JP2008220106A - Pwm controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a PWM controller which is free from control instability and induction failure at a transient voltage fluctuation and has an excellent control response characteristic in the whole speed areas and causes no grating noise. <P>SOLUTION: A PWM inverter, including a non-synchronous mode having a carrier not synchronous with a voltage command and a synchronous mode having the carrier synchronous with the voltage command and capable of carrying out one pulse operation saturated in a PWM waveform, is operated in the non-synchronous mode at a speed operated at a variable voltage to limit the voltage modulation rate so that the PWM waveform is not transiently saturated. While, at a speed when the voltage is at the maximum, the inverter is operated in the synchronous mode, without limiting the voltage modulation rate. When switched from the non-synchronous mode to the synchronous mode, the limit of the modulation rate is gradually increased up to the maximum value after being switched to the synchronous mode. When switched from the synchronous mode to the non-synchronous mode, the synchronous mode is switched to the non-synchronous mode after the limit of the modulation rate is gradually decreased down to the value where the PWM waveform is not saturated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a PWM inverter that controls an AC motor, and particularly to suppress transient control instability, inductive failure, and annoying noise.

  FIG. 2 shows a block diagram of a conventional PWM control apparatus as an example, and the conventional technique will be described based on this figure.

The voltage command generator 3 receives the torque command T *, the primary current of the motor 1 detected by the current detector 2, and the motor angular velocity ω, which is the angular velocity of the motor 1, and inputs a modulation factor command α ₀ voltage using vector control or the like. Outputs phase command θ. The maximum value of the modulation factor command α ₀ is 1.

Modulation factor corrector 5, when the modulation ratio command alpha ₀ is 0.9 or less and outputs a modulation rate instruction alpha ₀ as the modulation index correction value alpha _n, when the modulation ratio command alpha ₀ is more than 0.9, based on a function A value larger than the modulation rate command α ₀ is output as a modulation rate correction value α _n .

The voltage command calculator 6 receives the modulation factor correction value α _n and the voltage phase command θ, and outputs three-phase voltage commands Vu *, Vv *, Vw * according to (1) to (3).

  The asynchronous carrier frequency generator 7 generates a constant or variable asynchronous carrier frequency fca_a. The synchronous carrier frequency generator 8 receives the voltage phase command θ and outputs the carrier frequency fca_s calculated by the equation (4) synchronized with the voltage phase command θ.

  Here, N is the number of synchronization pulses, and a value that is an odd product of 3 is used.

  The carrier mode switch 14 outputs the carrier mode signal Sca as 0 when the motor angular speed ω is equal to or lower than the switching angular speed ωp, and outputs the carrier mode signal Sca as 1 when the motor angular speed ω is equal to or higher than the switching angular speed ωp. The switch 10 outputs the asynchronous carrier frequency fca_a as the carrier frequency fca when the carrier mode signal Sca is 0, and outputs the synchronous carrier frequency fca_s as the carrier frequency fca when the carrier mode signal Sca is 1.

  The carrier generator 11 outputs a triangular wave with a carrier frequency fca as a frequency and a magnitude of 1 to −1 as a carrier car. The carrier comparator 12 compares the voltage commands Vu *, Vv *, Vw * and the carrier car and outputs three-phase switching commands su, sv, sw. The switching command is obtained by the following calculation.

  The power converter applies three-phase output voltages Vu, Vv, Vw to the motor 1 based on 13 switching commands su, sv, sw.

Here, the reason for correcting the modulation factor when the modulation factor command α ₀ exceeds 0.9 will be described. When the modulation factor command α ₀ exceeds 0.9, the PWM waveform is gradually oversaturated, and the modulation factor command α ₀ and the amplitude of the fundamental component of the output voltages Vu, Vv, Vw are not proportional. Therefore, when the modulation rate command α ₀ exceeds 0.9, correction is performed so that the amplitude of the fundamental component of the modulation rate command α ₀ and the output voltages Vu, Vv, and Vw is proportional, and the modulation rate command α ₀ When the value becomes 1, the PWM voltage waveform is completely saturated so that a one-pulse operation that becomes a rectangular wave is performed.

  With the above configuration, when the motor angular speed ω is lower than the switching angular speed ωp, the carrier and the voltage command are not synchronized, and when the motor angular speed ω is higher than the switching angular speed ωp, the carrier and the voltage command are synchronized. It becomes.

  When one-pulse operation is attempted in the asynchronous mode, the carrier and the voltage command are not synchronized. Therefore, the complete one-pulse waveform is not necessarily obtained as shown in FIG. 3, which causes control instability and induction failure. On the other hand, when one-pulse operation is performed in the synchronous mode, by setting the modulation factor corrector 5 appropriately, a complete one-pulse waveform can be obtained as shown in FIG. 4, and control instability and induction failure can be prevented. It is.

  In the motor control for a vehicle, since the voltage is approximately proportional to the speed in the low speed range, the operation is performed with the variable voltage in the low speed range, and when the voltage reaches the maximum value, the operation is performed with the maximum voltage value. Therefore, by setting the switching angular speed ωp to an angular speed lower than the angular speed at which the voltage reaches the maximum voltage, complete one-pulse operation can be automatically performed in the speed range where the voltage reaches the maximum value, and stable control becomes possible.

  Even at a speed at which the voltage reaches the maximum value, the modulation rate command may decrease transiently. By performing one-pulse operation using a carrier in the synchronous mode, a high response can be obtained because a PWM voltage waveform is automatically obtained when the modulation rate is transiently lowered.

JP 2000-14200 A

  Even at a speed at which the voltage does not reach the maximum value in a steady state, the voltage may reach the maximum value and become saturated due to a torque command variation or the like. When the voltage is transiently saturated, the asynchronous mode does not become a complete one-pulse waveform, which causes control instability and induction failure. Therefore, it is necessary to switch to the synchronous mode at a speed much lower than the speed at which the voltage reaches the maximum value. However, in the synchronous mode, the carrier frequency changes greatly depending on the speed, and the control response characteristic changes greatly. Since there is an upper limit of the carrier frequency depending on the control processing time and the performance of the power converter, the carrier frequency is much lower in the synchronous mode at a lower speed than in the asynchronous mode, and the control response characteristic is deteriorated.

  In particular, when an AC motor having a large inductance is used as the motor 1, the above problem is likely to occur because transient voltage saturation is likely to occur and control response characteristics are significantly degraded due to a decrease in carrier frequency.

  In order to suppress the change of the carrier frequency, there is a method of changing the number N of synchronization pulses in the synchronization mode so that the carrier frequency is within a certain range. However, when the pulse mode changes, the noise changes discontinuously, which is undesirable.

  According to the first aspect of the present invention, the voltage command generator for inputting the motor angular velocity, the primary current, and the torque command and outputting the modulation rate command and the voltage phase command, and when the modulation rate command is 0.9 or less, the modulation rate command When the modulation rate command is 0.9 or more, a modulation rate corrector that outputs a value larger than the modulation rate command based on a certain function, the output of the modulation rate correction unit and the voltage phase command, and a three-phase A voltage command computing unit that outputs a voltage command, an asynchronous carrier frequency generator that outputs an asynchronous carrier frequency, a synchronous carrier frequency generator that receives the voltage phase command and outputs a synchronous carrier frequency, and a carrier mode signal A switch that selects either the asynchronous carrier frequency or the synchronous carrier frequency and outputs it as a carrier frequency, and a triangular wave having the carrier frequency as a frequency. A carrier generator that generates a carrier comparator that compares the voltage command with the carrier and outputs a three-phase switching command, and a power converter that applies a three-phase voltage to the motor based on the switching command. A modulation rate limiter that limits the modulation rate command, which is an input of the modulation rate corrector, with a modulation rate limit value, and synchronizes the output of the switch when the motor angular velocity exceeds a predetermined value. After outputting a carrier mode signal having a carrier frequency, the modulation factor limit value is increased to a maximum value over a predetermined time, and when the motor angular velocity falls below a predetermined value, the modulation factor limit value is decreased to a predetermined value over a predetermined time. It further comprises a modulation rate limit value calculator for outputting a carrier mode signal whose output is the asynchronous carrier frequency later.

  According to a second aspect of the present invention, in the PWM control device of the first aspect, the predetermined time for changing the modulation factor command value is set to a sufficiently short time.

  According to a third aspect of the invention, in the PWM control device of the first aspect, the synchronous carrier frequency and the asynchronous carrier frequency at the switching speed coincide with each other.

  Furthermore, the modulation rate in the asynchronous mode is limited to a value that does not saturate the PWM waveform. When transitioning from the asynchronous mode to the synchronous mode, the modulation rate limit is raised to the maximum value in a predetermined time after switching to the synchronous mode. When transitioning from the synchronous mode to the asynchronous mode, the modulation rate limit is lowered to a value that does not saturate the PWM for a predetermined time, and then the mode is switched to the asynchronous mode.

  According to the present invention, the switching angular velocity ωp can be matched with the angular velocity at which the voltage reaches the maximum value. For this reason, since the asynchronous mode is set in the speed range where the variable voltage is operated, no change in control response characteristics or discontinuous noise occurs. In addition, in the asynchronous mode, the modulation rate is limited to a value that does not saturate the PWM waveform. Therefore, when the voltage is transiently saturated, it does not cause control instability or induction failure. On the other hand, in the speed range where the voltage reaches the maximum value, one-pulse operation is performed in the synchronous mode.

  Asynchronous mode with a modulation rate limited to 0.9 is used in the low speed region, and synchronous mode with the modulation rate limited to 1.0 in the region where the voltage is maximum. When switching from the asynchronous mode to the synchronous mode, the modulation rate limit is gradually increased from 0.9 to 1 after switching to the synchronous mode. When switching from the synchronous mode to the asynchronous mode, the modulation rate limit is gradually lowered from 1 to 0.9, and then the asynchronous mode is switched.

  FIG. 1 is a block diagram showing an embodiment of the present invention representing claim 1 and will be described based on this figure, but the description of the same parts as those of the prior art will be omitted.

When the motor angular velocity ω is equal to or lower than the switching angular velocity ωp, the modulation factor limiting value calculator 9 _{outputs the} modulation factor limiting value α _lmt as 0.9 and the carrier mode signal Sca as 0, and when the motor angular velocity ω exceeds the switching angular velocity ωp. Then, after changing the carrier mode signal Sca to 1, the modulation factor limit value α _lmt is raised to 1 over a predetermined time Tα. When the motor angular velocity ω changes from a state where the motor angular velocity ω exceeds the switching angular velocity ωp to a state lower than the switching angular velocity ωp, the carrier mode signal Sca is set to 0 after the modulation factor limit value α _lmt is lowered to 0.9 over a predetermined time Tα. To change.

Modulation rate limiter 4, the modulation ratio command alpha ₀ is limited to the case exceeds the modulation rate limit value alpha _lmt modulation rate limit value alpha _lmt.

  In the asynchronous mode, since the modulation rate is limited to 0.9, the PWM waveform does not saturate even if the voltage is transiently saturated. Therefore, there is no problem even if the switching angular velocity ωp is matched with the angular velocity at which the voltage reaches the maximum value.

Since the synchronous mode is used only in the speed range where the voltage reaches the maximum value, one-pulse operation is performed in the steady state where the modulation factor limit α _lmt is 1. During one-pulse operation, the output waveform does not change even if the synchronization pulse number N changes. Therefore, even if the pulse number is changed so that the carrier frequency is within a certain range, no harsh noise is generated. It is possible to ensure control response characteristics by changing.

  An embodiment of the invention of claim 2 will be described, but the same parts as those of Embodiment 1 are omitted.

  In the PWM control apparatus of the first embodiment, the predetermined time Tα is set to a sufficiently short time.

When the modulation factor α does not reach 1, carrier frequency component noise occurs, and when the modulation factor α reaches one pulse, no carrier frequency component noise occurs. That is, in the asynchronous mode in which the modulation factor α is limited, the noise of the component of the asynchronous carrier frequency fca_a is generated. Before the modulation factor α _lmt reaches 1 in the synchronous mode, the noise of the component of the synchronous carrier frequency fca_s is generated and modulated in the synchronous mode. When the rate limit α _lmt reaches 1 and the modulation rate α is 1, no noise of the carrier frequency component occurs. Therefore, in the configuration of the first embodiment, since the noise having the synchronous carrier frequency fca_s is generated between the state where the noise of the asynchronous carrier frequency fca_a is generated and the state where the noise of the carrier frequency component is not generated, the asynchronous carrier frequency fca_s is generated. Discontinuous noise occurs when switching between mode and synchronous mode.

  By setting the predetermined time Tα to a sufficiently short time, it becomes a noise as if transitioning from a state where the noise of the asynchronous carrier frequency component fca_a is generated to a state where the noise of the carrier frequency component is not generated, Discontinuous noise that is annoying is not recognized and does not cause a problem. Note that if the predetermined time Tα is too short, torque instability occurs, so the time is such that torque instability does not occur.

  An embodiment of the invention of claim 3 will be described, but the same parts as those of the embodiment 1 are omitted.

  In the PWM control apparatus of the first embodiment, the switching angular velocity ωp is determined by the equation (5) using the asynchronous carrier fca_a and the number of synchronization pulses N.

  By determining the switching angular velocity ωp by the equation (5), when switching between the synchronous mode and the asynchronous mode, the asynchronous carrier frequency fca_a and the synchronous carrier frequency fca_s coincide with each other, so that discontinuous noise does not occur.

  The present invention is applicable to all vehicle motors such as electric railways, electric vehicles, hybrid vehicles, and fuel cell vehicles. Further, the electric motor 1 can be applied to various AC motors such as an induction motor, a permanent magnet type synchronous motor, and a synchronous reluctance motor, and can be widely used.

It is a block diagram showing one Example of Claim 1. FIG. It is a block diagram of the PWM control apparatus by a prior art. It is a one-pulse waveform in the asynchronous mode. It is one pulse waveform in synchronous mode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric motor 2 Current detector 3 Voltage command generator 4 Modulation rate limiter 5 Modulation rate corrector 6 Voltage command calculator 7 Asynchronous carrier frequency generator 8 Synchronous carrier frequency generator 9 Modulation rate limit value calculator 10 Switch 11 Carrier generation 12 Carrier comparator 13 Power converter 14 Carrier mode switch

Claims (3)

A voltage command generator for inputting a motor angular velocity, a primary current, and a torque command and outputting a modulation rate command and a voltage phase command; and when the modulation rate command is 0.9 or less, the modulation rate command is output and the modulation rate command is 0.9 A modulation rate corrector that outputs a value larger than the modulation rate command based on a certain function, and a voltage command computing unit that outputs the modulation rate corrector output and the voltage phase command as inputs and outputs a three-phase voltage command. An asynchronous carrier frequency generator that outputs an asynchronous carrier frequency, a synchronous carrier frequency generator that receives the voltage phase command and outputs a synchronous carrier frequency, and outputs the asynchronous carrier frequency and the synchronous carrier frequency by a carrier mode signal. A switch that selects either of them and outputs it as a carrier frequency, and a carrier generation that generates a triangular wave having the carrier frequency as a carrier. PWM control comprising a generator, a carrier comparator that compares the voltage command with the carrier and outputs a three-phase switching command, and a power converter that applies a three-phase voltage to the motor based on the switching command In the apparatus, a modulation rate limiter for limiting the modulation rate command, which is an input of the modulation rate correction unit, with a modulation rate limit value, and when the motor angular velocity exceeds a predetermined value, the output of the switch is set as a synchronous carrier frequency. After the carrier mode signal is output, the modulation factor limit value is increased to a maximum value in a predetermined time, and when the motor angular velocity falls below a predetermined value, the modulation factor limit value is decreased to a predetermined value in a predetermined time. A PWM control device comprising a modulation rate limit value calculator that outputs a carrier mode signal whose output is the asynchronous carrier frequency.   2. The PWM control device according to claim 1, wherein the predetermined time for changing the modulation factor command value is a sufficiently short time. 2. The PWM control device according to claim 1, wherein the synchronous carrier frequency and the asynchronous carrier frequency at the switching speed coincide with each other.

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