Motor drive device

Abstract

An electric motor drive device of an embodiment includes an electric motor, a main circuit, a current sensor, and a control unit. The electric motor includes a plurality of windings. The main circuit converts electric power of an alternating-current power supply into alternating-current electric power and supplies the alternating-current electric power to the plurality of windings, respectively. The current sensor detects load currents flowing to the plurality of windings, respectively. The control unit controls the main circuit on the basis of current values detected by the current sensor. The control unit controls an amount of electric power supplied from the main circuit to the electric motor on the basis of a magnitude of the load current associated with detection of an under-voltage state of the alternating-current power supply using a conversion rule that defines an index value relative to the magnitude of the load current flowing to the plurality of windings from the main circuit.

Description

Technical Field

[0001] Embodiments of the present invention relate to electric motor drive devices. Background Technology

[0002] The motor drive unit converts the power supplied from the AC power source to drive a multiphase AC motor (simply referred to as a motor). Due to the instability of the AC power supply voltage, the motor drive unit sometimes detects a voltage drop (undervoltage condition) on the AC power supply side. Power outages and momentary voltage drops are examples of undervoltage conditions. If the motor drive unit detects this voltage drop, it temporarily interrupts the AC power supply to the motor. If the voltage drop disappears, it resumes the AC power supply. However, if the motor drive unit resumes the AC power supply as described above, causing the motor to restart, it results in a drastic change in the load on the motor drive unit, potentially causing an overcurrent that affects both the motor drive unit and the operation of the motor.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2013-039033 Summary of the Invention

[0006] The problem that the invention will solve

[0007] The purpose of this invention is to provide an electric motor drive device that improves the convenience of resuming electric motor operation.

[0008] Methods for solving problems

[0009] The electric motor drive device of this embodiment includes an electric motor, a main circuit, a current sensor, and a control unit. The electric motor has multiple windings, and the main circuit converts AC power into AC power and supplies the AC power to the multiple windings respectively. The current sensor detects the load current flowing to each of the multiple windings respectively. The control unit controls the main circuit based on the current values ​​detected by the current sensors. The control unit uses a transformation rule that defines an index value relative to the magnitude of the load current flowing from the main circuit to the multiple windings, and controls the electrical power supplied from the main circuit to the electric motor based on the magnitude of the load current, which is associated with the detection of an undervoltage state in the AC power supply. Attached Figure Description

[0010] Figure 1 This is a configuration diagram of the electric motor drive device according to the implementation method.

[0011] Figure 2This is a diagram showing the configuration of the control unit in the implementation method.

[0012] Figure 3 This is a schematic diagram of the main circuit configuration for the implementation method.

[0013] Figure 4 This is a configuration diagram of the speed control unit in the implementation method.

[0014] Figure 5 This is a configuration diagram of the modulation rate conversion unit in the implementation method.

[0015] Figure 6 This is a diagram used to illustrate the transformation rules of the implementation method.

[0016] Figure 7 This is a diagram of a table used to illustrate the transformation rules for implementing the method.

[0017] Figure 8 This is a flowchart illustrating the general steps of the process for determining the DC voltage reference in the implementation method.

[0018] Figure 9 This is a timing diagram of a power outage occurring in the implementation method.

[0019] Figure 10 This is a schematic diagram of an FPGA that includes a portion of the modulation rate conversion unit in the variant example.

[0020] Figure 11A This is a flowchart illustrating the process of determining the DC voltage reference VDC_F0 in an FPGA based on a variant example.

[0021] Figure 11B This is a flowchart illustrating the process of determining the DC voltage reference VDC_F0 in an FPGA based on a variant example. Detailed Implementation

[0022] Hereinafter, the electric motor drive device according to the embodiments will be described with reference to the accompanying drawings.

[0023] In the following description, the variable speed motor drive unit will be referred to simply as a motor drive unit. Furthermore, components with the same or similar functions will be labeled with the same reference numerals. Also, repeated descriptions of these components will sometimes be omitted. Additionally, electrical connections will sometimes be referred to simply as "connections". The "PWM control" shown in the following description refers to Pulse Width Modulation control, sometimes simply referred to as PWM. PWM control can apply a carrier comparison PWM method using a triangular wave or sawtooth wave carrier. "Fundamental wave" refers to the lowest frequency component in a specific AC voltage waveform. "AC power supply undervoltage state" in the implementation refers to a state where the effective value of the AC voltage does not meet a specified value, and also includes so-called power outage states, instantaneous voltage drops, etc. "Speed" in the implementation refers to angular velocity, and the angular velocity of the motor rotor will be referred to simply as "speed".

[0024] Figure 1 This is a configuration diagram of the electric motor drive device 1 according to the embodiment.

[0025] The motor drive unit 1 includes, for example, a motor 2, a transformer 3, a rectifier 4, a capacitor 5, an inverter 6, a DC voltage sensor 7, a current sensor 8, an AC voltage sensor 9, and a control unit 10.

[0026] The electric motor 2 (M) has multiple windings. For example, the electric motor 2 has three windings supplied with three-phase AC power. The three windings are connected in a star (Y) configuration within the electric motor 2. The electric motor 2 can be, for example, an induction motor, but is not limited thereto. The various parts of the electric motor drive unit 1 drive the electric motor 2 based on AC power supplied from the AC power source G.

[0027] Transformer 3 converts the voltage (called the power supply voltage) of the AC power supplied from AC power source G into a specified voltage. An instrument transformer VT is installed on the primary side of transformer 3. The instrument transformer VT detects the AC voltage based on the power supply voltage on the primary side of transformer 3 and feeds back the input voltage to the VAC output.

[0028] Rectifier 4 rectifies the AC power supplied from AC power source G and outputs the desired voltage (DC voltage) between the negative terminal N and the positive terminal P of the DC link connected to the output. For example, capacitor 5 smooths the voltage between the negative terminal N and the positive terminal P of the DC link. Inverter 6 converts the DC power supplied via the DC link into AC power and outputs it.

[0029] DC voltage sensor 7, for example, detects the voltage applied to the DC link and outputs a corresponding DC voltage feedback VDC. For instance, DC voltage sensor 7 can also detect the voltage between the negative terminal N and the positive terminal P of the DC link.

[0030] Current sensor 8 detects the phase current of each phase of the multiphase AC power flowing to the output side of inverter 6 and outputs the corresponding current feedback. Variable transformer (CT) is an example of current sensor 8.

[0031] AC voltage sensor 9 detects the line voltage (voltage between two lines) of each phase of the multi-phase AC inverter 6 at the output side. For example, AC voltage sensor 9 detects the U-phase line LU of a three-phase AC inverter. Figure 3 ) and V phase line LV ( Figure 3 The AC voltage sensor 9 detects the AC voltage between the two phase lines LV and W phase lines LW, and uses this voltage as the output voltage feedback V_UV_FBK. Figure 3 The AC voltage between the two lines is used as the output voltage feedback V_VW_FBK output.

[0032] The control unit 10 sends a gate pulse GP to the inverter 6 based on the speed reference SP_REF to control the power conversion amount of the inverter 6. For example, the control unit 10 can control the inverter 6 based on the detection results of each sensor, including the DC voltage sensor 7, the current sensor 8, the AC voltage sensor 9, and the instrumentation variable frequency drive VT. In the following description, an example of the control unit 10 performing VVVF (variable voltage variable frequency) control on the motor 2 will be described.

[0033] Figure 2 This is a configuration diagram of the control unit 10 in the embodiment.

[0034] The control unit 10 includes a PWM control unit 11 (marked as PWM in the figure), a DQ inverse conversion unit 12, a DQ conversion unit 13, an absolute value calculation unit 14 (marked as ABS in the figure), a speed control unit 15 (marked as ASR in the figure), a current control unit 17 (marked as ACR in the figure), and a monitoring unit 19.

[0035] The PWM control unit 11 generates gate pulses GP for controlling the inverter 6 through PWM control based on the voltage command ER and the triangular wave carrier Car, which will be described later.

[0036] The DQ inverse transformation unit 12 uses a defined operation on the reference phase QO to transform a signal in a rotating coordinate system (called the dq coordinate system) with mutually orthogonal d-axis and q-axis into a stationary coordinate system (called the uvw coordinate system) with three axes corresponding to the uvw phases. The voltage command ER is an example of a signal in the uvw coordinate system.

[0037] The DQ transformation unit 13 transforms the signal in the uvw coordinate system into a signal in the dq coordinate system by using the prescribed operation of the reference phase QO. The transformation process performed by the DQ inverse transformation unit 12 is the opposite of the transformation process performed by the DQ transformation unit 13.

[0038] For example, the DQ conversion unit 13 generates d-axis current feedback ID_FBK and q-axis current feedback IQ_FBK based on the instantaneous values ​​of the phase currents detected by the current sensor 8. The instantaneous values ​​of the phase currents detected by the current sensor 8 are represented by IU_F, IV_F, and IW_F. Alternatively, they can be at least two of the three phase values.

[0039] The absolute value calculation unit 14 generates a current value representing the magnitude of the current detected by the current sensor 8. The output current I1_F is an example of this current value. The output current I1_F can be the root of the sum of the squares of the d-axis current feedback ID_FBK and the q-axis current feedback IQ_FBK.

[0040] The speed control unit 15 generates a speed correction signal EQ_REF corrected to the speed reference SP_REF, and a reference phase QO, based on the speed reference SP_REF specifying the speed of the motor 2, the line voltage detected by the AC voltage sensor 9, and the output current I1_F. Output voltage feedback V_UV_FBK and output voltage feedback V_VW_FBK are examples based on the voltage between the two lines detected by the AC voltage sensor 9. The reference phase QO corresponds to the angle between the reference axis of the dq coordinate system and the reference axis of the uvw coordinate system. The details of the speed control unit 15 will be described later. Furthermore, when the motor 2 is an induction motor, the speed control unit 15 can infer the slip angular frequency and correct the reference phase QO based on this slip angular frequency.

[0041] The current control unit 17 generates the d-axis voltage reference VD_REF and the q-axis voltage reference VQ_REF based on the speed correction signal EQ_REF, the d-axis current feedback ID_FBK, the q-axis current feedback IQ_FBK, and the reference phase QO. The d-axis voltage reference VD_REF and the q-axis voltage reference VQ_REF become the input signals of the DQ inverse converter unit 12.

[0042] The monitoring unit 19 monitors the control status based on the output current I1_F, the detection results of the primary side voltage of transformer 3 (i.e., AC voltage VAC, DC voltage VDC, speed reference SP_REF, and reference phase QO).

[0043] For example, monitoring unit 19 detects the power outage (undervoltage state) and restoration (elimination of undervoltage state) of AC power supply G based on AC voltage VAC, and outputs restart signal A and restart signal B (described later) according to the aforementioned states. Monitoring unit 19 detects whether the speed of motor 2 is following the speed reference SP_REF based on the speed reference SP_REF and the reference phase QO. For example, monitoring unit 19 can also determine that the speed of motor 2 is following the speed reference SP_REF if the deviation between the speed reference SP_REF and the reference phase QO is smaller than a specified value for more than a specified time. Monitoring unit 19 can release restart signal A based on the determination that the speed of motor 2 has returned to following the speed reference SP_REF. Additionally, monitoring unit 19 can release restart signal B after a specified time has elapsed since the power restoration was detected.

[0044] Reference Figure 3 The main circuit 20 of the implementation method will be described. Figure 3 This is a configuration diagram of the main circuit 20 in the implementation method.

[0045] The main circuit 20 includes, for example, a transformer 3, a rectifier 4, a capacitor 5, an inverter 6, a DC voltage sensor 7, a current sensor 8, and an AC voltage sensor 9. Alternatively, the DC voltage sensor 7, the current sensor 8, and the AC voltage sensor 9 can be configured externally to the main circuit 20.

[0046] For example, the main circuit 20 is configured independently for each phase, namely U-phase, V-phase, and W-phase. Figure 1 The diagrams showing each configuration are labeled with the characters U, V, and W to indicate the configuration of each phase. Furthermore, the positive terminal configuration is identified by adding the character P, and the negative terminal configuration by adding the character N. Additionally, configurations that are equivalent to DC polarity are identified by adding the characters A or B.

[0047] Here, we will use phase U as an example for explanation.

[0048] Transformer 3U, for example, has a primary winding and two secondary windings. The primary winding is connected to the AC side of rectifier 4UA via connecting terminals. The secondary winding is connected to the AC side of rectifier 4UB via connecting terminals. The DC sides of rectifier 4UA and rectifier 4UB are connected in series, with their ends connected to the positive and negative terminals of the U-phase DC link, respectively. Rectifiers 4UA and 4UB rectify the AC power supplied to them.

[0049] In the attached diagram, UC represents the neutral point of the U-phase DC system. The potential of the neutral point UC is the midpoint between the positive and negative terminals of the U-phase DC link. The terminals of capacitor 5UP are connected to the positive terminal of the U-phase DC link and the neutral point UC. The terminals of capacitor 5UN are connected to the negative terminal of the U-phase DC link and the neutral point UC.

[0050] Inverter 6, for example, includes bridge arms 6UA and 6UB, forming a full-bridge configuration. Inverter 6 can also be configured as a single-phase output type with bridge arms 6UA and 6UB. Each bridge arm can be either an NPC-type three-level type or, alternatively, a two-level type. Each bridge arm 6UA and 6UB has multiple switching elements. These multiple switching elements can, for example, be of the same type. The type of switching element is not limited. Examples of switching elements include IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors). A freewheeling diode connected in reverse parallel can also be provided in the switching element.

[0051] For example, when bridge arms 6UA and 6UB are NPC (Neutral-Point-Clamped) type, they are connected to the positive and negative terminals of the DC link of phase U and the neutral point UC, respectively. The output terminal of bridge arm 6UA is connected to terminal TU. The output terminal of bridge arm 6UB is connected to the AC side neutral point ACN. The U-phase winding of motor 2 is connected to terminal TU.

[0052] A current sensor 8U is provided on the connection line LU from the output terminal of bridge arm 6UA to the terminal TU. The current sensor 8U detects the current flowing in the connection line LU and the U-phase winding of motor 2.

[0053] Transformer 3U, rectifier 4UA, rectifier 4UB, capacitor 5UP, capacitor 5UN, neutral point UC, bridge arm 6UA, bridge arm 6UB, terminal TU, current sensor 8U, and connecting line LU are related to U.

[0054] The transformer is 3V, the rectifier is 4VA, the rectifier is 4VB, the capacitor is 5VP, the capacitor is 5VN, the neutral point is VC, the bridge arm is 6VA, the bridge arm is 6VB, the terminal is TV, the current sensor is 8V, and the connecting wire is LV, which is related to the V phase. The structure of the V phase is the same as that of the U phase. For detailed explanation, please refer to the explanation of the U phase.

[0055] The components are: transformer 3W, rectifier 4WA, rectifier 4WB, capacitor 5WP, capacitor 5WN, neutral point WC, bridge arm 6WA, bridge arm 6WB, terminal TW, current sensor 8W, and connecting wire LW, all related to phase W. The structure of phase W is identical to that of phase U; for detailed instructions, refer to the instructions for phase U.

[0056] The composition of those that do not belong to the above-mentioned phases will be explained.

[0057] AC voltage sensor 9 is connected to connecting lines LU, LV, and LW respectively, for example, to detect the voltage between connecting lines LU and LV, LV and LW, and LW and LU. As described above, at least two of these voltages can be output.

[0058] In addition, the input voltage feedback VAC can include input voltage feedbacks VCU, VCV, and VACW output from the instrumentation variable instruments VTU, VTV, and VTW of each phase, respectively.

[0059] Reference Figure 4 The speed control unit 15 of the embodiment will be described. Figure 4 This is a configuration diagram of the speed control unit 15 according to the embodiment. The speed control unit 15 receives the speed reference SP_REF supplied from the control device described above.

[0060] For example, the speed control unit 15 includes a frequency correction unit 151, a speed phase setting unit 152, a frequency range adjustment unit 153, a DQ conversion unit 154, a VF control unit 155, a modulation rate conversion unit 156, a voltage feedback adjustment unit 157, and a magnetic flux control unit 159.

[0061] The frequency correction unit 151 corrects the velocity reference SP_REF in a way that avoids frequencies that would cause mechanical resonance. For example, the frequency correction unit 151 includes calculation modules 151a to 151d. Calculation module 151a internally has a frequency limit table defining a limited frequency band and performs a velocity estimation calculation, comparing the estimated velocity (frequency) with the frequency limit table to correct the velocity reference SP_REF in a way that avoids frequencies defined in the frequency limit table. This correction is called a frequency jump. The calculation process used to estimate the velocity can use known calculation methods.

[0062] Operational modules 151b and 151c limit the rate of change by absorbing sharp changes in the signal output from operational module 151a. For example, the characteristics of operational module 151c are set to make the system response slower compared to the characteristics of operational module 151b. More specifically, the characteristics of operational module 151c can be determined so that signals that change sharply relative to the response characteristics of motor 2 are not supplied to motor 2. Operational module 151d is a switch. Operational module 151d selects one of the outputs of operational modules 151b and 151c based on the restart signal A and outputs the selected signal. For example, operational module 151d selects the output of operational module 151b when the logic value of restart signal A is 0, and selects the output of operational module 151c when the logic value of restart signal A is 1. The logic value of restart signal A is 0 when it is different from that at restart time, and 1 at restart time.

[0063] The speed phase setting unit 152 includes calculation modules 152a to 152d. Calculation module 152a sets the speed reference to compensate for the minimum speed of the motor 2 based on the speed reference corrected by the frequency correction unit 151. Calculation module 152b limits the upper limit of the speed reference corrected by the frequency correction unit 151. Calculation module 152c is a switch. Based on the restart signal B, calculation module 152c selects one of the speed reference SP_R from calculation module 152b and the speed reference SP_RSU from the VF control unit 155 (described later), and outputs the selected signal as the speed reference SP_R_VF. For example, when the logic value of the restart signal B is 0, calculation module 152c selects the speed reference SP_R; when the logic value of the restart signal B is 1, it selects the speed reference SP_RSU and outputs it as the speed reference SP_R_VF. The logic value of the restart signal A is 0 when it differs from the normal value during restart, and 1 during restart. The computation module 152d integrates the velocity reference SP_R_VF to generate the reference phase QO.

[0064] The frequency range adjustment unit 153 includes arithmetic modules 153a to 153d. Arithmetic module 153a is a multiplier. Arithmetic module 153a multiplies the velocity reference SP_R_VF by the flux reference FL_R and outputs the result. Arithmetic module 153b limits the rate of change by absorbing abrupt changes in the signal output by arithmetic module 153a. Arithmetic module 153c selects one of the output values ​​of arithmetic module 153a and arithmetic module 153b based on the restart signal B, and outputs the selected signal as the velocity reference EQ_REF0. For example, arithmetic module 153c selects the output value of arithmetic module 153a when the logic value of the restart signal B is 0, and selects the output value of arithmetic module 153b when the logic value of the restart signal B is 1, and generates the velocity reference EQ_REF0. Arithmetic module 153d is an adder. The arithmetic module 153d adds the speed reference EQ_REF0 to the correction signal VSM_EQ_PR (described later) and outputs the result as the speed reference EQ_REF.

[0065] The DQ conversion unit 154 acquires at least two line voltages of the two phases detected by the AC voltage sensor 9 and generates line voltages of each axis component in the uvw coordinate system. The DQ conversion unit 154 performs DQ conversion on the line voltages of each axis component according to the reference phase QO, thereby outputting the d-axis voltage feedback ED_FBK and q-axis voltage feedback EQ_FBK of each axis component in the dq coordinate system.

[0066] The VF control unit 155 includes arithmetic modules 155a to 155c. Arithmetic module 155a performs, for example, a PI operation with a defined transfer characteristic. This is called PI control. In other words, PI control extracts the low-frequency component from the frequency band of the voltage feedback and extracts its phase component. For example, arithmetic module 155a obtains the d-axis voltage feedback ED_FBK and the q-axis voltage feedback EQ_FBK, and performs a PI operation on the magnitude (amplitude) of the obtained voltage feedback, for example, with a defined gain characteristic (transfer characteristic) depending on the frequency, generating a signal VF_IPLL_OUT. Arithmetic module 155b obtains at least two line voltages of two phases detected by the AC voltage sensor 9, and based on this, detects the fundamental frequency of the AC, generating a signal FSEEK_SP_F representing the detected frequency. Arithmetic module 155c is an adder that adds the signal VF_IPLL_OUT to the signal FSEEK_SP_F to generate a speed reference SP_RSU. This speed reference SP_RSU is used during startup.

[0067] For example, the signal VF_IPLL_OUT generated by the above calculation changes in accordance with the magnitude (amplitude) of the output voltage feedback, represented as d-axis voltage feedback ED_FBK and q-axis voltage feedback EQ_FBK. The signal FSEEK_SP_F changes in accordance with the frequency of the fundamental frequency of the output voltage feedback. For example, it can be specified that when the frequency of the fundamental frequency of the output voltage feedback increases, the value of the signal FSEEK_SP_F becomes larger, and when the frequency of the fundamental frequency of the output voltage feedback decreases, the value of the signal FSEEK_SP_F becomes smaller. However, this is not limited to this, and known VVVF control methods can also be used.

[0068] The modulation rate conversion unit 156 generates the q-axis voltage feedback EQ_FBK0 based on the q-axis voltage feedback EQ_FBK and the output current I1_F. Details of the modulation rate conversion unit 156 will be described later.

[0069] The voltage feedback adjustment unit 157 includes arithmetic modules 157a and 157b. Arithmetic module 157a is a switch. The input side of arithmetic module 157a is connected to the output of modulation rate conversion unit 156, and the output side of arithmetic module 157a is connected to the input of arithmetic module 157b. Arithmetic module 157a switches between ON and OFF based on a restart signal B, controlling whether to output the signal from its input side to its output side. For example, when the logic value of the restart signal B is 0, arithmetic module 157a becomes OFF, disconnecting its input and output sides. When the logic value of the restart signal B is 1, arithmetic module 157a becomes ON, connecting its input and output sides. Arithmetic module 157b receives the output of arithmetic module 157a and outputs a corresponding correction signal VSM_EQ_PR. In addition, when the arithmetic module 157a is turned off, the input bias of the arithmetic module 157b is the initial value PRESET, and the signal of the magnitude corresponding to the initial value PRESET is output as the correction signal VSM_EQ_PR.

[0070] The flux control unit 159 generates a flux reference FL_R for controlling the magnitude of the flux in the motor 2. The flux control unit 159 can also be configured to implement weak flux control, etc., and can be implemented in a conventional manner.

[0071] Figure 5 This is a configuration diagram of the modulation rate conversion unit 156 in the embodiment.

[0072] The modulation rate conversion unit 156 includes arithmetic modules 156a to 156e.

[0073] The calculation module 156a infers a DC voltage reference VDC_F0 relative to the output current I1_F. The calculation module 156a may have pre-defined transformation rules for inferring the DC voltage reference VDC_F0 based on the output current I1_F. These transformation rules can be tabulated, written into software, or formed as a combination of both.

[0074] The arithmetic module 156b is a multiplier that multiplies the two constant values ​​described below and outputs the product. The two constant values ​​are the rated value of the q-axis voltage CS_EQUIP_VOLT and the rated value of the DC voltage CS_DC_VOLT. The arithmetic module 156c is a divider that divides the product calculated by the arithmetic module 156b by the DC voltage reference VDC_F0 to determine the modulation ratio k0. In addition, the relationship between the modulation ratio k0 and other variables is shown in equation (1).

[0075] k0=((CS_EQUIP_VOLT)×(CS_DC_VOLT)) / (VDC_F0) (1)

[0076] The arithmetic module 156d is a multiplier that multiplies the q-axis voltage feedback EQ_FBK by the modulation ratio k0 to calculate the q-axis voltage feedback EQ_FBK1. The arithmetic module 156e is a first-order hysteresis filter that receives the q-axis voltage feedback EQ_FBK1 and calculates the q-axis voltage feedback EQ_FBK0. The q-axis voltage feedback EQ_FBK0 is obtained by allowing the frequency band of the frequency components of the q-axis voltage feedback EQ_FBK1 up to a specified frequency to pass through, and attenuating the frequency components exceeding the specified frequency.

[0077] Reference Figure 6 The transformation rules related to the modulation rate conversion unit 156 of the embodiment will be explained. Figure 6 This is a diagram used to illustrate the transformation rules of the implementation method.

[0078] The calculation module 156a sets the output current I1_F as the input variable and the DC voltage reference VDC_F0 as the output variable. Furthermore, the calculation module 156a sets current thresholds IFCHG1 to IFCHG5 and voltage setting values ​​VFR1 to VFR5 to define the transformation rules. The calculation module 156a can tabulate and maintain the current thresholds IFCHG1 to IFCHG5 and the voltage setting values ​​VFR1 to VFR5.

[0079] The transformation rules are modeled and illustrated graphically. Phase current is assigned to the x-axis of the graph, and a voltage reference is assigned to the y-axis. The values ​​on the x-axis and y-axis correspond to the magnitudes of the phase current and voltage reference, respectively.

[0080] Connect the current thresholds IFCGHG1 to IFCGHG5 with Figure 6 The values ​​xa to xe on the x-axis are shown to establish a correspondence. In this case, it is stipulated that each threshold increases sequentially according to the current threshold IFCHG1 to the current threshold IFCHG5.

[0081] Set the voltage setting values ​​VFR1 to VFR5 and... Figure 6 The values ​​ya to ye on the y-axis are established in correspondence. In this case, the voltage values ​​specified for each setting value increase sequentially from voltage setting value VFR1 to voltage setting value VFR5.

[0082] As shown in the diagram, when the output current I1_F is below the current threshold IFCHG1, the calculation module 156a outputs the voltage setting value VFR1 as the DC voltage reference VDC_F0. When the output current I1_F exceeds the current threshold IFCHG1 but is below the current threshold IFCHG2, the calculation module 156a outputs the voltage setting value VFR2 as the DC voltage reference VDC_F0. When the output current I1_F exceeds the current threshold IFCHG2 but is below the current threshold IFCHG3, the calculation module 156a outputs the voltage setting value VFR3 as the DC voltage reference VDC_F0. When the output current I1_F exceeds the current threshold IFCHG3 but is below the current threshold IFCHG4, the calculation module 156a outputs the voltage setting value VFR4 as the DC voltage reference VDC_F0. When the output current I1_F exceeds the current threshold IFCHG4 but is below the current threshold IFCHG5, the calculation module 156a outputs the voltage setting value VFR5 as the DC voltage reference VDC_F0.

[0083] The arithmetic module 156a may also have a table storing fixed data corresponding to the above-mentioned transformation rules for outputting the DC voltage reference VDC_F0.

[0084] Reference Figure 7 An example of a table specifying the rules for changing the implementation method will be explained. Figure 7 It is a diagram used to illustrate the transformation rules that specify the implementation methods.

[0085] The table includes items for the current range, table number iX, and DC voltage reference. The current range item indicates the ranges for differentiating the load current magnitude. The table number iX item is identification information used to identify the current range and output voltage. The DC voltage reference item indicates the voltage setting value related to the DC link voltage, determined based on the load current magnitude. The voltage setting value related to the DC link voltage is one example, but not limited to, of the physical quantity used as an indicator value.

[0086] The transformation rules specified in this table can be, for example, stipulated that the larger the load current, the larger the voltage setting value related to the DC link voltage. By setting it in this way, it is possible to specify that the electrical force corresponding to the voltage setting value (index value) increases.

[0087] As shown in the table above, the voltage setpoint (index value) can be determined as one of several discrete values. These discrete values ​​can be set to desired values, and can be set to different values. Based on the example above, the voltage setpoint (index value) corresponds to the magnitude of the DC voltage of the DC link.

[0088] Reference Figure 8 The processing of the DC voltage reference VDC_F0 that determines the implementation method will be explained.

[0089] Figure 8 This is a flowchart illustrating the general steps of the process for determining the DC voltage reference VDC_F0 in the implementation method.

[0090] In the speed control unit 15, the calculation module 156a of the modulation rate conversion unit 156 obtains the output current I1_F based on the load current detected by the current sensor 8 (step SA1). The calculation module 156a uses current thresholds IFCHG1 to IFCHG5 to determine the magnitude of the output current I1_F (step SA2) and determines the corresponding table number iX (step SA3). The calculation module 156a determines the DC voltage reference VDC_F0 based on the voltage value corresponding to the table number iX (step SA4) and outputs the DC voltage reference VDC_F0.

[0091] Reference Figure 9 Explain the actions to be taken when a power outage occurs. Figure 9 This is a timing diagram of a power outage occurring in the implementation method.

[0092] from Figure 9 Starting from the upper section, the restart signal A, restart signal B, input AC voltage, speed, and load current are arranged sequentially. Figure 9The horizontal axis represents the elapsed time. Restart signal A and restart signal B are binary logic signals that take values ​​of 0 or 1. The input AC voltage represents the change in input voltage feedback VAC detected by the instrumentation variable VT. The speed represents the change in reference phase QO. Reference phase QO_1 and reference phase QO_2 represent two cases with different characteristics. The load current represents the change in load current and the change in the corresponding output current I1_F.

[0093] Until the power outage occurs at time t1, the system is in a state where the AC voltage of the desired amplitude is supplied from the AC power source G, and the motor 2 is driven at a speed equivalent to the speed reference SP_REF1. Therefore, the logic values ​​of both the restart signal A and the restart signal B are 0.

[0094] For example, if a power outage occurs due to a drop in the input AC voltage (at time t1), the control unit 10 (monitoring unit 19) detects this situation based on the detection result of the instrument variable VT. The monitoring unit 19 sets the logic values ​​of both the restart signal A and the restart signal B to 1. Furthermore, the control unit 10 maintains the magnitude of the load current at this timing (the value of the output current I1_F) in the registry 221, and then stops the output of the load current from the inverter 6 (referred to as stopping the inverter 6). As a result, the load current becomes 0, and the actual speed of the motor 2 gradually decreases.

[0095] As described above, the control unit 10 stops the output of the load current but continues its control. For example, the speed control unit 15 generates a speed reference SP_RSU based on the magnitudes of the d-axis voltage feedback ED_FBK and q-axis voltage feedback EQ_FBK corresponding to the line voltage detected during a power outage, using a low-frequency component of that magnitude. The speed control unit 15 uses the speed reference SP_RSU instead of the speed reference SP_R based on the speed reference SP_REF1 to maintain the voltage reference EQ_REF during the shutdown period of the inverter 6.

[0096] Furthermore, the speed control unit 15 determines the DC voltage reference VDC_F0 based on the value of the output current I1_F, and prepares to restart with a modulation rate k0 of the same magnitude as that at the time of the power outage when power is restored.

[0097] The control unit 10 (monitoring unit 19) detects that the power is restored at time t2 based on the detection result of the AC voltage on the input side of the instrument variable VT. The monitoring unit 19 maintains the logic values ​​of the restart signal A and the restart signal B as 1, and starts a timer to set the logic value of the restart signal B to 0 after a predetermined period of time from this moment.

[0098] Upon detecting the power restoration, the control unit 10 resumes the output of AC power from the inverter 6 and resumes the drive of the motor 2 based on the inverter 6.

[0099] Furthermore, in the comparative example, there was a situation where the load current increased sharply, and the speed of motor 2 became unstable. In contrast, the control unit 10 of the embodiment sets the logic values ​​of both restart signal A and restart signal B to 1 as described above, so the speed control essentially continues in the same control state as during a power outage.

[0100] If the timer period for restart signal B expires at time t3, the monitoring unit 19 sets the logic value of restart signal B to 0 accordingly. Thus, the speed control of the control unit 10 reverts to its normal control system state.

[0101] However, the speed control of the frequency correction unit 151 remains unchanged from the restart setting.

[0102] Subsequently, the speed of motor 2 further increases, and monitoring unit 19 detects that the speed represented by reference phase QO becomes equal to the speed equivalent to speed reference SP_REF1 (time t4). Based on this detection, monitoring unit 19 sets the logic value of restart signal A to 0, ending the restart process.

[0103] According to the above-described embodiment, the control unit 10 uses a transformation rule that specifies an index value corresponding to the magnitude of the load current flowing in the multiple windings of the motor 2 in the main circuit 20. After the AC power supply G becomes undervoltage, the control unit 10 controls the electrical force supplied from the main circuit 20 to the motor 2. The control unit 10 uses the transformation rule to control the electrical force based on the magnitude of the load current associated with the detected undervoltage state of the AC power supply G. This further improves the stability of control when restarting the motor 2 after the AC power supply G recovers from the undervoltage state, thus further improving the convenience of restarting the motor.

[0104] Furthermore, the control unit 10 can use a transformation rule that specifies the correspondence between the magnitude of the load current and the index value to control the electrical force. Figure 6 The transformation rules shown Figure 7 The table shown is an example of the transformation rules described above.

[0105] The control unit 10 can use a transformation rule to control the effective electrical force supplied from the main circuit 20 to the motor 2 based on the magnitude of the load current before the undervoltage state is detected.

[0106] The control unit 10 can control the electrical power supplied from the main circuit 20 to the motor 2 when it detects that the AC power supply G is in an undervoltage state, and when it detects that the undervoltage state has been eliminated and resumes the AC power supply from the main circuit 20 to the motor 2, thereby controlling the electrical power supplied from the main circuit 20 to the motor 2.

[0107] (Modifications of the implementation method)

[0108] A variation of the implementation method will be described.

[0109] This variation can be applied when the modulation rate conversion unit 156 is partially or entirely constructed using the FPGA 200. In the following description, an example focusing on the arithmetic module 156a will be given, but the entire modulation rate conversion unit 156 can also be housed in the FPGA 200.

[0110] Reference Figure 10 The FPGA200, which is modeled as a part of the modulation rate conversion unit 156, namely the arithmetic module 156a, will be described. Figure 10 This is a schematic diagram of the configuration of an FPGA 200, which includes a portion of the modulation rate conversion unit 156 in the modified example.

[0111] FPGA 200 is an example of a configuration using an FPGA. For example, it includes table 211 (first table), table 212 (second table), registry 221 (first variable processing unit), registry 222 (second variable processing unit), registry 223 (third variable processing unit), table number assignment unit 231, and comparison and calculation unit 232.

[0112] Table 211 is a lookup table containing current thresholds IFCHG1 to IFCHG5. Table 211 selects and outputs the current threshold corresponding to the table number ix output by the table number designation unit 231 described later from the current thresholds IFCHG1 to IFCHG5.

[0113] Table 212 is a lookup table containing voltage setting values ​​VFR1 to VFR5. Table 212 selects and outputs the voltage setting value corresponding to table number ix from voltage setting values ​​VFR1 to VFR5.

[0114] Registry 221 writes the output current I1_F at a predetermined time when specified conditions are met and holds it. For example, registry 221 includes a selector 221S and a storage area 221R. The selector 221S switches between the output current I1_F supplied from the outside and the signal output from the storage area 221R at a predetermined time within the control cycle, and supplies the result to the input of the storage area 221R.

[0115] The timing that meets the specified conditions can be correlated with the timing that detects the AC power supply G as being in an undervoltage state. For example, the aforementioned timing can be synchronized with the timing that detects the AC power supply G as being in an undervoltage state.

[0116] Registry 222 holds a value (IFCHG*) from the current threshold IFCHG1 to the current threshold IFCHG5 read from table 211. For example, registry 222 includes a selector 222S and a storage area 222R. Selector 222S switches between a signal (IFCHG*) supplied from table 211 and a signal output from storage area 222R at a predetermined timing within a control cycle, and supplies the result to the input of storage area 222R.

[0117] Registry 223 retains one of the voltage settings VFR1 to VFR5 read from table 212 (VFR*) and outputs it as the DC voltage reference VDC_F0.

[0118] Furthermore, selectors 221S, 222S, 223S, and 231S can be switched either by separately synchronized signals or by signals set to generate a predetermined time difference between each other. Storage areas 221R, 222R, 223R, and 231R obtain and update the values ​​of the input signals through separately synchronized clock signals CLK.

[0119] The table numbering unit 231 generates a table number ix for reference to tables 211 and 212. If the table numbering unit 231 is set to an initial value of 1 as the table number ix, it retains that initial value.

[0120] For example, the table numbering unit 231 includes a selector 231S, a storage area 231R, and an adder 231AD. The selector 231S switches between a signal representing the initial value 1 and a signal representing the result of the operation of the adder 231AD at a predetermined timing within the control cycle, and supplies the result to the input of the storage area 231R. The adder 231AD adds the output of the storage area 231R to the logic value (0 or 1) output by the comparison operation unit 232, which will be described later.

[0121] If the result of the comparison operation unit 232 is 0, which indicates a negative result, the table number designation unit 231 adds 1 to the held table number ix; if the result of the comparison operation unit 232 is 1, which indicates a positive result, the value of the held table number ix is ​​maintained and that value is retained.

[0122] The comparison unit 232 compares the output value of registry 221 with the output value of registry 222 and outputs the result. For example, if the output value of registry 221 is lower than the output value of registry 222, the comparison unit 232 outputs 0; otherwise, it outputs 1.

[0123] Figure 11A and Figure 11B This is a flowchart illustrating the process of determining the DC voltage reference VDC_F0 based on a variant of the FPGA 200.

[0124] Registry 221 writes the output current I1_F at the allowed time interval as described above (step SB1).

[0125] The table numbering unit 231 writes the initial value 1 as the table number ix into the storage area 231R and retains the initial value (step SB2).

[0126] The table number designation unit 231 determines whether the table number ix is ​​1 (step SB11).

[0127] When table number ix is ​​1, table 211 outputs the current threshold IFCHG1 referenced according to table number ix. Registry 222 reads the current threshold IFCHG1 from table 211, writes the current threshold IFCHG1 and stores it in storage area 222R (step SB12).

[0128] The comparison and calculation unit 232 determines whether the output value of the registry 221 is lower than or equal to the output value of the registry 222 (step SB13).

[0129] If the output value of registry 221 is lower than the output value of registry 222, table 212 outputs the voltage setting value VFR1 referenced according to table number ix. Registry 223 reads the voltage setting value VFR1 from table 212 (step SB14).

[0130] If the output value of registry 221 exceeds the output value of registry 222, the table number designation unit 231 adds 1 to the table number ix, writes the result to the storage area 231R and updates the value of the table number ix (step SB15), causing the process to proceed to step SB11.

[0131] If the table number ix is ​​not 1, the process starting from step SB21 is executed. The table number assignment unit 231 determines whether the table number ix is ​​2 (step SB21).

[0132] When table number ix is ​​2, table 211 outputs the current threshold IFCHG2 referenced according to table number ix. Registry 222 reads the current threshold IFCHG2 from table 211, writes the current threshold IFCHG2 to and holds it in storage area 222R (step SB22).

[0133] The comparison and calculation unit 232 determines whether the output value of the registry 221 is lower than or equal to the output value of the registry 222 (step SB23).

[0134] If the output value of registry 221 is lower than the output value of registry 222, table 212 outputs the voltage setting value VFR2 referenced according to table number ix. Registry 223 reads the voltage setting value VFR2 from table 212 (step SB24).

[0135] If the output value of registry 221 exceeds the output value of registry 222, the table number designation unit 231 adds 1 to the table number ix, writes the result to the storage area 231R and updates the value of the table number ix (step SB25), causing the process to proceed to step SB21.

[0136] If table number ix is ​​not 2, proceed from step SB31. Figure 11B The process begins with the table number specification section 231 determining whether table number ix is ​​3 (step SB31).

[0137] When table number ix is ​​3, table 211 outputs the current threshold IFCHG3 referenced according to table number ix. Registry 222 reads the current threshold IFCHG3 from table 211, writes it to and holds it in storage area 222R (step SB32).

[0138] The comparison and calculation unit 232 determines whether the output value of the registry 221 is lower than or equal to the output value of the registry 222 (step SB33).

[0139] If the output value of registry 221 is lower than the output value of registry 222, table 212 outputs the voltage setting value VFR3 referenced according to table number ix. Registry 223 reads the voltage setting value VFR3 from table 212 (step SB34).

[0140] If the output value of registry 221 exceeds the output value of registry 222, the table number designation unit 231 adds 1 to the table number ix, writes the result to the storage area 231R and updates the value of the table number ix (step SB35), causing the process to proceed to step SB31.

[0141] If the table number ix is ​​not 3, the process starting from step SB41 is executed. The table number assignment unit 231 determines whether the table number ix is ​​4 (step SB41).

[0142] When table number ix is ​​4, table 211 outputs the current threshold IFCHG4 referenced according to table number ix. Registry 222 reads the current threshold IFCHG4 from table 211, writes it to and holds it in storage area 222R (step SB42).

[0143] The comparison and calculation unit 232 determines whether the output value of the registry 221 is lower than or equal to the output value of the registry 222 (step SB43).

[0144] If the output value of registry 221 is lower than the output value of registry 222, table 212 outputs the voltage setting value VFR4 referenced according to table number ix. Registry 223 reads the voltage setting value VFR4 from table 212 (step SB44).

[0145] If the output value of registry 221 exceeds the output value of registry 222, the table number designation unit 231 adds 1 to the table number ix, writes the result to the storage area 231R and updates the value of the table number ix (step SB45), causing the process to proceed to step SB41.

[0146] If table number ix is ​​not 4, table 212 outputs the voltage setting value VFR5 referenced according to table number ix. Registry 223 reads the voltage setting value VFR5 from table 212 (step SB54).

[0147] After completing one of the processes in steps SB14, SB24, SB34, SB44, and SB54, registry 223 outputs one of the read voltage setting values ​​VFR1 to VFR5 as the DC voltage reference VDC_F0 (step SB61).

[0148] According to this variation, Table 211 holds multiple current thresholds with different values. Table 212 holds multiple voltage settings with different values. Registry 221 holds the value of the load current (output current I1_F) at a timing established with the detection that the AC power supply G is in an undervoltage state. Registry 222 holds one of the multiple current thresholds held in Table 211. Registry 223 determines a voltage setting value from the multiple voltage settings held in Table 212 based on the difference between the load current value held by Registry 221 and the current threshold held by Registry 222. This allows the computation module 156a to be constructed using a smaller FPGA 200, while achieving the same effect as in the previous implementation.

[0149] At least according to the above-described embodiments, the motor drive device 1 includes a motor 2, a main circuit 20, a current sensor 8, and a control unit 10. The motor 2 has multiple windings. The main circuit 20 converts the power from the AC power supply G into AC power and supplies the AC power to the multiple windings respectively. The current sensor 8 detects the load current flowing to each of the multiple windings respectively. The control unit 10 controls the main circuit 20 based on the current value detected by the current sensor 8. Furthermore, the control unit 10 uses a transformation rule that specifies an index value relative to the magnitude of the load current flowing from the main circuit 20 to the multiple windings, and controls the electrical power supplied from the main circuit 20 to the motor 2 based on the magnitude of the load current associated with the detected undervoltage state of the AC power supply. As a result, the motor drive device 1 can further improve the convenience of restarting the motor 2.

[0150] The control unit 10 of the aforementioned electric motor drive device 1 can be implemented in at least part by a software function unit that performs the function by executing a program by a processor such as a CPU, or it can be implemented entirely by a hardware function unit such as an LSI.

[0151] While several embodiments of the invention have been described, these embodiments are provided as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included within the scope and spirit of the invention, as well as within the scope of the claims and their equivalents.

[0152] In the above description of the embodiments, an example was described where the AC power supply G is detected to be in an undervoltage state, and the modulation rate k0 of the motor 2 is controlled based on the magnitude of the load current at that timing. The timing for identifying the magnitude of the load current could also be a timing before the AC power supply G is about to become undervoltage. In this case, the speed control unit 15 could also be configured to periodically and repeatedly sample the value of the load current regardless of whether the AC power supply G is in an undervoltage state, and not to perform the aforementioned periodic sampling during the period when the AC power supply G is in an undervoltage state. Thus, the speed control unit 15 (registration 221) can utilize the value of the output current I1_F before a power outage occurs.

[0153] Explanation of reference numerals in the attached figures

[0154] 1…motor drive unit, G…AC power supply, 2…motor, 3…transformer, 4…rectifier, 5…capacitor, 6…inverter, 7…DC voltage sensor, 8…current sensor, 9…AC voltage sensor, 10…control unit, 15…speed control unit (ASR), 20…main circuit, VT…instrument variable.

Claims

1. An electric motor drive apparatus, characterized by comprising: Possessing: An electric motor, possessing a plurality of windings; A rectifier, rectifying power of an alternating current power supply; A capacitor, smoothing a voltage output from the rectifier to a direct current link; An inverter, converting direct current power, after the voltage is smoothed, to alternating current power, and supplying the alternating current power to the plurality of windings respectively; A current sensor, detecting load currents flowing to the plurality of windings respectively; And A control section, controlling the inverter based on a current value detected by the current sensor and a speed reference for adjusting a speed of the electric motor, The control section is formed using a conversion rule that defines a direct current voltage reference relative to a magnitude of the load currents flowing from the inverter to the plurality of windings, The control section calculates a direct current voltage reference using the conversion rule based on a magnitude of the load currents associated with detection of an under-voltage state of the alternating current power supply, The control section generates a speed correction value by correcting the speed reference based on the calculated direct current voltage reference, The control section adjusts the load currents of the inverter using the generated speed correction value in a case where the under-voltage state is eliminated and supply of alternating current power from the inverter to the electric motor is started again, thereby controlling an amount of power conversion of the inverter.

2. The electric motor drive device according to claim 1, wherein The control section controls the amount of power conversion of the inverter using the conversion rule that defines a correspondence between the magnitude of the load currents and the direct current voltage reference.

3. The electric motor drive device according to claim 1, wherein The control section controls an effective amount of power supplied from the inverter to the electric motor using the conversion rule based on a magnitude of the load currents before detection of the under-voltage state.

4. The electric motor drive device according to claim 1, wherein The conversion rule is defined such that the greater the magnitude of the load currents, the greater the value of the direct current voltage reference.

5. The electric motor drive device according to claim 4, wherein The control section determines the value of the direct current voltage reference in correspondence with the magnitude of the load currents before the under-voltage state of the alternating current power supply.

6. The electric motor drive device according to claim 1, wherein The control section determines a modulation ratio by dividing a product of a rated value CS_EQUIP_VOLT of a first axis voltage of a rotating coordinate system related to control of the electric motor and a rated value CS_DC_VOLT of a direct current voltage by the direct current voltage reference VDC_F0, and generates a speed correction value by correcting the speed reference using the modulation ratio.

7. The electric motor drive device according to claim 1, wherein The control section implements current control that adjusts a magnitude of a current supplied from the inverter to the electric motor to a magnitude of the load currents before the under-voltage state in a case where supply of alternating current power from the inverter to the electric motor is limited in accordance with detection of the under-voltage state of the alternating current power supply, and detection of elimination of the under-voltage state.

8. The motor driving device according to claim 1, wherein the control section includes: a first table that holds a plurality of current threshold values that differ from each other in value in correspondence with table numbers; a second table that holds a plurality of voltage setting values that differ from each other in value as the value of the direct-current voltage reference in correspondence with table numbers; a first variable processing section that holds the value of the load current at a time when association is established with detection that the alternating-current power source is in an under-voltage state; a second variable processing section that holds one of the plurality of current threshold values held in the first table; and a third variable processing section that determines a table number for which the difference between the value of the load current held by the first variable processing section and the current threshold value held by the second variable processing section corresponding to the same table number is within a prescribed range, and determines one voltage setting value corresponding to the determined table number from among the plurality of voltage setting values held in the second table. ​ ​ ​ ​ ​ ​ ​

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