Power conversion method and power conversion device

Abstract

To provide a power conversion method for achieving PWM control for suppressing a ripple current of one smoothing capacitor shared by each switching circuit in an electric power conversion device for performing power control of three or more AC motors, and to provide the electric power conversion device.SOLUTION: Provided is a power conversion method executed in an electric power conversion device including: a switching circuit connected with each of three or more AC motors; a power storage element provided parallel to a DC terminal of the switching circuit; and a control section for performing PWM control individually using each carrier wave with the same carrier frequency with respect to each switching circuit. The power conversion method determines a mutual phase difference between the carrier waves on the basis of a direction of torque output by each AC motor.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a power conversion method and a power conversion device. [Background technology]

[0002] Patent Document 1 discloses one aspect of PWM (Pulse Width Modulation) control of a power conversion device that adjusts the power supplied to a three-phase AC motor. In particular, Patent Document 1 discloses control of a power conversion device in which switching circuits (inverters) that control two AC motors share a single smoothing capacitor. When such a circuit configuration is adopted, ripple currents generated in the smoothing capacitor due to the operation of each switching circuit overlap, causing heat generation and noise vibration.

[0003] In contrast to this, in Patent Document 1, the ripple current generated in the smoothing capacitor is reduced by appropriately adjusting the phase difference (carrier phase difference) between the carrier waves used to generate the PWM signals of the respective switching circuits. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-300800 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the power conversion device of Patent Document 1 is premised on power control for two AC motors, and is not intended to be applied to a motor control system that controls the power of three or more AC motors.

[0006] Therefore, an object of the present invention is to realize PWM control capable of suppressing ripple current in one smoothing capacitor shared by each switching circuit in a power conversion device that controls the power of three or more AC motors. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a power conversion method executed in a power conversion device including switching circuits connected to three or more AC motors, storage elements provided in parallel with the DC ends of the respective switching circuits, and a control unit that performs PWM control individually on the respective switching circuits using carrier waves having the same carrier frequency. The phase currents of each AC motor are obtained, and the AC motor showing the largest phase current is determined as the reference motor. A reference phase, which is the phase of the carrier wave used for PWM control of the reference motor, is determined. One or more same-output torque direction motors that output torque in the same direction as the reference motor, and one or more different-output torque direction motors that output torque in a different direction are identified. A same-output torque direction phase, which is the phase of the carrier wave used for PWM control of the same-output torque direction motor, and a different-output torque direction phase, which is the phase of the carrier wave used for PWM control of the different-output torque direction motor, are determined. The same-output torque direction phase is determined to have a predetermined specified phase difference from the reference phase depending on the total number of reference motors and same-output torque direction motors, and the different-output torque direction phase is determined to be the same as the reference phase. [Effects of the Invention]

[0008] According to the above aspect, when adjusting the power of three or more electric motors while sharing one power storage element (smoothing capacitor), it is possible to suppress the ripple current occurring in the smoothing capacitor. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating the configuration of a motor control system to which a power conversion device according to an embodiment of the present invention is applied. [Figure 2] FIG. 2 is a block diagram illustrating the configuration of the PWM control device. [Figure 3] FIG. 3 is a flowchart illustrating the control logic for determining each carrier phase in each PWM control. [Figure 4A] FIG. 4A is a diagram for explaining the effects of the control logic of FIG. [Figure 4B] FIG. 4B is a diagram for explaining the effect of the control logic of FIG. [Figure 5] FIG. 5 is a diagram for explaining a specific application example of the control logic of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0011] [First embodiment] 1 is a diagram illustrating the configuration of a motor control system 100 to which a power conversion device 10 according to this embodiment is applied. The motor control system 100 is mounted on a vehicle (EV or hybrid vehicle) that is equipped with three or more AC motors as driving sources for traveling, or that is equipped with a total of three or more AC motors as driving sources for traveling and AC motors as generators.

[0012] As shown in the figure, the motor control system 100 mainly includes a power conversion device 10, a battery 12 as a DC power supply, a smoothing capacitor 14, and N motors M1 to M2 (N is a natural number of 3 or more). N and,

[0013] In the following, for the sake of simplicity, "m" will be used as a symbol representing any number between 1 and N.

[0014] The power conversion device 10 includes: m Switching circuit B functions as a power conversion circuit (inverter) according to the number of cm Each switching circuit B cm and the DC system including the battery 12 (i.e., each switching circuit B cm A smoothing capacitor 14 is provided at the DC end of each switching circuit B. cm It functions as a common smoothing storage element connected in parallel to the

[0015] Each switching circuit B cm is a three-phase bridge circuit consisting of multiple semiconductor switching elements provided for each phase (u phase, v phase, w phase). cm The driving circuit α ​​for driving each switching element is mThe driving circuit α m is a command (duty command signal D um ) and drives each of the switching elements in a switching pattern according to the command.

[0016] In particular, the PWM control device 50 controls the speed of each motor M m Phase current (i um ,i vm ,i wm ) and the detected values ​​of each motor M m The desired voltage command value (v um * ,v vm * ,v wm * ) based on the input signal, each switching circuit B cm A duty command signal D that defines the switching pattern in um and each driver circuit α m This outputs to each switching circuit B cm DC current I input / output from cm is adjusted. DC current I cm The positive and negative of each motor M m In particular, in this embodiment, the DC current I cm In the direction of the smoothing capacitor 14 (battery 12), cm (Each motor M m ) is positive, and each switching circuit B cm The direction from the center toward the smoothing capacitor 14 is defined as negative.

[0017] In particular, each motor M m When the motor M m When the output torque is positive, the DC current I cm is generally positive. m When regenerative operation (motor M m When the output torque is negative, the DC current I cm is generally negative.

[0018] In the following, for the sake of simplicity, "x" will be used as a symbol to represent one of the phases (u, v, w).

[0019] 2 is a block diagram illustrating the configuration of the PWM control device 50. The PWM control device 50 has a carrier wave clock generating unit 19, carrier signal generating units 20-m, and PWM signal generating units 22-m.

[0020] The carrier wave clock generating unit 19 generates a reference signal (reference clock) for synchronizing each PWM control, and outputs it to each carrier signal generating unit 20-m.

[0021] The carrier signal generating unit 20-m receives a reference signal as an input and generates a predetermined carrier frequency f sw and phase current i xm The carrier phase θ determined based on m Carrier signal S that defines the carrier wave (such as a triangular wave) that takes cwm The carrier signal generating unit 20-m generates the generated carrier signal S cwm is output to the PWM signal generating unit 22-m.

[0022] The PWM signal generating unit 22-m is a m The voltage command value v is determined according to the required output (required driving force for the vehicle) xm * , and the carrier signal S cwm is used as input, and the duty command signal D xm Specifically, the PWM signal generating unit 22-m generates a carrier wave and a voltage command value v xm * Based on the comparison result, a pulse signal consisting of a combination of ON pulses and OFF pulses is generated as a duty command signal D xm The PWM signal generating unit 22-m generates the generated duty command signal D xm The drive circuit α m Output to.

[0023] Next, the carrier signal S from each carrier signal generating unit 20-m cwm The generation of is now explained in more detail.

[0024] First, as a premise, as shown in FIG. 1, the current I flowing through the smoothing capacitor 14 is c is the DC current I cm The sum of (I c1 +I c2 I cN ) Therefore, the carrier component of the ripple current flowing through the smoothing capacitor 14 is determined by each carrier signal S cwm Each DC current I is specified based on cm The total effective value of multiple signals with the same frequency varies depending on the phase difference between each signal. For this reason, in each PWM control, the same carrier frequency f sw When is used, each carrier phase θ m (hereinafter referred to as "carrier phase difference Δθ m By appropriately adjusting the capacitance (also referred to as "capacitor capacitance"), the carrier component of the ripple current flowing through the smoothing capacitor 14 can be reduced.

[0025] More specifically, the carrier phase θ m and the magnitude of the ripple current generated in the smoothing capacitor 14 (the ripple current effective value I c_sw The relationship between the magnitude of the

[0026]

number

[0027] Here, "A" in the formula m " is the direct current I cm is the amplitude of the carrier component in the ripple current contained in b " is the carrier phase θ m A phase selected from the above (hereinafter referred to as the reference phase θ b ").

[0028] Here, the amplitude A on the right side of equation (1) m , and carrier frequency f sw are determined depending on the operating conditions of the power conversion device 10. Therefore, the effective value I c_sw is the phase difference Δθ m (m=1, 2...) is a variable. Therefore, theoretically, the ripple current effective value I c_sw Each carrier phase difference Δθ takes the minimum value m can be determined as an optimum value that can suppress the ripple current.

[0029] However, the operating conditions of the on-board power conversion device 10 change from moment to moment depending on the running state of the vehicle, etc. Therefore, the amplitude A m , and carrier frequency f sw Therefore, the function form of Equation (1) changes at each control timing, and each carrier phase difference Δθ m It is practically difficult to adopt a control logic that continuously calculates the optimum value of

[0030] In contrast, in this embodiment, each motor M m Depending on the output torque direction (particularly, based on whether the output torque directions are the same or not), the carrier phase difference Δθ that can suppress the ripple current m Each motor M m Each carrier phase θ used for PWM control m The following is established.

[0031] Below, each carrier phase θ m The control logic for determining the above will be described in detail below.

[0032] Figure 3 shows the carrier phase θ m 3 is a flowchart illustrating a process for determining the PWM control signal 20-m at predetermined calculation intervals. The processes shown in FIG.

[0033] First, in step S110, the motor speeds M m Phase current i xm The phase current effective value is calculated from the phase current i xm is a three-phase AC current, the effective values ​​of the phase currents of each phase are assumed to be the same.

[0034] In step S120, the calculation result of step S110 is referred to, and the reference motor M having the largest phase current effective value is selected. b If necessary, each motor M m A part of the reference motor M b You may exclude them from the list of candidates.

[0035] In step S130, the reference motor M b The carrier signal S used to adjust the input and output power of cwb The phase of the reference phase θ b It is determined as follows.

[0036] In step S140, the reference motor M b Each motor other than M m Among these, the reference motor M b The motor M having the same output torque direction as the motor M and the motor M having a different output torque direction are identified. In particular, the identification of these motors M is performed by m For the sake of convenience, the torque command value for the reference motor M b The motor M that has the same output torque direction as the motor M is appropriately referred to as the "same torque direction motor M" k_h (k is a natural number from 1 to N-1 that is different from j), and the motor M that has different output torque directions is called the "different torque direction motor M j_d ” (j is a natural number between 1 and N-1, different from k).

[0037] And the torque direction motor M k_h Carrier signal S related to cwk_h (hereinafter referred to as "output torque direction phase θ k_h") is determined by the following formula (2).

[0038]

number

[0039] On the other hand, the different torque direction motor M j_d Carrier signal S related to cwj_d (hereinafter referred to as "different output torque direction phase θ j_d ") is the reference phase θ b That is, the reference phase θ b Each different output torque direction phase θ 1_d ,θ 2_d The phase difference between ... is set to zero.

[0040] By performing the above-described processes, the carrier phase difference Δθ can be reduced by using simple control logic. m Carrier phase θ that realizes m The following describes in more detail the effects that can be obtained by adopting the above control logic.

[0041] FIG. 4A shows the reference phase θ determined by the above control logic. b and the output torque direction phase θ k_h Each carrier signal S is determined based on cw1 ,S cwk_h 4B shows the pulse waveform of the duty signal obtained from the reference phase θ b and different output torque direction phase θ j_d Each carrier signal S is determined based on cw1 ,S cwj_d 1 shows the pulse waveform of the duty signal obtained from

[0042] In particular, in FIG. 4A(a), the total number of motors in the same torque direction N 1+k Example where is 2 (reference motor M b and one of the same torque direction motor M 1_hOn the other hand, Fig. 4A(b) shows the pulse waveform assuming the case where the total number of motors in the same torque direction, N 1+k Example where is 3 (reference motor M b and two motors M 1_h ,M 2_h Furthermore, FIG. 4B shows a pulse waveform assuming a case where one different torque direction motor M 1_d The pulse waveform is shown assuming an example in which

[0043] First, in the example shown in FIG. 4A(a), the output torque direction phase θ 1_h is the reference phase θ b Therefore, the torque direction motor M 1_h The phase of the pulses related to the reference motor M b Therefore, the DC current I cb and DC current I c1_h Since the mutual overlap of these can be suppressed, the total DC current I c The ripple current effective value I of the smoothing capacitor 14 according to c_sw can be reduced.

[0044] Next, in the example shown in FIG. 4A(b), the output torque direction phase θ 1_h ,θ 2_h are the reference phases θ b Therefore, the torque direction of the motor M 1_h ,M 2_h The phase of each pulse of the reference motor M b Therefore, the DC current I cb , direct current I c1_h , and DC current I c2_h Since the overlapping of the ripple currents can be suppressed, the effective value I c_sw can be reduced.

[0045] In particular, in this example, each output torque direction phase θ 1_h ,θ 2_h is the reference motor M with the largest phase current effective value. b Reference phase θ b With a base point, a certain deviation width (specified phase difference Δθ 1_h ,Δθ 2_h Therefore, the reference phase θ , which has a strong influence on the increase of the ripple current of the smoothing capacitor 14, is b Originating DC current I cb Furthermore, the output torque direction phase θ 1_h ,θ 2_h Originating DC current I c1_h ,I c2_h Therefore, the occurrence of a situation where the ripple current effective value I c_sw The reduction effect is further improved.

[0046] On the other hand, in the example shown in FIG. 4B, the different output torque direction phase θ 1_d is the reference phase θ b Here, the different torque direction motor M 1_d DC current I determined by PWM control cw1_d is the reference motor M b DC current I determined by PWM control cb Therefore, the direction of the different output torque phase θ 1_d The reference phase θ b By making it the same as the different output torque direction phase θ 1_d Originating DC current I c1_d Therefore, the reference phase θ b Originating DC current I cb Therefore, the ripple current effective value I c_sw can be reduced.

[0047] In particular, according to the control logic (especially steps S120 and S140) described in FIG. 3, the different torque direction motor M 1_dis the reference motor M with the largest phase current effective value. b Therefore, the output torque direction of the motor M is different from that of the motor M. 1_d The reference phase θ b By using the same control logic as cb Therefore, the ripple current effective value I c_sw The reduction effect is further improved.

[0048] The above-mentioned effects can be achieved by the specific torque direction motor M shown in FIGS. 4A and 4B. k_h The number of motors and the torque direction of the motor M j_d That is, for example, there are three or more motors M k_h and / or two or more different torque direction motors M j_d The same holds true when there exists a

[0049] Next, a more specific system configuration will be considered to explain the application of the above control logic.

[0050] FIG. 5 shows two drive motors (first drive motor M D1 and second drive motor M D2 ) and one power generating motor M used to generate the electricity required to run the vehicle. G 5 shows a motor control system 100 including a reference motor M b The candidate for the first drive motor M D1 and second drive motor M D2 and the generator motor M G is assumed not to be a candidate.

[0051] Therefore, based on the logic explained in step S120, the first drive motor M D1 and second drive motor M D2 The one with the largest phase current effective value is the reference motor M b Here, the first drive motor MD1 and second drive motor M D2 Normally, both motors are in power running mode. Therefore, the output torque direction of these motors can be considered to be the same. Therefore, when one of the motors is the reference motor M b , the other is the same torque direction motor M 1_h It is determined as follows.

[0052] On the other hand, the generator motor M G During normal operation (power generation), the drive motor M D1 ,M D2 Therefore, the output torque direction is different from that of the generator motor M G The torque direction of the motor M 1_d is set to

[0053] Then, based on the control logic explained in Fig. 3, each carrier phase θ b ,θ 1_h ,θ 1_d By determining this, the above-described effects explained with reference to FIGS. 4A(a) and 4B can be realized.

[0054] The configuration and effects of the power conversion method of the present embodiment described above will now be described.

[0055] According to this embodiment, three or more AC motors (each motor M m ) connected to each of the switching circuits B cm and each switching circuit B cm The storage element (smoothing capacitor 14) is connected in parallel to the DC end of each of the switching circuits B cm For the same carrier frequency f sw and a control unit (PWM control device 50) that performs PWM control individually using each carrier wave having a carrier wave having a phase difference Δθ m ) for each motor M mis determined based on the direction of the torque output.

[0056] This allows each of the three or more motors M m In the power conversion device 10 that performs PWM control of each of the motors M m The DC current I according to the direction (positive or negative) of the torque output by cm A suitable carrier phase difference Δθ taking into consideration the overlap and / or cancellation of m is determined, the ripple current of the smoothing capacitor 14 can be effectively suppressed.

[0057] In particular, each motor M m By focusing on the direction of the torque output by the smoothing capacitor 14, the carrier phase difference Δθ m In comparison with the case where the above formula (1) is directly calculated, a calculation logic that is significantly simplified to a practical level can be realized.

[0058] More specifically, in this embodiment, each motor M m Phase current i xm (Step S110), the motor M showing the largest phase current (effective phase current value) is selected as the reference motor (reference motor M b ) (step S120), and the reference motor M b The reference phase θ is the phase of the carrier wave used for PWM control of b is determined (step S130), and the reference motor M b One or more same-output torque direction motors (same-torque direction motors M) that output torque in the same direction as the k_h ), and the reference motor M b One or more different torque direction motors (different torque direction motors M) that output torque in different directions. j_d ) is identified (step S140), and the torque direction motor M 1_h The output torque direction phase θ is the phase of the carrier wave used for PWM control of k_h , and different torque direction motor M 1_d The phase of the carrier wave used for PWM control is the phase of the different output torque direction θ j_dThe following is established.

[0059] In particular, the output torque direction phase θ k_h is the reference phase θ b Reference motor M b and the torque direction motor M 1_h The total number N 1+k A predetermined specified phase difference Δθ according to k_h (Step S150). j_d is the reference phase θ b (phase difference is zero) (step S160).

[0060] This allows each of the three or more motors M m In the power conversion device 10 that performs each of the PWM controls, a suitable carrier phase difference Δθ that can be suppressed by the smoothing capacitor 14 is m A more specific control logic for determining is realized.

[0061] In particular, the output torque direction phase θ k_h The reference phase θ b With respect to the predetermined specified phase difference Δθ k_h By setting the reference motor M b DC current I derived from PWM control cb In contrast, the same torque direction motor M 1_h DC current I derived from PWM control ck_h This makes it possible to more reliably avoid situations where the two signals overlap.

[0062] In addition, the different output torque direction phase θ j_d and the reference phase θ b By making them the same, the different torque direction motor M j_d DC current I derived from PWM control cj_d is the reference motor M b DC current I derived from PWM control cb This can further enhance the canceling effect.

[0063] In particular, in this embodiment, the specified phase difference Δθ k_his defined as the second term on the right side of the above equation (2).

[0064] This allows the reference phase θ b and each output torque direction phase θ k_h A more specific calculation logic for determining is realized.

[0065] The above describes embodiments of the present invention, but the above embodiments merely illustrate some of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments. [Explanation of symbols]

[0066] 10 Power conversion device 12 Battery 14 Smoothing capacitor 20 Carrier signal generator 22 PWM signal generator 30 Carrier wave clock generation unit 50 PWM control device 100 Motor Control System Medium motor

Claims

1. A power conversion method executed in a power conversion device including: switching circuits connected to three or more AC motors, respectively; storage elements provided in parallel to DC ends of the respective switching circuits; and a control unit that performs PWM control individually on the respective switching circuits using carrier waves having the same carrier frequency, acquiring a phase current of each of the AC motors; determining the AC motor showing the largest phase current as a reference motor; determining a reference phase, which is the phase of the carrier wave used for PWM control of the reference motor; Identifying one or more same-output torque direction motors that output torque in the same direction as the reference motor, and one or more different-output torque direction motors that output torque in a different direction from the reference motor, determining a same output torque direction phase, which is the phase of the carrier wave used for PWM control of the same output torque direction motor, and a different output torque direction phase, which is the phase of the carrier wave used for PWM control of the different output torque direction motor; the output torque direction phase is determined to have a predetermined specified phase difference with respect to the reference phase according to the total number of the reference motors and the output torque direction motors, The different output torque direction phase is determined to be the same as the reference phase. Power conversion methods.

2. 2. The power conversion method according to claim 1, The specified phase difference is determined based on the following formula (1): [Equation 1] (However, N in the formula １＋ｋ represents the total number of the reference motor and the same output torque direction motor, and k is a natural number that uniquely corresponds to each of the same output torque direction motors. Power conversion methods.

3. A power conversion device comprising: switching circuits connected to three or more AC motors, respectively; storage elements provided in parallel to DC ends of the respective switching circuits; and a control unit that performs PWM control on the respective switching circuits individually using carrier waves having the same carrier frequency, The control unit acquiring a phase current of each of the AC motors; determining the AC motor showing the largest phase current as a reference motor; determining a reference phase, which is the phase of the carrier wave used for PWM control of the reference motor; Identifying one or more same-output torque direction motors that output torque in the same direction as the reference motor, and one or more different-output torque direction motors that output torque in a different direction from the reference motor, determining a same output torque direction phase, which is the phase of the carrier wave used for PWM control of the same output torque direction motor, and a different output torque direction phase, which is the phase of the carrier wave used for PWM control of the different output torque direction motor; the output torque direction phase is determined to have a predetermined specified phase difference with respect to the reference phase according to the total number of the reference motors and the output torque direction motors, The different output torque direction phase is determined to be the same as the reference phase. Power conversion device.

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