JPS61262084A - Current detector of inverter - Google Patents

Abstract

PURPOSE:To detect a power regenerative current of an inverter without using a current detector which is expensive and has a large volume by selecting a current that flows through each switch of a switch group on the positive or negative side of the inverter to detect the current. CONSTITUTION:Positive main switch groups 3a-3c are connected in a direction for making a current flow the positive electrode of a DC power source 1 to an AC motor 2, and negative main switch groups 5a-5c are connected in a direction for making a current flow from an AC motor 2 to the negative electrode of the power source 1. Current detecting resistors 7a-7c are connected in series with the main switch groups 5a-5c. Current detecting resistors 7a-7c are connected in series with the switch groups 5a-5c. A current detector is formed of the resistors 7a-7c, current selecting switches 8a-8c and an inverting amplifier 9, and the output is fed back to a current control amplifier 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a current detection device for an inverter.

[Technical background of the invention and its problems]

This type of device includes, for example, "New Drive Electronics" (written by Naohiko Ueyama, Denkishoin), P. 94, No. 3.
．． Figure 35 The AC servo circuit using a synchronous motor is well known, and its configuration is shown in Figure 4.

In Fig. 4, 1 is a DC power supply, 2 is an AC motor, 31 is an inverter bridge, 32a, 32b, 32c.
18 is a current detector, 18 is a position detector, 0 is a ROM in which a current pattern is written in advance, 34 is a multiplier, 35a
, 35b, 35c are current control amplifiers, 36 is PWM
It is a logic circuit.

The operation of the apparatus having the above configuration is well known, so a description thereof will be omitted. Next, problems with the above-mentioned device will be described.

In other words, the magnetic current detector 32a used in this device
, 32b, 32c E requires insulation means,
Generally, a two-hole current detector or a resistor and an isolated amplifier are used. However, these detectors are generally expensive and have a large volume, making it difficult to miniaturize the device.

Furthermore, a device having the configuration shown in FIG. 5 is also known.

In Figure 45, 1 is a DC power supply, 2 is an AC motor, and 3a.

3b, 3c, 5m, 5b, 5c are semiconductor switches; 4a;

4b, 4c*6a*6b, and f3c are diodes, and 41 is a current detection resistor.

Although the device configured as described above can detect current with a single resistor, it has the disadvantage that regenerative current cannot be detected.

[Purpose of the invention]

An object of the present invention is to provide a small and inexpensive inverter current detection device that can detect the regenerative magnetic current of an inverter without using an expensive and bulky current detector such as an insulated amplifier or a Hall current detector. Obtaining 1: There is.

[Summary of the Invention] The present invention is characterized in that current is detected by selecting each swing f (=flowing current) of the positive side switch group or negative side switch group of the inverter.

[Embodiments of the invention]

An embodiment of the present invention is shown in FIGS. 1 and 2.

In Fig. 1, 1 is a DC power supply, 2 is an AC motor, and 3a.

3b, 3c are positive side main switches, 4a, 4b, 4c are positive side diode groups, 5a, 5b, 5c are negative side main switch groups, 6a, 6b, 6c are negative side diode groups, 7
a, 7b.

7c is a current detection resistor group, 8a, 8b, 8c is a first current selection switch group, 9 is an inverting amplifier, 10 is a second current selection switch, 11 is a current control amplifier, 12 is a zero cross comparator, and 13 is an absolute value circuit, 14 C triangular wave generation circuit, 15 comparator, 16 P9VM logic circuit,
17 is a distributor, and 18 is a position detector.

FIG. 2 is a detailed diagram of the PWM logic circuit 16. In FIG. 2, 21 to 26 are AND circuits, 27, 28, and 29 are OR circuits, and 30 is a logic inversion circuit.

Hereinafter, the operation of the embodiment will be explained using FIG. 1, FIG. 2, and FIG. 3.

First, the overall circuit operation will be explained with reference to FIG.

The current command value and the current feedback value I are proportionally and integrally controlled by the current control amplifier 11 (2) to obtain the voltage command value E*. A pulse signal B* rwm,su1(: is converted) with a duty width proportional to the absolute value of the voltage command value B*.

Further, the polarity of the voltage command value f is determined by the zero cross comparator 12, and signE*7□ is obtained.

On the other hand, the distribution signals U' to Z' by the distributor 17 are as shown in FIG.
As shown in Figure 2, the signal is logic 1 during the 12σ period and logic 0 during the 240° period in the order of V→2′→1→X′→W′→Y′. However, the voltage command value? The logics of U' and x', v' and y', and w' and z' are switched depending on the sign of the polarity "sigh Ii".As the distributor 17, for example, ICμPC1246c manufactured by NEC Corporation may be used.

The signal B"FW'X~1,U' obtained in this way
~2' is converted by the PWM logic circuit 16 into a control signal U-Z for each arm of the inverter bridge.

Next, the operation of the PWM logic circuit 16 will be explained using FIG. Now, the distribution signals U' and 2' are logical 1 and the other parts. This corresponds to time t0 in FIG.

At this time, v, y, w are logical 0, Z is logical 1°, U is E*
The same logic as wja4, X is the inverted logic of R''cross vffln.

Therefore, in Fig. 1, each main switch of the inverter is 5C is conductive, 3b m 3c * sb is non-conductive, and 3a and 5a are E
”: Alternately conducting and non-conducting with the duty width of PWJLXl.

That is, in the inverter bridge, the negative side switch of a certain phase is conductive, the positive side and negative side switches of one of the other phases perform PWM control, and the remaining switches are nonconductive.

Now, how the current detection circuit of the present invention operates according to the above control method will be described.

The current detection portion in FIG. 1 is a current detection resistor 7a.

7b, 'Ic and current selection switch? 8a, 8b, 8
c, 10, and an inverting amplifier 9.

The first current selection switch includes three switches 8a.

gb, 8c, and distributed signals X', Y'.

Only one is shorted by 2' and the other two are open. The polarity of the selected signal wire / has not been determined as a detected magnetic current, and the second current selection switch 10 selects the I /
Or select -I, / and give feedback including polarity! get.

The operation of the current detection circuit will be specifically explained while following the current path. However, the direction in which the current flows from the negative side switch of the inverter to the negative pole of the DC power supply is defined as positive.

Now, distribution signals U' and Z' are logic 1, other distribution signals v',
Assume that w', x', and y' are in a logical 0 state.

This corresponds to time t0 in FIG.

(1) In case of power line mode (1) From DC power supply 1 to AC motor 2 (When supplying two power, the current path is from DC power supply 1 to positive main switch 3a -
, AC motor 2→negative side main switch 5c→current detection resistor 7c+DC′ source 1.

(1) When current circulates between the inverter bridge and the AC motor 2, the current path is AC motor 2 → negative side main switch 5C → current detection resistor 7c → ゛ current detection resistor 7a →
The negative side diode 6a becomes the AC motor 2.

Therefore, (+), (1) In either case, the current I/ selected by the first current selection switch in the row mode is the current flowing through the current detection resistor 7c.

Its polarity is positive.

(2) In the case of regeneration mode (1) When regenerating power from the AC motor s2 to the DC power supply 1, the current path is from the AC motor 2 to the positive diode 4a.
→DC source 1→Current detection resistor 7c→Negative diode 6
c→AC motor 2.

(W) When current circulates between the inverter bridge and the AC motor 2, the current path is as follows: AC motor 2 → negative side main switch 5a → 'transfer current detection resistor 7a → current detection resistor 7c
→ Becomes a negative side diode 6c.

Therefore, (1) (1) In both cases, in regeneration mode.

The signal line selected by the first current selection switch is a current flowing through the current detection resistor 7C, and its polarity is negative.

From the above explanation, the first current selection swing j8g.

The signal f' selected by 8b and 8c is a current flowing through the current detecting resistor 7G both during travel and during regeneration, and only its polarity is different.

On the other hand, depending on the polarity sigHg of the voltage command value, the distributor 1
Distribution signals U' to z', U' and X', v' and Y
'.

Since the logics of W' and 2' are switched, it is necessary to switch the polarity of the signal If' selected by the first current selection switches y-Ba, 8b, and 8c at the same time. SW: 7-10 and inverting amplifier 9 are in charge.

In other words, the detected feedback flow rate f' is selected by the second current selection switch, If' is selected in a certain rotational direction when traveling, -I is selected when regenerating, and / is selected in the other direction. In the rotational direction, -It/ is selected during forward movement, and -It/ is selected during regeneration, and it is important to note that current can be detected in all cases.

Furthermore, we will explain the case where the polarity of the two-sulfur flow command value 1 is reversed, and as a result, the polarity of the voltage command value E* is reversed, causing forced braking. In this case, the distribution signals U' and 2
' is at logic 1 and the other distribution signals are at logic 0.

Just before the voltage command value polarity SIgh]13* is reversed,
``The current path is (1) AC motor 2 → negative side main switch f5
c→Current detection resistor 7c −+ @Current detection resistor 7a→
Is the current circulating between the inverter bridge of the negative side diode 6a → AC motor 2 and the AC motor?
) DC power supply 1 → positive side main switch f3a → AC motor 2 → negative side main switch f 504 Current detection resistor 7c → DC power supply 1 of DC power source 1 is supplying power to the AC motor. In either case, the signal I, / selected by the first current selection switch is a single current flowing through the magnetic current detection resistor 7c, and its polarity is positive.

Now, when the polarity sigr+E'' of the voltage command value is reversed, the distribution signals W' and X' become logic 1, and the other distribution signals become logic 0.The current path is as follows: SWITCH f 5c -+ Magnetic current detection resistor 7cm + '4 Current detection resistor 7a → negative side diode 6a → Is the current circulating between the inverter bridge of AC motor 2 and the AC motor? (2) AC motor 2→Positive diode 4C→
This is the case where power is transferred from the AC motor 2 of the can motor 2 to the DC power supply 1. In either case, the signal I/ selected by the first current selection switch is a current flowing through the current detection resistor 7m, and its polarity is negative. However, the second current selection switch 10 is switched at the same time as the polarity of the voltage command value is reversed, and the detected feedback current I/ has different polarities before and after the polarity of the magnetic pressure command value is reversed. It's continuous.

Therefore, current can be detected even when the polarity of the magnetic current command value controller 9 is reversed and forced (=braking) is performed.

The embodiment described above is an example in which the present invention is applied to a triangular wave comparison PWM inverter. This embodiment is a relatively small-sized, high-output PWM inverter constructed in a compact and inexpensive manner, and can be applied as a servo device by adding a two-speed control system.

〔Effect of the invention〕

According to the present invention, the four regenerative currents of the inverter can be detected using a resistor without using an insulating means such as an insulating amplifier or a Hall current detector, so that the inverter can be constructed in a small size and at low cost.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an inverter current detection device according to one embodiment of the present invention, and the second factor is the PWM logic circuit 16 in FIG.
Figure 3 is a timing diagram necessary for a detailed explanation of the present invention, and Figure 4 is a configuration diagram showing different embodiments of a conventional inverter current detection device. Yes. l...DC power supply 2...AC motor 3m, 3b, 3c, 5a, sb, 5c"・
Semiconductor switch 4a, 4b, 4c, 6m, 6b
, 6c...Diode 7m, 7b, 7c...
・Current detection resistor 8m, 8b, gc, io-・-
Switch 9... Inverting amplifier (7317) Agent Patent attorney Noriyuki Chika (and 1 other person) Figure 5 Z' t. Figure 3

Claims (1)

[Claims] A group of positive main switches connected in a direction to flow current from the positive pole of the DC power source to the load, a group of negative main switches connected in a direction to flow current from the load to the negative pole of the DC power source, and either the positive or negative switch described above. or a current detection resistor inserted in series with each switch in one switch group and on the DC power supply side, and a diode connected in antiparallel to each of the positive and negative main switches, in which the current A first current selection switch that selects the terminal voltage of the detection resistor, an inverting amplifier that inverts only the polarity of the selected signal, and selects either the signal with the polarity inverted or the signal before inversion. An inverter current detection device comprising a second current selection switch.