ELECTRIC POWER CONTROL APPARATUS

Abstract: When an abnormality is detected during driving of an inverter, the output of the inverter is interrupted for a period of several milliseconds and then operated again. If at this time no abnormality is detected, driving is continued, while if an abnormality is again detected, driving is stopped.

Description: Background of the Invention Field of the Invention The present invention relates to a retry control apparatus, particularly to an inverter which converts DC electric power into AC electric power. Description of the Prior Art An inverter apparatus uses semiconductor elements such as a transistor and a thyristor, and thus has a relatively small thermal overload capacity, as well as having weak resistance to surge. Therefore, it is generally provided with a protective capability which functions to interrupt output with a relatively short rise in voltage/current when abnormalities such as abnormal rises in output voltage and electric current are produced. However, the conventional inverter apparatus involves the problem that the protective capability is likely to function when transient abnormalities are produced by noise, and operation is consequently stopped on such occasions. Thus, as described in Japanese Patent Publication No. 20273/1984, it has been proposed that such abnormalities be observed and inhibited immediately after the signs of the abnormalities are detected so as to prevent the occurrence of output interruption. This proposal involves observation of the voltage on the output side of the inverter during regenerative braking and relaxing of regenerative braking when this voltage exceeds a prescribed value. It does not work effectively for all abnormality producing factors. Prior art document FR-A-2 244 282 discloses a fault detector circuit which interrupts power supply to a DC motor. The power supply is controlled by a power switching device. When the conductivity of the power switching device remains high for an unduly long period of time the circuit interrupts power supply to a DC motor. After a certain delay time, power again is supplied to the DC motor, nevertheless, the switching device is furtheron observed and when it again remains opened for an unduly long period of time power supply will be definitely switched off. Then, the apparatus has to be manually reset. Prior art document GB-A-2 152 308 discloses a fault detection apparatus for an air-conditioner. This apparatus interrupts power supply to a compressor only when within a certain first time interval a predetermined number of overcurrent pulses are detected. Power supply is then interrupted for a certain period of time. After lapse of this period of time power is again supplied to the compressor. It is the object of the present invention to provide a control apparatus for an inverter capable of continuously driving the inverter substantially free from changes resulting from transient abnormalities produced by noise, and capable of displaying an adequate protective capability with respect to permanent abnormalities. This object is solved in accordance with the independent claim, dependent claims are directed on preferred embodiments of the present invention. Brief Description of the Drawings Fig. 1 is a block diagram which shows an embodiment of the electric power control apparatus of the present invention. Fig. 2 is a block diagram which shows an embodiment of the retry control circuit shown in Fig. 1. Fig. 3 is a tie chart which shows the action of the circuit shown in Fig. 2 when no abnormality occurs after the retry action. Fig. 4 is a time chart which shows the action of the circuit shown in Fig. 2 when an abnormality occurs after the retry action. Fig. 5 is a block diagram which shows another embodiment of the retry control circuit. Fig. 6 is a time chart which shows the action of the circuit shown in Fig. 5 when abnormalities occur again much later after the retry action. Fig. 7 is a time chart which shows the action of the circuit shown in Fig. 5 when abnormalities occur again immediately after the retry action. Fig. 8 is a block diagram which shows another embodiment of the retry control circuit. Fig. 9 is a flow chart explaining the program structure of the control circuit shown in Fig. 8. Description of the Preferred Embodiments In Fig. 1, reference numeral 1 is a three-phase AC power source, reference numeral 2 is a power rectifier which receives electric power from the power source 1 and rectifies it, reference numeral 3 a condenser which smooths the output of the power rectifier 2, reference numeral 4 is a main circuit portion of the power inverter which receives the DC electric power smoothed by the condenser 3, converts it into three phase AC, and provides it to a load 5, reference numeral 6 is a switching control circuit which forms a portion of the power inverter, reference numeral 7 is a shunt resistance which acts as a current detector and detects the magnitude of input current of the power inverter, and reference numeral 8 is a voltage detector which detects the magnitude of the voltage of the condenser 3 at both ends thereof. The main circuit 4 of the power inverter comprises transistors Q₁ to Q₆ as the main switching elements and flywheel elements D₁ to D₆ connected to each of the main switching elements in inverse parallel. The transistors Q₁ and Q₂, Q₃ and Q₄, and Q₅ and Q₆ are connected in series, respectively, and their both ends are connected to the both ends of the condenser 3. One terminal of the load 5 is connected to each of the series connecting points P₁, P₂, and P₃. The switching control circuit 6 has a speed dispatching apparatus 101 therewithin and is constructed such as to control each of the main switching elements Q₁ to Q₆ so that the output voltage and output frequency of the power inverter correspond to the outputs of the speed dispatching apparatus. That is to say, reference numeral 102 is a slow-acceleration and deceleration dispatching circuit lump circuit which softens the rapid change in output of the speed dispatching apparatus 101. Reference numeral 103 is a voltage dispatching circuit which dispatches the magnitude of the voltage in agreement with the output of the slow-acceleration and deceleration dispatching circuit 102 and reference numeral 104 is a frequency dispatching circuit which dispatches the frequency in agreement with the output of the slow-acceleration and acceleration dispatching circuit 102. Reference numeral 105 is a sine wave generating circuit which generates a sine wave having a frequency in agreement with the output of the frequency dispatching circuit 104 and at a voltage in agreement with the output of the voltage dispatching circuit 103 and reference numeral 106 is a carrier wave generating circuit. Reference numeral 107 is a pulse width modulation circuit which modulates a pulse width by comparing the output of the sine wave generating circuit 105 with that of the carrier wave generating circuit 106. Reference numeral 108 is an AND circuit which logically operates the outputs of the pulse width modulation circuit 107 and of the retry control circuit 11 and the output of this circuit becomes a base signal of the main switching element Q₁. Reference numeral 109 is an inversion circuit which inverts the output of the pulse width modulation circuit 107, reference numeral 110 is an AND circuit which logically operates the outputs of the inversion circuit 109 and of the retry control circuit 11 and the output of this circuit becomes the base signal of the main switching element Q₂. The retry control circuit 11 is constructed as shown in Fig. 2. Reference numeral 31 is a latch circuit of base breaking signal b, reference numeral 32 is a first timer circuit, reference numeral 33 is a latch circuit of the output of the first timer circuit, reference numeral 34 is a latch circuit of a retry prohibition signal g, reference numerals 35 and 36 are AND circuits, and reference numeral 37 is an OR circuit. In addition, a₁, a₂, and a₃ are abnormality detecting signals. The abnormality detecting signal a₁ among them is constructed such as to indirectly judge the temperature of the electronic thermal circuit 38 or the load 5 from the outputs of the frequency dispatching circuit 104 and the current detector 7 when the load 5 is an electric motor and to be output when it judges that the temperature rise has reached a constant value. Detailed description of the electronic thermal circuit 38 is given in the specification of US-4,527,214. The abnormality detecting signal a₂ is output from a comparator 40 when the output of the voltage detector 8 is above the output of the command circuit 41. The OR circuit 37 sets the latch circuit 31 when the abnormality detecting signals a₁, a₂, and a₃ or the retry prohibition signal g is output. Therefore, the latch circuit 31 outputs the base breaking signal b. The AND circuits 108 and 110 function to inhibit the base driving signal so that it is not output when the base breaking signal b is input. The first timer circuit 32 is triggered by the signal c from the AND circuit 35 and functions to generate the pulse signal d of a relatively narrow width after a first fixed time T₁. The latch circuit 33 is triggered by the pulse signal d and functions to generate a signal e which is maintained at a high level during driving. The latch circuit 34 is set by a signal f which appears as the AND conditions of the signals b and e and functions to latch the retry prohibition signal g. Furthermore, the latch circuit 31 of the base breaking signal b is reset by the pulse signal d which is the output of the timer circuit 32 but the latch circuit 33 and that of the retry prohibition signal g are reset when the starting button 50 (see Fig. 1) of the inverter apparatus is opened. The starting button 50 is maintained in a closed state during driving. Next, the working of the embodiment will be explained by the time chart shown in Fig. 3. First, Fig. 3 shows the operation when abnormalities are transiently produced by noise during the driving of the inverter. When any one of the abnormality detecting signals a₁ to a₃ rises as a result of a transient abnormality at a time t₀, the latch circuit 31 is set thereby, the base breaking signal b rises, and thus the output of the inverter main circuit is broken at this time t₀. Since the latch circuit 33 is not driven at this time, the output signal e is at a low level, and the base breaking signal b is input to the timer circuit 32 through the AND circuit 35 thereby, so that the timer circuit 32 is triggered at the time t₀ and begins to measure a time T₁. After the time T₁ has elapsed from the time t₀, the pulse signal d is output from the timer circuit 32 at the time t₁, the latch circuit 31 is reset and the base breaking signal b decays. Thus the base driving signal is again input to the inverter main circuit 4 from the AND circuits 108 and 110, and the Ac output is thereby provided to the load 5 from the main circuit. Therefore, according to this embodiment, it is possible to continue the driving in its existing state and to remove the necessity for restarting when a transient abnormality is produced by noises during driving of the inverter because in this case the AC output is temporarily broken by the base breaking but then the AC output again appears by retrying at t₁ after the short time T₁ has passed. At this time, the shorter the time T₁ determined by the time constant of the timer 32, the smaller the shock experienced when retrying. However, if this time T₁ is too short, the inverter is retried before the abnormality subsides after the time t₀ when it is produced, and thus one of the abnormality detecting signals a₁ to a₃ appears again, causing the driving to the discontinued. Therefore, the value of the time T₁ should be determined at a suitable figure by considering the above conditions, though it is suitable for the value to be determined at several milliseconds, for example, 1 to 2 milliseconds, from the practical point of view. Next, Fig. 4 explains the operation when a permanent abnormality is produced by some troubles of the apparatus, and not by noises. When an abnormality is detected at the time t₀ and any one of the signals a₁ to a₃ appears, the base breaking is carried out by the signal b and the abnormality detecting signals a₁ to a₃ are immediately caused to decay. Therefore, after the time T₁ which is established by the timer circuit 32, the pulse signal d is generated at the time t₁ for retry, the base breaking condition is removed, and the inverter main circuit 4 begins to generate the AC output. However, as described above, since in this case the permanent abnormality is produced at the time t₀, when retrying is again effected at the time t₁ and the inverter again starts to act, the abnormality detecting signals a₁ to a₃ appear again at the time t₂ slightly after the time t₁, the base breaking signal b rises, the retrying thus being cancelled, the base breaking is again carried out, and the AC output of the inverter becomes zero. However, at this time, the latch circuit 33 moves after the time t₁ and its output signal e reaches a high level. Therefore, in this case, the AND circuit 35 is prevented from functioning, and the AND circuit 36 is activated, whereby the base breaking signal b passes through the AND circuit 36 and becomes a signal f, the latch circuit 34 is set, the signal g rises at the time t₂, the signal g is latched thereafter, and resetting of the latch circuit 31 is prevented. Thus, according to this embodiment, when the abnormality detecting signal a appears again between the base breaking triggered by the abnormality detection and by stopping driving after retrying, it is possible to prohibit retrying after the time t₂, to stop driving the inverter, and to adequately attain protection with respect to permanent abnormality. Furthermore, when driving is stopped, the starting button is opened and thus the latch circuits 33 and 34 are reset Fig. 5 is another embodiment of the retry control circuit 11. The difference between what is indicated by reference numeral 6 shown in Fig. 2 and this embodiment is that the second timer circuit 33' is provided in the place of the latch circuit 33 in Fig. 2. A time T₂ which is maintained at a high level from the trigger time t₁ of the second timer 33' is established, and prevention of retrying is maintained only when the abnormality detecting signals a₁ to a₃ again appear within the time T₂ after the pulse signal d is generated from the timer circuit 32 in order to carry out retrying. In this manner, when any one of the abnormality detecting signals a₁ to a₃ is generated within the time T₂ after the retrying effected at the time t₁, the retrying is again carried out at the time t₃, as shown in Fig. 6. However, when the abnormality is again produced before the time T₂, such retrying is not carried out again, as shown in Fig. 7, wherein the driving of the load 5 is stopped by disengaging the starting button 50. Starting is effected by again pushing the push button 50. Furthermore, as seen from the above description, the establishment of too long a time interval T₂ leads to the inability to retry in the case of production of abnormality by noise and facilitates stopping driving the inverter, while too short a time interval causes retrying to be repeated after a short time and trouble in the inverter main circuit is thereby induced. Thus, from a practical viewpoint, it is suitable to select a time interval of about ten times the time T₁, for example about 50 milliseconds. The above described embodiment shows practice of the present invention as hardware. However, recently, microcomputers as shown in Fig. 8 is have been used with versatility to control an inverter apparatus. Therefore, the present invention can be practiced as one of the control programs of the inverter effected by microcomputer 200. An example of such treatment by this embodiment is shown by the flow chart in Fig. 9. This comprises the central processing unit of the microcomputer 200 (expressed as CPU hereinafter), a read only memory ROM 202 (expressed as ROM hereinafter), a random access memory RAM 203 (expressed as RAM hereinafter), a signal input interface circuit 204, and a signal output interface circuit 205. The abnormality detecting signals a₁ to a₃ are input from the signal input interface circuit 204 and the base breaking signal b is output from the signal output interface circuit 205 to the AND circuits 108 and 110 shown in Fig. 1. As shown in Fig. 9, CPU assumes that the abnormality detecting signals a₁ to a₃ enter the signal input interface circuit at step S1. As a result, if the abnormality detecting signals do not enter it, the program goes to a step S2 and continues driving. The presence of the abnormality detecting signals a₁ to a₃ is observed by returning to the step S1 during driving. As a result of the judgement at the step S1, when the abnormality detecting signals are shown, the program goes to a step S3 and immediately outputs the base breaking signal b through the signal output interface circuit 205, and the output of the inverter thereby goes OFF. Then, the program goes to step S4 and judges that the timer function corresponding to the timer 33' in CPU is under calculation. If under calculation, the program goes to step S5 and latches the base breaking signal b. When not under calculation, the program goes to step S6 and the function corresponding to the timer 32 in CPU starts to calculate in the same manner. Next, the program goes to step S7 and then to step S8 after the established time corresponding to the timer 32, and the retry signal (the signal d shown in Fig. 4) is output here. Then, the program goes to a step S9 and the timer function corresponding to the timer 33' starts to calculate. Then the program returns to step S1. In addition, the program for moving the microcomputer 200 along the flow chart shown in Fig. 9 is memorized in RAM 203 and ROM 203 is used to write data for a while for the purpose of activating the microcomputer 200 on the basis of the flow chart shown in Fig. 9.

Claims: A retry control apparatus for a power inverter which converts DC into AC and which has an AC motor connected to an output thereof, abnormality detecting means (7, 8, 38, 40, 42) for detecting an electric abnormality at the input and/or output side of said power inverter, retry means (11) which starts when said abnormality detecting means (7, 8, 38, 40, 42) detect an abnormality and which interrupts output of said inverter immediately and removes an output interruption of said power inverter after elapse of a first fixed time interval (T₁), and a signal latch means (31) which is operated upon a further detection of an abnormality occuring within a second fixed time interval (T₂) after the output interruption has been removed by said retry means, so that removing of the further output interruption by said retry means (11) is inhibited by the output signal of said signal latch means (31), wherein said first fixed time interval (T₁ ) is determined in the range of several milliseconds according to a time duration of a typical transient type abnormality to either one of input voltage level or input current level of the inverter, so that after elapse of said first fixed time interval (T₁) the driving of the motor is continued in its existing state, and said second fixed time interval (T₂) is about more than ten times said first time interval (T₁). An apparatus according to claim 1, wherein the first fixed time interval (T₁) is determined to be between 1 and 2 milliseconds. An apparatus according to claim 1 or 2, wherein the second fixed time interval (T₂) is determined to be 50 milliseconds.

Inventors: HATTORI, MOTONOBU, SHIMONABE, HIDEYUKI, TSUJI, NORITOSHI
Applicants: HITACHI, LTD.
Application year: 1985
Main classification: H02H7
IPC codes: H02M7, H02H7, H02H3