Power conversion device, power conversion control method and computer-readable recording medium

Abstract

This invention provides a power conversion device, a power conversion control method, and a computer-readable recording medium to suppress fluctuations in the DC voltage output of the converter. The power conversion device includes a converter that converts AC voltage to DC voltage; a smoothing capacitor that suppresses fluctuations in the DC voltage; and an inverter that converts the DC voltage charged in the smoothing capacitor into AC power. It further includes: a DC voltage detector for detecting the DC voltage; a current detector for detecting the AC power supply side current; a DC voltage controller for generating a converter input current command such that the DC voltage matches the DC voltage command value; a converter output current controller for controlling the converter AC voltage so that the AC power supply side current matches the generated converter input current command; and an adder for adding a converter-side power compensation value to the converter input current command.

Description

Technical Field

[0001] This invention relates to a power conversion device having a converter and an inverter, and particularly to a power conversion device, a power conversion control method, and a power conversion control program capable of suppressing DC voltage fluctuations of the converter that accompany rapid load changes. Background Technology

[0002] Power conversion devices are known to convert AC power into power with variable voltage and frequency. The main circuit of these devices consists of a converter that converts AC voltage to DC voltage, a DC circuit with a large-capacity smoothing capacitor, and an inverter that converts DC power to AC power. In particular, the smoothing capacitor occupies a large proportion of the overall volume of the power conversion device, and its miniaturization is essential for the compactness of the power conversion device.

[0003] One of the functions of a smoothing capacitor is to suppress DC voltage fluctuations caused by inconsistencies in power transfer between the converter and the inverter. Therefore, if DC voltage fluctuations can be further reduced, the capacitor capacitance can be reduced, enabling compact design. For example, the following techniques are disclosed in Patent Documents 1 and 2.

[0004] (1) The output current of the converter is controlled according to the output value of the DC voltage controller that controls the DC voltage to a predetermined value, so that the DC voltage is controlled to be constant (see Patent Document 1).

[0005] (2) A signal corresponding to the load (power) change on the inverter side is transmitted to the converter, and the transmitted signal is used to control the current of the converter (see Patent Document 2).

[0006] Patent Document 2 discloses a technique in which a signal corresponding to a change in load (power) on the inverter side is transmitted to the converter, and the transmitted signal is used to control the output current of the converter. However, the technique described in Patent Document 2 requires a transmission circuit for sending and receiving current commands between the converter and the inverter. These transmission circuits use wiring and signal transmission and reception circuits, thus requiring additional components to be added to the power conversion device.

[0007] Especially in power conversion devices used in steel rolling equipment, there are cases where a single converter applies DC voltage to multiple inverters. In this case, the number of transmission circuits used to connect the converter and the inverters needs to be equal to the number of inverters connected to the single converter.

[0008] Furthermore, due to the use of a transmission circuit, a transmission delay occurs when sending and receiving the current command signal. Therefore, the current command signal received by the converter is delayed relative to the current command signal sent by the inverter. In this case, the converter uses the delayed received signal to control the current, thus creating an inconsistency in power transfer between the converter and the inverter, resulting in fluctuations in the output DC voltage.

[0009] Patent Document 1: Japanese Patent Application Publication No. 61-109491

[0010] Patent Document 2: Japanese Patent Application Publication No. 3-245793 Summary of the Invention

[0011] The present invention was made in view of the above circumstances, and its object is to provide a power conversion device, a power conversion control method, and a power conversion control program capable of suppressing fluctuations in the DC voltage output of the converter.

[0012] The power conversion device (100) of the present invention includes: a converter (converter power conversion section 21) for converting AC voltage (Vs) to DC voltage (Vdc); smoothing capacitors (22, 23, 32, 33) for suppressing fluctuations in the DC voltage; and an inverter (31) for converting the DC voltage charged in the smoothing capacitor into AC power. The power conversion device (100) further includes: DC voltage detectors (25, 26) for detecting the potential difference of the smoothing capacitor; a current detector (7) for detecting the AC power supply side current (I_c) of the converter; a DC voltage controller (52) for generating a converter input current command (AVROUT) such that the DC voltage detection signal (Vdc) of the DC voltage detectors (25, 26) matches the DC voltage command value (Vref) of the converter; and a converter output current controller (current controller 53) for controlling the DC voltage (Vdc) output by the converter such that the converter... The AC power supply side current (I_c) is consistent with the generated converter input current command (AVROUT); the converter side DC power current calculation unit (73) calculates the converter side DC power current estimate (Idch_c) based on the converter's AC power supply side current (I_c); the variable power current calculation unit (74) calculates the variable power current estimate (ΔIdch) based on the converter's DC voltage detection signal (Vdc); the converter side power compensation conversion unit (75) multiplies the inverter side DC power current estimate (Idch_i) obtained by subtracting the variable power current estimate (ΔIdch) from the converter side DC power current estimate (Idch_c) by the inverse conversion gain (1 / Kdc) to generate the converter side power compensation value (POBSOUT); and the adder (56) adds the converter side power compensation value (POBSOUT) to the converter input current command (AVROUT). In addition, the reference numerals or text in parentheses are reference numerals or text used in the embodiments and are not intended to limit the present invention.

[0013] According to the present invention, fluctuations in the DC voltage output by the converter can be suppressed. Attached Figure Description

[0014] Figure 1 This is an overall structural diagram of the power conversion device according to the first embodiment of the present invention.

[0015] Figure 2 The converter unit and control circuit of the first embodiment of the present invention are illustrated in the block diagram.

[0016] Figure 3 This is an overall structural diagram of the power conversion device, which serves as the first comparative example of the present invention.

[0017] Figure 4 This is an overall structural diagram of the power conversion device, which serves as a second comparative example of the present invention.

[0018] Figure 5 A block diagram is used to illustrate the converter unit and control circuit of the second embodiment of the present invention.

[0019] Figure 6 This is an overall structural diagram of the power conversion device according to the third embodiment of the present invention.

[0020] Figure 7 The converter unit and control circuit of the third embodiment of the present invention are illustrated in the block diagram.

[0021] Figure 8 This indicates the elapsed time of the DC voltage waveform when the converter is started.

[0022] Figure 9 This is an overall structural diagram of the power conversion device according to the fourth embodiment of the present invention.

[0023] Figure 10 The converter unit and control circuit of the fourth embodiment of the present invention are illustrated in the block diagram. Detailed Implementation

[0024] Hereinafter, embodiments of the present invention will be described using the accompanying drawings and other references. The following embodiments represent specific examples of the invention, but the invention is not limited to these embodiments. Within the scope of the technical concept disclosed in this specification, those skilled in the art can make various changes and modifications.

[0025] Figure 1 This is an overall structural diagram of the power conversion device according to the first embodiment of the present invention.

[0026] The power conversion device 100 includes: a converter unit 2 that converts AC power (three-phase AC power) from an AC power source 1 with voltage Vs into DC power; an inverter unit 3 that converts the DC power output from the converter unit 2 into the desired AC power; a motor 4 that is driven by the AC power output from the inverter unit 3; a converter control device 5a that controls the converter unit 2; and an inverter control device 6 that controls the inverter unit 3.

[0027] Converter unit 2 is a so-called 3-level converter that converts AC power from AC power source 1 into DC power with a positive potential (first potential), a neutral point (zero) potential (second potential), and a negative potential (third potential). Inverter unit 3 is a so-called 3-level inverter that converts the DC power with the positive potential (first potential), neutral point (zero) potential (second potential), and negative potential (third potential) into AC power supplied to motor 4. The positive potential levels of converter unit 2 and inverter unit 3 are connected via P wiring 40, the neutral point potential level via C wiring 41, and the negative potential level via N wiring 42.

[0028] The converter unit 2 includes a converter power conversion section 21, a series circuit of a converter P-side smoothing capacitor 22 and a converter N-side smoothing capacitor 23 for suppressing DC voltage fluctuations, a converter P-side DC voltage detector 25 for measuring the inter-terminal voltage of the converter P-side smoothing capacitor 22, and a converter N-side DC voltage detector 26 for measuring the inter-terminal voltage of the converter N-side smoothing capacitor 23. The converter P-side smoothing capacitor 22 and the converter N-side smoothing capacitor 23 may be of the same capacitance, but they may not be of the same capacitance.

[0029] The power conversion unit 21 of the converter is configured to have four IGBTs (Insulated Gate Bipolar Transistors) for each phase, namely transistors T1, T2, T3, and T4, four freewheeling diodes D1, D2, D3, and D4, and two diodes D5 and D6. Each phase of the AC power supply 1 is connected to the emitter of transistor T2 and the collector of transistor T3. The collector of transistor T2, the emitter of transistor T1, and the cathode of diode D5 are connected, and the emitter of transistor T3, the collector of transistor T4, and the anode of diode D6 are connected. A DC voltage is generated between the junction of the anode of diode D5 and the cathode of diode D6 and the collector of transistor T1, and a DC voltage is generated between the junction of the anode of diode D5 and the cathode of diode D6 and the emitter of transistor T4.

[0030] The P-side smoothing capacitor 22 of the converter is connected between the junction of the anode of diode D5 and the cathode of diode D6 and the collector of transistor T1. The N-side smoothing capacitor 23 of the converter is connected between the junction of the anode of diode D5 and the cathode of diode D6 and the emitter of transistor T4. The P-side DC voltage detector 25 of the converter measures the voltage between the terminals of the P-side smoothing capacitor 22. The N-side DC voltage detector 26 of the converter measures the voltage between the terminals of the N-side smoothing capacitor 23. The PN DC voltage signal Vdc is the sum of the voltage between the terminals of the P-side smoothing capacitor 22 and the voltage between the terminals of the N-side smoothing capacitor 23.

[0031] Similar to converter unit 2, inverter unit 3 includes inverter power conversion section 31, inverter P-side smoothing capacitor 32, and inverter N-side smoothing capacitor 33. Here, inverter P-side smoothing capacitor 32 is connected in parallel with converter P-side smoothing capacitor 22, and inverter N-side smoothing capacitor 33 is connected in parallel with converter N-side smoothing capacitor 23.

[0032] The converter control device 5a consists of a CPU (Central Processing Unit) and a storage unit (not shown). It performs the following functions by executing programs stored in the storage unit: The converter control device 5a controls the converter power conversion unit 21 to ensure the converted DC power reaches the desired value. The inverter control device 6 controls the inverter power conversion unit 31 to ensure the output torque and speed of the motor 4 meet the desired characteristics.

[0033] In this embodiment, the power conversion device operates in two modes: power operation and regeneration. The power operation mode refers to a mode that accelerates the motor or applies a load. In this mode, the inverter control device 6 operates to draw the power required for motor operation from the smoothing capacitor in the DC circuit. At this time, the DC voltage decreases, so the converter control device 5a operates to maintain a constant DC voltage by drawing AC power from the AC power source 1 into the DC circuit side. On the other hand, the regeneration mode refers to a mode that decelerates the motor or applies a load in reverse. In this mode, the inverter control device 6 operates to return the regenerated power generated in the motor 4 to the smoothing capacitor in the DC circuit. At this time, the DC voltage increases, so the converter control device 5a operates to maintain a constant DC voltage by returning power from the DC circuit to the AC power source 1.

[0034] The power conversion device 100 also includes: a current detector 7, which detects the input AC current (AC power supply side current) of the converter unit 2; a speed detector 8, which is directly connected to the motor 4 and detects the speed of the motor 4; and a current detector 9, which detects the output AC current (motor side AC current) of the inverter unit 3. When the inverter control device 6 performs regenerative control, the current detector 7 detects the output current of the converter unit 2.

[0035] The converter input current I_c and PN DC voltage signal Vdc detected by the current detector 7 are input to the converter control device 5a. The converter control device 5a performs various calculations based on the input detection values ​​and outputs control signals for controlling the converter power conversion unit 21.

[0036] The signals (output signals) of the detected values ​​from the speed detector 8 and the current detector 9 are input to the inverter control device 6. The inverter control device 6 performs various calculations based on the input detected values ​​and outputs control signals for controlling the inverter power conversion unit 31.

[0037] The converter control device 5a includes a DC voltage command generator 51, a DC voltage controller 52, a current controller 53, a pulse generator 54, a power observer unit 55a, and an adder unit 56.

[0038] The DC voltage command generator 51 outputs a converter DC voltage command value Vref to the DC voltage controller 52, which represents the voltage value of the DC voltage output from the converter unit 2.

[0039] The DC voltage controller 52 calculates the converter input current command value AVROUT based on the converter DC voltage command value Vref input from the DC voltage command generator 51 and the PN DC voltage signal Vdc input from the DC voltage detector 25 on the P side of the converter and the DC voltage detector 26 on the N side of the converter, and outputs it to the adder 56. Specifically, the DC voltage controller 52 calculates the converter input current command value AVROUT so that the sum of the DC voltage detection values ​​(PN DC voltage signal Vdc) input from the DC voltage detector 25 on the P side of the converter and the DC voltage detector 26 on the N side of the converter is consistent with the converter DC voltage command value Vref.

[0040] The adder 56 adds the converter input current command value AVROUT to the calculated value output by the power observer 55a, and outputs the converter output current command value I_cref, which is the result of the addition, to the current controller 53.

[0041] The current controller 53 calculates the converter voltage command value so that the AC power supply side current of the converter power conversion unit 21 (= the converter input current I_c detected by the current detector 7) matches the converter input current command value AVROUT input from the adder 56, and outputs the calculated converter voltage command value to the pulse generator 54.

[0042] The pulse generator 54 calculates the pulse signal used to control the on / off switching of each switching element of the converter power conversion unit 21 so that the value of the converter output voltage obtained by the converter power conversion unit 21 is consistent with the converter output voltage command value input from the current controller 53, and outputs the calculated pulse signal to the converter power conversion unit 21.

[0043] The inverter control unit 6 includes a speed command generator 61, a speed controller 62, a current controller 63, and a pulse generator 64.

[0044] The speed command generator 61 outputs a speed command value to the speed controller 62, representing the speed at which the motor 4 operates. The speed controller 62 calculates the inverter output current command value to make the speed detection value input from the speed detector 8 consistent with the speed command value input from the speed command generator 61, and outputs the calculated inverter output current command value to the current controller 63.

[0045] The current controller 63 calculates the inverter voltage command value to make the inverter output current detection value input from the current detector 9 consistent with the inverter output current command value input from the speed controller 62, and outputs the calculated inverter voltage command value to the pulse generator 64.

[0046] The pulse generator 64 calculates the pulse signals used to control the switching elements of the inverter power conversion unit 31 to turn on / off, so that the value of the inverter output voltage obtained by the inverter power conversion unit 31 is consistent with the inverter output voltage command value input from the current controller 63, and outputs the calculated pulse signals to the inverter power conversion unit 31.

[0047] Next, the structure related to the power observer in the power conversion device 100 will be described. The converter control device 5a of the power conversion device 100 includes a power observer unit 55a, which outputs the calculation result to the addition unit 56.

[0048] The power observer unit 55a outputs a converter-side power compensation signal POBSOUT based on the PN DC voltage signal Vdc input from the DC voltage detector 25 on the P side of the converter and the DC voltage detector 26 on the N side of the converter, and the converter input current detection value output from the current detector 7. The adder unit 56 adds the converter-side power compensation signal POBSOUT calculated by the power observer unit 55a to the converter input current command value output from the DC voltage controller 52.

[0049] Figure 2 The converter unit and control circuit of the first embodiment of the present invention are illustrated in the block diagram.

[0050] As described above, the converter control device 5a ( Figure 1 It includes a DC voltage command generator 51, a DC voltage controller 52, an adder 56, and a current controller 53. Figure 1 ), pulse generator 54 ( Figure 1 ) and power observer section 55a.

[0051] The current controller 53, pulse generator 54, and converter power conversion unit 21 are represented by the converter output current unit 70. When the current controller 53 controls the converter input current command value I_cref in a small loop so that it matches the converter power supply side current (= converter input current I_c), the converter input current I_c follows the converter input current command value I_cref with a first-order delay transfer function. That is, the converter output current unit 70 is represented by a first-order delay transfer function of the converter current controller response time constant Tcc.

[0052] The converter-side DC power current conversion unit 71 obtains the converter-side DC power current Idc_c by multiplying the converter input current I_c output by the converter current unit 70 by the converter-side DC power current conversion gain Kdc. That is, the ratio of the AC power supply side current (converter input current I_c) to the output DC current (converter-side DC power current Idc_c) of the converter power conversion unit 21 is constant.

[0053] Subtractor 78 and DC voltage unit 72 represent the voltage-current relationship of the four capacitors (inverter P-side smoothing capacitor 32, converter P-side smoothing capacitor 22, inverter N-side smoothing capacitor 33, and converter N-side smoothing capacitor 23). That is, capacitor C represents the total capacitance of the four capacitors. Subtractor 78 calculates the variable power current ΔIdc by subtracting the inverter-side DC power current Idc_i from the converter-side DC power current Idc_c. DC voltage unit 72 uses a transfer function to represent the four capacitors, showing how the PN DC voltage signal Vdc changes due to the variable power current ΔIdc.

[0054] The inverter-side DC power current Idc_i is simulated based on factors such as motor load interference on the inverter side to represent the DC power current generated on the inverter side.

[0055] Here, the converter output current section 70 is represented by equation (1), the converter-side DC power current conversion section 71 is represented by equation (2), and the DC voltage section 72 is represented by equation (3).

[0056] I_c=I_cref×1 / (1+Tcc·S) (1)

[0057] Idc_c=I_c×Kdc (2)

[0058] Vdc=ΔIdc×1 / (C·S) (3)

[0059] Where Tcc is the converter current controller response time constant, Kdc is the converter-side DC power current conversion gain, and C is the smoothing capacitor electrostatic capacitance.

[0060] exist Figure 2In the middle, the power observer unit 55a includes a converter-side DC power current calculation unit 73, a variable power current calculation unit 74, a converter-side power compensation conversion unit 75, and a subtractor 79.

[0061] The converter-side DC power current calculation unit 73 calculates the converter-side DC power current estimation value Idch_c based on the converter input current I_c output from the converter output current unit 70. The variable power current calculation unit 74 calculates the variable power current estimation value ΔIdch based on the PN DC voltage signal Vdc.

[0062] Subtractor 79 subtracts the estimated DC power current from the converter side calculated by the DC power current calculation unit 73 on the converter side from the estimated variable power current calculated by the variable power current calculation unit 74, and outputs the estimated DC power current value Idch_i on the inverter side.

[0063] In addition, the converter-side power compensation conversion unit 75 multiplies the inverter-side DC power current estimation value Idch_i by the inverse conversion gain of the converter-side DC power current conversion gain Kdc, and outputs the converter-side power compensation signal POBSOUT.

[0064] The DC power current calculation unit 73 on the converter side is expressed by equation (4), the variable power current calculation unit 74 is expressed by equation (5), and the power compensation conversion unit 75 on the converter side is expressed by equation (6).

[0065] Idch_c=I_c×Kdc (4)

[0066] ΔIdch=Vdc×C·S (5)

[0067] POBSOUT=1 / Kdc×Idch_i (6)

[0068] As explained above, the power observer unit 55a of this embodiment can estimate the power change on the inverter side by means of the input current (converter input current I_c) and DC voltage (PN DC voltage signal Vdc) on the converter side.

[0069] (First comparative example)

[0070] Figure 3 This is an overall structural diagram of the power conversion device, which serves as the first comparative example of the present invention.

[0071] With power conversion device 100 ( Figure 1Similarly, the power conversion device 101 includes a converter unit 2, an inverter unit 3, and a motor 4. However, the power conversion device 101 differs from the power conversion device 100 in that it includes a converter control device 5 (5e) and an inverter control device 6B. The inverter control device 6B includes a load compensation calculation unit 65, which calculates the DC power current value on the inverter side based on the current detection value and voltage detection value of the motor, and outputs a value converted into a power compensation value on the converter side.

[0072] The power compensation value calculated by the load compensation calculation unit 65 on the converter side is transmitted to the converter control device 5e via a transmission circuit consisting of wiring and signal transceiver circuitry. The converter control device 5e's adder 56 adds the converter input current command value AVROUT output from the DC voltage controller 52 to the power compensation value on the converter side, thereby suppressing DC voltage fluctuations caused by inconsistencies in power transfer between the converter and the inverter. Therefore, the power conversion device 102 requires a transmission circuit (load compensation calculation unit 65 and transmission line 66) for transmitting and receiving signals between the converter and the inverter.

[0073] In contrast, if it is the power conversion device 100 of the first embodiment ( Figure 1 , 2 The DC power current value on the inverter side is estimated and calculated within the converter control device 5a, so there is no need to send or receive signals between the converter and the inverter, and there is no need for the transmission circuit required in the power conversion device 101.

[0074] Furthermore, in the case of the power conversion device 100 of the first embodiment, even in the presence of control response delay of the DC voltage controller of the converter constituting the power converter and signal transmission delay between the converter and the inverter, the DC voltage fluctuation of the converter can be suppressed even for a sudden load change on the inverter side, such as a sudden change in the speed or load of the AC motor.

[0075] (Second Comparative Example)

[0076] Figure 4 This is an overall structural diagram of a power conversion device, which serves as a second comparative example of the present invention, showing a device that supplies DC power to multiple inverters through a single converter.

[0077] The power conversion device 102 supplies DC power to multiple inverter units 3a, 3b, and 3c through one converter unit 2. In the power conversion device 102, each inverter control device 6a, 6b, and 6c calculates the DC power current value on the inverter side based on the driving state of the motors 4a, 4b, and 4c controlled by each inverter, and transmits the converted power compensation value on the converter side from each inverter side to the converter control device 5f through a transmission circuit.

[0078] At this point, it is difficult to install a transmission circuit for the number of inverters that need to be connected to the converter in devices with a large number of inverter connections.

[0079] In contrast, if the converter control device 5a of the first embodiment of the present invention is used, the sum of the DC power current values ​​of all inverters connected to the converter is estimated and calculated internally. Therefore, even in the power conversion device 102 ( Figure 4 It is also possible to eliminate the need for transmission circuits in this process.

[0080] As described above, in the first embodiment of the present invention, the estimated value of DC power current on the inverter side, Idch_i, is calculated based solely on the signal within the converter control device 5a. After being converted into the converter-side power compensation signal POBSOUT, it is added to the output of the DC voltage controller 52. Thus, even without a transmission circuit between the inverter and the converter, DC voltage fluctuations can be suppressed.

[0081] (Second Implementation)

[0082] In the second embodiment, compared to the first embodiment, the power observer section is modified to remove the influence of noise signals contained in the PN DC voltage signal Vdc.

[0083] Figure 5 The converter unit and control circuit of the second embodiment of the present invention are illustrated in the block diagram.

[0084] Power observer section 55b relative to power observer section 55a ( Figure 2 A filter / power compensation gain adjustment unit 76 is added. The filter / power compensation gain adjustment unit 76 performs filtering and compensation adjustment on the inverter-side DC power current estimation value Idch_i, and calculates the inverter-side DC power current adjustment value Idcfil_i. Then, the converter-side power compensation conversion unit 75 inputs the inverter-side DC power current adjustment value Idcfil_i, multiplies it by the inverse conversion gain of the converter-side DC power current conversion gain Kdc, and outputs the converter-side power compensation signal POBSOUT.

[0085] The function of the filter / power compensation gain adjustment unit 76 is represented by equation (7).

[0086] Idcfil_i=Idch_i×Kb / (1+Tb·S) (7)

[0087] Where Kb is the power compensation gain and Tb is the filter time constant.

[0088] The variable power current calculation unit 74 performs differentiation operations, so when a noise signal is superimposed on the PN DC voltage signal Vdc, the noise signal may be amplified. When the converter is driven based on a compensation signal that has been amplified by the noise signal, the DC voltage fluctuates and becomes the cause of fault detection, and in the worst case, it can cause damage to the power conversion device.

[0089] Furthermore, the adder 56 adds the converter input current command value AVROUT to the converter-side power compensation signal POBSOUT, thereby suppressing fluctuations in the PN DC voltage signal Vdc. However, since the control responses of the DC voltage controller 52 and the power observer 55a differ, the control may become unstable depending on the distribution ratio between the outputs of the DC voltage controller 52 and the power observer 55a, due to the relationship between stability and responsiveness.

[0090] Therefore, considering the presence of noise in the PN DC voltage signal Vdc, a filter / power compensation gain adjustment unit 76 is added between the subtractor 79 and the converter-side power compensation conversion unit 75. The filter / power compensation gain adjustment unit 76 is composed of a filter (1 / (1+Tb·S)) for noise removal and a power compensation gain Kb shared by the outputs of the DC voltage controller 52 and the power observer unit 55b. It takes Idch_i as input, performs calculations, and outputs Idcfil_i.

[0091] As explained above, in the second embodiment, by adding a filtering process to the inverter-side DC power current estimate and setting the power compensation gain Kb to adjust the compensation amount, the filtering / power compensation gain adjustment unit 76 calculates the inverter-side DC power current adjustment value Idcfil_i, thereby removing the influence of noise signals contained in the PN DC voltage signal Vdc, thereby preventing excessive compensation signals from being added to the output of the DC voltage controller 52.

[0092] Furthermore, by adjusting the power compensation gain Kb according to the control response of the separately designed DC voltage controller 52 and power observer unit 55, the distribution ratio between the output of the DC voltage controller 52 and the output of the power observer unit 55 can be optimally set. This allows for optimal overall control characteristics in terms of stability and responsiveness.

[0093] (Third Implementation)

[0094] In the third embodiment, a technique for properly smoothing the initial charging of the capacitor will be described.

[0095] Figure 6 This is an overall structural diagram of the power conversion device according to the third embodiment of the present invention.

[0096] Power conversion device 103 relative to power conversion device 100 ( Figure 1 It includes a charging power supply 80, a charging circuit 81, and a switching signal generation unit 57.

[0097] Before the operation of converter unit 2 and inverter unit 3 begins, charging power supply 80 and charging circuit 81 charge converter P-side smoothing capacitor 22, converter N-side smoothing capacitor 23, inverter P-side smoothing capacitor 32 and inverter N-side smoothing capacitor 33 (initial charging).

[0098] The switching signal generation unit 57 outputs one of the following signals based on the converter's driving status: (a) a signal to start the timer during initial charging, (b) a signal for a normal stop command, or (c) a signal for a fault stop command. The switching signal generation unit 57 includes a timer unit 57a that outputs a signal to start the timer.

[0099] Figure 7 A block diagram is used to illustrate the converter unit and control circuit of the third embodiment of the present invention.

[0100] Power observer section 55c is relative to power observer section 55a ( Figure 2 An additional selection unit 77 is provided, which switches the output of the converter-side power compensation signal based on (a) a signal to start the timer during initial charging, (b) a signal to stop the normal operation, and (c) a signal to stop the fault, which are output from the switching signal generation unit 57.

[0101] As described above, the power observer unit 55a adds the converter-side power compensation signal POBSOUT to the converter output current command value AVROUT output from the DC voltage controller 52 inside the converter controller. As a result, even if there is a sharp change in the speed command of the controlled motor 4 or a change in the load, the DC voltage fluctuation of the converter can be suppressed, and the PN DC voltage signal Vdc is consistent with the DC voltage command value Vref of the converter.

[0102] However, since the power observer unit 55a uses the DC voltage detection value to calculate the converter-side power compensation signal POBSOUT as a correction signal, even if the PN DC voltage signal Vdc changes due to reasons other than changes in the inverter-side DC power current Idc_i, it will mistakenly assume that the inverter-side DC power current Idc_i has changed and perform an incorrect correction. If the converter is driven based on the incorrect correction signal, the DC voltage fluctuation will become the cause of the detected fault, and in the worst case, it will become the cause of damage to the power conversion device.

[0103] Therefore, when the value of the PN DC voltage signal Vdc changes due to reasons other than the change in the DC power current Idc_i on the inverter side, the power observer unit 55c does not add the converter-side power compensation signal calculated by the power observer to the converter output current command output by the DC voltage controller, in order to avoid error correction by the power observer, according to the drive state of the converter unit 2.

[0104] Figure 8 This indicates the elapsed time of the DC voltage waveform when the converter is started.

[0105] The vertical axis represents the voltage [V] of the PN DC voltage signal Vdc, and the horizontal axis represents time [t]. τ1 is the time from the start of charging to the completion of charging, and τ2 is the time from the completion of charging until the DC voltage matches the converter's DC voltage command value Vref. When starting the converter, the converter P-side smoothing capacitor 22, the converter N-side smoothing capacitor 23, the inverter P-side smoothing capacitor 32, and the inverter N-side smoothing capacitor 33, which are connected to the converter and inverter, need to be pre-charged.

[0106] To charge the smoothing capacitor 22 on the P side of the converter, the smoothing capacitor 23 on the N side of the converter, the smoothing capacitor 32 on the P side of the inverter, and the smoothing capacitor 33 on the N side of the inverter, the power conversion device 103 includes a charging power supply 80 and a charging circuit 81. Furthermore, after charging is completed, the converter is started, and time is required until the PN DC voltage signal Vdc matches the converter DC voltage command value Vref. Figure 8 The DC voltage varies between τ1 and τ2 because the PN DC voltage signal Vdc is inconsistent with the converter DC voltage command value Vref. Therefore, the DC voltage varies for different reasons than the DC current variation on the inverter side.

[0107] Therefore, this embodiment includes: a start timer unit 57a that counts the power observer start-up standby time TS, wherein the power observer start-up standby time TS is the sum of the interval (τ1+τ2) from the start of charging until the DC voltage matches the command value and the preset useless time τ3 after the DC voltage matches the converter DC voltage command value Vref; and a selection unit 77 that outputs zero before the start timer unit 57a completes counting, and switches to outputting the converter-side power compensation signal POBSOUT after counting is completed. This prevents the erroneous compensation signal from the power observer unit 55c from being added to the output of the DC voltage controller 52 when the converter starts up.

[0108] In addition, during maintenance of the power conversion device 103, a normal stop command needs to be sent to the converter unit 2 to stop it. Furthermore, in the event of a malfunction or abnormality in the power conversion device 101 or other equipment, the converter unit 2 needs to be immediately and urgently stopped to ensure safety.

[0109] When converter unit 2 is stopped, if the converter controller receives a stop command, it stops the pulse signal output from pulse generator 54. As a result, DC voltage control stops, and therefore the DC voltage fluctuates.

[0110] As described above, since the power observer unit 55c uses the DC voltage detection value to estimate the inverter-side DC power current Idc_i as a correction signal, even if the value of the PN DC voltage signal Vdc changes due to the converter stopping, it will mistakenly assume that the inverter-side DC power current Idc_i has changed and make an incorrect correction.

[0111] Therefore, in this embodiment, when the selection unit 77 receives a normal stop command and a fault stop command from the switching signal generation unit 57, the selection unit 77 switches the output switch to make the converter-side power compensation signal POBSOUT zero. This prevents the incorrect compensation signal from the power observer unit 55c from being added to the output of the DC voltage controller 52 when the converter stops.

[0112] (Fourth Implementation)

[0113] In the fourth embodiment, a technique for dealing with transient lows generated in the AC power supply 1 is described.

[0114] Figure 9 This is an overall structural diagram of the power conversion device according to the fourth embodiment of the present invention.

[0115] The power conversion device 104 is configured to be equivalent to the power conversion device 100 of the first embodiment described above. Figure 1The system includes a synchronization power transformer 11 that steps down the voltage Vs of AC power supply 1 to generate a synchronization power signal, and an instantaneous low voltage calculation unit 58 that calculates the instantaneous voltage drop of AC power supply 1 from the synchronization power signal.

[0116] Synchronous power transformer 11 is connected to AC power supply 1, and steps down the AC voltage supplied to the converter to a voltage that can be processed by the converter control unit, generating a synchronous power signal. Instantaneous quantity calculation unit 58 calculates the voltage fluctuation of AC power supply 1 from the synchronous power signal generated by synchronous power transformer 11.

[0117] Figure 10 A block diagram is used to illustrate the converter unit and control circuit of the fourth embodiment of the present invention.

[0118] Power observer section 55e is in power observer section 55a ( Figure 2 The input signal of voltage fluctuation output from the instantaneous low quantity calculation unit 58 makes the converter-side DC power current conversion gain Kdc (KdcA) used in the converter-side DC power current calculation unit 73 and the converter-side power compensation conversion unit 75 variable.

[0119] Here, the DC power current conversion gain KdcA on the converter side is expressed by equation (8).

[0120]

[0121] Where Vs is the voltage of AC power supply 1, and Vdc is the DC voltage output by converter unit 2.

[0122] The voltage Vs of AC power supply 1 is typically supplied to converter unit 2 at a constant voltage. Furthermore, the DC voltage Vdc output by converter unit 2 is controlled to a constant value by the converter controller. Therefore, for the voltage Vs of AC power supply 1 and the DC voltage Vdc output by converter unit 2, the converter-side DC power current conversion gain Kdc (KdcB) of converter-side DC power current conversion unit 71 and the converter-side DC power current conversion gain Kdc (KdcA) used in converter-side DC power current calculation unit 73 and converter-side power compensation conversion unit 75 are typically fixed values.

[0123] However, the voltage Vs of AC power supply 1 may sometimes fluctuate or decrease instantaneously due to natural factors such as lightning strikes, excessive loads, or insufficient power supply.

[0124] When the voltage Vs of AC power supply 1 changes / decreases instantaneously, according to equation (8), the DC power current conversion gain Kdc (KdcB) used by the DC power current conversion unit 71 on the converter side will change according to the change / decrease of the voltage of AC power supply 1.

[0125] As described above, when the converter-side DC power current calculation gain Kdc (KdcA) used by the converter-side DC power current calculation unit 73 and the converter-side power compensation calculation unit 75 is set to a fixed value, when the voltage of the AC power supply 1 changes, it becomes inconsistent with the converter-side DC power current calculation gain Kdc (KdcB) of the converter-side DC power current calculation unit 71, resulting in incorrect correction. If the converter is driven based on the incorrect correction signal, the DC voltage change becomes a fault detection, and in the worst case, it becomes the cause of damage to the power conversion device.

[0126] Therefore, in this embodiment, based on the instantaneous low quantity output from the instantaneous low quantity calculation unit 58, the converter-side DC power current conversion gain setting value Kdc (KdcA) used by the converter-side DC power current calculation unit 73 and the converter-side power compensation conversion unit 75 can be varied.

[0127] As explained above, in this embodiment, based on the instantaneous low quantity output from the instantaneous low quantity calculation unit 58, the converter-side DC power current conversion gain setting value Kdc (KdcA) used in the converter-side DC power current calculation unit 73 and the converter-side power compensation conversion unit 75 is made variable. Thus, even if the voltage of the AC power supply 1 changes, by making it consistent with the converter-side DC power current conversion gain Kdc (KdcB) of the converter-side DC power current conversion unit 71, the accurate compensation signal can be added to the output of the DC voltage controller.

[0128] The above embodiments were described using a 3-level device, but the present invention can also be applied to a 2-level device.

[0129] Explanation of reference numerals in the attached figures

[0130] 1. AC power supply

[0131] 2 Converter Unit

[0132] 3 Inverter Unit

[0133] 4, 4a, 4b, 4c motors

[0134] 5a, 5b, 5c, 5d, 5e Converter control unit

[0135] Inverter control devices 6, 6a, 6b, 6c

[0136] 7, 9 Current detectors

[0137] 21. Converter Power Conversion Section (Converter)

[0138] 22 Converter P-side smoothing capacitor

[0139] 23. N-side smoothing capacitor of converter

[0140] 25 DC voltage detector on the P side of the converter

[0141] 26 DC voltage detector on the N side of the converter

[0142] 31. Inverter power conversion section (converter)

[0143] 32. Smoothing capacitor on the P-side of the inverter

[0144] 33. N-side smoothing capacitor of inverter

[0145] 55 Power Observer Section

[0146] 51 DC Voltage Command Generator

[0147] 52 DC Voltage Controller

[0148] 53, 63 Current Controller

[0149] 54, 64 pulse generator

[0150] 55a, 55b, 55c, 55d, 55e Power Observation Unit

[0151] 56. Addition Department

[0152] 57 Switching Signal Generation Unit

[0153] 57a Start Timer Section

[0154] 58 Instantaneous Low Quantity Calculation Unit

[0155] 66 Transmission Line

[0156] 70 Converter Current Section

[0157] 72 DC Voltage Section

[0158] 73 DC power current calculation unit on the converter side

[0159] 74 Variable Power Current Calculation Unit

[0160] 75 Converter-side power compensation conversion unit

[0161] 76 Filter / Power Compensation Gain Adjustment Section

[0162] 77 Selection Department

[0163] 80 charging power supply

[0164] 81 Charging Circuit

[0165] 100, 101, 102, 103, 104 Power conversion devices

[0166] I_cref Converter input current command value

[0167] Input current of I_c converter (AC power supply side current)

[0168] Idc_c converter-side DC power current

[0169] Idc_i Inverter-side DC power current

[0170] Vdc PN DC voltage signal (DC voltage)

[0171] Idch_c Converter-side DC power current estimate

[0172] Idch_i Estimated DC power current on the inverter side

[0173] POBSOUT converter-side power compensation signal

[0174] AVROUT converter input current command value.

Claims

1. A power conversion device provided with a converter that converts an alternating voltage into a direct voltage, a smoothing capacitor for suppressing variation of the direct voltage, and an inverter that converts the direct voltage charged in the smoothing capacitor into an alternating power, characterized by comprising: a direct voltage detector that detects a potential difference of the smoothing capacitor; a current detector that detects an alternating power source side current of the converter; a direct voltage controller that generates a converter output current command so that a direct voltage detection signal of the direct voltage detector coincides with a direct voltage command value of the converter; a converter output current controller that controls a direct voltage output from the converter so that the alternating power source side current of the converter coincides with the generated converter output current command; a converter side direct current power current operation section that operates a converter side direct current power current estimation value in accordance with the alternating power source side current of the converter; a variation power current operation section that differentiates the direct voltage detection signal of the converter with respect to an electrostatic capacitance of the smoothing capacitor to obtain a variation power current estimation value; a filter / power compensation gain adjustment section that performs a process of adjusting a filter time constant and a compensation amount with respect to an inverter side direct current power current estimation value obtained by subtracting the variation power current estimation value from the converter side direct current power current estimation value; a converter side power compensation conversion section that generates a converter side power compensation value by multiplying an inverter side direct current power current adjustment value output from the filter / power compensation gain adjustment section by an inverse conversion gain; and an adder that adds the converter side power compensation value to the converter output current command and outputs an addition result to the converter output current controller.

2. A power conversion device provided with a converter that converts an alternating voltage into a direct voltage, a smoothing capacitor for suppressing variation of the direct voltage, and an inverter that converts the direct voltage charged in the smoothing capacitor into an alternating power, characterized by comprising: a direct voltage detector that detects a potential difference of the smoothing capacitor; a current detector that detects an alternating power source side current of the converter; a direct voltage controller that generates a converter output current command so that a direct voltage detection signal of the direct voltage detector coincides with a direct voltage command value of the converter; a converter output current controller that controls a direct voltage output from the converter so that the alternating power source side current of the converter coincides with the generated converter output current command; a converter side direct current power current operation section that operates a converter side direct current power current estimation value in accordance with the alternating power source side current of the converter; a variation power current operation section that operates a variation power current estimation value in accordance with the direct voltage detection signal of the converter; and a converter side power compensation conversion section that generates a converter side power compensation value by multiplying an inverter side direct current power current estimation value obtained by subtracting the variation power current estimation value from the converter side direct current power current estimation value by an inverse conversion gain. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ an adder that adds the converter-side power compensation value to the converter output current command and outputs the addition result to the converter output current controller; and a selection unit that switches the output value of the converter-side power compensation conversion unit based on a signal of a start timer unit, a signal of a normal stop command, and a signal of a failure stop command, the selection unit has a start timer unit that counts a start time that is a time from when the smoothing capacitor starts charging to when charging is completed, a time from when charging is completed to when the DC voltage detection signal coincides with the DC voltage command value, and a time obtained by adding a useless time that is set in advance after the DC voltage detection signal coincides with the DC voltage command value, the selection unit switches the output of the converter-side power compensation conversion unit to zero before the start timer unit completes counting, and switches to output the operation result of the converter-side power compensation conversion unit after the start timer unit completes counting.

3. The power conversion device according to claim 2, wherein the selection unit switches the output of the converter-side power compensation conversion unit to zero according to a stop signal.

4. A power conversion device that has a converter that converts an alternating-current voltage into a direct-current voltage, a smoothing capacitor that suppresses variation of the direct-current voltage, and an inverter that converts the direct-current voltage charged in the smoothing capacitor into an alternating-current power, the power conversion device has a DC voltage detector that detects a potential difference of the smoothing capacitor; a current detector that detects an alternating-current power source side current of the converter; a DC voltage controller that generates a converter output current command so that a DC voltage detection signal of the DC voltage detector coincides with a DC voltage command value of the converter; a converter output current controller that controls a direct-current voltage output from the converter so that the alternating-current power source side current of the converter coincides with the generated converter output current command; a converter-side DC power current operation unit that operates a converter-side DC power current estimation value based on the alternating-current power source side current of the converter; a variation power current operation unit that operates a variation power current estimation value based on the DC voltage detection signal of the converter; a converter-side power compensation conversion unit that generates a converter-side power compensation value by multiplying an inverter-side DC power current estimation value obtained by subtracting the variation power current estimation value from the converter-side DC power current estimation value by an inverse conversion gain; an adder that adds the converter-side power compensation value to the converter output current command and outputs the addition result to the converter output current controller; and a transient low amount operation unit that detects a decrease amount of the alternating-current voltage, the gain of the converter-side DC power current operation unit and the converter-side power compensation conversion unit is decreased or increased according to the variation / decrease amount of the alternating-current voltage detected by the transient low amount operation unit. ​ 5. A power conversion control method executed by a control device of a power conversion device, the power conversion device including a converter that converts an alternating voltage into a direct voltage, a smoothing capacitor that suppresses variation of the direct voltage, an inverter that converts the direct voltage charged in the smoothing capacitor into an alternating power, a direct voltage detector that detects a potential difference of the smoothing capacitor, and a current detector that detects an alternating current source side current of the converter, characterized in that the power conversion control method implements the following functions: a direct voltage controller that generates a converter output current command so that a direct voltage detection signal of the direct voltage detector coincides with a direct voltage command value of the converter; a converter output current controller that controls the direct voltage output from the converter so that the alternating current source side current of the converter coincides with the generated converter output current command; a converter side direct current power current operation section that operates a converter side direct current power current estimation value in accordance with the alternating current source side current of the converter; a variation power current operation section that differentiates the direct voltage detection signal of the converter with respect to an electrostatic capacitance of the smoothing capacitor to obtain a variation power current estimation value; a filter / power compensation gain adjustment section that performs processing of adjusting a filter time constant and a compensation amount with respect to an inverter side direct current power current estimation value obtained by subtracting the variation power current estimation value from the converter side direct current power current estimation value; a converter side power compensation conversion section that generates a converter side power compensation value by multiplying an inverter side direct current power current adjustment value output from the filter / power compensation gain adjustment section by an inverse conversion gain; and an adder that adds the converter output current command to the converter side power compensation value and outputs an addition result to the converter output current controller.

6. A computer readable recording medium that stores a power conversion control program executed by a control device of a power conversion device, the power conversion device including a converter that converts an alternating voltage into a direct voltage, a smoothing capacitor that suppresses variation of the direct voltage, an inverter that converts the direct voltage charged in the smoothing capacitor into an alternating power, a direct voltage detector that detects a potential difference of the smoothing capacitor, and a current detector that detects an alternating current source side current of the converter, characterized in that the power conversion control program causes the control device to implement the following functions: a direct voltage controller that generates a converter output current command so that a direct voltage detection signal of the direct voltage detector coincides with a direct voltage command value of the converter; a converter output current controller that controls the direct voltage output from the converter so that the alternating current source side current of the converter coincides with the generated converter output current command; a converter side direct current power current operation section that differentiates the alternating current source side current of the converter with respect to an electrostatic capacitance of the smoothing capacitor to obtain a converter side direct current power current estimation value; a variation power current operation section that differentiates the direct voltage detection signal of the converter with respect to the electrostatic capacitance of the smoothing capacitor to obtain a variation power current estimation value; a filter / power compensation gain adjustment section that performs processing of adjusting a filter time constant and a compensation amount with respect to an inverter side direct current power current estimation value obtained by subtracting the variation power current estimation value from the converter side direct current power current estimation value; a converter side power compensation conversion section that generates a converter side power compensation value by multiplying an inverter side direct current power current adjustment value output from the filter / power compensation gain adjustment section by an inverse conversion gain; and an adder that adds the converter output current command to the converter side power compensation value and outputs an addition result to the converter output current controller. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ a fluctuation power current operation section that operates a fluctuation power current estimation value based on a DC voltage detection signal of the converter; a filter / power compensation gain adjustment section that performs processing of adjusting a filter time constant and a compensation amount on an inverter-side DC power current estimation value obtained by subtracting the fluctuation power current estimation value from the converter-side DC power current estimation value; a converter-side power compensation conversion section that generates a converter-side power compensation value by multiplying the inverter-side DC power current adjustment value output from the filter / power compensation gain adjustment section by an inverse conversion gain; and an adder that adds the converter-side power compensation value to the converter output current command and outputs an addition result to the converter output current controller.

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