: N m) for the motor characteristics when driven by the conventional PWM method (pseudo-sine wave output method: carrier frequency 1 kHz) and the motor characteristics when driven by the moving average method of this embodiment are shown in FIGS. 8 and 9.

[0064] As shown in Figure 8, when a three-phase squirrel-cage induction motor is driven using a general PWM modulation method, the starting current reaches a maximum of approximately 43 A, and it can be seen that even after reaching a steady state (after approximately 0.5 seconds), oscillations remain in the waveforms of the electromagnetic torque Te and the stator current Is.

[0065] In contrast, as shown in Figure 9, when a three-phase squirrel-cage induction motor is driven using the voltage control method based on the moving average method of this embodiment, the maximum starting current is limited to approximately 36 A, significantly lower than the typical PWM modulation method (approximately 43 A). This suggests low loss and minimal impact of overcurrent on the inverter. Furthermore, after reaching a steady state (approximately 0.5 seconds), there is almost no disturbance in the waveform of the stator current Is, and the waveform of the electromagnetic torque Te is also almost free of pulsation. As mentioned above, although the PWM voltage waveform appears distorted, this is likely due to the smoothing of the magnetic flux, which plays a key role in electromechanical energy conversion, achieved by the moving average operation. Furthermore, the spatial distribution of the magnetic flux becomes a sine wave with fewer harmonic components when using the voltage control method based on the moving average method of this embodiment, as can be confirmed by the fact that the waveform of the stator current Is in Figure 9 is a sine wave with fewer harmonic components than that in Figure 8. Furthermore, since the stator current is a sine wave with few harmonic components (the spatial distribution of magnetic flux is a sine wave with few harmonic components), it is presumed that the rotor current Ir, electromagnetic torque Te, and rotational speed are stable.

[0066] Although various embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be modified without departing from the spirit of the present invention.

[0067] For example, in this embodiment, as one aspect of the present invention, an aspect has been described in which a two-level inverter that changes the output voltage to only two values, 0 or |V0|, according to the moving average value is targeted, but the present invention is not limited to this embodiment. For example, the present invention can also be targeted at an inverter with three levels (for example, an output voltage that can take 0, |V0 / 2|, |V0|) or more.

[0068] Furthermore, in this embodiment, as one aspect of the present invention, a PWM method for smoothing magnetic flux is used to generate PWM pulses that output a predetermined voltage along a time axis in accordance with a moving average value. However, the present invention is not limited to this embodiment, and can also be applied to a PAM method that changes the voltage amount in accordance with a moving average value or a PDM method that changes the pulse density. [Explanation of symbols]

[0069] 10: voltage control device, 12: modulated wave generating unit, 14: calculation unit, 16: control pulse generating unit, 17: CPU, 18: interface, 19: memory, 20: inverter, 22A, 22B, 22C, 24A, 24B, 24C: switching elements, 30: motor, 40: DC power supply, 100: system

Claims

1. A voltage control device that controls an output voltage by turning on and off a switching element using a control pulse, a modulated wave generating unit that generates a sine wave based on a drive voltage and a drive frequency as a modulated wave; A calculation unit that calculates a moving average value of a voltage [v] output at an arbitrary discrete time [t] for each time width [δ] smaller than the time period of the modulated wave, over a time [t-Nδ to t-δ] going back from the discrete time [t] to N (positive integer) steps before the discrete time [t] according to the following formula (1); a control pulse generating unit that generates the control pulse in accordance with a comparison result between the moving average value and an instantaneous value of the modulated wave at a discrete time [t]; A voltage control device comprising: [Equation 1]

2. The control pulse generating unit generates a pulse voltage of 0 when the moving average value is positive and larger than the instantaneous value of the modulated wave, and generates a pulse voltage [+V 0 ], when the moving average value is negative and is greater than the instantaneous value of the modulated wave, a negative pulse voltage [-V 0 2. The voltage control device according to claim 1, wherein when the moving average value is negative and smaller than the instantaneous value of the modulated wave, a control pulse is generated that outputs a voltage of 0.

3. A voltage control method for controlling an output voltage by turning on and off a switching element using a control pulse, comprising: A sine wave based on a drive voltage and a drive frequency is generated as a modulated wave, At any discrete time [t], a moving average value of the voltage [v] output for each time width [δ] smaller than the time period of the modulated wave is calculated for a time [t-Nδ to t-δ] going back from the discrete time [t] to N (positive integer) steps before the discrete time [t] according to the following formula (1): generating the control pulse in accordance with a comparison result between the moving average value and the instantaneous value of the modulated wave at a discrete time [t]; Voltage control method. [Equation 2]

4. When the moving average value is positive and is larger than the instantaneous value of the modulated wave, the value is 0. When the moving average value is positive and is smaller than the instantaneous value of the modulated wave, the value is a positive pulse voltage [+V 0 ], when the moving average value is negative and is greater than the instantaneous value of the modulated wave, a negative pulse voltage [-V 0 4. The voltage control method according to claim 3, further comprising generating a control pulse for outputting a voltage of 0 when the moving average value is negative and smaller than the instantaneous value of the modulated wave.

5. A rotating electric machine comprising the voltage control device according to claim 1 or 2.

6. A ship equipped with the voltage control device according to claim 1 or 2.

7. 3. An automobile equipped with the voltage control device according to claim 1 or 2.

8. An aircraft equipped with the voltage control device according to claim 1 or 2.

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