JP2662967B2 - Load current voltage over / under detection circuit of uninterruptible power supply - Google Patents

Description

The present invention relates to a load current voltage excess / deficiency detection circuit of an uninterruptible power supply, and particularly to simplification of the circuit configuration.

(Prior art and its problems) As an uninterruptible power supply, power is supplied to a rectifier load D from a commercial frequency power supply S at all times as shown in FIG. 1, and the loss of the power supply voltage V _S is detected when the commercial frequency power supply S fails. inverter I which is activated together with interruption of the switch SW ₁ by the output of the power failure detection circuit a, for example, controlled by the switching transistor T _r1, T _r2 are alternately turned on by circuit G, the output transformer in the opposite direction current alternately T Primary winding N
By passing the _11, N _12, using an inverter device I for generating a square wave alternating voltage in the secondary winding N _2, and supplies immediately load D loss power according to the power failure has been conventionally used widely.

Incidentally, in this case, for example, when an overcurrent occurs due to an overload or the like on the load D side, it is necessary to protect the commercial frequency power supply circuit and the inverter device. Therefore, conventionally, when the load current is detected and exceeds a predetermined value, A signal is transmitted so that an alarm is issued or the commercial frequency power supply S or the inverter device is disconnected from the load D.

However, in this case, the voltage waveform of the commercial frequency power supply S is a sine waveform as shown in FIG. 2A, while that of the inverter device I is a rectangular wave alternating power supply as shown in FIG. The voltage waveform applied to the IC is different. Therefore, the waveform of the current flowing to the load D by the commercial frequency power supply S is as shown in FIG. 2B, and the waveform of the current flowing from the inverter device I is as shown in FIG. 3B. Therefore, when the same power as the supply power of the commercial frequency power supply S due to the power failure is supplied by the inverter device I, the effective value of the flowing current is different, and the effective value of the current in the case of the inverter device is about 1 / of that of the commercial frequency power supply. It becomes 2.

Therefore, when performing overcurrent detection, it is necessary to separately set overcurrent detection points in consideration of the difference between the effective values of the respective currents.

Therefore, conventionally, a method as shown in FIG. 1 has been adopted. That is, current detectors, for example, current transformers CT ₁ and CT ₂ are provided exclusively for the commercial frequency power supply circuit and the inverter device circuit, and their detection outputs are introduced into overcurrent detection circuits E and F, respectively, and their rectifying and smoothing circuits RC are provided. the average value by _1, RC _2,
This is configured to be compared with reference voltages E ₁ and E ₂ for setting overcurrent detection points by the comparators CM ₁ and CM ₂ , respectively.
Then, when each load current exceeds the overcurrent detection point set by the reference voltages E ₁ and E ₂ , an output is sent out, and the switch SW ₁ inserted in series to the commercial frequency power supply circuit is output by this output. The inverter is shut off, or the operation of the inverter device is stopped or an alarm is generated under the control of the control circuit G.

However, such a method requires two sets of overcurrent detection circuits including a current transformer or the like, and thus has a disadvantage that the circuit becomes complicated and expensive.

(Object of the Invention) The present invention has been made to provide a current detecting means which is simpler and cheaper than the above-mentioned conventional one.

(Means for Solving the Problems) The features of the present invention are as follows. That is, in the uninterruptible power supply device, the load currents in the power supply mode using the commercial frequency power supply and the power supply mode using the inverter device do not flow simultaneously but occur in series. Therefore, even if the input current of the load is detected by one current transformer, if the detection output is separated by the power supply mode, it is possible to detect whether the input current is from the commercial frequency power supply or from the inverter device.

The difference between the current detection points based on the difference between the waveforms of the load current generated by the commercial frequency power supply and the load current generated by the inverter device is determined by calculating the average value of the detected currents, dividing the average value so that it is the same, and comparing the average value with the reference voltage. Separation according to the power supply mode allows comparison between the same current level detection points. Accordingly, the present invention has been made with an idea that overcurrent can be detected by using one set of current detection circuits, and the circuit can be made simple and inexpensive. Next, the present invention will be specifically described with reference to examples.

(Embodiment) FIG. 4 is a circuit diagram of one embodiment of the present invention, in which S is a commercial frequency power supply, I is an inverter device, and their output sides are connected in parallel to form a rectifier and a load D connection. Is done. A power failure detection circuit, SW ₁ is a cut-off switch of the commercial frequency power supply S, or configuration action of is the same as the conventional circuit.

H denotes a power supply detection circuit, which includes the following units. A current transformer CT is connected to a circuit connecting the parallel connection point of the commercial frequency power supply S and the inverter device I to the load D, and is used for detecting respective load currents based on both power supplies. RC is a rectifying / smoothing circuit that calculates an average voltage based on both power supplies detected by the current transformer CT. RT is a voltage dividing circuit,
This is connected between both ends of the series voltage dividing resistors R ₁ , R ₂ , R ₃ and the resistor R ₃ and is in an ON state when power is supplied from the commercial frequency power supply S. It is formed by a mode changeover switch MS which is turned off by an output signal of the power failure detection circuit A at the time of power supply by I.

And the event of a short circuit of the resistor R ₃ by turning the switch MS, partial pressure ratio R ₂ / R ₁ + R ₂ when off switch _{MS, R 2 + R 3 /} R 1 + R 2 + R 3 resistors R _1, R _2, R _3, the average voltage V _S of the load current by the commercial frequency power supply S obtained by the rectifying and smoothing circuit RC.
And the divided voltage of the average value voltage V _I of the load current by the inverter device I, that is, V _S (R ₂ / R ₁ + R ₂ ), V _I (R ₂ + R ₃ / R ₁ + R ₂ + R ₃ ) are equal. It is configured to be. Note that a transistor photocoupler can be used as the switch MS as a relay contact or a semiconductor switch.

CM comparison circuit, E is a reference comparison voltage for setting a detection point of the overcurrent, is compared with the output voltage V ₀ which voltage divider circuit RT. AD ₁ and AD ₂ are AND circuits, respectively. The output signal of the comparison circuit CM is applied to one input terminal of each, and the output signal of the power failure detection circuit A is applied to the other terminal of AD ₁ .
Tama to the other terminal of AD ₂ is added a signal for detecting the on-state cutoff switch SW _1, the commercial and the current detection signal at the time of power supply by the frequency power source S, the current detection at the time of power supply by the inverter I Separate from the signal. The output signal of the AND circuit AD ₁ to stop circuit of the control circuit G of the inverter I Kuwaerae, the output signal is the alarm circuit DR of the AND circuit AD _2, but not further shown, the cut-off switch SW ₁ in Connected to trip circuit. In general, the commercial frequency power supply S has a large overload withstand capability, so that only an alarm may be used.

(Operation) When the power is supplied from the commercial frequency power supply S, there is no output from the power failure detection circuit A. Accordingly, the mode switch MS is in the ON state, and the voltage V _S detected by the current transformer CT and averaged by the rectifying / smoothing circuit CR is R ₂ / R ₁ + R
The voltage is divided by the division ratio of ₂ and applied to the comparison circuit CM. In this state, since the divided voltage is smaller than the level of the reference voltage E, no output is sent from the comparison circuit CM, and the alarm circuit DR does not operate.

When an overcurrent flows beyond the load, the voltage divider RT
Output exceeds the level of the reference voltage E, the comparison circuit CM
It is inputted to the AND circuit AD ₂ by sending an output, wherein A
On signal blocking switch SW _{1 in} is added to the other input terminal of the D _2. Therefore, the AND circuit AD ₂ is connected to the alarm circuit DR.
To notify that an overcurrent has flowed through the commercial frequency power supply circuit, and to take measures against it.

On the other hand, the commercial frequency power supply S is a power failure detection circuit A power failure in addition to sending an output to the control circuit G of the inverter I perform startup of the inverter apparatus I, in addition to as a trip signal to the cutoff switch SW ₁ in the same time This is turned off, and the power supply by the commercial frequency power supply S is stopped. Current detected by the current transformer CT based on the power supply by the inverter I is averaged valued by the rectifying smoothing circuit RC, the voltage V _I enters the dividing circuit RT. Here the mode switch MS is because the resistor R ₃ is inserted is turned off by the output of the power failure detection circuit A, the average value voltage V _I is divided by the division ratio of _{R 2 + R 3 / R 1} + R 2 + R 3 This voltage is lower than the overcurrent detection point voltage set by the reference voltage E. Therefore, the comparison circuit CM does not send a signal, and the inverter device I continues to supply power.

When a current exceeding the load D flows, the voltage divider circuit
Since the output of RT exceeds the level of the reference voltage E, the comparison circuit
CM adds in AD ₁ by sending the output, where since the other input terminal of the AD ₁ output signal of the power failure detection circuit A has been added, AD ₁ is the inverter apparatus I by sending the output In addition to the control circuit G, the inverter device I immediately stops its operation to stop supplying power, and sends out an alarm by a circuit (not shown) as necessary.

(Other Embodiments) One embodiment of the present invention has been described above.
Instead, a current divider can be used, and a DC transformer whose tap is switched by a mode switch can be used instead of the voltage dividing resistor of the voltage dividing circuit RT.

In the above description, the present invention is applied to the detection of overcurrent, but can be applied to, for example, detection of undercurrent. For example, when the load is zero, only a small current required for the light current smoothing circuit is required to flow. Therefore, there is no need to connect a commercial frequency power supply or an inverter device. It is therefore necessary to interrupt when the current through the current transformer falls below a certain value. At this time, the power supply may be stopped by setting the undercurrent detection point by the reference voltage E, and sending the output from the comparison circuit when the divided average voltage drops below the reference voltage E.

Further, the case where the excess or deficiency of the current is detected has been described above, but the present invention can also be applied to the detection of the excess or deficiency of the load input voltage based on, for example, a change in load. In this case, a transformer or a voltage divider may be used instead of the current transformer.

(Effects of the Invention) As is apparent from the above, according to the present invention, a simple and inexpensive circuit is used to detect the excess or deficiency of the load current or voltage of the uninterruptible power supply comprising the applicable frequency power supply and the inverter, and to obtain the required power supply. Protection can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a conventional uninterruptible power supply, and FIGS.
FIG. 4 is a voltage / current waveform diagram when power is supplied from the commercial frequency power supply and the inverter device, and FIG. 4 is a circuit diagram of one embodiment of the present invention.

Claims (1)

(57) [Claims] A power supply circuit for continuously supplying power to a rectifier load from a commercial frequency power supply and supplying the power lost by the inverter device when the commercial frequency power supply fails, a load input current or voltage detection circuit of the uninterruptible power supply; A voltage dividing circuit that switches the voltage dividing ratio between power supply and power outage to generate the same average value output from the detected output of the load input current or voltage at the time of power supply by the commercial frequency power supply and at the time of power outage. A circuit for transmitting an output when the output of the voltage dividing circuit exceeds or falls short of the set detection point voltage, and a circuit for separating an output signal of the circuit into a commercial frequency power supply circuit and an inverter device circuit. Load current voltage over / under detection circuit of power failure power supply.