Power Conversion Equipment

Abstract

To make it possible to reduce harmonic currents and reduce losses occurring in an AC motor, and suppress the fluctuation of output torque, without increasing the complexity in pulse mode switching control.SOLUTION: An electric power conversion device 100 selects a pulse mode in accordance with a modulation factor α, outputs a carrier and a carrier peak value from the pulse mode and an angular frequency, executes one time only processing of selecting a 7-pulse mode after selecting a (9+6(k-1))-pulse mode (k is an integer of 1 or greater) while the modulation factor rises, and executes one time only processing of selecting a (9+6(k-1))-pulse mode after selecting the 7-pulse mode while the modulation factor falls. A waveform of the 7-pulse mode causes an OFF signal to be generated before and after a 120-degree phase, respectively. A waveform from 180 degrees to 360 degrees in phase is a waveform where an ON signal and the OFF signal are switched with each other in a waveform from 0 degree to 180 degrees in phase.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a power conversion device that converts DC power into AC power by switching switching elements based on pulse width modulation. [Background technology]

[0002] Conventionally, a method of controlling a power conversion device that drives an induction motor for an electric vehicle has often been used in which asynchronous control is performed when the vehicle is traveling at low speed, and synchronous control is performed when the vehicle is traveling at high speed.

[0003] Fig. 7 is a diagram showing an example of the configuration of a general power conversion device. As shown in Fig. 7, a power conversion device 90 includes a reactor 3, a capacitor 4, a power converter 5, a current detector 6, a current command generator 11, a voltage command generator 12, a voltage phase / angular frequency calculator 14, and a PWM signal generator 25.

[0004] The power converter 5 converts the DC power supplied from the DC power supply 2 into AC power in order to drive the AC motor 1 using the DC power supply 2. Specifically, the power converter 5 includes a switching element, and by switching the switching element, converts the DC power from the DC power supply 2 into AC power and supplies it to the AC motor 1. The switching of the power converter 5 can be performed by a PWM (Pulse Width Modulation) method in which a switching element is switched on and off by a PWM control signal with a different pulse width according to a comparison between a carrier and a control command.

[0005] The current command generating unit 11 generates a current command using at least the torque command.

[0006] The voltage command generating unit 12 generates a voltage command from the current command generated by the current command generating unit 11. Specifically, the voltage command generating unit 12 generates d-axis and q-axis voltage commands using the deviation between the current command from the current command generating unit 11 and the current value from the current detector 6.

[0007] A voltage phase / angular frequency calculation unit 14 calculates the voltage phase and angular frequency to be output from the power converter 5 using the voltage command from the voltage command generation unit 12 .

[0008] The PWM signal generating unit 25 generates a PWM signal using the voltage command generated by the voltage command generating unit 12 and the voltage phase and angular frequency calculated by the voltage phase / angular frequency calculating unit 14, and using a carrier such as a triangular wave.

[0009] The power converter 5 uses the PWM signal generated by the PWM signal generating unit 25 to switch the switching elements, thereby converting DC power into AC power and outputting it to the AC motor 1.

[0010] Generally, when the frequency of the output voltage of the AC power output from the power converter 5 exceeds a threshold value, the control is switched from asynchronous control to synchronous control such as 9 pulses or 15 pulses. Thereafter, for example, when the voltage command increases due to an increase in the speed of an electric vehicle having an AC motor 1 that outputs AC power, an overmodulation state occurs in which the amplitude of the modulated wave (dashed line in FIG. 8) exceeds the amplitude of the carrier (solid line in FIG. 8), as shown in FIG. 8. In the overmodulation state, pulses are missing, and the mode eventually becomes one-pulse mode. The one-pulse mode is a state in which one cycle of output voltage is generated by one pulse.

[0011] The current detector 6 converts the stator current of the AC motor 1 into a d-axis current id and a q-axis current iq, which are current components on the d-axis and q-axis in a rotating Cartesian coordinate system, and outputs them. When the AC motor 1 is an induction motor, the d-axis is generally defined as the direction of the secondary flux linkage vector of the AC motor 1, and when the AC motor 1 is a permanent magnet synchronous motor, the d-axis is generally defined as the N-pole direction of the permanent magnet of the rotor of the motor.

[0012] However, in the above-mentioned technique, as shown in FIG. 8, in an overmodulation region in which the amplitude of the modulated wave exceeds the amplitude of the carrier, loss in the AC motor 1 due to harmonic currents may become large.

[0013] Therefore, the invention described in Patent Document 1 prepares a table of pulse patterns capable of reducing harmonic currents in advance, and switches the pulse mode between 9-pulse mode, 7-pulse mode (P7-pulse mode), 5-pulse mode (N5-pulse mode), and 3-pulse mode (N3-pulse mode) according to the modulation rate, thereby reducing harmonic currents in the overmodulation region. Note that the 7-pulse mode, 5-pulse mode, and 3-pulse mode are states in which one cycle of output voltage is generated by 7, 5, and 3 pulses, respectively. In other words, the pulse mode is the number of pulses that constitute one cycle of the output voltage. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] JP 2020-137385 A Summary of the Invention [Problem to be solved by the invention]

[0015] However, in the invention described in Patent Document 1, since the carrier phase differs for each pulse mode, it is necessary to change the carrier frequency when switching the pulse mode. This may cause fluctuations in the torque output from the motor. In addition, since the carrier frequency is changed multiple times, the control becomes complicated.

[0016] In view of the above problems, an object of the present invention is to provide a power conversion device that can reduce harmonic currents and losses generated in an AC motor, while also preventing complicated control for switching pulse modes and suppressing fluctuations in output torque. [Means for solving the problem]

[0017] In order to solve the above problems, a power conversion device according to the present invention is a power conversion device that converts DC power to AC power by switching a switching element based on pulse width modulation, and includes: a current command generation unit that generates a current command using at least a torque command; a voltage command generation unit that generates a voltage command from the current command; a modulation factor calculation unit that calculates a modulation factor from the voltage command; a voltage phase / angular frequency calculation unit that calculates a voltage phase and angular frequency of an output voltage from the voltage command; and a PWM signal generation unit that generates a PWM signal from the modulation factor, the voltage phase, and the angular frequency, wherein the PWM signal generation unit changes a pulse mode, which is the number of pulses constituting one period of the output voltage, using the modulation factor and the angular frequency, changes a carrier frequency in accordance with the pulse mode, and generates a carrier; a modulated wave generation unit that calculates a modulated wave by referring to a modulated wave ratio calculation table using the modulation factor and the voltage phase, and compares the carrier with the modulated wave, and outputs the PWM signal to a power converter in accordance with a comparison result. the carrier generating unit comprises a pulse mode selector which selects the pulse mode in which a harmonic current becomes the lowest according to the modulation factor, and a carrier generator which outputs the carrier and a peak value of the carrier from the pulse mode and the angular frequency, the pulse mode selector executes only a process of selecting a (9+6(k-1)) pulse mode (k is an integer of 1 or more) and then selecting a 7-pulse mode once while the modulation factor is increasing, and executes only a process of selecting the 7-pulse mode and then selecting the (9+6(k-1)) pulse mode once while the modulation factor is decreasing, the waveform of the 7-pulse mode is a waveform which generates an ON signal between a phase of 30 degrees and 210 degrees in a 1-pulse mode, generates an ON signal before a phase of 30 degrees, generates an OFF signal after a phase of 30 degrees, and generates an OFF signal before and after a phase of 120 degrees, and the waveform between a phase of 180 degrees and 360 degrees is a waveform in which an ON signal and an OFF signal are swapped in a waveform between a phase of 0 degrees and 180 degrees.

[0018] Furthermore, in the power conversion device control device of the present invention, the modulated wave generating unit is further characterized in that it is further provided with a modulated wave ratio calculation table that pre-stores a correspondence between the pulse width at which the harmonic current is at its lowest for the modulation factor and the ratio of the modulated wave for outputting the pulse width to the peak value of the carrier, and converts the modulated wave calculated by the modulation factor calculation unit into a ratio to the peak value of the carrier, and a modulated wave calculator that calculates the modulated wave from the ratio converted by the modulated wave ratio calculation table and the peak value of the carrier generated by the carrier generating unit. Effect of the Invention

[0019] According to the present invention, by reducing the harmonic current in the region where an overmodulation state occurs, it is possible to reduce losses generated in an AC motor and to reduce fluctuations in output torque when switching pulse modes while simplifying control. [Brief description of the drawings]

[0020] [Figure 1] 1 is a diagram illustrating an example of the configuration of a power conversion device according to an embodiment of the present invention. [Diagram 2] 2 is a diagram illustrating an outline of a configuration example of a PWM signal generating unit illustrated in FIG. 1. [Diagram 3] 3 is a diagram illustrating an example of the configuration of a carrier generating unit illustrated in FIG. 2. [Figure 4] 3 is a diagram illustrating an example of the configuration of a modulated wave generating unit illustrated in FIG. 2. [Diagram 5] FIG. 11 is a diagram showing an example of a phase voltage waveform in the NP7 pulse mode as viewed from the neutral point. [Figure 6] 1 is a diagram comparing harmonic currents in the prior art with harmonic currents in the present embodiment; [Figure 7] FIG. 1 is a diagram illustrating an example of the configuration of a general power conversion device. [Figure 8] FIG. 13 is a diagram showing an overmodulation state in a 9-pulse mode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, a power conversion device 100 according to an embodiment of the present invention will be described with reference to the drawings. The same functional units as those of the power conversion device 90 described with reference to FIG. 7 are denoted by the same reference numerals, and the description thereof will be omitted. In addition, the power conversion device 100 according to this embodiment uses a triangular wave with a constant slope as a carrier, and can change the carrier frequency by changing the crest value of the carrier. In addition, the pulse mode of the synchronous control when the power conversion device 100 according to this embodiment switches from asynchronous control to synchronous control will be described as a 9-pulse mode.

[0022] FIG. 1 is a diagram showing an example of the configuration of a power conversion device 100 according to this embodiment.

[0023] As shown in Fig. 1, the power conversion device 100 includes a reactor 3, a capacitor 4, a power converter 5, a current detector 6, a current command generating unit 11, a voltage command generating unit 12, a modulation factor calculating unit 13, a voltage phase / angular frequency calculating unit 14, and a PWM signal generating unit 15. The power conversion device 100 converts DC power into AC power by switching a switching element based on pulse width modulation. The power conversion device 100 of this embodiment includes the PWM signal generating unit 15 instead of the PWM signal generating unit 25 in the conventional power conversion device 90 shown in Fig. 7, and further includes a modulation factor calculating unit 13 between the voltage command generating unit 12 and the PWM signal generating unit 15.

[0024] The modulation factor calculation unit 13 calculates a modulation factor α from the voltage command generated by the voltage command generation unit 12. Here, the modulation factor α is the ratio of the output voltage calculated from the voltage command when the possible output voltage in the one-pulse mode is set to 1.

[0025] A voltage phase / angular frequency calculation unit 14 calculates a voltage phase and an angular frequency from the voltage command generated by the voltage command generation unit 12 .

[0026] The PWM signal generating unit 15 generates a PWM signal from the modulation factor α calculated by the modulation factor calculating unit 13 and the voltage phase and angular frequency calculated by the voltage phase / angular frequency calculating unit 14. The PWM signal generating unit 15 outputs the PWM signal to the power converter 5.

[0027] FIG. 2 is a diagram showing an outline of a configuration example of the PWM signal generating unit 15. As shown in FIG.

[0028] The PWM signal generating unit 15 includes a carrier generating unit 151 , a modulated wave generating unit 152 , and a comparator 153 .

[0029] Carrier generating unit 151 uses modulation factor α calculated by modulation factor calculation unit 13 and the angular frequency generated by the voltage phase / angular frequency calculation unit to change the pulse mode, which is the number of pulses that constitute one cycle of the output voltage, and changes the carrier frequency according to the pulse mode to generate a carrier. Carrier generating unit 151 outputs the carrier to comparator 153.

[0030] The modulated wave generating unit 152 calculates a modulated wave by referring to a modulated wave ratio calculation table using the modulation factor α calculated by the modulation factor calculating unit 13 and the voltage phase calculated by the voltage phase / angular frequency calculating unit 14. The modulated wave generating unit 152 outputs the modulated wave to the comparator 153.

[0031] Comparator 153 compares the carrier generated by carrier generation unit 151 with the modulated wave generated by modulated wave generation unit 152, and outputs a PWM signal to power converter 5 according to the comparison result.

[0032] FIG. 3 is a diagram showing an example of the carrier generation unit 151. As shown in FIG.

[0033] The carrier generation unit 151 includes a pulse mode selector 154 and a carrier generator 155 .

[0034] The pulse mode selector 154 selects a pulse mode in which the harmonic current is the lowest according to the modulation factor α calculated by the modulation factor calculation unit 13. Specifically, the pulse mode selector 154 selects a 9-pulse or 7-pulse pulse mode according to the modulation factor α calculated by the modulation factor calculation unit 13, and outputs the selected pulse mode to the carrier generator 155. More specifically, the pulse mode selector 154 executes only a process of selecting the 9-pulse mode and then the 7-pulse mode once while the modulation factor α is increasing, and executes only a process of selecting the 7-pulse mode and then the 9-pulse mode once while the modulation factor α is decreasing. A specific method in which the pulse mode selector 154 selects the pulse mode will be described in detail later.

[0035] Carrier generator 155 outputs a carrier and a peak value of the carrier from the pulse mode selected by pulse mode selector 154 and the angular frequency calculated by voltage phase / angular frequency calculation unit 14. Specifically, carrier generator 155 generates a carrier from the pulse mode and angular frequency, outputs it to comparator 153, and also calculates the peak value of the carrier and outputs it to modulated wave generation unit 152.

[0036] 4 is a diagram showing an example of the modulated wave generating unit 152. The modulated wave generating unit 152 includes a modulated wave ratio calculation table 156 and a comparison value calculator 157.

[0037] The modulation wave ratio calculation table 156 stores the ratio of the modulation wave for outputting the pulse width at which the harmonic current is minimum to the peak value of the carrier in advance in correspondence with the modulation factor α (comparison value in FIG. 4), and converts the modulation factor calculated by the modulation factor calculation unit 13 to the ratio to the peak value of the carrier. Specifically, the modulation wave ratio calculation table 156 stores the ratio to the peak value of the carrier in advance in correspondence with the modulation factor α calculated by the modulation factor calculation unit 13 and the voltage phase calculated by the voltage phase / angular frequency calculation unit 14. Then, the modulation wave ratio calculation table 156 calculates the ratio of the peak value of the modulated wave to the peak value of the carrier using the modulation factor α calculated by the modulation factor calculation unit 13 and the voltage phase calculated by the voltage phase / angular frequency calculation unit 14, and outputs it to the modulation wave calculator 157.

[0038] The modulated wave calculator 157 calculates the modulated wave from the ratio of the peak value of the modulated wave to the peak value of the carrier converted by the modulated wave ratio calculation table 156 and the peak value of the carrier generated by the carrier generating unit 151. The modulated wave calculator 157 outputs the modulated wave to the comparator 153.

[0039] Next, a method of calculating the pulse mode switching point and the modulated wave ratio used in pulse mode selector 154 and modulated wave ratio calculation table 156 will be described.

[0040] When the power conversion device 100 of this embodiment switches from asynchronous control to synchronous control, the synchronous control uses a 9-pulse mode in which control is performed with 9 pulses in one period. Therefore, in order to reduce harmonic currents, the power conversion device 100 of this embodiment reduces harmonic currents by introducing multiple pulses between the 9-pulse mode and the 1-pulse mode.

[0041] Possible pulses that can be introduced between 9 pulses and 1 pulse are 7 pulses, 5 pulses, and 3 pulses. Here, we consider inserting 0 vectors at two locations in the 3-pulse mode (N3-pulse mode) in which no 0 vector is inserted. In other words, when the waveform in the 7-pulse mode is a waveform in which an ON signal is output between the phase of 30 degrees and 210 degrees in the 1-pulse mode, an ON signal is generated before the 30-degree phase, an OFF signal is generated after the 30-degree phase, and an OFF signal is generated before and after the 120-degree phase, respectively, and the waveform with a phase of 180 degrees to 360 degrees is a waveform in which the ON signal and the OFF signal are swapped in the waveform with a phase of 0 degrees to 180 degrees. The phase in which an OFF signal is generated before and after the 120-degree phase, respectively, has a phase width of θ with a phase of 120 degrees as the center. 071 In the following description, the phase width of the OFF signal is θ 072 In the following description, the 7-pulse mode generated in this way will be referred to as an NP 7-pulse mode.

[0042] FIG. 5 is a diagram showing an example of a phase voltage waveform at the neutral point in the NP7 pulse mode. In the NP7 pulse mode, as shown in FIG. 071 and θ 072 , and θ which is the phase width of the ON signal generated 30 degrees before the phase 070 By changing the three phases (pulse widths) of the θ 072 When it becomes 0, the waveform becomes N3 pulse mode.

[0043] First, from the phase voltage waveform shown in Figure 5, the variable pulse width θ 700 , θ 071 , and θ 072 By varying the above, the harmonic current is calculated.

[0044] Specifically, the phase voltage waveform shown in Fig. 5 is the U-phase voltage waveform v u The voltage waveform of U phase v u The waveform delayed 120 degrees from the V phase voltage waveform v v, U-phase voltage waveform v u The waveform delayed by 240 degrees from the W phase voltage waveform v w Then, a three-phase composite wave v is created using equation (1).

[0045]

number

[0046] The voltage waveform of the three-phase composite wave v is subjected to FFT (Fast Fourier Transform) analysis to calculate the peak value of the voltage of each order. The magnitude of the harmonic current is calculated by calculating the square root of the sum of the squares of the values ​​obtained by dividing the peak value of the voltage of each order by the respective orders. The magnitude of the harmonic current calculated at this time is calculated as a ratio with the magnitude of the harmonic current in one pulse mode taken as 1. At this time, the modulation factor α is also derived. Then, the above-mentioned pulse width θ 700 , θ 071 , and θ 072 By changing the modulation factor α, the pulse width θ 700 , θ 071 , and θ 072 is derived.

[0047] The solid line in Fig. 6 indicates the harmonic current value according to the modulation factor α in the power conversion device 100 of this embodiment. The dashed line in Fig. 6 indicates the change in the harmonic current value when the power conversion device 90 in the conventional technology (specifically, the technology described in Patent Document 1) changes the pulse mode. In Fig. 6, when the modulation factor α becomes from less than 0.7 to 0.7 or more, the 9-pulse mode is switched to the NP7-pulse mode. Then, when the modulation factor α is 0.87 or more, the harmonic current becomes larger than that of the conventional technology, and at 0.98, the harmonic current is equivalent to that of the conventional technology.

[0048] The power conversion device 100 of the present embodiment can reduce harmonic current more than the conventional power conversion device 90 by switching from the 9-pulse mode to the NP7 pulse mode at a modulation factor α that is about 8% lower than when the power conversion device 90 of the conventional technology switches from the 9-pulse mode to the P7 pulse mode. In the process of accelerating an electric vehicle driven by AC power converted by the power conversion device 100, the time during which the modulation factor α is 0.87 or more and less than 0.98 and the harmonic current is higher than that of the conventional technology is short. Therefore, in the present embodiment, even during the time during which the harmonic current in the acceleration process is higher than that of the conventional technology, the power conversion device 100 continues to use the NP7 pulse mode, thereby reducing the number of switching controls and avoiding the execution of complicated control.

[0049] In addition, as described above, θ 072 By setting to 0, the NP7 pulse mode becomes the N3 pulse mode. Therefore, the power conversion device 100 of the present embodiment can switch the pulse mode by changing only the modulated wave without changing the carrier, and can switch continuously without requiring complicated control.

[0050] Considering the above, the power conversion device 100 of this embodiment can reduce harmonic current in the region where overmodulation occurs while avoiding or reducing fluctuations in output torque by simple control of switching from the 9-pulse mode to the NP7-pulse mode, thereafter continuously changing the output according to the modulation factor α, and transitioning to the N3-pulse mode when the 0 vector disappears. As shown in FIG. 3, the pulse mode selector 154 is set with the switching points of the pulse mode derived as described above (from 9-pulse to NP7-pulse mode, from NP7-pulse mode to 9-pulse mode). Also, as shown in FIG. 4, the modulation wave ratio calculation table 156 of FIG. 4 is set with information indicating the pulse width at which the harmonic current is at its lowest.

[0051] In the above-described embodiment, an example of introducing the NP7 pulse mode between the 9-pulse mode and the 1-pulse mode has been described. However, by using a semiconductor element having a wide band gap such as silicon carbide (SiC) to reduce switching losses, the power conversion device 100 is not limited to 9 pulses, and can also reduce harmonic currents in the region where the modulation factor α is lower than 0.7 by switching from a (9+6(k-1)) pulse mode (k is an integer equal to or greater than 1) (e.g., 15-pulse mode, 21-pulse mode) to the NP7 pulse mode.

[0052] As described above, by introducing the pulse mode in the region where the overmodulation state occurs after switching to the synchronous control mode, it is possible to reduce harmonic currents. The reduction in harmonic currents makes it possible to reduce losses generated in the AC motor.

[0053] Although the invention has been described, it is to be understood that these embodiments are presented as examples and are not intended to limit the scope of the invention. [Industrial Applicability]

[0054] The present invention is useful for electric vehicles that are driven by AC power converted by a power conversion device. [Explanation of symbols]

[0055] 1 AC motor 2 DC power supply 3 Reactor 4 Capacitors 5. Power Converter 6 Current detector 11 Current command generation section 12 Voltage command generator 13 Modulation rate calculation section 14 Voltage phase and angular frequency calculation section 15 PWM signal generation section 100 Power conversion device 151 Carrier Generation Unit 152 Modulation wave generator 153 Comparator 154 Pulse mode selector 155 Carrier Generator 156 Modulation Wave Ratio Calculation Table 157 Modulation Wave Calculator

Claims

1. A power conversion device that converts DC power into AC power by switching a switching element based on pulse width modulation, a current command generating unit that generates a current command using at least a torque command; a voltage command generating unit that generates a voltage command from the current command; a modulation factor calculation unit that calculates a modulation factor from the voltage command; a voltage phase and angular frequency calculation unit that calculates a voltage phase and an angular frequency of an output voltage from the voltage command; a PWM signal generating unit that generates a PWM signal from the modulation factor, the voltage phase, and the angular frequency, The PWM signal generating unit a carrier generating unit that uses the modulation rate and the angular frequency to change a pulse mode, which is the number of pulses that constitute one cycle of the output voltage, changes a carrier frequency in accordance with the pulse mode, and generates a carrier; a modulated wave generating unit that calculates a modulated wave by referring to a modulated wave ratio calculation table using the modulation factor and the voltage phase; a comparator that compares the carrier with the modulated wave and outputs the PWM signal to a power converter according to a comparison result; The carrier generating unit includes: a pulse mode selector that selects the pulse mode that minimizes the harmonic current in response to the modulation factor; a carrier generator that outputs the carrier and a peak value of the carrier based on the pulse mode and the angular frequency, the pulse mode selector executes only a process of selecting a (9+6(k-1)) pulse mode (k is an integer equal to or greater than 1) and then a 7-pulse mode once while the modulation rate is increasing, and executes only a process of selecting the (9+6(k-1)) pulse mode and then a 7-pulse mode once while the modulation rate is decreasing; A power conversion device characterized in that the waveform in the 7-pulse mode is a waveform in which an ON signal is generated between a phase of 30 degrees and 210 degrees in a 1-pulse mode, an ON signal is generated before a phase of 30 degrees, an OFF signal is generated after a phase of 30 degrees, and an OFF signal is generated both before and after a phase of 120 degrees, and a waveform from a phase of 180 degrees to 360 degrees is a waveform in which the ON signal and the OFF signal are swapped in a waveform from a phase of 0 degrees to 180 degrees.

2. The modulated wave generating unit includes: a modulation wave ratio calculation table that stores in advance a pulse width at which a harmonic current is at a minimum for the modulation factor and a ratio of a modulation wave for outputting the pulse width to a peak value of the carrier in correspondence with each other, and converts the modulation factor calculated by the modulation factor calculation unit into a ratio to the peak value of the carrier; a modulated wave calculator that calculates the modulated wave from the ratio converted by the modulated wave ratio calculation table and a peak value of the carrier generated by the carrier generation unit; The power conversion device according to claim 1 , further comprising:

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