JP2023127250A - converter - Google Patents

Abstract

To provide a converter that can start in a stable state when rebooting a switching element of the converter while a load to which a driving power supply is supplied is in operation.SOLUTION: A converter of an embodiment of the present invention, which is a device for generating an electric power source to operate a load, comprises: a smoothing capacitor connected in series between the forward side and reverse side DC buses; a full-wave rectifier circuit connected between each phase terminal of a three-phase AC power supply and the forward side or reverse side DC bus; a switching element arranged in an energization route from each phase terminal to the node of the capacitor; a current detection unit for detecting a current supplied from the three-phase AC power supply; a voltage phase detection unit for detecting a voltage phase of the three-phase AC power supply; and a control circuit for controlling the operation of the switching element based on the voltage phase and the current. The control circuit stops the switching element in a state of operating the load. After that, when rebooting the switching element to operate, the control circuit advances the voltage phase to output to the voltage phase of the three-phase AC power supply.SELECTED DRAWING: Figure 1

Description

Embodiments of the present invention relate to a converter that rectifies three-phase AC power and supplies DC power to a load.

For example, a multilevel converter called the VIENNA rectifier is used in AC applications that require a small electrical circuit volume and low harmonic current, such as battery charging circuits installed in electric vehicles and aircraft equipment. - Applied to DC conversion circuits. By employing a multilevel converter, it is possible to downsize components that have relatively large volumes, such as reactors and EMI filters.

Although there are multiple circuit configurations of the VIENNA rectifier, for example, Patent Document 1 discloses one configured with a diode bridge, a switching element, and a diode. Hereinafter, this will be referred to as a diode bridge type. Since the diode bridge type has fewer switching elements than other circuit configurations, the circuit for driving the elements can also be simplified. Furthermore, since the voltage applied to each component is half that of a two-level converter, this is an advantageous configuration from the viewpoint of the withstand voltage of the circuit elements.

European Patent No. 0660498

A converter made of such a diode bridge type converter operates as a full-wave rectifier when the driving of the switching element is stopped. Therefore, even if the driving of the switching element is temporarily stopped when an abnormality occurs in the converter operation, the inverter, which is the load to which driving power is supplied from the converter, is still driving the motor, etc. For example, the driving state of the motor can be maintained regardless of whether the switching element is stopped. Particularly in equipment such as air conditioners, if a compressor driven by a motor stops frequently, it creates an unpleasant environment for users, which is very inconvenient. For this reason, it is desirable to continue operating the compressor motor while it is in operation without stopping it as much as possible. In this respect, it is preferable to employ this type of converter.

After the switching element has stopped, it is possible to restore the operation of the switching element if a predetermined condition is satisfied. For example, it is assumed that the switching operation is stopped when the DC output voltage of the converter becomes excessively boosted, and the switching operation is restarted when the DC output voltage drops to a predetermined value.

However, in the diode bridge type converter, since the upper and lower arms are diodes, current cannot flow between the upper and lower arms. Therefore, when the switching element is stopped, as shown in FIG. 8, the reactor L provided on the three-phase power supply side causes the power factor to change from "1" due to the phase difference between the power supply voltage Vs and the current JwLI by θ. It will be out of place. If the converter is started in such a state, the timing will deviate between the switching control based on the power supply voltage phase and the actual current flowing JwLI, making the control unstable and causing abnormalities such as overcurrent to occur again. This will cause the converter to have to be stopped again. Frequent operation and stopping of the switching elements of the converter as described above is undesirable because it may reduce the durability of the converter and the load. Furthermore, while the engine is stopped, the power factor is not 1 during operation, resulting in a decrease in the power utilization rate.
Therefore, the present invention provides a converter that can be started in a stable state when restarting a switching element of the converter while a load supplying driving power is in operation.

The converter of the embodiment generates a power source for operating a load, and includes a smoothing capacitor formed by connecting capacitors in series between the positive side and negative side DC buses, and each phase terminal of the three-phase AC power source and the positive side. and a full-wave rectifier circuit connected between the negative DC bus and the negative side DC bus, a switching element placed in the current-carrying path from each phase terminal to the connection point of the capacitor, and detecting the current input from the three-phase AC power supply. A current detection section, a voltage phase detection section that detects a voltage phase of a three-phase AC power source, and a control circuit that controls the operation of the switching element based on the voltage phase and current, and the control circuit is configured to control the load. After stopping the operation of the switching element while operating the switching element, when restarting the operation of the switching element, the phase of the output voltage is advanced with respect to the voltage phase of the three-phase AC power source.

Further, the control circuit of the converter according to the embodiment stops the operation of the switching element while the load is operating, and then restarts the operation of the switching element when the value of the current falls below a threshold value.

The first embodiment is a circuit diagram and a functional block diagram showing the configuration of the converter. Flowchart mainly showing the processing contents of the control circuit A diagram showing the waveforms of each signal when the control of the first embodiment is not applied. A diagram showing the waveform of each signal when the control of the first embodiment is applied This is a second embodiment, and is a flowchart mainly showing the processing contents of the control circuit. A diagram showing the waveforms of each signal when the control of the second embodiment is applied This is the third embodiment, and is a flowchart mainly showing the processing contents of the control circuit. Diagram explaining the current phase when the converter is stopped

(First embodiment)
The converter of the first embodiment will be described below. As shown in FIG. 1, the R, S, and T phase output terminals of the three-phase AC power supply 1 are connected to the AC input terminals of bidirectional switching circuits 3R, 3S, and 3T via reactors 2R, 2S, and 2T of the converter 27. are connected to one side of each. The cathodes of positive diodes 5Ra, 5Sa, and 5Ta are commonly connected to the positive DC bus 4a, and the anodes of negative diodes 5Rb, 5Sb, and 5Tb are commonly connected to the negative DC bus 4b. Note that the configurations of the switching circuits 3R, 3S, and 3T are symmetrical, so unless there is a particular need to distinguish between phases, the explanation will be made without adding R, S, or T to the reference numerals.

The switching circuit 3 is configured by connecting, for example, an N-channel MOSFET 7 as a switching element between the cathode side and the anode side of a full-wave rectifier circuit in which four diodes 6 are bridge-connected. A common connection point where two diodes 6 are connected in series serves as an AC input terminal. The power supply side of the DC output terminal of the switching circuit 3 is connected to the anode of the positive side diode 5a, and the ground side thereof is connected to the cathode of the negative side diode 5b.

A smoothing capacitor 8 consisting of a series circuit of two capacitors 8a and 8b is connected between the DC buses 4a and 4b. The other AC input terminal of the switching circuit 3 is connected to a common connection point of capacitors 8a and 8b. The circuit elements connected between the above DC buses 4a and 4b constitute a converter main circuit 9. Note that the number of capacitors is not limited to two, and each of the capacitors 8a and 8b may be configured by a parallel connection or series connection circuit of a plurality of capacitors.

The switching of FET 7 of each switching circuit 3 is controlled by control calculation device 10 which is a control circuit of converter 27 . An input terminal of a power supply phase detection device 11 corresponding to a voltage phase detection section is connected to each phase output terminal of the three-phase AC power supply 1. The power supply phase detection device 11 detects the phase θ of the voltage input from the three-phase AC power supply 1 and outputs it to the control calculation device 10 . The power supply phase detection device 11 includes a detection circuit that normally detects the zero cross timing of an AC power supply, and divides the interval, that is, the time, between the zero cross timings of any phase into 180 degrees and counts the phase at that point. Determine θ.

Current sensors 12R, 12T, which are current detection units, are arranged between the reactors 2R, 2T and the AC input terminals of the switching circuits 3R, 3T. The current sensors 12R and 12T output the detected alternating currents i _L2 and i _L1 to the control calculation device 10. The control calculation device 10 uses the fact that the sum of the three-phase currents is "0" to calculate the current value of the remaining one phase by calculating i _L3 =-(i _L1+ i _L2 ). Incidentally, current sensors may be provided for all three phases to directly detect the current values of the three phases without performing any calculation, and input the detected current values to the control calculation device 10. Voltage sensor 13 detects voltage v _DC between DC buses 4 a and 4 b, and voltage sensor 14 detects voltage v _C1 of capacitor 8 b and inputs it to control calculation device 10 .

The abc/dq conversion circuit 15 of the control calculation device 10 converts the three-phase currents i _L2 , i _L1 , and i _L3 into currents i _q , i _d on the dq axis coordinates based on the power supply voltage phase θ, and outputs the converted currents. Currents i _q and i _d are input to PI controllers 17q and 17d via subtracters 16q and 16d. The subtracter 16q is given "0" as a subtraction value, and the subtracter 16d is given the output signal of the PI controller 18 as a subtraction value.

A subtracter 19 is provided at the front stage of the PI controller 18 , and the subtracter 19 inputs the difference between the output voltage command value V _{DC_ref} of the converter main circuit 9 and the voltage v _DC detected by the voltage sensor 13 to the PI controller 18 . do. The PI controller 18 performs proportional-integral control on the difference, and inputs the control result to the subtractor 16d as the d-axis current command value i _{d_ref} . Thereby, feedback control is performed so that the output DC voltage v _DC of the converter 27 becomes the voltage command value V _{DC_ref} .

The outputs of the PI controllers 17q and 17d are input to the dq/abc converter 20 as q-axis and d-axis voltage commands. The dq/abc converter 20 converts the voltages v _q and v _d on the dq axis coordinates into three-phase voltages based on the power supply phase θ, and outputs the three-phase voltages to the subtracters 22R, 22S, and 22.

Subsequently, processing is performed to equalize, that is, balance the voltages of the capacitors 8a and 8b connected in series. In this process, the voltage v _C1 detected by the voltage sensor 14 is multiplied by a coefficient “2” in the multiplier 23 and input to the subtracter 24 . The subtracter 24 subtracts the double value of the voltage v _C1 from the voltage v _DC , and the subtraction result is multiplied by a gain K in the gain adding section 25 and input to the subtracters 22R, 22S, and 22T. The subtracter 22 subtracts the output of the gain applying section 25 from the output of the dq/abc converter 20 and inputs the result to the PWM signal generating section 26 . Here, if the voltage v _DC and the double value of the voltage v _C1 are the same, the voltages of both capacitors 8a and 8b are balanced, so there is no addition by the gain K. On the other hand, if the voltages of the capacitors 8a and 8b are not balanced, the value obtained by multiplying the voltage difference (v _DC -v _C1 ×2) by the gain K is subtracted. Here, as an example, the voltage v _DC and the voltage v _C1 are detected and compared, but the voltages of the capacitors 8a and 8b, the voltage v _C1 and the voltage v _C2 , are detected and controlled so that both voltages match. It's okay.

The PWM signal generation unit 26 uses the input from the subtracter 22 as a three-phase voltage command value and compares it with the carrier signal to generate a three-phase voltage PWM signal and outputs it to the gate as a gate drive signal. This controls the on/off operation of each phase FET 7. In the process of generating this three-phase voltage PWM signal, since the converter 27 is of a rectifying type, the three-phase voltage command value is converted into an absolute value and compared with the carrier wave signal so that the three-phase voltage command value does not become negative. The above constitutes the converter 27. Note that the DC power generated by the converter 27 is supplied as a driving power to an inverter (not shown), which is an example of a driving circuit that operates a motor as a load. Further, the motor driven by this inverter drives the compression mechanism of the rotary compressor in the refrigeration cycle. Furthermore, this refrigeration cycle is incorporated into air conditioners, heat pump water heaters, and the like.

Next, the operation of this embodiment will be explained. As shown in FIG. 2, when the control calculation device 10 detects an abnormality such as an overcurrent detected by the current sensor 12 or an overvoltage detected by the voltage sensor 13 (S1; Yes), the control calculation device 10 turns off all FETs 7 of the converter main circuit 9 and operates. (S2). This state continues until the detected abnormality is resolved (S3; No). At this time, the inverter continues to operate. Therefore, the compressor and refrigeration cycle continue to operate.

When the abnormality is resolved (S3; Yes), the converter 27 restarts. At the time of restart, the voltage phase is advanced by a phase α with respect to the phase θ detected by the power supply phase detection device 11, switching by the FET 7 is started, and the converter 27 is operated (S4). If no abnormality is detected after the restart (S5; No), switching control of the FET 7 is performed so that the advanced phase α gradually becomes "0" (S6). If an abnormality is detected after restarting (S5; Yes), the process returns to step S2. Until the advanced phase α becomes "0" (S7; No), the process returns to step S5, and when the advanced phase α becomes "0" (Yes), the restart process is ended and normal continuous operation is performed.

Figure 3 shows each signal waveform when the converter is restarted without applying the control of this embodiment, that is, without advancing the voltage phase, after an abnormality occurs in the converter and the switching control is temporarily stopped. show. At the time of restart, a disturbance occurs in the waveform indicating the R-phase duty value near the zero-crossing point of the R-phase voltage. Due to this influence, the operation of the converter becomes unstable, and the difference between the d-axis current command value i _{d_ref} and the d-axis current i _d gradually increases, causing the control to diverge. When the time is 1.1, the control breaks down and the operation of the converter 27 is stopped.

On the other hand, when the control of this embodiment shown in FIG. 27 was successfully restarted, and even after that, stable control continued without any disturbance in the R-phase duty waveform. Although FIGS. 3 and 4 show an example in which the PWM signal generation unit 26 generates a two-phase modulation PWM signal, the same applies if it generates a three-phase modulation PWM signal.

As described above, according to this embodiment, the converter 27 generates driving power to be supplied to the inverter that operates the motor. The converter main circuit 9 includes a smoothing capacitor 8 formed by connecting capacitors 8a and 8b in series between the positive and negative DC buses 4a and 4b, and each phase terminal of the three-phase AC power supply 1 and the DC buses 4a and 4b. A full-wave rectifier circuit in which a diode 6 is bridge-connected is connected between the two, and an FET 7 is provided in a current-carrying path from each phase terminal to a common connection point of capacitors 8a and 8b.

The converter 27 also includes a current sensor 12 that detects the current input from the three-phase AC power supply 1, a power supply phase detection device 11 that detects the voltage phase of the three-phase AC power supply 1, and a power supply phase detection device 11 that detects the voltage phase of the three-phase AC power supply 1. A control calculation device 10 that controls switching of the FET 7 is provided. The control calculation device 10 advances the phase of the output voltage with respect to the voltage phase of the three-phase AC power supply 1 when restarting the control after stopping the control while the inverter is operating the motor. . Thereby, the converter 27 can be restarted in a state where the power factor is close to "1", and stable control can be continued.

(Second embodiment)
Hereinafter, parts that are the same as those in the first embodiment are given the same reference numerals and explanations will be omitted, and different parts will be explained. As shown in FIG. 5, in the second embodiment, when steps S1 to S3 are executed, it is determined whether the current value i detected by the current sensor 9 at that time is greater than or equal to the threshold value is (S11). If the current value i is greater than or equal to the threshold value is (Yes), the control calculation device 10 instructs the device controlling the inverter to gradually reduce the output frequency A (S12). Then, it is determined whether the current value i has become less than the threshold value is (S13). If it is determined "No" here, the process returns to step S12.

If the current value i becomes less than the threshold value is (S13; Yes) or if it is determined "No" in step S11, the phase of the output voltage is not advanced with respect to the phase of the input current, that is, α=0. Switching control of FET 7 of converter main circuit 9 is started, and converter 27 is restarted (S14).

As shown in FIG. 6, when the converter 27 is restarted when the amplitude of the R-phase input current becomes smaller than that shown in FIG. 4, the power factor remains close to "1" as in FIG. The converter 27 has been restarted.

As described above, according to the second embodiment, the control calculation device 10 controls the effective value of the current input from the AC power source 1 after stopping the control of the converter 27 while the inverter is operating the motor. When the value i is larger than the threshold value is, the converter 27 continues to be stopped, and when the current value i is less than the threshold value is, the converter 27 is restarted without advancing the phase. This allows stable restart of the converter 27.

However, with this method, the converter 27 cannot be started until the input current value i becomes smaller than the threshold value is, so during that time the power factor decreases and the converter is operated with reduced efficiency. Become. In order to reduce the operating time during which efficiency is reduced, the rotation speed of the motor driven by the inverter, which is the load of the converter 27, is temporarily lowered, the current i is proactively reduced, and the converter 27 is started. It is also possible to combine the controls.

(Third embodiment)
As shown in FIG. 7, in the third embodiment, steps S1 to S3 and S11 are executed similarly to the second embodiment, and if it is determined that "No" here, that is, the current value i is small, there is no phase shift. Step S14 of activating the converter 27 is executed. On the other hand, if it is determined "Yes" that the current value i is large, the voltage phase is advanced by the phase α, switching by the FET 7 is started, and the converter 27 is restarted, as in step S4 of the first embodiment. The phase α is variably set as follows (S15).
α=B×(i-is)
B is a proportional coefficient, and the phase α is set according to the difference between the current value i and the threshold value is. Then, similarly to the second embodiment, steps S5 to S7 are executed. By changing the advance phase in accordance with the current value i in this way, more stable restart is possible depending on the situation.

(Other embodiments)
The switching element is not limited to MOSFET.
The configuration of the main circuit of the converter is not limited to that shown in the drawings, and any configuration known as a VIENNA rectifier can be applied.

Although several embodiments of the invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention, as well as within the scope of the invention described in the claims and its equivalents.

In the drawing, 1 is a three-phase AC power supply, 3 is a switching circuit, 4a, 4b are DC buses, 7 is an N-channel MOSFET, 8 is a smoothing capacitor, 9 is a converter main circuit, 10 is a control circuit, and 11 is a power supply phase detection device , 12 is a current sensor, and 13 and 14 are voltage sensors.

Claims (2)

Generates power to drive loads.
A smoothing capacitor formed by connecting a capacitor in series between the positive and negative DC buses,
a full-wave rectifier circuit connected between each phase terminal of a three-phase AC power supply and the positive side and negative side DC buses;
a switching element disposed in a current-carrying path from each phase terminal to a connection point of the capacitor;
a current detection unit that detects a current input from the three-phase AC power supply;
a voltage phase detection unit that detects the voltage phase of the three-phase AC power supply;
a control circuit that controls the operation of the switching element based on the voltage phase and the current,
The control circuit outputs a voltage phase of the three-phase AC power supply when restarting the operation of the switching element after stopping the operation of the switching element while the load is operating. A converter that advances the phase of voltage. A smoothing capacitor formed by connecting a capacitor in series between the positive and negative DC buses,
a full-wave rectifier circuit connected between each phase terminal of a three-phase AC power supply and the positive side and negative side DC buses;
a switching element disposed in a current-carrying path from each phase terminal to a connection point of the capacitor;
a current detection unit that detects a current input from the three-phase AC power supply;
a voltage phase detection unit that detects the voltage phase of the three-phase AC power supply;
a control circuit that controls the operation of the switching element based on the voltage phase and the current,
The control circuit is a converter that stops the operation of the switching element while the load is operating, and then restarts the operation of the switching element when the value of the current becomes less than a threshold value.

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