JP5334093B2 - Inverter - Google Patents

Description

  The present invention relates to an inverter that converts DC power into AC power, and more particularly to a technique for reducing a decrease in output AC voltage during a period in which output AC current is limited.

Conventionally, inverters that convert DC power into AC power are known (see, for example, Non-Patent Documents 1, 2, and 3). If a load such as a transformer or an induction motor that flows a large inrush current is connected to the inverter, such as a transformer or an induction motor, the inverter may stop due to overcurrent protection of the inverter. Therefore, when such an excessive output AC current flows, if the output AC current value exceeds the current limiter level (a constant value), the voltage applied to the gate of the semiconductor switching element constituting the inverter is changed. The semiconductor switching element is turned off (gate block), and when the output AC current value falls below the current limiter level, the switching element is turned on by changing the voltage applied to the gate of the semiconductor switching element constituting the inverter (deblocking). ) Is used to limit the output AC current to a certain value so that the inverter does not stop.
Electrical Engineering Handbook 6th edition The Institute of Electrical Engineers of Japan Published February 20, 2001, pages 830-835 Hirata Tagao "Power Electronics" Kyoritsu Publishing Co., Ltd. Published October 5, 1995, pages 32 to 38 Supervised by Eisuke Shoda, Tadashi Fukao, Ryuichi Shimada, and Atsio Kawamura “All about Power Electronics” Ohmsha, Ltd. October 20, 1995, pages 28-29

However, in the above method, the output AC voltage of the inverter greatly decreases during the period when the output AC current is limited, affects other load devices, stops other load devices, and the operation is unstable. There was a problem that it might become.
Therefore, the problem to be solved by the present invention is to solve the above-mentioned problems and to provide an inverter that can reduce the decrease in the output AC voltage of the inverter during the period in which the output AC current is limited as compared with the prior art. That is.

In order to solve the above problems, the first invention in the present invention is an inverter that converts DC power into AC power, and generates an error signal when the temperature of the semiconductor switching element at the output stage of the inverter rises to a predetermined temperature. When the current command value of the inverter that is the target value of the alternating current supplied from the inverter to the load exceeds the predetermined value, the current command value is limited by the predetermined value, and the current command value When the current command value is equal to or less than the predetermined value, the current command value is not limited, and when there is the error signal, the predetermined value of the current command value is decreased, and when there is no error signal, the current command value is reduced. An inverter comprising: current limiting means for repeatedly performing control to increase the predetermined value of the current command value. Here, the “semiconductor switching element” is, for example, an IGBT, a thyristor, or a GTO.

According to the first aspect of the present invention, in the inverter that converts DC power into AC power, when the current limit value of the inverter, which is the target value of the AC current supplied from the inverter to the load, exceeds the predetermined value, The command value is limited by the predetermined value, and when the current command value is equal to or less than the predetermined value, the current command value is not limited. Further, the error signal generating means generates an error signal when the temperature of the semiconductor switching element at the output stage of the inverter rises to a predetermined temperature. In the current limiting means , if there is the error signal, the current command Since the control for decreasing the predetermined value of the value and increasing the predetermined value of the current command value when there is no error signal is repeatedly performed , the temperature of the semiconductor switching element is prevented from exceeding the predetermined value, and the output it is possible to reduce the decrease in the output AC voltage while limiting the AC current, further, Ru can output an output AC current from the inverter to the capacity last minute of the semiconductor switching element.

Further, a second invention in the present invention is the inverter described as the first invention , wherein the error signal generating means forms a diode on the same chip as the semiconductor switching element, and a forward current flows in the diode. The diode temperature is measured by measuring the forward voltage drop of the diode, and the measured temperature is regarded as the temperature of the semiconductor switching element. An inverter is characterized by generating an error signal when exceeded.

According to the second aspect of the invention, the error signal generating means measures a forward voltage drop of the diode when a forward current is supplied to the diode formed on the same chip as the semiconductor switching element, and detects the temperature of the diode. Since the measured temperature of the diode is regarded as the temperature of the semiconductor switching element and an error signal is generated when the measured temperature exceeds a predetermined allowable value, the temperature of the semiconductor switching element is An error signal can be generated when the allowable value is exceeded.

Furthermore, a third invention in the present invention is the inverter described as the first invention, wherein the semiconductor switching element is turned off for a predetermined time when the error signal is generated. It is.

According to the third aspect , when the error signal is generated, the semiconductor switching element is turned off for a predetermined time, so that the temperature of the semiconductor switching element exceeds an allowable value and the semiconductor switching element is destroyed. Can be surely prevented.

According to the first invention described above, it is possible to reduce the decrease in the output AC voltage when the output AC current of the inverter is limited as compared with the prior art , and further, the output AC from the inverter to the limit of the capacity of the semiconductor switching element. Ru can output current.
Furthermore, according to the second invention described above, together with the effect of the first invention, an error signal can be generated when the temperature of the semiconductor switching element exceeds a predetermined allowable value.
Furthermore, according to the third invention described above, together with the effect of the first aspect of the present invention, the semiconductor switching element can be reliably prevented from being destroyed by the temperature rise.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 is a block diagram of an inverter according to an embodiment of the present invention, FIG. 2 is a detailed circuit diagram of a part of FIG. 1, and FIG. 3 shows error signal generating means for one phase of the inverter of FIG. 4 is a flowchart showing the operation of the inverter of FIG. FIG. 5 shows the output AC current and output AC voltage of the inverter of FIG. Further, FIG. 6 shows the experimental results when the current limiter (current limit value) is kept constant at 75 A, and FIG. 7 shows the experimental results when the initial current limiter is set to 90 A and the current limiter value is reduced by 15 A in one step of the error signal. FIG. 8 shows the result of simulation under the same conditions as the experiment assuming that the current limiter is set to the initial value 75A and no error signal is detected. Further, FIG. 9 shows an experimental result in which the initial current limiter is set to 70 A, and the current limiter is lowered by 10 A with one error signal. FIG. 10 sets the initial current limiter to 70 A, and the current limiter is set with one error signal. It is an experimental result in which the current limiter is increased by 10 A in 1 second by reducing 10 A.

  As shown in FIG. 1, the inverter 10 of the present invention converts DC power into AC power, and includes an output stage 20 and a control circuit 30. The control circuit 30 includes a PWM control circuit 31, a current control circuit 32, a voltage control circuit 33, a current limiting means (current limiter circuit) 35, and an error signal generating means 40 (see FIG. 3). The control circuit 30 is connected to the output stage 20.

The output stage 20 is an IPM (Intelligent Power Module) which is a three-phase module, and the semiconductor switching element 22 of each phase is an IGBT. A diode 23 is connected in antiparallel to the IGBT.
Specifically, as shown in FIG. 2, a DC voltage stored in a capacitor 2 is used as the DC power source 1. The DC power source 1 is supplied to the semiconductor switching element 22 of the output stage 20. The capacitor 2 is, for example, an electric double layer capacitor (EDLC). Specifically,
As shown in FIG. 3, the capacitor 2 is charged with a DC voltage obtained by rectifying an AC voltage of a three-phase AC power source (AC power source) 3 with a rectifier circuit 4.

  As shown in FIG. 2, the transformer 62 converts the magnitude of the AC voltage supplied from the inverter 10 into an AC voltage having an optimum magnitude for the load 50. The filter 63 includes a reactor 63a and a capacitor 63b. The filter 63 absorbs harmonics of the AC voltage and AC current supplied from the inverter 10 to the load 50, and generates a clean sine wave AC voltage and AC current. Reactor 63a is connected in series to each phase of the transmission line, and capacitor 63b is connected between the transmission lines of each phase.

  The voltage control circuit 33 of the control circuit 30 shown in FIG. 1 operates as follows. That is, the voltage difference between the voltage command value and the voltage value of the capacitor 63 b of the filter 63 (the AC voltage of the load 50) is taken, and this voltage difference is input to the voltage control circuit 33. The voltage control circuit 33 adjusts and outputs the current command value so that the AC voltage of the load 50 becomes equal to the voltage command value based on the voltage difference value. Specifically, when the voltage difference value is positive (when the AC voltage of the load 50 is lower than the voltage command value), the current command value is increased, and when the voltage difference value is negative (the AC voltage of the load 50 is the voltage command). If higher than the value), the current command value is lowered.

The current limiting means 35 limits the current command value of the inverter 10 with the predetermined value when the current command value of the inverter 10 serving as the target value of the alternating current supplied from the inverter 10 to the load 50 exceeds the predetermined value. In other words, when the current command value of the inverter 10 is less than the predetermined value, the current command value of the inverter 10 is not limited.
Specifically, the current command value output from the voltage control circuit 33 is input to the current limiting unit 35, and the current limiting unit 35 directly accepts the current command value when the current command value is lower than the current limiter value (predetermined value). When the current command value is higher than the current limiter value (predetermined value), the current command value is replaced with the current limiter value (predetermined value) and output.
Further, the current transformer 61 detects the output AC current of the inverter 10, and a value obtained by reducing the detected output AC current value at a constant ratio is led to the control circuit 30, and the value led to the control circuit 30 is the current limit. Compared with the output of the means 35, the alternating current output from the inverter 10 is limited to a predetermined value.

The difference between the current command value output from the current limiting means 35 and the output AC current of the inverter 10 detected by the current transformer 61 is taken, and this difference is input to the current control circuit 32. The current control circuit 32 adjusts the amplitude of the reference signal (for example, a sine wave signal) so that the output AC current of the inverter 10 becomes equal to the current command value based on the current difference value, and outputs the result. Specifically, when the current difference value is positive (when the output AC current of the inverter 10 is lower than the current command value), the amplitude of the reference signal is increased, and when the current difference value is negative (the output of the inverter 10). When the alternating current is higher than the current command value), the amplitude of the reference signal is reduced.
The reference signal is input to the PWM control circuit 31, and the PWM control circuit 31 compares the reference signal with a carrier wave signal (for example, a triangular wave signal) to create a pulsed PWM control signal. This PWM control signal is input to the gate of the IGBT serving as the semiconductor switching element 22.

The error signal generator 40 generates an error signal Fo when the temperature of the semiconductor switching element 22 rises to a predetermined temperature.
The error signal Fo is input to the current limiting means 35. When there is an error signal Fo, control is performed to decrease the current limiter value (predetermined value) of the current limiting means 35, and when there is no error signal Fo, control to increase the limiter value (predetermined value) of the current limiting means 35. Do. Thus, the limit level of the output alternating current of the inverter 10 is raised or lowered according to the temperature of the semiconductor switching element 22 so that the output alternating current can be output from the inverter 10 to the limit of the capability of the semiconductor switching element 22.
That is, the current limiting means 35 reduces the predetermined value of the alternating current supplied from the inverter 10 to the load 50 when there is an error signal Fo, and supplies it from the inverter 10 to the load 50 when there is no error signal Fo. The predetermined value of the alternating current to be generated is increased.
As described above, current limit control is performed by repeating the gate block and deblocking of the IGBT serving as the semiconductor switching element 22 by using the current limiter value whose level changes dynamically according to the temperature of the semiconductor switching element 22. .

As shown in FIG. 3, the error signal generating means 40 measures the forward voltage drop of the diode 41 when the forward current is supplied to the diode 41 formed on the same chip 21 as the semiconductor switching element 22, and the diode 41. The temperature of the diode 41 is measured, and the measured temperature of the diode 41 is regarded as the temperature of the semiconductor switching element 22, and the error signal Fo is generated when the measured temperature exceeds a predetermined allowable value.
Specifically, when the diode 41 is a silicon diode, if the forward current If of the diode 41 is constant, the forward voltage Vf of the diode 41 is proportional to the absolute temperature T. Therefore, at the reference temperature. The forward voltage Vf of the diode 41 is measured in advance, and the forward voltage Vf of the diode 41 when the semiconductor switching element 22 is operating is measured and compared. That is, the temperature during operation of the semiconductor switching element 22 can be measured.
Further, when the error signal Fo is generated, the semiconductor switching element 22 is turned off for a predetermined time (for example, several ms).

  Specifically, when the IPM receives the trigger signal from the sensor circuit 42, the IPM sets the state of the heating protection circuit 43, the error signal output circuit 44 outputs the error signal Fo, and simultaneously disables the PWM control input signal. The drive circuit 45 (driving the gate of the IGBT serving as the semiconductor switching element 22) is stopped. In the heat protection, if it is less than the set value after several ms after the trip, the state of the heat protection circuit 43 is reset and returns to the normal operation. The drive circuit 45 is supplied with a power supply voltage from the power supply circuit 46. The error signal Fo is taken out via an interface (I / F) 47.

The inverter 10 having the above configuration operates as follows.
As shown in FIG. 2, the transformer 62 is connected to the output side of the inverter 10, and the induction motor 52 is connected in parallel to the load 50 by the three-phase switch 51 (step S1 in FIG. 4). At this time, the inverter 10 is connected to the induction motor 52 and the load 50 connected in parallel. Then, the inverter 10 is operated. Next, an initial setting of a current limiter (current limit value) is performed (step S2 in FIG. 4).
When the current command value of the inverter 10 that is the target value of the alternating current supplied from the inverter 10 to the load (50, 52) exceeds the predetermined value, the current limiting means 35 limits the current command value with the predetermined value. When the current command value is less than or equal to the predetermined value, the current command value is not limited (step S3 in FIG. 4).
Further, the error signal generating means 40 generates an error signal Fo when the temperature of the semiconductor switching element 22 of the output stage 20 of the inverter 10 rises to a predetermined temperature. When there is an error signal Fo (step S4 in FIG. 4), the current limiting means 35 reduces the predetermined value of the current command value (step S6 in FIG. 4), and when there is no error signal Fo. (Step S4 in FIG. 4), since the current limiting means 35 increases the predetermined value of the current command value (Step S7 in FIG. 4), the temperature of the semiconductor switching element 22 is prevented from exceeding the predetermined value, and the output AC A reduction in output AC voltage when the current is limited can be reduced.

  Further, when the error signal Fo is generated, the semiconductor switching element 22 is turned off for a predetermined time (step S5 in FIG. 4), so that the temperature of the semiconductor switching element 22 exceeds the allowable value and the semiconductor switching element 22 is destroyed. Can be surely prevented.

  Further, the error signal generation means 40 measures the voltage of the diode 41 by measuring the voltage drop of the diode 41 when a current is supplied to the diode 41 formed on the same chip 21 as the semiconductor switching element 22. Since the measured temperature of the diode 41 is regarded as the temperature of the semiconductor switching element 22 and the error signal Fo is generated when the measured temperature exceeds a predetermined allowable value, the temperature of the semiconductor switching element 22 is set to the predetermined allowable value. The error signal Fo can be generated when the value exceeds.

  In this way, the output AC current and output AC voltage of the inverter 10 at the time of starting the induction motor 52 as shown in FIG. 5 are obtained. Here, the horizontal axis represents time (seconds), and the vertical axis represents current (A) and voltage (V). Thus, during the DC / AC conversion operation of the inverter 10, the temporary decrease in the output AC voltage during the period in which the output AC current of the inverter 10 is limited can be reduced, and the load 50 (including other load devices) can be reduced. The influence on the operation can be minimized.

  Furthermore, when electric power was supplied from the capacitor 2 charged to 100 V to the load 50 having a current value set to 1 A, the no-load induction motor 52 was activated to generate an inrush current. The waveforms of each inverter current, load line voltage, and load line voltage effective value are shown below. The load line voltage effective value was calculated from the voltage value until one cycle before using a moving average.

  FIG. 6 shows an experimental result when the current limiter is set to be constant at 75A. The overcurrent could be suppressed by the current limiter after the induction motor 52 was turned on, and the switching was not stopped without the error signal Fo.

  FIG. 7 shows the experimental results when the initial current limiter is set to 90A and the value of the 15A limiter is decreased in the error signal Fo1 step. The error signal Fo is detected once. At that time, switching of the inverter 10 is stopped for 1.8 ms, the value of the current limiter is reduced from 90 A to 75 A, and the overcurrent is suppressed. However, regarding the effective voltage value, it took time to return to the steady state rather than the effective voltage value when 75 A is constant. This is presumably because the error signal Fo was not detected when 75A was constant, and the inverter 10 operated stably without stopping.

  FIG. 8 shows the result of simulation under the same conditions as in the experiment, assuming that the current limiter is set to the initial value 75A and the error signal Fo is not detected. The current limiter was increased by 15 A 0.1 seconds after the induction motor 52 was turned on and changed from 75 A to 90 A. Since the effective value of the load voltage returns to the state before being turned on when the current limiter is increased, it can be said that the influence on the load 50 can be reduced as compared with the case where the effective value of the load voltage is fixed by increasing the limiter.

  As shown in FIG. 9, when the initial current limiter is set to 70A and the current limiter is lowered by 10A every time the error signal Fo is generated once, the error signal Fo is output three times, but the induction motor 52 is operating normally. Rotating and the load voltage returns to normal after 1.75 seconds. In FIG. 9, the first error signal Fo1 and the second error signal Fo2 are displayed in an overlapping manner, and the third error signal Fo3 is displayed with a delay.

  As shown in FIG. 10, when the initial current limiter is set to 70A and the control is performed to decrease the current limiter by 10A every time the error signal Fo is generated once, the current limiter is gradually increased by 10A in 1 second. Although it was output three times, the induction motor 52 operated normally, and the load voltage returned to the normal state after 0.8 seconds. Therefore, the load voltage returned to the normal state earlier in the case of FIG. 10 than in the case of FIG. In FIG. 10, the first error signal Fo1, the second error signal Fo2, and the third error signal Fo3 are displayed separately.

  In the above-described embodiment, the IGBT is used as the semiconductor switching element 22. However, the present invention is not limited to this, and any power switching element can be used.

It is a block diagram of the inverter which concerns on embodiment of this invention. FIG. 2 is a detailed circuit diagram of a part of FIG. 1. It is explanatory drawing which shows the error signal generation means for 1 phase of the inverter of FIG. It is a flowchart which shows operation | movement of the inverter of FIG. It is a graph which shows the output alternating current and output alternating voltage of the inverter of FIG. An experimental result in the case where the current limiter is made constant at 75 A is shown. This is an experimental result when the initial current limiter is set to 90 A and the current limiter value is reduced by 15 A in one step of the error signal. This is a result of performing a simulation under the same conditions as in the experiment, assuming that the current limiter is set to an initial value of 75 A and no error signal is detected. This is an experimental result in which the initial current limiter is set to 70 A and the current limiter is lowered by 10 A with one error signal. This is an experimental result in which the initial current limiter is set to 70A, the current limiter is lowered by 10A in one error signal, and the current limiter is increased by 10A in one second.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Inverter 20 Output stage 21 Chip 22 Semiconductor switching element 30 Control circuit 31 PWM control circuit 32 Current control circuit 33 Voltage control circuit 35 Current limiting means 40 Error signal generating means 41 Diode

Claims (2)

In an inverter that converts DC power to AC power,
Error signal generating means for generating an error signal when the temperature of the semiconductor switching element at the output stage of the inverter rises to a predetermined temperature;
When the current command value of the inverter, which is the target value of the alternating current supplied from the inverter to the load, exceeds a predetermined value, the current command value is limited by the predetermined value, and the current command value is less than the predetermined value Does not limit the current command value, and when there is the error signal, decreases the predetermined value of the current command value, and when there is no error signal, the predetermined value of the current command value An inverter comprising: current limiting means for repeatedly performing control to increase the current. An inverter according to claim 1,
An inverter, wherein the semiconductor switching element is turned off for a predetermined time when the error signal is generated .

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