JP2001086764A - Inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an inverter which can be surely protected, while eliminating errors in interruption of operation by detecting overload of a brake circuit accurately, without requiring an overload detecting means including a thermal relay or a thermostat. SOLUTION: Short time power capacity characteristics of a brake resistor 4 are stored as data, in a characteristics table 22, and a protective operating section 21 determines the magnification a (=p/P) between an instantaneous power p determined by the resistance of the brake resistor and the power capacity P of the brake resistor. An integrated on-time t allowable for a magnification a is then determined from the short time power capacity characteristics of the brake resistor, and on/off state of a brake switch is detected through sampling. A short time withstanding capacity and use rate are then monitored by integrating or subtracting the integrated on-time of the brake resistor every sampling period. When the integrated on-time exceeds an allowable value, a decision is made that the brake circuit is overloaded, and an alarm output and the like is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter for absorbing regenerative power from a motor in a braking circuit, and more particularly to a protection device for a braking circuit.

[0002]

2. Description of the Related Art FIG. 6 shows a braking circuit of an inverter and a protection device therefor. The inverter main circuit obtains DC power from AC power in the forward converter 1, smoothes it with the smoothing capacitor 2, and obtains AC power in which the voltage and frequency are controlled by the inverse converter 3 which becomes a voltage form, and controls the motor as a load. Drive.

When a motor is driven at a variable speed by this inverter, regenerative power generated when the motor is decelerated is:
It is taken in to the DC side through the flywheel diode of the inverse converter 3. This regenerative power is regenerated as charging power for the capacitor 2. If the regenerative power is large, the voltage of the capacitor 2 rises to a rated value or more.

Therefore, a series circuit of a braking resistor 4 and a braking switch 5 is provided on the DC side, and when the DC voltage approaches the overvoltage level, the switch 5 is turned on, and the regenerative power flows through the braking resistor 4 to generate heat energy. Absorb as. The braking switch 5 is a self-extinguishing semiconductor device such as a bipolar transistor or IGBT.

The ON control of the switch 5 is performed by detecting a DC voltage by a DC / DC converter 6, and when the detected voltage exceeds a value close to an overvoltage level set in a comparator (hysteresis comparator) 7, the comparison is performed. The detection signal is detected as an inverted output of the switch 7, and the detection signal is power-amplified by the drive circuit 8 to obtain an on-gate output of the switch 5.

In such a braking circuit, when the regenerative power is larger than expected at the time of design, the braking resistor 4
However, there is a risk of overheating and burning due to overload. In addition, a current higher than the rated current may flow through the brake switch 5 and damage the current. Further, when the braking switch 5 is short-circuited, a current continues to flow through the braking resistor 4 even when the motor is driven, which causes a loss of the inverter function.

A device for protecting a braking circuit for solving such inconveniences includes a thermal relay 9 provided in series with the braking resistor 4 or a thermostat 1 directly attached to the braking resistor.
0 forms a protection sequence. The thermal relay 9
The presence or absence of an overload of the braking resistor is monitored based on the current flowing therethrough, and when the overload is detected, the electromagnetic contactor 11 on the AC input side of the forward converter 1 is shut off. The thermostat 10 monitors the surface temperature of the braking resistor 4 and shuts off the electromagnetic contactor 11 when detecting an overload. A flywheel diode 12 protects the brake switch 5 from a spike voltage generated by a braking resistor when the brake switch 5 is turned off.

The interruption of the electromagnetic contactor 11 eliminates the amount of current flowing from the forward converter 1 to the braking circuit, and eliminates an overload state and a short-circuit state of the braking resistor and the braking switch.

[0009]

The conventional protection device for a braking circuit requires a thermal relay 9 and a thermostat 10 externally connected to an inverter main circuit, and a sequence circuit for shutting off the electromagnetic contactor 11 with these detection signals. In addition, wiring and installation space for connecting these circuits are required.

Further, since the thermal relay 9 and the thermostat 10 are inferior in detection sensitivity and responsiveness, in order to surely detect an overload, the overload detection level is set low. For this reason, even when the braking resistor 4 and the braking switch 5 are not in an overload state, they may be erroneously detected as an overload, and the electromagnetic contactor 11 may be frequently shut off. The interruption of the electromagnetic contactor is the same as the power failure of the inverter, and the stop of the power causes the motor to stop.

An object of the present invention is to provide an inverter which does not require an overload detecting means such as a thermal relay or a thermostat, detects an overload of a braking circuit with high accuracy, and can surely protect the overload and eliminate an erroneous operation stop. Is to do.

[0012]

In order to solve the above-mentioned problems, the present invention provides an instantaneous power p determined by a resistance value R of a braking resistor and a DC voltage V applied thereto and a magnification a of a power capacity P of the braking resistor. (= P / P), the allowable on-time t at the magnification a is obtained from the short-time power capacity characteristic of the braking resistor, and the on / off state of the braking switch is detected by sampling. When the braking resistor is in the ON state, the ON integrated time is calculated, and when the braking resistance is OFF, the process of subtracting the OFF integrated time by the ratio of the usage rate (the ratio of the amount of time when integrating and the amount of time when subtracting) is repeated. When the on-integration time exceeds the permissible on-integration time t in this processing state, it is determined that the braking circuit is overloaded, and is characterized by the following configuration.

A braking circuit in which a braking resistor and a braking switch are connected in series is provided on the DC side of the inverting unit, and the braking switch is turned on when the DC side approaches an overvoltage level with regenerative power from a motor driven at a variable speed. In an inverter that absorbs regenerative power with a braking resistor, the inverter includes a data storage unit that stores a short-time power capacity characteristic of the braking resistor, and a protection operation unit that determines and protects an overload of the braking circuit, The protection operation unit is configured to determine whether the braking resistor is allowed to be turned on based on a ratio of an instantaneous power applied to the braking resistor to a power capacity of the braking resistor and the short-time power capacity characteristic obtained from the data storage unit. Means for calculating an integrated time, and an ON product obtained by integrating an ON time during which a voltage is applied to the braking resistor in a sampling cycle for detecting an ON / OFF state of the brake switch. Means for determining time, means for subtracting the on-integrated time at a fixed rate in the off state where no voltage is applied to the braking resistor in the sampling cycle, and when the on-integrated time exceeds the permissible on-integrated time. Means for determining that the braking circuit is overloaded.

The data storage means stores the short-time power capacity characteristics for each type of the braking resistor, and the protection calculating means sets the braking resistance when the type of the braking resistor is set. The protection operation is performed by taking in the short-time power capacity characteristic according to the type of the above.

[0015]

FIG. 1 is a block diagram of an inverter braking circuit and a protection device according to an embodiment of the present invention. 6 differs from FIG. 6 in that a protection operation unit 21 and a short-time power capacity characteristic table 22 are provided instead of the protection device using the thermal relay 9 and the thermostat 10.

The power capacity of the braking resistor 4 has a short-time rated capacity characteristic. For example, for a given enamel resistor, the 30 second rated capacity is six times the continuous rated capacity, and the 180 second rated capacity is twice the continuous rated capacity. That is, the resistor does not overheat or burn for a short time even if the power consumed by the resistor is large, and the short-time rated capacity is larger than the continuous rated capacity. FIG. 2 shows the short-time power capacity characteristic of the enamel resistor. As the power consumption becomes shorter, the magnification with respect to the continuous rated capacity becomes higher as the time becomes shorter.

A characteristic table 22 serving as data storage means
Stores the short-time power capacity characteristic of the braking resistor 4 as table data.

The protection calculation unit 21 determines the control state (on / off state) of the brake switch 5 by using the brake switch state detection circuit 2.
3 to monitor whether the overload of the braking resistor and the braking switch is determined based on whether or not the detected on-integration time of the braking resistor 4 exceeds the allowable on-integration time of the braking resistor. The protection calculation unit 21 outputs an overload alarm when an overload determination is obtained, and further shuts off the electromagnetic contactor 11.

Here, the allowable on-time of the braking resistor is calculated as
The power capacity and resistance value of the braking resistor, the usage rate, and the short-time power capacity characteristic are calculated and calculated from the data in the table 22. The on-time of the braking resistor is obtained as an integrated value of the on-time during which the DC voltage is applied.

However, in the off state where no DC voltage is applied, the on integration time is subtracted by the ratio of the usage rate. The usage rate is represented by ON time / (ON time + OFF time), and is set at a time ratio at which heat generated during the ON time can be radiated during the OFF time.

The protection operation unit 21 and the characteristic table 2
The protection device for the braking circuit composed of 2 is configured in hardware or software, and can be configured to be provided separately from the control circuit of the inverter, or can be configured to have a function added to the control circuit of the inverter.

FIG. 3 is a control flow in the case where the protection device of the braking circuit has a software configuration. Hereinafter, steps S1 to S8 will be described in order.

(S1) As the constant setting input of the protection operation unit 21, the power capacity P, the resistance value R, and the usage rate% ED are input. When obtaining the overload judgment according to the usage environment of the inverter, the ambient temperature of the braking resistor is also set, and
The short-time power capacity characteristic of the braking resistor having the ambient temperature as a parameter is used.

(S2) The instantaneous power p consumed by the braking resistor 4 when the braking switch 5 is turned on is determined. This operation is obtained by p = V ² / R. V is the DC voltage of the inverter (fixed value).

Further, the magnification a of the instantaneous power p and the power capacity P
(= P / P), and the allowable on-integration time t at the magnification a is determined from the short-time power capacity characteristic of the braking resistor 4 read from the characteristic table 22 (FIG. 2).

(S3) The output state of the brake switch state detection circuit 23 (the ON / OFF state of the brake switch 5) is sampled. This sampling period is determined by the braking switch 5
The on-time and the off-time are obtained with high accuracy by making the on-off frequency predicted several tens to several hundreds of times. Note that sampling can be performed on a gate voltage that is output from the comparator 7.

(S4) The ON / OFF state of the brake switch 5 is determined from the sampling result in each sampling cycle.

(S5) If the sampling result is ON (the brake switch 5 is ON), the ON integration time is added for a time corresponding to the sampling cycle.

(S6) Current ON accumulated time value and processing S2
Compare the magnitude with the permissible on-time calculated in the above.

(S7) When the ON cumulative time is equal to or longer than the allowable ON cumulative time, an overload alarm is output, and further, the shut-off output of the electromagnetic contactor 11 is obtained.

(S8) When the sampling result is off (the brake switch 5 is off), the time obtained by multiplying the time corresponding to the sampling period by the usage rate% ED is subtracted from the on-integrated time.

FIG. 4 is a time chart showing the above control. When the brake switch is continuously turned on for a long time or is repeatedly turned on and off with a high on-time ratio, and an on-brake time reaches an allowable on-time integration time, an overload alarm is generated.

Therefore, in order to protect the braking circuit, the allowable on-time is obtained from the resistance value of the braking resistor and the short-time power capacity characteristic, and the on / off state of the braking switch is detected at the sampling cycle. When the braking resistor is ON, the process of integrating the ON integration time is repeated, and when the braking resistor is OFF, the process of subtracting the ON integration time by the ratio of the usage rate is repeated, and braking is performed based on whether the ON integration time exceeds the allowable ON integration time. Monitor the resistance and braking switch overload conditions. Thus, the overload state of the braking resistor can be reliably detected and protected. Furthermore, a short-circuit failure of the brake switch can be detected by comparing and determining the integrated ON time and the ON time allowed for the brake switch.

The short-time power capacity of the braking resistor is several times larger than its continuous rated capacity, and the overload state is determined based on the short-time power capacity. Compared to the thermostat method, it is possible to obtain an accurate overload judgment expanded to the capacity permitted by the short-time power capacity characteristic.

In the above embodiment, the protection method in the case where the type of the braking resistor is predetermined is shown. However, there are several types of the braking resistor used in the braking circuit, such as enamel, steel, cement, etc. The short-time power capacity characteristics of the resistor have different characteristics as shown in FIG. In the case of a braking circuit that uses different braking resistances, characteristics for each type of resistance are stored in the characteristic table 22 of FIG.
By setting the type of the braking resistor as an input of step S1, the table data for each type of the braking resistor can be read and the overload can be protected.

[0036]

As described above, according to the present invention, the allowable on-time is obtained from the short-time power capacity characteristic of the braking resistor, and the on / off state of the braking switch is detected by sampling. By integrating or subtracting the on-time of the braking resistor every time, the short-time tolerance and the usage rate are monitored, and when the on-time exceeds the permissible on-time, it is determined that the braking circuit is overloaded. In addition, it is possible to detect the overload state of the braking circuit by reliably expanding the capacity of the braking resistor to the capacity allowed by the short-time power capacity characteristic, thereby to protect the protection circuit and eliminate erroneous operation stop of the inverter.

Further, the configuration of the protection device may be a configuration in which functions are added to the control circuit of the inverter and the like, which is simpler than a conventional protection device using a thermal relay or a thermostat.

[Brief description of the drawings]

FIG. 1 shows an inverter braking circuit and a protection device according to an embodiment of the present invention.

FIG. 2 shows the short-term power capacity characteristics of a braking resistor.

FIG. 3 is a control flow of a protection operation unit according to the embodiment.

FIG. 4 is a control time chart of the protection device in the embodiment.

FIG. 5 is a graph showing short-time power capacity characteristics for each type of braking resistor.

FIG. 6 shows a conventional inverter braking circuit and protection device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 forward conversion unit 3 reverse conversion unit 4 braking resistor 5 braking switch 6 DC / DC converter 7 comparator 8 driving circuit 11 electromagnetic contactor 21 protection calculation unit 22 short-time power capacity characteristic table 23 ... Brake switch state detection circuit

Claims (2)

[Claims] 1. A braking circuit in which a braking resistor and a braking switch are connected in series on the DC side of an inverting section, and the braking switch is turned on when the DC side approaches an overvoltage level with regenerative power from a motor driven at a variable speed. An inverter that absorbs regenerative power with a braking resistor and has a data storage unit that stores a short-time power capacity characteristic of the braking resistor and a protection calculation unit that determines and protects an overload of the braking circuit. The protection operation means is allowed for the braking resistance based on a ratio of an instantaneous power applied to the braking resistance to a power capacity of the braking resistance and the short-time power capacity characteristic obtained from the data storage means. Means for determining an allowable on-time, and an on-time obtained by integrating an on-time during which a voltage is applied to the braking resistor in a sampling cycle for detecting an on / off state of the brake switch. Means for calculating an integration time; means for subtracting the on-integration time at a fixed ratio in the off state where no voltage is applied to the braking resistor in the sampling period; and wherein the on-integration time exceeds the permissible on-integration time. Means for determining when the braking circuit is overloaded. 2. The data storage means stores short-time power capacity characteristics for each type of the braking resistor, and the protection calculation means sets the braking resistance when the type of the braking resistor is set. The inverter according to claim 1, wherein the protection operation is performed by taking in the short-time power capacity characteristic according to the type of the inverter.