JP2595717B2 - Inverter output current effective value detection circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter output current effective value detection circuit that approximates an effective value of an output AC current by an input current from a DC power supply side in a voltage type inverter. .

[Conventional technology]

Conventionally, the effective value of the AC output current of this type of inverter is detected by a dedicated effective value detection circuit which receives the detection signal of the AC output current by an AC current transformer as shown in the circuit diagram of FIG. Things are known.

In this connection, in FIG. 4, the voltage-transistor type inverter 1, the motor 2 driven by the inverter, C _i is the output side capacitor of the DC intermediate circuit comprising a DC power supply of the inverter, the DC link 7 Inverter input current detection signal _Sa and its setting signal S _as passing through the DC link section shown by reference character A between the circuit and the inverter 1
Comparator generates an output in the overcurrent state of the input current becomes larger than compared with the signal S _a is S _{the as} the door, the 8
A base drive circuit that receives a PWM reference signal and outputs a control signal to each switching transistor of the inverter 1; a protection 9 that receives an abnormality detection signal such as an output signal of the comparator 7 and outputs an operation stop command to the base drive circuit 8; circuit, 10 is the effective value of outputting the effective value detection signal S _bE of the detection signal S _b and input the inverter output current by the AC current transformer of the inverter output current passing through the code B shown section at the output of the inverter 1 It is a detection circuit.

FIGS. 5A and 5B are current waveform diagrams of the inverter input current and output current, respectively.
As shown in the figure, the input current has a pulse-like waveform, and the output current has a waveform in which harmonics are superimposed on a sine wave.

[Problems to be solved by the invention]

However, the conventional method of detecting the effective value of the inverter output current as described above requires a current transformer for detecting the inverter output current whose frequency fluctuates and contains a harmonic component and a dedicated effective value detection circuit.

In view of the above, the present invention eliminates the need for both the current transformer and the effective value detection circuit, and calculates and outputs an approximate value of the effective value of the output current from the input current detection signal of the inverter. The purpose is to provide.

[Means for solving the problem]

In order to achieve the above object, an inverter output current effective value detection circuit of the present invention is an output current effective value detection circuit of a voltage type inverter, and a detection circuit of the inverter input current flowing from the DC power supply, A peak charging circuit that receives the output signal of the detection circuit as an input and charges the peak value thereof, and outputs the signal obtained by attenuating the input signal according to an attenuation program with a plurality of long and short time constants using the output signal of the peak charging circuit as an input. An input attenuating circuit serving as a signal, and detecting a period in which the output signal of the peak charging circuit is larger than the output signal of the inverter input current detecting circuit, and outputting a time signal according to a predetermined program in the detecting period. A timer circuit for advancing an attenuation program of the input attenuation circuit according to a time signal, and an output signal of the input attenuation circuit; Envelope trajectory of the peak value of the inverter input current detection signal was collected using those formed by the detection signal of the output current effective value of the inverter drives out.

[Action]

If the power loss in the inverter and the harmonic component in the output power of the inverter are omitted, the inverter is given as a product of the DC voltage given by the DC intermediate circuit and the pulsed current as shown in FIG. 5 corresponds to the effective value of the AC current and the effective value of the AC voltage having a phase difference determined by the load circuit constant and the phase difference as shown in FIG. 5 (b). It is equal to the output power of the inverter given as the product of the power factor and a constant determined by the number of load phases. Therefore, the peak value of the pulse-like inverter input current as described above is proportional to the effective value of the fundamental wave of the inverter output current as described above.

According to the present invention, the envelope trajectory of each peak value of the pulse-like inverter input current is calculated and detected as described above, and the detected trajectory is approximated as an effective value variation trajectory of the inverter output current. The creation of the envelope locus is performed by connecting each peak value of the input current with an attenuation curve having a plurality of attenuation time constants. Therefore, a peak charging circuit for detecting the peak value of the input current and the peak charging circuit And a timer circuit for driving and advancing the attenuating circuit according to a predetermined time program.

The progress speed of the time program by the timer circuit is appropriately determined so as to obtain an envelope locus having the highest degree of approximation in relation to the repetition period of the input current pulse.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is an operation waveform diagram of each circuit in FIG.

In FIG. 1, components having the same functions and signals having the same character as those in FIG. 4 are denoted by the same reference numerals.

FIG. 1 shows the above-mentioned attenuation curve connecting between the pulse peak values of the inverter input current by using two types of long and short time constants τ _1.
And it shows the case of constituting the two sets of curves corresponding to the tau _2, the peak and 3 of illustration and inputs the detection signal S _a of the input current of the inverter 1 through the DC link section of an A portion It is a peak charging circuit that charges a value. The circuit comprising the capacitor C _p resistor R ₁ and R ₂ and time constant switching switch 6 which is long time constant tau ₁ is switched by the switch _{(tau 1 =} R ₁ C _p) a short time constant tau ₂ (Τ ₂ = R ₂ C _p )
A damping curve composed of two sets of curves each having a damping characteristic corresponding thereto, attenuating an output signal of the charging circuit according to the curve, and _a peak value of the signal Sa corresponding to an effective value of the inverter output current. the input attenuation circuit for outputting an envelope signal S _bE. The comparator of 4 is the signal S _a
The large and small compared to the signal S _a and S _BE outputs the signals S ₁ when there within or equal a predetermined deviation S _BE, 5 timers that time limit operation during the application of the signals S ₁ those discontinued outputs a signal S ₂ from the annihilation time after a period T, to change the selector switch 6 by the signal S ₂ that the time constant tau ₁ is switched constantly from the closed side b to the open-side a to tau ₂ It is.

Figure 2 is a respective units operation waveform diagram corresponding to the above such operation in the first view, FIG and (b) FIG and (b) FIG and (c) and the signal S ₂ / S _BE and S _1, respectively It illustrates the S _2. When the degree of approximation of the envelope trajectory S _be shown in FIG. 3A to the effective value of the inverter output current is insufficient, the time constants τ ₁ and τ ₂ are further subdivided into τ ₁ , τ ₂ , τ ₃ . Then, the time T corresponding to the time constant switching is set to T ₁ , T ₂ , T ₃ .
It is only necessary to subdivide appropriately.

In addition, the inverter input current collecting part may be changed from the part A shown in FIG. 1 to the part C of the inverter main circuit diagram in FIG. 3 in which the connection point of the freewheel diode of the inverter main circuit is changed. The same result as in FIG. 1 can be obtained.

〔The invention's effect〕

According to the present invention, the waveform peak values of the voltage-type inverter input current having a pulse-like waveform are connected by a curve having an appropriate attenuation characteristic to calculate an envelope locus of the respective wave peak values. Obtaining the output current effective value of the inverter eliminates the need for an AC current transformer for detecting the output current effective value and a dedicated effective value detection circuit, thereby simplifying the configuration of the inverter device and reducing the cost. Becomes

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG.
FIG. 3 is an operation waveform diagram of each part of the circuit, FIG. 3 is an inverter main circuit diagram showing a second embodiment of the present invention, FIG. 4 is a circuit diagram showing a prior art embodiment, and FIG. FIG. 4 is a current waveform diagram of an input current and an output current in an inverter. 1 ... (voltage-source transistor type) inverter 2 ... motor 3 ... peak charging circuit 4 ... comparator 5
... Timer, 6 Time constant changeover switch, 7 Comparator, 8 Base drive circuit, 9 Protection circuit, 10
… Effective value detection circuit, C _i , C _p …… Capacitor, R ₁ , R ₂ ……
resistance.

Claims (1)

(57) [Claims] 1. An output current effective value detection circuit for a voltage type inverter, comprising: a detection circuit for detecting an input current of the inverter flowing from a DC power supply; and an output signal of the detection circuit as an input to charge a peak value thereof. A peak charging circuit, an input attenuating circuit which receives the output signal of the peak charging circuit as an input, attenuates the input signal in accordance with an attenuation program with a plurality of long and short time constants, and forms an output signal thereof, and an output signal of the peak charging circuit A timer circuit for detecting a period in which the output signal of the inverter input current detection circuit is larger than the above, outputting a time signal according to a predetermined program in the detection period, and executing an attenuation program of the input attenuation circuit according to the time signal. And an envelope of a peak value of the inverter input current detection signal obtained as an output signal of the input attenuation circuit. Inverter output current effective value detection circuit, characterized in that forming the marks and a detection signal of the output current effective value of the inverter I following.