JP2015023601A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device that shortens a discharge time by controlling on/off switching elements of an inverter circuit.SOLUTION: An inverter section 10 of the power conversion device includes: switching elements Q1, Q2, Q3 and Q4 connected in series from a positive input section to a negative input section of a DC power supply smoothed by smoothing capacitors C1, C2; resistors R3 and R4 connected in parallel with the switching elements Q2 and Q3, respectively; and a control section connected to respective gate terminals of the switching elements Q1-Q4 to control on/off the four switching elements individually. The control section turns on the switching elements Q1 and Q4 and turns off the switching elements Q2 and Q3 to discharge charges stored in the smoothing capacitors C1, C2 via the resistors R3, R4 as well as via resistors R1, R2.

Description

  Embodiment of this invention is applied to the power converter device which can shorten the discharge time of the smoothing capacitor inside a power converter device.

  Usually, a power conversion device such as an inverter device or a converter device is provided with a discharge circuit for discharging electric charge remaining in a smoothing capacitor inside the device. This discharge circuit is for preventing an electric shock to the human body when the inside of the apparatus is inspected and repaired for maintenance or the like.

  This discharge circuit discharges the residual charge of the smoothing capacitor, and a specified safety voltage (for example, 50 [V]) that does not adversely affect the human body within a specified time (for example, 10 [min]). ). As a method of reducing the residual voltage of the smoothing capacitor, a method of discharging using an external discharge circuit or a method of limiting the discharge current according to the residual voltage is known (for example, see Patent Document 1). .

JP 2009-112156 A

  The above-described method of providing a discharge circuit externally has a problem that the discharge circuit also becomes large because the discharge current becomes large as the power capacity controlled by the power converter increases. Further, the discharge current limiting method described in Patent Document 1 relates to a method of suppressing power loss during operation by performing constant power discharge, and does not aim at shortening the discharge time.

  As described above, when the electric power capacity of the electric motor controlled by the power conversion device is large, the residual charge amount of the smoothing capacitor when the DC power supply to the power conversion device is shut off also becomes a large value. Since it is as long as 10 [min] as in the case of the above example, a method of easily discharging in a short time is desired.

  The present invention has been made to solve the above-described problems, and provides a power conversion device that shortens a discharge time by controlling on / off of a switching element of a conventional inverter circuit. Objective.

  In order to achieve the above object, a power conversion device according to claim 1 of the present invention includes a smoothing unit that smoothes a DC power supplied via a switch that turns on and off the supply of DC power, and a smoothing unit. An inverter unit that converts a DC power supplied via an AC power source to the AC power source, wherein the smoothing unit includes a + side input unit and a reference potential of the DC power supplied via the switch Connected in parallel to the first smoothing capacitor, the second smoothing capacitor connected between the negative input side of the DC power supply and a reference potential, and the first and second smoothing capacitors First and second resistors, wherein the inverter unit is connected in series from a + side input unit to a − side input unit of a DC power source smoothed by the smoothing capacitor. 3rd and 4th switching element A third and a fourth resistor connected in parallel to the second switching element and the third switching element, respectively, and a connection point between the second switching element and the third switching element; Connected to an inverter output terminal for supplying AC power to an externally connected load and to the respective gate terminals of the first to fourth switching elements, the four switching elements are turned on / off. A control unit that individually controls the control unit, and when the switch is turned off and the supply of DC power is cut off, the control unit turns on the first and fourth switching elements, and the second and second control elements. By turning off the switching element 4, the charge charged in the first and second smoothing capacitors is discharged through the third and fourth resistors.

1 is a circuit diagram of a power conversion apparatus according to Embodiment 1. FIG. The timing chart explaining operation | movement of an inverter part. FIG. 6 is a diagram showing discharge characteristics according to Example 1. The circuit diagram of the power converter device which concerns on Example 2. FIG.

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

  FIG. 1 is a circuit diagram of a power conversion apparatus 100 according to Embodiment 1 of the present invention. The power conversion apparatus 100 includes a smoothing unit 1 and 2, a snubber unit 3 and 4, a U-phase inverter unit 10 and a V-phase inverter unit 20, a W-phase inverter unit 30, a control unit 50, and the like.

  FIG. 1 shows a DC power source P for supplying power to the power conversion device 100, switches SW1 and SW2 for turning on / off the DC power supplied from the DC power source P to the power conversion device 100, and power conversion. A description will be given assuming that the electric motor 40 is connected as a load of the apparatus.

  The smoothing unit 1 includes a smoothing capacitor C1 (first smoothing capacitor) and a bleeder resistor R1 (first resistor) connected in parallel to the capacitor C1. When the switches SW1 and SW2 are turned on, the voltage ± E [V] is supplied from the DC power source P to the power converter 100. Since this DC power supply P uses a power supply immediately after rectification, the DC power supply P includes a pulsating flow. The smoothing capacitor C1 absorbs the pulsating flow and smoothes it. There is an effect of keeping the voltage constant by supplying the variable power to the load.

  By connecting the bleeder resistor R1 in parallel to the smoothing capacitor C1, the bleeder resistor R1 has an effect of constantly flowing a predetermined current and stabilizing the output voltage when the output of the smoothing unit 1 is no load or light load.

  The snubber unit 3 absorbs the spike voltage when the switching elements Q1 (first switching element) to Q4 (fourth switching element) of the U-phase inverter unit 10 are turned on / off. Since the spike voltage has a high frequency component, the spike voltage is absorbed by the diode D11 and the resistor R11 after passing through the capacitor C11.

  The inverter unit includes a U-phase inverter unit 10, a V-phase inverter unit 20, and a W-phase inverter unit 30. Since these inverter units have the same configuration, the configuration of the U-phase inverter 10 will be described.

  In the U-phase inverter unit 10, four switching elements Q1 to Q4 are connected in series to both ends of the supplied DC power sources + E and -E. As the switching element, for example, an IGBT (Insulated Gate Bipolar Transistor) is used. Diodes D3 to D6 (freewheeling diodes) are connected in antiparallel to the switching elements Q1 to Q4, respectively. Also, clamp diodes D1 and D2 for clamping the output voltage of each phase (in this case, the U phase) to a neutral point are connected to the three-level inverter shown in the present embodiment. In the case shown in the figure, by turning on switching elements Q2 (second switching element) and Q3 (third switching element), the U-phase output voltage (hereinafter referred to as U-phase voltage) Vu is neutral. Can be clamped to. Details will be described later.

  In this embodiment, a resistor R3 (third resistor) and a resistor R4 (fourth resistor) are connected in parallel with the switching elements Q2 and Q3, respectively. This means that the resistors R3 and R4 are connected between the U-phase voltage Vu and the neutral point via the clamp diodes D1 and D2, and the U-phase inverter output voltage at the time of switching element failure is stabilized. ing.

  Since the V-phase inverter unit 20 and the W-phase inverter unit 30 are the same as the U-phase inverter unit 10, description thereof is omitted.

  The control unit 50 is connected to the gate terminals of the switching elements Q1 to Q4 constituting the U-phase inverter unit 10, the V-phase inverter unit 20, and the W-phase inverter unit 30, and performs on / off control of the switching elements Q1 to Q4. Do.

  FIG. 2 is a timing chart for explaining the operation of the inverter unit (a general term for the U-phase inverter unit 10, the V-phase inverter unit 20, and the W-phase inverter unit 30). The horizontal axis indicates the phase angle [rad] of each phase. Q1 to Q4 indicate ON / OFF (OFF) states of the switching elements Q1 to Q4 of the U-phase inverter unit 10. The switching element is electrically connected between the collector terminal and the emitter terminal when turned on, and is cut off when turned off.

  The U-phase voltage Vu is obtained by performing on / off control of the switching elements Q1 to Q4 at the illustrated timing. An example of the operation will be briefly described.

  When switching element Q1 is on, Q2 is on, Q3 is off, and Q4 is off (for example, at T1 in FIG. 2), + E [V] is output as U-phase voltage Vu.

  When the switching element Q1 is off, Q2 is on, Q3 is on, and Q4 is off (for example, at T2 in FIG. 2), the U-phase voltage Vu is 0 [V].

  When switching element Q1 is off, Q2 is off, Q3 is on, and Q4 is off (for example, at T3 in FIG. 2), -E [V] is output as U-phase voltage Vu.

  When the switching element Q1 is off, Q2 is on, Q3 is on, and Q4 is off (for example, at T4 in FIG. 2), the U-phase voltage Vu is 0 [V].

  When switching element Q1 is on, Q2 is on, Q3 is off, and Q4 is off (for example, at time T5 in FIG. 2), + E [V] is output as U-phase voltage Vu. T5 is the same as T1 after one cycle, and is repeatedly output in the same manner.

  As apparent from the above description, the three-level inverter outputs three-level voltages of + E [V], 0 [V], and −E [V].

  The control unit 50 performs control so that the V-phase voltage Vv delayed by 2π / 3 from the U-phase voltage Vu is output.

  Similarly, the control unit 50 performs control so that the W-phase voltage Vw delayed by 2π / 3 from the V-phase voltage Vv is output.

  Moreover, the line voltage of each phase is shown by the following formula.

Line voltage Vuv between U and V: Vuv = Vu−Vv (1)
Line voltage Vvw between V and W: Vvw = Vv−Vw (2)
Line voltage Vwu between W and U: Vwu = Vw−Vu (3)
As is apparent from FIG. 2, an AC voltage having a maximum voltage ± 2E [V] is output as each line voltage.

  Here, a method for shortening the discharge time according to the first embodiment will be described with reference to FIG.

  When the power conversion apparatus 100 is in operation, the switch SW1 and the switch SW2 are in the on state, and the smoothing capacitor C1 is charged as described above.

  In this state, when the switches SW1 and SW2 of the power conversion apparatus 100 are turned off, the charge of the smoothing capacitor C1 is discharged in the direction of the arrow A1 through the bleeder resistor R1. The discharge time constant τ1 is expressed by the following equation (4).

τ1 = C1 ・ R1 (4)
In this embodiment, in order to cause the discharge through the resistors R3 and R4 along with the discharge through the resistor R1, the control unit 50 turns on the switching elements Q1 on, Q2 off, Q3 off, Q4 on, The electric charge charged in the smoothing capacitor C1 is discharged through the path of the capacitor C1, the switching element Q1, the resistance R3, the resistance R4, the switching element Q4, and the capacitor C2. As a result, the electric charge of the smoothing capacitor C1 can be discharged in the illustrated arrow A2 method via the resistors R3 and R4.

  The discharge time constant τ 2 is expressed by the following equations (5) and (6) because C 1 and C 2 are connected in series, and resistors R 3 and R 4 are connected in series to the capacitors C 1 and C 2. It is.

τ2 = (C1 · C2 / (C1 + C2)) · (R3 + R4) ·· (5)
When C1 = C2 and R3 = R4, τ2 = C1 · R3 (6)
From the above formulas (4) and (6), the capacitor C1 can be handled equivalently to the resistor R1 and the resistor R3 connected in parallel, so the time constant τ is given by the following formula (7). Indicated.

τ = C1 · ((R1 · R3) / (R1 + R3)) (7)
FIG. 3 is a diagram illustrating discharge characteristics according to the first embodiment. The discharge voltage V is expressed by the following formula (8), where the charging voltage is V ₀ .

Safety voltage during electric shock V = 50 [v]
Charging voltage V ₀ = 2430 [v]
Time to reach safe voltage (conventional time) ta = 543 [s]
The time constant τa at this time is expressed by the following equation (9) by substituting a numerical value into the above equation (8).

  In this example, by performing the discharge through the resistors R3 and R4 described above, the time ta until reaching the safe voltage could be 296 [s]. The time constant τb at this time is expressed by the following equation (10) by setting tb = 296 [s] in the equation (9).

τb = 296 / 3.88 = 76.3 (10)
Since the discharge voltage Vτ with the time constant τ is the discharge voltage when t = τ in the above equation (8), it is expressed by the following equation (11).

  In FIG. 3, the above-described values are plotted. From the time constant τa (= 139.9) of the conventional discharge characteristic A, discharge through the resistors R3 and R4 is performed. The time constant τb (76.3) of the characteristic B can be obtained, and as a result, the discharge time can be shortened by about 45% from the time 543 [s] until reaching the safe voltage to 296 [s].

  Since the discharge method according to the first embodiment uses a resistor built in the inverter circuit, not only does not need an external discharge facility, but also the discharge time is shortened. The effect of preventing electric shock during repair can be obtained.

  FIG. 4 is a circuit diagram of the power conversion apparatus according to the second embodiment. In the second embodiment, the control unit 50 includes a comparison unit 51 and a notification unit 52.

  Connected to the comparison means 51 are the + side input portion N1 of the DC power supply, the neutral point G, and the − side input portion N2 of the DC power supply. When the switches SW1 and SW2 are turned on and DC power is supplied from the DC power supply P to the power conversion device 100, the voltage of the DC power supply P is output to the + side input unit N1 and the − side input unit N2. In this state, when the switches SW1 and SW2 are turned off, the power supply from the DC power source P is cut off, so that the charging voltage + E [v] of the smoothing capacitor C1 is output to the + side input unit N1, and similarly − The charging voltage −E [v] of the smoothing capacitor C2 is output to the side input unit N2. This voltage is input to the comparison means 51 of the control unit 50.

  The comparing means 51 compares whether or not the absolute value of the input charging voltage exceeds 50 [v] set as a safety voltage. The notifying means 52 is notified of the result of this comparison. When the safety voltage exceeds 50 [v], the smoothing capacitor is in a charged state, and even when the switches SW1 and SW2 are turned off, electric charges remain in the smoothing capacitor. Because direct contact is dangerous, it alerts the operator.

  The comparison means 51 only has to compare the input voltage and the set voltage using a comparator, and can be configured by a known technique. Further, the notification unit 52 receives the result of the comparison unit 51 and notifies the operator by a display or an alarm.

  In addition, when the discharge time is shortened by the control unit 50 described in the first embodiment, the display time or alarm time by the notification unit is shortened.

  As described above, according to the second embodiment, it is possible to visually check whether or not the discharge voltage has reached a safe voltage or less, so that the effect of preventing electric shock at the time of inspection and repair inside the apparatus is improved.

Q1 to Q4 Switching elements D1 to D6 Diodes R1 to R4 Resistance Vu U phase voltage Vv V phase voltage Vw W phase voltage Vuv U-V line voltage Vvw V-W line voltage Vwu W-U line voltage 1 2 Smoothing section 3 4 Snubber section 10 U-phase inverter section 20 V-phase inverter section 30 W-phase inverter section 40 Electric motor (load)
50 control unit 100 power conversion device

Claims (4)

Power conversion comprising a smoothing unit for smoothing a DC power supplied via a switch for turning on / off the supply of the DC power and an inverter for converting the DC power supplied via the smoothing unit into an AC power A device,
The smoothing part is
A first smoothing capacitor connected between a + side input portion of a DC power source supplied via the switch and a reference potential; and a first smoothing capacitor connected between a − side input portion of the DC power source and a reference potential. Two smoothing capacitors;
First and second resistors connected in parallel to the first and second smoothing capacitors,
The inverter unit is
First, second, third, and fourth switching elements connected in series from a + side input unit to a − side input unit of a DC power source smoothed by the smoothing capacitor;
A third resistor and a fourth resistor respectively connected in parallel to the second switching element and the third switching element;
An inverter output terminal connected to a connection point of the second switching element and the third switching element, and for supplying an AC power to a load connected to the outside;
A control unit connected to the respective gate terminals of the first to fourth switching elements and individually controlling on / off of the four switching elements;
With
The controller is
When the switch is turned off and the supply of DC power is cut off, the first and second switching elements are turned on, and the second and fourth switching elements are turned off. An electric power converter that discharges the electric charge charged in the smoothing capacitor through the third and fourth resistors. A smoothing unit for smoothing the DC power supplied via a switch for turning on / off the DC power supply, a U-phase inverter for converting the DC power supplied via the smoothing unit into a three-phase AC power source, V A power converter comprising a phase inverter unit and a W phase inverter unit,
The smoothing part is
A first smoothing capacitor connected between a + side input portion of a DC power source supplied via the switch and a reference potential; and a first smoothing capacitor connected between a − side input portion of the DC power source and a reference potential. Two smoothing capacitors;
First and second resistors connected in parallel to the first and second smoothing capacitors,
The U-phase, V-phase, and W-phase inverter units are
First, second, third, and fourth switching elements connected in series from a + side input unit to a − side input unit of a DC power source smoothed by the smoothing capacitor;
A third resistor and a fourth resistor respectively connected in parallel to the second switching element and the third switching element;
An inverter output terminal connected to a connection point of the second switching element and the third switching element, and for supplying an AC power to a load connected to the outside;
A control unit connected to the respective gate terminals of the first to fourth switching elements and individually controlling on / off of the four switching elements;
With
The controller is
When the switch is turned off and the supply of DC power is cut off, the first and fourth switching elements of each phase are turned on, and the second and fourth switching elements are turned off, thereby An electric power converter characterized by discharging electric charges charged in the first and second smoothing capacitors through the third and fourth resistors of the respective phases. The controller is
Comparison means for comparing the charging voltage of the smoothing capacitor with a set safety voltage;
Notification means for notifying that charging is being performed when the charging voltage of the capacitor exceeds the safe voltage as a result of comparison by the comparison means;
The power converter according to claim 1 provided with. Comparison means for comparing the charging voltage of the smoothing capacitor with a set safety voltage;
Notification means for notifying that charging is being performed when the charging voltage of the capacitor exceeds the safe voltage as a result of comparison by the comparison means;
The power converter according to claim 2 provided with.

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