JP3239426B2 - Drive device for brushless DC motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive device for a brushless DC motor using an inverter circuit, which is used for driving a compressor of a variable capacity air conditioner.

[0002]

2. Description of the Related Art In a brushless motor driving device,
In order to detect the relative position between the stator winding and the rotor of the permanent magnet, there is a method that uses a terminal voltage including an induced voltage generated in the stator winding without using a position detecting element such as a Hall element. Are known. Further, in order to stabilize the operation, the power factor is calculated based on the waveform of the current flowing to the input side of the inverter circuit, that is, the DC side portion, instead of the terminal voltage, and the power factor is advanced and delayed. And the power factor is 1
A method is known in which the voltage and frequency applied to the inverter circuit are feedback-controlled so that

[0003]

However, in this method, the power factor of 1 is known from the current waveform of the DC section, but when the power is advanced or delayed, the absolute value of the power factor is It was unknown, and the current phase could not be freely controlled. This makes it difficult to optimally control the operation efficiency and control the expansion of the operation range. Furthermore, analog signal processing is required in the motor control circuit,
The design was complex and costly. In addition, since it is necessary to detect the current of the DC section, it is necessary to use an expensive DC current detector (DCCT). In the current detection, since the control circuit and the motor main circuit are electrically connected, reliability is reduced.

[0004] Further, at the time of power factor detection, an error occurs due to the effect of a chopping component (carrier) in the inverter circuit, and furthermore, it is impossible to sufficiently remove this carrier with a filter. When the value was high, the operation was unstable (if a filter was used, it was difficult to determine the power factor from the current waveform). Further, conventionally, the phase command has been set to around 0 in order to always aim for the optimum efficiency from the start to the maximum speed. For this reason, at a low frequency such as at the time of startup, the operation is likely to be unstable, and there is a case where a step-out occurs. When the inverter reaches its maximum voltage, further high-speed rotation becomes impossible.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problem, and obtains a current phase based on a voltage phase at the time of zero crossing of a motor current without using a current flowing in a DC side portion of an inverter circuit. By controlling the current phase to a desired value, it is possible to control the current phase to an arbitrary value, and to achieve stable operation, optimization of operation efficiency, high reliability, and low cost of a brushless DC motor. It is an object to provide a driving device. Also, by giving the current phase command according to the frequency of the inverter circuit,
It is an object of the present invention to provide a brushless DC motor drive device that stabilizes operation from startup to high speed.

[0006]

According to a first aspect of the present invention, there is provided an inverter circuit comprising a switching element for converting a DC voltage into an AC voltage and supplying the voltage to a brushless DC motor. A brushless DC motor driving device, comprising: a current detecting means for detecting a motor current; and a control circuit for driving and controlling a switching element of the inverter circuit based on a detection signal from the current detecting means. A current phase detecting means for detecting a motor voltage phase at the time of current zero crossing by the current detecting means, and detecting a motor current phase with reference to the voltage phase; Computing means for computing a voltage command or a frequency command to the inverter circuit so that the current phase becomes In which the it was to control the inverter circuit based on the calculation result of the calculating means.

According to a second aspect of the present invention, in the device of the first aspect, an AC current detector is used for the motor current detecting means, and a microcomputer capable of detecting zero crossing is used for the control circuit. According to a third aspect of the present invention, in the device according to the first aspect, an AC current detector is used as the motor current detecting means, and the detected current output is passed through a low-pass filter to remove a carrier component. is there.

According to a fourth aspect of the present invention, in the device of the first aspect, a desired current phase arbitrarily designated is changed according to the frequency of the inverter circuit. According to a fifth aspect of the present invention, in the device according to the fourth aspect, a delay phase command is output at a low frequency such as at the time of starting. According to a sixth aspect of the present invention, in the device according to the fourth aspect, a leading phase command is output at a high frequency. Claim 7
According to the invention described in the fourth aspect, the inverter circuit outputs a leading phase command so that the inverter circuit does not have the maximum voltage output.

[0009]

According to the first to third aspects of the present invention, the control circuit detects the motor voltage phase at the time of the current zero crossing detected by the current detecting means, and detects the motor current phase based on the voltage phase. A voltage command or a frequency command to the inverter circuit is calculated so that the detected current phase becomes a desired current phase command specified from the outside. By driving and controlling the inverter circuit based on the calculation result, operation at an arbitrary current phase can be performed. Also,
According to the configuration of the fourth to seventh aspects, the current phase can be appropriately given from the time of startup to the time of high speed according to the frequency of the inverter circuit.

[0010]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the overall configuration of a driving device for a brushless DC motor. In FIG. 1, an AC power supply 1 is a full-wave rectifier circuit 2.
The smoothing capacitor 3 is connected to a DC output terminal of the full-wave rectifier circuit 2, and further, an inverter circuit 4 is connected. A voltage Vdc is applied to the DC output terminal.
Is obtained. The inverter circuit 4 is formed, for example, by connecting six transistors as three switching elements in a three-phase bridge, converting a DC voltage into an AC voltage, and changing the frequency and voltage of the AC fundamental wave to arbitrary values by PWM (pulse width modulation). It can be controlled. The AC output voltage of the inverter circuit 4 is supplied to a star-connected three-phase stator winding of the brushless DC motor 5. The brushless DC motor 5 includes a stator winding and a permanent magnet type rotor. The brushless DC motor 5 is housed in a compressor 6 and drives a compression element 7. The compressor 6 is connected via an accumulator 8 to a refrigeration circuit including a heat exchanger and the like (not shown).

From the inverter circuit 4 to the brushless motor 5
AC current detector (ACC)
T) 9 is provided, and a detection output of the ACCT 9 is input to a control circuit 11 that drives and controls a switching element of the inverter circuit 4 via a filter circuit 10. The control circuit 11 comprises a microcomputer or the like, and
9 and a detection signal from the filter circuit 10, a current phase with respect to the voltage phase at the time of zero crossing of the motor current is obtained. It has the function of controlling the applied voltage and frequency.

FIG. 4 is a time chart of one phase (here, W phase) voltage (fundamental wave and PWM waveform) of the motor, a W phase voltage phase angle θv as an internal variable, a W phase current waveform, and a filter output. Show. This example shows a case where the current phase is delayed with respect to the voltage. The one-phase motor current detected by the ACCT 9 is governed by the fundamental wave and the PWM carrier component as shown in the figure. In order to detect the power factor of the fundamental wave to be obtained, it is desirable to remove the carrier component. Therefore, the filter circuit 10 is provided at the output terminal of the ACCT 9 as described above. In FIG. 4, T1 is one cycle of the power supply in the inverter circuit, and when the power supply frequency is f, T1 = 1 / 2πf.

An embodiment of the filter circuit 10 is shown in FIG.
Gain characteristics and delay phase (θfilt) for that frequency
The characteristics are shown in FIGS. This characteristic is used as a correction table (filter constant table). As illustrated, the filter circuit 10 is a low-pass filter including a resistor R and a capacitor C. Generally, the frequency of the fundamental wave of a brushless DC motor for a compressor is about 20 to 300 Hz, and the carrier frequency is about 3 kHz. As described above, since the frequency ratio is only about 10 times, it is difficult to obtain ideal characteristics (the phase delay is very small for the fundamental wave and the gain is very small for the carrier frequency). is there.

Here, a filter is designed such that the fundamental wave phase is not delayed as much as possible within a range where the zero-cross signal does not cause chattering due to the carrier component. Actually, since there is a phase delay with respect to the fundamental wave for the above reason, the bold line shown in FIG. 3B is stored in advance in a table on the memory to correct the effect of the filter. Used. The microcomputer constituting the control circuit 11 operates at a single voltage of 5 V and is capable of performing a zero-cross interrupt on the AC input. As a result, the present invention can be implemented with less hardware.

Next, the PW performed in the control circuit 11
The software processing of the M control will be described. This general function is shown in the dashed block in FIG. The current phase detection block 12 reads the voltage phase angle φv which is a variable in the circuit at the time of a zero-cross interruption of the current, and calculates the current phase φ ′ including the influence of the filter. In the correction block 13,
The filter delay amount φfilt for the current operation frequency is read from the table, corrected by subtraction, and the true current phase φ is obtained.

The PI control block 14 performs PI (proportional integration) control on the frequency and the voltage by a predetermined algorithm so that the phase difference becomes a desired value. In the adder 15,
The specified initial frequency command f from the command block 17
By adding the PI calculation results Δf and Δv to 0 and the voltage command v0, a final voltage and frequency command for the PWM calculation output block 16 is created.

The details of the software processing will be described with reference to the flowcharts of FIGS. First, the interruption process of the current zero cross will be described with reference to FIG. Control circuit 11
Detects the current zero crossing, and enters an interrupt process.
First, the voltage phase θv (angle), which is an internal variable of the microcomputer, is read (# 1). Then, it is checked whether the current rises (# 2). If the current rises, the current phase including the influence of the filter circuit 10 is detected. φ ′ is set to −θv (# 3). This corresponds to the processing of the current phase detection block 12. Next, the frequency (internal variable) f is read (#
4) Further, the delay phase θfilt with respect to the frequency is read from the filter constant table (# 5), and the actual current phase φ is obtained as φ′−θfilt (# 6) in order to correct the influence of the filter. Correction of the effect of this filter is performed by correction block 1
This corresponds to the process of No. 3. This actual current phase φ is stored in the memory (# 7), and the interrupt processing ends.

In step # 2, if the current is not rising but falling, it is checked whether the voltage phase θv is positive (# 8). The current phase φ ′ including the influence of the filter circuit 10 is set to −θv + π (# 9). If the voltage phase θv is not positive, the current phase φ ′ including the influence of the filter circuit 10 is set to −θv−π (# 10). In each case, the process proceeds to # 4.

Next, the interrupt processing of the PWM control will be described with reference to FIG. This process is performed at the carrier frequency, that is, P
This is performed for each control cycle of the WM inverter. The current phase command φref arbitrarily specified is read (# 11), then the actual current phase φ is read from the memory (# 12), and the current phase difference Δφ is calculated as φ−φref (# 13).
Next, frequency PI control (# 14) and voltage PI control are performed (# 15). This corresponds to the processing of the PI control block 14, and the frequency Δf and the voltage Δv for the fine adjustment are obtained by the following equations. Here, Kpf and Kpv are gain (constant), Ti
f and Tiv are integration times (constants), T is the control cycle, and the subscript k is the number of interrupts. In the case of a phase delay, the frequency is controlled to increase, but the voltage is controlled to decrease, so that Kpf <0 and Kpv> 0.

[0020]

(Equation 1)

Next, a frequency command f for PWM control of the inverter circuit is given by f = f0 + Δf, and a voltage command v is given by
The calculation is performed using the equation v = v0 + Δv (# 16). Then, the voltage vector is determined and the switching signal is output as the PWM waveform calculation (# 17), and the interrupt processing is completed. By the above processing, control is performed such that the difference between the current phase command φref and the actual current phase φ becomes zero.

FIG. 7 shows the overall configuration of a brushless DC motor driving apparatus according to another embodiment. In the above embodiment, the current phase is arbitrarily set to a desired value. However, the control circuit 11 in the embodiment shown in FIG. 7 changes the current phase command according to the frequency of the inverter circuit. ing. That is, the control circuit 11 has a preset phase command table 18, reads the frequency command f output from the adder 15, and reads the current phase command φref from the phase command table 18 according to the frequency command f. Are supplied to the PI control block 14. The reading process from the phase command table 18 corresponds to the process of # 11 in FIG. The other processes of the current zero cross interrupt and the PWM control interrupt are the same as those described above.
Duplicate description is omitted.

FIGS. 8A and 8B show examples of the current phase command φref according to the frequency f and the inverter output voltage value at that time in this embodiment. As shown in the figure,
At the time of low frequency such as at the time of startup, the delay phase command is output with emphasis on stability. At the time of high frequency, the advance phase command is output to increase the frequency limit. At that time, the leading phase is set so that the output voltage of the inverter circuit does not reach the maximum voltage so that the voltage control for stabilization always functions.

The present invention is not limited to the configuration of the embodiment described above, and various modifications are possible. For example, in the above, only one phase of the motor current is detected. Is detected, the stability can be further improved. If the stability is high, Kpf
Alternatively, one of Kpv may be set to zero.

[0025]

As described above, according to the first aspect of the present invention,
At the time of zero crossing of the motor current, the current phase with respect to the voltage phase is detected, and the command frequency and the command voltage to the inverter are controlled so that the current phase becomes a specified desired command value. The phase difference of the current can be controlled to an arbitrary phase from the leading to the lag, so that the optimum control of the efficiency and the control of expanding the operation range can be performed.

According to the second aspect of the present invention, since the motor current is detected by the ACCT and the control circuit capable of detecting the zero crossing is used, in addition to the above effects, the control circuit portion is insulated from the motor main circuit, and noise and the like are generated. Elimination of erroneous operation can be prevented, and design can be easily performed with a small number of parts, thereby achieving cost reduction.

According to the third aspect of the present invention, the ACCT output can be passed through the low-pass filter to appropriately eliminate the carrier component. And a highly reliable and high-performance brushless DC motor driving device can be realized.

According to the fourth to seventh aspects of the present invention, the current phase command is changed according to the frequency of the inverter, so that appropriate operation can be performed while ensuring stability in the entire operation range from the start to the high speed. .

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a driving device of a brushless DC motor according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of an embodiment of a filter circuit in the device.

FIG. 3 is a characteristic diagram of the filter circuit.

FIG. 4 is a time chart of voltage and current waveforms in the device.

FIG. 5 is a flowchart of a current zero cross interruption process in the device.

FIG. 6 is a flowchart of a PWM control interrupt process in the same device.

FIG. 7 is a configuration diagram of a driving device of a brushless DC motor according to another embodiment of the present invention.

FIG. 8 is a diagram showing an example of a current phase command according to a frequency and an inverter output voltage value at that time in the other embodiment.

[Description of Signs] 4 Inverter circuit 5 Brushless DC motor 9 AC current detector 10 Filter circuit 11 Control circuit 12 Current phase detection block 13 Correction block 14 PI control block 16 PWM calculation output block 17 Command block 18 Phase command table

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-15271 (JP, A) JP-A-3-31778 (JP, A) JP-A-3-215173 (JP, A) 57285 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) H02P 6/18

Claims (7)

(57) [Claims] 1. A brushless DC motor driving device having an inverter circuit comprising a switching element for converting a DC voltage into an AC voltage and supplying a voltage to the brushless DC motor, a current detecting means for detecting a motor current. A control circuit that drives and controls a switching element of the inverter circuit based on a detection signal from the current detection means.The control circuit detects a motor voltage phase at the time of current zero crossing by the current detection means, Current phase detection means for detecting a motor current phase based on a voltage phase, and a voltage command or a frequency command to the inverter circuit so that the detected current phase becomes a desired current phase arbitrarily specified. Calculating means for calculating, and controlling the inverter circuit based on the calculation result of the calculating means. A driving device for a brushless DC motor, characterized in that: 2. The brushless DC motor drive device according to claim 1, wherein an AC current detector is used as the motor current detecting means, and a microcomputer capable of detecting zero crossing is used as the control circuit. 3. The brushless DC motor according to claim 1, wherein an AC current detector is used as the motor current detecting means, and the detected current output is passed through a low-pass filter to remove a carrier component. Drive. 4. A brushless DC motor drive device according to claim 1, wherein a desired current phase arbitrarily specified according to claim 1 is changed in accordance with a frequency of said inverter circuit. 5. The brushless DC motor drive device according to claim 4, wherein a delay phase command is output at a low frequency such as at the time of starting. 6. The brushless DC motor driving device according to claim 4, wherein a leading phase command is output at a high frequency. 7. The brushless DC motor driving device according to claim 4, wherein the inverter circuit outputs a leading phase command so as not to output the maximum voltage.