JP2012223019A - Inverter device - Google Patents

Abstract

Disclosed is a small current detection device capable of detecting a current using an emitter sense terminal even in a high output inverter.
An inverter apparatus according to the embodiment is connected to a DC power source, it includes an emitter sense terminal _ES U switching element comprising a ~ES _{Z S} U ~S _Z and a reflux diode _D U to D _Z, the switching element Is generated at the emitter sense terminal, an inverter that converts the DC voltage into an AC voltage having a predetermined magnitude and frequency and supplies AC power to the load 105, control means for controlling the inverter, Conversion means for converting a voltage signal to be converted into a first PWM signal, and insulation means for insulating the first PWM signal and transmitting it to the control means as a second PWM signal,
The control means includes estimation means for estimating a phase current of the inverter from the second PWM signal.
[Selection] Figure 1

Description

  Embodiments of the present invention relate to an inverter device that converts DC power into AC power having a desired frequency and magnitude and drives an electric motor, and more particularly, to miniaturization of a current detection system that detects the magnitude of an inverter output current. .

  An inverter is used when driving a load by converting DC power into AC power. In particular, in an electric vehicle or a hybrid vehicle, an inverter is used for the purpose of converting DC power supplied from a battery into AC power, driving an electric motor, and controlling its rotation. The inverter is composed of switching elements such as IGBTs and MOSFETs, and converts power by turning on / off the switching elements.

  In an electric vehicle and a hybrid vehicle, downsizing of an inverter is desired by securing a boarding space and increasing a battery volume. There are a switching element, a capacitor, a switching element drive board, and the like that constitute the inverter.

  When controlling a load such as an electric motor to a target rotational speed or torque, or in order to protect an inverter so that an excessive current does not flow, it is necessary to detect a phase current flowing from the inverter to the load.

  A method of detecting a current by using a Hall element and converting the intensity of a magnetic field generated from the current into an electric signal is generally widespread. A current sensor using a Hall element can detect a current value in a non-contact manner, and thus has a great merit in that it is possible to easily insulate a high output voltage inverter from a control circuit.

  However, the output range of electric vehicles and hybrid vehicles has been increased, and the current range to be detected has become wider accordingly. The above-described current sensor requires a large sensor in order to detect a large current, which is a problem for downsizing the inverter.

  In the conventional system, there is a system for estimating the phase current of the inverter using the emitter sense terminals of the three switching elements constituting the low side arm of the inverter and the current sensor installed in the DC input unit. This emitter sense terminal is a terminal added to the switching element in order to detect the emitter current of the switching element constituting the inverter. When the emitter sense terminal and the emitter terminal are connected by a resistor or the like, a current proportional to the emitter current flows through the emitter sense terminal. In such a system, the current flowing through the emitter sense terminal is converted into a voltage by a resistor and input to a controller such as a microcomputer as a current detection value. The microcomputer controls the electric motor based on the input current detection value.

  Such a system is advantageous in terms of low cost and miniaturization because an expensive non-contact current sensor is not required and the current detection system can be mounted on the drive substrate of the switching element.

JP 2007-159346 A

  In an inverter having a small capacity, since the fluctuation of the reference voltage (emitter voltage) of the low side arm is small, there is no problem even if the voltage detection signal is directly input to the controller without being insulated. However, in an inverter of an electric vehicle or a hybrid vehicle having a large output, a large current flows between the emitters of the switching element, a voltage drop occurs due to a parasitic inductance or a resistance component, and the reference voltage fluctuates. .

  Embodiments of the present invention have been made to solve the above-described problem, and an object of the present invention is to provide a small-sized current detection device that can detect a current using an emitter sense terminal even in a high-power inverter. .

  An inverter device according to an embodiment includes a switching element and a free-wheeling diode connected to a DC power source and having an emitter sense terminal, and the DC voltage is changed to an AC voltage having a predetermined magnitude and frequency by on / off control of the switching element. An inverter for converting and supplying AC power to a load; a control means for controlling the inverter; a conversion means for converting a voltage signal generated at the emitter sense terminal into a first PWM signal; and insulating the first PWM signal And an insulating means for transmitting to the control means as a second PWM signal, the control means comprising an estimation means for estimating a phase current of the inverter from the second PWM signal.

The circuit block diagram of the inverter apparatus which concerns on 1st Embodiment. The detailed block diagram of the insulation circuit which concerns on 1st Embodiment. The wave form diagram of the voltage signal which concerns on 1st Embodiment. The circuit block diagram of 2nd Embodiment. The wave form diagram of the voltage signal which concerns on 2nd Embodiment.

  Embodiments of a switching element driving circuit according to the present invention will be described below with reference to the drawings.

[First Embodiment]
[Constitution]
First, the configuration of the first embodiment will be described with reference to FIG.

  FIG. 1 is a diagram showing a configuration example of an embodiment when an inverter device according to the present invention is applied to an electric vehicle. The inverter device according to the present embodiment can be applied not only to electric vehicles but also to hybrid vehicles, electric propulsion ships, and the like.

This inverter device 102 receives the torque command value Trq ^* 103 from the accelerator device 101, converts the output power of the DC voltage source 104 such as a battery into desired AC power in accordance with the torque command value Tq ^* 103, and 105 is driven to control the rotation of the wheel 106.

In the inverter 100, a capacitor 107 that smoothes a DC voltage is provided in an input stage, and a U-phase, V-phase, and W-phase bridge circuit is configured by a switching element. In the U-phase bridge circuit, the connection point between the switching element S _U and the switching element S _X is connected to the U-phase winding of the electric motor 5. Free-wheeling diodes D _U and D _X are respectively connected in antiparallel to switching element S _U and switching element S _X.

Switching element _{S V} and _{S Y,} the bridge circuit of the V-phase consists of a freewheeling diode _{D V} and _{D Y,} the switching element _{S W} and _{S Z,} also bridge circuit composed W phase reflux diode _{D W} and _{D Z} It is constituted similarly.

The switching elements S _U , S _V , S _W , S _X , S _Y , S _Z have emitter sense terminals ES _U , ES _V , ES _W , ES _X , ES _Y , ES _Z , respectively. In this structure, a current obtained by dividing the main current flowing to the emitter sense terminals ES _{U to} ES _Z flows. The emitter sense terminals ES _{U to} ES _Z are connected to the emitters of the switching elements through resistors, and voltage drops VE _{U to} VE _Z proportional to the main current occur at both ends of the resistors R _{U to} R _Z (see FIG. 2). The voltages VE _{U to} VE _Z are input to the control arithmetic unit 109 through the insulating circuit 108.

The control arithmetic unit 109 includes a phase current estimation unit 110 and a current control unit 111 as shown in FIG. The phase current estimator 110 generates phase currents I _U and I _V based on a PWM (Pulse Width Modulation) signal (described later) obtained from the insulating circuit 108 based on the voltages VE _{U to} VE _Z and a voltage command value. , I _W is estimated.

Torque command value Trq ^* 103, phase current 112 estimated by phase current estimation unit 110, and electrical angle 114 obtained from motor angle detector 113 are input to current control unit 111. The current control unit 111 performs vector control of the motor based on the torque command value Trq ^* 103, the electrical angle 114, and the phase current 112, generates a gate signal 115 that obtains a desired motor current, and outputs the gate signal 115 to the gate drive circuit 116. . The gate drive circuit 116 is connected to all the gates with the switching element _S U to S _Z, a gate signal 115 which is input from the control arithmetic unit 110 amplifies the power switch on and off the switching element _S U to S _Z I do.

  The control arithmetic unit 109, the insulation circuit 108, and the gate drive circuit 116 constitute inverter control means. Therefore, the inverter device 102 includes the inverter 100 and inverter control means (108, 109, 116).

Hereinafter, isolation circuit 108, as an example emitter sense terminal ES _U of the switching elements _{S U,} it will be described with reference to FIG. Resistor _R the voltage _{V EU} generated in _U is amplified to a voltage signal 202 through the operational amplifier 201, is compared with the output triangular wave of the triangular wave generating circuit 203 by the comparator 204, it is converted into a PWM signal 205. The operational amplifier input circle indicates that it is an inverting terminal. Here, the triangular wave frequency of the triangular wave generating circuit 203 is much higher (for example, several hundred times) than the frequency of the emitter current. PWM signal 205 is a pulse train of equal amplitude, the pulse width (duty ratio) is substantially proportional to the amplitude of the voltage V _EU, is one pulse generated per cycle of the triangular wave. The PWM signal 205 is input to the control arithmetic unit 109 through an insulating element 206 such as a phototransistor.

The triangular wave generation circuit 203 and the insulating element 206 are also installed in the switching elements S _{V to} S _Z , respectively, and the PWM signal is transmitted to the control arithmetic device 109. Since the reference potentials of the switching elements S _X , S _Y and S _Z are equal to each other, the triangular wave generation circuit 203 can be used in common for the elements S _X , S _Y and S _Z.

  The above is the configuration of the entire inverter device.

[Action]
The operation of the present embodiment configured as described above will be described in detail.

3A and 3B show current waveforms at various parts, where FIG. 3A shows a U-phase current I _U , FIG. 3B shows a collector current IC _U , IC _X , and FIG. 3C shows a collector current detection period T _O (described later). This is a current waveform when compensating In FIG. 3B, one pulse-like waveform is composed of a plurality of calculation values based on the pulse widths of a plurality of (for example, several tens) PWM pulses. Hereinafter, a method for estimating the phase current I _U will be described using the U-phase current as an example.

To estimate the U-phase current, the emitter sense currents of the switching element S _U and the switching element S _X are used. When the U-phase current I _U is positive as shown in FIG. 1, the emitter sense current of the switching element S _U is used, and when the U phase current I _U is negative, the emitter sense current of the switching element S _X is used.

A current proportional to the collector current IC _U flowing through the switching element S _U flows through the emitter sense terminal. Therefore, the emitter sense terminal ES _U and resistance R _U connected between emitter voltage proportional to the collector current IC _U is generated.

Switching element S _U has repeatedly turned on / off at a certain frequency, flows a collector current IC _U only ON period. However, due to the inductance component of the load circuit, the U-phase current I _U flows through the freewheeling diode D _X even during the OFF period of the switching element S _U , so that a non-detection period T ₀ of the U-phase current I _U occurs. The same applies to the switching element S _X, the ON period flows a collector current IC _X is, since the off period the current flows through the freewheeling diode D _U, non-detection period T ₀ is generated.

It is necessary to transmit the voltage VE _U generated in the resistor R _U in the processing device 109, the emitter voltage of the switching element S _U will same high voltage and DC input voltage 104 when the switching element S _U is turned on The Therefore, it is necessary to insulate the control arithmetic unit 109 operating at a low voltage from the switching element side.

Therefore, by comparing the output triangular wave of the triangular wave generating circuit 203 with the signal 202 obtained by amplifying the voltage V _EU by the operational amplifier by the comparator 204, the voltage V _EU is converted into the PWM signal 205 and passed through the insulating element 206 such as a phototransistor. It transmits to the control arithmetic unit 109.

A phase current estimation unit 110 is provided in the control arithmetic unit 109. Phase current estimation unit 110, reads the PWM signal 205 that is input, estimates the phase current _{I U.}

Current value in the non-detection period T ₀ is to the current value obtained in the last sampling detection period immediately before the non-detection period T ₀ and the same value, the IC _U equivalent signal 302 to restore the voltage signal V _EU obtain. Similarly, for the switching element S _X , a compensated signal is obtained as shown in FIG. 3C, and the value of the negative current period of the phase current I _U can be estimated.

In this way, the U-phase current can be estimated, but the V and W-phase currents can also be estimated by the same method. Further, since the addition of the three-phase currents results in zero, for example, even if only the two phases of the U and W phases are estimated, the V-phase current can be obtained by the following equation.

[effect]
In the conventional example, since the signal of the emitter sense terminal is directly input to the control arithmetic unit, when a large current flows through the inverter 100, the reference potential fluctuates and the phase current estimation accuracy deteriorates. In the worst case, the control side circuit may be destroyed.

  According to this embodiment, since the detection signal is transmitted after being insulated, the phase current can be accurately estimated without being affected by the fluctuation of the reference potential of the inverter 100, and the reliability of the control side circuit is improved.

Further, the switching element S _U constituting the upper arm by an _insulating, allows detection S _V, also the current of S _W, as in the prior art DC current sensor without even the phase current can be estimated. For this reason, a current detection system can be configured without using any non-contact current sensor or shunt resistor, which contributes to downsizing and cost reduction of the entire system.

[Second Embodiment]
[Constitution]
Next, a second embodiment of the inverter device according to the present invention will be described. In addition, the same code | symbol is attached | subjected to the structure same as 1st Embodiment, and the overlapping description is abbreviate | omitted.

  In the first embodiment described above, when the frequency at which the switching element is turned on / off (hereinafter referred to as switching frequency) increases, the number of samples of the current amplitude value that can be transmitted by PWM during one period of the collector current decreases. When the switching frequency is increased to near the frequency of the output triangular wave of the triangular wave generating circuit 203, the collector current amplitude cannot be accurately restored by the control arithmetic unit 109. In the second embodiment, it is avoided that the PWM isolation method described in the first embodiment cannot be used when the switching frequency is high.

As in the first embodiment, the configuration of the second embodiment will be described with reference to FIG. 4 using the switching element _SU as an example. The inverter device 102 according to the present embodiment includes a filter circuit 401 and an insulating circuit 108, and the insulating circuit 108 corresponds to a circuit including the circuits 203 to 206 shown in FIG. That is, the configuration of this embodiment is a configuration in which a filter circuit 401 is provided instead of the operational amplifier 201 of FIG.

Voltage VE _U generated in the resistor _{R U} is converted into a voltage signal 402 which is continuous through the filter circuit 401. Similarly to the first embodiment, the voltage signal 402 is converted into a PWM signal 403 through the insulating circuit 108 and input to the control arithmetic unit 109.

The filter circuit 401 and the insulating circuit 108 are also installed in the switching elements S _{V to} S _Z , respectively, and the PWM signal is transmitted to the control arithmetic unit 109.

[Action]
The operation of the present embodiment configured as described above will be described with reference to FIG. 5A shows the U-phase current I _U , FIG. 5B shows the collector current IC _U , the emitter sense terminal voltage V _EU indicating IC _X , FIG. 5C shows the output voltage waveform of the filter circuit 401, and FIG. It is a phase delay signal waveform of the collector current shown in (a).

The filter circuit 401 converts the emitter sense terminal voltage V _EU as shown in FIG. 5B into a continuous signal 402 as shown in FIG. 5C. Time constant of the filter circuit 401 is greater than the switching period of the switching element, it must be smaller than the period of the period or the output AC voltage of the collector current I _U. The time constant may be changed according to the frequency of the output AC voltage. By making the voltage V _EU of the emitter sense terminal into such a continuous signal, it can be converted into a PWM signal and insulation can be realized. However, the output signal 402 of the filter circuit 401 has an amplitude peak value smaller than the base signal IC _U due to the influence of the non-detection period and the frequency characteristics of the filter circuit 401. Further, the filter circuit 401 has a phase delay δ.

  As in the first embodiment, the triangular wave generation circuit output signal and the signal 402 are compared by a comparator to generate a PWM signal 403, which is transmitted to the control arithmetic unit 109 through an insulating element such as a phototransistor. The phase current estimation unit 110 restores the signal based on the duty ratio of the PWM signal 403.

As described above, the restored signal is attenuated in amplitude by the filter circuit 401 as compared with the original phase current, and a phase delay δ is generated. The phase current estimation unit 110 compensates the attenuated amplitude by using the frequency characteristic of the filter that is known in advance to obtain a signal 501 in FIG. Signal 501 is the amplitude attenuation due to non-detection period and the filter is compensated, that the phase is delayed is different for the phase current I _U. As for the phase currents I _V and I _W , estimated phase current values whose phases are delayed by δ are obtained.

Compensation of the phase delay δ is performed in the current control unit 111 at the time of three-phase → dq conversion used for vector control. The three-phase → dq conversion is expressed by the following equation.

Here, θ is an angle between the stationary coordinate and the rotational coordinate, and particularly represents a rotational angle of the magnetic field when the electric motor is a permanent magnet motor. Since the frequency characteristic of the filter circuit 401 is known in advance, the phase delay δ is obtained. Since the phase of the detected phase current is delayed by δ, the following equation is used to obtain the dq axis current.

  In this way, the dq-axis current is obtained, and the phase delay caused by the filter circuit can be compensated.

[effect]
The switching frequency has been increasing year by year due to the higher speed of switching elements. Insulation can be realized if the frequency of the PWM signal, that is, the frequency of the output triangular wave of the triangular wave generating circuit is sufficiently higher than the switching frequency, but the speed of the duty ratio calculation of the control arithmetic unit is limited. Furthermore, the accuracy of the PWM signal is significantly deteriorated due to variations in the triangular wave generation circuit and the phototransistor.

  By converting to a continuous signal using a filter circuit as in the second embodiment, the frequency of the PWM signal can be determined regardless of the switching frequency, and the phase current can be estimated without degrading accuracy.

  The above description is an embodiment of the present invention, and does not limit the apparatus and method of the present invention, and various modifications can be easily implemented. For example, various inventions can be configured by appropriately combining a plurality of constituent elements disclosed in the embodiment.

DESCRIPTION OF SYMBOLS 100 ... Inverter, 101 ... Accelerator apparatus, 102 ... Inverter apparatus, 103 ... Torque command value, 104 ... DC power supply, 105 ... Electric motor, 106 ... Wheel, 107 ... Smoothing capacitor, 108 ... Insulation circuit, 109 ... Control arithmetic unit, 110 ... phase current estimation unit, 111 ... current control unit, 112 ... estimated phase current, 113 ... angle sensor, 114 ... electrical angle, 115 ... gate signal, 116 ... gate drive circuit, 201 ... op amp, 202 ... amplified signal, 203 ... Triangle wave generation circuit, 204 ... Comparator, 205 ... PWM signal, 206 ... Insulating element, 301 ... Signal corresponding to collector current IC _U , 302 ... Non-detection period compensation signal, 401 ... Filter circuit, 402 ... Continuous signal, 403 ... PWM signal 501... Phase delay signal.

Claims (8)

A switching element connected to a DC power source and including a switching element having an emitter sense terminal and a freewheeling diode. The DC voltage is converted into an AC voltage having a predetermined magnitude and frequency by on / off control of the switching element, and AC power is supplied to the load. An inverter to supply;
Control means for controlling the inverter;
Conversion means for converting a voltage signal generated at the emitter sense terminal into a first PWM signal;
Insulating means for insulating the first PWM signal and transmitting it to the control means as a second PWM signal;
The said control means is an inverter apparatus provided with the estimation means which estimates the phase current of the said inverter from the said 2nd PWM signal.   The said estimation means makes the electric current value of the said non-current detection period of the said emitter sense terminal the same value as the electric current estimated value immediately before this non-current detection period, and compensates for the said non-current detection period. Inverter device. A switching element connected to a DC power source and including a switching element having an emitter sense terminal and a freewheeling diode. The DC voltage is converted into an AC voltage having a predetermined magnitude and frequency by on / off control of the switching element, and AC power is supplied to the load. An inverter to supply;
Control means for controlling the inverter;
Filter processing means for filtering the voltage signal generated at the emitter sense terminal to generate a continuous signal;
Conversion means for converting the continuous voltage signal into a first PWM signal;
Insulating means for insulating the first PWM signal and transmitting it to the control means as a second PWM signal;
The said control means is an inverter apparatus provided with the estimation means which estimates the phase current of the said inverter from the said 2nd PWM signal.   4. The inverter apparatus according to claim 3, wherein the control means includes means for compensating for attenuation and phase delay generated in the filtering process.   5. The inverter apparatus according to claim 4, wherein the control means performs the phase delay compensation at the time of three-phase → dq conversion in vector control.   6. The inverter device according to claim 3, wherein the filter processing unit sets a filter time constant to a value longer than a switching cycle of the switching element and shorter than a cycle of the AC voltage. .   6. The inverter device according to claim 3, wherein the filter processing unit changes a time constant according to a frequency of the AC voltage. An inverter control device that includes a switching element having an emitter sense terminal, controls an on / off of the switching element, and controls an inverter that converts a DC voltage into an AC voltage having a predetermined magnitude and frequency;
Conversion means for converting a voltage signal generated at the emitter sense terminal into a first PWM signal;
Insulating means for insulating the first PWM signal and transmitting it to the control means as a second PWM signal;
Means for estimating a phase current of the inverter from the second PWM signal;
An inverter control device comprising:

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