JP2015029395A - Air conditioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air conditioner that protects switching elements against thermal destruction without the addition of new components.SOLUTION: The air conditioner of the present invention includes a motor control device. The motor control device has: a three-phase inverter circuit having the switching elements to convert DC power to three-phase AC power; a motor control section for drivingly controlling a three-phase motor by means of the three-phase inverter circuit; a current detection section for detecting a current flowing through the three-phase inverter circuit; a junction temperature estimation section for estimating a temperature of junctions of the switching elements; and a control section for stopping driving the three-phase motor if the current detected by the current detection section exceeds an overcurrent threshold set beforehand as a standard of overcurrent determination. The overcurrent threshold is set so as to decrease with increasing junction temperature and increase with decreasing junction temperature. The junction temperature estimation section estimates the temperature of the junctions of the switching elements on the basis of the detection result of the current detection section and a detection result of an outside air temperature thermistor.

Description

  The present invention relates to an air conditioner.

  In a three-phase inverter circuit that has a plurality of switching elements and converts DC power to three-phase AC power, the switching elements are sequentially turned on / off to generate three-phase AC power and drive the three-phase synchronous motor. When a three-phase synchronous motor is driven at high speed, a large current flows through the switching element, and the junction temperature of the switching element may exceed the maximum rating and generate heat. In order to prevent such heat generation of the switching element and thermal destruction due to heat generation, an inverter circuit device described in Patent Document 1 has been proposed.

  Patent Document 1 discloses a switching circuit that controls the rotation of a motor, a drive signal that drives the switching circuit using a pulse wave-modulated rectangular wave, and a temperature sensor that captures a gentle resistance value change of the thermistor accompanying a temperature change. A temperature detection circuit that outputs a detection signal and an overcurrent detection circuit that outputs an abnormal signal when the motor current exceeds a predetermined value. If the temperature detection circuit changes, the drive circuit A technique is disclosed that immediately stops the output of the drive circuit when the output is changed and the abnormal signal changes.

JP 2008-29198 A

  However, when the technique according to Patent Document 1 is applied to an air conditioner, a thermistor must be newly added to the switching element that controls the rotation of the motor. For this reason, it is necessary to increase the cost by adding a thermistor and to redraw the wiring pattern.

  An object of this invention is to protect a switching element from a thermal destruction, without adding a new component in an air conditioner.

The air conditioner of the present invention includes an indoor unit and an outdoor unit, the indoor unit includes an indoor heat exchanger and an indoor fan, and the outdoor unit includes an outdoor heat exchanger, an outdoor fan, a motor control device, and an outdoor temperature thermistor. And an outdoor heat exchanger thermistor for measuring the temperature of the outdoor heat exchanger, the motor control device includes a switching element, a three-phase inverter circuit for converting DC power into three-phase AC power, and a three-phase inverter A motor control unit that drives and controls a three-phase motor by a circuit, a current detection unit that detects a current flowing in a three-phase inverter circuit, a junction temperature estimation unit that estimates a temperature of a junction of a switching element, and a current detection unit A controller that stops driving of the three-phase motor when the detected current exceeds a preset overcurrent threshold that is set in advance to determine whether or not it is an overcurrent; and
The overcurrent threshold is set to be lower as the junction temperature is higher and lower as the junction temperature is lower, and the junction temperature estimation unit is based on the detection result of the current detection unit and the detection result of the outside temperature thermistor. Estimate the temperature of the junction of the switching element.

  According to the present invention, the junction temperature estimation unit estimates the junction temperature of the switching element based on the detection result of the current detection unit and the detection result of the outside air temperature thermistor, so a new temperature detection unit is added to the air conditioner. Without addition, the switching element can be protected from thermal destruction.

Block diagram showing overall configuration of motor controller The figure showing overcurrent threshold information and current limit threshold information with respect to junction temperature

The air conditioner of the present embodiment includes an indoor unit and an outdoor unit, the indoor unit includes an indoor heat exchanger and an indoor fan, and the outdoor unit includes an outdoor heat exchanger, an outdoor fan, a motor control device, and an outdoor air temperature. The motor control device has a thermistor and an outdoor heat exchanger thermistor that measures the temperature of the outdoor heat exchanger, and includes a three-phase inverter circuit that has a switching element and converts DC power to three-phase AC power; A motor control unit that drives and controls a three-phase motor with an inverter circuit, a current detection unit that detects a current flowing through the three-phase inverter circuit, a junction temperature estimation unit that estimates a temperature of a junction of the switching element, and a current detection unit A controller that stops driving of the three-phase motor when the current detected in step exceeds an overcurrent threshold that is set in advance to determine whether or not it is an overcurrent; and
The overcurrent threshold is set to be lower as the junction temperature is higher and lower as the junction temperature is lower, and the junction temperature estimation unit is based on the detection result of the current detection unit and the detection result of the outside temperature thermistor. Estimate the temperature of the junction of the switching element. According to the air conditioner of the present embodiment, the junction temperature estimation unit estimates the temperature of the junction of the switching element based on the detection result of the current detection unit and the detection result of the outside air temperature thermistor. Thus, the switching element can be protected from thermal destruction without adding a temperature detector.

  First, an air conditioner to which the motor control device of this embodiment is applied will be described. The air conditioner includes a refrigeration cycle in which a compressor, an outdoor heat exchanger, an expansion valve, and an indoor heat exchanger are sequentially connected by refrigerant piping. The air conditioner includes an indoor unit and an outdoor unit. The indoor unit includes a housing having an air inlet and an air outlet, an indoor heat exchanger that exchanges heat with indoor air, a blower fan that blows out the indoor air sucked from the air inlet and exchanged with the indoor heat exchanger from the air outlet And a wind direction plate for controlling the air blown out from the air outlet. The outdoor unit includes a compressor that compresses refrigerant, an outdoor heat exchanger that exchanges heat with outdoor air, an outdoor fan that flows outdoor air through the outdoor heat exchanger, an outdoor temperature thermistor that measures outdoor temperature, and an outdoor heat exchanger. An outdoor heat exchanger thermistor for measuring temperature and a motor control device are provided. The motor control device converts AC power into DC and provides it to an inverter circuit for driving the motor, and drives, for example, a three-phase synchronous motor arranged inside the compressor.

  The configuration of the motor drive device will be described. FIG. 1 is a block diagram showing the overall configuration of the motor control device. The motor control device includes a three-phase inverter circuit that drives a three-phase motor, and a switching element is used for the inverter circuit. In this embodiment, in order to estimate the temperature of the switching element, information on the thermistor mounted on the air conditioner and the rotational speed of the outdoor unit fan is used. The thermistor attached to the air conditioner includes an outside temperature thermistor and a heat exchanger temperature detection thermistor (hereinafter referred to as “DEF thermistor”). The number of rotations of the outdoor unit fan is used to estimate the amount of air that hits the attached heat radiating fins in order to improve the heat dissipation of the switching element.

  The motor control device includes a DC power supply, a three-phase inverter circuit for driving and controlling a three-phase synchronous motor, an electromagnetic induction type overhead wire current sensor, a junction temperature estimation unit, an overcurrent stop control unit, an inverter drive circuit, .

  In addition, as a direct current power supply, what is comprised from an alternating current power supply and the converter circuit (For example, a reactor, a full wave rectifier circuit, and a smoothing circuit not shown) connected to this alternating current power supply is employ | adopted. May be.

  The three-phase inverter circuit has first to sixth switching elements. An IGBT or a MOSFET is used as the switching element. The three-phase inverter circuit converts DC power supplied from a DC power source into three-phase AC power, which is a pseudo sine wave of U phase, V phase, and W phase, based on a pulse width modulated wave signal (PWM signal). The three-phase synchronous motor is driven and controlled by supplying three-phase AC power, which is a pseudo sine wave after return, to the three-phase synchronous motor.

  The overhead wire current sensor detects a circuit current flowing from the DC power source to the three-phase inverter circuit. The circuit current detected by the overhead wire current sensor is sent to the junction temperature estimation unit and the overcurrent determination unit.

  The junction temperature estimation unit of the present embodiment estimates the junction temperature of the first to sixth switching elements from the temperature information of the outside temperature thermistor and the current information of the overhead wire current sensor. Specifically, first, based on the temperature information obtained by actually measuring the circuit current by the overhead wire current sensor and the temperature of the switching element, the table data obtained by previously obtaining the correlation between the circuit current by the overhead wire current sensor and the temperature of the switching element. Create The junction temperature estimation unit estimates the element temperature based on the circuit current measured by the overhead wire current sensor based on the table data, and further considers the influence of the outside air temperature on the element from the temperature information of the outside air temperature. Accurately estimate the temperature of the element.

  Next, the overcurrent threshold determined based on the temperature of the junction element estimation unit and the circuit current will be described. FIG. 2 is a diagram illustrating overcurrent threshold information and current limit threshold information with respect to the junction temperature.

  The maximum rated current of the switching element (here, the maximum rated current is a relative maximum rated current having temperature characteristics, which is different from the absolute maximum rated current). The outside air temperature (ambient temperature) of the element Fluctuates following the change in the junction temperature of the element so that it is high when the element is low and low when the outside air temperature of the element is high. Temporarily, if the overcurrent threshold value used as a reference when determining whether or not it is an overcurrent is set to a low fixed value based on the case where the element junction temperature is high, if the actual element junction temperature is low, Although there is a margin to the overcurrent, it is determined that the set overcurrent has been reached, and the drive of the motor is interrupted. In this case, the motor cannot be driven efficiently in consideration of the point that the maximum rated current of the switching element has temperature characteristics.

  Therefore, in the motor control device of the present embodiment, the overcurrent threshold that is set in advance to determine whether or not the overcurrent is high is set when the element junction temperature is low, and the element junction temperature is high. The temperature characteristic is set so as to be variable according to the change in the junction temperature of the element so as to be low when it is high. Similarly, the current limit threshold value used as a reference for determining whether or not to limit the current before the current value reaches the overcurrent threshold value is high when the element junction temperature is low, and the element junction temperature is high. It is set so as to have a temperature characteristic that can be changed in accordance with a change in the junction temperature of the element so that it becomes low when the value is high.

  Thus, in this embodiment, the overcurrent threshold information is high in the region where the junction temperature detected by the junction temperature detector is low (40 to 50 ° C.) as shown in FIG. The temperature is set so as to be variable according to the change in the junction temperature so as to be low in the high temperature region (50 to 90 ° C.). Actually, the overcurrent threshold information is set with appropriate temperature characteristics in consideration of the temperature characteristics of the maximum rated currents of the first to sixth switching elements.

  As for the current limit threshold information, as shown in FIG. 2, the first, second, and third deceleration regions are provided in regions where the current is lower than the overcurrent threshold information, and the current is limited step by step. . In the first deceleration region, the limit current value is set higher, but in the third deceleration region, it is set lower and the current is more rapidly limited.

  Here, since the radiating fin is attached to the switching element, the element temperature can be estimated more accurately by reading the information of the wind that hits the radiating fin. The information on the wind that hits the heat radiating fins is influenced by the air volume of the outdoor unit fan. Furthermore, since the wind by the outdoor unit fan releases the temperature of the heat exchanger, the temperature of the wind can be measured based on the temperature information of the DEF thermistor. With these two pieces of information, it is possible to estimate the air volume and temperature of the radiating fin. From this information, the overcurrent threshold information and current limit threshold information are offset higher when the air volume is high and the temperature is low. When is high, it is possible to perform control such as offsetting to a low level. In other words, in addition to the temperature information of the outside temperature thermistor and the current information of the overhead wire current sensor as described above, the rotational speed of the outdoor fan and the detection result of the outdoor heat exchanger thermistor are used to more accurately detect the switching element. The junction temperature can be estimated.

Claims (2)

An indoor unit and an outdoor unit,
The indoor unit includes an indoor heat exchanger and an indoor fan,
The outdoor unit includes an outdoor heat exchanger, an outdoor fan, a motor control device, an outdoor air temperature thermistor, and an outdoor heat exchanger thermistor that measures the temperature of the outdoor heat exchanger,
The motor control device
A three-phase inverter circuit that has a switching element and converts DC power to three-phase AC power;
A motor control unit for driving and controlling a three-phase motor by the three-phase inverter circuit;
A current detector for detecting a current flowing in the three-phase inverter circuit;
A junction temperature estimation unit for estimating the temperature of the junction of the switching element;
A controller that stops driving of the three-phase motor when the current detected by the current detector exceeds a reference overcurrent threshold that is set in advance to determine whether the current is an overcurrent;
Have
The overcurrent threshold is set to be lower as the junction temperature is higher, and higher as the junction temperature is lower,
The said junction temperature estimation part is an air conditioner which estimates the temperature of the said junction part of the said switching element based on the detection result of the said electric current detection part, and the detection result of the said external temperature thermistor.   In Claim 1, The said junction temperature estimation part is based on the detection result of the said electric current detection part, the detection result of the said external temperature thermistor, the rotation speed of the said outdoor fan, and the detection result of the said outdoor heat exchanger thermistor. An air conditioner that estimates the temperature of the joint of the switching element.