JP4887216B2 - Power converter for driving refrigeration cycle compressor and refrigeration system using the same - Google Patents

Description

  The present invention relates to a power conversion device that drives a compressor of a refrigeration cycle such as an air conditioner and a refrigeration device, and more particularly to a power conversion device that drives a refrigeration cycle compressor at a variable speed.

  In general, a power converter that drives a refrigeration cycle compressor at a variable speed includes a converter circuit that converts AC power input from an AC power source through a reactor into DC, and a smoothing connected in parallel to the DC output of the converter circuit. A capacitor and an inverter circuit that converts the DC power smoothed by the smoothing capacitor into AC power having a variable frequency and a variable voltage are provided. In addition, PWM control is performed on the switching elements of the upper and lower arms of the converter circuit based on the DC output command voltage and the phase of the power supply voltage, and PWM control of the switching elements of the upper and lower arms of the inverter circuit is performed. Thus, the AC output of variable frequency and variable voltage is supplied to the motor of the refrigeration cycle compressor. Recently, power converters in which a converter circuit, an inverter circuit, and a microcomputer that controls these semiconductor switching elements are modularized have been used (for example, Patent Document 1).

  Further, in Patent Document 1, in order to omit the detector that detects the AC input current of the converter circuit, the DC current of the converter circuit and the converter circuit are considered in view of the fact that the DC current of the converter includes information on the AC current. It has been proposed to obtain the alternating current on the input side of the converter circuit based on the operation mode of the semiconductor switching element.

JP 2006-67754 A

  However, Patent Document 1 does not consider the converter control at the time of starting to start the operation of the converter circuit. That is, since the phase information of the power supply voltage is necessary when starting the converter circuit, it is necessary to provide a phase detector of the power supply voltage. However, there is a problem that the manufacturing cost increases by providing the phase detector.

  Therefore, it is desired to detect the phase of the power supply voltage when starting the converter circuit based on the direct current of the converter circuit without providing a phase detector for the power supply voltage.

  However, since the inverter circuit is not operated when the converter circuit is activated, the converter circuit only has a charging current that temporarily flows through the smoothing capacitor when the power is turned on. Therefore, the phase of the power supply voltage cannot be detected with high accuracy.

  The problem to be solved by the present invention is to detect the power supply voltage phase before starting the converter circuit based on the direct current of the converter circuit and to improve the detection accuracy of the power supply voltage phase.

  The present invention provides a converter circuit that converts AC power input from an AC power source through a reactor into DC, a smoothing capacitor connected in parallel to a DC output of the converter circuit, and DC power smoothed by the smoothing capacitor. PWM control based on the voltage command of the DC output and the phase of the power supply voltage for the inverter circuit for converting to AC power of variable frequency and variable voltage, and the switching elements of the upper and lower arms of the bridge circuit constituting the converter circuit And a converter control means that performs variable speed driving of the refrigeration cycle compressor by the AC output of the inverter circuit.

  In order to solve the above problems, the converter control means of the power conversion device of the present invention includes a voltage phase detection means for detecting a power supply voltage phase, and the voltage phase detection means is configured to detect the upper arm before starting the converter circuit. Alternatively, turn on the switching elements of each phase of the lower arm in turn at a frequency higher than the AC power supply frequency, detect the DC output current of the converter circuit, and detect the zero current phase range where the DC output current becomes zero The phase of the power supply voltage is detected based on the detected zero current phase range.

  That is, for example, there are six regions in which the magnitude relationship between the three-phase (u, v, w) voltages changes every 60 ° electrical angle. When the switching elements of each phase of, for example, the lower arm of the converter circuit connected in a three-phase bridge are sequentially turned on at a frequency higher than that of the AC power supply, the DC output current of the converter circuit is changed according to the magnitude relationship of the three-phase voltages. A period of zero occurs. Further, since the center phase of the zero current phase range corresponds to the phase of the voltage maximum value of any one of the u, v, and w phases, the phase of the power supply voltage can be detected based on the zero current phase range. .

  By the way, in general, since external noise is superimposed on the commercial power supply, it is preferable to set a large zero current determination value with a margin. However, since the level of the DC current at the time of starting the converter circuit is small, it is difficult to detect the phase range in which the DC output current becomes zero. Therefore, according to the present invention, when the phase of the power supply voltage is detected, a command for causing the inverter circuit to operate with a load equal to or higher than the set value is output so that the DC current at the time of starting the converter circuit flows more than a certain value. It is characterized by that.

  In the case of a general power converter, it is difficult to operate the inverter circuit with a load equal to or higher than a set value at the time of startup. However, when the load of the inverter circuit is a refrigeration cycle compressor, there is no problem because the state of the refrigeration cycle does not change abruptly even if the refrigeration cycle compressor is operated with a load of about a set value at the time of startup.

  ADVANTAGE OF THE INVENTION According to this invention, the power supply voltage phase at the time of starting of a converter circuit can be detected based on the direct current of a converter circuit, and the detection accuracy of a power supply voltage phase can be improved. As a result, since it is not necessary to provide a phase detector for the power supply voltage, the cost of the power conversion device can be reduced.

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

  FIG. 1 shows an overall configuration diagram of a power conversion apparatus according to an embodiment of the present invention, and FIG. 2 shows a voltage phase detection processing procedure according to features of the present embodiment.

  As shown in FIG. 1, the power conversion device 14 of the present embodiment includes a three-phase converter circuit 1 that converts AC power input from an AC power supply 6 through a reactor 7 into DC, and a DC output of the converter circuit 1. Are connected in parallel to each other, a three-phase inverter circuit 2 for converting the DC power smoothed by the smoothing capacitor 10 into AC power of variable frequency and variable voltage, and a refrigeration connected to the AC output of the inverter circuit 2 A motor 8 for driving the cycle compressor is provided. The motor 8 is configured, for example, by arranging a plurality of windings for forming an alternating magnetic field around a rotor of a permanent magnet.

  The converter circuit 1 is configured by three-phase bridge connection of three switching arms formed by connecting semiconductor switching elements Q1, Q2, Q3, Q4, Q5, and Q6 in series for each of u, v, and w phases. Diodes D1 to D6 are connected in parallel with opposite polarities to the semiconductor switching elements Q1 to Q6. The connection points of the upper and lower arms of each phase of the converter circuit 1 are connected to the AC power source 6 via the reactor 7. Like the converter circuit 1, the inverter circuit 2 is configured by connecting six semiconductor switching elements and six diodes connected in parallel with opposite polarity in a three-phase bridge connection, and the upper and lower arms of each phase. The connection point is connected to the motor 8. The semiconductor switching elements of the converter circuit 1 and the inverter circuit 2 are controlled by PWM (pulse width modulation) by drive signals output from the driver circuits 18 and 19, respectively.

  The current detector 3 is provided on the negative side (N) line between the converter circuit 1 and the DC output smoothing capacitor 10, and the negative side (N) line between the inverter circuit 2 and the DC input smoothing capacitor 10 is provided. A current detector 4 is provided. A voltage detector 20 that detects a DC output voltage from the terminal voltage of the smoothing capacitor 10 is provided.

  The driver circuits 18 and 19 are controlled by the control circuit 11. The control circuit 11 includes an analog / digital (A / D) converter 21 that converts current / voltage information of the DC section detected by the current detectors 3 and 4 and the voltage detector 20 into a digital signal, a converter control circuit 20, An inverter control circuit 23 is provided. The A / D converter 21 converts an analog value of any one of the PWM pulse signals 12 and 13 and an amplifier such as an OP amplifier that amplifies the current voltage information detected by the current detectors 3 and 4 and the voltage detector 20. It is configured to operate as a timing signal to be captured. The A / D converter 21 is configured to have a sample hold function and an A / D conversion function. The A / D converter 21 converts the captured analog value into a digital value and converts it into the converter circuit control circuit 20 and the inverter circuit control circuit 23. Output.

  The converter control circuit 20 generates the PWM pulse signal 12 and outputs it to the driver circuit 18 so that the DC output voltage matches the DC voltage command value. That is, the converter control circuit 20 creates the input current command value i * so as to reduce the deviation between the DC output voltage E output from the A / D converter 21 and the DC voltage command value E *. The value i * is converted into an AC signal in accordance with the power supply voltage phase θ and compared with a PWM carrier wave (generally, a triangular wave) to generate a PWM pulse signal. The power supply voltage phase θ is a known current estimation calculation method or current reproduction method for estimating and calculating the input current of the AC unit based on the DC current detected by the current detector 3 (for example, see Japanese Patent Application Laid-Open No. 2003-250298). ). The outline of the current estimation calculation method is to calculate an AC input current based on the operation mode of the upper and lower arm semiconductor switch elements of each phase and the detected DC current.

  The inverter control circuit 23 controls the frequency of the output AC voltage so as to reduce the speed deviation between the speed command of the motor 8 and the detected speed, and generates an output current command so as to reduce the speed deviation. 4 generates an AC output voltage command so as to reduce the deviation between the AC output current detected by 4 and the AC output current command, converts the AC output voltage command into an AC signal in accordance with the AC output voltage phase θ, and generates a PWM carrier wave ( In general, the PWM pulse signal 13 is generated as compared with a triangular wave. Also for the AC output current at this time, the output current of the AC section of the inverter circuit 2 can be estimated and calculated based on the DC current detected by the current detector 4 by current estimation calculation method or current reproduction method.

  The A / D converter 21, the converter control circuit 20, and the inverter control circuit 23 are realized by a single semiconductor integrated circuit. The driver circuits 18 and 19 amplify the PWM pulse signals 12 and 13 and apply the amplified PWM pulse signals to the gates of the semiconductor switch elements of each phase. Each semiconductor switch element performs a switching operation according to the pulse signal. Further, when shunt resistors are used as the current detectors 3 and 4, one end of these shunt resistors is connected to the N line side connected to the smoothing capacitor 10, and the other end is connected to the A / D converter 21. input. Thereby, even when the reference potential varies due to external noise or the like, the relative relationship between the two current detectors does not change, so that the relative error can be reduced. The current detectors 3 and 4 are not limited to shunt resistors, and may be configured using a CT (current transformer), a Hall element, or the like. In this case as well, current detection can be performed with the same potential as a reference.

  Hereinafter, the processing procedure of the voltage phase detection means for detecting the power supply voltage phase before starting the converter circuit 1 which is the characteristic part of the present embodiment will be described with reference to the flowchart of FIG. The voltage phase detection means is incorporated in the inverter control circuit 20.

  As shown in FIG. 2, first, when the power is turned on before starting the converter circuit 1 (S1), the smoothing capacitor 10 is charged by the rectification operation by the diodes D1 to D6 of the converter circuit 1. Subsequently, when a start command based on the set load is output to the inverter circuit 2, the motor 8 is started by the electric power stored in the smoothing capacitor 10 (S2). Next, as shown in FIG. 3, pulsed drive signals P1 to P3 are output to the semiconductor switching elements Q2, Q4, and Q6 of the lower arm of the converter circuit 1 through the drive circuit 18 (S3). The pulse-shaped drive signals P1 to P3 are generated by a PWM switching circuit (not shown) of the converter control circuit 20 and the semiconductor switching element Q2 corresponding to the u, v, and w phases with a certain interval in electrical angle of the PWM carrier wave. , Q4, Q6 occur in order.

  Here, as shown in FIG. 4, the magnitude relationship between the three-phase AC phase voltages eu, ev, and ew is divided into six regions I to VI that change every 90 °. For example, in the regions I and II, the u-phase voltage eu is higher than ev and ew. Therefore, when the semiconductor switching element Q2 is turned on, an input current flows through a path indicated by a dotted line in FIG. DC current does not flow through. The magnitude of the current can be adjusted by adjusting the pulse width of the pulse-like drive signals P1 to P3. In particular, in order to suppress the inrush current flowing through the smoothing capacitor 10, it is preferable to gradually widen the pulse width of the drive signals P1 to P3 from near zero.

  On the other hand, in the regions IV and V, since the u-phase voltage eu is lower than ev and ew, a direct current flows through the smoothing capacitor 10 as shown in FIG. The Similarly, in the regions III and VI, since the u-phase voltage eu is lower than ev or ew, a direct current is detected by the current detector 3.

  In short, when no current flows through the current detector 3 when the u-phase lower arm semiconductor switching element Q2 is turned on, the relationship between the phase voltages eu, ev, and ew is the regions I and II in FIG. Can be identified. Similarly, when no current flows through the current detector 3 when the semiconductor switching element Q4 is turned on, the relationship between the phase voltages eu, ev, and ew is regions III and IV, and when the semiconductor switching element Q6 is turned on. When no current flows through the current detector 3, it can be specified that the relationship between the phase voltages eu, ev, and ew is the regions V and VI.

  As described above, when the DC output current detected by the current detector 3 with each of the semiconductor switching elements Q2, Q4, Q6 turned on is decomposed according to the phase of the on state, the waveform shown in FIG. 7 is obtained. From FIG. 7, since the start point and end point of the section where the phase of the power supply voltage and the DC output current detected by the current detector 3 become zero coincide with each other, the power supply voltage is detected by detecting the start point and the end point. Can be detected. Further, the phase sequence of the power source can be determined from the order of the sections in which the DC output current becomes zero. Further, the power supply frequency can be calculated from the time difference between the sections of the phases where the DC output current becomes zero.

  With reference to FIG. 8, a specific example of determining the zero interval of the DC output current and detecting the phase of the power supply voltage will be described. In FIG. 8, the horizontal axis represents time, and the vertical axis represents the DC output current waveform and the counter count value. In the figure, if the current waveform 33 is a DC output current waveform corresponding to the u phase, the phase of the power supply voltage at the time point (start point A) t1 when the current of the current waveform 33 becomes zero from positive is about 30 °, from zero. The phase of the power supply voltage at the time point (end point B) t2 when becoming positive is about 150 °. However, since the start point A and the end point B are slightly shifted due to the influence of the power source inductance and the load, if the midpoint C of t1 and t2 is detected as 90 °, the detection accuracy is improved. The counter is reset at time t0 when the detection of the power supply voltage phase is started, and counts up the count value every PWM carrier wave period. Then, each time the current of the current waveform 33 is sampled, the voltage phase detection means obtains a difference obtained by subtracting the current sampling value from the previous sampling value, and the difference is less than or equal to a determination value set in consideration of noise. The starting point A is detected, and the count value N1u at that time is held. Subsequently, a difference obtained by subtracting the current sampling value from the previous sampling value is obtained, an end point B where the difference exceeds a determination value set in consideration of noise is detected, and the count value N2u at that time is held. Based on the count values N1u and N2u held in this way, the phase θd of the power supply voltage at an arbitrary time point D (= t3) is obtained by the following equation. In the equation, N is a count value at an arbitrary time t3, and Δθ is an increase in phase per count cycle.

θd = (N− (N2u−N1u) / 2) × Δθ + 90 °
Δθ = 360 ° × power supply frequency / count cycle In this way, the count values N1u, N2u, Nv1, Nv2, Nw1, Nw2 of each phase are detected and held, so that the u, v, w phases at an arbitrary time point Can be detected. Further, if the count value of each phase increases in the order of u, v, and w, the phase rotation can be determined as normal order, and if the count value increases in the order of w, v, and u, the phase rotation can be determined as reverse order. Further, the power supply frequency can be obtained from the difference between the count value N1u and the count value N2u of each phase or the difference between the count value N1u of 1 and the next count value N1u.

  By the way, in general, since external noise or the like is superimposed on a commercial power supply, it is preferable to set a large zero current determination value with a margin. However, when the load of the inverter circuit 2 is small, the detection value of the current detector 3 is also small, so the difference when no current is flowing is small, the error of zero detection is large, and the DC output current is zero. It is difficult to detect the range. If the phase detection error increases, it affects the start of converter operation.

  Therefore, in the present embodiment, as shown in step S2 of FIG. 2, when detecting the power supply voltage phase, a command for operating the inverter circuit 2 with a load equal to or greater than a set value is output. Thereby, since the DC current at the time of starting of the converter circuit 1 flows over a certain value, the zero current phase range can be reliably detected even if the zero current determination value is set to be large with a margin.

  By the way, although it is difficult to operate the inverter circuit 2 at a constant set value frequency at the time of startup in the case of a general power converter, the motor 8 that is the load of the inverter circuit 2 drives the refrigeration cycle compressor. In this case, even if the refrigeration cycle compressor is operated with a small set load at the time of start-up, there is no problem because the state of the refrigeration cycle does not change rapidly.

  Further, in step S4 in FIG. 2, when the captured DC output current is smaller than the set value, a command can be sent to the inverter control circuit 23 to increase the inverter frequency.

  In the example shown in FIG. 3, the example in which the semiconductor switching elements in the lower arm of the converter circuit 1 are turned on in order to detect the zero current phase range has been described. It goes without saying that the zero current phase range can be detected by turning on.

  FIG. 9 shows a perspective view of an example in which the power conversion device of FIG. 1 is modularized. As shown in the figure, the power converter 14 is integrally formed by mounting a converter circuit 302, an inverter circuit 303, and a microcomputer 16 on the same substrate. That is, the converter circuit 302 and the inverter circuit 303 that are connected via a DC circuit are mounted on the substrate 300. A microcomputer 16 that controls a plurality of semiconductor switch elements of the converter circuit 302 and the inverter circuit 303 is also mounted on the substrate 300.

  The substrate 300 is provided with an AC terminal 305 a connected to the converter circuit 302 and an AC terminal 305 b connected to the inverter circuit 303. Further, the board 300 is provided with a connector 307 connected to an external control device such as a host control device. In addition, the substrate 300 is provided with two current detectors 304 that detect a current flowing through the DC line of the converter circuit 302.

  Further, as shown in FIG. 9, in the power conversion device 14 of the present embodiment, the power system including the semiconductor switch element is disposed on the back surface, and the control system such as the computer 16 is disposed on the front surface. It is not affected by the noise generated from the system.

  Furthermore, the schematic diagram of the outdoor unit 500 which applied the power converter device 14 of this embodiment to the compressor drive of a freezing apparatus in FIG. 10 is shown. The power conversion device 14 mounted and configured on one substrate is connected to the compressor 503 by a wiring 502, and drives the motor 8 in the compressor 503 to compress the refrigerant. The compressed high-pressure refrigerant passes through the pipe 504, passes through the heat exchanger 505, and releases heat. Although not shown in FIG. 10, there is an indoor unit that is paired with the outdoor unit 500. The refrigerant becomes a low pressure in the heat exchanger of the indoor unit, absorbs the theory, and returns to the compressor 503. In the cooling operation and the heating operation, the refrigerant flow is reversed, and heat is released by the heat exchanger of the indoor unit. By mounting the power conversion device 14 on one board, maintenance at the time of failure becomes easy.

  This refrigeration apparatus controls the air conditioning environment of the space in which the indoor unit is installed. The heat capacity of the space is relatively large. For example, when the space is cooled, the output frequency of the power converter 14 is increased in order to increase the refrigeration capacity of the outdoor unit 500. However, since the heat capacity to be air-conditioned is large, the power converter 14 continues to have a high output frequency for a while. It takes a relatively long time for the air-conditioned space to reach the desired temperature. Since it takes time to change the temperature of the air-conditioned space in this way, the temperature of the air-conditioned space is increased even if the output frequency of the power converter 14 is increased only for a short time when the power supply voltage phase is detected at the start of the converter operation. It doesn't change much.

It is a whole lineblock diagram of the power converter of one embodiment of the present invention. It is a flowchart which shows the process sequence of the voltage phase detection which is the characterizing part of this invention. It is a figure explaining the operation | movement which turns on the semiconductor switching element of a lower arm in order at the time of voltage phase detection. It is a figure explaining the magnitude relationship of each phase of a three-phase power supply voltage. It is a figure explaining the magnitude relation state of each phase voltage from which the detection current of a current detector becomes zero when one of the semiconductor switching elements of a lower arm is turned on. It is a figure explaining the magnitude relation state of each phase voltage from which the detection current of a current detector becomes non-zero when one of the semiconductor switching elements of a lower arm is turned on. It is the wave form diagram which decomposed | disassembled and showed the direct-current output current which flows when the semiconductor switching element of a lower arm is turned on in order according to the phase of an ON state. It is a figure explaining the specific example which determines the zero area of DC output current and detects the phase of a power supply voltage. It is a perspective view of one embodiment which modularized the power converter of the present invention. It is a schematic diagram of the outdoor unit of the freezing apparatus of an example to which the power converter of this invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Converter circuit 2 ... Inverter circuit 3 ... Current detector 4 ... Current detector 6 ... AC power supply 7 ... Reactor 8 ... Motor 10 ... Smoothing capacitor 11 ... Control circuit 18, 19 ... Driver circuit 20 ... Converter control circuit 21 ... A / D converter 23 ... Inverter control circuit

Claims (3)

A converter circuit for converting AC power input from an AC power source through a reactor into DC, a smoothing capacitor connected in parallel to the DC output of the converter circuit, and DC power smoothed by the smoothing capacitor with variable frequency and variable Converter control for PWM control of the inverter circuit for converting the voltage into AC power and the switching elements of the upper and lower arms of the bridge circuit constituting the converter circuit based on the voltage command of the DC output and the phase of the power supply voltage A power converter for driving the refrigeration cycle compressor at a variable speed by an AC output of the inverter circuit,
The converter control means includes voltage phase detection means for detecting a power supply voltage phase,
The voltage phase detection means, prior to activation of said converter circuit, outputs a command to operate at more than the set value of the load to the inverter circuit, from the AC power source frequency of each phase of the switching elements of the upper arm or the lower arm The DC output current of the converter circuit is detected by sequentially turning on the electrical frequency of the PWM carrier wave at a high frequency in order to detect the DC output current, and the zero current phase range where the DC output current becomes zero is detected. power converter, wherein the benzalkonium detecting the phase of the supply voltage on the basis of the zero current phase ranges. The power conversion device according to claim 1,
The voltage phase detection means includes a counter that measures an elapsed time in parallel with the detection of the DC output current, and obtains the phase of the power supply voltage based on the count values of the counter at the start point and the end point of the zero current phase range. The power converter characterized by this. The power conversion device according to claim 2,
The voltage phase detection means obtains the phase sequence and frequency of a power source based on the count values of the counter at the start point and end point of the zero current phase range.

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