Conversion device and power conversion system

Abstract

The present application provides a general-purpose conversion device capable of being combined with various power conversion systems to suppress high-order harmonic currents and a power conversion system provided with the same. The conversion device (4) includes external terminals (Pp, Pn), smoothing capacitors (C1, C2), a current detector (8), three-phase bidirectional current switches (SW(r, s, t)), and a conversion controller (7). The three-phase bidirectional current switches (SW(r, s, t)) are respectively provided between one end of a three-phase AC reactor (2) and a midpoint node (Nm) of the smoothing capacitors (C1, C2). The conversion controller (7) has a start-up judging device that compares a current value of a three-phase current detected by the current sensor (8) with a pre-set start-up judging value and outputs an internal start-up signal when the current value exceeds the start-up judging value, and a switch control that activates the three-phase bidirectional current switches (SW(r, s, t)) in response to the internal start-up signal.

Description

Technical Field

[0001] This invention relates to conversion devices and power conversion systems, such as techniques for suppressing high-order harmonic currents. Background Technology

[0002] For example, Patent Document 1 shows a method in which a bidirectional energizing switch corresponding to the phase with the intermediate potential of the three-phase power supply is switched on during the period before and after the voltage of the intermediate potential becomes 0, thereby reducing the high-order harmonic components of the power supply current.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2012-60801. Summary of the Invention

[0006] The problem the invention aims to solve

[0007] For example, power conversion systems driving three-phase AC motors are becoming increasingly common in various industrial sectors, such as refrigeration equipment. In these systems, a three-phase diode bridge is typically used to convert the input three-phase AC power to DC. However, this process generates a significant amount of high-order harmonics in the power supply current, and its adverse effects on the power transmission network are becoming a social problem. Therefore, in recent years, high-order harmonic limits have been established in Europe, China, Japan, and other countries, represented by the IEC (International Electrotechnical Commission) high-order harmonic limits (IEC 61000-3-2 (phase current < 16A) and IEC 61000-3-12 (16A < phase current < 75A)).

[0008] To address such high-order harmonic limitations, there are situations where it is desirable to embed a conversion device (in other words, a PFC (Power Factor Correction) unit) for suppressing high-order harmonic currents into an existing system comprising a three-phase AC power supply, a three-phase diode bridge, and a smoothing capacitor. The PFC unit preferably operates in the presence of a load connected in front of the smoothing capacitor, and with a certain level of current flowing through that load based on the high-order harmonic limitation.

[0009] Here, as shown in Patent Document 1, in a system where a PFC unit is pre-integrated, for example, the PFC unit can be started based on the load current of the load. However, if the PFC unit is to be embedded in the system after installation, there is a possibility that the PFC unit may not be able to start properly. For example, if the existing system does not have a pre-existing mechanism for detecting the load current and outputting the detection result to the outside, it may be difficult to start the PFC unit properly.

[0010] The present invention is made in view of the following circumstances, and one of its objectives is to provide a highly versatile conversion device and a power conversion system having the same, which can be combined with various power conversion systems to suppress high-order harmonic currents.

[0011] The above and other objects and novel features of the present invention will be explained in accordance with the description and drawings in this specification.

[0012] Technical means for solving problems

[0013] A brief summary of representative embodiments disclosed in this application is provided below.

[0014] A representative embodiment of the present invention provides a conversion device applied in a power conversion system comprising: a three-phase diode bridge for rectifying an input three-phase AC power supply; and a three-phase AC reactor inserted in a current path between the three-phase AC power supply and the three-phase diode bridge, the conversion device suppressing high-order harmonic currents generated in the three-phase AC power supply. The conversion device includes first and second external terminals, first and second smoothing capacitors, a current sensor, three-phase bidirectional energizers, and a conversion controller. The first and second external terminals are respectively connected to a pair of output nodes of the three-phase diode bridge. The first smoothing capacitor is connected between the first external terminal and the midpoint node, and the second smoothing capacitor is connected between the second external terminal and the midpoint node. The current sensor detects the three-phase current of the three-phase AC power supply. The three-phase bidirectional energizers are respectively disposed between the nodes on the three-phase diode bridge side of the three-phase AC reactor and the midpoint node. The conversion controller has a start-up judgment device that compares the current value of the three-phase current detected by the current sensor with a preset start-up judgment value, and outputs an internal start-up signal when the current value exceeds the start-up judgment value. The conversion controller responds to the internal start-up signal to activate the three-phase bidirectional energizing switch.

[0015] The effects of the invention

[0016] The effects obtained by using representative embodiments of the invention disclosed in this application will be briefly described, demonstrating that a highly versatile conversion device can be combined with various power conversion systems to suppress high-order harmonic currents. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating a structural example of a power conversion system according to Embodiment 1 of the present invention.

[0018] Figure 2 It means Figure 1 The circuit diagram shows a detailed example of the structure of a bidirectional switching circuit.

[0019] Figure 3 It means Figure 1 A block diagram of the structure of the conversion controller in the example.

[0020] Figure 4 It means Figure 3 A detailed structural example of the power supply voltage phase operator is shown in the diagram.

[0021] Figure 5 It means Figure 4 The timing diagram of the operation example of the power supply voltage phase operator.

[0022] Figure 6 It means Figure 3 A detailed structural example of the current controller in the diagram is shown.

[0023] Figure 7 It means Figure 6 A diagram of a variation.

[0024] Figure 8 This is a circuit diagram illustrating a typical boost converter circuit structure.

[0025] Figure 9 From Figure 1 A diagram of the boost circuit section is shown in the power conversion system.

[0026] Figure 10 This refers to the conversion device in Embodiment 2 of the present invention. Figure 1 A block diagram of the structure of a conversion controller. Detailed Implementation

[0027] Hereinafter, embodiments of the present invention will be described in detail based on the accompanying drawings. In all the drawings used to illustrate the embodiments, the same reference numerals are generally used for the same components, and repeated descriptions are omitted.

[0028] (Implementation Method 1)

[0029] <Overview of the Power Conversion System>

[0030] Figure 1 This is a schematic diagram illustrating a structural example of a power conversion system according to Embodiment 1 of the present invention. Figure 1The power conversion system shown includes a three-phase AC reactor 2, a three-phase diode bridge 3, a smoothing capacitor Co, a conversion device 4, a DC voltage detector (voltage sensor) 11, an inverter 13, an inverter controller 12, and a monitor 16. The three-phase AC reactor 2 is inserted into the current path between the three-phase AC power supply 1 and the three-phase diode bridge 3 to smooth the power supply current. The three-phase diode bridge 3 performs full-wave rectification of the input three-phase AC power supply 1 via the three-phase AC reactor 2. The smoothing capacitor Co smooths the output voltage of the three-phase diode bridge 3 (the output voltage VCC on the positive side with the negative side set to ground voltage GND).

[0031] A DC voltage detector (voltage sensor) 11 detects the voltage (output voltage VCC) at the output node of the three-phase diode bridge 3 through a resistor divider, and outputs a voltage detection signal Vdc. The inverter 13 includes multiple switching elements that convert the DC voltage (output voltage VCC) generated at the output node of the three-phase diode bridge 3 into a three-phase AC voltage. The inverter 13 then uses this three-phase AC voltage to drive a three-phase AC motor 14 (e.g., a motor for a refrigerator).

[0032] The conversion device 4 includes functions for suppressing high-order harmonic currents generated in the three-phase AC power supply 1 and controlling the output voltage VCC (boost function), as detailed later. In this example, the load supplied with the output voltage (DC voltage) VCC of the three-phase diode bridge 3 is the inverter 13, but it is not limited to this; it can be any load device that consumes DC power, such as a DC motor.

[0033] Monitor 16 is installed in a higher-level device, such as a personal computer, to monitor the operating status of inverter controller 12 (and conversion controller 7 described later). Monitor 16 communicates with inverter controller 12 (conversion controller 7) via communication paths 17 and 15, for example, based on wired communication standards such as RS-232C, RS-422, RS-485, USB, Ethernet, or wireless communication standards such as Bluetooth (registered trademark) and Wi-Fi.

[0034] The inverter controller 12 is, for example, composed of a microcontroller. The inverter controller 12 generates a PWM (Pulse Width Modulation) signal based on the operation command and speed command input from the monitor 16, and uses the PWM signal to control the switching of multiple switching elements in the inverter 13.

[0035] <Details of the conversion device>

[0036] The conversion unit (in other words, the PFC unit) 4 is, for example, a wiring circuit board on which various components are mounted, configured as a separate device from the inverter unit, which includes the inverter controller 12 and the inverter 13. The conversion unit 4 includes external terminals Pr1, Ps1, Pt1, Pr2, Ps2, Pt2, Pp, Pn, Pd, and Pc.

[0037] External terminals Pr1, Ps1, Pt1 and external terminals Pr2, Ps2, Pt2 are sequentially arranged in the current path between the three-phase AC reactor 2 and the three-phase diode bridge 3. External terminals Pp and Pn are respectively connected to a pair (positive side and negative side) of the output nodes of the three-phase diode bridge 3. For external terminal Pd, the voltage detection signal Vdc from the DC voltage detector (voltage sensor) 11 is input. External terminal Pc is the communication terminal with the monitor 16.

[0038] Additionally, the conversion device 4 includes: a voltage phase detector 5, a bidirectional switching circuit 6 comprising three-phase bidirectional energized switches SWr, SWs, and SWt, a conversion controller 7, a current detector (current sensor) 8, a buffer circuit 10, and smoothing capacitors C1 and C2. The current detector 8 is located between external terminals Pr1, Ps1, and Pt1 and external terminals Pr2, Ps2, and Pt2, detecting the three-phase current of the three-phase AC power supply 1. The current detector 8 is, for example, composed of a shunt resistor element or a current transformer (CT), and here, it detects the phase currents of phases R and T, outputting a current detection signal Ir for phase R and a current detection signal It for phase T.

[0039] A smoothing capacitor C1 is connected between the external terminal Pp and the midpoint node Nm, and a smoothing capacitor C2 is connected between the external terminal Pn and the midpoint node Nm. Three-phase bidirectional energizers SWr, SWs, and SWt are respectively located between the nodes on the three-phase diode bridge 3 side of the three-phase AC reactor 2 and the midpoint node Nm. More specifically, one end of each of the three-phase bidirectional energizers SWr, SWs, and SWt is connected to external terminals Pr2, Ps2, and Pt2, respectively, and is connected to external terminals Pr1, Ps1, and Pt1, respectively, via current sensors 8. The other end of each of the three-phase bidirectional energizers SWr, SWs, and SWt is connected to the midpoint node Nm via a buffer circuit 10 composed of inductors and multiple diodes.

[0040] Voltage phase detector 5 is connected to external terminals Pr2, Ps2, and Pt2, and outputs voltage phase signals Vrn, Vsn, and Vtn for detecting the voltage phase of the three-phase AC power supply 1 by resistive voltage division of the voltages at external terminals Pr2, Ps2, and Pt2. The conversion controller 7 is, for example, a microcontroller. The conversion controller 7 receives the voltage phase signals Vrn, Vsn, and Vtn, current detection signals Ir and It, the voltage detection signal Vdc from external terminal Pd, and various signals from external terminal Pc. It uses PWM signals Gr, Gs, and Gt to control the switching of bidirectional energized switches SWr, SWs, and SWt, respectively.

[0041] Alternatively, the conversion device 4 may be configured to include one or both of the three-phase AC reactor 2 or the three-phase diode bridge 3, depending on the circumstances. In this case, the positions of the external terminals Pr1, Ps1, Pt1, Pr2, Ps2, and Pt2 can also be appropriately changed according to the structure.

[0042] <Details of the bidirectional switching circuit>

[0043] Figure 2 It means Figure 1 The circuit diagram shows a detailed example of the structure of a bidirectional switching circuit. Figure 2 In this circuit, the three-phase bidirectional switches SWr, SWs, and SWt are each composed of a single-phase diode bridge and an IGBT (Insulated Gate Bipolar Transistor). Each IGBT within the bidirectional switches SWr, SWs, and SWt is controlled by PWM signals Gr, Gs, and Gt, respectively. Furthermore, the bidirectional switches SWr, SWs, and SWt are not limited to this structure; any other structure and semiconductor element can be used as long as they can be controlled to turn on / off in accordance with the PWM signals Gr, Gs, and Gt from the conversion controller 7.

[0044] <Details of the conversion controller>

[0045] Figure 3 It means Figure 1 A block diagram of the structure of the conversion controller in the example. Figure 3 The conversion controller 7 shown includes: a power supply voltage phase operator 20, a PI controller 21, a modulation wave multiplier 22, a PWM controller 23, a circuit breaker 24, a current controller 25, a start-up detector 26, a carrier generator 27, and a start-up mode switch 28. These modules are mainly implemented through program processing by the CPU (Central Processing Unit) within the microcontroller, achieved by appropriately utilizing analog-to-digital converters and timers within the microcontroller during program processing.

[0046] However, the modules of the conversion controller 7 are not limited to microcontrollers; they can also be partially or entirely constructed from hardware such as FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit). Furthermore, the modules of the conversion controller 7 are not limited to using a CPU; they can also be implemented using program processing such as DSP (Digital Signal Processor). Thus, the modules of the conversion controller 7 can be appropriately constructed using hardware, software, or a combination thereof.

[0047] The conversion controller 7 uses these modules to control the switching of each bidirectional energized switch SWr, SWs, and SWt within the bidirectional switching circuit 6, with the phase difference between the voltage and current phases of the three-phase AC power supply 1 approximately approaching zero. As a result, the conversion controller 7 improves the power factor and suppresses high-order harmonic currents. At the same time, the conversion controller 7 can also monitor the voltage detection signal Vdc while maintaining the output voltage (DC voltage) VCC at a constant level.

[0048] Regarding power supply phase detection

[0049] Figure 4 It means Figure 3 A detailed structural example of the power supply voltage phase operator is shown in the diagram. Figure 4 The power supply voltage phase operator 20 includes a voltage divider circuit 33, a comparator circuit 31, and an internal phase generator 30. In simple terms, it generates an internal phase θs synchronized with the voltage phase of the three-phase AC power supply 1. The voltage divider circuit 33 generates a reference voltage Vref based on the average value of the three-phase voltage phase signals Vrn, Vsn, and Vtn from the voltage phase detector 5. The comparator circuit 31 compares the voltage phase signals Vrn, Vsn, and Vtn with the reference voltage Vref and replaces them with pulse signals. The internal phase generator 30 includes a basic power supply frequency setter 32, a phase error operator 34, a PI controller 35, and a phase updater 36. It detects the timing (hereinafter referred to as the edge) of the pulse signal change from the comparator circuit 31 and generates the internal phase θs.

[0050] Figure 5 It means Figure 4 The timing diagram of the operation example of the power supply voltage phase operator. For example... Figure 5As shown, the pulse signal and the power supply voltage are in phase, resulting in high / low levels respectively. For example, when the power supply phase is 0°, the Vrn pulse signal becomes a rising edge, and when it is 120°, the Vsn pulse signal becomes a rising edge. This relationship varies with the magnitude of the reference voltage Vref, but by using the voltage divider circuit 33 to generate the average value of the three phases, the effects caused by power supply voltage fluctuations become difficult to generate.

[0051] Figure 4 In the internal phase generator 30, the phase updater 36 generates an internal phase θs based on the frequency command value fs. Specifically, the internal phase θs is as follows: Figure 5 As shown, for example, it is the count value of a counter that repeatedly performs a "360×N" counting operation according to the power supply frequency (power supply phase period of 360 degrees). The frequency command value fs indicates the counting speed of the counter.

[0052] The phase error calculator 34 generates a phase update setting value θget whenever it detects the edge of a pulse signal of the voltage phase signals Vrn, Vsn, and Vtn (in this example, every electrical angle of 60 degrees per power supply phase cycle). The phase update setting value θget represents the expected count value, and is a value such as "60×N", "120×N", etc., every 60 degrees. In addition, the phase error calculator 34 detects the phase error Δθs between the internal phase θs (the actual count value) from the phase updater 36 and the phase update setting value θget (the expected count value).

[0053] The PI controller 35 uses PI (proportional-integral) control to calculate a frequency correction value Δfs to bring the phase error Δθs close to zero. For the frequency command value fs, it is updated with the sum of the specified power frequency setpoint fs0 (e.g., a value of 50-60Hz) from the basic power frequency setter 32 and the frequency correction value Δfs, updated every 60 degrees in this example. The phase updater 36 updates the internal phase θs to the phase update setpoint θget every 60 degrees and performs a counting operation based on the frequency command value fs.

[0054] Furthermore, here, operations are performed using two edges every 60 degrees, but processing can also be done using a single edge (either the falling edge or the rising edge). Therefore, performing operations every 120 degrees reduces the processing load on the microcontroller, etc. Alternatively, instead of using all three phases, both the falling and rising edges of two phases can be used. This reduces the processing load on the microcontroller and lowers costs by eliminating one phase of circuitry.

[0055] Furthermore, to prevent fluctuations caused by noise, the calculation can be performed every 360 degrees of electrical angle. Specifically, the phase error Δθs every 60 degrees of electrical angle can be averaged over 360 degrees of electrical angle, and the frequency correction value Δfs can be calculated using this average value. Additionally, a power frequency setting value fs0, such as 50Hz or 60Hz, can be preset in the basic power frequency setter 32. In this case, even if a power frequency setting value fs0 such as 55Hz is set, a predetermined frequency correction value Δfs (e.g., ±5Hz) can be obtained, and the result is compatible with both 50Hz and 60Hz. Furthermore, the power frequency setting value fs0 can be automatically set by measuring the interval of the pulse signal edges using a timer such as a microcontroller.

[0056] Additionally, it is also possible to set other settings based on Figure 4 An anomaly detector uses the power supply voltage phase operator 20 to detect anomalies in its signal. For example... Figure 5 As shown, the power supply voltage phase operator 20 generates pulse signals of voltage phase signals Vrn, Vsn, and Vtn. The anomaly detector compares and judges each edge of these pulse signals, such as by equalizing the edge spacing, thereby detecting anomalies such as three-phase imbalance and phase loss in the power supply.

[0057] Regarding current detection

[0058] Figure 3 In simple terms, the current controller 25 determines the duty cycle command values ​​(Khr, Khs, Kht) of the PWM signals Gr, Gs, and Gt required to bring the phase difference between the voltage phase and the current phase close to zero, based on the internal phase θs from the power supply voltage phase operator 20 and the current detection signals Ir and It from the current detector (current sensor) 8. In other words, the current controller 25 determines the duty cycle command values ​​(Khr, Khs, Kht) required to bring the three-phase currents of the three-phase AC power supply 1 close to an ideal sinusoidal current. Furthermore, the current detector 8 only needs to be able to detect the phase currents of at least two of the R-phase, S-phase, and T-phase.

[0059] Figure 6 It means Figure 3 A detailed structural example of the current controller in the diagram is shown. Figure 6The current controller 25 shown includes a current command arithmetic unit 251, a current reproducing unit 252, and PI controllers 253r, 253s, and 253t. The current reproducing unit 252 calculates the current detection signal Is of the remaining phase based on the current detection signals Ir and It of two phases (specifically, digital signals obtained through an analog-to-digital converter). That is, because the sum of the three-phase current detection signals Ir, Is, and It is zero, the current reproducing unit 252 can calculate the current detection signal Is of the remaining phase (=-Ir-It). Furthermore, the current reproducing unit 252 calculates the current values ​​(e.g., RMS values ​​Irms) of the three-phase currents flowing through the three-phase AC power supply 1 based on the three-phase current detection signals Ir, Is, and It.

[0060] The current command arithmetic unit 251 generates three-phase current commands Ir', Is', It' (specifically, time-varying digital signals) representing ideal sinusoidal currents of the three phases, based on the internal phase θs generated by the power supply voltage phase arithmetic unit 20 and the current values ​​(RMS values ​​Irms) of the three-phase currents detected by the current reproducing unit 252 (and the current detector 8). PI controllers (duty cycle controllers) 253r, 253s, and 253t perform PI control based on the errors ΔIr, ΔIs, and ΔIt between the three-phase current commands Ir', Is', It' and the current detection signals Ir, Is, It from the current reproducing unit 252 (and the three-phase currents detected by the current detector 8). Thus, the PI controllers 253r, 253s, and 253t calculate the modulation waves (duty cycle command values) Khr, Khs, and Kht that bring the errors ΔIr, ΔIs, and ΔIt close to zero.

[0061] Figure 7 It means Figure 6 A diagram of a variation. For example... Figure 7 As shown, the current controller 25 can use a PI controller 253r to perform PI control on one of the three phases (here, phase R) to calculate the modulation wave Khr. The three-phase reproducer 256 then calculates the modulation waves Khs and Kht for the other two phases. Specifically, the three-phase reproducer 256 advances the phase of the modulation wave Khr by 120 degrees to generate the modulation wave Khs, and advances it by 240 degrees to generate the modulation wave Kht.

[0062] On Modulated Wave Multipliers

[0063] Figure 3The PI controller (voltage controller) 21 performs PI control based on the error ΔVdc between the voltage value (digital value after analog-to-digital conversion) represented by the voltage detection signal Vdc from the external terminal Pd and the preset voltage command value Vdc*, thereby calculating the modulation wave gain (operating quantity) Kv that makes the error ΔVdc close to zero. The modulation wave multiplier 22 weights the modulation waves (duty cycle command values) Khr, Khs, and Kht from the current controller 25 according to the modulation wave gain Kv from the PI controller 21 and then outputs them to the PWM controller 23.

[0064] Specifically, when the voltage value represented by the voltage detection signal Vdc is less than the voltage command value Vdc*, the PI controller 21 increases the modulation wave gain Kv. The modulation wave multiplier 22 multiplies the modulation waves Khr, Khs, and Kht by this modulation wave gain Kv, thereby increasing the multiplied modulation waves Khr', Khs', and Kht' output to the PWM controller 23. On the other hand, when the voltage value represented by the voltage detection signal Vdc is greater than the voltage command value Vdc*, the PI controller 21 decreases the modulation wave gain Kv, and correspondingly, the modulation wave multiplier 22 decreases the multiplied modulation waves Khr', Khs', and Kht'. In this way, control is performed so that the output voltage VCC is equal to the voltage command value Vdc*.

[0065] About PWM controllers

[0066] Figure 3 The PWM controller 23 generates three-phase PWM signals Gr', Gs', and Gt' based on the multiplied modulated waves (duty cycle command values) Khr', Khs', and Kht' obtained from the modulated wave multiplier 22 of the current controller 25, and uses them to control the switching of the three-phase bidirectional energized switches SWr, SWs, and SWt. Specifically, the PWM controller 23 generates PWM signals Gr', Gs', and Gt' by comparing the multiplied modulated waves Khr', Khs', and Kht' with the carrier wave (triangular wave or sawtooth wave) Fc generated by the carrier wave generator 27. At this time, the frequency of the carrier wave Fc is determined, for example, to a value preset in a microcontroller or the like.

[0067] "Instructions for Starting the Machine"

[0068] Figure 3 The start-up judgment unit 26 compares the effective value (Irms) of the three-phase current detected by the current detector (current sensor) 8 and calculated by the current controller 25 with a preset start-up judgment value Ith. When the effective value Irms exceeds the start-up judgment value Ith, it outputs an internal start-up signal 29a. The start-up judgment value Ith is set to a value corresponding to the rated current value of the system, for example, based on the IEC standard for high-order harmonic limits.

[0069] in addition, Figure 3 The external start signal 29b from Figure 1 The monitor 16 is input via an external terminal Pc. The start mode switch 28 asserts the start signal 29c in response to either the internal start signal 29a from the start determination unit 26 or the externally input external start signal 29b. At this time, the start mode switch 28 determines, for example, whether to select the internal start signal 29a or the external start signal 29b based on a selection signal input from the monitor 16 via the external terminal Pc, or a selection switch mounted on the wiring circuit board constituting the switching device 4.

[0070] Figure 3 The switching controller 7 activates the switching control of the bidirectional switching circuit 6 in response to the start signal 29c (internal start signal 29a or external start signal 29b). In this example, a circuit breaker 24 is provided. When the start signal 29c is asserted (enabled), the circuit breaker 24 outputs the PWM signals Gr', Gs', and Gt' from the PWM controller 23 as PWM signals Gr, Gs, and Gt. On the other hand, when the start signal 29c is negated (negated), the circuit breaker 24 cuts off the output of the PWM signals Gr', Gs', and Gt', fixing the PWM signals Gr, Gs, and Gt at the off level.

[0071] Alternatively, the start mode switch 28 can output the start signal 29c using both the internal start signal 29a and the external start signal 29b. For example, the start mode switch 28 can invalidate the start signal 29c even when the start signal 29c is asserted in response to the assertion of the internal start signal 29a, or when the external start signal 29b is invalidated (in other words, when an external cut-off signal is input), thereby suspending the switch control.

[0072] Thus, for example, Figure 1 During the normal operation of the power conversion system (and consequently, during the period when the conversion controller 7 performs switching control in response to the internal start signal 29a), in the event of an abnormality such as overcurrent in the inverter 13, protection can be achieved by urgently stopping the operation of the conversion controller 7. Specifically, when the monitor 16 detects an abnormality in the inverter 13 via the inverter controller 12, it can simply invalidate the external start signal output to the conversion controller 7 (in other words, output an external cut-off signal).

[0073] and then, Figure 3 The start-up detector 26 can also perform start-up determination based on the signal from the power supply voltage phase operator 20. Specifically, it can be as follows: Figure 4 and Figure 5 As shown, an anomaly detector is also provided to detect anomalies such as three-phase imbalance and phase loss of the power supply based on the signal from the power supply voltage phase operator 20. This anomaly detector may also be installed in the start-up detector 26, for example.

[0074] In this case, when an anomaly is detected by the anomaly detector, the start-up detector 26 fixes the internal start-up signal 29a to an invalid level. Specifically, the start-up detector 26 is configured to not assert the internal start-up signal 29a (and start-up signal 29c) even if the effective value Irms exceeds the start-up judgment value Ith when an anomaly is detected by the anomaly detector. Furthermore, the start-up detector 26 is configured to invalidate the internal start-up signal 29a (and start-up signal 29c) if an anomaly is detected by the anomaly detector while the internal start-up signal 29a has already been asserted.

[0075] Furthermore, circuit breaker 24 can simply switch the switching control of the bidirectional switching circuit 6 to active / inactive, and there is no particular need to set it at the output stage of the transfer controller 7. For example, circuit breaker 24 can suspend the switching control by cutting off the input to the internal phase θs of the current controller 25, or it can suspend the switching control by suspending the operation of the entire transfer controller 7.

[0076] in addition, Figure 1 Alternatively, the system can be configured such that the monitor 16 is not provided, and the conversion controller 7 is operated solely by the internal start signal 29a, thereby independently operating the inverter controller 12. Alternatively, the system can be configured such that the monitor 16 is not provided, and the conversion controller 7 and inverter controller 12 can communicate directly.

[0077] <Regarding the boosting action>

[0078] use Figure 1 In power conversion systems, for example, it is also possible to... Figure 3 The voltage command value Vdc* is set to a higher value than the normal output voltage VCC, which is determined based on the voltage amplitude of the three-phase AC power supply 1, and a boost operation is performed. Figure 8 This is a circuit diagram illustrating a typical boost converter circuit structure. Figure 8 The boost circuit shown includes a DC power supply 1', an inductor 2', a switching element 6', a diode 3', and a smoothing capacitor C12, which supplies a voltage greater than that of the DC power supply 1' to the resistor 13', which serves as a load.

[0079] In this boost circuit, during the period when the switching element 6' is on, power is stored in the reactor 2'. During the period when the switching element 6' is off, the power stored in the reactor 2' is transferred to the smoothing capacitor C12 via the anti-reverse current diode 3', thereby performing the boost operation. The boost capability is determined based on the operating frequency of the switching element 6', the inductance value of the reactor 2', and the magnitude of the current flowing through the reactor 2'. That is, to actively boost the voltage, the operating frequency of the switching element 6', the inductance value, or the current flowing through the reactor 2' can be increased.

[0080] In practical circuits, changing the inductance value of reactor 2' requires wiring work during operation, making it difficult to apply. Therefore, in practice, it is preferable to increase the current flowing through reactor 2' or increase the operating frequency of switching element 6'. When using the former method, the voltage across the smoothing capacitor C12 can be monitored while controlling the switching time of switching element 6' to be appropriately increased.

[0081] Figure 9 From Figure 1 A diagram of the boost circuit section is shown in the power conversion system. Figure 8 The reactor 2', switching element 6', diode 3', smoothing capacitor C12, and resistor 13' in the diagram correspond to respectively Figure 9 The components include a three-phase AC reactor 2, a bidirectional switching circuit 6, a three-phase diode bridge 3, smoothing capacitors C1 and C2, and an inverter 13.

[0082] so, Figure 9 In power conversion systems, there exists... Figure 8 It uses the same components as the boost circuit, so it can perform boost operation using the same working principle. Figure 8 and Figure 9 The difference lies in that the DC power supply 1' is replaced by a three-phase AC power supply 1. When using the three-phase AC power supply 1, the boost circuit switches between phases in response to the phase changes of the three-phase AC power supply 1, performing an alternating and repeated boosting operation. At this time, Figure 3 The modulation wave multiplier 22 boosts the output voltage VCC by weighting the modulation wave (duty cycle command value) Khr, Khs, and Kht based on the error between the voltage value represented by the voltage detection signal Vdc and the voltage command value Vdc*.

[0083] <Main Effects of Implementation Method 1>

[0084] As described above, by using Embodiment 1, as a first effect, a highly versatile conversion device that can be combined with various power conversion systems to suppress high-order harmonic currents can be achieved. As a specific example, it is envisioned that it is pre-configured integrally... Figure 1The situation is that of a power conversion system. In this case, Figure 1 The smoothing capacitor Co is replaced with a structure of smoothing capacitors C1 and C2, and the inverter controller 12 and other controllers respond to the detected load current to start the conversion controller 7 appropriately.

[0085] On the other hand, it is conceivable to be from Figure 1 In the power conversion system, the existing system omits the conversion device 4 by retrofitting the embedded conversion device 4. In this case, in order for the conversion controller 7 to start properly, the inverter controller 12 and the like need to output a start signal to the conversion controller 7. However, existing systems may not have a mechanism to output such a start signal. In contrast, Figure 1 The conversion device 4 includes a current detector (current sensor) 8 and Figure 3 The start-up judgment unit 26, etc., enables the start-up unit to start the machine based on its own judgment even when there is no start-up signal input from the outside.

[0086] Furthermore, one end of the bidirectional switching circuit 6 is connected to the midpoint Nm of the smoothing capacitors C1 and C2, but in existing systems including the smoothing capacitor Co, it may be difficult to obtain such a midpoint Nm. In contrast, Figure 1 The conversion device 7 includes smoothing capacitors C1 and C2, thereby enabling it to form a midpoint node Nm. Therefore, a highly versatile conversion device can be realized.

[0087] Furthermore, as a second effect, it allows for the appropriate determination of the period for suppressing higher harmonics. Specifically, in limiting higher harmonics, it is necessary to limit the higher harmonics in the power supply current of the three-phase AC power supply 1. Therefore, in order to appropriately determine the period for suppressing higher harmonics, it is preferable to detect the power supply current with higher precision. Figure 1 In the case of the conversion device 4, the power supply current can be detected with high accuracy at the position of the current detector 8.

[0088] On the other hand, as a comparison, as described above, when the inverter controller 12 outputs a start signal, the power supply current of the three-phase AC power supply 1 is estimated, for example, based on the output power of the inverter 3 (the input voltage of the inverter 3 or the output current of the inverter 3). That is, the inverter controller 12 typically outputs a start signal based on the result obtained by detecting the input voltage or the output current of the inverter 3 using a sensor. However, the relationship between the power supply current of the three-phase AC power supply 1 and the output power of the inverter 3 actually varies due to power conversion efficiency and power factor, etc., so it is not always possible to estimate the power supply current of the three-phase AC power supply 1 with high accuracy.

[0089] Furthermore, as a third effect, the suppression effect of higher harmonics can be easily improved by using the current detector 8. For example, consider not performing current detection, but pre-determining the method of changing the duty cycle to make the current waveform approximate a sine wave through simulation or the like, and pre-registering it in a table. In this case, the optimal value that should be registered in the table may also change when various driving conditions change, so there may be a need to appropriately edit the table, etc. On the other hand, Figure 1 The conversion device 7 uses a current detector 8 to directly observe the current waveform and uses... Figure 3 The current controller 25 calculates the appropriate duty cycle, thus enabling the current waveform to closely approximate a sine wave even under various changing drive conditions.

[0090] (Implementation Method 2)

[0091] <Details of the conversion controller>

[0092] Figure 10 This refers to the conversion device in Embodiment 2 of the present invention. Figure 1 A block diagram illustrating the structure of a conversion controller. (The above...) Figure 3 and Figure 9 In the structural example, the modulation wave multiplier 22 adjusts the duty cycle by weighting the modulation waves Khr, Khs, and Kht according to the modulation wave gain (operational quantity) Kv from the PI controller (voltage controller) 21, thereby achieving constant control of the output voltage VCC. On the other hand, Figure 10 In the structural example, the output voltage VCC is kept constant by changing the frequency of the carrier Fc used in the PWM controller 23 based on the modulation wave gain Kv from the PI controller 21.

[0093] Figure 10 Structural examples and Figure 3 Compared to the previous example, the output target of the modulation wave gain Kv from the PI controller 21 is different. Figure 10 In this circuit, the carrier generator 27 controls its operating frequency based on the modulation gain Kv, thereby causing the frequency of the carrier Fc (and the switching frequency of the bidirectional switching circuit 6) to vary based on the modulation gain Kv. Specifically, when the voltage value represented by the voltage detection signal Vdc is less than the voltage command value Vdc*, the modulation gain Kv increases, and the frequency of the carrier Fc increases. Conversely, when the voltage value represented by the voltage detection signal Vdc is greater than the voltage command value Vdc*, the modulation gain Kv decreases, and the frequency of the carrier Fc decreases.

[0094] <Main Effects of Implementation Method 2>

[0095] As described above, by using Embodiment 2, the same effects as those described in Embodiment 1 can be obtained. Furthermore, as shown in Embodiment 1, in the method of controlling the duty cycle by keeping the frequency of the carrier Fc constant, switching losses are suppressed, but the accuracy decreases when the current waveform approaches a sine wave. In contrast, in Embodiment 2, the accuracy is improved when the current waveform approaches a sine wave, thus enhancing the suppression effect of higher harmonics.

[0096] The invention described above is based on specific embodiments, but the invention is not limited to the above embodiments and various modifications can be made without departing from its spirit. For example, the above embodiments are described in detail for ease of understanding and are not limited to having all the structures described. In addition, a part of the structure of a certain embodiment can be replaced with the structure of another embodiment, and the structure of another embodiment can be added to the structure of a certain embodiment. Furthermore, for a part of the structure of each embodiment, other structures can be added, deleted, or replaced.

[0097] Symbol Explanation

[0098] 1 Three-phase AC power supply

[0099] 2 Three-phase AC reactor

[0100] 3 Three-phase diode bridge

[0101] 4. Conversion device

[0102] 7. Conversion Controller

[0103] 8. Current detector (current sensor)

[0104] 12 Inverter Controller

[0105] 13 Inverters

[0106] 16 monitors

[0107] 20 Power Supply Voltage Phase Calculator

[0108] 21. PI Controller (Voltage Controller)

[0109] 22 Modulated Wave Multiplier

[0110] 23 PWM Controller

[0111] 25 Current Controller

[0112] 26 Startup Detector

[0113] 27. Carrier Generator

[0114] 29a Internal start signal

[0115] 29b External start signal

[0116] C1, C2, Co smoothing capacitors

[0117] Fc carrier

[0118] Gr, Gs, Gt PWM signals

[0119] Ith Startup Judgment Value

[0120] Khr, Khs, Kht Modulation Waves (Duty Cycle Command Values)

[0121] Kv Modulation gain (operational variable)

[0122] Nm midpoint node

[0123] External terminals Pr1, Ps1, Pt1, Pr2, Ps2, Pt2, Pp, Pn, Pd, Pc

[0124] SWr, SWs, SWt bidirectional power switches

[0125] VCC Output Voltage (DC Voltage)

[0126] Vdc voltage detection signal

[0127] Vdc* Voltage command value

[0128] θs internal phase

Claims

1. A conversion device applied in a power conversion system having a three-phase diode bridge that rectifies a three-phase alternating-current power source inputted, and a three-phase alternating-current reactor inserted in a current path between the three-phase alternating-current power source and the three-phase diode bridge, the conversion device suppressing a high-order harmonic current generated in the three-phase alternating-current power source, characterized in that, has: a first external terminal and a second external terminal connected to a pair of output nodes of the three-phase diode bridge, respectively; a first smoothing capacitor connected between the first external terminal and a midpoint node; a second smoothing capacitor connected between the second external terminal and the midpoint node; a current sensor that detects three-phase currents of the three-phase AC power supply; three-phase bidirectional current switches respectively provided between nodes on the three-phase diode bridge side of the three-phase AC reactor and the midpoint node; and a switching controller that performs switching control of the three-phase bidirectional current switches, the switching controller has a start-up determiner that compares a current value of the three-phase currents detected by the current sensor with a pre-set start-up determination value, and outputs an internal start-up signal when the current value exceeds the start-up determination value, and the switching controller activates the switching control in response to the internal start-up signal.

2. The switching device according to claim 1, characterized by: further having a third external terminal that inputs an external start-up signal, the switching controller activates the switching control in response to either of the internal start-up signal and the external start-up signal.

3. The switching device according to claim 1, characterized by: further having a third external terminal that inputs an external start-up signal, the switching controller suspends the switching control in response to invalidity of the external start-up signal.

4. The switching device according to claim 1, characterized by: further having a fourth external terminal and a fifth external terminal that are provided in series on a current path between the three-phase AC reactor and the three-phase diode bridge, the current sensor is provided between the fourth external terminal and the fifth external terminal, one end of the three-phase bidirectional current switches is connected to the fourth external terminal via the current sensor.

5. The switching device according to claim 1, characterized in that: the switching controller further has: a power supply voltage phase calculator that generates an internal phase that is synchronized with a voltage phase of the three-phase AC power supply; a current controller that calculates a duty command value required to make the three-phase currents close to an ideal sinusoidal current, based on the internal phase generated by the power supply voltage phase calculator and the three-phase currents detected by the current sensor; and a PWM controller that generates three-phase PWM signals based on the duty command value from the current controller, and performs switching control of the three-phase bidirectional current switches using the three-phase PWM signals. has:

6. The conversion device of claim 5, wherein, a sixth external terminal that inputs a voltage detection signal that takes as a detection object a voltage of the output nodes of the three-phase diode bridge; a voltage controller that calculates an operation amount that makes an error between a voltage value indicated by the voltage detection signal and a pre-set voltage command value close to zero, based on the error; and a modulation wave multiplier that weights the duty command value from the current controller by the operation amount from the voltage controller, and outputs the result to the PWM controller. has:

7. The conversion device of claim 5, wherein, ​ a sixth external terminal that inputs a voltage detection signal that detects a voltage at the output node of the three-phase diode bridge; a voltage controller that calculates an operation amount that makes an error between a voltage value indicated by the voltage detection signal and a voltage command value set in advance close to zero based on the error; and a carrier generator that generates a carrier used in the PWM controller, the frequency of the carrier being changed based on the operation amount from the voltage controller.

8. A power conversion system having: a three-phase diode bridge that rectifies a three-phase alternating-current power source inputted; a third smoothing capacitor that smoothes an output voltage of the three-phase diode bridge; a three-phase alternating-current reactor that is inserted in a current path between the three-phase alternating-current power source and the three-phase diode bridge; and a conversion device that suppresses a high-order harmonic current generated in the three-phase alternating-current power source, the power conversion system being characterized in that the conversion device has: a first external terminal and a second external terminal that are connected to a pair of output nodes of the three-phase diode bridge, respectively; a first smoothing capacitor that is connected between the first external terminal and a midpoint node; a second smoothing capacitor that is connected between the second external terminal and the midpoint node; a current sensor that detects a three-phase current of the three-phase alternating-current power source; three-phase bidirectional current switches that are respectively provided between nodes on the three-phase diode bridge side of the three-phase alternating-current reactor and the midpoint node; and a conversion controller that performs switching control on the three-phase bidirectional current switches, the conversion controller having a start-up determiner that compares a current value of the three-phase current detected by the current sensor with a start-up determination value set in advance, and outputs an internal start-up signal when the current value exceeds the start-up determination value, the conversion controller activating the switching control in response to the internal start-up signal.

9. The power conversion system of claim 8, wherein, has: an inverter that includes a plurality of switching elements, and converts a direct-current voltage generated at the output node of the three-phase diode bridge into a three-phase alternating-current voltage; an inverter controller that performs switching control on the plurality of switching elements in the inverter; and a monitor that monitors an operation of the inverter controller, the conversion device having a third external terminal that is a communication terminal with the monitor.

10. The power conversion system according to claim 9, characterized in that: the third external terminal is capable of inputting an external start-up signal, the conversion controller suspending the switching control in response to invalidation of the external start-up signal.

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