JP6213155B2 - Digital filter - Google Patents

Description

  The present invention relates to a digital filter.

  A hybrid vehicle, an electric vehicle, a fuel cell vehicle and the like equipped with an electric motor as a driving source are known. Such a vehicle supplies electric power to an electric motor, for example, a power supply device such as a battery or a capacitor, a converter for stepping up or down a voltage, and an electric device such as an inverter for converting direct current to alternating current Is provided.

  For the digital filter, calculate the servo data calculation parameters, determine the operation mode based on these parameters, change the filter parameters according to the operation mode, and set the initial values of the filter internal variables to appropriate values. Thus, a technique for preventing the filter output from becoming discontinuous when the filter characteristic is changed is known (see, for example, Patent Document 1).

  Also, a feedback signal calculation unit that calculates and outputs the output signal of the digital filter, a feedforward signal calculation unit that calculates and outputs the input signal of the digital filter, and an output of the feedback signal calculation unit There is known a technique for changing the filter coefficient of a digital filter including an adder that adds the output of the feedforward signal calculation unit and the output of the feedforward signal calculation unit to obtain an output signal of the digital filter. In this technique, all the filter coefficients of the digital filter are sequentially set to 0, the filter coefficients in the feedback signal calculation unit are sequentially updated to the changed coefficients, and the filter coefficients in the feedforward signal calculation unit are sequentially changed coefficients. (For example, refer to Patent Document 2).

JP-A-11-112289 Japanese Patent Laid-Open No. 02-252307

  In the technique of changing the filter parameters in accordance with the operation mode, the integration control is performed in order to suppress the discontinuity of the filter output value when the filter constant is changed, so that complicated arithmetic processing is required.

  In the technique of sequentially setting all the filter coefficients of the digital filter to 0 and updating the filter coefficients in the feedback signal calculation unit to the coefficients after being sequentially changed, the amount of calculation for sequentially setting all the filter coefficients to 0 increases. Since all the filter coefficients are sequentially set to 0, a time during which filtering cannot be performed occurs and filtering is delayed.

  An object of the present invention is to improve the characteristics of the output waveform of a digital filter when the filter constant is changed.

The digital filter of an embodiment of the disclosure is
This is a digital filter that receives the voltage of a power converter that electrically generates AC power from DC power, can remove noise superimposed on the power supply voltage, and variably controls the cutoff frequency. And
When changing the carrier frequency for adjusting the amount of power supplied to the power converter, so that the filter constant of the digital filter is switched in the state of the higher carrier frequency among the carrier frequencies before and after the change , The order of timing for switching the filter constant of the digital filter and the timing for changing the carrier frequency of the power converter is determined, and filtering is performed based on the filter constant switched at the timing of switching the filter constant of the digital filter.

  According to the disclosed embodiment, it is possible to improve the characteristics of the output waveform of the digital filter when the filter constant is changed.

It is a figure which shows an example of a control circuit. It is a figure which shows one Example of a control circuit. It is a figure which shows one Example of operation | movement of a control circuit. It is a figure which shows the output waveform of the digital filter of one Example of a control circuit.

Next, the form for implementing this invention is demonstrated, referring drawings based on the following Examples. Examples described below are merely examples, and embodiments to which the present invention is applied are not limited to the following examples.
In all the drawings for explaining the embodiments, the same reference numerals are used for those having the same function, and repeated explanation is omitted.

<Example>
<Control circuit>
FIG. 1 shows an example of the control circuit.

  An example of the control circuit supplies power to the motor 400. The control circuit is mounted on a hybrid vehicle, an electric vehicle, a fuel cell vehicle, or the like that has a motor as a drive source.

  The control circuit includes a converter 200 and an inverter 300. Inverter 300 drives motor 400. Converter 200 supplies necessary power to inverter 300.

  Converter 200 performs boost control. Converter 200 uses a voltage (VH voltage) obtained by removing switching noise and motor noise of inverter 300 with a filter for boost control. Converter 200 includes a reactor 202, two transistors TrbH 204 and TrbL 206, and two diodes 208 and 210. An example of the transistors TrbH204 and TrbL206 are npn transistors. Reactor 202 has one end connected to the positive electrode side of battery 100 and the other end connected to a connection point of two transistors.

  The two transistors TrbH204 and TrbL206 are connected in series. Diodes 208 and 210 are connected between the collectors and emitters of the transistors TrbH204 and TrbL206 so that current flows from the emitter side to the collector side.

  By controlling the gate voltages of the two transistors TrbH204 and TrbL206 to be on or off, the amount of power supplied to the inverter 300 is adjusted.

  The transistors TrbH204 and TrbL206 may be composed of IGBTs (Insulated Gate Bipolar Transistors). Instead of the transistor, a power switching element such as a power MOSFET (Metal Oxide Semiconductor Field-Effect Transistor) may be used.

  When the electric power discharged from the battery 100 is supplied to the motor 400, the voltage is boosted by the switching operation of the converter 200. Conversely, when charging the battery 100 with the power generated by the motor 400, the voltage is stepped down by the converter 200.

  The inverter 300 is a power conversion device having a power supply circuit that electrically generates AC power from DC power. Inverter 300 has a U-phase arm 302, a V-phase arm 304, and a W-phase arm 306. U-phase arm 302, V-phase arm 304, and W-phase arm 306 are connected in parallel. The U-phase arm 302 has two transistors 308 and 310 connected in series. The V-phase arm 304 has two transistors 312 and 314 connected in series. The W-phase arm 306 has two transistors 316 and 318 connected in series. An example of the transistors 308 to 318 is an npn transistor.

  A diode 320 is connected between the collector and emitter of the transistor 308 to allow current to flow from the emitter side to the collector side. A diode 322 that flows current from the emitter side to the collector side is connected between the collector and emitter of the transistor 310. A diode 324 is connected between the collector and emitter of the transistor 312 to flow current from the emitter side to the collector side. A diode 326 that allows current to flow from the emitter side to the collector side is connected between the collector and the emitter of the transistor 314. A diode 328 that allows current to flow from the emitter side to the collector side is connected between the collector and the emitter of the transistor 316. A diode 330 is connected between the collector and emitter of the transistor 318 to allow current to flow from the emitter side to the collector side.

  A connection point of each transistor in each arm is connected to an end portion different from a neutral point (not shown) of each coil (not shown) of the motor 400.

  The inverter 300 converts a direct current supplied from the battery 100 into an alternating current and supplies the alternating current to the motor 400. Further, the inverter 300 converts the alternating current generated by the motor 400 into a direct current.

  The smoothing capacitor 102 is charged by the battery 100.

  The time for turning on and turning off the gate voltages of the two transistors TrbH204 and TrbL206 is set based on the power supply voltage Vs_inv of the inverter 300. That is, the inverter power supply voltage Vs_inv is used as one parameter when controlling the time to turn on and off the gate voltages of the two transistors TrbH204 and TrbL206. Specifically, when the power supply voltage Vs_inv of the inverter 300 is lower than the target voltage, control is performed to increase the power supply amount. Conversely, when the power supply voltage Vs_inv of the inverter 300 is higher than the target voltage, power supply is performed. Control to reduce the amount.

  Let us consider a case where noise is superimposed on the power supply voltage Vs_inv of the inverter 300. In this case, the time for turning on and turning off the gate voltages of the TrbH 204 and the TrbL 206 is controlled based on the power supply voltage Vs_inv with noise superimposed on the original power supply voltage Vs_inv.

  The noise superimposed on the power supply voltage Vs_inv of the inverter 300 is predominantly a component proportional to the rotation speed of the motor 400 such as motor noise or a component proportional to the carrier frequency of the inverter 300 such as switching noise of the inverter 300.

  Corresponding to the rotation speed of the motor 400, a filter constant such as a cutoff frequency is set from the control side. Since the rotation speed of the motor 400 changes continuously, the filter constant set from the control side also changes continuously. For this reason, no glitch occurs in the output of the digital filter.

  Corresponding to the carrier frequency of the inverter 300, a filter constant such as a cutoff frequency is set from the control side. The carrier frequency of the inverter 300 is discontinuously changed from the control side by the change of the running mode with respect to the rotation speed of the motor. For this reason, when the carrier frequency is switched, the filter constant is also switched discontinuously.

  That is, of the noise superimposed on the power supply voltage Vs_inv of the inverter 300, the noise having a large amplitude remaining in the output of the digital filter depends on the carrier frequency of the inverter 300. Here, the carrier frequency of the inverter 300 is a frequency at which the gate voltages of the transistors TrbH204 and TrbL206 are turned on or off. Therefore, noise can be reduced by calculating the frequency of noise based on the carrier frequency and performing appropriate filtering.

  Since the carrier frequency needs to be changed as appropriate according to the operation mode and operation state of the motor 400, a digital filter having a variable cutoff frequency is used.

  By changing the cutoff frequency, the filter constant of the digital filter is changed. Therefore, when the carrier frequency is changed discontinuously, the filter constant of the digital filter is also changed discontinuously. In this case, along with the discontinuous change of the filter constant, a narrow pulse such as a wave or a jump is generated in the waveform filtered by the digital filter. This thin pulse is sometimes called a glitch. Due to the influence of the glitch, the difference between the voltage after filtering by the digital filter and the actual power supply voltage Vs_inv of the inverter 300 becomes large. For this reason, a voltage different from the power supply voltage Vs_inv of the inverter 300, that is, the power supply voltage Vs_inv on which noise is superimposed is used for boost control, and the controllability deteriorates.

  In general, noise that is superimposed (ridden) on the power supply of the inverter 300 that drives the three-phase motor is often generated by switching on or off the transistors 308 to 318 of the inverter 300 in synchronization with the carrier frequency. Current is supplied to the motor 400 from the power supply line of the inverter 300 in synchronism with (in synchronization with) the timing of switching the transistors 308 to 318 of the inverter 300 on or off.

  However, since a transient current change cannot be supplied by the converter 200, a transient current is supplied by disposing the capacitor 212 between the power supply and the GND. However, when a transient current is charged or discharged from the capacitor 212, a voltage fluctuation corresponding to the amount of charge / discharge of the current may occur.

  Control for turning on or off the transistors 308 to 318 of the inverter 300 is performed by pulse width modulation (PWM) control at the carrier frequency. Therefore, the higher the carrier frequency, the shorter the time for turning on the transistor is controlled, and the lower the carrier frequency, the longer the time for turning on the transistor.

  Since the charge / discharge amount of current has a positive correlation with the time during which the transistor is on, the charge / discharge amount decreases as the carrier frequency increases. As the charge / discharge amount decreases, the voltage fluctuation decreases and the noise depending on the carrier frequency also decreases.

  Conversely, the charge / discharge amount increases as the carrier frequency decreases. As the charge / discharge amount increases, the voltage fluctuation increases, and the noise depending on the carrier frequency increases.

  When the carrier frequency is high, the noise superimposed on the power supply voltage Vs_inv of the inverter 300 is small, and when the carrier frequency is low, the noise superimposed on the power supply voltage Vs_inv of the inverter 300 is large.

  One embodiment of the control circuit reduces glitches by adjusting the timing of changing the filter constant. Specifically, the switching of the filter constant of the digital filter is executed in a high frequency state among the carrier frequencies before and after switching. By performing switching of the filter constant of the digital filter in a high frequency state, switching can be performed in a state where noise superimposed on the power supply voltage Vs_inv of the inverter 300 is small, so that glitches can be reduced. By reducing the glitch, the characteristics of the filter output value when the filter constant is changed can be improved.

<One Example of Control Circuit>
FIG. 2 shows an embodiment of the control circuit.

  The control circuit shown in FIG. 2 includes a converter control unit 500 in the control circuit described with reference to FIG. Converter control unit 500 includes an integrated circuit such as an ASIC (application specific integrated circuit). By using an integrated circuit, the speed of the converter can be increased.

  Converter control unit 500 is connected to converter 200 and inverter 300. Converter control unit 500 obtains carrier frequency change timing information and carrier frequency change value information of inverter 300. Converter control unit 500 adjusts the timing for switching the filter constant of the digital filter based on the change from the current carrier frequency to the change value of the carrier frequency.

  Specifically, converter control unit 500 switches the carrier frequency of inverter 300 after switching the filter constant of the digital filter when the change value of the carrier frequency is higher than the current carrier frequency. . Conversely, when the current carrier frequency is equal to or less than the change value of the carrier frequency, converter control unit 500 switches the carrier frequency of inverter 300 and then switches the filter constant of the digital filter.

<Function of Converter Control Unit 500>
Converter control unit 500 includes A / D conversion unit 502, digital filter 504, boost control unit 506, and inverter control unit 508.

  The A / D conversion unit 502 converts the inverter power supply voltage Vs_inv of the inverter 300 into a digital value and inputs the digital value to the digital filter 504.

  The inverter control unit 508 controls the inverter 300. The inverter control unit 508 controls the inverter 300 by turning on or off the gate voltage of the transistors 308-318. Moreover, the inverter control unit 508 acquires carrier frequency change timing information and carrier frequency change value information of the inverter 300. The inverter control unit 508 adjusts the timing for switching the filter constant of the digital filter based on the change from the current carrier frequency to the changed value of the carrier frequency.

  Specifically, when the change value of the carrier frequency is higher than the current carrier frequency, the inverter control unit 508 executes the filter constant switching control of the digital filter 504, and then performs the carrier frequency of the inverter 300. The switching control is executed. Conversely, when the current carrier frequency is equal to or less than the change value of the carrier frequency, the inverter control unit 508 executes the switching control of the carrier constant of the inverter 300 and then the switching control of the filter constant of the digital filter. To do.

  Further, the inverter control unit 508 inputs a filter constant such as a cutoff frequency to the digital filter 504.

  The digital filter 504 is connected to the A / D conversion unit 502 and the inverter control unit 508. The digital filter 504 removes noise superimposed on the inverter power supply voltage Vs_inv converted into a digital value input from the A / D conversion unit 502. Specifically, the digital filter 504 removes noise of a component proportional to the carrier frequency of the inverter 300 by performing filtering based on a filter constant such as a cutoff frequency from the inverter control unit 508.

  The digital filter 504 inputs the inverter power supply voltage Vs_inv from which noise has been removed to the boost control unit 506.

  Boost control unit 506 is connected to digital filter 504. Boost control unit 506 controls the time for turning on and turning off the gate voltages of TrbH 204 and TrbL 206 of converter 200 based on inverter power supply voltage Vs_inv from which noise from digital filter 504 has been removed.

<One Example of Operation of Control Circuit>
FIG. 3 shows an embodiment of the operation of the control circuit. In step S302, a request for switching the carrier frequency of the inverter 300 is generated in the control circuit.

  In step S304, it is determined whether or not the current carrier frequency is higher than the change value of the carrier frequency.

  In step S306, when it is determined that the current carrier frequency is higher than the change value of the carrier frequency, the filter constant of the digital filter 504 is switched. For example, when changing from a high carrier frequency (5 kHz) to a low carrier frequency (2 kHz), the filter constant is switched by setting a cutoff frequency before changing to a low carrier frequency. The digital filter 504 performs filtering based on the switched filter constant.

  In step S308, the carrier frequency of the inverter 300 is switched. For example, change to a lower carrier frequency.

  In step S310, when it determines with the present carrier frequency being below the change value of a carrier frequency, switching of the carrier frequency of the inverter 300 is implemented. For example, when changing from a low carrier frequency (2 kHz) to a high carrier frequency (5 kHz), the filter constant is changed to a low carrier frequency before switching the filter constant by setting a cutoff frequency.

  In step S312, the filter constant of the digital filter 504 is switched. For example, the filter constant is switched by setting a cutoff frequency. The digital filter 504 performs filtering based on the switched filter constant.

<Effect of one embodiment of control circuit>
FIG. 4 shows the output waveform of the digital filter in one embodiment of the control circuit.

  In FIG. 4, the upper diagram shows the switching timing of the filter constant, and the lower diagram shows the power supply voltage waveform of the inverter and the output waveform from the digital filter.

  In FIG. 4, the left figure shows the output characteristics of the conventional control circuit, and the right figure shows the output characteristics of the control circuit of this embodiment.

  According to the conventional control circuit, the switching of the filter constant of the digital filter and the switching of the carrier frequency are performed at the same timing regardless of the level of the carrier frequency before and after switching, so the carrier frequency is changed from a high frequency to a low frequency. A glitch occurs either when switching or when switching from a low frequency to a high frequency.

  In contrast to the conventional control circuit, in the control circuit of this embodiment, the filter constant of the digital filter is switched at a higher frequency among the carrier frequencies before and after switching, so that glitches are reduced.

  According to one embodiment of the control circuit, when the carrier frequency of the inverter is switched, the filter constant of the digital filter is switched at the timing of the higher frequency of the carrier frequencies before and after the switching. Can be reduced. That is, glitches can be reduced without stopping filtering by controlling the order of switching the filter constant of the digital filter and the timing of switching the carrier frequency of the inverter.

  Although the present invention has been described above with reference to specific embodiments and modifications, each embodiment and modification is merely illustrative, and those skilled in the art will recognize various modifications, modifications, alternatives, and substitutions. You will understand examples. For convenience of explanation, an apparatus according to an embodiment of the present invention has been described using a functional block diagram, but such an apparatus may be implemented in hardware, software, or a combination thereof. The present invention is not limited to the above-described embodiments, and various variations, modifications, alternatives, substitutions, and the like are included without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 100 Battery 102 Smoothing capacitor 200 Converter 202 Reactor 204, 206 Transistor 208, 210 Diode 212 Capacitor 300 Inverter 302 U-phase arm 304 V-phase arm 306 W-phase arm 308, 310, 312, 314, 316, 318 Transistor 320, 322, 324 326, 328, 330 Diode 400 Motor 500 Converter control unit 502 A / D conversion unit 504 Digital filter 506 Boost control unit 508 Inverter control unit

Claims (1)

A power supply voltage of a power conversion device that electrically generates AC power from DC power is input, noise superimposed on the power supply voltage can be removed, and the filter constant can be changed by changing the cutoff frequency. Is a digital filter to be changed ,
When changing the carrier frequency for adjusting the amount of power supplied to the power converter, so that the filter constant of the digital filter is switched in the state of the higher carrier frequency among the carrier frequencies before and after the change , The order of timing for switching the filter constant of the digital filter and the timing of changing the carrier frequency of the power converter is determined, and filtering is performed based on the filter constant switched at the timing of switching the filter constant of the digital filter. Digital filter.

Images