JP2016086492A - Capacitor discharge device and control method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that when lowering the voltage in a short time by discharging a smoothing capacitor, it is required to set a large power consumption of a discharge resistor, and as a result, the physique of a resistor increases, thus increasing the cost and the size for implementation.SOLUTION: A capacitor discharge device for discharging a smoothing capacitor connected in parallel with a voltage type inverter circuit performing power conversion by using a power supply exceeding DC voltage 60 V, as an input power supply, includes a power consumption circuit having at least one power consumption resistor connected in parallel with both terminals of the smoothing capacitor, a discharge circuit for controlling a current flowing through the resistor to a substantially constant first predetermined value, and a power supply circuit supplying a power for driving the discharge circuit from both terminals of the smoothing capacitor.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a smoothing capacitor discharging apparatus and a control method thereof.

  A voltage source inverter (hereinafter referred to as an inverter in the present invention) is a power converter that converts a DC voltage into an AC voltage, and is widely used for variable speed driving of an AC motor. It is also one of the core components of hybrid electric vehicles and electric vehicles that are expanding the market scale against the backdrop of heightened environmental awareness.

  In these automobile applications, in particular, in order to protect the passenger from danger caused by some trouble, various abnormality detection means are provided, and the system is shifted to a safe operation state according to the abnormality detection result.

  Further, when the DC voltage supplied to the inverter exceeds 60V, the power consuming means for discharging the charge of the smoothing capacitor connected in parallel to the inverter within a predetermined time in order to remove the voltage ripple associated with the switching operation. When the vehicle is stopped by turning off the ignition or in the event of an accident, etc., when the system determines that it is necessary, the power consuming means is operated, the capacitor is discharged, and the voltage is Safety is ensured at a level where there is no human shock (less than 60V).

  Note that at least two means are required to be used as power consuming means (redundancy), and the discharge time is, for example, within 5 s for the first means and less than 60 V within 5 minutes for the second means. There is a need.

  Such a technique is described in, for example, Patent Document 1 and Patent Document 2.

Japanese Utility Model Publication No. 63-29391 Japanese Patent No. 4418318

  First, in the method described in Patent Document 1, as a power consuming means for discharging the charge of the smoothing capacitor within a predetermined time, a circuit in which a circuit in which a discharge resistor and a switch element are connected in series is connected in parallel to the smoothing capacitor (discharge) Circuit) and some control is described. However, details of the control are not described.

  On the other hand, in the method described in Patent Document 2, for example, a method for controlling the discharge circuit exemplified in Patent Document 1 is shown in detail. According to this method, the voltage of the smoothing capacitor voltage is detected, the ignition is turned off, and the detection is performed at predetermined time intervals based on the time when an open command of the contactor connected in series between the DC battery and the inverter is given. A change in voltage value is calculated, and the result is compared with a predetermined threshold value to determine whether the capacitor discharge is normally performed. Thereby, for example, when the contactor has failed and is against the command and forms a closed circuit, it can be determined that there is an abnormality, and the discharge operation is stopped to cause a malfunction of the discharge resistance (such as burning due to overheating). Can be prevented.

  However, this method requires a complicated process of calculating and comparing the voltage change, and a predetermined time is required for confirming the diagnosis. There is a case where it is required to continue discharging for a period. Since the diagnosis time is determined systematically, it is longer than the diagnosis time for each unit. And if you set the rated power of the discharge resistor in consideration of the power consumed until the diagnosis result is confirmed, the physique of the resistor will increase, and eventually the size for cost increase and mounting will increase. There were issues such as.

In order to solve the above-described problems, a capacitor discharge device according to the present invention discharges a charge of a smoothing capacitor connected in parallel with a voltage source inverter circuit that performs power conversion using a power supply exceeding a DC voltage of 60 V as an input power supply A power consumption circuit having at least one power consumption resistor connected in parallel to both terminals of the smoothing capacitor, and a discharge circuit for controlling a current flowing through the resistor to a substantially constant first predetermined value; ,
A power supply circuit for supplying power for driving the discharge circuit from both terminals of the smoothing capacitor.

  Also, the control method of the capacitor discharge device according to the present invention controls the capacitor discharge device that discharges the electric charge of the smoothing capacitor connected in parallel with the voltage source inverter circuit that performs power conversion using the power source exceeding the DC voltage of 60V as the input power source. A method of controlling a power consumption circuit by controlling a current flowing through a power consumption circuit having at least one power consumption resistor connected in parallel to both terminals of the smoothing capacitor to a substantially constant first predetermined value. A power source for driving the circuit is supplied from both terminals of the smoothing capacitor.

  If the capacitor discharge device or the method for controlling the capacitor discharge device according to the present invention is employed, the smoothing capacitor can be discharged and the voltage thereof can be reduced to a safe value (less than 60 V).

It is a whole circuit block diagram of the drive system which concerns on this embodiment. It is a circuit diagram centering on the discharge circuit regarding this embodiment. 6 is a waveform diagram in which an output of a current detection resistor 25 is detected through a low-pass filter circuit 23. FIG. The voltage across the capacitor 12 and the current flowing through the discharge resistor 20 are shown. FIG. 3B shows the voltage across the capacitor 12 and the current flowing through the discharge resistor 20 when the time axis from 0.5 s to 0.6 s in FIG. In the example described in Patent Document 2, the voltage across the smoothing capacitor after the contactor is determined to be normal and the current flowing through the discharge resistor are shown. 2 is a discharge characteristic when the operation of the discharge circuit is prohibited by the circuit diagram shown in FIG. 2 according to the present embodiment. 6 is a circuit diagram centering on a discharge circuit according to Embodiment 2. FIG. The discharge characteristic of the capacitor | condenser 12 at the time of applying this Example 2 is shown.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is an overall circuit configuration diagram of a drive system according to the present embodiment. As shown in FIG. 1, a variable speed drive system for an AC motor for automobile use includes a high-voltage battery 1, an inverter 2, an AC motor 3, a DC input voltage detector 4, current detectors 5 to 7 for AC output, and rotation. It comprises a position detector 8, a control circuit 9, a gate drive circuit 10, and a switching power supply 11 necessary for control and gate drive. The inverter 2 is connected in parallel with a smoothing capacitor (C0) 12 and a capacitor (C1) 13 and a capacitor (C2) 14 connected in series. For example, the capacitor C0 is as large as 800uF, and the capacitor C1 and the capacitor C2 are each as small as 0.1uF. A discharge circuit 15 is further connected in parallel to the inverter 2.

  As shown in FIG. 1, for example, the control circuit 9 and the gate drive circuit 10 to which the operating voltage is applied from the low-voltage battery 17 from the switching power supply 11 to which 12V is input, the inverter 2 outputs its output based on a command from a host controller (not shown). The current is controlled so as to become a predetermined value, and the motor 3 performs an electric or power generation operation.

  The contactor 16 connected in series to the DC bus (+) (−) is opened and closed by a high voltage battery controller (not shown), for example, and forms a closed circuit between the high voltage battery 1 and the inverter 2 during operation. . In the electric operation, current flows from the battery 1 to the inverter 2, and in the power generation operation, current flows from the inverter 2 to the battery 1.

  FIG. 2 is a circuit diagram centering on the discharge circuit according to the present embodiment. A discharge circuit 26 and a power supply circuit 27 that drives the discharge circuit 26 are connected to the DC bus (+) (−) connected to the capacitor 12.

  The discharge circuit 26 includes a discharge resistor 20 as a power consumer, a switch element 21 for controlling the current of the discharge resistor 20 to be constant, a current detection resistor 25, a current command setting circuit 24, a low-pass filter circuit 23, And a hysteresis comparator circuit 22.

  The hysteresis comparator circuit 22 corresponds to a predetermined current by dividing the voltage obtained through the current detection resistor 25 and passing through the low-pass filter circuit 23 proportional to the current flowing through the discharge resistor and the power supply voltage of the discharge circuit 26 with a voltage dividing resistor. The switch element 21 is turned on / off using the set voltage as an input.

  The power supply circuit 27 includes a resistor for limiting the current, a Zener diode connected in series to the resistor and obtaining a predetermined substantially constant voltage, a ripple removing capacitor connected in parallel to the Zener diode, It is composed of

  3 (a) to 3 (c) show the results of simulating the voltage at both ends of the DC bus (+) (−) and the current flowing through the discharge resistor by SPICE during the discharging operation of the circuit shown in FIG. Show.

  The smoothing capacitor capacitance C0 of the capacitor 12 is 800 uF, the resistance value of the discharge resistor 20 is 120Ω, the resistance value of the current detection resistor 25 is 0.2Ω, and the hysteresis width of the hysteresis comparator 22 is +/− 5 mV, The voltage reference (current command) to be compared is set to 54 mV, that is, the discharge resistance current command is set to 0.27 A.

  Then, due to the load dump (the contactor 16 was opened during the motor power generation operation), the initial voltage of the smoothing capacitor increased from the high voltage battery voltage 400V (maximum value) to 550V.

  FIG. 3A is a waveform diagram in which the output of the current detection resistor 25 is detected through the low-pass filter circuit 23. The horizontal axis is time, and the vertical axis is voltage value. In general, the current command can be controlled up to 0.8 s, but after that, it decreases with respect to the command current. The power consumption at the discharge resistor 20 is 8.7 W up to 0.8 s and decreases thereafter.

  FIG. 3B shows the voltage across the capacitor 12 and the current flowing through the discharge resistor 20. FIG. 3C shows the voltage across the capacitor 12 and the current flowing through the discharge resistor 20 when the time axis from 0.5 s to 0.6 s in FIG. 3B is expanded.

  Referring to FIG. 3C, it can be seen that the discharge resistance current is controlled in a pulse shape by the switch element 21. FIG. In the hysteresis width for controlling the set switch, the switching frequency is about 500 Hz. During the discharge operation, the loss associated with the switching and the conduction loss of the switch element 21 are added to the power consumption to assist the capacitor discharge.

  The voltage between both ends of the capacitor 12 is approximately 1.7 s and less than 60V. In addition, it becomes 270V or less after 0.8s. On the other hand, the current limiting resistor used in the power circuit 27 was 150 kΩ, and the Zener voltage was 12V. In the element model used for SPICE simulation, the Zener voltage of 12V (power supply voltage) cannot be maintained due to the balance of current supply to the hysteresis comparator circuit 22 at 1.8mA (= 270 / 150e3) or less. As a result, it was found that the current corresponding to the current command generated by dividing the power supply voltage also decreases, so that the current flowing through the discharge resistor 20 decreases.

  When a certain time elapses, the discharge resistance current falls below a predetermined value, but the discharge can be continued. It was confirmed that the discharge was possible to 60 V or less within a predetermined time. Here, the power supply voltage range of the used comparator element is 2 to 36V, and the gate threshold voltage of the switch element is at least 3.5V.

  FIG. 4 shows, for example, the voltage across the smoothing capacitor and the current flowing through the discharge resistor after the contactor is normally determined in the embodiment described in Patent Document 2. The switch element 21 connected in series with the discharge resistor is controlled to be always on, and the discharge resistance current decreases with a decrease in the voltage across the smoothing capacitor. The discharge resistance is set to 1000Ω, which can discharge to 60V or less in about 1.7s.

  In the example of FIG. 4, the average current flowing through the resistor for 2 seconds is about 0.28A. Therefore, the average power consumption at the discharge resistance is 78.4 W, which is about 10 times larger than 8.7 W or less of the present invention.

  Furthermore, when there is no abnormality determination and the discharge is performed while the contactor is in the closed circuit formation state, the high voltage battery voltage 400V is applied to the discharge resistance as the power consumption. As a result, power consumption reaches 160W.

  From these results, it can be seen that by applying the present invention, predetermined discharge can be achieved in a short time and the power consumption of the discharge resistor can be significantly reduced. As a result, the discharge circuit can be reduced in size and cost.

  Furthermore, since the power supply for operating the discharge circuit is obtained from both ends of the capacitor 12, if the voltage is 60 V or higher, the discharge operation continues even when the low-voltage battery that is the power supply for the control circuit 9 is disconnected. It also has a unique effect of being able to.

  Further, since the power source for operating the discharge circuit discharges the capacitor 12, it can be utilized as a constant discharge circuit that is required to be mounted separately from a circuit that can realize discharge in an early time for ensuring sufficient safety.

  FIG. 5 shows the discharge characteristics of the smoothing capacitor (C0) 12 with the switch element 21 of FIG. 2 held off. It became 60V or less in about 270s (5 minutes or less).

FIG. 6 is a circuit diagram centering on the discharge circuit according to the second embodiment. The difference from the first embodiment is that a discharge circuit 60 to which a comparator circuit 61, a voltage threshold setting circuit 62, and a high voltage detection circuit 63 are added is used instead of the discharge circuit 26 described in the first embodiment.
The voltage threshold setting circuit 62 divides the power supply voltage and sets a voltage value detected as an overvoltage in the control circuit 9 shown in FIG.

  The high voltage detection circuit 63 supplies a voltage obtained by dividing the voltage across the capacitor 12 to the (−) input of the comparator circuit 61 and the output voltage of the voltage threshold setting circuit 63 to the (+) input. Then, the open collector output of the comparator circuit 61 is connected to the output of the low-pass filter circuit 23.

  This operation will be described. The output of the comparator circuit 61 is turned on when the voltage across the smoothing capacitor C0 exceeds the overvoltage value set as the threshold voltage by the input connection as described above.

  This output is connected to the output stage of the current detection path, and in the ON state, the current detection value is held at “0” regardless of the actual current. As a result, since it is below the set value of the current command setting circuit 24, the switch element 21 is always on.

  Then, discharge at the discharge resistor 20 is performed. The voltage across the smoothing capacitor (C0) 12 decreases, and the open collector output of the comparator circuit 61 is turned off when the voltage falls below a threshold set as an overvoltage. As a result, the current detection value becomes a value corresponding to the actual current, and the hysteresis comparator circuit 22 performs the on / off operation based on the setting value of the current designation setting circuit 24. The discharge action as described in the first embodiment is brought about.

  When the overvoltage threshold is exceeded, the switch element 21 continues to be turned on as in the conventional method. If the contactor 16 is not opened, the voltage does not exceed the maximum value of the high voltage battery (the reason is that the minimum voltage value is obtained when multiple voltage sources are connected in parallel). A diagnostic process for determining contactor abnormality is unnecessary.

  FIG. 7 shows the discharge characteristics of the capacitor 12 when Example 2 is applied. The overvoltage threshold is set to 460V that can protect the inverter circuit. And the maximum value of high voltage battery is 400V.

  According to the present example, the time to reach 60 V or less by discharge is 1.45 s, which is shorter than 1.7 s of Example 1. In addition, the resistance power consumption during the ON period of the switch element 21 is over 2kW, but the application time is as short as 30ms, and up to about 1000 times the rated power can be allowed by using a resistor with high surge resistance. It is. Therefore, the discharge circuit can be reduced in size and cost.

  Further, if this embodiment is adopted, the overvoltage state can be quickly eliminated, and an inverter circuit 2 connected to the high voltage battery 1 or a DCDC converter circuit that performs power conversion from the high voltage battery 1 (not shown) to the low voltage battery 17 is usually used. Enable operation.

  As a result, the discharge of the capacitor 12 can be assisted using these circuits. As a result, the power consumed by the discharge resistor 20 can be reduced, and the size and cost of the discharge circuit can be reduced.

  The present invention can be applied to an inverter connected to a high voltage battery for automobile use.

DESCRIPTION OF SYMBOLS 1 ... High voltage battery, 2 ... Inverter, 3 ... Motor, 4 ... DC voltage detector, 5-7 ... Current detector, 8 ... Rotation position detector, 9 ... Control circuit, 10 ... Gate drive circuit, 11 ... Switching power supply 12-14: Capacitor, 15 ... Discharge circuit, 16 ... Contactor, 17 ... Low voltage battery, 20 ... Discharge resistor, 21 ... Switch element, 22 ... Hysteresis comparator circuit, 23 ... Low pass filter circuit, 24 ... Current command setting circuit, 25 ... Current detection resistor, 26 ... Discharge circuit, 27 ... Power supply circuit, 28 ... Discharge circuit, 61 ... Comparator circuit, 62 ... Voltage threshold setting circuit, 63 ... High voltage detection circuit, C0 ... Capacitor (and its capacity), C1 ... Capacitor (and its capacity), C2 ... Capacitor (and its capacity), Tu + ... Transistor, Tv + ... Transistor, Tw + ... Transistor, Tu -... Transistor, Tv -... Transistor, Tw -... Transistor, Du + ... Diodes, Dv + ... Diodes, Dw + ... Diodes, Du -... Diodes, Dv -..., Dw -... Diodes

Claims (6)

A capacitor discharge device that discharges the charge of a smoothing capacitor connected in parallel with a voltage source inverter circuit that performs power conversion using a power supply exceeding a DC voltage of 60 V as an input power supply,
A power consuming circuit having at least one power consuming resistor connected in parallel to both terminals of the smoothing capacitor;
A discharge circuit for controlling the current flowing through the resistor to a substantially constant first predetermined value;
A capacitor discharge device comprising: a power supply circuit that supplies power for driving the discharge circuit from both terminals of the smoothing capacitor. The capacitor discharge device according to claim 1,
The capacitor discharge device in which the current value controlled to be substantially constant is set so that the time until the voltage across the smoothing capacitor becomes less than 60 V is less than or equal to a predetermined value. The capacitor discharging device according to claim 1 or 2,
A voltage detection circuit for detecting a voltage across the smoothing capacitor;
A voltage threshold setting circuit for setting a predetermined voltage value;
A comparator circuit that compares the voltage value detected by the voltage detection circuit with the predetermined voltage value set by the voltage threshold setting circuit;
When the discharge circuit determines that the voltage across the smoothing capacitor exceeds an overvoltage protection threshold for protecting the voltage source inverter circuit based on the comparison result of the comparator circuit, the current flowing through the resistor is the first current flowing through the resistor. A capacitor discharge device that controls to be a second predetermined value that is greater than one predetermined value. A method for controlling a capacitor discharge device that discharges a charge of a smoothing capacitor connected in parallel with a voltage source inverter circuit that performs power conversion using a power supply exceeding a DC voltage of 60 V as an input power supply,
Controlling a current flowing in a power consumption circuit having at least one power consumption resistor connected in parallel to both terminals of the smoothing capacitor to a substantially constant first predetermined value;
A method for controlling a capacitor discharge device, wherein a power source for driving a circuit for controlling the power consumption circuit is supplied from both terminals of the smoothing capacitor. It is a control method of the capacitor discharge device according to claim 4,
The method for controlling a capacitor discharge device, wherein the current value controlled to be substantially constant is set such that the time until the voltage across the smoothing capacitor is less than 60 V is less than or equal to a predetermined value. A method for controlling a capacitor discharge device according to claim 1 or 2,
Compare the voltage value detected the voltage across the smoothing capacitor and the predetermined voltage value,
Based on the comparison result, when it is determined that the voltage across the smoothing capacitor has exceeded the overvoltage protection threshold for protecting the voltage source inverter circuit, the current flowing through the power consumption circuit is greater than the first predetermined value. A method for controlling a capacitor discharge device that controls the second predetermined value.