Power conversion device, power conversion system, and control method

Abstract

This power conversion device is capable of controlling an AC output voltage of a single-phase full-bridge cell unit to zero voltage. The power conversion device comprises a single-phase full-bridge cell unit and a control unit. When setting an AC output voltage to zero voltage by stopping switching of a semiconductor switching element of the positive electrode side arm or the negative electrode side arm of the cell unit, the control unit controls one of the semiconductor switching elements of the positive electrode side arm and the negative electrode side arm to be in an on state and the other thereof to be in an off state according to the temperatures of the semiconductor switching elements in the cell unit.

Description

Power conversion device, power conversion system, and control method

[0001] Embodiments of the present invention relate to a power conversion device, a power conversion system, and a control method.

[0002] There is a power conversion device in which the AC sides of a plurality of single-phase full-bridge type cell units are connected in series. In such a power conversion device, in order to stop the switching of some cell units, the switching of the positive electrode arm or the negative electrode arm in the cell unit is stopped, and one of them is made conductive, so that the output of the stopped cell unit may be set to zero voltage. In such a case, a bias may occur in the current burden of the elements in the cell unit. In order to protect the elements from heat generation due to such a bias in the current burden, if the derating is increased, the performance of the elements cannot be fully exhibited, and the convenience may decrease.

[0003] Japanese Patent Application Laid-Open No. 2021-069171

[0004] An object of the present invention is to provide a power conversion device, a power conversion system, and a control method capable of enhancing the convenience of the power conversion device.

[0005] The power conversion device according to the embodiment can control the AC output voltage of a single-phase full-bridge type cell unit to zero voltage. The power conversion device includes a single-phase full-bridge type cell unit and a control unit. When the control unit stops the switching of the semiconductor switching element of the positive electrode arm or the negative electrode arm of the cell unit to make the AC output voltage zero voltage, the control unit turns on one of the semiconductor switching elements of the positive electrode arm and the negative electrode arm and turns off the other according to the temperature of the semiconductor switching element in the cell unit.

[0006] A diagram showing an example of the power conversion system of the embodiment. A diagram of the configuration of a cell unit of the embodiment. A diagram of the configuration of multiple cascaded cell units of the embodiment. A diagram illustrating an example of the configuration of the control system of the power conversion system of the embodiment. A diagram illustrating the output voltage of the cell unit of the embodiment. A diagram of the configuration of the cell unit control unit within the cell unit of the embodiment. A diagram illustrating the idle control of the cell unit of the embodiment. A diagram illustrating an example of the configuration of the control system of the power conversion system of the embodiment.

[0007] The power conversion device, power conversion system, and control method of the embodiment will be described below with reference to the drawings. In the following description, components having the same or similar functions will be denoted by the same reference numerals. Duplication of these components may be omitted. For the sake of clarity, the drawings referenced below may omit illustrations of control gate wiring and other components.

[0008] The power conversion system of this embodiment forms a multi-cell type power conversion system. The multi-cell type power conversion system comprises a plurality of cell units. Here, the "positive electrode P" and "negative electrode N" within the plurality of cell units are first defined. "Positive electrode P" refers to the part of the cell unit that is at a positive potential when the power conversion system 1 is operating. "Negative electrode N" refers to the part of the cell unit that is at a negative potential when the power conversion system 1 is operating.

[0009] The power conversion system 1 of the embodiment will be described with reference to Figures 1 to 5. Figure 1 is a diagram showing an example of the power conversion system 1 of the embodiment. In Figure 1, the electrical circuit system is shown as a single line, and switches and other components are omitted from the illustration. The power supply side of the power conversion system 1 is connected to an AC power source 2 via, for example, a circuit breaker. The power conversion system 1 converts the AC power supplied from the AC power source 2 into DC power, and then converts the converted DC power back into AC power of a desired frequency and voltage and supplies it to the motor 3. The motor 3 is, for example, a three-phase induction motor, but is not limited to this.

[0010] In this embodiment, an example is described in which the power conversion system 1 comprises a plurality of cell units 6s. The power conversion system 1 comprises, for example, an input transformer 5, a plurality of cell units 6s, a control device 7, and a current sensor AM.

[0011] AC power is supplied to the input transformer 5 from the AC power source 2. The input transformer 5 transforms the voltage of the AC power supplied from the AC power source 2 (primary voltage) to a desired secondary voltage and supplies the AC power of the secondary voltage to each of the multiple cell units 6s. The input transformer 5 has a primary winding and multiple groups of windings (secondary windings) that are insulated from each other. The primary winding and the secondary windings are also insulated from each other.

[0012] The multiple cell units 6s include, for example, three first-phase load cell units 6A1, 6A2, 6A3 (indicated as U1, U2, U3 in the figure), three second-phase load cell units 6B1, 6B1 (indicated as V1, V2, V3, 6B3 in the figure), and three third-phase load cell units 6C1, 6C2, 6C3 (indicated as W1, W2, W3 in the figure). The cell units 6A1, 6A2, 6A3, 6B1, 6B1, 6B3, 6C1, 6C2, 6C3 have the same circuit configuration, and when describing them without distinction, they are simply referred to as cell unit 6. For example, multiple cell units 6s is an example of multiple slave stations, and cell unit 6 is an example of a slave station. Each cell unit 6 converts the three-phase AC power supplied from the secondary winding of the input transformer 5 into DC power, and then converts the converted DC power back into AC power of the desired frequency and voltage for output.

[0013] For example, the first group of secondary components of input transformer 5 is connected to the input of cell unit 6A1. The second group of secondary components of input transformer 5 is connected to the input of cell unit V1. The third group of secondary components of input transformer 5 is connected to the input of cell unit W1. The fourth group of secondary components of input transformer 5 is connected to the input of cell unit 6A2. The fifth group of secondary components of input transformer 5 is connected to the input of cell unit 6B2. The sixth group of secondary components of input transformer 5 is connected to the input of cell unit 6C2. The seventh group of secondary components of input transformer 5 is connected to the input of cell unit 6A3. The eighth group of secondary components of input transformer 5 is connected to the input of cell unit 6B3. The ninth group of secondary components of input transformer 5 is connected to the input of cell unit 6C3.

[0014] In this embodiment, the outputs of cell units 6A1, 6A2, and 6A3 are electrically connected in series with respect to each other in the order shown. The output terminal of cell unit 6A3 that is not connected to cell unit 6A2 is connected to the first phase (U phase) of the motor 3. The output terminal of cell unit 6A1 that is not connected to cell unit 6A2 is connected to the neutral point. In this embodiment, the outputs of cell units 6B1, 6B2, and 6B3 are electrically connected in series with respect to each other in the order shown. The output terminal of cell unit 6B3 that is not connected to cell unit 6B2 is connected to the second phase (V phase) of the motor 3. The output terminal of cell unit 6B1 that is not connected to cell unit 6B2 is connected to the neutral point. In this embodiment, the outputs of cell units 6C1, 6B2, and 6B3 are electrically connected in series with respect to each other in the order shown. The output terminal of cell unit 6C3 that is not connected to cell unit 6C2 is connected to the third phase (W phase) of the motor 3. The output terminals of cell unit 6C1 that are not connected to cell unit 6C2 are connected to the neutral point. This allows the power conversion system 1 to supply a large amount of AC power to the motor 3.

[0015] Current sensors AM1 and AM2 are examples of current sensors AM, and they detect the load current (phase current) flowing between the inverter 13 (Figure 2) and the motor 3 of the power conversion system 1. Note that current sensors AM may be omitted if the system has a configuration for generating an estimated value of the load current. Temperature sensors are provided on the heat sinks of each cell unit 6.

[0016] The control device 7 is an example of a higher-level control device that controls or protects each cell unit 6. The control device 7 includes, for example, a storage unit 71, an operation control unit 72, a control state estimation unit 73, and a braking control unit 74.

[0017] The memory unit 71 stores various data related to the control of multiple cell units 6s. This data includes, for example, the number of cell units 6 connected in a daisy chain, the received value and transmitted value of the control signal α, and the operating status of each cell unit 6.

[0018] The operation control unit 72 generates a control signal α for controlling the semiconductor switching element 13S (Figure 3A) contained in each cell unit 6 based on the data stored in the memory unit 71. The operation control unit 72 controls each cell unit 6 by sending the generated control signal α to each cell unit 6. The operation control unit 72 may also acquire a signal indicating the control status of the electric motor 3 (for example, a rotational speed feedback signal) and control each cell unit 6 based on the feedback signal. Alternatively, the control device 7 may acquire a control command signal for the electric motor 3 from another device and control each cell unit 6 based on the control command signal.

[0019] The control state estimation unit 73 estimates the operating state of the power conversion system 1 based on the reception state of the control signal α and the information contained in the received control signal α. The details of this will be described later.

[0020] The braking control unit 74 controls each cell unit 6 based on the estimated operating state of the power conversion system 1, and controls each part to brake the electric motor 3 based on the control state.

[0021] Next, the cell unit 6 will be described. Figure 2A is a diagram showing the configuration of the cell unit 6 in the embodiment. Figure 2B is a diagram showing the configuration of a plurality of cascaded cell units 6s in the embodiment.

[0022] The cell unit 6 includes, for example, a single-phase cell inverter 6IV and a cell unit control unit 6CUC.

[0023] The single-phase cell inverter 6IV is, for example, a single-phase AC output type inverter. The single-phase cell inverter 6IV includes, for example, a diode converter 12, an inverter 13, a smoothing capacitor 14, and resistors 15 and 16. The DC output of the diode converter 12 and the DC input of the inverter 13 are electrically connected to each other via a DC link, with their positive (P) terminals to each other and their negative (N) terminals to each other. The smoothing capacitor 14 is provided on the DC link, and the terminals of the smoothing capacitor 14 are electrically connected to the positive and negative terminals of the DC link.

[0024] The following explanation uses cell unit 6A1 as an example to illustrate the connection relationship with the outside world. The same applies to the other cell units 6.

[0025] The diode converter 12 is a three-phase AC input type forward converter, and its input section is electrically connected to one group on the secondary side of the input transformer 5. The diode converter 12 converts the AC power input from the input transformer 5 into DC power by rectifying the AC. The smoothing capacitor 14 smooths the DC voltage after conversion.

[0026] The inverter 13 is an example of a single-phase AC output type power converter. The inverter 13 includes, for example, a semiconductor switching element 13S that converts DC power on the DC side into AC power, and a reverse-connected diode 13D that is connected in antiparallel to the semiconductor switching element 13S. The semiconductor switching element 13S is an example of a semiconductor switching element. The inverter 13 is connected so that the DC side is connected to the DC output of the diode converter 12, and the AC side is connected in series with the output of the motor 3 or another cell unit 6. The inverter 13 outputs the converted AC power to the first phase of the motor 3. The heat sink of this inverter 13 is provided with temperature sensors 13TSP and 13TSN. For example, the temperature sensor 13TSP is positioned to easily detect the temperature of the positive electrode side arm 13PA. The temperature sensor 13TSN is positioned to easily detect the temperature of the negative electrode side arm 13NA.

[0027] A resistor (not shown) may be provided to discharge the charge accumulated in the smoothing capacitor 14.

[0028] The cell unit control unit 6CUC generates signals to control the semiconductor switching elements constituting the diode converter 12 and inverter 13 based on control from the control device 7. The cell unit control unit 6CUC uses the generated signals to control the semiconductor switching elements constituting the diode converter 12 and inverter 13. The cell unit control unit 6CUC collects the DC voltage Vdc, the P-side element temperature Tp, the N-side element temperature Tn detected by the temperature sensors 13TSP and 13TSN, and outputs them via communication.

[0029] For example, the inverter 13, although its detailed internal connection configuration is omitted, is equipped with one or more semiconductor switching elements, which convert power through switching. The types of semiconductor switching elements may include IGBTs (Insulated Gate Bipolar Transistors), IEGTs (Injection Enhanced Gate Transistors), and MOSFETs (metal-oxide-semiconductor field-effect transistors). The inverter 13 functions as an inverter that generates AC power through control, and works in conjunction with other inverters connected to its output to supply current to the windings of the motor 3.

[0030] Figure 3A is a diagram of the configuration of the cell unit 6 of the embodiment. The cell unit 6 comprises semiconductor switching elements GAP and GBP on the positive side arm and semiconductor switching elements GA_N and GB_N on the negative side arm 13NA. Semiconductor switching elements GA_P and GA_N form a first leg, and semiconductor switching elements GB_P and GB_N form a second leg. Each semiconductor switching element in the cell unit 6 is configured as a single-phase full-bridge type. Note that the semiconductor switching elements GAP and GBP and semiconductor switching elements GA_N and GB_N described above are examples of the semiconductor switching element 13S mentioned above. Each semiconductor switching element shown in this figure is an IGBT, but is not limited to this.

[0031] Figure 3B is a diagram illustrating the output voltage of the cell unit 6 in the embodiment. The output voltage of the cell unit 6 can be changed by turning on two of each semiconductor switching element in the cell unit 6. For example, by turning on the semiconductor switching element GA_P on the positive side arm 13PA and the semiconductor switching element GB_N on the negative side arm 13NA, the output voltage of the cell unit 6 becomes a positive voltage. By turning on the semiconductor switching element GA_N on the negative side arm 13NA and the semiconductor switching element GB_P on the positive side arm 13PA, the output voltage of the cell unit 6 becomes a negative voltage. Alternatively, by turning on two semiconductor switching elements GA_P and GB_P on the positive side arm 13PA, or two semiconductor switching elements GA_N and GB_N on the negative side arm 13NA, the output voltage of the cell unit 6 becomes zero voltage.

[0032] There are two methods for controlling the semiconductor switching elements when stopping the cell unit 6. As described above, the cell unit 6 can be stopped by simultaneously turning on the two semiconductor switching elements GA_P and GB_P on the positive side arm 13PA, or the two semiconductor switching elements GA_N and GB_N on the negative side arm 13NA. For example, when the cell unit control unit 6CUC identifies that a predetermined condition has been met, it is preferable to control the two semiconductor switching elements GA_P and GB_P on the positive side arm 13PA, or the two semiconductor switching elements GA_N and GB_N on the negative side arm 13NA, to turn on simultaneously. This allows the cell unit 6 to be stopped by control from the cell unit control unit 6CUC.

[0033] By the way, even when the cell unit 6 is stopped, if current is still flowing, heat is generated due to losses in the semiconductor switching elements along the current path, and the longer the energizing time, the higher the temperature due to the heat generation.

[0034] Figure 4A is a diagram showing the configuration of the cell unit control unit 6CUC within the cell unit 6 of the embodiment. Figure 4B is a diagram illustrating the pause control of the cell unit 6 of the embodiment. As shown in Figure 4A, the cell unit control unit 61CUC of the cell unit 61 is equipped with a control signal α receiving port αI as a port for receiving signals from the outside, and a control signal α transmission port αO and a gate pulse output port GPO as ports for outputting signals to the outside.

[0035] The cell unit control unit 61CUC further comprises processing blocks 101, 102, 111 to 114.

[0036] The control signal α is supplied to the control signal α receiving port αI from the preceding cell unit 6 or control device 7. The inputs of processing blocks 101, 111 and 112 are connected to the control signal α receiving port αI.

[0037] Processing block 101 extracts a control command from the control signal α and calculates a control amount for control targeting this command. The output signal of the control amount is a pulse converted to a binary value by PWM control or the like. Processing block 102 (GB) limits the output of gate pulses corresponding to the pulses output by processing block 101 based on the PGON and NGON signals output by processing block 114. For example, when the logic of the PGON signal is logic 1 and the logic of the NGON signal is logic 0, processing block 102 fixes the output of the gate pulse to the positive side arm to a logic that makes the element of the positive side arm conduct, thereby limiting the output of the gate pulse to the negative side arm. When the logic of the PGON signal is logic 0 and the logic of the NGON signal is logic 1, processing block 102 fixes the output of the gate pulse to the negative side arm to a logic that makes the element of the negative side arm conduct, thereby limiting the output of the gate pulse to the positive side arm. In cases other than those described above, the processing block 102 outputs a gate pulse corresponding to the output signal of the processing block 101.

[0038] Processing block 111 detects that a control signal α is being supplied. Processing block 111 outputs a logic 0 when it detects that the supply of control signal α is being supplied, and outputs a logic 1 when it detects that the supply of control signal α has been interrupted for a predetermined time. The output of processing block 111 is connected to the input of processing block 114.

[0039] Processing block 112 extracts CELL_NUM and the pause stage command from the control signal α. Processing block 112 generates an updated CELL_NUM by adding 1 to it and outputs a signal to processing block 113 that replaces the CELL_NUM in the control signal α. This pause stage command is a signal that specifies which cell units 6 out of multiple cell units 6s should be put into a pause state in units of stages. If the pause stage command is constructed using binary logic, it is preferable to pre-determine whether this logical value is, for example, an odd or even stage. For example, processing block 112 determines the value of CELL_NUM based on the pause stage command as described above. For example, if the pause stage command is even and the value of CELL_NUM above is even, it generates a logic 1, and otherwise generates a logic 0. Processing block 112 supplies the result of the determination of the pause stage command to processing block 114.

[0040] The processing block 113 acquires the P-side element temperature Tp and the N-side element temperature Tn from temperature sensors 13TSp and 13TSN, respectively, generates a PN selection command, and outputs it to the processing block 114. The processing block 113 adds the P-side element temperature Tp, the N-side element temperature Tn, and the PN selection command to the control signal α and outputs it to the next stage.

[0041] Processing block 114 outputs a logical value of 1 as its initial value. When both processing block 111 and processing block 112 supply a logical value of 1, processing block 114 generates and outputs signals PGON and NGON based on the PN selection command from processing block 113. Processing block 114 outputs signals PGON and NGON with a predetermined delay period.

[0042] As shown in FIG. 4B, the processing block 113 generates a PN selection command based on the temperature difference between the P-side element temperature Tp and the N-side element temperature Tn. When the N-side element temperature Tn is lower than the P-side element temperature Tp, the processing block 113 generates a PN selection command to turn on the negative electrode side arm. When the N-side element temperature Tn is higher than the P-side element temperature Tp, the processing block 113 generates a PN selection command to turn on the positive electrode side arm.

[0043] Upon receiving the PN selection command, the processing block 114 ensures sufficient time so that excessive current does not flow through the cell unit 6 when switching the PN selection command. Further, the processing block 114 provides a delay time to suppress the switching frequency so that the switching does not become frequent due to the determination result of the PN selection command. Thereby, it is possible to suppress the occurrence of fluctuations in the PN selection command when the temperature difference between the P-side element temperature Tp and the N-side element temperature Tn is small.

[0044] (Modification examples of the processing block 113 and the processing block 114) The processing block 113 may determine the logical value of the PN selection command based on the detected value or estimated value of the temperature. The P-side element temperature Tp and the N-side element temperature Tn are examples of the detected value or estimated value of the temperature. For example, the P-side element temperature Tp is the estimated value or detected value of the temperature of the semiconductor switching element of the P-side arm. The N-side element temperature Tp is the estimated value or detected value of the temperature of the semiconductor switching element of the N-side arm. The output PN selection command takes a logical value.

[0045] For example, when the relationship between the P-side element temperature Tp and the N-side element temperature Tn is such that the P-side element temperature Tp is higher than the N-side element temperature Tn, the processing block 113 sets the PN selection command to the logical value for turning on the semiconductor switching element of the N-side arm. When the relationship between the P-side element temperature Tp and the N-side element temperature Tn is such that the P-side element temperature Tp is lower than the N-side element temperature Tn, the processing block 113 sets the PN selection command to the logical value for turning on the semiconductor switching element of the P-side arm.

[0046] Processing block 114 generates a gate control signal (P-side gate on signal) for the semiconductor switching element of the P-side arm and a gate control signal (N-side gate on signal) for the semiconductor switching element of the N-side arm based on the logical value of the PN selection command. Processing block 114 has a pulse delay function for extending the pulse width of the PN selection command, and does not generate a P-side gate on signal and an N-side gate on signal that are shorter than a predetermined time defined by at least the pulse delay function. Also, the P-side gate on signal and the N-side gate on signal do not both become logical values specifying an on state.

[0047] For the sake of simplicity of explanation, in the following description, various processes performed by each cell unit control unit 6CUC may be described as processes of each cell unit 6.

[0048] The control device 7 includes a control signal α transmission port for transmitting a control signal α for controlling the operating state of each cell unit 6 to the cell unit 63 (second slave station) among the cell units 6, and a control signal α reception port for receiving the control signal α from the cell unit 61 (first slave station) among the cell units 6. Explanation regarding these will be described later.

[0049] Configuration example of the power conversion system 1 of the embodiment: Referring to FIG. 5, a configuration example of the control system of the power conversion system 1 will be described. FIG. 5 is a diagram for explaining a configuration example of the control system of the power conversion system 1 of the embodiment. The system shown in FIG. 5 includes a control device 7 (cell control command board), three cell units 6 (61, 62, 63), and a daisy chain communication path 8 for sending signals of the control system. The control device 7 may be referred to as the master station, and the cell unit 6 may be referred to as the slave station. The range shown here exemplifies the range corresponding to the U-phase of the motor 3 among the phases of the motor 3 divided.

[0050] The daisy-chain communication path 8 connects the control device 7 to a plurality of cell units 6s. Reference numerals 81 to 84 are examples of connecting media that constitute the daisy-chain communication path 8. The connecting media 81 to 84 in this embodiment are isolated from each other. The daisy-chain communication path 8 is configured to communicate in at least one direction. For example, the daisy-chain communication path 8 is configured to send at least a control signal α.

[0051] For example, one end of the connecting medium 81 is connected to the control signal α transmission port of the control device 7, and the other end of the connecting medium 81 is connected to the control signal α receiving port of the cell unit 63. One end of the connecting medium 82 is connected to the control signal α transmission port of the cell unit 63, and the other end of the connecting medium 82 is connected to the control signal α receiving port of the cell unit 62. One end of the connecting medium 83 is connected to the control signal α transmission port of the cell unit 62, and the other end of the connecting medium 83 is connected to the control signal α receiving port of the cell unit 61. One end of the connecting medium 84 is connected to the control signal α transmission port of the cell unit 61, and the other end of the connecting medium 84 is connected to the control signal α receiving port of the control device 7.

[0052] As described above, the signals transmitted using the daisy-chain communication channel 8 include control signals α. These control signals α include control signals for controlling the power converters of each cell unit 6.

[0053] Before explaining the details of control using the daisy-chain communication channel 8, we will first describe the function of the cell unit 6 alone and the control of the electric motor 3.

[0054] As described above, the multiple cell units 6s are configured such that each cell unit 6 has a single-phase cell inverter 6IV (power converter) connected to an electric motor 3 (load device) to supply power to the electric motor 3. The multiple cell units 6s supply power to the electric motor 3 (load device) by switching between "operation" to supply power from the power converter and "stop" to interrupt the power supply from a specific cell unit 6 by setting the output voltage of that cell unit 6 to 0 voltage. Even if the output voltage of a specific cell unit 6 is set to 0 voltage and the power supply from that cell unit 6 is stopped, power from the other cell units 6 is supplied to the electric motor 3 (load device).

[0055] As described above, there are two methods for controlling the semiconductor switching elements when each cell unit 6 is put into a stopped state. However, if the control device 7 individually specifies the control for putting each cell unit 6 into a stopped state, the control becomes complicated. Therefore, in this embodiment, a method for simplifying the above control is proposed. Each scenario to which this control can be applied will be explained in turn by illustrating examples.

[0056] Scenario 1: Each cell unit control unit 6CUC (control unit) may control the operating state of its own cell unit 6 so that the temperature rise of the semiconductor switching elements within its own cell unit 6 is uniform, based on commands from the control device 7 of the higher-level device, the state of its own cell unit 6, or both commands from the higher-level device and the state of its own cell unit 6. For example, each cell unit control unit 6CUC may pause the switching of the semiconductor switching elements of the positive-side arm 13PA or the negative-side arm 13NA of its own cell unit 6 to set the AC output voltage to zero. In this case, each cell unit control unit 6CUC (control unit) may control either the semiconductor switching elements of the positive-side arm 13PA or the negative-side arm 13NA to the ON state and the other to the OFF state depending on the temperature of the semiconductor switching elements within its own cell unit 6. As a result, each cell unit control unit 6CUC (control unit) can output zero voltage from its own cell unit 6. Furthermore, the state of the self-cell unit 6 may be determined by using one or more of the following: the temperature of the semiconductor switching element, the magnitude of the conduction current of the semiconductor switching element, the polarity of the conduction current, or the continuous duration of the ON state of the semiconductor switching element.

[0057] Scenario 2: If the continuous ON state of one of the semiconductor switching elements, the positive electrode arm 13PA or the negative electrode arm 13NA, exceeds a predetermined time, each cell unit control unit 6CUC may switch one semiconductor switching element to the OFF state and the other semiconductor switching element to the ON state.

[0058] Scenario 3: Each cell unit control unit 6CUC may switch the semiconductor switching element that is in the ON state of the positive electrode side arm 13PA and the negative electrode side arm 13NA to the OFF state and the other semiconductor switching element to the ON state if the temperature of the ON semiconductor switching element of the positive electrode side arm 13PA is higher than the temperature of the other semiconductor switching element.

[0059] Scenario 4: Each cell unit control unit 6CUC may delay the timing of switching between the on and off states of the semiconductor switching element that is currently in the on state and the other semiconductor switching element by a predetermined time.

[0060] Next, we will explain the details of the control using the daisy-chain communication channel 8.

[0061] Multiple cell units 6s receive control commands for power converters from a master station, either directly or indirectly. In this embodiment, each cell unit 6 is daisy-chained with a wired communication path (daisy-chain communication path 8). The power conversion system 1 uses the daisy-chain communication path 8 for communication between the master station and the cell units 6, and between each cell unit 6. The power conversion system 1 uses this communication to control the power converters within each cell unit 6, thereby supplying power to the load devices connected to the power converters within each cell unit 6. In supplying power, the power conversion system 1 switches between "operation" to supply power from the power converters and "stop" to interrupt the power supply.

[0062] (Control using control signal α) The control device 7 and each cell unit 6 send a control signal α to each cell unit 6 using the daisy-chain communication path 8.

[0063] For the sake of explanation, in the following, the cell that directly receives the control signal α output by the control device 7 will be referred to as the uppermost cell unit, and the cell that sends the control signal α back to the control device 7 will be referred to as the lowermost cell unit. The lowermost cell unit is an example of a first slave station, and the uppermost cell unit is an example of a second slave station. In Figure 5, the uppermost cell unit is cell unit 63, and the lowermost cell unit is cell unit 61.

[0064] (Control and status monitoring using control signal α) Of the pair of cell units 6 (slave stations) facing each other across each wiring section, the cell unit 6 on the transmitting side of the control signal α identifies its own number (hereinafter simply referred to as MYNUM), which is defined as the cell stage count CELL_NUM (hereinafter simply referred to as CELL_NUM). The cell unit 6 on the transmitting side of the control signal α includes this CELL_NUM in the control signal α.

[0065] The control signal α contains the value of CELL_NUM as its data. Each cell unit 6 adds 1 to the CELL_NUM of the control signal α received from the upper row (CELL_NUM++) and sets this value as identification information for relatively identifying its own position in MYNUM, and transmits its own MYNUM as CELL_NUM to the lower row. The value of CELL_NUM corresponds to the number of times the control signal α has been relayed by cell unit 6. The above relationship is shown in the following equations (1) and (2). These equations indicate that the result of the operation on the right side is set to the value of the variable on the left side.

[0066] MYNUM=CELL_NUM+1 (1) CELL_NUM=MYNUM (2)

[0067] According to the above embodiment, the power converter can control the AC output voltage of a single-phase full-bridge type cell unit to zero voltage. The power converter comprises a single-phase full-bridge type cell unit and a control unit. When the control unit pauses the switching of the semiconductor switching elements of the positive-side arm 13PA or the negative-side arm 13NA of the cell unit to set the AC output voltage to zero voltage, it controls one of the semiconductor switching elements of the positive-side arm 13PA and the negative-side arm 13NA to the ON state and the other to the OFF state according to the temperature of the semiconductor switching elements in the cell unit. This improves the convenience of the power converter.

[0068] In the power conversion system equipped with the power conversion device of the above embodiment, the power conversion device including a plurality of cell units 6s is configured as a multilevel inverter having a single-phase circuit in which a plurality of single-phase full-bridge type cell units 6s are connected in series, with a number of single-phase circuits corresponding to the number of phases. Each cell unit 6 is associated with a cell unit control unit 6CUC that controls each cell unit 6. Each cell unit control unit 6CUC receives commands from the control device 7 (higher-level device).

[0069] For example, the transmission system for the control signals of each cell unit control unit 6CUC is daisy-chained for each group of cell units 6s in which the AC sides of multiple cell units 6s are connected in series. In this case, each cell unit control unit 6CUC identifies the cell unit 6 to be put into a paused state from among the multiple cell units 6s, according to its position within the daisy-chain connection and a command from the control device 7.

[0070] Each cell unit control unit 6CUC identifies the cell unit 6 to be put into a paused state from among the multiple cell units 6s based on whether or not it meets the conditions specified by the command word from the control device 7.

[0071] According to at least one embodiment described above, the power converter can control the AC output voltage of a single-phase full-bridge type cell unit to zero voltage. The power converter comprises a single-phase full-bridge type cell unit and a control unit. When the control unit pauses the switching of the semiconductor switching elements of the positive or negative electrode arm of the cell unit to set the AC output voltage to zero voltage, it controls one of the semiconductor switching elements of the positive or negative electrode arm to be in an ON state and the other to be in an OFF state according to the temperature of the semiconductor switching elements in the cell unit. This enhances the convenience of the power converter.

[0072] In the power conversion system 1 of the embodiment described above, some or all of the functional units of the control device 7 and the cell unit control unit 6CUC are software functional units realized by, for example, a program (computer program, software component) stored in the computer's memory being executed by the computer's processor (hardware processor). Some or all of the functional units of the control device 7 and the cell unit control unit 6CUC may be realized by hardware such as an LSI (Large Scale Integration), ASIC (Application Specific Integrated Circuit), or FPGA (Field-Programmable Gate Array), or by a combination of software functional units and hardware.

[0073] Although several embodiments have been described above, the configuration of the embodiments is not limited to the examples above. For example, the configurations of each embodiment may be combined with each other and can be applied to components that have not been described. For example, the description of the first phase, U phase, of the electric motor 3 above may be applied to the second phase, V phase, and the third phase, W phase, of the electric motor 3.

[0074] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

[0075] Furthermore, the daisy-chain communication channel 8 may be a communication channel using electrical signals or a communication channel using optical signals.

[0076] (Note) This embodiment can be configured as follows: (1) One embodiment is a power conversion device capable of controlling the AC output voltage of a single-phase full-bridge type cell unit to zero voltage, comprising: a single-phase full-bridge type cell unit; and a control unit that, when the switching of the semiconductor switching elements of the positive-side arm or the negative-side arm of the cell unit is suspended to set the AC output voltage to zero voltage, controls one of the semiconductor switching elements of the positive-side arm and the negative-side arm to an ON state and the other to an OFF state according to the temperature of the semiconductor switching elements in the cell unit. (2) In the power conversion device of (1) above, the control unit may control one of the semiconductor switching elements of the positive-side arm and the negative-side arm to an ON state in order to output zero voltage, based on a command from a higher-level device, the state of its own cell unit, or both, so that the temperature rise of the semiconductor switching elements is uniform. (3) In the power conversion device described in (1) above, the state of the self-cell unit may be any of the following: the temperature of the semiconductor switching element, the magnitude of the conduction current of the semiconductor switching element, the polarity of the conduction current, or the continuous duration of the ON state of the semiconductor switching element. (4) In the power conversion device described in (1) above, the control unit may switch one of the semiconductor switching elements of the positive side arm and the negative side arm to the OFF state and the other semiconductor switching element to the ON state if the continuous duration of the ON state of one of the semiconductor switching elements of the positive side arm and the negative side arm exceeds a predetermined time. (5) In the power conversion device described in (1) above, the control unit may switch one of the semiconductor switching elements of the positive side arm and the negative side arm that is in the ON state to the OFF state and the other semiconductor switching element to the ON state if the temperature of the one semiconductor switching element that is in the ON state is higher than the temperature of the other semiconductor switching element. (6) In the power conversion device described in (1) above, the control unit may delay the timing of switching between the on state and the off state of one semiconductor switching element and the other semiconductor switching element by a predetermined time.(7) A power conversion system according to one embodiment includes the power conversion device described in (1) above, wherein the power conversion device is configured as a multilevel inverter having a number of single-phase circuits for each phase in which a plurality of single-phase full-bridge type cell units are connected in series, and each cell unit is associated with a control unit that controls the respective cell unit, and each control unit may receive commands from a higher-level device. (8) In the power conversion system described in (7) above, if the transmission system for the control signals of each control unit is daisy-chained for each group of cell units in which the AC sides of the plurality of cell units are connected in series, each control unit may identify the cell unit to be shut down from among the plurality of cell units according to its position in the daisy-chain connection and the command from the higher-level device. (9) In the power conversion system described in (7) above, each control unit may identify the cell unit to be shut down from among the plurality of cell units based on whether or not it meets the conditions specified by the command word from the higher-level device.

[0077] 1...Power conversion system, 3...Electric motor, 6...Cell unit (power conversion device), 6s...Multiple cell units, IV...Single-phase cell inverter (power conversion device), 6CUC...Cell unit control unit (control unit), 7...Control device (higher-level device), 8...Daisy-chain communication channel

Claims

1. A power conversion device capable of controlling the AC output voltage of a single-phase full-bridge type cell unit to zero voltage, comprising: a single-phase full-bridge type cell unit; and a control unit that, when the switching of the semiconductor switching elements of the positive-side arm or the negative-side arm of the cell unit is suspended to set the AC output voltage to zero voltage, controls one of the semiconductor switching elements of the positive-side arm and the negative-side arm to an ON state and the other to an OFF state according to the temperature of the semiconductor switching elements in the cell unit.

2. The power conversion device according to claim 1, wherein the control unit controls either the semiconductor switching element of the positive electrode arm or the negative electrode arm to the ON state in order to output a zero voltage so that the temperature rise of the semiconductor switching elements is uniform, based on a command from a higher-level device, the state of the self-cell unit, or both.

3. The power conversion device according to claim 1, wherein the state of the self-cell unit is any of the temperature of the semiconductor switching element, the magnitude of the conduction current of the semiconductor switching element, the polarity of the conduction current, or the continuous duration of the ON state of the semiconductor switching element.

4. The power conversion device according to claim 1, wherein the control unit switches one of the semiconductor switching elements, the positive side arm and the negative side arm, to the OFF state and the other semiconductor switching element to the ON state if the continuous ON state of one of the semiconductor switching elements exceeds a predetermined time.

5. The power conversion device according to claim 1, wherein the control unit switches one semiconductor switching element to the OFF state and the other semiconductor switching element to the ON state when the temperature of one of the positive-side arm and the negative-side arm that is in the ON state is higher than the temperature of the other semiconductor switching element.

6. The power conversion device according to claim 5, wherein the control unit delays the timing of switching between the on state and the off state of one semiconductor switching element and the other semiconductor switching element by a predetermined time (suppressing the switching frequency).

7. A power conversion device as described in claim 1, wherein the power conversion device is configured as a multilevel inverter having a number of single-phase circuits for each phase, each of which is a single-phase full-bridge type cell unit connected in series, and each cell unit is associated with a control unit that controls the cell unit, and each control unit is a power conversion system that receives commands from a higher-level device.

8. The power conversion system according to claim 7, wherein, when the transmission system for the control signals of each control unit is daisy-chained for each group of cell units in which the AC sides of the plurality of cell units are connected in series, each control unit identifies the cell unit to be shut down from among the plurality of cell units in accordance with the position within the daisy-chain connection and a command from the higher-level device.

9. The power conversion system according to claim 7, wherein each control unit identifies the cell unit to be shut down from among the plurality of cell units based on whether or not it meets the conditions specified by the command word from the higher-level device.

10. A control method for a power converter capable of controlling the AC output voltage of a single-phase full-bridge type cell unit to zero voltage, the method comprising, when the switching of the semiconductor switching elements of the positive-side arm or the negative-side arm of the single-phase full-bridge type cell unit is suspended to set the AC output voltage to zero voltage, controlling one of the semiconductor switching elements of the positive-side arm and the negative-side arm to an ON state and the other to an OFF state according to the temperature of the semiconductor switching elements in the cell unit.

11. The control method according to claim 10, which includes controlling either the semiconductor switching element of the positive electrode arm or the negative electrode arm to the ON state in order to output a zero voltage so that the temperature rise of the semiconductor switching elements is uniform, based on a command from a higher-level device, the state of the self-cell unit, or both.

12. The control method according to claim 10, wherein the state of the self-cell unit is any of the temperature of the semiconductor switching element, the magnitude of the conduction current of the semiconductor switching element, the polarity of the conduction current, or the continuous duration of the ON state of the semiconductor switching element.

13. The control method according to claim 10, which includes switching one of the semiconductor switching elements, the positive side arm and the negative side arm, to the off state and the other semiconductor switching element to the on state if the continuous time of the on state of one of the semiconductor switching elements exceeds a predetermined time.

14. The control method according to claim 10, which includes switching one semiconductor switching element to the OFF state and the other semiconductor switching element to the ON state when the temperature of one of the positive electrode side arm and the negative electrode side arm that is in the ON state is higher than the temperature of the other semiconductor switching element.

15. The control method according to claim 14, further comprising delaying the timing of switching between the on state and the off state of one semiconductor switching element and the other semiconductor switching element by a predetermined time.

16. A control method according to claim 10, wherein the power converter is configured as a multilevel inverter having a number of single-phase circuits for each phase, in which a plurality of single-phase full-bridge type cell units are connected in series, each cell unit is associated with a control unit that controls the respective cell unit, and the control method includes each control unit receiving commands from a higher-level device.

Images