JP2582071B2 - Pulse width modulation type inverter control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable voltage / variable frequency (VVVF) inverter using a pulse width modulation method, and more particularly to an inverter suitable for controlling an induction motor for driving an electric vehicle. Related to the device.

[Conventional technology]

2. Description of the Related Art In recent years, an induction motor driven by an inverter has been used for driving an electric vehicle, which has greatly contributed to cost reduction and simplified maintenance.

By the way, drive the induction motor in such a case
In the VVVF inverter device, a so-called PWM control method of converting a modulated wave signal, which is a basic component of the output voltage, and a carrier wave such as a triangular wave into a pulse signal is conventionally employed. There are a synchronous control method in which the zero-cross point of the modulated wave and the carrier wave always coincide with each other, and an asynchronous control method in which the carrier is fixed regardless of the modulated wave.

First, the synchronous control method is widely used in the field of electric railways in which it is necessary to limit the switching frequency of the inverter and suppress induction failure, but there is a problem in torque control at low speed.

On the other hand, the asynchronous control system is superior in control at low speed and has a fast response to torque fluctuation.On the other hand, when the number of pulses is reduced in a high speed region, the torque becomes unbalanced due to a phase shift, and the operation becomes unstable. There was a problem.

For example, Japanese Patent Application Laid-Open No. Sho 60-174088 discloses a control device which switches between asynchronous control at low speed and synchronous control at high speed by utilizing the advantages of synchronous control and asynchronous control.

[Problems to be solved by the invention]

In the above prior art, asynchronous control and synchronous control are controlled by simply switching only the inverter frequency.However, in an ultra-low frequency range using asynchronous control, accurate PWM control is required. However, there is a possibility that torque pulsation may occur in an extremely low frequency range.

An object of the present invention is to provide a PWM inverter control device that can perform sufficiently accurate PWM control even at a low speed and that can be used for driving an induction motor to sufficiently suppress torque pulsation.

[Means for solving the problem]

An object of the present invention is to provide an arithmetic processing unit that software-generates an output frequency command signal and an output voltage command signal of an inverter,
A first pulse width modulation unit that receives the output frequency command signal and the output voltage command signal and outputs a pulse width-modulated pulse synchronized with the inverter output AC; An arithmetic processing unit for generating pulse width data asynchronous to the inverter output AC in a software manner and a second pulse width modulation unit for outputting a pulse width modulated pulse from the pulse width data are used. This is achieved by selectively controlling the main circuit switching element of the inverter by the appropriate pulse width modulated pulse and the pulse width modulated pulse synchronized with the inverter output AC.

(Operation)

According to the present invention, in order to perform accurate PWM control at low speed, asynchronous control mainly by software processing is performed, and at high speed, the operation responsibilities of arithmetic processing means such as a computer are reduced. Synchronous control for processing by dedicated hardware is performed based on the command.

As a result, at the time of low speed, the ratio of the portion executed as software in the control processing is increased, so that the high precision particularly required at low speed can be easily obtained. Therefore, high-speed processing can be performed while reducing the load on software processing, and as a result, appropriate control can always be obtained from low speed to high speed.

〔Example〕

Hereinafter, a PWM inverter control device according to the present invention will be described in detail with reference to the illustrated embodiments.

FIG. 1 shows an embodiment in which the present invention is applied to the control of an induction motor for driving an electric vehicle. In FIG. 1, reference numeral 1 denotes a CPU of a micro computer, which is a forward / reverse signal F, R of an operation command, a power running / braking. Signal P, B, brake handle output B _r , load-response signal PD,
The rotation frequency detector output f _{r of the} induction motor, the filter capacitor voltage E _cf , and the motor current I _M are converted into digital quantities and taken in, and the notch signal 71 of the operation command unit 7 and the brake handle output B _r which input the operation command are inputted. , The load signal PD and the filter capacitor voltage _Ecf are input to the slip frequency pattern generator 3, the powering current pattern generator 5, and the braking current pattern generator 6, respectively, to generate each pattern. Then, enter the respective pattern output 31,51,61 and the motor current I _M slip frequency calculating unit 4, determines a slip frequency signal f _s.

On the other hand, in the frequency detector 2, the rotational frequency detector output _fr
Outputting a rotational frequency signal f _R from obtaining inverter operating frequency f _i0 by adding a slip frequency signal f _s by the adder 13.

Further, the pulse mode control unit 8 determines the inverter output AC 1 based on this f _i0 and the filter capacitor voltage E _cf.
A pulse mode signal PM for designating the number of pulses in a cycle is determined and output to the outside.

Further, the modulation factor calculating section 9 can output a required inverter output voltage and an inverter device according to _Ecf so that the modulation factor signal γ and V / F are constant from f _i0 , E _cf and I _M. Calculate the percent output voltage _VMD , which is the ratio of the maximum voltage,
The modulation degree signal γ is output to the outside.

At this time, the inverter operating frequency f _i0 is set to E _cf to suppress the vibration due to the resonance of the filter existing in the main circuit.
Then, an adder 14 adds the damping signal DP generated by the damping control unit 12 to the inverter frequency signal _fi1 and outputs the determined signal to the outside.

In this embodiment, the processing of the asynchronous control is mainly performed by the software of the CPU 1, and therefore, the asynchronous operation
In 10, from f _i1 and PM and percentages output voltage V _MD, create operation data POT, NOT the control switching signal 11 and asynchronous control PWM signal, and outputs it to the outside. The asynchronous control circuit 100 synthesizes the waveforms from the POT and NOT to form the asynchronous control P.
The WM signal 101 is generated.

On the other hand, in the synchronous control PWM circuit 200, the outputs f _i1 ,
PM and γ are input, the modulation wave and the carrier wave are compared, and a synchronization control PWM signal 201 is generated.

Then, the control switch 15 switches the PWM signal 131 to either 101 or 201 according to the control switch signal 11, and the gate pulse generator 16 generates the gate signal 141.

Here, the output from the CPU 1 to the outside is the inverter operating frequency signal f _i1 , the pulse mode signal PM, the modulation factor signal γ and the control switching signal 11, and the arithmetic data POT, NOT for asynchronous control PWM signal generation.
The asynchronous control processing is mostly performed by software using the CPU 1, and the PWM signal can be obtained only by setting the operation data 122 to the timer. Therefore, there is an effect that a control device for a PWM inverter having a simple circuit configuration can be realized.

Next, generation of the asynchronous control PWM signal will be described with reference to FIGS. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals. Phase calculating unit the phase of the fundamental wave of the output voltage from the inverter frequency signal f _i1 in the CPU 1 110
, And outputs its output to the sine wave conversion unit 111 and the switching control unit 112.
Output to Sine wave conversion signal 121 and percent output voltage V
_The multiplication unit 113 multiplies the _MD to calculate instantaneous output voltage value data 122, sets the output data in the timer P114 and the timer N115, and supplies each timer output POT, NOT to the waveform synthesizing circuit 116 to perform asynchronous control PWM. A signal 101 is generated.

The switching control unit 112 includes the fundamental wave phase 120 and the pulse mode signal PM
Then, the control switching signal 11 is created and output to the outside.

The operation of each unit will be described with reference to FIG. The phase operation value 120 is 1
Since computing the period the sawtooth wave, the terms of this value in a sine wave, multiplies the percentage voltage V _MD. If the value of _VMD is 100% as shown in FIG. 3, the instantaneous output voltage value data 122 as a result of the multiplication is a sine wave of maximum + 100% and minimum -100%.
The magnitude of the amplitude changes depending on the value of _MD .

In this embodiment, the operation cycle of the timers P and N is
Of it so that to perform the sampling time T _s, the value of T _s /2.5ms is requested from the operating stability of the inverter device. Therefore, if T _s = 2.5 ms, the timer sets the instantaneous output voltage value data every T _{s in} FIG.

The operation at the bottom of Figure 3, showing an extended T _s. That is, the timer P114 every T _s, to excisional alternately data to the timer N115. When excisional data to the timer N115 at time t _1, the timer N115 and outputs by controlling the delay time T _N in accordance with the data, to excisional data to the timer P114 at time t _2,
Timer P114 and outputs the control delay time T _P in accordance with the data. Then, the timer outputs POT and NOT are combined into a waveform and asynchronous P
The WM signal 101 is generated. PWM with sampling time T _s twice
Since a signal is generated, when T _s = 2.5 ms, a PWM signal having a constant frequency of 200 Hz can be obtained.

Next, generation of the synchronous control PWM signal will be described with reference to FIG. 4, the same parts as those in FIG. 1 are denoted by the same reference numerals. Although it is possible to generate a PWM signal by software processing in the synchronous control as in the asynchronous control, the duty of the CPU becomes stricter as the frequency increases, and the sampling time must be reduced. Less, dedicated hardware is suitable as in this embodiment.

The inverter frequency signal f _i1 and the pulse mode signal PM, which are the outputs from the CPU 1, are input to the counter 210, and the output signal 220 corresponding to the phase of the inverter output voltage is output.
The addresses of the EPROMs 211, 212, and 213 storing the carrier waves are swept to obtain carrier wave data 221, 222, and 223. Comparators 214,215,2
16, the modulation degree signal γ from the CPU 1 and the carrier wave data 221, 22
2,223 is compared digitally, and the comparison result is a waveform generation circuit 217
To the synchronous control PWM signal 201 by the counter output 210.
Get.

Here, the carrier data of a half cycle (180 °) is divided into three and stored in the EPROMs 211, 212 and 213 every 60 °, and the comparison accuracy near the zero level between the modulated wave and the carrier is increased and the comparison level is unified. For this purpose, the level of the carrier is made to be the inverse of the sine wave.

Data at every 60 ° of the EPROMs 211, 212, and 213 is compared with the modulation degree signal γ, and the comparison result is combined for each zero cross signal of the counter output 210 to generate a PWM signal.

Next, the control mode switching operation will be described with reference to FIG. Here, a switching operation from asynchronous control to synchronous control is shown.

As apparent from FIG. 5, the control switch 15 is not immediately perform the switching operation also control switching signal 11 is generated at t _10, the output voltage of computing within CPU1 fundamental wave phase 12
0 of a zero crossing point and summer to switch the synchronous control at t ₂₀ is rising, no Torukushiyotsuku the phase is continuous with this. Switching from synchronous control to asynchronous control is also performed at the zero crossing point. The same effect can be obtained by using the inverter frequency _fi0 or the vehicle speed instead of the pulse mode signal PM input to the switching control unit 112.

Therefore, according to this embodiment, the speed control of the induction motor can be performed with high accuracy while sufficiently suppressing the torque pulsation at a low speed, and the running of the electric vehicle can be smoothly controlled.

Further, in this embodiment, as described above, since the switching operation of the control mode is performed without changing the phase of the fundamental wave of the output voltage, a torque shock does not appear in the induction motor and a smooth operation can be obtained. Can be

〔The invention's effect〕

According to the present invention, since the main processing of the asynchronous control in the low-frequency region is performed by the CPU, it is possible to generate a PWM signal with high accuracy. In consideration of this, it is decided to use dedicated hardware, so that the sharing of processing between software and hardware is optimized, the need for an interface between the CPU and hardware can be minimized, and the circuit configuration is simple The effect is as follows.

[Brief description of the drawings]

FIG. 1 is a control block diagram showing one embodiment of the present invention, and FIG.
FIG. 3 is a control block diagram showing an embodiment of an asynchronous control PWM circuit, FIG. 3 is a waveform diagram for explaining the operation of FIG. 2, FIG. 4 is a control block diagram showing an embodiment of a synchronous control PWM circuit, FIG. FIG. 5 is a waveform chart for explaining the control mode switching operation. 1 CPU 15 Control switcher 100 Asynchronous control PWM circuit 200 Synchronous control PWM circuit 110 Phase calculation unit 111
... Sine wave converter, 112 ... Switching controller, 113 ... Multiplier, 114
…… Timer P, 115 …… Timer N, 116 …… Waveform synthesis circuit, 210
…… Counter, 211-213 …… EPROM, 214-216 …… Comparator,
217 ... Waveform generation circuit.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tokunosuke Tanamachi 4026 Kuji-cho, Hitachi, Japan Inside Hitachi, Ltd.Hitachi, Ltd. Inside

Claims (7)

(57) [Claims] 1. A pulse width for selecting and outputting a pulse width-modulated pulse asynchronous to an inverter output AC and a pulse width modulated pulse synchronized to an inverter output AC for a main circuit switching element of an inverter. In a control device for a modulation type inverter, a first arithmetic processing means for creating an output frequency command signal and an output voltage command signal of the inverter in accordance with a predetermined calculation procedure, and inputting the output frequency command signal and the output voltage command signal A first pulse width modulation means for outputting a pulse width modulated pulse synchronized with the inverter output AC; and pulse width data asynchronous to the inverter output AC determined in advance from the output frequency command signal and the output voltage command signal. Second arithmetic processing means created according to the calculated arithmetic procedure, and the asynchronous pulse width data Second pulse width modulation means for outputting a pulse width-modulated pulse from the data, an output of the first pulse width modulation means, and an output of the second pulse width modulation means. Means for selecting based on a selection signal generated from the signal and the output voltage command signal. 2. The control device for a pulse width modulation type inverter according to claim 1, wherein said first arithmetic processing means and said second arithmetic processing means are constituted by a common computer. 3. The control device for a pulse width modulation type inverter according to claim 1, wherein the selection signal is generated according to a predetermined calculation procedure. 4. The apparatus according to claim 1, wherein said selecting means comprises: an output of said first pulse width modulating means at a point where a phase of said inverter output AC becomes zero phase; A pulse width modulation type inverter control device for switching between the output of a width modulation means. 5. The apparatus according to claim 1, wherein said second arithmetic processing means comprises: a phase arithmetic means for outputting a phase of an output voltage fundamental wave of said inverter from said output frequency command signal; A sine wave generating means for outputting a sine wave from the phase of the fundamental wave; a means for generating an instantaneous output voltage command from the sine wave and the output voltage command signal; operating at a constant sampling cycle; Means for outputting pulse width data according to the instantaneous output voltage command value. 6. The control device for a pulse width modulation type inverter according to claim 5, wherein said constant sampling period is made coincident with a sampling period of said second arithmetic processing means. 7. A pulse mode signal according to claim 1, wherein said first pulse width modulating means outputs a pulse mode signal for specifying the number of pulses in one cycle of the inverter output AC generated according to a predetermined calculation procedure. A counter that inputs and generates an output corresponding to the phase of the inverter output AC based on the pulse mode signal and the output frequency command signal; a storage unit that sweeps an address by this counter output and outputs carrier wave data; Means for comparing a carrier wave data with the output voltage command value signal and outputting a pulse width-modulated pulse.