JP7601809B2 - Power conversion device, power conversion method, and industrial equipment - Google Patents

Description

The present invention relates to a power conversion device, a power conversion method, and industrial equipment.

Permanent magnet synchronous motors, which are more efficient than conventional induction motors, are becoming popular in industrial fields such as refrigeration equipment. However, because permanent magnet synchronous motors have a permanent magnet in the rotor, when a magnetic field of a certain value or more is applied to the permanent magnet, irreversible demagnetization occurs, and the magnetic force of the permanent magnet weakens, which can reduce the torque of the motor. Because the magnetic field applied to the permanent magnet is proportional to the current value flowing through the motor, a demagnetization start current value, which is the upper limit of the current value for preventing irreversible demagnetization, is set for permanent magnet synchronous motors, and it is necessary to control the permanent magnet synchronous motor below this current value. Therefore, when driving a permanent magnet synchronous motor, a power conversion device equipped with an overcurrent protection circuit is connected to the permanent magnet synchronous motor to prevent an overcurrent exceeding the demagnetization start current value from flowing.

When controlling a permanent magnet synchronous motor with a power conversion device, it is common to first convert the AC voltage to a DC voltage using a smoothing circuit consisting of a rectifier diode bridge using multiple diode elements and a smoothing capacitor for smoothing the voltage, and then convert the DC voltage back to an AC voltage using a switching element such as an IGBT (Insulated Gate Bipolar Transistor).

When controlling the switching elements, it is common to use sensorless vector control, in which a current detector detects the three-phase current flowing through the permanent magnet synchronous motor and estimates the magnetic pole position of the permanent magnet from the current information detected by the current detector. In addition to estimating the magnetic pole position, the current detector also monitors whether a current greater than the demagnetization start current value flows, and if a current exceeding the demagnetization start current value flows, it turns off the switching element and operates to prevent the permanent magnet synchronous motor from being irreversibly demagnetized. The demagnetization start current value of each permanent magnet synchronous motor is set in advance in the power conversion device, and the motor is protected so that it operates above the rated current and below the demagnetization start current. In general, the rated current value and demagnetization start current value of a permanent magnet synchronous motor are designed and set with a margin, so there is no need for precision in the current value at which the overcurrent protection operates.

However, in recent years, due to the rising prices of rare earths such as neodymium, which are the raw materials for permanent magnets, and copper, which is used in motor coils, there have been many cases where the raw materials and the number of turns of the coils of permanent magnet synchronous motors have to be changed. For example, the raw materials used for permanent magnets are being changed from neodymium to ferrite, which tends to have a lower demagnetization start current. As for coils, the number of turns of the coils is being reduced to reduce usage costs. The demagnetization start current value of a permanent magnet synchronous motor is lowered by ferrite, so there are cases where the margin between the rated current value and the demagnetization start current value is reduced. In addition, the impedance of a permanent magnet synchronous motor is reduced by reducing the inductance due to the reduction in the number of turns of the coil. Therefore, when the same voltage is applied to a permanent magnet synchronous motor after the number of turns of the coil is reduced, a large current is more likely to flow than before the reduction in the number of turns of the coil. Due to these factors, if the accuracy of the overcurrent protection circuit is low, a current that exceeds the demagnetization start current value flows through the permanent magnet synchronous motor, and the permanent magnet synchronous motor is expected to experience irreversible demagnetization.

As an example of a conventional overcurrent protection circuit, Patent Document 1 discloses a method of constructing an overcurrent protection circuit by detecting the current by measuring both ends of a resistor and comparing it with a reference power supply.

JP 2005-45853 A

However, the technology described in Patent Document 1 is based on the premise that there is no fluctuation in the reference voltage used when detecting the current, and if the reference voltage fluctuates due to fluctuations in the control voltage that occur during power reception fluctuations, load fluctuations, or temperature changes, there are cases in which overcurrent cannot be detected accurately. In other words, since it is necessary to set the overcurrent value in advance taking into account the variation in the control voltage so that the permanent magnet synchronous motor is not demagnetized, setting the overcurrent value too low may result in the permanent magnet synchronous motor being unable to make full use of the torque it can output.

The present invention aims to provide a power conversion device that can accurately detect the current of a permanent magnet synchronous motor and maximize the torque of the permanent magnet synchronous motor without demagnetizing it, even when the control voltage fluctuates due to power fluctuations, load fluctuations, and temperature changes.

The following is a brief summary of the representative inventions disclosed in this application:

A power conversion device according to a representative embodiment of the present invention is a power conversion device including a DC conversion unit that converts an externally supplied power source into DC, a smoothing unit that smooths the DC current output from the DC conversion unit, a power conversion unit that switches the smoothed current output from the smoothing unit, and a control unit that controls the power conversion unit. The power conversion device includes a transformer unit that is connected in parallel with the smoothing unit and generates a power supply voltage for the control unit, a constant voltage output unit that outputs an analog constant voltage even when the smoothed current fluctuates, a storage unit that pre-stores the analog constant voltage as a reference digital voltage, a first analog detection unit that converts the analog constant voltage output from the constant voltage output unit into a digital constant voltage, and a correction calculation unit that compares the digital constant voltage with the reference digital voltage, calculates a correction coefficient to correct the power supply voltage of the control unit, and corrects the power supply voltage. The maximum analog voltage that the first analog detection unit can convert is the power supply voltage of the control unit.

The effects obtained by the representative inventions disclosed in this application can be briefly explained as follows. According to the representative embodiment of the present invention, even when the control voltage fluctuates due to power fluctuations, load fluctuations, and temperature changes, the current of a permanent magnet synchronous motor can be detected with high accuracy, and maximum torque can be utilized without demagnetizing the permanent magnet synchronous motor.

FIG. 1 is a block diagram showing an overall configuration of a power conversion device according to a first embodiment. FIG. 2 is a block diagram showing the internal configuration of the control circuit unit according to the first embodiment. FIG. 3 is a diagram showing the relationship between the detected current I of the current detector and the current detector output voltage Vout according to the first embodiment. FIG. 4 is a diagram showing the relationship between the CT output voltage and the current detected by the microcomputer according to the first embodiment. FIG. 5 is a diagram showing the relationship when the power supply voltages supplied to the CT and the microcomputer according to the first embodiment are different. FIG. 6 is a flowchart showing an example of the operation of the power conversion device according to the first embodiment. FIG. 7 is a diagram showing a configuration of an output function and the like of a power conversion device according to the second embodiment.

In the following embodiments, when necessary for convenience, they will be divided into multiple sections or embodiments for explanation; however, unless otherwise specified, they are not unrelated to each other, and one is a partial or complete modification, detail, supplementary explanation, etc., of the other. Furthermore, in the following embodiments, when the number of elements (including the number, numerical value, amount, range, etc.) is mentioned, it is not limited to that specific number, and may be more or less than the specific number, except when otherwise specified or when it is clearly limited in principle to a specific number.

Although each embodiment of the present invention will be described with reference to the drawings, the disclosure is merely an example, and appropriate modifications that a person skilled in the art can easily conceive of while maintaining the gist of the invention are naturally included within the scope of the present invention. In addition, in order to make the explanation clearer, the drawings may show the width, thickness, shape, etc. of each part in a schematic manner compared to the actual embodiment, but these are merely examples and do not limit the interpretation of the present invention.

Furthermore, in the following embodiments, the components (including element steps, etc.) are not necessarily essential unless otherwise specified or considered to be clearly essential in principle. Similarly, in the following embodiments, when referring to the shape, positional relationship, etc. of components, etc., it is intended to include those that are substantially similar or similar to the shape, etc., unless otherwise specified or considered to be clearly not essential in principle. The same applies to the above numerical values and ranges.

The following describes in detail an embodiment of the present invention with reference to the drawings. In all the drawings used to explain the embodiment, the same components are generally given the same reference numerals, and repeated explanations are generally omitted. In the following, the following description will be given using as an example a power conversion device connected to electrical equipment including rotating machines such as fans, pumps, and compressors.

<First embodiment>
The first embodiment will be described with reference to FIGS. 1 to 6. FIG.

[Overall configuration of power conversion device]
1 is a diagram showing an example of the overall configuration of a power conversion device. The power conversion device 100 includes a main circuit section 110, a control circuit unit 120, a control power supply generating circuit section 130, a current detection section 3, etc., and a microcomputer mounted on the control circuit unit 120 controls the operation of the power conversion device 100. The power conversion device 100 converts a three-phase AC power supply 1 into a DC power supply, supplies the DC power to a switching circuit 113, and operates a rotating machine 2 by the switching operation of the switching circuit 113. As described above, the rotating machine 2 is incorporated into an electric device such as a fan, a pump, or a compressor.

Furthermore, we will specifically explain this power conversion device and the components connected to this power conversion device.

(Three-phase AC power supply 1)
The three-phase AC power source 1 is, for example, a three-phase AC power source generated at a power plant. R, S, and T of the power source are supplied to the main circuit unit 110. Note that the power source supplied to the main circuit unit 110 is not limited to a three-phase AC power source. For example, the power source may be a single-phase AC power source, a battery, or a DC power source supplied from a power conditioner. However, when the power source is a single-phase AC power source or a DC power source, the configuration of the main circuit unit 110 also changes. For example, the diode bridge 111 may be modified for a single-phase AC power source or omitted. In the following description, components of the main circuit unit 110 and the like will be described using a case where the power source is a three-phase AC power source 1 as an example.

(Main circuit section 110)
The main circuit section 110 includes a diode bridge 111 connected to the three-phase AC power source 1 and functioning as a DC converter, a smoothing capacitor 112 connected in parallel to an output terminal from which DC power is output by the diode bridge 111, and a switching circuit 113 functioning as a power converter for converting DC power to AC power. The AC power output from the switching circuit 113 is output to the rotating machine 2, and the rotating machine 2 is rotated by the AC power. The switching circuit 113 is controlled by a microcomputer mounted on the control circuit unit 120 so that the frequency and voltage of the AC power are set to arbitrary values. That is, the waveforms of switching signals SG1, SG2, SG3, SG4, SG5, and SG6 applied to gates G1, G2, G3, G4, G5, and G6 of transistors such as IGBTs constituting the switching circuit 113 are controlled by the microcomputer mounted on the control circuit unit 120.

(Current detection unit 3)
The current detection unit 3 is provided on a conductor that electrically connects the rotating machine 2 to the switching circuit 113 that functions as a power conversion unit. The current detection unit 3 is a current sensor such as a Hall sensor. The current detection unit 3 has a function of placing at least two current sensors such as Hall sensors close to the conductor and detecting the current flowing through the rotating machine 2. For example, a Hall sensor is an element that detects the magnetic flux generated when a current value I flows and outputs an analog voltage signal Vout, and the relationship between I and Vout is I = Vout G (G = gain). The gain differs for each Hall sensor, so it is a value selected depending on the current value to be detected.

Figure 3 shows the relationship between the detected current I (A) and the voltage signal Vout in the case where the Hall sensor outputs a voltage signal Vout of 0 to +5V when it detects a current of -25A to +25A. The vertical axis on the right side of Figure 3 shows the magnitude of the detected current of the Hall sensor, and the vertical axis on the left side of Figure 3 shows the magnitude of the voltage signal Vout, which is the output of the Hall sensor. The horizontal axis of Figure 3 represents the sine wave input to the Hall sensor as a function of time. The Hall sensor uses 2.5V, which is half the maximum output voltage of 5V, as the reference voltage, and outputs the reference voltage as an offset value when the current is 0A. Therefore, when the Hall sensor detects -25A, the voltage signal Vout is 0V, and when the Hall sensor detects +25A, the voltage signal Vout is 5V.

This offset value of 2.5V is also constantly output from a port Vref other than Vout, allowing the reference voltage of the Hall sensor to be monitored externally. The reference voltage of 2.5V output from port Vref does not change even if the power supply voltage of the current detection unit 3 changes. However, if the power supply voltage of the current detection unit 3 falls below approximately 2.5V, the reference voltage cannot maintain an output of 2.5V. This offset value of 2.5V may be output from another constant voltage element. An example of a constant voltage element is a constant voltage diode.

(DC voltage detection unit 4)
The DC voltage detection unit 4 steps down the voltage across the smoothing capacitor 112 using a circuit configuration such as a voltage divider resistor, and outputs the change in the voltage across the smoothing capacitor 112 according to a voltage range that can be input by the control circuit unit 120. For example, if the maximum voltage that can be applied across the smoothing capacitor 112 is +5 V, then the DC voltage detection unit 4 outputs a voltage in the range of 0 to +5 V as a voltage signal Vedc to the control circuit unit 120. In other words, the DC voltage detection unit 4 functions to enable the control circuit unit 120 to monitor fluctuations in the DC voltage that has been converted from the input voltage by the diode bridge 111 and the smoothing capacitor 112.

(Temperature detection unit 5)
The temperature detection unit 5 has a function of outputting temperature information as a voltage signal utilizing the characteristic that the resistance value of the thermistor built in the switching circuit 113 changes with temperature change. For example, a resistor is connected in series with the thermistor, and 5V is applied to one end of the thermistor or the resistor, and 0V is applied to the other end. In this configuration, when the resistance value of the thermistor changes, the voltage division ratio of the thermistor and the resistor changes. Therefore, when the voltage of any point of the resistor is detected, the voltage of the point changes in response to the change in the resistance value of the thermistor. If the temperature of the thermistor and the voltage of the point are associated and stored in advance in the built-in memory of the microcomputer described later, the temperature of the thermistor can be converted from the voltage of the point. Note that the thermistor does not have to be built in the switching circuit 113, but may be mounted as an external component. For example, it may be directly attached to the switching circuit 113.

(External Interface Unit 6)
The external interface unit 6 can be configured as a circuit unit capable of transmitting and receiving information to and from an external device 7, which will be described later, by wire or wirelessly. For example, the external interface unit 6 can receive instructions for the rotating machine 2 from the external device 7, and execute starting of the rotating machine 2, decelerating and accelerating the rotation of the rotating machine 2, stopping of the rotating machine 2, and the like, via a control circuit unit 120, which will be described later. The external interface unit 6 can also receive a program from the external device 7, and store it in a storage unit (not shown) of the control circuit unit 120. The control circuit unit 120 can control the rotating machine 2 based on the program. Furthermore, new characteristic information of the current detection unit 3, the DC voltage detection unit 4, and the temperature detection unit 5 can also be input from the external device 7. For example, the new characteristic information may be information such as upgrade information or coefficients associated with replacement of at least one of the current detection unit 3, the DC voltage detection unit 4, and the temperature detection unit 5.

The external interface unit 6 can also output information such as the operating state and fault state of the rotating machine 2 to the external device 7. For example, when an overcurrent flows through the rotating machine 2, the current detection unit 3 detects the overcurrent, stops the rotating machine 2, and outputs information that the overcurrent has been detected and the rotating machine 2 has been stopped to the external device 7. If the external device 7 includes an abnormality alarm buzzer, the abnormality alarm buzzer will sound. If the external device 7 includes an indicator lamp and an operation panel, abnormality information of the rotating machine 2 can be displayed on the indicator lamp and output to the operation panel. The overcurrent processing unit 129 that detects the overcurrent can be realized by the configuration in embodiment 3.

(External device 7)
The external device 7 is a device that transmits and receives information to and from the power conversion device 100. Examples of the external device 7 include an operation panel, an indicator lamp, a communication device, and an abnormality alarm buzzer. The external device 7 can execute instructions to the power conversion device 100 and monitor the operation state of the rotating machine 2. The communication device can also function as a relay device and relay information to an operation monitoring center or the like that is located outside or in a remote location. The operation monitoring center may be a place that collects information from various locations and manages it centrally.

(Control power supply generating circuit section 130)
The control power supply generating circuit unit 130 generates a control voltage (power supply voltage) on the secondary side of the transformer unit 131 from the DC voltage smoothed by the smoothing capacitor 112, by using the transformer unit 131 and the switching circuit 132. The switching IC is composed of a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) and the like, and is controlled by the control power supply adjusting unit 133. The control power supply adjusting unit 133 feeds back the voltage of the secondary winding of the transformer unit 131 and controls it to be a constant voltage. However, when there are multiple secondary windings, the voltage of the winding that is not feedback controlled fluctuates depending on the voltage of the primary winding and the load of the secondary winding. Furthermore, when the smoothed DC voltage fluctuates, the voltage of the secondary winding fluctuates.

(Control circuit unit 120)
The configuration and operation of the control circuit unit 120 will be described with reference to Figures 1 and 2. As shown in Figure 2, the control circuit unit 120 includes a PWM output unit 121, a first analog detection unit 123, a second analog detection unit 122, a third analog detection unit 124, an external interface processing unit 125, and a control unit 126. An example of the control unit 126 is a microcomputer. Therefore, the control unit 126 can be read as a microcomputer. The control circuit unit 120 further includes a correction calculation unit 140 and a storage unit 150.

The control circuit unit 120 drives the rotating machine 2 in response to the conditions set from the external interface unit 6. The driving of the rotating machine 2 can be controlled each time based on the instructions input from the external interface unit 6. It is also possible to store a program input from the external interface unit 6 in the memory unit 150 and control the rotating machine 2 by the program.

The PWM output unit 121 outputs switching signals SG1, SG2, SG3, SG4, SG5, SG6, etc., which are PWM signals applied to gates G1, G2, G3, G4, G5, G6 of transistors such as IGBTs that constitute the switching circuit 113 that outputs drive pulses for rotating the rotating machine 2. Information on the relationship between the PWM signals and the rotation state of the rotating machine 2 can be stored in the memory unit 150 of the control unit 126.

The control circuit unit 120 has multiple analog detection units, and converts the analog values detected by the current detection unit 3, the DC voltage detection unit 4, and the temperature detection unit 5 into digital values and transmits them to a microcomputer, which is an example of the control unit 126. At this time, the microcomputer performs calculations including conversion processing on the analog voltage values input from each analog detection unit using a conversion gain preset in the memory unit 150 of the microcomputer. Using the processed information, the microcomputer controls the rotating machine 2 using a control method such as vector control or V/F control. Furthermore, if the converted current value, voltage value, or temperature is an abnormal value, the control circuit unit 120 is configured to be able to perform protective processing operations such as stopping the rotating machine 2 or limiting operation.

For example, the first analog detection unit 123 detects information such as the value and phase of the current flowing through the rotating machine 2, and outputs the detected information to the control unit 126. The control unit 126 uses the detected information to estimate the magnetic pole position of the rotating machine 2 and executes feedback control. Furthermore, when it is recognized that the load on the rotating machine 2 is large and the current value is increasing, it executes control to reduce the rotation speed of the rotating machine 2 or control to stop the rotating machine 2.

When the third analog detection unit 124 detects an abnormal voltage value indicating an undervoltage or overvoltage in the output voltage value of the diode bridge 111, which is a DC conversion unit, the third analog detection unit 124 outputs abnormal voltage information to the control unit 126, and the control unit 126 that receives the abnormal voltage information executes a process of stopping the rotating machine 2. Note that a voltage abnormality may occur when the voltage of the three-phase AC power source 1 fluctuates. Also, a voltage abnormality may occur when an abnormality occurs in the circuit of the diode bridge 111. Furthermore, a voltage abnormality may occur due to an overvoltage that rises due to a regenerative voltage generated by a sudden deceleration of the rotating machine 2. Since the third analog detection unit 124 can detect the abnormal voltage value, the control unit 126 can protect the power conversion device 100. For example, when the control unit 126 detects an abnormal voltage higher than the withstand voltage of the smoothing capacitor 112, it controls the rotating machine 2 to protect the power conversion device 100. Also, the DC voltage information is used for vector control and V/F control of the rotating machine 2. The control unit 126 adjusts the output voltage to the rotating machine by controlling the switching interval of the switching circuit 113 according to the DC voltage value.

The second analog detection unit 122 monitors the temperature detected by the temperature detection unit 5, and when the temperature is low, for example when the temperature drops below freezing, the control unit 126 can execute anti-freeze operation to keep the rotating machine 2 running at a low speed so that the water in the pump equipped with the rotating machine 2 does not freeze. In addition, when the temperature is high, the control unit 126 can execute control to reduce the rotation speed of the rotating machine 2 or to stop it in order to protect the parts so that they do not break down or have their lifespan shortened.

Note that in this specification, the first analog detection unit 123, the second analog detection unit 122, and the third analog detection unit 124 may be collectively referred to as the analog detection units.

The external interface processing unit 125 has a function of converting information input and output via the external interface unit 6. For example, it is possible to convert a wireless signal into a signal that can be recognized by the control unit 126, and to convert a signal that can be recognized by the control unit 126 into a wireless signal. Also, when the information input via the external interface unit 6 is an analog signal, it is possible to perform AD conversion and convert it into a digital signal that can be recognized by the control unit 126. The signals output from the external interface processing unit 125 will be further explained in the description of FIG. 7 described later.

The storage unit 150 may be a computer-readable recording medium. For example, the storage unit 150 may be composed of at least one of a ROM (Read Only Memory), a RAM (Random Access Memory), etc. In addition to a ROM and a RAM, the storage unit 150 may be composed of at least one of an EPROM (Erasable Programmable ROM), an EEPROM (Electrically Erasable Programmable ROM), etc. The storage unit 150 may be called a register, a cache, a main memory (primary storage device), etc. The storage unit 150 may also store programs, software modules, etc. that are executable to perform processing according to an embodiment of the present disclosure.

The memory unit 150 is also capable of storing information input to the control unit 126, inputting and outputting information between the correction calculation unit 140 in the control unit 126, and storing the information that is input and output. Furthermore, the memory unit 150 is also capable of storing information between each functional block (not shown) in the control unit 126. Furthermore, the memory unit 150 is also capable of storing information that is to be output from the control unit 126.

Furthermore, the memory unit 150 can store digital information that the reference voltage input by the first analog detection unit 123 is 2.5 V as a reference digital voltage. Therefore, no matter what digital value the digital constant voltage output by the first analog detection unit 123 takes, the control unit 126 can recognize whether or not it deviates from the reference digital voltage.

When the power supply voltage supplied to the analog detection unit fluctuates, the output voltage of the analog detection unit contains an error, and the correction calculation unit 140 has a function to correct the error. The details are explained step by step below.

<<Explanation of the error correction principle>>
4 shows the relationship between the output voltage of a CT (Current Transformer), which is an example of the current detection unit 3, and the detected current of a microcomputer, which is an example of the control unit 126. Different power sources are provided to the CT and the microcomputer from the control power supply generation circuit unit 130, and the voltage value of the provided power source becomes the maximum output voltage value of the CT and the maximum detected voltage value of the microcomputer. In other words, the CT and the microcomputer cannot process as information a signal voltage that is greater than the supplied voltage.

For example, when the same voltage of 5V is supplied to the CT and the microcomputer, the signal voltage values in the CT and the microcomputer can be treated as values having the same meaning. That is, the voltage value generated in the CT corresponding to the current flowing through the CT and the voltage value detected by the microcomputer from the output of the CT are the same. However, when the voltages supplied as the power supply voltage to the CT and the microcomputer are different, even if the signal voltage values in the CT and the microcomputer are the same, the signal voltage values cannot be treated as values having the same meaning. That is, the signal voltage value output by the CT is not recognized as the same value due to the power supply voltage supplied to the microcomputer. That is, if the power supply voltages of the CT and the microcomputer are different, the signal voltage value output by the CT will be detected as a different voltage value by the microcomputer. Below, a case where the power supply voltages supplied to the CT and the microcomputer are different will be described. In this embodiment, it is assumed that the power supply voltage supplied to the analog detection unit and the power supply voltage supplied to the microcomputer are the same. It is also assumed that the reference voltage (Vref) of the AD converter of the analog detection unit is the power supply voltage. However, the reference voltage (Vref) of the AD converter of the analog detection unit may be a voltage that varies linearly with the variation of the power supply voltage. For example, it may be a voltage obtained by dividing the power supply voltage.

Figure 5 shows the correlation when the power supply voltages supplied to the CT and the microcomputer are different. Figure 5 shows the case where the power supply voltage supplied to the CT is 5V and the power supply voltage supplied to the microcomputer is 4V. The CT has a maximum output voltage of 5V, and outputs a voltage according to the current flowing through the CT, using the intermediate voltage of 2.5V as the reference voltage to express positive and negative depending on the direction of the current being detected. On the other hand, the power supply voltage supplied to the microcomputer is 4V, so the microcomputer detects 4V as the maximum detectable voltage value, and recognizes any voltage above 4V as the maximum voltage value. The microcomputer also recognizes 2V, half of 4V, as the reference voltage value. This is because the microcomputer recognizes half of the maximum detectable voltage value as the reference voltage value.

Detection errors (see Figure 5) occur due to differences in recognition of reference voltage values, etc. However, since the CT has a terminal that outputs an analog constant voltage that is not affected by the supply voltage, the microcomputer can use this analog constant voltage to correct the signal voltage value output from the CT in response to changes in the current flowing through the CT, thereby eliminating the detection error. In Figure 5, the value of this analog constant voltage is the reference voltage, which is 2.5V. In Figure 5, the microcomputer recognizes 2V, half of the maximum detectable voltage of 4V, as the reference voltage value, but the reference voltage value output from the CT is 2.5V, resulting in a detection error. Note that the microcomputer can also correct the detection error using constant voltage output elements such as regulators and Zener diodes that output a constant voltage value without being affected by the supply voltage.

The detection error correction can be configured to be executed by a correction calculation unit 140 configured inside the control unit 126 such as a microcomputer. One example of a specific detection error correction method is a method of calculating the ratio between a reference digital voltage stored in the microcomputer and a voltage as a reference voltage output from the CT to the microcomputer, taking into consideration positive and negative, and calculating the detection error. As an example, as described above, the reference voltage value output by the CT is an analog constant voltage of 2.5 V if the power supply voltage supplied to the CT is a predetermined voltage or higher, so the microcomputer detects the reference voltage value output from the CT and executes the calculation of formula (1) or formula (2).
Error [ratio] = 1 - CT reference voltage terminal output detection value [V] ÷ setting value 2.5 [V] - (1)
Error [%] = Error [ratio] x 100 - (2)

(Output detection value [V] of CT's reference voltage terminal) is the voltage value recognized by the microcomputer after AD conversion of the voltage value output from the CT's reference voltage terminal. Specifically, it indicates the digital constant voltage converted by the first analog detection unit 123 from the analog constant voltage output from the constant voltage output unit included in the current detection unit 3. In the example of Figure 5, the voltage value output from the CT's reference voltage terminal is 2.5V, and the microcomputer detects the voltage value output from the CT's reference voltage terminal as 2V, so the digital constant voltage, which is the output detection value, is 2V.

(Set value 2.5 [V]) is a reference digital voltage stored in the memory unit 150 of the microcomputer, and is a digitized value of the voltage value output from the reference voltage terminal of the CT. The voltage value output from the reference voltage terminal is a value determined by the CT used. Therefore, the set value is not a fixed value limited to 2.5 V, but the explanation is given for the case where the voltage value output from the reference voltage terminal of the CT used in the current detection unit 3 of this embodiment is 2.5 V. Therefore, for example, when performing detection error correction based on a Zener diode that outputs a constant value of 3 V, the set value should be 3 V.

The (output detection value [V] of the reference voltage terminal of the CT ÷ set value [V]) in formula (1) may be called the correction coefficient. The microcomputer uses the correction coefficient to calculate the voltage value detected by the microcomputer, thereby enabling the correction process of the detection error to be performed. Specifically, the voltage value output by the CT can be accurately detected by dividing the voltage value detected by the microcomputer by the correction coefficient in formula (1) and regarding the divided value as the voltage value detected by the microcomputer. In the case of FIG. 5, the reference voltage terminal of the CT outputs 2.5V, and the microcomputer detects the 2.5V as 2.0V. Therefore, the error [ratio] is 0.2 from formula (1), and the error [%] is 20%. The correction coefficient is also 0.8. In other words, the microcomputer can recognize by calculation that the voltage detected by the microcomputer is 20% lower than the actual voltage output by the CT.

The microcomputer also calculates the reciprocal of the correction coefficient as a conversion gain, and multiplies the conversion gain by other analog detection quantities, thereby enabling accurate and high-speed correction calculations of analog detection quantities. For example, by multiplying the output value of the second analog detection unit 122 in FIG. 2 by the conversion gain, the temperature of the switching circuit 113, which is the power conversion unit detected by the temperature detection unit 5 in FIG. 1, can be accurately and quickly corrected. Furthermore, by multiplying the output value of the first analog detection unit 123 by the conversion gain, or by multiplying the output value of the third analog detection unit 124 in FIG. 2 by the conversion gain, the DC voltage value through the diode bridge 111 and smoothing capacitor 112, which are the DC conversion units in FIG. 1, can be accurately and quickly corrected. In this way, by using the conversion gain to perform corrections on the analog values (voltages) detected by the microcomputer, it becomes possible to accurately detect the output voltage of the detection unit even between circuits with different supply voltages.

[Example of correction process of power conversion device]
FIG. 6 is a flowchart showing an example of a procedure for executing the correction process of the power conversion device 100.

In step S601, the first analog detection unit 123 inputs an analog voltage obtained by converting the current detected by the current detection unit 3 into a voltage, and converts it into a digital value. The first analog detection unit 123 also inputs an analog constant voltage output from a constant voltage output unit (not shown) that is built into the current detection unit 3 or is provided outside the current detection unit 3, and converts it into a digital value.

In step S 602 , the correction calculation unit 140 receives the reference digital voltage stored in the storage unit 150 from the storage unit 150 .
The order of execution of steps S601 and S602 may be reversed. For example, in step S601, the correction calculation unit 140 can input a reference digital voltage stored in the storage unit 150 from the storage unit 150. Then, in step S602, the first analog detection unit 123 can input an analog voltage obtained by converting a current detected by the current detection unit 3 into a voltage, and convert it into a digital value. Also, the first analog detection unit 123 can input an analog constant voltage output from a constant voltage output unit (not shown) built into the current detection unit 3 or provided outside the current detection unit 3, and convert it into a digital value.

In step S603, the correction calculation unit 140 calculates the error [ratio] using formula (1). Alternatively, the correction calculation unit 140 calculates a correction coefficient by dividing the digital constant voltage by the reference digital voltage. When the correction calculation unit 140 calculates a correction coefficient, it calculates the reciprocal of the correction coefficient to calculate the conversion gain.

In step S604, the correction calculation unit 140 multiplies the voltage values AD converted by the first analog detection unit 123, the second analog detection unit 122, and the third analog detection unit 124 by a conversion gain to calculate corrected voltage values.

In step S605, the control unit 126 uses the corrected voltage value to control the rotating machine 2 controlled by the power conversion device 100, or electrical equipment such as a pump or compressor that includes the rotating machine 2. The control unit 126 can also display the corrected voltage value on the external interface unit 6.

In step S606, the control unit 126 determines whether the control operation of the rotating machine 2 or the electrical equipment including the rotating machine 2 has ended. If the control operation has ended (step S606: YES), the power conversion device 100 ends the processing. If the control operation has not ended (step S606: NO), the power conversion device 100 returns to step S601.

By performing the above-mentioned correction calculation in real time, it becomes possible to accurately detect the analog voltage value even if the supply voltage supplied to the microcomputer's power supply fluctuates.

For example, in a factory that uses a large amount of power, a stable voltage is normally supplied to the power conversion device, but during lunch breaks and at night, the receiving voltage rises because other equipment does not use power. In this case, if no correction processing is performed, errors will occur in the analog detection values during lunch breaks and at night. For example, this may affect the current value that vector controls the rotating machine 2, reducing the operating efficiency of the rotating machine 2. In addition, detection errors will occur in temperature detection and voltage detection when the receiving voltage rises, resulting in false detection of abnormalities and affecting the monitored values if values are being monitored. By correcting these in real time, stable analog detection can be performed. Furthermore, this correction makes stable analog detection possible even in emerging countries where power transmission facilities are not fully developed, or when unstable power sources are supplied from solar power generation or hydroelectric power generation.

In other words, according to the configuration of the above-mentioned embodiment 1, it is possible to provide a power conversion device that can accurately detect the current of a permanent magnet synchronous motor and utilize the maximum torque without demagnetizing the permanent magnet synchronous motor even when the control voltage fluctuates due to power receiving fluctuations, load fluctuations, and temperature changes. Furthermore, according to the configuration of the above-mentioned embodiment 1, even when the control voltage fluctuates due to power receiving fluctuations, load fluctuations, and temperature changes, the input analog voltage and current values are corrected in real time, allowing the power conversion device to accurately control the electrical equipment to be controlled.

<Embodiment 2>
The configuration and operation of the second embodiment will be described with reference to FIG.

In the first embodiment, the detection of the microcomputer was described, but in the second embodiment, the control of the microcomputer using the correct correction value obtained by performing the correction in the first embodiment will be described. Specifically, the analog output unit 128, which outputs the correction value output from the microcomputer, which is an example of the control unit 126, as analog information, and the FM output unit 127, which creates pseudo-analog information, will be mainly described. The analog output unit 128 and the FM output unit 127 are included in the control circuit unit 120, and output information obtained by converting the correction value output from the microcomputer.

That is, the output function of the power conversion device 100 is shown in FIG. 7. The external interface unit 6 inputs a speed command from the external device 7 and outputs the operating state of the rotating machine 2 to the external device 7. The control unit 126 outputs the operating state of the power conversion device 100, for example, information on the operating frequency, various current and voltage information, and temperature information of the thermistor, to an external higher-level electronic device. In this case, by using the correction value corrected in the first embodiment, it becomes possible to output the analog value with high accuracy via the analog output unit 128. The analog output unit 128 has a function of converting the digital correction value output by the microcomputer into an analog correction value. In addition, the microcomputer performs ON/OFF operation and converts the digital correction value into a frequency by changing the frequency of the ON/OFF operation. The FM output unit 127 can output the state of the power conversion device as an FM output in the same way as the analog output. When the input of the external device 7 is a pulse counter or the like, the FM output unit 127 counts the frequency output, and the external device 7 can detect the state of the power conversion device. The microcomputer correction value may include information inside the microcomputer, such as the operating state, fault state, detected current value, detected voltage value, detected temperature value, operating time, etc. Note that the operation command from the external device 7 may be input as an analog value. For example, when the power conversion device 100 controls the compressor, an external pressure sensor is attached, and PI control processing is performed so that the pressure is constant. In this case, the external interface unit 6 inputs the analog value that is the output of the pressure sensor.

According to the configuration and operation of the second embodiment described above, by performing the correction calculation in real time, it becomes possible to accurately detect the analog voltage value and output it to the outside even if the supply voltage supplied to the power supply of the microcomputer fluctuates.

<Third embodiment>
The configuration and operation of the third embodiment will also be described with reference to Fig. 7. The third embodiment relates to the configuration and operation of the overcurrent processing unit 129 in Fig. 7.

7, the corrected voltage value that should be judged as an overcurrent and the analog voltage value obtained by correcting the output voltage value of the first analog detection unit 123 are input. The overcurrent processing unit 129 includes a comparator (not shown), and is configured so that the output signal of the comparator is inverted when the corrected analog voltage value exceeds the voltage value that should be judged as an overcurrent. When the microcomputer, which is an example of the control unit 126, detects the inversion edge, it controls the switching circuit 113 so that the current value output from the switching circuit 113 becomes smaller. The voltage value that should be judged as an overcurrent varies depending on the characteristics of the rotating machine 2, but it is possible to store it in advance in the storage unit 150 of the control unit 126 from the external device 7. In addition, the voltage value that should be judged as an overcurrent varies depending on the ambient temperature, but the ambient temperature can be estimated from the temperature of the thermistor. Therefore, the control unit 126 can determine the voltage value that should be judged as an overcurrent based on the estimated ambient temperature. Since the method of estimating an overcurrent from the ambient temperature is a known technology, a detailed description is omitted.

According to the configuration and operation of the third embodiment, when the power conversion device 100 drives the rotating machine 2, for example, it is possible to monitor the current value and execute overcurrent processing to protect the rotating machine 2 from demagnetization if the current value exceeds a certain level. The overcurrent level is controlled by analog output from a microcomputer. The overcurrent level can be adjusted according to the characteristics of the connected rotating machine 2 and the ambient temperature to change the correction value, thereby enabling overcurrent protection to be executed with high precision.

In addition, the configurations and operations of embodiments 1 to 3 further enable the following effects to be achieved.

For products equipped with an analog detection unit, for example, the gain of the analog detection is adjusted during shipping testing to eliminate variations in the electrical characteristics of individual analog detection units. As a specific example, two different voltage values are applied to the analog detector from an external device (e.g., a test device). For example, when 1V and 4V are applied to the analog detection unit as different voltage values, the microcomputer stores the analog values obtained for 1V and 4V in the memory unit. Assume that the internal value of the microcomputer is 819 digits at 1V and 3276 digits at 4V (4095 digits is the maximum internal value for a 12-bit analog detector). Using the voltage (V) as the vertical axis and digits as the horizontal axis, a linear function passing through two points is derived using the above values. (x, y) = (1, 819), (4, 3276)

The slope of the above linear function is a = gain, and the intercept b = offset. a and b are stored in the memory of the microcomputer when the product equipped with the analog detection unit is shipped.

However, according to the configurations and operations of the first to third embodiments, the gain adjustment is performed in real time, making the gain adjustment during the shipping test described above unnecessary. Also, if the value output from the correction calculation unit 140 of the embodiment is not 0, it may be possible to discover that there is an abnormality in the circuit.

The disclosure made by the inventor has been specifically described above based on the embodiments, but it goes without saying that the present disclosure is not limited to the above embodiments and can be modified in various ways without departing from the gist of the disclosure. Furthermore, for example, the above embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to having all of the configurations described. Furthermore, it is possible to add, delete, or replace part of the configuration of the above embodiments with other configurations.

Furthermore, the above-mentioned configurations, functions, processing units, processing means, etc. may be realized in part or in whole in hardware, for example by designing them as integrated circuits. Furthermore, the above-mentioned configurations, functions, etc. may be realized in software by a processor interpreting and executing a program that realizes each function. Information on the programs, tables, files, etc. that realize each function can be stored in a recording device such as a memory, a hard disk, or an SSD (Solid State Drive), or in a recording medium such as an IC card, an SD card, or a DVD.

In addition, in each of the above diagrams, the control lines and information lines shown are those considered necessary for explanation, and do not necessarily show all of the control lines and information lines in the actual implementation. In reality, it can be assumed that almost all components are interconnected.

1... Three-phase AC power supply 2... Rotating machine 3... Current detection unit (including constant voltage output unit)
REFERENCE SIGNS LIST 4 DC voltage detection section 5 Temperature detection section 6 External interface section 7 External device 100 Power conversion device 110 Main circuit section 111 Diode bridge (DC conversion section)
112...Smoothing capacitor (smoothing section)
113...Switching circuit (power conversion section)
120...Control circuit unit (control unit)
REFERENCE SIGNS LIST 121: PWM output section 122: Second analog detection section 123: First analog detection section 124: Third analog detection section 125: External interface processing section 126: Control section 127: FM output section 128: Analog output section 129: Overcurrent processing section 130: Control power supply generating circuit section 131: Transformer section 132: Switching circuit 133: Control power supply adjustment section 140: Correction calculation section 150: Storage section

Claims (12)

A DC converter that converts an externally supplied power source into DC;
a smoothing unit that smoothes the direct current output from the direct current conversion unit;
a power conversion unit that switches a smoothed current output from the smoothing unit;
A power conversion device including a control unit that controls the power conversion unit,
a transformer section connected in parallel with the smoothing section and generating a power supply voltage for the control unit;
a constant voltage output unit that outputs a constant analog voltage even when the smoothing current fluctuates;
a storage unit that stores the analog constant voltage as a reference digital voltage in advance;
a first analog detection unit that converts the analog constant voltage output from the constant voltage output unit into a digital constant voltage;
a correction calculation unit that compares the digital constant voltage with the reference digital voltage, calculates a correction coefficient for correcting a power supply voltage of the control unit, and corrects the power supply voltage;
A power conversion device in which the maximum analog voltage that the first analog detection unit can convert is the power supply voltage of the control unit. A current detection unit converts the current output from the power conversion unit into a voltage and outputs the voltage as a detected output voltage.
The power conversion device according to claim 1 , wherein the first analog detection unit converts the detected output voltage, which is an analog voltage, into a digital detected output voltage. the constant voltage output unit is provided to the current detection unit, and the detected output voltage of the current detection unit is a voltage corresponding to a direction in which a current to be detected flows and a magnitude of the current to be detected, with the analog constant voltage of the constant voltage output unit as a center voltage;
The power conversion device according to claim 2 , wherein the current detection unit outputs the analog constant voltage from a terminal different from a terminal from which the detected output voltage is output. The power conversion device according to claim 2 or 3, wherein the control unit corrects the voltage information and current information input from outside the control unit using the correction coefficient, performs an internal calculation using the corrected voltage information and current information, and outputs internal calculation information based on the internal calculation. The power conversion device according to claim 4, wherein the internal calculation information can be output as FM signal information, digital information, and analog information. the correction calculation unit corrects the detected output voltage of the current detection unit using the correction coefficient, and outputs a corrected detected output voltage;
The power conversion device according to claim 4 , wherein the control unit controls the power conversion section using the corrected detected output voltage as one piece of control information. The power conversion device according to claim 6, further comprising an overcurrent processing unit that determines whether the corrected detection output voltage is a voltage corresponding to a current exceeding an overcurrent of an electrical device connected to the power conversion unit. The power conversion unit is provided with a temperature detection unit, and further includes a second analog detection unit that converts an analog temperature voltage output by the temperature detection unit into a digital temperature voltage,
the correction calculation unit corrects the digital temperature voltage output from the second analog detection unit using the correction coefficient, and outputs a corrected digital temperature voltage;
The power conversion device according to claim 6 , wherein the control unit controls the power conversion section based on the control information including the corrected digital temperature voltage. a third analog detection unit for converting an analog power supply voltage of the control unit into a digital power supply voltage;
the correction calculation unit corrects the digital power supply voltage output by the third analog detection unit using the correction coefficient, and outputs a corrected digital power supply voltage;
The power conversion device according to claim 6 , wherein the control unit controls the power conversion section based on the control information including the corrected digital power supply voltage. the power source supplied from the outside is a three-phase AC power source,
The power conversion device according to claim 2 , wherein the current detection unit is attached to at least two of three phases. A power conversion method for a power conversion device including a DC conversion unit that converts an externally supplied power source into a DC current, a smoothing unit that smoothes a DC current output from the DC conversion unit, a power conversion unit that switches a smoothed current output from the smoothing unit, and a control unit that controls the power conversion unit,
a transformer section connected in parallel with the smoothing section generating a power supply voltage for the control unit;
a constant voltage output unit outputting an analog constant voltage even when the smoothing current fluctuates;
A storage unit of the control unit stores the analog constant voltage in advance as digital voltage value information;
A first analog detection unit of the control unit converts the analog constant voltage of the constant voltage output unit into a digital constant voltage;
a correction calculation unit of the control unit comparing the digital constant voltage with the digital voltage value information, and calculating and outputting a correction coefficient for correcting the power supply voltage of the control unit;
A power conversion method, wherein the maximum analog voltage that the first analog detection unit can convert is the power supply voltage of the control unit. The power conversion device according to any one of claims 1 to 10,
and an electric device including a rotating machine controlled by the power conversion device.

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