JPH03135385A - Method of protecting overheat of damping resistor - Google Patents

Abstract

PURPOSE:To prevent the overheat of a damping resistor safely at low cost without using a temperature sensor and a thermal relay by obtaining the comparison value of the maximum power consumption value of the damping resistor and a rated power value and turning a switching transistor ON-OFF. CONSTITUTION:When voltage V at both ends of a smoothing capacitor 4 exceeds a breakdown setting level SO in an inverter 2, the excess of the breakdown setting level SO is detected by a comparator 7A, a transistor 5 is turned ON through an AND gate 8, and discharge is started. An output from the AND gate 8 is introduced to the arithmetic section 9 of the time-lag of first order, and the output is multiplied by a power-consumption coefficient set value from a setter 11 by a multiplying section 10 and the ratio of the temperature rise value of a damping resistor to a temperature rise value at the time of rated power consumption is acquired. When an output from the multiplying section 10 exceeds an overheat detecting setting level S2, an overheat detecting signal C1 normally brought to a high value is brought to a low level, and the transistor 5 for discharge is turned OFF by the AND gate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for overheating protection of a braking resistor when regenerated power from a motor driven via an inverter is discharged to the braking resistor through a switching transistor.

(Prior Art) Conventionally, as this type of protection method, there have been methods such as attaching a temperature sensor directly to the outer sheath of the braking resistor, and attaching a thermal relay to the braking resistor circuit.

[Problem to be solved by the invention]

However, in the case where the temperature sensor is attached to the outer sheath of the braking resistor, there is a problem that when the braking resistor rapidly generates heat, the temperature gradient between the inside of the braking resistor and the outer sheath increases, making it difficult to protect against overheating.

On the other hand, in the thermal relay one-way type, it is necessary to install a thermal relay, and additional equipment is required for the inverter.

Therefore, an object of the present invention is to protect a braking resistor from overheating inexpensively and safely without using a temperature sensor or a thermal relay.

[Means to solve the problem]

When discharging regenerative power from a motor driven via an inverter to a braking resistor through a switching transistor, a first-order lag calculation is performed on the drive signal of the switching transistor according to a preset thermal time constant of the braking resistor. Then, the calculation result is multiplied by the ratio of the maximum power consumption value of the braking resistor to the rated power value (power consumption coefficient), and when this exceeds a preset overheat detection level, the switching transistor is turned off. to prevent overheating of the braking resistor.

[Effect]

To protect a braking resistor from overheating simply by monitoring a drive signal of a discharge control transistor for the braking resistor, and to eliminate the need for a special overheat detection sensor or the like.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 1 is a converter section, 2 is an inverter section, 3 is a motor, 4 is a smoothing capacitor, 5 is a discharge transistor, 6 is a braking resistor, 7A, 7B, 7C are comparators, 8
is an AND gate, 9 is a first-order delay operation section, 10 is a multiplication section,
11 is a power consumption coefficient setting section.

When the voltage of the DC intermediate circuit, that is, the voltage V across the smoothing capacitor 4 exceeds the discharge start setting level SO, the inverter detects this with the comparator 7A, turns on the transistor 5 via the AND gate 8, and starts discharging. do. As a result, when the voltage across the smoothing capacitor 4 decreases, the transistor 5 is turned off. If the regenerative power from the motor is large and the voltage of the DC intermediate circuit further increases during discharge and exceeds the set level 5l (Vov), the comparator 7B detects this and sends a signal C2 to the inverter section 2.
to stop this and perform overvoltage protection. For this reason,
The voltage applied to the braking resistor 6 during discharge corresponds to the value vov (V) of the overvoltage protection setting level 31 at the maximum. From this, the maximum power consumption Pmax of the braking resistor 6 during discharging
is expressed as follows. However, R indicates the resistance value [Ω] of the braking resistance.

On the other hand, since the temperature increase value θ (deg) of the braking resistor becomes a -order lag function of the power consumption P (W), the following relationship holds true.

=V ov”/ (RxP o) −(4)
While the discharge is stopped, T represents the thermal time constant (S) of the braking resistance.

Also, if the rated power value of the braking resistor is Po (W), then (
2) The formula is as follows.

... (3) However, θ0 indicates the temperature rise value at the time of rated power consumption.

Since the overvoltage protection setting level S1 and the discharge start setting level SO are set close to each other, the power consumption of the braking resistor 6 during discharging becomes approximately equal to the value of equation (1).

Therefore, from equations (1) and (3), the relationship between the temperature rise of the braking resistor 6 during discharge and the power consumption is as follows. By calculating this equation (4) or (5), θl/θO when the temperature of the braking resistor increases and decreases can be determined, and when this value reaches the overheat detection setting level 82 or higher, the transistor 5 is turned off. For example, overheating of the braking resistor can be prevented.

However, in this embodiment, instead of calculating equations (4) and (5), the output of the AND gate 8 is guided to the first-order lag calculation section 9, and the power consumption coefficient from the setting device 11 is applied to the output by the multiplication section IO. By multiplying by the set value Vov''/(RXPO), quantities equivalent to θ and I/θ0 are obtained. Therefore, when the output of the multiplier 10 exceeds the overheating detection setting level S2, it is normally high. The overheating detection signal C1 becomes low level, and the AND gate 8 turns off the discharging transistor 5, thereby preventing the braking resistor 6 from overheating.

FIG. 2 is a block diagram showing another embodiment of the present invention, and is an example using a processing unit (CPU).

In recent imparks, various processes including generation of output waveforms are often executed by a processing unit CPU. Therefore,
In this embodiment, the drive signal a of the discharging transistor 5 (output of the AND gate 8) is input to the CPU 12, and the calculations from the first-order lag calculation section 9 in FIG. 1 to the comparator 7C are performed therein. , the other details are the same as in FIG. At this time, since the drive signal a takes only two values, high or low level, there is no need to use an interface such as an A/D converter, and it can be easily input into the CPU. Also, regarding the −th order lag calculation, it is sufficient to perform the following calculation instead of formulas (4) and (5).

Y (N)=Y (N-1) Δt + (X (N) -Y (N-1))Y(N
) : Output Y (N-1
): Output of the previous primary lag calculation unit etc. will also change, so it goes without saying that we need to be able to deal with this.

〔Effect of the invention〕

According to this invention, it is possible to protect the braking resistor from overheating simply by monitoring the drive signal of the discharge control transistor for the braking resistor, and there is an advantage that there is no need to provide a special sensor for detecting overheating. can get.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the invention, and FIG. 2 is a block diagram showing another embodiment of the invention. Code explanation 1... converter section, 2... inverter section, 3...
・Motor, 4... Smoothing capacitor, 5... Discharging transistor, 6... Braking resistor, 7A, 7B, 7C...
- Comparator, 8... AND gate, 9...-Next lag calculation section, 10... Multiplication section, 11... Power consumption coefficient setting section, 12... CPU (processing device). v1 diagram

Claims (1)

[Scope of Claims] 1) In discharging regenerative power from a motor driven via an inverter to a braking resistor through a switching transistor, the thermal time constant of the braking resistor is set in advance with respect to the drive signal of the switching transistor. After performing the corresponding first-order delay calculation, the calculation result is multiplied by the ratio of the maximum power consumption value of the braking resistor to the rated power value, and when this exceeds a preset overheat detection level, the switching A braking resistor overheat protection method characterized by turning off a transistor to prevent overheating of the braking resistor.