JPH04217875A - Method for generating sine-wave pwm control signal of inverter - Google Patents

Abstract

PURPOSE:To use saw tooth carriers having a width which is 1/2 of the period of the sine-wave PWM of an inverter and, at the same time, to make a required PWM command signal coincident with the central point of time of the period of the carriers when the sine-wave PWM of the inverter is calculated. CONSTITUTION:One CPU performs logical operations by successively repeating various kinds of calculation, such as the calculation of the 1/2 value of the pulse width of a required PWM command signal, etc., by dividing the calculation into two routes prior to required points of time by making interrupting operations at every 1/2 period of saw tooth carriers, forms a required pulse by symmetrically distributing the results of the logical operations before and after the central point of time of the corresponding period of the carriers which becomes the required point of time in accordance with the results of the logical operations and setting the logical output between designated two points of time at an 'H' level, and obtains required PWM command signals constituting a pulse string by forming the required pulse at every period of the carriers.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a PW in an inverter.
This invention relates to a method of generating an M control signal.

0002

2. Description of the Related Art As a conventional method for generating a sine wave PWM control signal of this type, a method whose basic operation is shown in the operational waveform diagrams of FIGS. 5 and 6 is known. FIG. 5 shows a case where a sawtooth wave whose peak value is constant and whose width is equal to its period is used as a carrier wave to be compared with the sine wave control signal, and the sawtooth wave indicated by Vc1 in the figure is used. The shaped carrier wave forms a signal train with a constant peak value, with its period being T. Further, Vs is the sine wave control signal, and what is shown is a schematic representation of the state of the control signal between time (n-1)T and time (n+2)T and its vicinity. Furthermore, signal PWM・S
is an inverter sine wave PWM control signal whose time width is the period during which the control signal Vs is larger than the carrier wave Vc1 and is formed in a pulse train for each cycle of the carrier wave Vc1.

Next, FIG. 6 shows a case where a triangular wave Vc2 having a constant peak value and a width equal to its period T is used as a carrier wave to be compared with the sine wave control signal Vs. Sine wave PWM control signal
PWM·S is also obtained in the same manner as in the case shown in FIG.

0004

However, in the conventional sine wave PWM control signal generation method as described above, when using the sawtooth carrier wave Vc1 as shown in FIG. Wave PWM control signal P
The center time and therefore the center phase point of each pulse of WM.S does not coincide with the center time and therefore the center phase point of each corresponding cycle of the carrier wave Vc1, but is unevenly located to the left thereof. Now, the signal PWM・S as mentioned above is 120
If a three-phase AC voltage obtained by controlling a three-phase inverter is organized into three sets of control signals having a phase difference of degrees, and a three-phase AC voltage is obtained, the vibration of the motor can be reduced. As a countermeasure to this problem, if a correction operation is performed to match the center of each pulse width of the signal PWM・S with the center of each cycle of the carrier wave Vc1, the detected Calculation of 1/2 of the time width (or phase width) of each pulse of the signal PWM・S, calculation of the center time (or center phase point) of each cycle of the carrier wave Vc1, and further calculation of the calculation time (or phase point) ) This results in an increase in required calculations such as allocating 1/2 value of the pulse time width (or phase width) before and after the pulse time width (or phase width).

Further, when using a triangular wave Vc2 as shown in FIG. 6 as a carrier wave, it is necessary to find the intersections of the two signals Vs and Vc2 at two locations in order to obtain the signal PWM·S, as shown in FIG. As in the case, the required calculations will increase. Therefore, in both cases, the conventional methods illustrated in FIGS. 5 and 6 result in an increase in the calculation processing time on the software and an increase in the cost of both the software and the hardware.

In view of the above, the present invention provides a sine wave PWM for an inverter that solves various problems during operation of the induction motor without causing problems in both software and hardware as described above.
The object of the present invention is to provide a control signal generation method.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the method for generating a sine wave PWM control signal for an inverter according to the present invention is such that the frequency thereof is equal to the output frequency of the inverter, and the amplitude of each signal is equal to the output frequency of the inverter. An instantaneous value comparison is made between a sine wave control signal having a value proportional to , and a sawtooth carrier wave having a constant peak value, and according to the comparison result, the switching elements constituting the main circuit of the inverter are turned on or off for each period of the carrier wave. In the method for generating a sine wave PWM control signal for an inverter that determines the pulse width of the off control pulse, the width of the sawtooth carrier wave is set to 1/2 of the period of the carrier wave.
and calculates a pulse signal having a pulse width twice as long as the pulse width obtained by comparing the instantaneous values of the sine wave control signal and the carrier wave, and whose center is the center point in the corresponding period of the carrier wave. The pulse signals are synthesized to form a required PWM control signal, and the n-th signal between time nT and time (n+1)T of the signal train whose period is T is
Regarding the calculation for creating a pulse-like PWM control signal corresponding to the n-th carrier wave, the elapsed time tn from the time nT of the intersection of the n-th carrier wave and the sine wave control signal.
Then, the time difference ΔT between the conjugate operation of cutoff and conduction of both switching elements provided to prevent a short circuit of the DC main power supply due to simultaneous conduction of the switching elements of both the upper and lower arms of each phase of the inverter main circuit bridge configuration is calculated from the time tn. ton, which is obtained by subtracting and has a time width of 1/2 of the pulse width of the PWM control signal, and time tun, which is ahead by the time width ton with respect to time (n+1/2)T, and also by the time width ton. Various calculations related to the delayed time tdn are sequentially repeated every 1/2 cycle T/2 of the carrier wave from time (n-3/2) T in the order of tn-ton-tun-tdn of the various quantities, and It is assumed that the logical output level of the PWM control signal is set to H level at the above-mentioned time tun and set to L level at time tdn, and is sequentially created for number n to form a signal pulse train.

[0008]

[Operation] When obtaining a sine wave PWM control signal for an inverter main circuit switching element by instantaneous value comparison between a sine wave control signal and a sawtooth carrier wave signal, the waveform width of the carrier wave is set to 1/2 of its period. By doing this, the center time of each cycle of the carrier wave is automatically determined, and further, a logical operation using a sine table or the like or an analog voltage comparison of the two signals is performed to compare the instantaneous values between the two signals, and the result of the comparison is By distributing and synthesizing pulse waveforms whose width is the obtained time width before and after the center time of each cycle of the corresponding carrier wave, the pulse width is set to be twice the time width obtained by the instantaneous value comparison. A required sine wave PWM control signal whose center coincides with the center time of each cycle of the carrier wave can be obtained. Note that the time t that defines the instantaneous values of both signals is the angular velocity ω with the sine wave control signal as a reference.
If so, there is a relationship between the phase angle θ and θ=ωt, and according to this relationship, the center time and time width can be equivalently converted into a center phase point (or center phase angle) and a phase width, respectively.

[0009] The present invention obtains the required sine wave PWM control signal according to the above-described logical operation by the CPU, and the time nT of the sawtooth carrier wave signal whose period is T and whose time width is T/2. In obtaining the sine wave PWM control signal corresponding to the n-th waveform between time (n+1)T, the elapsed time from the time nT to the point in time when the sawtooth carrier signal becomes larger than the sine wave control signal. t
n, and a time which is obtained by subtracting the operating time difference ΔT for preventing simultaneous conduction of the switching elements of both upper and lower arms of the inverter bridge from the time tn, and which is 1/2 of the pulse width of the required sine wave PWM control signal. width ton, and the time nT+T/2 is the center time, and the time to is before and after that.
The times tun and tdn obtained by dividing
/2) tn-ton-tun-t every T/2 period from T
This is repeated in the order of dn, and the logic output level between the times tun and tdn is set to H to produce a required sine wave PWM control signal.

0010

[Math 1]

[0011] However, λ=Es/Ec, Es is the amplitude of the sine wave control signal, and Ec is 1 of the peak value of the sawtooth carrier wave.
/binary value, θna is the time nT~(n
+1) is the average phase angle between T.

0012

[Embodiments] Examples of the present invention will be explained below with reference to the drawings. First, FIG. 1 is an operational waveform diagram showing the relative relationship between a sine wave PWM control signal PWM·S, a sine wave control signal Vs, and a sawtooth carrier signal Vc obtained according to the present invention. In FIG. 1, the signal Vc has a period of T and a time width of T.
/2, and the illustrated signal Vs has a period (n-1)T to (n+1)th pulse from the (n-1)th pulse to the (n+1)th pulse of the signal Vc.
+1) This is a partial display of the sine wave control signal near T. Further, taking as an example a period nT to (n+1)T corresponding to the n-th pulse of the signal Vc, time tn indicates the elapsed time from time nT to the point in time when the signal Vc becomes larger than Vs, The time ton is the time tn minus the operating time difference ΔT for preventing simultaneous conduction of the upper and lower arm switching elements of the inverter main circuit bridge, and the signal PWM·S is the center time nT+T/2 of the period nT to (n+1)T. The above-mentioned time ton is distributed before and after to create a pulse with a width of 2 tons, and such an operation is performed at each time...(n-1)T-nT-(n+1)T... to make each pulse width・・2・to(n−1) −2
・ton −2・to(n+1) . . . This is a pulse train.

Next, FIG. 2 shows one of the signals Vc in FIG.
FIG. 2 is an enlarged view of the signal Vc and the signal Vs in a period of /2, and shows the principle of calculating the time tn. In this figure, the amplitude Ec, which is 1/2 of the peak value of the signal Vc, is used as a reference value, and the magnitudes of the signal Vc and the signal Vs are made dimensionless, and both signals are expressed by the following equations (
2) It was done as follows.

[0014]

[Math 2]

Note that Es is the amplitude of the signal Vs. Further, 1/2 period T/2 of the signal Vc and 1 period of the signal Vs
/2 period π/ω has a relationship of T/2≪π/ω, therefore, the signal Vs in the illustrated period 0 to T/2 is expressed as λ・sinθna using the average value θna of the phase angle in the period.
can be approximated as a constant value. Therefore, the time tn is defined as the elapsed time when Vc=Vs in the period 0 to T/2 excluding time T/2, as shown in the following equation (3), and the CPU sequentially performs logic for each number n using a sine table. Calculated.

[0016]

[Math 3]

Next, FIGS. 3 and 4 show the PWM control signal PWM・S according to various quantities defined by the above equation (1).
These are a time chart and a flowchart of the creation operation, in which the various quantities of the above formula (1) are obtained by logical operations using a CPU, and the various operations are performed using 1/2 of the sawtooth carrier wave signal (carrier signal) Vc. The signal n is sequentially processed by software interrupt operations at intervals of T/2. As shown in FIG. 3, for example, the calculation of various quantities of the signal PWM·S corresponding to the pulse waveform of the n-th signal Vc between time nT and (n+1)T is performed at time (n-3/2)T.
Therefore, due to the interrupt every T/2, the above tn-ton-
The n-th pulse waveform of the signal PWM.S is completed by setting the logical output level of the CPU to H level between the tun and tdn. Note that in each interrupt interval after time (n-1/2)T, various quantity calculations corresponding to the (n+1)th pulse waveform of the signal PWM・S centered at time (n+3/2)T are performed. t(n+1) -to(n+1)
-tu(n+1) -td(n+1) The processes are proceeded in parallel in the following order. Further, FIG. 4 shows the calculation flow in the CPU for various quantity calculations corresponding to FIG. 1/2)T
For example, with respect to the number n, tn
The route is divided into two routes: -tun and ton-tdn.

[0018]

According to the present invention, regarding a method of generating a sine wave PWM control signal for an inverter by comparing instantaneous values of a sine wave control signal and a sawtooth carrier wave signal, the waveform width of the sawtooth wave constituting the carrier wave can be The various calculations related to the generation of the sine wave PWM control signal are sequentially repeated by the CPU using an interrupt operation every 1/2 period of the carrier wave signal as 1/2 of the period of the carrier wave, and logical operations are performed. By dividing the various calculations in the CPU into two routes depending on whether the timing is at the center point or at the end of the period of the carrier wave signal, it is possible to determine the center point between the required sine wave PWM control signal and each period of the carrier wave signal. The matching operation of points or central phase angles can be easily and reliably performed by one CPU without increasing the calculation time on software or increasing the size and cost of hardware; It is possible to avoid an increase in vibration and noise or a decrease in efficiency in an induction motor that serves as a load for an inverter that is subjected to sinusoidal PWM control using a sawtooth carrier wave.

[Brief explanation of the drawing]

FIG. 1 is an operational waveform diagram of a sine wave PWM control signal PWM·S, a sine wave control signal Vs, and a sawtooth carrier signal Vc obtained according to the present invention.

FIG. 2 is an enlarged view of the sawtooth carrier signal Vc and the sine wave control signal Vs in 1/2 period of the signal Vc;

[Figure 3] Figure 1
Creation operation time chart of sine wave PWM control signal PWM・S corresponding to

[Figure 4] Sine wave PWM control signal corresponding to Figure 1 PWM
・S creation operation flowchart

FIG. 5 is an operation waveform diagram corresponding to FIG. 1 and showing a first method example according to the prior art;

FIG. 6 is an operation waveform diagram corresponding to FIG. 1 and illustrating a second method example according to the prior art;

[Explanation of symbols]

tn Time ΔT when the above-mentioned Vc and Vs become Vc≧Vs Operation command time difference ton between switching elements
1/2 value tun of the nth waveform pulse time width of the above PWM・S Output H level command time tdn for creating the nth waveform of the above PWM・S Output L for creating the nth waveform of the above PWM・S Level command time

Claims (2)

[Claims] Claims: 1. Instantaneous value comparison between a sine wave control signal whose frequency is equal to the output frequency of an inverter and whose amplitude is proportional to the output voltage of the inverter and a sawtooth carrier wave having a constant peak value; In the method for generating a sine wave PWM control signal for an inverter, the pulse width of an on/off control pulse for a switching element constituting a main circuit of the inverter is determined for each period of the carrier wave according to a comparison result, wherein the width of the sawtooth carrier wave is determined. 1 of the period of the carrier wave
/2, and has a pulse width twice as long as the pulse width obtained by comparing the instantaneous values of the sine wave control signal and the carrier wave, and whose center is the center point in one period corresponding to the carrier wave. 1. A method for generating a sine wave PWM control signal for an inverter, the method comprising: calculating and synthesizing the pulse signals to generate a required PWM control signal. [Claim 2] Sine wave PWM of the inverter according to Claim 1.
In the control signal generation method, regarding the calculation for creating a pulse-like PWM control signal corresponding to the n-th carrier wave between time nT and time (n+1)T of a signal train whose period is T, the n-th To prevent short-circuiting of the DC main power supply due to the elapsed time tn from the time nT of the intersection of the carrier wave and the sine wave control signal, and the simultaneous conduction of the switching elements of both the upper and lower arms of each phase of the inverter main circuit bridge configuration. ton, which is obtained by subtracting the time difference ΔT between the conjugate operations of cutoff and conduction of both of the provided switching elements from the time tn, and has a time width of 1/2 of the pulse width of the PWM control signal, and time (n+1/2). Various operations regarding the time tun, which is ahead by the time width ton with T as the center, and the time tdn, which is also delayed by the time width ton, are performed at the time (n-3/n-3/) in the order of the various quantities tn-ton-tun-tdn. 2) From T to 1/2 period T/ of the carrier wave
The logic output level of the PWM control signal is set to H level at the time tun, and the logic output level of the PWM control signal is set to H level at the time t.
1. A method for generating a sine wave PWM control signal for an inverter, characterized in that a signal pulse train is generated by sequentially generating a signal pulse train with respect to number n by setting the signal pulse train to L level at dn.