JP2011004539A - Inverter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exact sensorless vector control regardless of the operation state of a motor.SOLUTION: A first current detection mode, a second current detection mode, and a third current detection mode are executed by switching according to the operation state of the motor 6. In the first current detection mode, current values detected with shunt resistors 12 and 13 for phase currents are used. In the second current detection mode, a current value detected with a shunt resistor for a phase current is used in other than the range of the specified angle, and in the range of the specified angle, a current value detected at the time of 180° before is substituted for the current value in the range of the specified angle, or the present current value is computed by computation from the current value detected by the shunt resistor for a phase current in its vicinity, and the computed value is substituted for the current value in the range of the specified angle. In the third current detection mode, a current value detected with a shunt resistor for a bus current is used.

Description

  The present invention relates to an inverter device that controls an electric motor by a sensorless vector method without using a magnetic pole position sensor.

  Conventionally, when operating a brushless motor (motor) with sensorless vector control, the rotor position is estimated from the phase current flowing through the inverter main circuit, and the voltage command value, rotation speed (angular frequency), and phase are calculated. However, a small and inexpensive shunt resistor is used as a device for detecting this phase current. There are basically two types of methods using this shunt resistor. One is a method (one shunt method) for detecting the bus current of the inverter device by one shunt resistor (for example, see Patent Document 1), and the other is This is a method (two-shunt method) in which currents flowing in two phases of the three arms of the inverter main circuit are detected by a shunt resistor (see, for example, Patent Document 2).

JP 2007-312511 A JP 2000-262088 A

  However, the one-shunt method disclosed in Patent Document 1 is likely to generate noise and vibration, and in a low load state, the ON period of the switching element of the inverter main circuit is shortened so that only the current for one phase can be detected. Further, there is a problem that the dq current used in the vector control cannot be calculated only with the current for one phase.

  On the other hand, the two-shunt method disclosed in Patent Document 2 has a problem in that the ON period of the switching element of the lower arm is shortened at a specific phase in a high load state, and the phase current cannot be detected.

  The present invention has been made to solve the conventional technical problem, and in an inverter device that performs drive control of a motor using a shunt resistor, accurate sensorless vector control is performed regardless of the operating state of the motor. It is intended to be able to realize.

  In order to solve the above-described problems, an inverter device according to the present invention connects three arms formed by connecting two switching elements that perform ON / OFF operations that are contradictory to each other in series to a DC power source in a three-phase bridge shape. Inverter main circuit that applies three-phase pseudo AC voltage of phase PWM system to the motor, bus current shunt resistor connected to DC power source in series with the bus of this inverter main circuit, and three arms of inverter main circuit , Detecting a phase current shunt resistor connected to a DC power source in series with at least two arms, and a current flowing through the shunt resistor at a predetermined cycle, and switching each of the inverter main circuits based on the detected current Control means for controlling the ON / OFF operation of the element, and this control means is a shunt resistor for phase current according to the operating state of the motor. In the first current detection mode that uses the current value detected in the above and the current value detected by the shunt resistor for the phase current except for the range of the specific angle, 180 ° before the specific angle range. The current value detected in time is used in place of the current value in the range of this specific angle, or the current value detected by the phase current shunt resistor in the vicinity thereof is calculated and calculated. A second current detection mode that uses the calculated value in place of a current value within a specific angle range and a third current detection mode that uses the current value detected by the shunt resistor for bus current are switched and executed. It is characterized by that.

  In the inverter device according to the second aspect of the present invention, the control means executes the first current detection mode based on the voltage command value for controlling the inverter main circuit when the motor is not in a high load state. If the load fluctuation and the voltage fluctuation are not large in the load state, the second current detection mode is executed. If the load fluctuation and / or the voltage fluctuation is large in the high load state, the third current detection mode is executed. A current detection mode is executed.

  According to the present invention, the first current detection mode using the current value detected by the phase current shunt resistor connected to the two arms of the inverter main circuit according to the operating state of the electric motor, and the specific angle The current value detected by the shunt resistor for the phase current is used outside the range of the current range. In the specific angle range, the current value detected at a time 180 degrees before is changed to the current value in the specific angle range. A second current that is used or calculated by calculating the current value from the current value detected by the phase current shunt resistor in the vicinity thereof, and replacing the calculated value with a current value within a specific angle range Since the detection mode and the third current detection mode using the current value detected by the shunt resistor for bus current connected to the bus of the inverter main circuit are switched and executed, for example, the inverter main circuit is Based on the voltage command value for controlling, the first current detection mode is executed when the electric motor is not in a high load state, and the second change is performed when the load fluctuation and the voltage fluctuation are not large in the high load state. When the current detection mode is executed and the load fluctuation and / or the voltage fluctuation is large in the high load state, the third current detection mode is executed, so that the operation state of the motor from the low load to the high load is achieved. Regardless, it is possible to realize accurate sensorless vector control that uses only the advantages of each current detection mode, is resistant to fluctuations, and suppresses noise and vibration.

It is a circuit block diagram of the inverter apparatus of one Embodiment to which this invention is applied. It is another circuit block diagram of the inverter apparatus of FIG. It is a figure which shows the ON / OFF state and voltage command value of the switching element of the lower arm within 1 carrier frequency of the inverter apparatus of FIG. FIG. 3 is still another circuit configuration diagram of the inverter device of FIG. 1. FIG. 5 is a characteristic diagram of three-phase modulation when the voltage command value is approximately 100% duty for explaining the operation of the control device of the inverter device of FIG. 4. It is a figure which shows the functional block of the control apparatus of FIG. 1, an inverter main circuit, and an electric motor. It is the figure explaining the pros and cons of each current detection mode by the control device of FIG. 2 is a flowchart for explaining a current detection mode switching operation by the control device of FIG. 1.

  Hereinafter, embodiments of the present invention will be described in detail. FIG. 1 is an electric circuit diagram of an inverter device 1 for an air conditioner or a car air conditioner to which the present invention is applied. In this figure, 3 is a three-phase PWM (Pulse Width Modulation) type inverter main circuit. The inverter main circuit 3 converts the voltage supplied from the DC power supply unit 4 into a three-phase pseudo AC voltage having an arbitrary variable voltage and variable frequency, and outputs the converted voltage to form an electric motor (for example, a refrigerant circuit of an air conditioner). Compressor drive motor (for example, synchronous motor) 6 is supplied.

  The inverter main circuit 3 connects three arms formed by connecting two switching elements (7u to 7w, 8u to 8w) that perform opposite ON / OFF operations in series to the DC power supply unit 4 in a three-phase bridge shape. Configured. That is, the inverter main circuit 3 includes a U-phase upper arm switching element 7u, a U-phase lower arm switching element 8u, a V-phase upper arm switching element 7v, and a V-phase lower arm switching element. 8v, W-phase upper arm switching element 7w and W-phase lower arm switching element 8w are provided, and each switching element 7u, 8u, 7v, 8v, 7w, 8w flows in the winding of the motor 6. A diode for circulating current is connected in reverse parallel.

  Note that an IGBT (Insulated Gate Bipolar Transistor) is used as the switching element (the same applies hereinafter). The switching elements 7u, 8u, 7v, 8v, 7w, and 8w are turned on when the pulse signal input to the gate is at “H” level, and turned off when the pulse signal is at “L” level.

  The shunt resistor 2 for bus current is connected in series to the DC bus of the inverter main circuit 3 and the DC power supply unit 4, and the DC bus current Idc (one shunt current) flows through the shunt resistor 2. ing.

  The phase current shunt resistors 12 and 13 are connected in series to the V-phase lower arm, the W-phase lower arm, and the DC power supply unit 4, respectively. The shunt resistor 12 has a V-phase current Iv. The shunt resistor 13 is configured to pass a W-phase current Iw (two shunt currents).

  The control device (control means) 11 according to the present invention detects the current of the electric motor 6 and estimates the rotor position, so that the first current detection mode using the two-shunt method and the second method using the two-shunt current copy method. There are three current detection modes: a current detection mode and a third current detection mode using a single shunt method. Each current detection mode will be described below.

(1 shunt method: 3rd current detection mode)
First, the third current detection mode by the one shunt method will be described. In this third current detection mode, the control device (control means) 11 has a shunt resistance 2 in a predetermined cycle (cycle of the carrier signal) based on the pulse signals U, Ubar, V, Vbar, W, Wbar output by itself. Is detected, and the detected DC bus current Idc is distributed to the respective phases, so that the three-phase current flowing to the motor 6, that is, the U-phase current Iu, the V-phase current Iv, and the W-phase The phase current Iw of is estimated.

  FIG. 6 shows functional blocks of the control device 11. The bus current Idc flowing through the shunt resistor 2 is taken into the current detection unit 21, and the current detection unit 21 obtains three-phase phase currents Iu, Iv, and Iw. In this case, in the range where the voltage command values Vu, Vv, and Vw are separated, for example, the DC bus current Idc is detected within the period (1) and (2) as shown in FIG.

  In the period (1), as shown in FIG. 1, the switching element 7u for the upper arm for the U phase is ON, the switching element 8v for the lower arm for the V phase is ON, and the switching element 8w for the lower arm for the W phase is Since it is ON, the U-phase phase current Iu (sign is negative) is estimated to be the DC bus current Idc detected in the period (1).

  In the period (2), as shown in FIG. 2, the U-phase upper arm switching element 7u is ON, the V-phase upper arm switching element 7v is ON, and the W-phase lower arm switching element 8w is ON. Since it is ON, the W-phase phase current Iw (sign is negative) is estimated to be the DC bus current Idc detected in the period (2).

  Further, since the sum of the U-phase phase current Iu, the V-phase phase current Iv, and the W-phase phase current Iw becomes zero, the V-phase phase current Iv is also estimated by Iv = − (Iu + Iw). In this way, the phase currents Iu, Iv, and Iw are obtained.

(Two shunt method: About the first current detection mode)
Next, the first current detection mode by the two shunt method will be described. In this first current detection mode, the control device (control means) 11 has a shunt resistor 12 in a predetermined cycle (carrier signal cycle) based on the pulse signals U, Ubar, V, Vbar, W, Wbar output by itself. And the V-phase phase current Iv and the W-phase phase current Iw flowing through the first and second currents 13 and 13 are detected. The V-phase current Iv and the W-phase current Iw flowing through the shunt resistors 12 and 13 are taken into the current detection unit 21 in FIG. 6, and the current detection unit 21 obtains the three-phase phase currents Iu, Iv, and Iw. It is done.

  In this case, as shown in FIG. 4, the switching element 7u for the upper arm for the U phase is ON, the switching element 8v for the lower arm for the V phase is ON, and the switching element 8w for the lower arm for the W phase is ON. Thus, the V-phase current Iv (sign is negative) is detected by the shunt resistor 12, and the W-phase current Iw (sign is negative) is detected by the shunt resistor 13. Further, since the sum of the U-phase phase current Iu, the V-phase phase current Iv, and the W-phase phase current Iw becomes zero, the U-phase phase current Iu is also obtained by Iu = − (Iv + Iw). In this way, the phase currents Iu, Iv, and Iw are obtained.

(Two-shunt current copy method: Second current detection mode)
Next, the second current detection mode by the two-shunt current copy method will be described. Here, in the two-shunt method, when the voltage command value is in a high load state with a duty of approximately 100%, for example, the switching element 8v for the V-phase lower arm around the phase 90 ° (range of specific angle) in FIG. Is turned off in substantially the entire region of one carrier frequency, so that the V-phase current Iv cannot be detected in the vicinity of the phase of 90 °. Similarly, the W-phase current Iw cannot be detected in the vicinity of the phase 210 ° (in a specific angle range).

  On the other hand, the current value of the phase (time) 180 degrees before the present is opposite in polarity to the current current value and has substantially the same absolute value. Also, the current value of the phase in the vicinity of 180 ° before is opposite to the current current value and has almost the same absolute value. Therefore, in this second current detection mode, the duty of voltage command values Vv, Vu, Vw, which will be described later, is less than 100% (for example, 85%, or any value from 85% to 95%, below). When the value H · Duty is exceeded, the current detection unit 21 does not detect the phase current Iv of the V phase and the phase current Iw of the W phase and does not estimate the phase current Iu of the U phase.

  Then, the current detection unit 21 obtains the current current value by calculation from the current value of the phase 180 ° before the current phase or a phase near 180 ° before. For example, if the duty of the voltage command value exceeds H · Duty in phase P2 of FIG. 5, it is determined that the V-phase current Iv cannot be detected, and the phase P3 (or a phase in the vicinity thereof) 180 ° before that is determined. It is assumed that the phase current Iv of the V phase is adopted and the phase current Iv having the same value with the polarity reversed is currently flowing. The same applies to the phase current Iw of the W phase.

  In this case, the current detection unit 21 assumes that the rotation speed (estimated value) is the same at the time of sampling before the phase P2 (that is, it is rotating at the same speed), and at that rotation speed until the next sampling. The phase (θ2) at present (P2) is grasped as advanced. Then, the phase 180 ° before the phase of P2 or the phase P3 in the vicinity of 180 ° is specified.

  In the second current detection mode, the phase currents Iu, Iv, Iw are determined from the current values detected by the shunt resistors 12, 13 in the same manner as in the first current detection mode, except in the range of the specific angle. Ask for. The switching of these current detection modes will be described in detail later.

(About motor control)
In the current detection unit 21 of the control device 11, the phase currents Iu, Iv, Iw are obtained in this way. Next, in the three-phase / two-phase coordinate conversion unit 22, the phase currents Iu, Iv, and Iw obtained by the current detection unit 21 are three-phase / two-phase converted, and the q-axis current Iq and the d-axis current Id are calculated. The Next, in the position / velocity estimator 23, the q-axis current Iq and the d-axis current Id calculated by the three-phase two-layer coordinate conversion unit 22 and the q-axis current control unit 24 and the d-axis current control unit 26 are calculated. The rotation speed of the electric motor 6 and the magnetic pole position of the rotor (rotor) are estimated using the q-axis voltage and the d-axis voltage.

  Next, in the speed control unit 27, PI is calculated from the rotational speed estimated by the position / speed estimator 22 and the target rotational speed (for example, calculated based on the temperature of the conditioned room air-conditioned by the air conditioner). A target q-axis current (q-axis current is proportional to torque) is calculated by the control. Next, in the q-axis current control unit 24, the q-current is calculated by PI control from the target q-axis current calculated by the speed control unit 27 and the actual q-axis current Iq calculated by the three-phase two-phase coordinate conversion unit 22. A shaft voltage is calculated.

  On the other hand, in the flux weakening control unit 28 (control to reduce the induced voltage), the rotational speed (estimated value) estimated by the position / speed estimator 23 and the target q-axis current calculated by the speed control unit 27 are used. From the target d-axis current. Next, in the d-axis current control unit 26, the target d-axis current calculated by the magnetic flux weakening control unit 28 and the actual d-axis current Id calculated by the three-phase two-phase coordinate conversion unit 22 are used to perform d control by PI control. A shaft voltage is calculated.

  In the two-phase / three-phase coordinate conversion unit 29, the U-phase voltage is converted by two-phase / three-phase conversion of the q-axis voltage and the d-axis voltage calculated by the q-axis current control unit 24 and the d-axis current control unit 26. A command value Vu, a V-phase voltage command value Vv, and a W-phase voltage command value Vw are calculated. These three-phase voltage command values Vu, Vv, Vw are further pulse width modulated, and pulse signals for ON / OFF control of the switching elements 7u, 8u, 7v, 8v, 7w, 8w of each arm of the inverter main circuit 3, respectively. U, Ubar, V, Vbar, W, Wbar are generated.

  In the inverter main circuit 3, the switching elements 7u, 8u, 7v, 8v, 7w, 8w are ON / OFF controlled by the pulse signals U, Ubar, V, Vbar, W, Wbar, and the operation of the motor 6 is controlled. is there. In this way, the control device 11 performs sensorless vector control of the electric motor 6.

(About switching the current detection mode)
Next, the switching operation of the current detection mode in the current detection unit 21 of the control device 11 will be described with reference to FIGS. As described above, in the single shunt method, only a phase current for one phase can be detected at a low load. Also, noise and vibration are likely to occur. This is periodically when the two-phase voltage command values are substantially the same. At that time, only one-phase current can be detected in the one-shunt method. Therefore, in order to detect the two-phase current even in such a situation, a correction is performed to shift the two-phase voltage command values up and down so that the voltage command values are substantially the same. This is because the command value deviates from the original sine wave, which causes noise and vibration of the motor 6. On the other hand, the two-shunt method can suppress noise and vibration compared to the one-shunt method, but has a problem that the phase current cannot be detected at a high load. Further, in the two-shunt current copy method, the current value is obtained by changing the previous current value or by calculating from the previous current value. Therefore, when the load fluctuation or the voltage fluctuation of the DC power supply unit 4 increases, There is a problem that the difference between the current values becomes large and the system cannot be used (the problem in each method is indicated by x in FIG. 7).

  Therefore, the current detection unit 21 of the control device 11 switches and executes the first to third current detection modes according to the operation state of the electric motor 6 and the state of the DC power supply unit 4. Next, the switching operation of the current detection mode for the detection and estimation of the phase current in the current detection unit 21 will be described using the flowchart of FIG.

  That is, in step S1 of FIG. 8, it is determined whether the electric motor 7 is currently in a high load state based on the voltage command values Vu, Vv, Vw. When the current voltage command value is equal to or less than the predetermined value and the operation state of the motor 7 is not a high load state, the process proceeds to step S4 to execute the first current detection mode of the two-shunt method described above, and each phase current Iu, Iv and Iw are obtained. As a result, the motor 6 is operated with reduced noise and vibration compared to the single shunt method.

  Next, when the current voltage command value is larger than the predetermined value and in a high load state in step S1, the process proceeds to step S2, whether or not the load fluctuation is large based on the voltage command value, and the DC power supply unit 4 It is determined whether or not the voltage value varies greatly. When the load fluctuation range within the predetermined period is within the predetermined value and the voltage fluctuation range is also within the predetermined value, the process proceeds to step S3 and the second current detection mode of the above-described two-shunt current copy method is performed. In a specific angle range, the phase currents Iu, Iv, Iw are replaced with the previous ones, or replaced with those calculated from the vicinity thereof. This makes it possible to estimate the phase current in a high load state with a duty of approximately 100%, which was impossible with the two-shunt method.

  On the other hand, if the load fluctuation range within the predetermined period is larger than the predetermined value in step S2 or the voltage fluctuation range is larger than the predetermined value, there is a problem in the two-shunt current copy method. The third current detection mode of the one shunt method is executed to obtain each phase current Iu, Iv, Iw. By switching each current detection mode in this way, from the low load to the high load, regardless of the operating state of the electric motor 6, only the advantages of each current detection mode are used, and it is resistant to fluctuations, and noise and vibration are reduced. Suppressed and accurate sensorless vector control can be realized.

  In the above-described embodiment, the change in step S2 in FIG. 8 is determined based on the load change and the voltage change. However, the determination is not limited to this, and only the load change of the electric motor 6 may be determined. However, the switching from the second current detection mode to the first current detection mode can be performed more accurately by taking into account the voltage fluctuation of the DC power supply unit 4 as in the embodiment.

  In the embodiment, in the second current detection mode, the current current value is calculated from the current value of the phase before 180 ° or a phase in the vicinity thereof. However, the present invention is not limited to this, for example, two phases before and after 180 ° Or the current value at a plurality of phases 180 degrees before and in the vicinity thereof, and the current value may be calculated from them using a predetermined calculation formula (calculation). Good. By doing so, it is possible to estimate the current value more accurately.

DESCRIPTION OF SYMBOLS 1 Inverter apparatus 2, 12, 13 Shunt resistance 3 Inverter main circuit 4 DC power supply part 6 Electric motor 7u-7w, 8u-8w Switching element 11 Control apparatus 21 Current detection part

Claims (2)

Inverter that connects three switching elements that perform opposite ON / OFF operations in series to a DC power supply and connects three arms in a three-phase bridge shape to apply a three-phase PWM three-phase pseudo-AC voltage to the motor The main circuit;
A shunt resistor for bus current connected to the DC power source in series with the bus of the inverter main circuit;
Of the three arms of the inverter main circuit, a shunt resistor for phase current connected to the DC power supply in series with at least two arms,
Control means for detecting a current flowing through the shunt resistor at a predetermined period and controlling the ON / OFF operation of each switching element of the inverter main circuit based on the detected current;
The control means, according to the operating state of the electric motor,
A first current detection mode using a current value detected by the phase current shunt resistor;
The current value detected by the phase current shunt resistor is used in a range other than the specific angle range. In the specific angle range, the current value detected at a time 180 degrees before the current value is detected. The current value is used by calculation instead of the current value detected by the phase current shunt resistor in the vicinity of the current value, and the calculated value is used as the current value in the specific angle range. A second current detection mode used instead,
An inverter device characterized by switching and executing a third current detection mode using a current value detected by the bus current shunt resistor. The control means executes the first current detection mode when the electric motor is not in a high load state based on a voltage command value for controlling the inverter main circuit,
When the load fluctuation and the voltage fluctuation are not large in the high load state, execute the second current detection mode,
2. The inverter device according to claim 1, wherein the third current detection mode is executed when the load variation and / or the voltage variation is large in a high load state.

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