JP2016019336A - Motor drive system and dc short-circuit detection device for motor drive system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor drive system presenting equal effects to monitoring at two positions by monitoring a discharge current from a short-circuit detection capacitor of small capacity which is connected to a DC link capacitor in a three-level inverter in parallel, with a current sensor at one position in place of monitoring a discharge current from the DC link capacitor with current sensors at two positions in the case of DC short-circuiting, and a DC short-circuit detection device for the motor drive system.SOLUTION: In a DC short-circuit detection device 20, between P and C, a first charging circuit is provided which includes a connection point P1 where a short-circuit detection capacitor CP2 and a forward diode D1 are connected in series from a P pole side. In C and B, a second charging circuit is provided which includes a connection point P2 where a forward diode D2 and a short-circuit detection capacitor CN2 are connected in series from a C pole side. Further, between the second connection point and the first connection point, a discharging circuit is provided in which a third diode and a current sensor CT are connected in series from the side of the second connection point.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an electric motor drive system and a DC short-circuit detection device for the electric motor drive system.

  FIG. 5 shows a DC short-circuit detection method in a conventional DC short-circuit detection device for an electric motor drive system. In the case of a three-level inverter, in order to monitor the DC short-circuit between two DC links (between P pole and C pole) and (between C pole and N pole), charging / discharging currents for DC link capacitors (smoothing capacitors) CP1 and CN1 Need to be monitored.

  In FIG. 5, Vu, Vv, and Vw are connected to the motor side. The DC link capacitor CP1 is charged by a charging current 1a from a power supply side converter (not shown), and the discharge current 1b of the DC link capacitor CP1 is supplied to the U-phase inverter 30, the V-phase inverter 40, and the W-phase inverter 50 during normal operation of the motor. The Similarly, the DC link capacitor CN1 is charged by the charging current 2a, and the discharge current 2b of the DC link capacitor CN1 is supplied to the U-phase inverter 30, the V-phase inverter 40, and the W-phase inverter 50 during normal operation of the motor.

  The charging current 1a and discharging current 1b of the DC link capacitor CP1 are detected by the current sensor CT1. Similarly, the charging current 2a and discharging current 2b of the DC link capacitor CN1 are detected by the current sensor CT2.

  Signals detected by these two current sensors CT1 and CT2 are monitored by a monitoring circuit (not shown), and are connected to the DC link, for example, the U-phase inverter 30, for some reason IGBTQ1, IGBTQ2, IGBTQ3. When a short circuit occurs between CP1 and IGBTQ1 → IGBTQ2 → IGBTQ3 → diode D9, the DC link capacitor current is monitored, and the healthy inverter V-phase and W-phase arm gate blocks Preventing the spread of damage. Since two DC links in the case of a three-level inverter are connected in series (between P pole and C pole, between C pole and N pole), the currents of the two DC links were monitored at two locations.

Japanese Patent No. 4769390 (Overall)

  At the time of DC short-circuit, the discharge currents from the DC link capacitors CP1 and CN1 were monitored by current sensors arranged at two locations, respectively. However, since the discharge current becomes a large current, the economy and space associated with the downsizing of the device Improvement of the factor was anxious.

  The present invention has been made in view of the above. When a DC short circuit occurs, instead of monitoring discharge currents from the DC link capacitors CP1 and CN1 at two locations, a small-capacity short circuit connected in parallel to the DC link capacitor. An object of the present invention is to provide a motor drive system and a DC short-circuit detection device for the motor drive system that monitor the discharge current from the sensing capacitor at one place and have the same effect as the above-mentioned two-place monitoring.

  In order to achieve the above object, an electric motor drive system of the present invention is connected between a P pole, a C pole and an N pole for supplying DC power, and a P pole and a C pole constituting the power supply section. In order to monitor the current of the first DC link capacitor and the second DC link capacitor connected between the C pole and the N pole, and the current of the first DC link capacitor and the second DC link capacitor, A first charging circuit having a first connection point in which a first short-circuit detecting capacitor and a first diode arranged in a forward direction are connected in series from the P pole side between the P pole and the C pole; A second charging circuit having a second connection point in which a second diode and a second short-circuit detection capacitor arranged in a forward direction from the C pole side are connected in series between the C pole and the N pole; Second connection point and the first connection A discharge circuit in which a third diode and a current sensor are connected in series from the second connection point side, so that the discharge current can be monitored in one place when a DC short-circuit occurs. Features.

  According to the present invention, instead of monitoring the discharge current from the DC link capacitors CP1 and CN1 at two locations when a DC short circuit occurs, the discharge current from the small-capacity short-circuit detection capacitor connected in parallel to the DC link capacitor is 1 It is possible to provide a motor drive system and a DC short-circuit detection device for the motor drive system that are monitored at locations and have the same effect as the above-described two-site monitoring.

1 is a circuit diagram (charging current) of an electric motor drive system according to Embodiment 1 of the present invention. The circuit diagram (discharge current) of the electric motor drive system which concerns on Example 1 of this invention. The figure explaining the capacity | capacitance of the DC link capacitor | condenser which concerns on Example 1 of this invention, and the capacity | capacitance of a short circuit detection capacitor | condenser. The figure explaining the DC link capacitor current (main current) and short circuit detection capacitor current concerning Example 1 of the present invention. The circuit diagram of the DC short circuit detection apparatus of the conventional motor drive system.

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

  FIG. 1 is a circuit diagram of an electric motor drive system 100 according to a first embodiment of the present invention, in which a charging current path is shown. The motor drive system 100 includes a DC power input unit having P poles, C poles, and N poles, a DC link unit 10 that processes a ripple current of the DC power input from the DC power input unit, and a DC short circuit detection device 20. And inverter units 30-50.

  The DC power source input section is E [V] between P pole and C pole (hereinafter referred to as between P and C), and E [V between C pole and N pole (hereinafter referred to as between C and N). ] Is supplied.

  The DC link unit 10 includes a DC link capacitor CP1 (first DC link capacitor) connected between P and C and a DC link capacitor CN1 (second DC link capacitor) connected between C and N. Configured. A bleeder resistor may be connected in parallel to the DC link capacitors CP1 and CN1, but is omitted here. Further, a snubber circuit may be connected in parallel to the DC link unit 10 in order to remove harmonic components mixed in the DC power supply, but it is omitted because it is not directly related to the gist of the present invention.

  In the DC short-circuit detection device 20, a short-circuit detection capacitor CP2 (first short-circuit detection capacitor) and a diode D1 (first diode) arranged in the forward direction are connected in series between the P-pole and the C-pole from the P-pole side. A first charging circuit having a connected connection point P1 (first connection point) is provided. Further, a connection point P2 in which a diode D2 (second diode) and a short-circuit detection capacitor CN2 (second short-circuit detection capacitor) arranged in the forward direction from the C-pole side are connected in series between the C-pole and the N-pole. A second charging circuit having (second connection point) is provided. Furthermore, a discharge circuit in which a third diode and a current sensor CT are connected in series from the second connection point side is provided between the second connection point and the first connection point.

  The inverter unit includes a U-phase inverter unit 30, a V-phase inverter unit 40, and a W-phase inverter unit 50. Since the configuration of each inverter unit is common, the configuration of the U-phase inverter unit 30 will be described.

  In the U-phase inverter unit 30, four switching elements Q1 to Q4 are connected in series to both ends of DC power supplies E [V] and E [V] to be supplied. As the switching elements Q1 to Q4, for example, an IGBT (Insulated Gate Bipolar Transistor) is used. Diodes D4 to D7 (freewheeling diodes) are connected in antiparallel to the switching elements Q1 to Q4, respectively. Also, clamp diodes D8 and D9 for clamping the output voltage of each phase (in this case, the U phase) to the neutral point C0 are connected to the three-level inverter shown in the present embodiment.

  With the above configuration, the U-phase voltage Vu is generated by switching the switching elements Q1 to Q4 on and off at a set timing.

  The V-phase inverter unit 40 and the W-phase inverter unit 50 are configured in the same manner as the U-phase inverter unit 30, and the V-phase voltage is changed by switching on and off the switching elements constituting the inverter unit at a set timing. Vv and W phase voltage Vw are generated.

  Through the above processing, three-phase AC voltages Vu, Vv, Vw are generated, and three-phase AC power is supplied to a load (not shown).

  When E [V] is supplied between PCs of electric motor drive system 100 having the above configuration, and E [V] is supplied between CNs, charging current 1a1 flows through DC link capacitor CP1, and the above-described first The charging current 1a2 flows through the short-circuit detecting capacitor CP2 by the charging circuit 1.

  Similarly, the charging current 2a1 flows through the DC link capacitor CN1, and the charging current 2a2 flows through the short-circuit detection capacitor CN2 by the above-described second charging circuit.

  FIG. 2 is a circuit diagram of the electric motor drive system according to the first embodiment of the present invention, and shows a path of a discharge current during normal operation of the electric motor. The discharge current 1b1 of the DC link capacitor CP1 in FIG. 2 and the discharge current 2b1 of the DC link capacitor CN1 have the same action as the discharge current path 1b of the DC link capacitor CP1 and the discharge current path 2b of the DC link capacitor CN1 in FIG. Therefore, here, the path of the discharge current from the short-circuit detection capacitors CP2 and CN2 during normal operation of the motor will be described.

  The discharge current 1b2 (solid arrow) based on the electric charge charged in the short-circuit detection capacitor CP2 is supplied from the short-circuit detection capacitor CP2 to the inverter units 30 to 50, and is converted into an alternating current by the inverter units 30 to 50 and supplied to the load. Then, the signal is fed back to the short-circuit detection capacitor CP2 via a neutral point C0 → diode D2 → diode D3 → current sensor CT.

  Similarly, the discharge current 2b2 (broken arrow) based on the electric charge charged in the short-circuit detection capacitor CN2 is supplied to the short-circuit detection capacitor CN2, the diode D3, the current sensor CT, the diode D1, the neutral point C0, and the inverter units 30 to 50. Then, an alternating current is supplied to the load by the inverter units 30 to 50 and then fed back to the short-circuit detection capacitor CN2.

  As described above, during normal operation of the motor, the discharge currents 1b2 and 2b2 from the short-circuit detection capacitors CP2 and CN2 both pass through the current sensor CT. The discharge current from CN2 can be detected.

  FIG. 3 is a diagram for explaining the capacity of the DC link capacitors (CP1 and CN1) and the capacity of the short circuit detection capacitors (CP2 and CN2) according to the first embodiment of the present invention.

  The capacity ratio of the short-circuit detection capacitor capacity to the general DC link capacitor capacity is set to about 0.1%. For example, in an inverter device that outputs a voltage of 3.3 [kV], if the DC link capacitor capacity for 1 BNK (UVW phase) is 2000 [μF] (between PC and C-N), short circuit detection The capacitor capacity is 2 [μF].

Also in the first embodiment, as shown in FIG. 3, the same capacitor capacity as described above is used. The motor drive system (device) output power (apparent power) Po and the motor drive system (device) are assumed when a DC link voltage of 3 [kV] × 2 is used to output the voltage, and a device of 4000 [kVA] is assumed. ) The output current Io is expressed by the following formulas (1) to (3).
DC link voltage Vpc = Vcn = 3 [kV] (1)
Device output power Po = 4000 [kVA] (2)
Device output current Io = 4000 kVA / (√3 × 3300 V)
= 700 [Arms] ... (3)
[rms] is (root mean square value: effective value), and the above formula (3) indicates that the effective value of current is 700 [A].

  If the wiring inductance connecting the DC link capacitors CP1 and CP2 shown in FIG. 3, the inductance of the BUS bar (not shown) connecting the DC link capacitor and the inverter unit, and the inductances of the short-circuit detection capacitors CP2 and CN2 are ignored, The discharge current values ICP2 and ICN2 from the sensing capacitors CP2 and CN2 are indicated by the capacitance ratio of the capacitor to the discharge current values from the DC link capacitors CP1 and CN1.

That is, the discharge currents ICP2 and ICN2 of the short-circuit detection capacitors CP2 and CN2 when the device is short-circuited are the DC link capacitors CP1 and CN1 and the short-circuit detection capacitors CP2 and CN2 with respect to the device output current value Io expressed by the above equation (3). The capacitor capacity ratio can be expressed by the following formulas (4) to (5).
DC link capacitor CP1 capacitance: short-circuit detection capacitor CP2 capacitance = 2000 μF: 2 μF = 1000: 1 (4)
Short-circuit detection capacitor current ICP2 = Io / 1000 = 0.7 [Arms] (5)
The DC link capacitor CN1 capacity: short circuit detection capacitor CN2 capacity is calculated in the same manner as in the above (4), and the short circuit detection capacitor current ICN2 is calculated in the same manner as in the above equation (5).

  When a DC short-circuit occurs in the motor drive system 100 according to the first embodiment, a discharge current flows as a short-circuit current from the DC link capacitors CP1 and CP2, and the short-circuit current is 700 as shown by the above equation (3). Since a large current exceeding [Arms] is required, a large-capacity current sensor is required to detect this large current with the current sensor. However, when the DC short circuit occurs, the short circuit detection capacitors CP2 and CN2 change the current sensor to the current sensor. The flowing current is 0.7 Arms as shown in the above formula (5), and only 1/1000 of the discharge current flows as a short-circuit current compared to the discharge currents from the DC link capacitors CP1 and CN2.

  That is, the capacitance of the short-circuit detection capacitor CP2 can be set smaller than the capacitance of the DC link capacitor CP1, and the capacitance of the short-circuit detection capacitor CN2 can be set smaller than the capacitance of the DC link capacitor CN1. Thus, it is possible to detect a DC short circuit of the electric motor drive system 100 with a small-capacity current sensor.

FIG. 4 illustrates the DC link capacitor current ICP1 flowing from the DC link capacitor CP1 and the discharge current ICP2 (corresponding to the discharge current 1b2 shown in FIG. 2) flowing from the short circuit detection capacitor CP2. Here, the main currents Ir, Is, It constituting the DC link capacitor current ICP1 are calculated by the following equations (6) to (8). Further, the maximum current ICP1m at that time is calculated by the following equation (9) from the above equation (3).
Ir = ICP1m · sin ωt (6)
Is = ICP1m · sin (ωt−2π / 3) (7)
It = ICP1m · sin (ωt−4π / 3) (8)
ICP1m = √2Io = √2 × 700 = 990 [A] (9)
Similarly, since the short-circuit detection capacitor current ICP2 is 1/1000 of the main current Ir, Is, It, the current flows as main currents Ir / 1000, Is / 1000, It / 1000. is there. The maximum current ICP2m at that time is calculated from the above equation (5) by the following equation (10).
ICP2m = √2Io / 1000 = 0.99 [A] (10)
The calculated current value is shown in FIG.

  As is apparent from the above description, according to the present embodiment, in the DC short-circuit detecting device of the motor drive system using the three-level inverter, when the DC short-circuit is detected, the discharge current (large current) from the DC link capacitors CP1 and CP2 is 2 To provide a motor drive system and a DC short-circuit detection device for a motor drive system having the same effect as two-position monitoring by monitoring discharge current (small current) from a short-circuit detection capacitor at one place instead of monitoring at a place. Can do.

DESCRIPTION OF SYMBOLS 10 DC link part 20 DC short circuit detection apparatus 30-50 Inverter part CP1 DC link capacitor (smoothing capacitor) connected between CP
CP2 Short-circuit detection capacitor connected between CP and CN1 DC link capacitor (smoothing capacitor) connected between CN
CN2 Short-circuit detection capacitor CT connected between C-N Current sensors Q1 to Q4 Switching elements D1 to D3 Diodes D4 to D7 Diode (freewheeling diode)
D8 ~ D9 Clamp diode

Claims (5)

A DC power supply input section having P pole, C pole and N pole for supplying DC power;
A first DC link capacitor connected between the P pole and the C pole constituting the DC power supply input unit, and a second DC link capacitor connected between the C pole and the N pole;
A DC short-circuit detecting device provided between the P pole and the N pole in order to monitor currents of the first DC link capacitor and the second DC link capacitor;
An inverter unit that receives supply of the DC power and converts it into AC power;
An electric motor drive system comprising: The DC short-circuit detection device is
A first charging circuit having a first connection point in which a first short-circuit detecting capacitor and a first diode arranged in a forward direction are connected in series from the P pole side between the P pole and the C pole;
A second charging circuit having a second connection point in which a second diode and a second short-circuit detecting capacitor arranged in a forward direction from the C pole side are connected in series between the C pole and the N pole;
A discharge circuit in which a third diode and a current sensor are connected in series from the second connection point side between the second connection point and the first connection point;
The motor drive system according to claim 1, further comprising:   The capacity of the first short-circuit detecting capacitor is set to be smaller than the capacity of the first DC link capacitor, and the second short-circuit capacitor capacity is smaller than the capacity of the second DC capacitor. The electric motor drive system according to claim 2, wherein the electric motor drive system is set. DC power supply input section having P pole, C pole and N pole for supplying DC power supply, first DC link capacitor connected between P pole and C pole constituting the DC power supply input section, and C pole and N pole A second DC link capacitor connected between the poles, and a DC short circuit detection provided between the P pole and the N pole to monitor the current of the first DC link capacitor and the second DC link capacitor. A DC short-circuit detection device of an electric motor drive system comprising: a device; and an inverter unit that receives the supply of the DC power and converts the AC power into an AC power source,
A first charging circuit having a first connection point in which a first short-circuit detecting capacitor and a first diode arranged in a forward direction are connected in series from the P pole side between the P pole and the C pole;
A second charging circuit having a second connection point in which a second diode and a second short-circuit detecting capacitor arranged in a forward direction from the C pole side are connected in series between the C pole and the N pole;
A discharge circuit in which a third diode and a current sensor are connected in series from the second connection point side between the second connection point and the first connection point;
An apparatus for detecting a DC short circuit in an electric motor drive system.   The capacity of the first short circuit detection capacitor is set to be smaller than the capacity of the first DC link capacitor, and the capacity of the second short circuit detection capacitor is smaller than the capacity of the second DC capacitor. The DC short-circuit detection device for an electric motor drive system according to claim 4, wherein

Images