KR20140142604A - Method for estimating capacitance of capacitors in brushless dc motor drive system - Google Patents

Abstract

The present invention relates to a method for estimating capacitance of a capacitor in a BLDC motor drive system. According to an embodiment of the present invention to diagnose degradation state and to predict status of a capacitor by measuring capacitance of the capacitor in a BLDC motor drive system, the method includes the steps of: calculating an average value of a charging current charged in a capacitor connected to a front of an inverter circuit in parallel, when a BLDC motor is decelerated in a generator mode where energy is delivered by direct current electricity by converting a three-phase alternate current from rotation of a BLDC motor; calculating variation as to time of a charging voltage measured at both ends of the capacitor; and estimating capacitance of the capacitor from the average value of the charging current and the variation of the charging voltage.

Description

[0001] METHOD FOR ESTIMATING CAPACITORS IN CAPACITORS IN BRUSHLESS DC MOTOR DRIVE SYSTEM [0002]

The present invention relates to a method of estimating capacitor capacitance of a VDC motor drive system, and more particularly, to a method of estimating capacitor charge current in a generator mode or a converting mode when decelerating from a rotation state of a motor in a VDC motor drive system, To a method for estimating the capacitance of a capacitor using a voltage rise.

Compared to general DC motors, BID-DC motors have low commutator and brushes, so they have low noise and no frictional losses caused by commutator, so maintenance and repair costs are low, long service life and high reliability. Also, the inertia of the rotor is low, and the torque-to-inertia ratio, that is, the power density is larger than that of the conventional DC and induction machine.

The driving system of a general three-phase VDC motor includes a capacitor for supplying a DC voltage, a three-phase PWM inverter connected to a stator winding of a three-phase VDC motor, three Hall sensors sensor, a current sensor for measuring the phase current of the motor, and a controller for motor control.

1 is a conceptual diagram showing a configuration of a general three-phase BDD motor drive system.

In general, an inverter, which is a power conversion device that generates AC power from a DC power source for driving and controlling a motor, is used. In order to drive and control the 3-phase VDC motor, the system is constituted by a 3-phase PWM inverter. The three-phase inverter consists of three poles that can operate independently of each other and can control the output phase voltage, the output line voltage, and the load phase voltage of the inverter according to the switching state of each pole.

In the motor drive system, the direction of energy transfer varies depending on the operating conditions. In the motor mode (motor mode) in which energy is transferred from the DC power source to the 3-phase AC power source by rotation of the motor and the rotation of the motor, And a generator mode (generator mode) in which energy is transferred to the DC power source.

In order to examine the operation of the two driving modes of the motor driving system in the three-phase BDD motor driving system, the operation modes of the motor driving system are shown in FIG. 2 through FIG. Here, the input / output current of the inverter is I _dc , the input / output current of the power _source is I _source , the phase current of the inverter is I _phase , the capacitor current is I _C , and the capacitor voltage is V _C.

FIG. 2 is a conceptual diagram illustrating a circuit operation of the PWM section in the motor mode (inverting) of the three-phase VDC motor drive system according to one embodiment.

In FIG. 2- (a), the discharged capacitor current and the power supply current are inputted to the motor through the inverter to drive the motor. In FIG. 2 (b), since no current is input to the inverter, Is used.

3 is a conceptual diagram illustrating a circuit operation of a PWM section in a generator mode (Converting) of a three-phase VDE motor drive system according to an embodiment of the present invention.

In FIG. 3 (a), current is applied from the rotating motor to the capacitor and the power source through the conversion, but all the currents applied as the reverse bias of the diode rectifier circuit are used as the capacitor charging current. In Figure 3 (b), the current applied from the motor stays in the inverter through the reflux diode and no current is applied to the capacitor or power supply.

On the other hand, a smooth power supply voltage is required for driving the BIEDY motor, and this role is taken up by the current-termination capacitor.

However, the reduction of the capacitance due to the deterioration of the capacitor causes a deterioration of the filter performance. As a result, the unbalance of the phase current and the increase of the DC voltage pulsation result in the deterioration of the control performance and the secondary failure of the system.

KR 10-0829188 B1 KR 10-1175415 B1

In order to solve the problems derived from the prior art, it is an object of the present invention to diagnose a deterioration state and to predict a state of a capacitor by measuring a capacity of the capacitor in the VDD motor drive system.

According to an embodiment of the present invention, when the hybrid vehicle is decelerated in a generator mode in which three-phase alternating-current power is converted from rotation of a hybrid electric motor and energy is transmitted to a direct-current power source, Calculating an average value of charge currents charged in the capacitors connected in parallel; Calculating a variation with time of the charge voltage measured across the capacitor; And estimating a capacitance of the capacitor based on an average value of the charging current and a variation amount of the charging voltage.

Preferably, in the step of calculating the average value of the charging current, the generator mode is a period during which the rotational speed of the VDD motor decelerates from the rated speed.

Preferably, the DC power source converted in the step of calculating the average value of the charging current is controlled by pulse width modulation (PWM) to charge the capacitor.

에 의해 산출되는 것을 특징으로 한다. 여기서, I_{C (n)}은 PWM 제어에서 n번째 커패시터 전류(펄스)이고, Duty ratio_(n)은 PWM 제어에서 on/off 듀티비이다.Preferably, the average value I _{C ( avg )} of the charging current charged in the capacitor is calculated by the following equation

Is calculated by the following equation. Where I _{C (n)} is the nth capacitor current (pulse ₎ in PWM control and Duty ratio _(n) is the on / off duty ratio in PWM control.

Preferably, the charging current at the step of calculating the average value of the charging current is measured by using a current sensor connected to the front end of the inverter circuit.

Preferably, the step of calculating the amount of change of the charging voltage with respect to time is characterized by calculating a variation with time of the charging voltage in a period in which the charging voltage across the capacitor rises.

에 의해 상기 커패시터의 용량(C)이 추정되는 것을 특징으로 한다. 여기서, I_{C ( avg )}는 커패시터 충전전류의 평균값이고, dv_c는 커패시터 충전전압 변화량이고, v_{c ( t1 )}은 t₁ 시간에 샘플링한 커패시터 전압이고, v_{c ( t2 )}은 t₂ 시간에 샘플링한 커패시터 전압이다.Preferably, in the step of estimating the capacity of the capacitor,

The capacity C of the capacitor is estimated by the following equation. Here, I _{C (avg)} is the average value of the capacitor charge current, dv _c is the capacitor charging voltage variation, v _{c (t1)} is the capacitor voltage sampled in t ₁ sigan, v _{c (t2)} is t ₂ hours It is the sampled capacitor voltage.

According to the method of estimating the capacitance of the BDDi motor drive system of the present invention as described above, the following effects can be obtained.

First, since the topology of the existing motor drive system can be used as it is, no additional hardware is needed and the cost can be reduced.

Second, the addition of a simple algorithm makes it easy to estimate the capacity of a capacitor.

Third, it is possible to estimate the capacitor capacity of a wide range of motor drive systems from small capacity to large capacity.

Fourth, the capacitor estimation operation according to the present invention has no effect on the operation of the entire system.

Fifth, a high resolution A / D converter is not required, and capacitor capacity can be accurately estimated.

1 is a conceptual diagram showing the configuration of a general VDD motor drive system,
FIG. 2 is a conceptual diagram illustrating a circuit operation of a PWM section in the motor mode (inverting) of a three-phase VDE motor drive system,
3 is a conceptual diagram illustrating a circuit operation of a PWM section in a generator mode (Converting) of a three-phase VDC motor drive system,
FIG. 4 is a graph for explaining characteristics of circuit operation for each section of FIGS. 2 to 3,
FIG. 5 is a flowchart illustrating a method of estimating a capacitance of a BD drive motor drive system according to an embodiment of the present invention,
FIG. 6 is a graph showing the amount of change of the voltage raised by the conversion in the section (C) of FIG. 3 with respect to time.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Brief Description of Drawings FIG. 1 is a block diagram of a computer system according to an embodiment of the present invention; FIG. 2 is a block diagram of a computer system according to an embodiment of the present invention; FIG.

1 to 3 as in the prior art, and prior to describing a capacitor capacity estimation method of a BDDY motor drive system according to an embodiment of the present invention, The characteristics of the circuit operation for each section of FIG. 2 to FIG. 3 will be described with reference to FIG.

First, (A) section is a section of the motor mode (inverting mode), in which the speed is increased in order to start the motor drive for the first time and reach the rated speed. To increase the speed, the phase current should be given as the maximum value. The current and voltage of the capacitor are repeatedly charged and discharged due to the pulse width modulation (PWM) control, and the phase current becomes maximum at this time. Here, for the sake of convenience, the graphs for charging and discharging are not shown, and the capacitor voltage is represented by the average voltage only.

Next, the section (B) is an interval of the motor mode as in the section (A), and the motor speed rises to reach the desired speed or the rated speed, thereby performing normal operation. Since the speed has already risen to the target value, it is a section having a constant speed, and the speed is maintained only by the minimum phase current. In this section, the current and voltage of the capacitor are repeatedly charged and discharged due to the pulse width modulation control.

Next, (C) is the section where the deceleration of the motor starts. It is a section of the generator mode (converting mode) in which the speed of the motor is not maintained or driven, and thus the energy is no longer transferred from the power source and the energy is reversely transferred from the rotation of the motor. This interval is used for the practice of the present invention, and the capacity is estimated by charging the capacitor using the current received from the motor. Of course, the speed decelerates from the rated speed. Since it is the generator mode, an arbitrary phase current is generated from the motor, so that the current of the capacitor is constantly transmitted, and the voltage across the capacitor gradually increases due to the constant charging current. Since the pulse width modulation control is performed in the generator mode, the actual phase is transmitted in the form of a pulse differently from that shown in the figure.

Next, the section (D) is a section for decelerating or stopping the motor as in the section (C), and is a section of the generator mode. (C), which is a section for estimating a capacitor in the entire section for decelerating or stopping the motor, and a section (D) for estimating the remaining capacity, ) Section. Thus, the (D) interval is the last interval until stopping, which completes the capacitor estimation and slows down only by the load of the motor.

As shown in FIG. 5, the method of estimating the capacitance of a BDDC motor drive system according to an embodiment of the present invention based on the above description is characterized in that a three-phase AC power source is converted from a rotation of a VDD motor, Calculating (S101) an average value of a charging current charged in a capacitor connected in parallel to a front end of the inverter circuit when the VDD motor is decelerated in a generator mode in which energy is transferred; Calculating a change amount with respect to time of a charge voltage measured at both ends of the capacitor (S103); Estimating a capacity of the capacitor based on an average value of the charging current and a variation amount of the charging voltage (S105).

In the step S101 of calculating the average value of the charging currents, all the current from the inverter due to the reverse bias of the diode rectifier in the generator mode is used as the charging current of the capacitor. At this time, as described above, the generator mode is a period in which the rotation speed of the VDD motor decelerates from the rated speed, and the converted DC power is charged to the capacitor by PWM control.

Here, the average value I _{C ( avg )} of the charging current charged in the capacitor is calculated by the following equation (1).

In Equation (1), I _{C (n)} is an n-th capacitor current (pulse ₎ in PWM control, and duty ratio _(n) is an on / off duty ratio in PWM control.

Meanwhile, the charging current in step S101 of calculating the average value of the charging current may be measured using a current sensor connected to the front end of the inverter circuit. The current sensor may be variously determined according to the state or condition of the system Of course, be selected.

The step (S103) of calculating the variation with respect to time of the charging voltage is a step of calculating a variation with respect to time of the charging voltage in a period in which the charging voltage across the capacitor rises. At this time, the rising variation of the charging voltage may appear as shown in FIG. 5, and it is well known that the variation varies depending on the capacity of the capacitor and the state of the generator mode.

In the step S105 of estimating the capacitance of the capacitor, the capacitance C of the capacitor can be estimated by the following equation (2).

In the above Equation 2 I _{C (avg)} is the average value of the capacitor charge current, dv _c is a capacitor and the charging-circuit voltage variation, v _{c (t1)} is the capacitor voltage sampled in t ₁ sigan, v _{c (t2)} is t _It is the capacitor voltage sampled in ₂ hours.

As described above, according to the present invention, it is possible to effectively estimate the capacitor capacity of the VDD motor drive system by using the capacitor charging current and the charging voltage. By estimating the capacitances of the VDD motor drive system, it is possible to predict the performance degradation due to the capacitor capacitance change. In addition, capacity estimation can be implemented without any additional hardware to check the capacity of the capacitor, and capacity estimation can be realized even with one sampling without high resolution A / D converter. In addition, by estimating the capacity of the capacitor of the motor drive system and estimating the replacement period, it is possible to prevent human and material damage due to malfunction of the non-Diesel motor.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the claims of the invention to be described below may be better understood. The embodiments described above are susceptible to various modifications and changes within the technical scope of the present invention by those skilled in the art. These various modifications and changes are also within the scope of the technical idea of the present invention and will be included in the claims of the present invention described below.

Claims (7)

When the VDD motor is decelerated in a generator mode in which energy is transferred from a 3-phase AC power source to a DC power source by rotation of the VDD motor, an average value of the charging current charged in the capacitor connected in parallel to the preceding stage of the inverter circuit is calculated ;
Calculating a variation with time of a charging voltage measured across the capacitor; And
Estimating a capacitance of the capacitor from an average value of the charging current and a variation amount of the charging voltage;
Wherein the capacitor capacity estimating method of the BDDi motor drive system comprises: The method according to claim 1,
Wherein the generator mode is a period during which the rotation speed of the VDD motor decelerates from the rated speed in the step of calculating the average value of the charging current. The method according to claim 1,
Wherein the converted DC power is charged to the capacitor by PWM control of the converted DC power in the step of calculating the average value of the charging current. The method of claim 3,
The average value I _{C ( avg )} of the charging current charged in the capacitor is calculated by the following equation

(Where I _{C (n)} is the nth capacitor current (pulse ₎ in PWM control and Duty ratio _(n) is the on / off duty ratio in PWM control).
And calculating the capacitance of the capacitor of the BDDY motor drive system. The method according to claim 1,
Wherein the charge current in the step of calculating the average value of the charge current is measured using a current sensor connected to the front end of the inverter circuit. The method according to claim 1,
Wherein the step of calculating the variation with respect to time of the charging voltage calculates a variation with time of the charging voltage in a period in which the charging voltage across the capacitor rises, . The method according to claim 1,
In the step of estimating the capacity of the capacitor,

(Where, I _{C (avg)} is the average value of the capacitor charge current, dv _c is a capacitor charging a voltage change amount, v _{c (t1)} is the capacitor voltage sampled in t ₁ sigan, v _{c (t2)} is t ₂ sigan Is the capacitor voltage sampled at.
Wherein the capacitance (C) of the capacitor is estimated based on the capacitance of the capacitor.

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